Challenge in Tunnelling for Kolkata East West Metro – Passage of underground twin tunnels in the vicinity of Brabourne Road Flyover

The global trend of development of underground urban infrastructural facilities have come across in India too as majority of MRTS corridor projects involves tunnelling in busy districts of the city. In the context of the city of Kolkata, which is developed over a span of more than 300 years in changing regime with heterogeneous development authorities and policies, planning for an underground metro corridor encompasses diverse administrative & technological challenges. A major challenge of crossing of underground tunnel of East West Metro corridor in close vicinity of pile foundation of an extremely busy flyover viaduct structure is showcased in this paper to demonstrate the successful mitigation of this criticality by adopting systematic analysis & procedures. In this context, the paper covers Geomorphology & Geotechnical investigation & its impact on choice of tunnel boring machine, building condition survey and structural impact assessment and mitigative planning adopted. The theoretical prediction of tunnelling impact is compared with actual settlement and other tunnelling parameters.