Effect of specimen confinement method on simple shear test of clay

Abstract

The simple shear test has been employed regularly during the last few decades in soil characterisation studies for earthquakes, liquefaction, offshore construction and other applications. A variety of simple shear devices are available and the main difference between them is the method of applying the horizontal confining stress. According to the ASTM (D6528-07) standard for direct simple shear testing of cohesive soils, circular specimens are generally confined by a wire reinforced membrane or stacked rings. In this paper a comparison of results from monotonic undrained simple shear tests with wire reinforced and flexible membranes is reported. A simple shear apparatus is utilized in which lateral confinement of the specimens can be achieved, either by flexible membrane and confining pressure applied to the specimen through compressed air to maintain K0 condition during compression, or by conventional wire reinforced membrane without confining pressure. It is shown that the membrane confinement method influences the measured undrained strength. For the normally consolidated specimens reported herein the shear strength using a flexible membrane is higher than for the wire reinforced membrane when the confining stress is adjusted to keep the vertical stress constant and is similar when the confining stress is kept constant throughout the shearing stage.