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Ahmedabad UG Metro Project: TBM launched without D Wall, 1st for any Metro project in India

by Rishika Choudhury

Date & Time: Sep 10, 2022 8:00 AM

Read Time: 3 minute

An innovation can significantly alter the course of events while paving the way for record-breaking milestones. For the first time in India, Tunnel Boring Machines (TBM) were launched without a Diaphragm Wall (D Wall) at the Ahmedabad Underground Metro Project (UG-1).

This alternate methodology aided in the completion of the Kankaria Metro Station and, eventually, the tunnelling for the remainder of the project.

Afcons building two underground stations
Afcons is building two underground stations, twin tunnels totaling about 3.5km in length, a cut and cover section, and a ramp connecting elevated and underground sections for the Ahmedabad Metro's UG-1 project.

The first TBM, which was ready for commissioning, could not be started because the headwall construction was halted due to a delay in the handover of land for Kankaria Station and other issues. To reduce delays and accelerate execution, the project team at Kankaria Station implemented a new TBM passthrough without a D-Wall methodology.

The station box D-Wall is placed before the TBM passthrough in top-down construction methodology, which was not possible at Kankaria Station. This novel methodology ensured that the delay did not have a cascading effect. To accommodate the unique TBM manoeuvre, the station's width was increased from 20m to 22m.

TBMs were launched from launching shaft
Explaining the process, Project Manager S Nakkiran said, “The TBMs were launched from launching shaft as tunnelling started for both east-bound and west-bound routes. The tunnelling for both routes was completed smoothly by constructing permanent rings, and the TBMs were then retrieved at Kalupur Station. As far as Kankaria Station was concerned, the D-Wall of the main station box was constructed in a phased manner once the land was handed over in phases.”

For the first time in India this method has been used in a metro project. Previously, it was adopted in Istanbul Metro.

Developed in-house calibration unit for earth pressure censor
To ensure the smooth functioning of TBM, the team also developed an in-house calibration unit for the earth pressure censor. “Sometimes, the sensors gave a deviated value of earth pressure when the face of the censor was covered by muck. Hence, its calibration was required. However, getting calibration done from the manufacturer every time, or, renting a unit for it was not cost-effective, and it was time consuming. Therefore, the team developed a calibration unit in-house to address the issue," Nakkiran said.

To expedite work at Kankaria Station, parallel construction was adopted instead of the sequence method. “We could complete the construction of the main station box four months ahead of schedule, and the erection of the Over Track Exhaust (OTE) duct was done five months ahead of schedule. The efforts were also appreciated by the client (Gujarat Metro Rail Corporation),” he added.

The Ahmedabad Metro (UG-1) Project is about to be inaugurated, and Afcons has completed it without compromising on health and safety parameters. The project has accumulated 11.5 million Safe Man Hours.
Following an extensive evaluation of health and safety management on site, the site received a four-star rating from the National Safety Council of India and the Safety Innovation Award from The Institute of Engineers (India). The British Safety Council has also issued a certificate of appreciation.

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