Undrained Triaxial Compression Testing of Sand-Low Plastic Silt Mixtures

Abstract

This study presents some consolidated undrained triaxial compression (CU) tests of sand-low plastic silt (ML) mixtures, with ML contents of 0 %, 10 %, 20 %, 30 %, 40 %, and 50 %. The tests were performed on each mixture at three effective consolidation stresses (ECSs) of 50, 100, and 150 kPa. Triaxial testing equipment equipped with submersible local linear variable differential transformers (LVDTs) was employed to obtain accurate non-linear stiffness responses of the tested specimens over the course of the test. The testing results showed that the minimum and maximum void ratios (e_min and e_max) of the specimens decreased until 20 % ML additions and then increased. Increasing the ECS of the test increased the deviatoric stress, contractive volumetric response and secant modulus (E_u) of all mixtures. Increasing the ML content at a given ECS decreased the deviatoric stress of the mixtures. The ML additions increased the excess pore water pressure (PWP) of the mixtures. The sand with low ML contents (0, 10, and 20 %) exhibited an initial contractive behaviour, followed by a dilative response. However, sand mixed with 30, 40, and 50 % ML were dominated by contractive response. The E_u values of sand decreased with the ML additions. Consequently, these suggest that sand grains can retain their dilative nature and stability when the ML contents are low (i.e., sand-dominated soil matrix). However, when ML dominates the soil matrix, the mixtures exhibited a dominant contractive response with decreasing mean effective stress in their stress paths.