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Implementation of the state‐of‐the‐art understanding of the mechanics of unsaturated soils into geotechnical engineering practice is partly limited due to the lack of quick, reliable, and economical techniques for matric suction measurement. Matric suction is one of the key stress state variables that significantly influences the hydro‐mechanical behavior of unsaturated soils. In this paper, to address this objective, two artificial intelligence (AI) models were developed for estimating matric suction in unsaturated soils based on the particle swarm optimization support vector regression (PSO‐SVR) and multivariate adaptive regression spline (MARS) algorithms. The results suggest that both these models can reasonably estimate matric suction. Compared to the MARS model, the PSO‐SVR model can achieve higher accuracy. Nonetheless, the MARS model facilitates the sensitivity analysis and the selection of essential inputs. A novel integrated framework is proposed and validated, leveraging the strengths, and alleviating the limitations of the PSO‐SVR and MARS algorithms for reliable and rapid estimation of matric suction in the range of 0–1500 kPa for low plastic soils (0 < Ip ≤ 7). Six inputs are required to use this model successfully; some can be measured using conventional laboratory tests, and others can be calculated from mass‐volume relationships. [ABSTRACT FROM AUTHOR]

This study proposed an analytical approach for predicting the end-bearing capacity of driven piles that are subjected to axial loads in saturated and unsaturated soils. This is a generalized approach in which the stress characteristic method is employed successfully for both saturated and unsaturated soils. An iterative technique computer code was developed for the proposed analytical approach extending the finite difference method to develop solutions with the aid of MATLAB (version 2019a) that provides graphical output to visualize the results. The results from the proposed approach were compared against measurements for 13 pile load tests that include 11 in saturated soils and 2 in unsaturated soils, with good agreement. In addition, numerical analyses were performed using ABAQUS (version 6.14) to simulate the driven pile penetration and pile loading by employing the arbitrary Lagrangian–Eulerian adaptive mesh methods. The comparisons between the numerical predictions and measurements from a published model pile test suggested that the ultimate bearing capacity is well predicted by the finite-element model in comparison to the proposed analytical method. However, the proposed analytical method was simple for use in engineering practice applications to estimate the end-bearing capacity of pile foundations in both saturated and unsaturated soils. [ABSTRACT FROM AUTHOR]

Studies about the strain-softening behavior of unsaturated soils published in the literature during the past three decades are summarized under three categories; namely: (i) mechanical characteristics and micromechanisms, (ii) prediction models for shear strength, and (iii) numerical methods for modeling strain-softening behavior of unsaturated soils. In addition, the influence of the soil–water characteristic curve and time effects on the strain-softening behavior of unsaturated soils are discussed. Various experimental studies related to the strain-softening behavior of unsaturated soils are summarized to interpret the mechanical behavior characteristics and micromechanisms of the strain-softening under large shear deformation. The widely used empirical/semi-empirical prediction models from the literature for interpreting the peak, critical, and residual shear strength of unsaturated soils are comprehensively summarized considering the influence of soil fabric and water phase on the shear strength. Several numerical methods (i.e., conventional plasticity, bounding surface plasticity, disturbed state concept, and elasto-viscoplasticity) of modeling the strain-softening behavior of unsaturated soils are discussed, highlighting their strengths and limitations. The comprehensive details summarized in this paper related to the strain-softening behavior is valuable for the rational analysis and design of geostructures in unsaturated soils that undergo large shear deformation. In several scenarios, unsaturated soils exhibit strain-softening behavior when they undergo a large deformation during the shearing stage. In other words, there is reduction in the shear strength from a peak to a residual value associated with the evolution of a shear band where the dilation is localized. Shear deformations behavior in geo-infrastructures constructed in unsaturated soils are sensitive to the wetting conditions associated with rainfall infiltration. Therefore, shear strength in the geostructures varies between peak and residual value according to the magnitude of corresponding shear deformation. For this reason, the strain-softening behavior should be considered for reliable analyses and design of geo-infrastructure in unsaturated soils undergoing large shear deformation. This paper provides a comprehensive review of the studies about the physical mechanisms and numerical modeling methods of strain-softening behavior of unsaturated soils. The contents summarized in this article assist geotechnical engineers to understand how the strain-softening occurs in unsaturated soils under shearing, and how the shear strength reduction due to strain-softening behavior can be modeled in engineering practice applications. [ABSTRACT FROM AUTHOR]

Geotechnical and geo-environmental engineers are interested in the desiccation-induced cracks as they significantly influence the performance of geotechnical structures. A comprehensive understanding is required for developing rational tools for the design of geotechnical structures taking account of the morphological characteristics of desiccation-induced cracks. This study provides a critical review based on more than 100 publications related to the morphological characteristics of cohesive soil desiccation cracks from in situ investigations as well as laboratory studies during the past several decades. Both the in situ and laboratory characterization techniques are comprehensively reviewed, and their advantages and limitations are summarized. The mixture of the hexagonal pattern and the orthogonal pattern is typically observed in desiccation cracks, which is a combined result of the simultaneous strain energy release and the successive interaction between the generated stress field and the existing or induced heterogeneities. A theoretical equation is proposed to estimate the crack block size considering the effects of soil layer thickness, base friction, and environmental factors. It has been found that the crack depth increases linearly with the increasing crack width based on limited measurements at different scales. A reliable in situ characterization technique for the three-dimensional crack morphology and a more effective and fully coupled numerical modelling technique for the multi-physical and multi-scale desiccation cracking behavior are recommended for future works. [ABSTRACT FROM AUTHOR]

The hydromechanical behavior of compacted clayey soils is significantly influenced by its microstructure. The microstructural void ratio is a key parameter that is strongly associated with the microstructural state. The objective of this study is to provide a practical and reliable estimation approach for predicting the evolution of the microstructural void ratio of compacted clay soils subjected to wetting and drying paths. In this paper, the microstructural evolution of 12 clayey soils was investigated quantitatively using the mercury intrusion porosimetry (MIP) results. Based on this study, a comprehensive criterion has been developed for identifying different pore populations of compacted clayey soils for interpreting the MIP results. The "as-compacted state line" was proposed to estimate the initial microstructural void ratio of clayey soils at the as-compacted state. An incremental linear constitutive model was proposed for correlating the microstructural void ratio to the "microstructural average skeleton stress" in compacted clayey soils following monotonic wetting and drying paths. The developed approach is validated by providing comparisons between the predicted and interpreted microstructural void ratios for all the examined soils. The proposed approach can be extended in constitutive modeling of the hydromechanical behavior of compacted clayey soils by incorporating explicitly the microstructural information. [ABSTRACT FROM AUTHOR]

Pile foundations are widely used in regions with expansive soils to transfer the loads from superstructures to a rigid soil stratum, thereby alleviating stability and deformation problems. However, current design procedures for pile foundations are typically based on saturated soil mechanics principles assuming drained conditions, despite the fact expansive soils surrounding the piles are typically in an unsaturated state. Volume changes of expansive soil induced by matric suction changes upon seasonal wetting and drying can significantly influence the pile load-transfer mechanisms. In this paper, using unsaturated soil mechanics as a tool, theoretical models are introduced for estimations of pile shaft friction and pile base resistance considering both the influences of matric suction changes and matric suction variation-induced volume changes of expansive soil around the pile. The commonly used shear displacement method for interpreting the pile mechanical behaviors is modified by including these models to extend their application to piles in unsaturated expansive soils. The proposed modified shear displacement method (MSDM) is interpreted and successfully validated using a pile infiltration test conducted in the laboratory along with another case study from published literature. The results of investigation studies using the proposed MSDM suggest that it can be a valuable tool for practicing engineers to make reasonable predictions of mechanical behaviors of piles in unsaturated expansive soils. [ABSTRACT FROM AUTHOR]

A well-established framework for the design of excavation support systems (ESSs) is not available in the literature. Several guidelines that have evolved from engineering practice are conventionally used in the design of ESSs. The key indicators for judging the performance of ESSs are wall deformation, internal wall stresses, and surface soil settlement information. There is evidence from several case studies that the measured wall deformations are typically lower than the predicted values. Such behavior may be attributed to ignoring the influence of capillary suction. The key objective of the study presented in this paper is twofold; the first is highlighting limitations in the current design practice and the second is to pave the way for comprehensive design of ESSs. This is achieved by undertaking numerical analysis on a silty clay taking account of the influence of saturated and unsaturated soil conditions to investigate the performance of ESSs based on a rational design approach. In addition, the proposed approach is validated based on wall deflections information using the published results of a case history. The proposed approach is promising for implementing the mechanics of unsaturated soils in geotechnical engineering practice for the rational design of ESSs. The paper also highlights some limitations of the present study and the need for future studies to provide verifications using more case histories. [ABSTRACT FROM AUTHOR]

In this paper, two artificial intelligence (AI) models (i.e., artificial neural networks (ANN) and multivariate adaptive regression splines (MARS)) were developed using cumulative percentiles from the grain-size distribution (GSD) curve as input information to predict the soil-water characteristic curve (SWCC). The importance of each input variable was testified using two different sensitivity analyses. The results show a strong correlation between the SWCC and GSD curves based on large volume of datasets. The ANN provides higher accuracy due to its unique structure; however, the MARS model facilitates in developing a regression equation that contributes to stable performance. The SWCC can be reliably predicted with the MARS regression equation using one data point from the GSD curve and bulk density information. Sensitivity analysis suggests that the prediction of the SWCC is also possible with a reasonable degree of accuracy by using single data point information from the GSD curve as an input variable. Finally, a novel AI aid design method is proposed by combining the MARS regression equation along with physico-empirical model and fitting equation that provides a rapid and reliable technique for predicting the SWCC of sands. [ABSTRACT FROM AUTHOR]

Several of the geotechnical structures constructed with unsaturated soils undergo a large deformation prior to reaching failure conditions (e.g., progressive failure of a soil slope). During this process, the shear stress in soils typically increases initially and then reduces with an increase in the shear strain. The prediction of the stress–strain relationship is critical for reasonable interpretation of the mechanical behavior of those geo-structures that undergo large deformation. This paper introduces a model based on the disturbed state concept (DSC) to predict the variation of shear stress in unsaturated soils during the strain-softening process under consolidated drained triaxial compression condition. In this model, the apparent stress–strain relationship is formulated as a weighted average of a hyperbolic hardening response extending the pre-peak state stress–strain curve and a linear response extending the critical state stress–strain curve with an assumed disturbance function as the weight. The prediction procedure is described in detail and the proposed model is validated using several sets of published data on unsaturated soils varying from coarse- to fine-grained soils. Finally, a comprehensive error analysis is undertaken based on an index of agreement approach. [ABSTRACT FROM AUTHOR]

A comprehensive experimental program was performed in order to understand the mechanical behavior of model piles associated with water infiltration in collapsible loess. Real-time measurements were recorded for pile head settlement, pile shaft friction, and pile base resistance, as well as for the soil behavior, including soil settlement, volumetric water content, and soil suction. The experimental results suggest that both the pile head settlement and pile base resistance increased with water infiltration. The linear pile axial force distribution gradually changed to a "D" shape, with the maximum pile axial force occurring in the middle instead of the end stage of water infiltration. Such behavior can be attributed to a reduction in the contribution of soil suction, degradation of the pile–soil interface shear strength, and settlement of the collapsible soil. In addition, a softening model was proposed by modifying the traditional shear displacement method for interpretation of the mechanical behavior of piles in collapsible loess. There was good agreement between our experimental results and those from the literature and the results predicted using the proposed model, suggesting that the model can be used as a tool in the rational design of pile foundations in collapsible soils. [ABSTRACT FROM AUTHOR]

• The soil freezing characteristic curve is modeled using thermodynamics principles. • Links with well-known soil water characteristics curve models are presented. • Influence of salinity and initial water content on SFCCs are successfully predicted. Experimental studies related to the thermo-hydro-mechanical-chemo (THMC) behaviors of unsaturated frozen soils are cumbersome, expensive, and time consuming. For this reason, several researchers suggested mathematical models exploiting the strong relationships between the soil freezing characteristics curve (SFCC) and the THMC behavior of unsaturated frozen soils. However, the physical meanings of parameters in the available models are not clearly defined; hence there are limitations in providing rational interpretation of the frozen unsaturated soils behavior. In the present study, SFCC models with well-defined model parameters are developed extending thermodynamics principles and are linked to well-known soil–water characteristics curves (SWCC) models from the literature. Various zones in the SFCC are discussed along with providing rational explanation for the hysteretic effects using the proposed models. In addition, comparisons are provided between the measured results from experimental studies and the predicted results using the proposed models successfully highlighting the effects of salinity and the initial water content on the frozen unsaturated soils. The SFCC models proposed in this paper are promising and can be used for rigorous interpretation and in the prediction of the complex THMC behaviors of frozen unsaturated soils. [ABSTRACT FROM AUTHOR]

In this paper, water flow in a 4 m height column with an unsaturated soil that is subjected to multiple infiltration events for a 62 day period is investigated. One-dimensional (1D) numerical analysis is also undertaken to analyze the flow, extending the seepage theory for unsaturated soils. Results highlight the formation of two wetting fronts; namely, wetting front I and wetting front II that are induced by the first and subsequent infiltration events, respectively. There is a stable zone where the water content is approximately constant; it forms between the two fronts. A conceptual model of the suction profile is proposed for interpreting in situ water flow by dividing the unsaturated zone into four distinct zones; namely, active, steady, transition, and capillary fringe zones. This division is helpful for providing a rational explanation of water flow in different zones. Novel contributions from this study include a relationship between the hydraulic properties in the steady zone and the flow velocity, which is determined by an average influx rate. In addition, the rate of groundwater recharge can also be estimated using the average influx rate. Results of the present study are useful to understand and interpret the relationship between water infiltration and suction or water content profile in the unsaturated zone as well as variation of groundwater table level. [ABSTRACT FROM AUTHOR]

In this paper, the volumetric collapse of an unsaturated soil, upon soaking to saturation under a certain stress level, is referred to as soaking collapse. The soaking collapse for a soil under virgin condition is assumed equal to the difference between the soil's virgin compression line (VCL) and its normal consolidation line (NCL) at saturated condition based on results of oedometric constant water content compression and soaking tests performed on a compacted Nanyang expansive clay. A one-parameter model is proposed to describe the variation of the soaking collapse with the pre-soaking degree of saturation under virgin condition once (1) a soil's yielding point can be clearly defined and (2) the degree of saturation during virgin compression is known. This model can be used to predict the VCL from the NCL. Data of the Nanyang expansive clay, along with published data of nine soils that were derived from constant water content or constant suction compression tests (including oedometric and triaxial compression), were used to calibrate and validate the model. It is shown that the model, when combined with a degree of saturation-volume model and the information of yielding and NCL, can predict reasonable VCLs for all examined soils and suitably capture several characteristics of the VCL including the nonlinearity and pressurised saturation. A constant model parameter of 1.5 is found suitable for all examined soils. The model is also used to predict the VCLs of two compacted soils from the constant degree of saturation compression, which is a recently developed testing technique to evaluate the compression behaviour of unsaturated soils, with reasonable agreement achieved. [ABSTRACT FROM AUTHOR]

Several pipeline projects have been proposed in the world in recent years owing to the rapid growth of the petroleum industry. Onshore pipeline systems are usually buried above the natural groundwater table, where the soil is typically in an unsaturated condition. Rational interpretation of these pipelines is possible by extending the mechanics of unsaturated soils. In this paper, the axial force exerted by way of the relative movement on a prototype steel pipeline in sand under both saturated and unsaturated conditions is determined from laboratory investigations using specially designed equipment. The test results under the unsaturated condition showed significantly higher axial force on the pipeline compared to the saturated condition, attributable to the contribution from matrix suction. Two analytical models proposed in this study, which take into account the influence of matrix suction and dilation, successfully predicted the peak and residual skin friction along the pipe surface. The framework developed, based on experimental studies and analysis of the results and the proposed models that use saturated shear strength parameters and the soil-water characteristic curve, is promising for generating simple tools for the design of pipeline infrastructure buried in sands to ensure their stability and safety, and at the same time provide economical solutions. [ABSTRACT FROM AUTHOR]

A series of shaking table tests were conducted to investigate the failure mechanism of slope models prepared using sand and gravel mixtures derived from open pit slopes by subjecting them to vibration for extended periods of time. The dynamic response is analyzed based on the acceleration amplifications measured at different elevations. The horizontal PGA amplification factors first increase and then decrease with an increase in frequency, reaching a peak value at the natural frequency of 20 Hz. The horizontal PGA amplification factors increased for frequency values lower than 20 with an increase in the input amplitude; however, they decreased for frequency values higher than 20. An increase in excitation duration typically contributes to trigger slope deformation; however, its effect increases rapidly for longer excitation periods. A novel technique is developed for the estimation of the deformation in slope models using an image processing program for this study based on image recognition and data extraction. Furthermore, the slope stability behavior is analyzed based on the numerical simulations considering the disturbed state concept (DSC) for rigorous analyses. Results of this study are of interest in engineering practice applications for taking measures to prevent natural disasters associated with open pit slopes formed due to mining activity. [ABSTRACT FROM AUTHOR]

The soil–water characteristic curve (SWCC) is widely used as a tool in geotechnical, geo-environmental, hydrology, and soil science fields for predicting and interpreting hydro-mechanical behaviors of unsaturated soils. Several previous studies focused on investigating the influence of initial water content, stress history, temperature, and salt content on the SWCC behavior. However, there is still limited understanding to be gained from the literature on how we can systematically incorporate the influence of complex thermo-hydro-mechanical-chemo (THMC) effects into interpreting and predicting the behavior of unsaturated soils. To address that knowledge gap, in this study, the coupled influence of temperature, initial stress state, initial density, soil structure, and chemical solution effects was modeled using established SWCC equations from the literature. The methodology for incorporating the coupled effects of these influential factors is presented herein. Furthermore, we evaluated the SWCC models proposed in this study, enabling us to provide a comprehensive discussion of their strengths and limitations, using the published SWCC data from the literature. The developments outlined in this paper contribute toward facilitating a rigorous approach for analyzing the THMC behaviors of unsaturated soils. [ABSTRACT FROM AUTHOR]

Abstract A three-step computer program is developed for simulating the load-displacement response of a single pile in unsaturated expansive soil taking account of influence of water infiltration. In the first step, peak and residual pile-interface shear strength variation with suction are estimated. The relationship between interface shear strength and pile-soil relative displacement and pile base resistance and pile base settlement is achieved by modifying universal transfer curve model, in the second step. Lastly, traditional load transfer method was modified for analyzing the load-displacement response. The validity of program is verified using a laboratory model test and a field investigation case study. [ABSTRACT FROM AUTHOR]

Buried pipeline systems form vital infrastructure, all over the world, to transport resources such as water, oil, and gas from the production stage to the locations of consumption. Failure or rupture in pipelines in general and oil or gas pipelines in particular lead to not only economic losses that are expensive, but also cause extensive damage to the environment in several scenarios. One of the key reasons for buried pipeline systems failure is associated with excavation or soil trenching within the proximity of pipelines. Soil deformation associated with excavation causes relative displacement between the pipeline and the surrounding soil, which contributes to external as well as internal stresses and strains on the pipelines. In this study, numerical analyses are carried out to investigate the behaviors of buried rigid and flexible pipelines by extending the effective stress analysis and the modified effective stress analysis approaches for saturated and unsaturated soils, respectively. The pipe displacement, strains, and internal force results from the study suggest that soil trenching in unsaturated soils contribute to limited deformations within the proximity of the embedded pipelines and result in lower internal forces. The proposed methodology can be used to determine the safe depths of unsupported excavations in unsaturated soils without causing excessive strains or internal forces in the ring of rigid and flexible pipes. [ABSTRACT FROM AUTHOR]

It is widely accepted that the results of wetting tests conducted on collapsible soils by reducing matric suction in consecutive steps in the laboratory provide reliable experimental data for interpreting the soil collapse behavior. The variation of void ratio derived using such a testing technique is similar to that of water content in response to decrease associated with matric suction. For this reason, van Genuchten's equation for the soil-water characteristic curve was extended to fit the measured data of collapse behavior to describe the variation of void ratio with matric suction. Two of the three fitting parameters in the extended equation, n and m, change negligibly with the applied stress, p whereas another parameter, a, could be represented as a power function of p at a given initial matric suction. For this reason, using the results of two wetting tests performed on identical soil specimens under different applied stresses, the power function is developed for a and the values of n and m are determined; thus, the collapse behavior can be predicted. A good agreement is observed between the collapse behavior predicted using the proposed method and the measured data on collapsible soils in the literature. The proposed method requires less experimental data and hence is simple for use in engineering practice applications. [ABSTRACT FROM AUTHOR]

The influence of tensile strength on the behaviour of cohesionless soils is typically ignored in geotechnical engineering practice. However, the tensile cracking and subsequent failure characteristics of earth structures, such as dams, slopes and embankments, are significantly influenced by the tensile strength. For this reason, a semi-empirical model is proposed for predicting the variation of the tensile strength of unsaturated cohesionless soils with the degree of saturation, using the soil-water characteristic curve (SWCC) as a tool. The proposed model is capable of predicting the tensile strength arising from matric suction and surface tension, which are related to saturated pores and to the air–water interface associated with water bridges around interparticle contacts in unsaturated pores, respectively. Information about (i) the matric suction (ua – uw), the capillary degree of saturation (Sc), and the residual degree of saturation (Sr) derived from the SWCC; (ii) the mean particle size (d50) and the coefficient of uniformity (Cu) from the grain-size distribution curve; (iii) the void ratio (e); and (iv) the friction angle (--> ϕ t -->) at low normal stress level is required to employ this model. The proposed model is validated by comparing the prediction results with measured tensile strength of 10 different unsaturated cohesionless soils (including five sandy soils and five silty soils). The proposed model is promising for use in engineering practice applications as it only requires conventional soil properties, alleviating the need for cumbersome experimental studies for the determination of tensile strength of unsaturated cohesionless soils. [ABSTRACT FROM AUTHOR]

The resilient modulus is a key parameter required in the mechanistic design of pavements. Experimental determination of the resilient modulus requires elaborate equipment for testing and requires trained personnel; for this reason, it is expensive. There are several models for predicting the resilient modulus for unbound road materials that take into account the influence of wetting and drying conditions. However, well-established models are not available for the prediction of the resilient modulus of these materials in a frozen state. In this paper, a semi-empirical model, which uses a soil-freezing characteristic curve as a tool, is proposed for predicting the variation of the resilient modulus with subzero temperature and the associated cryogenic suction for frozen soils. Experimental data on seven different pavement unbound materials were used to validate the proposed model. It is shown that the model can reasonably predict the resilient modulus of the investigated soils that are in a frozen state. More investigations on different types of soils would be useful to better understand the strengths and limitations of the proposed model. [ABSTRACT FROM AUTHOR]

In this paper, an analytical method and semi-empirical equations are presented for determining the bearing capacity failure envelopes for foundations subjected to inclined or eccentric loads in unsaturated soils considering the influence of steady and transient state flow conditions. Firstly, the analytical method is proposed extending the slip line theory coupled with analytical solutions for different matric suction profiles. The failure envelopes in the V - H (Vertical - Horizontal) and V - M (Vertical - Moment) loading spaces for two fine-grained soils were investigated by conducting parametric studies using the proposed method. The influence of the ground water table depth variation, internal friction angles, surface flux boundary conditions and different infiltration durations were considered. Based on the parametric studies results, semi-empirical equations were proposed for the failure envelopes in the two loading spaces. The validity of the proposed failure envelope equations is examined by providing comparisons with the proposed analytical method and published results from the literature. Good agreement is found between the fitted failure envelopes and that obtained from the analytical method and published studies. [ABSTRACT FROM AUTHOR]

The water infiltration characteristics associated with irrigation activities which contribute to the slope stability failures of Heifangtai loess highland of China from the mid-1980s are still not well understood. For this reason, infiltration characteristics of loess were studied from 1D column test by adding water at daily intervals for a long period of time. Experimental results of the 1D column test were numerically simulated along with 2D simulation studies for a typical Heifangtai slope for studying the water infiltration characteristics and its influence on the slope stability for a 33 years period. Numerical simulation results highlight that the infiltration characteristics in the 1D column and 2D slope are similar and can be explained by dividing the unsaturated zone into three different zones. Simulation results of the 2D slope were valuable to understand how the irrigation activities affect the hydraulic behavior and the slope stability. The initial hydraulic state with low water content and no GWT condition transforms into a new hydraulic equilibrium state with a constant water content in the unsaturated zone and a stable GWT. This process can be divided into four different stages. The safety factor ( F s ) of the slope decreases during the first three stages; however, it is stable in the fourth stage when a hydraulic equilibrium condition is reached. Slopes in Heifangtai can fail during any of the first three stages due to different triggering factors. The most feasible way to control the occurrence of landslides is to control or reduce the total amount of irrigation water per year. The results summarized in the present study are useful to better understand the cumulative effects of infiltration events on stability of slopes. [ABSTRACT FROM AUTHOR]

Lateral swelling pressure (LSP) can pose significant threats to the safety and stability of the geo-infrastructure. For this reason, it is necessary to take into account the influence of LSP in the design of geo-infrastructure such as basement walls, retaining walls, pile foundations, and pipelines built within or adjacent to expansive soils upon water infiltration. A relationship is developed to calculate the LSP upon free swelling from the vertical swelling pressure (VSP), which can be measured from conventional laboratory tests. This relationship is extended to calculate (1) the lateral earth pressure (LEP) behind a retaining structure with expansive soils as backfill material, and (2) the uplift friction along a single pile placed in expansive soils upon infiltration. Experimental results from large-scale tests and centrifuge tests from published literature are used to validate the proposed methods. The studies presented in this paper not only highlight the influence of LSP on the geo-infrastructure but also provide simple tools for taking account of it in the conventional geotechnical engineering practice for both saturated and unsaturated expansive soils. [ABSTRACT FROM AUTHOR]

Experimental and numerical modeling studies related to the behavior of pile foundations are conventionally undertaken based on the assumption that the surrounding soils are in a state of saturated condition. Such an assumption may contribute to erroneous estimations of the stability and settlement behavior of pile foundations installed in unsaturated soils due to neglecting the influence of soil suction. In this paper, the behavior of a single friction pile loaded in drained and undrained conditions in a compacted glacial till is modeled using finite-element analyses (FEAs). The influence of the soil suction on (1) the shear strength and the modulus of elasticity of the soil and (2) the shear strength of the pile-soil interface derived from the experimental studies is discussed and considered in the FEA. There is reasonable agreement between the load-settlement behavior and the bearing capacity of the friction pile modeled using the FEA and the measured results from experimental studies. This study highlights the significant influence of the soil suction on the behavior of single friction pile and suggests a relatively simple approach to reasonably model the pile behavior using the FEA. [ABSTRACT FROM AUTHOR]

The resilient modulus ( M R ) of pavement materials is a key parameter required in the mechanistic pavement design methods. Seasonal moisture regime and suction ( s ) fluctuations exert remarkable influence on the M R which should be measured or predicted to assist in the analysis of pavement distress and service life. This paper presents extensive experimental investigations to determine the M R - s relationship for three Canadian subgrade soils (a silty clay from Toronto, a marine clay from Ottawa and a glacial till from Indian Head) using two different experimental methods. Following the first method, glacial till specimens were consolidated to known stress and suction levels using the axis-translation technique before subjecting to cyclic loading tests to determine the M R . In the second method, equilibrium conditions were achieved with respect to different moisture contents for specimens of the silty clay and marine clay before cyclic loading tests. Suction was measured after the completion of cyclic loading tests using the filter paper method. Experimental results suggest varying degrees of non-linear relationships between the M R and the suction, gravimetric water content and external stress for different soils. A simple model, which is based on the soil-water characteristic curve and M R values at saturated and optimum moisture content conditions for prediction, is used to predict the measured M R - s relationship for the three soils. Same measurements were also predicted using two rigorous models from the literature that were proposed based on different approaches. It is shown that the simple model, compared with other two models, provides equally good predictions but requires remarkably less experimental data. The simple model therefore can be used in practice as a reliable tool for predicting the influence of suction and moisture content on the resilient modulus of subgrade soils. [ABSTRACT FROM AUTHOR]

In this paper, equations that were proposed in the literature over the past four decades to estimate or predict the variation of the resilient modulus with respect to soil suction for pavement base-course materials and subgrade soils are summarized into three groups: (1) empirical relationships, (2) constitutive models incorporating the soil suction into applied shearing or confining stresses, and (3) constitutive models extending the independent stress state variable approach. Two equations selected from each of the groups (a total of six equations) are used to predict the resilient modulus-soil suction correlations for three compacted subgrade soils. Strengths and limitations of these widely used equations are discussed based on the comparisons between the measurements and predictions. The key objective of the state-of-the-art research summarized in this paper is for assisting practicing engineers to choose suitable equations for the rational prediction of the resilient modulus taking into account the influence of the soil suction. [ABSTRACT FROM AUTHOR]

The one-dimensional (1-D) potential heave (or swell strain) of expansive soil is conventionally estimated using the swelling pressure and swelling index values that are determined from different types of oedometer test results. The swelling pressure of expansive soils is typically measured at saturated condition from oedometer tests. The experimental procedures of oedometer tests are cumbersome as well as time-consuming for use in conventional geotechnical engineering practice and are not capable of estimating heave under different stages of unsaturated conditions. To alleviate these limitations, semi-empirical models are proposed to predict the variation of swelling pressure of both compacted and natural expansive soils with respect to soil suction using the soil-water retention curve (SWRC) as a tool. An empirical relationship is also suggested for estimating the swelling index from plasticity index values, alleviating the need for conducting oedometer tests. The predicted swelling pressure and estimated swelling index are then used to estimate the variation of 1-D heave with respect to suction for expansive soils by modifying Fredlund's 1983 equation. The proposed approach is validated for eight field sites from six countries - namely, Saudi Arabia, Australia, Canada, China, USA, and UK - and on six different compacted expansive soils from USA. [ABSTRACT FROM AUTHOR]

• Three simple models are proposed for predicting hysteretic behaviors of SWCC including the scanning curves based on the soil pore-size distribution curve for coarse-grained soils. • The SWCC of fine-grained soils were successfully predicted taking account of the influence of stress state and soil structure associated with different initial water contents. • A coupled SWCC model is proposed that can be used for explaining the influence of multiple soil parameters. The focus of this paper is directed towards developing models for predicting the soil–water characteristic curves (SWCCs) for coarse- and fine-grained soils taking account influence of hysteresis and various factors such as the stress state and soil structure, respectively. For achieving this objective, several novel models are derived from the pore-size distribution (PoSD) curve of the SWCC and linked to the well-known SWCC fitting equations. Three simple methods are developed from the proposed model that can be used for predicting the scanning SWCCs of coarse-grained soils. A modified SWCC model is built based on the theoretical background developed for the PoSD curve that is capable for predicting the of fine-grained soils taking account influence of the initial water content and stress state. In addition, a coupled SWCC model is proposed that can be used for explaining the influence of multiple soil parameters. The proposed novel, yet simple models can be used in numerical modeling of complex coupled hydromechanical problems and for predicting of various properties of unsaturated soils. [ABSTRACT FROM AUTHOR]

• Three simple models are proposed for predicting hysteretic behaviors of SWCC including the scanning curves based on the soil pore-size distribution curve for coarse-grained soils. • The SWCC of fine-grained soils were successfully predicted taking account of the influence of stress state and soil structure associated with different initial water contents. • A coupled SWCC model is proposed that can be used for explaining the influence of multiple soil parameters. The focus of this paper is directed towards developing models for predicting the soil–water characteristic curves (SWCCs) for coarse- and fine-grained soils taking account influence of hysteresis and various factors such as the stress state and soil structure, respectively. For achieving this objective, several novel models are derived from the pore-size distribution (PoSD) curve of the SWCC and linked to the well-known SWCC fitting equations. Three simple methods are developed from the proposed model that can be used for predicting the scanning SWCCs of coarse-grained soils. A modified SWCC model is built based on the theoretical background developed for the PoSD curve that is capable for predicting the of fine-grained soils taking account influence of the initial water content and stress state. In addition, a coupled SWCC model is proposed that can be used for explaining the influence of multiple soil parameters. The proposed novel, yet simple models can be used in numerical modeling of complex coupled hydromechanical problems and for predicting of various properties of unsaturated soils. [ABSTRACT FROM AUTHOR]

In this paper, an analytical method is proposed for estimating the bearing capacity of soil within the framework of slip line theory. The method incorporates a closed-form solution taking account the transient unsaturated vertical flow conditions. The proposed framework is validated for both level and sloping ground scenarios considering saturated and unsaturated soil conditions. More specifically, the bearing capacity of a strip foundation located on an unsaturated soil slope under the influence of different rainfall infiltration conditions is evaluated. A comprehensive parametric study is also conducted taking account the influence of the rainfall influx, rainfall duration, slope angle, foundation setback distance, soil type, and the depth of the ground water table. In addition, the contribution of matric suction towards the bearing capacity under transient flow conditions is evaluated. Results of this study provide a rigorous understanding of the performance of foundations on sloping ground extending the mechanics of unsaturated soils. [ABSTRACT FROM AUTHOR]

The influence of the stress regime change and associated softening can be significant on unsaturated expansive soil slope stability due to soil swelling upon wetting, which cannot be considered in conventional hydrological models. In this paper, the shallow expansive soil slope failure mechanism is addressed in the framework of an infinite slope formulation. The unsaturated soil elasto-plastic constitutive relationship is utilized for interpretation of stress regime evolution induced by expansive soil swelling during infiltration. The extended Mohr–Coulomb failure criterion for unsaturated soils is used as the yield surface, under which the nonlinear elastic behavior is considered by quantifying the effect of two stress state variables (net stress and suction) on elasticity parameters. The strain softening behavior in unsaturated soils is accounted for via reducing the material parameters of the yield surface with respect to plastic deviatoric strain. A numerical exercise is performed on a relatively gentle slope in Regina, Canada with highly expansive soil properties, using the developed computer program that implements the constitutive model into infinite slope formulation. The results suggest that neglecting the swelling-induced stress change and associated softening behavior can significantly overestimate the stability of expansive soil shallow layer under infiltration, in terms of both failure occurrence and failure time. Additional parametric study shows that all the considered parameters (including initial stress condition, softening rate and slope angle) have a considerable effect on the failure time and failure depth of the shallow deposit, which have important implications for the engineering design of expansive soil slopes. [ABSTRACT FROM AUTHOR]

Rain-induced surficial slope failures in expansive soils are frequently reported in the literature. These failures are primarily attributed to the shear strength reduction due to the loss of suction associated with the water infiltration. For this reason, slope stability is conventionally evaluated taking account of the hydraulic response of the soil to infiltration of water. The unsaturated expansive soil swells significantly upon wetting; the associated hydro-mechanical coupling effect on the slope stability of expansive soils is not considered in conventional geotechnical engineering practice. This paper aims to numerically evaluate the coupling effect or swelling on the hydraulic response as well as the stability of surficial layer of a typical expansive soil slope. Both hydro-mechanical (coupled) and hydraulic (uncoupled) responses of the slope to a low intensity prolonged rainfall are modeled using the commercial software SIGMA/W and SEEP/W, respectively. Subsequently, the infinite slope formulation is used to compute the factors of safety (FS) profiles extending both coupled (SIGMA/W) and uncoupled (SEEP/W) analysis. The results of the study presented in this paper show that coupled analysis (considering swelling) leads to different suction (negative pore water pressure (PWP)) and FS profiles within the surficial layer from those resulting from uncoupled analysis at the same elapsed time. The wetting fronts in the PWP profile from coupled analysis advance at a relatively faster rate in comparison to uncoupled analysis contributing to more critical FS values or failure conditions. The study highlights the coupled hydro-mechanical behavior of expansive soil has an adverse effect on the slope stability and hence should be taken into account in practice for estimating reliable values of FS. [ABSTRACT FROM AUTHOR]

Soil suction (ψ) is one of the key factors that influence the resilient modulus (MR) of pavement subgrade soils. There are several models available in the literature for predicting the MR-ψ correlations. However, the various model parameters required in the existing models are generally determined by performing regression analysis on extensive experimental data of the MR-ψ relationships, which are cumbersome, expensive, and time-consuming to obtain. In this paper, a model is proposed to predict the variation of the MR with respect to the ψ for compacted fine-grained subgrade soils. The information of (i) the MR values at optimum moisture content condition (MROPT) and saturation condition (MRSAT), which are typically determined for use in pavement design practice; (ii) the ψ values at optimum moisture content condition (ψOPT); and (iii) the soil-water characteristic curve (SWCC) is required for using this model. The proposed model is validated by providing comparisons between the measured and predicted MR-ψ relationships for 11 different compacted fine-grained subgrade soils that were tested following various protocols (a total of 16 sets of data, including 210 testing results). The proposed model was found to be suitable for predicting the variation of the MR with respect to the ψ for all the subgrade soils using a single-valued model parameter ξ, which was found to be equal to 2.0. The proposed model is promising for use in practice, as it only requires conventional soil properties and alleviates the need for experimental determination of the MR-ψ relationships. [ABSTRACT FROM AUTHOR]

In this paper, a novel coupled hydro-mechanical model for unsaturated expansive soils and a constitutive model for unsaturated pile-soil interfaces are implemented into ABAQUS for performing 3-D finite element analysis of single piles in expansive soils during infiltration. Some key features of coupled thermal–mechanical model from ABAQUS are used to formulate coupled hydro-mechanical model developing five independent user-material subroutines. User-defined field subroutine (USDFLD) is used to access the stress and strain and transfer these values to other subroutines. Three subroutines including user-defined material subroutine (UMAT), user-defined thermal material subroutine (UMATHT), and user-defined thermal expansion subroutine (UEXPAN) are developed and used to calculate the stress-deformation, the hydraulic behavior, and the expansion strain, respectively. In addition, an unsaturated soil-structure interface model is implemented into user-defined friction behavior subroutine (FRIC) to calculate the friction stress between soil and pile. The program is successfully validated using experimental results performed on a single model pile in an expansive soil. The modeling results are consistent with the experimental results which suggest that a decrease in matric suction can contribute to the reduction in the shaft friction as more load is transferred to the pile resulting in an increase in the pile head settlement and pile base resistance. The modeling approach presented in this paper is promosing and can be extended by the practitioners in the rational design of pile foundations in expansive soils. [ABSTRACT FROM AUTHOR]

The behavior of annulus stone columns in soft clays is significantly influenced by the outer-to-inner diameter ratio. For this reason, in the present study, a comprehensive experimental investigation program was undertaken in the laboratory on a soft clay from Warangal, India, by varying its water content for achieving different undrained shear strength values and to determine the load-carrying capacity of conventional and annulus stone columns with different outer-to-inner diameter ratios that were double-encapsulated with geotextile. Investigations were also extended to determine the optimum L/D ratio and spacing between the groups of annulus stone columns. Based on these studies, a theoretical framework is developed for interpreting and determining the load-carrying capacity of the stone columns. The studies presented in this paper offer a novel ground improvement technique to enhance the load-carrying capacity of soft soils. Conventional in situ pile foundations and stone columns have been extensively used in geotechnical engineering to support widespread loads arising from infrastructure, such as oil storage tanks and embankments on soft soils. However, stone columns typically fail, due to bulging action. Therefore, the geotechnical engineering community uses pile foundations to alleviate failures and support widespread loads on soft soils. However, a significant decrease in the cost of the project and carbon footprint is realized when stone columns replace conventional pile foundations. Therefore, the proposed geosynthetic double-encapsulated annulus stone columns with enhanced confining resistance could be a suitable replacement for conventional stone columns and pile foundations to support widespread loads. The results presented in this paper show a significant reduction in bulging when the conventional stone columns are replaced with annulus stone columns. However, the installation technique adopted in the model tests differs from those in the field. Full-scale field testing of the proposed technique is required to understand the strengths and limitations of the proposed design approach. [ABSTRACT FROM AUTHOR]

The bearing capacity of unsaturated soils is commonly estimated using the conventional shear-strength parameters determined from drained loading conditions regardless of soil type and drainage condition. However, the use of drained shear-strength parameters to interpret the bearing capacity of unsaturated fine-grained soils is not reliable because there are uncertainties with respect to the drainage conditions of both the pore-air and pore-water pressures. In the current study, a series of model footing tests is conducted in statically compacted unsaturated fine-grained soils. The model footing test results are interpreted using the modified effective-stress and total stress approaches considering the influence of matric suction. In addition, the validity of the modified total stress approach is tested using in situ plate-load test results in unsaturated fine-grained soils. The advantages, disadvantages, and limitations of using the modified effective-stress and modified total-stress approaches for engineering practice applications are discussed in this paper. [ABSTRACT FROM AUTHOR]

The design of soil nail systems used in engineering practice is either based on conventional soil mechanics or empirical procedures, and generally ignores the influence of matric suction. An experimental program was conducted to investigate the influence of matric suction on the pullout capacity of soil nails installed in compacted sand under both saturated and unsaturated conditions. Pullout tests were performed on soil nails installed vertically, horizontally, and at an inclination of 15° to the vertical in a specially designed test box. A strong relationship was observed between the pullout capacity and matric suction. A semiempirical method is proposed for the estimation of the pullout capacity of soil nails by using the average matric suction value and the saturated soil strength parameters, and . There is a reasonably good agreement between the measured and estimated pullout capacity of soil nails using the results of the present research program as well as the data from the literature. [ABSTRACT FROM AUTHOR]

Simple relationships are proposed in this paper by modifying the Schmertmann's equation for settlement estimations of footings (i.e., B/L ≈ 1) carrying vertical loads in saturated and unsaturated sandy soils. The modified method is developed using model plate load tests (PLTs) and cone penetration tests (CPTs) results conducted in saturated and unsaturated sand in a controlled laboratory environment. Seven in-situ large-scale footings tested under both saturated and unsaturated conditions in sands were used to validate the proposed technique. The results of the study are encouraging as they provide reliable estimates of the settlement of shallow footings in both saturated and unsaturated sands using the conventional CPT results. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical method for estimating the load versus displacement curves for laterally loaded rigid piles in unsaturated soils taking account the influence of matric suction. The distribution of lateral soil resistance along the pile in this method considers three distinct states: (i) pre-tip yield state; (ii) post-tip yield state; and (iii) ultimate limiting state. The lateral earth pressure coefficient, K c required in this method is derived by extending the three-dimensional (3D) effect factor for drained loading. A numerical technique is also proposed which incorporates a user-defined subroutine (USDFLD) into ABAQUS for simulating the behavior of laterally loaded piles extending 3D finite element analysis taking account of nonlinear behavior of shear strength and modulus of elasticity with respect to matric suction. The proposed analytical method and numerical techniques were validated, respectively using the results of seven field studies and two laboratory tests published from the literature. In addition, close agreement was observed between the predictions of the proposed analytical method and numerical technique for a single pile example problem placed in a soil with varying groundwater table conditions. The summarized studies are promising for use in practice for the rational design of laterally loaded piles in unsaturated soils. [ABSTRACT FROM AUTHOR]

The bearing capacity and settlement of foundations are determined experimentally or modelled numerically based on conventional soil mechanics for saturated soils. In both methods, bearing capacity and settlement are estimated based on the applied vertical stress versus surface settlement relationship. These methods are also conventionally used for soils that are in an unsaturated condition, ignoring the contribution of matric suction. In this study, a methodology is proposed to estimate the bearing capacity and settlement of shallow foundations in unsaturated sands by predicting the applied vertical stress versus surface settlement relationship. The proposed method requires soil parameters obtained under only saturated conditions (i.e., effective cohesion, effective internal friction angle, and modulus of subgrade reaction from model footing test) along with the soil-water characteristic curve (SWCC). In addition, finite element analyses are undertaken to simulate the applied vertical stress versus surface settlement relationship for unsaturated sands. The proposed method and finite element analyses are performed using an elastic - perfectly plastic model. The predicted bearing capacities and settlements from the proposed method and finite element analyses are compared with published model footing test results. There is good agreement between measured and predicted results. La capacité portante et le tassement de fondations sont déterminés expérimentalement ou numériquement d'après le modèle classique de la mécanique des sols pour les sols saturés. Pour les deux méthodes, la capacité portante et le tassement sont estimés d'après la relation entre la contrainte normale verticale appliquée en fonction du tassement de surface. Ces méthodes sont également utilisées conventionnellement pour les sols qui sont dans un état non saturé en ignorant la contribution de la succion matricielle. Dans la présente étude, une méthodologie est proposée afin d'estimer la capacité portante et le tassement des fondations peu profondes dans les sols sableux non saturés en prédisant la relation entre la contrainte verticale appliquée et le tassement de surface. La méthode proposée ne requiert que les paramètres du sol obtenus sous des conditions saturées (c.-à-d. cohésion effective, angle de friction interne effectif, et module de réaction du sol obtenu lors d'essais de semelle à échelle réduite) ainsi que sa courbe de rétention d'eau (« SWCC »). En outre, des analyses par éléments finis sont également entreprises afin de simuler la relation entre la contrainte verticale appliquée et le tassement de surface de sols sableux non saturés. La méthode proposée et les analyses par éléments finis sont effectuées en utilisant le modèle élastique - parfaitement plastique. La capacité portante et le tassement prédits par la méthode proposée et l'analyse par éléments finis sont comparés avec les résultats publiés des essais de semelles à échelle réduite. Il existe une bonne concordance entre les mesures et les résultats prédits. [ABSTRACT FROM AUTHOR]

Abstract: Stability analyses for a homogeneous compacted embankment were undertaken considering infiltration of water into the embankment. The analyses include several different practical scenarios: (i) saturated condition, (ii) ponding (or runoff) along with saturated condition, (iii) short term analysis for unsaturated conditions, and (iv) long term analysis for unsaturated conditions. The appropriate shear strength parameters of the compacted soil required for analyzing different practical scenarios were determined using conventional and modified triaxial shear apparatus. The results of the study show that typically shallow circular failures above water front occur due to infiltration rather than the conventional infinite slope type failures. [Copyright &y& Elsevier]

A semi-empirical model is proposed in this paper to predict the variation of modulus of elasticity with respect to matric suction for unsaturated sandy soils using the soil-water characteristic curve (SWCC) and the modulus of elasticity under saturated conditions. Using this model, comparisons are provided between the predicted and measured moduli of elasticity and elastic settlements from model footing test results on three different sandy soils. The results of this study are encouraging as there is good agreement between the predicted and measured moduli of elasticity and settlements. [ABSTRACT FROM AUTHOR]

This paper introduces a hypothesis to link the soil pore size distribution curve (PSDC) to the bimodal soil–water characteristic curve (SWCC). The relationships between the PSDC and the bimodal SWCC equations are discussed extending a novel modeling method using two equations; namely, the rigid equation and the simplified equation extending two well-known traditional unimodal SWCC equations from the literature. The calibration processes built for both the equations performance was evaluated for various types of soils. The results suggest that both the modified equations provide excellent comparisons with the measured data. The rigid equations provide comprehensive information about the macropores and the micropores of the bimodal SWCC; however, the simplified equations facilitate a flexible and simple curve-fitting process. The relationships between the proposed equations and the available methods for the bimodal SWCC from the literature are also discussed. In addition, a technique is developed based on regression analysis to estimate the key features for bimodal SWCC without bias. Similar to the unimodal SWCC equations the proposed equations are promising tools for predicting the properties of unsaturated soils; they are also valuable for use in numerical techniques for addressing complex nonlinear problems in engineering practice for unsaturated soils. [ABSTRACT FROM AUTHOR]

This paper presents the design details of a simple compressible air column pressure gauge system. The main components of this pressure gauge consist of a Mariotte bottle, plastic tubing, and a graduated scale. This low-cost gauge design is based on applying the principle of Boyle’s law for gases, which makes it particularly well-suited for the measurement of soil–water characteristics of coarse-grained soils, which desaturate at a faster rate, particularly in the low matric suction range of 0–10 kPa. Among its many uses, this precise gauge is best employed in the axis translation technique to measure matric suction in the range of 0–700 kPa. [ABSTRACT FROM AUTHOR]

• Various factors influencing groundwater hydrochemistry are discussed. • Ground and surface water interactions developed based on thermodynamics. • Recharge sources and ratios of groundwaters were quantified for a reservoir. Xiluodu Reservoir is the third-largest dam worldwide constructed in 2012. Significant changes in the hydrogeological conditions and regional groundwater-surface water (GW-SW) interactions associated since the dam impoundment in 2012 contributed to the river valley contraction (RVC). In this study, various factors that influence hydrochemistry and isotopic characteristics of GW-SW distribution interactions along with their migration patterns are extensively discussed. Based on these studies, the saturation index (SI) of different minerals during the GW-SW interaction in different periods was quantified considering the ion activity. The confined limestone GW and phreatic basalt GW are dominating GW in the dam site that play a predominant role in the regional GW-SW interactions. The impoundment strengthened the water–rock interaction and promoted the dissolution of minerals in limestone and basalt, contributing to an increase in the SI of different minerals in SW and GW. The primary recharge source for the limestone GW is Lake water; however, the secondary basalt GW recharge shifts from Ditch water to Reservoir water. The comprehensive studies summarized in this paper lays a foundation for rigorous understanding of the RVC mechanism that can be extended to other large reservoir projects in the world. [ABSTRACT FROM AUTHOR]

• Cementation and FT cycles reduce soils' water retention capacity. • Moisture sensitivity of M R , q u , E 1% , S u1% reduce upon cementation and FT cycles. • Proposed equations to predict the M R for cementation and FT influenced soils. This study evaluates the effects of post-compaction wetting–drying (WD) process, freeze–thaw (FT) cycles and cement content (CC) on the microstructure, volumetric strain (ε v), soil–water characteristic curve (SWCC), resilient modulus (M R), unconfined compressive strength (q u), and reloading modulus (E 1%) and axial stress (S u1%) at 1% strain level of a cement-stabilized expansive soil. The specimens compacted with different CC (i.e. 0%, 2%, 4% and 6%) were subjected to different number of FT cycles (i.e. N FT = 0, 1, 3 and 10). They were then dried or wetted to different moisture contents before the determination of the (i) SWCC using filter paper method, (ii) M R from cyclic triaxial tests, and (iii) q u , E 1% , and S u1% from unconfined compression tests. The microstructural changes in the test specimens were determined using mercury intrusion porosimetry and scanning electron microscope tests. Experimental results reveal that cement stabilization and cracks induced during FT cycles cause a significant reduction in the specimen's water retention capacity and the scale of volumetric strain upon moisture content fluctuation. The M R , q u , E 1% and S u1% typically decrease with N FT but increase with CC. However, their variation with moisture content changes is less significant after stabilization or FT cycles. Performance of several empirical models for predicting the M R , q u , E 1% or S u1% was examined. Similar trends in behavior were found for M R - q u , M R - E 1% and M R - S u1% relationships for the specimens tested with different CC, N FT and water content. A simple hyperbolic model proposed in this study for predicting these relationships is validated. The studies presented in this paper are helpful for the design and analysis of stabilized expansive soils used as pavement subgrade considering the influence of complex environmental factors. [ABSTRACT FROM AUTHOR]

The resilient modulus (M R) is a key parameter used in the mechanistic-empirical methods for the rational design of pavement structures. In permafrost and seasonally frozen regions, the M R of subgrade soils is significantly influenced by the variations in moisture content and temperature. The M R typically reduces due to the weathering action associated with wetting and freeze-thaw (F-T) cycles, which contributes to the reorientation of soil particles, loss in suction and cohesion, and formation of cracks in the subgrade soils. In the present study, the M R values of five Canadian soils that are widely used as pavement subgrades were determined under wetting and F-T conditions. The key findings from the extensive experimental investigation suggest: (i) the M R values of the soils at their respective optimum water contents significantly reduce up to the critical F-T cycle, which is typically the first or second F-T cycles; (ii) there is little change in the M R values from the critical to the tenth F-T cycle; (iii) the percentage of reduction in the measured M R at the optimum water content after the critical F-T cycle is strongly related to the soils plasticity index; (iv) the measured M R values are typically low for the specimens subjected to wetting, and the effect of F-T cycles on these specimens is insignificant; and (v) the effect of stress levels on the M R values is dependent on the initial water contents of the specimens and soil types. In addition, an artificial neural network (ANN) model was proposed and validated for estimating the M R of the tested soils taking account of various influencing factors. Both the experimental data and the developed ANN model provide valuable information for the rational design of pavements in Canada. • The M R of four soils tested decrease significantly after first or second F-T cycles. • The reduction in M R at the optimum water content is related to the plasticity index. • The effect of F-T cycles is insignificant when the specimens have high water contents. • The effect of stress levels is dependent on initial water contents and soil types. [ABSTRACT FROM AUTHOR]

Limited information is available in the literature for interpreting the influence of water infiltration process that contributes to in-situ collapse in loess deposits. For this reason, the focus of the present investigation has been directed to studying the collapse deformation with respect to time in Heifangtai, China, where significant wetting-induced collapse deformation is widespread due to multiple years of irrigation activities. A method that is based on easy-to-obtain parameters from constant water content oedometer tests and the wetting soil-water characteristic curve is used for predicting the long-term wetting-induced collapse deformation. The proposed method is validated using a field infiltration test. The wetting-induced collapse behavior in Heifangtai is interpreted using the proposed method. Results of the study suggest that there is a significant difference in total subsidence between the irrigation and non-irrigation areas. The collapse in the irrigation area occurs during the period when the wetting front advances and the groundwater table (GWT) forms and rises until the formation of a new hydraulic equilibrium state, which is significantly different from its initial condition. However, the collapse in the non-irrigation area is mainly related to the GWT variation. The difference in the total subsidence between the irrigation and non-irrigation areas is predominantly associated with the propagation of the wetting front. The proposed method is simple and can be extended in practical applications for reliably estimating the in-situ collapse deformation associated with the water infiltration process. • A simple method is proposed for predicting wetting-induced collapse deformation associated with infiltration process. • Difference in total subsidence between irrigation and non-irrigation areas is mainly due to wetting front propagation. • The wetting-induced collapse deformation is strongly related to the water infiltration process. [ABSTRACT FROM AUTHOR]