ABSTRACT
Adoption of a tunnel pressure, and the required volume of air to maintain that pressure, is currently based on judgement or oversimplified formulae. The risks associated with leakages of air from tunnels are not addressed by these methods. Such risks include surface settlement, uplift of structures and development of air paths to other structures or excavations. Furthermore, it is considered that standard ground investigations do not provide the parameters necessary for carrying out analysis if a method did exist. A series of experiments has been carried out on a small-scale physical model of a tunnel in sand to demonstrate the mechanisms of air flow through soils, including the behaviour of the ground during a blow-out, the settlement of the surface and the changes in soil condition after a blow-out. The observations are presented and a more rigorous method for the prediction of tunnel pressure, air consumption and the zone influenced by the air flow is discussed.
