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Although the undrained anisotropic behaviour of sand has been extensively studied, little is known about undrained anisotropy and liquefaction susceptibility of silt soil. This paper presents a systematic experimental study on the undrained response of a silt soil under different patterns of principal stress rotation, including the 90° jump of principal stress and the continuous rotation of principal stress. Particular attention has been focused on the influence of the cyclic stress path and the influence of cyclic stress ratio (CSR) on the pore pressure ratio ru and the deviatoric strain amplitude γqa. A remarkable finding of this study is that, for all loading patterns investigated, the pore pressure ratio ru is uniquely related to the deviatoric strain amplitude γqa, rather than to the CSR. Based on the experimental data, an explicit expression is proposed to relate γqa and ru, which can be used to predict the onset of failure as well as the build-up of pore water pressure at a specific strain level. The study also found that the relationship between the CSR and the number of cycles required to failure (Nf) is dependent on cyclic loading patterns and stress paths. However, by defining a unit cyclic stress ratio (USR) as a new index for cyclic resistance, a virtually unique relationship between USR and Nf can be established for all cyclic loading patterns and stress paths considered.

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This paper systematically investigates the dynamic behavior of sandy soils mixed with recycled tire rubber over a wide strain range in the order of 10[Formula: see text]–10[Formula: see text], using combined resonant column and cyclic triaxial tests for measurement of the shear modulus and damping ratio. The experiment integrates small-strain tests using a resonant column apparatus and large-strain tests using a cyclic triaxial apparatus. The results demonstrated that the addition of rubber particles significantly enhances the linear elastic properties of the host sandy soils and improves the critical shear strain from which the rubber–sand mixtures change from linear to nonlinear stress–strain behavior. The critical shear strain is therefore introduced as the function of rubber content (RC), to identify the influence of RC on the strain-dependent dynamic properties of the host sandy soils. Then, a well-calibrated prediction formula is applied in conjunction with the concept of binary packing material to describe the behavior of the host sandy soils with various RC. Remarkably, the obtained normalized shear modulus and damping ratio vs. shear strain relationships address the limitations of existing testing methods to simultaneously capture the soil dynamic properties at low-strain (stiffness) and the large-strain (energy dissipation) regimes. The model constants can be simply determined through a unique set of explicit expressions which incorporate some basic index properties of the host sand and recycled tire rubber. In this regard, the proposed procedure provides a significant advantage in the evaluation of strain-dependent dynamic properties of rubber–sand mixtures in practice.