Prediction of valley shrinkage deformation in Xiluodu Hydropower Plant based on the hydraulic responses of a confined aquifer

The Xiluodu high-arch dam is situated in a synclinal basin, and one of the typical hydrogeologic features is that there exists an intact and regionally extended confined aquifer consisting of Yangxin limestone buried beneath the riverbed. Remarkable valley shrinkage deformation has been detected on both the upstream and downstream of the dam since the impoundment. The valley shrinkage deformation is speculated to be due to the expansion, which is associated with the decrease in the effective stress of the Yangxin limestone formation and the increase in the hydraulic uplift pressure imposed on the bottom plane of the relatively impervious formation, which result from the increase in pore water pressure when responding to the change of the reservoir stage. Based on the patterns of hydrualic responses of the Yangxin confined aquifer, an analytical model is established to calibrate and predict the valley shrinkage deformation of each measuring line. Furthermore, the convergence time and values of each line are predicted under two prescribed convergence principles with the respect of deformation rate, i.e., less than 0.01 mm/d and 0.001 mm/d. Overall, the proposed analytical model yields fairly good calibration performance, revealing that the valley shrinkage deformation is highly correlated with the change of the reservoir stage. The prediction results demonstrate that the valley shrinkage deformation of the Xiluodu Hydropower Plant is approaching the convergence condition.