Resilient Roads in Challenging Terrain: A Case Study of Siddhartha Highway in Nepal

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Chhetri, Rishav Jaiswal, Rabina Poudel This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4505046/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract Nepal is a country known for its diverse and challenging topography, and it relies heavily on a robust road infrastructure network to connect its remote regions and urban centers. This study addresses the critical need for enhanced road safety and infrastructure resilience on the Siddhababa road section of the Siddhartha Highway, Nepal, notorious for its high accident rates and susceptibility to landslides. Given the road's strategic importance in connecting remote regions and its challenging topographical conditions, our research aimed to identify the most suitable pavement type to mitigate these issues. Through a detailed examination incorporating eight different soil tests, alongside evaluations of traffic loads, weather conditions, and existing pavement performance, we adopted a comparative analysis methodology to assess the viability of flexible versus rigid pavements within this unique context. Results revealed that the soil composition and environmental conditions of the Siddhababa section significantly influence pavement performance, with specific gravity, moisture content, and California Bearing Ratio (CBR) tests indicating a nuanced suitability for both pavement types under varying circumstances. Our analysis concluded that, despite the economic and staged reinforcement benefits of flexible pavements, the durability, safety, and maintenance considerations favor the adoption of rigid pavement for the Siddhababa road section. However, acknowledging the economic constraints, a hybrid approach is recommended, emphasizing rigid pavements for the most vulnerable sections and flexible pavements elsewhere. This study contributes to the pavement engineering field by providing a model for pavement type selection in mountainous regions, aiming to enhance road safety and durability amidst challenging environmental conditions. challenging topography road network flexible and rigid pavement road safety and durability Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1. Introduction Nepal's road infrastructure plays a pivotal role in its socio-economic development, connecting remote and rugged terrains with urban centers and facilitating trade, tourism, and access to education and healthcare. However, the country's diverse and challenging geographical conditions, characterized by mountainous regions, steep slopes, and seismic activity, pose significant challenges to road construction and maintenance. The rugged terrain not only complicates the design and construction process but also increases vulnerability to natural disasters such as landslides, floods, and earthquakes, which can severely impact road safety and durability (Hearn & Shakya, 2017; Yousefi et al., 2022). These challenges underscore the importance of selecting appropriate pavement types that can withstand Nepal's unique environmental conditions and ensure reliable and safe road transportation. The selection between flexible and rigid pavements is a critical decision in road construction that significantly affects the infrastructure's long-term performance, safety, and cost-effectiveness. The literature provides extensive insights into the advantages, challenges, and application contexts of both pavement types, drawing from experiences and studies conducted globally and within Nepal's unique topographical settings. Flexible pavements, composed of layers of materials with decreasing stiffness from the top (surface) layer down to the subgrade, flex under load, distributing stresses over a broader area of the subgrade. The studies by Laldintluanga et al. (2023) and Rashid & Gupta (2017) have underscored the cost-effectiveness and ease of repair of flexible pavements, particularly in developing countries with limited resources. However, the long-term performance of flexible pavements can be significantly affected by moisture infiltration, requiring effective drainage solutions to maintain their structural integrity and prevent premature failure (Laldintluanga et al., 2023; Aghamelu & Okogbue, 2011). Rigid pavements, primarily composed of Portland cement concrete, are characterized by their ability to distribute loads over a small area of the subgrade without significant bending or flexing. Their inherent strength and stiffness make them less dependent on the subgrade for structural support, offering superior durability and resistance to traffic loads and environmental conditions. According to Bansal (2018), rigid pavements exhibit better performance in resisting deformation and cracking over time, making them a cost-effective solution in the long run despite their higher initial construction cost (Bansal, 2018; Aryal, 1999). The environmental sustainability of pavement materials and construction methods has also become a significant consideration in pavement selection. Research by Papagiannakis and Masad (2008) highlights the potential for both flexible and rigid pavements to incorporate recycled materials and innovative technologies to reduce their environmental impact. These considerations are particularly relevant in the context of Nepal's commitment to sustainable development and environmental conservation (Papagiannakis & Masad, 2008; Sadek, Kaysi, & Bedran, 2000). The design of pavements in mountainous regions like Nepal presents unique challenges, including variable weather conditions, steep gradients, and susceptibility to natural hazards. Shrestha et al. (2014) conducted a multi-objective analysis of rural road networks in the hilly regions of Nepal, emphasizing the importance of integrating transportation research with local geographical and socio-economic factors (Shrestha et al., 2014). Comparative studies in the Himalayan regions have shown that the choice between flexible and rigid pavements must consider factors such as slope stability, potential for seismic activity, and the need for regular maintenance (Hearn & Shakya, 2017; Yousefi et al., 2022; Bayan, 2013). The integration of geotechnical engineering principles with pavement design is essential to ensure the safety and reliability of road infrastructure in these challenging environments (Choudhary, Garg, & Jain, 2024; Sauer, 1967). In response, this study aims to systematically evaluate the performance of different pavement types in the context of the Siddhababa road section to identify the most suitable pavement design that enhances safety and durability. Specifically, the study seeks to: 1. Conduct comprehensive soil tests to assess the subgrade conditions unique to the Siddhababa road section. 2. Compare the advantages and limitations of flexible and rigid pavements, considering the local environmental and traffic conditions. 3. Propose a pavement design that addresses the identified challenges, aiming to reduce accident rates and improve the longevity of the road infrastructure. The significance of this study extends beyond the Siddhababa road section, offering valuable insights for the construction and maintenance of roads in similar mountainous terrains within Nepal and other countries with comparable geographical challenges. By providing evidence-based recommendations for pavement selection and design, this research contributes to the broader goal of enhancing road safety, reducing maintenance costs, and improving transportation efficiency in regions where road travel is fraught with risks due to natural and man-made factors. Ultimately, the study aims to support the development of more resilient and reliable road infrastructure, thereby supporting Nepal's ongoing efforts towards sustainable development and improved quality of life for its citizens. 2. Study Area Description The Siddhababa road section, part of the crucial Siddhartha Highway in Nepal, stretches for 3.5 kilometers from Golpark in Butwal Sub Metropolitan City (ward no. 3) to Dobhan in Tinau Rural Municipality (ward no. 3), Palpa. This segment is renowned not only for its vital role in connecting urban and rural locales but also for its challenging terrain that typifies Nepal's rugged landscape. The road's geographical features include steep gradients and close proximity to the Tinau River valley, heightening the risk of landslides and erosion, particularly during the monsoon season. Climatically, the area is subject to a subtropical highland climate, with a pronounced wet season bringing heavy rainfall and a dry season marked by dust and potential water scarcity. Traffic along this road is diverse, encompassing local commuters, long-distance travelers, and heavy trucks, underscoring the need for a pavement design that can withstand such varied use while ensuring safety and efficiency. Adding to the complexity of the Siddhababa road section is its cultural and environmental significance, highlighted by the presence of the Siddhababa Temple, a site of high ritual value that attracts pilgrims and increases pedestrian traffic. The existence of a perennial spring and additional seasonal springs along the road further influences its hydrological dynamics and the surrounding ecosystem. These factors together necessitate a multifaceted approach to road design and maintenance, one that considers the safety of both vehicular and pedestrian traffic, the preservation of cultural sites, and the mitigation of environmental impacts. This intricate blend of geographical, climatic, traffic, and cultural considerations makes the Siddhababa road section a compelling case study for developing resilient and sustainable road infrastructure in mountainous regions. 3. Soil Testing and Analysis In the study, various soil testing methods such as Grain Size Analysis, Specific Gravity Test, Density Test, Direct Shear Test, and Atterberg Limits Test were conducted. These tests were crucial for understanding the characteristics of the soil, including its gradation, density, shear strength, and plasticity. For example, the Grain Size Analysis helped determine soil gradation, essential for assessing drainage and stability, while the Specific Gravity and Density Tests provided insights into the soil's load-bearing and compaction capabilities. The Direct Shear and Atterberg Limits Tests revealed the soil's shear strength and plasticity, respectively, which are critical for assessing its suitability under different loading and environmental conditions. 3.1 Grain Size Analysis (Sieve Analysis) : The test separates soil particles into different size ranges by passing them through a series of sieves of decreasing mesh size. Samples were collected at various depths and locations along the road section to ensure representativeness of the soil types of present. This test is done to determine the soil gradation, which is crucial for assessing the soil's drainage capacity and stability as a base/subbase material. The soils were predominantly classified as well-graded sand and soil (A-1-a, A-1-b, A-3), indicating good drainage characteristics and suitability for use in pavement layers with proper compaction. 3.2 Specific Gravity Test (Pycnometer Method) : This test measures the ratio of the density of the soil solids to the density of water, using a pycnometer. Small, oven-dried soil samples were used to minimize moisture content's effect on the measurement. This test is done to assess the soil particles' density, affecting the soil's load-bearing capacity and compaction characteristics. Table 1 Specific Gravity of each sample Sample S.N. Parameters 1 2 3 4 1 Wt. of Pycnometer Bottle (W1) 703 703 703 703 2 Wt. of Pycnometer + dry soil (W2) 987 993 999 985 3 Wt. of Pycnometer + dry soil + water (W3) 1.752 1768 1746 1740 4 Wt. of Pycnometer + water 1.591 1591 1592 1591 5 Specific Gravity (G) 2.309 2.566 2.099 2.12 The average specific gravity was found to be 2.476, suggesting that the soil particles are denser than many types of soils, which is favorable for providing a stable foundation. 3.3 Density Test (Optimum Moisture Content and Maximum Dry Density) : The Density Test, specifically the Standard Proctor Test, plays a pivotal role in road construction and pavement foundation design by determining the soil's Optimum Moisture Content (OMC) and Maximum Dry Density (MDD). This test method involves compacting soil samples at varying moisture levels within a mold to identify the moisture content that allows the soil to reach its maximum density. The results from the Density Test for the Siddhababa road section reveal varying OMC and MDD values across the four samples, with an average OMC of 12.265% and an average MDD of 1.809 g/cm³. These values are within the ideal range for road construction, indicating that with proper compaction and moisture control, the soil can provide a stable and durable foundation for the pavement. 3.4 Direct Shear Test In our study of the Siddhababa road section, the Direct Shear Test was employed to evaluate the shear strength properties of soil samples under varying conditions of normal stress. The analysis involved subjecting four distinct soil samples to normal stresses of 0.5 kg/cm², 1 kg/cm², and 1.5 kg/cm², and recording the resultant shear stress at various levels of settlement. The Direct Shear Test measures the maximum shear stress that soil can resist under a given normal stress, providing insights into its shear strength parameters, namely cohesion (C) and angle of internal friction (Φ). The area of the sampler was consistently set to 36 mm² to ensure precise application of forces. The Direct Shear Test results reveal a progressive increase in shear stress with settlement under each level of normal stress, indicating the soil's capacity to resist higher shear forces as compaction increases. Notably, Sample 1 demonstrated significant shear strength, particularly under a normal stress of 1.5 kg/cm², reaching a shear stress of 0.239 kg/cm², suggesting robust resistance to lateral forces. The calculated shear forces and corrected areas enabled the determination of specific shear stress values, offering a granular view of soil behavior under load. The derived values of cohesion (C) and angle of internal friction (Φ) across the samples ranged from 19.61KPA to 29.42KPA for C, and 17 to 20 degrees for Φ, respectively, with average values computed as C = 23 KPA and Φ = 18.375 degrees. These parameters are instrumental for pavement material selection and structural design, indicating that the soils possess adequate shear strength for supporting anticipated loads. 3.5 Atterberg Limits Test Analysis The Atterberg Limits Test, comprising the Liquid Limit and Plastic Limit tests, was conducted to characterize the plasticity and workability of soil samples from the Siddhababa road section. Liquid Limit (LL) determines the moisture content at which soil transitions from a plastic to a liquid state. It indicates how much water a soil can absorb before behaving as a liquid. Plastic Limit (PL) identifies the moisture content at which soil changes from a plastic to a semi-solid state. This limit reflects the soil's ability to be molded or shaped. Plasticity Index (PI) is the difference between the Liquid Limit and the Plastic Limit, representing the range of moisture content where the soil exhibits plastic properties. The results for each sample are summarized as follows in Table 2 . Table 2 Atterberg Limits Test Results - Soil Classification Sample Liquid Limit Plastic Limit Plasticity Index A-Line Classification Soil Type 1 50% 17% 33% 21.9% MH or OH High/Inorganic Clay 2 62.5% 20.4% 42.1% 31.02% CH High plasticity clay 3 75% 27.3% 47.4% 40.15% CH High plasticity clay 4 58% 26% 32% 40.15% CH High plasticity clay The average values across the samples were found to be: Liquid Limit = 61.25%, Plastic Limit = 22.675%, and Plasticity Index = 38.625%. The Atterberg Limits Test reveals significant variability in the plasticity of the soil samples, with Plasticity Index values ranging from 33–47.4%. The high Plasticity Index values observed in Samples 2, 3, and 4 (all classified as CH) indicate soils with high plasticity, which can undergo significant volume changes with moisture variations. 3.6 Moisture Content Tests Using the Oven Dry Method In the context of the Siddhababa road section study, moisture content tests were conducted using the Oven Dry Method to establish the water content of soil samples. The Oven Dry Method involves weighing a soil sample before and after oven drying to determine its moisture content. This process removes all moisture from the soil, allowing for the calculation of water content based on weight loss. The following table summarizes the moisture content test results for four soil samples collected from the study area: To calculate the moisture content, the weight of the dry soil was determined by subtracting the weight of the container (M1) from the oven-dried weight (M3). The weight of moisture was then obtained by subtracting the weight of dry soil from the wet soil weight (M2 - M3). Finally, the total moisture content percentage was calculated using the formula: $$Moisture content \left(\%\right) = \frac{Weight of moisture}{Weight of dry soil}X 100$$ 1 The moisture content tests revealed variations in water content across the samples, with values ranging from 7.53–13.64%. The average moisture content for the soil samples was calculated at 9.575%, indicating the soil's natural condition in terms of water content. 3.7 California Bearing Ratio (CBR) Test Analysis The CBR test measures the resistance of the soil to penetration by a standardized plunger under controlled density and moisture conditions. The test results are expressed as a percentage of the resistance to penetration compared to a standard crushed rock material. This test is critical for designing the pavement thickness by assessing the load-bearing capacity of the soil. Similarly, we would assess the CBR value of each sample using the formulations- $$CBR = \frac{Std Load at Penetration}{Test Load at Penetration}X 100\%$$ 2 The CBR test results reveal a range of soil strength across the samples, with samples 2 and 4 showing higher bearing capacities, making them more suitable for supporting pavements subjected to regular and potentially heavy traffic. Samples 1 and 3, with lower CBR values, might require soil improvement techniques such as stabilization or the use of geotextiles to enhance their load-bearing capabilities. 3.8 Unconfined Compression Test Analysis This test involves compressing a cylindrical soil sample at a constant rate until failure, measuring the axial load and deformation. The test is performed without lateral confinement, allowing the determination of the soil's Unconfined Compressive Strength (UCS) and providing an indirect measure of the soil's shear strength under saturated conditions. The axial stress at failure divided by the initial cross-sectional area of the sample gives the UCS, which is a crucial parameter in evaluating soil stability and suitability for construction projects. The average UCS value for the tested samples was found to be less than 0.25 N/mm², with an average undrained shear strength of 0.105 N/mm², indicating that while some samples exhibit adequate strength for standard pavement applications, others may require stabilization or reinforcement to meet the demands of higher traffic loads or environmental stressors. 4. Pavement Condition Assessment The Siddhababa road section, known for its scenic beauty, is also notorious as one of Nepal's most hazardous routes. This segment has been the site of numerous accidents, prompting an in-depth analysis to identify underlying issues and propose viable solutions. Herein, we outline the principal challenges faced and recommend remedial measures to enhance road safety and efficiency. 4.1 Pothole Formation Potholes were observed approximately every meter along the road, affecting not only flexible but also rigid pavement sections. The primary causes of these potholes include moisture infiltration, the absence of a prime or tack coat between layers, and typically stem from neglected alligator cracking. Given that nearly all potholes were in a severe state, a full-depth replacement patch is recommended. 4.2 Faulting in Rigid Pavements Faulting, characterized by differential settlement at pavement joints, can be seen thoroughly the section which arises from subgrade softening and base course weakening. Temperature fluctuations contribute to slab curling, further accentuating the problem. Implementing dowel bar retrofits for faulting between 3 mm and 12.5 mm can effectively mitigate this issue. Faults exceeding 12.5 mm necessitate complete pavement reconstruction to ensure structural competence and user safety. 4.3 Alligator Cracking Alligator cracking were found in the region of repeated traffic loading. The reason is inadequately designed pavements leading to surface, base, or subgrade failures, manifesting as alligator cracking. Targeted full-depth patching followed by milling and resurfacing of the affected sections are recommended to address these structural failures comprehensively. 4.4 Rutting Heavy traffic from large vehicles such as trucks and tippers frequently using this road segment leads to the formation of ruts, which are grooved depressions in the pavement. This issue primarily arises from several factors: inadequate thickness of the pavement, insufficient compaction of the asphalt, stone base, or underlying soil, the use of weak asphalt mixtures, or the penetration of moisture. For minor or stabilized ruts, overlay techniques suffice. However, severe deformations require excavation and replacement with appropriately designed materials to restore functionality. 4.5 Water-Induced Damage Water poses a significant threat to pavement integrity, as evidenced by photos showing damage to the road section surrounding spring water. This issue also leads to slippery pavement surfaces, increasing the risk of accidents. Implementing an effective drainage system, along with an underground drainage system, is recommended to redirect water away from the pavement and towards the opposite side, such as the Tinau River. 4.6 Inadequate Roadside Barriers The Siddhababa road section, situated on high embankments and within hilly terrain, stands approximately 400 meters above sea level. Its proximity to the Tinau River, characterized by a large number of significant boulders, further amplifies the danger of this road section. Consequently, there's a pressing need for critical road safety infrastructure treatments to redirect out-of-control vehicles back onto the road. It has been observed that there are no safety measures in place along the roadside, which poses a serious concern. To enhance safety, the implementation of guard rails, Longitudinal Channelizing Devices (LCDs), and concrete barriers is recommended. 4.7 Slope Stabilization Challenges Given the rocky nature of the hills and the prevalence of large rocks, landslides pose a significant threat in this area, leading to loss of lives, damage to vehicles, and disruptions in reaching destinations. During the rainy season, landslides occur almost daily, making the situation even more perilous. While completely preventing landslides may not be feasible, several precautionary measures and strategies can be employed to mitigate the risk of small landslides and manage smaller rocks. These measures include removing part of the soil or rock, or the load from the top of the slope, to decrease the shear stresses on critical planes. The use of concrete gravity walls, cantilever walls, gabion structures, baby crib walls, and embankment piles can provide necessary resistance against the slope's tendency to topple. Although this section is challenged by heavy rocks, smaller rocks can be managed by installing draped mesh or netting to control their movement. The major issues identified on the Siddhababa road section highlight significant safety and infrastructure concerns, including the presence of heavy vehicles leading to rutting, widespread potholes, faulting in rigid pavements, challenges posed by spring water and poor drainage, dangers associated with high embankments and rocky terrain prone to landslides, and the lack of critical road safety measures. Beyond these substantial problems, there are also numerous other issues such as the absence of essential traffic signboards indicating turns, slippery roads, accident-prone areas, landslide zones, speed limits, construction activities, and parking for Siddhababa temple, among others. Addressing these concerns, even with relatively minor safety precautions, has the potential to significantly reduce the risk of accidents and save lives. The implementation of recommended measures such as improving drainage, installing road safety barriers, stabilizing slopes, and enhancing traffic sign visibility could greatly enhance the safety and functionality of the Siddhababa road section. This underscores the importance of proactive infrastructure management and safety interventions to protect road users in this challenging terrain. 5. Suitability of Pavement Types The comprehensive evaluation of the Siddhababa road section, which suffers from various types of pavement failures, underscores the critical need for thoughtful pavement selection to enhance road safety, durability, and travel efficiency. The decision-making process for pavement type involves considering the subgrade strength, traffic conditions, environmental factors, and economic and safety implications. The 10% California Bearing Ratio (CBR) value of the subgrade suggests a strong foundation, making flexible pavement an appealing choice due to its adaptability to subgrade strength. Flexible pavements offer the advantage of being constructed and reinforced incrementally to accommodate increasing traffic demands. Their initial and maintenance costs are generally lower compared to rigid pavements, providing a cost-effective solution for road construction. The challenging environmental conditions, characterized by frequent landslides and large stones, alongside the road's designation as an accident-prone area, necessitate a pavement solution that prioritizes durability and safety. Rigid pavement, with its robust structure, is capable of maintaining its form under traffic loads and offers superior durability, making it a suitable choice for areas requiring high safety standards and longevity. Although the initial costs of concrete pavement are higher, the long-term benefits of reduced maintenance and a longer design life can justify the investment. Given the diverse needs and challenges of the Siddhababa road section, a balanced approach that considers both economic efficiency and safety is essential. For the 3.5km stretch of Siddhababa road, which presents significant safety concerns and challenging environmental conditions, a strong rigid pavement is recommended. This choice is driven by the need for durability and safety in a national highway context, where preserving life and ensuring reliable transportation are paramount. For the remaining sections of the Siddhartha highway, flexible pavement is suggested, capitalizing on its cost-effectiveness, ease of maintenance, and adaptability to traffic growth. This dual approach allows for the optimization of resources, ensuring both economic and safety objectives are met. By taking a holistic view of the project's requirements, considering the site visits, and analyzing the overall scenario, the conclusion is drawn that adopting a combination of rigid pavement for the high-risk, accident-prone Siddhababa section, and flexible pavement for the rest of the highway, offers the best compromise between safety, durability, and cost-efficiency. 5.1 Design of Flexible Pavement To clarify and structure the explanation for the calculation of the design thickness of a flexible pavement based on the given data and requirements, we'll break down the process into its fundamental steps and formulas. Given Data 1. Average Daily Traffic of Heavy Vehicles (P): 1250 cvpd (commercial vehicles per day) 2. Number of heavy vehicles per day after adjustment for growth (A): 1393.229 cv/day 3. Cumulative Number of Standard Axles (Ns) over the design life: 13.5 million standard axles (msa) 4. Sub-grade California Bearing Ratio (CBR) values from samples: Sample 1: 11.67%; Sample 2: 13.86%; Sample 3: 9.73% and Sample 4: 11.45% Steps and Formulations Step 1: Calculation of Adjusted Daily Traffic The adjusted daily traffic A is calculated using the formula: $$A = p {\left(1+r\right)}^{y}$$ 3 where, 𝑃 is the initial traffic load, 𝑟 is the annual growth rate, and 𝑦 is the number of years considered. For this study, the adjusted traffic resulted in 1393.229 cv/day, assuming a typical growth rate over the specified period. Step 2: Cumulative Number of Standard Axles (Ns) The formula used here is: $${N}_{s}=\frac{365 X A X VDF X LDF X ({\left(1+r\right)}^{n}-1)}{r}$$ 4 where, VDF is the Vehicle Damage Factor, LDF is the Lane Distribution Factor, 𝑟 is the growth rate, and 𝑛 is the number of years in the design life. This calculation yielded an Ns of approximately 13.5 msa. Step 3: Determination of 90th Percentile CBR The 90th percentile CBR is interpolated between the 75th and 100th percentile values, simplifying the design CBR to 10% for practical application purposes, facilitating subsequent calculations. Step 4: Pavement Layer Thickness Design Based on the IRC standard table for flexible pavements and the given cumulative traffic load (Ns) of 13.5 msa along with a sub-grade CBR of 10%, the layer thicknesses are proposed. The calculation involves interpolation between known points for 10 and 20 msa: • For 10 msa, thicknesses are: BC = 40 mm, DBM = 50 mm, Total = 540 mm • For 20 msa, thicknesses are: BC = 40 mm, DBM = 75 mm, Total = 565 mm Given Ns of 13.5 msa, the total thickness is then the sum of these layers plus the base and sub-base layers, equating to 550 mm. Hence, this gets finalized as 40mm as W/C, 60 mm as Binder layer, 250mm as base layer and 200 mm as subbase layer. This detailed explanation illustrates the methodology behind designing the thickness of flexible pavements to accommodate traffic loads and sub-grade conditions effectively. 5.2 Design of Rigid Pavement Step 1: Initial Assumptions and Data • Traffic growth rate ( r ): 7.5% • Design life ( n ): 20 years. • Construction period ( y ): 3 years • Modulus of subgrade reaction ( k ): 8 kg/cm³ • Flexural strength of concrete: 40 kg/cm² • Modulus of Elasticity ( E ): 3××10⁵ kg/cm² • Poisson’s ratio ( µ ): 0.15 • Thermal expansion coefficient of concrete: 10×10 − 6 /°C Given Temperature Gradient: • For Hilly region: 13.1°C at 20 cm, 14.3°C at 25 cm • For Terai region: 16.4°C at 20 cm, 16.6°C at 25 cm The trial slab thickness starts at 20 cm, based on standard practices and initial estimates of pavement performance under anticipated loads and environmental conditions. Step 2: Calculate the Radius of Relative Stiffness (l) for the Initial Trial Thickness Using the initial trial thickness ( h ) of 20 cm: \(l = \sqrt[4]{\frac{E {h}^{3}}{12 \left(1-{\mu }^{2}\right)k}}\) =71.11cm ( 5 ) This calculation is crucial for understanding how the slab will behave under load, considering the stiffness of both the concrete and the subgrade. Step 3: Determine L/l and W/l Ratios With L = 4.5m and W = 3.5m, the ratios are calculated as: L / l = 6.32 and W / l = 4.92 Since L / l > W / l , L / l is the critical condition for design considerations, focusing on the slab's length. Step 4: Interpolate the Coefficient Cv Given L / l ratios, Cv is interpolated for pavement design, resulting in Cv = 0.9 for the initial thickness of 20 cm. Step 5: Average Temperature Gradient and Adjusting for Trial Thickness The average temperature gradient (Δ t ) is calculated by taking the average of the provided gradients for both Hilly and Terai regions. Since the Siddhababa section is not fully in either, an average is used, yielding Δ t = 14.75°C for initial calculations. This step is critical in determining the thermal stresses the pavement will experience. Step 6: Calculate Temperature Edge Stress (fte) Using Cv = 0.9 and the average Δ t , fte is calculated, resulting in 20 kg/cm² for the initial 20 cm thickness. Step 7: Residual Stress and Factor of Safety for the Initial Thickness Residual Stress is calculated as 20 kg/cm² (40 kg/cm² − 20 kg/cm²) and factor of Safety ( fos ) is calculated as 0.714, which is less than 1, indicating the initial thickness is not adequate. Due to the insufficient fos , the trial thickness is increased to 23 cm to improve safety and performance. Step 8: Recalculate L/l, and W/l for Adjusted Thickness For h = 23 cm, l is recalculated, resulting in l = 84.86 cm, and the critical ratios are updated accordingly. Step 9: Interpolate Cv for Adjusted Thickness With the adjusted ratios, Cv is now 0.8, reflecting changes in slab behavior and stress distribution with the increased thickness. Step 10: Recalculate Temperature Edge Stress (fte) for Adjusted Thickness Using the new Cv and an interpolated Δ t for 23 cm, fte is found to be 17 kg/cm². Step 11: Final Factor of Safety and Thickness Determination Residual Stress is now found to be 23 kg/cm² (40 kg/cm² − 17 kg/cm²) and fos i mproves to 1.02, indicating the adjusted thickness is safe. Considering the daily traffic and its growth over the design life, the final thickness is determined as 25 cm (23 cm + 2 cm for traffic adjustments). This comprehensive approach illustrates the iterative process of pavement design, starting from initial assumptions, through critical ratio analysis and thermal stress calculation, to final adjustments based on safety and performance criteria. The increase in trial thickness from 20 cm to 23 cm, followed by the final adjustment to 25 cm, ensures the pavement can safely support expected traffic loads and environmental conditions. 6. Conclusions and Discussions The comprehensive study on the Siddhababa road section of the Siddhartha Highway in Nepal has provided valuable insights into the critical decision-making process involved in selecting the most appropriate pavement type for mountainous terrains, faced with unique environmental challenges and safety concerns. The analysis, grounded in extensive soil testing, traffic load evaluation, and environmental condition assessments, highlighted the nuanced performance of flexible and rigid pavements under the specific conditions of the Siddhababa road section. Despite the initial cost-effectiveness and adaptability of flexible pavements, the study concluded that the durability, safety, and reduced long-term maintenance requirements of rigid pavements offer a more viable solution for this particularly vulnerable road segment. The recommendation for a hybrid approach, utilizing rigid pavement for the most susceptible sections to natural hazards and flexible pavement elsewhere, underscores the importance of a balanced and context-sensitive strategy in pavement engineering to enhance road safety, durability, and economic efficiency. This study contributes significantly to the field of pavement engineering, especially in the context of developing countries like Nepal, where road infrastructure must contend with complex topographical, environmental, and socio-economic factors. By adopting a holistic approach that integrates geotechnical assessments with pavement design principles, the research offers a model for addressing the challenges of road construction in mountainous regions. Moreover, the emphasis on a hybrid pavement solution not only paves the way for safer and more resilient road infrastructure but also aligns with sustainable development goals by considering the long-term environmental and economic impacts of road construction projects. Future research could further explore innovative materials and technologies in pavement construction to enhance the sustainability and efficiency of road infrastructure in similar challenging environments. Declarations Conflict of interest On behalf of all authors, the corresponding author states that there is no confict of interest. Funding: The authors did not receive any fnancial support from any organisation for the submitted work. Author Contribution The contribution of individual co-authors is as follows: Nishesh-conceptualization, methodology, laboratory testing, writing; R. Jaiswal-conceptualization, methodology, data analysis, writing, and editing; Rabina-conceptualization, methodology, laboratory testing, writing Acknowledgement This paper is based on the author’s own intellectual construction and is not tied to any grant funding. References Laldintluanga, H., Ramhmachhuani, R., Mozumder, R. A., & Lalbiakmawia, F. (2023). Hydrogeological Effects on Premature Failure of Flexible Pavement in Hilly Area Along State Highway-I in Mizoram, India. Indian Geotechnical Journal, 53 (1), 29–41. Kumar, A., & Jain, A. (2023). Penetration Characteristics Optimization and Design of Hilly Rural Road. International Journal of Pavement Research and Technology, 1–15. Shrestha, J. K., Benta, A., Lopes, R. B., & Lopes, N. (2014). A multi-objective analysis of a rural road network problem in the hilly regions of Nepal. Transportation research part A: policy and practice, 64 , 43–53. Bansal, P. (2018). Evaluation of Design and Cost Aspects of Flexible and Rigid Pavements. Papagiannakis, A. T., & Masad, E. A. (2008). Pavement design and materials . John Wiley & Sons. Choudhary, Ankit, Rahul Dev Garg, and S. S. Jain. "Safety impact of highway geometrics and pavement parameters on crashes along mountainous roads." Transportation Engineering 15 (2024): 100224. Yousefi, S., Jaafari, A., Valjarević, A., Gomez, C., & Keesstra, S. (2022). Vulnerability assessment of road networks to landslide hazards in a dry-mountainous region. Environmental Earth Sciences, 81 (22), 521. Hearn, G. J., & Shakya, N. M. (2017). Engineering challenges for sustainable road access in the Himalayas. Quarterly Journal of Engineering Geology and Hydrogeology, 50 (1), 69–80. Sadek, S., Kaysi, I., & Bedran, M. (2000). Geotechnical and environmental considerations in highway layouts: an integrated GIS assessment approach. International Journal of Applied Earth Observation and Geoinformation, 2 (3–4), 190–198. Sauer, E. K. (1967). The Application of Geotechnical Principles in Road Design Problems . University of California, Berkeley. Aghamelu, O. P., & Okogbue, C. O. (2011). Geotechnical assessment of road failures in the Abakaliki area, southeastern Nigeria. Int J Civil Environ Eng, 11 (2), 12–24. Bayan, G. K. (2013). Critical problems and their solution for hilly road pavement with particular reference to nh-52 (a)–a new avenue. Int. J. of Civil, Structural, Env. and Infrastructure Eng. Res. and Dev.(IJCSEIERD), 3 (4), 47–58. Rashid, Z. B., & Gupta, R. (2017). Review paper on defects in flexible pavement and its maintenance. Int. J. Adv. Res. Educ. Technol, 4 (2), 74–77. Aryal, M. P. (1999). Damage assessment and life-span prediction of cement concrete pavements in Nepal. In Concrete Durability and Repair Technology: Proceedings of the International Conference Held at the University of Dundee, Scotland, UK on 8–10 September 1999 (p. 335). Thomas Telford Publishing. Choudhary, A., Garg, R. D., & Jain, S. S. (2024). Safety impact of highway geometrics and pavement parameters on crashes along mountainous roads. Transportation Engineering, 15 , 100224. Dahal, R. K. (2019). Rockfall mitigation practices in Nepal. In IAEG/AEG Annual Meeting Proceedings, San Francisco, California, 2018-Volume 5: Geologic Hazards: Earthquakes, Land Subsidence, Coastal Hazards, and Emergency Response (pp. 131–136). Springer International Publishing. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 01 Jul, 2024 Reviews received at journal 27 Jun, 2024 Reviews received at journal 27 Jun, 2024 Reviewers agreed at journal 23 Jun, 2024 Reviewers agreed at journal 20 Jun, 2024 Reviewers agreed at journal 18 Jun, 2024 Reviewers invited by journal 18 Jun, 2024 Editor assigned by journal 14 Jun, 2024 Submission checks completed at journal 10 Jun, 2024 First submitted to journal 30 May, 2024 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-4505046","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":317947093,"identity":"0d82aa17-4908-4ea0-87a6-967eef72f8a6","order_by":0,"name":"Nishesh P. Chhetri","email":"","orcid":"","institution":"Pokhara University","correspondingAuthor":false,"prefix":"","firstName":"Nishesh","middleName":"P.","lastName":"Chhetri","suffix":""},{"id":317947094,"identity":"d2852416-fda5-4cd7-b78f-5c42abe0ff5d","order_by":1,"name":"Rishav Jaiswal","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA30lEQVRIiWNgGAWjYBACxgbGBiBlI0eyljRjCDeBeJ2HExuI1sLcfrj5M+8e5vS17acTP/78YZPPwH74AX6H9SS2SfM8Y8vddiZ3szRPQpplA0+aAX4tDYltzDkHeHK33eDdIM2QcNiAQYKBgJb+h82fcw5IpJvd4N3880fCf6AW9g/4tcxIbJDOOWCQANSyTYIn4QBQCw8BW2Y8bJP+cyDBEOiXbdY8ackGbDw5BXi1GPanP/4448B/ebPjZzff/GFjZ8DPfnwDfi0N6CJseNUDgTwhBaNgFIyCUTAKGACTYke4rsFeUQAAAABJRU5ErkJggg==","orcid":"","institution":"McMaster University","correspondingAuthor":true,"prefix":"","firstName":"Rishav","middleName":"","lastName":"Jaiswal","suffix":""},{"id":317947095,"identity":"1bb52da0-1510-4d9c-a46f-826528a1a0dc","order_by":2,"name":"Rabina Poudel","email":"","orcid":"","institution":"Pokhara University","correspondingAuthor":false,"prefix":"","firstName":"Rabina","middleName":"","lastName":"Poudel","suffix":""}],"badges":[],"createdAt":"2024-05-30 20:38:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4505046/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4505046/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":59292490,"identity":"422dad05-5032-41f0-abf8-2a895ba72c4b","added_by":"auto","created_at":"2024-06-28 18:53:13","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":88412,"visible":true,"origin":"","legend":"\u003cp\u003eGeographical Map of Nepal showcasing Siddhababa road section (Dahal, 2019)\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4505046/v1/c9445c5aa854c42491213b66.jpg"},{"id":59293179,"identity":"e941bbd4-a921-43c1-a415-36b48df41254","added_by":"auto","created_at":"2024-06-28 19:01:13","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":80432,"visible":true,"origin":"","legend":"\u003cp\u003eOptimum Moisture Content and Maximum Dry Density of each sample\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4505046/v1/4243bd47a5b08b00fffcdd45.jpg"},{"id":59292498,"identity":"d3b46a06-adf4-49c9-85ca-5722cda81d7e","added_by":"auto","created_at":"2024-06-28 18:53:14","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":42889,"visible":true,"origin":"","legend":"\u003cp\u003eNormal Stress vs. Shear Stress for all samples\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4505046/v1/19ac98838b09d3d3499463ff.jpg"},{"id":59293182,"identity":"4b8dcc6f-2670-47e9-b706-b339c45731e7","added_by":"auto","created_at":"2024-06-28 19:01:14","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":25693,"visible":true,"origin":"","legend":"\u003cp\u003eTotal Moisture Content of each sample\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4505046/v1/9a10e1128e4128acf56e6db7.jpg"},{"id":59292492,"identity":"d4f2d50c-596e-4b9f-92ec-6941ae39c3da","added_by":"auto","created_at":"2024-06-28 18:53:13","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":71113,"visible":true,"origin":"","legend":"\u003cp\u003eLoad vs Penetration Plot for each sample\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4505046/v1/9b818efcba38f7dcf764fc5a.jpg"},{"id":59292495,"identity":"df16356c-eaff-49e9-8cf5-7ccb8b688f2e","added_by":"auto","created_at":"2024-06-28 18:53:14","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":32633,"visible":true,"origin":"","legend":"\u003cp\u003eCBR value of each sample\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4505046/v1/8e9be32eb3aa2030c1311970.jpg"},{"id":59292494,"identity":"8d5da736-406c-42ca-a8ed-67c49dbdabe1","added_by":"auto","created_at":"2024-06-28 18:53:13","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":39913,"visible":true,"origin":"","legend":"\u003cp\u003eStress versus strain curve of each soil sample\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4505046/v1/2fc1978be47292d6b56d863b.jpg"},{"id":59293180,"identity":"d4e0cbf0-198a-482f-b3c6-c0332998816e","added_by":"auto","created_at":"2024-06-28 19:01:13","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":62066,"visible":true,"origin":"","legend":"\u003cp\u003ePothole at Siddhababa road section\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4505046/v1/2950003cea2e1a5e958978ec.jpg"},{"id":59292497,"identity":"d8d74f0d-46ce-443e-9dbb-0de0c76ef035","added_by":"auto","created_at":"2024-06-28 18:53:14","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":63456,"visible":true,"origin":"","legend":"\u003cp\u003eFaulting in rigid pavement of Siddhababa road section\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4505046/v1/8f7d1ef47845e02c95624ec3.jpg"},{"id":59292502,"identity":"f20a81c7-fa6f-4974-b4b1-51f01ea488f2","added_by":"auto","created_at":"2024-06-28 18:53:15","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":68968,"visible":true,"origin":"","legend":"\u003cp\u003eAlligator cracking seen at road section\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4505046/v1/940d409ff67b7d62d12dc488.jpg"},{"id":59292496,"identity":"2e84d15e-6793-4745-a5a5-bb42607690bd","added_by":"auto","created_at":"2024-06-28 18:53:14","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":94149,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Springs at various section of the road and (b) Water induced pavement damage\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4505046/v1/2f8391e226ecc865b9adfdc3.jpg"},{"id":59292500,"identity":"e61dd32f-f6bd-4736-a721-ea262f4dc090","added_by":"auto","created_at":"2024-06-28 18:53:14","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":90481,"visible":true,"origin":"","legend":"\u003cp\u003e(a) and (b) Landslides seen at different sections of the road\u003c/p\u003e","description":"","filename":"12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4505046/v1/4475b3f7248d8035d7daaefe.jpg"},{"id":59293500,"identity":"798bfd04-45b6-4d01-9d88-a8129db86ecc","added_by":"auto","created_at":"2024-06-28 19:09:14","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1406889,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4505046/v1/83cbe5ad-277c-4fc3-a498-3868d9963060.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Resilient Roads in Challenging Terrain: A Case Study of Siddhartha Highway in Nepal","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eNepal's road infrastructure plays a pivotal role in its socio-economic development, connecting remote and rugged terrains with urban centers and facilitating trade, tourism, and access to education and healthcare. However, the country's diverse and challenging geographical conditions, characterized by mountainous regions, steep slopes, and seismic activity, pose significant challenges to road construction and maintenance. The rugged terrain not only complicates the design and construction process but also increases vulnerability to natural disasters such as landslides, floods, and earthquakes, which can severely impact road safety and durability (Hearn \u0026amp; Shakya, 2017; Yousefi et al., 2022). These challenges underscore the importance of selecting appropriate pavement types that can withstand Nepal's unique environmental conditions and ensure reliable and safe road transportation.\u003c/p\u003e \u003cp\u003eThe selection between flexible and rigid pavements is a critical decision in road construction that significantly affects the infrastructure's long-term performance, safety, and cost-effectiveness. The literature provides extensive insights into the advantages, challenges, and application contexts of both pavement types, drawing from experiences and studies conducted globally and within Nepal's unique topographical settings. Flexible pavements, composed of layers of materials with decreasing stiffness from the top (surface) layer down to the subgrade, flex under load, distributing stresses over a broader area of the subgrade. The studies by Laldintluanga et al. (2023) and Rashid \u0026amp; Gupta (2017) have underscored the cost-effectiveness and ease of repair of flexible pavements, particularly in developing countries with limited resources. However, the long-term performance of flexible pavements can be significantly affected by moisture infiltration, requiring effective drainage solutions to maintain their structural integrity and prevent premature failure (Laldintluanga et al., 2023; Aghamelu \u0026amp; Okogbue, 2011).\u003c/p\u003e \u003cp\u003eRigid pavements, primarily composed of Portland cement concrete, are characterized by their ability to distribute loads over a small area of the subgrade without significant bending or flexing. Their inherent strength and stiffness make them less dependent on the subgrade for structural support, offering superior durability and resistance to traffic loads and environmental conditions. According to Bansal (2018), rigid pavements exhibit better performance in resisting deformation and cracking over time, making them a cost-effective solution in the long run despite their higher initial construction cost (Bansal, 2018; Aryal, 1999).\u003c/p\u003e \u003cp\u003eThe environmental sustainability of pavement materials and construction methods has also become a significant consideration in pavement selection. Research by Papagiannakis and Masad (2008) highlights the potential for both flexible and rigid pavements to incorporate recycled materials and innovative technologies to reduce their environmental impact. These considerations are particularly relevant in the context of Nepal's commitment to sustainable development and environmental conservation (Papagiannakis \u0026amp; Masad, 2008; Sadek, Kaysi, \u0026amp; Bedran, 2000). The design of pavements in mountainous regions like Nepal presents unique challenges, including variable weather conditions, steep gradients, and susceptibility to natural hazards. Shrestha et al. (2014) conducted a multi-objective analysis of rural road networks in the hilly regions of Nepal, emphasizing the importance of integrating transportation research with local geographical and socio-economic factors (Shrestha et al., 2014). Comparative studies in the Himalayan regions have shown that the choice between flexible and rigid pavements must consider factors such as slope stability, potential for seismic activity, and the need for regular maintenance (Hearn \u0026amp; Shakya, 2017; Yousefi et al., 2022; Bayan, 2013). The integration of geotechnical engineering principles with pavement design is essential to ensure the safety and reliability of road infrastructure in these challenging environments (Choudhary, Garg, \u0026amp; Jain, 2024; Sauer, 1967).\u003c/p\u003e \u003cp\u003eIn response, this study aims to systematically evaluate the performance of different pavement types in the context of the Siddhababa road section to identify the most suitable pavement design that enhances safety and durability. Specifically, the study seeks to:\u003c/p\u003e \u003cp\u003e1. Conduct comprehensive soil tests to assess the subgrade conditions unique to the Siddhababa road section.\u003c/p\u003e \u003cp\u003e2. Compare the advantages and limitations of flexible and rigid pavements, considering the local environmental and traffic conditions.\u003c/p\u003e \u003cp\u003e3. Propose a pavement design that addresses the identified challenges, aiming to reduce accident rates and improve the longevity of the road infrastructure.\u003c/p\u003e \u003cp\u003eThe significance of this study extends beyond the Siddhababa road section, offering valuable insights for the construction and maintenance of roads in similar mountainous terrains within Nepal and other countries with comparable geographical challenges. By providing evidence-based recommendations for pavement selection and design, this research contributes to the broader goal of enhancing road safety, reducing maintenance costs, and improving transportation efficiency in regions where road travel is fraught with risks due to natural and man-made factors. Ultimately, the study aims to support the development of more resilient and reliable road infrastructure, thereby supporting Nepal's ongoing efforts towards sustainable development and improved quality of life for its citizens.\u003c/p\u003e"},{"header":"2. Study Area Description","content":"\u003cp\u003eThe Siddhababa road section, part of the crucial Siddhartha Highway in Nepal, stretches for 3.5 kilometers from Golpark in Butwal Sub Metropolitan City (ward no. 3) to Dobhan in Tinau Rural Municipality (ward no. 3), Palpa. This segment is renowned not only for its vital role in connecting urban and rural locales but also for its challenging terrain that typifies Nepal's rugged landscape. The road's geographical features include steep gradients and close proximity to the Tinau River valley, heightening the risk of landslides and erosion, particularly during the monsoon season. Climatically, the area is subject to a subtropical highland climate, with a pronounced wet season bringing heavy rainfall and a dry season marked by dust and potential water scarcity. Traffic along this road is diverse, encompassing local commuters, long-distance travelers, and heavy trucks, underscoring the need for a pavement design that can withstand such varied use while ensuring safety and efficiency.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAdding to the complexity of the Siddhababa road section is its cultural and environmental significance, highlighted by the presence of the Siddhababa Temple, a site of high ritual value that attracts pilgrims and increases pedestrian traffic. The existence of a perennial spring and additional seasonal springs along the road further influences its hydrological dynamics and the surrounding ecosystem. These factors together necessitate a multifaceted approach to road design and maintenance, one that considers the safety of both vehicular and pedestrian traffic, the preservation of cultural sites, and the mitigation of environmental impacts. This intricate blend of geographical, climatic, traffic, and cultural considerations makes the Siddhababa road section a compelling case study for developing resilient and sustainable road infrastructure in mountainous regions.\u003c/p\u003e"},{"header":"3. Soil Testing and Analysis","content":"\u003cp\u003eIn the study, various soil testing methods such as Grain Size Analysis, Specific Gravity Test, Density Test, Direct Shear Test, and Atterberg Limits Test were conducted. These tests were crucial for understanding the characteristics of the soil, including its gradation, density, shear strength, and plasticity. For example, the Grain Size Analysis helped determine soil gradation, essential for assessing drainage and stability, while the Specific Gravity and Density Tests provided insights into the soil's load-bearing and compaction capabilities. The Direct Shear and Atterberg Limits Tests revealed the soil's shear strength and plasticity, respectively, which are critical for assessing its suitability under different loading and environmental conditions.\u003c/p\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e3.1 Grain Size Analysis (Sieve Analysis)\u003c/b\u003e:\u003c/h2\u003e \u003cp\u003eThe test separates soil particles into different size ranges by passing them through a series of sieves of decreasing mesh size. Samples were collected at various depths and locations along the road section to ensure representativeness of the soil types of present. This test is done to determine the soil gradation, which is crucial for assessing the soil's drainage capacity and stability as a base/subbase material. The soils were predominantly classified as well-graded sand and soil (A-1-a, A-1-b, A-3), indicating good drainage characteristics and suitability for use in pavement layers with proper compaction.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e3.2 Specific Gravity Test (Pycnometer Method)\u003c/b\u003e:\u003c/h2\u003e \u003cp\u003eThis test measures the ratio of the density of the soil solids to the density of water, using a pycnometer. Small, oven-dried soil samples were used to minimize moisture content's effect on the measurement. This test is done to assess the soil particles' density, affecting the soil's load-bearing capacity and compaction characteristics.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSpecific Gravity of each sample\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"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 \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c6\" namest=\"c3\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS.N.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eParameters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWt. of Pycnometer Bottle (W1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e703\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e703\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e703\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e703\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWt. of Pycnometer\u0026thinsp;+\u0026thinsp;dry soil (W2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e987\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e993\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e999\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e985\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWt. of Pycnometer\u0026thinsp;+\u0026thinsp;dry soil\u0026thinsp;+\u0026thinsp;water (W3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.752\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1768\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1746\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1740\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWt. of Pycnometer\u0026thinsp;+\u0026thinsp;water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.591\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1591\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1592\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1591\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpecific Gravity (G)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.309\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.566\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.099\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe average specific gravity was found to be 2.476, suggesting that the soil particles are denser than many types of soils, which is favorable for providing a stable foundation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e3.3 Density Test (Optimum Moisture Content and Maximum Dry Density)\u003c/b\u003e:\u003c/h2\u003e \u003cp\u003eThe Density Test, specifically the Standard Proctor Test, plays a pivotal role in road construction and pavement foundation design by determining the soil's Optimum Moisture Content (OMC) and Maximum Dry Density (MDD). This test method involves compacting soil samples at varying moisture levels within a mold to identify the moisture content that allows the soil to reach its maximum density. The results from the Density Test for the Siddhababa road section reveal varying OMC and MDD values across the four samples, with an average OMC of 12.265% and an average MDD of 1.809 g/cm\u0026sup3;. These values are within the ideal range for road construction, indicating that with proper compaction and moisture control, the soil can provide a stable and durable foundation for the pavement.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Direct Shear Test\u003c/h2\u003e \u003cp\u003eIn our study of the Siddhababa road section, the Direct Shear Test was employed to evaluate the shear strength properties of soil samples under varying conditions of normal stress. The analysis involved subjecting four distinct soil samples to normal stresses of 0.5 kg/cm\u0026sup2;, 1 kg/cm\u0026sup2;, and 1.5 kg/cm\u0026sup2;, and recording the resultant shear stress at various levels of settlement. The Direct Shear Test measures the maximum shear stress that soil can resist under a given normal stress, providing insights into its shear strength parameters, namely cohesion (C) and angle of internal friction (Φ). The area of the sampler was consistently set to 36 mm\u0026sup2; to ensure precise application of forces.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Direct Shear Test results reveal a progressive increase in shear stress with settlement under each level of normal stress, indicating the soil's capacity to resist higher shear forces as compaction increases. Notably, Sample 1 demonstrated significant shear strength, particularly under a normal stress of 1.5 kg/cm\u0026sup2;, reaching a shear stress of 0.239 kg/cm\u0026sup2;, suggesting robust resistance to lateral forces. The calculated shear forces and corrected areas enabled the determination of specific shear stress values, offering a granular view of soil behavior under load. The derived values of cohesion (C) and angle of internal friction (Φ) across the samples ranged from 19.61KPA to 29.42KPA for C, and 17 to 20 degrees for Φ, respectively, with average values computed as C\u0026thinsp;=\u0026thinsp;23 KPA and Φ\u0026thinsp;=\u0026thinsp;18.375 degrees. These parameters are instrumental for pavement material selection and structural design, indicating that the soils possess adequate shear strength for supporting anticipated loads.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Atterberg Limits Test Analysis\u003c/h2\u003e \u003cp\u003eThe Atterberg Limits Test, comprising the Liquid Limit and Plastic Limit tests, was conducted to characterize the plasticity and workability of soil samples from the Siddhababa road section. Liquid Limit (LL) determines the moisture content at which soil transitions from a plastic to a liquid state. It indicates how much water a soil can absorb before behaving as a liquid. Plastic Limit (PL) identifies the moisture content at which soil changes from a plastic to a semi-solid state. This limit reflects the soil's ability to be molded or shaped. Plasticity Index (PI) is the difference between the Liquid Limit and the Plastic Limit, representing the range of moisture content where the soil exhibits plastic properties. The results for each sample are summarized as follows in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAtterberg Limits Test Results - Soil Classification\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLiquid Limit\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePlastic Limit\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePlasticity Index\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eA-Line\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eClassification\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSoil Type\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e21.9%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMH or OH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eHigh/Inorganic Clay\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e62.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20.4%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e42.1%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e31.02%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eHigh plasticity clay\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27.3%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e47.4%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e40.15%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eHigh plasticity clay\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e58%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e32%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e40.15%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eHigh plasticity clay\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe average values across the samples were found to be: Liquid Limit\u0026thinsp;=\u0026thinsp;61.25%, Plastic Limit\u0026thinsp;=\u0026thinsp;22.675%, and Plasticity Index\u0026thinsp;=\u0026thinsp;38.625%. The Atterberg Limits Test reveals significant variability in the plasticity of the soil samples, with Plasticity Index values ranging from 33\u0026ndash;47.4%. The high Plasticity Index values observed in Samples 2, 3, and 4 (all classified as CH) indicate soils with high plasticity, which can undergo significant volume changes with moisture variations.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Moisture Content Tests Using the Oven Dry Method\u003c/h2\u003e \u003cp\u003eIn the context of the Siddhababa road section study, moisture content tests were conducted using the Oven Dry Method to establish the water content of soil samples. The Oven Dry Method involves weighing a soil sample before and after oven drying to determine its moisture content. This process removes all moisture from the soil, allowing for the calculation of water content based on weight loss. The following table summarizes the moisture content test results for four soil samples collected from the study area:\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo calculate the moisture content, the weight of the dry soil was determined by subtracting the weight of the container (M1) from the oven-dried weight (M3). The weight of moisture was then obtained by subtracting the weight of dry soil from the wet soil weight (M2 - M3). Finally, the total moisture content percentage was calculated using the formula:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$Moisture content \\left(\\%\\right) = \\frac{Weight of moisture}{Weight of dry soil}X 100$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe moisture content tests revealed variations in water content across the samples, with values ranging from 7.53\u0026ndash;13.64%. The average moisture content for the soil samples was calculated at 9.575%, indicating the soil's natural condition in terms of water content.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.7 California Bearing Ratio (CBR) Test Analysis\u003c/h2\u003e \u003cp\u003eThe CBR test measures the resistance of the soil to penetration by a standardized plunger under controlled density and moisture conditions. The test results are expressed as a percentage of the resistance to penetration compared to a standard crushed rock material. This test is critical for designing the pavement thickness by assessing the load-bearing capacity of the soil.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSimilarly, we would assess the CBR value of each sample using the formulations-\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$CBR = \\frac{Std Load at Penetration}{Test Load at Penetration}X 100\\%$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe CBR test results reveal a range of soil strength across the samples, with samples 2 and 4 showing higher bearing capacities, making them more suitable for supporting pavements subjected to regular and potentially heavy traffic. Samples 1 and 3, with lower CBR values, might require soil improvement techniques such as stabilization or the use of geotextiles to enhance their load-bearing capabilities.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.8 Unconfined Compression Test Analysis\u003c/h2\u003e \u003cp\u003eThis test involves compressing a cylindrical soil sample at a constant rate until failure, measuring the axial load and deformation. The test is performed without lateral confinement, allowing the determination of the soil's Unconfined Compressive Strength (UCS) and providing an indirect measure of the soil's shear strength under saturated conditions. The axial stress at failure divided by the initial cross-sectional area of the sample gives the UCS, which is a crucial parameter in evaluating soil stability and suitability for construction projects.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe average UCS value for the tested samples was found to be less than 0.25 N/mm\u0026sup2;, with an average undrained shear strength of 0.105 N/mm\u0026sup2;, indicating that while some samples exhibit adequate strength for standard pavement applications, others may require stabilization or reinforcement to meet the demands of higher traffic loads or environmental stressors.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Pavement Condition Assessment","content":"\u003cp\u003eThe Siddhababa road section, known for its scenic beauty, is also notorious as one of Nepal\u0026apos;s most hazardous routes. This segment has been the site of numerous accidents, prompting an in-depth analysis to identify underlying issues and propose viable solutions. Herein, we outline the principal challenges faced and recommend remedial measures to enhance road safety and efficiency.\u003c/p\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003e4.1 Pothole Formation\u003c/h2\u003e\n \u003cp\u003ePotholes were observed approximately every meter along the road, affecting not only flexible but also rigid pavement sections. The primary causes of these potholes include moisture infiltration, the absence of a prime or tack coat between layers, and typically stem from neglected alligator cracking. Given that nearly all potholes were in a severe state, a full-depth replacement patch is recommended.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003e4.2 Faulting in Rigid Pavements\u003c/h2\u003e\n \u003cp\u003eFaulting, characterized by differential settlement at pavement joints, can be seen thoroughly the section which arises from subgrade softening and base course weakening. Temperature fluctuations contribute to slab curling, further accentuating the problem. Implementing dowel bar retrofits for faulting between 3 mm and 12.5 mm can effectively mitigate this issue. Faults exceeding 12.5 mm necessitate complete pavement reconstruction to ensure structural competence and user safety.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n \u003ch2\u003e4.3 Alligator Cracking\u003c/h2\u003e\n \u003cp\u003eAlligator cracking were found in the region of repeated traffic loading. The reason is inadequately designed pavements leading to surface, base, or subgrade failures, manifesting as alligator cracking. Targeted full-depth patching followed by milling and resurfacing of the affected sections are recommended to address these structural failures comprehensively.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n \u003ch2\u003e4.4 Rutting\u003c/h2\u003e\n \u003cp\u003eHeavy traffic from large vehicles such as trucks and tippers frequently using this road segment leads to the formation of ruts, which are grooved depressions in the pavement. This issue primarily arises from several factors: inadequate thickness of the pavement, insufficient compaction of the asphalt, stone base, or underlying soil, the use of weak asphalt mixtures, or the penetration of moisture. For minor or stabilized ruts, overlay techniques suffice. However, severe deformations require excavation and replacement with appropriately designed materials to restore functionality.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n \u003ch2\u003e4.5 Water-Induced Damage\u003c/h2\u003e\n \u003cp\u003eWater poses a significant threat to pavement integrity, as evidenced by photos showing damage to the road section surrounding spring water. This issue also leads to slippery pavement surfaces, increasing the risk of accidents. Implementing an effective drainage system, along with an underground drainage system, is recommended to redirect water away from the pavement and towards the opposite side, such as the Tinau River.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\n \u003ch2\u003e4.6 Inadequate Roadside Barriers\u003c/h2\u003e\n \u003cp\u003eThe Siddhababa road section, situated on high embankments and within hilly terrain, stands approximately 400 meters above sea level. Its proximity to the Tinau River, characterized by a large number of significant boulders, further amplifies the danger of this road section. Consequently, there\u0026apos;s a pressing need for critical road safety infrastructure treatments to redirect out-of-control vehicles back onto the road. It has been observed that there are no safety measures in place along the roadside, which poses a serious concern. To enhance safety, the implementation of guard rails, Longitudinal Channelizing Devices (LCDs), and concrete barriers is recommended.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\n \u003ch2\u003e4.7 Slope Stabilization Challenges\u003c/h2\u003e\n \u003cp\u003eGiven the rocky nature of the hills and the prevalence of large rocks, landslides pose a significant threat in this area, leading to loss of lives, damage to vehicles, and disruptions in reaching destinations. During the rainy season, landslides occur almost daily, making the situation even more perilous.\u003c/p\u003e\n \u003cp\u003eWhile completely preventing landslides may not be feasible, several precautionary measures and strategies can be employed to mitigate the risk of small landslides and manage smaller rocks. These measures include removing part of the soil or rock, or the load from the top of the slope, to decrease the shear stresses on critical planes. The use of concrete gravity walls, cantilever walls, gabion structures, baby crib walls, and embankment piles can provide necessary resistance against the slope\u0026apos;s tendency to topple. Although this section is challenged by heavy rocks, smaller rocks can be managed by installing draped mesh or netting to control their movement.\u003c/p\u003e\n \u003cp\u003eThe major issues identified on the Siddhababa road section highlight significant safety and infrastructure concerns, including the presence of heavy vehicles leading to rutting, widespread potholes, faulting in rigid pavements, challenges posed by spring water and poor drainage, dangers associated with high embankments and rocky terrain prone to landslides, and the lack of critical road safety measures. Beyond these substantial problems, there are also numerous other issues such as the absence of essential traffic signboards indicating turns, slippery roads, accident-prone areas, landslide zones, speed limits, construction activities, and parking for Siddhababa temple, among others.\u003c/p\u003e\n \u003cp\u003eAddressing these concerns, even with relatively minor safety precautions, has the potential to significantly reduce the risk of accidents and save lives. The implementation of recommended measures such as improving drainage, installing road safety barriers, stabilizing slopes, and enhancing traffic sign visibility could greatly enhance the safety and functionality of the Siddhababa road section. This underscores the importance of proactive infrastructure management and safety interventions to protect road users in this challenging terrain.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"5. Suitability of Pavement Types","content":"\u003cp\u003eThe comprehensive evaluation of the Siddhababa road section, which suffers from various types of pavement failures, underscores the critical need for thoughtful pavement selection to enhance road safety, durability, and travel efficiency. The decision-making process for pavement type involves considering the subgrade strength, traffic conditions, environmental factors, and economic and safety implications.\u003c/p\u003e \u003cp\u003eThe 10% California Bearing Ratio (CBR) value of the subgrade suggests a strong foundation, making flexible pavement an appealing choice due to its adaptability to subgrade strength. Flexible pavements offer the advantage of being constructed and reinforced incrementally to accommodate increasing traffic demands. Their initial and maintenance costs are generally lower compared to rigid pavements, providing a cost-effective solution for road construction.\u003c/p\u003e \u003cp\u003eThe challenging environmental conditions, characterized by frequent landslides and large stones, alongside the road's designation as an accident-prone area, necessitate a pavement solution that prioritizes durability and safety. Rigid pavement, with its robust structure, is capable of maintaining its form under traffic loads and offers superior durability, making it a suitable choice for areas requiring high safety standards and longevity. Although the initial costs of concrete pavement are higher, the long-term benefits of reduced maintenance and a longer design life can justify the investment.\u003c/p\u003e \u003cp\u003eGiven the diverse needs and challenges of the Siddhababa road section, a balanced approach that considers both economic efficiency and safety is essential. For the 3.5km stretch of Siddhababa road, which presents significant safety concerns and challenging environmental conditions, a strong rigid pavement is recommended. This choice is driven by the need for durability and safety in a national highway context, where preserving life and ensuring reliable transportation are paramount. For the remaining sections of the Siddhartha highway, flexible pavement is suggested, capitalizing on its cost-effectiveness, ease of maintenance, and adaptability to traffic growth. This dual approach allows for the optimization of resources, ensuring both economic and safety objectives are met.\u003c/p\u003e \u003cp\u003eBy taking a holistic view of the project's requirements, considering the site visits, and analyzing the overall scenario, the conclusion is drawn that adopting a combination of rigid pavement for the high-risk, accident-prone Siddhababa section, and flexible pavement for the rest of the highway, offers the best compromise between safety, durability, and cost-efficiency.\u003c/p\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Design of Flexible Pavement\u003c/h2\u003e \u003cp\u003eTo clarify and structure the explanation for the calculation of the design thickness of a flexible pavement based on the given data and requirements, we'll break down the process into its fundamental steps and formulas.\u003c/p\u003e \u003cp\u003e \u003cb\u003eGiven Data\u003c/b\u003e \u003c/p\u003e \u003cp\u003e1. Average Daily Traffic of Heavy Vehicles (P): 1250 cvpd (commercial vehicles per day)\u003c/p\u003e \u003cp\u003e2. Number of heavy vehicles per day after adjustment for growth (A): 1393.229 cv/day\u003c/p\u003e \u003cp\u003e3. Cumulative Number of Standard Axles (Ns) over the design life: 13.5\u0026nbsp;million standard axles (msa)\u003c/p\u003e \u003cp\u003e4. Sub-grade California Bearing Ratio (CBR) values from samples: Sample 1: 11.67%; Sample 2: 13.86%; Sample 3: 9.73% and Sample 4: 11.45%\u003c/p\u003e \u003cp\u003e \u003cb\u003eSteps and Formulations\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 1: Calculation of Adjusted Daily Traffic\u003c/em\u003e \u003c/p\u003e \u003cp\u003eThe adjusted daily traffic \u003cem\u003eA\u003c/em\u003e is calculated using the formula:\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$A = p {\\left(1+r\\right)}^{y}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere, \u0026#119875; is the initial traffic load, \u0026#119903; is the annual growth rate, and \u0026#119910; is the number of years considered. For this study, the adjusted traffic resulted in 1393.229 cv/day, assuming a typical growth rate over the specified period.\u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 2: Cumulative Number of Standard Axles (Ns)\u003c/em\u003e \u003c/p\u003e \u003cp\u003eThe formula used here is:\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$${N}_{s}=\\frac{365 X A X VDF X LDF X ({\\left(1+r\\right)}^{n}-1)}{r}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere, \u003cem\u003eVDF\u003c/em\u003e is the Vehicle Damage Factor, \u003cem\u003eLDF\u003c/em\u003e is the Lane Distribution Factor, \u0026#119903; is the growth rate, and \u0026#119899; is the number of years in the design life. This calculation yielded an \u003cem\u003eNs\u003c/em\u003e of approximately 13.5 msa.\u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 3: Determination of 90th Percentile CBR\u003c/em\u003e \u003c/p\u003e \u003cp\u003eThe 90th percentile CBR is interpolated between the 75th and 100th percentile values, simplifying the design CBR to 10% for practical application purposes, facilitating subsequent calculations.\u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 4: Pavement Layer Thickness Design\u003c/em\u003e \u003c/p\u003e \u003cp\u003eBased on the IRC standard table for flexible pavements and the given cumulative traffic load (Ns) of 13.5 msa along with a sub-grade CBR of 10%, the layer thicknesses are proposed. The calculation involves interpolation between known points for 10 and 20 msa:\u003c/p\u003e \u003cp\u003e\u0026bull; For 10 msa, thicknesses are: BC\u0026thinsp;=\u0026thinsp;40 mm, DBM\u0026thinsp;=\u0026thinsp;50 mm, Total\u0026thinsp;=\u0026thinsp;540 mm\u003c/p\u003e \u003cp\u003e\u0026bull; For 20 msa, thicknesses are: BC\u0026thinsp;=\u0026thinsp;40 mm, DBM\u0026thinsp;=\u0026thinsp;75 mm, Total\u0026thinsp;=\u0026thinsp;565 mm\u003c/p\u003e \u003cp\u003eGiven \u003cem\u003eNs\u003c/em\u003e of 13.5 msa, the total thickness is then the sum of these layers plus the base and sub-base layers, equating to 550 mm. Hence, this gets finalized as 40mm as W/C, 60 mm as Binder layer, 250mm as base layer and 200 mm as subbase layer. This detailed explanation illustrates the methodology behind designing the thickness of flexible pavements to accommodate traffic loads and sub-grade conditions effectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Design of Rigid Pavement\u003c/h2\u003e \u003cp\u003e \u003cem\u003eStep 1: Initial Assumptions and Data\u003c/em\u003e \u003c/p\u003e \u003cp\u003e\u0026bull; Traffic growth rate (\u003cem\u003er\u003c/em\u003e): 7.5%\u003c/p\u003e \u003cp\u003e\u0026bull; Design life (\u003cem\u003en\u003c/em\u003e): 20 years.\u003c/p\u003e \u003cp\u003e\u0026bull; Construction period (\u003cem\u003ey\u003c/em\u003e): 3 years\u003c/p\u003e \u003cp\u003e\u0026bull; Modulus of subgrade reaction (\u003cem\u003ek\u003c/em\u003e): 8 kg/cm\u0026sup3;\u003c/p\u003e \u003cp\u003e\u0026bull; Flexural strength of concrete: 40 kg/cm\u0026sup2;\u003c/p\u003e \u003cp\u003e\u0026bull; Modulus of Elasticity (\u003cem\u003eE\u003c/em\u003e): 3\u0026times;\u0026times;10⁵ kg/cm\u0026sup2;\u003c/p\u003e \u003cp\u003e\u0026bull; Poisson\u0026rsquo;s ratio (\u003cem\u003e\u0026micro;\u003c/em\u003e): 0.15\u003c/p\u003e \u003cp\u003e\u0026bull; Thermal expansion coefficient of concrete: 10\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e /\u0026deg;C\u003c/p\u003e \u003cp\u003eGiven Temperature Gradient:\u003c/p\u003e \u003cp\u003e\u0026bull; For Hilly region: 13.1\u0026deg;C at 20 cm, 14.3\u0026deg;C at 25 cm\u003c/p\u003e \u003cp\u003e\u0026bull; For Terai region: 16.4\u0026deg;C at 20 cm, 16.6\u0026deg;C at 25 cm\u003c/p\u003e \u003cp\u003eThe trial slab thickness starts at 20 cm, based on standard practices and initial estimates of pavement performance under anticipated loads and environmental conditions.\u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 2: Calculate the Radius of Relative Stiffness (l) for the Initial Trial Thickness\u003c/em\u003e \u003c/p\u003e \u003cp\u003eUsing the initial trial thickness (\u003cem\u003eh\u003c/em\u003e) of 20 cm:\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(l = \\sqrt[4]{\\frac{E {h}^{3}}{12 \\left(1-{\\mu }^{2}\\right)k}}\\)\u003c/span\u003e \u003c/span\u003e=71.11cm (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eThis calculation is crucial for understanding how the slab will behave under load, considering the stiffness of both the concrete and the subgrade.\u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 3: Determine L/l and W/l Ratios\u003c/em\u003e \u003c/p\u003e \u003cp\u003eWith \u003cem\u003eL\u003c/em\u003e\u0026thinsp;=\u0026thinsp;4.5m and \u003cem\u003eW\u003c/em\u003e\u0026thinsp;=\u0026thinsp;3.5m, the ratios are calculated as:\u003c/p\u003e \u003cp\u003e \u003cem\u003eL\u003c/em\u003e/\u003cem\u003el\u003c/em\u003e\u0026thinsp;=\u0026thinsp;6.32 and \u003cem\u003eW\u003c/em\u003e/\u003cem\u003el\u003c/em\u003e\u0026thinsp;=\u0026thinsp;4.92\u003c/p\u003e \u003cp\u003eSince \u003cem\u003eL\u003c/em\u003e/\u003cem\u003el\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;\u003cem\u003eW\u003c/em\u003e/\u003cem\u003el\u003c/em\u003e, \u003cem\u003eL\u003c/em\u003e/\u003cem\u003el\u003c/em\u003e is the critical condition for design considerations, focusing on the slab's length.\u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 4: Interpolate the Coefficient Cv\u003c/em\u003e \u003c/p\u003e \u003cp\u003eGiven \u003cem\u003eL\u003c/em\u003e/\u003cem\u003el\u003c/em\u003e ratios, \u003cem\u003eCv\u003c/em\u003e is interpolated for pavement design, resulting in \u003cem\u003eCv\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.9 for the initial thickness of 20 cm.\u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 5: Average Temperature Gradient and Adjusting for Trial Thickness\u003c/em\u003e \u003c/p\u003e \u003cp\u003eThe average temperature gradient (Δ\u003cem\u003et\u003c/em\u003e) is calculated by taking the average of the provided gradients for both Hilly and Terai regions. Since the Siddhababa section is not fully in either, an average is used, yielding Δ\u003cem\u003et\u003c/em\u003e\u0026thinsp;=\u0026thinsp;14.75\u0026deg;C for initial calculations. This step is critical in determining the thermal stresses the pavement will experience.\u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 6: Calculate Temperature Edge Stress (fte)\u003c/em\u003e \u003c/p\u003e \u003cp\u003eUsing \u003cem\u003eCv\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.9 and the average Δ\u003cem\u003et\u003c/em\u003e, \u003cem\u003efte\u003c/em\u003e is calculated, resulting in 20 kg/cm\u0026sup2; for the initial 20 cm thickness.\u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 7: Residual Stress and Factor of Safety for the Initial Thickness\u003c/em\u003e \u003c/p\u003e \u003cp\u003eResidual Stress is calculated as 20 kg/cm\u0026sup2; (40 kg/cm\u0026sup2; \u0026minus;\u0026thinsp;20 kg/cm\u0026sup2;) and factor of Safety (\u003cem\u003efos\u003c/em\u003e) is calculated as 0.714, which is less than 1, indicating the initial thickness is not adequate. Due to the insufficient \u003cem\u003efos\u003c/em\u003e, the trial thickness is increased to 23 cm to improve safety and performance.\u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 8: Recalculate L/l, and W/l for Adjusted Thickness\u003c/em\u003e \u003c/p\u003e \u003cp\u003eFor \u003cem\u003eh\u003c/em\u003e\u0026thinsp;=\u0026thinsp;23 cm, \u003cem\u003el\u003c/em\u003e is recalculated, resulting in \u003cem\u003el\u003c/em\u003e\u0026thinsp;=\u0026thinsp;84.86 cm, and the critical ratios are updated accordingly.\u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 9: Interpolate Cv for Adjusted Thickness\u003c/em\u003e \u003c/p\u003e \u003cp\u003eWith the adjusted ratios, \u003cem\u003eCv\u003c/em\u003e is now 0.8, reflecting changes in slab behavior and stress distribution with the increased thickness.\u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 10: Recalculate Temperature Edge Stress (fte) for Adjusted Thickness\u003c/em\u003e \u003c/p\u003e \u003cp\u003eUsing the new \u003cem\u003eCv\u003c/em\u003e and an interpolated Δ\u003cem\u003et\u003c/em\u003e for 23 cm, \u003cem\u003efte\u003c/em\u003e is found to be 17 kg/cm\u0026sup2;.\u003c/p\u003e \u003cp\u003e \u003cem\u003eStep 11: Final Factor of Safety and Thickness Determination\u003c/em\u003e \u003c/p\u003e \u003cp\u003eResidual Stress is now found to be 23 kg/cm\u0026sup2; (40 kg/cm\u0026sup2; \u0026minus;\u0026thinsp;17 kg/cm\u0026sup2;) and \u003cem\u003efos i\u003c/em\u003emproves to 1.02, indicating the adjusted thickness is safe.\u003c/p\u003e \u003cp\u003eConsidering the daily traffic and its growth over the design life, the final thickness is determined as 25 cm (23 cm\u0026thinsp;+\u0026thinsp;2 cm for traffic adjustments).\u003c/p\u003e \u003cp\u003eThis comprehensive approach illustrates the iterative process of pavement design, starting from initial assumptions, through critical ratio analysis and thermal stress calculation, to final adjustments based on safety and performance criteria. The increase in trial thickness from 20 cm to 23 cm, followed by the final adjustment to 25 cm, ensures the pavement can safely support expected traffic loads and environmental conditions.\u003c/p\u003e \u003c/div\u003e"},{"header":"6. Conclusions and Discussions","content":"\u003cp\u003eThe comprehensive study on the Siddhababa road section of the Siddhartha Highway in Nepal has provided valuable insights into the critical decision-making process involved in selecting the most appropriate pavement type for mountainous terrains, faced with unique environmental challenges and safety concerns. The analysis, grounded in extensive soil testing, traffic load evaluation, and environmental condition assessments, highlighted the nuanced performance of flexible and rigid pavements under the specific conditions of the Siddhababa road section. Despite the initial cost-effectiveness and adaptability of flexible pavements, the study concluded that the durability, safety, and reduced long-term maintenance requirements of rigid pavements offer a more viable solution for this particularly vulnerable road segment. The recommendation for a hybrid approach, utilizing rigid pavement for the most susceptible sections to natural hazards and flexible pavement elsewhere, underscores the importance of a balanced and context-sensitive strategy in pavement engineering to enhance road safety, durability, and economic efficiency.\u003c/p\u003e \u003cp\u003eThis study contributes significantly to the field of pavement engineering, especially in the context of developing countries like Nepal, where road infrastructure must contend with complex topographical, environmental, and socio-economic factors. By adopting a holistic approach that integrates geotechnical assessments with pavement design principles, the research offers a model for addressing the challenges of road construction in mountainous regions. Moreover, the emphasis on a hybrid pavement solution not only paves the way for safer and more resilient road infrastructure but also aligns with sustainable development goals by considering the long-term environmental and economic impacts of road construction projects. Future research could further explore innovative materials and technologies in pavement construction to enhance the sustainability and efficiency of road infrastructure in similar challenging environments.\u003c/p\u003e"},{"header":"Declarations","content":" \u003cp\u003e \u003cstrong\u003eConflict of interest\u003c/strong\u003e \u003cp\u003eOn behalf of all authors, the corresponding author states that there is no confict of interest.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eThe authors did not receive any fnancial support from any organisation for the submitted work.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eThe contribution of individual co-authors is as follows: Nishesh-conceptualization, methodology, laboratory testing, writing; R. Jaiswal-conceptualization, methodology, data analysis, writing, and editing; Rabina-conceptualization, methodology, laboratory testing, writing\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThis paper is based on the author\u0026rsquo;s own intellectual construction and is not tied to any grant funding.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLaldintluanga, H., Ramhmachhuani, R., Mozumder, R. A., \u0026amp; Lalbiakmawia, F. (2023). Hydrogeological Effects on Premature Failure of Flexible Pavement in Hilly Area Along State Highway-I in Mizoram, India. Indian Geotechnical Journal, \u003cem\u003e53\u003c/em\u003e(1), 29\u0026ndash;41.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKumar, A., \u0026amp; Jain, A. (2023). Penetration Characteristics Optimization and Design of Hilly Rural Road. International Journal of Pavement Research and Technology, 1\u0026ndash;15.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShrestha, J. K., Benta, A., Lopes, R. B., \u0026amp; Lopes, N. (2014). A multi-objective analysis of a rural road network problem in the hilly regions of Nepal. Transportation research part A: policy and practice, \u003cem\u003e64\u003c/em\u003e, 43\u0026ndash;53.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBansal, P. (2018). Evaluation of Design and Cost Aspects of Flexible and Rigid Pavements.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePapagiannakis, A. T., \u0026amp; Masad, E. A. (2008). \u003cem\u003ePavement design and materials\u003c/em\u003e. John Wiley \u0026amp; Sons.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChoudhary, Ankit, Rahul Dev Garg, and S. S. Jain. \"Safety impact of highway geometrics and pavement parameters on crashes along mountainous roads.\" Transportation Engineering 15 (2024): 100224.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYousefi, S., Jaafari, A., Valjarević, A., Gomez, C., \u0026amp; Keesstra, S. (2022). Vulnerability assessment of road networks to landslide hazards in a dry-mountainous region. Environmental Earth Sciences, \u003cem\u003e81\u003c/em\u003e(22), 521.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHearn, G. J., \u0026amp; Shakya, N. M. (2017). Engineering challenges for sustainable road access in the Himalayas. Quarterly Journal of Engineering Geology and Hydrogeology, \u003cem\u003e50\u003c/em\u003e(1), 69\u0026ndash;80.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSadek, S., Kaysi, I., \u0026amp; Bedran, M. (2000). Geotechnical and environmental considerations in highway layouts: an integrated GIS assessment approach. International Journal of Applied Earth Observation and Geoinformation, \u003cem\u003e2\u003c/em\u003e(3\u0026ndash;4), 190\u0026ndash;198.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSauer, E. K. (1967). \u003cem\u003eThe Application of Geotechnical Principles in Road Design Problems\u003c/em\u003e. University of California, Berkeley.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAghamelu, O. P., \u0026amp; Okogbue, C. O. (2011). Geotechnical assessment of road failures in the Abakaliki area, southeastern Nigeria. Int J Civil Environ Eng, \u003cem\u003e11\u003c/em\u003e(2), 12\u0026ndash;24.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBayan, G. K. (2013). Critical problems and their solution for hilly road pavement with particular reference to nh-52 (a)\u0026ndash;a new avenue. Int. J. of Civil, Structural, Env. and Infrastructure Eng. Res. and Dev.(IJCSEIERD), \u003cem\u003e3\u003c/em\u003e(4), 47\u0026ndash;58.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRashid, Z. B., \u0026amp; Gupta, R. (2017). Review paper on defects in flexible pavement and its maintenance. Int. J. Adv. Res. Educ. Technol, \u003cem\u003e4\u003c/em\u003e(2), 74\u0026ndash;77.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAryal, M. P. (1999). Damage assessment and life-span prediction of cement concrete pavements in Nepal. In \u003cem\u003eConcrete Durability and Repair Technology: Proceedings of the International Conference Held at the University of Dundee, Scotland, UK on 8\u0026ndash;10 September 1999\u003c/em\u003e (p. 335). Thomas Telford Publishing.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChoudhary, A., Garg, R. D., \u0026amp; Jain, S. S. (2024). Safety impact of highway geometrics and pavement parameters on crashes along mountainous roads. Transportation Engineering, \u003cem\u003e15\u003c/em\u003e, 100224.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDahal, R. K. (2019). Rockfall mitigation practices in Nepal. In \u003cem\u003eIAEG/AEG Annual Meeting Proceedings, San Francisco, California, 2018-Volume 5: Geologic Hazards: Earthquakes, Land Subsidence, Coastal Hazards, and Emergency Response\u003c/em\u003e (pp. 131\u0026ndash;136). Springer International Publishing.\u003c/span\u003e\u003c/li\u003e\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":"discover-civil-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Civil Engineering](https://www.springer.com/journal/44290)","snPcode":"44290","submissionUrl":"https://submission.nature.com/new-submission/44290","title":"Discover Civil Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"challenging topography, road network, flexible and rigid pavement, road safety and durability","lastPublishedDoi":"10.21203/rs.3.rs-4505046/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4505046/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eNepal is a country known for its diverse and challenging topography, and it relies heavily on a robust road infrastructure network to connect its remote regions and urban centers. This study addresses the critical need for enhanced road safety and infrastructure resilience on the Siddhababa road section of the Siddhartha Highway, Nepal, notorious for its high accident rates and susceptibility to landslides. Given the road's strategic importance in connecting remote regions and its challenging topographical conditions, our research aimed to identify the most suitable pavement type to mitigate these issues. Through a detailed examination incorporating eight different soil tests, alongside evaluations of traffic loads, weather conditions, and existing pavement performance, we adopted a comparative analysis methodology to assess the viability of flexible versus rigid pavements within this unique context. Results revealed that the soil composition and environmental conditions of the Siddhababa section significantly influence pavement performance, with specific gravity, moisture content, and California Bearing Ratio (CBR) tests indicating a nuanced suitability for both pavement types under varying circumstances. Our analysis concluded that, despite the economic and staged reinforcement benefits of flexible pavements, the durability, safety, and maintenance considerations favor the adoption of rigid pavement for the Siddhababa road section. However, acknowledging the economic constraints, a hybrid approach is recommended, emphasizing rigid pavements for the most vulnerable sections and flexible pavements elsewhere. This study contributes to the pavement engineering field by providing a model for pavement type selection in mountainous regions, aiming to enhance road safety and durability amidst challenging environmental conditions.\u003c/p\u003e","manuscriptTitle":"Resilient Roads in Challenging Terrain: A Case Study of Siddhartha Highway in Nepal","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-28 18:53:08","doi":"10.21203/rs.3.rs-4505046/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-07-01T12:41:13+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-27T21:05:21+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-27T16:02:23+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"332856568166025030296712229458378965044","date":"2024-06-23T17:58:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"249229558428249040332052185642205791426","date":"2024-06-20T16:07:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"332018680972769294106112836403104767018","date":"2024-06-18T10:31:14+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-06-18T09:59:12+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-06-14T12:21:26+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-06-10T06:53:30+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Civil Engineering","date":"2024-05-30T20:32:04+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-civil-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Civil Engineering](https://www.springer.com/journal/44290)","snPcode":"44290","submissionUrl":"https://submission.nature.com/new-submission/44290","title":"Discover Civil Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"928ef3cb-93f7-4153-abe6-a42a6d1386db","owner":[],"postedDate":"June 28th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-09-09T08:19:48+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-28 18:53:08","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4505046","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4505046","identity":"rs-4505046","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}