Packing properties and steady strength of cemented loose granular materials

Abstract

We study samples composed of loose cemented assemblies of particles under isotropic compression and biaxial shearing by means of a discrete-element approach. Compression tests are undertaken by consolidation of grains initially not presenting contacts under varying level of cementation and increasing confining pressure. We find a nonlinear evolution of the solid fraction with pressure that is described using the evolution of granular connectivity and the collapse of pores under homogeneous load. The poral space is characterized in terms of probability of void size number and volume distribution which, surprisingly, can contain voids as 30 times the size of an average particle. Under steady flow, the shear strength turned out to evolve non linearly with the cementation level. For cementation strengths below the confining pressure, the cementation between particles has little effect upon macroscopic friction angle. For greater values of cementation, a rapid increase of macroscopic friction occurs despite a drop in grain connectivity. Macroscopic cohesion is, in turn, small when compared with the interparticle bonding strength for highly cemented samples. The increment of macroscopic strength is found to deeply depend on the anisotropy of contact forces despite a homogeneous distribution of contact orientations and lower connectivity for highly cemented samples.