Developing the Metro 3 corridor could be a challenging task for authorities, as it is the first underground metro project in Mumbai that involves boring 33.5km long twin tunnels.
Unlike underground metro projects in other Indian cities, tunnels in Mumbai have to be carved out of basalt rock.
The task could be even more challenging if there is a mix of soil and rock. According to Mumbai Metro Rail Corporation (MMRC) officials, a tunnel boring machine (TBM) was stuck underground for several months in Chennai, after it encountered a mix of soil and rock.
Keeping this in mind, officials have asked the prospective contractors to bring TBMs with certain specifications. “Our geo-technical study shows there is basalt rock underground. However, there could be soil at certain places, which poses more difficulties for boring. So we have asked contractors to get TBM machines with predefined parameters to avoid any glitches,” said an MMRC official, who requested anonymity.
MMRC is a joint venture of the Mumbai Metropolitan Region Development Authority (MMRDA), the Centre and the state government, for the development of metro projects in Mumbai.
According to officials, the construction of tunnels is to be divided into seven parts. While a single contractor is to be awarded a package for one part only, two packages can be given if the contractor’s credentials are more than double the criteria sought.
The tendering process is underway and actual construction work is expected to start by the middle of next year.
Fourteen consortia have expressed their interest in constructing the 33.5-km long twin tunnels, each 5.2-metre in diameter, and 26 underground stations for the Metro 3 Colaba-Bandra-Seepz corridor.
Contractors will have to bring two to four TBMs for each part.
In a bid to ensure the speedy execution of the tunnelling works, MMRC wants the contractors to use at least one new TBM.
MMRC managing director Sanjay Sethi said, “As per our condition, contractors will have to bring at least one newly-manufactured TBM for each part.”
Most underground stations will be built using the cut-and-cover method, except for the ones at Hutatma Chowk, Kalbadevi and Grant Road, which will be constructed using the New Austrian Tunnelling Method.