Pair of Crossover TBMs Completes Triple Tunnel Drives in Mumbai
Jul 28, 2021
Robbins XRE TBMs cross the Finish Line in Massive Metro Project
The tunnel drives were a triumph for joint venture contractor Larsen & Toubro and the Shanghai Tunnel Engineering Company (L&T – STEC), as the crew and equipment overcame unpredictable terrain, high-pressure water ingress, and government-imposed lockdown orders during the Covid-19 pandemic.
The two custom-built machines were selected to bore parallel 2.9 km (1.8 mi) tunnels between the Cuffe Parade station and CST stations, breaking through into several station sites along the way. “It is the first time in India that Dual Mode, Crossover type TBMs equipped with a horizontal screw conveyor and high torque / high speed (two-speed) cutterhead drives were used. Overall, the performance of the Crossover TBMs was found satisfactory and we are in the process of shifting these TBMs for the L&T Chennai Metro project,” said Mr. Palwinder Singh, Head – Tunnel Construction for the L&T – STEC JV.
“This requires fine control on the operational parameters of the TBM because only 25% of the cutterhead is excavating the rock mass, while the remaining 75% of the cutterhead has no contact with rock or soil. In addition, the TBM was relaunched without using a reaction frame, instead taking reaction from half segments erected during the benching of the NATM Platform Tunnel. These innovative concepts were accomplished for the first time in India at Mumbai Metro Line-3, Package 1, and I therefore have many reasons to feel proud on the completion of tunneling,” said Singh.
L&T – STEC made impressive progress throughout tunneling despite the many exacting circumstances surrounding the scope of work. Above ground, the joint venture not only had to navigate the restrictions of working within an urban environment, such as limited work hours and the slow removal of muck due to minimal space and traffic, but also faced concern for major structures such as the Mittal Towers and the historic Bhikha Behram Well located along the tunneling route.
Underground, L&T – STEC faced a complex geological mix of fresh greyish basalt, soft volcanic tuffs, shale, and breccias—consolidated rocks of angular fragments of disintegrated volcanic rock. One of the biggest concerns, however, came from the tunnels’ proximity to the coastline of the Arabian Sea. During one point, TBM 1 was only 25 m (82 ft) from the coastline, with the invert level of the tunnel running approximately 22 m (72 ft) below mean sea level. As anticipated with circumstances such as these, the Crossovers faced a significant amount of groundwater with up to 300 liters/min during their excavation.
Despite these obstacles, the TBMs were still able to maintain impressive rates. TBM 2 even completed one push in a swift 14 minutes. “In fact, the boring rate of the Crossover TBMs was never an issue for us. It was only limited by the rate of muck removal and we could have finished the tunnels much faster,” said Singh.
Each milestone reached on this project is another step closer toward significantly improving the lives of Mumbai residents. As the financial capital of India and one of the most populated cities in the world, Mumbai is faced with an excessive amount of road traffic. It currently takes up to two hours to drive the 25 km (15 mi) distance from Cuffe Parade to the airport—the same trip on the finished metro will take a mere 50 minutes. The completion of Mumbai Metro Line 3, which is expected in 2025, will not only save residents transit time, but is expected to initially decrease road traffic in the area by 35%, reducing daily fuel consumption by 460,000 liters.
The News in Brief:
- The second of two 6.65 m (21.8 ft) Robbins Crossover XRE TBMs made it’s final breakthrough at India’s Mumbai Metro Line 3 in spring 2021.
- The two Robbins XRE TBMs were uniquely designed for basalt, tuff, shale and breccias, and featured a screw conveyor as well as two-speed cutterhead drives.
- JV contractor L&T-STEC achieved good advance rates in tough ground conditions, completing a push in as little as 14 minutes.
- The Robbins Crossover TBMs are the first in India to be used in the benching of a NATM tunnel as they passed through an intermediate station site.
- The completion of Mumbai Metro Line 3, which is expected in 2025, will decrease road traffic by 35% and correspondingly reduce daily fuel consumption by 460,000 liters.
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