Abstract: It is not unusual in the construction of an urban rail transit tunnel underneath the existing structures. However, it is rare for a shielded tunnel that is over crossing the existing operating metro tunnel at a close distance. The challenge in the construction was the safety as well as the stability of both new shielded tunnel and the exiting operating metro tunnel. This paper presents a case history of constructing the shielded tunnel zone in Qianwan Station of No.5 Line. The new shielded tunnel would over cross the existing operating No. 11 tunnel between Nanshan and Qianwan stations at a very close distance. The measures to ensure the construction safety and stability were used. These measures included soil improvement, excavation parameter control of the shielded tunnel excavation, automatic and live construction instrumentation monitoring as well as emergency response backups.

Key words: Shielded Tunnel Excavation, Close Distance, Over Crossing, Construction Measures, Construction Controls