防渗墙作用下堤防保护区地下水动态数值模拟分析 Ⅲ:多元结构堤基条件下的数值模拟

Numerical Simulation on Groundwater Regime in Land Protected by Dyke with Cut-off Wall Ⅲ:Numerical Simulation for Dyke Foundation of Multiple Layers

对长江重要堤防的典型多元结构堤基地下水流运动进行了数值模拟。二维模拟结果表明:未被河流切割的含水层受江水位的影响很小;未被防渗墙截断的含水层受防渗墙的影响也很小;被河流切割的承压含水层与江水位关系密切,但布置半封闭式防渗墙后会制约堤防保护区地下水动态对江水位的响应,承压含水层渗透性越强,其动态受江水位影响越大,修建防渗墙后受到的制约作用也越显著;潜水含水层受江水位的影响小得多,受半封闭式防渗墙的影响也小得多。三维模拟结果说明了防渗墙端部绕渗影响:防渗墙端部绕渗会使墙端附近承压含水层动态受防渗墙的制约作用降低;绕渗对潜水含水层的作用很有限,一般可以忽略不计。与二元结构堤基相比,多元结构堤基中含水层受江水位影响较小,半封闭式防渗墙对地下水动态的影响小于全封闭式防渗墙;同样的自由绕渗条件下,半封闭式防渗墙端部绕渗影响小于全封闭式防渗墙。

The ground water movement in response to hydrological and metrological processes is simulated with saturated-unsaturated flow model for typical dyke foundation of multiple layers in lower and middle Yangtze Valley. 2D model simulation results show the ground water regime of the unconfined ＆ confined aquifer, and the regime differences under conditions with and without cut-off wall. The confined aquifer not cut by the river and not penetrated by cut-off wall would be little influenced by the river and by the cut-off wall respectively. There is close hydraulic relationship between the river level and confined aquifer cut by the river, which would be greatly restricted by cut-off wall of semi-closure type penetrating the aquifer. The higher the permeability of the confined aquifer, the more greatly the cut-off wall influences on its ground water regime. The unconfined aquifer responds less to the river water level change, and would be little influenced by cut-off wall of semi-closure type. 3D model simulation results demonstrate the influence of water flow moving around the lateral ends of the cut-off wall. It would lower the influence of the cut-off wall on the ground water regime of confined aquifer near the ends. The more permeable the confined aquifer, the more greatly the by-pass flow would appear. The influence of the by-pass flow on the unconfined aquifer is little and could be neglected. The river water level fluctuation effects less on the aquifer in the foundation of multiple layers than on that in the foundation of double layers. In comparison with the cut-off wall of closure type, the cut-off wall of semi-closure type changes less ground water regime in the area protected by dyke, and the influence of water flow moving around its lateral ends is also less.