Experimental study on rockbolt anchoring performance and its influencing factors under confining stress effect

Confining stress is one of the key factors affecting the anchoring performance of rockbolts. To investigate the effect of confining pressure on rockbolt anchoring performance and its influencing factors, the anchor pull-out tests under the conditions of the surrounding rock properties and stress environment were carried out using the self-developed rockbolt confining pressure pull-out test device. The influence of factors, such as confining pressure, rockbolt diameter, anchoring length and surrounding rock strength, on the anchoring performance of rockbolts was investigated. The results show that confining pressure is a critical factor influencing rockbolt anchoring performance. With increasing confining stress, the lateral constraint exerted by the surrounding rock on the anchoring interface strengthens, leading to an approximately linear increase in the ultimate anchoring force of the rockbolt at a rate of 4.28 kN/MPa. This manifests as a significant improvement in the overall bearing capacity of the rockbolt anchoring system. Under constant confining pressure, the rockbolt diameter and anchoring length exhibit a positive correlation with the ultimate anchoring force. The larger rockbolt diameters and longer anchoring lengths enhance the anchoring force more effectively, although this enhancement is limited by the material strength of the rockbolt and the bearing capacity of the surrounding rock. The anchoring performance of rockbolt is highly sensitive to the strength of the surrounding rock. Under the same confining stress, the anchoring force of rockbolt is positively correlated with the strength of the surrounding rock, and the stronger surrounding rock provids better anchoring conditions and greater system stability. Furthermore, recommendations to improve rockbolt anchoring performance in coal mine roadway support were proposed, which is valuable for the design and optimization of deep coal mine roadway support under complex geological conditions.