Evolution of 3D Stress Arch in Surrounding Rock During Segmented Excavation of a Circular Tunnel

Investigating the evolution of the pressure arch in rock masses undermining conditions is crucial for safe tunnel excavation. This study developed a mechanical model of the surrounding rock pressure arch, inspired by a domestic hydropower station's water diversion tunnel project. The characteristics of pressure arch formation and elastic energy changes during segmented excavation were examined through theoretical and numerical simulations. Results show that as excavation progresses, energy in the surrounding rock transfers, increasing energy concentration and the affected area. A symmetric pressure arch forms due to the overlying strata's gravity. The horizontal axis lengths of the pressure arch's boundaries exceed the vertical axis lengths, and the arch zone's thickness continuously increases. The mining-induced unloading effect releases elastic energy from the roof, accumulating within the pressure arch's inner boundary. When the working face reaches 30–40 m, the inner and outer boundary heights increase while the span decreases, indicating effective stress distribution and transfer by the arch structure. The arch foot, typically an area of energy concentration, determines the tunnel roof's failure characteristics along its strike. Stress concentration and elastic energy at the arch foot are critical for predicting the surrounding rock's stability in the tunnel roof.