The tunnel is part of the Janakpuri West–RK Ashram Marg extension of the Magenta Line.
DMRC said the tunnelling work between Pulbangash and Sadar Bazar stations was especially challenging as trains on the busy Red Line above were not halted for a single day, even as the TBM constructed the tunnel below the elevated viaduct on which trains were operational.
The Red Line viaduct stands on open foundations with a balanced cantilever span, so several engineering precautions were used to ensure its safety.
Tube a manchette grouting, with 180 TAM boreholes, was used to strengthen the ground around the viaduct. Also, instrumentation and real-time monitoring were deployed to monitor ground movement, pier behaviour, and building safety. The equipment included surface settlement markers, deep inclinometers, building settlement points, pier tilt meters and load cells.
Specialised personnel were deployed around the clock to monitor the readings. DMRC said all parameters remained well within permissible limits during the entire operation.
“The construction of the downline tunnel on this section has now been completed. Work on the upline tunnel is under way with the same level of precautions and monitoring. This was an extremely critical construction work since the Red Line, on average, carries about 700,000 passengers every day,” DMRC said.
