Abstract: The theoretical and technical principles of self-expanding bolt with large amounts of expansion agents were first proposed, and its economic benefits and the effect of improving the ultimate pullout resistance were addressed. However, excessive expansion agent would generate cracks in the surrounding rock caused self-expanding bolt, and it is highly important to determine the limit content of the expansion agent. Therefore, two prerequisites for the application of self-expanding bolt were proposed, and experimental study were performed based on the clarification of experimental purposes from two levels. The former one is expansion cracking method. Firstly, the bursting and cracking test of surrounding rock was carried out to obtain the change law of normal stress at the interface and the failure law of surrounding rock. The evolution law of the cracking and failure of the moderately weathered argillaceous siltstone under the action of self-expanding anchor body was also explained. A calculation models of radial self-expansion stress at different positions were established. Based on the radial expansion stress of the contact surface, a prediction model of the critical content of the expansion agent of the anchor body was obtained, and the critical content of the expansion agent of the moderately weathered argillaceous siltstone was predicted to be 28.98%. The latter one is elastic analysis method. Based on the problem of uniform compression of circular holes in the infinite medium and stress concentration at the edges of the holes, a model for the expansion and failure of surrounding rocks under the action of self-expanding anchors body was established. A set of formulas for predicting the stress distribution of surrounding rock under the action of self-expanding anchors body was obtained, and a critical cracking equation for surrounding rock under radial expansion stress was derived. In order to reduce the field test cycle and cost, a formula for predicting the tensile strength of the moderately weathered argillaceous siltstone was established based on the acoustic-rebound value. Finally, the parameter correction of the critical cracking equation is completed based on the incompleteness of the surrounding rock and the softening effect of the surrounding rock soaking. Combined with the critical admixture value, the safety reserve coefficient was introduced, and the design formula for the limit content of self-expanding anchor body was established. According to the design formula, it is calculated that the limit content of the self-expanding anchor solid expansion agent for moderately weathered muddy siltstone is 26.5%. The paper can provide technical support for the application of self-expanding bolt in geotechnical, mining and water conservancy fields.

Key words: self-expanding anchor body, limit content of expansion agent, radial expansion stress, rock tensile strength, ultrasonic- rebound combined method