Experimental Investigation on the Crack Propagation and Coalescence in Rock-Like Specimens with Pre-existing Cracks Under Compressive Loading

Abstract

The mechanical behavior of a rock mass is ruled by its embedded discontinuities such as cracks and joints. Uniaxial compression experiments were carried out on rock-like materials with man-made flaws to study the effects of flaw parameters on the mechanical behavior of rock samples under uniaxial compression. Crack initiation, propagation and coalescence near the pre-existing cracks were investigated by rock-like cylinder shaped specimens with different geometries. The samples were prepared by increasing the angle of the flaws by 15°, and the number of pre-existing flaws. The flaws were made by pulling out a metal shim located in the sample before a curing process. Based on complete axial stress–strain curves of the loading process using a servo-controlled testing system, the effect of flaw geometry and number of flaws on the strength and deformation behavior of specimens were fully analyzed. Also, crack propagation and coalescence mechanisms, leading to progressive failure processes in rock masses under compressive loading were carefully observed with a high speed recording digital camera. In all samples, it was observed that wing cracks produced at the first stage of loading and propagate in the direction of uniaxial compressive loading. Moreover, it is shown that the uniaxial compressive strength, elastic modulus and peak axial strain of specimens with pre-existing flaws are lower than those of the specimens without pre-existing flaws. The mechanism of crack initiation, propagation and coalescence is described in the present study and the outcomes are summarized according to various parameters.