Interfacial Behaviour in Tunnel Engineering

Abstract

The stress induced in an underground tunnel due to the applied stress of a tunnel boring machine (TBM) is studied to understand the mechanisms which lead to tunnel collapse. An investigation of the classical plane strain gravitational problem in a purely elastic medium shows that any fractures due to gravitational effects alone would occur at the base of the tunnel rather than the apex. Ignoring gravity we then explore an elastic/plastic solution in an idealized soil with no cohesion. To simulate the action of the TBM a point source is imparted on the medium extending in the horizontal direction. This model decouples into an elastostatic problem that predicts a wedge shaped region of plasticity extending from the point source and a hyperbolic flow problem in the plasticized region. Using a similarity solution, it is shown that the behaviour of the medium is very sensitive to the parameters that characterize the soil.