Evaluation of Soil Response to EPB Shield Tunneling

Earth pressure balance (EPB) shields can be operated so that soil is forced away from its face; this heaving process may cause smaller surface settlements than would result from tunneling, without inducing any initial heave. Field observations made at the first EPB project in the U.S. and finite element analyses results of that project are compared to gain a better understanding of ground behavior around EPB shields. Field observations indicated that the ground response was both three-dimensional and time-dependent. To keep computational costs within reason, the EPB tunneling process was simulated in a finite element analysis using two, two-dimensional models. Besides approximating EPB shield tunneling effects, the finite element simulations explicity account for pore pressure mobilization and dissipation in time. Results of parametric studies indicate that intentionally induced heave decreases the net movement into the tail void gap behind the shield at the expense of increasing consolidation settlements at the surface.