Lunar soil can be classified as silty sand according to its particle size distribution. The Lunar environment is quite different from on the earth (such as with no water

low gravitational fields

very low atmospheric pressure

etc.). The Van der Waals forces between soil particles proposed by Perko et al. (2001) is taken into consideration in the simplified lunar siol contact model

which is then implanted into PFC2D. With this model several biaxial compression tests are simulated by the discrete element method (DEM). The effects of Van der Waals forces on the mechanical behavior of samples and the average coordination number of samples are then studied. The results show that the Van der Waals force is a very important factor in controlling the peak strength; and it will lead to extensive dilatancy of the samples.