河谷演化控制下的覆盖型岩溶区地下岩溶分层——以白石窑水电站为例

Underground Karst Stratification in Covered Karst Areas Under Control of River Valley Evolution: A Case Study of Baishiyao Hydropower Station

覆盖型岩溶区的河谷地下岩溶总体上具有上强下弱的垂直分带特征,但这种垂直分带的成因众说纷纭,给工程实际运用带来不少困惑。为此,通过找出河谷由峡谷期向盆地期演化过程的最大岩溶作用水头、最大强化作用水头和最新强化作用水头等特征作用水头,把河谷岩溶的多期叠加成层模型简化为河谷地下岩溶的三期叠加强化模型,即由下至上划分为深层孤立洞隙层、中层强化岩溶层和现代岩溶影响层。借助于白石窑水电站为工程实例进行了河谷演化及其地下岩溶剖面分层分析,提出坝基现代岩溶影响层发育强烈,是防渗的重点,岩溶最大防渗深度进入中层强化岩溶层,大大减少坝基岩溶渗漏防渗处理工程量,节约工程投资。经多年渗漏量观测,防渗效果良好。覆盖型岩溶区地下岩溶分层研究具有一定的应用意义,可供类似的坝基防渗工程参考和使用。

The underground karsts of the river valley in the covered karst area generally have the characteristics of vertical zoning with a strong upper part and a weak lower part.The causes of such vertical zoning are still unclear, which brings difficulties to practical engineering applications.Therefore, the multi-phase superimposed stratification model of river valley karsts is simplified to the three-phase superimposed strengthening model of underground karsts of the river valley.The simplification is conducted on the basis of finding out the characteristic karstification heads such as the maximum karstification head, the maximum strengthening head, and the latest strengthening head in the evolution process of the river valley from the canyon period to the basin period.The three-phase superimposed strengthening model is divided into the deep isolated cave layer, middle enhanced karst layer, and modern karst-influenced layer from bottom to top.Taking the Baishiyao Hydropower Station as an engineering example, this study analyzes the evolution of the river valley and the stratification of the underground karst profile.It is proposed that as the modern karst-influenced layer of the dam foundation is strongly developed, it is the key point of anti-seepage.The maximum anti-seepage depth of karsts should enter the middle enhanced karst layer to greatly lessen the anti-seepage treatment of karst leakage of the dam foundation and save engineering investment.Years of leakage observation suggest that the anti-seepage effect is good.The underground karst stratification in the covered karst area is of certain practical significance and can be used as a reference for the seepage prevention engineering of similar dam foundations.