Fracture evolution characteristics of sandstone containing double fissures and a single circular hole under uniaxial compression

The uniaxial compression experiments on the sandstone samples containing double fissures and a single circular hole were carried out by using electro-hydraulic servo universal testing machine to investigate the effect of rock bridge angle β and fissure angle α on mechanical properties and evolution characteristics of cracks. The results show that the peak strength, peak strain and elastic modulus of defected specimens decrease comparing with those for intact sample, and show a decreased trend firstly and then increase with β changing from 0° to 90°. The peak strength and elastic modulus achieve the minimum value as the rock bridge angle is 60°, while the peak strain reaches the minimum value with the rock bridge angle of 45°. The crack initiation of tested rock samples occurs firstly in stress concentration areas at tips of prefabricated fissures under uniaxial compression, and then propagates constantly and coalescences with the prefabricated hole. Some secondary cracks initiate and propagate as well until buckling failure happens. The rock bridge angle has a great influence on crack initiation, coalescence, final failure mode, crack initiation stress and transfixion stress. The peak strength varies significantly, while the elastic modulus and peak strain change slightly, and the failure modes are also different due to the influence of fissure angle.