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AbstractExcess pore water pressure (EPWP) induced by shield tunneling has a significant influence on the stability of the tunnel face, post-construction settlement, and the mechanical behavior of the tunnel lining. However, the three-dimensional and unsaturated property of the soil field is seldom considered in current research. Considering the non-uniform radial convergence model, a modified three-dimensional displacement solution induced by shield tunneling was established first. Then based on unsaturated EPWP elastic theory, a reliable and efficient method is developed to expedite the evaluation of EPWP distribution in three-dimensional saturated and unsaturated clay soil. The validity of the method is confirmed through comparison with field test and numerical outcomes. The analysis examples demonstrate that negative and positive EPWP are generated above the tunnel crown and beneath the tunnel invert, respectively. In the vertical direction, the negative EPWP exhibits a decreasing trend ahead of the heading face and an increasing trend behind it. Along the longitudinal direction, the influence zone of EPWP extends to 1D ahead of and 6D behind the heading face. With the decrease of soil saturation, the EPWP values tend to diminish. The maximum EPWP values observed in saturated conditions can be 16.13 times higher than those under unsaturated conditions. [ABSTRACT FROM AUTHOR]

Taking Bingham slurry as the research object, an infiltration diffusion model of Bingham slurry in unsaturated soil is established based on the seepage theory of unsaturated porous media, which takes into account the displacement effect and the viscosity time-varying characteristics of slurry. Combined with the seepage motion equation, relevant boundary conditions and interface conditions, the Bingham slurry diffusion equation considers grouting parameters and mechanical parameters is obtained. The research results are degraded to the saturated state and compared with the existing theoretical results. Numerical examples are used to study the influence of the above parameters on grouting pressure and slurry diffusion radius, then the diffusion mechanism of Bingham slurry is verified and analysed by model test. The above analysis and test results confirm the effectiveness and applicability of the research results, which can provide reliable theoretical support and technical reference for the design and construction of grouting engineering in unsaturated soil areas. [ABSTRACT FROM AUTHOR]

The combination of permeable and impermeable columns is commonly employed to enhance the stability of natural ground and expedite the consolidation process while effectively reducing foundation settlement. This study presents a comprehensive investigation of the consolidation characteristics of unsaturated composite foundations (USCF) using various methods. Firstly, a mathematical model is developed under the assumption of equal strain, considering depth‐dependent initial stress. To obtain more generalized analytical solutions for excess pore pressures and foundation settlement, separation of variables, Laplace transformation, and inversion Laplace transformation are employed. Secondly, the accuracy of the proposed analytical solutions is validated by comparing them with two specific cases reported in the existing literature, achieved by reducing the compression modulus of columns. Lastly, a series of parameters are investigated to examine the consolidation characteristics of USCF considering depth‐dependent initial stress. The results demonstrate that the final settlement of the foundation will be overestimated while the variation of vertical stress along the depth is neglected. Furthermore, adjusting the values of area replacement ratios proves to be more effective and straightforward than modifying the compression modulus of columns in the reinforcement treatment of USCF. [ABSTRACT FROM AUTHOR]

Energy piles are often partially or fully embedded in unsaturated soils, particularly in arid and semiarid regions; however, suction effects on their thermomechanical behavior have not been fully understood. In this study, a series of physical modeling tests were carried out to investigate the behavior of energy piles in unsaturated soils. The soil used for testing is completely decomposed granite, which is a type of clayey sand sampled from Hong Kong. Five constant-temperature pile load tests and three constant-load heating and cooling tests were conducted under different conditions of pile surface roughness and initial soil suction. It is observed that the ultimate capacity of the energy pile (Qult) increases as the initial suction increases from 0 to 90 kPa, the pile roughness increases from 0.05 to 1, and the temperature increases from 10°C to 21°C. Moreover, the effects of roughness are more significant in unsaturated conditions than in saturated states. A suction increment can increase both shaft and toe resistance, while temperature and roughness mainly affect the shaft resistance. During cyclic heating and cooling, suction and roughness increment reduces the irreversible pile head settlement due to the increment of shaft resistance. Furthermore, the irreversible pile head settlement is greatly affected by vertical load. When the working load is relatively small (smaller than 0.5Qult in this study), the settlement increases with the number of thermal cycles but at a decreasing rate for both saturated and unsaturated conditions, and finally reaches a stable state. When the working load is relatively high (0.7Qult in this study), the response of the pile does not reach a stable state in saturated conditions even after five thermal cycles. These observations should be treated with caution because they may be specific and only applicable to the case of no overburden pressure. Exercising caution is crucial when interpreting these observations, particularly at a quantitative level, because they may be limited to the test soil and the low stress level utilized in the physical model tests. [ABSTRACT FROM AUTHOR]

Precipitation is one of the most important factors inducing shallow slope failures, and the shallow slope covering bedrocks is prone to instability after heavy rainfall. In one-dimensional (1D) seepage–deformation coupling issues, permeability coefficient and moisture vary with matric suction in unsaturated soil. Combining mass conservation, Darcy's law, and elastic theory, an analytical solution for coupled seepage–deformation in unsaturated soil slopes during rainfall infiltration is derived using the Fourier integral transformation method. The analytical solution can be applied to a 1D seepage problem in a soil slope with flux at the top and impervious bedrock in the base under heavy precipitation, and is conducive to study infiltration into the slope under rainfall conditions. To validate the accuracy of the proposed analytical solution in this study, it is compared with monitored pore-water pressure data from the Gufenping Landslide in the red-bed region located in Nanjiang, Sichuan, China. The compared result shows a good consistency between the analytical solution and the measured results, with a minor relative error. Investigation of the parameters demonstrates that the water-level rise is closely related to the coupling, which is influenced by precipitation duration, precipitation intensity, soil properties, and slope angle. The bottom boundary of the slope is considered to be impermeable in this study, which leads to rainfall accumulation at the base over time, and the coupled effect becomes more pronounced at the bottom boundary. [ABSTRACT FROM AUTHOR]

Understanding the moisture migration of unsaturated soil in response to temperature changes is essential in soil science and geosystems applications. The coupling of thermohydro (TH) processes is a result of changes in fluid density and viscosity; however, gravity can disrupt the moisture migration of unsaturated sand initiated by a thermal gradient when the sand is considerably porous. Moreover, the moisture redistribution caused by the gravity effect is influenced by the imposed boundary temperature and initial moisture content of the unsaturated sand. Therefore, this paper presents heating tests performed on sand specimens of different gradations and subjected to various thermal gradients in a modified and well-controlled soil testing cell to evaluate the coupling behavior of TH processes in unsaturated sand. Two sands were tested in the soil testing cell, which was equipped with thermocouples (TCs) to measure the temperature and time-domain reflectometry (TDR) sensors to measure the apparent dielectric constant (Ka); three temperature boundary conditions were imposed on the soil testing cell to create two thermal gradients. This study shows that gravity, thermal boundary conditions, initial moisture content, and matric suction influence the migration of moisture: the silty sand, as compared with pure sand, more properly displayed the phenomenon of coupled TH processes in unsaturated soil when tested at a temperature gradient of 200°C/m and initial moisture content of 6%. The study provides an advanced understanding of the paired migration of heat and moisture in porous media under various conditions, including thermal gradient, initial moisture content, and gradation. When unsaturated soils are under a temperature gradient, the pore water tends to move from the heat source to a cooler end in search of moisture equilibrium. Temperature-driven moisture flow is commonly investigated in soil science, agriculture, and geosystems. For example, the soil surrounding a geosystem (electrical cables and ground heat exchangers) experiences heating and cooling cycles when heat energy is exchanged from buildings to the soil via the geosystem. This heat exchange can effectively cool the buildings in the summer and heat the buildings in the winter. To maintain effective heat transfer in the soil, it is necessary to investigate the temperature-driven moisture flow, as it has been established that redistributed moisture also significantly impacts heat transport. At the same time, the moisture flow is also influenced by gravity, particularly for coarse sands. Moisture flow in coarse sands is more prone to the effect of gravity than that in fine sands. This paper evaluates how the physical and hydraulic properties of the soil, such as gradation and suction, can affect the coupled thermal and hydraulic processes. The gravitational effect can dominate the moisture redistribution depending on the direction of the temperature gradient. [ABSTRACT FROM AUTHOR]

In unsaturated soil mechanics, the soil–water characteristic curve (SWCC) is the most fundamental soil attribute. All seepage analyses require SWCC to generate the pore-water pressure and water content distribution within the soil layers. SWCC is often determined using laboratory procedures. However, the expensive cost, long testing time, and difficulty of the SWCC tests hinder the use of unsaturated soil mechanics in engineering practice. Models for predicting SWCC have been proposed in the literature; however, the equations cannot be applied to soils of a wide variety, and their parameters lack physical significance. This work used a modified lognormal distribution function to generate the equations that best suit the grain-size distribution (GSD) and the model that estimates SWCC for a wide range of soil types. The parameters of the proposed GSD equation have well-defined physical meanings. The model for estimating SWCC was established based on the link between soil pore-size distribution and dry density, void ratio, and saturated water content. The air-entry value of coarse-grained soil is a function of inflection point of SWCC and percentage of coarse particle. The air-entry value of fine-grained soil is a function of saturated water content. Experiments were carried out as part of this study to evaluate the proposed equation as well as its model. The proposed model to estimate SWCC was compared with other models. The proposed model is better than other models in the estimation of SWCC from GSD. [ABSTRACT FROM AUTHOR]

This study presents a semi‐implicit MPM to adequately characterize the mechanical behavior of unsaturated soil based on Biot's mixture theory. To represent the dependency of the degree of saturation on the suction, we employ the VG model along with a soil‐water characteristic curve, which determines a functional form of permeability called the Mualem model. Hencky's hyperelastic model and the Drucker‐Prager model assuming nonassociativity are adopted for elastic and plastic deformations, respectively. The novelty of this study is the incorporation of the fractional‐step method into the MPM framework so that the pore water pressure is obtained by implicitly solving the pressure Poisson's equation, which reduces numerical instability and improves computational efficiency. Also, because the drag force between solid and liquid phases is evaluated using the intermediate velocity of pore water relative to the intermediate velocity of solid skeleton, the time increment can be chosen without considering the magnitude of water permeability. In addition, to suppress “odd‐even” oscillation, we employ a sub‐grid method in which two grids with different spatial resolutions are used for the velocities and pore water pressure. Furthermore, considering the advantages and disadvantages of two different interpolation schemes for pore water pressure, we suggest switching the schemes depending on the model conditions. Several numerical examples are presented to demonstrate the performance of the proposed method. Specifically, unidirectional consolidation and leak flow analyses are performed for verification purposes, followed by validation analysis of a model experiment of infiltration‐induced landslides. [ABSTRACT FROM AUTHOR]

This study proposes a closed‐form solution for axisymmetric electro‐osmotic consolidation of unsaturated soil under semi‐permeable boundary conditions. The governing equations are formulated to allow for vertical and radial flows of liquid and air phases. The techniques of eigenfunction expansion and Laplace transformation are employed to develop the exact solution for excess pore‐air (EPAP) and pore‐water pressures (EPWP). The proposed solution is first validated by comparing it to an existing solution, followed by verification through finite element simulations. Both methods of validation confirm the accuracy of the analytical solution. Then, based on the obtained solution, the effects of vertical flow, semi‐permeable boundary conditions, electrical voltage, electro‐osmosis conductivity and spacing ratio re/rw on the consolidation profile have been further investigated. Parametric studies show that the EPWP at the steady state depends on the electro‐osmosis conductivity and applied electricity gradient. In addition, the dissipation rates of EPWP and EPAP in the axisymmetric electro‐osmotic consolidation would be underestimated if the vertical flows are neglected. The semi‐permeable boundary conditions have great influences on the dissipation rate and the steady‐state solution. The proposed solution could serve as a theoretical basis for axisymmetric electro‐osmotic consolidation of unsaturated soil. [ABSTRACT FROM AUTHOR]

While the shear behavior of granular soils is directly related to the microstructure of contacts which often leads to the coaxiality between Cauchy stress and Satake fabric tensors, it is generally accepted by the geomechanics and geotechnical engineering community that the capillary effects are isotropic. At low saturation levels, however, the pore fluid tends to form interparticle menisci that can also manifest an anisotropic structure, which may result in the development of anisotropic capillarity in wetted granular media. To study the interplay between the solid grain contacts and the liquid bridges at the micro-scales, this study adopts a coupled discrete element method that utilizes a linear contact model combined with a capillary model, and explores their effects by conducting a series of numerical experiments. The distributions of contact and capillary force orientations during the experiment are further investigated to better understand how their alignments affect the global response of the granular assembly subjected to a deviatoric loading. The results indicate that the global shear stress response is not only affected by the contact fabric but also by the network of liquid bridges, and we also observe that the particles may lose contact while the pendular menisci may not be destroyed during the elastic unloading. [ABSTRACT FROM AUTHOR]

The rock walls of Valles Marineris (VM) valleys on Mars reveal significant gravitational failures, resulting in a sequence of massive landslides spanning several hundred cubic kilometers in volume. For further Mars exploration missions, it is critical to understand which characteristics impact the stability of these rock walls. In this work, ArcGIS is used to identify 30 steep slopes. Utilizing the finite element method, we calculate the proposed seven possibly landslide-prone slopes based on geometry in VM. Using Strength Reduction Method (SRM) in Midas GTS NX, the impacts of variations in cohesion, internal friction angle, unit weight, and elastic modulus of soil and rock on the slope safety factor against landslides are evaluated. The Strength Reduction Method (SRM) is a widely used approach in geotechnical engineering to assess slope stability. It involves systematically reducing the strength parameters of the soil and rock materials within the slope until failure occurs. By iteratively reducing the strength parameters, the SRM calculates the factor of safety against landslides. Internal friction angle is the most critical factor in determining the stability of a slope under low gravity circumstances since it has the widest range of possible alterations. Furthermore, the material's cohesion and unit weight significantly impact the safety factor, although elastic modulus barely affects slope stability. A modulus of elasticity of more than 35 GPa will not enhance the factor of safety. There is no significant difference in soil suction between Earth and Martian gravities near the surface water table. However, as the groundwater depth increases, soil suction under Martian gravity becomes notably lower than that on Earth. Additionally, consistent with prior investigations, the Vadose zone on Mars is positioned at higher elevations relative to Earth, indicating the presence of a higher capillary fringe. Furthermore, the factor of safety for slope stability consistently outperforms Earth for equivalent slope configurations under unsaturated conditions, with approximately 2.5 times higher factor of safety for higher suctions and approximately 1.5 times higher factor of safety for lower suctions compared to Earth. [ABSTRACT FROM AUTHOR]

Microbial induced calcium carbonate precipitation (MICP) offers a sustainable technique to improve geologic properties of soils in engineering structures. The applications encompass improved soil strength, scour mitigation, fracture sealing, and in situ contaminant immobilization. Previous studies have presented fundamental processes and implementation in lab- and field-scale. Most of these studies were examined in saturated conditions despite many MICP applications including those in coastal and riverside areas which will likely take place under unsaturated conditions. The study herein investigated the effect of soil water retention curve (SWRC) parameters and attachment coefficient (Kat) on CaCO3 precipitation in sand. Using numerical analyses, a continuum model was developed in which unsaturated flow and transport were coupled with biological and chemical reactions in variably saturated conditions. Predictive modeling results compare mass percentage of calcium carbonate resulting from MICP at degrees of soil water saturations of 20%, 40%, 80%, and 100% in sandy soil media. The results indicate the bacteria attachment coefficient increases by a factor of 3 as the degree of saturation is decreased from 100% to 20%, as the higher suctions at lower saturation levels improve bacteria fixation. The drying branch of SWRC versus wetting front yields higher CaCO3 for identical MICP treatment. Numerical results show the trend in hydraulic conductivity with increasing cementation level. [ABSTRACT FROM AUTHOR]

This paper aims at proposing a calculation model to deal with the face stability of shield tunnels in unsaturated soil. Based on the existing results of centrifugal test and numerical simulation, a new failure mechanism is proposed, which combines the logarithmic spiral with upper loosening arch mechanisms. The failure mechanism considers the influence of the soil arching effect and the logarithmic spiral height coefficient. Formulas for calculating the loosening earth pressure of unsaturated soil are deduced. Subsequently, this model of loosening earth pressure is introduced into an analytical model to compute the limit support pressure on the tunnel face. Compared with other height coefficients and the degree of soil arching effect, when the height coefficient is 0.95 and the degree of soil arching effect is 10%–30%, the limit support pressure proposed in this paper is in good agreement with the centrifugal test results. Finally, comparisons are performed with the proposed model and classical models as well as typical centrifuge model tests. The comparative analysis shows that the proposed theoretical model is in good agreement with the numerical simulation. The outline of the failure zone by the theoretical model in this paper is in good agreement with the centrifuge results. [ABSTRACT FROM AUTHOR]

Borehole thermal energy storage (BTES) is an innovative renewable energy technology for building heating and cooling. The lack of studies about BTES in unsaturated soils acts as a barrier to further implementation. In this study, the research obstacles, progress, hotspots, and differences between countries of BTES systems in unsaturated soils were described in detail based on a literature review, bibliometric analysis, technology roadmap, and data visualizations. The results show that the process of coupled heat and moisture transfer has been a research hotspot in recent years, and the thermo‐hydraulic properties increase the complexity of analysis. There are few studies on experimental data and engineering practices of BTES systems in unsaturated soils. China is leading in publications number, but European and North American countries perform better in international cooperation and policy incentives. Technology development will be directly driven by policy momentum, followed by the gradual establishment of a complete research, design, and evaluation system, which helps accelerate the replacement of traditional fossil energy with renewable energy. In an attempt to improve society's awareness and move forward with scientific foresight of BTES systems in unsaturated soils, this review has revealed the evolutionary process, identified its current status, and depicted the future development from political, economic, social, and other dimensions. [ABSTRACT FROM AUTHOR]

It is important to understand the shear behavior of oil-contaminated soils in many geotechnical problems, such as the analysis of pipelines and storage tanks affected by oil leakage. In this study, the shear behavior of a silt permeated with silicone oil/water (denoted by OS and WS, respectively) was investigated through direct shear tests. The residual shear strength was measured at various degrees of liquid saturation (65–100%) and net normal stresses (50 to 400 kPa). The oil and water retention curves were measured and used to explain the shear behavior. The results show that the residual friction angle of OS is 30% larger than that of WS. This is likely because OS and WS show aggregated and matrix structures, respectively, as evidenced by the Scanning Electron Microscope (SEM) test. The former structure includes more particle contacts than the latter one. These structural differences can be attributed to varying fluid properties, such as wettability, viscosity, and dielectric constant. When the volumetric degree of water saturation decreases, the total cohesion of WS increases substantially because of the strengthening effects of air-water interfaces on the soil skeleton. In contrast, the degree of oil saturation has minuscule effects on these variables, mainly because OS has a low oil retention ability and the air-oil suction remains very low (i.e., less than 2 kPa) during the desaturation process. [ABSTRACT FROM AUTHOR]

Permeability tests on unsaturated frozen sand and gravel In artificial ground freezing applications, frozen saturated soil is assumed to be practically impervious. However, in the case of partial initial saturation, this is no longer the case. As part of a pilot study, permeability tests were carried out in the laboratory on cohesionless, loose, partially saturated, frozen soil samples. Mineral oil was used as the flow medium. Since no standardized apparatus exists, suitable experimental techniques and evaluation procedures had to be developed. The permeability of unfrozen, fully saturated soil was also determined for reference. Due to the loose packing and the low degree of saturation, the partially saturated soils exhibited a significant permeability, which is in the same order as the value of the corresponding water‐saturated, unfrozen soils. [ABSTRACT FROM AUTHOR]

Field compaction control is arguably the most common yet critical quality control procedure in geotechnical engineering. Since the early 1930s, the systematic process for performing quality control of compacted soils has often been implemented by measuring the in-place dry unit weight (or density) and as-compacted soil moisture content after placement in a fill. However, the current practice overlooks several facts resulting from comparing soil prepared and compacted in the laboratory to soils placed and compacted in the field. These issues include comparing the compaction energy in the lab versus what is applied in the field, and the behavior of saturated soils in the laboratory to the performance of unsaturated soils in the field. To address some of these gaps, this study presents a new saturation-based framework for compaction quality control. The aim of this new framework is to reduce the uncertainties and assumptions of the compaction control process and provide practicing engineers with further insight into the key engineering attributes of compacted soils. The proposed saturation-based approach compares a degree of saturation difference with a normalized dry unit weight ratio, making saturation upon compaction the controlling diagnostic variable and the focus of the monitoring effort. In essence, the optimal compaction conditions will be referenced to a characteristic saturation state near 80%. Compared with the conventional quality control system for field compaction, the saturation-based approach is developed with the same field and reference data collected for most earth fill projects. The results of this approach enhance the engineering judgment required to match the laboratory reference values to the field conditions. For the purposes of illustration, the proposed saturation-based framework is applied to compaction control data of a large earth dam and compared against the conventional method side by side. [ABSTRACT FROM AUTHOR]

Rainwater infiltration is one of the main triggering factors in slope failure. Therefore, exploring the unsaturated slope behavior is essential. However, studies generally ignored the impact of soil-water characteristic curve (SWCC) hysteresis caused by wet-dry cycles in engineering practice. SWCC measured in the drying process is commonly used to estimate slope behavior in the wet-dry cycle. Three soils of Toyoura sand, Hiroshima decomposed granite soil (Masado soil), and DL clay will be taken as examples to examine the infinite slope stability under the effect of SWCC hysteresis. Firstly, this research examines soils' SWCC and suction stress characteristic curves (SSCC). Then, the factor of safety (FOS) changes are further analyzed when suction stress is considered the confining pressure. The results indicate that FOS for soils with small cohesion and air-entry value is greatly affected by SWCC hysteresis. As the depth between the selected slip surface and slope surface increases, the disparity between FOSs calculated through wetting FOS and drying FOS will decrease sharply. Therefore, for shallow slope stability analysis, only using the SWCC measured during the drying process to evaluate the entire wet-dry cycle might lead to underestimating slope failure potentiality. [ABSTRACT FROM AUTHOR]

Rainfall and earthquakes are two major triggering factors for landslides. Previous studies have often used critical rainfall for assessment of occurrence of landslides induced by simultaneous rainfall and earthquakes; there has been minimal exploration of antecedent rainfall, which directly affects water content and saturation degree of soil before landslides occur due to both rainfall and earthquakes. Here, this study developed a model to assess the landslide probability of an unsaturated slope considering earthquake effect and under different critical and antecedent rainfall conditions. The proposed model includes two steps. In step 1, antecedent and critical rainfall are used as initial and boundary conditions, respectively, to simulate rainfall infiltration into an infinite unsaturated soil slope; this determines the depth of the wet zone. In step 2, factor of safety is calculated with consideration of seismic effects in the infinite slope model, using the wet zone depth determined in step 1. The spatial distribution of these factors of safety is used to classify susceptibility levels of landslide occurrence. The proposed model was assessed using data from a landslide event in Atsuma, Japan that had been caused by rainfall and earthquakes. The results showed that the area under the receiver operating characteristic curve was 83.4%, while confusion matrix-based accuracy was 63.7%. The proposed model was applied to Mt. Umyeon, Korea to evaluate the likelihood of landslide occurrence due to rainfall and earthquakes, according to four susceptibility levels: very low, low, moderate, and high. The results indicated that antecedent rainfall strongly affects the spatial probability of landslides induced by simultaneous rainfall and earthquakes. The proposed method may provide reasonable predictions for landslide susceptibility assessments. [ABSTRACT FROM AUTHOR]

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Soil-water characteristic curve (SWCC) is an essential parameter in unsaturated soil mechanics, and it plays a significant role in geotechnical engineering to enhance theoretical analysis and numerical calculations. This study investigated the effects of key factors, such as the percentage of sand, initial degree of saturation, and initial dry unit weight, on the SWCC of expansive soil by measuring the matric suction using a pressure apparatus method. The empirical equation of SWCC was obtained using the Van Genuchten and Fredlung Xing models, and the processing of experimental data checks the fitting of the two empirical models. The findings revealed that the Fredlung Xing model fit the relationship between matric suction and volumetric water content of expansive soil better than the Van Genuchten model, indicating that the pressure apparatus approach's experimental data are correct and acceptable. The study also found that the matric suction increased with decreasing percentage of added sand at the same volumetric moisture content, and the increase in initial dry unit weight increased the matric suction, with the water retention capacity decreasing significantly after adding 20% sand. Moreover, as the initial degree of saturation increased, the volumetric water content decreased, and the characteristic curves became identical when the initial saturation degree reached 90%. Finally, to minimize the water retention capacity of expansive soils, the study recommended adding a percentage of sand not less than 30% to the expansive clay sample. [ABSTRACT FROM AUTHOR]

Abstract While the shear behavior of granular soils is directly related to the microstructure of contacts which often leads to the coaxiality between Cauchy stress and Satake fabric tensors, it is generally accepted by the geomechanics and geotechnical engineering community that the capillary effects are isotropic. At low saturation levels, however, the pore fluid tends to form interparticle menisci that can also manifest an anisotropic structure, which may result in the development of anisotropic capillarity in wetted granular media. To study the interplay between the solid grain contacts and the liquid bridges at the micro-scales, this study adopts a coupled discrete element method that utilizes a linear contact model combined with a capillary model, and explores their effects by conducting a series of numerical experiments. The distributions of contact and capillary force orientations during the experiment are further investigated to better understand how their alignments affect the global response of the granular assembly subjected to a deviatoric loading. The results indicate that the global shear stress response is not only affected by the contact fabric but also by the network of liquid bridges, and we also observe that the particles may lose contact while the pendular menisci may not be destroyed during the elastic unloading.

Abstract The issue of rainfall-induced slope failure has attracted more attention from geotechnical engineers as a consequence of global warming. Current cumulative waste disposal has generated scientific interest in the utilization of waste materials in geotechnical design for climate change adaptation measures. Taking into consideration the effect of slope height and angle, steel slag—a waste product derived from the production of steel—was investigated as a slope cover against rainfall. To assess the stability of the slope and the infiltration of water into the soil, numerical analyses were conducted using both SEEP/W and SLOPE/W software in conjunction with rainfall conditions. Based on the findings, it can be concluded that increasing the slope's elevation and inclination will have an adverse effect on its safety factor. Steel slag can nevertheless be utilized for minimizing rainwater infiltration into the slope, as indicated by the pore-water pressure variations and graphs of the safety factor versus time. For a 20-m slope height, steel slag slopes have demonstrated a lower factor of safety difference in comparison to the initial slope without remediation. Regardless of slope angle and slope height, the safety factor reduces marginally during rainfall.

Suction stress is one of the most significant factors affecting the serviceability and stability of soil structures. This study presents a framework for analyzing the stability of geosynthetic reinforced soil (GRS) walls and slopes under unsaturated conditions. An analytical formulation of suction stress-based effective stress was implemented into a limit equilibrium solution, namely, the top-down procedure. The developed framework enables the prediction of the tensile load distribution and connection load between the reinforcement and wall face considering the pullout resistance of reinforcements in GRS walls backfilled with granular and marginal soils under unsaturated conditions. The applicability of the framework was demonstrated by providing an illustrative example followed by three series of parametric studies to understand the effects of pore size distribution, air entry pressure, and infiltration rate on the performance of an unsaturated GRS wall. The results quantify the impact of suction, showing that as it increases, the maximum tensile loads and connection loads decrease while pullout resistance increases. Mostly affected by the suction effect are upper reinforcement layers, where combined effects of reduced tensile load and increased pullout resistance decrease connection load and reinforcement length requirements. The current study strongly discourages counting on the contribution of suction for the design of new GRS walls. The suction value cannot be accurately and reliably determined for the entire lifespan of the GRS wall, and it may decrease or diminish in an uncontrolled and random manner under infiltration. However, by quantifying the effect of suction, the proposed framework in this study provides a valuable tool for analysis purposes, enabling a rigorous interpretation of field-measured reinforcement loads during wall service as well as evaluation of the forensics of failed GRS walls. [ABSTRACT FROM AUTHOR]

Desiccation cracks are the most prevalent cause of engineering geological problems with expansive soils, and tensile strength is the major restricting component for crack formation and development. To promote the development of the connection between tensile strength and other mechanical indexes, a test procedure was established that can measure uniaxial tensile strength and unconfined compressive strength in the same conditions. Uniaxial tensile and compressive tests were performed on compacted expansive soils with water contents that varied from 12% to 24% and dry densities ranging from 1.4 g/cm3 to 1.6 g/cm3. The suction and pore surface fractal dimensions of the specimens were also measured. The experimental findings reveal that the uniaxial tensile strength and unconfined compressive strength followed similar trends as degree of saturation increases and are significantly reliant on suction variations. Then, tensile-compressive-strength ratio and pore surface fractal dimension are subsequently employed to develop tensile strength prediction models. The models presented above have specific physical implications that compensate for the limitations of the fitted models. Finally, the applicability and limits of suggested models for future applications are examined. [ABSTRACT FROM AUTHOR]

Abstract\nHIGHLIGHTSAccurate knowledge of hydraulic properties of unsaturated soil is vital to modelling water and solute transport process and addressing soil salinisation problems. Due to the defect that the van Genuchten (VG) model cannot represent soil water characteristics (SWC) during the drying stage, we have introduced a modified model, which combines capillary flow with film flow models to describe the unsaturated hydraulic conductivity. The capillary SWC is obtained by assuming the specific water capacity function with lognormal distribution. The film SWC is modified using the logarithmic nonlinear expression by introducing a modification coefficient into the Campbell equation, and the film relative hydraulic conductivity (RHC) is obtained based on the logarithmic nonlinear relationship. The calculated modification coefficient values range from 0.99 to 2.49. Finally, the proposed model’s rationality and applicability are validated through root mean square error (RMSE) analysis with measured values and comparison with the VG model. While the calculation RMSEs of SWC in the two models are basically consistent, the RMSEs of RHC in the proposed model are around 1–10 times smaller than those of the VG model, indicating its superiority in calculating the hydraulic conductivities over the entire matric head.A modified model describing the variably saturated hydraulic conductivity is presented combining the capillary with film flow model.A logarithmic nonlinear expression with a modification coefficient is introduced in the film soil water characteristic model.The fitting parameters for relative hydraulic conductivity are determined and root mean square errors are chosen for evaluating the modified model. [ABSTRACT FROM AUTHOR]

We develop an analytical solution to the problem of one‐dimensional consolidation of unsaturated soil subjected to cyclic loads with arbitrary waveforms. The solution predicts the excess pore water and pore air pressures and the accompanying vertical compression in a poroelastic, unsaturated soil material. Cyclic loading occurs in a variety of engineering applications and often generates higher excess pore fluid pressures and larger vertical compression than does a time‐invariant load. In the present study, the loading function is allowed to take on any arbitrary waveform represented by a Fourier trigonometric series. Analytical solution to the boundary‐value problem in one dimension is given in closed form describing the frequency‐independent and frequency‐dependent components of the poroelastic response. We verify the analytical solution through representative examples involving cyclic loads with square and triangular patterns. Apart from the shape of the forcing function, we also investigate the effects of initial water saturation, soil texture, and excitation frequency on the system response. [ABSTRACT FROM AUTHOR]

A viscoplastic constitutive model is developed to describe the viscoplastic behavior of unsaturated soils. The proposed model accounts for the stain‐rate and suction effects on yield by adopting an unsaturated isotach concept. The nonstationary flow surface theory (NSFS) is applied for modeling the viscoplastic behavior, with the yield surface which can evolve with the viscoplastic strain, viscoplastic strain rate and suction. Meanwhile, the progressively hardening concept is adopted for reproducing the viscoplastic behavior of soil at an over‐consolidated state. For the validation, a series of loading conditions are considered based on the data from the literature. Results show that the proposed model is able to reproduce the main viscoplastic behaviors of unsaturated highly compacted Gaomiaozi (GMZ) bentonite, Glenroy silt and Qianjiangping landslide (QL) soil, including CRS compression tests, rate‐dependent triaxial shear tests, and triaxial creep tests. [ABSTRACT FROM AUTHOR]

The stratigraphic uncertainty and rotated anisotropy of soil properties exist widely in nature. Recent studies have shown that the slope stability was significantly influenced by these two uncertainties. However, there is no proper method for simulating these two uncertainties at the same time, and the influence of the two uncertainties has not been considered in previous unsaturated soil slope stability analysis. This paper aims to propose a coupled method for characterizing the stratigraphic uncertainty and rotated anisotropy of soil properties, and investigate the unsaturated soil slope stability considering the two uncertainties. Through a slope case, the proposed method for characterizing the two uncertainties is examined. The effect of rotational angle on the slope stability and groundwater table is studied. In addition, four different uncertainty considerations are chosen to compare their influence on the slope stability and groundwater table. The results show that the proposed method can well characterize the two uncertainties at the same time. The rotational anisotropy of soil properties has a substantial impact on the slope stability and groundwater table. The rotational angles corresponding to the maximum and minimum reliability index of slope depend on the uncertainty considerations in the slope stability analysis. The slope reliability index only considering stratigraphic uncertainty is the highest, and the slope reliability index considering stratigraphic uncertainty and rotated anisotropy of soil properties is the lowest. [ABSTRACT FROM AUTHOR]

This work investigates the rainfall infiltration process within homogeneous and stratified colluvial deposits caused by short (1–3 h) and intense (40–90 mm/h) rainfall, using both analytical and numerical infiltration modelling. The findings of the investigation demonstrate that the classic Green–Ampt model can be employed effectively to study homogeneous colluvial covers with permeability equal to or lower than kw = 10−5 m/s and that are subject to a 1 h rainfall with intensity I ≥ 45–50 mm/h. In these circumstances, a top-down saturation front forms within the colluvial deposit, leading to the saturation of a 70–100 cm-thick layer. This critical condition occurs every 5–10 years in the mountain area of the Friuli Venezia Giulia Region (NE Italy), which corresponds to a lower return period of critical hydrologic events when compared with other mountain basins in the Alps due to the higher initial degree of saturation characterising colluvial covers in this area (70–95%). When analysing stratified colluvial covers, the Dagan–Bresler approximate model, as well as the numerical modelling, emphasised the strong influence that abrupt variations in the permeability of the various soil layers have on the infiltration process at depth. In particular, the presence of a top organic soil horizon that is rich in macro-pores and is characterised by a higher permeability (k = 10−4 m/s) actually reduces the possibility of surficial ponding, which is the basic condition of the "piston" models. The highly permeable top soil allows for a rapid downward infiltration up to contact with the underlying colluvial material, which is less permeable (k = 10−5 m/s). Therefore, a perched water table forms starting from the organic soil–colluvium interface, originating pore–water overpressures within the colluvial deposit, with maximum values in the order of 5–10 kPa. [ABSTRACT FROM AUTHOR]

Describing the hydraulic conductivity of unsaturated soil is very important in predicting water transport. Most current models have complex forms and generally need to be calibrated by the measured unsaturated hydraulic conductivity curve. A simple model, by which it is possible to conveniently predict the unsaturated hydraulic conductivity, is proposed in this study. The soil–water characteristic curve and hydraulic conductivity curve are separated into three parts. The soil–water characteristic curve is represented by Fredlund and Xing's equation. A simple model composed of three lines is proposed for estimating the hydraulic conductivity of unsaturated soil. The model parameters can be conveniently calibrated from the measured soil–water characteristic curve and saturated hydraulic conductivity. Finally, the proposed model is validated by the experimental data from different soils. The proposed model provides a simple approach to estimating the hydraulic conductivity of unsaturated soil, which is more convenient for practical application. [ABSTRACT FROM AUTHOR]

An elastoplastic analysis scheme for the cylindrical cavity expansion in offshore islands unsaturated soils considering anisotropy is established. The hydraulic properties and anisotropy caused by stress of unsaturated soils are coupled in an elastoplastic constitutive matrix for unsaturated soil to obtain the governing equations for the cylindrical cavity expansion problem, with an analytical solution that utilizes the original hydro-mechanical state of the soil as the initial conditions. Through a comparative analysis with other analytical solutions, the effectiveness of the new solution is verified. Moreover, the swelling response of the cylindrical cavity expansion in unsaturated soils is examined by systematically analyzing different parameters of the surrounding soil. The findings reveal that the development and rate of anisotropy in normal consolidated soil and over-consolidated soil exert a significant impact on the soil's mechanical characteristics. Nevertheless, the alteration in the model constant h has little effect on the soil's mechanical characteristics. The analytical solution introduces anisotropy and broadens the expansion theory of unsaturated soils to yield a more comprehensive theoretical framework for the comprehensive analysis of offshore islands' unsaturated soils. [ABSTRACT FROM AUTHOR]

Unsaturated soil covers a significant part of the world, and studying the behavior of deep foundations in this medium is an important step in increasing accuracy and economic efficiency in geotechnical studies. This paper presents an analytical solution to investigate the load-carrying characteristics of single piles embedded in unsaturated soils, accounting for the effect of groundwater level on the pile's response. For this purpose, relationships for shear modulus and Poisson's ratio for unsaturated soils were collected from the literature to consider their effects as key parameters on pile performance. A parametric study was conducted to evaluate the effect of soil moisture content on the behavior of the pile-soil system for different soil types, and the effect of pile slenderness on its load-settlement behavior was studied for varying soil moisture contents. The results indicate that the pile stiffness increases as the soil suction increases while below a critical slenderness value, hence increasing the pile load capacity. However, this improvement occurs within a limited range of soil suction that is narrower for coarse-grained soils. The pile settlement corresponding to soil failure was also evaluated by modifying the existing solutions for unsaturated soils. The developed solutions were verified against the predictions of published solutions as well as the results of finite element analysis and pile load tests. It was found that the system stiffness decreases by 50% when the water table rises from the pile toe level to the ground surface in the studied soil. [ABSTRACT FROM AUTHOR]

Landslides due to catastrophic weather events, especially heavy rainfall, have risen significantly over the last several decades, causing significant damage and affecting the health and livelihoods of millions of people. Using tree roots to bio-engineer shallow slopes has been proven to be a cost-effective, sustainable measure and thus has gained increasing popularity. As slope failure often occurs under heavy precipitation, it is important to understand the mechanical interactions in the soil matrix surrounding a root to better estimate the reinforcement capacity of a root system, especially as the soil undergoes wetting from drier conditions. However, very few studies of root reinforcements have considered the effects of degree of saturation on behaviour. In this study, steel wires are used as a root analogue to explore the impact of root geometry, soil dilation and soil saturation on the pull-out behaviour of a root and three commonly used unsaturated soil strength models have been used to interpret the pull-out results. It was found that roots with larger diameter did not contribute to additional resistance. Also, a linear relationship between degree of saturation and pull-out strength was identified over a large range of suctions and one of the unsaturated soil strength models seemed to provide a more reasonable interpretation. The results will help future bioengineering slope design by improving the understanding of soil-root interface behaviour, including the effect of root diameter in slippage failure and greater emphasis on the importance of taking degree of saturation into account in unsaturated soil strength models. [ABSTRACT FROM AUTHOR]

The presence of unsaturated soil is critical in geotechnical engineering since the matric suction may aid in accommodating the pile shaft capacity. The design of piles can be optimized by incorporating unsaturated soil mechanics principles. Hence, the amount of waste materials can be reduced, the duration of pile installation can be expedited, and the amount of energy used for casting the pile can be optimized, resulting in more sustainable design and construction of piles. Conventional α, β, and λ methods and modified α, β, and λ methods are the common models that are used for calculating the shaft capacity by incorporating soil–water characteristic curves (SWCCs). However, in our opinion, we feel that the investigation of the influence of seepage infiltration due to rainfall on the shaft capacity of piles, calculated using both analytical means and numerical analysis, has been dealt with inadequately in past studies. The objective of this study is to investigate changes in the shaft pile capacity according to suction changes due to rainwater infiltration for the greater reliability of the pile design, using both analytical and numerical studies with the finite element method (FEM). Sand and kaolin, which are typical components of coarse-grained and fine-grained soil, are used in this study. The laboratory results were incorporated into PLAXIS 3D (Version 22), and a coupled analysis was carried out, utilizing the meteorological conditions in Astana. The results showed that the decreases in matric suction in sand and kaolin are similar after their subjection to rainfall, yet sand produces a higher shaft capacity compared to kaolin. The modified β method offers a higher shaft capacity compared to the other methods due to the effective stress factors being taken into account. The modified α and λ methods are recommended for short piles because they are more sustainable, whilst the modified β method is preferable for long piles. Overall, unsaturated soil conditions should be applied to optimize the foundation design since they generate a higher shaft capacity. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology 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.)

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology 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.)

Purple soil is widely distributed in southwestern China and is one of the important natural resources. Because of the loose parent rock and low degree of differentiation, purple soil is characterized by a loose structure that is easily eroded and high soil fertility. Soil erosion is very serious in the purple soil region, which is one of the main sources of sediment in the upper reaches of the Yangtze River, and has a certain impact on the agricultural production and engineering development in the purple soil region. After erosion, purple soil shows the characteristics of reduced dry density of soil and serious loss of fine particles, which affects its water-holding characteristics. In order to explore the changes of soil water-holding properties of purple soil after rainfall erosion, this study was carried out to analyze the effect of missing grain groups on the water-holding properties of sandy clayey purple soil under rainfall conditions by selecting three test methods, namely, axial translation technique, filter paper method, and saturated salt saturated saline solution vapor equilibrium technique for the three grain groups which are the most susceptible to changes in the rainfall conditions, and carrying out the Soil-Water Characteristic Curve (SWCC) test with the absence of grain groups within the full suction range to analyze the effect of the missing grain groups on the water-holding properties of sandy clayey purple soil. The results show that: 1) the missing grain group reduces the water-holding characteristics of sandy clayey purple soil, which is most obvious in the boundary effect zone and transition zone, and has less effect on the residual zone. The mass of the missing grain group is inversely proportional to the air intake value and the residual water content. 2) Using the grain size parameters (Constrained diameter、Average diameter、Median diameter、Effective diameter) to characterize the soil grading condition, the relationship between the soil grading curves and the characteristic values of SWCC was established. It was found that except for effective diameter, the other parameters were linearly inversely related to the air intake value and residual water content; 3) The data obtained from different methods were fitted using the Fredlund-Xing model, and it was found that the results of the data obtained from a single test method fitted better, but the SWCC significantly deviated from the test data points in the boundary effect zone and the transition zone. Root mean square error (RMSE)、 percent bias (PB) and mean absolute percent relative error (MAPRE) were introduced as evaluation indexes, and it was found that the suction range was the main factor affecting the fitting effect of SWCC, and within a certain suction range, the larger the range of data points involved, the better the model fitting effect was, and after a certain suction value was reached, the suction range had very little effect on the model fitting effect. It is proposed that to obtain the accurate SWCC of purple soil quickly, only the maximum suction value needs to be determined, and the number of test points with high suction is reduced, which can effectively shorten the SWCC test period. The results lay a foundation for the subsequent study of the role of soil erosion and water-holding characteristics of purple soil, and also provide reliable ideas for the prevention of soil erosion and the application of soil-water characteristic curves in the Three Gorges Reservoir area. [ABSTRACT FROM AUTHOR]

This paper presents a coupled hydro-mechanical peridynamic (PD) model to simulate unsaturated seepage and crack propagation due to moisture change in unsaturated expansive soils. The PD form of the nonlinear moisture diffusion equation is derived by using the PD differential operator (PDDO). The bond-based PD equilibrium equation includes the effect of elastic strain due to moisture change. These coupled field equations are solved by employing explicit schemes. Their accuracy is established by simulating the transient flow in the unsaturated soil pillar, steady flow in the unsaturated soil dam, and crack propagation in the cylinder soil specimens. The PD fluid pressure predictions are in good agreement with the analytical and numerical results. The crack propagation process and crack patterns are similar to the experimental observation. The results show that coupled hydro-mechanical PD model can capture realistic hydraulic and mechanical behaviors of unsaturated expansive soils. [ABSTRACT FROM AUTHOR]

It is well-recognised that stress can greatly affect the pore characteristics of unsaturated soil, such as pore size distribution (PSD) and pore shape (PS). So far, the effects of PSD and PS on the drying and wetting water retention curve at different stresses have not been well understood. To fill the knowledge gap, eight water retention tests were carried out to evaluate the effects of PSD and PS on hysteretic water retention behaviour at different stresses. Soil specimens purposely prepared at two compaction water contents and two initial void ratios were subjected to drying and wetting under two different net stresses (0 and 50 kPa). Moreover, mercury intrusion porosimetry (MIP) and micro-X-ray computed tomography (µ-XCT) were used to quantify the microstructure of specimens. The results showed an important role of pore structure in the hysteretic SDSWRCs. Compared to the specimens prepared on the dry side, specimens compacted on the wet side of the optimum are highly aggregated, possessing a lower water retention ability but a higher degree of hysteresis. The higher hysteresis observed in the highly aggregated specimens can be explained by the irregular-shaped pore characteristics observed in µ-XCT tests. [ABSTRACT FROM AUTHOR]

The analytical representation of kinematic interaction between pipe pile and unsaturated soil subjected to vertical SH-waves is revisited using three-dimension continuum modelling. The fractional-order standard line solid (FSLS) model is employed in the governing equation of unsaturated soil to refine the characterization of the flow-independent viscosity of the soil skeleton. The Timoshenko beam theory is utilized to describe the horizontal dynamic behavior of pipe pile. A closed series form solution of horizontal kinematic response for a pipe pile embedded in unsaturated soils under the action of vertical SH-waves is deduced theoretically with boundary conditions of pile-soil system. The solutions of the proposed model are compared with those captured from existing solutions. Finally, the effects of physical parameters in pile-soil system on the horizontal kinematic response of pipe pile under SH-waves are evaluated with analytical examples and parametric study. The results indicate that FSLS model parameters have significant impact on the horizontal kinematic response of the pipe pile, changes in the soil saturation have a relatively slight effect on the horizontal kinematic response of the pipe pile, and the length and radii of pipe pile should be moderate rather than too large or too small to make the pipe pile play a better seismic performance. [ABSTRACT FROM AUTHOR]

The soil–water characteristic curve (SWCC) plays an important role in solving the stability and deformation problems of unsaturated soils. In many practical situations, soils are usually experienced by both deformations and thermal conditions. In this interest, the paper proposes a simple and effective model to predict the combined effect of initial density and temperature on the SWCC and to be able to quantify the changes in thermal-hydro-mechanical behavior of unsaturated soils. In the first step, an initial density-dependent SWCC model is presented using the translation principle between particle-size distribution curve and soil–water characteristic curve. In the second part, a non-isothermal model is proposed to predict the effect of temperature on the SWCC. The key to the non-isothermal model is considering five different temperature-dependent functions, which are surface tension, contact angle, particle-size expansion, void ratio, and water density. On the basis of 22 data sets of thermal volume change, this study also developed further a theoretical correlation between void ratio and temperature that is directly related to soil plasticity. It was observed that the value of the thermal void ratio increases as soil plasticity increases, and there is a nonlinear relationship between the plasticity index and the void ratio. Because of this, soils with high plasticity are more susceptible to volume changes caused by temperature fluctuations than soils with low plasticity. A coupled mechanical–thermal model is then produced which is capable to predict separately or simultaneously the effect of temperature and initial density on SWCC. The proposed model is validated against several test data sets available in the literature. The results show that the proposed model has a good performance in predicting the variation in SWCC with arbitrary temperature and initial density. [ABSTRACT FROM AUTHOR]

Since the mid-1990s, several empirical unsaturated shear strength equations have been proposed for use in geotechnical engineering practice. Most of the equations have been based on information associated with the measured drying soil-water characteristic curve (SWCC) in combination with the effective shear strength parameters of the saturated soil. There have been few studies, however, undertaken on verifying and comparing the suitability of the proposed unsaturated shear strength equations. This study involves consideration of a wide range of possible drying SWCCs plotted as a relationship between the degree of saturation and suction (saturation soil-water characteristic curve (S-SWCC)). The study forms the basis for comparing five methodologies that have been proposed for the estimation of the shear strength of unsaturated soils. The SWCCs are defined by the fitting parameters for the Fredlund and Xing (1994) sigmoidal equation. This study supports the use of unsaturated soil shear strength empirical estimation methods using the S-SWCC anchor points of air-entry value and residual suction of the soil. [ABSTRACT FROM AUTHOR]

The soil–water characteristic curve (SWCC) is a key constitutive relationship for unsaturated soil which can be unimodal or bimodal. For the fine-grained compacted subgrade soil with a bimodal pattern, the determination of SWCC is complicated and needs a wide-range suction measurement. In this paper, the bimodal SWCC of a subgrade soil derived from the compaction condition was measured and determined by incorporating pore size distribution. For this purpose, a series of laboratory tests were conducted, including the pressure plate method, filter paper method, and vapor equilibrium method, which were used to measure SWCC at the low, medium, and high suction range, respectively. The pore size distribution (PSD) data were obtained by mercury intrusion porosimetry (MIP) tests and used to predict SWCC. Based on the analysis of hydraulic paths and SWCC-PSD correlations, the SWCC of the subgrade soil should be determined to follow the actual hydraulic path. SWCC within a low suction range can be filled by PSD-based data to improve the fitting accuracy. Then, a graphical method is applied to predict the bimodal SWCC by combining the filter paper method, vapor equilibrium method, and PSD-based data. The prediction curves fit well with the test data for all selected compaction conditions. Furthermore, the prediction method can still provide good prediction performance in the absence of high suction section data, which is beneficial for the application of bimodal SWCC. [ABSTRACT FROM AUTHOR]

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Adsorption-desorption experiments of three heavy metal ions (i.e., lead, copper, cadmium) in silty soil were carried out at different temperatures, and the microscopic characteristics of silty soil loaded with the three heavy metal ions were analyzed. A one-dimensional soil column was used to discuss the influences of heavy metal ion types and concentrations on the soil moisture distribution and the migration level of different heavy metal ions, especially during the dynamic change process from an unsaturated state to a saturated state. Studies show that the adsorption of heavy metal ions onto silty soil is closely related to the mineral composition and functional groups in silty soil. In addition to physical adsorption, the adsorption of heavy metal ions is closely related to the hydrolysis reaction of mineral components such as kaolinite, calcite, dolomite, plagioclase and quartz. Under constant temperature, the types and concentrations of heavy metal ions play an important role in the moisture migration of unsaturated soil. In the presence of heavy metal ions, the penetration of lead ions is the greatest, followed by copper ions and then cadmium ions. The greater the ion concentration is, the stronger the penetration of heavy metal ions in silty soils.