Numerical investigation on impact of excavations in influence zone of existing MRT tunnels

Abstract

ABSTRACT Due to a high demand of space utilisation in metropolitan area, the existing tunnels, which are normally used for underground transportation and service utilities, can be suffered from the impacts caused by the adjacent constructions. In general, the protection zone of a tunnel is developed based on the assumption of shear plane of soil, rather than the soil–structure interaction. The assessment of the impacts of new construction nearby the existing tunnel is thus essential for improving the protection zone. 3D finite-element analyses are conducted for the case of the mass rapid transit (MRT) tunnels in soft ground. The impacts on the MRT tunnels from two possible underground construction cases (i.e. open cut and pipe jacking) are investigated in terms of tunnel deformations and changes in tunnel lining moment. The advantages of using 3D analysis are to model the realistic soil–structure interactions and to observe the multidirectional impacts on MRT tunnels. The results show that the bending moments increased by both open cut and pipe jacking construction activities are relatively small. For the tunnel deformations, most cases are sufficiently secure, but only in some cases, the deformations of tunnel lining almost reach the limit of 6 mm. However, it is highly recommended that they are still required to numerically examine in case by case