摘要
坋質砂土，在台灣南部之曾文溪以南，台南、高雄一帶分佈極廣。其#200篩以下的細顆粒含量相當大，又不具凝聚性，故抗沖蝕能力差，易為滲流水沖離，導致土壤細顆粒流失，產生管湧破壞。鑑於此，本研究探討坋質砂土做為填土材料，或地下開挖時之管湧產生特性，並研提防治管湧所需的過濾料設計。研究中進行1.基礎土壤基本性質試驗：探討基礎土壤之一般物理性質，滲透係數及材料之c、ψ值。2 .管湧試驗：分別探討坋質砂土作為填土材料，或地下開挖時之管湧潛能。3.過濾料試驗：參考Sherard 等（1989）發表之「無沖蝕過濾料試驗」，進行過濾料選定試驗，研提防治管湧所需的過濾料設計。由試驗結果顯示，坋質砂土發生管湧的潛能，隨材料乾密度增加，而顯著降低。開挖時，發生管湧破壞的潛能，隨開挖面增加而遞增，且隨材料乾密度增加而顯著降低。因此，坋質砂土不論做為填土材料或地下開挖，均應注意材料乾密度的控制，以降低管湧發生的潛能。防治此坋質砂土管湧所需過濾料之D_(15b)，介於0.85~2.10mm；並隨#200篩以下細顆粒含量增加，呈線性遞減。而U. S. Anny之過濾料設計準則D_(15)/d_(85) ≤5（D及d 分別代表濾料及土壤的粒徑），應用於坋質砂土，雖較保守，但考慮現場施工，易造成粒料分離，則尚屬合理。
並列摘要
This study investigates the piping problem of silty sands. Filter requirement of the silty sands is discussed to provide design criteria in preventing for piping failure. Soil property and its piping potential are examined by using proper test set-up and ＂no erosion filter test＂ suggested by Sherard et al. (1989) is proceeded to design proper filter to prevent silty sands from piping. Test results indicate that by increasing the soil dry density (or the compaction ratio), the piping potential of silty sands decrease significantly. The result is true for silty sands employed as fill material, or arching action manifests owing to underground excavation. The filter boundary D_(15b) of silty sands is in the range of 0.85mm to 2.10mm and decreases linearly when fine content increase. The current filter criterion D_(15)/d_(35) ≤ 5 (D and d are diameter for filter and soil separately) suggested by U. S. Army et al. (1971) is conservative for silty sands; but it is reasonable if the segregation phenonienon is considered.