承压含水层中非达西径向稳定流动抽水模拟试验

为分析抽水井附近水流的非达西流动,采用装填均质河砂的扇形密闭水槽模拟承压含水层,开展了外边界水头恒定条件下的定流量抽水试验,获得到了水流稳定流动时的水头降深曲线。通过比较试测水头降深与达西流动理论水头降深,以及比较相邻两压力传感器之间的平均水力梯度与相同流速下的达西水力梯度,进行了非达西流动的判别,比较结果发现本试验条件下存在明显的非达西流动现象。同时,应用基于Izbash方程的非达西稳定流动水头降深解析解,对不同流量下的试验数据进行了拟合分析,发现抽水流量对非达西稳定流动的Izbash方程系数值影响较小。通过不同平均方法获得了描述本试验中非达西流动的Izbash方程系数的适宜取值为k=7.17×10-7,n=1.65,此时不同抽水流量下拟合水头降深曲线与试测水头降深曲线吻合良好,表明基于Izbash方程的非达西稳定流动水头降深解析解可较好地描述抽水井附近的非达西径向稳定流动。

A laboratory experiment on radial non-Darcian flow in confined aquifer under steady-state conditions

In order to analyze the non-Darcian radial flow near the pumping well in confined aquifer, a series of constant pumping tests were conducted in a converging permeameter of 60° under constant head at the inlet and outlet boundaries in laboratory. The tank was filled with river sand with diameter of 0.3~0.6 mm to simulate the confined aquifer. Pressure transducers were installed in different distances along the radial direction, and the measurement of the pressure head was used to obtain the steady state drawdown curves in different radial distances. Both the measured drawdown and the mean hydraulic gradient between two adjacent pressure transducers were used to identify the occurrence of non-Darcian flow. The results show that non-Darcian flow occurs in the test with different pumping rates. The analytical solution of non-Darcian steady state flow on the basis of the power function was used to fit the experimental drawdown data. The results show that the pumping rate has slight effect on the values of the coefficients of the Izbash equation. With the average coefficients values, i.e. the non-Darcian hydraulic conductivity k=7.17×10-7 and the power index n=1.65, the calculated drawdown match the measured data well for different pumping rates, indicating that the analytical solution is capable of describing the radial non-Darcian flow.