Discussion on the change rule of different characteristic parameters with Depth in expansion soil graben slopes

Discussion on the change rule of different characteristic parameters with Depth in expansion soil graben slopes | 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 Article Discussion on the change rule of different characteristic parameters with Depth in expansion soil graben slopes Chaozheng Shen, Xueyun Miao, Yongqiang Li This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5008337/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 31 Mar, 2025 Read the published version in Scientific Reports → Version 1 posted 8 You are reading this latest preprint version Abstract Expansive soil due to wet expansion and dry contraction of engineering properties, resulting in the stability of the riffle slope, has been one of the key issues in the expansion of soil area earthworks; this paper, through the three representative riffle slope site field visits and indoor tests, respectively, from the dry bulk weight, unconfined compressive strength, three-way expansion force and expansion with the change rule of the Depth of the law to be explored. The three-way expansion force test shows that the extension and proximity direction of the horizontal expansion force are the same. The vertical direction is greater than the horizontal direction, and its ratio is about 0.5. Further analysis of the relationship between the characteristics of the parameters with the Depth can be seen: the surface soil indicators are more varied, between 0.5-1.0 m, the soil layer dry density is small, the expansion of the soil wet expansion and drying shrinkage is significant, and the unconfined compressive strength is close to or has reached the lowest value; expansion force and expansion volume test indicators along the Depth of the graben slope, the expansion force and expansion volume test indicators are more varied. Expansion force and expansion amount test indexes change along the Depth of the riffle slope but remain unchanged after 2.0 m. Therefore, the damage of the expansion soil riffle slope mainly occurs in the soil layer near the Depth of 1.0 m, which is manifested explicitly as a failure to adapt to the change of stress in the soil and the inability to adjust to the atmospheric natural camping force. Earth and environmental sciences/Natural hazards Physical sciences/Engineering Expansive soil slope depth range dry bulk density unconfined compressive strength three-dimensional expansion force expansion amount Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 0 Introduction As China's rail transportation sector continues to evolve, the incidence of projects within expansive soil regions rises annually. Given the subpar engineering characteristics of expansive soil, newly excavated riffle slopes may undergo rapid deformation if timely slope stabilization measures are not implemented. The instability of these riffle slopes poses significant risks to the safe operation of the infrastructure, potentially resulting in substantial economic repercussions [ 1 – 2 ] . Due to its unique expansion, contraction, and fracture, expansive soil often causes slope instability and structural damage in engineering practice, which has become an important research topic in geotechnical engineering. In recent years, scholars at home and abroad have conducted extensive research on the stability, destabilization mechanism, and management technology of expansive soil slopes, and significant progress has been made. However, there are still some deficiencies that need to be further explored. In studying the stability of expansive soil slopes, Ning Xinyang [ 3 ] constructed a prediction model based on the statistical law of crack distribution, which provided theoretical support for slope stability analysis. On the other hand, Chen Dongyu [ 4 ] analyzed the destructive modes of expansive soil slopes in detail from the destabilization mechanism and characteristics and proposed corresponding management measures, which achieved good engineering results. These studies provide essential references for the stability assessment and management of expansive soil slopes. Still, they mainly focus on the analysis at the macro level and lack a systematic study of the internal characteristic parameters of the soil body and its Depth of influence. In protecting and managing expansive soil slopes, Xu et al. [ 5 – 7 ] used geo-bagging slope protection technology, which effectively prevented crack development and improved the mechanical properties of slopes by isolating the external environmental influencing factors and blocking the internal moisture variation of the soil body. Guo Yipeng et al. [ 8 ] explored the application effect of new geomaterials in expansive soil slopes through experimental research, providing new ideas for protecting expansive soil slopes. Zhang Yang [ 9 ] and others studied the construction technology and quality control points of the "quicklime + curing agent" combination of reinforced expansive soil slopes, which provides a reference for similar projects. In addition, Katti et al. [ 10 ] and Clayton et al. [ 11 ] proposed a new design method for expansive soil retaining walls, which further enriched the protection technology system of expansive soil slope. Ning Xinyang et al. [ 12 ] proposed a new flexible integrated protection technology based on "pressure fast drainage", which can effectively control slope seepage and improve slope stability. Gong Bi-wei [ 13 ] and Zhu Wu et al. [ 14 ] explored the performance of EPS drag-reducing expansive soil retaining walls through indoor modelling tests and theoretical analysis. They proposed a new form of double-layer protection structure. These studies demonstrated the diversity of expansion soil slope protection techniques. Still, they mainly focused on engineering applications and lacked an in-depth evaluation of the applicability and long-term effects of the methods. Although the existing research in the stability analysis of expansive soil slopes, destabilization mechanism, and protection technology has achieved significant results, the lack of in-depth study of the soil body parameters' internal characteristics mainly focused on the macro level of slope stability analysis. In contrast, the internal factors of the soil body parameters (such as dry weight, three-way expansion force, expansion, etc.) and their impact on the Depth of the study are more scarce. Secondly, there is insufficient attention to the long-term stability of the riffle slope. Expanded soil riffle slopes will experience a long-term evolution process from the "unadaptive stage" to the "adaptive stage" after excavation. At the same time, the existing studies are primarily focused on the analysis of short-term stability, and there is a lack of analysis of the long-term slope that has been stabilized. Analysis. Based on the above shortcomings, this paper selects different working points of the expanded soil graben slope, systematic research on the internal characteristics of the soil body parameters of the law of change and the Depth of influence, aimed at providing a more scientific theoretical basis for the design and management of the expanded soil graben slope. 1 Overview of the excavation slope work site Because the Graben Valley slope is directly affected by the natural camping force and human factors, the indicators change with the Depth. To study the Depth of its influence, through the field investigation of Ankang Xiangyu line K312 + 650 section, Xixiang Yangan line K211 + 320 section, and Mianxi Yangan line K72 + 200 section of the railroad graben valley slopes, the field test map as shown in Fig. 1 - Fig. 3 . Soil samples were taken for an indoor characteristic parameter test to seek the change rule with Depth; the specific workplace profile is shown in Table 1 below. Table 1 Overview of expansive soil trench slope index test site Site name mileage slope height slope Forms of protection epigenetic characterization fracture Ankang City, Shaanxi Province Xiangyu line K312 + 650 above the first level platform on the left side of the line 12m 1:1.5 2.5×2.5m sheet rock lattice berm with internal turf planting Brownish red contains ferromanganese nodule Fissures are developed, and cut soils are prismatic or vertically prismatic. Xixiang County, Hanzhong City, Shaanxi Province Yangan line K211 + 320 above the first level platform on the right side of the line 10m 1:1.5 Supported infiltration trenches spaced 10m apart, slopes planted with Sophora japonica Brownish-red, greyish-green, wormlike bands of greyish-white, greyish-green clay with ferromanganese nodules Fissures are developed, some with smooth and abraded fissure surfaces, easily weathered into grains Mianxi County, Hanzhong City, Shaanxi Province Above the highway on the right side of line K72 + 200 of the Yangan Line 8m 1:1.5 Natural slopes of farmland, no more cultivation within 1.5×1.5m around the observation site, no protection Brownish red, containing ferromanganese nodules Fissure development, easy to weather into loose grains 2 Soil Sample Collection and Testing Program 2.1 Soil Sample Collection The sampling is done by a thin-walled in-situ soil sampler, which takes in-situ soil samples vertically on the riffle slope to different depths within the riffle slope. All three work sites are carried out in March of the dry season to facilitate the sampling and field test. According to the Standard for Geotechnical Test Methods (GBT 50123 − 2019) [ 15 ] , the fundamental physical and mechanical property tests are conducted on expanded soil samples collected from various working points. The parameters of the physical and mechanical properties of the assessed working points are presented in Table 2 . Subsequently, in line with the Special Geotechnical Investigation Procedures for Railway Engineering (TB 10038 − 2022) [ 16 ] , the free expansion rate index is employed to categorize the soil samples from the three working points into expansive soil classifications. The Ankang expansive soil exhibits a free expansion rate of 67%, which falls within the 60–90% range, thus classifying it as moderately expansive. In contrast, the free expansion rates of the Xixiang and Mianxi expansive soils are approximately 60%, positioned within the 40–60% range, thereby categorizing them as weakly expansive soils. Table 2 Parameters of physical and mechanical properties of the site observation site Depth range (m) natural capacity \(\:{\gamma\:}(\text{g}/\text{c}{\text{m}}^{3})\) Natural moisture content \(\:{\text{w}}_{0}\) (%) plastic limit \(\:{\text{w}}_{\text{P}}\) (%) liquid limit \(\:{\text{w}}_{\text{L}}\) (%) plasticity index \(\:{\text{I}}_{\text{P}}\) free inflation rate \(\:{\text{F}}_{\text{s}}\) (%) Ankang 0-0.5 2.03 22.45 20.7 46.8 26.1 67 0.5-1.0 2.20 23.02 21.2 47.0 25.8 63 1.0–2.0 2.24 24.28 23.8 48.5 24.7 70 >2.0 2.20 27.43 24.2 49.8 25.6 71 Xixiang 0-0.5 1.98 22.43 20.1 39.5 19.4 57 0.5-1.0 2.11 24.12 20.9 41.0 20.1 60 1.0–2.0 2.22 24.56 22.4 41.7 19.3 59 >2.0 2.20 26.28 23.5 42.5 19.0 63 Mianxi 0-0.5 2.02 22.39 21.5 40.5 19.0 59 0.5-1.0 2.14 24.03 22.0 41.0 19.0 61 1.0–2.0 2.19 23.98 23.5 42.3 18.8 62 >2.0 2.23 25.56 24.7 42.8 18.1 67 2.2 Research protocol 2.2.1 Sample Preparation The in-situ soil samples underwent complete crushing and were sieved through a 2 mm mesh to determine the wet bulk density. Subsequently, the dry bulk densities at three distinct working points were derived from the samples' natural moisture content. A remoulded ring cutter sample with a height of 20 mm and a diameter of 61.8 mm was created using a hydraulic press (refer to Figure. 4) and subsequently placed in a humidor for over 24 hours for preservation. 2.2.2 Test Methods In this experiment, dry bulk weight, unconfined compressive strength, three-way expansion force, and unloaded expansion rate tests were conducted, and the matrix of the tests is shown in Table 3 . Table 3 Experimental matrix table Experimental items Testing methods Parameters Depth ranges(m) Dry weight test By the Standard for Geotechnical Test Methods (GBT 50123 − 2019) Dry weight (g/cm³) 0-0.5,0.5-1.0, 1.0–2.0, > 2.0 Unconfined compressive strength test Use of YYW-2 type unconfined pressure gauge Unconfined compressive strength (kPa) Three-way expansion force test Using a three-way expansion meter Vertical expansion force and horizontal expansion force (kPa) Loadless Expansion Rate Test Using WZ-1 type expansion meter Expansion volume (%) (1)Unconfined compressive strength test The unconfined compressive strength is used to investigate the deformation and damage exhibited by the in-situ soil samples when subjected to pressure without lateral constraints to determine their strength and mechanical properties. The strength of expansive soils is mainly controlled by the distribution of fissure surfaces, density, shape, water content status on the fissure surfaces, and filling materials, so the field unconfined compressive strength test was used. The test was chosen for the dry season to minimize the influence of the difference in water content at different depths on the strength. The test apparatus was a YYW-2 type unconfined compression apparatus (refer to Fig. 5 (a)); its main parameters are shown in Table 4 . Table 4 Test parameters of unconfined compressive strength specimens \(\:{\text{ℎ}}_{0}\) (mm) \(\:{\text{D}}_{0}\) (mm) \(\:{\text{A}}_{0}\) ( \(\:{\text{c}\text{m}}^{2}\) ) quantitative force loop coefficient (Kg/mm) Screw rise height per handwheel revolution (mm) 100 39.5 12.2 22.65 0.2 (2)Three-way expansion force test In expansive soil slope within a unit, when the water content changes, the unit soil body in the surrounding soil body constraints under the expansion of the force state is three-dimensional nature, and the stability of the slope plays a role in addition to the vertical expansion force, but also includes the horizontal expansion force pointing to the side of the slope face as well as due to the repeated drying and wetting and expansion of some of the cracks caused by the three-way expansion force. Hence, the study of the three-way expansion force is essential. In this test, a square specimen was cut by a square ring cutter according to the sampling orientation (vertical direction Z, graben slope extension horizontal direction X, and airside horizontal direction Y) and put into the three-way expansion meter (refer to Fig. 5 (b)) according to the orientation. Under the condition of controlling the deformation amount to be zero, the specimen's top and bottom were immersed in water simultaneously to get the specimen's expansion force in the three directions. (3)Loadless Expansion Rate Test The unloaded expansion rate test is designed to simulate the loading state of foundation soil to understand its expansion process. The test adopts an expansion meter (Fig. 5 (c)). The deformation of the specimen in contact with water does not exceed 0.01mm within 6 hours, which is considered stable. The test is generally stabilized after 24 to 36 hours. 3 The change rule of different characteristic parameters with Depth 3.1 Variation of natural dry weight with Depth Figure 6 plots the variation of natural dry bulk weight with Depth. The Figure shows that the riffle slopes of the three work sites all significantly change surface dry bulk weight in the depth range of 1.0 m, especially at 0.5 m, followed by a gradual stabilization. Numerically, the surface riffle slopes in Xixiang showed the most significant change, increasing from 1.43 \(\:\text{g}/\text{c}{\text{m}}^{3}\) at 0.2 m to 1.63 \(\:\text{g}/\text{c}{\text{m}}^{3}\) at 0.5 m, i.e., the dry bulk density increased by 14%. Ankang, due to the lattice berm protection, had a more minor change than the Xixiang riffle slope, which was only protected by the supporting seepage trench. Some of the data nodes were taken for further analysis, and if the dry weight value at 3.0 m is used as unit 1, the calculation of the dry weight ratio at different depths is included in Table 5 below. Table 5 Dry bulk density and ratio of trench slopes at different depths Sampling depth (m) Ankang Xixiang Mianxi \(\:{{\gamma\:}}_{\text{d}}\) ( \(\:\text{g}/\text{c}{\text{m}}^{3}\) ) Ratio \(\:{{\gamma\:}}_{\text{d}}\) ( \(\:\text{g}/\text{c}{\text{m}}^{3}\) ) Ratio \(\:{{\gamma\:}}_{\text{d}}\) ( \(\:\text{g}/\text{c}{\text{m}}^{3}\) ) Ratio 0.2 1.51 0.90 1.43 0.84 1.42 0.85 0.5 1.61 0.96 1.63 0.96 1.53 0.91 1.0 1.66 0.99 1.69 0.99 1.62 0.96 2.0 1.67 1 1.70 1 1.67 0.99 3.0 1.67 1 1.70 1 1.68 1 It is clear from Table 5 that the dry capacity of the Ankang and Xixiang riffle slopes at 1.0 m is 0.99 of the dry capacity at 3.0 m, and it remains the same when it reaches 2.0 m. The dry capacity of the riffle slopes at 1.0 m is 0.99 of the dry capacity at 3.0 m. Therefore, it can be assumed that for the general turf and Sophora japonica-protected Graben Valley slope, the dry weight corresponds to a depth of about 2.0 meters when keeping the original soil. The Mianxi Graben Valley slope depth of 2.0 meters below the dry weight remains unchanged; the reason is that the Mianxi slope is a natural slope of farmland, planting crops twice a year, farmers frequently cultivate, the application of organic fertilizers to make the soil loose, destroying the continuous growth of the plant root system, it is difficult to form the surface of the protective role of the root layer of the plant. 3.2 Variation of unconfined compressive strength with Depth The Fig. 7 shows that the graphs of unconfined compressive strength with Depth for the three work sites are incredibly similar. These curves can be divided into a 4-stage change process by Depth: firstly, the depth range of 0-0.5 m; the curve begins to decline slowly and reaches a minimum value when the Depth is 0.5 m; 0.5-1.0 m; the unconfined compressive strength at this stage starts to increase gradually from the minimum value; 1.0–2.0 m. continue to grow, but the growth rate is reduced compared to the previous stage; when the depth range reaches 2.0 m or less, at this time, the curve change amplitude tends to flatten, the unconfined compressive strength slightly up and down, and finally stabilized. Specific causes can be analyzed in each section, showing different strength characteristics and forms of damage: ① Depth range 0-0.5 m, the surface soil after repeated dry and wet cycles and achieving a certain degree of remodelling. There are plant roots intertwined, the strength of a large extent by the influence of the root system, with the Depth of the large to small, the specimen was bulging type broken cup, in the damage can be seen in several pulled plant root system. ② Depth range of 0.5-1.0 m, the layer of soil dry weight analyzed in the previous section also gradually increased from small to large values due to the influence of wet and dry cycles, cracks are highly developed, the specimen was bulging type damage and the appearance of many open fissures as the primary form of damage, the strength of the minimum value in this layer. ③ The depth range of 1.0–2.0 m, the fissures gradually become smaller in this layer due to a slight increase in dry bulk weight. Specimen damage has a clear rupture surface, and part of the fissure surface overlaps or is close to the fissure surface; when the fissure surface and the angle are close to \(\:{45}^{\text{o}}+{\phi\:}/2\) , the intensity is low, and vice versa is high. ④ Depth range below 2.0 m, the analysis within the layer is known to be dry bulk weight remains unchanged, the fissures can be considered to belong to the primary fissures and unloading fissures, weathering has been reduced to a lower degree, the destruction of the specimen is the same form as in the upper layer when the strength increases or decreases slightly about the degree of destruction along the fissure surface. 3.3 Variation of three-way Expansion Force with Depth From the test data results, the riffle slope extension direction horizontal expansion force \(\:{\text{P}}_{\text{o}\text{x}}\) compared to the proximity direction horizontal riffle force \(\:{\text{P}}_{\text{o}\text{y}}\) . However, along the depth direction of the riffle, the slope is from small to large, but with the same Depth \(\:{\text{P}}_{\text{o}\text{x}}\) and \(\:{\text{P}}_{\text{o}\text{y}}\) equal, there is no excavation of the riffle slope due to the proximity of the direction of the \(\:{\text{P}}_{\text{o}\text{y}}\) trend to reduce. Therefore, in Fig. 8 , for the sake of eye-catching, only draw a horizontal direction of the expansion force \(\:{\text{P}}_{\text{o}\text{x}}\) and a vertical direction \(\:{\text{P}}_{\text{o}\text{z}}\) . As can be seen from Fig. 8 , close to the surface, the dry weight of the specimen is minimal, so the expansion force is also minimal; with the increase in Depth, the dry weight increases, and the expansion force also increases, to reach a depth of 2.0 meters below, the expansion force is unchanged. Further analysis shows that: ①There is a difference between the expansion force in the horizontal direction and the expansion force in the vertical direction of the original soil specimens of the expansion soil graben slope. It shows that the expansion force is anisotropic when the water content changes in three directions. The horizontal expansion force is smaller than the vertical expansion force, and the ratio is around 0.5. ②Numerically, the three selected work points show similar expansion force after stabilization due to the relatively close soil property index; specifically, the vertical direction expansion force is generally around 20-30kPa, and the horizontal direction expansion force is generally around 5-15kPa. ③Three kinds of natural moisture content state of the original soil, expansion force test of the post-test moisture content are minimal change, \(\:\varDelta\:\text{W}=1-2\text{%}\) . It shows that most of the natural state of the expansion of the soil, in the case of volume unchanged after the water expansion of the water content change, is relatively small. 3.4 Variation of Expansion with Depth Figure 9 plots the curves of expansion with Depth. These curves can be equally divided into four segments according to Depth: first depth range 0-0.5 m, the curve decreases rapidly; when the Depth of 0.5 m, close to the minimum; 0.5-1.0 m, the curve continues to decrease in this stage, but the rate of decline slows down, reaching 1.0 m, the minimum occurs; 1.0–2.0 m, the amount of expansion with the Depth of the increase in the amount of expansion slightly increased; when the depth range reaches 2.0 m below when the magnitude of the curve change tends to flatten out, and the amount of expansion rises and falls slightly, remaining essentially constant. Specific analysis can be seen: ①Depth range 0-0.5 m, because the closer to the surface, the initial dry weight of the specimen is smaller, the dry shrinkage and wet expansion is more prominent, so the soil curing cohesion is closer to the complete loss of the soil, thus showing remodelling of the expansion characteristics of the soil, i.e., the expansion of a large amount of the expansion limit of the soil layer is enormous. Hence, the expansion of the Depth of the decreasing rate is swift. The Depth of 0.5 meters is close to the minimum expansion amount. ②Depth range of 0.5-1.0 meters, with the depth increase, the expansion continues to decrease, to a depth of 1.0 meters has had the characteristics of the original state of the soil is not close to the minimum amount of expansion; ③Depth range of 1.0–2.0 meters, the expansion of the amount of Depth with the depth increase and a slight increase in the reason is that with the Depth of change in the dry bulk weight of the slight increase due to the depth change; ④Depth range of 2.0 meters below the measured expansion of the water content is only slightly increased 23% more than the natural moisture content; ④The depth range is below 2.0 meters, and the water content after swelling was measured to be only slightly increased by 2–3% compared to the natural water content, so the amount of swelling remains unchanged. 4 Discussion of test results 4.1 Discussion of the law between the characteristic parameters Analyzing Figs. 6 , 7 , 8 , 9 , and Table 5 , it is found that the characteristic parameters roughly coincide with the deformation stratification of the graben slope. The indicators change most significantly when the Depth is near 0–1.0 m. Among them, the lowest value of unconfined compressive strength occurs due to the expansion limit of the surface specimen water content being very high; after rainfall can be fully absorbed, the expansion of a more significant amount, so the surface layer of sliding slump mainly occurs here, that is, in the expansion of the soil in the strong activity layer [ 17 ] .2.0 m near the indicators and the Depth of the in situ soil is not much difference, are tending to stabilize. The specific change rule of each characteristic parameter with Depth is shown in Table 6 . Table 6 Variation of different characteristic parameters of expansive trench slope with Depth Depth range (m) dry weight \(\:{{\gamma\:}}_{\text{d}}(\text{g}/{\text{c}\text{m}}^{3}\) ) Unconfined compressive strength \(\:{\text{q}}_{\text{u}}\) (kPa) Three-way expansion force \(\:{\text{P}}_{\text{o}\text{z}}\) , \(\:{\:\text{P}}_{\text{o}\text{x}}\) , \(\:{\:\text{P}}_{\text{o}\text{y}}\) (kPa) unlimited expansion \(\:{\text{V}}_{\text{H}}\) (%) 0-0.5 The surface soil is highly loose with minimal dry bulk weight, which gradually increases with Depth Strength is strongly influenced by the plant root system, ranging from large to small, with Depth In the surface layer, due to the minimum dry weight, the three-way expansion force increases gradually with Depth after reaching the minimum, \(\:{{\text{P}}_{\text{o}\text{z}}＞{\text{P}}_{\text{o}\text{x}}\text{、}{\text{P}}_{\text{o}\text{y}}；{\:\text{P}}_{\text{o}\text{x}}\approx\:\text{P}}_{\text{o}\text{y}}\) The surface layer exhibits the swelling characteristics of a remodelled soil, i.e., a large amount of swelling, ranging from large to small with Depth, and a high water content after swelling 0.5-1.0 The dry mass continues to increase, reaching 1.0 m, essentially 99% of the deep dry mass. The strength increases after the minimum value occurs, and the specimen's damage is bulging, cracking, or cracking. Continued slow increase Expansion continues to decrease, reaching 1.0 m, essentially the minimum expansion 1.0–2.0 Slight increase in dry weight, reaching 2.0 m, essentially the same as the deeper layers Strength continues to increase; specimen destruction has more apparent damage to the surface Continuing to increase slowly. But the rise is even smaller Swelling increases slightly with Depth, which is associated with a slight increase in dry bulk weight >2.0 Dry weight remains constant A slight increase or decrease in strength is related to the proportion of damage along the cleavage plane, but overall strength remains constant. Expansion force remains essentially unchanged. The expansion amount stays the same, and the water content after expansion slightly increases by 2–3% compared with the natural water content. 4.2 Analysis of the damage mechanism of the surface layer of the riffle slope Through the analysis of experimental data, it is evident that the failures of these slopes predominantly originate from the surface layer. This indicates that when excavating slopes in expansive soil areas, the surface soil layers are the first to be unacclimatized to the new environment. The main aspects of their maladaptation to the environment are as follows: (1)The soil is not well-suited to changes in stress levels. When expansive soil is in its original super-consolidated state, inherent internal stress exists within the soil. Following the excavation of the riffle slope, the stress acting on the surface soil rapidly diminishes to zero. This results in a re-adjustment process of soil stress that gradually occurs from the surface of the riffle slope to the interior soil layer. The transition of the soil body's stress from a state of non-adaptation to one of adaptation is critical. Once the adaptation phase is attained, the riffle slope can be generally stable over the long term. However, if this stage concludes without achieving adaptability, the condition of the riffle slope will inevitably worsen, potentially leading to its failure. (2) Inadequate adaptation to natural atmospheric forces may occur following the excavation of the graben slope, where the newly exposed surface becomes directly subjected to the effects of atmospheric conditions. Consequently, this surface layer quickly encounters erosion and infiltration from wind, sunlight, and rainfall. As a result, the soil undergoes repeated cycles of drying and shrinking, followed by wetting and expanding annually, ultimately forming a weathering layer that has adapted to atmospheric conditions. If this cyclical process fails to establish a proper adaptation, it could result in detrimental geological phenomena such as erosion, slope failure, and sliding. 5 Conclusions Unlike Ning Xinyang [ 3 ] , who focused on macro-stability analysis, this paper goes deep into the soil body. It reveals the differences in the characteristics at different depths, especially the significant changes in the depth indexes of 0–1.0 m. Compared with Chen Dongyu [ 4 ] , who mainly analyzed the damage patterns of expansive soil slopes and proposed measures to manage them, this paper reveals the variation rules of the characteristic parameters with the Depth through the experimental data and finds that the expansion force of expansive soils in three directions is more significant than that in the horizontal direction, and fills the gap of its failure to analyze the anisotropy of expansion force. This paper fills the gap of not investigating the anisotropy of expansion force; Xu et al. [ 5 – 7 ] focus on geotechnical bag type slope protection technology engineering applications, not in-depth analysis of the internal characteristics of the soil body parameter changes, while this paper through the different sites of expansion of the soil riffle slope of the field and indoor testing, systematic study of the dry bulk weight, unconfined compressive strength, three-way expansion force and expansion with the change rule of the Depth of the expansion of the soil riffle slope surface damage mechanism. The main research conclusions developed in this paper are as follows. (1) The wet expansion and dry contraction characteristics of expansive soils lead to the loosening of the surface layer of the riffle slope in the range of 0–1.0 meters, and the dry weight and strength are significantly reduced while the changes in various indexes in the range of 1.0–2.0 meters are relatively small. (2) The Expansive soil rift slope original soil is anisotropic; the vertical expansion force is greater than the horizontal expansion force, and the ratio is about 0.5. (3) The expansion of in-situ soil under natural water content conditions is minimal, and the water content increases by only 2–3% after expansion, indicating that the water in the expanded soil can seep through the cracks to the deeper soil layers. (4) Expansive soil riffle slope damage begins at the surface. A lack of adaptation to changes in soil stresses and the natural camping forces of the atmosphere primarily characterizes it. Regarding the research on expansive soil graben slopes and slopes, long-term monitoring studies should be carried out in the future to monitor expansive soil graben slopes in the long term and assess their stability changes under different seasons and climatic conditions to validate the conclusions of the existing studies further; moreover, multidisciplinary knowledge such as geology, hydrology, and ecology should be combined to explore the stability mechanism of expansive soil slopes in-depth and to probe for more effective protection techniques; further exploration is needed for the It is necessary to examine further the application of new geomaterials and reinforcement techniques in expansive soil slopes to improve the long-term stability of slopes. Declarations Author Contribution Chaozheng Shen (First Author): Conceptualization, Data Curation, Formal Analysis, Investigation, Methodology, Writing-Original Draft, Writing-Review & Editing;Xueyun Miao (Corresponding Author): Funding Acquisition, Resources, Supervision, Writing-Original Draft, Writing-Review & Editing;Yongqiang Li (Third Author): Methodology, Supervision.All authors participated in the manuscript review. Data Availability Data is provided within the manuscript or supplementary information files. References Liao Shiwen. Expansive soil and railway engineering[M]. Beijing: China Railway Publishing House, 1984. Xiao Shiguo. Stability analysis of expansive soil cutting slope[J]. Rock and Soil Mechanics, 2001, (02): 152-155. Ning Xinyang,ZENG Jun,LV Guoliang. Stability Analysis and Reinforcement Design of Expansive Soil Slope Considering Fracture Statistical Distribution[J]. Water Resources and Hydropower Engineering,2022,53(S1):436-441. Chen Dongyu. Comprehensive treatment of expansive soil slope collapse[J]. China High and New Technology,2022,(10):118-120. XU Y F, HUANG J, DU Y J, et al. Earth reinforcement using soilbags[J]. Geotextiles and Geomembranes, 2008, 26(3): 279-289. XU Y F, HUANG J. Case study on earth reinforcement using soilbags[C]// Proceedings of the 4th Asian Regional Conf on Geosynthetics. Shanghai, 2008. MATSUOKA H, LIU S H. New earth reinforcement method by soil bags ("do now")[J]. Soils and Foundations, 2003, 43(6): 173-188. Guo Yipeng, Nie Rusong, ZHANG Xiong, Zhang Yongjie, Chen Jiejin, Zou Quan. Experimental study on water migration of expansive soil treated by new geotextiles[J]. Journal of Railway Science and Engineering:1-10. Zhang Yang. "Lime + curing agent" composite improved expansive soil slope backfill construction technology[J]. Science and Technology Innovation,2022,(18):137-140. KATTI RK, BHANGALE E S, MOZA K K. Lateral pressure in expansive soil with and without a cohesive non-swelling soil layer-application to earth pressures on cross drainage structures in canals and key walls in dams (Studies on K0 Condition)[R]. New Delhi: Central Board of Irrigation and Power, 1983. CLAYTON C R I, SYMONS I F, HIEDRA-COBO J C. The pressure of clay backfill against retaining structures[J]. Canadian Geotechnical Journal, 1991, 28(2): 282-297. Ning Xinyang, Zeng Jun, Zeng Linghua. Research on flexible, comprehensive protection scheme of expansive soil slope based on "pressure and fast drainage"[J]. Water Resources and Hydropower Express,2022,43(02):52-56+62. Gong Biwei. Fractures, Strength, and Relationship between Expansive Soil and Slope Stability[J]. Journal of Yangtze River Research Institute,2022,39(10):1-7. Zhu Wu, Dou Hao, Yin Nazheng, Cheng Yiqing, Zhang Shuangcheng, Zhang Qin. Analysis of Deformation Characteristics of Expansive Soil Slope Based on Combined InSAR and SSA: A Case Study of South-to-North Water Diversion Project[J]. Journal of Surveying and Mapping,2022,51(10):2083-2092. GB/T 50123-2019, Standard for geotechnical test methods[S]. State Railway Administration. TB 10038−2022, Regulations for special geotechnical investigation of railway engineering [S] Beijing: China Railway Press, 2022. Zhang Delong, Miao Xueyun, Shen Chaozheng. Study the Mechanism of Expansive Ripping Soil Disease and Comprehensive Control Measures[J]. Shanxi Architecture, 2024, 50 (03): 82-85+89. Additional Declarations No competing interests reported. Supplementary Files Rawdata.xlsx Cite Share Download PDF Status: Published Journal Publication published 31 Mar, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Accepted 25 Mar, 2025 Reviews received at journal 20 Mar, 2025 Reviewers agreed at journal 19 Mar, 2025 Reviews received at journal 19 Mar, 2025 Reviewers agreed at journal 19 Mar, 2025 Reviewers invited by journal 19 Mar, 2025 Submission checks completed at journal 18 Mar, 2025 First submitted to journal 27 Feb, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5008337","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":430939233,"identity":"3ad0d9cb-0831-40f8-94a0-4eb93670bb8c","order_by":0,"name":"Chaozheng Shen","email":"","orcid":"","institution":"School of Transportation Engineering, Nanjing University of Technology, Nanjing 210009","correspondingAuthor":false,"prefix":"","firstName":"Chaozheng","middleName":"","lastName":"Shen","suffix":""},{"id":430939234,"identity":"f1d2c024-313d-4136-bf60-3434096a9f88","order_by":1,"name":"Xueyun Miao","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAsklEQVRIiWNgGAWjYFAC5gMHEgxsePj5G4jWwpZ44EFFmozkjANEa+ExPvjgzGEbg4YEIjXwTztjcCCx7TyPAcMBxg8fc4jQInE7rQCo5TaPOXMDs+TMbcRYczt5A1iLZcMBNmZeYrTI304AOewcj8GBBCK1GNxOASo+c4AELYa30xIOJFQk80jOONhMnF/kbicf/vjDwM6en7/54IePRHkfARgbSFM/CkbBKBgFowA3AACxOz3E+W652QAAAABJRU5ErkJggg==","orcid":"","institution":"China Railway Northwest Research Institute Co.., Ltd., Lanzhou 730000","correspondingAuthor":true,"prefix":"","firstName":"Xueyun","middleName":"","lastName":"Miao","suffix":""},{"id":430939237,"identity":"6fe2a628-70d6-490f-9c3e-4b74f08a56bf","order_by":2,"name":"Yongqiang Li","email":"","orcid":"","institution":"China Railway Northwest Research Institute Co.., Ltd., Lanzhou 730000","correspondingAuthor":false,"prefix":"","firstName":"Yongqiang","middleName":"","lastName":"Li","suffix":""}],"badges":[],"createdAt":"2024-08-31 09:54:06","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5008337/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5008337/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-96062-y","type":"published","date":"2025-03-31T15:57:49+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":79068350,"identity":"2ea53338-78ac-41a0-9c98-7c647672700e","added_by":"auto","created_at":"2025-03-24 05:09:37","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":262180,"visible":true,"origin":"","legend":"\u003cp\u003eStudy site of K312+650 section of Xiangyu Line in Ankang\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5008337/v1/8c3e143ab3243c0ba0ea18c0.png"},{"id":79069987,"identity":"0dd88c98-329c-4ca6-9ca3-847178b92611","added_by":"auto","created_at":"2025-03-24 05:41:37","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":194879,"visible":true,"origin":"","legend":"\u003cp\u003eStudy site of K211+320 section of Xixiang Yangan line\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5008337/v1/205a8303ca17c3c72130e3c5.png"},{"id":79068353,"identity":"e7e8aca0-bf45-4af2-9499-42e82eb0f8d3","added_by":"auto","created_at":"2025-03-24 05:09:38","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":237942,"visible":true,"origin":"","legend":"\u003cp\u003eStudy site of K72+200 section of Mianxi Yang'an Line\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5008337/v1/0369a7c9689b98bb160579a8.png"},{"id":79068368,"identity":"39e26c20-5c77-443d-9a41-2302ac1e1938","added_by":"auto","created_at":"2025-03-24 05:09:38","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":166155,"visible":true,"origin":"","legend":"\u003cp\u003eExpansive soil specimens\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5008337/v1/746e3601b9e98fdec4e6c499.png"},{"id":79068365,"identity":"0cb5f00a-cbfd-4d11-b21f-2417d272223d","added_by":"auto","created_at":"2025-03-24 05:09:38","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":398010,"visible":true,"origin":"","legend":"\u003cp\u003eTest Instruments\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5008337/v1/1b7b143bec351d4188a80d95.png"},{"id":79068346,"identity":"f5d7e6e6-19b2-4680-b09c-17e901606acc","added_by":"auto","created_at":"2025-03-24 05:09:37","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":69482,"visible":true,"origin":"","legend":"\u003cp\u003eVariation curve of natural dry bulk density with Depth\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5008337/v1/fbb375bb4caf1b25184668cc.png"},{"id":79068348,"identity":"c1e04663-210e-4858-a5ba-c1b90aed71fa","added_by":"auto","created_at":"2025-03-24 05:09:37","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":67161,"visible":true,"origin":"","legend":"\u003cp\u003eUnconfined compressive strength with Depth\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5008337/v1/177358ca89fd722f25684ed4.png"},{"id":79068371,"identity":"26ebe472-2f45-4398-8827-c3835e5da47c","added_by":"auto","created_at":"2025-03-24 05:09:38","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":82507,"visible":true,"origin":"","legend":"\u003cp\u003eThree-way expansion force with Depth\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5008337/v1/bdb59170a96d56cd4860afb4.png"},{"id":79068351,"identity":"de913afb-7df7-4f19-89bc-6a14b17f79c8","added_by":"auto","created_at":"2025-03-24 05:09:37","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":61265,"visible":true,"origin":"","legend":"\u003cp\u003eExpansion as a function of depth h\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-5008337/v1/510b550309b7961c0a768751.png"},{"id":80082469,"identity":"78293529-ee08-4534-904e-59a48be88257","added_by":"auto","created_at":"2025-04-07 16:09:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2943841,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5008337/v1/0d946fa8-e7a8-4989-9c4c-cb5deb46fa1d.pdf"},{"id":79068343,"identity":"5b3508ef-733c-4622-9cbf-3093a6ffc2ec","added_by":"auto","created_at":"2025-03-24 05:09:37","extension":"xlsx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":71426,"visible":true,"origin":"","legend":"","description":"","filename":"Rawdata.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-5008337/v1/4e1b2a58fa917ab4edf29d74.xlsx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Discussion on the change rule of different characteristic parameters with Depth in expansion soil graben slopes","fulltext":[{"header":"0 Introduction","content":"\u003cp\u003eAs China's rail transportation sector continues to evolve, the incidence of projects within expansive soil regions rises annually. Given the subpar engineering characteristics of expansive soil, newly excavated riffle slopes may undergo rapid deformation if timely slope stabilization measures are not implemented. The instability of these riffle slopes poses significant risks to the safe operation of the infrastructure, potentially resulting in substantial economic repercussions\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eDue to its unique expansion, contraction, and fracture, expansive soil often causes slope instability and structural damage in engineering practice, which has become an important research topic in geotechnical engineering. In recent years, scholars at home and abroad have conducted extensive research on the stability, destabilization mechanism, and management technology of expansive soil slopes, and significant progress has been made. However, there are still some deficiencies that need to be further explored.\u003c/p\u003e \u003cp\u003eIn studying the stability of expansive soil slopes, Ning Xinyang \u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e constructed a prediction model based on the statistical law of crack distribution, which provided theoretical support for slope stability analysis. On the other hand, Chen Dongyu \u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e analyzed the destructive modes of expansive soil slopes in detail from the destabilization mechanism and characteristics and proposed corresponding management measures, which achieved good engineering results. These studies provide essential references for the stability assessment and management of expansive soil slopes. Still, they mainly focus on the analysis at the macro level and lack a systematic study of the internal characteristic parameters of the soil body and its Depth of influence.\u003c/p\u003e \u003cp\u003eIn protecting and managing expansive soil slopes, Xu et al. \u003csup\u003e[\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e used geo-bagging slope protection technology, which effectively prevented crack development and improved the mechanical properties of slopes by isolating the external environmental influencing factors and blocking the internal moisture variation of the soil body. Guo Yipeng et al. \u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e explored the application effect of new geomaterials in expansive soil slopes through experimental research, providing new ideas for protecting expansive soil slopes. Zhang Yang \u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e and others studied the construction technology and quality control points of the \"quicklime\u0026thinsp;+\u0026thinsp;curing agent\" combination of reinforced expansive soil slopes, which provides a reference for similar projects. In addition, Katti et al. \u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e and Clayton et al. \u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e proposed a new design method for expansive soil retaining walls, which further enriched the protection technology system of expansive soil slope. Ning Xinyang et al. \u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e proposed a new flexible integrated protection technology based on \"pressure fast drainage\", which can effectively control slope seepage and improve slope stability. Gong Bi-wei \u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e and Zhu Wu et al. \u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e explored the performance of EPS drag-reducing expansive soil retaining walls through indoor modelling tests and theoretical analysis. They proposed a new form of double-layer protection structure. These studies demonstrated the diversity of expansion soil slope protection techniques. Still, they mainly focused on engineering applications and lacked an in-depth evaluation of the applicability and long-term effects of the methods.\u003c/p\u003e \u003cp\u003eAlthough the existing research in the stability analysis of expansive soil slopes, destabilization mechanism, and protection technology has achieved significant results, the lack of in-depth study of the soil body parameters' internal characteristics mainly focused on the macro level of slope stability analysis. In contrast, the internal factors of the soil body parameters (such as dry weight, three-way expansion force, expansion, etc.) and their impact on the Depth of the study are more scarce. Secondly, there is insufficient attention to the long-term stability of the riffle slope. Expanded soil riffle slopes will experience a long-term evolution process from the \"unadaptive stage\" to the \"adaptive stage\" after excavation. At the same time, the existing studies are primarily focused on the analysis of short-term stability, and there is a lack of analysis of the long-term slope that has been stabilized. Analysis. Based on the above shortcomings, this paper selects different working points of the expanded soil graben slope, systematic research on the internal characteristics of the soil body parameters of the law of change and the Depth of influence, aimed at providing a more scientific theoretical basis for the design and management of the expanded soil graben slope.\u003c/p\u003e"},{"header":"1 Overview of the excavation slope work site","content":"\u003cp\u003eBecause the Graben Valley slope is directly affected by the natural camping force and human factors, the indicators change with the Depth. To study the Depth of its influence, through the field investigation of Ankang Xiangyu line K312 + 650 section, Xixiang Yangan line K211 + 320 section, and Mianxi Yangan line K72 + 200 section of the railroad graben valley slopes, the field test map as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e1\u003c/span\u003e - Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Soil samples were taken for an indoor characteristic parameter test to seek the change rule with Depth; the specific workplace profile is shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e below.\u003c/p\u003e \u003cdiv class=\"gridtable\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\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\u003eOverview of expansive soil trench slope index test site\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSite name\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003emileage\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eslope height\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eslope\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eForms of protection\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eepigenetic characterization\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003efracture\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnkang City, Shaanxi Province\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eXiangyu line K312 + 650 above the first level platform on the left side of the line\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12m\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1:1.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.5×2.5m sheet rock lattice berm with internal turf planting\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBrownish red contains\u003c/p\u003e \u003cp\u003eferromanganese nodule\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eFissures are developed, and cut soils are prismatic or vertically prismatic.\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eXixiang County, Hanzhong City, Shaanxi Province\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eYangan line K211 + 320 above the first level platform on the right side of the line\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10m\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1:1.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSupported infiltration trenches spaced 10m apart, slopes planted with Sophora japonica\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBrownish-red, greyish-green, wormlike bands of greyish-white, greyish-green clay with ferromanganese nodules\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eFissures are developed, some with smooth and abraded fissure surfaces, easily weathered into grains\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMianxi County, Hanzhong City, Shaanxi Province\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAbove the highway on the right side of line K72 + 200 of the Yangan Line\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8m\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1:1.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNatural slopes of farmland, no more cultivation within 1.5×1.5m around the observation site, no protection\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBrownish red, containing ferromanganese nodules\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eFissure development, easy to weather into loose grains\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e "},{"header":"2 Soil Sample Collection and Testing Program","content":"\u003ch2\u003e2.1 Soil Sample Collection\u003c/h2\u003e\u003cp\u003eThe sampling is done by a thin-walled in-situ soil sampler, which takes in-situ soil samples vertically on the riffle slope to different depths within the riffle slope. All three work sites are carried out in March of the dry season to facilitate the sampling and field test.\u003c/p\u003e\u003cp\u003eAccording to the Standard for Geotechnical Test Methods (GBT 50123 − 2019)\u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e, the fundamental physical and mechanical property tests are conducted on expanded soil samples collected from various working points. The parameters of the physical and mechanical properties of the assessed working points are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Subsequently, in line with the Special Geotechnical Investigation Procedures for Railway Engineering (TB 10038 − 2022)\u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e, the free expansion rate index is employed to categorize the soil samples from the three working points into expansive soil classifications. The Ankang expansive soil exhibits a free expansion rate of 67%, which falls within the 60–90% range, thus classifying it as moderately expansive. In contrast, the free expansion rates of the Xixiang and Mianxi expansive soils are approximately 60%, positioned within the 40–60% range, thereby categorizing them as weakly expansive soils.\u003c/p\u003e\u003cdiv class=\"gridtable\"\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=\"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=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\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\u003eParameters of physical and mechanical properties of the site\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e\u003ccolgroup cols=\"8\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eobservation site\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDepth range (m)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003enatural capacity\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\gamma\\:}(\\text{g}/\\text{c}{\\text{m}}^{3})\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNatural moisture content\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{w}}_{0}\\)\u003c/span\u003e\u003c/span\u003e(%)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eplastic limit\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{w}}_{\\text{P}}\\)\u003c/span\u003e\u003c/span\u003e(%)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eliquid limit\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{w}}_{\\text{L}}\\)\u003c/span\u003e\u003c/span\u003e(%)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eplasticity index\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{I}}_{\\text{P}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003efree inflation rate\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{F}}_{\\text{s}}\\)\u003c/span\u003e\u003c/span\u003e(%)\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eAnkang\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0-0.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.03\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e22.45\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e20.7\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e46.8\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e26.1\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e67\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.5-1.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.20\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e23.02\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e21.2\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e47.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e25.8\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e63\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.0–2.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.24\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e24.28\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e23.8\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e48.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e24.7\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026gt;2.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.20\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e27.43\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e24.2\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e49.8\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e25.6\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e71\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eXixiang\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0-0.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.98\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e22.43\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e20.1\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e39.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e19.4\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e57\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.5-1.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.11\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e24.12\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e20.9\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e41.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e20.1\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.0–2.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.22\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e24.56\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e22.4\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e41.7\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e19.3\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e59\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026gt;2.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.20\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.28\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e23.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e42.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e19.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e63\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eMianxi\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0-0.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.02\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e22.39\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e21.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e40.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e19.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e59\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.5-1.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.14\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e24.03\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e22.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e41.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e19.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e61\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.0–2.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.19\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e23.98\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e23.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e42.3\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e18.8\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e62\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026gt;2.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.23\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e25.56\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e24.7\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e42.8\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e18.1\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e67\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e\u003ch3\u003e2.2 Research protocol\u003c/h3\u003e\u003ch2\u003e2.2.1 Sample Preparation\u003c/h2\u003e\u003cp\u003eThe in-situ soil samples underwent complete crushing and were sieved through a 2 mm mesh to determine the wet bulk density. Subsequently, the dry bulk densities at three distinct working points were derived from the samples' natural moisture content. A remoulded ring cutter sample with a height of 20 mm and a diameter of 61.8 mm was created using a hydraulic press (refer to Figure. 4) and subsequently placed in a humidor for over 24 hours for preservation.\u003c/p\u003e\u003ch3\u003e2.2.2 Test Methods\u003c/h3\u003e\u003cp\u003eIn this experiment, dry bulk weight, unconfined compressive strength, three-way expansion force, and unloaded expansion rate tests were conducted, and the matrix of the tests is shown in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e\u003cdiv class=\"gridtable\"\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\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\u003eExperimental matrix table\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExperimental items\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTesting methods\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eParameters\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDepth ranges(m)\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDry weight test\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBy the Standard for Geotechnical Test Methods (GBT 50123 − 2019)\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDry weight (g/cm³)\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e0-0.5,0.5-1.0, 1.0–2.0, \u0026gt; 2.0\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUnconfined compressive strength test\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUse of YYW-2 type unconfined pressure gauge\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUnconfined compressive strength (kPa)\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThree-way expansion force test\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUsing a three-way expansion meter\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVertical expansion force and horizontal expansion force (kPa)\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLoadless Expansion Rate Test\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUsing WZ-1 type expansion meter\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eExpansion volume (%)\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e\u003ch2\u003e(1)Unconfined compressive strength test\u003c/h2\u003e\u003cp\u003eThe unconfined compressive strength is used to investigate the deformation and damage exhibited by the in-situ soil samples when subjected to pressure without lateral constraints to determine their strength and mechanical properties. The strength of expansive soils is mainly controlled by the distribution of fissure surfaces, density, shape, water content status on the fissure surfaces, and filling materials, so the field unconfined compressive strength test was used. The test was chosen for the dry season to minimize the influence of the difference in water content at different depths on the strength. The test apparatus was a YYW-2 type unconfined compression apparatus (refer to Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a)); its main parameters are shown in Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e\u003cdiv class=\"gridtable\"\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\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTest parameters of unconfined compressive strength specimens\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{ℎ}}_{0}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003e(mm)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{D}}_{0}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003e(mm)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{A}}_{0}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003e(\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{c}\\text{m}}^{2}\\)\u003c/span\u003e\u003c/span\u003e)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003equantitative force loop coefficient\u003c/p\u003e \u003cp\u003e(Kg/mm)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eScrew rise height per handwheel revolution\u003c/p\u003e \u003cp\u003e(mm)\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e39.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12.2\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e22.65\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e\u003ch3\u003e(2)Three-way expansion force test\u003c/h3\u003e\u003cp\u003eIn expansive soil slope within a unit, when the water content changes, the unit soil body in the surrounding soil body constraints under the expansion of the force state is three-dimensional nature, and the stability of the slope plays a role in addition to the vertical expansion force, but also includes the horizontal expansion force pointing to the side of the slope face as well as due to the repeated drying and wetting and expansion of some of the cracks caused by the three-way expansion force. Hence, the study of the three-way expansion force is essential. In this test, a square specimen was cut by a square ring cutter according to the sampling orientation (vertical direction Z, graben slope extension horizontal direction X, and airside horizontal direction Y) and put into the three-way expansion meter (refer to Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b)) according to the orientation. Under the condition of controlling the deformation amount to be zero, the specimen's top and bottom were immersed in water simultaneously to get the specimen's expansion force in the three directions.\u003c/p\u003e\u003ch3\u003e(3)Loadless Expansion Rate Test\u003c/h3\u003e\u003cp\u003eThe unloaded expansion rate test is designed to simulate the loading state of foundation soil to understand its expansion process. The test adopts an expansion meter (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e5\u003c/span\u003e(c)). The deformation of the specimen in contact with water does not exceed 0.01mm within 6 hours, which is considered stable. The test is generally stabilized after 24 to 36 hours.\u003c/p\u003e"},{"header":"3 The change rule of different characteristic parameters with Depth","content":"\u003ch2\u003e3.1 Variation of natural dry weight with Depth\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e6\u003c/span\u003e plots the variation of natural dry bulk weight with Depth. The Figure shows that the riffle slopes of the three work sites all significantly change surface dry bulk weight in the depth range of 1.0 m, especially at 0.5 m, followed by a gradual stabilization. Numerically, the surface riffle slopes in Xixiang showed the most significant change, increasing from 1.43\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{g}/\\text{c}{\\text{m}}^{3}\\)\u003c/span\u003e\u003c/span\u003e at 0.2 m to 1.63\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{g}/\\text{c}{\\text{m}}^{3}\\)\u003c/span\u003e\u003c/span\u003e at 0.5 m, i.e., the dry bulk density increased by 14%. Ankang, due to the lattice berm protection, had a more minor change than the Xixiang riffle slope, which was only protected by the supporting seepage trench.\u003c/p\u003e\u003cp\u003eSome of the data nodes were taken for further analysis, and if the dry weight value at 3.0 m is used as unit 1, the calculation of the dry weight ratio at different depths is included in Table\u0026nbsp;\u003cspan refid=\"Tab8\" class=\"InternalRef\"\u003e5\u003c/span\u003e below.\u003c/p\u003e\u003cdiv class=\"gridtable\"\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=\"left\" 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=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003ctable float=\"Yes\" id=\"Tab7\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDry bulk density and ratio of trench slopes at different depths\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSampling depth\u003c/p\u003e \u003cp\u003e(m)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eAnkang\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eXixiang\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003eMianxi\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{{\\gamma\\:}}_{\\text{d}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003e(\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{g}/\\text{c}{\\text{m}}^{3}\\)\u003c/span\u003e\u003c/span\u003e)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRatio\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{{\\gamma\\:}}_{\\text{d}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003e(\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{g}/\\text{c}{\\text{m}}^{3}\\)\u003c/span\u003e\u003c/span\u003e)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRatio\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{{\\gamma\\:}}_{\\text{d}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003e(\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{g}/\\text{c}{\\text{m}}^{3}\\)\u003c/span\u003e\u003c/span\u003e)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eRatio\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.51\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.90\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.43\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.84\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.42\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.85\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.61\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.96\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.63\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.96\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.53\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.91\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.66\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.69\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.62\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.96\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.67\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.70\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.67\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.67\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.70\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.68\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e\u003cp\u003eIt is clear from Table\u0026nbsp;\u003cspan refid=\"Tab8\" class=\"InternalRef\"\u003e5\u003c/span\u003e that the dry capacity of the Ankang and Xixiang riffle slopes at 1.0 m is 0.99 of the dry capacity at 3.0 m, and it remains the same when it reaches 2.0 m. The dry capacity of the riffle slopes at 1.0 m is 0.99 of the dry capacity at 3.0 m. Therefore, it can be assumed that for the general turf and Sophora japonica-protected Graben Valley slope, the dry weight corresponds to a depth of about 2.0 meters when keeping the original soil. The Mianxi Graben Valley slope depth of 2.0 meters below the dry weight remains unchanged; the reason is that the Mianxi slope is a natural slope of farmland, planting crops twice a year, farmers frequently cultivate, the application of organic fertilizers to make the soil loose, destroying the continuous growth of the plant root system, it is difficult to form the surface of the protective role of the root layer of the plant.\u003c/p\u003e\u003ch2\u003e3.2 Variation of unconfined compressive strength with Depth\u003c/h2\u003e\u003cp\u003eThe Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows that the graphs of unconfined compressive strength with Depth for the three work sites are incredibly similar. These curves can be divided into a 4-stage change process by Depth: firstly, the depth range of 0-0.5 m; the curve begins to decline slowly and reaches a minimum value when the Depth is 0.5 m; 0.5-1.0 m; the unconfined compressive strength at this stage starts to increase gradually from the minimum value; 1.0–2.0 m. continue to grow, but the growth rate is reduced compared to the previous stage; when the depth range reaches 2.0 m or less, at this time, the curve change amplitude tends to flatten, the unconfined compressive strength slightly up and down, and finally stabilized.\u003c/p\u003e\u003cp\u003eSpecific causes can be analyzed in each section, showing different strength characteristics and forms of damage: ① Depth range 0-0.5 m, the surface soil after repeated dry and wet cycles and achieving a certain degree of remodelling. There are plant roots intertwined, the strength of a large extent by the influence of the root system, with the Depth of the large to small, the specimen was bulging type broken cup, in the damage can be seen in several pulled plant root system. ② Depth range of 0.5-1.0 m, the layer of soil dry weight analyzed in the previous section also gradually increased from small to large values due to the influence of wet and dry cycles, cracks are highly developed, the specimen was bulging type damage and the appearance of many open fissures as the primary form of damage, the strength of the minimum value in this layer. ③ The depth range of 1.0–2.0 m, the fissures gradually become smaller in this layer due to a slight increase in dry bulk weight. Specimen damage has a clear rupture surface, and part of the fissure surface overlaps or is close to the fissure surface; when the fissure surface and the angle are close to \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{45}^{\\text{o}}+{\\phi\\:}/2\\)\u003c/span\u003e\u003c/span\u003e, the intensity is low, and vice versa is high. ④ Depth range below 2.0 m, the analysis within the layer is known to be dry bulk weight remains unchanged, the fissures can be considered to belong to the primary fissures and unloading fissures, weathering has been reduced to a lower degree, the destruction of the specimen is the same form as in the upper layer when the strength increases or decreases slightly about the degree of destruction along the fissure surface.\u003c/p\u003e\u003ch2\u003e3.3 Variation of three-way Expansion Force with Depth\u003c/h2\u003e\u003cp\u003eFrom the test data results, the riffle slope extension direction horizontal expansion force \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{P}}_{\\text{o}\\text{x}}\\)\u003c/span\u003e\u003c/span\u003e compared to the proximity direction horizontal riffle force \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{P}}_{\\text{o}\\text{y}}\\)\u003c/span\u003e\u003c/span\u003e. However, along the depth direction of the riffle, the slope is from small to large, but with the same Depth \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{P}}_{\\text{o}\\text{x}}\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{P}}_{\\text{o}\\text{y}}\\)\u003c/span\u003e\u003c/span\u003e equal, there is no excavation of the riffle slope due to the proximity of the direction of the \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{P}}_{\\text{o}\\text{y}}\\)\u003c/span\u003e\u003c/span\u003e trend to reduce. Therefore, in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e8\u003c/span\u003e, for the sake of eye-catching, only draw a horizontal direction of the expansion force \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{P}}_{\\text{o}\\text{x}}\\)\u003c/span\u003e\u003c/span\u003e and a vertical direction \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{P}}_{\\text{o}\\text{z}}\\)\u003c/span\u003e\u003c/span\u003e. As can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e8\u003c/span\u003e, close to the surface, the dry weight of the specimen is minimal, so the expansion force is also minimal; with the increase in Depth, the dry weight increases, and the expansion force also increases, to reach a depth of 2.0 meters below, the expansion force is unchanged.\u003c/p\u003e\u003cp\u003eFurther analysis shows that: ①There is a difference between the expansion force in the horizontal direction and the expansion force in the vertical direction of the original soil specimens of the expansion soil graben slope. It shows that the expansion force is anisotropic when the water content changes in three directions. The horizontal expansion force is smaller than the vertical expansion force, and the ratio is around 0.5. ②Numerically, the three selected work points show similar expansion force after stabilization due to the relatively close soil property index; specifically, the vertical direction expansion force is generally around 20-30kPa, and the horizontal direction expansion force is generally around 5-15kPa. ③Three kinds of natural moisture content state of the original soil, expansion force test of the post-test moisture content are minimal change, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:\\text{W}=1-2\\text{%}\\)\u003c/span\u003e\u003c/span\u003e. It shows that most of the natural state of the expansion of the soil, in the case of volume unchanged after the water expansion of the water content change, is relatively small.\u003c/p\u003e\u003ch2\u003e3.4 Variation of Expansion with Depth\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e9\u003c/span\u003e plots the curves of expansion with Depth. These curves can be equally divided into four segments according to Depth: first depth range 0-0.5 m, the curve decreases rapidly; when the Depth of 0.5 m, close to the minimum; 0.5-1.0 m, the curve continues to decrease in this stage, but the rate of decline slows down, reaching 1.0 m, the minimum occurs; 1.0–2.0 m, the amount of expansion with the Depth of the increase in the amount of expansion slightly increased; when the depth range reaches 2.0 m below when the magnitude of the curve change tends to flatten out, and the amount of expansion rises and falls slightly, remaining essentially constant.\u003c/p\u003e\u003cp\u003eSpecific analysis can be seen: ①Depth range 0-0.5 m, because the closer to the surface, the initial dry weight of the specimen is smaller, the dry shrinkage and wet expansion is more prominent, so the soil curing cohesion is closer to the complete loss of the soil, thus showing remodelling of the expansion characteristics of the soil, i.e., the expansion of a large amount of the expansion limit of the soil layer is enormous. Hence, the expansion of the Depth of the decreasing rate is swift. The Depth of 0.5 meters is close to the minimum expansion amount. ②Depth range of 0.5-1.0 meters, with the depth increase, the expansion continues to decrease, to a depth of 1.0 meters has had the characteristics of the original state of the soil is not close to the minimum amount of expansion; ③Depth range of 1.0–2.0 meters, the expansion of the amount of Depth with the depth increase and a slight increase in the reason is that with the Depth of change in the dry bulk weight of the slight increase due to the depth change; ④Depth range of 2.0 meters below the measured expansion of the water content is only slightly increased 23% more than the natural moisture content; ④The depth range is below 2.0 meters, and the water content after swelling was measured to be only slightly increased by 2–3% compared to the natural water content, so the amount of swelling remains unchanged.\u003c/p\u003e"},{"header":"4 Discussion of test results","content":"\u003ch2\u003e4.1 Discussion of the law between the characteristic parameters\u003c/h2\u003e\u003cp\u003eAnalyzing Figs.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e6\u003c/span\u003e, \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e7\u003c/span\u003e, \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e8\u003c/span\u003e, \u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e9\u003c/span\u003e, and Table\u0026nbsp;\u003cspan refid=\"Tab8\" class=\"InternalRef\"\u003e5\u003c/span\u003e, it is found that the characteristic parameters roughly coincide with the deformation stratification of the graben slope. The indicators change most significantly when the Depth is near 0–1.0 m. Among them, the lowest value of unconfined compressive strength occurs due to the expansion limit of the surface specimen water content being very high; after rainfall can be fully absorbed, the expansion of a more significant amount, so the surface layer of sliding slump mainly occurs here, that is, in the expansion of the soil in the strong activity layer\u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e.2.0 m near the indicators and the Depth of the in situ soil is not much difference, are tending to stabilize. The specific change rule of each characteristic parameter with Depth is shown in Table\u0026nbsp;\u003cspan refid=\"Tab9\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e\u003cdiv class=\"gridtable\"\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\u003ctable float=\"Yes\" id=\"Tab9\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eVariation of different characteristic parameters of expansive trench slope with Depth\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDepth range\u003c/p\u003e \u003cp\u003e(m)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003edry weight\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{{\\gamma\\:}}_{\\text{d}}(\\text{g}/{\\text{c}\\text{m}}^{3}\\)\u003c/span\u003e\u003c/span\u003e)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUnconfined compressive strength\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{q}}_{\\text{u}}\\)\u003c/span\u003e\u003c/span\u003e(kPa)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eThree-way expansion force\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{P}}_{\\text{o}\\text{z}}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\:\\text{P}}_{\\text{o}\\text{x}}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\:\\text{P}}_{\\text{o}\\text{y}}\\)\u003c/span\u003e\u003c/span\u003e(kPa)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eunlimited expansion\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{V}}_{\\text{H}}\\)\u003c/span\u003e\u003c/span\u003e(%)\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0-0.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThe surface soil is highly loose with minimal dry bulk weight, which gradually increases with Depth\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eStrength is strongly influenced by the plant root system, ranging from large to small, with Depth\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eIn the surface layer, due to the minimum dry weight, the three-way expansion force increases gradually with Depth after reaching the minimum, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{{\\text{P}}_{\\text{o}\\text{z}}＞{\\text{P}}_{\\text{o}\\text{x}}\\text{、}{\\text{P}}_{\\text{o}\\text{y}}；{\\:\\text{P}}_{\\text{o}\\text{x}}\\approx\\:\\text{P}}_{\\text{o}\\text{y}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eThe surface layer exhibits the swelling characteristics of a remodelled soil, i.e., a large amount of swelling, ranging from large to small with Depth, and a high water content after swelling\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5-1.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThe dry mass continues to increase, reaching 1.0 m, essentially 99% of the deep dry mass.\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eThe strength increases after the minimum value occurs, and the specimen's damage is bulging, cracking, or cracking.\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eContinued slow increase\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eExpansion continues to decrease, reaching 1.0 m, essentially the minimum expansion\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.0–2.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSlight increase in dry weight, reaching 2.0 m, essentially the same as the deeper layers\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eStrength continues to increase; specimen destruction has more apparent damage to the surface\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eContinuing to increase slowly. But the rise is even smaller\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSwelling increases slightly with Depth, which is associated with a slight increase in dry bulk weight\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u0026gt;2.0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDry weight remains constant\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eA slight increase or decrease in strength is related to the proportion of damage along the cleavage plane, but overall strength remains constant.\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eExpansion force remains essentially unchanged.\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eThe expansion amount stays the same, and the water content after expansion slightly increases by 2–3% compared with the natural water content.\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e\u003ch2\u003e4.2 Analysis of the damage mechanism of the surface layer of the riffle slope\u003c/h2\u003e\u003cp\u003eThrough the analysis of experimental data, it is evident that the failures of these slopes predominantly originate from the surface layer. This indicates that when excavating slopes in expansive soil areas, the surface soil layers are the first to be unacclimatized to the new environment. The main aspects of their maladaptation to the environment are as follows:\u003c/p\u003e\u003cp\u003e(1)The soil is not well-suited to changes in stress levels. When expansive soil is in its original super-consolidated state, inherent internal stress exists within the soil. Following the excavation of the riffle slope, the stress acting on the surface soil rapidly diminishes to zero. This results in a re-adjustment process of soil stress that gradually occurs from the surface of the riffle slope to the interior soil layer. The transition of the soil body's stress from a state of non-adaptation to one of adaptation is critical. Once the adaptation phase is attained, the riffle slope can be generally stable over the long term. However, if this stage concludes without achieving adaptability, the condition of the riffle slope will inevitably worsen, potentially leading to its failure.\u003c/p\u003e\u003cp\u003e(2) Inadequate adaptation to natural atmospheric forces may occur following the excavation of the graben slope, where the newly exposed surface becomes directly subjected to the effects of atmospheric conditions. Consequently, this surface layer quickly encounters erosion and infiltration from wind, sunlight, and rainfall. As a result, the soil undergoes repeated cycles of drying and shrinking, followed by wetting and expanding annually, ultimately forming a weathering layer that has adapted to atmospheric conditions. If this cyclical process fails to establish a proper adaptation, it could result in detrimental geological phenomena such as erosion, slope failure, and sliding.\u003c/p\u003e"},{"header":"5 Conclusions","content":"\u003cp\u003eUnlike Ning Xinyang \u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e, who focused on macro-stability analysis, this paper goes deep into the soil body. It reveals the differences in the characteristics at different depths, especially the significant changes in the depth indexes of 0–1.0 m. Compared with Chen Dongyu \u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e, who mainly analyzed the damage patterns of expansive soil slopes and proposed measures to manage them, this paper reveals the variation rules of the characteristic parameters with the Depth through the experimental data and finds that the expansion force of expansive soils in three directions is more significant than that in the horizontal direction, and fills the gap of its failure to analyze the anisotropy of expansion force. This paper fills the gap of not investigating the anisotropy of expansion force; Xu et al. \u003csup\u003e[\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e–\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e focus on geotechnical bag type slope protection technology engineering applications, not in-depth analysis of the internal characteristics of the soil body parameter changes, while this paper through the different sites of expansion of the soil riffle slope of the field and indoor testing, systematic study of the dry bulk weight, unconfined compressive strength, three-way expansion force and expansion with the change rule of the Depth of the expansion of the soil riffle slope surface damage mechanism.\u003c/p\u003e\u003cp\u003eThe main research conclusions developed in this paper are as follows.\u003c/p\u003e\u003cp\u003e(1) The wet expansion and dry contraction characteristics of expansive soils lead to the loosening of the surface layer of the riffle slope in the range of 0–1.0 meters, and the dry weight and strength are significantly reduced while the changes in various indexes in the range of 1.0–2.0 meters are relatively small.\u003c/p\u003e\u003cp\u003e(2) The Expansive soil rift slope original soil is anisotropic; the vertical expansion force is greater than the horizontal expansion force, and the ratio is about 0.5.\u003c/p\u003e\u003cp\u003e(3) The expansion of in-situ soil under natural water content conditions is minimal, and the water content increases by only 2–3% after expansion, indicating that the water in the expanded soil can seep through the cracks to the deeper soil layers.\u003c/p\u003e\u003cp\u003e(4) Expansive soil riffle slope damage begins at the surface. A lack of adaptation to changes in soil stresses and the natural camping forces of the atmosphere primarily characterizes it.\u003c/p\u003e\u003cp\u003eRegarding the research on expansive soil graben slopes and slopes, long-term monitoring studies should be carried out in the future to monitor expansive soil graben slopes in the long term and assess their stability changes under different seasons and climatic conditions to validate the conclusions of the existing studies further; moreover, multidisciplinary knowledge such as geology, hydrology, and ecology should be combined to explore the stability mechanism of expansive soil slopes in-depth and to probe for more effective protection techniques; further exploration is needed for the It is necessary to examine further the application of new geomaterials and reinforcement techniques in expansive soil slopes to improve the long-term stability of slopes.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eChaozheng Shen (First Author): Conceptualization, Data Curation, Formal Analysis, Investigation, Methodology, Writing-Original Draft, Writing-Review \u0026amp; Editing;Xueyun Miao (Corresponding Author): Funding Acquisition, Resources, Supervision, Writing-Original Draft, Writing-Review \u0026amp; Editing;Yongqiang Li (Third Author): Methodology, Supervision.All authors participated in the manuscript review.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData is provided within the manuscript or supplementary information files.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eLiao Shiwen. Expansive soil and railway engineering[M]. Beijing: China Railway Publishing House, 1984.\u003c/li\u003e\n\u003cli\u003eXiao Shiguo. Stability analysis of expansive soil cutting slope[J]. Rock and Soil Mechanics, 2001, (02): 152-155.\u003c/li\u003e\n\u003cli\u003eNing Xinyang,ZENG Jun,LV Guoliang. Stability Analysis and Reinforcement Design of Expansive Soil Slope Considering Fracture Statistical Distribution[J]. Water Resources and Hydropower Engineering,2022,53(S1):436-441.\u003c/li\u003e\n\u003cli\u003eChen Dongyu. Comprehensive treatment of expansive soil slope collapse[J]. China High and New Technology,2022,(10):118-120.\u003c/li\u003e\n\u003cli\u003eXU Y F, HUANG J, DU Y J, et al. Earth reinforcement using soilbags[J]. Geotextiles and Geomembranes, 2008, 26(3): 279-289.\u003c/li\u003e\n\u003cli\u003eXU Y F, HUANG J. Case study on earth reinforcement using soilbags[C]// Proceedings of the 4th Asian Regional Conf on Geosynthetics. Shanghai, 2008.\u003c/li\u003e\n\u003cli\u003eMATSUOKA H, LIU S H. New earth reinforcement method by soil bags (\u0026quot;do now\u0026quot;)[J]. Soils and Foundations, 2003, 43(6): 173-188.\u003c/li\u003e\n\u003cli\u003eGuo Yipeng, Nie Rusong, ZHANG Xiong, Zhang Yongjie, Chen Jiejin, Zou Quan. Experimental study on water migration of expansive soil treated by new geotextiles[J]. Journal of Railway Science and Engineering:1-10.\u003c/li\u003e\n\u003cli\u003eZhang Yang. \u0026quot;Lime + curing agent\u0026quot; composite improved expansive soil slope backfill construction technology[J]. Science and Technology Innovation,2022,(18):137-140.\u003c/li\u003e\n\u003cli\u003eKATTI RK, BHANGALE E S, MOZA K K. Lateral pressure in expansive soil with and without a cohesive non-swelling soil layer-application to earth pressures on cross drainage structures in canals and key walls in dams (Studies on K0 Condition)[R]. New Delhi: Central Board of Irrigation and Power, 1983.\u003c/li\u003e\n\u003cli\u003eCLAYTON C R I, SYMONS I F, HIEDRA-COBO J C. The pressure of clay backfill against retaining structures[J]. Canadian Geotechnical Journal, 1991, 28(2): 282-297.\u003c/li\u003e\n\u003cli\u003eNing Xinyang, Zeng Jun, Zeng Linghua. Research on flexible, comprehensive protection scheme of expansive soil slope based on \u0026quot;pressure and fast drainage\u0026quot;[J]. Water Resources and Hydropower Express,2022,43(02):52-56+62.\u003c/li\u003e\n\u003cli\u003eGong Biwei. Fractures, Strength, and Relationship between Expansive Soil and Slope Stability[J]. Journal of Yangtze River Research Institute,2022,39(10):1-7.\u003c/li\u003e\n\u003cli\u003eZhu Wu, Dou Hao, Yin Nazheng, Cheng Yiqing, Zhang Shuangcheng, Zhang Qin. Analysis of Deformation Characteristics of Expansive Soil Slope Based on Combined InSAR and SSA: A Case Study of South-to-North Water Diversion Project[J]. Journal of Surveying and Mapping,2022,51(10):2083-2092.\u003c/li\u003e\n\u003cli\u003eGB/T 50123-2019, Standard for geotechnical test methods[S].\u003c/li\u003e\n\u003cli\u003eState Railway Administration. TB 10038\u0026minus;2022, Regulations for special geotechnical investigation of railway engineering [S] Beijing: China Railway Press, 2022.\u003c/li\u003e\n\u003cli\u003eZhang Delong, Miao Xueyun, Shen Chaozheng. Study the Mechanism of Expansive Ripping Soil Disease and Comprehensive Control Measures[J]. Shanxi Architecture, 2024, 50 (03): 82-85+89.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Expansive soil slope, depth range, dry bulk density, unconfined compressive strength, three-dimensional expansion force, expansion amount","lastPublishedDoi":"10.21203/rs.3.rs-5008337/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5008337/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eExpansive soil due to wet expansion and dry contraction of engineering properties, resulting in the stability of the riffle slope, has been one of the key issues in the expansion of soil area earthworks; this paper, through the three representative riffle slope site field visits and indoor tests, respectively, from the dry bulk weight, unconfined compressive strength, three-way expansion force and expansion with the change rule of the Depth of the law to be explored. The three-way expansion force test shows that the extension and proximity direction of the horizontal expansion force are the same. The vertical direction is greater than the horizontal direction, and its ratio is about 0.5. Further analysis of the relationship between the characteristics of the parameters with the Depth can be seen: the surface soil indicators are more varied, between 0.5-1.0 m, the soil layer dry density is small, the expansion of the soil wet expansion and drying shrinkage is significant, and the unconfined compressive strength is close to or has reached the lowest value; expansion force and expansion volume test indicators along the Depth of the graben slope, the expansion force and expansion volume test indicators are more varied. Expansion force and expansion amount test indexes change along the Depth of the riffle slope but remain unchanged after 2.0 m. Therefore, the damage of the expansion soil riffle slope mainly occurs in the soil layer near the Depth of 1.0 m, which is manifested explicitly as a failure to adapt to the change of stress in the soil and the inability to adjust to the atmospheric natural camping force.\u003c/p\u003e","manuscriptTitle":"Discussion on the change rule of different characteristic parameters with Depth in expansion soil graben slopes","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-24 05:09:32","doi":"10.21203/rs.3.rs-5008337/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Accepted","date":"2025-03-25T14:47:03+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-03-20T05:21:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"263139049095678401321667553329961382447","date":"2025-03-19T09:10:28+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-03-19T07:24:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"216155258719755137833495823579087717393","date":"2025-03-19T06:56:44+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-03-19T06:39:30+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-03-18T13:58:14+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-02-27T08:52:55+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"babe351a-3b04-4c9a-8232-f22d0cf12bf4","owner":[],"postedDate":"March 24th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":45897360,"name":"Earth and environmental sciences/Natural hazards"},{"id":45897361,"name":"Physical sciences/Engineering"}],"tags":[],"updatedAt":"2025-04-07T16:07:50+00:00","versionOfRecord":{"articleIdentity":"rs-5008337","link":"https://doi.org/10.1038/s41598-025-96062-y","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-03-31 15:57:49","publishedOnDateReadable":"March 31st, 2025"},"versionCreatedAt":"2025-03-24 05:09:32","video":"","vorDoi":"10.1038/s41598-025-96062-y","vorDoiUrl":"https://doi.org/10.1038/s41598-025-96062-y","workflowStages":[]},"version":"v1","identity":"rs-5008337","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5008337","identity":"rs-5008337","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}