Analysis of unsteady seepage field and surrounding rock stability of underground cavern excavation

Abstract

During the cavern excavation, the underground seepage boundaries are constantly changing, and the seepage field is in an unstable state. Meanwhile, most underground caverns are not constructed with grouting curtains and drainage holes during excavation. The caverns are subject to high osmotic pressure, which is prone to water inrush and seepage failure. Based on the Signorini’s type variational inequality, the variable bandwidth iteration method is proposed to effectively simulate the potential overflow boundary in unsteady seepage by loosing restrictions for non-overflow nodes. The advantage of this methods over traditional methods is fast convergence and relatively high accuracy. Subsequently, a simulation method of unsteady seepage field in the cavern excavation process is proposed, and following this we applied the corresponding unsteady seepage load to the surrounding rocks to evaluate the stability of the cavern. The above methods were further applied to the excavation process of Azad hydropower station powerhouse. The results show that during the cavern excavation, the groundwater surface gradually decreases and the flow rate of the cavern generally increases. In addition, although the osmotic load has an adverse effect on the stability of the cavern, the impact is not significant. This research has proofed guiding significance for maintaining stability throughout the underground cavern excavation process.