One dimensional compression behavior of poorly graded soils and their mixtures have been investigated using the discrete element method PFC3D software package with spherical particles and a size-related linear elastic contact model. Simulation results show that, for soil samples of the same grading that were compressed from different initial solid fractions, there exists a unique relationship between solid fraction and vertical stress at high stress levels. Contact force distributions of these different samples fall on a similar distribution curve in the same stress range. There is also a convergence for the size distributions of particles involved in the transmission of greater-than-average (strong) contact forces in each system. The results are mainly presented for a sand-like monodisperse material and a best packing efficiency mixture material. Cumulative contributions of individual contact forces to the deviator stress were calculated and the results show that the deviator stress is primarily attributed to the strong forces for both monodisperse and mixture materials.