Analytical study of steel bolt profile and its influence on bolt load transfer

Abstract

The load transfer capacity of fully grouted steel bolts has been the subject of research for the past three decades. Experimental studies have confirmed that the bolt surface profile plays an important role in load transfer of fully grouted rock bolting systems. This research work seeks to lay the foundation for the role of the bolt profile in rock bolting mechanisms. A shear failure surface which is parallel to the bolt surface has been assumed and investigated using stress analysis. The stress field within the resin introduced by the axial load of the bolt has been formulated based on the half space theory, and the influence of the bolt profile configuration on rock bolting failure is identified under Mohr–Coulomb's failure criterion. Parametric studies show that bolts with smaller rib face angles or smaller profile height to length ratios are favourable to transfer load radially. Hence, they should be used in hard rock environments. On the contrary, bolts with large rib face angles and higher rib height to length ratios will transfer the major part of axial load into the resin in a direction parallel to the bolt surface. Thus, they should be used in soft rock conditions.