Dynamic Modelling of Tunnel Failure

Rupture dynamics along a relatively wide fault zone intersecting an underground tunnel is studied in the framework of recently developed damage-breakage rheological model. The propagating rupture produces rock damage and granulation in the process zone ahead of the rupture front, where intense torsion is simulated. It also produces an out-of-fault damage zone, of which the volume is calculated and compared with analytical predictions using the point source approximation. Interaction between propagating rupture and tunnel significantly enhances stresses around the tunnel leading to its failure with significant implosive component. Tunnel failure may occur with a certain delay after the rupture front passed, depending on the initial tunnel strength. This time delay is defined by the time needed to accumulate damage in the rock mass around the tunnel. In some cases such tunnel failure maybe interpreted as an independent implosive seismic event. Model results provide an insight into the near- and intermediate fields of seismic radiation produced by seismic sources close to and intersecting an underground tunnel. Energy dissipation in the process zone in front of the propagating rupture due to the damage–breakage mechanism significantly affects the S-wave radiation in the direction of the rupture propagation. On top of that the tunnel failure process, especially if it is surrounded by relatively weak and damaged rock, significantly reduces S-wave radiation also in the directions normal to the fault zone.