Experimental Study on Pull-Out Behavior of Wedge-Grouted Rockbolt in Wind Turbine Tower Foundation

To investigate the the pull-out behaviors of wedge-grouted rockbolts and grouted rockbolts in strongly weathered and moderately weathered rocks, the rockbolts with lengths of 8.0 m, 10.5 m and 13.0 m were tested under freeze–thaw cycle and cyclic load. The test result shows that the minimum anchoring length of wedge-grouted rockbolt is less than 3.0 m and of grouted rockbolt is less than 4.0 m in the strongly weathered or moderately weathered rock. The effect of the wedge head on restricting the deformation of the rockbolt is not obvious when the anchoring length is less than 6.0 m. Freeze–thaw cycle had little effect on the stiffness and deformation of the two kinds of rockbolts. The wedge-grouted rockbolts have better deformation performance than the grouted rockbolts. The bonding force between the rockbolt and the grout or the grout and the surrounding rock is greater than the tensile strength of the rockbolt. Furthermore, the calculation models of shear stress and axial strain can provide reasonable predictions for two kinds of rockbolts, and the development trends of strain and shear stress under different pullout loads were calculated.