Time-dependant infiltration and groundwater flow in a face stability analysis

ABSTRACT: In slurry or EPB shields a bentonite slurry or a foam may be injected by the TBM into the soil. These injections will displace part of the pore water before the TBM and, especially in fine sands, will cause excess pore pressures in front of the TBM, which lower the effective stresses in the soil and thereby the stability of the tunnel face. These excess pore pressures increase during boring and dissipate during stand-stills. Using a time-dependant groundwater flow model this behaviour has been included in a limit equilibrium model, in order to predict the pore pressures measured in front of the TBM. The results have been compared to field measurements.