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This paper presents a two-surface constitutive model for describing thermomechanical behaviour of saturated fine-grained soils at both normally consolidated and overconsolidated states. A thermal-dependent stress ratio-state parameter relation is adopted to account for the effects of temperature on the shape of the state boundary surface (SBS) of soils. In the model, both the size and the shape of the SBS are allowed to vary with temperature, which is evidenced by thermal variation of the mechanical yield loci and the shifts of the normal consolidation line (NCL) and the critical state line (CSL) upon heating and (or) cooling. A thermal yield surface is added for modelling the isotropic thermal deformation of soils more accurately, in particular at overconsolidated states. The mechanical and thermal yield mechanisms are coupled through the temperature-dependent preconsolidation pressure that is controlled by a volumetric hardening law. Based on experimental observations, a nonlinear relationship between the spacing ratio and temperature changes is defined and a simple thermal dependent non-associated flow rule is proposed. The model is validated against some selected experimental results of several soils tested under various mechanical and thermal paths such as drained isotropic heating and cooling, drained and undrained triaxial compression at non-isothermal conditions.

This paper presents a theoretical study on a hybrid fabric evolution law for modelling anisotropic behaviour of granular media. In the hybrid evolution law, the rate of a contact normal-based fabric tensor is related to the rates of both stress ratio tensor and plastic strain. Assumptions and principles that were adopted for the development of the fabric evolution law are presented and discussed at first. Its accuracy is then examined by comparing with discrete element modelling (DEM) results under proportional loading and experimental data under complex loading and unloading processes. It is found that fabric evolution at low stress ratios is closely related to the stress-rate driven term of the hybrid law, while the strain-rate driven term dominates at high stress ratios. The hybrid evolution law satisfies the uniqueness requirement of fabric at the critical state by introducing an ‘attractor’ concept. Overall, fabric evolutions predicted by the hybrid law show a close agreement with DEM simulation results and experimental data.

This paper presents rigorous analytical solutions for cavity contraction analysis of a thick-walled cylinder/sphere after an arbitrary magnitude of expansion. Closed-form solutions are given for the distribution of stress and displacement within the cylinder/sphere of soil that is subjected to constant external pressure and monotonically decreasing internal pressure. The soil is modelled as an elastic-perfectly plastic material obeying the Mohr-Coulomb yield criterion and a non-associated flow rule. Large strain effects are taken into account by adopting the logarithmic strain definition in the plastic deformation analysis. The new solutions are validated with published results at first, then parametric studies are carried out. It is shown that the reference stress state (e.g. in-situ, elastic, partially plastic and fully plastic) and the cavity geometry ratio may greatly affect the unloading behaviour, in particular, when the cavity geometry ratio is smaller than a limit value. Finally, three typical applications of the solutions are demonstrated, including (i) design of the thickness of frozen cylinder walls accounting for large deformation effects, (ii) interpretation of laboratory pressuremeter tests with consideration of effect of the constant stress boundary, and (iii) shakedown analysis of a soil cylinder/sphere considering its geometry changes upon cyclic loading and unloading.

To provide precise prediction of tunnelling-induced deformation of the surrounding geomaterials, a framework for derivation of rigorous large-strain solutions of unified spherical and cylindrical cavity contraction is presented for description of confinement-convergence responses for deep tunnels in geomaterials. Considering the tunnelling-induced large deformation, logarithmic strains are adopted for cavity contraction analyses in linearly elastic, non-associated Mohr–Coulomb, and brittle Hoek–Brown media. Compared with approximate solutions, the approximation error indicates the importance of release of small-strain restrictions for estimating tunnel convergence profiles, especially in terms of the scenarios with high stress condition and stiffness degradation under large deformation. The ground reaction curve is therefore predicted to describe the volume loss and stress relaxation around the tunnel walls. The stiffness of circular lining is calculated from the geometry and equivalent modulus of the supporting structure, and a lining installation factor is thus introduced to indicate the time of lining installation based on the prediction of spherical cavity contraction around the tunnel opening face. This study also provides a general approach for solutions using other sophisticated geomaterial models, and serves as benchmarks for analytical developments in consideration of nonlinear large-deformation behaviour and for numerical analyses of underground excavation.

In this paper, a noncoaxial plane strain soil model is developed in the framework of initial soil strength anisotropy that is described by taking the internal friction angle to be a function of principal stress orientations. The conventional Mohr-Coulomb (M-C) yield criterion is generalized to give an anisotropic yield criterion, with the curve in the deviatoric stress space forming an ellipse. Both rotational and eccentric ellipses are discussed. The formulation of noncoaxial constitutive equations is described by a general form in terms of the plastic strain rate. In this form, the plastic strain rate is divided into two parts: the conventional component that is derived from the classical plastic potential theory and the noncoaxial component that is assumed to be tangential to the yield surface. The newly proposed model is validated by the analytical calculations and discrete element modeling (DEM) simulation results in simple shear tests. Conclusions can be drawn that this model is generally capable of capturing the DEM observations of simple shear testing.