Tunnel face stability analysis based on pressure field surface's normal vector for earth pressure balanced shield

Under extremely unpredictable geological and hydrogeological conditions the tunnel face instability would occur during the earth-pressure-balance (EPB) shield working. It is thus significant to judge the face stability online based on the pressure sensors set inside the shield chamber. In this paper, a new numerical method based on the geometrical characteristics of the pressure field surface in work chamber for analysing the tunnel face stability of the EPB shield, is presented. The normal vector of the pressure field surface is derived by the discrete derivatives calculated from the signals sampled through the pressure sensors, by which real-time analysis can be made on the change situation of active and passive earth pressures for the ground in front of the tunnel face. This mechanism provides the basis for ensuring the tunnelling safety and automatic controlling of the EPB shield tunnel process. Finally, a simulation is given to demonstrate feasibility of the proposed method.