Kolkata: The tunnel boring machines (TBMs) that will be used to construct the 5 km underground section of the Joka-Esplanade Metro or the Purple line are expected to arrive from Germany next Jan. They will be assembled and deployed for tunnelling work between Kidderpore and Esplanade through Maidan in March 2025, Metro Railway saidon Tuesday.
The twin TBMs from Herrenknecht are due to be launched from a shaft inside St Thomas’ Boys School in Kidderpore.“The tunnel borers will need a wall through which they will punch in and start digging. Construction of this diaphragm or D-wall started last Thursday. The 65m-long D-wall inside the school will be constructed in two months,” a Metro Railway official said.
VNL and contractors L&T have started casting the diaphragm wall for Victoria station. “The D-wall will be extended to become a part of the station box,” an engineer said.
The tunnels from Park Street to Esplanade will be built in the cut-and-cover method because a crossover needs to be constructed between the two stations. TBMs dig in a linear fashion and are incapable of turning to create crossovers.
Additionally, at RVNL’s casting yard in Sarkarpool, 1.4m-wide tunnel precast segments are being built. Six segments will be used to build a ring for the inner 5.8m diameter.