Tunnel Works: Mg Road-Shivajinagarmost Complex Section On Metro Phase 2 | Bangalore News
This is mainly done when the cutting discs are worn or proper discs need to be fitted to cut through rocky ground or rocks depending on the geological conditions.
“A mix of rocks and soil on the course meant that the blade discs had to be changed often when a rock was encountered. These discs are mounted on the cutting head of the tunnel boring machines. The number of cutting discs depends on the actual hardness of the rock,” explained BMRCL (underground) chief engineer Subrahmanya Gudge.
For example, 325 cutter discs were replaced in TBM Avni, which drilled between Shivajinagar and MG Road (1,086 m, south direction) in 388 days. TBM Lavi, which was building a tunnel on the same section (1076m, northbound), required 295 discs.
Another official said, “Each cutting disc costs contractors around Rs 1.5-3 lakh. But most are beyond repair and often cannot be used again because they are damaged when they encounter hard rocks or boulders in the ground.
“In addition to the cutter discs, missing/non-functioning parts will also result in the need to stop the bore for maintenance. This will slow down the job from 1.5 days to seven days, depending on the severity of the situation,” Gudge said.
“Normally, the average daily digging of a tunnel is around 2.4m in mixed/hard rock conditions and 5m in favorable soil/conditions. On April 25, the tunnel boring machine Urja, which was tunneling between Cantonment and Pottery Town, achieved a record 27m progress,” Gudge said. However, the average Lavi TBM progress was only 2.7 million days between Shivajinagar and MG Road (northbound) due to complex geology. Nevertheless, the Phase 2 tunneling work is progressing well compared to the Phase 1 underground work, which has been marred by delays.
“We have completed 40% of the digging work so far. We plan to complete it in 1.5 years. Metro operations on the pink line will begin by 2025,” Gudge added.
TBM Lavi won
The MG Road-Shivajinagar section is part of the longest underground metro corridor in the city – between Dairy Circle and Nagawara (14 km) on the Gottigere-Nagawara section (pink line). No less than 713 interventions were required by engineers and contractors for the seven tunnel boring machines each time a maintenance or repair problem arose.
Of the seven, TBM Lavi needed the most interventions (203). It was followed by TBM Avni (193). The construction of tunnels between Cantonment and Shivajinagar was also a complex task. “While the TBM Vidhya, which was tunneling between Cantonment and Shivajinagar (859 m, southbound) saw 93 interventions, the TBM Urja (867 m, northbound) had 88,” said one. responsible.
Similarly, the Rudra TBM (to the north) and the Vamika TBM (to the south), which drilled 613 m each, recorded 35 and 57 operations respectively. The Varada tunnel boring machine which dug a 595 m tunnel between Vellara Junction and Langford Town faced 44 interventions.