Concrete finish for Glendoe repair Dec 2011
TunnelTalk reporting
About half of the 6.2km long headrace at Glendoe in Scotland will be shotcrete lined as part of the extensive repair programme to restore the stricken hydro station to commercial operation.
  • Mesh installation ahead of shotcrete lining

    Mesh installation ahead of shotcrete lining

  • Upstream junction of the bypass and the TBM headrace

    Upstream junction of the bypass and the TBM headrace

A 100mm thick lining of steel fibre and mesh reinforced shotcrete secures long sections of the TBM driven headrace with an extra 500mm of secondary shotcrete lining applied in the recovery bypass to increase waterproofing and lining strength through the fault zone that caused failure of the 5m diameter unlined TBM tunnel back in August 2009. The opportunity is also being used to apply a 100mm of fibre reinforced shotcrete lining in the tailrace to increase its durability and prevent erosion that occurred during the few months that the plant was in operation between December 2008 and shutdown following a major rockfall in August 2009.

Fig 1. Plan of the repair works

BAM Nuttall secured the recovery contract for Scottish and Southern Energy (SEE) hydro plant in February 2010. As well as clearing an estimated 20,000m3 of debris, the repair contract involved drill+blast excavation of a 560m adit around the underground power station on the original downstream access route to the headrace drive, and a 600m drill+blast bypass of the collapsed zone about 2km into the headrace from the upstream reservoir intake (Fig 1).
The lining is designed to extend the design life of the new hydro scheme built into the mountains above Scotland's famous Loch Ness into which the scheme's tailrace discharges.
Two massive 14m long concrete plugs will seal off each end of the bypass to direct water around the collapsed section.

Finishing up the downstream concrete plug

The lower concrete plug is installed and work has begun for the upstream plug. In all, about 60,000 tonne of concrete will be used on the project with Dramix RC65/35BN steel fibre from Bekaert used in much of the immediate support and lining shotcrete.
Douglas Gilchrist, the project's Community Liaison Officer for SEE, said that some 240 staff are on site, working 24hr/day, 7 days/week to meet target deadlines. The aim is to complete the civil works by May next year, he said, adding: "The process of re-filling the reservoir should begin at the end of this winter season and electricity generation should resume in the first half of 2012." The site will close down for about two weeks over the Christmas and New Year holidays with a holding team on site.
Glendoe recovery progress - TunnelTalk, August 2011
Recovery contract for failed headrace at Glendoe - TunnelTalk, Feb 2010
Glendoe rockfalls more serious than initial fears - TunnelTalk, Oct 2009

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