Even as the city’s development authority has started the tendering process for the Colaba-Bandra-Seepz Metro, the construction work may start only by October 2015, as the city’s first underground Metro will require special tunnel boring machines that will have to be newly manufactured for the project.
The Mumbai Metro Rail Corporation (MMRC) had issued the documents for financial bidding to the nine shortlisted companies last month. The potential bidders have time until February end to submit their tenders.
Sanjay Sethi, managing director , MMRC, said although underground Metro corridors had been constructed in cities such as Delhi and Chennai, constructing such a fully-underground corridor in Mumbai will require different tunnel boring machines as the city’s underground strata is very different.
“Mumbai’s underground strata is made of basalt rock. The complexity levels are slightly more. In Chennai and Delhi, the strata is mostly a combination of soil and rock. We need full rock tunnel boring machines. The companies getting the civil works contracts will take about six to eight months in manufacturing the tunnel boring machines,” Sethi said.
The MMRC has invited tenders for the civil work of the Rs 23,136-crore Metro, which will be 33.5 kilometre long, in six packages. The underground tunnels, which would be at a depth of 15 to 25 metre on an average, will be constructed using tunnel boring machines. These machines are used to excavate tunnels using a circular cross. Although expensive, they limit the disturbance to surrounding areas making them ideal for heavily urbanised settings.
“Every package will require about three tunnel boring machines. We have said that of these at least one should be new. After awarding contracts, the companies may begin some ground work such as mobilising people and machinery, but construction work is likely to start only after the monsoon next year,” Sethi said.
The underground stations will be constructed using other methods such as cut and cover and the new Austrian tunneling method according to site requirements. The Austrian tunneling method enables blasting the underground by drilling a small hole on the surface, keeping it intact, and is useful for underground construction in congested areas.
The MMRC had originally hoped to start construction by May 2014 when it invited pre-qualification bids for the Colaba-Bandra-Seepz Metro in September 2013. However, it was unable to shortlist potential bidders until the middle of this year as there was a delay in reconstituting its board.