Analytical solutions for excess pore water pressures generated by TBM tunnelling in a semi-confined aquifer

Tunnel-boring machine (TBM) tunnelling through an aquifer will generate excess pore water pressures in the soil around the tunnel face. Accurately predicting the magnitude of the excess pore water pressures is significant because it directly determines the effective face support pressure. In this study, an analytical solution for transient cylindrical flow caused by TBM tunnelling considering the elastic storage of the aquifer is developed. Furthermore, a quasi-static solution to couple the effect of slurry infiltration with the elastic storage is presented. It is shown that the pore water pressures derived from the analytical solution match quite well with the measurements obtained in proximity to as well as far away from the TBM. The coupled quasi-static solution also agrees with the measurements for the places close to the tunnel face, but underestimates the observations far away from the tunnel face. The results also show that a larger infiltration distance leads to a slower dissipation of excess pore water pressures, which does not make a difference during excavation (when excavation velocity is faster than the pore fluid velocity).