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Tunnel Refurbishment - Gripforce ® Rockbolts

Case Study Project Info
Project Title Conisbrough Tunnel Refurbishment
Client Railtrack
Main Contractor Amalgamated Construction Co. Ltd
Featured Products Weldgrip Gripforce ® Rockbolts

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The refurbishment of Conisbrough tunnel is part of Railtrack’s ongoing programme of improving the rail network. The tunnel is 235 metres long on the main line between Doncaster and Sheffield. The 6.1m wide tunnel was causing speed restrictions on the line due to inadequate clearances and repairs were required in two areas.

The repairs involved taking out the existing brick lined steel arch reinforcement from previous repairs carried out in the late 1800’s.

Can Geotechnical
An additional 10 Gripforce ®, 31/15 rockbolts 10 metre's long, were used at 3 metre's above rail height inclined into the roof, to reinforce a fractured section of the existing brickwork. These were installed using the internal bore of the Gripforce ® Rockbolt as a breather tube.

The Gripforce ® Rockbolt and a plastic grout tube was installed into each inclined hole and expanding foam used to form a seal. Cementitious grout was pumped through the grout tube filling the hole from the sealed entrance to the top of the hole, until grout started to flow from the Gripforce ® tube. The orifice of the tube was then plugged with a stainless steel peg.

The advantages of using Gripforce ® fibreglass rockbolts in Conisbrough tunnel were:

  • Ease of installing 12 metre lengths by being able to bend the bolts in the confined space of the 6.1m Wide tunnel.
  • Tube delivers the cementitious grout to the back of the hole and displaces build up of water.
  • Ease of transportation into the tunnel.
  • High tensile strength.
  • High corrosion resistant particularly important in the wet conditions.
  • Improved tube/grout interface bond strength.
 

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