Kolkata TBM failure causes extensive damage (TunnelTalk)

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Tailseal failure on the EPBM [earth pressure balance machine] operating on a running tunnel drive for the Kolkata Metro is reported to be the cause of an uncontrollable inrush of water and material that led to major damage and collapse of buildings. Having started in the evening of Saturday 2 September, the inrush took until end of Sunday 3 September to control, with residents evacuated from dangerously damaged and collapsing homes and businesses in the central Bowbazar area.

The incident occurred 1.6km into the lead heading of the 2.45km running tunnel drives for the new East-West Metro line, which will run from Esplanade to Sealdah Stations (Fig 1). According to senior executives of the Kolkata Metro Rail Corporation (KMRC), the machine had just taken a tight radius turn into an alignment under Ganguly Street, placing severe pressure on the three-row wire brush tailseal. The turn occurred as the machine entered a reportedly unexpected geological deposit of highly water-charged sand. The inrush of water and sand through the damaged tailseal – described as a ferocious flow – quickly became uncontrollable, flooding the tunnel and the TBM, and causing collapse damage on the surface.

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Written by Long Branch Mike