An experimental study on foam infiltration into saturated sand and its consequence for EPB shield tunneling

Abstract With reference to the Earth Pressure Balance (EPB) shield tunneling, the pressure infiltration of foam into saturated sand has been investigated in a laboratory set-up that could provide a comparable hydraulic gradient as in field conditions. The focus is to investigate the foam infiltration characteristics in comparison with slurry infiltration. Results suggest that a pressure drop can be realized over the foam infiltrated area during the foam spurt period, suggesting that the supporting pressure can be applied to the soils in front of a tunnel face during standstill. Development of pore pressures shows that the foam infiltrated area functions similarly to an internal cake at the tunnel face of a slurry shield. Verification tests indicate that the permeability of the whole system is determined by the foam infiltrated sand instead of the foam itself, different to the situation in a slurry infiltration. In the meanwhile, further infiltration of foam bubbles in the saturated sand was found in the experiment to be the main process after the foam spurt period. General agreement was found when comparing the experimental results with field measurement data from the Botlek Rail Tunnel.