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To elucidate the degradation mechanism of expansive soil–rubber fiber (ESR) under freeze–thaw cycles, freeze–thaw cycle tests and consolidated undrained tests were conducted on the saturated ESR. The study quantified the elastic modulus and damage variables of ESR under different numbers of freeze–thaw cycles and confining pressure, and proposed a damage constitutive model for ESR. The primary findings indicate that: (1) The effective stress paths of ESR exhibit similarity across different numbers of freeze–thaw cycles, the critical stress ratio slightly decreased by 8.8%, while the normalized elastic modulus experienced a significant reduction, dropping to 42.1%. (2) When considering the damage threshold, the shear process of ESR can be divided into three stages: weak damage, damage development, and failure. As strain increases, the microdefects of ESR gradually develop, penetrating macroscopic cracks and converging to form the main rupture surface. Eventually, the damage value reaches 1. (3) Due to the effect of freeze–thaw cycles, initial damage exists for ESR, which is positively correlated with the number of freeze–thaw cycles. The rubber fibers act as tensile elements, and the ESR damage evolution curves intersect one after another, showing obvious plastic characteristics in the late stage of shear. (4) Confining pressure plays a role in limiting the development of ESR microcracks. The damage deterioration of ESR decreases with an increase in confining pressure, leading to an increase in ESR strength. (5) Through a comparison of the test curve and the theoretical curve, this study validates the rationality of the damage constitutive model of ESR under established freeze–thaw cycles. Furthermore, it accurately describes the nonlinear impact of freeze–thaw cycles and confining pressure on the ESR total damage. [ABSTRACT FROM AUTHOR]

Efficient data use for early warnings is a critical component of failure management, which encompasses activities such as vulnerable zone mapping, prediction, warning elements, prevention, planning, and action. This study proposes an early warning protocol (EWP) against highway embankment (HWE) failures constructed on expansive soil, implementing in filed situ/lab testing, instrumentation, geophysical testing, 2D/3D finite element method (FEM) analysis, development of machine learning-based predictive models, and analysis of the slope vulnerability index (SVI) factor. Six referenced HWEs were investigated, instrumented, monitored, and considered to measure their evaluative parameters (soil in situ, soil index properties, and factor of safety). The field-recorded data were validated using 2D electrical resistivity imaging. The 2D/3D FEM numerical models were developed based on the field-recorded rainfall volume to analyze the flow and coupled flow deformation of the HWEs' slopes. Predictive models were implemented to analyze the SVI, and the EWP was developed. The action plan was found to be the main component of the proposed EWP. Observing, planning, deciding, and acting are the proposed EWP's key predecessors. The developed EWP for embankment slope failure mitigation could benefit various public and private transportation agencies. [ABSTRACT FROM AUTHOR]

Large volumes of waste tires are generated due to the rapid growth of the transportation industry. An effective method of recycling waste tires is needed. Using rubber from tires to improve problematic soils has become a research topic. In this paper, the dynamic response of rubber fiber-reinforced expansive soil under freeze–thaw cycles is investigated. Dynamic triaxial tests were carried out on rubber fiber-reinforced expansive soil subjected to freeze–thaw cycles. The results showed that with the increase in the number of freeze–thaw cycles, the dynamic stress amplitude and dynamic elastic modulus of rubber fiber-reinforced expansive soils first decrease and then increase, and the damping ratio first increases and then decreases, all of which reach the turning point at the 6th freeze–thaw cycle. The dynamic stress amplitude and dynamic elastic modulus decreased by 59.4% and 52.2%, respectively, while the damping ratio increased by 99.8% at the 6th freeze–thaw cycle. The linear visco-elastic model was employed to describe the hysteretic curve of rubber fiber-reinforced expansive soil. The elastic modulus of the linear elastic element and the viscosity coefficient of the linear viscous element first decrease and then increase with the increase in the number of freeze–thaw cycles; all reach the minimum value at the 6th freeze–thaw cycle. The dynamic stress–dynamic strain curve calculation method is established based on the hyperbolic model and linear visco-elastic model, and the verification shows that the effect is better. The research findings provide guidance for the improvement of expansive soil in seasonally frozen regions. [ABSTRACT FROM AUTHOR]

Expansive soil is widely distributed and often needs to be improved for engineering and construction needs. Using blast furnace slag and fly ash as precursors and NaOH as an alkali activator, a geopolymer was prepared to solidify expansive soil, and the effect of nano-SiO2 on the compressive strength and water stability of the geopolymer-solidified expansive soil was further studied. The effects of alkali addition ratio, nano-SiO2 addition ratio, and curing agent addition ratio on the unconfined compressive strength and water stability of the cured soil were studied through unconfined compressive strength tests, and the curing mechanism was analyzed by electron microscopy scanning. The experimental results showed that the unconfined compressive strength and water stability of geopolymer-stabilized soil first increased and then decreased with an increase in alkali activator dosage. The optimal dosage of alkali activator was found to be 12.5%. Furthermore, it was found that adding nano-SiO2 can further enhance the strength and water stability of solidified soil. When the content of nano-SiO2 was 3%, the unconfined compressive strength was increased by 15%. With an increase in the content of nano-SiO2 doped polymer (GFNS), the unconfined compressive strength and water stability of the solidified soil showed a trend of first increasing and then decreasing, reaching a peak at a content of 20%. The cementitious materials, such as hydrated calcium silicate and hydrated calcium silicate aluminate, generated by the reaction between nano-SiO2 and geopolymer played a role in bonding and filling in the solidified soil. Under the joint action of the two, the structural arrangement between the solidified soil particles became more compact, which improved the strength of the solidified soil. [ABSTRACT FROM AUTHOR]

To simulate the influence of rainfall on the internal forces of expansive soil slope retaining structures, an approximate calculation method for the humidity stress field of expansive soil is proposed in this study. Considering both rainy and non-rainy conditions, on a high expansive soil slope, a numerical model is constructed for a combining supporting structure, which is composed of upper and lower anti-sliding piles and anchor rods/cable frames. Furthermore, the distribution of internal forces in the retaining structure is studied, and design optimization is performed. The research findings reveal that the bending moment profile along the longitudinal axis of the lower anti-sliding pile demonstrates a distinctive "W" pattern, which is characterized by initial reduction, following augmentation, a subsequent reduction, and final amplification. In contrast, the upper anti-sliding pile experiences an ascending trend, followed by a descending trend, and then a subsequent ascending trend. Interestingly, the introduction of rainfall grants an escalation in both the shear force exerted along the entire length of the upper and lower anti-sliding piles and the bending moment encountered by the lower anti-sliding pile. The determination of the internal force distribution of the expansive soil slope retaining structures under different conditions, using the proposed calculation method, provides a further optimization in their design. [ABSTRACT FROM AUTHOR]

This study evaluates the impact of compaction on the soil–water characteristic curve of unsaturated remodeled weakly expansive soils by assessing changes in soil pore structure resulting from variations in compaction. The remodeled weakly expansive soil in the Xinjiang Hami area is taken as the research subject to investigate how compaction affects microscopic pore structure using mercury intrusion testing. Subsequently, mercury intrusion porosimetry is employed to examine pore structure and distribution patterns at different dry densities. Based on the capillary principle and experimental methods (filter paper method and pressure plate method test), modified soil–water characteristic curves are obtained by fitting them with a three-parameter model law. The results indicate that higher dry density leads to an increased air intake value and significantly reduces the total volume of large pores within samples. Both the Fredlund and Xing model and the three-parameter model effectively capture the influence of initial dry density on the development pattern of the soil–water characteristic curve. [ABSTRACT FROM AUTHOR]

Expansive soil is prone to rapid strength degradation caused by repeated volume swelling and shrinkage under alternating dry–wet conditions. Basalt fiber (BF) and cement are utilized to stabilize expansive soil, aiming to curb its swelling and shrinkage, enhance its strength, and ensure its durability in dry–wet cycles. This study examines the impact of varying content (0–1%) of BF on the physical and mechanical characteristics of expansive soil stabilized with a 6% cement content. We investigated these effects through a series of experiments including compaction, swelling and shrinkage, unconfined compressive strength (UCS), undrained and consolidation shear, dry–wet cycles, and scanning electron microscope (SEM) analyses. The experiments yielded the following conclusions: Combining cement and BF to stabilize expansive soil leverages cement's chemical curing ability and BF's reinforcing effect. Incorporating 0.4% BFs significantly improves the swelling and shrinkage characteristics of cement-stabilized expansive soils, reducing expansion by 36.17% and contraction by 28.4%. Furthermore, it enhances both the initial strength and durability of these soils under dry–wet cycles. Without dry–wet cycles, the addition of 0.4% BFs increased UCS by 24.8% and shear strength by 24.6% to 40%. After 16 dry–wet cycles, the UCS improved by 38.87% compared to cement-stabilized expansive soil alone. Both the content of BF and the number of dry–wet cycles significantly influenced the UCS of cement-stabilized expansive soils. Multivariate nonlinear equations were used to model the UCS, offering a predictive framework for assessing the strength of these soils under varying BF contents and dry–wet cycles. The cement hydrate adheres to the fiber surface, increasing adhesion and friction between the fibers and soil particles. Additionally, the fibers form a network structure within the soil. These factors collectively enhance the strength, deformation resistance, and durability of cement-stabilized expansive soils. These findings offer valuable insights into combining traditional cementitious materials with basalt fiber to manage expansive soil hazards, reduce resource consumption, and mitigate environmental impacts, thereby contributing to sustainable development. [ABSTRACT FROM AUTHOR]

Investigating crack evolution characteristics in expansive soil under dry–wet cycle conditions is essential for analyzing the shallow instability of embankments and roadbeds filled with this type of soil. Indoor tests on remolded expansive soil specimens were performed under dry–wet cycle conditions, and digital image processing technology (PCAS) was used to quantitatively analyze the process of crack evolution. The study examined how initial moisture content, compaction degree, thickness, and expansibility affect crack development in expansive soil. Additionally, the study discussed the mechanism of crack evolution, considering the characteristics of crack structures in expansive soil. The findings suggest that crack development in expansive soil specimens is influenced by various factors including initial moisture content, compaction degree, thickness, and expansibility. The crack ratio increases with the initial moisture content, thickness, and expansibility, but decreases with the compaction degree. Furthermore, a significant linear relationship exists between the attenuation rate of soil strength and the crack ratio. The development of cracks is governed by the variance in soil shrinkage, which leads to the formation of distinct shrinkage centers at various locations and is markedly influenced by the soil's thickness. This research explores the laws governing the evolution of cracks in expansive soils, elucidating the mechanisms by which these cracks evolve under the influence of various factors. It addresses a significant gap in the theoretical understanding of crack evolution in expansive soils under conditions of multiple influences, thereby offering crucial insights into the characteristics of soil evolution. [ABSTRACT FROM AUTHOR]

In recent years, many researchers have evaluated the sustainable use of waste tire rubber as an aggregate in soil. Its effectiveness has been widely acknowledged. The main objective of this work is to study the influence of rubber fibers on shear strength and pore structure characteristics in relation to expansive soil. In this context, we conducted a series of experiments that were carried out on reinforced expansive soil with rubber fiber contents of 0, 5, 10, 15, and 20%. The results show that the shear strength and maximum dilatation angle increase gradually with rubber fiber content. Due to the pore water pressure and creep effects, the deviator stress and effective cohesion of the samples under the consolidated drained conditions were higher than those under the undrained conditions. The converse was true for the internal angle. The addition of an appropriate amount of (5–10%) rubber fiber can effectively inhibit the development of soil cracks and reduce the porosity of the samples. The results obtained can highlight the beneficial effects of rubber fiber, which is highly desirable in many backfill applications. [ABSTRACT FROM AUTHOR]

Featured Application: This research paper encourages repurposing waste material for ground improvement. The results of this study contribute towards a greater understanding of the strength and durability performance of treated soils under normal, fluctuating, and adverse moisture conditions. Expansive soil underlying structures pose a significant risk to the integrity of superstructures. Chemical soil stabilization can be used to strengthen soils due to the cost and impracticality of mechanical approaches. Waste materials such as recycled gypsum and rice husk ash have been considered alternatives because of their sustainable and economic advantages. A combination of these additives was used to address the high absorption of gypsum and the lack of cohesion of the pozzolan. The study assessed the short-term and long-term performance of expansive soil treated with recycled gypsum and rice husk ash under normal and fluctuating moisture conditions. Direct shear tests indicated ductile and compressive soil behavior with improved shear strength. A good approximation of stress–strain response was made with a modified hyperbolic model for treated soils that exhibited strain hardening and compressive volumetric strain. Durability and water immersion tests were performed for samples after varying curing periods and cycles of capillary soaking to assess the behavior when exposed to varied environmental conditions. Samples under the modified durability test experienced significant strength loss, with decreasing compressive strength as curing durations increased. Specimens in the modified water immersion test experienced significant strength loss; however, it was determined that curing durations did not contribute to the change in the strength of the sample. Expansion index tests also determined that the treatment effectively mitigated expansivity and collapsibility in all samples. Despite improvement in shear strength and expansion potential, further investigation is needed to enhance the durability of soil treated with gypsum and rice husk ash. [ABSTRACT FROM AUTHOR]

Expansive soil exhibits significant swellings and shrinkages, which may result in severe damage or the collapse of structures built upon it. Calcium-based admixtures, such as lime, are commonly used to improve this problematic soil. However, traditional chemical additions can increase significant environmental stress. This paper proposes a sustainable solution, namely, the use of lignin fiber (LF) from the paper industry to partially replace lime as an amendment for expansive soils. Both the macroscopic and microscopic characteristics of the lignin fiber-treated expansive soil are extensively studied. The results show that the mechanical properties of expansive soil are improved by using lignin fiber alone. Under the condition of an optimal dosage of 8%, the compressive strength of lignin fiber-modified soil can reach 193 kPa, the shear strength is increased by 40% compared with the untreated soil, and the water conductivity is also improved with the increase in dosage. In addition, compared with 2% lime-modified soil, the compressive strength of 8% lignin fiber- and 2% lime composite-treated expansive soil increased by 50%, the cohesion increased by 12%, and the water conductivity decreased significantly. The microstructure analysis shows that at an 8% lignin fiber content, lignin fibers interweave into a network in the soil, which effectively enhances the strength and stability of the improved soil. Simultaneously, the fibers can form bridges across the adjacent micropores, leading to the merging of pores and transforming fine, dispersed micropores into larger, connected macropores. Lime promotes the flocculation of soil particles, forming larger aggregates and thus resulting in larger pores. The addition of fibers exerts an inhibitory effect on the flocculation reaction in the composite-improved soil. In conclusion, lignin fibers are an effective addition used to partially replace calcium admixture for the treatment of expansive soil, which provides a sustainable and environmentally friendly treatment scheme for reducing industrial waste. [ABSTRACT FROM AUTHOR]

Expansive soils exhibit directionally dependent swelling that traditional isotropic models fail to capture. This study investigates the anisotropic swelling characteristics of expansive soil with a medium swelling potential through the use of modified oedometric testing. Vertical swelling strains can reach up to 1.71 times that of the horizontal movements, confirming intrinsic anisotropy. A nonlinear elastic constitutive model incorporates vertical and horizontal elastic moduli with respect to matric suction to characterize anisotropy. Three elastic parameters were determined through the experiments, and predictive equations were developed to estimate the unsaturated moduli. The constitutive model and predictive techniques provide practical tools to better assess expansive soil pressures considering anisotropy, offering guidelines for utilization and design. The outcomes advance understanding of these soils' directionally dependent behavior and stress–strain–suction response. [ABSTRACT FROM AUTHOR]

The pore size distributions of an expansive soil under different simulated rainfall conditions were studied using nuclear magnetic resonance (NMR) techniques. Four sets of treatments with different rainfall intensities (light, moderate, heavy, and rainstorm) and durations (0.5 d, 1 d, 2 d, and 3 d) were designed to analyze the effects of rainfall on the microstructure of the expansive soil. Results show that with increasing rainfall duration, micropores gradually form and develop, enlarge, and interconnect in the soil, eventually forming stable seepage channels. Under light and moderate rain conditions, the proportion of micropores gradually decreases, while the proportions of mesopores and macropores gradually increase. Under heavy and rainstorm conditions, the proportion of micropores sharply decreases and then stabilizes, while the proportions of mesopores and macropores increase. With increasing rainfall intensity, the dominant pore size and porosity both initially increase and then stabilize. A quantitative relationship model between pore size, porosity, and rainfall conditions is established and the fitting effect is good. This study shows that rainfall alters the microstructure of expansive soils, which stabilizes after dynamic equilibrium. This provides a theoretical basis for predicting and controlling the engineering behavior of expansive soils under different rainfall conditions. [ABSTRACT FROM AUTHOR]

Natural biopolymers offer a sustainable alternative for improving soil behavior due to their inert nature, small dosage requirement, and applicability under ambient temperatures. This research evaluates the efficacy of natural biopolymers for ameliorating an expansive soil by using a 0.5% dosage of cationic chitosan, charge-neutral guar gum, and anionic xanthan gum during compaction. The results of laboratory investigations indicate that the flow through and volume change properties of the expansive soil were affected variably. The dual porosity, characterized by low air entry due to inter-aggregate pores (AEV1 of 4 kPa) and high air entry due to the clay matrix (AEV2 of 200 kPa) of the soil, was healed using chitosan and guar gum (AEV of 200 kPa) but was enhanced by the xanthan gum (AEV1 of 100 kPa and AEV2 of 200 kPa). The s-shaped swell–shrink path of the soil comprised structural (e from 1.23 to 1.11), normal (e from 1.11 to 0.6), and residual stages (e ranged from 0.6–0.43). This shape was converted into a j-shaped path through amendment using chitosan and guar gum, showing no structural volume change, with e from about 1.25 to 0.5, but was reverted to a more pronounced form by xanthan gum, with e from 1.5 to 1.32, 1.32 to 0.49, and 0.49 to 0.34 in the three stages, respectively. The consolidation behavior of the soil was largely unaffected by the addition of biopolymers such that the saturated hydraulic conductivity decreased from 10−9 m/s to 10−12 m/s over a void ratio decrease from 1.1 to 0.6. At a seating stress of 5 kPa, the swelling potential (7.8%) of the soil slightly decreased to 6.9% due to the addition of chitosan but increased to 9.4% and 12.2% with guar gum and xanthan gum, respectively. The use of chitosan and guar gum will allow the compaction of the investigated expansive soil on the dry side of optimum. [ABSTRACT FROM AUTHOR]

This study investigates the effect of nanosilica and plantain leaf ash on the sustainable stabilization of expansive soil. This study conducted various strength tests, including Unconfined Compressive Strength (UCS), direct shear, and California Bearing Ratio (CBR) tests, to analyze the enhancement of mechanical properties by adding nano silica and plantain leaf ash. Scanning Electron Microscopy (SEM) analysis was conducted to investigate the interaction mechanism between the soil and the combination of nano silica and plantain leaf ash. Three different combinations of plantain leaf ash were utilized, ranging from 5% to 15%, alongside nano silica ranging from 0.4% to 1.2%. The reinforced soil's compressive strength, shear strength, and bearing capacity were assessed through UCS, direct shear, and CBR tests. The results demonstrated significant improvements in compressive strength, up to 4.6 times, and enhancements in cohesion and frictional angle, up to 3.3 and 1.6 times, respectively, at 28 days. Moreover, the addition of nano silica and plantain leaf ash led to increased bearing capacity and reduced soil swelling potential, contributing to the overall stability and strength improvement in expansive soil. The SEM test results demonstrate that maximum bonding and compaction occur when 1.2% nano silica and 15% plantain leaf ash are added to the soil. [ABSTRACT FROM AUTHOR]

Expansive soils are distributed across a wide area in China, and land transport and surface construction will inevitably involve these soils. To mitigate the deficiencies of single-method expansive soil modification, it is highly important to adopt the use of polyvinyl alcohol (PVA) to improve expansive soils and enhance the strength and toughness of modified soils. In addition, solidification technology can be utilized for the resource utilization of expansive soils. In this study, triaxial testing is employed to evaluate the mechanical properties of solidified soil. When the confining pressure is the same and with increasing PVA content, soil particles and PVA combine to form a cemented substance, which fills the internal pores of the soil samples, enhances the cohesion between soil particles, and improves the bearing capacity of the soil. The stress–strain curve for the modified soil first increases and then decreases. The shear strength peaks at a PVA content of 3%. Based on the improved soil with a 3% PVA content, GDS dynamic triaxial tests were carried out to investigate the effects of different confining pressures and frequencies on the dynamic stress–strain curves, dynamic modulus of elasticity, and variation rule for the damping ratio of the improved soil. The results show that the dynamic stress–strain curve for the improved soil increases with increasing confining pressure and frequency and that the dynamic stress–strain backbone curves exhibit significant nonlinearities at different frequencies and circumferential pressures. The dynamic elastic modulus increases with increasing confining pressure and frequency and decreases gradually with increasing dynamic strain. The initial dynamic modulus of elasticity increases with increasing envelope pressure and frequency but is less affected by frequency, and the damping ratio decreases with increasing confining pressure and frequency. Soil treatment can improve the pore distribution, inhibit the extension of soil cracks, and enhance soil compactness. [ABSTRACT FROM AUTHOR]

The structure of a bridge has certain peculiarities, and its pile foundations are susceptible to uplift or settlement deformation due to various factors. This can result in bridge deck cracking, structural instability, tilting, and even irreversible damage, which significantly impacts the bridge's stability and driving safety. This study focuses on the Shiyangtai No.1 Bridge and aims to investigate the factors that cause abnormal rise and fall deformations of bridge pile foundations. The study combines macro and micro analysis, physical characteristic testing of the overlying soil under the bridge pile foundation, and numerical simulation of the bridge pile foundation in the goaf. The study discusses in-depth the formation mechanism of the abnormal uplift of some pile foundations of the Shiyangtai No.1 Bridge based on the analysis of the factors influencing the abnormal rise and fall deformation of the bridge pile foundations at home and abroad. The expansive soil beneath the pile foundation is weak, and the force generated by the water expansion is insufficient to cause the pile foundation to rise to 309 mm. The results indicate that the pile foundation of the bridge is not affected by the expansion characteristics of the overlying soil. The collapse of the goaf roof generates double lateral thrust from the accumulation body at the bottom of the goaf and the upper collapse arch. This causes staggered bending uplift of the sandstone soil layer, resulting in upward squeezing pressure that causes the bridge pile foundation to rise. Therefore, the coal mining area is the main factor influencing the abnormal uplift of the pile foundation of the Shiyangtai No.1 Bridge. [ABSTRACT FROM AUTHOR]

With the development of the Belt and Road Initiative in China, high-speed railways are booming and inevitably pass through seasonal frost regions. In Nanyang basin, due to seasonal changes, railway subgrades will undergo frost heaving and thawing subsidence. The freezing characteristics of the soil are characterized by the freezing characteristic curve, and the important factors affecting the freezing characteristic curve are the content of expansive clay minerals in the soil and the salt solution. Therefore, three soil samples with different montmorillonite contents were saturated with salt solutions of different concentrations, and the freezing temperature of the soil samples was controlled by a cold bath. After the temperature equilibrium, the frozen stable soil samples were put into a nuclear magnetic resonance instrument to test the unfrozen water content, and the relationship between the freezing temperature and the unfrozen water content of expansive soil under different salt solution concentrations was obtained. Additionally, a unified model was used to simulate the test results. The results show that SFCC shifts to the left, that is, the sodium chloride salt solution reduces the freezing point of the soil sample so that it has more unfrozen water at the same temperature. At the same time, the soil's freezing characteristic curves are closely related to content of expansive clay minerals in the soil. The more expansive clay mineral content, the greater the corresponding unfrozen water content. These results provide some basic insights for improving the frost heave and thaw subsidence problems of railway subgrades in seasonal permafrost regions, which will have a positive impact on promoting the management and rational application of land resources and the promotion of sustainable development. [ABSTRACT FROM AUTHOR]

This study investigates the critical behavioral characteristics of pile foundations in expansive soil foundations through a series of model tests, including settlement, axial force, and side frictional resistance. The experiment initially utilized sand, bentonite, and gypsum as the fundamental materials for the preparation and composition research of expansive soil simulant materials. Subsequently, the performance of different types of model piles under various loads and water immersion conditions was analyzed. The results indicate that non-cased piles exhibit typical friction pile behavior, while PVC-cased and steel-cased piles effectively reduce side frictional resistance, resulting in a more uniform distribution of axial force along the pile. After immersion, the model test materials experience expansion, with a faster initial expansion rate and a more gradual later expansion rate. Different types of model piles exhibit different displacement characteristics, and the presence of an outer casing can reduce the uplift of the inner pile. Furthermore, PVC casing demonstrates better performance in handling negative frictional effects. This study provides valuable insights for the design and construction of pile foundations in expansive soil foundations. [ABSTRACT FROM AUTHOR]

Expansive soils change volume due to changes in moisture content, which results in ground movement. Lightweight shallow-depth structures such as pavements, residential footings, and pipelines can suffer distress as they face additional stresses from the moving ground. The soil reactivity (the ability of soil to expand or contract due to change in moisture content) and the interactions at the soil-atmosphere-vegetation boundary are two of the major contributing factors to the ground movement. The current methodology used in design to account for ground movement is based on limited field and laboratory observations. Aiming at a better understanding of the interaction at the soil-atmosphere-vegetation boundary and its correlation with ground movement, this paper presents results from a field study. The research site was located in a semi-arid climate area and consisted of moderately to highly reactive clay soils. Part of the site was vegetated with mature trees, and part was occupied by grass. The order of 10 s of mm difference was observed in the magnitude of movement across the site owing to site soil variability as well as differences in vegetation. The areas with large trees showed relatively lower ground movement over the study period compared to the area occupied by grass, which was attributed to the microclimate created by the tree canopy and the already established deeper drying of the soil near the trees. [ABSTRACT FROM AUTHOR]

The impact of reinforcing vegetation roots on the stability of expansive soil slopes with moisture absorption and expansion was investigated. Then, poinsettia is selected as the slope protection plant, and ABAQUS software (version 2022) with secondary development is used to simulate the moisture absorption and expansion of the expansive soil slope. After that, the strength reduction method is employed to study the effects on the displacement and plastic zone, and on the shallow layer of the expansive soil slope at different rainfall conditions. The following points are revealed: (1) The roots of the poinsettia can reduce the displacement of the slope. But, when the rainfall intensity exceeds the soil permeability coefficient, the soil reinforcement effect decreases. (2) The poinsettia root system can alleviate the concentration of plastic strain, disperse the plastic zone, and increase slope stability along the distribution of the roots. (3) The poinsettia roots can improve the shallow stability of the slope. But when the rainfall intensity exceeds the surface permeability coefficient, the magnitude of the reinforcement decreases. The results demonstrate that the poinsettia roots can enhance shallow slope stability. However, with increasing rainfall intensity, the ability of the poinsettia roots to enhance shallow slope stability gradually weakens. [ABSTRACT FROM AUTHOR]

Taking the expansive soil near Hefei Xinqiao International Airport as the research subject, indoor dynamic triaxial tests were conducted to investigate the influence of different loading methods on the dynamic pore pressure of saturated remolded expansive soil on the basis of maximally simulating the real characteristics of subway loading. Furthermore, the action laws of three factors, namely intermittent loading ratio, static deviator stress, and cyclic stress ratio, on the accumulated pore pressure of saturated remolded expansive soil under intermittent subway cyclic loading were analyzed. The research results indicate that the loading method significantly affects the development trend of the accumulated pore pressure. Under similar conditions, a larger intermittent loading ratio leads to smaller accumulated pore pressure values and a slower initial development rate of pore pressure under the same cycle vibration. Increasing static deviatoric stress promotes the accumulation of pore pressure. The influence of the cyclic stress ratio is dependent on the intermittent loading ratio and does not follow a consistent pattern. [ABSTRACT FROM AUTHOR]

Soil, a naturally occurring resource, is increasingly used as a construction material. Stabilisation strengthens soil, which is weak as an engineering material. Stabilising soil changes its physical qualities, enhancing its strength. Soil stabilisation increases the shear strength and load-bearing capacity. Soil stabilisation refers to any endeavour to change natural soil for engineering purposes using physical, chemical, mechanical, or biological methods, or a mix of these. Strengthening road pavements includes improving the load-bearing capacity, tensile strength, and performance of unstable subsoils, sands, and waste materials. Due to market demands and scientific advances, the number of soil-stabilising additives has increased. These innovative stabilisers include reinforcing fibres, calcium chloride, sodium chloride, and cross-linking water-based styrene acrylic polymers, which are geopolymers that boost the load-bearing capacity and tensile strength of soil. Many materials are being explored for soil stabilisation. In this article, the authors investigated the direction of soil stabilisation research. Scientometric analysis identifies stabilisation challenges and research trends in the field. This study analysed research patterns by countries, authors, institutions, keywords, and journals from 1959 to 2023; in 2021, 150 articles were published, which was the highest number in a year. Citations peaked at 3084 in 2022. With 253 publications and 3084 citations, India was the most productive country. Iran and France published the fewest, 34 and 33, respectively. The Islamic Azad University and the National Institute of Technology had the fewest published articles with 17 articles. This work can help track soil stabilisation research and will serve as an information document for future research. [ABSTRACT FROM AUTHOR]

Expansive soil near Hefei Xinqiao International Airport was selected as the research focus. The effects of different loading modes on the dynamic strain of the saturated remodeled expansive soil was investigated by indoor dynamic triaxial tests and the effect of three factors, intermittent loading ratio, static deviatoric stress, and cyclic stress ratio, on the accumulated plastic strain of saturated remodeled expansive soil under intermittent subway cyclic loading was analyzed. Finally, the corresponding accumulated plastic strain calculation model was established based on the test results. The research results show that the loading modes do not affect the overall development mode of the strain and, under intermittent loading, the strain tends to be more stable. Under intermittent loading, when the number of cycles is the same, the larger the intermittent loading ratio, the smaller the accumulated plastic strain. The effect of static deviatoric stress and cyclic stress ratio on strain accumulation is significant. Based on the hyperbolic model, an accumulated plastic strain calculation model related to the number of cycles of remolded expansive soil under the load of the Hefei subway was proposed, which has a certain reference significance for the design, safety assessment, and safe operation of the Hefei subway. [ABSTRACT FROM AUTHOR]

The water-sensitive effect of expansive soil (ES) poses a serious challenge to the safety and durability of infrastructure. To reduce the effect of water sensitivity on expansive soil, a new powder soil passivator with polyacrylic (PA) as the main component was proposed. In this paper, a series of macroscopic and microscopic tests were conducted to evaluate the water-sensitive passivation effect and mechanism of PA-ES composites. The results showed that PA significantly attenuated the water sensitivity of ES. With the increase in PA content in the PA-ES composites, the water sensitivity of the composites decreased, swelling and shrinkage deformation decreased, and the strength of the composites increased significantly. In addition, when the content of PA in the PA-ES composite is 6%, it can significantly alleviate the deformation of the composite and improve the saturated shear strength of the composite, meeting the requirements of ES engineering disposal. Finally, the results show that the mechanism of PA passivation of ES water-sensitive effect mainly includes adsorption, binding, and filling. The study shows that PA has a broad engineering application prospect as an ES passivator. [ABSTRACT FROM AUTHOR]

The present work determined the influence of superhydrophobic nano-SiO2 on the hydraulic conductivity and pore size distribution of expansive soil, and analysed the mechanism of modification between superhydrophobic nano-SiO2 and expansive soil from a microscopic view. Superhydrophobic nano-SiO2 was added to expansive soil as a modifier. Our samples were of two types, i.e., unmodified (without nano-SiO2) and modified (with 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% nano-SiO2 by weight of the parent soil). The hydraulic conductivity decreased with increasing nano-SiO2 content. Fourier transform mid-infrared test revealed that some silanols in soil and nano-SiO2 were dehydrated and condensed to form siloxanes. We inferred that nano-SiO2 can attach onto the surface of soil particles to form a hydrophobic membrane, which reduced the soil expansion and the change in pore size distribution. And microscopic tests showed that the pore volume and hydrophilicity of the soil samples decreased with increasing SiO2 content. According to the Young–Laplace equation, the minimum permeable pore radius was calculated in the hydraulic-conductivity test. With increasing nano-SiO2 content, the volume of permeable pore decreased. It had an excellent linear relationship with the hydraulic conductivity and permeable pore volume of samples containing different nano-SiO2 contents. Therefore, superhydrophobic nano-SiO2 could effectively reduce hydraulic conductivity by changing the pore size distribution of expansive soil. [ABSTRACT FROM AUTHOR]

Expansive soil is prone to shrinkage and cracking during the drying process, leading to strength and permeability problems that exist widely in water conservancy projects and geotechnical engineering, including foundation pits and cracks at the bottom of channels and slopes. Such problems are closely related to the tensile strength of the soil. In this study, Nanyang expansive soil is taken as the research object and radial splitting tests were performed using a particle image velocimetry (PIV) test system on both undisturbed and remolded expansive soil during the drying process. The results indicated that the load–displacement curve of the undisturbed and remolded expansive soil specimens showed a strain-softening phenomenon and that the peak load increased with decreasing water content. Under the same other conditions, the peak load of the remolded expansive soil specimen was higher than that of the undisturbed soil specimen, with the undisturbed soil specimen having distinctive structural and fractural features. The load–displacement relation curve, displacement vector field, and fracture characteristics had an obvious one-to-one correspondence in the stage division. The compression deformation stage, crack development stage after the peak value, crack maturity stage, and failure stage could be observed via the PIV technique. Moreover, the fracture characteristics of the remolded specimens were more regular than those of the undisturbed specimens. The above research results provide a scientific basis for the design and construction of geotechnical engineering related to expansive soil. [ABSTRACT FROM AUTHOR]

Expansive soils in the field are typically exposed to cyclic wetting and drying due to climatic fluctuations and subjected to a variety of stress conditions in nature or when used as compacted layers for the construction of hydraulic barriers or waste disposal facilities. The hysteric behavior of the soil-water characteristic curve (SWCC) is a key parameter for understanding, modeling, and interpreting the unsaturated behavior of these soils under such conditions. This study investigates the effect of stress states on the hysteresis behavior of soil-water characteristic curves (SWCCs) for compacted highly expansive clay over a range of matric suction between 0 and 1500 kPa. Two test series were performed, the first test series investigated the effect of stress states on the hysteresis of SWCCs during a single drying-wetting (DW) cycle. The second test series studied the combined effect of stress applied and multiple drying-wetting cycles on the SWCC hysteresis. For the sake of comparison, the overall SWCC hysteresis due to drying-wetting cycles was quantified using the average degree of hysteresis in terms of volumetric water content (ADHθ). Furthermore, contributors to the observed hysteresis were defined using two newly proposed measures; namely, average degree hysteresis in terms of gravimetric water content (ADHw) and in terms of volume change (ADHe*). The outcomes of this study indicate that consideration of stress states on the hysteresis of SWCC for expansive clay is of great importance. The results show a dual trend for the variation of ADHθ with applied vertical stress. Furthermore, multiple DW cycles induced a significant reduction in the hysteresis (ADHθ) under low- and high-stress states up to a certain level of DW cycles, then, no further changes in the hysteresis trend were detected. It was also found that hysteresis loops under a low-stress state were concentric in shape while hysteresis loops for specimens under a high-stress state were non-concentric, with a downward shift in hysteresis loops with the increase in DW cycles. [ABSTRACT FROM AUTHOR]

Expansive soil covers the vast area of Mengzi, Yunnan, China, and creates numerous hazards for construction projects. When treating expansive soil, a modifier is usually added to inhibit its expansion and increase its strength. Lignin and its derivatives can better meet the requirements of expansive soil treatment and have become the preferred choice to replace traditional inorganic modifiers. Lignin is a green and environmentally friendly physical improvement material. In this study, lignin was used to improve soil, alone and combined with its derivatives, and the physical and mechanical properties of the improved soil were studied. Combined with an unconfined compressive strength test, a low-stress direct shear test, and a scanning electron microscopy test, the mechanism of lignin and its derivatives for the improvement of expansive soil is discussed. When calcium lignosulfonate alone was added, the improved soil's expansion rate decreased, the soil's water-holding capacity decreased, and its strength increased. Furthermore, the inclusion of 3% calcium lignosulfonate was the best. When the expansive soil was improved with the optimal calcium lignosulfonate content (3% CL) and composite lignin fibers, the strength of the soil body was further improved, the toughness was enhanced, and it shows plastic swelling failure and good water stability. 3% calcium lignosulfonate and 1.5% lignin fiber was the best for composite improvement as; it offered the optimal degree of particle aggregation and the development of pores and cracks was better inhibited, even though the fiber distribution was messy. This study shows that lignin and its derivatives can be used instead of inorganic modifiers to treat expansive soils to reduce the number of inorganic modifiers, and provided a sustainable treatment plan for reducing industrial waste. [ABSTRACT FROM AUTHOR]

Expansive soil swells with water and shrinks with water loss, causing serious safety problems for construction projects. This study emphasizes alkali-activated binder (NaOH excited fly ash) stabilized expansive soil. We found that swelling decreased with an increase in the amount of NaOH in alkali-activated binder. It was found that the alkali-activated binder stabilized expansive soils (AABS) had higher shear strength than untreated expansive soils (US), manifested by increased cohesion and friction angle. In AABS, the highest cohesion and the highest shear strength were found when the NaOH mass was 6% of the fly ash mass. The strength of AABS was similar to that of US without curing. AABS had higher strength than US after 7 and 14 days of curing. The unconfined compressive strength increased with extension of curing time. Combined with XRD and SEM analysis, it was shown that the mechanism of AABS was the formation of C–S–H and (C,N)–A–S–H and the change in the internal structure of expansive soil. This investigation can solve both the expansive soil problem and provide new concepts for green development. [ABSTRACT FROM AUTHOR]

Highlights: What are the main findings? Digital image correlation (DIC) method was applied to monitor the slope surface deformation and crack development. Deformation and failure processes of the expansive soil slope had an obvious crack control effect. The SLO method should be preferentially used to forecast the failure of expansive soil slopes with "step-like" displacement. What is the implication of the main findings? The main findings are helpful for forecasting expansive soil landslides and providing guidance for controlling landslide hazards in expansive soil areas. Expansive soil is one of the most widely distributed special soils in the world. It is widely developed in Henan, Anhui, Guangxi and other places in China, and highly overlaps with densely populated and economically active areas. Expansive soil is considered a typical "problematic soil" because its mechanical behaviour is very sensitive to water content changes; such behaviour mainly manifests as swelling upon wetting and shrinking upon drying, so the presence of expansive soil is an important factor in mountain landslide disasters in southern China. Because the particularities of its constituent materials are related to typical physical and mechanical properties, forecasting the failure times of expansive soil slopes remains a global problem. In this study, a series of in situ artificial rainfall experiments were conducted on an excavated expansive soil slope; then, the digital image correlation (DIC) method was applied to monitor the slope surface deformation and crack development. Finally, the failure time of the slope was forecasted using the inverse velocity (INV) and slope (SLO) models. The study results show that the deformation and failure processes of the analysed expansive soil slope had an obvious crack control effect, and the displacement–time curve derived by the DIC method had an obvious "phased change law". The data points calculated by the INV method were discrete and had high linear fitting requirements, resulting in large failure time forecasts. When the SLO method was used to forecast the failure time, because the values derived in the stable deformation stage were relatively concentrated in the calculation process, an obvious linear relationship was found in only the accelerated deformation stage, so the prediction results were more accurate. Therefore, the SLO method should be preferentially used to forecast the failure of expansive soil slopes with "step-like" displacement. These results enabled us to characterize slide processes and identify the mechanism responsible for the movement of a rainfall-induced expansive soil landslide. The stage deformation and failure mode of expansive soil landslide under rainfall infiltration: "slow deformation—stable deformation—accelerated deformation—instability failure" was revealed. This study is helpful for determining the deformation and failure mechanism of rainfall-induced expansive soil landslide and forecasting expansive soil landslides and providing guidance for controlling landslide hazards in expansive soil areas. [ABSTRACT FROM AUTHOR]

To reasonably analyze the bearing characteristics of curved beam bridge pile foundation under the combined action of vertical force (V) and torque (T) in expansive soil, a method of determining Tu (limit torque) under the action of V is proposed. Considering the effects of expansive force and ground heave after immersion, the load transfer function at the pile–soil interface with positive and negative friction resistance is established. The nonlinear solution of a single pile under vertical load is achieved by the finite difference method. Subsequently, the circumferential limit friction resistance is modified, and a loop iteration program is compiled through MATLAB. Thus, the bearing capacity of single pile under the loading path of V→T is obtained. The corresponding failure envelope curve is drawn and verified by laboratory model tests. Based on the verified solution, the bearing capacity envelope curve and deformation characteristics of single pile are analyzed. The influence of the expansion rate on the bearing capacity envelope curve is discussed, and reasonable engineering suggestions are put forward. [ABSTRACT FROM AUTHOR]

This study investigated the crack propagation law of expansive soil slopes under drying–wetting conditions and the influence of cracks on slopes by conducting a large-scale indoor slope test subjected to drying–wetting cycles. The change in soil moisture content at different depths during the drying–wetting cycles was monitored using a moisture content sensor, and the variation in crack depths in the expansive soil during the drying process was measured using a crack depth detector. The cracks on the slope's surface were processed using a self-made binarization program, and the crack evolution mechanism of the expansive soil during the drying process was analyzed. The rainfall-induced change in moisture content in the fractured soil was used to obtain the influence of moisture content change on expansive soils, and to analyze the dry–wet cycle failure mode of surface soil. The surface cracks of the soil were quantified by binary processing, and the area of the cracks and the area ratio of cracked soil to intact soil were calculated. Finally, by using PFC simulation software with the slope cracks and quantitative analysis results as parameters, it was confirmed that the greater the number of drying–wetting cycles, the greater the number of cracks, and the greater the damage to the slope. [ABSTRACT FROM AUTHOR]

This research developed a numerical-hierarchical framework that captured surface conditions and climate parameters. Volume changes under distinct scenarios of surface boundary, antecedent moisture, and meteorological parameters were predicted using a coupled seepage-deformation model. Risk was hierarchically based on expert judgment for surface scenarios (Stage-I indices) and normal distribution for antecedent moisture and atmospheric parameters scenarios (Stage-II indices). Results indicated seasonal volumetric changes with minor variations of −5 mm from January to April, a steady settlement of −17 mm by June, and a gradual heave of +8 mm by December. All Stage-I indices showed similar trends such that the fluctuations were highest for vegetation, followed by slope, then by cover, and lowest for loading. Volume changes gradually reduced with depth and diminished at 3.1 m. Similar seasonal and profile trends were generally found for most Stage-II indices. Nonetheless, different trends under wet and dry conditions were observed for initial water content, precipitation, and air temperature. For the datum scenario, risk was non-existent till February, increased to 2.3 by June, diminished by October, and rose back to 1.0 by December. Similar values of cyclic variations in risk were found in most urban facilities. Volume changes were found to be two times higher in parks, insignificant for roads, half for five story buildings, and one-fourth for pipes under roads. Among the Stage-II indices, risk for the initial water content inhibited seasonal variations whereas that for precipitation was about half with a wider distribution; all the other indices showed about one-third the values. Under a higher occurrence probability of 0.129, a magnified risk was observed for all the indices such that the most critical were the initial water content and precipitation. [ABSTRACT FROM AUTHOR]

Expansive soils exist in many countries worldwide, and their characteristics make them exceedingly difficult to engineer. Due to its significant swelling and shrinkage characteristics, expansive soil defies many of the stabilization solutions available to engineers. Differential heave or settlement occurs when expansive soil swells or shrinks, causing severe damage to foundations, buildings, roadways, and retaining structures. In such soils, it is necessary to construct a foundation that avoids the adverse effects of settlement. As a result, building the structure's foundations on expansive soil necessitates special consideration. Helical piles provide resistance to uplift in light structures. However, they may not fully stabilize foundations in expansive soils. A granular anchor pile is another anchor technique that may provide the necessary resistance to uplift in expansive soils using simpler methods. This review and numerical study investigate the fundamental foundation treatments for expansive soils and the behavior of granular anchors and helical piles. Results indicate that granular anchor piles performed better than helical piles for uplift and settlement performance. For heave performance, the granular anchor and helical piles perform nearly identically. Both achieve heave reductions greater than 90% when L/H > 1.5 and D = 0.6 m. [ABSTRACT FROM AUTHOR]

Featured Application: This study attempts to identify optimal dosage ranges of lime and PG for maximizing the strength performance of stabilized expansive soils. The study involved the utilization of an industrial waste product, Phosphogypsum (PG) as an additive to lime for the stabilization of soil. Three lime dosages, viz. initial consumption of lime (ICL), optimum lime content (OLC) and less than ICL (LICL) were adopted for stabilizing the soil. The study investigated the stress-strain characteristics of soil composites stabilized with these three lime contents modified with optimum dosages of PG. Mineralogical studies were performed on the spent samples used for a series of determinations of unconfined compression strength tests with various combinations of lime and optimum PG content. The addition of an optimum dosage of PG resulted in an early strength gain of 8.8%, 14.1% and 13.9% and a delayed strength gain of 9.9%, 19% and 19.7% for 3%, 5.5% and 7% for the lime-stabilized soil, respectively. It was found that the addition of PG to the lime resulted in enhanced stiffness, residual strength and reduced brittleness due to the PG amendment of the stabilization reactions. However, in terms of the overall improvement of soil properties, the most favorable benefit was obtained by optimal PG modification of ICL rather than OLC. Microanalysis of the X-ray diffraction scatter also supported the results revealed through stress-strain characteristics. ICL with its optimal PG dosage showed a better progression of pozzolanic reactions when compared to the other two in terms of reduction of peaks of soil minerals and increase in peaks of CSH. [ABSTRACT FROM AUTHOR]

Lightweight structures built on expansive soils are susceptible to damage caused by soil movement. Financial losses resulting from the improper design of structures on expansive soils can be significant. The interactions and failure mechanisms of different geotechnical structures constructed on such soils differ depending on the structure type, site characteristics, and climatic conditions, as the behaviour of expansive soils is influenced by moisture variations. Therefore, the performance of different geotechnical structures (e.g., lightweight footings for residential buildings) is expected to be adversely affected by climate change (especially rainfall and temperature change), as geotechnical structures are often designed to have a service life of 50–100 years. Some structures may even fail if the effect of climate change is not considered in the present design. This review aims to provide insights into problems associated with expansive soils that trigger the failure of lightweight structures, including current investigations and industry practices. This review recognises that although the soil moisture conditions govern expansive soil behaviour, limited studies have incorporated the effect of future climate changes. In addition, this review identifies the need to improve the current Australian design practice for residential footings through the inclusion of more site-specific investigations and expected climate changes. [ABSTRACT FROM AUTHOR]

With the rapid development of road engineering today, a large number of high-grade highways need to pass through expansive soil distribution areas. At present, the research on expansive soil slope mainly focuses on the newly excavated cutting slope. However, according to engineering experience, a landslide of fill embankment on expansive soil foundation is also very common. The expansive soil layer is heterogeneous. There are many weak intercalations or large fissures under the ground, which are generally parallel to the trend, with low strength and high permeability. After rainfall, the strength of the weak interlayer and large fissures will be further reduced after moisture absorption, and the sliding surface is easily formed under the load of filler, which is the main factor inducing embankment landslide. On the basis of landslide investigation and a laboratory test, a FORTRAN calculation program is developed in this paper, which can comprehensively consider the special moisture absorption and softening characteristics of expansive soil. Taking a high fill embankment slope with a soft interlayer in the Baoshan area of Yunnan Province as an example, the stability and instability characteristics of the fill slope on the expansive soil foundation are analyzed, and the influence of moisture absorption and softening on the expansive soil slope is emphatically discussed. Finally, this paper puts forward the reinforcement method of the high fill embankment slope on the soft expansive soil foundation, which is proven to have a good reinforcement effect through calculation analysis and field practice. For expansive soil foundation with weak interlayer, it is better to directly reinforce the weak layer through rigid piles. [ABSTRACT FROM AUTHOR]

Resistance value (R-value) is one of the basic subgrade stiffness characterizations that express a material's resistance to deformation. In this paper, artificial intelligence (AI)-based models—especially M5P, support vector machine (SVM), and Gaussian process regression (GPR) algorithms—are built for R-value evaluation that meets the high precision and rapidity requirements in highway engineering. The dataset of this study comprises seven parameters: hydrated lime-activated rice husk ash, liquid limit, plastic limit, plasticity index, optimum moisture content, and maximum dry density. The available data are divided into three parts: training set (70%), test set (15%), and validation set (15%). The output (i.e., R-value) of the developed models is evaluated using the performance measures coefficient of determination (R2), mean absolute error (MAE), relative squared error (RSE), root mean square error (RMSE), relative root mean square error (RRMSE), performance indicator (ρ), and visual framework (Taylor diagram). GPR is concluded to be the best performing model (R2, MAE, RSE, RMSE, RRMSE, and ρ equal to 0.9996, 0.0258, 0.0032, 0.0012, 0.0012, and 0.0006, respectively, in the validation phase), very closely followed by SVM, and M5P. The application used for the aforementioned approaches for predicting the R-value is also compared with the recently developed artificial neural network model in the literature. The analysis of performance measures for the R-value dataset demonstrates that all the AI-based models achieved comparatively better and reliable results and thus should be encouraged in further research. Sensitivity analysis suggests that all the input parameters have a significant influence on the output, with maximum dry density being the highest. [ABSTRACT FROM AUTHOR]

Using tire waste rubber reinforced expansive soil (ESR) can modify its poor engineering characteristics. The damping properties of ESR at different temperatures may vary dramatically. Two kinds of rubber Ra (large particle size) and Rb (small particle size) are mixed with expansive soil according to gradient ratio. The backbone curves, dynamic shear modulus, and damping ratio of expansive soil in varying temperature fields of 20 °C, −5 °C, and −15 °C are investigated. The Hardin-Drnevich model can well fit the backbone curves of ESR specimens in various temperature fields. Dynamic triaxial results show that 5–10% Ra rubber can withstand higher shear stress in all temperature fields; Rb rubber can increase the dynamic shear modulus of expansive soil and reach the peak value with 10% rubber content. The damping ratio can be significantly improved by using 10% Ra rubber at room temperature, while the ESR damping ratio in a temperature field of −5 °C does not change significantly with increasing shear strain or even decreases; Ra increases the damping ratio of expansive soils in the temperature field of 15 °C while small particle size Rb decreases the damping ratio of expansive soils. The experimental results validate the effectiveness of ESR in the frozen soil area. In an engineering sense, local temperature needs to be considered to use an appropriate ESR, which can provide effective seismic isolation and damping. [ABSTRACT FROM AUTHOR]

Soil's consolidation is a geotechnical problem resulting from a stress-transfer process that initiates when the load is applied to the water contained in the soil, producing a reduction in pore water pressure and rearranging the solid particles, and thus causing a decrease in soil volume. Therefore, consolidation is a coupled flow–mechanical problem. Coupled models have been developed to simulate this phenomenon while considering different theories, providing consistent results. This paper presents an elastoplastic coupled model of consolidation under Terzaghi's effective stress formulated using the equations of transient flow, balance moment, motion, and the critical state model that considered elastoplastic strains. The coupled model algorithm provided fast and easy results due to its flexibility, as it allowed combinations in loading and boundary conditions. Additionally, it considered the external/internal water flow as an inflow or outflow, which modified the pore water pressure and produced changes in the horizontal and vertical displacements. The numerical results obtained showed an appropriate behavior of the consolidation phenomenon, as well as the evolution of the vertical U y and horizontal U x displacements, water pressure p w , volumetric ε v and deviatoric ε q strain, mean σ p and deviatoric σ q stress, volumetric variation ∆ ε v , and elastic/plastic behavior of the finite elements while considering the yield surface of the critical state. [ABSTRACT FROM AUTHOR]

Volume change of expansive soils is a challenging issue, which affects various engineering structures all over the world. Consequently, we need environmentally-friendly and cost-effective soil stabilizers to address the challenges related to expansive soils. The utilization of natural fibers allows for the reduction in environmental impact since they are renewable and biodegradable raw materials. Moreover, the current article presents an experimental approach to study the effect of natural fibers on the mechanical behavior of expansive soils. Various experimental tests—such as Atterberg limits, standard compaction, direct shear, swelling potential, and swelling pressure—were conducted on control and treated soil samples using different percentages of fibers. The results of measurements of the physico-mechanical properties after reinforcement of the soil with 1%, 5%, and 10% of natural fibers indicate that the mechanical behavior of expansive soils is greatly influenced by the addition of natural fibers. To conclude, 86% reduction was observed in the swelling coefficient of treated soil. Future research can be done to check the durability of the current practice in detail. [ABSTRACT FROM AUTHOR]

The role of gypsum level on the long-term strength and expansion of soil stabilised with different lime contents is not well understood. This research, therefore, studied the effect of varying gypsum concentrations of 0, 3, 6, and 9 wt% (equivalent to the sulfate contents of 0, 1.4, 2.8, and 4.2%, respectively) on the performance of sulfate soil stabilised with two lime levels (4 and 6 wt%). This was carried out to establish the threshold level of gypsum/lime (G/L) at which the increase in G/L ratio does not affect the performance of lime-stabilised sulfate soil. Both unconfined compressive strength (UCS) and expansion, along with the derivative thermogravimetric (DTG) analysis, were adopted to accomplish the present objective. Accordingly, the result indicated that the strength and expansion were proportional to the lime and sulfate content, of which a G/L ratio of 1.5 was the optimum case scenario for UCS, and at the same time, the worst-case scenario for expansion. This discovery is vital, as it is anticipated to serve as a benchmark for future research related to the design of effective binders for suppressing the sulfate-induced expansion in lime-stabilised gypseous soil. [ABSTRACT FROM AUTHOR]

To study the influence of dehydration conditions on the pore structure and the mechanical property of expansive soil, two experimental conditions with high-temperature drying (temperature 50 °C-humidity 10%) and high-temperature humid (temperature 50 °C-humidity 70%) were carried out. Taking the remolded expansive soil in the province of Anhui in China as the research object, this paper used mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) to analyze the pore size distribution and pore structure of remolded expansive soil samples under different dehydration conditions and duration. After these tests, their mechanical properties were further obtained by uniaxial compression tests. The results showed that the distribution of pore structure of expansive soil was various under different dehydration conditions. Under high temperature and dry environment, the volume of large pores decreased first and then increased with the time of dehydration, while the medium pore volume decreased until the dehydration was stable. Under high temperature and humid environment, the volume of large pore and medium pore both showed a trend of decrease until the dehydration kept stable. The pore volume of expansive soil did not change significantly under the two dehydration conditions. The uniaxial compressive strength (UCS) of remolded expansive soil samples in high temperature and dry environment reached the highest on the 5th day of dehydration, and then the soil strength decreased slightly until it stabilized. The UCS of remolded expansive soil reached the highest on the 15th day of dehydration under high temperature and humidity environment, and the soil strength changed little after continual dehydration. These tests showed that the UCS of dehydrated expansive soil samples under the condition of high temperature and humidity is higher than that of dehydrated expansive soil samples under the condition of high temperature and dry environment. [ABSTRACT FROM AUTHOR]

Loss of matric suction during rain has an important effect on the instability of expansive soil slope. A new device was designed for testing the expansive force in order to propose and determine the equivalent expansive force corresponding to the matric suction. First, the internal relation between the matric suction and the corresponding equivalent expansive force of unsaturated expansive soil was analyzed. Then, numerical algorithm implementation of the equivalent expansive force was discussed, and the equivalent expansive force was introduced into the strength reduction finite element method (FEM). Finally, the equivalent effects of the matric suction and the equivalent expansive force were compared and analyzed by evaluating the stability of an unsaturated expansive soil slope. The results show that the new testing device significantly improves the accuracy of the expansive force test and shortens the testing time. The relation between the matric suction and the equivalent expansive force with the change in initial water content is obvious. The equivalent expansive force can reflect the macro contribution of matric suction to unsaturated expansive soil, and the developed strength reduction FEM based on the equivalent expansive force can be used to evaluate the rainfall-induced instability of an expansive soil slope caused by the decrease in matric suction resulting from the rainfall infiltration. [ABSTRACT FROM AUTHOR]

Ankang Airport is constructed on an expansive soil-fill platform in Shaanxi Province, Central China. Since its completion in 2020, it has suffered surface deformation caused by the consolidation and settlement of the fill layer and instability of the expansive soil slope. Exploring the special deformation law of expansive soil regions by remote sensing and analyzing the deformation characteristics of airports in mountainous areas have always been key issues in related disaster research. Based on the intensity and phase observation data of 37 Sentinel-1 synthetic aperture radar images, this study obtained the spatio-temporal distribution of the deformation of Ankang Airport from May 2020 to October 2021. First, phase optimization was performed on the original interferograms. Second, the persistent scatterer synthetic aperture radar interferometry (PS-InSAR) method was applied to extract the surface deformation information of Ankang Airport, and the accuracy was evaluated. Finally, the singular spectrum analysis method was introduced to jointly analyze the deformation information obtained by the InSAR technology in combination with geological and climatic data. The results show that the excavation area of Ankang Airport was basically stable, the filling area had obvious surface and uneven deformation, and the expansive soil fill slope exhibits deformation characteristics strongly related to slope, rainfall, and fill depth. The deformation was mainly caused by consolidation and settlement, supplemented by the expansion and shrinkage deformation of the expansive soil. [ABSTRACT FROM AUTHOR]

In view of the fact that it is easy for the ancient city soil site of Cai Kingdom to expand and crack when encountering water, this paper explores the methods to improve the expansion and shrinkage deformation, dry shrinkage cracks and easy water absorption characteristics of the expanded site soil based on a lime and silicone hydrophobic agent. In this paper, the expansive clay in the old city site of Cai Kingdom in Zhumadian was taken as the research object, and the dry-shrinkage fissure test of saturated expansive soil was carried out, to study the influencing factors of the dry-shrinkage cracking of expansive soil in this area. The site soil was modified with lime and glue powder, and the fissure image was quantitatively analyzed by MATLAB. The test shows that the smaller the particle size, the faster the evaporation of water and the smaller the surface fissure rate; the thicker the thickness of the soil sample, the greater the surface fissure rate and the greater the crack width; and with the increase in the number of drying and wetting cycles, the surface fissure rate of the soil sample increases. In this paper, lime and waterproof materials are used to improve the expansive soil. This not only reduces the dry shrinkage crack rate, but also improves the waterproof performance and durability of expansive soil. [ABSTRACT FROM AUTHOR]

In this study, cement, zeolite powder and three industrial by-products (blast furnace slag, steel slag, and fly ash) were selected as additives to study their effects on the swelling potential of red clay with different curing ages and dosages. At the same time, the mechanism of additives reducing the swelling potential of red clay was analyzed by scanning electron microscope (SEM) and X-ray fluorescence (XRF) tests. The X-ray diffraction (XRD) test was used to detect the clay mineral content of the red clay specimens before and after the modification to determine the change in the clay mineral content of the specimens. The direct shear test was used to explore the influence of additives on the strength of red clay. The results show that with 9% cement content, the no loading swelling potential of specimens can be reduced by 82.5% under 28 days of curing, and the cohesion of the specimens can be greatly increased by 82%. However, the specimens with cement have an increase in no loading swelling potential under the condition of no curing. In contrast, when steel slag is used as an additive to modify the swelling properties of red clay, the swelling potential can be reduced without curing, but the addition of steel slag will reduce the cohesive strength of specimens. XRD testing shows that the clay mineral composition in cement-modified specimens and steel slag-modified specimens experienced a relative change, the relative content of montmorillonite and illite decreased, and the relative content of kaolinite increased. Combined with SEM and XRF test results, it is concluded that cement's reduction in the swelling potential of red clay depends on pozzolanic reaction products filling the pores in specimens and bonding clay particles, so as to reduce the permeability of red clay and increase the resistance during swelling. The addition of cement can also convert hydrophilic clay minerals into nonhydrophilic clay minerals. Compared with cement, the reduction in swelling potential caused by steel slag mainly depends on the adsorption of ions to reduce the adsorption of water molecules on the surface of clay slices. [ABSTRACT FROM AUTHOR]

Expansive soil is widely distributed in seasonally frozen areas worldwide. Due to the special expansion and shrinkage characteristics of expansive soil related to water content, there are potential engineering disasters in the subgrade and slope engineering. To investigate the physical and mechanical changes within the expansive soil slope, four freeze-thaw cycles tests were performed on expansive soil slope models in an environmental chamber with slope ratios 1:1.5, 1:1 and 1:0.5. Nuclear magnetic resonance (NMR) technology is used to explain the pore changes in expansive soil during freezing and thawing. Model tests were carried out to monitor the changes in cracks, moisture content, temperature, displacement and soil pressure of the slope model. The results show an increase in the slope ratio may give rise to more intense temperature changes, promote the development of cracks in the model, and increase the temperature gradient and moisture migration rate during freezing and thawing. Following freeze-thaw cycling, the soil structure is destroyed and reassembled, and the soil pressure decreases as the slope ratio increases. Combined with the displacement of slope model and NMR test results, the slope can maintain a stable state after multiple freezing–thawing cycles under a specific moisture content ω s . [ABSTRACT FROM AUTHOR]

Cost efficient and robust transport systems are of critical importance to future economic prosperity as well as for the society's social and environmental well-being. However, current performance shortcomings in the transport infrastructure formations induced by extreme climatic events cause excessive maintenance requirements with increased costs and disruptions to commuters and loss of productivity in the freight services. This is particularly important in locations where soils are sensitive to moisture changes caused by extreme climatic events. In this paper the role of soil stabilisation in halting volumetric deformation and associated reduction in shear strength derived from the wetting processes (e.g., rainfall periods) is examined for an expansive soil. Two stabilizers commonly used in road construction are examined, i.e., hydrated lime and Portland cement. An additional non-traditional stabiliser composed of a blend of ground granulated blast furnace slag and hydrated lime is also considered. A series of one-dimensional swelling and direct shear box tests were conducted adopting vertical stresses relevant for pavements and simulate wetting process that can take place after a period of rainfall. Results indicate that while all stabilizers contribute to a reduction of swelling and smaller losses in shear strength upon wetting, the blend of blast furnace slag and hydrated lime is the most favourable in terms of carbon footprint. [ABSTRACT FROM AUTHOR]