Dynamic mechanical responses and failure characteristics of fractured rocks with hydrostatic confining pressures: An experimental study

Abstract

A precise understanding of the dynamic mechanical responses and failure characteristics of fractured rock with hydrostatic confinements is of paramount importance for the safety of deep underground engineering construction. In the present investigation, a modified split Hopkinson pressure bar (SHPB) apparatus was used to carry out the tri-axial dynamic tests on sandstone specimens with multiple parallel flaws under different strain rates in a range of 100–200 s−1 and four hydrostatic confining pressures varying from 5.7 to 22.7 MPa. The tested results indicate that the dynamic strength, elastic modulus and peak strain are all positively correlated with hydrostatic confining pressure. As the flaw intensity increases, both the dynamic strength and elastic modulus commonly decrease, and the dynamic peak strain decreases first and then slightly increases. Meanwhile, the energy utilization efficiency slightly declines with rising hydrostatic confining pressure, and features positive correlation to the flaw intensity but is not sensitive to the strain rate. The flaw intensity and strain rate both promote the energy dissipation density of the fractured rocks. By the post-mortem examination, ten crack categories are classified for fractured rock specimens subjected to dynamic loading with hydrostatic confinement, and the coalescence of such cracks causes different final failure patterns. Generally, with increasing flaw intensity, the failure pattern of fractured rock changes from shear dominant to shear-tensile mixed failure. Under higher hydrostatic confining pressure, the fractured rock usually exhibits conjugated X-shape failure patterns which are quite different from the specimens with lower confining pressure.