Mechanism of confining stress effects on rock fracture toughness and fracture characteristics

To investigate the effects of confining stress on the fracture behavior of rock masses under deep high-stress environments, this study employed stereolithography 3D printing technology to fabricate rock-like specimens featuring Cracked Chevron Notched Brazilian Disc (CCNBD) geometry. Static fracture tests under varying confining stress were conducted using a custom-designed confining stress loading system. The key findings are as follows: 1) Fracture toughness exhibited a linear increase with confining stress. When the confining stress reached 1.168 MPa, the fracture toughness increased to 2.86 times that of the unconfined specimen. 2) Crack propagation paths were influenced by confining stress. Under zero confinement, cracks propagated straight through the specimen. Increasing confining stress caused significant deflection in the crack propagation path. Concurrently, the fractal dimension of the fracture surface showed a positive correlation with increasing confining stress. 3) Confinement constrained lateral deformation and altered fracture characteristics. The presence of confining stress constrained lateral deformation under load. As confining stress increased, the resulting fracture surfaces became progressively rougher, and the corresponding energy release rate of the specimens demonstrated an increasing trend. These research outcomes hold significant theoretical and practical importance for enriching the understanding of fracture mechanisms in deep rock masses subjected to external loads.