Sumit Kumar, Patna. The first Tunnel Boring Machine (TBM) “Mahavir”, which was launched 16 feet below ground for Patna Metro underground excavation from Moinul Haque Stadium to Patna University, has covered a distance of 85 meters. With this, the initial drive for the construction work of the underground metro station of the stadium has been completed. TBM has started main drive journey from Friday. According to metro officials, now the digging of the tunnel will be automatic, due to which the time will be reduced. TBM may take time till November-December to break through the remaining distance till University. This distance is about 1.3 km.
Construction of underground metro line in three phases
DMRC official told that the construction of underground metro line by tunnel boring machine is mainly divided into three phases. In this, the first stage is the initial (primary) drive, in which the TBM starts digging the tunnel from the launching shaft. In this stage, the initial ring segments are fixed manually, due to which the thrust jacks fitted in the machine propel the TBM forward with the help of these temporary ring segments. After this the TBM reaches the main drive, in which the TBM constructs the tunnel by installing permanent ring segments along with the excavation.
The cutting head fitted in the front shield will cut the soil
According to the officials, the tunnel boring machine is divided into different parts. The most advanced part of TBM is the cutting head in the front shield, with the help of which TBM digs the tunnel while cutting the soil. It will be automatically used in the main drive. There is also a system for sprinkling a special type of chemical in the cutting head, which is sprayed on the soil through a nozzle mounted on the cutting head. Due to this chemical, the soil does not stick to the cutter head and easily moves to the rear of the machine with the help of the conveyor belt fitted in the machine. From here the soil is brought out of the tunnel through a trolley and sent to the dumping area.
Excavation to install Di-wall cage at Rajendra Nagar Metro Station begins
After Moinulhaq Stadium and Akashvani underground metro station, excavation has started for the construction of Rajendra Nagar underground station to put “Di-wall cage”. This digging is being done in front of Rajendra Nagar Terminal. According to DMRC, the “Di-wall cage” is made of iron bars and strong concrete, which is inserted deep into the ground. It protects the surrounding ground surface from collapse during wall tunneling, underground excavation, slab construction or track work. Before Rajendra Nagar, near Moinul Haq Stadium, the di-wall was inserted in an 82 feet deep pit while near Akashwani (Fraser Road) it was about 25 to 30 meters deep and about 1.5 meters wide.
First U-Garder launched for ISBT elevated metro station construction
The elevated stations of Patna Metro are starting to take shape. On Friday, the first U-Garder was launched for the construction of ISBT metro station on Priority Corridor (Malahi Pakdi to ISBT). It is near to New Patliputra Bus Terminal. DMRC officials said that U-girders are placed on the pier caps placed on the pillars. The station is built on these U-girders only.
Two metro lines will be ready for 18 km long underground section
In Corridor Two of Patna Metro, two metro lines will be ready for an 18 km long underground section on the Patliputra ISBT station to Patna Junction route. For this, TBM (Tunnel Boring Machine) will excavate a total of 36 km from Patna Junction to Malahi Pakdi before adding cutter cover. Rest of the work from Malahi Pakdi to Patliputra bus stand will be elevated. The tunnel boring machine that came out of Moinulhaq Stadium will reach the University after covering a distance of one km and 400 meters. The second TBM running at an interval of one month will also reach the other end.
TBM will reach Gandhi Maidan after re-launching from University
According to DMRC officials, when both the TBMs leave the university, they will be launched again from the other end to Gandhi Maidan. This TBM will not be taken out in PMCH. Both the TBMs will be taken out to Gandhi Maidan after passing through the drag. Then at the other end of this station (TBM) will start. In this way both TBMs will complete the work. Two more TBMs are in this package. One will start from Gandhi Maidan and end before Patna Junction. After this, work will start at the other end of Moinul Haq station and before Malahi Pakdi, the cutter will come out in the cover tunnel.
Patna Metro work will be completed in four to five years
According to the Director (Works) of Patna Metro, the tunnel work will be completed in four years and the station work in five years. It also takes a long time to prepare and integrate air conditioning, signalling, track, traction and automatic fare collection gate etc. for the Metro.
One TBM equal to the weight of 60 elephants
According to metro officials, the weight of TBM is equal to the weight of 60 elephants. This TBM has been designed and manufactured by CRCHI (China Railway Construction Heavy Industries Corporation Limited) keeping in view the soft soil and ground pressure balance of Patna. The length of the main body of the TBM is about nine meters while the full length of the earth pressure balance is about 95 meters. During operation of TBM, a continuous process of mining, grouting, ring building along with ground monitoring information analysis will be completed. According to officials, small sections of concrete set in the steel reinforcement cage fitted in the TBM are used to form the permanent layer of the tunnel. Each tunnel ring locks the system by connecting six segments together. It also helps the tunnel boring machine to move forward.
