Study on the influence of fracture distribution on mechanical properties of limestone

In order to study the dependence of the mechanical properties of fractured hard rocks，including their strength，deformability，failure mode，characteristic of energy dissipation and bursting liability，on fracture distribution and volumetric or areal damage variable，uniaxial compression tests were carried out on limestone specimens with a single fracture，three coplanar and non-coplanar fractures at different inclination angles. The results show that：(1) the elastic deformation is mainly affected by the volumetric damage variable，while the strength is mainly affected by the areal damage variable. For the specimens with a single fracture，the unified Young′s modulus and peak strength increase monotonically with the fracture inclination angle，and the relation between the unified Young′s modulus or peak strength and the component of Oda′s second-order volumetric damage tensor or areal damage vector along the loading direction，can be well fitted with an inverse proportional power function. For the specimens with three coplanar or non-coplanar fractures，both the curves of the unified Young′s modulus and peak strength with the fracture inclination angle are W and V shapes respectively，and prediction for their upper limit and average can be given by the above relations with the component of volumetric and areal damage tensors obtained from the specimens with a single fracture respectively. (2) In general，the fractured limestone specimen may undergone three damage evolution stages，i.e.，initiation and propagation of cracks，formation of macroscopic failure surface(zone) and residual deformation. There are three basic failure modes：split，stepped and blocky failure. (3) Some of the limestone specimens show certain degree ductile characteristics due to the existence of the fractures，namely，their stress-strain curves change from single peak to multi-peaks. For the specimens with single peak stress-strain curve(type I)，the elastic energy accumulated before the peak stress is rapidly transformed into dissipated energy. For the specimens with multi-peaks stress-strain curves(type II and III，multi-peaks during softening and hardening stages，respectively)，the elastic energy accumulated before each peak stress is released and transformed into dissipated energy step by step. Both the unified total strain energy and energy storage limit of the specimen may increase linearly with the unified peak strength，and therefore is inversely proportional to the component of the two damage tensors. and (4) Both the intact and fractured limestone specimens at failure appeared different degrees of bursting phenomena such as particle ejection and making sound. Compared with the elastic strain energy index and bursting energy index，the comprehensive index of elastic strain and bursting energy(the ratio of the elastic strain energy before the peak strength to the total strain energy)，can more reasonably represent the bursting liability of the fractured specimens with multi-peaks stress-strain curve，and coincide very well with the degrees of bursting intensity observed in the test. © 2024 Academia Sinica. All rights reserved.