Energy analysis during compression tests of rock samples

Uniaxial compression tests on coarse-grained sandstone samples carried out in a stiff testing machine have shown that the stress-strain curves are not smooth on account of the local maxima and drops of stresses. According to the investigations performed by Minh (1989) the stress drops are caused by new cracks appearing in the rock sample. In this work Minh’s hypothesis for the determination of the fracture surface energy consumed for the creation of new cracks in the pre-failure part of stress-strain relation was applied. An introduction of the new expression in the energy balance does not globally change the values of energy indexes characterizing the rock burst susceptibility and which, contrary to expectation, remain greater for water saturated than for dry samples.