Empirical estimation of strength of jointed rocks traversed by rock bolts based on experimental observation

Engineering behaviour of jointed rocks is substantially incompetent as compared to intact rocks due to the presence of joints. Rock bolts are routinely used to reinforce jointed rocks at project sites. The assessment of the strength behaviour of bolt-reinforced jointed rock is a challenging task due to the complex interaction between the joints and the bolts. The present paper attempts to resolve this issue through an experimental study. Natural rock cores with a natural joint, and synthetic rock cores with smooth joint have been tested under uniaxial compression. The tests have been performed on specimens without and with bolt. Grouted steel bolt was used to reinforce the rock. Results from the tests indicate that the provision of the bolt alters the failure mode of jointed rock, and enhances the strength and modulus values. Strength and modulus of the reinforced rock were found to be correlated with each other. It is proposed that the strength of reinforced rock can be obtained from strength and modulus of the intact rock and the modulus of the reinforced rock. The intact rock strength and modulus may be obtained from laboratory tests and the modulus of the reinforced rock may be obtained by back analysing the deformations observed in the field. Sakurai's critical strain concept has been analysed and it is observed that the correlations suggested through proposed empirical approach closely commensurate with critical strain approach and hence give scale free results.