A novel framework for nonlinear thermal elastic-viscoplastic (TEVP) constitutive relationships was proposed in this study, incorporating three distinct thermoplasticity mechanisms. These four TEVP formulations, combined with an existing TEVP constitutive equation presented in the companion paper, were integrated into a coupled consolidation and heat transfer (CHT) numerical model. The CHT model accounts for large strain, soil selfweight, creep strains, thermal-induced strains, the relative velocity of fluid and solid phases, varying hydraulic conductivity and compressibility during consolidation process, time-dependent loading, and heat transfer, including thermal conduction, thermo-mechanical dispersion, and advection. The performance of CHT model, incorporating different TEVP constitutive equations, was evaluated through comparing the simulation results with measurements from laboratory oedometer tests. Simulation results, including settlement, excess pore pressure and temperature profiles, showed good agreement with the experimental data. All four TEVP constitutive relationships produced identical results for the consolidation behavior of soil that in the oedometer tests. The TEVP constitutive equations may not have a significant effect on the heat transfer in soil layers because of the identical performance on simulating soil compression. The CHT model, incorporating the four TEVP constitutive equations, was then used to investigate the long-term consolidation and heat transfer behavior of a four layer soil stratum under seasonally cyclic thermal loading in a field test, with excellent agreement observed between simulated results and measured data.

A numerical model that accounts for fully coupled long-term large strain consolidation and heat transfer provides a more realistic analysis for various applications, including geothermal energy storage and extraction, buried power cables, waste disposal, groundwater tracers, and landfills. Despite its importance, existing models rarely simulate fully coupled large-strain long-term consolidation and heat transfer effectively. To address this research gap, this study presents a numerical model, called Consolidation and Heat Transfer (i.e., CHT), designed for one-dimensional (1D) coupled large-strain consolidation and heat transfer in layered soils, with the added capability to account for thermal creep. The model employs a piecewise-linear approach for the coupled long-term finite strain consolidation and heat transfer processes. The consolidation algorithm extends the functionality of the CS-EVP code by incorporating thermally induced strains. The heat transfer algorithm accounts for conduction, thermomechanical dispersion, and advection, assuming local thermal equilibrium between fluid and solid phases. Heat transfer is consistent with the spatial and temporal variation of void ratio and seepage velocity in the long-term consolidating layer. This paper details the development of the CHT model, presents verification checks against existing numerical solutions, and demonstrates its performance through several simulations. These simulations illustrate the effects of seepage velocity, thermal boundary conditions, and layered soil configurations on the coupled heat transfer and consolidation behavior of saturated compressible soils.

The behavior of soft soils distributed in coastal areas usually exhibits obvious time-dependent behavior after loading. To reasonably describe the stress-strain relationship of soft soils, this paper establishes a viscoelastic-viscoplastic small-strain constitutive model based on the component model and the hardening soil model with small-strain stiffness (HSS model). First, the Perzyna's viscoplastic flow rule and the modified Hardin-Drnevich model are introduced to derive a one-dimensional incremental Nishihara constitutive equation. Next, the flexibility coefficient matrix is utilized to extend the one-dimensional model to three-dimensional conditions. Then, by combining the HSS elastoplastic theory with the component model, the viscoelastic-viscoplastic small-strain constitutive model is subsequently established. To implement the proposed model for numerical analysis, the corresponding UMAT subroutine is developed using Fortran. After comparing the results of numerical simulations with those of existing literature, the reliability of the constitutive model and the program written in this paper is verified. Finally, numerical examples are designed to further analyze the effects of small-strain parameters and viscoelastic-viscoplastic parameters on the time-dependent behavior of soft soils.

The rate effect of cavity expansion is not only related to the drainage conditions of the soil surrounding the cavity, but also closely associated with the rate-dependent mechanical properties of the soil. Most existing cavity expansion theories primarily focus on the rate effect caused by partial drainage conditions, with little attention given to the combined influence of drainage conditions and the rate-dependent mechanical behavior of soil. By employing numerical analysis and utilizing the overstress elasto-viscoplastic (EVP) model, the study focuses on the partial drainage conditions during cylindrical cavity expansion. The analysis indicates that when only the effect of partial drainage conditions is considered, the total radial stress and shear stress decrease monotonically as the expansion velocity increases, and the expansion velocity ranging from 10(-4) to 10(-1) mm/s has a small impact on the total radial stress during the initial expansion stage. When the effect of partial drainage conditions and rate-dependent behavior is considered simultaneously, the total radial stress and shear stress gradually increase with the increase of expansion velocity during initial expansion stage, which is consistent with the results of in-situ self-boring pressuremeter tests conducted on the Burswood clay and Zhanjiang clay. With the cavity expansion, the radial total stress and shear stress show a pattern of first decreasing and then increasing with the increase of expansion velocity. Sensitivity analysis of the soil's viscoplastic parameters (gamma(vp) and n ) reveals that, for a given expansion velocity, the total radial stress, shear strength, and initial shear modulus gradually decrease as gamma(vp) or n increase, with the rate of decrease diminishing over time. The expansion velocity, permeability coefficient, and overconsolidation ratio of the soil significantly impact the drainage conditions at the cavity wall, while the influence of gamma(vp) and n is relatively minor. The drainage conditions of the soil can be assessed using a dimensionless velocity V , with values of V corresponding to partial drainage conditions ranging from 0.04 to 250. It is suggested that the time-dependent mechanical behavior should be considered when applying cylindrical cavity expansion theory to analyze geotechnical problems related to cohesive soils.

Polymer-blend geocell sheets (PBGS) have been developed as substitute materials for manufacturing geocells. Various attempts have been made to test and predict the behaviors of commonly used geogrids, geotextiles, geomembranes, and geocells. However, the elastic-viscoplastic behaviors of novel-developed geocell sheets are still poorly understood. Therefore, this paper investigates the elastic-viscoplastic behaviors of PBGS to gain a comprehensive understanding of their mechanical properties. Furthermore, the tensile load-strain history under various loading conditions is simulated by numerical calculation for widespread utilization. To achieve this goal, monotonic loading tests, short-term creep and stress relaxation tests, and multi-load-path tests (also known as arbitrary loading history tests) are performed using a universal testing machine. The results are simulated using the nonlinear three-component (NLTC) model, which consists of three nonlinear components, i.e. a hypo-elastic component, a nonlinear inviscid component, and a nonlinear viscid component. The experimental and numerical results demonstrate that PBGS exhibit significant elastic-viscoplastic behavior that can be accurately predicted by the NLTC model. Moreover, the tensile strain rates significantly influence the tensile load, with higher strain rates resulting in increased tensile loads and more linear load-strain curves. Also, parametric analysis of the rheological characteristics reveals that the initial tensile strain rates have negligible impact on the results. The rate-sensitivity coefficient of PBGS is approximately 0.163, which falls within the typical range observed in most geosynthetics. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Rainfall-induced landslides are common natural hazards, particularly in cases involving unsaturated soils. Slope instability issues may arise due to extreme climate events, while, creep effects can also contribute to landslide problems. In this study, a modified ViscoElastic-ViscoPlastic constitutive model is developed to more accurately characterise the mechanical properties of unsaturated loess, considering stress-level dependency of stiffness and creep properties. In addition, to better characterise the collapsibility of loess, the relationship between strengths and matric suction has been introduced. The infiltration process of an unsaturated porous medium is illustrated by the Van Genuchten model and the generalized Darcy ' s law. Additionally, the atmospheric boundary condition is incorporated in the numerical simulations, considering factors such as runoff generation and various climate events. In the context of slope stability analysis, a numerical approach has been developed to determine the safety factor of the slopes, by using displacement changes as the key assessment criterion. A good agreement between numerical and analytical results has been observed, verifying the proposed approach to determining safety factor. Finally, in parametric analyses, the effects of creep and matric suction on safety factor have been identified. Slope stability of unsaturated loess slopes subjected to different rainfall intensities and rainfall durations has been studied. The maximum depth of the sliding part increases obviously when considering the contribution of creep deformations, which is crucial in analysing slope stability.

This paper presents a semi-analytical solution for calculating soil stresses and pore pressures in the vicinity of an expanding cylindrical cavity. The main features of the solution are: i) realistic modelling of time-dependent soil behaviour, by means of an elastic-viscoplastic constitutive model, and ii) accurate prediction of soil strength under the stress path followed during plane-strain undrained cavity expansion, by using the transformed stress method to formulate the solution in the three-dimensional stress space and adopting an appropriate failure criterion. Predictions of the presented solution are benchmarked against a published solution, and are comprehensively analysed to identify the effect of the failure criterion and of the cavity expansion rate on the soil stresses and pore pressures developing in the vicinity of the cavity, and the associated stress paths.

This paper presents a novel elastic-viscoplastic constitutive model for reproducing the time-dependent behaviour of coarse-grained soil considering particle breakage, by integrating the Unified Hardening (UH) model, the elastic-viscoplastic (EVP) model and the overstress theory. The relationship between the degree of particle breakage and the loading rate is established, and the state variables associated with the critical state of coarsegrained soil are derived to jointly consider both time and particle breakage. A new three-dimensional elasticviscoplastic constitutive model is then constructed through combining the one-dimensional viscoplastic hardening parameter with a secondary consolidation coefficient considering particle breakage. The proposed model requires 19 parameters and it can well describe the influence of time-dependency and particle breakage to the shear, dilatancy, and compression behaviours of coarse-grained soil with various confining pressures or initial void ratios. Comparisons between the model predictions and experimental data are employed to validate the capability of the proposed model to replicate the time-dependent behaviour of coarse-grained soil.