The Stress Distribution around Fully Grouted Rockbolts in a Fractured Rock Mass

A fully grouted rockbolt is the most common method for rock-mass reinforcement, of which stress distribution is an important basis for the design of supporting works. To investigate the stress distribution around a rockbolt in a fractured rock mass, in this study, laboratory-similar material tests and numerical simulation [discrete-element software PFC2D (two-dimensional Particle Flow Code, version 3.0)] were conducted on rockbolt-supported intact and fractured rock masses, taking the Hongtoushan Copper Mine as the background. By comparing the stress distribution of rockbolts in intact and fractured rock masses, fractures were found to affect the stress distribution around a fully grouted rockbolt. When a certain rock deformation is reached, a tensile stress relief zone is formed in the rockbolt near the fracture, leading to lower stress at this location compared with the rockbolt on the two sides of the fracture. Meanwhile, the stress distribution curve exhibits double peaks instead of a single peak, and the peak stress in the deep part gradually exceeds that in the shallow part. When the surrounding rock mass is damaged and becomes unstable, the stress in the rockbolt near the fracture suddenly increases, becoming the only peak in the stress distribution curve. Therefore, field monitoring of the stress in the rockbolt shall be conducted. If the stress in the rockbolt near a fracture gradually changes from the local minimum to the local maximum, instability or failure of surrounding rock mass is imminent, and safety measures should be implemented.