深厚覆盖层坝基水文地质结构控渗机理研究

STUDY ON SEEPAGE CONTROL MECHANISM OF HYDROGEOLOGICAL STRUCTURE IN DEEP OVERBURDEN DAM FOUNDATION

厚度大且为强-弱-强渗透性组合的覆盖层在我国西南河流中分布较广。为研究此类夹层型水文地质结构覆盖层中坝基渗流场的特征及其影响因素,利用Visual MODFLOW模拟了给定覆盖层厚度下强弱渗透性层组的不同渗透性比值、不同厚度比值,和变覆盖层厚度下不同弱透水层厚度这两种类型16种工况下的渗流场,通过监测坝基渗流场中弱透水层顶底板的水头差和水力坡度,研究弱透水层渗透性和厚度对渗流场的影响。结果表明:强-弱-强夹层型水文地质结构的坝基平面渗流场受上层强透水覆盖层性质控制;给定覆盖层厚度工况中,弱透水层顶底板的水头差与强弱透水层渗透性比值相关,两者先表现出正相关的关系,当强弱透水层渗透性比值大于500时,弱透水层顶底板的水头差变化不再明显;变覆盖层厚度工况中,弱透水层顶底板的水头差也呈现出先增大后趋于稳定的趋势,转折点发生在弱透水层厚度20m的工况条件下;变覆盖层厚度工况中水力坡度则有着随着弱透水层厚度增大而变小的规律。综上所述,在夹层型水文地质结构中,弱透水层厚度与渗透性对渗流场起控制作用。研究结果可为深厚覆盖层河谷区的水电水利工程坝基水害防治提供依据。

The overburden layer with large thickness and strong-weak-strong permeability combination is widely distributed in valleys of southwestern China.This paper studies the characteristics and influencing factors of the dam foundation seepage field in the interbed type hydrogeological structure.It uses Visual MODFLOW to simulate the seepage field of 16 working conditions with two types of constant thickness and variable thickness.It analyzes the influence of permeability and thickness of the weak permeable layers to the seepage field morphology,by the change of head difference and hydraulic gradient of roof and floor of the weak permeable layer.The paper reaches the following conclusions.The plane seepage field of dam foundation is strongly influenced by the property of strong permeable cover in upper layer.In constant thickness condition,the head difference of weak permeable roof and floor is related to the permeability ratio of strong permeable layer to weak permeable layer.When the permeability ratio of strong and weak permeable layers is greater than 500,the head difference of weak permeable roof and floor changes slightly.In variable thickness condition,the head difference of weak permeable roof and floor increases with the thickness of weak permeable layer.When the thickness of weak permeable layer is greater than 20m,the head difference changes weakly.Hydraulic gradient decreases with increasing thickness of weak permeable layer.In conclusion,the thickness and permeability of the weak permeable layer play a controlling role in the seepage field in the interlayer hydrogeological structure.The research results can provide support for water prevention and control of dam foundation of water conservancy and hydropower projects in deep covered valley.