Study on the influence of far-field cracks on tunnel stability and fracture properties under compression loads

Numerous cracks in the surrounding rock mass will be formed when a tunnel suffers from explosive loads, resulting in a fractured surrounding rock and the stability of the tunnel will be reduced. To investigate the evolution of the stability of the fractured surrounding rock, the fracture modes of a tunnel with a far-field crack located in the vault under compressive load are studied. Numerical simulation and experiment are implemented, the stress intensity factor of the far-field crack and stress clouds of the fractured tunnel are calculated by using ABAQUS code, green sandstone is chosen for experiments to make specimens, digital image correlation technology was employed to study the real-time strain field. The test results indicate that the far-field crack located in the vault reduces the stability of the fractured surrounding rock. The failure of the tunnel is more likely to occur from the side near the crack tip. When the crack inclination angle θ = 0°, the stability of the tunnel is the best and the stability is the worst at θ = 30°. However, when the crack inclination angle θ = 45°, the tunnel's strength significantly increases. In addition, when the crack inclination angle θ ranges from 0° to 75°, there is a strong tendency for the crack to connect with the surrounding rock but at θ = 90°, reconnecting becomes challenging. Furthermore, five failure modes are classified according to the destruction mechanism and position, among which tension cracks comprise the largest proportion (48.4 %).