A SIMPLE STRESS-STRAIN RELATION BASED ON STRESS-PATH BEHAVIOR IN STRAIN-PATH CONTROLLED TRIAXIAL TESTS

Abstract

ABSTRACT A new devise is developed for conducting a strain-path controlled test with a conventional triaxial test apparatus. By controlling lateral stress during axial strain controlled test, this devise can keep the principal strain increment ratio, Re , defined as a ratio between axial and lateral strain increments, constant. Toyoura sand specimens at relative densities of 55% and 80%, consolidated under four different initial confining stresses, are axially loaded with a Re -value between — 0.5 and 1.0. The specimens are then unloaded to the initial stress states and reloaded with different Re -values. The test results during compression show that the principal stress ratio, K, converges at a constant value. The converged K- value is strongly dependent on the Re -value but insensitive to the strain history and the initial stress state. There is a well-defined relationship between the principal stress ratio K and the total strain ratio Re,t where the K-value decreases with decreasing Re,t-value. The K-Re,t relation is independent of its strain path and uniquely expressed in terms of the internal friction angle and the dilatancy angle of the sand. Based on the K-Re,t relationship, a simple equivalent linear constitutive model for axisymmetric condition is developed. Two series of stress-controlled drained triaxial compression tests are performed, and the results are compared with those simulated by the model. The computed results show excellent agreements with the test results, indicating that the proposed constitutive model, although based on the equivalent linear concept, is promising for simulating a stress-strain relation including dilatancy behavior of sand in the stress-controlled triaxial test.