Experimental Study on Prestress Loss and Pull-out Behavior of Rock Bolts

Abstract

For mountain wind power towers, the foundation adopts rock anchor foundation, which can fully utilize the bearing capacity of the bedrock and achieve the goal of shortening the construction period and saving investment. However, there is still few studies on the mechanical properties of prestressed wedge-grouted rock bolts (PWRBs). The research on rock bolts under prestressed conditions is also limited to scale experiments and steel casing experiments, lacking accurate and reliable on-site full-scale prestressed rock bolt pull-out test results and analysis. Therefore, field pull-out tests in weathered rock formations for prestressed grouted rock bolts (PGRBs) and PWRBs with lengths of 8.0 m, 10.5 m, and 13.0 m, respectively, were conducted to investigate the pull-out behavior and prestress loss of these two types of rock bolts. The test results show that the prestress loss ratio of two types of rock bolts is generally around 15%, and the maximum prestress loss ratio can reach 25%. Besides, the failure mode of two types of rock bolts was that the the steel bars fractured in the free section and were not pulled out. The pull-out bearing capacity of PWRBs is higher than that of PGRBs. Using the prestressed rock bolts with 8.0 m bolt length (6.0 m anchored length) to construct wind turbine tower foundation in strongly weathered rocks can meet the design requirements.