Direct numerical simulation techniques for particulate flow by the fictitious boundary method (FBM) are presented. The flow is computed by a multigrid finite element solver and the solid particles are allowed to move freely through the computational mesh which can be chosen independently from the particles of arbitrary shape, size and number. The interaction between the fluid and the particles is taken into account by the FBM in which an explicit volume based calculation for the hydrodynamic forces is integrated. A new collision model based on papers by Glowinski, Joseph, Singh and coauthors is examined to handle particle-particle and particle-wall interactions. Numerical tests show that the present method provides a very efficient approach to directly simulate particulate flows with many particles.