Abstract:
A selfexpanding anchor rod with more HCSAtype expansion agent has been developed to increase the ultimate pullout resistance of the anchor rod. But for media with low rigidity and easy deformation,the main factors to increase the anchoring force of selfexpanding bolts are still uncertain. In order to prove the lifting effect of the selfexpanding anchor rod in the anisotropic initial insitu stress soft rock,three kinds of wall thickness steel pipes are used to simulate surrounding rock with different radial stiffness,and different expansion agent content is added to the inside of the steel pipe. Selfexpanding anchoring material,by testing the evolution law of the radial expansion stress and deformation of the anchoring structure,the analytical formula for the expansion stress and displacement of the selfexpanding anchor rod in the anisotropic initial ground stress is deduced,and the stress,deformation and steel pipe are established. The relationship between wall thickness and expansion agent content.Based on the ABAQUS numerical simulation method,the formula is verified to be consistent with the experiment,and the expansion law of the selfexpanding anchor in the lowrigidity rock and soil body and the improvement effect of the ultimate pullout resistance are obtained through the pullout simulation.The research results show that:① When reducing the wall thickness of the steel pipe,the stressdeformation change trend of the selfexpanding anchor rod with different expansion agent content is highly consistent. When the content of the expansion agent is large,the steel pipe wall thickness is reduced,and the radial expansion stress is only reduced. 8.6%,but the radial deformation increased by 117%,indicating that the enlarged head effect is more obvious. ② The ultimate pullout resistance of selfexpanding bolts with an expansion agent content of 25% is similar in the surrounding rock with different stiffness,but the selfexpanding bolts have a significantly greater increase in the energy before the peak of the pullout force in relatively high surrounding rocks.Reaching 819%. It shows that the frictional force has a better effect on the anchoring performance of selfexpanding bolts than the expansion effect. Finally,a design formula for expansion agent content based on the strength parameters of weak surrounding rock and initial stress is established,and field tests are carried out on a rock slope. The test results verify the feasibility of the formula.