Axial load transfer mechanisms of rock bolts with modified surface profiles for various geotechnical conditions

Axial load transfer mechanisms of rock bolts with modified surface profiles for various geotechnical conditions

Fully grouted rock bolts, anchored using resin or cementitious grout, are widely used in mining and civil engineering to transfer loads from unstable rock to more competent strata, preventing further deformation. The surface geometry of rock bolts, including rib profile shape, height, angle of wrap, and rib spacing, significantly affects load transfer efficiency. This study aims to enhance bond resistance by optimizing rib spacing and introducing grooves along the bolt. A comprehensive experimental and numerical investigation was conducted, including 56 small-scale and 12 large-scale pull-out tests. Small-scale tests utilized steel sleeves with varying rib spacings and grooves to evaluate axial bond resistance. Large-scale tests extended the analysis to rock bolts embedded in concrete of different strengths (20, 40, and 60 MPa), simulating weak to medium-strength host rock conditions. Results indicated that increasing rib spacing and adding grooves generally improved bond resistance. However, in low-strength concrete, failure shifted from the rock bolt-grout interface to the grout-concrete interface, reducing ultimate bond resistance. Numerical modelling provided deeper insights into axial load transfer mechanisms. Variables such as borehole diameter, grout strength, resin properties, and seismic conditions were analysed. Sensitivity analyses revealed that larger borehole diameters improved bond performance, particularly for bolts with modified ribs and grooves. Increasing borehole diameter from 36 mm to 50 mm enhanced ultimate bond resistance by up to 35%. Large-scale simulations highlighted the crucial role of host rock strength and encapsulation length in bond performance. In weak concrete (20 MPa), optimised rock bolts exhibited lower axial bond resistance than standard designs in a 36 mm borehole. However, increasing borehole diameter enhanced bond resistance by increasing the surface area for axial load transfer. Simulations also demonstrated that grooves improved stress distribution within the grout. Under seismic loads, rock bolts with grooves exhibited superior pull-out resistance, confirming that geometric optimisation enhances load-bearing capacity under real-world conditions.

Files associated with this item cannot be displayed due to copyright restrictions.