Model For Unsaturated Soils Research Articles

A hydromechanical model for unsaturated soils based on state boundary hypersurface

A hydromechanical model for unsaturated soils based on state boundary hypersurface

Cyclic response of unsaturated weathered red mudstone: Experimental investigation and a cyclic model

The mechanical properties and constitutive model of unsaturated soils under cyclic loading are crucial for understanding the behavior of foundations and slopes subjected to dynamic motions such as earthquakes and traffic loading. In this study, multilevel strain-controlled cyclic simple shear tests of unsaturated weathered red mudstone (WRM) were conducted. The detailed investigation focused on cyclic responses, including shear stress-strain behavior and volume change, strain-dependent secant shear modulus and damping ratio, and stress–dilatancy behavior. This study revealed the significant influences of the degree of saturation and vertical stress on these responses, with the initial static shear stress mainly affecting the shear stress-strain behavior and volume changes at the initial loading stage. Based on the experimental observations, a cyclic constitutive model was proposed for unsaturated WRM. The model incorporates a slightly revised Davidenkov model and Masing criterion to generate shear stress-strain hysteresis loops with or without initial static shear stress. Additionally, a stress-dilatancy equation was included to capture the volume changes during cyclic loading. The proposed model was verified by comparing representative test data and calculation results, demonstrating the excellent performance of the proposed model in modeling the main features of unsaturated WRM under cyclic loading.

Numerical simulation of rainfall-induced deformations of embankments considering the coupled hydro-mechanical behavior of unsaturated soils

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.

Thermo-hydro-mechanical behaviour of energy tunnel in unsaturated soils

Soils surrounding energy tunnels are often unsaturated, particularly in areas with a low water table. All studies of the mechanical behaviour of energy tunnels focused on saturated or dry soils. Through numerical simulations using a coupled thermo-hydro-mechanical model for unsaturated soils, this study aims to improve the understanding of the interactions between energy tunnels and unsaturated ground. The influences of water table position and soil type on the mechanical behaviour of energy tunnels were investigated. Results show that the thermally-induced lining convergence of energy tunnels does not change much with the water table position. Nevertheless, the other mechanical responses (e.g., settlements of ground and tunnel and lining stress changes) highly depend on the water table position. These mechanical responses are more significant when the water table is higher than the tunnel center, except for the larger settlements at a lower water table in clay. Furthermore, the above responses are underestimated if soils above the water table are assumed to be completely dry. The degree of underestimation is most significant for the clay, followed by silt and sand, e.g., a maximum of 54%, 23% and 10% in the change of circumferential stress, respectively. These results highlight that the unsaturated soil model should be used to evaluate the thermo-hydro-mechanical responses of energy tunnels in unsaturated soils, particularly for the clay ground.

Thermal effects on the strain rate-dependent behavior of highly compacted GMZ01 bentonite

Investigation of thermal effects on the strain rate-dependent properties of compacted bentonite is crucial for the long-term safety assessment of deep geological repository for disposal of high-level radioactive waste. In the present work, cylindrical GMZ01 bentonite specimens were compacted with suction-controlled by the vapor equilibrium technique. Then, a series of temperature- and suction-controlled stepwise constant rate strain (CRS) tests was performed and the rate-dependent compressibility behavior of the highly compacted GMZ01 bentonite was investigated. The plastic compressibility parameter λ, the elastic compressibility parameter κ, the yield stress p0, as well as the viscous parameter α were determined. Results indicate that λ, κ and α decrease and p0 increases as suction increases. Upon heating, parameters λ, α and p0 decrease. It is also found that p0 increases linearly with increasing CRS in a double-logarithm coordinate. Based on the experimental results, a viscosity parameter α(s, T) was fitted to capture the effects of suction s and temperature T on the relationship between yield stress and strain rate. Then, an elastic-thermo-viscoplastic model for unsaturated soils was developed to describe the thermal effects on the rate-dependent behavior of highly compacted GMZ01 bentonite. Validation showed that the calculated results agreed well to the measured ones.

Preliminary Experiences in Determining the Soil–Water Characteristic Curve of a Sandy Soil Using Physical Slope Modeling

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.

A Hyperelastic Bounding Surface Plasticity Model for Unsaturated Granular Soils

A Hyperelastic Bounding Surface Plasticity Model for Unsaturated Granular Soils

Seismic Response Study of S-Wave Incident Stratified Unsaturated Soil Site Under Thermal Effects

ABSTRACT Drawing upon the fundamental principles of mixture continuum and thermodynamics, planar S-wave incident model for layered unsaturated soil is formulated. Employing the Helmholtz vector decomposition principle, the wave field within the layered unsaturated soil is analyzed using the transfer matrix method, accounting for the influence of thermal effects. An analytical solution is obtained for the seismic response in layered unsaturated soil under the action of thermal effect. The results of the numerical analyses show that the thermo-physical parameters such as relative heat of solid, temperature, and thermal expansion coefficient have a notable effect on the seismic response of the site.

Numerical modeling bearing capacity in wetting unsaturated expansive soils

To address the load-bearing deterioration of expansive soils uplift pile foundation after moisture absorption, a coupled seepage-soil deformation model for unsaturated expansive soils is implemented into ABAQUS. This modeling work consists primarily of two aspects: (1) The total strain of expansive soils has been decoupled into two parts, i.e., one caused by external loads and calculated by using Mohr-Coulomb plasticity model, and the other induced by wetting swelling and modeled by defining the moisture-swelling relation curve of expansive soils; (2) User-defined field subroutine (USDFLD) is developed by defining suction-dependent soil’s parameters (elastic modulus, cohesion and internal friction angle), and employed to simulate softening behaviors of expansive soils after moisture absorption. he above model is subsequently used to perform 3D finite element modeling and hydraulic-stress coupling analysis on the bearing capacity of pile in expansive soils before and after rainfall. Eventually, the proposed numerical method is validated by simulating a group of full-scale tests.

Constitutive and experimental study of unsaturated fine-grained soils over a wide suction range

The instabilities exhibited by unsaturated fine-grained soil, stemming from coupled hydro-mechanical phenomena, represent crucial engineering characteristics essential for geotechnical designs. This study introduces a constitutive model for unsaturated fine-grained soils, incorporating the framework of sub-loading surface plasticity. The model integrates Bishop’s effective stress and capillary degree of saturation as basic variables, while also addressing the distinct influences of soil volume change on capillarity and adsorption mechanisms. Validation of the proposed model is conducted using a diverse set of experimental data derived from suction-controlled triaxial compression tests conducted under low and high suction conditions. The results demonstrate that the new constitutive model can achieve a reasonable agreement with the observed data.

Temperature-Dependent SWCC Model for Unsaturated Soil

Temperature-Dependent SWCC Model for Unsaturated Soil

Hydromechanical modeling of unsaturated soils considering compaction effects on soil physical and hydraulic properties

Hydromechanical modeling of unsaturated soils considering compaction effects on soil physical and hydraulic properties

Analytical solution of a pollutant transport model for unsaturated soil considering the effects of consolidation and temperature

The migration behavior of pollutants is affected by consolidation and temperature when using thermal desorption technology to clean contaminated sites. Based on a one-dimensional consolidation model for unsaturated soil and the traditional heat conduction equation, a pollutant transport model accounting for the combined effects of consolidation and temperature was established in this paper. An analytical solution was obtained by using the separation of variables method and the integral transformation method. In addition, the correctness of the proposed model was verified via a comparison between the existing analytical solution and the theoretical model. Finally, adopting benzene as the research object, the influence of different factors on pollutant migration was studied. It was found that the growth rate of the pollutant concentration increased with increasing consolidation pressure, and the final pollutant concentration decreased with increasing consolidation pressure. The pollutant concentration increment due to temperature first increased and then decreased with increasing migration distance. The higher the Soret coefficient and volumetric moisture content are, the higher the pollutant concentration.

An effective stress-based approach to modeling the hydro-mechanical behavior of unsaturated soils

A constitutive model of unsaturated soils is developed by incorporating the concept of intergranular stress into the framework of the modified Cam–Clay model. Within this context, the degree of saturation is viewed as an internal state variable, so that the soil–water retention function appears naturally as an evolution equation for the volume fraction of water. The new model not only has a neat structure but also includes fewer material parameters compared to the other models. A new volumetric-hardening law is proposed by taking into account the effect of wetting-induced pore collapse. It is shown that the collapsing void ratio (the current void ratio minus the void ratio at full saturation under the same effective stress) is dominated by the degree of pore air saturation (one minus the degree of water saturation) and practically independent of intergranular pulling forces, highlighting the important effect of soil fabric on the wetting-induced pore collapse. The proposed model is applied to simulate different types of experiments on unsaturated soils subjected to various combined hydraulic and mechanical loadings, showing its capability and diversity in modeling the hydraulic and mechanical behavior of unsaturated soils.

Study on coupled heat-water-vapor transfer in buffer material based on SPH method

To study the hydrothermal evolution law in buffer materials, based on the heat balance equation of unsaturated soil and the quality control equation of water migration, a coupled heat-water-vapor model of unsaturated soil is proposed. This model comprehensively considers the transition process of water vapor, the heat transfer caused by water flow and vapor migration, as well as the influence of temperature potential on water flow and vapor migration. The smoothed particle hydrodynamics (SPH) method can be used to calculate their evolution process conveniently. In the solution, the vapor content of heat balance equation is solved first, and then the water content and temperature field are solved, so as the coupling of temperature field between water and vapor field is implemented. The rationality of the model is verified by the tested results of soil column test. According to the established theoretical model, the heat-water-vapor three-field coupling problem of the buffer material in the repository was simulated and studied, and the hydrothermal evolution law inside the buffer material was revealed. On this basis, the influence of the change of groundwater pressure and heat source temperature on the hydrothermal evolution law of buffer material was further analyzed.

On vibration response of heavy hammer self-falling pile driver in uneven unsaturated soil – Experimental and analytical study

The goal of this study is to determine the scope of the impact of pile driving construction vibration on surrounding residential houses and buildings during engineering construction. Firstly, introducing the gradient factor of unsaturated soil, proposed a model for non-uniform variation of pores with depth. Secondly, Consider the coupling between the model and soil skeleton density, relative fluid density, relative gas density, pore fluid, pore gas, and shear modulus. Finally, coupling the pile with the driving depth and propose a pile driving vibration model for non-uniform unsaturated soil. Proposed a new method for solving coupled equations using Hankel transform. Moreover, the analytical solution of this study was validated through on-site experiments. Results show that, deeper the pile is inserted into the soil, the greater the peak vertical velocity at different measuring points. The vibration of the pile is strongest at the last 1 m into the soil. When close to the vibration source, the amplitude values in the three directions are: maximum in vertical direction, followed by horizontal and radial direction, and minimum in horizontal and tangential direction. When pile driving construction is carried out outside the range of vibration influence, the seismic damage generated is equivalent to the seismic intensity below V (excluding V). The rate amplitude calculated by the model established in this study is closer to the measured value. Therefore, using the model established in this work can more accurately evaluate the impact of pile driving vibration during the construction process of highways and high-speed railways.

Fractal thermal conductivity of unsaturated soils considering pore heterogeneity

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.

The UTUH model: a time-dependent unified hardening constitutive model for unsaturated soils

AbstractAn advanced constitutive framework for unsaturated soils, the UTUH model, is proposed in this paper, which considers the joint effect of time, suction and overconsolidation within the framework of sub-loading surface plasticity. A reference line, namely the instantaneously normal compression line (INCLs) for unsaturated soils, is introduced from a conceptual framework drawn from constant rates of strain test results to determine creep time and overconsolidation states of unsaturated soils. Subsequently, an isotropic elasto-viscoplastic constitutive model for unsaturated soils is produced by combining viscous deformation with mechanical and hydraulic deformation through overconsolidation parameter. Net stress, suction and time are adopted as fundamental constitutive variables and time-dependent loading collapse yield surface is derived to characterize the relationship between yield stress, suction, and time. Then, an extension to a triaxial stress state is built in the space of mean effective stress, suction, deviator stress and time variable. The hardening of yield surface and sub-loading surface is controlled by viscoplastic volumetric strain and unified hardening parameter. The performance of the proposed UTUH model is addressed through four numerical studies, and the proposed model is validated against experimental data from the literature.

Experimental study and numerical modeling of the thermo-hydro-mechanical process in unsaturated soil under freeze-thaw cycles

Hydropower resources have been developed to the cold regions in the west of China recently, wherein the dam will be subjected to high frequency of repeated freeze-thaw action during the construction process in winter, and thus will cause safety and stability problems of these projects. According to the actual construction situations of Lianghekou hydropower station located in Sichuan Province, one-side freezing and two-side thawing tests of unsaturated core-wall soil samples in a closed system are carried out, and the evolution of temperature, water and displacement as well as their interaction are tested and analyzed. The results show that with the increasing of freeze-thaw cycles, water migration results in a decrease of water content in the unfrozen zone and an increase in the frozen zone, and the water concentration area is formed in the soil column. Simultaneously, a deeper freezing depth accompanied with a shorter thawing duration after 10 freeze-thaw cycles is observed through the temperature field results, whereas a steady fluctuation of the deformation field is showed after the 7th freeze-thaw cycle. Moreover, based on the test results and exiting researches, a thermo-hydro-mechanical coupling model for unsaturated soils subjected to cyclic freeze-thaw action is proposed, in which both the permeability and compressibility are inextricably related to the void ratio, and vary in different calculated areas. Additionally, the effects of number of cycles on initial conditions and model parameters are also considered. Comparisons with the experimental data demonstrate the validity and adaptability of the proposed model in describing the freeze-thaw process of unsaturated soil. Through the combination of experiments and numerical simulation, the freeze-thaw process can be more clearly understood, and related engineering problems can be predicted with the help of the mathematical model in this paper.

A viscoplastic constitutive model for unsaturated soils based on nonstationary flow surface theory

AbstractA viscoplastic constitutive model is developed to describe the viscoplastic behavior of unsaturated soils. The proposed model accounts for the stain‐rate and suction effects on yield by adopting an unsaturated isotach concept. The nonstationary flow surface theory (NSFS) is applied for modeling the viscoplastic behavior, with the yield surface which can evolve with the viscoplastic strain, viscoplastic strain rate and suction. Meanwhile, the progressively hardening concept is adopted for reproducing the viscoplastic behavior of soil at an over‐consolidated state. For the validation, a series of loading conditions are considered based on the data from the literature. Results show that the proposed model is able to reproduce the main viscoplastic behaviors of unsaturated highly compacted Gaomiaozi (GMZ) bentonite, Glenroy silt and Qianjiangping landslide (QL) soil, including CRS compression tests, rate‐dependent triaxial shear tests, and triaxial creep tests.