STRESS-STRAIN ANALYSIS OF SAND SUBJECTED TO TRIAXIAL LOADING

An influence of the end boundary conditions to distribution of stress and strains in a soil specimen during conventional compression triaxial tests is analyzed by the experimental and numerical methods. An evaluation of actual stress state is important when determining the shear strength parameters of soil. These methods are used in this paper to investigate and simulate the contact between the testing equipment and ends of sand specimen during the test. Two different conditions of sample boundaries are analyzed: the first case, when the friction between the sample ends and testing machine is not eliminated (fixed ends); the second case, when the friction between the sample ends and testing machine is eliminated (free ends). The friction is eliminated by allowing the sample base to move freely in any horizontal direction. Simulation results of stress-strain distribution in the sample by using the finite element method show that the shear stress at the contact plane increases for the sample with fixed ends. The stress restricts the displacement of sample ends in the horizontal direction. In the case of free ends the horizontal displacement of sample base occurs. Similar to simulation results have been obtained from the laboratory tests performed with triaxial compression apparatus.