Recently, the second roadheader of two Robbins cross-mode XRE (Merged Earth Pressure Balance and Hard Rock Mode) with a diameter of 6.65 meters achieved the third and final breakthrough on Line 3 of the Mumbai Metro in India. . The first machine has achieved the final pass of the project at the end of April. The completion of this tunnel is a victory for a joint venture between Larsen&Toubro and Shanghai Tunnel Engineering Company (L&T-STEC). Because during the new crown epidemic, construction personnel and equipment have overcome many difficulties, including unpredictable geology, high-pressure water gushing, and government-enforced blockade orders.

 The two custom-made cross-modes excavated two parallel tunnels with a length of 2.9 kilometers between the Cuffe Parade station and the CST station, passing several stations along the way. "This is the first time that India has used a cross mode equipped with a horizontal screw conveyor and a high-torque, high-speed two-speed cutter head drive to excavate a tunnel. In general, the performance of the cross mode roadheader is very satisfactory. The equipment was transferred to L&T’s new Chennai Metro project for use,” said Mr. Palwinder Singh, head of tunnel construction at the L&T-STEC joint venture.

These two devices also set another milestone for India on this project. The two devices use unique technology in the 554-meter-long section from Hutatma Chowk to CST station. They use the platform tunnel excavated by NATM, and the bottom basalt rock is excavated stepwise (after the top rock is conventionally excavated, the remaining rock at the bottom of the station is excavated). "This requires fine control of the operating parameters of the roadheader, because only 25% of the cutterheads are excavating the rock mass, and 75% of the cutterheads are not in contact with the rock or soil. In addition, no countermeasures are used when restarting the roadheader. Force frame, but from the half section erected during the construction of the new Austrian method platform tunnel steps, the reaction force is used to advance the tunneling machine. These innovative concepts are the first realization of the Mumbai Metro Line 3 Mark 1 in India, so I have many reasons for I am proud of the completion of this tunnel project." Mr. Singh continued.

 Although there are many harsh conditions in the construction, the progress of the entire tunnel boring operation of the contractor is very impressive. On the ground, the contractor must not only overcome the various constraints of construction in the urban environment, such as limited construction time, and slow down the progress of the silt removal work due to space and traffic restrictions. In addition, the equipment must also consider the impact on the structure of major landmarks, such as the Mittal Tower and the historic Biha Behram oil well located along the tunnel. When the cross-mode roadheader excavates, there is only a buried depth of 15 to 20 meters, which separates the equipment from these important building structures. Instruments must be used in real time during construction to monitor vibration, movement, and potential settlement.

Underground, the equipment faces a complex geological combination of fresh gray basalt, soft volcanic tuff, shale and breccia, which consist of horn-shaped fragments of decomposed volcanic rock. However, one of the biggest challenges comes from the proximity of the tunnel to the Arabian Sea coastline. In a section, the first roadheader was only 25 meters away from the coastline, and the top of the tunnel was excavated about 22 meters below the average sea level. In this case, the roadheader needs to resist huge water inrush while excavating. According to records, the highest gushing water flow rate is 300 liters per minute.

Faced with these difficulties, the roadheader can still maintain a satisfactory speed. The second roadheader can even complete a fast-stroke advance in 14 minutes. "In fact, the boring speed of the cross-mode tunnel boring machine has never been a problem for us. Just because the city is restricted by the progress of the silt removal work, otherwise we can complete the tunnel faster," Mr. Singh said.

In this project, engineers from L&T, one of the contractors, worked closely with Robbins, and were highly involved in the specification and design of the equipment, and were fully prepared for the challenges of the project. Although L&T has a wealth of tunneling experience, it is the first time for them to use a cross-mode roadheader. To this end, Robbins provided a key service team for the project, giving L&T training in all aspects of machine design and operation. "The cooperation with the Robbins field service team is very satisfying. Even if the new crown pneumonia is raging, the Robbins field service team provides support for us 24 hours a day, 7 days a week." Mr. Singh exclaimed.

Pudong factory acceptance equipment

As the financial capital of India and one of the most populous cities in the world, Mumbai suffers from overloaded traffic. Currently, it takes two hours to drive 25 kilometers from Cuffe Parade to the airport, and after the project is completed, it will only take 50 minutes by subway. Therefore, every milestone of the Mumbai Metro Line 3 project is another step towards improving the lives of Mumbai residents. The entire Mumbai Metro Line 3 is expected to be completed in 2025. This will not only save residents' traffic time, but also is expected to reduce road traffic in the area by 35% and reduce daily fuel consumption by 460,000 liters.Editor/Baohongying