Numerical investigation on the mechanical and stress characteristics of rock containing a spherical defect under uniaxial compression

Spherical defects widely exist in natural rock and severely affect the stability of rock material. Laboratory tests and numerical simulations are performed to reveal the influence of the size and the location of spherical defects on the mechanical properties, stress distribution, and fracture modes of specimens. The experimental results show that the uniaxial compressive strength (UCS) and elastic modulus of the specimen decrease with the increase in defective size. Compared with the complete specimen, the UCS and elastic modulus of specimen D5 are reduced by 48% and 53%, respectively. For specimens with different locations of spherical defect, the closer the defect is to the boundary of the specimen, the lower the UCS of the specimen. The result is P5 < P6 < P9 < P3 < P8 < P7 < P2 < P4 < P1. However, the location of the defect has minimal impact on the elastic modulus of the specimen. The stress distribution around the spherical defect was monitored by measuring balls. Numerical stress distribution results around the defect suggest that stress values near the defect are positively proportional to the defective size, while the stress values close to the model boundary are negatively proportional to the defective size. Simulation results of crack evolution reveal that the larger the defect is or the closer the defect is to the boundary, the earlier the arrival of crack initiation and propagation is. The failure characteristics and macroscopic fracture distribution from the numerical simulation agree with the experimental results. The research findings could supply a certain reference for stability analysis and control of rock material containing similar types of defects.