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The Glenholt Tunnel Maintenance Project formed part of Railtrack’s
continual upgrade to its rail network infrastructure.
Part of the tunnel maintenance involved stabilisation of an
air shaft above the tunnel, which had been filled in many years
earlier. Consolidation of the loose fill in the shaft had started
to affect the lining of the tunnel roof.
For repairs to be carried out in the tunnel, the air shaft had
to be excavated from the surface, down to the tunnel lining
— a depth of 8m.
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The shaft was opened up from
its original size of 3m diameter to a 4.5m square section. This
was achieved by excavating in 1m lifts and supporting the sides
with Weldgrip Fibregrip ® polyester
rockbolts and wire mesh panels.
The rockbolts were 22mm diameter x 1.8m long, with a tensile
strength of 470kN. These were installed into 28mm diameter holes
and spun into polyester resin capsules.
A standard 80kN nut and a 150 x 150mm square plastic end plate
was used to tighten the bolt end assembly to the wire mesh.
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The wire panels were flat and
self-coloured with dimensions of 2.6m x 1.2m, using 3mm wire
and an aperture size of 75mm x 75mm.
They were bent to the contours of the excavation.
The air shaft was sealed and capped after completion of the
tunnel lining repairs.
The Weldgrip Fibregrip
® Rockbolt system gave the following advantages:
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Bar
& 'AT' Rockbolts
Safe method of installation