非承压和非稳定抽水试验资料的有限单元分析

在抽水条件下水位随空间和时间变化的预测,依赖于潜水层的透水率和给水度的准确测定。如何利用抽水试验资料求这两种参数也是一个关键。这种相辅相成的关系是有效地开发利用地下水资源的前提。

FINITE ELEMENT ANALYSIS OF TIME-DEPENDANT PUMPING TEST DATA IN AN UNCONFINED AQUIFER

To obtain a solution for unsteady radial flow in an uncontrolled and unconfined aquifer under constant drawdown or discharge, a region is selected for finite element analysis by means of fictitious cut and subjected to flux boundary condition along the cut. This time-dependant boundary flux is expressed in terms of the unknown nodal head and then being able to cover implicitly the change of influence radius with time.The free surface in an aquifer under pumping is a moving boundary, at the end of each time step of computation, the vertical coordinate of all the nodals above the water level in the pumped well are then scaled down by a ratio of the free surface nodal elevation to its previous position, i.e. ht2*/ht1*, as a new grid for next time step.Solutions are presented by the use of dimensionless form, therefore the obtained relationships between well discharge, water level in the well and time are of general nature and can be applied by interpolation to any seepage flow problems having similar initial and boundary conditions as specified herein.Comparison of the digitally computed values of both free surface elevation and well discharge with the measured ones indicates that the flow characteristics of an unconfined aquifer can be determined only with a pumped well and without any necessity of observations wells.