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The deformation of expansive soil in seasonally frozen regions caused by freeze–thaw cycles has severely affected the long-term performance of engineering applications. The alteration of expansive soil microstructure has resulted in many geotechnical engineering failures, such as soil cracking and settlement. Consequently, the micropore contraction and expansion mechanisms of expansive soil have drawn extensive attention. Nuclear Magnetic Resonance (NMR) is widely used as a rapid, non-destructive detection technique for moisture monitoring and microstructure evolution characterization in porous media. In addition, Magnetic Resonance Imaging (MRI) can visualize the migration pattern of pore water under different numbers of freeze–thaw cycles. SEM is the most effective and direct method to reveal the structure of particle and micropore arrangement. This paper investigates the pore size evolution and pore structure distribution characteristics of saturated expansive soil via 6 freeze–thaw cycle tests using NMR and SEM techniques. The evolution law of saturated expansive soil under freeze–thaw cycles is obtained. The results show that pore water migrates from the center to the periphery under freeze–thaw cycles. The pore size decreases as the number of freeze–thaw cycles increases and small particles increase significantly. During the freeze–thaw cycle, the arrangement pattern changed from surface-surface contact to stacking. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil shrinkage leads to cracking of expansive soil during desiccation. Prevention of crack propagation in soil is of paramount importance. This research examines the effect of auxetic yarns, in control of expansive soil desiccation cracks. In this study, auxetic yarns with optimal properties were produced. Using an innovative test method, the influence of auxetic yarn structure on the prevention of soil crack propagation was investigated. It was found that the inclusion of auxetic yarns in the expansive soil results in a 9.94% reduction in crack propagation of the soil. In order to confirm the positive effect of auxetic yarns on the behavior of the soil samples, pull-out test was conducted on the auxetic yarns incorporated in the soil samples. The interaction between the soil and the auxetic yarn was found to be much higher than the interaction between the equivalent non-auxetic yarn and the same soil. This was not only attributed to the transverse expansion of auxetic yarn, but also to the helical structure that occurs in such yarn during the pull-out. The auxetic effect of the yarn results in a 27.3% increase in the force needed to pull the yarn from the soil matrix. [ABSTRACT FROM AUTHOR]

This study addresses the critical role of shaft friction of pile in the interaction with expansive soil under varying moisture content. A simplified estimation method is proposed, capturing the non-linear correlation between the interface relative displacement between the soil and pile and unit skin friction and during water infiltration. The approach integrates soil-pile displacement, interface shear strength parameters, and soil matric suction fluctuations. Tests on Nanyang expansive soil include a laboratory model with water infiltration, constant volume swelling, direct shear for interface shear strength, and a filter paper method for SWCC determination. Initial water content of 21% shows an increases swelling pressure more than 24% and 27%. Increasing soil water content reduces soil matric suction. Due to lower soil matric suction, cohesion, friction, and soil interface shear strength decreased. After the passage of the infiltration duration (specifically, 200 hours), ground heave peaks at 10.7 mm, potentially affecting pile axial forces. As matric suction diminishes, the pile's shaft friction reduces, transferring more weight to the pile base, leading to settlements. Experimental data validate the proposed shaft friction estimation method. The approach aligns with previous studies and laboratory models, providing a comprehensive understanding of soil-pile interaction in changing moisture conditions. [ABSTRACT FROM AUTHOR]

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]

Enzyme induced carbonate precipitation (EICP) is a new bio-cementation technique that utilizes plant-sourced urease to catalyze urea degradation and reaction with calcium iron, resulting in the formation of calcium carbonate (CaCO3) for soil improvement. EICP has considerable promise for novel and sustainable engineering applications such as soil strengthening, pollutant remediation, and other in situ field applications. In this study, the effect of EICP on the geotechnical characteristics of expansive soil is examined. A series of laboratory tests have been performed with an optimal concentration ratio of 0.75 mol/L. The outcomes of the compaction experiment indicated a slight increment in the dry density of the expansive soil from 15.78 to 16.71 kN/m3.Further, it diminished the optimal moisture content of the soil, decreasing it from 22.3 to 18.5%. The utilization of EICP improves the soil mechanical characteristics, reducing swelling pressure by 80% and increasing the UCS, cohesion, friction angle, unsoaked and soaked CBR by 66%, 44%, 49%, 441%, and 430%, approximately. Additionally, it leads to a significant decrease in soil permeability, approximately 63%. Moreover, SEM and XRD analysis confirmed the presence of CaCO3 content in the treated soil. The experimental findings indicated that the EICP method holds promise in enhancing expansive soil within engineering projects. [ABSTRACT FROM AUTHOR]

Index properties such as liquid limit, plasticity index, shrinkage index, colloidal content, and free swell index (FSI) are used to identify and classify the nature of soil expansivity. However, for these tests either powdered or remoulded soils are used for testing and do not reflect the field placement conditions and soil structure. Hence, the present article proposes a new Desiccated State Free Swell (DSFS) index to encompass the field placement conditions and soil structure. In this method, the small compacted soil specimens are subjected to two-stage process – desiccation followed by swell measurement. The compacted or undisturbed soil specimens are placed in 100 ml glass measuring jars and allowed to swell in distilled water, similar to the FSI test. The percentage increase in the volume of the desiccated soil specimens is measured, and the same is used for the classification of degree of soil expansion. A total of 21 soils covering a wide range of plasticity characteristics and swell potentials were used for the present study. Based on the DSFS test results, a new classification chart is proposed for the prediction of the degree of soil expansion. The experimental findings revealed that the soil expansion predicted using the DSFS method is superior to the conventional indirect methods and matches well with the oedometer swell potentials. [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]

Soils with a significant proportion of clay or silt tend to have poor geotechnical characteristics (such as volumetric change and low strength) when exposed to varying moisture contents. The chemical stabilizers currently used are costly and have negative effects on the environment. Arkansas, in the United States, is the leading producer of rice in the country. During rice production, ~20% of the harvested grain consists of rice husk (RH). The rice milling process produces ash with a considerable amount of silicate. Research is being conducted to address the environmental concerns associated with its disposal in Arkansas, as there is growing interest in using rice husk ash (RHA) as a stabilizing additive for problematic soils. For RHA to be effective, an activator such as lime may be needed. The present study focuses on investigating the effectiveness of RHA in stabilizing substandard soils, as no prior study has used RHA as a stabilizing agent in the United States. Additionally, the research aims to determine the optimal proportions of RHA, hydrated lime (HL), or a combination of both. The study employs varying percentages of RHA (3%, 6%, and 9%) and HL (1%, 3%, and 5%) in a unary system. In the binary system, 3%, 4%, and 5% of RHA are combined with 1% HL. The study includes a range of routine tests, such as assessments of Atterberg limits, modified proctor compaction, pH levels, California bearing ratio (CBR), unconfined compressive strength (UCS), and free swell (FS). Furthermore, results from scanning electron microscopy (SEM) coupled with X‐ray diffractometer analyses demonstrated significant improvements in UCS and CBR values for the treated soils, indicating enhanced strength and stability. Moreover, the FS test reveals a reduction in swelling characteristics for the stabilized soils. It was found the optimal dosages of RHA and HL were 6% and 3%, respectively. Notably, when RHA and HL were combined, a blend of these two stabilizing agents exhibited the most promising results in terms of improving the swelling. The optimum percentage of the combined stabilizing agents was 4% RHA + 1% HL. The findings of this proof‐of‐concept research hold substantial potential for the construction industry in Arkansas, offering cost‐effective alternatives to conventional soil stabilization methods while promoting the sustainable and environmentally conscious use of RHA. [ABSTRACT FROM AUTHOR]

Expansive soils, known for their significant volume change with variations in moisture content, are widely distributed around the globe. Due to their swelling properties, expansive soils pose significant engineering challenges, especially in rapidly developing countries like China. This study aims to investigate the swelling mechanisms of expansive soils, focusing on the influence of crack characteristics on swelling behavior. The research methodology includes field investigations, laboratory experiments, and theoretical modeling. By comprehensively considering crack rate, dry density, initial moisture content, and overburden load, a nonlinear regression swelling model is proposed in this research. The degree of crack development in expansive soils is quantitatively characterized by the content of filling materials, leading to the establishment of a crack rate model for expansive soils. Swelling tests on expansive soils with different crack contents were conducted. The results show that the swelling rate is negatively correlated with the initial moisture content and positively correlated with dry density and crack rate. Additionally, the larger the crack rate, the more significant the change in the swelling rate. Furthermore, model validation confirms that this nonlinear regression model accurately describes the relationship between swelling rate and influencing factors. It offers a more precise prediction tool for infrastructure design and maintenance in expansive soil areas, advancing geotechnical engineering practices. [ABSTRACT FROM AUTHOR]

In order to reveal the influence of expansive soil meso structure on the macro expansion, Nanning remolded expansive soil was studied. The macro test is carried out by self-developed three-dimensional dilatometer to obtain the influence law of dry density on expansion rate. The meso pore and soil particle structure are studied through CT scanning test. The meso characteristics and fractal characteristics of pores and particles are systematically analyzed based on Avizo software. Combined with three-dimensional macro test, the influence of meso structure characteristics on macro expansion deformation is revealed. The results show that the horizontal expansion rates of the sample are basically the same. The vertical expansion rate is greater than the horizontal expansion rate. With the increase of dry density, the ratio of horizontal-vertical expansion rate is close to 1. The ratio of vertical-horizontal porosity increases with the increase of dry density; When the ratio of horizontal-vertical expansion is close to 1, the ratio of vertical-horizontal porosity is larger, indicating that there is a good relationship between horizontal-vertical porosity and macro horizontal-vertical expansion. The ratio of vertical-horizontal soil particle size decreases with the increase of dry density. When the ratio of horizontal-vertical expansion rate is close to 1, the ratio of vertical-horizontal soil particle size is smaller, indicating that there is also a good relationship between horizontal-vertical soil particle size and three-dimensional expansion rate pore fractal dimension is used to characterize pore complexity, which is not directly related to three-dimensional expansion rate. [ABSTRACT FROM AUTHOR]

Freeze-thaw effects can significantly alter the volume of expansive soil due to the water-phase change and soil expansion. The montmorillonite content was an important factor influencing the expansibility of expansive soil. This paper investigated the micropore structure characteristics of expansive soil under freeze-thaw cycles with various montmorillonite contents. In addition, the micropore evolution of expansive soils and relationship between the unfrozen water content and temperature were also examined via X-ray diffraction (XRD) and nuclear magnetic resonance (NMR). The results indicated that: (1) the montmorillonite content affected the pore size distribution of expansive soil, and with increasing montmorillonite content, the relaxation time (T2) distribution curves changed from single-peak into double-peaks; (2) after multiple freeze-thaw cycles, the macropores in expansive soil increased and mesopore pores decreased; (3) considering the freezing point and capillary adsorption, the soil freezing characteristic curve (SFCC) could be divided into four stages, namely, unfrozen water, free water, freezing-capillary water, freezing-hydroscopic water; (4) the montmorillonite content only affected the unfrozen water content from 0°C to −5°C, while at temperatures lower than −5°C, the effect of the montmorillonite content on the unfrozen water content was negligible. [ABSTRACT FROM AUTHOR]

This paper introduces a rational method to analyze the inverted T-section strip footing resting on expansive soil. A computer program called SFOEES using the suggested analysis procedure was created to obtain the solution. The program SFOEES involves two major problems that are solved independently for simplicity. Firstly, estimating the distorted soil surface by solving Mitchell's suction diffusion equation using the FDM in 2D and using Wray's model to predict the soil movements. Secondly, analysis of the strip footing-distorted soil surface interaction using the FEM and the Vlasov model. The program's accuracy has been checked through comparison of its results with others' results and shown to be valid. The program was also used to investigate the behavior of the inverted T-section strip footings of different stiffnesses resting on expansive soil and subjected to columns' loads of a lightweight structure consisting of a 3-story. It is concluded that the case of edge heave is considered the critical case for the distortion criteria and the maximum positive bending moment whereas, with regard to the negative bending moment, the case of edge shrinkage is considered the critical case. [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]

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Abstract Expansive soils have a high tendency for volume change in case of fluctuations in moisture content, potentially causing significant damage to light structures, particularly road pavements. This paper investigates the influence of waste paper sludge ( $$\:WPS$$ ) as an alternative sustainable stabilizer on the volume change behavior of expansive road subgrade soils of different origins. For this purpose, $$\:WPS$$ was added to the expansive soils at ratios of 3%, 6%, 9%, 12%, and 15% by dry weight of the soils. A series of Atterberg’s limit, swelling, shrinkage, compaction, and consolidation tests were performed on pure soils and soil specimens with $$\:WPS$$ to attain a comprehensive understanding of the role that $$\:WPS$$ plays in the volume change behavior of expansive soils. The experimental test results showed that the addition of $$\:WPS\:$$ led to a considerable decrease in the plasticity and swell-shrink potentials of subgrade soils. The consolidation settlement of expansive road subgrades was also reduced to some extent with $$\:WPS$$ . Moreover, the statistical analysis of the test data indicated a significant relationship among different swelling-shrinkage parameters. The experimental results presented here suggest that the $$\:WPS$$ may be a cost-effective, environmentally friendly, and sustainable stabilizer to reduce the volume change sensitivity of expansive road subgrade soils.

The aim of this study is to analyze the stabilization effects of an expansive soil using three different nontraditional chemical additives, in this case: white cement and nano-silica as admixture, waste granite dust, and a new liquid polymer soil stabilizer (i.e. liquid granite). The engineering properties such as soil consistency, linear shrinkage and soil swelling behaviour of a bentonite treated with these stabilizing agents were investigated. Furthermore, the bearing capacity of the stabilized bentonite was analyzed through the California Bearing Ratio test (BCR) and a laboratory foundation model. The experimental program consisted of three series of tests. In the first series, the tests were performed on an expansive soil reinforced with 2%, 4%, 8%, and 10% of white cement combined with 2% of nano-silica. Another series of tests consisted of samples mixed with different percentages of granite powder (5%, 10%, 15%, and 20%). In the third series, liquid granite as a soil stabilizer was blended with soil specimens at various concentrations (1%, 2%, 3%, and 4%). For all admixtures, the results showed a marked improvement in soil consistency, an important decrease in linear shrinkage, a considerable reduction on the expansion index, and a significant improvement of CBR and soil bearing capacity. Moreover, two empirical correlations were proposed between the bearing capacity parameters (i.e. CBR and Improvement factor) and the expansion index. [ABSTRACT FROM AUTHOR]

Expansive soils cause frequent surface deformation due to their expansion and contraction, which is a serious engineering hazard, and long-term subsidence monitoring is a prerequisite for preventing and controlling expansive soil disasters. Currently, the conventional monitoring methods for the above issue include Interferometric Synthetic Aperture Radar (InSAR) technology, but InSAR is not suitable for uninterrupted monitoring of surface deformation and has low sensitivity. Meanwhile, it can't obtain multiple surface environmental parameters around the station. The Global Navigation Satellite System (GNSS), a system that can directly acquire surface deformation, has been widely used in landslide disaster monitoring, and in recent years, this technology has also been applied to the field of expansive soil disaster monitoring. At the same time, GNSS can also provide a constant stream of L-band microwave signals to obtain ground environmental information such as precipitable rainfall and soil moisture around the station. In previous studies of expansive soil hazards, GNSS technology has been mainly used to provide surface deformation information without exploring its potential to invert ground environmental information around stations. This paper proposes a ground-based GNSS remote sensing integrated monitoring system that integrates expanding land surface parameters such as "precipitable rainfall, soil moisture, and three-dimensional deformation" and analyses the ability of ground-based GNSS to be used for integrated monitoring of expanding soil hazards by combining ten years of consecutive observational data from GNSS stations along the coastal area of Houston. The experimental results show that the GNSS is capable of providing highly accurate time-series characterization of deformation, and inelastic subsidence in recent years has resulted in a cumulative permanent elevation loss of 2 cm along the Houston coast. The correlation coefficient between soil moisture extracted by the fifth-generation European reanalysis data (ERA5) and soil moisture inverted by ground-based GNSS is 0.514. At the same time, the GNSS was also able to monitor the zenithal precipitable water vapor (PWV) and soil moisture changes around the GNSS station and further analyze the response relationship among the three parameters, which could comprehensively evaluate the stability of expansive soils, avoiding the unreliability of relying on a single piece of monitoring information to assess the stability of expansive soils. We hope to construct a more comprehensive ground-based GNSS remote sensing monitoring system to better monitor expansive soil hazards. [ABSTRACT FROM AUTHOR]

Expansive soils are widespread in the world and coincide with areas of high human activity. The main cause of deep instability of expansive soil slopes is due to their softening caused by excavation and seepage. By developing a comprehensive numerical model based on the theory of unsaturated soil, this study examines the characteristics of stress and displacement distribution of expansive soil slopes through hydraulic‐mechanical coupled numerical simulation. This study analyzes the evolution patterns of slopes with excavation unloading and seepage of water storage to reveal the mechanisms of deep‐seated instability of expansive soil slopes. The findings demonstrate that: The instability of expansive soil slopes begins at the foot of the slope and propagates along the interlayer, affecting the entire slope. Excavation leads to the softening of the expansive soil interlayer and the transfer of shear stress. During water storage, the weakening of the soil strength results in slope instability along the weak interlayer slip. Softening of the expansive soil interlayer facilitates the redistribution of shear forces in the slope and alters the distribution law of the plastic zone in the deep layer. Overly slowing down the slope leads to significant excavation unloading, which is detrimental to the slope's stability. [ABSTRACT FROM AUTHOR]

Abstract The study investigated the reinforcing effect of vetiver root on soil by conducting outdoor planting tests and indoor root tests. The cracking indexes of soil specimens with varying root contents were analyzed, and a statistical model was established to determine the relationship between the cracking indexes, the number of dry and wet cycles, and the root content. The study revealed the crack evolution law of vetiver-reinforced expansive soil. The study explored the mechanism of the vegetation root in inhibiting the cracking of expansive soil and determined the optimal planting density of vetiver grass through outdoor planting tests. The results indicate that: The surface crack rate (CR), total crack length (CL), and crack number (CN) in the root-soil specimen exhibited exponential growth with an increase in the number of wet and dry cycles. This growth was more pronounced during the first and second cycles. The vetiver root could effectively reduce soil crack formation, and the specimen's cracking resistance is positively correlated with the root content. With the root content increased, the CR, CN, and CL decreased. The logistic model is suited to the CL of added root soil. The logistic model is more suitable for the growth model of the CR of the expansive soil with low root content, while the Boltzmann model is more suitable for the growth model of the CR of the expansive soil with high root content. Width of crack (CW) is better suited to the DoseResp growth model. The Boltzmann model is more applicable to the CN in expansive soils with low reinforcement, while the logistic growth model is more suitable for the development of CN above 0.21% root content. The development of the crack network was influenced by two key factors: the root content and the number of wet and dry cycles. Under the condition of planting roots, the development of crack networks in expansive soil differs from that of expansive soil with added roots, and there is no clear pattern to follow. The inhibitory effect of the vetiver root on cracking of expansive soil is related to the planting density of vetiver.

Soil stabilization offers an alternative solution to overcome the problem of expansive clay soil characteristics. Unconfined compressive strength tests were conducted on original and expansive clay soils containing cement and lime to investigate the effectiveness percentage of two pozzolan materials. The amount of material stabilization with percentages 2, 4, 7, 10 % cement, and 5% lime for each sample was adopted. The dimensions of the cylindrical sample were 3’’ in height and 3/2’’ in diameter. The relative density was 80% for all samples and sheared at a strain rate of 1 %. The properties of the original expansive clay soil are (w) 40.11%, (γd ) 1.3 gr/cm³, (Gs) 2.59, (LL) 60.05%, (PL) 38.16%, (IP) 21.88% and (qu) 0.61 kg/cm2. The test results indicate that the clay exhibits high plasticity. Based on the results, the effective combination percentage of two pozzolan materials to enhance the characteristics of expansive clay soil is 2% to 7 % cement and 5% lime. However, adding 10% cement and 5% lime causes the UCS value to decrease. The finding of this investigation shows the combination of two pozzolan materials, especially cement and lime, can effectively enhance the UCS values. This enhancement is observed at specific percentages of cement and lime addition. These results underscore the importance of carefully selecting proportions to achieve desired soil stabilization outcomes.

The study investigated the reinforcing effect of vetiver root on soil by conducting outdoor planting tests and indoor root tests. The cracking indexes of soil specimens with varying root contents were analyzed, and a statistical model was established to determine the relationship between the cracking indexes, the number of dry and wet cycles, and the root content. The study revealed the crack evolution law of vetiver-reinforced expansive soil. The study explored the mechanism of the vegetation root in inhibiting the cracking of expansive soil and determined the optimal planting density of vetiver grass through outdoor planting tests. The results indicate that: The surface crack rate (CR), total crack length (CL), and crack number (CN) in the root-soil specimen exhibited exponential growth with an increase in the number of wet and dry cycles. This growth was more pronounced during the first and second cycles. The vetiver root could effectively reduce soil crack formation, and the specimen's cracking resistance is positively correlated with the root content. With the root content increased, the CR, CN, and CL decreased. The logistic model is suited to the CL of added root soil. The logistic model is more suitable for the growth model of the CR of the expansive soil with low root content, while the Boltzmann model is more suitable for the growth model of the CR of the expansive soil with high root content. Width of crack (CW) is better suited to the DoseResp growth model. The Boltzmann model is more applicable to the CN in expansive soils with low reinforcement, while the logistic growth model is more suitable for the development of CN above 0.21% root content. The development of the crack network was influenced by two key factors: the root content and the number of wet and dry cycles. Under the condition of planting roots, the development of crack networks in expansive soil differs from that of expansive soil with added roots, and there is no clear pattern to follow. The inhibitory effect of the vetiver root on cracking of expansive soil is related to the planting density of vetiver. [ABSTRACT FROM AUTHOR]

In order to study the soil squeezing effect of pile sinking under vibration load in expansive soil layer, based on the mechanical properties of shear expansion and water softening of expansive soil, the key technology of "hydrodynamic method" assisted pile sinking is proposed. Through field test and finite element calculation, the changing rules of deep horizontal displacement and deep soil pressure of the soil around the H-type and O-type steel sheet piles during pile sinking are summarized. The results shows that the deep horizontal displacement and deep soil pressure around the pile are closely related to the properties and depth of soil layer, and the shear expansion of expanding soil can significantly enhance the soil squeezing effect of the pile sinking. Compared with the pile sinking without auxiliary measures, the maximum value of deep horizontal displacement and deep soil pressure around the pile can be reduced by more than 50% when the pile sinking is assisted by "hydrodynamic method" . The auxiliary measures of "hydrodynamic method" can significantly reduce the adverse effects of pile sinking on the surrounding environment, which provides important technical support for the design and construction of combined steel sheet pile support technology. [ABSTRACT FROM AUTHOR]

The stabilization/solidification method can improve the engineering properties and reduce the environmental risks of heavy metal-contaminated expansive soil. However, the solidification effects deteriorate for soils experiencing wetting–drying (W–D) cycles. For this objective, the expansion/shrinkage, cracking, and leaching behaviors, as well as the corresponding internal relations, of lime-solidified lead-contaminated expansive soil were investigated. The results showed that during the W–D process, the volumetric strain increased, particularly along the radial direction. The cracks gradually developed and increased in length, width, and surface-crack ratio. Contaminant leaching and mobility increased, increasing environmental risk. In addition, a higher Pb(II) concentration in the solidified soil exhibited a more notable expansion potential release, crack development, and leaching capacity. X-ray diffraction and scanning electron microscopy results revealed the redistribution of soil particles and pores rather than chemical changes in mineral components during the deterioration process, and increasing the lead concentration accelerated the deterioration of W–D cycles. Finally, based on the grey correlation analysis, deterioration effects in leaching behaviors were controlled by expansion/shrinkage exponential release for solidified soil experiencing lower W–D cycles and higher Pb(II) concentrations, whereas leaching behaviors were controlled by crack behavior for solidified soil experiencing higher W–D cycles and lower Pb(II) concentrations. [ABSTRACT FROM AUTHOR]

This study investigates the dynamic evolution of cracks in expansive soil under varying wet-dry cycles, employing a self-developed three-dimensional spatiotemporal crack evolution model testing system. The research includes experiments, spatial moisture migration analysis, resistivity monitoring, and crack distribution inference to elucidate the crack development mechanisms. The findings reveal distinct stages in moisture evaporation at different soil depths, characterized by initiation, stability, deceleration, and residual phases. The influence of wet-dry cycles on evaporation rates is pronounced, particularly in deep soil layers. Resistivity changes in expansive soil during moisture evaporation display specific phases, demonstrating their potential to characterize crack development. The study validates the feasibility of assessing crack development through soil resistivity changes. Crack formation initiates at weak points on the soil surface, with subsequent elongation and secondary crack development, resulting in a crack network. Further moisture evaporation and volume shrinkage widen cracks, while wetting leads to crack healing. Total crack length, average width, and area crack ratio decrease exponentially with soil depth, but increase at different depths with more wet-dry cycles. Volume crack ratio initially rises and then stabilizes, while volume shrinkage capacity diminishes until equilibrium. Wet-dry cycles promote crack development, modifying particle arrangements. This research underscores that soil cracking and crack development result from the evolving balance of moisture-induced stresses in space, stemming from non-uniform moisture distribution. In conclusion, this study sheds light on crack development mechanisms in expansive soil under wet-dry cycles, offering valuable insights for soil engineering and geotechnical applications. [ABSTRACT FROM AUTHOR]

Expansive soil poses significant challenges for civil engineers, leading to structural damage, particularly in lightly loaded structures. This study employs an innovative and sustainable recipe to stabilize highly expansive soil using the Microbial- Induced Calcium Carbonate Precipitation (MICP) technique by substituting conventional ingredients with olive mill wastewater and hydrated lime. A series of laboratory tests were performed to evaluate the improvement in Atterberg's limits, Free Swell, Unconfined Compressive Strength (UCS), and pH, in addition to a series of qualitative measurements, including X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Optical Microscopic Images, and bacteria growth rate. Different mellowing periods and different cementation concentrations were used. The proposed recipe results showed a 50% reduction in the soil's free swell value. The UCS of the treated soil using the proposed recipe was eight times that of the untreated soil and twice that of the soil treated with the traditional recipe. The SEM images showed flocculation and aggregation in the soil particles, with the voids becoming smaller and filled with calcium carbonate (CaCO3). The XRD results showed the formation of new CaCO3 particles. The optimized recipe demonstrated remarkable enhancement improvement and significant changes in soil physical properties and microstructure. [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]

Expansive soils are widely distributed around the world. They have significant characteristics of both hygroscopic expansion and water-loss shrinkage, which have caused serious damage to road paving, construction of low-rise houses, and construction of slopes along the banks of rivers. Similarly, the implementation of low impact development measures can cause considerable difficulties in the distribution area of expansive soil. The entire urban area of Hefei is situated on expansive soil. Although Hefei city has developed a sponge city plan, it has not been carried out on a large scale for implementation of low impact development technical measures. Experimental studies have shown that exposed expansive soils produce fissures that run up and down during wet and dry cycles. These fissures are extremely unfavorable to the infiltration of surface runoff formed by short-term heavy rainfall. This is also one of the reasons for short-term rainfall in Hefei city, resulting in serious flooding in low-lying areas with a poor drainage system. At the same time, initial rainfall is ineffective in cleaning up surface source pollution. Therefore, we can enhance the characteristics of expansive soil, keep the expansive soil unexposed, and maintain a certain level of humidity. These approaches can play a better role in the control of rainfall runoff and surface source pollution. The characteristics of expansive soils can be enhanced by mixing them with weathered sand, a physical improvement, to meet the technical requirements for infiltration, interception, and purification. It is recommended to carefully select low impact development measures in the distribution area of expansive soil to avoid the occurrence of wasteful investment and poor results. [ABSTRACT FROM AUTHOR]

In order to study the effect of alkali-excited low-calcium fly ash on the improvement of weak expansive soil, the effects of different amounts of alkaline excitation agent NaOH on the mechanical properties of low-calcium fly ash expansive soil were studied through expansion test, unconfined compressive strength test, environmental scanning electron microscope test and X-ray diffraction (XRD) phase analysis tests, and the soil microstructure and pore formation characteristics were analyzed and quantified. Based on XRD test, the change characteristics of mineral composition in soil were analyzed, and the mechanism of action between alkali excited fly ash and soil was revealed. The results show that alkaline activator can enhance the activity of fly ash, accelerate the hydration reaction, accelerate the development of early strength and improve the later strength. With the increase of alkali activator, the unconfined compressive strength of fly ash improved expansive soil first increases and then decreases, and 10% NaOH is the best content. The types of pores in the soil are complex, and the gel produced by the microscopic discovery of alkali-stimulated modified soil can fill the pores, and bond with the soil to reduce the pores. As an activator, NaOH can effectively improve the activity of fly ash and improve the basic properties of expansive soil. [ABSTRACT FROM AUTHOR]

Understanding expansive soil behavior under variable environmental conditions is crucial for environment and engineering contexts. This study investigates the deformation mechanism and mechanical behaviors of expansive soil with varied moisture contents under dry–wet cycles. Through theoretical analysis and laboratory tests, we first analyzed the elastic–plastic behavior of expansive soil under dry–wet cycles and then explored the elastic–plastic deformation, fracture characteristics, and mechanical properties therein. Results indicate that the soil aggregates evolve through the four stages of stable, compact, loose, and damaged structures under the dry–wet cycles. The swelling–shrinkage deformation consists of elastic and plastic components, and the magnitude of elastic expansion is always smaller than that of plastic expansion. Meanwhile, the cracks develop with the increased water content and the increased number of cycles. The aperture of the induced cracks increases as the water content increases. Accordingly, the shear strength sequentially decreases with the increasing number of cycles and the increasing moisture content. The decrease in shear strength with the increasing cycles is primarily due to structural damage accumulation followed by the reduction of cohesion, while the decrease with increasing water content is primarily due to the reduction in matric suction and the increased lubrication between soil particles and aggregates. In addition, the cohesion decreases with the increasing moisture content and the increasing number of cycles. However, the friction angle decreases only with a clear increase in the number of cycles, showing less sensitivity to dry–wet cycles in general. [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]

Horizontal drains have been widely installed along expansive soil slopes to maintain slope stability. However, these drains typically get clogged with clay particles after several years of operation and must be maintained and replaced regularly. This paper proposes a new type of horizontal drain with a replaceable tubular filter element (RTFE) to overcome the time-consuming nature and laborious replacement procedure of existing horizontal drains. Tests were conducted to compare its drainage performance with that of a conventional horizontal drain. The effects of horizontal drain clogging on the pore water pressure and slope stability were analyzed using the equivalent permeability coefficient of the expansive soil considering the adverse effects of cracks that are randomly distributed in the soil when the matrix suction exceeds the air-entry value. This coefficient was then used as one of the input parameters in the finite element analysis (FEA) for a hydro-mechanical coupling simulation. A replacement standard for the tubular filter element was established according to the numerical results, and the replacement method was explained. The study results showed that the RTFE-equipped horizontal drain was evidently superior to the conventional horizontal drain owing to the advantage of quick replacement. It can also effectively preserve the soil and prevent infiltration deformation caused by the loss of skeleton particles, implying a more economical, effective, and controllable means for the dewatering of expansive soil slopes. This study provides references for the construction and management of engineering projects involving horizontal drainage systems. [ABSTRACT FROM AUTHOR]

In order to explore the influence of vegetation root content on the water holding and permeability characteristics of expansive soil, samples with different root content were prepared by mixing bermudagrass roots with expansive soil from Nanning expansive soil area, and indoor pressure plate test and variable head permeability test were conducted, the Van Genuchten-Mualem model was used to predict the unsaturated permeability coefficient of expansive soil with different root contents. The results show that the water holding capacity of expansive soil decreases after the addition of roots, and the addition of roots increases the proportion of large and medium pores in the expansive soil. The higher the root content, the greater the proportion of large pore volume to total pore volume, and the greater the decrease in water holding capacity compared to pure soil. In saturated state, the permeability coefficient of expansive soil increases with the increase of root content. In unsaturated state, the permeability of expansive soil at low suction stage (0 ~ 25 kPa) increases with the increase of root content. As the matrix suction increases to high suction stage (200 ~ 1 000 kPa), the effect of root dominant flow decreases, and the permeability of expansive soil with roots gradually tends to be lower than that of pure soil. The mesoscopic results indicate that the incorporation of root system causes through cracks in the expansive soil, which is a key factor affecting the water holding and permeability of the expansive soil. This study further reveals the mechanism and regularity of the infiltration enhancement effect of vegetation roots on expansive soil, providing a reference for comprehensive evaluation of the effect of vegetation protection on expansive soil slopes. [ABSTRACT FROM AUTHOR]

The lateral pressure exerted by expansive soils on retaining walls constructed with expanded polystyrene geofoam blocks (EXRW-EPS), upon water infiltration to saturation, is crucial for designing these structures. In this study, model tests were employed to examine the behavior of EXRW-EPS subjected to water infiltration, with concurrent monitoring of deformation and lateral pressure. The results showed that the compressive deformation of the expanded polystyrene (EPS) geofoam block facilitated swelling deformations of the backfilled expansive soil, effectively mitigating the lateral pressure experienced by the retaining wall. Upon saturation of the backfilled expansive soil, the total lateral force on the wall decreased by approximately 44% by the EPS geofoam block with a density of 12 kg/m3. A practical method for predicting the lateral pressure on EXRW-EPS upon water infiltration to saturation was developed based on the relationship between the EPS geofoam block and the backfilled expansive soil. The reliability of this method was corroborated by the model test results. Additionally, the effects of the density and thickness of the EPS geofoam block on the lateral pressure of EXRW-EPS were analyzed using the prediction method. • Lateral pressures experienced by expansive soils on retaining walls are effectively reduced by EPS geofoam blocks. • A practical method for predicting lateral pressures upon water infiltration to saturation is proposed. • Effects of EPS geofoam block density and thickness on lateral pressures are analyzed using the proposed method. [ABSTRACT FROM AUTHOR]

In order to improve the unconfined compressive strength of expansive soil and reduce engineering hazards. Based on the research of lignin modified expansive soil, the influence of fiber length, fiber content and lignin content on the compressive strength of expansive soil was studied by single factor test. Based on the results of single factor test, the response surface test was carried out by BBD ( BOX-Behnken design ) response surface design method, and a quadratic regression model was established to study the effect of two-factor interaction on the unconfined compressive strength of expansive soil. The results show that under the action of single factor, the unconfined compressive strength of expansive soil increases first and then decreases under the action of each factor. When the two factors interact, the interaction between lignin content and polypropylene content is the best. The optimal combination obtained by the BBD response surface method is: the length of polypropylene fiber is 9 mm, the fiber content is 0. 3%, and the lignin content is 3% . The average compressive strength of the parallel test group under this variable is 552. 48 kPa, which is 76. 97% higher than the compressive strength of the plain expansion. It can be seen that this scheme has the best effect on the unconfined compressive strength of the plain expansive soil. The research results provide a reference for the improvement of weak expansive soil in Xinxiang area, and provide a new idea for the experimental design of composite improved soil. [ABSTRACT FROM AUTHOR]

The moisture and thermal characteristics of expansive soil slopes have a significant impact on the strength and overall stability of the soil. In this study, the medium-strength expansive soil vegetated slope in Baise, Guangxi, was taken as the research object. Through the combination of numerical simulation and measured meteorological data, the impact of moisture and heat characteristics on slope stability was then analyzed, and optimal geometric parameters conducive to the stability of vegetated slopes were proposed based on these findings. The research results indicate that under long-term climatic conditions, solar net radiation has the most sensitive effect on the evaporation of slope soil. During the evaporation process, vegetation transpiration dominates in the vegetation-covered layer, while below the depth of the vegetation cover layer, soil evaporation itself plays a dominant role. Under the conditions of evaporation-rainfall-evaporation, slopes with a smaller permeability coefficient in the vegetation cover layer have significantly higher safety factors than slopes with a larger permeability coefficient and bare slopes. A steep vegetated slope with a slope gradient of 50° can maintain slope stability with proper handling of its height. The research findings have reference value for the design and construction of vegetated slopes with expansive soil. [ABSTRACT FROM AUTHOR]

Microbial-induced carbonate precipitation (MICP) is a promising method for improving the properties of geotechnical engineering materials. However, little research has been conducted on the creep behavior and long-term strength of MICP-treated expansive soil. Therefore, this study performed triaxial consolidated undrained creep tests to investigate the improvement effect of MICP on the creep behavior and long-term strength of expansive soil. The results indicate that with the increase of deviatoric stress, the creep process of MICP-treated expansive soil includes four stages: instantaneous creep, decelerating creep, steady-state creep, and accelerated creep. Based on the creep test results, a calculation method has been proposed to quickly and accurately determine the long-term shear strength of MICP-treated expansive soil. Under different confining pressure conditions, the long-term shear strength of the improved expansive soil has been significantly increased, indicating that the MICP method can effectively enhance the long-term shear strength of expansive soil. Furthermore, both the long-term cohesion and the long-term internal friction angle of the MICP-improved expansive soil have been slightly reduced, with the long-term shear strength being approximately 65 to 70% of the short-term shear strength. This study confirms the positive effects of the MICP method on inhibiting the creep of expansive soil and enhancing its long-term strength. [ABSTRACT FROM AUTHOR]

Dried Athel leaves (DAL) are abundant agricultural waste that may have a detrimental effect on the environment due to improper disposal. The current paper is aimed at investigating the incorporation of DAL into lime treatment of heavy clays, presenting a novel sustainable waste management strategy. To the best of the authors' knowledge, this topic has not been investigated in the literature. The experimental programme is designed to thoroughly assess its effects on the hydro-mechanical properties of lime-treated clay in particular strength gain, swelling pressure and permeability. Tests were conducted on the specimens treated with different ratios of lime and DAL and cured under two different temperatures (i.e. 20 and 40 °C) for various periods. Moreover, microstructural analysis was undertaken to support the results. The results indicated that adding 2% DAL to lime-treated clay specimens cured at 20 °C for 3 months remarkably increased unconfined compressive strength by about 68% compared with those attained on lime-treated clay. Stress-strain relationships suggested that the specimens modified by DAL exhibited an enhanced ductile behaviour. Moreover, the incorporation of 2% DAL further reduced clay swelling pressure by 25% compared with those treated by lime only, resulting in a total swelling pressure reduction of 93.6% compared with that recorded on untreated specimens. Permeability enhancement in the specimens treated with lime and DAL was also observed and supported by the morphological analysis. The comprehensive experimental results confirmed the suitability of using DAL as an efficient enhancer to lime-treated clay. The research outcomes can provide valuable insights into the feasibility of DAL as an eco-friendly additive for improving geotechnical engineering practises. [ABSTRACT FROM AUTHOR]

Expansive clayey soils often pose challenges for construction projects due to their low bearing capacity, swelling, and shrinkage properties. While previous research has explored additives to enhance these soils' properties, the potential of sand remains underexplored. This study investigates the impact of varying sand percentages on expansive clayey soils' consistency, compaction, and permeability. This study examines how adding different percentages of sand influences the physical properties of expansive clayey soils. Laboratory tests involved systematic testing of texture, compaction, and permeability. Findings reveal a notable improvement in the physical properties of the soil with the addition of sand. Results from the laboratory tests provided data for empirical equations that facilitate the prediction of soil properties based on the sand content. The enhancement in soil properties underscores the potential of sand as an additive for expansive clayey soils. The empirical equations presented here provide practical benefits to geotechnical engineers and practitioners engaged in construction projects involving these soils, offering them valuable insights into the benefits of sand additives to improve physical characteristics. The insights gained from this research hold promising prospects for improving construction practices and addressing the challenges associated with these soils. [ABSTRACT FROM AUTHOR]

Expansive soil is one of the problematic soil types due to its potential to swell highly when moisture content increases and shrink when moisture decreases. The soil exhibits mechanical behavior that is highly sensitive to changes in natural moisture content influenced by environmental factors such as infiltration and evaporation. It has the potential to damage civil structures such as road pavement and lightweight buildings. An alternative method to overcome this phenomenon is the use of ground anchors, a structural element installed into a soil or rock layer to withstand the tension load. An expandable ground anchor is proposed as an alternative to overcome the drawback of a helical anchor. Wings are installed in such a way that additional passive pressure is developed. The study was firstly conducted by performing anchor pullout capacity tests on a dense sand layer, followed by a swelling test of expansive soil, and finally, the performance test of ground anchor to withstand swelling pressure using three different sizes of steel box anchor prototypes, 4 cm × 4 cm × 30.5 cm, 5.5 cm × 5.5 cm × 30.5 cm and 7 cm × 7 cm × 30.5 cm. A series of anchor pullout capacity tests were conducted on a 90 cm dense sand layer, continued by a swelling test of 25 cm expansive. The result indicates that an expandable anchor can significantly withstand the swelling of expansive soil. [ABSTRACT FROM AUTHOR]

Expansive soils exhibit a relatively low permeability coefficient when structurally intact, allowing for their treatment as a homogeneous medium in calculations. However, the susceptibility of the slope's shallow area to numerous primary and secondary cracks under the influence of wetting and drying cycles challenges this approach. Failing to account for the impact of these surface cracks on the soil's permeability can result in a significant discrepancy between calculated and actual conditions. This study initially validated a predictive model for the soil-water characteristic curve that incorporates the effects of wetting and drying cycles. Subsequently, leveraging the fracture volume ratio parameter (pv) and the bimodal distribution characteristics of the dual-pore structure, we proposed a permeability coefficient model for expansive soils that considers fracture effects. This model was integrated with the validated soil-water characteristic curve model to facilitate the analysis of expansive soil's infiltration characteristics under cyclic wetting and drying conditions. The findings indicate that the predictive model accurately captures the hysteresis effect of expansive soil's soil-water characteristics. Moreover, the permeability coefficient model, which accounts for fractures, effectively reflects the infiltration properties of cracked expansive soil and enables the prediction and calculation of its permeability under multiple cycles of wetting and drying. This study introduces a predictive model for the soil-water characteristic curve, leveraging the hysteresis properties of expansive soil. Additionally, it presents a model for calculating the permeability coefficient of expansive soil, utilizing a dual-peak characteristic function. The development of these models establishes a theoretical basis for the computation and analysis of the soil's permeability attributes.