基于承压含水层水力响应的溪洛渡水电工程区谷幅收缩变形预测研究

溪洛渡高拱坝位于一个向斜盆地内,区域水文地质的一个典型特征是盆地内下覆有一个完整延伸的阳新灰岩承压含水层。水库蓄水以来上下游库岸边坡发生了明显的谷幅收缩变形,主要是由于水库蓄水引起承压含水层孔隙水压力增加,从而引起灰岩地层因有效应力减小而产生膨胀,以及相对隔水层底板扬压力增加所引起的。基于承压含水层水力响应规律,建立了谷幅收缩变形反演及预测的解析模型,分别预测了在变形速率小于0.01,0.001mm/d两个收敛准则下的谷幅收缩变形收敛时间以及收敛值。所建立的反演预测模型能够较好地重现谷幅收缩变形历时曲线,反映出谷幅收缩变形与库水位变化具有高度的相关性。模型预测结果显示,溪洛渡水电工程的谷幅收缩变形已趋于收敛。

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.