The Bhoomipujan for the 32.5km-long Colaba-Bandra-SEEPZ underground metro rail project was held on Tuesday at Marol. The Rs23,136-crore project will connect Cuffe Parade, Nariman Point, Fort, Girgaum, Mahalaxmi, Worli, Bandra-Kurla Complex, Airport and SEEPZ. Construction work on the car depot planned at Aarey Colony will commence in September.
Union minister of urban development M Venkiah Naidu and chief minister Prithviraj Chavan were present for the function.
Q All stations will have platform screen doors
The 27 stations of the underground metro rail will have platform screen doors. The platform screen doors act as barriers that don't allow any commuters to fall on the tracks. These doors open only when doors of the metro rail and platform are parallel
to each other.
At least five construction methodology has been finalised for the project.
Q Cut and cover method for underground stations
In this method of construction a trench is excavated and roofed over. There are two basic forms of this method. They are the Bottom-up and Top-down methods. In the first, a trench is excavated, with ground support as necessary, and the opening is constructed within. The trench is then backfilled with precautions regarding balancing compaction of the backfill material, and the surface is reinstated. The second method is the most suitable method for underground stations. But the road will be shut for a period of six months to a year.
Q New Austrian Tunnelling Method (NATM)
The plan is to construct 11 stations using NATM. In this method, the surrounding rock or soil formation of a tunnel are integrated into an overall ring-like support structure. The connection to the surface for entry and exit is generally provided by means of two shafts located at both ends of a station.
Q Temporary traffic decking arrangements
This method will be effective to keep the city moving. In this, the king post will be useful. King post is a vertical structural support member to prevent the sagging of cross-beams. The prime objective is to support the traffic deck. In this temporary arrangement, construction of underground station will continue while the traffic is moving above.
Q Underground subways by Pipe Jacking Method
Aimed at not infringing with building foundations, construction of subways will be challenging. Several longitudinal support members (pipes) are inserted side by side through the ground beneath the existing street. Number of longitudinal support members is also inserted along the height of the wall of the subway to be formed.
Q Underground tunnel between stations by Tunnel Boring Machine
TBM, a highly-mechanised device, is an alternative to drilling and blasting. It's advantage is to limit disturbance to the surrounding ground, and reduces construction cost in urban areas. TBM is much more efficient and it reduces total project time affected by tunnelling.
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