本研究以美國水土保持局設計規範為依據，建立砂及礫石土層地下水觀測井回填濾料粒徑設計方法。首先收集了常見的設計規範，經歸納後推得濾料粒徑 D15上下限，並假設粒徑 D10至 D90之間呈對數直線分佈，推得 D10、D60及 D90與均勻係數 D15之公式，再以線性公式推得 D0及 D100，並以實例進行說明設計方法。隨後以無沖蝕濾料試驗進行規範驗證，發現美國水土保持局規範D15下限值4D15可成為良好的濾料，但上限值 4D85 試驗結果不佳；而若採用現行國內施行方式時，若 時，建議降低濾料粒徑之下限值，以避免土壤細粒料被洗出之問題。

Based on the nonn of Soil Conservation Service (1986)，United state， this study establishes the grain size distribution design method of filter backfill for Groundwater monitoring well (GMW) located in sand or gravel land. First， the design criteria of grain size distribution are collected. After reduction， we define the upper and lower limit of DI5. Assuming the log-linear distribution between DlO and D90， the fonnulas of DlO， D60 and D90 are obtained by unifonn coefficient and DI5. Liner theory is then used to detennine Doand DlOO• A field example illustrates the design step of grain size distribution for filter backfill. Moreover， no erosion filter test is utilized to verify the design nonns of filter backfill. Laboratory experiments showed that 4DI5， which is the lower limited of DI5 defined by the soil conservation bureau of America， can be a good filter， and poor test results on the limit of 4Ds5. On the other hand， when the existing nonn used in Taiwan is used， it is recommended to reduce the lower limit of particle size for filter with Cu>6， so as to avoid being washed out of small soil particles.