Calculation of grout compressive bearing capacity for compression anchor in rock mass

The lateral confinement of the rock mass can significantly enhance the grout compressive bearing capacity of compression anchors. However, this bearing capacity is difficult to quantify. Current specifications adopt empirical calculation methods, which tend to result in large deviations in calculation results. To address the aforementioned challenges in quantitative calculation, this paper develops a mechanical model that considers limited cracking depth of the rock mass surrounding the grout, derives a method for calculating the grout compressive bearing capacity, and systematically analyzes the influences of relevant parameters. The results indicate that when limited cracking is allowed in the surrounding rock mass, the axial stress sustained by the grouted body increases significantly. This stress shows a marked increase with the propagation of crack depth, ultimately reaching the compressive bearing capacity at the critical cracking depth. Under identical crack depths in the rock mass, the axial stress sustained by the grouted body significantly increases with the elastic modulus of the grout and the tensile strength of the rock mass, while it decreases notably with an increase in the Poisson's ratio of the grout and the elastic modulus of the rock mass. In contrast, the radius of the reinforcing bar and the Poisson's ratio of the rock mass have negligible effects on the axial stress of the grouted body. To verify the method proposed in this study, field tests were conducted in moderately weathered granite. Through comparative analysis, the calculated results from this study are slightly larger than the measured values, but the overall trend is consistent with a high degree of agreement, which verifies the validity of the proposed method. This method provides valuable references for further theoretical research and engineering design related to the grout compressive bearing capacity of compression anchors.