Patna Metro Project: First tunnel boring machine ‘Mahavir’ launched, will be used in tunnel digging

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The first of the four Tunnel Boring Machine (TBM) “Mahavir” of the Patna Metro project was launched at the under-construction Moinul Haq station in Patna on Monday. The tunnel will be excavated with this machine weighing about 420 metric tonnes. According to Delhi Metro Rail Corporation (DMRC) officials, this is the second time in the Patna Metro after Delhi, when the TBM was first assembled on the ground and then lowered with the help of a megalift on the cradle. The TBM was lifted along with the cage using four strand jacks with a capacity of 325 MT each. The mega lift will lift the cradle and then slowly lower it to the TBM lowering position (launching shaft). The TBM will then be lowered into the shaft, which is 16 meters below ground level after skidding.

TBM will take two to three weeks to fully connect

According to DMRC, bringing down the TBM is the first step in the tunneling for Patna Metro, which has started at Moinul Haq Stadium. After connecting other part of TBM, work of debris removal etc. will be done. The process of complete linking of TBM takes about two to three weeks. The weight of TBM is equal to the weight of about 60 elephants.

CRCHI designed and manufactured the TBM

According to officials, the soil of Patna situated on the southern bank of river Ganges is alluvial. Its ground water level is also very high. The TBM has been designed and manufactured by CRCHI (China Railway Construction Heavy Industries Corporation Limited) for Patna Metro keeping in view the pressure balance of soft soil and ground.

what is tbm

Earth pressure balance tunnel boring machine consists of a cutter head, front shield, middle shield, tail shield with backup gantry. The length of the main body of the TBM is about 9 metres, while the full length of the earth pressure balance is about 95 metres. Digging diameter is 6650 mm with pre-cast ring lining with outside diameter of 6350 mm and inside diameter of 5800 mm. About 49 cubic meters of land will be mined from each ring. During operation of TBM, a continuous process of mining, grouting, ring building along with ground monitoring information analysis will be completed.

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