Multistage Triaxial Testing: A Rational Procedure

Abstract

It is difficult to obtain enough undisturbed submarine samples from a particular location to carry out triaxial compression tests in the conventional manner using three samples at three different cell pressures. Multistage triaxial tests offer an attractive means for determining shear strength parameters of submarine soils since they use only a single sample. This paper presents a study through which a rational procedure for multistage undrained triaxial testing of submarine soils has been evolved. For this purpose tests were conducted on laboratory sedimented kaolinite. This rational procedure was then used to determine shear behavior of a submarine soil from off the west coast of India and then verified by comparing it with conventional tests. It is shown that to ensure sufficiently good correspondence between results obtained from conventional and multistage testing, the sample in multistage testing must not be sheared to failure in each stage. The sample should be sheared to about 2 to 4% axial strain in each stage, and then failure condition predicted by using Kondner's hypothesis and extrapolating to a finite strain. The influence of finite strain as well as the cell pressure to be used in successive stages of the multistage test has been studied and suitable recommendations have been made.