Analytical Study on the Actual Mechanical Behavior of Fully Grouted Bolts in Jointed Rock Masses

Joint development in rock masses results in complicated anchoring mechanisms of fully grouted bolts. This study offers a detailed analysis of the elastic–plastic deformation evolution of the bolts. A method was developed, taking the deflecting section as a hyperstatic structure with ends rotation, to predict bolt contribution and describe bolt shear behavior by incorporating beam bending theory and the coupling effect of external loads. Assuming elastic–perfectly plastic behavior in steel, the failure process of the bolts was described. As joint shear displacement increases, the bolts initially reach their elastic limit at the zero-shear force point, forming a plastic hinge under combined tension and bending. The plastic deformation zone then expands, leading to full yielding at the bolt–joint intersection under combined tension and shear, and the instability of the hyperstatic structure. Comparative analysis with other models and experimental data reveals accuracy improvements in bolt contribution by 2.0%–11.87% with corresponding end rotational angles from 0.090° to 4.701°, and the length of the deflecting section obtained with the developed method is closer to the test results than other predictions.