Testing of rock climbing anchors in weak sandstone

Abstract

Climbers sometimes rely on fixed anchors which are secured in drilled holes by mechanical expansion or with glue. Most rock climbing takes place on high strength rock and there has been considerable testing of anchors worldwide. However, there has only been limited testing of anchors in weaker rock. Over 60 anchors were tested in weak rock, failure loads of 8–48 kN were achieved. Chemically bonded anchors were the strongest, the 10 mm rings and 10 mm U-bolts were the only anchors that passed the European standard (EN 959). Older style anchors showed low strength and high variability. The relative strengths of single and twin holes anchors followed predictions based on interaction theory. The results also confirm the prediction of mixed glue/rock failure. The cyclic loading behaviour of anchors was explored, anchor with higher stiffness appeared to perform better; the U-bolts had the best fatigue performance.