The ball was set rolling for Metro Phase III with the lowering of the 80-metrelong tunnel boring machine at the Chelmsford Club on Tuesday . And DMRC is giving shape to another engineering marvel as it readies its machine to tunnel through the 9.5km stretch from Central Secretariat to Mandi House - a corridor that will take off the passenger load from Rajiv Chowk station which sees a footfall of at least 4 lakh a day. "Designing of the pit took six to eight months. Once that is through, the boring machine "Designing of the pit took six to eight months. Once that is through, the boring machine will be assembled in the shaft for excavation till Janpath" will be assembled in the shaft for excavation till Janpath," said Kumar Keshav, director, projects and planning, DMRC. The tunneling machine was assembled and meticulously checked in Chennai and then dismantled. It was then brought to Delhi where it will be reassembled at Chelmsford Club. The technology helps to balance displaced soft soil by creating equivalent air pressure. First the cutter head will be fixed over the tunnel eye to cut through the soil with the muck trails dispersing soil. This will then be picked up by gantries (cranes) and dumped into trucks. The reassembling of the 450 metric tonne machine will take three weeks and will be operational by February 18. The machine was bought from a German company Herrenknecht . It will excavate the twin tunnels from Central Secretariat to Janpath and Janpath to Mandi House. The machine will cut by Shangri La to reach Janpath in four months. "Two tunnels will be excavated from Central Secretariat to Janpath. Then the machine will be taken out since there is a station in between and then lowered again at Mandi House to resurface at Janpath," said Kumar Keshav. The depth of the tunnel at Janpath is 20 metre below the ground. Beyond Janpath, the depth increases to 25 metre below the ground. The Central Secretariat-Mandi House corridor plans to use the mass spring system technology to avoid vibrations being transferred to the tunneling surface. This comes after complaints from residents near the airport link that passing trains shook their homes. This phase will use a record 22 TBMs. Phase I made use of three TBMs and Phase II had more than 14. The Central Secretariat-Mandi House corridor, will have two stations that are slated to be operational by May 2014. Once the corridor becomes functional, Mandi House will serve as an interchange station allowing passengers from Noida and Okhla to board trains at Central Secretariat. DMRC chief Mangu Singh said at a place where there are so many machines in operation there is always a possibility of untoward incidents. "However , our work is to educate and train people who work at the construction sites. This time we have ensured that no person will work on site who has not received previous training ," he said.
How a tunnel boring machine works
1 Cutting wheel scrapes away layer of the earth
2 Drilling fluid continually removes earth
3 Tunnel wall is constructed within shield
4 Machine uses thrust cylinders to advance by pushing against concrete segments
An underground corridor of 9.3km comprising seven stations & a twin tube tunnel with an internal diameter of 5.8km (approx)
STATIONS: Central Sec, Janpath, Mandi House, ITO, Delhi Gate, Jama Masjid, Lal Quila & Kashmere Gate
INTERCHANGE STATIONS: Central Sec, Mandi House & Kashmere Gate
To pass through the vicinity of protected monuments like Jantar Mantar, Agrasen ki Baoli, Khooni Darwaza, Delhi Gate, Sunehri Masjid, Lal Quila & Kashmere Gate
EXPECTED RIDERSHIP IN 2016 1,34,879
Tunnel Rings
Tunnel rings are made of reinforced concrete. The individual segments, with carefully controlled material properties, are fully hardened, transported to the site in the shield and assembled into complete rings under the shelter of the tail skin. Machine advance is only possible if grouting mortar is perfectly filled in the gaps
Earth pressure balancing machine specifically being used, keeping in mind Delhi's soil condition. To balance the displaced soft soil, the machine will create an equivalent air pressure
Phase III will use a record of 22 TBMs. Phase I made use of three TBMs and Phase II had more than 14
