Coulomb stress changes: From earthquakes to underground excavation failures

Evidence from shallow tunnels and mines indicates that, in certain cases, deformation and failure are not confined to the vicinity of the excavation front, as is widely believed. This situation has recently been described as lateral strain propagation from a “source” to remote parts of the excavation through low-strength rocks. A similar situation is observed in deep excavations, mainly expressed by rock bursts and micro-earthquakes. We suggest that (slow) propagation or (seismic) radiation of deformation away from the excavation front can be explained on the basis of the theory of Coulomb failure stress changes, in analogy to faulting in large earthquakes: local increase of stresses due to the excavation or failure in a certain point leads to a slight increase of stresses around this point. If adjacent points are already at a critical level for failure, this slight increase triggers a laterally, domino-style propagating new failure. Yet, in contrast to earthquakes, triggered deformation in mining can, in principle, be predicted and counteracted.