A new analytical approach able to predict the mechanical behavior of rock bolts subjected to pull-out tests was proposed in this paper. Input parameters of such approach are: rib profile shape, height, width, angle of wrap and spacing, axial bolt pull-out force, and material properties. As for the analytical part, the basis of the new analytical solution for the prediction of the load displacement curve was developed. Derived mathematical equations enable calculations of grout displacement in elastic and elasto-plastic behaviour. In the experimental part, four examined bolts in situ pull-out tests were compared with the predictions of the new analytical approach, and this comparison led to the validation of this approach.
Rock bolts are widely used in mining and tunnel engineering to support underground excavation or to stabilize rock masses . A rock bolt consists of a bar inserted in a borehole that is drilled into the surrounding soil or rock mass and anchored to it by means of a fixture. A rock bolt reinforcement system has four principal components: the rock or soil, the reinforcing bar, the internal fixture to the borehole wall and the external fixture to the excavation surface . The reinforcing effect of a grouted bolt is by the longitudinal and shear displacement in the rock mass.
Thus the load transfer capacity of the bolt is governed by the shear strengths developed between the rock/grout and the grout/bolt surface . Pull-out tests are very useful to investigate the bonding capacity of rock bolts . The bonding capacity of the bolt, in turn, is influenced by the bolt profile configurations. The profile configuration is defined by the rib profile shape, and height, width, angle of wrap and spacing or distance between the ribs . The work currently undertaken by the authors tries to improve the knowledge acquired through these past studies. The pull-out test and the stress distribution in infinite elastic media are presented first. Later, the basis of the new analytical solution for the prediction of the load-displacement curve is developed. Finally, comparisons between the analytical solution and experimental data are shown, and the results are discussed.