Afcons has launched Tunnel Boring Machine (TBM) without Diaphragm Wall (D-wall) in the Underground (UG-1) Project of Ahmedabad Metro.
For the first time in India, such method has been used for any metro project. This method was previously used in the construction of Istanbul Metro.
Afcons is constructing two underground stations, twin tunnels of about 3.5 km length in total, a cut and cover section besides a ramp connecting elevated and underground sections in the UG-1 project of Ahmedabad Metro.
The first TBM, ready for commissioning, could not be set in motion as the headwall construction came to a standstill due to delay in handing over of land for Kankaria Station and various other issues.
To minimise the delay and speed up execution, the project team adopted a new methodology of TBM pass through without a D-Wall at Kankaria Station.
The station box D-Wall is placed before TBM pass through in top-down construction methodology, the contractor said, adding this was not possible at Kankaria Station.
This innovative methodology ensured the delay does not have a domino effect. The station’s width was subsequently increased from 20m to 22m to accommodate the unique TBM manoeuvre.
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,” he added.
To ensure the smooth functioning of TBM, the team also developed an in-house calibration unit for the earth pressure sensor.
“Sometimes, the sensors gave a deviated value of earth pressure when the face of the sensor was covered by muck. Hence, its calibration was required,” Nakkiran said.
“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,” he added.
Nakkiran further said parallel construction was adopted instead of the sequence method to expedite the work at Kankaria Station.
“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.
Ahmedabad Metro (UG-1) Project is slated for inauguration shortly and Afcons has completed the project without compromising on health and safety parameters.
The project has clocked twelve-and-half-million safe man hours.
The site has earned various accolades, including a four-star rating by the National Safety Council of India, and the Safety Innovation Award from The Institute of Engineers (India) after an extensive evaluation of health and safety management at site.
The British Safety Council has also issued an appreciation certificate, as per Afcons.
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