Face stability of slurry shield-driven tunnel in an aquifer

In this article the face stability of slurry shield-driven tunnel in an aquifer is investigated. The influences of slurry infiltration at the face and soil layering are taken into account. The results show that due to the infiltration an additional margin for the support pressure is required. At larger slurry infiltration distance or larger cover depth to tunnel diameter ratio (C/D), a higher margin is required. It also appears that soil layering affects the hydraulic gradient that stabilise the face of cohesionless soil. TBM excavation in a semi-confined aquifer (compared to an unconfined aquifer) leads to higher excess pore water pressures in the soil around the TBM and a reduced infiltration of slurry into the soil in front of the TBM. The excess pore water pressures in a semi-confined aquifer are present over a larger area than in an unconfined aquifer, increasing the risk of a blow-out during excavation.