ABSTRACT
Mumbai Metro Line – 3 (MML-3) is a 33.5 kilometer long underground corridor presently under construction. The project scope includes twin tube tunneling by Tunnel Boring Machines (TBM), 19 Cut and Cover Stations, 7 Stations, cross passages and cross overs using New Austrian Tunnelling Method. The city of Mumbai was formed by merging of seven islands through multiple land reclamations. Mumbai geology consists of soft ground followed by volcanic rocks such as Basalt, Breccia, Tuff and intertrappean sedimentary rocks such as Shale. The ground water table is shallow. The paper describes challenges including tunneling under mixed ground conditions, water drawdown and associated settlements. The observed settlements during TBM tunneling are analyzed to estimate a range of volume loss and trough width parameters for Mumbai geology. The paper illustrates the benefits of instrumentation and monitoring scheme to understand the ground and groundwater response in urban tunneling.
