Understanding of shear behavior of soils is very important in engineering application. There are many factors influencing to the shear behavior of soils. In the laboratory tests, end friction at the axial plate changes the result and many researchers try to reduce the effect of end friction by using lubricated plate and specimen area correction. In this study, the effect of boundary condition is studied by numerical simulation using DEM program. End friction increases the critical void ratio. The best method to calculate the deviator stress is suggested by comparison of various area correction methods. Shear behavior is not different according to specimen shape by comparison with triaxial test and true triaxial test. Thus the effect of specimen shape is found to be little in DEM simulation.
For safe design, it has been an issue to clarify the critical state of soils. In this study, the uniqueness of critical state is studied by comparison of the critical state parameters derived from various drainage conditions and densities. Critical state line is unique regardless of drained condition and density. By checking the local void ratio in the triaxial test with free wall boundary, the local area of a specimen in which the void ratio is similar to the critical state void ratio is found. The middle part of specimen with end friction has the void ratio similar to the critical state void ratio.