考慮井部分貫穿效應之定水頭試驗

Abstract

進行定水頭試驗時，需在抽水井中維持固定的水位高，並同時測量觀測井內洩降隨時間的變化。本研究考慮在非侷限含水層裡有一部分貫穿井作定水頭試驗，推導水層水位分佈之半解析解。本研究首先將部分貫穿井濾管部分設為定水頭邊界、盲管部分設為不透水邊界，接著以自由液面條件來描述非侷限含水層的上邊界，最後利用分離變數法及拉普拉斯轉換，推導得半解析解。此解可用來產生無因次洩降與時間之關係曲線，探討部分貫穿井在水層中所造成的垂直流問題，亦可利用試驗數據來推求水層的參數。

The constant head test is to keep constant water level in the pumping well while the drawdown into the observed well is measured. This study derives a semi-analytical solution for drawdown distribution during constant-head test at a partially penetrating well in an unconfined aquifer. The constant-head condition is used to describe the boundary along the screen while no-flow condition is employed to describe the boundary along the casing of the well. In addition, a free surface condition is utilized to delineate the upper boundary of the unconfined aquifer. The Laplace domain solution is then derived using separation of variables and Laplace transform. This solution can be used to produce the curves of dimensionless drawdown versus dimensionless time to investigate the effects of vertical-flow caused by the partially penetration well and free surface boundary in an unconfined aquifer or to identify the aquifer parameters from the data of constant-head test.