Excess pore pressures near a slurry tunnel boring machine

Modelling and measurements

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Abstract

In this thesis an investigation is performed into the rise of excess pore pressures in front of a slurry tunnel boring machine (TBM) during boring. Accurate prediction of excess pore pressures is particularly important when boring close to foundation piles or when boring with a small overburden. The existence of this phenomenon has been known for approximately two decades and several groundwater flow models have been derived since. Laboratory experiments are conducted to investigate the applicability of laboratory results as input for the existing groundwater flow models. Furthermore, a new relation to calculate excess pore pressures at the tunnel face is derived. The discharge from the tunnel face during boring is investigated as well. Calculations considering the cutter wheel configuration are compared with calculations considering a mean slurry infiltration time and show similar results. This research originated from the North/South metro line in Amsterdam, at which excess pore pressures presented a real challenge in crossing a historical bridge. Data from the Green Heart Tunnel is also used in this research to serve as validation.