Coupled fluid-mechanical analysis of DOT shield tunnel construction beneath adjacent existing underpass

Based on the construction of Shanghai Metro Line No. 10, the characteristic, magnitude and range of ground settlement and excess pore water pressure induced by double-o-tube (DOT) shield construction in free field were analyzed by means of tridimensional finite difference numerical simulation. Analysis results were compared with site monitoring results to get the parameters of simulation construction which could reflect actual construction level. The parameters of simulation construction were applied to the analysis of DOT shield driving beneath existing underpass to forecast the influence of shield tunnelling on the bottom slab of the underpass. The studies indicate that the positive excess pore pressure is hard to dissipate to external environment and the negative excess pore pressure is hard to get water replenishment from external environment induced by shield construction beneath adjacent existing underpass; in front of DOT shield's excavating face, the underpass's bottom slab is bearing extrusion force mainly composed of excess pore water pressure; the excess pore water pressure acting on the bottom slab is well distributed in transverse direction, however the soil grain's extrusion force mainly distribute around the centerline of bottom slab; the rigid displacement of the underpass is the main reason of bottom slab's settlement; and the structural deformation of bottom slab just induces less settlement; the interspaces of shield tail is the main reason for the deformation of soil mass and adjacent structures owing to shield tunnel construction.