The behaviour of tunnels at great depth under large static and dynamic pressures

Abstract

The main objective of the paper is to illustrate the range of conditions that can result from the presence of tunnels in, and the activity of driving tunnels through, competent hard rock under conditions of very high rock pressure. After briefly examining differences and similarities between the support design philosophies applied in these circumstances and those prevailing in most civil engineering tunnels, the paper goes on to suggest concepts that might prove useful in civil works under great depth of cover. The conviction is clearly explained and illustrated that the rock-anchoring tendons used under these conditions must possess sufficient yieldability to avoid tensile fracture under conditions of large and violent rock deformation. The containment support must also be appropriately compliant and must be properly coupled to the retaining rock tendons. Environmental impact statement: The environment in which tunnelling is undertaken through hard rock at great depth is harsh and sometimes dangerous. It has the potential to affect the health and safety of the workforce who constructed the tunnel and continue to use it after completion. There is no possibility that the underground situation can have any effect on the surface environment or any direct impact on the health and safety of its community. Insofar as they would have the objective of controlling the fracturing and potential disruption of the surrounding rock, the technologies implied or explicity advocated in the paper would improve the underground environment and substantially benefit the safety of the workforce.