Displacement of Rods During Pullout Failure of Rock Anchors: A Case Study

This paper focuses on a pullout failure of anchor rods used to stabilize rock slope at the sides of a road cut in a mountainous terrain. The objectives of this work are to analyze a case study of a pullout type of failure of anchor rods at highly fractured rock slope sides of a road cut called Dhila descent in Saudi Arabia, and also to investigate the possible mechanisms that caused this peculiar type of failure of the rock anchors and the landslides along the descent. Anchor rods exit out of the hole for a distance of few meters. Results of this analysis showed that the mechanism of this rock anchor failure is of the pullout type, caused apparently by the release of the energy stored in anchor rods at the post-tension stage during the construction period. This release is caused by the reduction of the bond strength between the rod and the grout at the anchorage end inside the hole. The displacements of the rods were computed based on the conservation of energy and work-energy principles. The amount of the displacements computed for a range of possibilities are comparable with those observed in the field. The bolt failure process is explained in terms of the debonding between the bolt and the grout. Recommendations were made to improve the design of such anchors. It is recommended to use fully-grouted, inclined, static rock bolts with a more ductile grout, and locked with nuts from both sides of the bearing block.