Uniaxial strength and failure in sandstone containing a pre-existing 3-D surface flaw

Abstract

A series of uniaxial compression experiments were performed on specimens of sandstone containing a pre-existing 3-D surface flaw in various configurations. The influence of the single flaw geometry on the stress-strain response and failure process was recorded and then analyzed in detail including real-time capture of surface cracking process by photographic monitoring. Uniaxial compressive strength drops of 25.7, 33.2 and 21.6 % were observed due to an increase in the flaw length (2a = 20-50 mm) and flaw depth (d = 4-20 mm) but a decrease in the inclination of the flaw (α = 75 • -15 • ). The generation of three typical surface cracking patterns, namely wing cracks, anti-wing cracks and far-field cracks were identified and these depend on the geometry of the preexisting surface flaw. Wing cracks initiate more readily from longer pre-existing flaws and those of deeper flaw depth or shallower flaw inclination while antiwing cracks develop in the converse situation. Impor-

Simulating damage evolution and fracture propagation in sandstone containing a preexisting 3‐D surface flaw under uniaxial compression

“…In this paper, the impact of varying the flaw angle on the fracture propagation and unconfined compressive strength (UCS) was considered. The work presented in this paper extended this investigation by including the variation of the flaw angle as well as the flaw depth and length and simulated the recent experiments of Lu et al…”

“…We simulated a block‐shaped sandstone specimen with a preexisting flaw undergoing uniaxial compression with dimensions of 20 × 70 × 120 mm 3 to replicate the experimental investigations of Lu et al, see Figure A. In the center of the front x 2 x 3 planar surface of the specimen, there was a single preexisting flaw, see Figure B.…”

“…Rock specimens contain preexisting flaws at a variety of length scales from microscopic cracks to macroscopic fissures, joints, and even continental faults. The deformation, damage evolution, and subsequent failure and crack propagation in rocks are largely dependent on the process of initiation, propagation, and coalescence of new cracks from preexisting flaws . A better understanding of the dynamic mechanisms and process of rock fracturing and the effect of preexisting flaws yield benefits in many areas from rock mechanics to mining engineering and fracture stimulation in unconventional oil and gas reservoirs to earthquake prediction.…”

“…Another experimental study by Yang and Jing was conducted to investigate the deformation, strength, and failure behaviour of precracked specimens with a single fissure under uniaxial compression. Extending earlier experiments on uniaxial compression tests of rocks with single preexisting flaws,() the study by Lu et al examined a series of experiments on sandstone specimens containing a single preexisting three‐dimensional surface flaw. Also, the authors systematically investigated the impact of the flaw geometry on the deformation and strength behaviour varying geometric parameters of the flaw, including flaw length, flaw depth, and flaw orientation.…”

“…Significantly, we ran parameter suites for varying flaw geometry while leaving the parameters relating to the damage evolution and rock heterogeneity unchanged in order to simulate the experiments more realistically and isolate the effect of the changing the flaw geometry alone. In particular, we compared our results with the experiments by Lu et al for sandstone but also considered work from other authors for similar experimental set‐ups. () We applied the elastic damage model based on the unified strength theory and RFPA code, but in contrast to the RFPA code, we used the FEM with tetrahedron elements on unstructured meshes.…”