Influence of excess pore pressures on the stability of the tunnel Face
W. Broere
Abstract
In shield tunnelling in loose and water bearing soils, a bentonite slurry is often used to help support the tunnel face. During excavation, the bentonite cake, which is intended to seal the face, is removed by the cutter bits and subsequently slurry will infiltrate the soil. This infiltration causes excess pore pressures in front of the TBM, which lower the stability of the face. The effect has been investigated using a stationary model as well as with a time-dependent groundwater flow model, linked to a limit equilibrium face stability model. This model can be used to predict the minimal required support pressure and also the build-up of excess pore pressures in front of the TBM over time. The calculated excess pore pressures compare well with field observations.