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Anchor Selection
Choosing The Right Anchor Type
The choice of bolt (fixing) type will take into account the environment, number of bolts to install and the rock type. Fatal accidents have been caused (e.g. Blue Mountains, Australia) by the installation of unsuitable bolts for the rock properties. Local experience / policy should be consulted before equipping in an unfamiliar area.
Glue-in anchors are increasingly recognised as the preferred type of fixing that offer better performance long term and can be used in any rock type.
Corrosion is an important consideration and local experience should always be a starting point for assessing which materials (stainless steel or titanium) have stood the test of time. For entirely new climbing areas, we can assist you with identifying the presence of compound salts on the rock surface, which can cause aggressive corrosion.
Equipping Soft Rock
Soft rock is typically defined as having an upper unconfined compressive strength (UCS) of 25MPa and poses particular problems when bolting. Where UCS values are too low, wedge bolts will fail to achieve sufficient torque due to the rock compressing as the clip slides over the wedge in the vicinity of the clip / wedge interface. Double wedge bolts were specifically designed for equipping conglomerate where drilling through a pebble can cause it to shatter and leave an air gap, which prevents the clip and wedge from engaging. A second wedge and clip increase the likelihood of a secure placement. The use of sleeve bolts can address poor wedge bolt performance however the strengths of glue-in fixings become evident.
Drilling and brushing holes in soft rock often results in enlargement that further supports the use of glue-in fixings. Tests conducted in the conglomerate rock of the Allgau region of Southern Germany demonstrated that in addition to using a glue-in, the fixing required sufficient embedment depth to achieve EN 959 performance in axial testing. 80mm leg length bolts failed below 10kN and 100mm deep glue-in bolts were marginal at achieving 15kN (failing at 13 to 14kN) thus ultra deep shaft lengths of 150mm were necessary, with increasing the bolt size (12mm to a 16mm hole) gave further strength increases (as would be expected).
Using 150mm deep glue-in bolts, placed in holes drilled through pebbles ensure sufficient matrix is able to absorb the force induced via the fixing during a fall.
