Delhi Metro tunnelling under Red Line viaduct: design and monitoring notes for engineers
Reviewed by Tom Sullivan
First reported on Tunnels & Tunnelling International – News
30 Second Briefing
Tunnelling for Delhi Metro’s Janakpuri West–RK Ashram Marg extension has completed the downline bore between Pulbangash and Sadar Bazar directly beneath the operational Red Line viaduct, which carries about 700,000 passengers daily. To protect the viaduct’s open foundations and balanced cantilever spans without halting traffic, engineers executed tube a manchette grouting through 180 TAM boreholes and installed dense instrumentation including surface settlement markers, deep inclinometers, pier tilt meters, building settlement points and load cells. Continuous real-time monitoring by dedicated staff kept ground movement, pier behaviour and building responses within permissible limits, and the upline tunnel is now being driven under the same regime.
Technical Brief
- Tube a manchette grouting via 180 TAM boreholes formed a pre-improvement umbrella around viaduct foundations.
- Open foundations supporting balanced cantilever spans were explicitly identified as vulnerable elements requiring pre-emptive ground treatment.
- TBM advance was sequenced to maintain viaduct stability while avoiding any interruption to Red Line operations.
- Instrumentation scope extended to adjacent buildings, treating them as critical assets within the influence zone.
- Dedicated monitoring teams worked 24/7, enabling immediate intervention had trigger levels been exceeded.
- DMRC confirmed all monitored parameters stayed within predefined permissible limits throughout the downline drive.
- The same protection, grouting and monitoring regime is being replicated for the parallel upline tunnel.
- For similar brownfield metro works, this approach reinforces the need for dense, real-time response monitoring under live structures.
Our Take
Within our 158 Infrastructure stories, DMRC appears regularly as one of the few urban rail operators pushing complex underground works in dense, built-up corridors, so the Janakpuri West–RK Ashram Marg extension reinforces its role as a reference client for difficult metro tunnelling in India.
Executing 180 TAM boreholes for grouting along sections like Pulbangash and Sadar Bazar on the Red Line signals that ground treatment is becoming a major cost and schedule driver for Delhi’s infill and extension works, which contractors will need to factor into bids more aggressively than on earlier phases.
Among the 357 tag-matched ‘Projects’ and ‘Safety’ pieces, only a small subset deal with intensive pre-support and grouting regimes, suggesting that DMRC’s approach here could set a higher baseline for pre-construction ground investigation and risk mitigation on future Indian metro projects.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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