Pull-Out Performance and Load Transfer Mechanism of Pressure-Type Rock Anchor with Grouted Interface

Pressure-type rock anchors transfer tendon force to the grouted body through an end bearing plate, placing the grout predominantly in compression; however, their load-transfer mechanisms and axisymmetric stress-field distributions under varying loads remain insufficiently understood. This study combines laboratory physical model testing and three-dimensional numerical simulations to investigate the vertical pull-out performance and load-transfer characteristics of pressure-type rock anchors. Scaled pull-out tests were first conducted to investigate the effects of anchorage length and anchor rebar diameter on load–displacement behavior and ultimate bearing capacity. A finite element model was then established and validated against the experimental results. The results indicate that the axial force of the grout exhibits a highly non-linear distribution, reaching its peak at the borehole bottom. An effective load-transfer length of approximately 3.5 to 3.7 m is identified, within which 90% of the axial force is dissipated. Unlike tension-type anchors, the anchor rebar functions as an integral tension-transmission member, maintaining a near-constant axial force profile outside the bottom boundary zone. Furthermore, the surrounding rock exhibits distinct axisymmetric responses, characterized by funnel-shaped vertical displacement diffusion and bulb-shaped principal stress contours. These findings provide a theoretical framework for optimizing anchorage length and understanding the symmetric mechanical boundary responses of pressure-type anchors in rock mass stabilization.