PATNA (Metro Rail News): The First of four Tunnel Boring Machines (TBM) of Patna Metro Project, nicknamed “Mahavir”, was lowered on Monday in Patna at Moin-Ul-Haq Station with a drive length of 1494m towards Patna University station. TBM Mahavir bearing serial number DZ1090 weighs around approx. 420 Metric Ton. The underground tunnelling work in Patna Metro Project will be done with the TBM machine. The lowering of the TBM is the first step of tunnelling for Patna Metro, which has commenced at Moin-Ul-Haq Stadium. Other parts of the TBM, which will be assisting in muck disposable, feeding of the tunnel segments shall be done subsequently; that is, after lowering the main part of the TBM, the process of complete assembling of the TBM takes about 2 to 3 weeks’ time. Once TBM is assembled in totality, the drive will start.
The TBM, if compared to that of the weight of an African Elephant; one elephant’s weight is approx. 7 Metric Ton, so the weight of TBM equals to that of 60 elephants’ weight.
This is the second in DMRC after Delhi that TBM was assembled first at the ground, and the same is lowered with the help of Mega Lifts on the cradle. TBM assembly was lifted with the cradle using strand jacks with a capacity of 325 Metric Ton each. Four-strand jacks are being used to lower the TBM at MUH. The Mega lift will lift the cradle and then push it up to TBM lowering position (Launching Shaft). Then TBM will be lowered into the shaft, which is approx. 16m below the ground level after skidding.
Patna is located on the south bank of the Ganges River in eastern India, which has alluvial soil. The groundwater level is also very high. As per the soil strata, soft soil Earth Pressure Balance (EPB) TBMs have been designed and manufactured for Patna Metro by CRCHI (China Railway Construction Heavy Industry Corporation Ltd.) The TBM shall first be launched from Moin Ul Haq Station towards Patna University station.
What is TBM
The Earth Pressure Balance (EPB) Tunnel Boring Machine (TBM) comprises a cutter head, front shield, middle shield, and tail shield, along with the backup gantries. The main body length of the TBM is approx. 9m with EPB full length of 95m approx. The excavation diameter is 6650mm, with the precast ring lining with an outer diameter of 6350mm and inner diameter of 5800mm. Approximately 49cum of the earth will be mined for every ring installed. Grouting behind the segmental lining shall be carried to ensure that full and immediate support is given to the rings as they emerge from the rear of the TBM. Thus, a continuous process of mining, grouting, and ring building, with ground monitoring information analysis, will be applied during the operation of the TBM.
