The role of dynamic measurements in characterizing the mechanical behaviour of a high porosity rock

In this paper some results from laboratory tests on a clastic rock (calcarenite) having a porosity of 0.3 are illustrated and discussed. The mechanical behaviour of the calcarenite has been investigated through measurements of its textural characteristics and of the seismic wave velocities in both dry and saturated conditions on unstressed specimens. To study the mechanical behaviour of the rock during loading, uniaxial and triaxial tests have been carried out; the static measurements have been supplemented by dynamic measurements of the P- and S-wave velocities in the direction of the applied load and in the transversal direction for the uniaxial compression tests. The results of the measurements have outlined that porosity alone is insufficient in evaluating the elastic properties of the rock, while it is important to gain a thorough understanding of its textural characteristic, which can determine a composite distribution of water inside the voids and large differences in the elastic moduli. Wave velocities and also wave amplitudes have been found to be a very sensitive index of textural variations.