Mineralogical and Geochemical Control on Swelling Behaviour of Expansive Soils in Navrongo, Ghana

Mineralogical and Geochemical Control on Swelling Behaviour of Expansive Soils in Navrongo, Ghana | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Mineralogical and Geochemical Control on Swelling Behaviour of Expansive Soils in Navrongo, Ghana Eric Enzula Bayari, Dickson Asante Armah, Prosper Aduah Akaba, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8408259/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 12 You are reading this latest preprint version Abstract Soils with expansive behaviour pose a great geotechnical impact on buildings in tropical regions, due to moisture variations causing severe volumetric changes. This study investigates the mineralogical, geochemical, and index property characteristics of expansive soils from Navrongo in the Upper East Region of Ghana to identify the controls on their swelling behaviour. An integrated methodology of X-ray diffraction (XRD), major oxide geochemistry, Atterberg limits, and the Weathering Index of Parker (WIP) was performed on four soil samples. Results reveal a dominant kaolinite-quartz assemblage indicating advanced tropical weathering, yet with spatial variability. One sample (NA0001) was found to contain sodium-rich montmorillonite (smectite), correlating with uniquely elevated geochemical concentrations of Fe 2 O 3 (8.83%) and MgO (1.57%) and a very high Plasticity Index (PI = 57.6%), classifying it as having high expansion potential. In contrast, the smectite-free samples exhibited significantly lower plasticity (PI = 20.3–43.2%). The data establish a causal chain of localised geochemical conditions, associated with an intermediate weathering stage, that stabilise expansive smectite clays, which in turn dictate high-index properties and severe swell potential. This study further interprets this variability within a classic tropical regolith profile, identifying the mottled weathering zone as a probable genesis horizon for expansive clays. The findings underscore that the swelling risk in Navrongo is not ubiquitous but confined to specific zones where smectite is present. Consequently, a multi-method approach that combines plasticity tests and mineralogical and geochemical analyses to identify these high-risk, spatially discrete soil units to inform geotechnical design and sustainable infrastructure development in Navrongo. Expansive Soils Smectite Geochemistry Plasticity Index Weathering Index Navrongo Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1 INTRODUCTION Expansive soils, which are a significant geotechnical challenge characterised by pronounced volume changes in response to moisture fluctuations, are found extensively in tropical and semi-arid regions worldwide. Their impact on construction is particularly acute and is a global problem. The distribution of these problematic soils appears to be widening with increased construction activity, especially in developing nations, where infrastructure expansion encounters previously uncharacterised deposits. This volumetric instability is fundamentally attributed to the presence of active clay minerals, such as 2:1 smectite (especially montmorillonite), which have a pronounced capacity to absorb water into their interlayer spaces, leading to swelling during wet periods and subsequent shrinkage upon drying [ 1 , 2 ]. Therefore, such soils, which usually contain more than 30% of 2:1 expanding type of the smectitic clay, are referred to as expansive soils. A soil is commonly considered to have expansive tendencies when the liquid limit is greater than 53% and the plasticity index is greater than 25% [ 3 ]. Osman [ 3 ] alternatively refers to these soils as shrink-swell soils. When they are dried, they shrink so greatly that they cause wide and deep cracks on the surface to depths often extending more than a meter downward [ 4 ]. These soils are referred to as deeply and widely cracking soils or simply cracking soils. They occur at a minimum depth of 50 cm, and in most cases, their engineering behavior depends mainly on the physicochemical characteristics of the clay component within the regolith. These expansive soils have been noted to pose a significant and widespread geotechnical challenge to civil infrastructure globally, with annual costs estimated in the billions of dollars, often exceeding the damage caused by natural disasters like earthquakes and floods [ 5 , 6 ] The primary mechanism of damage stems from the soil's volumetric changes, the swelling-shrinking effect, which exert substantial pressures on overlying structures. This phenomenon severely impacts building foundations, particularly those of lightweight residential and commercial buildings, where differential heave can lead to cracking in slabs-on-grade, walls, and in structural frames. Similarly, pavement systems, including roads and runways, are highly vulnerable; the uneven movement of the subgrade soil causes cracking, roughness, and premature failure of the asphalt or concrete surface, leading to increased maintenance costs and reduced service life [ 7 – 13 ]. The detrimental effects extend to linear infrastructure, where buried pipelines are at a high risk of failure owing to the cyclic forces imposed by moving soil. This can result in joint breaks, leaks, and costly service interruptions [ 14 , 15 ]. Significant effects have been reported in arid, semi-arid, and seasonally wet climates on all inhabited continents, including the United States, Canada, China, India, Australia, and a significant portion of Africa[ 1 , 3 , 16 ]. Expansive soils are a crucial factor in the creation of sustainable infrastructure globally because of their ubiquitous character, which calls for specialised and frequently expensive site study, design modifications, and soil stabilisation measures [ 17 ]. Heaving foundation issues are common in semi-arid and dry sub-humid regions of Africa and in many other parts of the world. This is because long stretches of dryness and heavy seasonal rainfall cause soils to alternate between desiccation and saturation [ 16 ]. The expansiveness of the expansive soils is fundamentally controlled by a geochemical and mineralogical property, primarily driven by the presence and activity of the hydrophilic mineral montmorillonite and other mixed clay, with montmorillonite being the most prevalent and influential species [ 8 , 10 , 18 ]. The exceptional swelling capacity of smectite originates from its unique 2:1 layered silicate structure, which consists of an alumina octahedral sheet sandwiched between two silica tetrahedral sheets. Crucially, isomorphous substitution, where atoms within the crystal lattice (e.g., Al 3+ for Si 4+ in the tetrahedral sheet or Mg 2+ for Al 3+ in the octahedral sheet) create a permanent negative charge, occurs. This charge is balanced by the adsorption of exchangeable cations (e.g., Na + and Ca 2+ ) and water molecules into the interlayer space between adjacent layers. It is this interlayer space that acts as the engine for expansion, as water molecules are strongly attracted to the charged mineral surfaces and to the hydrated cations, forcing the layers apart [ 19 ]. The intensity of this swelling is governed by the specific type of exchangeable cation and available soil moisture. For instance, sodium-saturated montmorillonite (Na-montmorillonite) can exhibit virtually unlimited interlayer expansion, absorbing water to several times its original volume, whereas calcium-saturated varieties (Ca-montmorillonite) exhibit more limited swell due to stronger electrostatic bonds [ 17 ]. Upon wetting, water is drawn into the interlayers through osmosis and strong surface adsorption, generating immense swelling pressures that can exceed 1 MPa, sufficient to lift heavy structures and causing cracks that may sometimes extend to a depth of 0.5 m below the surface and can be 5 to 20 mm wide [ 20 ]. Conversely, during drying, the loss of interlayer water causes the crystals to contract, leading to soil shrinkage and desiccation cracks. This reversible shrink-swell cycle, dictated by the mineral's response to environmental changes, is the direct cause of the severe distress observed in overlying foundations, pavements, and pipelines [ 21 ]. Structures constructed on such soils are subjected to uplift forces due to the swelling and shrinking characteristics [ 15 ]. Generally, light structures, particularly low-cost houses, have lightly loaded foundations typical of residential construction, and these safer differential heaves impose severe tensile and shear stresses on masonry and concrete, which are weak in resisting such forces, resulting in characteristic diagonal cracking in walls, jamming of doors and windows, and tilting of entire structures. This problem is often exacerbated by the common practice of constructing without a properly engineered, moisture-controlled, and compacted fill material, placing the foundation directly on the active, natural soil. In the developing world context such as in Navrongo in the Upper East Region of Ghana, where Bayari et al. [ 22 ], made reports on x-ray diffraction showing a strong montmorillonite mineral phase in some residual clay deposits in Navrongo the impact of this phenomenon of expansive soils is magnified by a confluence of socio-economic and technical factors. The high cost and limited availability of professional geotechnical services imply that most light buildings are erected without prior site investigation or appropriately engineered foundations, leaving homeowners unaware of the risk until damage manifests. Furthermore, a lack of robust building codes, enforcement, and awareness among informal builders leads to construction practices that inadvertently worsen the situation, such as the use of moisture-susceptible shallow strip footings and poor site drainage. When cracks appear, residents often resort to temporary cosmetic repairs that fail to address the underlying soil issue, initiating a destructive cycle of recurring damage. This not only depletes the limited financial resources of families but also perpetuates a state of unsafe housing and undermines long-term sustainable development, as the very fabric of the built environment remains chronically vulnerable to a predictable and manageable geotechnical hazard [ 23 ]. Despite the perceived challenges and anecdotal evidence, a comprehensive, multi-faceted study linking mineralogy and geochemistry to the geotechnical properties of these soils in Navrongo is lacking. Identified studies in Ghana on expansive soils have mainly focused on other regions (e.g., the Accra Plains or Kumasi) [ 24 ], leaving a knowledge gap for the Upper East Region. Reliance solely on basic geotechnical tests (e.g., Atterberg Limits) without corroboration with mineralogical data can lead to an incomplete understanding and misdiagnosis of the soil's expansive potential. This gap hinders effective land-use planning, safe construction practices, and the development of appropriate soil-stabilization techniques in the region. Therefore, this study seeks to provide a comprehensive characterization of the perceived expansive soils in Navrongo through an integrated mineralogical, geochemical, and geotechnical approach to determine their true expansive nature and potential engineering implications. The findings will provide a scientific database for engineers, urban planners, and developers working in the Navrongo area and the broader Upper East Region of Ghana. This integrated methodology can serve as a model for assessing problematic soils in other parts of Ghana with similar geological settings. The results will inform the development of appropriate foundation design and soil stabilization strategies, thereby enhancing the durability and safety of infrastructure. 2 MATERIALS AND METHODS 2.1 Study area 2.1.1 Location, climate, relief, drainage, and vegetation The study area, Navrongo, is a strategically important town and the administrative capital of the Kassena-Nankana Municipal District in the Upper East Region of Ghana. The Ghana Statistical Service[ 25 ] estimates that, approximately 99,895 people reside in the Kasena Nankana Municipal and the majority are subsistence farmers. Its geographical characteristics are typical of the broader Sudan-Savanna zone of West Africa, shaping the livelihoods and socio-economic activities of its predominantly agrarian population. Navrongo is situated in the northeastern corner of Ghana, close to the international border with Burkina Faso. Its precise coordinates are approximately 10° 53' 0" North latitude and 1° 5' 0" West longitude and is 30km North-West of Bolgatanga the Upper East Regional capital. This location places it within the Guinea Savanna agro-ecological zone [ 26 ]. The town serves as a major nodal point for trade and commerce in the region, linking Ghana to its Sahelian neighbors. Its position within the municipal makes it a central hub for administrative, educational, and health services for the surrounding rural settlements. Navrongo experiences a tropical continental (Sudanian) climate characterized by a pronounced unimodal rainfall pattern and high temperatures throughout the year. The climate is distinctly divided into two seasons: The Rainy Season, a single, intense wet season, lasts from approximately May to October, with its peak in August. The total mean annual rainfall is relatively low, ranging between 800 mm and 1,100 mm. and is highly erratic, both in terms of onset, duration, and intensity, making rain-fed agriculture a risky venture [ 16 ]. Intense storms often lead to high runoff and soil erosion rather than effective water infiltration [ 16 ]. From November to April, the region experiences a prolonged and severe dry season. This period is dominated by the dry and dusty Harmattan wind, which blows from the Sahara Desert. Humidity drops significantly, and temperatures can be very high during the day, often reaching 46°C, with monthly average temperatures ranging between 18°C and 45°C. The desiccating effect of the Harmattan further stresses the land, vegetation and leads to severe water scarcity [ 27 ]. The relief of the Navrongo area (Fig. 1 ) is generally flat to gently undulating, with an average elevation of around 200 meters above sea level [ 26 ]. The landscape is part of the vast Voltaian Basin, which is composed of ancient sedimentary rock. The topography is characterized by monotonous plains with occasional low-lying hills and inselbergs. While the overall relief is low, the gentle slopes are significant for surface hydrology, facilitating the rapid runoff of rainwater and contributing to the high erosion potential noted in the area[ 16 ]. The land is suitable for mechanized agriculture, but its flatness can lead to seasonal waterlogging in depressions. The drainage system in Navrongo is part of the Volta River Basin, drained by several seasonal streams and rivers, which are tributaries of the White Volta [ 16 ]. A defining feature of the drainage is the seasonality; rivers and streams flow only during and immediately after the rainy season, becoming completely dry or reduced to a series of stagnant pools for the rest of the year [ 16 ]. This temporal variability poses a major challenge for water supply, especially during the long dry season, and ultimately causes deep, wide cracks, sometimes several centimeters wide and over a meter deep. These cracks act as direct conduits, channelling moisture from deeper in the soil profile to the surface, where it is lost to the atmosphere. Navrongo falls within the Guinea Savanna woodland ecological zone, more specifically classified as the Sudanian Savanna [ 28 ]. The natural vegetation is a mosaic of grassland, dominated by tough, tussock-forming grasses that can withstand the long dry season and periodic wildfires. Scattered drought-resistant tree cover is open and consists of species adapted to moisture stress, such as Baobab (Adansonia digitata), Shea tree (Vitellaria paradoxa), and Acacia species (Acacia spp.). These trees are often stunted and have deep root systems or other xerophytic adaptations. However, natural vegetation has been significantly altered by prolonged human activity, including farming, fuelwood collection, and charcoal production. This has resulted in widespread land degradation and a reduction in biodiversity [ 29 , 30 ]. The landscape is now predominantly a cultivated savanna with small, scattered patches of protected woodland around sacred groves and settlements. The combined pressures of climate variability and anthropogenic activities continue to threaten the fragile vegetation cover in the area. 2.1.2 Geology From the perspective of the regional geology of Ghana, the geology of the study area (Fig. 2 ) falls within the eastern volcanic belt, a segment of the larger Bole-Nangodi greenstone belt, and a fairly complete succession of Paleoprotorozoic Birimian rocks exists in this area. It is characterized by a series of NEE to NE-trending structural zones dominated by metavolcanic and metasedimentary rocks intruded by various granitoid [ 31 – 33 ]. As noted by Melcher[ 34 ] and Attoh[ 35 ] the basement is underlain by Birimian granitoids interspersed with minor pyroclastic and volcaniclastic rocks. Metavolcanic rocks are a significant component of the area and are primarily basaltic to andesitic in composition. They have been metamorphosed to greenschist facies, resulting in mineral assemblages dominated by chlorite, actinolite, and epidote [ 36 ]. The presence of pyroclastic and volcaniclastic rocks indicates explosive volcanic activity and reworking of volcanic material, suggesting a complex volcanic-arc environment. Granitoid Intrusives are predominantly diorites to tonalites and granodiorites, which represent the plutonic roots of the Birimian volcanic arc system [ 37 ]. These intrusions are typically syn-to late-tectonic relative to the main Birimian deformation. Navrongo lies on the Bole-Navrongo structural zone, this zone is defined by a network of major, crustal-scale shear zones with a dominant NE-SW trend, consistent with the regional structural grain of the Birimian [ 38 ]. These shear zones are deep-seated structures that act as conduits for hydrothermal fluids. Geology directly controls the nature of the overlying soils. The deep chemical weathering of these Birimian rocks; particularly the ferromagnesian-rich metavolcanics and the potassic feldspars within the granitoids produces a clay-rich soil mantle [ 22 ]. The mineralogy of the parent rock is crucial; the weathering of mafic volcanic rocks can lead to the formation of smectite clays, which are highly expansive, while the weathering of granitoids typically yields kaolinite and illite [ 22 ]. The complex intercalation of different rock types means that soil properties can vary significantly over short distances. The NE-SW structural trends can also influence drainage patterns and groundwater flow, which in turn affects the moisture content and swell-shrink potential of soils derived from this bedrock. According to Foli et al. [ 39 ], the ochrosols are made up of shallow to deep soils, that have features of gravels and concretions and they overlie weathered granitic rocks. The ochrosols are usually hydromorphic in nature, well-drained, and have very high clay content, usually black or dark-grey clayey soils that are very suitable for cultivation because of the soil’s arability. The soil found in the study area is savannah ochrosols, which are porous, well-drained, loamy, mildly acidic, and interspersed with patches of dark-grey or black clay soils and groundwater laterites, which are developed mainly over shale and granite. 2.2 Subsurface Profile 2.2.1 Pitting To enable the visual examination of the subsurface material conditions, a suitable site was identified through an initial assessment of areas with low-lying or depositional areas, a cover of transported overburden forming the direct parent material of the soil, visible surficial cracks (Fig. 3 a), and structural failures such as cracks (Fig. (b-e) were identified. The depth of the regolith, a key indicator of the potential depth of clay-rich, expansive materials, was pitted to obtain information regarding the subsurface in-situ soil conditions and formations. 2.3 Sample Material Collection and Preparation For this experimental study, material (expansive soil) was collected from four sites, NA0001, NA0002, NA0003, and NA0004 (Fig. 1 (a-d)). The exact locations of these sites are shown in Fig. 1 . The individual samples were freed of stones and other unimportant things, such as dead plant roots. Some of the clay materials were slightly bulky; therefore, they were broken down into smaller pieces before placing them in zip-lock bags and labeling them, as shown in Fig. 4 a-d. The samples were air-dried for approximately 24 h and crushed into powder using a pestle and mortar at the Center for Scientific and Industrial Research (CSIR), Fumesua-Kumasi (Fig. 5 a). They were then sieved for very fine particles of the clay using the 0.425mm sieve (No.40) (Fig. 5 b). 2.4 Mineralogical and Geochemical analysis 2.4.1 X-Ray Diffraction (XRD) X-ray Powder Diffraction (XRD) analysis was used to test the mineralogical characteristics of the rock and soil samples. XRD is a technique that is widely used for identifying minerals and therefore will be very relevant in finding traces of montmorillonitic or other expansive clay minerals in the samples. This type of analysis is used because the minerals will diffract a beam of incident x-rays and this diffraction pattern actually differentiates each mineral species based on their properties [ 40 ]. XRD analysis was performed using X-ray Diffractometers. The samples were sent to the Department of Physics, University of Ghana, for preparation and analysis. The analysis was performed using an EMPYREAN diffractometer system. 2.4.2 Geochemical analysis All samples were analyzed for major and minor elements using an XRF spectrometer at the Geological Survey Authority (GSA) in Accra, Ghana. An X-ray Fluorescence Spectrometer-XRF (Model: VMR) from Olympus (Model: Adventurer-Pro AV 264), Mill/Mixture (Model: MM301), hydraulic press (Model: Specac), and sieve were used to carry out the final selected samples that showed variation in their texture and mineralogical composition. The samples were sieved using a sieve with a size of 75 µm. For each analysis, 5.0 g of the sieved sample was well mixed and homogenized with 0.9 g of a binder (Hoechst Wax) in a mill and pressed with 15 tons to a 32 mm pellet. Multi-element determinations from the prepared pellets were carried out using an energy-dispersive polarizing X-ray fluorescence (XRF) spectrometer ( VMR Vanta M Series) with a tube rating of 50 kV and 0.2 mA. The analytical quality was assessed by inserting quality control and assurance samples SRM 2711a from NIST and OxG180 from Rocklabs, respectively. The laboratory temperature was maintained at 20°C during the analysis. 2.4.3 Weathering Intensity assessment The engineering behaviour of rock materials depends not only on the stress state and stress history but also on the physical, mineralogical, and chemical changes in the rock materials due to weathering. Weathering indices are used to define these changes and quantify the engineering properties of regolith. Several weathering indices have been devised to quantify changes in the intrinsic properties of rocks from different perspectives, some of which can be related to the engineering properties of weathered rocks. The most commonly used methods can be broadly categorized as chemical, mineralogical-petrographical, petro-chemical, and engineering indices. The Weathering Index of Parker also known as Parker’s index [ 41 ] was applied to assess the degree of the decomposition of the regolith material that constitutes the expansive soil (clay) using Eq. 1. This weathering index among others is most appropriate application to weathering profile on heterogeneous (and homogeneous) parent rocks on the collective decomposition of multiple mineral phases [ 42 ]. WIP = \(\:\left[\right(\frac{Na}{0.35}\:+\frac{Mg}{0.9})\:+(\frac{K}{0.25}\:+\:\frac{Ca}{0.7}\left)\right]\:\times\:\:100\) Eq. 1 2.5 Index Properties 2.5.1 Atterberg Tests The Atterberg limits, comprising the liquid limit (w L ), plastic limit (w P ), and shrinkage limit (w S ), are fundamental indices that define the moisture content ranges at which fine-grained soil transitions between distinct consistency states (liquid, plastic, and semisolid). These tests, performed in accordance with ASTM D4318 [ 43 ], were conducted on the fraction of each soil sample passing a No. 40 sieve (0.425 mm aperture). Standard apparatus was employed for the determinations, including a porcelain mortar and pestle for sample preparation, evaporating dishes and spatulas for mixing and specimen molding, a thermostatically controlled drying oven maintained at 105°C, and a digital analytical balance for mass measurements. 2.5.2 Liquid Limit Test The liquid limit (w L ) was determined using the Casagrande percussion cup method, conforming to the standard procedure outlined in ASTM D4318 [ 43 , 44 ]. The primary apparatus consisted of a mechanical Casagrande device, standardized grooving tool, flat mixing board, and spatulas. The test procedure involved thoroughly mixing a portion of the prepared soil sample with distilled water to form a homogeneous paste. This paste was then placed in the brass cup of the liquid-limit device and levelled. A groove was cut through the soil pat along its centerline using a Casagrande grooving tool. The handle was then turned at a rate of approximately two blows per second, causing the cup to lift and drop repeatedly. The liquid limit was defined as the moisture content (determined gravimetrically) at which the two halves of the soil pat came into contact along the bottom of the groove for a distance of 0.5 inches (approximately 13 mm) after 25 blows. This test was repeated at varying moisture contents to obtain between three and five trials with blow counts of 25, enabling the derivation of the liquid limit from the plotted flow curve using Eq. (2). \(\:{{w}_{L}={w}_{N}\left(\frac{N}{25}\right)}^{tan\beta\:}\) Eq. 2 where w L is the Liquid Limit (%), w N is the measured moisture content at N blows (%), N = Number of blows (25), and tan β is the slope of the flow line. The standard allows the use of an approximation factor (k). For many soils, especially clays, a standard slope corresponding to k = 0.121 is used. 2.5.3 Plastic Limit Test The plastic limit (w p ) was determined in accordance with standard geotechnical procedures [ 43 , 44 ]. For each sample, a portion of the moist soil was shaped into a ball and repeatedly rolled on a glass plate to form a uniform thread of approximately 3 mm diameter (Fig. 6 a). The plastic limit was defined as the moisture content at which the thread crumbled and could no longer be rolled to the full 3 mm diameter without breaking apart. This procedure was replicated to obtain multiple subsamples. The moisture content was calculated gravimetrically from the mass loss upon oven-drying at 105°C to constant weight (Fig. 6 b). using Eq. 3, the plastic limit values were determined. \(\:{M}_{c}=\frac{{W}_{a}-\:{W}_{b}}{{W}_{b}-{W}_{c}}\times\:100\) Eq. 3 Where, M c is the moisture content, W a is mass of container and wet material (g).W b is mass of container and dry material (g), W c is container only (g). 2.5.4 Plasticity Index The plasticity index (PI) is a fundamental engineering parameter calculated as the numerical difference between the liquid limit and the plastic limit. It represents the range of moisture content over which the soil exhibits plastic behaviour. A higher PI generally indicates a greater proportion of active clay minerals and a greater potential for volume change and compressibility. This index (Eq. 4) is critical for soil classification systems, such as the Unified Soil Classification System (USCS) and AASHTO system [ 45 ], and serves as a key indicator of potential expansiveness in fine-grained soils. \(\:PI\:=\:wₗ\:-\:wₚ\) Eq. 4 2.5.5 Shrinkage Limit Test The shrinkage limit (W S ) was determined following ASTM D4943 [ 46 ]. A standardized shrinkage dish, lightly coated on the interior with petroleum oil to prevent adhesion, was used. A portion of the wet soil paste was consolidated into the dish in layers using a spatula and a glass plate to eliminate air voids and ensure full saturation. The mass of the dish containing the wet soil was recorded. The sample was subsequently oven-dried at 105°C to a constant mass. The volumetric displacement of the oven-dried soil cake was measured via the water displacement method. The shrinkage limit was then calculated using Eq. 5 by recording the masses and volumes to determine the moisture content at which further drying does not cause additional volumetric reduction. \(\:\text{w}\text{s}=\text{w}\text{i}-\frac{\left(\text{V}\text{i}-\text{V}\text{f}\right){\rho\:}\text{w}}{\text{m}\text{s}}\times\:100\text{%}\) Eq. 5 Where: wₛ = Shrinkage Limit (%), w i = Initial Moisture Content of the wet soil pat (%), V i = Initial Volume of the wet soil pat (cm³), V f = Final Volume of the oven-dried soil pat (cm³), ρw = Density of water (≈ 1 g/cm³), m s = Mass of the oven-dried soil solids (g). 3 RESULTS AND DISCUSSIONS 3.1.1 Regolith Profile Description Figure 7 presents a schematic regolith profile typical of tropical basement complex terrains, such as that found in Navrongo. This profile provides the essential genetic and stratigraphic context for understanding the formation and distribution of the expansive soils characterized in this study [ 47 ]. The profile is structured sequentially from the soil and duricrust horizon (0.00m – 0.85m), this uppermost zone comprises two sub-layers. The Clayey Sand Soil topsoil is a transported and bioturbated mixture of clay minerals and sand-sized particles, representing the immediate geotechnical material sampled in this study. Underlying it, the Clayey Lateritic Gravel/Duricrust is an indurated layer enriched in iron and aluminum oxides, forming a relatively impermeable capstone characteristic of advanced laterization [ 48 ]. Transitional Weathering Zone (1.85m – 3.70m) directly beneath the duricrust lies the Mottled/Arenose Zone (Clav Zone). This horizon is defined by its mottled coloration, resulting from the irregular leaching and precipitation of iron. It is a zone of active in-situ chemical weathering and neoformation of clay minerals, where bedrock is transformed into a porous matrix of clay and sand [ 49 ]. Weathered Bedrock (below 3.70m) forms the base of the profile and consists of the Saprock/Gruss, comprising physically disintegrated but chemically less-altered bedrock. This friable material, which retains the original rock structure, represents the initial weathering stage and the parent material for the overlying horizons. 3.2 XRD Analysis Based on the provided mineralogical data for samples from Navrongo, Upper East Ghana (Fig. 8 , Fig. 9 , Fig. 10 , Fig. 11 ). The identified minerals (Table 1 ) point to a complex soil system where swelling potential is not dominated by a single, highly expansive clay but is influenced by a mixture where even minor phases can have significant geotechnical implications. All four samples contain Aluminum Silicate Hydroxide (Kaolinite, Al 2 Si 2 O 5 (OH) 4 ). Kaolinite is a 1:1 layered clay mineral with strong hydrogen bonding between layers, resulting in a non-expansive nature and low cation exchange capacity (CEC) [ 19 , 50 ]. Its prevalence, especially in samples NA0001, NA0002, and NA0004, suggests these soils likely have a generally low to moderate inherent swelling capacity. The formation of kaolinite is typical in intensely weathered tropical environments with good drainage and leaching conditions, which aligns with the weathering profiles common in West Africa [ 51 ]. Its presence provides a stable, relatively inert matrix. Silicon Oxide (Quartz, SiO 2 ) is present in every sample. Quartz is a framework silicate, mechanically stable and non-reactive. Its primary role is as a diluent, reducing the overall proportion of clay-sized particles and active minerals that contribute to swelling [ 52 ]. A high quartz content typically correlates with lower plasticity and swell potential. Its ubiquity indicates these soils contain a significant silt or fine sand fraction [ 21 ]. The most mineralogically significant finding for understanding potential expansiveness is in sample NA0001, which contains Sodium Iron Silicate Hydroxide Hydrate (montmorillonite/bentonite). Montmorillonite is a smectite-group mineral, a 2:1 expandable clay with a very high CEC and specific surface area. Interlayer cations (like Na + here) and water molecules can cause significant volumetric change (up to 1500%) upon wetting [ 52 ]. The notation Na 0.3 suggests a sodium-rich variety (Na-montmorillonite), which is particularly prone to dispersion and severe swelling compared to calcium-saturated varieties [ 53 ]. Guimarães et al. [ 54 ] and Ramana [ 55 ] identified that a small percentage (often as little as 5–10%) of smectite within a kaolinitic or quartzose matrix can impart significant expansiveness. Its absence from the other three samples highlights the spatial variability of expansive risk. Sample NA0001 also lists anorthite sodian, and NA0003 lists anorthite (Al 2 CaO 8 Si 2 ) which is a calcium-rich plagioclase feldspar. Therefore, in this context of tropical soils, feldspars are weatherable primary minerals. Their presence, especially alongside kaolinite and smectite, indicates an incomplete weathering sequence. The weathering of plagioclase is a key source of calcium, sodium, and silica ions in pore water, which influence the geochemical environment controlling clay mineral stability and cation populations on exchange sites [ 45 ]. The coexistence of a primary mineral (anorthite), a stable secondary mineral (kaolinite), and a highly active secondary mineral (montmorillonite) in NA0001 suggests a geochemically transitional and heterogeneous weathering profile. The mineralogical suite dominated by kaolinite and quartz in samples NA0002, NA0003, and NA0004 suggests soils with inherently low swell potential. These would likely exhibit low plasticity and moderate strength, consistent with lateritic or residual soils described in the Basement Complex of Navrongo [ 39 , 56 ]. Sample NA0001 represents a high-risk scenario. Here, the soil matrix, while still containing kaolinite and quartz, is adulterated with sodium montmorillonite. This mineral's overwhelming affinity for water and its sodium-saturated state mean this soil will likely exhibit high swell pressure, high shrinkage limits, and severe volume changes with seasonal moisture fluctuations. The swelling behavior will be disproportionate to its total clay content because the smectite exerts a controlling influence [ 52 , 57 ] The occurrence of montmorillonite alongside anorthite and kaolinite may indicate specific the local conditions of perhaps poor drainage, a geochemical barrier (e.g., higher pH or silica activity), or weathering of a more mafic rock source that provides the necessary magnesium and iron. Montmorillonite often forms in less aggressive weathering environments than kaolinite or from the alteration of volcanic ash (bentonite), which could point to localized depositional history [ 58 ].The mineralogical analysis underscores that expansive soils in Navrongo are not ubiquitously hazardous but are spatially variable. The principal risk arises from localized pockets or layers containing smectite (montmorillonite), even as a minor constituent. Standard geotechnical classification (e.g., Atterberg limits) on bulk samples might not fully capture this risk if the smectite is unevenly distributed. Therefore, site investigations in this region should combine routine tests with detailed mineralogical identification (like XRD, as shown in Figs. 8 , 9 , 10 and 11 ) and swell-consolidation tests, especially where historical performance indicates distress. The critical finding is that the swelling influence is not from the dominant kaolinite but from the trace, yet potent, expansive clay minerals that may be present. Table 1 Summary of the minerals found in all four samples Sample Id Mineral Identified Compound Name NA0001 Al 2 Si 2 O 5 (OH) 4 SiO 2 Na 0.3 Fe 2 Si 4 O 10 (OH) 2 .4H 2 O All.55Ca0.55Na0.45O 8 Si2.45 Aluminum silicate Hydroxide (Kaolinite) Silicon Oxide Sodium Iron Silicate Hydroxide Hydrate (montmorillonite/bentonite) Anorthite Sodian NA0002 SiO 2 Al 2 Si 2 O 5 (OH) 4 Silicon Oxide Aluminum Silicate Hydroxide (kaolinite) NA0003 SiO 2 Al 2 CalO 8 Si 2 Silicon Oxide Anorthite NA0004 SiO 2 Al 2 Si 2 O 5 (OH) 4 Silicon Oxide Aluminum Silicate Hydroxide(kaolinite) Silicon oxide is a common compound/mineral that is found in almost all soils and therefore runs through all the clay samples. It can also be seen that kaolinite is a common mineral in the soils in Navrongo since it can be found in all except one of the samples. Other notable minerals that were identified by the XRD analysis are montmorillonite, sodian and anorthite. 3.3 Geochemical analysis The obtained geochemical data (Table 2 ) show that, the major oxide compositions are characteristic of intensely weathered tropical soils derived from parent rocks within the Basement Complex (Fig. 2 ), consistent with the regional geology of the study area [ 39 ]. The high percentages of SiO 2 (48.7–55.3%) and Al 2 O 3 (12.5–19.2%) quantitatively confirm the mineralogical dominance of quartz and kaolinite, respectively, as identified by XRD (Table 1 ). The strong correlation between total silica-alumina and the abundance of these two minerals reflects a geochemical system where mobile cations (Ca 2+ , Na + , K + ) have been extensively leached, a hallmark of laterization in humid tropical climates (Nesbitt and Young, 1982). Sample NA0001, which XRD identified as containing smectite, is geochemically distinct. It exhibits the lowest SiO 2 /Al 2 O 3 ratio and the highest concentrations of Fe 2 O 3 (8.83%) and MgO (1.57%) among the set. This chemistry is diagnostic of smectites, particularly the iron-magnesium-rich variety suggested by the XRD formula (Na 0.3 Fe 2 Si 4 O 10 (OH) 2 ·4H 2 O), require these elements for their 2:1 lattice structure. The elevated Fe and Mg in NA0001 provide the necessary chemical building blocks for smectite stability, likely sourced from the weathering of ferromagnesian minerals in the parent rock [ 53 ]. In contrast, NA0004, with 0% MgO and lower Fe 2 O 3 , lacks the chemical prerequisites for smectite formation, explaining its XRD assemblage of only kaolinite and quartz. The low concentrations of base cations (CaO, Na 2 O, K 2 O < 1.3%) across all samples underscore the advanced weathering stage and explain the general scarcity of primary feldspars, with the minor CaO in NA0003 (0.94%) corresponding to its detected anorthite. Table 2 Geochemical data of sampled clay Sample NA0001 NA0002 NA0003 NA0004 SiO 2 48.731 55.347 55.333 49.451 TiO 2 0.946 0.803 0.855 0.815 Al 2 O 3 19.243 16.128 12.518 18.156 Fe 2 O 3 8.825 6.125 5.558 7.657 MgO 1.567 1.026 1.049 0.000 MnO 0.076 0.080 0.072 0.074 CaO 0.492 0.351 0.941 1.299 Na 2 O 0.431 0.387 0.501 0.398 K 2 O 0.539 0.508 0.720 0.528 P 2 O 5 0.010 0.000 0.110 0.001 The overall Index of Alteration (IA) for these soils would be very high, approaching that of pure kaolinite, which aligns with the mineralogy. However, the local deviation in NA0001, where the leaching process was perhaps less complete or the parent material more basic, created a microenvironment with sufficient silica, iron, and magnesium activity to facilitate smectite formation instead of, or alongside, kaolinite [ 52 ]. This directly links geochemistry to the engineering property: the swell potential hazard in Navrongo is spatially coincident with these distinct geochemical anomalies. Therefore, the integration of data confirms that the pronounced swelling in specific locations is not merely a textural accident but is fundamentally governed by a less-advanced local weathering pathway that preserves expandable 2:1 clays, as signalled by enhanced Fe, Mg, and a reduced silica-to-sesquioxide ratio. 3.4 Weathering Intensity assessment and engineering implication All WIP values shown in Table 3 are significantly lower than that of fresh rock (typical values > 1000), confirming that all samples are products of substantial chemical weathering, consistent with the tropical climate of the Upper East Region [ 42 , 47 , 59 ]. Table 3 Weathering Index of Parker value describing the intensity of weathering Sample NA0001 NA0002 NA0003 NA0004 WIP 583 478 682 511 Interpretation Highly weathered Highly weathered Most weathered Highly weathered The range of values (478 to 682) reveals important variability in weathering intensity across the site. Sample NA0003 has the highest WIP (682), indicating it is the least chemically weathered of the set. This aligns perfectly with its mineralogy, which included primary anorthite (a calcium feldspar) alongside kaolinite and quartz. The persistence of this weatherable mineral is reflected in the higher retention of mobile bases, yielding a higher WIP. Sample NA0002 has the lowest WIP (478.09), signifying it has undergone the most intense chemical leaching. This correlates with its mineralogy (only kaolinite and quartz) and its geochemistry, which showed the lowest sum of base cations. It represents the most advanced end-member of the weathering sequence. The WIP for the smectite-bearing Sample NA0001 (583) is intermediate, not the lowest. This is a critical finding. It indicates that while weathering has occurred, the leaching of magnesium and iron, essential for smectite stability has been less complete here than in NA0002. This supports the earlier geochemical hypothesis that local conditions (e.g., poorer drainage, specific parent material) inhibited the full weathering progression to kaolinite, instead stabilizing the expansive smectite phase. The WIP confirms that the formation of the highly swelling clay is associated with a specific, less-advanced stage of weathering in a particular microenvironment [ 60 ]. 3.5 Atterberg Tests Using established classification of Peck et al. [ 65 ], the Plasticity Index (PI) data categorises the samples into distinct risk groups (Table 4 ). From Table 5 , it is observed that, Sample NA0001, with a PI of 57.6%, falls into the very high expansion potential category. This extreme plasticity is the direct geotechnical manifestation of its unique mineralogy, the presence of sodium montmorillonite (smectite) identified by XRD. Smectite's high cation exchange capacity and specific surface area enable it to absorb large quantities of water, dramatically increasing the range of moisture content over which the soil remains plastic [ 6 ]. This aligns perfectly with its distinct geochemistry, which showed elevated Fe 2 O 3 and MgO, the essential structural cations for this expansive clay mineral [ 61 ]. The exceptionally high Liquid Limit (LL = 81.8%) further confirms the enormous water-holding capacity imparted by the smectite. Table 4 Expansion Potential of Soils and Plasticity Index (after Peck et al., [ 65 ]). Plasticity Index Expansion Potential 0–15 Low 0–35 Medium 22–55 High > 55 Very high Table 5 Summary of Atterberg data Sample ID Atterberg limits (%) Expansion Potential (Peck et al., [ 65 ]) LL PL PI Linear shrinkage (%) NA0001 81.80 24.20 57.6 7.48 Very High NA0002 43.90 16.40 27.5 14.36 Medium NA0003 37.30 17.00 20.3 12.49 Medium NA0004 65.80 22.60 43.2 17.25 High In contrast, samples NA0002 (PI = 27.5%) and NA0003 (PI = 20.3%) exhibit medium expansion potential. Their mineralogy, dominated by kaolinite and quartz with no detectable smectite, results in a significantly narrower plastic range and lower LL values (43.9% and 37.3%, respectively). Their geochemistry, with lower Fe 2 O 3 and MgO, supports this mineralogically controlled, moderate plasticity. Sample NA0004 presents an interesting case with a PI of 43.2% (High expansion potential) despite its XRD analysis indicating only kaolinite and quartz. The high plasticity indices observed in Sample NA0004, particularly its liquid limit of 65.8% and PI of 43.2% present a notable geotechnical anomaly when contrasted with its XRD mineralogy, which identified only kaolinite and quartz. This discrepancy suggests that the soil's expansive behaviour is driven by factors beyond the detection limits of standard XRD analysis or by the physical characteristics of its clay fraction. This phenomenon is well-documented in international literature. A primary explanation is the presence of amorphous or poorly crystalline phases. A study on Nigerian lateritic soils [ 58 ] recorded high liquid limits (> 60%) in soils with XRD-dominant kaolinite and quartz, attributing the behaviour to significant fractions of amorphous alumino-silicate gels and ultra-fine kaolinite particles that disproportionately increase surface area and water adsorption. Similarly, research on Cameroonian tropical soils indicated that high clay activity could be linked to nano-sized oxides and disordered phases not quantified by XRD [ 60 ]. Furthermore, the physical dominance of a very fine clay fraction can elevate plasticity independently of mineralogy. Soils with a high proportion of particles < 0.2 µm, even if predominantly kaolinite, exhibit increased surface charge density and enhanced water retention on particle edges and fractures, leading to higher PI values [ 62 , 63 ]. Critically, standard XRD often fails to identify interstratified or poorly crystalline expansive minerals. Investigations have revealed that soils classified as kaolinitic by XRD can contain 10–20% of poorly crystalline smectitic/illitic material or mixed-layer clays, which are primary drivers of swell pressure and high Atterberg limits [ 64 ]. The Linear Shrinkage values offer a crucial complement to the PI data. Notably, the sample with the highest swell potential (NA0001) does not have the highest linear shrinkage; that value belongs to NA0004 (17.25%). This can be interpreted through the mechanism of shrinkage: upon drying, smectite-rich soils (NA0001) generate very high suction and interparticle stresses, leading to the formation of large, macroscopic cracks and a heterogeneous structure, rather than uniform, bulk dimensional decrease. The resulting shrinkage may be substantial but is often distributed across cracks. Conversely, a kaolinitic soil with a high PI (like NA0004) may shrink more uniformly, leading to a greater measured linear shrinkage, as its fabric contracts more homogeneously [ 52 ]. The medium-plasticity samples (NA0002, NA0003) show intermediate shrinkage. 3.5.1 Engineering Properties (Atterberg Tests) After the tests were performed, it was observed that the plasticity indexes of all the four clay samples showed that they had the potential of expanding. The plastic index of sample NA0001 which appears to be 57.6 shows that the clays at that particular location have a very high tendency of expanding or have a very high expansion potential(greater than 55) when compared to the standards of Pack et al. [ 65 ]. This means that when the area with these clays gets into contact with water, the clays will experience a high rate of expansion/swelling and then will also experience shrinking when the moisture leaves. The second sample NA0002, had a plasticity index of 27.5 and it can be deduced that the clay soils at the particular location where this sample was picked have medium to high expansion potentials when they are compared to the standards. This means that any form of moisture contact/absorption will cause these clays to experience significant swelling and volume changes. Sample EAM003 had a plasticity index of 20.3 which when compared to the accepted standards, can be said to have a medium expansion potential because it falls between 0–35. This shows that clays at this area have a lesser potential of expanding when they absorb water as compared to clays in the other areas The last sample NA0004 had a plasticity index of 43.2 and this figure falls in the category that shows the expansion potential is high. And from this, it can be deduced that the clays in this particular area where the sample was picked will show high swelling properties when there is a contact with moisture. The case of Sample NA0004 aligns with these contemporary findings. Its high LL (65.8%) and PI (43.2%), contrasted with a kaolinite + quartz XRD signature, strongly suggest the influence of either trace amounts of expansive or active clay minerals below ~ 2–5% XRD detection limits, or a dominant kaolinite fraction of exceptionally fine particle size. The WIP helps explain the swelling potential trend, highlighting the sample with the highest swell potential (NA0001) does not have the lowest WIP. Its intermediate weathering index reflects the unique geochemical conditions that preserved expansive minerals. The most weathered sample (NA0002) has a low WIP and correspondingly lower plasticity (PI = 27.5), reflecting a more stable, kaolinite-rich end product. The least weathered sample (NA0003) has a high WIP but low swell potential because its primary mineral (anorthite) is non-expansive, and its clay fraction is kaolinitic. 4 CONCLUSIONS This integrated study on expansive soils from Navrongo, Upper East Ghana, conclusively demonstrates that swelling potential is not a uniform area characteristic but a spatially variable geotechnical hazard, directly controlled by local variations in mineralogy and geochemistry. The main finding is that, the pronounced swelling behaviour is dominantly driven by the presence of smectite-group clay minerals, even in minor quantities, within a generally kaolinitic and quartzose soil matrix. The mineralogical (XRD) analysis established the foundational soil composition, revealing a prevalent kaolinite-quartz assemblage which indicates advanced tropical weathering. The single exception was Sample NA0001, where the identification of sodium-rich montmorillonite signaled a high-risk zone. The geochemical data provided the explanatory context for this anomaly, showing that NA0001 was uniquely enriched in iron (Fe 2 O 3 ) and magnesium (MgO), essential structural cations for smectite formation, thereby linking the soil geochemistry to the formation of expansive minerals. The geotechnical index testing quantitatively validated the engineering implications of the mineralogical composition. The Atterberg limits classified NA0001 with a Plasticity Index (PI) of 57.6%, corresponding to a very high expansion potential per established classification systems [ 65 ]. This extreme plasticity is interpreted as a direct behavioural consequence of the smectite content. The other samples exhibited lower, yet variable, plasticity (PI 20.3–43.2%), which is consistent with their kaolinitic dominated mineralogy, though high PI of sample NA0004 suggests possible undetected active clay or nano-clay particle effects. The datasets reveal a definitive causal chain, specific to local geochemical conditions (retention of Fe and Mg) permit the formation and stability of expansive clay minerals (smectite), which then dictate high-index properties (LL, PI), ultimately manifesting as severe volumetric instability. Furthermore, the case of NA0004 highlights the limitation of relying on any single analytical method; index properties can reveal high clay activity where standard XRD may not detect low concentrations of expansive or poorly crystalline phases. Therefore, for resilient infrastructure development in Navrongo and similar surrounding areas, site investigation must move beyond conventional classification. The Weathering Index of Parker provided a consistent geochemical framework that integrates and validates the mineralogical and geotechnical findings. It confirms the overall weathered nature of the soils and explains the variability in swelling behavior. The high-swelling hazard in Navrongo is not associated with the most intensely weathered material but with pockets of intermediately weathered soil where geochemical conditions (evident in the WIP and Fe/Mg enrichment) favored the formation and preservation of expansive smectite clays. This underscores the necessity of understanding the weathering pathway and local geochemical history to accurately predict geotechnical hazards in tropical soils. A multi-faceted protocol is recommended; the use of Atterberg limits (especially PI > 35%) and free swell tests as initial hazard indicators. Employ XRD on samples showing high plasticity to confirm the presence and type of expansive clays (e.g., smectite). Where discrepancies arise (e.g., high PI without clear smectite in XRD), integrate Cation Exchange Capacity (CEC) and methylene blue value (MBV) tests to quantify clay activity and detect amorphous or poorly crystalline phases. Finally, there is the need to recognise the high spatial variability and plan investigations to identify isolated high-risk smectitic pockets. Declarations Funding statement No funding was received to assist with the preparation of this manuscript. Author contributions statement E. E. B. Conceptualization, methodology, investigation, data curation, formal analysis, writing original draft and visualization. A. A. D. formal analysis; review and editing; P. A. A. writing of original draft, review, and editing. A. N. writing, review and editing of manuscript; C. K. K. writing, review and editing of original manuscript Corresponding author Correspondence to Eric Enzula Bayari Ethics Declarations Ethics approval and consent to participate Not Applicable Consent for publication Not applicable. Competing interests The authors declare no competing interests. Dual publication Not Applicable Availability of data and material The datasets used and/or analysed during this study are available from the corresponding author on reasonable request. Acknowledgement We acknowledge the overall support of the staff of the School of Physical Sciences. 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1","display":"","copyAsset":false,"role":"figure","size":842497,"visible":true,"origin":"","legend":"\u003cp\u003eAerial map showing the location of samples\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8408259/v1/77a0b16b6fe638afbb125267.png"},{"id":99793187,"identity":"7b0c7f6a-919d-48d2-bc86-30a28786f934","added_by":"auto","created_at":"2026-01-08 13:31:09","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":383989,"visible":true,"origin":"","legend":"\u003cp\u003eGeological map of Navrongo and surrounding areas\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8408259/v1/6351491489934c732d2a894c.png"},{"id":99793966,"identity":"91c25ad5-e828-4c2a-9807-9d951899ac31","added_by":"auto","created_at":"2026-01-08 13:33:38","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":711021,"visible":true,"origin":"","legend":"\u003cp\u003ePhotographs of structural cracks (a) crack on the ground (b) crack on a newly plastered building (c) crack in a local mud house (d) crack on the wall into a tiled base (e) crack inside a room wall\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8408259/v1/0c3c3d3bbabebd91f9d7047b.png"},{"id":99793015,"identity":"8435c9eb-c23f-4015-9fc3-d107b8d12096","added_by":"auto","created_at":"2026-01-08 13:30:49","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":589037,"visible":true,"origin":"","legend":"\u003cp\u003eClay (expansive soil) samples collected in sample bag (a) sample NA0001 (b) sample NA002 (c) sample NA0003 (d) sample NA0004\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8408259/v1/3693c1079a81d1e296c62bcc.png"},{"id":99606246,"identity":"62db336d-389d-439f-8a07-b0f9d2892cd3","added_by":"auto","created_at":"2026-01-06 11:28:34","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":690725,"visible":true,"origin":"","legend":"\u003cp\u003eSample preparation (a) crushing using mortar and pestle in the laboratory (b) sieved for very fine particles of the clay using a 0.425 mm sieve (No.40).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8408259/v1/9e7b09dcf352e039c82eae86.png"},{"id":99793892,"identity":"f81f2095-39f6-4f19-a368-4892f15f7eda","added_by":"auto","created_at":"2026-01-08 13:33:26","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":738105,"visible":true,"origin":"","legend":"\u003cp\u003ePlastic limit testing (a) sample shaped into a ball (b) Oven-drying of plastic limit samples.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8408259/v1/424d914d6ac6addb6396bb9e.png"},{"id":99606252,"identity":"e634c691-0ec3-4a2c-b70c-d3571c41a771","added_by":"auto","created_at":"2026-01-06 11:28:34","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":615243,"visible":true,"origin":"","legend":"\u003cp\u003eVertical section of the soil profile showing the regolith characteristics in the study area\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8408259/v1/05eb468bcdfd876b3a932c0f.png"},{"id":99793672,"identity":"ac7becf6-78b1-45a7-afca-4ee329ccf376","added_by":"auto","created_at":"2026-01-08 13:32:08","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":83863,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of sample NA0001\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-8408259/v1/7023cc8203249c4b624a063d.png"},{"id":99792839,"identity":"bca21b55-a411-4249-9d0e-0b8356f68928","added_by":"auto","created_at":"2026-01-08 13:26:51","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":65886,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of NA0002\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-8408259/v1/5ea42c239424c147b707382f.png"},{"id":99606256,"identity":"9d20fab1-8790-4da5-951e-27dde5e01883","added_by":"auto","created_at":"2026-01-06 11:28:34","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":89155,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of NA0003\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-8408259/v1/f281f8f8b01a7b8c591bc6aa.png"},{"id":99792730,"identity":"236784ca-a7f6-4330-beb6-994f9a01bb4d","added_by":"auto","created_at":"2026-01-08 13:25:26","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":60193,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of NA0004\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-8408259/v1/b236c06a8ea5d22aaba0586c.png"},{"id":100356161,"identity":"4701af59-4887-4551-9c5c-7bfdcdbe2522","added_by":"auto","created_at":"2026-01-16 06:54:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6907859,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8408259/v1/70651717-0202-478c-9675-a6dd4de2cb51.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Mineralogical and Geochemical Control on Swelling Behaviour of Expansive Soils in Navrongo, Ghana","fulltext":[{"header":"1 INTRODUCTION","content":"\u003cp\u003eExpansive soils, which are a significant geotechnical challenge characterised by pronounced volume changes in response to moisture fluctuations, are found extensively in tropical and semi-arid regions worldwide. Their impact on construction is particularly acute and is a global problem. The distribution of these problematic soils appears to be widening with increased construction activity, especially in developing nations, where infrastructure expansion encounters previously uncharacterised deposits. This volumetric instability is fundamentally attributed to the presence of active clay minerals, such as 2:1 smectite (especially montmorillonite), which have a pronounced capacity to absorb water into their interlayer spaces, leading to swelling during wet periods and subsequent shrinkage upon drying [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Therefore, such soils, which usually contain more than 30% of 2:1 expanding type of the smectitic clay, are referred to as expansive soils. A soil is commonly considered to have expansive tendencies when the liquid limit is greater than 53% and the plasticity index is greater than 25% [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Osman [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] alternatively refers to these soils as shrink-swell soils. When they are dried, they shrink so greatly that they cause wide and deep cracks on the surface to depths often extending more than a meter downward [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. These soils are referred to as deeply and widely cracking soils or simply cracking soils. They occur at a minimum depth of 50 cm, and in most cases, their engineering behavior depends mainly on the physicochemical characteristics of the clay component within the regolith.\u003c/p\u003e \u003cp\u003eThese expansive soils have been noted to pose a significant and widespread geotechnical challenge to civil infrastructure globally, with annual costs estimated in the billions of dollars, often exceeding the damage caused by natural disasters like earthquakes and floods [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] The primary mechanism of damage stems from the soil's volumetric changes, the swelling-shrinking effect, which exert substantial pressures on overlying structures. This phenomenon severely impacts building foundations, particularly those of lightweight residential and commercial buildings, where differential heave can lead to cracking in slabs-on-grade, walls, and in structural frames. Similarly, pavement systems, including roads and runways, are highly vulnerable; the uneven movement of the subgrade soil causes cracking, roughness, and premature failure of the asphalt or concrete surface, leading to increased maintenance costs and reduced service life [\u003cspan additionalcitationids=\"CR8 CR9 CR10 CR11 CR12\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The detrimental effects extend to linear infrastructure, where buried pipelines are at a high risk of failure owing to the cyclic forces imposed by moving soil. This can result in joint breaks, leaks, and costly service interruptions [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSignificant effects have been reported in arid, semi-arid, and seasonally wet climates on all inhabited continents, including the United States, Canada, China, India, Australia, and a significant portion of Africa[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Expansive soils are a crucial factor in the creation of sustainable infrastructure globally because of their ubiquitous character, which calls for specialised and frequently expensive site study, design modifications, and soil stabilisation measures [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Heaving foundation issues are common in semi-arid and dry sub-humid regions of Africa and in many other parts of the world. This is because long stretches of dryness and heavy seasonal rainfall cause soils to alternate between desiccation and saturation [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe expansiveness of the expansive soils is fundamentally controlled by a geochemical and mineralogical property, primarily driven by the presence and activity of the hydrophilic mineral montmorillonite and other mixed clay, with montmorillonite being the most prevalent and influential species [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The exceptional swelling capacity of smectite originates from its unique 2:1 layered silicate structure, which consists of an alumina octahedral sheet sandwiched between two silica tetrahedral sheets. Crucially, isomorphous substitution, where atoms within the crystal lattice (e.g., Al\u003csup\u003e3+\u003c/sup\u003e for Si\u003csup\u003e4+\u003c/sup\u003e in the tetrahedral sheet or Mg\u003csup\u003e2+\u003c/sup\u003e for Al\u003csup\u003e3+\u003c/sup\u003e in the octahedral sheet) create a permanent negative charge, occurs. This charge is balanced by the adsorption of exchangeable cations (e.g., Na\u003csup\u003e+\u003c/sup\u003e and Ca\u003csup\u003e2+\u003c/sup\u003e) and water molecules into the interlayer space between adjacent layers. It is this interlayer space that acts as the engine for expansion, as water molecules are strongly attracted to the charged mineral surfaces and to the hydrated cations, forcing the layers apart [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe intensity of this swelling is governed by the specific type of exchangeable cation and available soil moisture. For instance, sodium-saturated montmorillonite (Na-montmorillonite) can exhibit virtually unlimited interlayer expansion, absorbing water to several times its original volume, whereas calcium-saturated varieties (Ca-montmorillonite) exhibit more limited swell due to stronger electrostatic bonds [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Upon wetting, water is drawn into the interlayers through osmosis and strong surface adsorption, generating immense swelling pressures that can exceed 1 MPa, sufficient to lift heavy structures and causing cracks that may sometimes extend to a depth of 0.5 m below the surface and can be 5 to 20 mm wide [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Conversely, during drying, the loss of interlayer water causes the crystals to contract, leading to soil shrinkage and desiccation cracks. This reversible shrink-swell cycle, dictated by the mineral's response to environmental changes, is the direct cause of the severe distress observed in overlying foundations, pavements, and pipelines [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eStructures constructed on such soils are subjected to uplift forces due to the swelling and shrinking characteristics [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Generally, light structures, particularly low-cost houses, have lightly loaded foundations typical of residential construction, and these safer differential heaves impose severe tensile and shear stresses on masonry and concrete, which are weak in resisting such forces, resulting in characteristic diagonal cracking in walls, jamming of doors and windows, and tilting of entire structures. This problem is often exacerbated by the common practice of constructing without a properly engineered, moisture-controlled, and compacted fill material, placing the foundation directly on the active, natural soil.\u003c/p\u003e \u003cp\u003eIn the developing world context such as in Navrongo in the Upper East Region of Ghana, where Bayari et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], made reports on x-ray diffraction showing a strong montmorillonite mineral phase in some residual clay deposits in Navrongo the impact of this phenomenon of expansive soils is magnified by a confluence of socio-economic and technical factors. The high cost and limited availability of professional geotechnical services imply that most light buildings are erected without prior site investigation or appropriately engineered foundations, leaving homeowners unaware of the risk until damage manifests. Furthermore, a lack of robust building codes, enforcement, and awareness among informal builders leads to construction practices that inadvertently worsen the situation, such as the use of moisture-susceptible shallow strip footings and poor site drainage. When cracks appear, residents often resort to temporary cosmetic repairs that fail to address the underlying soil issue, initiating a destructive cycle of recurring damage. This not only depletes the limited financial resources of families but also perpetuates a state of unsafe housing and undermines long-term sustainable development, as the very fabric of the built environment remains chronically vulnerable to a predictable and manageable geotechnical hazard [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDespite the perceived challenges and anecdotal evidence, a comprehensive, multi-faceted study linking mineralogy and geochemistry to the geotechnical properties of these soils in Navrongo is lacking. Identified studies in Ghana on expansive soils have mainly focused on other regions (e.g., the Accra Plains or Kumasi) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], leaving a knowledge gap for the Upper East Region. Reliance solely on basic geotechnical tests (e.g., Atterberg Limits) without corroboration with mineralogical data can lead to an incomplete understanding and misdiagnosis of the soil's expansive potential. This gap hinders effective land-use planning, safe construction practices, and the development of appropriate soil-stabilization techniques in the region. Therefore, this study seeks to provide a comprehensive characterization of the perceived expansive soils in Navrongo through an integrated mineralogical, geochemical, and geotechnical approach to determine their true expansive nature and potential engineering implications.\u003c/p\u003e \u003cp\u003eThe findings will provide a scientific database for engineers, urban planners, and developers working in the Navrongo area and the broader Upper East Region of Ghana. This integrated methodology can serve as a model for assessing problematic soils in other parts of Ghana with similar geological settings. The results will inform the development of appropriate foundation design and soil stabilization strategies, thereby enhancing the durability and safety of infrastructure.\u003c/p\u003e"},{"header":"2 MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1 Study area\u003c/h2\u003e\n \u003cdiv id=\"Sec4\" class=\"Section3\"\u003e\n \u003ch2\u003e2.1.1 Location, climate, relief, drainage, and vegetation\u003c/h2\u003e\n \u003cp\u003eThe study area, Navrongo, is a strategically important town and the administrative capital of the Kassena-Nankana Municipal District in the Upper East Region of Ghana. The Ghana Statistical Service[\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e] estimates that, approximately 99,895 people reside in the Kasena Nankana Municipal and the majority are subsistence farmers. Its geographical characteristics are typical of the broader Sudan-Savanna zone of West Africa, shaping the livelihoods and socio-economic activities of its predominantly agrarian population.\u003c/p\u003e\n \u003cp\u003eNavrongo is situated in the northeastern corner of Ghana, close to the international border with Burkina Faso. Its precise coordinates are approximately 10\u0026deg; 53\u0026apos; 0\u0026quot; North latitude and 1\u0026deg; 5\u0026apos; 0\u0026quot; West longitude and is 30km North-West of Bolgatanga the Upper East Regional capital. This location places it within the Guinea Savanna agro-ecological zone [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. The town serves as a major nodal point for trade and commerce in the region, linking Ghana to its Sahelian neighbors. Its position within the municipal makes it a central hub for administrative, educational, and health services for the surrounding rural settlements. Navrongo experiences a tropical continental (Sudanian) climate characterized by a pronounced unimodal rainfall pattern and high temperatures throughout the year. The climate is distinctly divided into two seasons: The Rainy Season, a single, intense wet season, lasts from approximately May to October, with its peak in August. The total mean annual rainfall is relatively low, ranging between 800 mm and 1,100 mm. and is highly erratic, both in terms of onset, duration, and intensity, making rain-fed agriculture a risky venture [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]. Intense storms often lead to high runoff and soil erosion rather than effective water infiltration [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]. From November to April, the region experiences a prolonged and severe dry season. This period is dominated by the dry and dusty Harmattan wind, which blows from the Sahara Desert. Humidity drops significantly, and temperatures can be very high during the day, often reaching 46\u0026deg;C, with monthly average temperatures ranging between 18\u0026deg;C and 45\u0026deg;C. The desiccating effect of the Harmattan further stresses the land, vegetation and leads to severe water scarcity [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eThe relief of the Navrongo area (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) is generally flat to gently undulating, with an average elevation of around 200 meters above sea level [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. The landscape is part of the vast Voltaian Basin, which is composed of ancient sedimentary rock. The topography is characterized by monotonous plains with occasional low-lying hills and inselbergs. While the overall relief is low, the gentle slopes are significant for surface hydrology, facilitating the rapid runoff of rainwater and contributing to the high erosion potential noted in the area[\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]. The land is suitable for mechanized agriculture, but its flatness can lead to seasonal waterlogging in depressions.\u003c/p\u003e\n \u003cp\u003eThe drainage system in Navrongo is part of the Volta River Basin, drained by several seasonal streams and rivers, which are tributaries of the White Volta [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]. A defining feature of the drainage is the seasonality; rivers and streams flow only during and immediately after the rainy season, becoming completely dry or reduced to a series of stagnant pools for the rest of the year [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]. This temporal variability poses a major challenge for water supply, especially during the long dry season, and ultimately causes deep, wide cracks, sometimes several centimeters wide and over a meter deep. These cracks act as direct conduits, channelling moisture from deeper in the soil profile to the surface, where it is lost to the atmosphere.\u003c/p\u003e\n \u003cp\u003eNavrongo falls within the Guinea Savanna woodland ecological zone, more specifically classified as the Sudanian Savanna [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e]. The natural vegetation is a mosaic of grassland, dominated by tough, tussock-forming grasses that can withstand the long dry season and periodic wildfires. Scattered drought-resistant tree cover is open and consists of species adapted to moisture stress, such as Baobab (Adansonia digitata), Shea tree (Vitellaria paradoxa), and Acacia species (Acacia spp.). These trees are often stunted and have deep root systems or other xerophytic adaptations. However, natural vegetation has been significantly altered by prolonged human activity, including farming, fuelwood collection, and charcoal production. This has resulted in widespread land degradation and a reduction in biodiversity [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e]. The landscape is now predominantly a cultivated savanna with small, scattered patches of protected woodland around sacred groves and settlements. The combined pressures of climate variability and anthropogenic activities continue to threaten the fragile vegetation cover in the area.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\n \u003ch2\u003e2.1.2 Geology\u003c/h2\u003e\n \u003cp\u003eFrom the perspective of the regional geology of Ghana, the geology of the study area (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) falls within the eastern volcanic belt, a segment of the larger Bole-Nangodi greenstone belt, and a fairly complete succession of Paleoprotorozoic Birimian rocks exists in this area. It is characterized by a series of NEE to NE-trending structural zones dominated by metavolcanic and metasedimentary rocks intruded by various granitoid [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e]. As noted by Melcher[\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e] and Attoh[\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e] the basement is underlain by Birimian granitoids interspersed with minor pyroclastic and volcaniclastic rocks. Metavolcanic rocks are a significant component of the area and are primarily basaltic to andesitic in composition. They have been metamorphosed to greenschist facies, resulting in mineral assemblages dominated by chlorite, actinolite, and epidote [\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e]. The presence of pyroclastic and volcaniclastic rocks indicates explosive volcanic activity and reworking of volcanic material, suggesting a complex volcanic-arc environment. Granitoid Intrusives are predominantly diorites to tonalites and granodiorites, which represent the plutonic roots of the Birimian volcanic arc system [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]. These intrusions are typically syn-to late-tectonic relative to the main Birimian deformation.\u003c/p\u003e\n \u003cp\u003eNavrongo lies on the Bole-Navrongo structural zone, this zone is defined by a network of major, crustal-scale shear zones with a dominant NE-SW trend, consistent with the regional structural grain of the Birimian [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]. These shear zones are deep-seated structures that act as conduits for hydrothermal fluids. Geology directly controls the nature of the overlying soils. The deep chemical weathering of these Birimian rocks; particularly the ferromagnesian-rich metavolcanics and the potassic feldspars within the granitoids produces a clay-rich soil mantle [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e]. The mineralogy of the parent rock is crucial; the weathering of mafic volcanic rocks can lead to the formation of smectite clays, which are highly expansive, while the weathering of granitoids typically yields kaolinite and illite [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e]. The complex intercalation of different rock types means that soil properties can vary significantly over short distances. The NE-SW structural trends can also influence drainage patterns and groundwater flow, which in turn affects the moisture content and swell-shrink potential of soils derived from this bedrock. According to Foli et al. [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e], the ochrosols are made up of shallow to deep soils, that have features of gravels and concretions and they overlie weathered granitic rocks. The ochrosols are usually hydromorphic in nature, well-drained, and have very high clay content, usually black or dark-grey clayey soils that are very suitable for cultivation because of the soil\u0026rsquo;s arability. The soil found in the study area is savannah ochrosols, which are porous, well-drained, loamy, mildly acidic, and interspersed with patches of dark-grey or black clay soils and groundwater laterites, which are developed mainly over shale and granite.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2 Subsurface Profile\u003c/h2\u003e\n \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n \u003ch2\u003e2.2.1 Pitting\u003c/h2\u003e\n \u003cp\u003eTo enable the visual examination of the subsurface material conditions, a suitable site was identified through an initial assessment of areas with low-lying or depositional areas, a cover of transported overburden forming the direct parent material of the soil, visible surficial cracks (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea), and structural failures such as cracks (Fig. (b-e) were identified. The depth of the regolith, a key indicator of the potential depth of clay-rich, expansive materials, was pitted to obtain information regarding the subsurface in-situ soil conditions and formations.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3 Sample Material Collection and Preparation\u003c/h2\u003e\n \u003cp\u003eFor this experimental study, material (expansive soil) was collected from four sites, NA0001, NA0002, NA0003, and NA0004 (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e(a-d)). The exact locations of these sites are shown in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The individual samples were freed of stones and other unimportant things, such as dead plant roots. Some of the clay materials were slightly bulky; therefore, they were broken down into smaller pieces before placing them in zip-lock bags and labeling them, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea-d. The samples were air-dried for approximately 24 h and crushed into powder using a pestle and mortar at the Center for Scientific and Industrial Research (CSIR), Fumesua-Kumasi (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea). They were then sieved for very fine particles of the clay using the 0.425mm sieve (No.40) (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e2.4 Mineralogical and Geochemical analysis\u003c/h2\u003e\n \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n \u003ch2\u003e2.4.1 X-Ray Diffraction (XRD)\u003c/h2\u003e\n \u003cp\u003eX-ray Powder Diffraction (XRD) analysis was used to test the mineralogical characteristics of the rock and soil samples. XRD is a technique that is widely used for identifying minerals and therefore will be very relevant in finding traces of montmorillonitic or other expansive clay minerals in the samples. This type of analysis is used because the minerals will diffract a beam of incident x-rays and this diffraction pattern actually differentiates each mineral species based on their properties [\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e]. XRD analysis was performed using X-ray Diffractometers. The samples were sent to the Department of Physics, University of Ghana, for preparation and analysis. The analysis was performed using an EMPYREAN diffractometer system.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\n \u003ch2\u003e2.4.2 Geochemical analysis\u003c/h2\u003e\n \u003cp\u003eAll samples were analyzed for major and minor elements using an XRF spectrometer at the Geological Survey Authority (GSA) in Accra, Ghana. An X-ray Fluorescence Spectrometer-XRF (Model: VMR) from Olympus (Model: Adventurer-Pro AV 264), Mill/Mixture (Model: MM301), hydraulic press (Model: Specac), and sieve were used to carry out the final selected samples that showed variation in their texture and mineralogical composition.\u003c/p\u003e\n \u003cp\u003eThe samples were sieved using a sieve with a size of 75 \u0026micro;m. For each analysis, 5.0 g of the sieved sample was well mixed and homogenized with 0.9 g of a binder (Hoechst Wax) in a mill and pressed with 15 tons to a 32 mm pellet. Multi-element determinations from the prepared pellets were carried out using an energy-dispersive polarizing X-ray fluorescence (XRF) spectrometer ( VMR Vanta M Series) with a tube rating of 50 kV and 0.2 mA. The analytical quality was assessed by inserting quality control and assurance samples SRM 2711a from NIST and OxG180 from Rocklabs, respectively. The laboratory temperature was maintained at 20\u0026deg;C during the analysis.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\n \u003ch2\u003e2.4.3 Weathering Intensity assessment\u003c/h2\u003e\n \u003cp\u003eThe engineering behaviour of rock materials depends not only on the stress state and stress history but also on the physical, mineralogical, and chemical changes in the rock materials due to weathering. Weathering indices are used to define these changes and quantify the engineering properties of regolith. Several weathering indices have been devised to quantify changes in the intrinsic properties of rocks from different perspectives, some of which can be related to the engineering properties of weathered rocks. The most commonly used methods can be broadly categorized as chemical, mineralogical-petrographical, petro-chemical, and engineering indices. The Weathering Index of Parker also known as Parker\u0026rsquo;s index [\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e] was applied to assess the degree of the decomposition of the regolith material that constitutes the expansive soil (clay) using Eq.\u0026nbsp;1. This weathering index among others is most appropriate application to weathering profile on heterogeneous (and homogeneous) parent rocks on the collective decomposition of multiple mineral phases [\u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eWIP = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left[\\right(\\frac{Na}{0.35}\\:+\\frac{Mg}{0.9})\\:+(\\frac{K}{0.25}\\:+\\:\\frac{Ca}{0.7}\\left)\\right]\\:\\times\\:\\:100\\)\u003c/span\u003e\u003c/span\u003e Eq. 1\u003c/p\u003e\u003cspan\u003e\n \u003ch3\u003e\u003cstrong\u003e2.5 Index Properties\u003c/strong\u003e\u003c/h3\u003e\u003cspan\u003e\n \u003ch3\u003e\u003cstrong\u003e2.5.1 Atterberg Tests\u003c/strong\u003e\u003c/h3\u003e\n \u003c/span\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003c/span\u003e\n \u003cp\u003eThe Atterberg limits, comprising the liquid limit (w\u003csub\u003eL\u003c/sub\u003e), plastic limit (w\u003csub\u003eP\u003c/sub\u003e), and shrinkage limit (w\u003csub\u003eS\u003c/sub\u003e), are fundamental indices that define the moisture content ranges at which fine-grained soil transitions between distinct consistency states (liquid, plastic, and semisolid). These tests, performed in accordance with ASTM D4318 [\u003cspan class=\"CitationRef\"\u003e43\u003c/span\u003e], were conducted on the fraction of each soil sample passing a No. 40 sieve (0.425 mm aperture). Standard apparatus was employed for the determinations, including a porcelain mortar and pestle for sample preparation, evaporating dishes and spatulas for mixing and specimen molding, a thermostatically controlled drying oven maintained at 105\u0026deg;C, and a digital analytical balance for mass measurements.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\n \u003ch2\u003e2.5.2 Liquid Limit Test\u003c/h2\u003e\n \u003cp\u003eThe liquid limit (w\u003csub\u003eL\u003c/sub\u003e) was determined using the Casagrande percussion cup method, conforming to the standard procedure outlined in ASTM D4318 [\u003cspan class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e]. The primary apparatus consisted of a mechanical Casagrande device, standardized grooving tool, flat mixing board, and spatulas. The test procedure involved thoroughly mixing a portion of the prepared soil sample with distilled water to form a homogeneous paste. This paste was then placed in the brass cup of the liquid-limit device and levelled. A groove was cut through the soil pat along its centerline using a Casagrande grooving tool. The handle was then turned at a rate of approximately two blows per second, causing the cup to lift and drop repeatedly. The liquid limit was defined as the moisture content (determined gravimetrically) at which the two halves of the soil pat came into contact along the bottom of the groove for a distance of 0.5 inches (approximately 13 mm) after 25 blows. This test was repeated at varying moisture contents to obtain between three and five trials with blow counts of 25, enabling the derivation of the liquid limit from the plotted flow curve using Eq.\u0026nbsp;(2).\u003c/p\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:{{w}_{L}={w}_{N}\\left(\\frac{N}{25}\\right)}^{tan\\beta\\:}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e Eq.\u0026nbsp;2\u003c/p\u003e\u003cp\u003ewhere w\u003csub\u003e\u003cstrong\u003eL\u003c/strong\u003e\u003c/sub\u003e is the Liquid Limit (%), w\u003csub\u003eN\u003c/sub\u003e is the measured moisture content at N blows (%), N\u0026thinsp;=\u0026thinsp;Number of blows (25), and tan \u0026beta; is the slope of the flow line. The standard allows the use of an approximation factor (k). For many soils, especially clays, a standard slope corresponding to k\u0026thinsp;\u003cstrong\u003e=\u003c/strong\u003e\u0026thinsp;0.121 is used.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\u003ch2\u003e2.5.3 Plastic Limit Test\u003c/h2\u003e\u003cp\u003eThe plastic limit (w\u003csub\u003ep\u003c/sub\u003e) was determined in accordance with standard geotechnical procedures [\u003cspan class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e]. For each sample, a portion of the moist soil was shaped into a ball and repeatedly rolled on a glass plate to form a uniform thread of approximately 3 mm diameter (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea). The plastic limit was defined as the moisture content at which the thread crumbled and could no longer be rolled to the full 3 mm diameter without breaking apart. This procedure was replicated to obtain multiple subsamples. The moisture content was calculated gravimetrically from the mass loss upon oven-drying at 105\u0026deg;C to constant weight (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eb). using Eq.\u0026nbsp;3, the plastic limit values were determined.\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:{M}_{c}=\\frac{{W}_{a}-\\:{W}_{b}}{{W}_{b}-{W}_{c}}\\times\\:100\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e Eq. 3\u003c/p\u003e\n \u003cp\u003eWhere, M\u003csub\u003ec\u003c/sub\u003e is the moisture content, W\u003csub\u003ea\u003c/sub\u003e is mass of container and wet material (g).W\u003csub\u003eb\u003c/sub\u003e is mass of container and dry material (g), W\u003csub\u003ec\u003c/sub\u003e is container only (g).\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\n \u003ch2\u003e2.5.4 Plasticity Index\u003c/h2\u003e\n \u003cp\u003eThe plasticity index (PI) is a fundamental engineering parameter calculated as the numerical difference between the liquid limit and the plastic limit. It represents the range of moisture content over which the soil exhibits plastic behaviour. A higher PI generally indicates a greater proportion of active clay minerals and a greater potential for volume change and compressibility. This index (Eq.\u0026nbsp;4) is critical for soil classification systems, such as the Unified Soil Classification System (USCS) and AASHTO system [\u003cspan class=\"CitationRef\"\u003e45\u003c/span\u003e], and serves as a key indicator of potential expansiveness in fine-grained soils.\u003c/p\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:PI\\:=\\:wₗ\\:-\\:wₚ\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e Eq.\u0026nbsp;4\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\n \u003ch2\u003e2.5.5 Shrinkage Limit Test\u003c/h2\u003e\n \u003cp\u003eThe shrinkage limit (W\u003csub\u003eS\u003c/sub\u003e) was determined following ASTM D4943 [\u003cspan class=\"CitationRef\"\u003e46\u003c/span\u003e]. A standardized shrinkage dish, lightly coated on the interior with petroleum oil to prevent adhesion, was used. A portion of the wet soil paste was consolidated into the dish in layers using a spatula and a glass plate to eliminate air voids and ensure full saturation. The mass of the dish containing the wet soil was recorded. The sample was subsequently oven-dried at 105\u0026deg;C to a constant mass. The volumetric displacement of the oven-dried soil cake was measured via the water displacement method. The shrinkage limit was then calculated using Eq.\u0026nbsp;5 by recording the masses and volumes to determine the moisture content at which further drying does not cause additional volumetric reduction.\u003c/p\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{w}\\text{s}=\\text{w}\\text{i}-\\frac{\\left(\\text{V}\\text{i}-\\text{V}\\text{f}\\right){\\rho\\:}\\text{w}}{\\text{m}\\text{s}}\\times\\:100\\text{%}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e Eq. 5\u003c/p\u003e\u003cp\u003eWhere: wₛ = Shrinkage Limit (%), w\u003csub\u003ei\u003c/sub\u003e = Initial Moisture Content of the wet soil pat (%), V\u003csub\u003ei\u003c/sub\u003e = Initial Volume of the wet soil pat (cm\u0026sup3;), V\u003csub\u003ef\u003c/sub\u003e = Final Volume of the oven-dried soil pat (cm\u0026sup3;), \u0026rho;w\u0026thinsp;=\u0026thinsp;Density of water (\u0026asymp;\u0026thinsp;1 g/cm\u0026sup3;), m\u003csub\u003es\u003c/sub\u003e = Mass of the oven-dried soil solids (g).\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"3 RESULTS AND DISCUSSIONS","content":"\u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003cdiv class=\"Heading\"\u003e3.1.1 Regolith Profile Description\u003c/div\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e presents a schematic regolith profile typical of tropical basement complex terrains, such as that found in Navrongo. This profile provides the essential genetic and stratigraphic context for understanding the formation and distribution of the expansive soils characterized in this study [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe profile is structured sequentially from the soil and duricrust horizon (0.00m \u0026ndash; 0.85m), this uppermost zone comprises two sub-layers. The Clayey Sand Soil topsoil is a transported and bioturbated mixture of clay minerals and sand-sized particles, representing the immediate geotechnical material sampled in this study. Underlying it, the Clayey Lateritic Gravel/Duricrust is an indurated layer enriched in iron and aluminum oxides, forming a relatively impermeable capstone characteristic of advanced laterization [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. Transitional Weathering Zone (1.85m \u0026ndash; 3.70m) directly beneath the duricrust lies the Mottled/Arenose Zone (Clav Zone). This horizon is defined by its mottled coloration, resulting from the irregular leaching and precipitation of iron. It is a zone of active in-situ chemical weathering and neoformation of clay minerals, where bedrock is transformed into a porous matrix of clay and sand [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. Weathered Bedrock (below 3.70m) forms the base of the profile and consists of the Saprock/Gruss, comprising physically disintegrated but chemically less-altered bedrock. This friable material, which retains the original rock structure, represents the initial weathering stage and the parent material for the overlying horizons.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e3.2 XRD Analysis\u003c/h2\u003e \u003cp\u003eBased on the provided mineralogical data for samples from Navrongo, Upper East Ghana (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e). The identified minerals (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) point to a complex soil system where swelling potential is not dominated by a single, highly expansive clay but is influenced by a mixture where even minor phases can have significant geotechnical implications. All four samples contain Aluminum Silicate Hydroxide (Kaolinite, Al\u003csub\u003e2\u003c/sub\u003eSi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e(OH)\u003csub\u003e4\u003c/sub\u003e). Kaolinite is a 1:1 layered clay mineral with strong hydrogen bonding between layers, resulting in a non-expansive nature and low cation exchange capacity (CEC) [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. Its prevalence, especially in samples NA0001, NA0002, and NA0004, suggests these soils likely have a generally low to moderate inherent swelling capacity. The formation of kaolinite is typical in intensely weathered tropical environments with good drainage and leaching conditions, which aligns with the weathering profiles common in West Africa [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. Its presence provides a stable, relatively inert matrix. Silicon Oxide (Quartz, SiO\u003csub\u003e2\u003c/sub\u003e) is present in every sample. Quartz is a framework silicate, mechanically stable and non-reactive. Its primary role is as a diluent, reducing the overall proportion of clay-sized particles and active minerals that contribute to swelling [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. A high quartz content typically correlates with lower plasticity and swell potential. Its ubiquity indicates these soils contain a significant silt or fine sand fraction [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The most mineralogically significant finding for understanding potential expansiveness is in sample NA0001, which contains Sodium Iron Silicate Hydroxide Hydrate (montmorillonite/bentonite). Montmorillonite is a smectite-group mineral, a 2:1 expandable clay with a very high CEC and specific surface area. Interlayer cations (like Na\u003csup\u003e+\u003c/sup\u003e here) and water molecules can cause significant volumetric change (up to 1500%) upon wetting [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. The notation Na\u003csub\u003e0.3\u003c/sub\u003e suggests a sodium-rich variety (Na-montmorillonite), which is particularly prone to dispersion and severe swelling compared to calcium-saturated varieties [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. Guimar\u0026atilde;es et al. [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e] and Ramana [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e] identified that a small percentage (often as little as 5\u0026ndash;10%) of smectite within a kaolinitic or quartzose matrix can impart significant expansiveness. Its absence from the other three samples highlights the spatial variability of expansive risk.\u003c/p\u003e \u003cp\u003eSample NA0001 also lists anorthite sodian, and NA0003 lists anorthite (Al\u003csub\u003e2\u003c/sub\u003eCaO\u003csub\u003e8\u003c/sub\u003eSi\u003csub\u003e2\u003c/sub\u003e) which is a calcium-rich plagioclase feldspar. Therefore, in this context of tropical soils, feldspars are weatherable primary minerals. Their presence, especially alongside kaolinite and smectite, indicates an incomplete weathering sequence. The weathering of plagioclase is a key source of calcium, sodium, and silica ions in pore water, which influence the geochemical environment controlling clay mineral stability and cation populations on exchange sites [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. The coexistence of a primary mineral (anorthite), a stable secondary mineral (kaolinite), and a highly active secondary mineral (montmorillonite) in NA0001 suggests a geochemically transitional and heterogeneous weathering profile.\u003c/p\u003e \u003cp\u003eThe mineralogical suite dominated by kaolinite and quartz in samples NA0002, NA0003, and NA0004 suggests soils with inherently low swell potential. These would likely exhibit low plasticity and moderate strength, consistent with lateritic or residual soils described in the Basement Complex of Navrongo [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. Sample NA0001 represents a high-risk scenario. Here, the soil matrix, while still containing kaolinite and quartz, is adulterated with sodium montmorillonite. This mineral's overwhelming affinity for water and its sodium-saturated state mean this soil will likely exhibit high swell pressure, high shrinkage limits, and severe volume changes with seasonal moisture fluctuations. The swelling behavior will be disproportionate to its total clay content because the smectite exerts a controlling influence [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eThe occurrence of montmorillonite alongside anorthite and kaolinite may indicate specific the local conditions of perhaps poor drainage, a geochemical barrier (e.g., higher pH or silica activity), or weathering of a more mafic rock source that provides the necessary magnesium and iron. Montmorillonite often forms in less aggressive weathering environments than kaolinite or from the alteration of volcanic ash (bentonite), which could point to localized depositional history [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e].The mineralogical analysis underscores that expansive soils in Navrongo are not ubiquitously hazardous but are spatially variable. The principal risk arises from localized pockets or layers containing smectite (montmorillonite), even as a minor constituent. Standard geotechnical classification (e.g., Atterberg limits) on bulk samples might not fully capture this risk if the smectite is unevenly distributed. Therefore, site investigations in this region should combine routine tests with detailed mineralogical identification (like XRD, as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e,\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e and \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e) and swell-consolidation tests, especially where historical performance indicates distress. The critical finding is that the swelling influence is not from the dominant kaolinite but from the trace, yet potent, expansive clay minerals that may be present.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of the minerals found in all four samples\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample Id\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMineral Identified\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCompound Name\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNA0001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eSi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e(OH)\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003cp\u003eNa\u003csub\u003e0.3\u003c/sub\u003eFe\u003csub\u003e2\u003c/sub\u003eSi\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e10\u003c/sub\u003e (OH)\u003csub\u003e2\u003c/sub\u003e.4H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003cp\u003eAll.55Ca0.55Na0.45O\u003csub\u003e8\u003c/sub\u003eSi2.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAluminum silicate Hydroxide (Kaolinite)\u003c/p\u003e \u003cp\u003eSilicon Oxide\u003c/p\u003e \u003cp\u003eSodium Iron Silicate Hydroxide Hydrate (montmorillonite/bentonite)\u003c/p\u003e \u003cp\u003eAnorthite Sodian\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNA0002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eSi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e(OH)\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSilicon Oxide\u003c/p\u003e \u003cp\u003eAluminum Silicate Hydroxide (kaolinite)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNA0003\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eCalO\u003csub\u003e8\u003c/sub\u003eSi\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSilicon Oxide\u003c/p\u003e \u003cp\u003eAnorthite\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNA0004\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eSi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e(OH)\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSilicon Oxide\u003c/p\u003e \u003cp\u003eAluminum Silicate Hydroxide(kaolinite)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eSilicon oxide is a common compound/mineral that is found in almost all soils and therefore runs through all the clay samples. It can also be seen that kaolinite is a common mineral in the soils in Navrongo since it can be found in all except one of the samples. Other notable minerals that were identified by the XRD analysis are montmorillonite, sodian and anorthite.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Geochemical analysis\u003c/h2\u003e \u003cp\u003eThe obtained geochemical data (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) show that, the major oxide compositions are characteristic of intensely weathered tropical soils derived from parent rocks within the Basement Complex (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), consistent with the regional geology of the study area [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. The high percentages of SiO\u003csub\u003e2\u003c/sub\u003e (48.7\u0026ndash;55.3%) and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (12.5\u0026ndash;19.2%) quantitatively confirm the mineralogical dominance of quartz and kaolinite, respectively, as identified by XRD (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The strong correlation between total silica-alumina and the abundance of these two minerals reflects a geochemical system where mobile cations (Ca\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e) have been extensively leached, a hallmark of laterization in humid tropical climates (Nesbitt and Young, 1982).\u003c/p\u003e \u003cp\u003eSample NA0001, which XRD identified as containing smectite, is geochemically distinct. It exhibits the lowest SiO\u003csub\u003e2\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e ratio and the highest concentrations of Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (8.83%) and MgO (1.57%) among the set. This chemistry is diagnostic of smectites, particularly the iron-magnesium-rich variety suggested by the XRD formula (Na\u003csub\u003e0.3\u003c/sub\u003eFe\u003csub\u003e2\u003c/sub\u003eSi\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e10\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO), require these elements for their 2:1 lattice structure. The elevated Fe and Mg in NA0001 provide the necessary chemical building blocks for smectite stability, likely sourced from the weathering of ferromagnesian minerals in the parent rock [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. In contrast, NA0004, with 0% MgO and lower Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, lacks the chemical prerequisites for smectite formation, explaining its XRD assemblage of only kaolinite and quartz. The low concentrations of base cations (CaO, Na\u003csub\u003e2\u003c/sub\u003eO, K\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;\u0026lt;\u0026thinsp;1.3%) across all samples underscore the advanced weathering stage and explain the general scarcity of primary feldspars, with the minor CaO in NA0003 (0.94%) corresponding to its detected anorthite.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eGeochemical data of sampled clay\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNA0001\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNA0002\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNA0003\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNA0004\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e48.731\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e55.347\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e55.333\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e49.451\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.946\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.803\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.855\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.815\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e19.243\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e16.128\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e12.518\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e18.156\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8.825\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.125\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5.558\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e7.657\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMgO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.567\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.026\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.049\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMnO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.076\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.080\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.072\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.074\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCaO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.492\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.351\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.941\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.299\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.431\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.387\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.501\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.398\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.539\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.508\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.720\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.528\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.010\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.110\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe overall Index of Alteration (IA) for these soils would be very high, approaching that of pure kaolinite, which aligns with the mineralogy. However, the local deviation in NA0001, where the leaching process was perhaps less complete or the parent material more basic, created a microenvironment with sufficient silica, iron, and magnesium activity to facilitate smectite formation instead of, or alongside, kaolinite [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. This directly links geochemistry to the engineering property: the swell potential hazard in Navrongo is spatially coincident with these distinct geochemical anomalies. Therefore, the integration of data confirms that the pronounced swelling in specific locations is not merely a textural accident but is fundamentally governed by a less-advanced local weathering pathway that preserves expandable 2:1 clays, as signalled by enhanced Fe, Mg, and a reduced silica-to-sesquioxide ratio.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Weathering Intensity assessment and engineering implication\u003c/h2\u003e \u003cp\u003eAll WIP values shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e are significantly lower than that of fresh rock (typical values\u0026thinsp;\u0026gt;\u0026thinsp;1000), confirming that all samples are products of substantial chemical weathering, consistent with the tropical climate of the Upper East Region [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eWeathering Index of Parker value describing the intensity of weathering\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNA0001\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNA0002\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNA0003\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNA0004\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWIP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e583\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e478\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e682\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e511\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInterpretation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHighly weathered\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHighly weathered\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMost weathered\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eHighly weathered\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe range of values (478 to 682) reveals important variability in weathering intensity across the site. Sample NA0003 has the highest WIP (682), indicating it is the least chemically weathered of the set. This aligns perfectly with its mineralogy, which included primary anorthite (a calcium feldspar) alongside kaolinite and quartz. The persistence of this weatherable mineral is reflected in the higher retention of mobile bases, yielding a higher WIP. Sample NA0002 has the lowest WIP (478.09), signifying it has undergone the most intense chemical leaching. This correlates with its mineralogy (only kaolinite and quartz) and its geochemistry, which showed the lowest sum of base cations. It represents the most advanced end-member of the weathering sequence. The WIP for the smectite-bearing Sample NA0001 (583) is intermediate, not the lowest. This is a critical finding. It indicates that while weathering has occurred, the leaching of magnesium and iron, essential for smectite stability has been less complete here than in NA0002. This supports the earlier geochemical hypothesis that local conditions (e.g., poorer drainage, specific parent material) inhibited the full weathering progression to kaolinite, instead stabilizing the expansive smectite phase. The WIP confirms that the formation of the highly swelling clay is associated with a specific, less-advanced stage of weathering in a particular microenvironment [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e \u003cb\u003e3.5 Atterberg Tests\u003c/b\u003e \u003c/p\u003e\u003cp\u003eUsing established classification of Peck et al. [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e], the Plasticity Index (PI) data categorises the samples into distinct risk groups (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). From Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, it is observed that, Sample NA0001, with a PI of 57.6%, falls into the very high expansion potential category. This extreme plasticity is the direct geotechnical manifestation of its unique mineralogy, the presence of sodium montmorillonite (smectite) identified by XRD. Smectite's high cation exchange capacity and specific surface area enable it to absorb large quantities of water, dramatically increasing the range of moisture content over which the soil remains plastic [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. This aligns perfectly with its distinct geochemistry, which showed elevated Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and MgO, the essential structural cations for this expansive clay mineral [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]. The exceptionally high Liquid Limit (LL\u0026thinsp;=\u0026thinsp;81.8%) further confirms the enormous water-holding capacity imparted by the smectite.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExpansion Potential of Soils and Plasticity Index (after Peck et al., [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e]).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePlasticity Index\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eExpansion Potential\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0\u0026ndash;15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLow\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0\u0026ndash;35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMedium\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e22\u0026ndash;55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHigh\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVery high\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of Atterberg data\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSample ID\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003eAtterberg limits (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eExpansion Potential (Peck et al., [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e])\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLL\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePL\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePI\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLinear shrinkage (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNA0001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e81.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e24.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e57.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e7.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eVery High\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNA0002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e43.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e16.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e27.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e14.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMedium\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNA0003\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e37.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e17.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e12.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMedium\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNA0004\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e65.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e22.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e43.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e17.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eHigh\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn contrast, samples NA0002 (PI\u0026thinsp;=\u0026thinsp;27.5%) and NA0003 (PI\u0026thinsp;=\u0026thinsp;20.3%) exhibit medium expansion potential. Their mineralogy, dominated by kaolinite and quartz with no detectable smectite, results in a significantly narrower plastic range and lower LL values (43.9% and 37.3%, respectively). Their geochemistry, with lower Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and MgO, supports this mineralogically controlled, moderate plasticity. Sample NA0004 presents an interesting case with a PI of 43.2% (High expansion potential) despite its XRD analysis indicating only kaolinite and quartz. The high plasticity indices observed in Sample NA0004, particularly its liquid limit of 65.8% and PI of 43.2% present a notable geotechnical anomaly when contrasted with its XRD mineralogy, which identified only kaolinite and quartz. This discrepancy suggests that the soil's expansive behaviour is driven by factors beyond the detection limits of standard XRD analysis or by the physical characteristics of its clay fraction. This phenomenon is well-documented in international literature.\u003c/p\u003e \u003cp\u003eA primary explanation is the presence of amorphous or poorly crystalline phases. A study on Nigerian lateritic soils [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e] recorded high liquid limits (\u0026gt;\u0026thinsp;60%) in soils with XRD-dominant kaolinite and quartz, attributing the behaviour to significant fractions of amorphous alumino-silicate gels and ultra-fine kaolinite particles that disproportionately increase surface area and water adsorption. Similarly, research on Cameroonian tropical soils indicated that high clay activity could be linked to nano-sized oxides and disordered phases not quantified by XRD [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e]. Furthermore, the physical dominance of a very fine clay fraction can elevate plasticity independently of mineralogy. Soils with a high proportion of particles\u0026thinsp;\u0026lt;\u0026thinsp;0.2 \u0026micro;m, even if predominantly kaolinite, exhibit increased surface charge density and enhanced water retention on particle edges and fractures, leading to higher PI values [\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e, \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e]. Critically, standard XRD often fails to identify interstratified or poorly crystalline expansive minerals. Investigations have revealed that soils classified as kaolinitic by XRD can contain 10\u0026ndash;20% of poorly crystalline smectitic/illitic material or mixed-layer clays, which are primary drivers of swell pressure and high Atterberg limits [\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe Linear Shrinkage values offer a crucial complement to the PI data. Notably, the sample with the highest swell potential (NA0001) does not have the highest linear shrinkage; that value belongs to NA0004 (17.25%). This can be interpreted through the mechanism of shrinkage: upon drying, smectite-rich soils (NA0001) generate very high suction and interparticle stresses, leading to the formation of large, macroscopic cracks and a heterogeneous structure, rather than uniform, bulk dimensional decrease. The resulting shrinkage may be substantial but is often distributed across cracks. Conversely, a kaolinitic soil with a high PI (like NA0004) may shrink more uniformly, leading to a greater measured linear shrinkage, as its fabric contracts more homogeneously [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. The medium-plasticity samples (NA0002, NA0003) show intermediate shrinkage.\u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003e3.5.1 Engineering Properties (Atterberg Tests)\u003c/h2\u003e \u003cp\u003eAfter the tests were performed, it was observed that the plasticity indexes of all the four clay samples showed that they had the potential of expanding. The plastic index of sample NA0001 which appears to be 57.6 shows that the clays at that particular location have a very high tendency of expanding or have a very high expansion potential(greater than 55) when compared to the standards of Pack et al. [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e]. This means that when the area with these clays gets into contact with water, the clays will experience a high rate of expansion/swelling and then will also experience shrinking when the moisture leaves.\u003c/p\u003e \u003cp\u003eThe second sample NA0002, had a plasticity index of 27.5 and it can be deduced that the clay soils at the particular location where this sample was picked have medium to high expansion potentials when they are compared to the standards. This means that any form of moisture contact/absorption will cause these clays to experience significant swelling and volume changes.\u003c/p\u003e \u003cp\u003eSample EAM003 had a plasticity index of 20.3 which when compared to the accepted standards, can be said to have a medium expansion potential because it falls between 0\u0026ndash;35. This shows that clays at this area have a lesser potential of expanding when they absorb water as compared to clays in the other areas The last sample NA0004 had a plasticity index of 43.2 and this figure falls in the category that shows the expansion potential is high. And from this, it can be deduced that the clays in this particular area where the sample was picked will show high swelling properties when there is a contact with moisture. The case of Sample NA0004 aligns with these contemporary findings. Its high LL (65.8%) and PI (43.2%), contrasted with a kaolinite\u0026thinsp;+\u0026thinsp;quartz XRD signature, strongly suggest the influence of either trace amounts of expansive or active clay minerals below ~\u0026thinsp;2\u0026ndash;5% XRD detection limits, or a dominant kaolinite fraction of exceptionally fine particle size.\u003c/p\u003e \u003cp\u003eThe WIP helps explain the swelling potential trend, highlighting the sample with the highest swell potential (NA0001) does not have the lowest WIP. Its intermediate weathering index reflects the unique geochemical conditions that preserved expansive minerals. The most weathered sample (NA0002) has a low WIP and correspondingly lower plasticity (PI\u0026thinsp;=\u0026thinsp;27.5), reflecting a more stable, kaolinite-rich end product. The least weathered sample (NA0003) has a high WIP but low swell potential because its primary mineral (anorthite) is non-expansive, and its clay fraction is kaolinitic.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4 CONCLUSIONS","content":"\u003cp\u003eThis integrated study on expansive soils from Navrongo, Upper East Ghana, conclusively demonstrates that swelling potential is not a uniform area characteristic but a spatially variable geotechnical hazard, directly controlled by local variations in mineralogy and geochemistry. The main finding is that, the pronounced swelling behaviour is dominantly driven by the presence of smectite-group clay minerals, even in minor quantities, within a generally kaolinitic and quartzose soil matrix.\u003c/p\u003e \u003cp\u003eThe mineralogical (XRD) analysis established the foundational soil composition, revealing a prevalent kaolinite-quartz assemblage which indicates advanced tropical weathering. The single exception was Sample NA0001, where the identification of sodium-rich montmorillonite signaled a high-risk zone. The geochemical data provided the explanatory context for this anomaly, showing that NA0001 was uniquely enriched in iron (Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) and magnesium (MgO), essential structural cations for smectite formation, thereby linking the soil geochemistry to the formation of expansive minerals.\u003c/p\u003e \u003cp\u003eThe geotechnical index testing quantitatively validated the engineering implications of the mineralogical composition. The Atterberg limits classified NA0001 with a Plasticity Index (PI) of 57.6%, corresponding to a very high expansion potential per established classification systems [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e]. This extreme plasticity is interpreted as a direct behavioural consequence of the smectite content. The other samples exhibited lower, yet variable, plasticity (PI 20.3\u0026ndash;43.2%), which is consistent with their kaolinitic dominated mineralogy, though high PI of sample NA0004 suggests possible undetected active clay or nano-clay particle effects.\u003c/p\u003e \u003cp\u003eThe datasets reveal a definitive causal chain, specific to local geochemical conditions (retention of Fe and Mg) permit the formation and stability of expansive clay minerals (smectite), which then dictate high-index properties (LL, PI), ultimately manifesting as severe volumetric instability. Furthermore, the case of NA0004 highlights the limitation of relying on any single analytical method; index properties can reveal high clay activity where standard XRD may not detect low concentrations of expansive or poorly crystalline phases. Therefore, for resilient infrastructure development in Navrongo and similar surrounding areas, site investigation must move beyond conventional classification.\u003c/p\u003e \u003cp\u003eThe Weathering Index of Parker provided a consistent geochemical framework that integrates and validates the mineralogical and geotechnical findings. It confirms the overall weathered nature of the soils and explains the variability in swelling behavior. The high-swelling hazard in Navrongo is not associated with the most intensely weathered material but with pockets of intermediately weathered soil where geochemical conditions (evident in the WIP and Fe/Mg enrichment) favored the formation and preservation of expansive smectite clays. This underscores the necessity of understanding the weathering pathway and local geochemical history to accurately predict geotechnical hazards in tropical soils.\u003c/p\u003e \u003cp\u003eA multi-faceted protocol is recommended; the use of Atterberg limits (especially PI\u0026thinsp;\u0026gt;\u0026thinsp;35%) and free swell tests as initial hazard indicators. Employ XRD on samples showing high plasticity to confirm the presence and type of expansive clays (e.g., smectite). Where discrepancies arise (e.g., high PI without clear smectite in XRD), integrate Cation Exchange Capacity (CEC) and methylene blue value (MBV) tests to quantify clay activity and detect amorphous or poorly crystalline phases. Finally, there is the need to recognise the high spatial variability and plan investigations to identify isolated high-risk smectitic pockets.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding statement\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo funding was received to assist with the preparation of this manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eE. E. B. Conceptualization, methodology, investigation, data curation, formal analysis, writing original draft and visualization. A. A. D. formal analysis; review and editing; P. A. A. writing of original draft, review, and editing. A. N. writing, review and editing of manuscript; C. K. K. writing, review and editing of original manuscript\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorresponding author\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence to Eric Enzula Bayari\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics Declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDual publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and material\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during this study are available from the corresponding author on reasonable request.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe acknowledge the overall support of the staff of the School of Physical Sciences. We appreciate the laboratory support provided by the Council of Scientific \u0026amp; Industrial Research (CSIR)-Building and Road Research Institute (BRRI), Fomesua, Kumasi, and the Ghana Geological Survey Authority, Accra, for providing help, guidance, and the needed facilities for conducting the experiments of this work. Special thanks go to Mr. Usman Farouk (BRRI) for granting assistance with the geotechnical testing.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eFiroozi AA, Guney Olgun C, Firoozi AA, Baghini MS. Fundamentals of soil stabilization. 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November, 2013.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePack R, Hanson W, Thornburn T. \u0026lsquo;Foundation Engineering - second edition\u0026rsquo;, 1974.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-applied-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Applied Sciences](https://link.springer.com/journal/42452)","snPcode":"42452","submissionUrl":"https://submission.springernature.com/new-submission/42452/3","title":"Discover Applied Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Expansive Soils, Smectite, Geochemistry, Plasticity Index, Weathering Index, Navrongo","lastPublishedDoi":"10.21203/rs.3.rs-8408259/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8408259/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSoils with expansive behaviour pose a great geotechnical impact on buildings in tropical regions, due to moisture variations causing severe volumetric changes. This study investigates the mineralogical, geochemical, and index property characteristics of expansive soils from Navrongo in the Upper East Region of Ghana to identify the controls on their swelling behaviour. An integrated methodology of X-ray diffraction (XRD), major oxide geochemistry, Atterberg limits, and the Weathering Index of Parker (WIP) was performed on four soil samples. Results reveal a dominant kaolinite-quartz assemblage indicating advanced tropical weathering, yet with spatial variability. One sample (NA0001) was found to contain sodium-rich montmorillonite (smectite), correlating with uniquely elevated geochemical concentrations of Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (8.83%) and MgO (1.57%) and a very high Plasticity Index (PI\u0026thinsp;=\u0026thinsp;57.6%), classifying it as having high expansion potential. In contrast, the smectite-free samples exhibited significantly lower plasticity (PI\u0026thinsp;=\u0026thinsp;20.3\u0026ndash;43.2%). The data establish a causal chain of localised geochemical conditions, associated with an intermediate weathering stage, that stabilise expansive smectite clays, which in turn dictate high-index properties and severe swell potential. This study further interprets this variability within a classic tropical regolith profile, identifying the mottled weathering zone as a probable genesis horizon for expansive clays. The findings underscore that the swelling risk in Navrongo is not ubiquitous but confined to specific zones where smectite is present. Consequently, a multi-method approach that combines plasticity tests and mineralogical and geochemical analyses to identify these high-risk, spatially discrete soil units to inform geotechnical design and sustainable infrastructure development in Navrongo.\u003c/p\u003e","manuscriptTitle":"Mineralogical and Geochemical Control on Swelling Behaviour of Expansive Soils in Navrongo, Ghana","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-06 11:28:29","doi":"10.21203/rs.3.rs-8408259/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-14T12:00:47+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-18T08:53:16+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-14T12:08:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"251696461236858302599074901483615176318","date":"2026-02-03T13:56:39+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-01T10:54:55+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"27709280713092621060749636051177379598","date":"2026-02-01T03:48:30+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"183588924553045898305785770461688080893","date":"2026-01-30T04:13:29+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-01-29T10:57:45+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-01-29T09:34:20+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-24T05:21:37+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-24T05:20:17+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Applied Sciences","date":"2025-12-19T21:23:55+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-applied-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Applied Sciences](https://link.springer.com/journal/42452)","snPcode":"42452","submissionUrl":"https://submission.springernature.com/new-submission/42452/3","title":"Discover Applied Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0c5d5eff-eb47-4b2f-9ab5-d1d75220c692","owner":[],"postedDate":"January 6th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-08T06:23:58+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-06 11:28:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8408259","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8408259","identity":"rs-8408259","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}