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  Kolkata EW Metro - Removal of abandoned H-Piles using NATM in Soft Ground to facilitate the TBM operations in Package UG02

  Alignment of new EW (East-West) Metro Package 02, bored tunnels to new Esplanade Station, is crossing the existing (30-35 years old) Old Esplanade underground station, built with traditional bottom-up construction used in India in the 1980s. Newly proposed EW Metro tunnel alignment is running diagonally across this 250m long station (see Figure 2. below). There is 7.6m of vertical separation between the crown of the new tunnel and the bottom of the base slab of the existing Old Esplanade station. There were multiple steel double H-piles at approximately 3.0m centre to centre spacing, obstructing future TBM path, left in place during construction of Old Esplanade Station. These H-piles were removed before beginning of tunnelling to clear the TBM path. NATM drifts of four (4) meter diameter and 100 meters of length, from the New Esplanade underground station, were executed for removal of those abandoned H-piles from the ground after discarding the option of higher risk hyperbaric works from the TBM cutter head. This paper describes the approach of design and execution of these NATM tunnels in stiff clayey soils with pockets of silty sand with the high-water table in Kolkata region of India along with the impact of the construction on the existing Old Esplanade station.

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