Analytical methods in predicting excess pore water pressure in front of slurry shield in saturated sandy ground

Abstract

During mechanized tunnelling with a slurry shield in saturated sand, excess pore water pressures will generate in front of slurry shield. These excess pore water pressures can influence the stability of the tunnel face. The magnitude of the excess pore water pressures thus becomes of importance for the stability of the tunnel face. In this paper, two theories solutions are presented to describe the development and decline of the excess pore water pressures in front of slurry shield in saturated sandy ground. The first theory considers transient flow in a semi-confined aquifer with elastic storage, while the second one assumes different conditions of unconfined steady-state flow governed by the penetration of slurry into the soil in front of the tunnel face. Both methods are tested at different positions around the tunnel, during both drilling and standstill and compared with measurements performed at the Green Hart Tunnel and North/South line in the Netherlands. It is shown that both analytical theories can predict the excess pore water pressures in front of slurry shield. The second one seems more appropriate because it reflects the effect of slurry penetration. Furthermore, the measurements seem to indicate that the influence of elastic storage is not so big as assumed in the first theory.