Cutter Head Intervention by Grouting the Chamber in Weak Ground Condition & Heavy Water Ingress – Delhi Metro Rail Corporation (DMRC)

Tunneling in backfilled urban areas poses a risk of weak geological conditions. The case presents challenges of Cutter Head Intervention in weak ground conditions with extremely unstable tunnel face and no feasibility for hyperbaric intervention. Overburden consisted dense cover of dilapidated buildings.

The Study describes Intervention by injecting Cement grout in the excavation chamber. Owing to weak tunnel face, pressure leakage capillaries and high ingress of water, the hyperbaric intervention was not feasible at few locations for tunneling drive between Delhi Gate and Jama Masjid Stations of DMRC.

Accordingly, grout mix of Cement, Bentonite, and Admixtures was formulated. After successful trails for strength, temperature, and flow, it was pumped from working chamber to the cutter head. Parallelly, Bentonite was injected from Middle Shield to prevent backward flow and jamming of Main Body/ Articulation. Additional Bentonite filling in Screw conveyor was done to prevent setting. Injection Pressure and Chamber Pressure were maintained as per engineering calculations. Cutter head rotation, grease injection and articulation movement were maintained to prevent any blockage. Post completion of grouting, temperature monitoring was done until the steady and workable temperature was achieved in the chamber. Thereafter chamber was opened to check the Strength of cement Grout and on satisfactory results, excavation and cleaning were done to inspect and replace the cutter discs.