A novel method for determining the timing of support for roadway surrounding rock: the stress mutation method

The selection of the timing for roadway surrounding rock support is fundamental to ensuring the effectiveness of support. Previous studies on support timing primarily utilized the convergence-confinement method. However, the support timing determined by this method corresponds to a period where surrounding rock displacement is within a rapidly increasing stage of instability, making it difficult to guarantee the safety of support operations. Based on the continuous cusp mutation theory, this paper proposes a novel method for determining the optimal support timing for roadway surrounding rock-the stress mutation method. Firstly, using the stress from the monitoring cross-section during roadway excavation as the state variable, a continuous cusp mutation analysis model is established. Then, this model is employed to identify the location of stress mutation, pinpointing the critical instability point of the surrounding rock as the optimal support timing. Finally, the safety factors of the surrounding rock and the support structure are solved to evaluate the engineering stability achieved when supporting according to the new method. The rationality of the support timing determined by the new method is validated through an engineering case study. The results demonstrate that, compared to the convergence-confinement method, the support timing determined by the stress mutation method resulted in a displacement increment of the surrounding rock that was only 33.7% of that observed with the convergence-confinement method, while maintaining comparable levels of safety in both surrounding rock stability and support structure performance. Moreover, the collapse probability was reduced by 67%. The stress mutation method effectively circumvents the safety hazards associated with rapidly increasing surrounding rock displacement, ensuring support effectiveness. This demonstrates its stronger scientific validity and rationality. The findings provide a novel perspective for selecting support timing in roadway surrounding rock engineering.