Numerical analysis of stress-strain inhomogeneities in a triaxial test specimen

Inhomogeneities caused by end restraint and insufficient drainage during conventional compression triaxial tests are analyzed by a numerical method. A finite element model is presented to simulate the testing procedure. The soil-platen interaction is represented by contact elements which allow frictional sliding between contacting nodes. The soil mass is represented by the modified Cam clay model. Coupled hydro-mechanical analyses are carried out in order to simulate both drained and undrained tests. The distributions of stresses and strains in the specimen for different end conditions are compared with the ideal case where no end restraint exists, in order to find representative measuring positions in the sample. Different rates of axial strain are tested in order to study the inhomogeneities caused by insufficient drainage during drained tests. Simulated results show that both end restraint and insufficient drainage can cause the barrel shape deformation of the specimen. Stress-strain and strength properties based on global measurements are not a good representation of true soil behaviour when end restraint or insufficient drainage is present.