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AbstractRainfall infiltration is a primary cause of slope failure. Analyzing the entire process of a landslide triggered by rainfall is crucial for the design of infrastructure. However, the complexity associated with simulating large deformations has often hindered previous studies from modeling the entire landslide process subsequent to rainfall infiltration. This study aims to provide a method to simulate the entire process of landslides considering rainfall and more insight into the mechanism of landslides. The discrete element method (DEM) is first applied to model the entire process of shallow landslides triggered by rainfall. The numerical results indicate that the intensity and duration of rainfall infiltration have significant impacts on the slope stability. The particle displacement field, resulting from landslides due to rainfall, corresponds with three distinct stages within the landslide process. The increased rainfall intensity causes the area of the particles within failure mass grows rapidly during the initial stage of the landslide. The closer to the slope surface the faster the particle velocity. The simulations demonstrate that the slope surface transitions from a linear to a concave downward geometry during the landslides. Larger particles display greater displacement and velocity compared to smaller particles. [ABSTRACT FROM AUTHOR]

ABSTRACT Slopes in nature usually present layered characteristics, and its stability is susceptible to rainfall events. Considering that current analytical solutions are only suited to simulate the rainfall infiltration of double‐layered infinite unsaturated slopes, an analytical procedure is hence proposed in this study to tackle the consideration of multiple layers. The variable separation method and transfer matrix method are combined to derive the analytical solution of pore water pressure (PWP) for simulating rainfall infiltration in layered infinite unsaturated slopes. After having validated the proposed model and analytical solutions by comparing with existing literature and numerical simulation, the closed‐form solution of PWP is incorporated into the limit equilibrium for assessing slope stability. A three‐layer slope is selected as an example for further discussion. PWP distribution and factor of safety are calculated, considering the effects of saturated hydraulic conductivity and thickness of the upper layer, intensity of antecedent and subsequent rainfall, and varied soil unit weight along the depth. The slope stability subjected to rainfall effects is consistent with the variation of PWP. The proposed analytical solutions provide a simple and practical avenue for computing PWP distribution and evaluating the stability of multi‐layered slopes under rainfall conditions, which can also serve as a benchmark for numerical solutions. [ABSTRACT FROM AUTHOR]

Periodic wave barriers have been widely used to manipulate elastic waves propagating in saturated and single-phase soil due to their attenuation zone properties. However, it is difficult to promote application of periodic barriers in unsaturated soils due to their complex constitutive relationship. In this study, manipulation of surface waves by periodic in-filled trench barriers in unsaturated soil has been studied based on the periodic theory. The dispersion relations of a periodic structure for surface waves in unsaturated soil are determined. The attenuation mechanism of evanescent surface waves is revealed. Next, the effects of several key parameters of unsaturated soil on the attenuation zones of the periodic in-filled trench barriers are comprehensively discussed. It is found that in a particular range for material parameter, the surface waves are attenuated over the entire frequency range due to the viscosity of fluid. Finally, a periodic in-filled trench barrier is designed according to a field test of ground vibration induced by a train, and its performances in mitigating surface waves propagating in unsaturated and saturated soils are conducted and compared by conducting analysis in time domain. This investigation provides a new insight for manipulating surface waves by periodic barriers. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 1)'. [ABSTRACT FROM AUTHOR]

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]

Accurate 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. Highlights: 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]

Suffusion refers to the loss of small particles in a soil matrix without volume changes, caused by hydrodynamic forces and alternation of pore fluid chemistry. This study investigated the ionic concentration (IC)-induced suffusion of sand–clay mixtures under saturated and unsaturated conditions through laboratory soil-column experiments. The impacts of clay mineralogy and sand-grain size on suffusion were investigated based on the breakthrough curves (BTCs) obtained from the soil-column experiments. In addition, the degree of saturation during the experiments was measured to assess the impact of the saturation state on suffusion in the sand–clay mixtures. The observed BTCs in this study demonstrated that suffusion was more significant under saturated conditions than unsaturated conditions for the sand–kaolinite and sand–illite mixtures. In contrast, the sand–bentonite mixtures exhibited higher susceptibility to suffusion under unsaturated conditions. Moreover, for the sand–kaolinite mixtures, a higher susceptibility to suffusion was observed with smaller sand-grain sizes under saturated conditions, whereas the opposite trend was observed under unsaturated conditions. This study provides insights into the suffusion behavior of sand–clay mixtures, considering influential factors such as clay type, sand-grain size, and IC gradient under both saturated and unsaturated conditions, which highlight the importance of considering the saturation state for a comprehensive understanding of suffusion in the sand–clay mixtures. [ABSTRACT FROM AUTHOR]

The soil is usually unsaturated in practical engineering, and the slope failure surface generally presents three-dimensional (3D) characteristics. Therefore, the traditional plane problem calculation method does not accurately describe the slope's stability and safety assessment results strengthened through frame beam anchor plates (FBAPs). This work introduces a novel approach based on the limit analysis (LA) technique for assessing the 3D stability of unsaturated soil slopes supported by FBAPs to address this issue. The slope safety factor (Fs) expression was derived based on the energy balance principle. The soil slope stability the FBAP reinforces was quantitatively expressed as a function of slope parameters. Nonlinear distribution features of soil matrix suction and effective unit weight, as well as the internal energy dissipation rate created by the anchor plate, must be taken into account when calculating the internal energy dissipation and external work rate. The impact of the 3D effect, seismic parameters, unsaturated soil characteristics, and supporting structure on slope stability was discussed. Some design suggestions for slope reinforcement are put forward. According to the findings, the suction effect's beneficial effects on stability should be considered. Slopes with a width-to-height ratio (B/H) of less than 10 should consider the 3D effect's beneficial effects. The seismic action significantly negatively impacts slope stability, while using FBAP reinforcement structures can dramatically improve slopes' static and seismic stability. [ABSTRACT FROM AUTHOR]

The process of rainwater infiltration into unsaturated multi-layered slopes is complex, making it extremely difficult to accurately predict slope behaviors. The hydrological mechanisms in multi-layered slopes could be significantly influenced by the varying hydraulic characteristics of different soils, thus influencing slope stability. A numerical model based on Hydrus 2D was constructed to investigate the hydrological mechanisms of multi-layered slopes under different slope inclinations and rainfall intensities. The results revealed hydraulic processes in response to rainfall in unsaturated multi-layered slopes, in which layered soils retard the advance of wetting fronts and affect seepage paths in the slope. The results also showed the characteristics of hydraulic parameters, including pore water pressure and moisture content, under different conditions, and explained the crucial factors at play in maintaining slope stability. [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]

When remediating contamination in the vadose zone, which is a potential source of continuous groundwater and surface water pollution, technical challenges are often encountered. In this study, the feasibility of delivering sodium persulfate (SPS) oxidant to unsaturated soils was explored by integrating porous pipes, commonly used in agriculture, with in-situ chemical oxidation (ISCO). An evaluation of the operating characteristics of the pipe determined a recommended influent rate of < 0.1 L min−1 and an initial influent water pressure < 20 kPa to prevent percolation pore enlargement. Two-dimensional sandbox experiments revealed that pulse infiltration at an influent rate of 0.05 L min−1 was effective in creating matrix flow and lateral movement, minimizing preferential flow induced by continuous infiltration. Application of SPS (10% by wt.) under these conditions resulted in approximately 90% wetting of the sandbox area SPS flow at the experimental time that infiltrated from the pipe. After a 14-d post infiltration resting state, residual SPS concentrations ranged from 6,000 -12,000 mg/kg in soil, with soil pH levels of 3–4, ORP around 600 mV, and 40–60% decreases in soil organic carbon. This developed method helps retain the oxidant and promote chemical reactions, making ISCO a viable option for remediating unsaturated soil contamination. [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]

Pile response in unsaturated soils is an area of interest due to its prevalence in real-world scenarios. Significant differences exist in the lateral behavior of single piles in partially saturated soils due to increased soil stiffness. In this study, a single pile was monotonically loaded laterally to investigate the performance of piles in soils with variable water table levels. Pile head lateral response showed that a mix of unsaturated-saturated soil led to an increase in lateral loads on the pile at a similar displacement compared with the fully saturated or dry soil conditions. The lateral response of the pile was obtained based on the curvature data from the strain gauges. A derivative method was used to generate the shear force and lateral resistance along the pile length based on finite differences at the seven strain gauge locations, thereby eliminating errors associated with curve fitting. Various lateral response plots, such as the normalized p-y curves, M-y curves, and maximum bending moment response plots, were used to assess the response to lateral load. Further, the effect of two different loading rates were assessed on the fully saturated and unsaturated-saturated soil, and the range of loading rates evaluated had minimal influence on the pile lateral response. Results indicated that considering the influence of the unsaturated soil could increase lateral resistance under similar lateral displacements. However, there is a risk of inducing large pile bending moments, potentially leading to pile flexural failure if the pile plastic moment is reached. [ABSTRACT FROM AUTHOR]

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In this study, the performance of a Proportional-Integral (PI) automatic control system for the operation of the main channel of the northern branch of the Abshar irrigation network was evaluated under low-water operation scenarios. The actions taken to achieve the research objectives included:1) Development of a hydraulic flow simulation model in the main channel of the Abshar irrigation network using a simplified Integral-Delay (ID) mathematical model. 2) Development of a decentralized PI automatic control operation model. 3) Coupling the automatic operation control model with the hydraulic simulation model in MATLAB and determining the proportional and integral coefficients of each controller using system identification methods. 4) Simulation of the operation status using the designed automatic system under normal, low-water, and severe low-water operation scenarios with input fluctuations. The simulation results demonstrated that the controller had acceptable capability in implementing desirable operation under normal operation scenarios, with performance evaluation indices MAE, IAE, and STE fluctuating within the ranges of 0.11 to 0.140, 0.0013 to 0.0182, and 0.0001 to 0.0011, respectively. With the emergence of low-water scenarios and their intensification, water distribution conditions were assessed as desirable in upstream intakes but uncertain in downstream intakes. The calculated maximum error values in the lower intervals ranged from -10 to -20 and -35 to -45 centimeters, respectively. The results showed that the controller transferred the effects of low-water conditions and inflow fluctuations downstream, resulting in desirable surface water distribution for upstream intakes but inappropriate distribution for downstream intakes. [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]

Landslides or slope failure pose a significant risk to human lives and infrastructures. The stability of slopes is controlled by various hydrological processes such as rainfall infiltration, soil water dynamics, and unsaturated soil behavior. Accordingly, soil hydrological monitoring and tracking the displacement of slopes become crucial to mitigate such risks by issuing early warnings to the respective authorities. In this context, there have been advancements in monitoring critical soil hydrological parameters and slope movement to ensure potential causative slope failure hazards are identified and mitigated before they escalate into disasters. With the advent of the Internet of Things (IoT), artificial intelligence, and high-speed internet, the potential to use such technologies for remotely monitoring soil hydrological parameters and slope movement is becoming increasingly important. This paper provides an overview of existing hydrological monitoring systems using IoT and AI technologies, including soil sampling, deploying on-site sensors such as capacitance, thermal dissipation, Time-Domain Reflectometers (TDRs), geophysical applications, etc. In addition, we review and compare the traditional slope movement detection systems, including topographic surveys for sophisticated applications such as terrestrial laser scanners, extensometers, tensiometers, inclinometers, GPS, synthetic aperture radar (SAR), LiDAR, and Unmanned Aerial Vehicles (UAVs). Finally, this interdisciplinary research from both Geotechnical Engineering and Computer Science perspectives provides a comprehensive state-of-the-art review of the different methodologies and solutions for monitoring landslides and slope failures, along with key challenges and prospects for potential future study. [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]

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]

Unsaturated soil desiccation cracking is a coupled hydro-mechanical problem. It seriously weakens the hydraulic and mechanical characteristics of soil, causing various natural disasters potentially. For the unsaturated soil, the mechanism of moisture diffusion and deformation is more complicated compared with saturated soil, attracting wide attention. Thus, a coupled hydro-mechanical bond-based peridynamic (BB PD) model was proposed to explore the moisture diffusion and crack propagation in unsaturated soil. Specifically, the moisture diffusion equation for unsaturated soil was recast with the peridynamic differential operator, and an improved micro-modulus was adopted to revise the bond force density in the BB PD. In addition, a hybrid algorithm combining the explicit difference scheme for solving the diffusion equation and the implicit scheme for solving the motion equation was adopted, to avoid the incongruity of time steps for two types equations under the same explicit scheme. The validity of the proposed model and algorithm was verified by the examples on the desiccation of an unsaturated soil block and the desiccation cracking of a 3D unsaturated soil plate. The results show the potential of peridynamics in capturing desiccation cracks of unsaturated soil. [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]

Relating soil moisture content to soil suction, the soil–water characteristic curve (SWCC) represents an essential feature in unsaturated soil mechanics that enables estimation of different unsaturated soil property functions and modeling of the macro-scale soil behavior. However, depending on the soil and processes under consideration, proper hydraulic characterization of a soil through direct laboratory measurements can be difficult, time-consuming, and involve many uncertainties. In the case of uniformly graded sands, there is a highly nonlinear and steep shape of the SWCC, with only a few kPa of soil suction separating saturated and residual soil moisture conditions, which makes measurements for determinations of SWCC especially challenging. This study encompasses an investigation of the sandy type of soil's behavior and presents some preliminary results and experiences on the determination of SWCC through the use of physical slope model tests. The 30 cm deep slope, inclined at 35 degrees and instrumented with soil moisture and pore water pressure sensors, was exposed to series of rainfall intensities, ranging from 37 up to 300 mm/h. The results indicated that the data on hydraulic response in monitored points are not only useful for the determination of SWCC, but that the approach is useful for investigation of hydraulic hysteresis phenomena, as well as its effects on soil moisture and pore water pressure conditions, which also affects the stability conditions of a slope. In particular, the best-fit parameters of the van Genuchten model suggested air entry values of 1.6 and 1.1 kPa for the drying and the wetting curves of the SWCC, respectively, with the two branches shifted by about 1 kPa of soil suction. [ABSTRACT FROM AUTHOR]

Abstract 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.

Recently, rainfall-induced slope failure has struck Cimanggung village, West Java province, Indonesia. In order to anticipate future slope failures due to rainfall, an unsaturated slope stability analysis is compulsory. Precise information on the soil–water characteristic curve (SWCC) is required to conduct an accurate unsaturated soil analysis. In this article, a procedure to obtain SWCC by using a polymer tensiometer for Cimanggung village is proposed. Considering the long period of time needed to obtain the measured data, some prediction methods are available. The measured SWCCs are then compared with SWCCs based on two prediction methods. Chin’s 1-point and Perera et al.’s methods are applied as the prediction methods and then compared with the measured SWCCs. It could be concluded that Chin’s 1-point method yields a close estimation within the suction range. Meanwhile, the Perera et al. method underestimates the air entry value, and the predicted curve deviates significantly with the measured SWCC. Hence, Chin’s 1-point method is recommended for predicting SWCCs in Cimanggung Village.

Extreme rainfall significantly threatens the safety of the landfill cover system, especially under humid climates. This study aims to provide design recommendations for a sustainable landfill cover system consisting of a low-permeability soil layer underlying a two-layer capillary barrier for humid climates. First, the numerical back-analysis was conducted for verification against a series of flume model tests. Then, a parametric study was performed to investigate the effects of inclination angle, particle size and layer thickness on the lateral diversion length (DL) of the three-layer cover system under the 100-year return period rainfall of humid climates. The results show that the water lateral DL of the cover system can be greatly enhanced by increasing the inclination angle from 3° to 18°. Moreover, the bottom layer of the cover system with a coarser d10 was more susceptible to the impact of the heavy rainfall, while this can be alleviated by increasing the thickness of the bottom layer. A dimensionless number, defined as the ratio of thickness and d10 of the bottom layer, is proposed for designing lateral diversion of the three-layer cover system under humid climates. To preserve the maximum DL, it is suggested that the proposed dimensionless number should be larger than 95 and 110 for the design of rainfall events with 50-year and 100-year return periods for humid climates, respectively.

To address the engineering problem of wall collapse and destabilization during the construction of the slurry trench wall, the stability of the slurry trench wall under the condition of three-dimensional (3D) unsaturated stable seepage is studied using the upper limit analysis method and in combination with the three-dimensional rotating failure mechanism. The expression of the factor of safety (FS) for the unsaturated soil slurry trench was deduced by the gravity increase method. Additionally, a genetic algorithm was used to search for the minimum FS and the critical slip surface, and the obtained results were compared and validated with existing literature results. The effects of relevant parameters on the stability of the slurry trench under the condition of unsaturated seepage were analyzed in detail. The results of this paper indicated that ignoring the 3D effect of the slurry trench will underestimate the stability of the slurry trench. The presence of suction in unsaturated soil is beneficial to the stability of the slurry trench, and the impact of suction is closely associated with seepage conditions and the characteristics of the soil. The increase in surcharge load can lead to a decrease in the FS, and its effect on slurry trench stability increases with the enhancement of the three-dimensional effect. The impact of different seepage conditions on the sliding surface of the channel wall of clay strata is more significant, while the effect on the trench wall of sand strata is negligible. [ABSTRACT FROM AUTHOR]

Rainfall, evaporation, tides and waves make the soil at coastlines show dynamic unsaturated characteristics. In order to cope with landslides, collapses, and coastline receding, microbially induced calcium carbonate precipitation (MICP) was recently implemented to reinforce the soil in slopes and coastal zones using a spraying method. However, most of the researches on MICP focus on soil with a static saturation degree, and there are few numerical researches about the MICP reactions under dynamic saturation degree. Therefore, a coupled numerical model capable of describing the evolutions of bacteria, substance, calcium carbonate (CaCO3), porosity, and permeability in unsaturated soil over time reasonably was developed based on the convective–diffusion–reaction theory and the Richards' equation. The effect of MICP reactions on the parameters α, n, θs, θr in van Genuchten-Mualem (VG) model was considered. A large cylinder test (30 × 75 cm) about reinforcing sand based on the spraying method was carried out to validate the model. The CaCO3 distribution of the MICP infiltration and mineralization was fully reproduced and the concept of critical depth (Zcr) was proposed. The initial porosity, initial bacterial concentration, and spraying rate were the main parameters affecting the CaCO3 distribution and critical depth Zcr. When the bacterial concentration increased, the maximum CaCO3 content, critical depth Zcr, and normalized permeability coefficient (k/k0) indicated exponential increase, exponential increase, and exponential decrease. The saturated permeability coefficient of the sand was determined by the maximum calcium carbonate. The normalized permeability coefficient (k/k0) and critical depth Zcr showed an exponential decrease and a power function increase with the increase of the maximum CaCO3 content. [ABSTRACT FROM AUTHOR]

Realistic estimates of evaporation from unsaturated soils, which are important for many geotechnical and geoenvironmental applications, need to be considered in the context of soil settlement, and require thermohydromechanical (THM) analysis. Evaporation also depends on environmental parameters, including air temperature, air relative humidity, net radiation, and wind speed. Therefore, a consideration of atmospheric coupling in predicting evaporation is also necessary. In this study, the two-dimensional model EVAP1––which numerically estimates evaporation from unsaturated soil using THM and employing a soil–atmosphere model––was used to conduct a parametric study in order to investigate the effects of variation in environmental parameters and to study the effects of climate change on potential and actual evaporation and soil settlement. We found that the evaporation rate increased nonlinearly with increases in air temperature, net radiation, and wind speed, but decreases with an increase in relative humidity. However, the effect of a change in wind speed was less than the effect of a change in the three other environmental parameters. In addition, the change in evaporation rate differed in different regions with different air temperatures. For example, the temperature change had more of an effect on the evaporation rate at higher temperatures. In addition, neglecting soil settlement led to an overestimation of evaporation, albeit the amount of evaporation was almost the same whether soil settlement was considered or not, both at the beginning of the evaporation process, when potential evaporation was dominant, and at the end, when the water content in both cases had decreased almost to the residual water content, and the evaporation was minimized. The difference in the amount of evaporation was greater in the middle of the evaporation process, when actual evaporation dominated. [ABSTRACT FROM AUTHOR]

• Develop fiber-reinforced steel slag-bentonite mixture to construct hydraulic barrier. • This new material reduces desiccation cracks and ensures a low water permeability. • Fiber content and length affect hydro-mechanical properties and crack behavior. • Optimal use 0.3 % 9 mm-fiber to reinforce steel slag (90 %) mixed with bentonite (10 %) Desiccation-induced cracks in a compacted clay liner significantly deteriorate the hydraulic barrier performance of landfill covers. The present study explores the effects of polypropylene (PP) fiber reinforcement on the hydrological response and crack resistance of compacted steel slag (SS; 90 wt%) – bentonite (10 wt%) mixtures under drying and wetting cycles. Comprehensive tests were conducted to explore the impact of different fiber lengths (6–12 mm) and contents (0–0.4 % wt.%), including hydraulic conductivity tests for measuring the saturated hydraulic conductivity (k s), unconfined-penetration tests for measuring the tensile strength, small-sized plate tests for quantifying crack development, and large-sized bucket tests for studying the hydrological response and crack characteristics. Higher fiber contents and longer fiber lengths increased the k s -value of the specimens. For a 0.3 % fiber content, the tensile strength peaked for the 9-mm fiber. Consistently, the specimen reinforced with the 9-mm fibers exhibited significantly fewer cracks than those reinforced with the 6-mm and 12-mm fibers. It was because the 6-mm fibers had a shorter anchorage length, while the 12-mm fibers tended to agglomerate. The large-sized bucket tests showed that fiber reinforcement limited crack development significantly under wetting and drying cycles, reducing the rainfall infiltration by 40 % and enhancing the soil water retention capacity. Finally, a 0.3 wt% of 9-mm PP was recommended to reinforce the compacted SS-bentonite mixtures. [ABSTRACT FROM AUTHOR]

The effective interaction mechanisms in the pullout resistance of reinforcements include skin friction mobilized at the soil-solid surface, soil-soil shear resistance, and compressive resistance created against transverse elements. The third component is obtained from passive lateral pressure (LPM) or bearing capacity (BCM) methods. An analytical solution is proposed to determine the pullout capacity of geocell, geogrid, and strengthened geogrids embedded in ordinary and unsaturated soils. For unsaturated soils, the effective stress approach was employed. The solution-predicted results were compared with those obtained from large-scale pullout tests reported in the literature. Results indicated that considering LPM for 2D and 3D reinforcements better agrees with experimental results. The mobilized frictional rib-soil interfaces and the soil-soil shear resistance components generally contribute more to the pullout capacity of the geocell and geogrid, respectively. For the extensibility represented by m p i and flexibility of geocell denoted by α p i , the values of m p i = 1, 0.7, and 0.3 for the first, second, and third row of geocell, α p i = 0.4 for the first row of geocell and 0.25 for the second and subsequent rows are suggested to be considered. Parametric studies showed that the optimum transverse rib spacing is over 50 times the equivalent rib thickness (B eq). • To develop a solution based on the lateral earth pressure and bearing capacity methods to determine the pullout resistance of three-dimensional (3D) reinforcement such as geocell and two-dimensional (2D) reinforcement like geogrid and strengthened geogrids. • Validating the proposed equation for reinforcement pullout resistance in unsaturated soil, based on effective stress. • Investigating the present solution outcomes with 162 pullout tests performed on 28 different types of reinforcement, extracted from 10 case studies. • Proposing a method to reduce the passive resistance of geocell transverse ribs, related to the effects of extensibility and flexibility. • Presenting an evaluation method considering the geocell geometry and soil matric suction on the pullout capacity of geocells and the effects of the transverse rib spacing and width on the pullout capacity of geogrids. [ABSTRACT FROM AUTHOR]

The limit support pressure significantly influences the stability of the shield tunnel face and deformation control during tunneling. Current research predominantly focuses on soils under dried or saturated conditions. However, unsaturated soils, which are more commonly encountered in engineering practice and widely distributed, have not been as extensively studied. Based on limit equilibrium theory, a modified analytical wedge-prism model is proposed in this paper to predict the limit support pressure acting on the shallow shield tunnel face in unsaturated sandy soil where the soil arching effect is considered. Taking advantage of finite-element software ABAQUS (version 2021), a series of numerical trapdoor tests are conducted first to study the failure behavior of unsaturated sandy soil. Then, by combining the rotation trajectory of major principal stress with the shear strength theory of unsaturated soil, the loosening earth pressure solution above the shallow trapdoor can be derived analytically. The limit support pressure can be finally obtained through a force equilibrium analysis of the wedge body. The accuracy of the proposed model is validated by comparing the calculated results with current model tests and numerical simulations. Parameter analysis results reveal that both the loosening earth pressure and limit support pressure initially decrease and then increase with the rising degree of soil saturation. A critical saturation point is identified where the loosening earth pressure and the limit support pressure reach their minimum values, attributed to the full development of the soil arching effect. [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.

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]

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]

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]

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]

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]

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]

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]

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