Face Stability Calculation for a Slurry Shield in Heterogeneous Soft Soils

The minimal support pressure needed at the tunnel face can be calculated using a wedge stability analysis. Current methods have been presented only for a homogeneous soil at the tunnel face. This Paper investigates the influence of heterogenity of the soil on the angle of slip and the minimal support pressure. It is found that the influence of horizontal layer boundaries is si gnificant, especially at the top of the tunnel face. In case of a soft layer over a relatively stiff layer the minimal support pressure is greater than would be calculated by interpolation of the support pressures calculated for th e separate layers.