Experimental Evaluation of Sleeved Rock Bolts for Corrosion Resistance and Load Transfer Performance in Underground Reinforcement

Abstract Ground reinforcement using rock bolts is critical for long-term stability in underground excavations, but their effectiveness is highly dependent on their resistance to corrosion. While Corrosion Protection Sleeves (CPS) are widely used to mitigate corrosion in steel rock bolts, their mechanical integrity and influence on the overall system’s performance under axial and shear displacement remain unquantified. This study addresses this knowledge gap by conducting a comparative analysis of sleeved versus conventional rock bolts, investigating the influence of the host medium type, and assessing the integrity of the CPS under various loading conditions. The findings revealed that sleeved bolts show a more ductile response in pull-out tests compared to conventional bolts, allowing for greater roof convergence before debonding. This contrasts with conventional bolts, which demonstrate higher initial stiffness and bond strength. It was also found that, during axial loading, the main failure mode was debonding at the grout-CPS interface, which was similar to the previous studies. Furthermore, the study identified a critical shear displacement threshold of around 25 mm, beyond which the CPS shows visible cracking. This finding differs from previous studies that reported higher thresholds. The results also highlighted that the failure mode and load transfer capacity are influenced by the stiffness of the surrounding host medium, a factor that was not assessed sufficiently in the literature. These outcomes have significant implications for the design and maintenance of ground reinforcement systems. They highlight that while CPS enhances corrosion resistance, their mechanical performance is adversely affected by ground deformation. This research provided practical guidance for field engineers, emphasizing the need for a cautious design approach and continuous monitoring of sleeved rock bolts in highly deformable ground conditions. Meanwhile, the results can help engineers establish a guide for inspection routines and replacement strategies to ensure the long-term reliability and safety of underground excavations.