Climbers are warned about potential bolt failures in the slate quarries of North Wales. The BMC advise climbers to use caution with any loose expansion bolts used for protection and in particular for lower off's on popular routes. Resin bolts are not affected.
After a 10mm expansion bolt was reported to have failed on a popular route lower off on the Sidings, locally based instructor and coach Mark Reeves started checking bolts and lower offs on the most popular routes in the quarries. Mark used a hydraulic bolt testing rig to pull test a number of bolts. Several things became apparent:
A small number of 10mm expansion bolts pulled out at very low loads.
Heavily used lower off's appear to be affected.
Any bolt which can be moved must be considered dangerous.
The local bolt fund (NWBF) has been supporting volunteers undertaking this testing and remedial action replacing loose bolts on the most heavily used routes with resin bolts.
This work is being done by volunteers with limited resources, so it may be some considerable time before all loose bolts are checked and replaced.
TREAT LOOSE EXPANSION BOLTS ON SLATE WITH CAUTION
You may be asking how has this happened? During original testing the results with both 10mm and 12mm expansion bolts were good on slate. Follow up tests made more recently confirmed that when initially placed, expansion bolts appear to meet UIAA standards.
With heavy use, the softness of slate appears to allow degradation of the rock leading to movement and weakening of the bolt because it no longer securely fits into the drilled hole.
Resin bolts do not stress the rock except when loaded and spread the load more evenly so are a good choice for heavy usage situations and soft rock.
Photo: Mark Reeves replacing slate bolts
Big thanks are due to Mark Reeves for a huge amount of testing and bolt replacement. Check out his website: http://lifeinthevertical.co.uk
Contact the NWBF and donate by clicking here.
Article edited 26/03/2014
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