Search

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]

Most soils in the natural state are unsaturated. At present, the theoretical formulas for the shear strength of unsaturated soils are difficult to apply in engineering practice due to the difficulty in obtaining the physical parameters. While one of the factors determining the fundamental physical indices of soils is moisture content, is convenient to be obtained. Based on the indoor consolidation undrained shear test, analysis was done on how changing moisture contents and confining pressure affected the strength and deformation traits of remolded silty clay. Results show that the shear strength is affected by the combined effect of moisture content and confining pressure, the increase of confining pressure can significantly improve the shear strength of soil. Under the condition that the moisture content is maintained constant, the perimeter pressure has a positive relationship with the percentage increase in shear strength of unsaturated chalky clay. So, the formula for the total stress strength of unsaturated soil with the moisture content as the independent variable is established by curve fitting. The findings of this study can serve as a valuable guide for estimating the shear strength produced by the local change in groundwater level in silty clay layers. [ABSTRACT FROM AUTHOR]

The frame beam anchor plate (FBAP) is a new supporting structure to reinforce backfill. The current studies of slope stability concentrate on homogeneous isotropic dry or saturated slopes according to two-dimensional assumptions. In engineering practice, however, the soils are heterogeneous and anisotropic and exhibit evident unsaturated characteristics, and the failure surface shows obvious three-dimensional (3D) characteristics universally. A new method for evaluating the 3D stability of unsaturated soil slopes reinforced with FBAPs is established in this paper. The upper-bound analytical solution of slope safety factor (Fs) is derived based on the energy balance equation incorporated with the 3D spiral failure mechanism and the gravity increase method (GIM). Comparisons verified the effectiveness of the methodology and the optimization program. The influence of unsaturated characteristics, support structure design parameters, and seismic force on the 3D slope stability is evaluated through parameter analysis. The results show that the shear strength prediction model is crucial in slope stability assessments. The stability of slopes can be significantly improved by about 29%–52% by using FBAPs. Seismic action has a significant negative impact on the slope stability. When kh increases from 0 to 0.3, Fs generally decreases by about 40%–55%. [ABSTRACT FROM AUTHOR]

Compacted soils used as formation layers of railways and roads continuously undergo water content and suction changes due to seasonal variations. Such variations, together with the impact of cyclic traffic-induced loads, can alter the hydro-mechanical behaviour of the soil, which in turn affects the performance of the superstructure. This study investigates the impact of hydraulic cycles on the coupled water retention and cyclic response of a compacted soil. Suction-monitored cyclic triaxial tests were performed on a compacted clayey sand. The cyclic response of the soil obtained after applying drying and wetting paths was different to that obtained immediately after compaction. The results showed that both suction and degree of saturation are required to interpret the cyclic behaviour. A new approach was developed using (a) a hysteretic water retention model to predict suction variations during cyclic loading and (b) Bishop's stress together with a bonding parameter to predict accumulated permanent strain and resilient modulus. The proposed formulations were able to predict the water retention behaviour, accumulated permanent strains and resilient modulus well, indicating the potential capability of using the fundamentals of unsaturated soils for predicting the effects of drying and wetting cycles on the coupled soil water retention and cyclic response. [ABSTRACT FROM AUTHOR]

When the shield tunnel passes through the gas-bearing strata, gas and water leakage may occur depending on the sealing performance of the segment joints. This process involves the complex multiphase seepage flow phenomenon in unsaturated soil. In this study, a fully coupled solid-liquid-gas model of the GIL Utility Tunnel was established to investigate the influence of the high-pressure gas on the mechanical properties of the tunnel segments and joints. The constitutive model of the Extended Barcelona Basic Model was implemented to simulate the effect of the seepage process on soil deformation. The results show that significant upward displacement occurred in the gas reservoir and its overlying strata, and the maximum displacement reached 30 mm. In addition, during the leakage of the gas and the water, an increase in the average soil effective stress was observed. It would induce a reduction in the suction and expansion of the yield surface. The tunnel tended to be stable from 20 years onwards, thus the soil deformation due to the water leakage only occurred at the early stage. In addition, the joint opening under the most unfavorable internal force combination was 0.69 mm, and the corresponding bolt stress was 119.5 MPa, which is below the yield limit. The results of this study help to understand the influence of high-pressure gas on tunnel safety and the sealing performance of the joints. [ABSTRACT FROM AUTHOR]

This paper attempts to investigate the bearing capacity of a strip footing that rested on unsaturated homogenous sands and used upper bound finite-element limit analysis in association with linear optimization. The analysis is based on suction stress-based (σs) effective stress (σ′) analysis. Unlike the saturated soil, the size of the yield surface varies with the vertical position, and therefore, proper modifications are carried out in the upper bound formulations to incorporate the unsaturated soil property functions. A detailed investigation is carried out to estimate the load-carrying capacity of a strip footing that vary the mechanical strength, unsaturated soil properties, water table depth (hw), and climatic conditions. The numerical solutions are presented in terms of bearing capacity factors [BCF (Nγs, Nqs)] for the unit weight (γw) and surcharge pressure (qs). The nodal velocity patterns are drawn for several cases, and the presented solutions are compared with the available results. The design charts provided in this paper might be useful to design engineers. [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]

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]

The rhizosphere is the region of soil directly influenced by plant roots. The microbial community in the rhizosphere includes fungi, protists, and bacteria: all play significant roles in plant health. The beneficial bacterium Sinorhizobium meliloti infects growing root hairs on nitrogen-starved leguminous plants. Infection leads to the formation of a root nodule, where S. meliloti converts atmospheric nitrogen to ammonia, a bioavailable form. In soil, S. meliloti is often found in biofilms and travels slowly along the roots, leaving developing root hairs at the growing root tips uninfected. Soil protists are an important component of the rhizosphere system, able to travel quickly along roots and water films, who prey on soil bacteria and have been known to egest undigested phagosomes. We show that a soil protist, Colpoda sp., can transport S. meliloti down Medicago truncatula roots. Using model soil microcosms, we directly observed fluorescently labeled S. meliloti along M. truncatula roots and tracked the displacement of the fluorescence signal over time. Two weeks after co-inoculation, this signal extended 52 mm farther down plant roots when Colpoda sp. was also present versus treatments that contained bacteria but not protists. Direct counts also showed protists are required for viable bacteria to reach the deeper sections of our microcosms. Facilitating bacterial transport may be an important mechanism whereby soil protists promote plant health. IMPORTANCE Soil protists are an important part of the microbial community in the rhizosphere. Plants grown with protists fare better than plants grown without protists. Mechanisms through which protists support plant health include nutrient cycling, alteration of the bacterial community through selective feeding, and consumption of plant pathogens. Here, we provide data in support of an additional mechanism: protists act as transport vehicles for bacteria in soil. We show that protist-facilitated transport can deliver plant-beneficial bacteria to the growing tips of roots that may otherwise be sparsely inhabited with bacteria originating from a seed-associated inoculum. By co-inoculating Medicago truncatula roots with both S. meliloti, a nitrogen-fixing legume symbiont, and Colpoda sp., a ciliated protist, we show substantial and statistically significant transport with depth and breadth of bacteria-associated fluorescence as well as transport of viable bacteria. Co-inoculation with shelf-stable encysted soil protists may be employed as a sustainable agriculture biotechnology to better distribute beneficial bacteria and enhance the performance of inoculants. [ABSTRACT FROM AUTHOR]

Composite foundation is a widely used foundation treatment technology in geotechnical engineering. This study are derived governing equations to axisymmetric consolidation of unsaturated composite foundation (USCF) incorporating permeable columns and impermeable columns under instantaneous loading, and obtained the final solutions of excess pore pressures (EPPs) by using mathematical methods such as the variable separation, decoupling, finite Hankel transform and its inverse transform. The analytical solution obtained under free strain conditions is more general and representative, as it can be readily degraded to solutions for a variety of consolidation models and the EPPs can be conveniently calculated at any point in the calculation cell. Through degrading proposed solutions to the special case to verify their correctness, the comparative results were found well‐matched to the existing literature solutions. The effect of various parameters on the consolidation performance of USCF was analyzed, where the studied parameters include the compression modulus of columns, radius ratio for permeable columns, and the number of impermeable columns. The results show that increasing the compression modulus and area replacement rates of columns can accelerate consolidation and reduce settlement, and the latter is more effective. Compared to reinforced composite foundations with only a single form of the permeable or impermeable column, the combination of permeable and impermeable columns can significantly shorten the consolidation time and enhance the bearing capacity of the unsaturated ground. [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]

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]

Considering the flow‐independent viscosity of soil skeleton and the lateral inertia effect of pipe pile, the vertical dynamic behavior of a pipe pile embedded in unsaturated soil is investigated in this work when the pipe pile is subjected to the vertical dynamic loading. In order to model this problem, the fractional‐order standard linear solid (FSLS) model is introduced to characterize the flow‐independent viscosity of the soil skeleton, the Rayleigh‐Love rod model is employed to specify the lateral inertia effect of pipe pile, while both vertical and radial soil displacement are entirely considered. The analytical solution of the pipe pile complex impedance is obtained through the rigorous theoretical derivation. Numerical results with known analytical solution are finally presented to discuss the influence of the model parameters for the FSLS model, lateral inertia effect and geometrical characteristic for the pipe pile, and saturation degree and intrinsic permeability for the unsaturated soil on the vertical complex impedance of the pipe pile. The main results indicate that enlarging the fractional‐order index, raising the strain relaxation time, or shortening the stress relaxation time will reduce the oscillation amplitude and natural frequency for the dynamic stiffness and damping of the pipe pile but will improve their mean value. The lateral inertia effect of pipe pile has effect on its complex impedance only in the high‐frequency region. The outer and inner radii of pipe pile, pile length, soil saturation degree, and soil intrinsic permeability are highly correlated with the pipe pile complex impedance. [ABSTRACT FROM AUTHOR]

This study investigates the bearing capacity of strip footings resting on unsaturated soils subjected to combined loading using the lower-bound limit analysis coupled with the finite element discretization approach. In this regard, second-order cone programming (SOCP) is exploited to simulate the nonlinear form of the universal Mohr-Coulomb yield criterion during the process of stress field optimization. The significant influence of matric suction induced below the surface footing was accounted for by adopting the suction stress concept under the no-flow and steady-state infiltration/evaporation flow conditions. The eccentricity and inclination of the foundation loading are introduced into the equilibrium equations along the strip footing so as to render various combinations of moment (M), vertical (V) and shear (H) forces. The results stemming from the lower-bound finite element limit analysis are compared with several previous studies throughout the literature for verification of the model. The substantial contribution of suction stress to the evolution of failure loci and the distribution of subsurface stresses for the shallow foundation subjected to inclined and eccentric loadings is thoroughly discussed. A general three-dimensional failure envelope is presented for shallow foundations resting on partially saturated soils under combined vertical, horizontal and moment loadings. [ABSTRACT FROM AUTHOR]

This study presents a series of triaxial tests to highlight the effect of saturation degree ranging from 79.8% to 100% on the behavior of sand subjected to cyclic loading, the development of pore water pressure increment, the volumetric strain at liquefaction state, and the behavior of sand subjected to monotonic loading after liquefaction. The tested sand was Hostun RF sand, fine clear sand that has been widely used in laboratory testing in France. The results show that there is a difference between the behavior of samples having saturation degrees higher and lower than 95%. Besides, the development of pore water pressure increment is affected significantly by the value of cyclic stress ratio (CSR) and saturation degree. The Saturation degree also affects the appearance of criteria of liquefaction as Excess Pore-water Pressure (EPP) and Double Amplitude of axial strain (DA). The analysis of the effect of saturation degree on sample volumetric strain exhibits nonlinear liquefaction criteria for a given maximum value of CSR. The monotonic loading tests after liquefaction showed a small difference between the monotonic compressed behavior of the samples before and after liquefaction. [ABSTRACT FROM AUTHOR]

The plate load test (PLT) is the most reliable in situ testing for studying the load–settlement behaviour of footings on unsaturated collapsible soils. In these soils, the suction profile is not constant along the depth, and the scale effect between the prototype and footing leads to different suction averages and, consequently, different data. One method to eliminate the effect of soil suction on the test data is to fully saturate the soil prior to the test, which is also recommended at the design process for footing on collapsible soils. However, the inundation process on PLTs is expensive and time-consuming, which makes this procedure difficult to incorporate into engineering practice. This study presents a device that can be attached to flat dilatometer (DMT) to allow local inundation of the soil as part of the in situ test campaign and obtain the DMT-constrained modulus (MDMT) for both natural and inundated conditions. The MDMT presented an average reduction of 56% from natural to inundated condition. This parameter can be used in a model to predict load–settlement curves by DMT data considering the suction influence on this behaviour. The curves obtained from the prediction model were compared to curves determined by PLT conducted under the same in situ conditions. Good agreement was found between the curves predicted by DMT and those measured by PLT for both conditions. The proposed procedure, which uses a device attached to the DMT blade, provides an investigation method to obtain the load–settlement curve under different suction conditions, which can help in the selection and performance prediction of shallow foundations, taking into account suction and collapse phenomenon-related problems. [ABSTRACT FROM AUTHOR]

Based on the theory of single-phase elastic medium and unsaturated porous medium, the vibration isolation effect of composite multilayer wave impeding block (WIB) in the unsaturated ground under an underground dynamic load is investigated. The results show that the best vibration isolation effect can be obtained by designing the wave impedance ratio between the composite multilayer WIB and unsaturated ground. The composite multilayer WIB improves the vibration-damping bandwidth compared with the homogeneous WIB. The vibration isolation effect is better the closer the embedded depth of the composite multilayer WIB is to the vibration source, and its vibration isolation effect increases significantly with the increase of thickness, but when the thickness of the WIB exceeds a certain critical thickness, its vibration isolation effect decreases with the increase of thickness. Soil saturation has a significant effect on the vibration isolation effect of composite multilayer WIB in the unsaturated ground, and the composite multilayer WIB can achieve a better vibration isolation effect at low saturation. [ABSTRACT FROM AUTHOR]

Soils above the groundwater table and near the ground surface are often partially saturated, and the changes in the degree of saturation and matric suction caused by infiltration may have substantial effects on the stability of geotechnical systems. This work evaluates the significant effect of transient flow on the ultimate bearing capacity of strip footings founded on unsaturated soils under the simultaneous actions of vertical and horizontal loads and moment using the lower-bound theorems of the finite-element limit analysis and the incorporation of second-order cone programming. The unified effective stress theory is incorporated into the soil yield function to model the partially saturated state, and the closed-form solution for one-dimensional transient flow is adopted so as to evaluate the tempo-spatial variations of suction stress. For both sand and clay underlying soils, it is found that the increase of infiltration time leads to a notable decrease of the size of the normalized failure envelopes for either obliquely or eccentrically loaded shallow foundations. The impact of transient flow on the ultimate bearing capacity of surface footings is also observed to be greater for clay soils as compared with sand deposits due to the significant contribution of higher induced suction stress. [ABSTRACT FROM AUTHOR]

Rainfall infiltration can alter the pore-water pressure and decrease matric suction, which can lead to slope instability and landslides. Most of the previous numerical studies conducted on rain infiltration have assumed a two-dimensional (2D) failure mechanism, which neglects the three-dimensional (3D) characteristics of slopes. An analytical assessment framework was developed using the upper-bound theorem of limit analysis to determine the factor of safety and failure pattern in the case of a 3D vertical cut slope under diverse rainfall situations combined with the unsaturated soil mechanics. The Green–Ampt model was adopted to depict the infiltration process and the progression of the wetting front into the soil. The slope factor of safety was determined using the energy balance equation by adopting the strength reduction approach. The validity of the framework was verified using the numerical simulation method. The effects of duration, intensity, and patterns of rainfall and the 3D traits of slope on the slope failure pattern and stability were determined. A set of design charts was included for the preliminary design. The present study quantitatively determines the stability of slopes susceptible to rainfall infiltration. [ABSTRACT FROM AUTHOR]

This paper discusses the second-order reliability-based design optimization (SORBDO) of unsaturated finite slopes. An efficient search algorithm is proposed to locate the most probable slip surfaces using the Morgenstern–Price method of slices. The variability of fitting parameters of the soil water characteristic curve (SWCC) and shear strength parameters have been taken into account for evaluating the reliability of unsaturated finite slopes. Six unsaturated shear strength (USS) models are considered for the analysis of unsaturated soils. The most conservative model for the optimum design of finite slopes is recommended. Moreover, the results indicate that the mean and standard deviation of the fitting parameters of SWCC have a significant effect on the critical centers, critical slip surfaces, and reliability index of the unsaturated finite slopes. The results demonstrate a significant change in the critical centers associated with critical slip surfaces due to the change in the mean and coefficient of variation of the fitting parameters of SWCC. Statistical analysis of the experimental data shows that a positive correlation exists between fitting parameters of SWCC related to air entry value (af) and residual water content (mf). Negative correlations are found between the fitting parameters of SWCC related to air entry value (af) and slope (nf). Similarly, the SWCC fitting parameters related to residual water content (mf) and slope (nf) have negative correlations for clayey soils. It is observed that the correlated value of the reliability index is overestimated with reference to the uncorrelated value for clayey soil slopes. The proposed design charts are beneficial for engineers and practitioners for the sustainable design of unsaturated finite slopes. Overall, the developed rigorous SORBDO framework offers a more rational approach for assessing critical failure surfaces and critical centers, considering the interdependency of random variables. [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]

In the current state of the study regarding passive earth pressure, the majority of literature was limited in scope to dry or saturated cases. However, most soils in practical engineering are unsaturated. Based on the log-spiral failure mechanism, this paper develops a limit equilibrium (LE) analysis to evaluate the passive earth pressure under the effect of steady unsaturated seepage conditions. For assessing the effect of suction stress on passive earth pressure, a suction stress-based effective stress representation is incorporated into a limit equilibrium analysis. The analytical formula of passive earth pressure coefficient is derived using the moment equilibrium equation for the backfill defined by a log-spiral slip surface. An optimization procedure is developed to search for the minimum passive earth pressure coefficient and the critical failure surface via MATLAB. A parametric analysis is performed to investigate the effects of some key parameters on passive thrust. Besides, examples of two different cases are given to verify the effectiveness of theoretical results. Results indicate that suction stress can increase the magnitude of the passive earth pressure coefficient and the suction-induced effect highly depends on the seepage conditions and soil types. [ABSTRACT FROM AUTHOR]

A simplified analytical method is proposed for one-dimensional unsaturated soil consolidation theory. First, in the one-dimensional compression test of unsaturated soil, the effective stress principle of saturated soil under compression is introduced to replace the constitutive relation expressed by the state of double stress in Fredlund's theory. Based on this, the governing equations composed of two bi-variable partial differential equations are obtained. In the process of derivation, the dissipation law of pore pressure during the consolidation process is analyzed and the theoretical rationality is demonstrated. When solving the system of equations, considering that the initial excess pore water and the gas pressure are caused by instantaneous loading, Hilf's theory is improved to calculate the change of pore pressure. This improvement is more in line with the actual situation and simplifies the approximate calculation method to obtain the analytical solution when the coupling effect of water and gas is considered. This method is verified by comparing with Terzaghi's theory and Fredlund's theory. It is shown that the solution of Terzaghi's theory is a special case of this method for saturated soil, and the results of the dissipative process obtained with the method is close to Fredlund's theory. [ABSTRACT FROM AUTHOR]

In current study, a test program is designed to observe the influence of wetting stress paths on behavior and instability of unsaturated soil in stress state space. The mechanical behavior was studied by performing three test series in constant matric suction plane. In first series, water infiltration was performed together with shearing starting from zero (0 kPa) deviatoric stress. In second series, first water was infiltrated at zero (0 kPa) deviatoric stress then samples were sheared in drained pore water pressure conditions. In third series, water was first infiltrated at zero deviatoric stress then specimens were sheared in undrained pore water pressure conditions. Instability was studied in constant shear stress plane by first shearing soil up to predefined level of deviatoric stress then infiltrating water keeping deviatoric stress constant on the specimen. This research also describes how unsaturated soil behavior and instability is varied with variation in net confining stresses when suction is decreased from initial measured value to start water infiltration with different wetting stress paths and their effect on shear state and failure surface in stress state space. The test results revealed that the movement of stress paths was independent of net confining stress, matric suction and shearing conditions employed in the study. [ABSTRACT FROM AUTHOR]

The soil deposits for general constructions and mining are often under both saturated and unsaturated conditions at different overconsolidation ratios. Within the frameworks of the unified hardening unsaturated model, in this paper, a constitutive model is proposed for the unsaturated overconsolidated soil under drained and undrained conditions. This model is validated against the unsaturated experimental results, and the hydromechanical behavior of soil is thoroughly investigated considering the dilation behaviour under a high overconsolidation ratio. It is found that the prediction results for the volume change, deviator stress, and suction behavior determined by the proposed model agree well with the experimental results, particularly for the dilation behaviour. It can be concluded that this model can predict the hydromechanical behavior of the unsaturated overconsolidated soil under both the drained and undrained conditions. [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]

To consider the shape effect of prefabricated vertical drain (PVD), the elliptical cylindrical equivalent model (ECEM) is established for the consolidation of unsaturated soft foundations improved by PVD. Then, the associated analytical solutions of excess pore‐air and pore‐water pressures are derived under free strain and equal strain conditions, respectively. The rationality of proposed solutions is verified by comparing them with the existing solutions. Through conducting the parametric study, the effects of the permeability coefficients and the extent of influence zone on the dissipation of excess pore pressure and the consolidation settlement are investigated. Outcomes show that there is a plateau during the dissipation process of the excess pore‐water pressure. The consolidation behavior is dominated by the dissipation of the excess pore‐air pressure before the plateau, while it is governed only by the dissipation of the excess pore‐water pressure after the plateau. [ABSTRACT FROM AUTHOR]

The accelerating pace of development due to groundwater overwithdrawal throughout the world places increasing demands on the unsaturated zone. Estimating evaporation from unsaturated soil has been important for many geotechnical and geoenvironmental applications. As an example, the long-term performance of soil covers, which are widely used in mining and landfill applications to protect the environment, depends on evaporation from their surfaces. Evaporation, in turn, depends on moisture flow within an unsaturated soil mass, which is generally coupled with heat flow. Evaporation also depends on the void ratio and hydraulic and air conductivities of soil, which are, in turn, affected by stress and strain and the resulting soil settlement. As a result, a thermohydromechanical (THM) analysis for predicting evaporation is necessary. A two-dimensional (2D) finite-element program, θ-Stock, can perform THM analysis of unsaturated soil but works only within the soil, not in the atmosphere above the soil. In this study, a 2D model of soil–atmosphere interaction employing atmospheric coupling and using a modified Penman equation was implanted in θ-Stock to develop program EVAP1, which numerically estimates potential and actual evaporation from unsaturated soil using THM analysis. Because of the coupled character of the phenomena, the boundary conditions were determined by the soil state and the environmental data. The program EVAP1 was verified with published experimental and numerical studies on evaporation. The results of analyses using the verified program showed that neglecting THM behavior, and hence soil settlement, leads to an overestimation of evaporation from unsaturated soil surfaces. [ABSTRACT FROM AUTHOR]

The bearing capacity of foundations constructed on unsaturated soils depends on the soil saturation degree and thus the soil suction. This paper presents a simple limit equilibrium approach to compute the foundation bearing capacity on unsaturated soil using lateral earth pressure theory. An imaginary retaining wall is assumed to pass the edge of the foundation and active and passive lateral pressures on both sides of the wall are computed using the distribution introduced in an earlier study. Equating total active and passive thrusts on two sides of the wall gives the footing bearing capacity. The soil–water characteristic curve is used to obtain soil suction corresponding to different moisture contents and drained shear–strength parameters are used to determine the foundation bearing capacity. The developed method is applicable to sands and c-φ unsaturated soils with varying saturation degrees. The predicted results have been compared with data from seven case studies reported in the literature and found a satisfactory agreement. Parametric studies have been conducted to investigate effects of foundation embedded depths, two-layer soils, various suction stresses, and ground slope changes on the footing ultimate bearing capacity. The results show that with increasing the soil suction, the footing bearing capacity increases significantly. [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]

Insufficient bearing capacity of foundations is hazardous for construction engineering, and improper construction scheme can also lead to unexpected problems. Vertical drains are always installed in the soil foundations to accelerate the consolidation process and thus improve the bearing capacity. According to the consolidation theory proposed by Fredlund, the consolidation of unsaturated vertical drain foundation is investigated with analytical solutions, in which smear effect, drain resistance, and depth‐dependent initial excess pore pressures (i.e., excess pore‐air and pore‐water pressures) are considered. In the derivative process, the decoupling method and Fourier series expansion method are applied. The reliability of the current solutions is verified by comparing the degenerate ones with existing solutions. Sensitivity analysis is conducted to assess the consolidation characteristics of the proposed model against modeling sizes, smear coefficients, drain resistance factors, and distribution coefficients. The analytical model has the advantages of simplicity and easy to implement in practical engineering. [ABSTRACT FROM AUTHOR]

Constitutive coupled modeling has developed rapidly in recent decades, with numerous new models published. However, few models consider dynamic porosity, and experimental validation of such a model remains a challenge due to multiple variables. In this study, a new constitutive model for unsaturated soil with dynamic porosity was developed based on mixture theory and nonequilibrium thermodynamics, then the model was validated using test data from two experimental studies that yielded good results (relative average error AVRE = 0.8631–1.3046, R2 = 0.9028–0.9981). The sensitivity of the model to the four primary parameters was analyzed to investigate the influence of model properties on the hydraulic and mechanical behavior. Results show that the calculation of volumetric strain is most sensitive to Young's modulus (E), while the calculation of specific water volume is most sensitive to permeability (k). In addition, the sensitivity of the parameters changes with their value. Modeled results show that the porosity change significantly affects both hydraulic and mechanical behavior, even when soil undergoes relatively low deformation. Relative calculation error decreases notably after porosity change is considered (44.9% and 35.2% improvement in two different calculations). This study also finds that dynamic porosity affects the deformation energy of solids. [ABSTRACT FROM AUTHOR]

A novel semi-analytical solution is proposed to analyze the consolidation behavior of composite ground with a floating impervious column in unsaturated soil based on the equal-strain hypothesis. The basic governing equations in the reinforced zone and the underlying stratum are first obtained. Using the Laplace transformation and matrix analysis method, a final solution in the Laplace domain is derived. Afterwards, on the basis of Stehfest's method, an inverse Laplace transform is conducted to derive the solution in the time domain. The effectiveness of the proposed solution is then evaluated against the results of finite difference analysis. Moreover, a sensitivity analysis is performed to assess the effects of area replacement ratio, depth improvement ratio, and column stiffness on the dissipation of excess pore-water/air pressure and the average degree of consolidation. Results show that only vertical seepage occurs during the consolidation process of unsaturated composite ground under a condition of equal-strain. The consolidation rate of unsaturated soft ground can be improved by introducing floating impervious columns. The use of larger area replacement ratio, depth improvement ratio, and column stiffness can increase the consolidation speed and reduce the settlement of composite ground with a floating impervious column in unsaturated soil. [ABSTRACT FROM AUTHOR]

To explore the effect of suction stress on effective stress, shear strength, and the relationship with the soil–water characteristic curve of unsaturated reticulated red clay, a series of triaxial compression tests, soil–water retention tests, and particle flow code 3D (PFC3D) simulation under different matric suction and net confining pressure was conducted. The suction stress characteristic curve (SSCC) and soil–water characteristic curve (SWCC) of reticulated red clay was obtained. These test results show that the effective stress based on suction stress converged to the unique failure envelope and that there is an internal relationship between SSCC and SWCC. The simulation results of PFC3D were very close to the laboratory measurements in the observation peak value and variation laws of the stress–strain curve. Based on the discrete element method, PFC3D takes rigid spheres or disks as basic units and simulates practical problems through the motion and interaction of the basic units. The parameters obtained by inversion of the stress–strain curve of PFC3D simulation were basically the same as laboratory measurements. Therefore, PFC3D simulation can be used to obtain SSCC and SWCC. These results are expected to promote the development of unsaturated soil mechanics. [ABSTRACT FROM AUTHOR]

Liquefaction in soils has predominantly been associated with saturated soils. Under seismic activity, unsaturated soils are may also be susceptible to liquefaction. The implications of neglecting unsaturated soils that are close to saturation as the foremost rule for assessment of liquefaction can be risky and catastrophic. Hence, in this study, a cyclic double-walled triaxial device capable of applying suction via axis-translation technique was modified to conduct cyclic triaxial tests on suction-equilibrated specimens at a low suction state. In unsaturated soils, the presence of highly compressible air within the soil specimens may prevent the effective confining pressure from reaching zero, which is typically considered as initiation of liquefaction. Therefore, in this study, liquefaction was considered to occur when 5% double-amplitude strain was attained in the soil specimen. A series of suction-equilibrated cyclic triaxial test results on unsaturated soils were analyzed to study and verify the possibility of liquefaction in unsaturated soils. Additional suction-controlled monotonic triaxial tests were performed to compare the stress paths of the cyclic triaxial tests with their respective critical state lines to indirectly assess the hypothesis of liquefaction mitigation using an induced partial-saturation technique. It was observed that liquefaction was possible and detected in unsaturated cohesionless soils having relative density of 50% and a degree of saturation of above 70%. However, with desaturation the resistance to liquefaction in soils increased exponentially. This demonstrated the potential for induced partial saturation to mitigate liquefaction in moderately compacted soils whose degree of saturation is reduced to less than 70%. [ABSTRACT FROM AUTHOR]

In this work, a series of unconfined compression tests at different water contents were performed to investigate the mechanical behaviour of clay–sand mixtures compacted in standard Proctor conditions. For studying the effect of water content and suction on unconfined compressive strength (UCS) and on strain secant modulus (E50 modulus) of these mixtures, drying–wetting paths were defined by measuring the soil–water characteristic curves (SWCCs) using osmotic and salt solution techniques and filter paper method. The results highlighted that an increase in sand content of the mixture leads to an increase in the maximum dry densities and a decrease in the optimum water content of the materials. However, at the given state, when clay is mixed with 25% of sand, the UCS and E50 modulus increase to 37% and 70%, respectively, compared to those of clayey samples. But when clay is mixed with 50% of sand, the UCS and E50 modulus decrease to 38% and 46%, respectively, compared to those of clayey samples. The results also indicate that the UCS and E50 increase with a decrease in the water content and an increase in suction, irrespective of the sand content. [ABSTRACT FROM AUTHOR]

Unsaturated soil shear strength is a crucial and useful parameter for predicting geostructure stability, soil erosion, seasonal variation, and land management. Unsaturated shear strength measurement, however, is frequently costly, complex, and time-consuming. The main objective of this paper is to present a new generalized equation for the shear strength estimation of unsaturated soils. The proposed equation is derived from a micromechanical equilibrium condition considering the interaction of air, water, and solid phases. The particle contact area effect is taken into account in the proposed model, even though it is thought to be negligible in existing equations. In comparison with existing equations, the proposed one has the benefit of being able to capture the nonlinear influence of saturation degree and matric suction on unsaturated shear strength. The proposed equation is compared with several other existing equations as well as experimental data for four different soil types to verify its validity. The findings indicate that the proposed equation has a potential application in estimating unsaturated soil shear strength and that it outperforms existing equations. The stress state also has a substantial impact on the shear strength properties of unsaturated soils, which was extended to include in the proposed equation. The results reveal that the proposed equation is capable of accurately predicting the variation of the soil–water characteristic curve and unsaturated soil shear strength as a function of the stress state. [ABSTRACT FROM AUTHOR]

The effects of different types of earthen landfill covers and vapor on landfill gas emissions are not well understood. In this study, an existing theoretical model of water and multicomponent gas (methane, carbon dioxide, nitrogen, and oxygen) flow was improved by incorporating vapor flow. The model was validated using a published soil column test simulating landfill gas emissions through landfill covers. Numerical simulations were conducted to investigate landfill gas emissions through a single clay-layer cover, a cover with capillary barrier effects (CCBE), and a three-layer cover during continuous drying. The CCBE retained the lowest water content after drying, whereas the bottom clay layer in the three-layer cover stayed almost saturated due to the protection afforded by the top two layers. Accordingly, methane emissions from the CCBE were the highest, whereas those from the three-layer cover were the lowest. Ignoring vapor will predict a drier soil state, and hence will cause methane emissions to be overestimated by 1–2.5 times. Effects of vapor became more significant as the overall gas coefficient of permeability of the cover increased. [ABSTRACT FROM AUTHOR]

Civil engineers face significant challenges in the safe design and construction of durable road infrastructure in the presence of expansive soils. These problematic soils exacerbate undesirable serviceability concerns induced by pavement distress. Soil stabilisation has been recognised as a sustainable approach to alleviate the problematic nature of expansive subgrades. Road pavements constructed on top of expansive subgrade soils are generally under unsaturated conditions, where the moisture variations can significantly impact the pavement response. However, current pavement design and modelling frameworks overlook unsaturated soil behaviour by adopting simplified approaches. This study examines the hydraulic behaviour of expansive clayey soils stabilised with non-traditional and traditional chemical based additive. Tests were conducted to determine the state variation and stabilisation influence on the soil water characteristic curve using the dewpoint potentiometer for an expansive subgrade commonly found in Melbourne geology. Results show that the stabilisation has strong influence on soil hydraulic characteristics at various initial state conditions tested. Experimental data have been applied to illustrate the significance of incorporating realistic hydraulic response using a simulated practical application in road pavements. The research highlights the significance of incorporating accurate hydraulic characteristics for simulating and assessing the response of pavement constructed with stabilised unsaturated subgrade soils. [ABSTRACT FROM AUTHOR]

In the current study, three Ng tests were performed to simulate the LNAPL contaminants' transport and fate in the porous media. Through the tests, the efficacy of the soil–cement vertical barriers with a low permeability, which is among the most-used techniques in site remediations in practical projects, was assessed, and the results were compared to that of free field condition. Furthermore, extensive insight was achieved into the migration pattern of the LNAPL in unsaturated soil. All of the Ng tests were implemented at 40 g to simulate a voluminous spill of LNAPL in various timeframes. Consecutive imaging through the transparent front was used to gather data, and the LRV image processing technique was utilized to analyze these data. Reliable and effective performance of the barriers for containing the LNAPL spread was confirmed. Groundwater depression was observed in all three tests, particularly in the tests with using barriers. Nevertheless, using barriers restrained the contaminated soil and groundwater to the zones between the two barriers. Based on the observed LNAPL plume, the minimum depth of these barriers was recommended to account for the preferential flow. Three different methods were used for the validation of the image processing results. All in all, the accuracy of image processing was satisfactorily high. [ABSTRACT FROM AUTHOR]

Geosynthetic-reinforced soil (GRS) walls using marginal soils can operate under unsaturated conditions depending on climate conditions and drainage inside the reinforced zone. Geocomposite reinforcements have been suggested to act as internal drainage layers, but their hydraulic behavior can also be strongly affected by climate conditions. Numerical analyses were conducted to observe the impact of four distinct tropical climate conditions (arid, semi-arid, humid subtropical and humid tropical) on suction profiles and stability of reinforced soil walls constructed using geogrid and geocomposite reinforcements. The climate simulation involved the incorporation of a soil-atmosphere interaction on water balance and on the unsaturated transient infiltration. Results indicate the GRS walls can operate under relatively high suction levels under arid climates in which cumulative evaporation overcomes infiltration. Any climate that has rainy seasons with consecutive rainfalls with intensities close to the infiltration capacity of soil and/or monthly cumulative precipitation higher than 200 mm/day led to critical conditions in terms of soil water saturation and stability. Under unsaturated conditions of soil, the drainage effectiveness of geocomposites is significantly reduced and adverse capillary break effects become critical. • Evaporation has a significant effect on stability of geosynthetic reinforced soil structures. • Unsaturated condition was kept in climates which the monthly precipitation does not overcome the evaporation. • The critical FOS was reached in climates with monthly cumulative precipitation of 200 mm. • The pattern of rainy season has a significant effect on the FOS. • Under the real climate conditions, the effectiveness of draining geocomposite reinforcements is significantly reduced. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical model for evaluating the dynamic response of an underground railway tunnel in layered foundation soil with different saturations. The soil is modeled as layered media, and the circular tunnel lining is modeled as an infinite Flügge cylindrical shell. The separation of variables method is used to solve the motion equation of the shell, and the wave equation of the soil is solved using the Helmholtz decomposition theorem. A dynamic matrix reflecting the wave vectors of soil layers is established using the transfer matrix method. Based on boundary conditions, the tunnel-soil model is coupled using the transformation method of plane wave functions and cylindrical wave functions. The proposed model is validated by comparison with existing tunnel models, and the effects of saturation and the layered properties of soil on the dynamic response of a layered tunnel-soil system is demonstrated via case studies. [ABSTRACT FROM AUTHOR]

Rainfall infiltration causes the collapse of unsaturated embankments due to loss of suction. In this paper, the Barcelona Basic Model (BBM), a constitutive model developed for unsaturated soils, was implemented in Fast Lagrangian Analysis of Continua (FLAC) for simulating the effect of varying rainfall intensities on compacted embankments. It was observed that large vertical deformations occur and considerably high positive pore-water pressures get developed, accounting for the collapse of an embankment. The results also show that rainfall intensity and duration affect the slope stability. A comparison was made between the results obtained using the Mohr–Coulomb model and BBM. It was found that the soil undergoes larger deformations when modeled using BBM as BBM accurately models the loss of suction upon saturation. Reliability analysis of embankment shows that probabilistic analysis provides a better assessment of slope stability rather than the factor of safety and shows that suction and hydraulic conductivity are critical parameters influencing slope reliability for unsaturated soil slope embankments. [ABSTRACT FROM AUTHOR]

Traditionally, the seepage through embankments and other geotechnical structures is estimated using the hydraulic properties of saturated soil. In most cases, the soil is not fully saturated, and the use of saturated soil properties can lead to erroneous results. A reliable assessment of slope stability needs comprehensive characterization of both unsaturated and hydraulic properties of saturated soil. The permeability coefficient of unsaturated soil is usually estimated using existing permeability models derived from the soil water characteristic curve (SWCC) of soil. The performance of these prediction models has not been consistent in the past. A proper determination of unsaturated soil permeability properties will be needed for better stability designs and checks of earth structures. In this study, an experimental program is designed to evaluate the influence of matric suction, net confining stress, and wetting and drying cycles on the hydraulic conductivity of a clayey soil over a wide range of suction values. Modified suction-controlled triaxial equipment was used to apply and maintain suction and hydraulic head in a soil specimen to measure the coefficient of permeability for drying and wetting cycles. Additionally, a series of fully coupled hydromechanic numerical analyses was performed to examine the effect of hydraulic properties of unsaturated soil on pore water pressure response and safety factors of slope for transient seepage conditions during drawdown. The effects of stress-dependent hydraulic properties and hydraulic hysteresis on transient seepage were also investigated. The findings from this study highlight the role of hydraulic properties of partially saturated soil in seepage and slope stability analysis of earthen dams. [ABSTRACT FROM AUTHOR]

Band gaps or attenuation zones existing in periodic structures can filter out elastic waves propagating in both single-phase soils and saturated soils in specific frequency regions, which opens a window for designing new wave barriers to attenuate ambient vibration. However, vibration mitigation in unsaturated soil remains a significant challenge due to soil's constitutive relation strongly relying on saturation, especially by periodic wave barriers. Based on local resonance mechanism, the performance of a periodic in-filled barrier for isolating low-frequency ambient vibration is studied. The periodic in-filled barrier is filled with a viscous material. Investigations found that the attenuation zones of the periodic wave barrier are robust to saturation and the viscosity of the in-filled material can broaden the frequency range for vibration reduction. More interestingly, periodic wave barriers in unsaturated soils can produce attenuation zones for P1 waves, which is impossible in saturated soils. Therefore, this investigation provides a promising insight for the application of periodic wave barriers to unsaturated soils. • The complex band structures of bulk waves in an in-filled periodic barrier are obtained. • This periodic barrier provides a precise low-frequency attenuation zone which is robust to saturation. • The viscosity of the in-filled material can improve the mitigation performance outside the attenuation zone at the expense of weakening it inside the attenuation zone. [ABSTRACT FROM AUTHOR]

Post-wildfire mass wasting is a major problem throughout many regions worldwide. Recent dramatic increases in global wildfire activities coupled with a shift in wildfire-prone elevation to higher altitudes raise the need to better predict post-fire rainfall-triggered landslides. Despite its importance, only a limited number of studies have investigated landslide susceptibility in areas hit by wildfires using hydromechanical models. However, most of these studies follow either qualitative or semi-quantitative approaches without explicitly considering the fire's effects on the impacted area's physical behavior. This study aims to develop and employ a physics-based framework to generate susceptibility maps of rainfall-triggered shallow landslides in areas disturbed by wildfire. A coupled hydromechanical model considering unsaturated flow and root reinforcement is integrated into an infinite slope stability model to simulate the triggering of shallow landslides from rainfall. The impact of fire is considered through its effects on soil and land cover properties, near-surface processes, and canopy interception. The developed model is then integrated into a geographic information system (GIS) to characterize the regional distribution of landslide potential and its variability considering topography, geology, land cover, and burn severity. The proposed framework was tested for a study site in Southern California. The site was burned in the San Gabriel Complex Fire in June 2016 and experienced widespread landsliding almost three years later following an extreme rainstorm in January 2019. The proposed framework could successfully model the location of observed shallow landslides. The model also revealed a significantly higher likelihood for slope failure in areas burned at moderate to high severities as opposed to unburned and low-burn severity areas. The findings of this study can be employed to predict the timing and general locations of rainfall-triggered shallow landslides following wildfires. • Novel physics-based framework developed to predict post-fire rainfall-triggered landslides. • Integration of hydromechanical and infinite slope stability models considering fire effects. • Successful modeling of observed shallow landslides in a Southern California study site. • Higher likelihood of slope failure in areas burned at moderate to high severities revealed. [ABSTRACT FROM AUTHOR]

This paper focuses on the impact of elevated temperatures on the adsorptive and capillarity water retention mechanisms of unsaturated soils under constrained (constant volume) conditions. This topic is critical for simulating the thermo-hydraulic behavior of soils in hydrogeological or geotechnical applications, including climate change effects on near surface soils, energy piles or soil borehole thermal energy storage systems in unsaturated soil layers, and buffers for geological nuclear waste repositories. A nonisothermal soil water retention curve (SWRC) that separately considers the temperature-dependency of the key parameters governing adsorptive and capillarity water retention mechanisms and soil physical parameters (e.g., surface tension, contact angle, adsorption capacity, cation exchange capacity, mean cavitation suction, air entry value and equilibrium film thickness) was developed to provide insights into the impact of temperature on water retention over the full suction range. The nonisothermal SWRC was validated using experimental data on high plasticity clays, with a good prediction of temperature effects on adsorption and capillarity water retention mechanisms in constrained unsaturated soils. [ABSTRACT FROM AUTHOR]

Most previous experimental studies on the behavior of piles subjected to lateral loading have focused on testing model piles embedded in dry or fully saturated soils, and little attention has been paid to the impact of the soil partial saturation on the results. This paper presents results of 1g model tests on a single pile embedded in dry and unsaturated sand subjected to two-way constant displacement amplitude loading. The tests were aimed at examination of the effects of degree of soil saturation and density on the pile internal forces and lateral capacity and the deformation patterns of the adjacent soils. Five degrees of saturation (Sr = 0, 10, 20, 35 and 50%) for loose and medium-dense sand (Dr = 20% and 50%) were chosen and a 65-mm-diameter and 900-mm-long polyethylene model pile was used. Test results indicated that at each soil relative density, the pile head horizontal load, and the maximum bending moment, shear force, and soil reaction in the pile increase with increase in the degree of saturation up to about Sr = 35%. However, further increase in Sr led to decrease in these values. Moreover, the cyclic loading led to depressions in the surface of the dry sand and bulging associated with soil–pile separation in the unsaturated sand. For the model testing conditions used, results indicated that the sand degree of saturation can have a greater impact on the pile behavior than its density. [ABSTRACT FROM AUTHOR]