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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]

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]

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]

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

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

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

Traditional soil mechanics idealizes geomaterials as being in a dry or fully water-saturated state. However, there is a zone between the ground surface and the groundwater table, where the soil is unsaturated, which means the pore space is filled with air and water. This zone is affected by environmental changes during wetting and drying seasons through precipitation, evaporation, or evapotranspiration. The influence of water content, for instance, the degree of saturation, on the characteristics of soil under dynamic loading i.e. at small to intermediate strains, for example, small-strain shear modulus (Gmax), modulus degradation [G(γ)], and damping ratio [D(γ)] remain of interest in the geotechnical community due to the practical relevance of the problem. This study attempted to cover the existing gaps in the dynamic characteristics of soil with different degrees of saturation. Therefore, Hostun sand (HS) was mixed with 30% Amberger kaolin (AK) and compacted to Proctor density at the optimum water content. They were saturated in a special saturation cell applying back pressure. Then, the saturated samples were dried to different degrees of saturation. Resonant column (RC) tests were carried out on the prepared samples to determine the effect of the degree of saturation on Gmax, G(γ), and D(γ). Of note, in this series of tests, suction was not strictly controlled; however, the necessary volume change corrections were performed via various noncontact transducers. To describe the experimental observations and to evaluate the impact of the degree of saturation on Gmax, G(γ), and D(γ), the soil water characteristic curve (SWCC) of the adopted mixture was determined. The results showed a significant increase of Gmax with the degree of saturation following an S-phaped curve. Based on the new data, previous models to predict Gmax were inspected under a significantly wider range of the degrees of saturation and suction. In addition, the effect of the degree of saturation on the intermediate strain characteristics of the adopted mixture [G(γ)/Gmax] and D(γ) was evaluated, where modulus degradation was found almost unaffected by Sr while a moderate increase of damping ratio with Sr was observed. [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]

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

In the common practice of geotechnical design, the state of soil is considered fully saturated, while recent examples show the importance of the consideration of unsaturated conditions as well due to the location of the groundwater table at deeper levels. However, it is problematic to design a foundation and calculate bearing capacity as the internal stress in unsaturated conditions needs to be quantified. The mechanics of unsaturated soils are critical in geotechnical engineering, especially when the case of the foundation design is required. This study aims to investigate the influence of suction on the shaft capacity of pile foundations based on the data obtained from in situ and laboratory testing. The three modified methods (i.e., modified α, β, and λ) were implemented in this study in order to calculate the shaft capacity of the pile foundation incorporating unsaturated soil mechanics principles. In addition, the effect of varying matric suction on shaft capacity was discussed. The results of obtained changes show the importance of rain infiltration in the design of piles in unsaturated conditions. It can be concluded that the most conservative method is found to be the modified β method in designing pile foundations incorporating the suction changes due to rainwater infiltration. However, cost optimization shall be considered while choosing the method for the design. As for the increase in GWT, the modified λ method depicted the most conventional behavior. The possible rain infiltration decreases matric suction, mostly in the upper layers. [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]

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]

Ignoring the role of soil suction and implementing unsaturated soil mechanics when assessing slope stability in Indonesia is a common practice. One of the main reasons is due to the precognition that incorporating soil suction means using higher shear strength, which leads to less conservative analysis, while it is difficult to practically obtain accurate input parameters for unsaturated soil analysis. However, a number of slope failures occur all over the world due to rainfall, which becomes evidence that ignoring the role of soil suction may not necessarily lead to a conservative result. On 9 January 2021, rainfall-induced slope failure occurred at Cimanggung after four hours of heavy rainfall and killed 32 people. Many of them were injured, and houses were destroyed. This event shows the significance of considering the interaction between infiltration and soil suction when conducting slope stability analysis. Difficulties in obtaining input parameters for unsaturated soil analysis experimentally hindered practitioners in applying unsaturated soil mechanics. While the parameters can be estimated, it is always of question whether the estimated parameters are sufficiently accurate for practical purposes. In this paper, conventional site investigations were carried out while unsaturated soil parameters were estimated to study the mechanism which triggers the landslide that occurred at Cimanggung. It will be shown that estimating unsaturated soil parameters can be practically accurate and manage to capture the failure mechanism such as critical rainfall duration and critical slip surface. [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]

Prefabricated vertical drains (PVDs) are an established ground improvement method. Mimicking drinking straws, PVDs are installed to convey vacuum pressure in the ground and lift groundwater. However, the dewatering performance is suboptimal in consolidating fine-grained layers. Practical applications have shown that better dewatering performance is achieved through aiding the vacuum dewatering with an air-booster. Air-boosters are installed in an alternating pattern adjoining PVDs, increasing pore pressures and unclogging pores. This study presented a numerical model for this vacuum and air-booster combined dewatering solution. Taking account of the large strain deformation, this model used the Lagrangian-convective coordinate to track the global and local deformation of the soil layer separately, thus enabling accurate determination of consolidation. This model also considered air-booster induced unsaturated conditions and the associated effects on water flow. The numerical model was verified against field test results and laboratory measurements. [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]

Arsenic is a metalloid frequently found in contaminated sites, especially in the soil. In this regard, soil contamination has attracted researchers' attention because it affects soil suction, which is essential in unsaturated soil mechanics. Due to its reliability and low cost, the filter paper method is frequently used to evaluate soil suction. However, it is laborious and time consuming. As an alternative, different mathematical models have been developed to estimate natural soil's suction. The objective of this study was to elucidate if Fuentes' model (using fractal, Mualem, and Burdine restrictions) can be used to estimate the soil-water retention curve of an arsenic-contaminated soil by comparing it with the filter paper method data already reported. The results showed that under natural conditions, Fuentes' model provided similar results to those obtained by the filter paper method. The model also suggested modification of the soil's structure, observed by the increase in the soil's particle diameter after contamination. However, Fuentes' model was observed to overestimate the suction values for contaminated soils. This observation highlights the necessity to use a soil stabilization method to control the soil's volume variations. The data also showed that Fuentes' model overestimated the hydraulic conductivity function of the contaminated soil. Hence, the retention potential does not reflect the behavior of the contaminated soils and can induce misinterpretation of contaminant transport evaluation in soil. Nevertheless, further analyses should be performed to investigate the direct applicability of this model to soils contaminated with other substances. [ABSTRACT FROM AUTHOR]

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The humidity sensors based on metal halide perovskite have achieved outstanding improvement. However, there are few reports of perovskite nanocrystals for humidity sensors. Herein, CsPdBr3 nanocrystals with high surface‐to‐volume ratio are synthesized by the in situ spin‐coating method. Subsequently, the humidity sensor based on CsPdBr3 nanocrystals is prepared and the response mechanism is demonstrated to originate from the formation of the Pd––O bond on the surface by performing density functional theory calculation. The humidity sensor shows a fast response/recovery time of 0.68/2.43 s in a relative humidity range from 88.9%RH to 4.7%RH; the fast response/recovery properties are used to monitor human respiratory and noncontact switch. Moreover, the hydromechanical characteristics of unsaturated soil are obtained by noncontact testing with the humidity sensor for the first time in geological engineering, and the strong correlation between relative humidity and hydromechanical characteristics is revealed by mathematical derivation, which lays the theoretical foundation for the noncontact real‐time sensing of hydromechanical characteristics of unsaturated soil. These findings not only open the door to the development of perovskite nanocrystals materials for humidity measurement, but also offer a new method for nondestructive and real‐time test of the mechanical properties of soil in geological engineering. [ABSTRACT FROM AUTHOR]

The mechanisms of hydraulic collapse (wetting‐induced deformation) are studied through a series of simulations using a model for unsaturated soils. The model is a critical state soil model extended for unsaturated soils using Bishop's effective stress tensor, the state boundary surface (SBS) moving with the change in the degree of saturation, and a rational soil‐water characteristic curve that takes account of density and hydraulic hysteresis. Comparisons with published experimental data validate the proposed model. The simulation results show that the model adequately captures the hydraulic collapse behavior under both isotropic and anisotropic stress conditions. The effects of density, mean net stress, and deviatoric stress on the hydraulic collapse behavior are further investigated through a parametric calculation, and the mechanics of the wetting–induced instability are discussed. The effects of suction history, namely repeated wetting and drying cycles, on the deformation and failure, are also presented. The proposed model provides a validated method for modeling hydromechanical collapse in unsaturated soil and provides a better understanding of the mechanisms involved. [ABSTRACT FROM AUTHOR]

This paper presents numerical simulations of the deformation response of unsaturated embankments subjected to rainfall infiltration using a coupled hydro-mechanical constitutive model for unsaturated soils. The constitutive model accounts for the influence of degree of saturation on the stress–strain behavior and the influence of void ratio on the water retention behavior. The constitutive model was implemented in the finite difference program FLAC, calibrated using triaxial test data, and validated using measurements of wetting-induced deformations of embankment models from centrifuge tests. The validation demonstrates that the constitutive model can capture the coupled hydro-mechanical behavior of unsaturated soils under wetting conditions. Simulations of the hydro-mechanical response of unsaturated embankments subjected to rainfall infiltration indicate that the differential settlement across the top surface of the embankment between the centerline and shoulder increases significantly during rainfall infiltration, which could result in severe damage to overlying transportation infrastructure. As the rainfall infiltration increases, shear strains accumulate and form a potential failure surface at a shallow depth of approximately 2 m from the slope surface. Insights into the hydro-mechanical response of unsaturated embankments subjected to rainfall infiltration gained will be useful for considering climate change effects in design and construction of compacted embankments. [ABSTRACT FROM AUTHOR]

The stability of unsaturated slopes under seismic loading has become an important issue over the past few years which is the indication of its practical significance in geoengineering. This study aims at exploring the seismic stability of unsaturated sandy clay and silty clayey sand slopes using 2D limit equilibrium analysis for different slope geometries and ground water levels. To this end, the pseudo-static and the displacement-based sliding block Newmark's approaches are employed for parametric studies by considering the records of the 2003 earthquake that devastated the city of Bam, in the southeast of Iran. In all analyses, the unsaturated state of the soil materials is taken into account in accordance with the changes in the matric suction profile within the soil body using the effective stress approach of unsaturated soil mechanics. The research outcomes, in terms of the safety factor, are then analyzed and compared for different examined conditions. The parametric study in this research considered the method of analysis, slope geometry, ground water conditions, and soil type as the most influential parameters on the factor of safety. The results revealed that considering the unsaturated parameters for the examined soils results in higher factor of safety in comparison with the corresponding cases in which unsaturated parameters are not adopted. A comparative study was also carried out based on a threshold safety factor, in which the safety factors obtained from all analyses, undergoing various conditions and loadings, provide a preliminary insight into the prospective seismic microzonation of unsaturated slopes. [ABSTRACT FROM AUTHOR]

The Barcelona Basic Model (BBM) has been implemented in a finite difference-based computer program to simulate the behavior of unsaturated soils subjected to wetting. The BBM implementation was verified using analytical solutions, and the proposed model has been used to simulate the response of a compacted embankment under complete saturation and suction induced conditions. Numerical analyses indicate that considerable amount of total and differential settlements could develop at the top surface of the embankment. BBM is executed into FLAC2D extending a defined module for modified Cam Clay (MCC) and has been set up an analytical solution for suction-dependent stress and strain. Evaluating the effect of anisotropy and nonlinear apparent tensile strength in unsaturated soils, a modification to BBM formulation has been proposed and optimized by developing numerical analyses to reduce the size of elastic region of loading collapse (LC) curve. Then, an experimental study in the literature is investigated by utilizing comparative curves from BBM and modified BBM indicating well agreement with natural circumstances. As a result of the work presented in this research, finite difference codes with BBM and modified BBM has the capability of simulating the real behavior and is operational being applied to problems associated with earthen structures in unsaturated or partially saturated of expansive soils as a three-phases medium. [ABSTRACT FROM AUTHOR]

The experimental data dealing with the so-called small strain stiffness of soils are indispensable in developing and calibrating advanced numerical models. A literature review revealed a lack of such data for unsaturated soils. In this study, the laboratory measurements of very small and small strain stiffness are carried out in a double-walled triaxial cell using bender elements and LVDT transducers. The tested soil is a reconstituted silty clay, representing a typical soil encountered in engineering practice. A so-called effective stress for unsaturated soil is used in interpreting and numerically simulating the effects of suction magnitude, net stress magnitude and suction history on the initial elastic shear modulus, and on its decrease with increasing strain. The increase of both net stress and suction leads to increase in stiffness. This is observed by both elastic shear modulus and shear modulus reduction curve measurements. The "overconsolidation" by suction leads to the increase of stiffness, too. The experimental data are used for calibrating constitutive parameters and for assessing the capabilities of an advanced hypoplastic model for unsaturated soils. The model predictions are consistent with the laboratory measurements and the model can capture the increase of stiffness with respect to the increase of suction and net stress reasonably well. Moreover, the model is able to predict the increase of stiffness due to suction "overconsolidation". [ABSTRACT FROM AUTHOR]

A two-layer hydro-mechanically coupled material point method has been formulated in the framework of unsaturated soil mechanics. The method employs two layers of material points to represent coupling effects between the solid and fluid phases. Several numerical examples demonstrate unique features of the method, including free water infiltration into the unsaturated soil, dynamic soil–water interaction in an example of underwater soil collapse and initially saturated soil column collapse. Furthermore, rainfall-induced failure in unsaturated soil slopes is analyzed. The proposed method can well capture change in matric suction, development of shallow and deep-seated shear bands, and finally, large-deformation post-failure behavior. Parametric studies also demonstrate soil cohesion, dilatancy and friction angle play significant roles on the slope failure mechanisms. [ABSTRACT FROM AUTHOR]

The pivotal aim of this research is to investigate the radial consolidation behavior of unsaturated soil by vertical drains under various cyclic loadings. Based on Fredlund and Hasan's consolidation theory for unsaturated soil, the governing equations for radial consolidation of unsaturated soil are converted into a set of conventional diffusion equations by introducing two new variables. Then, the general solutions for time‐dependent loading are derived under free‐strain condition and equal‐strain condition. Furthermore, the complete analytical solutions are proposed for different cyclic loadings such as haversine cyclic loading, trapezoidal cyclic loading, rectangular cyclic loading, and triangular cyclic loading. The proposed solutions are verified by comparing with those available in the literature as a limiting situation and the results show a quite good agreement. Finally, the effects of different parameters on the radial consolidation of unsaturated soil subjected to various cyclic loadings are graphically presented and examined. [ABSTRACT FROM AUTHOR]

To investigate unsaturated soil‐water interaction at micro‐scale, this study extends the numerical manifold method (NMM) by incorporating a soil‐water coupling model considering specific capillary water distribution and capillary force calculation. The soil skeleton is constructed by a soil skeleton generation algorithm with random polygons. To more realistically capture the interaction between soil grains and capillary water, a capillary mechanics‐based geometric algorithm is proposed to iteratively calculate the capillary water distribution. The capillary forces corresponding to the capillary water distribution are calculated based on the Young‐Laplace equation. The proposed capillary water solving framework is first verified by reproducing the soil‐water characteristic curve and the capillary water distribution of an ideal contact‐disk model against analytical solutions. To further validate the ability of the capillary water solving framework to predict hydraulic behavior of the real soil, a laboratory test on the Toyoura sand is reproduced numerically. Then an ideal direct shear test is performed to further validate the two‐way soil‐water coupling procedure, in which a comparison between the numerical and analytical results regarding the shear strength and matric suction is presented. Finally, microscopic hydraulic and compression tests are conducted on two soil specimens with the same porosity and mean grain diameter but different uniformity coefficients. The results elucidate that the extended method is a potential tool to explore unsaturated soil behaviors at micro‐scale. [ABSTRACT FROM AUTHOR]

Most soil mechanics theories are limited to strain hardening and shrinkage under high compressive stresses, and there are some shortcomings in the selection of suction or degree of saturation as the water content state varies in the constitutive models of unsaturated soil. Based on the triaxial shear tests of unsaturated compacted soil (a silt of high plasticity) with different water content and confining pressure (low-confining), a shear dilatancy model of unsaturated soil based on the mass water content is proposed in this paper. The influence of the water content on the shear deformation characteristics of the unsaturated soil is analysed. The stress–dilatancy relationship and the prediction equation of the minimum dilatancy rate of the unsaturated soil under different water content and different confining pressure are provided. Selecting the mass water content as the state variable, a constitutive model suitable for the dilatancy of unsaturated soil is established. The method of determining model parameters based on the mass water content is analysed. The applicability of the model is verified by comparisons between the predicted and experimental results. [ABSTRACT FROM AUTHOR]

Climate change is increasing the frequency of extreme rainfall events and the snow cover to melt at high altitudes, which may exacerbate the threat posed by debris flows. Soil bed erosion, the process by which the bed material fails under loadings from a debris flow, is perhaps the most important momentum exchange process that governs the destructive potential of debris flows. Existing erosion theories adopt saturated soil mechanics to describe the failure of soil bed and place a strong emphasis on the basal friction induced shear stress as the driving mechanism. However, soil beds in nature are rarely saturated and field observations have hinted at the importance of collisional stresses as a driving mechanism. In this study, an unsaturated soil mechanics framework is used to characterize soil bed erosion by collisional flows. Experiments were conducted to model the erosion of unsaturated sandy beds with a wide range of initial matric suction values, which is a measure of capillary stresses, by gravel flows. Contrary to the existing literature, the rate of erosion does not increase linearly but demonstrates a parabola‐like relationship with the bed water content because the shear strength of unsaturated soil is governed by capillary stresses. The importance of collisional stresses on soil bed erosion is demonstrated by a newly proposed dimensionless number. Findings indicate that existing erosion models largely underestimate channel bed erosion, especially for soil beds with low water content, and stress the importance of hydro‐mechanical coupling to advance the current state of debris flow hazard delineation. Key Points: Soil bed erosion by debris flow exhibits a parabola‐like relationship with bed water content under the influence of capillary stressesBasal collisional stresses have been largely ignored but are a major contributing factor to soil bed erosion by debris flowThe effects of capillary and collisional stresses need to be captured in debris flow models to improve hazard delineation [ABSTRACT FROM AUTHOR]

• Develops a fractal thermal conductivity model of heterogeneous soils. • The model can predict the thermal properties of unsaturated fine-grained soils. • The model can capture the thermal conductivity evolution during soil deformation. • The developed fractal model performs better compared to other models. Accurately predicting the thermal conductivity of unsaturated soils is crucial for assessing and simulating the long-term environmental impact of subterranean engineering structures. This study presents a fractal thermal conductivity model for unsaturated soils that considers the influence of heterogeneous pore topology, water content and volumetric deformation. Based on the results from the scanning electron microscopy (SEM) and mercury intrusion-extrusion cyclic porosimetry (MIECP) tests on Shanghai clay and Kaolin, we introduce the pore-throat structure to describe the soil heterogeneity and deal with the coupling of solid-pore thermal properties through the mixing law at the pore scale. Together with the self-similar fractal law, the thermal conductivity model is upscaled from the pore scale to the representative element volume (REV) scale. During the process, heterogeneity factors are introduced to describe differences between local and bulk properties, such as porosity and saturation. Thermal property tests of Shanghai clay and Kaolin with varying porosities are then conducted to validate the proposed thermal conductivity model. Additionally, nineteen published datasets on thermal conductivity are also utilized to confirm the adaptability and robustness of the model. The results show that the proposed model predicts well the thermal conductivity of unsaturated soils. Moreover, when compared to existing models, the proposed model offers superior performance in describing the thermal properties of unsaturated soils. [ABSTRACT FROM AUTHOR]

Rainfall is one of the most significant natural factors for inducing landslides. The shallow saturated zone formed in slopes during rainfall is an important factor in inducing shallow landslides. In this paper, the characteristics and influencing factors of the saturated zone in soil slopes, and the relationship between the soil surface permeability coefficient and the rainfall intensity are analyzed. In this research, the equation that characterizes the rainfall intensity by the soil saturation is built based on the Mualem-van Genuchten model, which mathematically describes the soil water characteristics of unsaturated soils. Using this model, the target saturation of the slope surface during rainfall can be determined accurately, with an average deviation of − 0.008. Based on the equations, the innovative critical curve model of the rainfall intensity−time required to form the shallow saturated zone is established and calculated. The influence of the soil material, slope angle, rainfall intensity and antecedent rainfall on the critical curve for the shallow saturated zone is analyzed. The results indicate that for slopes of 30°~40°, it is easy for the shallow saturated zone to form, and the previous rainfall after more than 16 days has little impact on the critical curve. Furthermore, an innovative landslide prediction model, based on the critical curve for the shallow saturated zone and I-D modeling, is proposed to provide benchmarks for the prediction-specific characteristics of deep or shallow landslides, which is verified by the case of the Madiwan landslide. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) kinematic limit analysis of unsaturated hillslopes is presented in this paper. Different from the traditional two-dimensional (2D) mechanism based on the infinite slope model, the 3D failure mechanism is more rational for its advantage in taking the out-of-plane geometries and soil properties into consideration. The soils in engineering practice are mostly unsaturated in nature and are commonly characterized with an arbitrary distribution of the moisture content, i.e., the matric suction, and therefore the formation of the work balance equation becomes much more elaborated using traditional methods. To tackle the nonlinear features of matric suction, a semi-analytical method is presented and is validated through comparisons with the benchmark solutions. The hillslope stability under seismic and pore water pressure conditions are both numerically studied. The results are presented in forms of graphs for a practical range of parameters, indicating the significance in accounting for the influences of 3D constraints, seismic loads and pore water pressures in hillslope stability assessments. [ABSTRACT FROM AUTHOR]

This paper describes the application of unsaturated soil mechanics to an interstate connecting-ramp embankment that failed during construction. Specifically, matric suction is incorporated into the calculation of the tension crack (TC) depth induced by desiccation and strain incompatibility and the contribution of matric suction to embankment shear strength. The results are compared with field observations to assess the viability of unsaturated soil mechanics in modeling compacted embankments in stability analyses. Results from this study suggest that using unsaturated shear strength parameters while introducing a TC in the compacted fill yields a reasonable inverse analysis of this interstate embankment. This may be preferred in slope stability analyses to the current practice of using an undrained shear strength (i.e., cohesion) for the unsaturated compacted fill and including a TC to generate a reasonable factor of safety. [ABSTRACT FROM AUTHOR]

In mountainous western China, a large number of granular materials are used as construction materials in high-fill embankments. These granular fill materials in the embankments are typically unsaturated owing to the arid and semi-arid climates in this area. However, previous studies on unsaturated soils primarily focus on fine-grained soils. In this study, a series of triaxial tests were performed to determine the critical state parameters of a granular fill material in q– p ¯ , v–ln p ¯ , and vw–ln p ¯ planes. An upgraded double-cell triaxial system (DCTS) was used in net confining pressures ranging from 0 to 450 kPa and matric suctions ranging from 0 to 160 kPa. This study demonstrates the good performance of the upgraded DCTS in unsaturated soil testing. Experimental results show that the critical state lines are almost parallel to those of saturated soil in the q– p ¯ plane, suggesting that the friction angle is independent of suction. The total cohesion and hence the shear strength increase with suction. In the v–ln p ¯ plane, both the intercept and slope of the critical state line increase with suction. Finally, it is observed that the intercept and slope decrease with increasing suction in the vw–ln p ¯ plane. [ABSTRACT FROM AUTHOR]

Naturally, soil moisture reduces during dry seasons when the soil is in drying state; while it increases during wet seasons when the soil is in wetting state. Previous studies have shown that for an unsaturated soil sample, soil-water characteristic curves (SWCCs) do not match in wetting and drying paths. The differences between wetting and drying paths are called the hydraulic hysteresis. The hydraulic hysteresis plays an important role in mechanical properties of soil such as shear strength, volume change, and settlement. The objective of this research is to study the effects of drying and wetting on the effective stress and compressibility of unsaturated clayey fine-grained soils. To this end, saturated and unsaturated triaxial tests were performed on the soil samples under various normal mean stresses, and matrix suctions in drying and wetting paths. It was found that soil samples bear higher levels of effective stress in the drying path than the wetting path under a same level of suction. The attained values of effective stress parameter (?) showed that the Bishop's effective stress parameter (= Sr) is not properly applicable for the clayey soil. Moreover, the resulting loading-collapse curve (LC) revealed that the effective pre-consolidation pressure in the drying and wetting stages changed even with same degrees of matrix suction. [ABSTRACT FROM AUTHOR]

The complexity of unsaturated soil means that its permeability coefficient and seepage law are important topics in soil mechanics and geotechnical engineering. In this study, a new type of equipment for measuring the seepage of unsaturated soil was used to study the steady seepage of unsaturated loess soil collected from northern Shaanxi province in China. The entire process of the steady seepage of unsaturated soil under different seepage hydraulic gradients was obtained, and the permeability coefficient in the steady seepage state was measured. When the soil water content was low, the soil moisture remained only in small pores or at the junction of soil particles, the effective seepage area of the sample was reduced, and the seepage path was extended. Therefore, the lower the water content, the smaller the permeability coefficient of unsaturated soil and the longer the time required for the seepage to reach a steady state. The matric suction of the unsaturated loess soil was measured under different water contents. With decreasing water content, water remained only in the smaller pores, which provided shrink films with a smaller radius of curvature. This allowed the shrink films to withstand a larger pore air pressure and transmit a smaller pore water pressure, so that the matric suction of the loess soil increased with decreasing soil water content. The Gardner model provided an accurate fit of how the matric suction varied with the volumetric water content of the unsaturated soil. The seepage velocity and seepage hydraulic gradient were correlated well with a linear relationship, indicating that the seepage law of unsaturated loess soil accords with Darcy's law. The experimental results show that the new unsaturated soil permeameter has good performance and controllability, thereby providing support for studying the steady seepage of unsaturated soil. [ABSTRACT FROM AUTHOR]

In 1959, Bishop published his classic paper on “effective stress” in unsaturated soils, combining together the components of net stress and suction into a single stress variable using the empirical  factor. Jennings and Burland (1962) criticised this approach, identifying limitations in the use of an “effective stress”. In particular, the approach failed to explain volumetric collapse of soil when wetted. Burland followed up this criticism in 1965 by pointing out that the role of suction was two-fold; not only did it increase the contact stress between particles but the presence of air-water interfaces (menisci) also had a stabilising effect. He suggested that we should not try to combine the stress variables into a single “effective stress” but that we should treat the two stress components of net stress and suction differently. This approach was adopted by Fredlund and Morgenstern (1977) and led to the widely used  b approach. Thus, in critiquing the Bishop approach, John Burland had a highly significant input into the direction of unsaturated soil research and practice over a number of decades. In this paper, Burland’s contribution to the debate on stress components in unsaturated soils will be examined through reinterpretation of a set of experimental data from triaxial testing of an unsaturated lateritic gravel. The results confirm that attempting to combine net stress and suction into a single variable is not sufficient for interpreting unsaturated soil behaviour. [ABSTRACT FROM AUTHOR]

In order to study how shear strength and its change in unsaturated soils modified by hydrophobic agent, sandy soils hydrophobized by dimethyldichlorosilane (DMDCS) were prepared. The hydrophobic soils with different DMDCS volume by soil mass, water content and clay content were obtained respectively. Mixtures of sandy soils (DMDCS volume by soil mass were 2 mL:100 g and 3 mL:100 g, i.e., 2% and 3%, the same below) with 3%, 5%, 7%, 11% and 13% water content were prepared respectively. Meanwhile, the mixtures of clay and sandy soils (3% DMDCS) according to the clay mass fraction of 0, 5%, 10%, 15%, 20%, 25%, 30%, 40% and 50% were prepared respectively. Then the unsaturated direct shear tests were carried out by unsaturated direct shear apparatus. Four samples in each group were prepared under the normal pressure in 100, 200, 300 and 400 kPa, respectively. The horizontal shearing ratio was 0.8 mm/min and the shearing test lasted 6 min. The results showed that: 1) The mixtures of sandy soils and DMDCS presented extreme hydrophobicity. 2) The water repelling of mixtures of clay and sandy soils was affected by both DMDCS and clay content. The water repelling of mixtures was degraded with the increasing of clay content, and improved with the increasing of DMDCS volume by soil mass. 3) The Mohr-Coulomb strength criterion could be adopted to describe the shear strength of hydrophobic sandy soils with different DMDCS and water content. With the increasing of DMDCS volume by soil mass, the shear strength index of the hydrophobic soil was decreased to different extents. The cohesive force showed a steep-drop shape from soil without DMDCS addition to that with 1% DMDCS and a slow decline up to stabilize finally. The effect of DMDCS on the cohesive force of modified sandy soils was much greater than on the internal friction angle. The hydrophobic soils’ cohesion with the increasing of water content was decreased gradually, while the internal friction angle was increased firstly and decreased finally. The water content had a much effect on the shear strength of the hydrophobic sandy soils. The shear strength index were decreased with the increasing of DMDCS volume by soil mass: the cohesion was declined rapidly from 19.6 kPa (no DMDCS) to 10.4 kPa (1% DMDCS) and slowly from 10.4 kPa (1% DMDCS) to 9.3 kPa (3% DMDCS). The internal friction angle was declined slowly from 16.2° (no DMDCS) to 11.8° (3% DMDCS). The cohesion was decreased with the increasing of water content: the cohesion was declined from 15.5 kPa (3% water content) to 7.5 kPa (13% water content) with 2% DMDCS and from 15 kPa (3% water content) to 5.2 kPa (13% water content) with 3% DMDCS respectively; the internal friction angle was increased from 12.7° (3% water content) to 15.2° (11% water content) with 2% DMDCS and from 11.7° (3% water content) to 14.6° (7% water content) with 3% DMDCS, then decreased to 13.9° (13% water content) with 2% DMDCS and 11.9° (13% water content) with 3% DMDCS respectively. 4) The Mohr-Coulomb strength criterion could also be adopted to describe the shear strength of hydrophobic mixed soils with different clay content. The cohesion was increased remarkably with the increasing of clay content. The cohesion of sandy soils without clay was 9.3 kPa, then suddenly increased to 27.2 kPa and 55.1 kPa mixed with 5% and 50% clay mass fraction, respectively. The internal friction angle was increased from 12.1° (5% clay mass fraction) to 16.2° (15% clay mass fraction), and then decreased to 9.7° (50% clay mass fraction). All the analysis could be beneficial to analyze the shear strength of hydrophobized soils and apply in engineering. [ABSTRACT FROM AUTHOR]

Highlights • Repeat small scale flying plate test with soil blast over two plate sizes. • Soil characterisation for a sandy gravel soil. • Development of an FHWA soil material model. • Numerical validation and analysis using LS-DYNA. Abstract This paper presents the results of a combined experimental and numerical investigation into the blast loading generated by an explosive charge buried in an unsaturated soil. The dynamic response of the soil blast is quantified by its impulse imparted onto a high strength steel plate in a flying plate experiment. A 50 mm-thick plate of exposed area 500 mm by 500 mm is located at a constant stand-off distance of 400 mm above the surface of the soil. Upon detonation, the plate's heights are recorded and analysed using the initial velocity of the plate calculated from the flying time, while the rotation of the plates was shown to have negligible influence. Detailed unsaturated soil preparation, in-situ and laboratory characterisation as well as experimental setup are reported and compared to obtained meaningful parameters of the soil for the tests. The numerical model for the soil blast impact on the steel plates is developed based on the Arbitrary Lagrangian-Eulerian (ALE) method in the commercial simulation package LS-DYNA. Key soil properties, such as density, moisture content, bulk and shear moduli are characterised and utilised as input parameters into the FHWA material model in the numerical model. Results from a series of soil blast tests with 0.5 kg TNT charges on different plate sizes are presented and validated numerically. The numerical models agree generally well with the unsaturated soil blast test results, while the observed variations in the plate height are clearly attributed to the sensitivity of the soil properties. [ABSTRACT FROM AUTHOR]

The basic scheme of microscopic mechanical model is proposed to analyze the various mechanical behaviors of unsaturated coarse-grain soil. Physical quantities required for the proposed model are grain size distribution, soil particle density, void ratio and water content. The probability theory and inferential statistics are applied to relate the macroscopic physical quantities used in the conventional soil mechanics to the microscopic physical quantities in the proposed model. [ABSTRACT FROM AUTHOR]

Seasonal volume changes associated with wetting and drying conditions due to infiltration and evaporation of water significantly influence the mechanical behavior of expansive soils. For this reason, rational design of foundations in expansive soils has been a challenge for the geotechnical engineers. Pile foundations have been found to be more suitable in carrying loads from the superstructure to the expansive soil below alleviating stability and deformation problems in comparison to other types of foundations. However, there is a lack of simple procedures in the literature to estimate how the load transfers from pile to the soil, which is the key information required in the rational design of pile foundations in expansive soils. In this paper, the conventional shear deformation method is modified to estimate the load transfer mechanism from pile to expansive soil taking account of the influence of infiltration and evaporation of water. The proposed approach is based on the mechanics of unsaturated soils and can be extended for single pile considering the influence of volume change behavior in expansive soils. In addition, parametric analysis undertaken in the present study suggests that the pile diameter and pile length significantly influence the mechanical behavior of piles in expansive soils. Geotechnical engineers can use the proposed method in routine design of foundations for expansive soils as the complexity associated with the estimation of pile mechanical behavior in expansive soils is significantly reduced. [ABSTRACT FROM AUTHOR]

Summary: Strain localization has been the subject of extensive theoretical and numerical studies over the last four decades. The static and dynamic strain localization in both dry and water‐saturated geomaterials has widely been investigated numerically. However, studies on unsaturated geomaterials have been insufficient. This paper presents a computational model for nonlinear dynamic analysis of strain localization in multiphase geomaterials. The discretization of the governing equations is achieved using the finite element method in the finite deformation regime with the updated Lagrangian description. An elasto‐viscoplastic model extended to include the effect of suction on the behavior of partially saturated clay is used in the formulation. The nonlinear kinematic hardening rule and softening due to the structural degradation of soil particles are taken into account in the model. The inception and progression of localization in fully saturated and unsaturated clay under dynamic compressive loading are investigated. In the unsaturated case, the strain localization becomes more pronounced and much clearer shear bands are formed. More brittleness is observed in the unsaturated case due to the collapse of suction force caused by shearing. This demonstrates that even though suction improves the mechanical properties of soil, ie, increasing the stiffness and shear strength, the hypothesis of fully saturation is not at all on the side of safety due to the drastic loss of strength associated with the collapse of suction which may cause a strong strain localization. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • When saturation degree rises, shear strength of circular particles assembly rises. • For elliptical particles, shear strength rises with the saturation degree then drops. • The highest apparent-cohesion rise takes place for the highest eccentric particles. • Unsaturated assemblies contract more before the phase transfer point at low strains. • The highest coordination number and shear strength occurs at eccentricity 15%. Abstract The unsaturated soils mechanic is of significant importance for understanding and predicting the actual behavior of unsaturated soils in plenty of geo-environmental condition including tailing dams and earth dams during construction and operation, soil slopes, and shallow foundations. In this research, a micromechanical model for unsaturated assemblies composed of elliptical particles is presented so that the effect of capillary force, confining stress, and particle shape on unsaturated granular media behavior is analyzed in the pendular regime. As one of the early attempts, the toroidal liquid bridge for elliptical particles is studied in granular assemblies using modified ELLIPSE program, Discrete Element Method based program. The results show that although the strength of spherical particles grows when the saturated degree increases, the strength of elliptical particles rises and then decreases; however, the friction angle remains almost constant. Furthermore, the highest percentage of apparent-cohesion rise takes place at saturation degree of 10% at the highest eccentricity. As long as the eccentricity increases, the effect of capillary force on shear strength grows continuously. Not only do unsaturated assemblies contract more at low strains, but also they expand more after the phase transfer point at high stains. The assembly composed of particles with eccentricity of 0.15 has the highest coordination number. The coordination number constantly increases with the saturation degree for circular particles. In contrast, for elliptical particles assemblies, when degree of saturation increases, the coordination number increases at the beginning then drops. [ABSTRACT FROM AUTHOR]

This paper discusses the 2D plane strain consolidation problem of unsaturated soil considering the time-dependent drainage boundaries. A set of time-growing exponential functions are firstly used to describe the changes of excess pore-pressures at the drainage boundaries of an unsaturated soil layer. Then, a generalized analytical solution for the 2D plane strain consolidation under these boundaries and constant initial excess pore-pressures is obtained using the finite Fourier transform and Laplace transform methods. Further, the comparisons are presented to verify the accuracy of the proposed solution. It is shown that the proposed solution is more general in the drainage boundary, and in a good agreement with the analytical solution available in the literature and the finite difference solution. Finally, a worked example is presented to investigate the consolidation characteristics under four changing drainage parameters of time-dependent drainage boundaries. The average degrees of consolidation for both air and water phases as well as that for the soil layer are presented and discussed. [ABSTRACT FROM AUTHOR]

Abstract This study presents a new cavity expansion solution in unsaturated soils of finite radial extent. The solution is formulated for spherical and cylindrical cavities subjected to two boundary conditions under the drainage condition where the contribution of suction to the effective stress is constant. It is found that samples with a higher suction value are under more influence of the boundary size effect and this is more obvious with higher mean net stress and higher void ratio. Potential application of the solution in calibration chamber studies for in-situ tests in unsaturated samples is discussed. [ABSTRACT FROM AUTHOR]

The freezing-thawing behavior of soil plays a crucial role in frozen soil engineering. In this study, a soil freezing-thawing model is proposed from the perspective of statistical thermodynamics. First, the phase equilibrium relation for pore ice-water interface is deducted by applying statistical thermodynamics and the theoretical relationship is defined between the freezing temperature (i.e., the temperature at the ice-water interface) and the potential energy (i.e., total suction) of pore-water. This relation reveals that the matric suction of pore-water solely depends on the negative temperature at the pore ice-water interface for a given soil with constant osmotic suction and air pressure. Further, using the aforementioned relation and regarding the ice content of soil as an unknown variable, the thermo-hydraulic field in the soil freezing-thawing process can be solved by the mass and heat conversation. The governing equations related to this model are proposed in detail. Finally, to enhance the applicability of the proposed model, simplified forms in three typical conditions are provided, including the freezing process of saturated soil in artificial ground freezing technique, the capillary water migration coupled with freezing process of unsaturated soil in subgrade engineering and the vapor migration coupled with freezing process of semidry coarse soil under airport runways. Overall, the proposed model can be applied to various conditions and to other types of porous media (such as rock or concrete) that undergo freezing-thawing processes. [Display omitted] • A soil freezing-thawing model based on thermodynamics is proposed. • A new form of Clapeyron equation is deduced to characterize the phase equilibrium relation in porous media. • The potential energy of pore-ice is depending on its temperature. • The potential energy of pore-water is depending on its total suction. • Govern equations for solving soil ice content and temperature in freezing-thawing soil are proposed. [ABSTRACT FROM AUTHOR]

Rainfall and reservoir water level changes lead to changes in pore water pressures and in turn to changes in effective stresses and thus to landslide deformations. This is also a time dependent process and creep may occur on top of it. To explore their creep mechanics, four groups of isotropic compression creep tests on unsaturated soils have been conducted. We found that the volumetric strain had a linear relationship with logarithmic time under a constant net confining pressure or suction. The gradient of the straight line is independent of the net confining pressure and has an exponential relationship with suction, indicating that the creep formula proposed by Yin and Graham can be employed to describe the strain in unsaturated soil; however, the creep parameters must be expressed by a function that considers suction. In this study, we established a creep model for unsaturated materials based on plastic and rheological theories. The hardening parameters of the yield stress include the plastic volumetric strain and viscous volumetric strain. We established a time-dependent yield surface equation for unsaturated soils by introducing a conversion time variable into the yield surface equation of the Barcelona Basic Model. Subsequently, based on the associated flow rule and the Perzyna theory, we derived a viscoplastic strain rate equation for unsaturated soil. To verify the model, a set of unsaturated shear and creep tests have been performed and recorded the volumetric, axial strains and stress over time. The values predicted by the model agreed with our experimental results, indicating the reliability of the new creep model for unsaturated soil. • The isotropic compression creep tests of partially saturated soil are carried out to explore the volume creep law. • The functional relationship between creep parameter and suction is studied. • The elasto-viscoplastic model for partially saturated geomaterials is established in the critical state framework. [ABSTRACT FROM AUTHOR]