Action of fully-grouted bolts in jointed rock and factors of influence

Summary Bolting has been used in rock engineering for many years, but present knowledge and research experience supply only limited information concerning the action of rock bolts and the determination of the bearing capacity. To improve this unsatisfactory situation a test-based research programm has been carried out at the Rock Mechanics Laboratory of the Swiss Federal Institute of Technology.Based on recent publications treating rock bolting in theory and practice, about 70 laboratory and field tests have been carried out in order to explain the mode of action of fully-bonded, untensioned rock bolts in stratified or jointed rock masses. A three-dimensional model of a laboratory test was implemented using the Finite Element Method, with the aim to check the test observations and to furnish complete information for all stages of the shear tests.Through a systematic variation of the principal bolting parameters, their influence on the increase of the shear resistance of joints has been quantified. Formulae have been developed for the evaluation of the bearing capacity of fullygrouted bolts and for the prediction of the required shear displacements.