Effect of Initial Grain Size and Packing on the Evolution of Elastic Properties of Poorly Lithified Sandstones

In order to understand the effect of initial grain size and packing (porosity) on the deformation behavior of porous sandstone, we have conducted two series of triaxial experiments including hydrostatic and axisymmetric tests. We study the evolutionary pattern of elastic properties of our material. We investigate elastic moduli such as static bulk and shear moduli as well as dynamic and static M-moduli for the samples under compaction and shear. Our results show that initial packing (porosity) seems to be a more important factor than the initial grain size influencing the behavior of material under compaction. Higher confining pressure in the axisymmetric experiments impacts the onset of shear-enhanced compaction. Our investigation shows that static elastic moduli such as bulk and shear moduli and M-modulus vanish in the shear phase of the axisymmetric experiments indicating the effect of large strain and grain crushing in the samples. Whereas, the dynamic M-modulus increases along with compaction within the sample and is not sensitive to grain crushing observed in our final samples.