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Focusing mainly on the compressive-shear (C-S) stress, the existing soil strength theories fail to well describe the soil strength under tenso–shear (T-S) stress and are not suitable for analyzing the tensile strength and T-S coupling strength. Taking the T-S strength into account, a three-dimensional nonlinear strength model of soil is established. The failure function on the π plane is a Lade Lade-curved triangle in principal stress space, which reasonably reflects the effect of medium principal stress. The failure function on the triaxial compression meridian plane is divided into the T-S and C-S zones, in which the two failure functions are smoothly connected at the closed stress point. To easily combine it with the specific elastoplastic constitutive theory, the proposed strength model is transformed into the D-P criterion in transformed stress space using the transformation stress method, which provides a theoretical foundation for numerical calculations. Compared with the true triaxial test results and numerical slope examples, the proposed model gives a good description of the nonlinear soil strength under complex stresses and the instability failure mechanism of the slope. [ABSTRACT FROM AUTHOR]

The microstructure can have an important impact on the hydraulic and mechanical behaviors of unsaturated soil; therefore, it must be considered in constitutive models to enable accurate predictions of soil behavior. This paper focused on the constitutive modeling of soils that exhibited a dual porosity structure. Based on the assumption that macro and micropores contained in the double porosity structure had different influences on the mechanical and hydraulic behaviors, the effective degree of saturation (Se) was selected as a microstructural index. This microstructural index was implemented within Bishop's effective stress-based approach and the Glasgow coupled (GCM) and modified Cam-Clay models (MCC) were adopted as the basic framework for the development of a constitutive model. Typical samples of low expansive, nonexpansive, and collapsible soils with dual porosity were selected to validate the model's performance, and the model performed well when compared with experimental data for isotropic compression, triaxial shear, and wetting tests. [ABSTRACT FROM AUTHOR]

Shear strength (τ) analysis has received considerable attention, because of its importance when designing various geotechnical structures, such as tunnels, retaining walls, shallow foundations, and slopes. Predicting the unsaturated τ from water retention curves (WRCs) is an existing method. The validity of this method for the prediction of unsaturated τ over a wide suction (ψ) range has been discussed by several researchers. However, the existing method ignores the influence of void ratio (e), which plays a strong part in the water holding capacity and the τ analysis of unsaturated soils. Therefore, according to an existing WRC equation that distinguishes capillary water and adsorbed water, a new WRC equation was proposed to consider the effect of e on the water holding capacity. In addition, using the e dependent WRC, a new method that predicted the τ of unsaturated silts or silty clays at various e over a wide ψ range (that included the residual zone) was proposed. The prediction of τ by the proposed method produced better predictions for experimental data than that of the existing method. [ABSTRACT FROM AUTHOR]

Pore ice content is crucial in evaluating the mechanical properties of frozen soils. Existing strength criterion models are usually empirical and ignore the influence of pore ice content. By assuming that the critical state shear stress ratio of soil is a function of the stress level, a critical state line of frozen soil is proposed to consider pore ice content. By combining the Mohr–Coulomb (M–C) and Drucker–Prager strength criteria to describe the failure shape characteristics on the deviatoric plane, a new strength criterion is established for complex stress conditions. The proposed model is validated against existing models and measured data in the literature. In addition, the proposed model can uniformly describe the CSL of different types of geotechnical materials and has a clear physical meaning, which may provide a theoretical basis for constitutive models. [ABSTRACT FROM AUTHOR]

In the past, the capillary effect is rarely considered for microcontact models when two adjacent particles are separated by a certain distance. In this paper, a liquid-bridge contact model of unsaturated particles is presented, which is applied to the discrete-element software PFC. Based on this, simulations of uniaxial tensile for unsaturated soils under (2D) situation are carried out, and influence of a water retention angle on uniaxial tensile strength are studied. The simulation results show that the uniaxial tensile strength of unsaturated soil decreases gradually with the increase of the water retention angle, obvious cracks generate at both ends of the soil samples, and the soil sample possesses a residual strength. According to the particle displacement field, velocity field, and contact force chain, the failure forms of samples with different water retention angles are determined. Based on the rose diagram of normal contact force, the changes of its direction and value during failure process are observed directly, so as to analyze the evolution law of contact force for unsaturated soils. [ABSTRACT FROM AUTHOR]