Uniaxial compression of synthetic, poorly consolidated granular rock with a bimodal grain-size distribution

We attempted to gain some insight into the mechanical properties of poorly consolidated granular rock by preparing and testing synthetic rock specimens in which different cement content and bimodal grain-size distributions were used. We mixed various proportions of fine and coarse sand, Portland cement, and water. The mixture was cast in a mold and left pressure-free during curing, thus ensuring that the final material was poorly consolidated. The specimens were tested in a uniaxial press. During these tests, the static Young's modulus was measured by performing small stress excursions at discrete intervals along the stress-strain curve. We observed significant non-linear elasticity (i.e., Young's modulus increased with stress) in all the specimens. As expected, the uniaxial compressive strength increased with increasing cement content. Furthermore, we observed a transition from grain-size sensitivity of strength at cement contents less than 20-30% to grain-size independence above this value. At high cement content, the measured values of Young's modulus are relatively well explained by a model based on rigid inclusions embedded in a soft matrix. At low cement content, we suggest that modelling the individual cemented grain-to-grain contacts becomes necessary. But this could not be done here for lack of microstructural information.