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This study attempts to modify the unified strength theory by considering compression as a positive load in geotechnical engineering. It also aims to establish a unified elastoplastic strain softening constitutive model which can accurately describe the strain softening behavior of one kind of soft rocks distributed in Japan. The hardening function parameters of the unified elastoplastic strain softening constitutive model are determined from experiments. In addition, numerical simulations of this model are performed to compare the pre-peak, post-peak and the residual strengths of soft rock predicted by this study and experimental results. Simulation results demonstrated that the proposed constitutive equations in strain space can well describe the softening behavior and accurately predict the peak and residual strengths of soft rock. While the proposed equation is applicative for normally consolidated state and overconsolidated state according to the simulation results.

A pressure-dependent elastoplastic Cosserat continuum model for three-dimensional problems is presented in this paper. The nonassociated Drucker–Prager yield criterion is particularly considered. Splitting the scalar product of the stress rate and the strain rate into the deviatoric and the spherical parts, the consistent algorithm of the pressure-dependent elastoplastic model is derived in the three-dimensional framework of Cosserat continuum theory, i.e., the return mapping algorithm for the integration of the rate constitutive equation and the closed form of the consistent elastoplastic tangent modulus matrix. The matrix inverse operation usually required in the calculation of elastoplastic tangent constitutive modulus matrix is avoided, that ensures the second order convergence rate and the computational efficiency of the model in numerical solution procedure. A comparison is performed between the classical and Cosserat continuum model through the numerical results of three-dimensional shear structure, tensile specimen, footing on a soil foundation, and soil slope stability. It illustrates that mesh dependency and numerical difficulties exist in classical model, while Cosserat model possesses the capability and performance in keeping the well-posedness of the boundary value problems with strain softening behavior incorporated. The relationship between the internal length scale and the width of shear band and the load-carrying capability of the structure has also been demonstrated.

Mineralized collagen fibrils (MCFs) are important building blocks of bone at the submicroscale, and the mechanical performance of MCF arrays has a great influence on fracture resistance of bone at large length scales. In this study, we carry out the analyses of fracture process in MCF arrays under tensile loading. The plastic deformation of extrafibrillar matrix (EFM), post-yield behavior of MCFs, MCF breakage and debonding of the MCF-EFM interface are accounted for in the calculations. It is found that the fracture mechanisms of MCF arrays depend on the post-yield characteristics of MCFs. Shear-band-induced cracking of MCFs is the dominant fracture mechanism in the case of strain softening of MCFs, while strain hardening of MCFs promotes the MCF-EFM interfacial debonding, which controls fracture of MCF arrays. In addition, we reveal that plastic energy dissipation of MCFs and EFM provides major contribution to toughness of MCF arrays. Compared with the case of strain softening of MCFs, the MCFs exhibiting post-yield strain hardening can give rise to larger plastic deformation zone in MCFs and activate higher levels of plastic strain of EFM, enhancing plastic energy dissipation and thereby amplifying toughness of MCF arrays. The findings of this study shed new light on the fracture mechanisms of bone associated with alterations in submicroscale structure and composition.

This study attempts to modify the unified strength theory by considering compression as a positive load in geotechnical engineering. It also aims to establish a unified elastoplastic strain softening constitutive model which can accurately describe the strain softening behavior of one kind of soft rocks distributed in Japan. The hardening function parameters of the unified elastoplastic strain softening constitutive model are determined from experiments. In addition, numerical simulations of this model are performed to compare the pre-peak, post-peak and the residual strengths of soft rock predicted by this study and experimental results. Simulation results demonstrated that the proposed constitutive equations in strain space can well describe the softening behavior and accurately predict the peak and residual strengths of soft rock. While the proposed equation is applicative for normally consolidated state and overconsolidated state according to the simulation results.

The effects of various initial state variables on liquefaction resistance of sands are presented. The importance of adopting appropriate reconstitution technique in laboratory studies is highlighted by comparing the response of specimens at identical stress and density states, but reconstituted by different methods. Mobilised minimum undrained strength is shown to be highly dependent on the stress path. The correction factor K_σ is dependent on relative density, stress state, and loading mode. Significant differences are noted in the measured K_α values in a sub-rounded and generally strain softening sand compared to that of a sub-angular and relatively dilative sand at the same density and stress state. Over consolidation significantly increases the cyclic resistance, but it does not alter the normalized K_σ factor, implying the same factors reported in the literature for NC soils can be applied regardless of stress history.