The degradation of shear strength of soils due to prolonged contamination of soils is an emerging problem. The experiments conducted at New Jersey institute of Technology showed a gradual reduction of the unconfined compressive strength and the modulus of the contaminated soils with the increase in the amount of contamination. It was also found that the pore fluid viscosity was responsible for the degradation of the shear strength and the change in stress-strain behavior. In this paper a theoretical explanation is provided for the above observations with the aid of a microscopic model for soils. The microscopic model TRUBAL (Strack & Cundall, 1984), a computer program which was developed to model dry granular assemblies of spheres in three dimension, was modified and used in this study. To adopt the above model for this research, the computer program was first modified to accommodate the pore pressure changes. In order to model the degradation of shear strength of soils due to chemical contamination, the pore fluid in the granular assembly was replaced with fluids of different pore fluid viscosities. The influence of pore fluid viscosities on the granular assembly was modeled by introducing the theory on converging-diverging wedges in basic lubrication theory. The results show that the modified microscopic model is capable of explaining the experimental observations.