Study on the Structure and Mechanical Properties of an Innovative Type of Yielding Bolt in Squeezing Surrounding Rock Tunnel

Abstract

To address the challenges of large deformation, prolonged deformation time, and inadequate support force in squeezing surrounding rock tunnels, a novel graded yield bolt has been developed. The mechanical properties of this new yield bolt were investigated through laboratory tests and numerical simulations. The analysis focused on the effects of the wall thickness of both large and small gradient sleeves, as well as the length and inclination angle of the resistance‐increasing head on the mechanical properties of the bolt. Furthermore, based on deformation classification and utilizing numerical simulation software, the supporting effectiveness of the yielding anchor under various deformation levels was examined. The results indicate that the new yielding bolt exhibits a graded yielding function, which can be categorized into three stages: elastic deformation, first yielding, and second yielding. The yield load value increases with the wall thickness of the large gradient sleeve and the length of the resistance‐increasing head. The yield load initially increases and then decreases with increasing wall thickness of the small gradient sleeve, and it decreases with an increase in the inclination angle of the resistance‐increasing head. Regardless of the deformation grade, the performance of the new yield bolt surpasses that of conventional bolts, with the advantages of the new yield bolt becoming more pronounced at higher deformation grades.