Effects of rib distances on axial load transfer mechanisms of fully grouted rock bolts

Rock bolt systems are widely used for the reinforcement of underground coal mines after excavation. These systems consist of steel bolts installed in drill holes and encapsulated by resin or grout. The spacing between the rock bolt ribs is one of the factors affecting the axial load transfer mechanisms. Steel rebar with a 16 mm diameter, Stratabinder HS grout, and steel pipes with a diameter of 50 mm were used to simulate the rock bolt system. The distance between the ribs on the rebar was doubled for half of the samples to investigate the effects of rib spacing on the pull out capacity of grout encapsulated rock bolts. The water to grout ratio was set to 0.35. Pull-out testing of the samples with curing times 7, 14, and 28 days was carried out using the automated tensile testing machine at the Centre for Future Materials laboratory of the University of Southern Queensland. It was concluded that the ultimate load was increased when the spacing between the ribs was doubled. The results also showed curing time increases the ultimate pull-out load capacity.