After completing Mumbai Coastal Road’s two undersea tunnels, TBM awaits next assignment

Followed by much fanfare, the boring of the first tunnel began in January 2021 with the then chief minister Uddhav Thackeray doing a Bhoomipoojan ceremony at the launching site in Priyadarshini Park. The first breakthrough was achieved in January 2022 at the southern tip of the tunnel in Girgaon, following which Mavala was pushed leftwards by using a hydraulic-jack powered turn-table which helped in rotating the TBM by 180 degrees and in April, 2022 mining for the second tunnel began and the breakthrough was achieved in the presence of Chief Minister Eknath Shinde and Deputy CM Devendra Fadnavis.

Now two years later, and after digging more than 4 km (2 km each tunnel), Mavala’s next stop remains uncertain.
Mavala arrived in Mumbai’s Jawaharlal Nehru Port from Shanghai in April 2020, from where it was transferred to Priyadarshini Park via 17 different trucks since it was dismantled due to its massive size. The BMC assembled the TBM and brought it to the launching site in a 200-wheel self-propelled transporter and freight wings. Civic officials said that it took three months for them to assemble the entire TBM.

“The process of dismantling Mavala has already begun. We are systematically bringing out the pieces one by one and it will take us nearly 15 days to dismantle it completely,” said Mantayya Swami, chief engineer of MCRP.
“Initially it took us more time to assemble and reassemble the machine because we were starting from zero. This time, the machine will not be dismantled into very smaller pieces and will keep the basic size intact,” he said.

Swami said that at present the BMC doesn’t have any ownership on the machine as it is owned by the civic body’s appointed contractor, Larsen and Toubro. Swami said that once the dismantling is completed, a structural stability test of Mavala will be carried out, following which a decision on its future usage will be taken.

It is pertinent to note that in February 2023 a rubber-bearing of the TBM malfunctioned, which stopped the project for a period of three months. Later, the bearing was replaced with a new one, which was imported from Italy.
“The TBM have continuously mined through complex geological elements like breccia, basalt and shale. Mining underneath the Arabian Sea was also challenging. Therefore, there needs to be a check on the wear and tear of the parts of the machine,” said Swami.
“If the contractors feel that the TBM is fit for another new assignment, then they can deploy it there, and if they feel it needs to be replaced, then can sell it back to the manufacturer (CRCHIL) at a discounted rate, who may refurbish the product,” he said.
The TBM is 82 metres long and is divided into multiple sections, which includes the cutter-head in the front which has high-power spokes fitted on it.