一种确定超固结弱透水层水力参数的方法

A method for determining hydraulic parameters of an overconsolidated aquitard

弱透水层是含水层系统的重要组成部分。弱透水层的渗透系数K_v和弹性贮水率值S_(ske)对研究地面沉降及地下水资源评价具有重要的意义。在相邻含水层降深随时间周期性波动的条件下,推得了超固结弱透水层中无量纲形式的降深解析解,并基于该解析解进一步得到了超固结弱透水层累计变形量随时间变化的理论曲线。由于弱透水层的低渗透性,其变形总是滞后于相邻含水层的降深变化。根据弱透水层变形的滞后时间与含水层降深波动半周期的关系,提出了一种用以确定超固结弱透水层垂向渗透系数和弹性贮水率的方法,该方法对于弹性变形的超固结土具有很好的适用性。使用该方法之前,首先要根据分层标和水位资料确定含水层降深的变化周期以及弱透水层变形的滞后时间。应用该方法确定了上海地区f_(10-7)分层标处第2弱透水层的水力参数为K_v=4.12×10^(-10)m/s,S_(ske)=1.07×10^(-4) m^(-1)。经实例计算结果具有一定的可靠性。

Aquitard is an important part of the subsurface aquifer system. Hydraulic parameters of an aquitard, including the vertical hydraulic conductivity Kv and elastic specific storage Sske, are of great importance for the investigation of land subsidence and groundwater resources evaluation. An analytical solution for the flow in an overconsolidated aquitard is derived in dimensionless form under the condition of drawdown in adjacent aquifers fluctuating cyclically with time. The theoretical curve of cumulative deformation of the aquitard versus time is further derived in dimensionless form as well. Due to the low permeability of the aquitard, its deformation lags behind water level changes in adjacent aquifers. The relationship between the time delay in deformation and half cycle of aquifer drawdown is derived. Then a new method is proposed for estimating Kv and Sske. This method can be applied to an overconsolidated aquitard demonstrating elastic deformation. Before using the new method, the half cycle of cyclical aquifer drawdown and the time delay in aquitard deformation should be determined according to observed extensometer and hydrograph data. The new method is applied to obtain Kv and Sske of the second aquitard at the f10-7 extensometer site in Shanghai area. Field test results demonstrated that Kv and Sske are, respectively, 4.12 × 10^-10 rn/s and 1.07 × 10^-4 m^-1. The results are verified to be reliable.