Effect of large excavation on deformation of adjacent MRT tunnels

A large excavation of approximately 140 m wide, 200 m long and 15 m deep wa s made close to two Mass Rapid Transit (MRT) tunnels of 6 m diameter with i nvert depth of 15-27 m. In view of the scale and distance of excavation, si gnificant effects on the MRT tunnels were expected. The paper presents the monitoring of the tunnel deformations during the excavation. A sophisticate d monitoring system using a motorised total station was installed in the MR T tunnels to monitor their displacements and to ensure that the stringent r equirements for safeguarding the tunnels were not violated during any part of the excavation works. The paper also presents the modelling of the excav ation using a finite element program. The results obtained were reasonably close to the monitoring results. It was found that the stiffness of the tun nel lining has significant influence on the displacement and distortion of tunnels caused by an adjacent excavation. A stiffer lining undergoes less d isplacement and distortion but is likely to experience significantly greate r bending moments. (C) 2001 Elsevier Science Ltd. All rights reserved.