Fully Grouted Rock Bolts: An Analytical Investigation

This paper analytically investigates the performance of fully grouted rock bolts in typical scenarios, including pullout test, suspending loosened block, and increasing joint aperture, respectively. The interface shear stress distribution follows the model proposed by Li and Stillborg (Int J Rock Mech Mining Sci 36:1013-1029, 1999), while the axial behavior of the bolt shank obeys the elasto-plastic (yielding-hardening) constitutive model of steel. Three different failure modes are taken into account: tensile failure of bolt shank, bolt shank being pulled out along the bolt/rock interface, and loss of face plate. The evolution of the interface shear stress and the axial tensile stress are examined for both long and short bolts under displacement and load boundary conditions. The derived charts are able to predict the load capacity of fully grouted bolts in pullout test, the minimum length requirement of the bolt to suspend a loosened block, and the maximum allowed opening displacement of a rock joint for a fully grouted bolt. In addition, different potential failure modes are specified. Full range load-displacement curves are produced and compared for various failure modes. The derived charts could be directly used in rock-bolting design.