| 摘要: | 多深度微水試驗（multilevel slug test，MLST）利用單或雙封塞將井篩段區隔使水流僅能從測試段自由進出，更換測試段長度（ls）及封塞位置可獲得該井測試段周圍的水力傳導係數，K(z)。本研究目的探討MLST之測試段長度變化對推估K值的影響；在南部高滲透性砂質含水層井場以固定ls（=0.41m）於26個深度進行MLST，MLSTs之K(z)結果與地層資料柱狀圖比較，與現場地質情形大致符合，因此MLST可有效幫助了解該井場之K值空間上分布狀況。在三個特定深度分別變換5種測試段長度（ls=0.26、0.36、0.41、0.61和0.76m），由分析結果顯示當ls小於一個極限值（本場址ls≦0.41m），水位壓力資料不隨ls變化而改變，已無差異性，代表對垂直異質性變化已不敏感，然而K值推估卻受到形狀因子（F）影響，F與ls成正比，以致K值無法收斂而不相同；建議未來應發展新的形狀因子，當ls越小時F值會收斂趨於一個極限值。此外，本研究之全層貫穿整段井篩長度的平均K值，與幾何、調和、平方及數學等任一種數學平均算法之 比較皆偏小，但由文獻可知全層貫穿整段井篩長度之抽水試驗所推估平均K值卻可代表MLSTs之 ；需要更多研究來解決這項問題。 This study investigates the impact of the tested interval length ls of the multilevel slug test (MLST) on the estimates of hydraulic conductivity, K. In a single well located in a sandy aquifer in southern Taiwan, 26 MLSTs using a constant ls (=0.41 m) were conducted at 26 different depths, respectively. The estimated K(z) agrees well with the geologic interpretation made from core samples. At three specific depths, MLSTs were conducted using five tested screen lengths; i.e., ls = 0.26, 0.36, 0.41, 0.61, and 0.76m. The test responses do not change with ls when ls≦ 0.41m, indicating that the variation of vertical heterogeneity over a relatively small scale (e.g., less than 0.41 m) is insignificant. However, the estimated K(z) varies with ls when ls≦0.41 m, because the shape factor used depends on ls no matter how small ls is. Therefore, there is a need to derive new a shape factor that converges to a limiting value when ls is small. Moreover, Kavg determined using the full screen length is smaller than the geometric, harmonic, quadratic, or arithmetic mean of K(z). That is, Kavg is not representative of a mean value of K(z). This is in contradiction to literature where hydraulic conductivity estimated from a pumping test of a fully screened pumping well represents certain averaged value of K(z) determined from MLSTs. More research is needed to solve this issue. |
