ABSTRACT:

The resistance to lateral shearing is an important yet poorly understood component of the reinforcement provided by fully grouted rock bolts. Numerical models such as the FLAC3D finite difference code can be used to investigate the effect of shear resistance on roof stability. However, calibrating a numerical model to realistically simulate the complex processes that occur at the shearing interface can be challenging. This paper outlines recent work in which a systematic procedure was developed to match numerical model results to the measured shear response of fully grouted rock bolts. In this paper, results of the shear tests of reinforced rock joints published by Haas [1] and McHugh and Signer [2] were modeled with FLAC3D to identify and calibrate the critical parameters of the rock bolt model both in tension and in shear. In particular, the model response to changes of the bolt/joint angle and the surrounding rock type were calibrated and compared with the published tests results. It was found that the structural pile element in FLAC3D can be used to accurately represent grouted bolt shear and tensile behavior. The best approach to calibrate the FLAC3D structural pile element model was found to be: 1) select the structural element segment size less than half of the active length, 2) calibrate the shear spring cohesion and stiffness based on pull test results, and 3) calibrate the normal spring cohesion and stiffness based on shear test results. Using this method, the calibrated model results fit the test results very well.

1. INTRODUCTION

Immediately after development of an underground entry, the virgin stress field is redistributed to achieve a new stress equilibrium. Fully grouted roof bolts provide reinforcement by providing a resistance to both the vertical and horizontal displacements of the roof beam.

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