Simplified Constant Volume Simple Shear Tests on Clay

Abstract

This study investigates the shear parameter differences for an offshore clay tested under simplified constant volume direct simple shear (CDSS) and conventional non-constant volume Direct Simple Shear (DSS) conditions. Undrained test is achieved by maintaining constant specimen height against vertical movement in CDSS device. The change in vertical stress which occurs during shearing is assumed to be the equivalent pore water pressure in a truly undrained test. A series of undrained simple shear tests was performed at various vertical stresses, overconsolidation ratios (OCR) and shearing rates. The shear strength of clay specimen is overestimated when it is tested under conventional DSS device as compared to that under CDSS device. However, the secant modulus of normally consolidated local Terengganu Offshore Clay (TOC) specimens tested under CDSS device is at least two times greater than those under conventional DSS device. When offshore clay is tested under CDSS device, the normalized undrained strength of clay increases with OCR and the undrained shear strength of clay increases with shearing rate.