A Simplified Approach to Determine the Response of Unsaturated Soils Using Multistage Triaxial Test

Multistage triaxial tests offer a convenient alternative to determine the mechanical response of saturated and unsaturated soils. However, the primary challenge is to accurately identify the point of termination of the initial shearing stages prior to the failure of the brittle specimens. Hence, in this paper, the previous methodology used to define the point of termination of the shearing stages were studied in detail. Based on the limitations of methods used in the previous studies, a new twofold criterion integrating the variation of initial tangent modulus and the volumetric strain response with shearing has been proposed. The new approach was validated by comparing the results obtained from multistage triaxial tests and those from single-stage triaxial tests at low suction state under drained conditions. Each multistage test was performed on an isotropically consolidated specimen of silty soil at constant matric suction and different net confining pressures. Subsequently, it was confirmed that the shear strength parameters from both types of tests were practically identical.