Shear strength of liquefied soil can be determined by laboratory test methods and field test correlation methods. The strength determined by the former methods is termed as undrained steady state strength. A number of investigations show that the laboratory-tested strength of sand is usually much higher than the residual strength back calculated from actual seismic flow failures. Such uncertainty in the undrained steady state strength is generally considered as a result of scattering of laboratory test results and disturbance of soil samples....[ Read more ]

Shear strength of liquefied soil can be determined by laboratory test methods and field test correlation methods. The strength determined by the former methods is termed as undrained steady state strength. A number of investigations show that the laboratory-tested strength of sand is usually much higher than the residual strength back calculated from actual seismic flow failures. Such uncertainty in the undrained steady state strength is generally considered as a result of scattering of laboratory test results and disturbance of soil samples.

Some later investigations show that the steady state strength of sand is influenced by material inherent anisotropy. Due to inherent anisotropy, the strength of inherently anisotropic sand is dependent on the stress path and the mode of shear. Generally, conventional laboratory triaxial compression tests on samples taken along the axis of soil deposition usually overestimate the strength of such sand. It is considered that the common practice of using such test results in geotechnical designs and stability analyses without appropriate correction is non-conservative.

In this research, a method is proposed to quantify the influence of inherent anisotropy on the undrained steady state strength of sand. This method is derived based on the concept of critical state soil mechanics and under a framework for constitutive modelling. This theoretical approach of derivation is used in order to tackle the inherently anisotropic sand behaviour intrinsically. The output of the method is a set of reduction factors that can be applied to correct the laboratory-tested undrained steady state strength. This set of reduction factors is presented in manner that it can be easily incorporated into conventional geotechnical design and stability analysis procedures. This way of presentation is to allow engineers to account for the influence of inherent anisotropy in their work without a necessity of performing very complicated computations.