Repurposing of reception shaft, Mumbai Coastal Road Project – Case study

As part of Mumbai Coastal Road Project - the connection between Nariman Point and Bandra Worli, a total length of 10.58 km - Package IV (MCRP4) includes submarine twin tube tunnels. Current Package’s total length is 4,480 m, of which 2,008 m are excavated by means of one slurry shield and supported/lined by precast segments. Each tube will accommodate a three-lane carriageway, for an internal diameter of 11 m and an excavation diameter 12.19 m. To enable the launching and receiving of the TBM, two shafts were constructed at North end and South end of the package. The reception shaft is 42m long and 30m wide with a depth of 26m below the ground formation level at +3.0 msl. The intention was to disassemble the TBM after the first drive to reassemble and relaunch it from the original shaft – the “launching shaft”. However, due to logistical constraints, given the project location in a dense urban setting, and due to time delays, because of stoppage of works during Covid lockdown, the Contractor of the project decided to relaunch the TBM from the reception shaft itself by rotating the TBM and save approx. 60-75 days. Due to this dynamic need of the project, reception shaft was repurposed for relaunching with additional ancillary structures (like Heavy weight modular gantry crane foundations, TBM reaction frame, Slurry treatment plant on surface etc.,) in and around the shaft which weren’t foreseen during the excavation of shaft. This paper discusses design aspects with special focus on challenges which were needed for this repurposing of shaft.