THE SHEAR-STRENGTH OF REINFORCED ROCK JOINTS

The evaluation of the shear strength of rock joints, reinforced by mea ns of steel dowels, by both experimental measurements and numerical mo delling with the aim of determining a provisional tool for optimizatio n of dowel design is presented. The influence of some important parame ters of both the rock and the steel type on the mechanical behaviour o f the reinforced structure has been studied. The analysis of the mecha nical behaviour of the discontinuous rock mass-dowel system presented in this paper involved the following theoretical and experimental stud ies: laboratory tests on reinforced rock joints, Finite Element Method (FEM) modelling of the laboratory tests, analytical models for determ ination of the reinforced joint shear strength, comparison between the experimental and analytical results. The tests have been carried out in order to evaluate the influence of some important parameters on the mechanical behaviour of the reinforced structure: steel type, bar dia meter, reinforcement type (bars and tubes), rock material type. Shear resistance is heavily influenced by the quoted parameters. Yielding st eel provides the highest contribution to the global reinforced joint s hear resistance when using bars or tubes. Stronger and stiffer rock ma terials lead to higher shear stresses in the steel and consequently lo wer overall resistance. Two different mechanisms of reinforcement fail ure have been observed while varying the rock material characteristics . The analytical model has been set up in order to reproduce these two failure mechanisms, one involving a strong and stiff rock material wi th bar failure determined by shear and tensile stresses at the joint i ntersection; and the other involving weaker rock and the formation of two symmetric plastic hinges in the bar, with failure being due to eit her the tensile strength or the ultimate elongation of the reinforceme nt being reached. Finally, the analytical model has been validated by comparison with experimental results.