Preliminary Study on Small-Strain Triaxial Testing Method for Soft Shanghai Clays

摘要

Triaxial tests with local strain measurements can obtain the change of stiffness at small strain level. It can help to increase the accuracy of finite element analysis on the influence of underground constructions to surrounding environment. This study is a summary of the experience upon small strain triaxial tests on Shanghai clays. First, the principle and recommended methods for installation of Hall Effect device are introduced. The whole test procedure and key points are described in detail. Then some different approaches to attain modulus from stress-strain curves are presented and compared. It is concluded that the modulus is properly calculated based on the stress-strain curve that pass through the origin. Finally, an analysis on the influence of pre-contact forces Δq_(pre) to the small-strain stiffness is presented. The characterization of stiffness in small strain (0.001% ～ 0.1%) is evaluated for intact Shanghai clay under various drainage conditions. The decay curve of stiffness for specimen under consolidation drained triaxial shear test is more continuous than consolidation undrained shear test. The stiffness in early shear stage measured in this study is significantly higher than that measured from conventional triaxial tests. This research can contribute to establish a small strain testing standard.