Effect of Geotechnical Parameters in Design and Construction of Metro Tunnel below River Ganges in Kolkata, India-Paper

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The paper examines how geotechnical and hydrological conditions shaped the design and construction of Kolkata’s East–West Metro twin tunnels beneath the Ganges (Hooghly) River—the first transportation tunnel of its kind under a major Indian river. The 520 m crossing was excavated 16–19 m below the riverbed using earth pressure balance (EPB) tunnel boring machines and reinforced-concrete segmental linings.<br /><br />Investigations used marine boreholes, in-situ testing and laboratory analyses to characterize the young deltaic soils. The preferred tunnel horizon was firm to stiff clayey silt, selected for its low permeability and suitable strength. Alignment decisions also accounted for riverbed scour and silting, tidal conditions, existing and historic structures, land availability, navigation, and protection of Howrah Bridge. Soil cover was checked for flotation and for blowout risk under TBM face pressure.<br /><br />EPB machines were chosen because they can support the excavation face, control ground movement and reduce water inflow and ground loss. Their operation required careful calculation and monitoring of face pressures, including during stoppages. Foam additives were adjusted to produce a cohesive, plastic excavated soil mass suitable for pressurized tunneling.<br /><br />Lining design considered soil stiffness, groundwater pressure, construction sequence, consolidation and seismic loading. The analysis identified the river and shallow sections as particularly demanding.<br /><br />The paper concludes that successful underwater urban tunneling depends on thorough ground and hydrological investigation, appropriate alignment and machinery selection, strict control of excavation and grouting parameters, and reliable emergency procedures. The project provides a technical precedent for future underwater transport tunnels in India.

Keywords

Kolkata East-West Metro

Ganges River tunnel

Hooghly River crossing

EPB tunnel boring machine

geotechnical conditions

hydrological conditions

twin tunnels

segmental lining

deltaic soils

underwater urban tunneling