Determination method for influence zone of pumped storage underground cavern and drainage system

The construction and operation of underground cavern and drainage system for pumped storage are threatened by groundwater seepage. Numerical simulation methods are commonly used for seepage analysis of cavern and drainage system. However, the method for determining the influence zone of the cavern and drainage system is unclear. The model range is difficult to confirm, and the accuracy of the analysis results is unwarranted. In this study, the engineering and geological characteristics of 56 operational pumped storages were summarised. Numerical simulation experiments were conducted based on steady seepage analysis of simplified pumped storage with cavern and drainage system. The influences of the model range on the groundwater level and flow rate of the cavern and drainage system were investigated, and a method for determining the influence zone was proposed for the cavern and drainage system. The results indicated that unclear influence zone of the cavern and drainage system existed in numerous pumped storages. Moreover, a small model range strongly overstated the results regarding the flow rate and groundwater level, as the groundwater drawdown at the computation boundary was ignored. Increased influence factors, including the right and left bank groundwater surface slope ratio, maximum water head depth above the cavern, and volume of the cavern, delayed the stable tendencies of the changes of the flow rate and groundwater level with an increased model range. With a receivable flow rate threshold, the proposed method could be used to predict the influence zone for the cavern and drainage system, and the optimal model range could be confirmed to improve the calculation accuracy of seepage analysis.