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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. [ABSTRACT FROM AUTHOR]

The soil‒water characteristic curve (SWCC) defines the relationship between the amount of water in soil and soil suction. The SWCC is commonly used to estimate the hydraulic conductivity function (HCF) and the shear strength function (SSF). Therefore, an accurate determination of the SWCC is crucial for implementing the principles of unsaturated soil mechanics. The SWCC is commonly determined from a limited number of experimental data because SWCC measurements are time-consuming and costly. As a result, the minimum number of required soil specimens is crucial for a SWCC test when considering the accuracy of the determined SWCC and the experimental expenses. In this study, both engineered from sand and kaolin mixtures and residual soils from Bukit Timah Formation in Singapore are selected to prepare soil specimens for SWCC measurements. The SWCCs obtained from the specimens with engineered soil are consistent, while those from specimens with residual soil are slightly scattered. This indicates that one specimen is sufficient to determine the SWCC for engineered soil samples, while a minimum of two specimens should be prepared for the determination of SWCC for residual soil samples from Bukit Timah Formation. [ABSTRACT FROM AUTHOR]

Weathered rock (especially granite) slopes are prone to failure under the action of rainfall, making it necessary to study the response of weathered rock slope to rainfall infiltration for landslide prevention. In this study, a series of model tests of weathered rock slope under different conditions were conducted. The matric suction, volumetric water content, earth pressure and deformation of slope were monitored in real time during rainfall. The response of the slope to rainfall infiltration, failure process and failure mode of slope under different conditions were analyzed, and the early warning criterion for the failure of weathered rock slope caused by rainfall was studied. The results show that the slope deformation evolution process under rainfall condition was closely related to the dissipation of matric suction. When the distribution of the matrix suction (or water content) of slope met the condition that the resistance to sliding of the slip-mass was overcome, the displacement increased sharply and landslide occurred. Three factors including rainfall process, lithologic condition and excavation condition significantly affect the response of weathered rock slope to rainfall. It can be found from the test results under different conditions that compared with intermittent rainfall condition, the rainfall intensity and infiltration depth were smaller when the slope entering accelerated deformation stage under the condition of incremental rainfall. The accumulated rainfall when weathered clastic landslide occurring was greater than that of weathered granite, which results in greater disaster risk. The excavation angle and moisture distribution of a slope were the main factors affecting the stability of a slope. In addition, the evolution processes and critical displacement velocities of slopes were studied by combining the deformation curves and matrix suction curves, which can be used as reference for early warning of rainfall-induced weathered rock landslide. [ABSTRACT FROM AUTHOR]

Unsaturated soils with bimodal pore structures, such as many residual and colluvial soils, are widespread in nature. Bimodal pore structures can noticeably influence their soil–water retention behaviour. Estimating the bimodal soil–water retention curve (SWRC) accurately has become critical in both theoretical research and engineering practice. In this paper, a novel equation to simulate the bimodal SWRC of unsaturated soils is proposed. The proposed bimodal SWRC equation not only provides higher simulation accuracy for bimodal SWRCs compared to other equations, but it also shows good agreement with experimental data from different types of soils. Moreover, the relationships between bimodal SWRC variables (i.e., air entry value, inflection point, and slopes at transition zone) and the best fitting parameters are presented. Finally, a practical approach is developed to estimate the bimodal relative permeability of unsaturated soils based on the proposed bimodal SWRC equation. The results are convincingly demonstrated that there is good agreement between the predicted and measured relative permeability coefficients of unsaturated soils in the literature. [ABSTRACT FROM AUTHOR]

This study investigates experimentally the water retention behavior of granular soils from saturation to oven-dry state. The soil–water retention curve (SWRC) tests were conducted on a well-graded sand with clay using tensiometer and chilled-mirror hygrometer techniques. The soil samples were statically compacted at various water contents to different initial densities. The results showed that individual linear segments in the log–log graph could characterize the desorption process of capillary and adsorption water. A novel water retention model in a simple mathematical form was developed by conceptualizing the total water content as the sum of the suction-dependent capillary and adsorption components. The model parameters possess an unambiguous physical meaning. They can be easily calibrated based on the graphical properties of the test data using simple linear regression, which is a significant advantage over conventional SWRC models. The model was validated using the water retention data of the tested soil in this study and the available data of granular soils in the literature. The reproduced curves agree well with the experimental results. This study also analyzed the influence of compaction water content, initial density, and clay content on the capillary and adsorption components of the water retention curve. Additionally, the proposed framework provides a quick approximation method for the adsorption capacity, which plays an essential role in assessing the effective stress and the simulation of liquid film flow in unsaturated granular soils. [ABSTRACT FROM AUTHOR]

Torrential rainfall is one of the significant factors contributing to shallow slope failures. This study discusses the effect of the different filter gabion sizes against slope instability due to torrential rainfall numerically. The experimental investigation of effects of different filter gabion sizes was extensively investigated. The investigations were carried out in a two-dimensional domain using the saturated–unsaturated consolidation analysis method with an elastoplastic model for unsaturated soils considering two suction effects. Four different sizes of filter gabion were used in this investigation. The results of numerical simulations of slope model tests showed that, as rainwater accumulated at the slope toe, the pore water pressures (PWPs) near the slope toe increased to be positive or larger than the surface soil’s air entry PWP. The phreatic surface that appeared on the slope surface as the positive PWPs increased with the elapsed time. In the simulations, large displacement, considered surface failure, started once the phreatic surface reached the slope surface. The simulated phreatic surface appearance time on the slope surface extended as the filter gabion size became larger. Nevertheless, the results showed that the applied analysis method is powerful and reliable for simulating slope failure behaviours and their proper countermeasures under torrential rainfall. [ABSTRACT FROM AUTHOR]

Unsaturated soils are the major component of both natural and artificial earth structures, and they exhibit less predictable behavior than saturated soils. Presently, the world is experiencing pronounced impacts from climate change. Sudden heavy rainfalls and droughts both result in fluctuating soil moisture levels, meaning that soil responds differently to infrastructure loads. Accordingly, a better understanding is needed of failure causes in unsaturated soils. This research was conducted to investigate the coupled behavior of unsaturated soil with varying degrees of compaction and moisture change. Samples were prepared at 81% and 88% degrees of compaction with moisture content ranging from 10 to 25% on both sides of optimum moisture content for silty soil. Different parameters such as suction, porewater pressure, and deformation were carefully measured at every stage of the triaxial test, from sample placing to the shearing phase. The results show that there is more compressive soil behavior when there is a lower degree of compaction, i.e., 81%, along with moisture content of 15–25%. Where there is a higher degree of compaction at 88%, dilative behavior is more evident, which changes to compressive behavior as the moisture content increases. Any change in moisture content (increase or decrease) during the lifecycle of any earthen structure necessitates a long time to stabilize its suction value (decrease or increase) if it compacted to a degree that still exhibits a compressive response. This slow recovery of suction, specifically from the wetting to the drying cycle, is not favorable for soil stability upon loading. [ABSTRACT FROM AUTHOR]

The physical meaning of the neutral stress and effective stress for soils is still unclear, which leads to the neutral stress for unsaturated soils being totally ignored and increasingly complicated expressions for effective stress. To solve these problems, we establish an extended three-phase physical model for unsaturated soils, including capillary water, pore air, and generalized soil skeleton (GSS) and then derive a generalized Terzaghi's effective stress equation, stating that the effective stress is equal to total stress minus neutral stress. In our equation, the neutral stress consists of three components, i.e. the homogenized pore fluid pressure, the stress acting on the cross sections of soil particles, and the stress acting on the contacts between particles. The mechanical effects of the neutral stress can be appreciable, especially in unsaturated clays at a relatively low saturation. The effective stress is found to be the stress that is transmitted through GSS. The local stress, induced by physicochemical forces, cementation, and surface tension, is not transmitted through GSS, and thus, it should not be added into effective stress equation. The mechanical effects of the effective stress are controlled by the mechanical parameters of GSS expressed as a function of suction besides the effective stress itself. Integrating the mechanical effects of neutral stress and effective stress, a general framework is proposed for describing the mechanical behaviour of unsaturated soils. Under the framework, the proposed shear strength equation is in very good agreement with the experiment data reported in the literature. [ABSTRACT FROM AUTHOR]

Piles supporting large structures are often subjected to cyclic lateral loads due to natural phenomena, including earthquakes, winds, and waves. Such loads are main causes of progressive deterioration in the stiffness and reduce the lateral capacity of piles. However, the effects of unsaturated soil conditions on the lateral cyclic response of piles are not yet fully understood, and the p–y curves used in engineering practice are merely based on the assumption of full saturation or complete dry conditions. This study is aimed to investigate the pile performance under unsaturated soil conditions by performing monotonic, cyclic, and post-cyclic loading tests on piles installed in sand with a varying water table. A loading system was designed and constructed to carry out different types of cyclic loadings. It was observed that the lateral capacity of the pile is influenced by the average suction stress along the pile which increases with the depth of the water table. During the cyclic loading, gap formation is noticed around the pile head for tests conducted in unsaturated conditions, which results in significant stiffness degradation compared to the saturated state. However, post-cyclic loading tests showed that the ultimate lateral capacity of the pile is not affected by the cyclic loading history. Finally, a modified p–y curve is proposed for the piles embedded in unsaturated sandy soils, and a comparison of its performance with the observed results is promising. [ABSTRACT FROM AUTHOR]

When unsaturated soils are affected by thermal radiation such as sunlight, geothermal heat, nuclear waste, and biochemical reactions, the soil temperature will increase and accelerate soil moisture migration, resulting in soil deformation. Therefore, in this paper, by extending the SFG model of the unified yield surface to consider the effect of temperature change on the unified yield surface, a yield surface constitutive model which can simultaneously reflect temperature-suction-stress is proposed. In order to verify the applicability of the model, the triaxial test of Jiangxi laterite at different temperatures is carried out to determine the calculation parameters of the model, and the fitting results of the model are compared with the experimental results, and the model is fitted and analyzed by referring to the test data of remolded clay used by Uchaipichat. The results show that the model can well reflect the stress-strain characteristics of soil during compression rebound, dehumidification and shear at different temperatures, which provides a theoretical support for predicting and solving the influence of temperature change on the stress deformation and shear strength of unsaturated soil in the corresponding engineering environment in the future, thus further enriching the constitutive theory of unsaturated soil under the influence of temperature. [ABSTRACT FROM AUTHOR]

Thermal conductivity is a key parameter governing heat transfer in rocks and soils with applications to geothermal systems and groundwater studies. Its accurate measurement is crucial to understand energy exchange in the Earth's subsurface. This study explores the application of the percolation-based effective-medium approximation (P-EMA) model to a broad range of soil types using a database including 158 soil samples. The P-EMA model for soil thermal conductivity, introduced by Ghanbarian and Daigle, is validated through robust optimization of its parameters and by comparing with the laboratory measurements where we find an excellent match between the theory and the experiments. A regression-based model is developed to estimate the P-EMA model parameters directly from other soil properties, such as sand, clay, bulk density, and thermal conductivities at completely dry and full saturation. The proposed regression-based relationships are evaluated using unseen data from two databases: one from Kansas containing 19 soil samples and another from Canada containing 40 soil samples. These regression-based relationships offer an approximation for the P-EMA model parameters, providing a practical approach to estimate the thermal conductivity of soils. Furthermore, a curve-clustering approach is proposed to classify soil thermal conductivity curves based on their similarities, providing insights into the heterogeneity of samples. We find seven clusters for each of which the average P-EMA model parameters are reported. The classification and regression models generally extend the seamless applicability of the P-EMA model. [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]

Limited experimental and theoretical research has been conducted on the shear strength of unsaturated soils over a wide suction range. This study aimed to investigate the shear strength characteristics of a weakly expansive soil over a wide suction range (0.05–367 MPa) through a series of triaxial tests. The results of the experiments demonstrate that, under the same net confining stress, the shear strength increases with the suction over the entire suction range. Furthermore, an increase in suction leads to a change in the shape of the stress–strain curve, from strain-hardening to strain-softening. The effect of net confining stress on the stress–strain curve and volumetric strain-axial strain curve varies with suction. An additional analysis indicates that the cohesions and angles of internal friction acquired through net stress differ from those obtained through effective stress. The angles of internal friction at different suctions remain the same on the shear strength-net normal stress (τf−(σ−ua)) plane, while the cohesions increase exponentially with increasing suction. Based on these test results, a novel equation for the shear strength of unsaturated soil over a wide suction range is proposed by incorporating suction-dependent cohesion. The results of the study show excellent agreement between the predicted and measured shear strength results over a wide suction range, and its superior accuracy is demonstrated through comparisons with several existing models in the literature. [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]

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]

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]

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]

Utilizing the unsaturated porous elastic media theory, the study investigates the scattering of plane P-waves by a single-layer lined tunnel within an unsaturated half-space. The analysis employs the Fourier–Bessel series expansion for wave functions for this purpose. Through numerical examples, this study analyzes how physical and mechanical parameters like incident wave frequency, angle, saturation, and burial depth affect the surface displacement amplitude in a single-layer lined tunnel within an unsaturated soil half-space under P-wave incidence. Results indicate that saturation significantly influences the surface displacement amplitude. The maximum surface displacement amplitude in the single-layer lined tunnel at low saturation levels exceeds that observed at high soil saturation. The surface displacement amplitude inside the single-layer lined tunnel and on its left side varies sharply and remains high across different incident frequencies. Conversely, the surface displacement amplitude on the right side of the single-layer lined tunnel exhibits a relatively gentle change and is lower. This variation becomes more pronounced with increasing frequency. At a low wave frequency, the displacement amplitude of the single-layer lined tunnel decreases with the increase of the burial depth. When the incident wave frequency is high, the displacement amplitude of the single-layer lined tunnel exhibits a marked change with burial depth increment. [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]

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]

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]

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]

In cold regions, the environment dynamics lead to variations of soil temperature, water content, and deformation, which are characterized by highly coupled physical interplay. The hydraulic and thermal properties of unsaturated soils are highly nonlinear, which is further complicated when subjected to freezing. This paper presents a comprehensive multiphysics coupling model to evaluate these complex processes. The model considers the behaviors of unsaturated frozen soils. It accounts for the influences of meteorological, geothermal, and hydrological factors. The model is validated through two pavement case studies using Long-Term Pavement Performance (LTPP) road section data. The first case analysis is performed for a pavement section in Vermont, and the simulation lasted for 30 days during a non-freezing season on an hourly basis. The results validated the performance of the model considering unsaturated soil behaviors. The second case study is based on a daily analysis of a pavement section in South Dakota over a freezing–thawing cycle over 194 days. The results validated the model in considering the frozen unsaturated soil behaviors. Both case studies demonstrate the performance of this comprehensive model in quantifying the spatial and temporal variations of soil temperature and water content in response to environmental stressors. The capability of the model in accurately predicting the responses of pavement to the meteorological factors unleashes the potential of this model to assess the effects of climate and climate change on cold region pavement, as well as other types of geo-structures. [ABSTRACT FROM AUTHOR]

A fully-automated unsaturated triaxial device with continuous measurement of all variables is developed to investigate the hydromechanical behavior of unsaturated soils under different stress/strain paths, especially under anisotropic stress states. An experimental program including nine wetting paths was carried out to study the effect of initial shear stress on the hydromechanical behavior of unsaturated specimens of Gorgan loess, corroborating the functionality of the developed device. The results vividly show the important role of initial shear stress on the water absorption and deformation behavior of the reconstituted loessial soil under different mean net stresses. The application of initial shear stress on the tested collapsible soil specimens resulted in a higher collapse potential and larger volume decrease (i.e., up to a maximum increase of 4.6% in the volumetric strain) when the specimens were subjected to wetting, compared to the specimens wetted under an isotropic stress state with the same initial mean net stresses. Furthermore, in the case of the specimens wetted under the highest level of initial shear stress, at suctions lower than 15 kPa corresponding to the axial strains of about 30%, the critical state condition was achieved. Visual inspections of the failed specimens showed a bulging-type failure. Based on the effective stress theory, the analyzed results illustrated that for the same levels of initial mean effective stress, the initial shear stress caused a slight increase in suction stress values, except for the tests with the lowest level of initial mean effective stress in which this effect was negligible. [ABSTRACT FROM AUTHOR]

Aims: This study experimentally investigated the short-term (about 6 months) effects of roots of Cynodon dactylon on the gas permeability and gas diffusion coefficient of soils with different degrees of compaction. Methods: Compacted soil planted with Cynodon dactylon were left outdoors for about 6 months for plant growth. The measurements of rooted and bare soils included gas permeability, gas diffusion coefficient, root characteristics and soil microstructure. The relative effects of different root characteristic parameters on gas permeability and gas diffusion coefficient were compared through grey relational analysis. Results: The root volume ratio had a greater effect on gas permeability and gas diffusion coefficient, compared with root area index, root area ratio, root length density, and root biomass ratio. When the degree of compaction ≥ 85% (porosity ≤ 0.41, bulk density ≥ 1.56 g cm−3), the macro-pores at the root–soil interface increased gas permeability and gas diffusion coefficient, while negligible effects of roots on gas movement existed under degree of compaction of 80%. The increase in gas permeability by roots was more significant than that in gas diffusion coefficient. However, roots' increase of gas movement generally decreased at higher root volume ratio due to roots-occupied soil pores. Finally, gas permeability and gas diffusion coefficient of rooted soil were well predicted by newly-developed empirical models considering the effect of root volume ratio. Conclusions: Macro-pores at the root–soil interface tended to increase gas permeability and gas diffusion coefficient of soil with a degree of compaction ≥ 85%, while it is the opposite for root volume ratio. [ABSTRACT FROM AUTHOR]

Variations in the hydraulic and mechanical behaviour of soils caused by rainfall infiltration are major causes of slope failure. In previous studies, hydraulic hysteresis was commonly ignored to simplify seepage analysis, but this can cause an inaccurate representation of the hydromechanical behaviour of soils and the stability of the associated slopes. In the present study, the effects of hysteretic soil water characteristic curves (SWCC) on the hydromechanical behaviour and slope stability associated with rainfall were assessed, and the results were compared with those obtained using the non-hysteretic SWCC. Hysteresis associated with the capillary and air entrapment effects was considered, and these were incorporated into the analysis of the hydromechanical framework. The hydraulic response and slope stability were analyzed using numerical modelling. Effects of the hydraulic hysteresis on the hydromechanical behaviour within the slope under transient rainfall conditions were then explored. The infiltration fluxes linked to the non-hysteresis and hysteresis conditions differ, impacting the water flow regime and slope stability. Hysteresis involving higher air entrapment shortens the failure time compared to the non-hysteresis condition. The present study demonstrates that hydraulic hysteresis involving air entrapment is important for an adequate assessment of the hydromechanical response of silty soil and the stability of the associated slope. [ABSTRACT FROM AUTHOR]

This article primarily investigates the effect of transient flow and seismic loadings on the active and passive earth pressures developed in retained unsaturated backfills. The classical Rankine’s earth pressure theory for saturated soils is duly modified to account for the dynamic loadings and the partial saturation state of the soil under transient infiltration. The influence of the matric suction on the water content and flow rate is apprehended by incorporating a suitable soil water characteristics curve and a hydraulic conductivity function. The suction stress-based effective stress formulation is adopted for the purpose of analysis. The one-dimensional Richards' equation models the transient water flow in the vadose zone. The seismic loading is idealized as a statically applied inertial force by using the pseudo-static method. A comprehensive parametric study is carried out to investigate the impact of soil strength properties, hydromechanical parameters, seismic loading conditions, and flow behaviour (rate and duration) of the transient infiltration on the two failure states -- active and passive. The tension crack depths in the vadose zone under transient flow conditions are also calculated. [ABSTRACT FROM AUTHOR]

Soil shear strength is the most fundamental property when designing structures in the ground and should be carefully assessed and understood. Several empirical models were introduced to predict the shear strength of unsaturated soils. However, there is uncertainty regarding the applicability and sensitivity of these prediction models. This paper presents a comprehensive verification study to assess the reliability and validity of the existing theoretical models. The results obtained from the prediction models are compared to measured data using thirty experimental data sets. A performance classification program is also conducted to assess the suitability of the analytical models for different soil types as well as over a wide range of matric suctions, saturation degrees, soil densities, soil plasticity, and clay activity. The impact of each single parameter is clarified by the microstructure studies, which also provides insight into the mechanics of unsaturated soils. The results indicated that the applicability of models is more appropriate for sandy soils rather than for clayey ones. The performance of shear strength models tends to decrease with an increase in matric suction, initial density, plasticity index, and clay activity. It is, therefore, recommended that the shear strength estimation models should be carefully selected depending on the soil type and properties. Besides, the analysed results pointed out that the choice to assume the factor χ in the equation of Bishop equals the saturation degree is only suitable for medium-dense soils with low matric suction. This assumption is particularly not effective for clayey soils, or dense soils with high matric suction. [ABSTRACT FROM AUTHOR]

The frame beam anchor plate (FBAP) reinforced slope has been popularized and applied in some fill slope projects. Nevertheless, the existing design method ignores the influence of earthquake action and the suction effect of unsaturated soils. The stability of unsaturated soil slopes reinforced with FBAPs under an earthquake is analyzed based on the upper bound theorem of limit analysis and pseudo-dynamic method to solve the above problems. The influence of the suction effect on the effective weight and strength of unsaturated soils under one-dimensional steady seepage conditions was considered in the derivation of the energy balance equation. A simplified method based on the volume integral of the rotating body is used to calculate the external work rate. Two possible failure modes of anchorage structures are considered when solving internal energy dissipation. Results show that the influence of suction and seepage conditions on slope stability decreases with the increasing soil pore size distribution parameter n and saturated hydraulic conductivity ks. Also, the stability of the slopes is significantly improved with the increase of total rows of anchor plates. Likewise, the stability of slopes decreases with the increase in the horizontal seismic coefficient kh and amplification coefficient fa. [ABSTRACT FROM AUTHOR]

The tensile strength of unsaturated soils is a fundamental property in various geotechnical designs. Reliable estimation of the tensile strength of unsaturated soils, in particular fine-grained soils, is required in both theoretical research and engineering practice. Although several tensile strength models have been proposed in the literature, an overestimation may occur over a wide suction range, when applying them in the modelling of tensile strength of fine-grained soils. In this paper, the tensile strength of an unsaturated lean clay has been measured over a wide range of void ratio and water content by employing the Brazilian tensile strength test. A critical degree of saturation can be observed for specimens with different void ratios, at which the soil tensile strength reaches the peak. In addition, a predictive tensile strength model considering the effect of initial void ratio has been subsequently proposed for both coarse-grained and fine-grained unsaturated soils based on the interaction mechanisms between the adsorptive and capillary soil water. Finally, the proposed model has been demonstrated to be capable of modelling the tensile strength characteristic curve of various soil types ranging from clean sands to silty and clayey soils. [ABSTRACT FROM AUTHOR]

Plant microbial fuel cell (PMFC) newly emerges as a sustainable technology in green infrastructures such as green roofs, reactive barriers, and environmental biosensors. PMFCs generate bioelectricity driven by microbial redox reactions in the rhizosphere. However, the interactions between the bioelectricity and soil–water characteristics remain unknown, and PMFCs are vulnerable to drought stress. Therefore, this study aims to reveal the coupled bio-hydrological behaviors of PMFCs and propose biochar amendment on PMFCs for improving bioelectricity generation under drought conditions. Biochar-aided PMFCs were prepared by growing green-roof vegetation, Hydrocotyle vulgaris, on sandy lean clay with biochar at a mass ratio of 0, 5, and 10%. Bioelectricity (i.e., electrical potential and current) and unsaturated soil properties (i.e., suction and water content) were monitored simultaneously. Results showed that biochar increased the electrical power output of PMFCs by up to 30 times in unsaturated conditions. This may be because biochar-enhanced catalytic activities in redox reactions decreased soil electrical resistance and improved water retention. The bioelectricity was highly correlated with the suction, as the bioelectrical potential and current decreased by 90% with increasing suction. It was also found that the bioelectrical potential dropped rapidly by 67.6–87.2% when suctions were larger than the air entry values. This might be because air invasion led to the discontinuity of the liquid phase, hindering the ion transport of microbial redox reactions. The study implies that bioelectricity could be applied for field monitoring of soil–water characteristics, and biochar addition would enhance the drought resistance of PMFCs. [ABSTRACT FROM AUTHOR]

Currently, climate change has several negative impacts on the worldwide environment. One of them is land sliding due to rainfall precipitation. Commonly, mountainous areas have a high possibility of having such consequences. Unsaturated soil characterization is presented in this paper to demonstrate that the shifting of ground occurs at the surfaces of any slopes. The paper presents the simulation analysis on clayey soil slopes under extreme rainfall in Kazakhstan. The different slope heights and angles are selected to perform seepage and stability analysis in GeoStudio software. The results show that the slope is prone to failure due to the lower safety factor. It means the driving force is increasing during rainfall due to the increase in pore water pressures. As a result, the shear strength of the soil decrease. According to the results of the seepage analysis, the pore-water pressure has increased to almost 80 kPa at the mid-slope for each simulation. It leads to a decrease in suction and shear strength. The change of a factor of safety for the gentlest slope with 27 degrees angle is the lowest for 10 m slope height and the highest for 30 m slope height, whereas the change of safety factor for a slope with 45 degrees angle (9%) is almost the same for all slope heights. In other words, the factor of safety tends to reduce in all simulation cases, which confirms the loss of strength of soil due to a large amount of infiltration into the ground. [ABSTRACT FROM AUTHOR]

The water retention properties of soils present in formation layers of roads and railways continuously vary due to repeated traffic loads and periodic rainfall events. This is important because the accumulated deformation and resilient modulus of such soils under cyclic loading are profoundly affected by water retention properties. This paper discusses the cyclic and water retention response of a clayey sand subjected to repetitive cyclic loading and wetting stages. The results show that the accumulated permanent strains and resilient modulus of the tested soil are dependent on the suction level while the main wetting water retention curve of the soil dictates the variation of the suction measured during cyclic loading and wetting. This bounding effect of the water retention curve is found to be dependent on the void ratio where the suction can even increase due to the accumulation of strains under cyclic loading while the degree of saturation increases. This contradicts the suction reduction typically observed with an increase in the degree of saturation. A void ratio dependent water retention model is developed accounting for the observed bounding effect and employed to predict the measured suction during repetitive cyclic loading and wetting. The suction values predicted by the void ratio dependent water retention model are in good agreement with the experimental data. The predicted suctions are then used in semi-empirical formulations to obtain the accumulated permanent strains and resilient modulus. A better correlation between model predictions and experimental data is achieved where the suction values predicted by the void ratio dependent water retention model are used. The results imply that predictive frameworks proposed for the cyclic behaviour of road and railway formation layers require water retention counterparts that incorporate the bounding effect of void ratio on soil water retention curves. [ABSTRACT FROM AUTHOR]

The lateral response of piles is governed by the soil–pile interaction in the shallower layer of surrounding soil, which may be above the water level and thus is unsaturated. There is no comprehensive analytical model for the soil–pile interaction under lateral loads considering both linear and nonlinear behaviors in unsaturated soils. In this study, an analytical solution is proposed to simulate the linear and nonlinear load–displacement variations for laterally loaded piles supported by unsaturated soils. Analytical formulations are developed to determine the stiffness per unit pile length considering the influence of soil suction on the soil modulus of elasticity. Since the current p–y curves available in the literature are unable to adequately address the unsaturated soil reaction to piles, analytical p–y relations for three types of soil are developed regarding the soil suction parameter. In order to expand the scope of application of presented method, the developed solution is extended to step-tapered piles and to piles subjected to simultaneous horizontal and vertical loads. The developed solutions are validated with the results obtained from laterally loaded pile tests reported in the literature. Parametric studies evaluated the effects of pile length and cross-section configuration and applied vertical load on the pile lateral response under various soil unsaturation conditions. The results revealed that the stiffness of the pile–soil system and its load-deformation behavior are improved significantly as the soil suction pressure increases. Furthermore, the lateral pile displacement in unsaturated soil decreases as the pile length and diameter of the upper pile portion increase, and by considering the applied vertical load. Considering the positive effect of soil suction on reducing the lateral response of piles in unsaturated soil (in arid areas) in design may help shorten the pile length or reduce its diameter while achieving a desired force–deflection demand. [ABSTRACT FROM AUTHOR]

For unsaturated soils, Terzaghi's effective stress σ = σ tot - u has been generalized by Bishop to the form σ B = σ tot - χ u . Factor χ , for example χ (S) ≈ S , takes into account the degree of saturation S. However, σ B is unable to characterize strength and deformation of soil unless applied with suction. A new stress σ E = σ tot - χ E u with χ E (S , n) is proposed. It is likewise insufficient if applied without suction, but it has (at least) a clear physical meaning: σ E represents contact forces between grains in the static equilibrium in the same manner as the effective stress does in saturated soils. All grains must be entirely surrounded by free or capillary water. [ABSTRACT FROM AUTHOR]

An analytical study of the problem of water infiltration into a homogeneous unsaturated soil showed that, in the case of periodical water recharge through the soil surface, the character of the flow will tend to uniform with the depth. The stabilization of the flow was found to be due to the effect of two factors: capillary dissipation and nonlinearity. The role of each factor was studied by constructing appropriate exact solutions. An estimate was proposed for the depth at which flow variations become insignificant. This estimate takes into account the joint effect of both these factors. An explicit expression for it contains the hydraulic characteristics of the soil and the main characteristics of the surface recharge regime. The pumping effect was also studied and it was showed that, at some assumptions regarding the soil hydraulic characteristics, it manifests itself in that the time-averaged water content in the top soil layers is less than that at greater depth. [ABSTRACT FROM AUTHOR]

Shallow landslides in Souk Ahras region, NE Algeria, occur usually after prolonged rainfall events. Three localities which are Zaarouria, Hammam Tassa, and Mechroha were chosen to study these landslides and the conditions of their occurrences. They have been observed to affect mainly agricultural lands, main supplies, and the road network. This paper aims to find the relationship between the rainfall, the soil engineering properties, the geology, and the geomorphology. A number of field trips were organized to the study areas where landslide masses were described and mapped as well as some field measurement such as natural moisture content and sampling. In the laboratory, we establish gain size distribution, Atterberg limits, density, and effective cohesion and internal friction. Then we established the unsaturated soil property functions such as the soil water characteristic curve (SWCC) and the hydraulic function. The stability computation was undertaken using, GeoStudio software 2020, a coupled analysis where the Seep/W simulates the seepage and the Slope/W for the safety factor. The results show that the sector study containing: silty sand (SM), well graded sand with silt and gravel (SW-SM), and clayey sand with Gravel (SC) while hydraulic conductivity varies between 4.5. 10−6 for 4.10−5 and 10−3 m/s. The factor of safety varies between 0.8, 1.16, and 0.8. In conclusion, our study confirms the field observations as shallow landslides have been numerous in mars 2019 when rainfall reaches 110 mm. Moreover, high permeability soils, in Mechrouha, show a more dramatic decrease in the factor of safety as the 100 = -mm rainfall amount is reached while it decreases gradually for the other two less permeable soils of Zaarouria and Hammam Tassa. [ABSTRACT FROM AUTHOR]

The coexistence of air and water as a mixture in void spaces in unsaturated soils, makes its mechanical behaviour relatively complex and difficult to be addressed by classical saturated soil mechanics principles. In addition, many engineering problems encountered in practical situations had some part to deal with unsaturated soils and therefore the clear understanding of various behavioural patterns of unsaturated soils is crucial. To date, a large number of attempts are reported in evaluating the mechanical behaviour of unsaturated soils in different stress spaces. The present study evaluates the deviatoric behaviour of compacted unsaturated soils in deviator stress–specific water volume–mean net stress ( q , v w , p ) space. The effect of moisture content, confinement and the stress history on the behaviour of compacted unsaturated kaolin subjected to triaxial compression was assessed and the results showed that there exists a critical state surface for compacted unsaturated soils in q - v w - p space. [ABSTRACT FROM AUTHOR]

Unsaturated permeabilities of six different kaolin-sand mixtures named as 100K0S, 90K10S, 80K20S, 50K50S, 20K80S, and 10K90S were directly measured using a modified flexible wall triaxial permeameter system. 90K10S means that the soil mixture contains 90% kaolin and 10% sand by dry mass. Soil–water characteristic curves (SWCC) of the kaolin-sand soil mixtures were also measured for a wide range of suctions using a Tempe pressure cell, 5-bar pressure plate, 15-bar pressure plate, and saturated salt solutions. The unsaturated permeabilities of the soil mixtures were also estimated using ten different theoretical models using (1) the measured SWCC data over a complete suction range and (2) the measured SWCC data up to 100 kPa suction in combination with the estimated SWCC data at higher suction values. The directly measured unsaturated permeability of the soil mixtures was used to validate the estimated values of unsaturated permeability. The results showed that the unsaturated permeability estimation models could reasonably fit the directly measured unsaturated permeability data when both the data from the complete measurement of SWCC and the measured SWCC data up to 100 kPa suction in combination with the estimated SWCC data at higher suction values were used. [ABSTRACT FROM AUTHOR]

This study proposes a new soil-water characteristic model to predict the variation of volumetric water content with the matric suction pressure for unsaturated soil conditions. The proposed model has been built utilizing the nondestructive electrical properties of the unsaturated soil. In addition, nine previous models have been collected and used in parallel with the new model to predict the soil-water characteristic relationships for four sets of different experimental data. The study has clearly revealed that the new proposed model agreed very well with the experimental data with R2 values of 0.90, 0.93, 0.95, and 0.92 for the four studied cases respectively. However, none of the collected nine models had the power of the new proposed model in terms of predicting the experimental data for all the studied cases. Furthermore, it was concluded that the new model parameters have been correlated strongly with the final volumetric water content. [ABSTRACT FROM AUTHOR]

This research presents a modified numerical simulation approach for predicting approximate values of unsaturated soil parameters with low water content. In order to understand how unsaturated soils behave and to create the soil–water characteristic curve, the suggested model attempts to predict the following parameters. First, the relationship between the water content and the matric suction in terms of particle separation distance. Secondly, the relationship between the effective stress parameter χ and the filling angle θ when the separation distance between soil particles is taken into account. Thirdly, the relationship between suction stress and filling angle θ , in terms of particle separation distance. Fourthly, the effect of particle separation distance on the curve of tensile strength in terms of the degree of saturation. The updated model assumes that all the particles are equally dispersed spheres of the same size. In this study, the updated model is exclusively applied to simple cubic packing order with zero contact angle. The model may also be used to predict matric suction, effective stress parameter, suction stress, and tensile strength while combining experimentally determined soil properties. This removes the requirement for sophisticated measuring devices or specific test procedures to illustrate how the separation distance affects the behavior of unsaturated soils. Compared to the experimental data, our model has shown positive results. In this paper, all curves have been programmed using MATLAB. [ABSTRACT FROM AUTHOR]

Numerous important earthen heritage sites in northwestern China have survived until today because of the arid and semi-arid climate. However, most of them suffer from various types and degrees of deterioration, with many questions not answered. Scaling off is one of the main types of deterioration widely observed at the Site of Yar City. To clarify the underlying mechanisms of cracked surface crust formation, previous experimental achievements are reviewed in the framework of unsaturated soil mechanics in this paper. A series of laboratory tests on the properties of local soil during desiccation, including water retention, volumetric shrinkage, cracking and tensile strength, are presented and analyzed, with a particular emphasis on salinity effect. Results show that suction is the key factor controlling the soil behavior. With the decrease in water content, all suction components increased gradually. The presence of NaCl led to a large increase in total suction, but a negligible change in matric suction. The soil shrinkage characteristic curve, which can be divided into three zones, was not affected by NaCl. The suction-loading curve indicates that the change in void ratio was governed by matric suction. In addition, most of the drying shrinkage of soil took place in saturated and near-saturated conditions. According to the quantitative analysis of final crack patterns, the highly fragmented surface morphology tended to be induced in thinner, less salinized soil specimens. The soil tensile strength also increased during drying, which was further enhanced by the cementation of salt crystals between particles. These preliminary results can provide some insights in understanding the on-site deterioration of earthen heritage sites. [ABSTRACT FROM AUTHOR]

Electro-osmotic consolidation is taken as a valid and practical approach for soft ground improvement, and it is of vital significance to study the consolidation behaviour of electro-osmotic consolidation for the application purpose. This paper presents an analytical solution for two-dimensional (2D) electro-osmosis-enhanced preloading consolidation of unsaturated soil. The governing equations are first expanded using the eigenfunction expansion method in the y-direction, and then, the auxiliary function is constructed to rearrange the boundary conditions for mathematical convenience. The coupled partial differential equations are subsequently transformed into a system of ordinary differential equations (ODEs) containing only time t by adopting the eigenfunction expansion method in the x-direction. The exact solution is finally found by using the Laplace transform techniques to solve the ODEs system. Working example conducts a series of numerical simulations to validate the newly proposed solutions, and verification results demonstrate excellent agreement. Using the proposed solutions, this paper conducts parametric analyses to study the influences of coupled electro-osmosis and preloading on the consolidation behaviour. [ABSTRACT FROM AUTHOR]

Purpose: In the ground vibration control, most of the previous studies focused on the vibration isolation performance of the wave impeding block (WIB) in elastic foundation or saturated soil foundation, while there are few reports on the vibration isolation performance of the WIB in unsaturated soil foundation which is more universal in nature. Therefore, we study the propagation characteristics of S-wave passing through an elastic wave impeding block in the unsaturated soil. Methods: Based on the propagation theory of elastic waves in unsaturated porous medium and single-phase elastic medium, considering that an elastic wave impeding block with a certain thickness is set in the unsaturated soil foundation, and using the potential function and continuous boundary conditions, the analytical solution of the reflected/transmitted amplitude ratio of S-wave passing through the WIB in the unsaturated soil are derived in this paper. The variation of the reflected/transmitted amplitude ratio with the shear modulus and density of the WIB, incident angle and incident frequency is investigated by parametric studies. Conclusion: The results showed that incident angle, the shear modulus and density of the WIB have a significant influence on the vibration isolation performance of the WIB in the unsaturated soil foundation. It is verified that the better vibration isolation performance can be obtained by reasonably controlling the shear modulus and density of the WIB. [ABSTRACT FROM AUTHOR]

The Richards' equation describes the flow phenomenon in unsaturated porous media and is essential to hydrology and environmental science. This study evaluated the numerical stability of two different forms of the Richards' equation. Sensitivity analyses were performed to investigate the control parameters of the equation. The results show that the h-form Richards' equation has better applicability for calculating variable saturation flows than the θ-form Richards' equation. For the h-form Richards' equation, the hydraulic conductivity of the soil in the low-suction range and the specific moisture capacity in the high-suction range primarily influenced the solution. In addition, sensitivity analyses indicated that the saturated hydraulic conductivity, initial condition, and air-entry pressure have a higher sensitivity to the simulation results than the saturated water content, rainfall intensity, and decline rate of hydraulic conductivity. Moreover, their correctness needs to be guaranteed first in numerical simulations. The research findings can provide a helpful reference for improving the reliability of numerical simulations of unsaturated flows. [ABSTRACT FROM AUTHOR]

The present study aims at addressing the stability of homogenous soil slopes by duly considering the unsaturated properties of the soil above the water table. The variational technique which is developed on the framework of the limit equilibrium method is employed to determine the critical factor of safety and the corresponding critical slip surfaces. The unsaturated soil above the water table is modelled by incorporating the suitable soil water characteristics curve and hydraulic conductivity function and on the basis of the suction-stress-based effective stress approach. An extensive parametric study is carried out to understand the combined effect of slope geometry, strength properties, hydromechanical parameters, location of the water table, and the impact of climatic conditions. The flows within the soil are considered unidirectional and are of three types, namely, evaporation (positive), precipitation (negative), and no-flow type (zero flow). Stability charts and slip surfaces are produced to show the effect of fluctuations in the water table and climatic conditions. The computed solutions match quite well with the existing solutions available in the literature. [ABSTRACT FROM AUTHOR]

The mechanical behaviours of unsaturated soils are highly related to the water content and pore water and air distributions. Under the context of climate change, geo-disasters related to soil moisture change attract more and more research attentions. Due to the heterogeneity of soil textures and the complicated morphology of liquid phases, it is crucial to understand the microstructural features of unsaturated soils. This work presents a study based on a miniaturized suction controlled triaxial device which is suitable for micro-CT image analysis. A fine sand is sheared in this device under different suction levels while CT scans are taken at different strain stages. After image 3D reconstruction, image trinarization, label analysis, contact detection and other customized image analysis and calculations, the micro-mechanisms of unsaturated granular soils upon triaxial shearing are investigated. It is observed that the inter-particle contact coordination number is reduced after shearing due to the dilation behaviour and the sample with the highest capillary strength has the highest coordination number. Although there is an initial fabric anisotropy due to gravity and sample compaction, triaxial loading will further enlarge the fabric anisotropy of the solid phase and the solid fabric anisotropy is also associated with shear strength. With the development of shear band, water drains out and the quantity of small-volume liquid clusters in the liquid bridge increases. This shifts the distributions of inter-facial areas. The effective stress tensor is interpreted microscopically based on small RVEs. Based on the CT image analysis, the suction-induced stress component is not an isotropic term and the anisotropy of the water phase is increased with triaxial deformation as well as decrease in degree of saturation when there are more isolated water bridges formed around solid contacts. [ABSTRACT FROM AUTHOR]

An accurate assessment of the tunnel face excavated under rainfalls is commonly desired in the design and construction. The infiltrating rainfall usually needs to pass through unsaturated layers before reaching the water table. During this dynamic process, the response of the soil is complex due to the rainfall intensity and duration, hydraulic properties of soils, and soil geometries. To assess the tunnel face in unsaturated soils under transient flow conditions, an efficient general framework is established in this paper. An analytical suction stress-based formula for one-dimensional transient flow was derived, which is adaptive to express the tempo-spatial profiles of the suction head and suctions stress. A three-dimensional (3D) rotational failure mechanism was established with the discrete spatial technology, allowing the tempo-spatial changed unsaturated effect incorporated into the calculation. Then the proposed framework using the kinematic approach of limit analysis was applied to assess the tunnel face in three hypothetical soils, including the sands, silts, and clays. A numerical simulation was also conducted to validate the established analytical framework. Finally, several design charts of normalized safety factors obtained by the dichotomy and strength reduction method were provided for practical reference. [ABSTRACT FROM AUTHOR]