Mechanical response and fracture behavior of rock bolts under eccentric loading

: In infrastructure engineering such as tunnels and roadways, rock bolt support technology serves as a core method for maintaining surrounding rock stability. However, bolt failures pose serious threats to both the construction and operational safety of such engineering. In response to the frequent occurrence of bolt fractures in the Hongliulin Coal Mine, fractured bolts were collected on-site and bolt's fracture characteristics were analyzed. A mechanical model of the bolt under eccentric loading was further established, revealing the mechanical mechanism behind bolt fracture and proposing two fracture modes. Finally, laboratory tests and numerical simulations were carried out to uncover the entire process of bolts from tensile yielding to fracture, clarified the mechanical response characteristics of bolt under eccentric loading. Test results show that under eccentric loading, tensile-bending fracture occurs at the bolt's tail. Eccentric loading has little influence on the elastic and yield stages of the bolt but significantly inhibits the development of the strain hardening and necking stages. Under eccentric loading, the toughness reserve energy of the bolt decreases by 46.9 % and 72.5 %, respectively. In addition, the elongation of the bolt drops from 14.06 % to 5.63 % and 2.93 % due to the eccentric load. The use of spherical washers can compensate for the angular deviation between the tray and the nut, thereby regulating the effect of eccentric loading. The findings of this study provide guidance and reference for the design of bolt support in infrastructure engineering.