雙向反覆水流試驗評估土壤－地工織物過濾系統

Abstract

地工織物在控制土壤流失方面，已發展出了阻留準則，在維持土壤－地工織物系統的滲透性方面，則發展出了滲透性準則，但由於試驗條件較為簡單，並未考慮現地多種情況，如反覆水流之情況、覆土壓力與土壤配比等，因此在實際使用時，這些準則或公式是否符合現地需求，實有深入探討之必要。 本研究採用雙向水流儀，期能在模擬現地之環境上有一更好之效果。研究方法針對覆土壓力、土壤級配(包括黏土含量)、水流週期等影響過濾行為之因素加以改變。其中，覆土壓力分為70 kPa以及140 kPa，土壤級配採用90%的越南砂搭配10%的細粒料(6.5%粉土混合3.5%黏土，以及3.5%粉土混合6.5%黏土兩組)。在週期水流方面，有每週期為600秒、300秒、150秒、75秒四種週期。 試驗結果顯示黏土含量對於過濾行為有相當大的影響；經與無黏土之情況加以比較，更突顯黏土含量對於土壤－地工織物過濾系統的顯著影響。此外，水流週期之長短也會改變覆土壓力、黏土含量等變數對於土壤－地工織物過濾系統的影響。因此，本研究也對阻留準則及滲透性準則在雙向水流情況下之適用性作一檢討及建議。

In the research on geotextiles, it has developed the retention criteria in controlling soil loss and permeability criteria to drain water effectively. But most of research considered simpler conditions rather than real conditions in the field such as bi-directional cyclic flow condition, overburden pressure, and soil gradation. In this research, a bi-directional flow apparatus is adapted to simulate in-situ conditions considering the parameters: overburden pressure, soil composition, and cyclic flow period. These parameters are changed to analyze their effect on filtration behavior. Overburden pressures selected are 70 kPa and 140 kPa. The soil samples are composed of Vietnam sand and 0-10% fine material. The four flow periods are 600, 300, 150 and 75 seconds per cycle. From comparing the results of the sand and the sand with fines, it is found that the clay content plays a very important role in filtration behavior of soil-geotextile system. The flow period may change the filtration behavior that affected by overburden pressure and clay content. In addition to that, the retention and permeability criteria are also examined and suggestions from this research are made.