The macro and micro mechanical responses of the surrounding rock influenced by roadway contour excavation

Abstract

The challenge faced by roadway excavation methods lies in minimizing disturbance to the surrounding rock while maintaining driving speed. To minimize damage to the surrounding rock during roadway excavation, this study proposes a method of unloading the roadway contour to sever the connection between the excavated target rock mass and the retained surrounding rock mass. This approach initiates the propagation of cracks within the targeted rock mass, thereby releasing internal energy to facilitate rapid excavation. Through laboratory testing of contour excavation and coupled numerical testing of PFC3D-FLAC3D, the fracture mechanism of surrounding rock in roadway contour excavation is elucidated, and the impact of geometric parameters of contour excavation on surrounding rock disturbance is examined. The findings indicate that contour excavation does not result in structural impairment to the entire coal body, but instead leads to the formation of internal macroscopic fractures. The AE parameters (RA-AF total statistics, cumulative ringing count, cumulative energy), the range of high strain field, and the degree of internal fracture of the sample all exhibit a significant decrease as the length of cyclic excavation (LCE). This is evidenced by a decrease in development depth of roof cracks from 0.43 m to 0.20 m and a 33% reduction in the number of cracks. Selecting a lower LCE has the potential to substantially mitigate the adverse effects of contour excavation on the surrounding rock mass. The inner rock mass of the excavation target exhibits a reduced contact field, leading to a noticeable deterioration in the strength of the rock mass, thereby creating favorable conditions for subsequent cutting operations. The contour excavation method has the potential to mitigate the severe damage caused by traditional roadway excavation, transforming it into a more controlled and shallow cracking process. This allows for the implementation of precise local support design.