Tunnel Face Stability in the Soil Medium Under Collapse and Blowup Conditions

Earth Pressure Balance Tunnel Boring Machines (EPB TBM) are widely used for tunnel excavation in soft cohesive soil medium. The overall safety of the tunneling operations largely depends on the stability of the excavated face. EPB shield provides the required support pressure to the excavated face. The face will collapse if the applied pressure is less than the minimum required, and the ground in front of the TBM will blow up if the support pressure is too high. As a result, correct assessment of face pressure is extremely important for face stability. A 3D wedge-prism model has been considered for the face pressure calculation under the limit equilibrium method (LEM). A range of face pressure has been calculated considering the collapse of the tunnel face and blowup of the ground. Face pressure calculated by the present method is in close agreement with other researchers. A detailed parametric study has been carried out to explore the impacts of the soil property on the face pressure.