Air Shaft Stabilisation Gripforce ® Rockbolts & Welded Mesh Panels

Project Title Glenholt Tunnel Air Shaft Stabilisation Client Railtrack Main Contractor Amalgamated Construction Co. Ltd Featured Products Weldgrip Fibregrip ® Rockbolts & Welded Mesh Panels

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.

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. 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:

• Safe method of installation
• Quick and effective method of reinforcement
• Lightweight construction allows for better handleability in confined space

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Product Brochure - Soil Nails & Rockbolts - 620k