With 17 TBMs of different types and open-cut and NATM for 26 underground stations and associated structures, construction of the 33.5km underground alignment of the Mumbai Metro Line 3 had reached more than 80% by early March 2020. Started in early 2017, S K Gupta, Director (Projects) for the client MMRC, Mumbai Metro Rail Corporation, reported that “all the TBMs have performed well” and that the station and rail tunnel works “are on track to complete all excavations by June 2020”.
The geology is largely hard basalt and softer tuff and breccia geology with hard basalt rock at up to 125MPa in compressive strength to the south and softer breccia and tuff to the north. For the most part the hard rock excavations in rock Classes I and II are dry with groundwater ingress experienced in the fractured and jointed rock of Classes III, IV and V. Groundwater ingress, some at high volume and under hydrostatic pressures of up to 5 bar, is also experienced in mixed face conditions and through upper sedimentary overburden and in softer tuff and breccia deposits.