Twin Crossover TBMs prepare for Mumbai Metro drives 12 Jul 2018

The first of two Robbins Crossover XRE TBMs has arrived in Mumbai to excavate running tunnels for contract UGC-01 of the city’s Metro Line 3. The two 6.65m diameter Crossover machines combine the features of EPB and hard rock single shield TBM technology and will be operated by Larsen & Toubro as part of the Larsen & Toubro-Shanghai Tunnel Engineering (L&T-STEC) JV.

Robbins Crossover TBM ready for dispatch to Mumbai

During excavation of the parallel 2.8km tunnels, geologic conditions will include mixed ground and possible water pressures up to 2 bar. According to Singh, “a Crossover XRE was chosen because of the expected geology,” which includes basalt rock and transition zones consisting of black carbonaceous shale, tuff, and breccia. Rock strengths are expected to range between 15 MPa and 125 MPa in UCS. The machines will bore with about 15-20m of cover and will erect a reinforced concrete segmental lining with five segments and a key in each ring.

“During the factory acceptance testing in April, we observed that the machine and back-up system are robust enough for hard rock tunneling,” stated Palwinder Singh, Head of Tunnel Operations for L&T-STEC JV.

The metro tunnels will run between the Cuffe Parade Station and Hutatma Chowk station, passing through the Vidhan Bhavan and Church Stations. Both machines will be launched from a 25m deep x 22m long shaft at the Cuffe Parade Station. “The limited length of the shaft requires running the TBMs for the first 100m with some or all of the back-up decks at the surface connected with umbilical cables and hoses,” said Robbins Project Engineer JP Bayart. The Robbins Company will provide key personnel for the initial boring phase.

Senior managers during the factory testing

The TBMs will begin their drives in hard rock mode. “Each cutterhead is optimized for operation in rock, and can also operate in soft ground thanks to the screw conveyor with a bulkhead gate and a discharge gate,” said Bayart. “The Robbins torque-shift system, consisting of two-speed shifting gearboxes coupled to the main drive motors, allows for the high cutterhead torque required for soft ground operations.” The cutterhead of each machine is equipped with six muck buckets and six large internal muck loading plates. This design, in combination with the screw conveyor located at the centerline of each machine, will allow for the option of fully emptying the cutterhead chamber, resulting in minimal wear when EPB mode is not required. Muck will be removed from the tunnels in trains of muck cars.

Assembly for launch of the first XRE TBM began on 20 June and is estimated to take about six weeks. The second Robbins XRE TBM underwent factory acceptance testing at the end of May and will arrive at the jobsite at the end of July for its assembly.

Robbins personnel inspect TBM back-up system

“Our target is to achieve an average of 250m (820ft) of boring/month,” said Jim Clark, Robbins Projects Manager India. “The target is to complete the boring operations in 20 months, which includes the additional time required for the short start-up using umbilicals and operations to pull the machines through three station boxes.”

Contractor L&T plans to work crews on double shifts to cover a full day of operations in order to keep to this timeline. The machines will join two Robbins slurry machines boring a separate contract of the Mumbai Metro Line 3. The first of those machines will launch in August 2018.

Mumbai’s 33km all underground Metro Line 3 is estimated to be completed and in operation by 2021.