The experimental determination of shear stress distribution along fully grouted rock bolts with different bond lengths subjected to pull testing

Abstract

In this study, laboratory pull tests of rock bolts were conducted to verify and update existing stress transfer models. The rock bolt samples in the study had different bond lengths that were fully encapsulated in cementitious grout with different water-cement ratios. The test results show that the existing models do not correctly describe the shear stress distribution on the bond length in some loading stages. Three new models were proposed for the distribution of shear stress along the bond length. The first model describes cases where the bolt sample has a bond length that is much longer than the critical bond length, the second model describes cases where the bolt sample has a bond length slightly shorter than the critical bond length, and the third model describes cases where the bolt sample has a bond length that is much shorter than the critical bond length. In these models, the bolt is fully debonded along the section between the borehole collar and a depth of approximately one bolt diameter (db). The bolt is then partially debonded and the residual shear stress on the bolt increases with depth. In the first model, the shear stress reaches the maximum at a depth of approximately 3db. The shear stress then attenuates to zero at a depth of 25db. In the second and third models, the entire bond length is mobilized to carry load.