Undrained Shear Strength Anisotropy of Cohesive Soils Caused by the Principal Stress Rotation

Abstract

The construction of geotechnical structures, e.g. diaphragm walls, tunnels, pad foundations or embankments, on cohesive soils, requires assessing the bearing capacity in undrained conditions. For this purpose, it is necessary to determine the value of undrained shear strength. Undrained shear strength is not the same in the subsoil, because it depends on many factors. One of these factors is principal stress rotation caused by changing the stress state due to loading or unloading the subsoil. During determination of undrained shear strength in laboratory tests the influence of principal stress rotation on undrained shear strength is often overlooked because of difficulty of reflecting this phenomenon in laboratory research. A device that allows to determine the anisotropy of undrained shear strength in soils due to the principal stress rotation is a Torsional Shear Hollow Cylinder Apparatus (TSHCA). The paper presents test results performed in a TSHCA on undisturbed sandy silty clays (sasiCl) characterized by different index properties. The main objective of the research was determining the undrained shear strength at wide range of angle of the principal stress rotation. The results of laboratory tests allow assessing the influence of the principal stress rotation on the value of undrained shear strength that should be used to determine the bearing capacity of the subsoil.