Face stability of shallow tunnels in partially saturated soil: centrifuge testing and numerical analysis

In this paper the face stability of shallow tunnels in partially saturated soil is investigated by means of centrifuge testing and numerical analysis. A loess soil is chosen for this study and its properties are characterised by laboratory testing. Centrifuge model tests are carried out at different soil densities and with different depths of water table. The numerical analyses are performed with an advanced constitutive model for partially saturated soil. The constitutive model is implemented in a finite-element code using the Bishop's effective stress. The model parameters are calibrated based on drained triaxial compression tests on partially saturated soil. The wetting collapse of the tunnel face is simulated by imposing a zero pore pressure condition at the ground surface. The numerical results are compared with the centrifuge tests.