Afcons has launched tunnel boring machine (TBM) without Diaphragm Wall (D-wall) in the underground (UG-1) section of the Ahmedabad 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, 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 head-wall construction came to a standstill due to delay in handing over of land for Kankaria Station and various other issues. To minimize 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. 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 maneuver.
Project Manager S. Nakkiran informed that the TBMs were launched from the launching shaft as tunnelling started for both east-bound and west-bound routes. The tunneling for both routes was completed smoothly by constructing permanent rings and the TBMs were then retrieved at Kalupur Station. As far as Kankaria Station is concerned, the D-Wall of the main station box was constructed in a phased manner. To ensure smooth functioning of TBM, the team also developed an in-house calibration unit for the earth pressure sensor.