Deformation mechanism and mechanical response of coal mine roadway roof in the unsupported area during rapid tunneling

Aiming at the prominent problems in the rapid excavation of coal roadways, namely the complex factors affecting the stability of composite roofs and the restricted excavation efficiency caused by an overly small unsupported roof distance, this study takes the 1211(1) transportation roadway of Guqiao Coal Mine in Huainan Mining Area as the research object. Through numerical simulation, the influence of unsupported roof distance on roof stability is quantitatively analyzed. Considering the actual stress characteristics of the composite roof in the unsupported area of coal roadways, a thick plate mechanical model with three fixed edges and one simply supported edge is established. Based on elasticity theory, the deflection expression for any point on the composite roof is derived, the sensitivity of deflection and subsidence of the immediate roof in the unsupported area is analyzed, and the response surface methodology is used to determine the key factors dominating the deformation of the unsupported roof and their coupling relationships. The results show that under constant geological and engineering conditions, the unsupported roof distance is the most critical factor governing the deformation and failure of the unsupported roof; when it exceeds 2 m, the roof subsidence rate increases sharply and the difficulty of roof control increases significantly. Combined with the engineering geological conditions of the roadway, the optimal unsupported roof distance is determined as 1 m. After adopting the “one-cycle excavation and one-cycle support” protocol and high-prestressed bolt-cable combined support, the average roadway excavation speed is increased from 6 to 15–18 m/d, and the roof remains stable and controllable throughout the excavation process, verifying the rationality and engineering practicability of the research findings.