Chinese TBM for Mumbai coastal highway drives 30 Apr 2020

A 12.2m diameter slurry TBM supplied by Chinese manufacturer CRCHI is heading to India to work on the first stage of an ambitious project to construct a new coastal highway for Mumbai. The highway will include about 3km of TBM and cut-and-cover excavation between Naruman Point and Bandra Worli (Fig 1). In total, the first stage will run almost 10km of a planned 29km route to connect Marine Drive in the south and Kandivali in the north.

The underground alignment will consist of twin TBM drives of 1.9km long with three traffic lanes each. The southbound tube will include 660m of cut-and-cover at both ends, and the northbound drive has 410m of cut-and-cover at the Nariman Point end and 660m of cut-and-cover at the Banra Worli end. Ten cross passages will link the twin underground roadways.

Fig 1. Underground highway route between Naruman Point and Bandra Worli

CRCHI TBM, reportedly the largest diameter Chinese TBM in India

The tunnels will run at depths of about 70m through complex geological conditions that include basalt, breccia and shales, with maximum compressive strengths of up to 200MPa. The engaged contractor L&T, Larson & Toubro, has procured the CRCHI TBM for the project.

At 80m long and weighing 2,300 tonne, the CRCHI machine is claimed as the largest Chinese TBM exported to India. To excavate through the challenging geology, the slurry TBM is equipped with a mixed cutterhead, with eight spokes and panels, as well as a large-diameter slurry feed port and several slurry flushing lines to increase the flow rate of the slurry to the cutterhead. Additional features include:

• 20in disc cutters
• A dual-chamber indirect slurry control system
• A dual-circuit automatic pressure system
• A high torque, retractable main drive.

The machine is the fifth CRCHI machine manufactured for the Indian market, following four slurry TBMs ordered also by L&T for its Bangalore Metro Phase II contracts.

The twin tubes of the Mumbai road project will have a finished precast segmentally lined diameter of 11m, with a prefabricated, man-entry technical conduit in the invert. The cut-and-cover sections have a cross section of 11m x 6.5m. Ventilation in the operating highway will be provided by a Saccardo system.

In addition to the difficult geological conditions, the bored alignments run under several historic and high-rise buildings, requiring careful operation of the TBM. During excavation, surface monitoring will be undertaken with feedback provided to ensure appropriate operating parameters and mitigation measures are applied.

The underground section of the highway forms part of Package IV of the first phase of the project. In addition to the appointment of L&T as construction contractor, a JV of Yooshin Engineering and TEC-4 has been appointed as the project management consultant. Design work was undertaken by Lombardi.

Work on the project recently restarted after a December 2019 ruling by the Indian Supreme Court overturned a lower-court decision to halt the project over concerns of irregularities in the project approval process.