Dynamic fracture behaviors and fragment characteristics of pre-compressed flawed sandstones

Abstract

Because of tectonic stress and dynamic disturbance, underground rock masses containing pre-existing flaws usually undergo complex loading conditions combining static pre-stress (SPS) and external dynamic loads. Comprehending the mechanical behaviors of flawed rocks under coupled static-dynamic loads is helpful to assess the stability of underground engineering. This study presented a series of coupled static-dynamic compression experiments on sandstone containing two non-coplanar flaws. The results indicated that the dynamic strength of the flawed sandstone increased first and then decreased with the increase in the SPS for a given dynamic strain rate (DSR), and the coupled strength of the flawed sandstone was less dependent on the DSR under the SPS of 60% of the uniaxial compressive strength than the other SPS values. Low SPS and DSR generally induced an asymmetrically X-shaped shear failure mode of the specimen, while this failure pattern could be observed in the tests with high SPS and DSR. Moreover, both a greater SPS and a higher DSR could lead to smaller location parameter values in the generalized extreme value fitting and a higher fractal dimension of the rock fragments, resulting in a more severe crushing destruction of the flawed sandstone. In addition, this study demonstrates that both the fracture process zones and the higher-order stress terms in the Williams series expansion, which are often neglected in traditional related studies, cannot be thoughtlessly ignored when analyzing the crack initiation, propagation, and coalescence of flawed rocks.