New tunneling close to an existing tunnel may damage the existing tunnel lining if no appropriate measures are taken during construction. A series of centrifuge hmnel models with various cover-to-diameter ratios (C/D = 1,2, and 3) both in the plane strain condition and in the 3- dimensional condition were performed in an acceleration of 1OOg to investigate the distributions of earth pressure around tunnels and the bending moment on lining during the tail voids closures caused by nearby new tunneling. The failure mechanism and load mechanism are demonstrated in the paper.
Shield tunneling has become more and more widely used to subway construction in soft ground in order to reduce interference with surface traffic in Taiwan. However, subway authorities have been forced to make use of a limited public area (i.e. beneath existing streets) to build tunnels because of high density of development and the difficulty on land expropriation in crowed cities. A subway line generally consists of twin tunnel drives, the up track and down track tunnel, one of them is driven first and the other follows later. Tunneling in soft ground is usually driven by means of an earth pressure balance shield (EPB). The EPB shield is operated by the following sequence: As the shield advances by applying a pushing force through hydraulic jacks onto assembled segmental lining behind the shield, soils are excavated through slots in a rotating cutting head and deposit into a spoil retaining area. The soils are then removed from the enclosed spoil retaining area by a screw conveyor. The face stability is kept by the balance between the rate of soil removal and the advancing rate of shield, in other words, by reaching a state of equilibrium between the face pressure and the jacking force.