Visualizing the effect of excavation rate on rock deformation and fracturing of tunnels using a transparent soft rock surrogate

One of the most important problems during tunneling in soft rock is deformation and fracturing of the rock during tunneling. The problem was successfully explored by using a transparent rock surrogate to simulate the behavior of soft rock, which permitted visualizing conditions within the rock. Synthetic soft rock was made using consolidated fused quartz saturated with a blend of two mineral oils that have the same refractive index as the quartz. The tunnel was simulated using a smooth aluminum tube and two tunneling methods representing machining and blasting were considered. Two observation planes made of seeding particles were pre-placed within the model and used to track soil movements and crack propagation. Images of both planes were captured simultaneously using two orthogonal cameras. Rock deformations were concentrated in the vicinity of the tunnel face, and deformation rates behind the tunnel face were significantly greater than those ahead of the face. However, deformation rates and patterns varied considerably depending on the excavation method/rate. Fracturing mechanisms exhibited similar differences, for machining deformations occurred higher above the crown and propagated toward the tunnel face. Conversely for blasting deformations sprang from the crown upwards. These observations can assist with numerical simulations and in planning tunnel support systems.