反向水流對地工織物抗阻塞潛能影響之研究

A study on the Anti-Clogging Potential of Geotextile by the Reverse Flow

王國海(Kuo-Hai Wang)

指導教授 ： 張達德

中原大學/工學院/土木工程研究所/碩士(2001年)

https://doi.org/10.6840/cycu200100214

摘要

摘 要
地工織物在過濾/排水工程運用上，反向水流的存在，常容易產生管湧、滲流甚至土壤軟化(Soften)現象，使土體掏空以致於破壞；換言之，反向水流作用在系統未達管湧階段確實對織物過濾系統形成一抗阻塞效應，為探求反向水流對地工織物抗阻塞潛能影響，擬以模擬試驗進行探討。
改良Williams及Abouzakhm(1988)所提出之三軸儀水力傳導度比試驗，進行模擬正反雙向水流滲透試驗；評估反向水流對土壤-織物系統於過濾/排水行為中造成之阻塞(clogging)及土壤自濾層(filter layer)之形成是否有相當程度之影響。並針對水力傳導度比試驗無法掌握過濾系統內部水頭分佈之缺失，使用微電子水壓力計伸入柔性橡皮模內之試體，以準確掌握試體內水頭分佈之情形，並進行改良式水力坡降比試驗，以判別織物或土壤層阻塞與否。
本研究使用二種織物，二種級配土壤，及三種反向水力梯度，考慮細粒料含量多寡及反向水力梯度大小為可能的影響因子，配合試驗前後進行臨界氣泡法試驗對地工織物孔徑分佈之量測，了解地工織物在過濾/排水行為前後其孔徑分佈之變化。
根據研究結果歸納，反向水流作用對細粒料含量為10%之土樣整體系統導水度影響層面較大，尤其在高反向水力梯度(i ≥ 20)的條件下，被覆土壤管湧現象較易發生。細粒含量為30%的土樣，反向水流的影響趨勢則較為平緩，系統對土壤阻留效應呈現較正面的效益。經由改良式水力坡降比試驗結果，發現細粒含量少(10%)時主要為織物層的阻塞及堵塞效應嚴重，而細粒含量多(30%)時，土體本身薄層濾塊形成是導水度降低的主因。
在未達嚴重管湧(Piping)階段前，反向水流作用對織物抗阻塞潛能確實有正面的影響效益；似乎在過濾/排水工程上可運用反向水流的效應達到織物過濾/排水行為後阻塞之沖洗作用，以延長織物在過濾/排水功能上的使用壽命。

關鍵字

改良式水力傳導度比試驗 ； 臨界氣泡法 ； 反向水流 ； 阻塞 ； 微電子水壓力計 ； 改良式水力坡降比試驗 ； 管湧

並列摘要

ABSTRACT
In the application field of drainage/filtration of geotextile, the existing reverse water flows always makes the piping takes place much easier even soil soften. The soil mass was washed so that failure happened. However, reverse water flows that are acting on a filtration/drainage system under the unpiping stage will form an anti-clogging affection. A series of simulation tests will perform to study the affections of the reverse water flows to the anti-clogging performance of the geotextiles.
In order to estimate affections of the clogging behavior caused by reverse water flows to the soil-geotextiles filtration/drainage system and the performing of soil filtration layer. A test device modified from the Hydraulic Conductivity Ratio Test recommended by Williams and Abouzakhm was used to simulate the test with direct and reverse water flow in a soil. And a set of electronic water pressure transducers were involved into this test to overcome the disadvantage of HCR test which is not able to evaluate the water head distribution inside the soil mass. The electronic water pressure transducers penetrated in to the soil mass through the rubber membrane exactly measured the water pressure distribution inside the soil mass.
With consideration the content of fine particles and the gradient of the revere water flows would be the most important influence factors to this application study. There are two geotextiles, two grained soils were used in this study with three gradients of the reverse water flows. Beside, Bubble Point Method was also used to evaluate the pore size distribution of the geotextile before and after the filtration/drainage behavior, then the pore size change of the geotextile in the filtration/drainage behavior would be known.
Concluded with the tests results, the influence of reverse water flow to the conductivity of the system is more serious with the 10% fine particles content soil sample（i>=20）reverse water flow condition. The overlay soil would have more chance to perform a piping phenomenon. The influence of the reverse water flow with the 30% fine particles content soil sample the system also showed a better performance to retain the soil particles.
By analyzing the test results from modified HCR tests, when the fine particle content of soil sample is lower, the clogging and blocking effect with in the geotextile layer is more serious. And when the fine particle content of soil sample is higher, the main reason of the system conductivity goes down is because of the performing of impervious layer of the soil sample. Before the serious piping stage, reverse water flows perform a positive effect to the geotextile anti-clogging potential. It seems that the reverse water flow is valuable to applied the washing behavior with the geotextile in the filtration/drainage application in order to extend the lifetime of geotextile on filtration/drainage application field.

並列關鍵字

clogging ； bubble point method ； modified the conductivity ratio test ； electronic micro pore water pressure gauge ； modified the hydraulic gradient ratio test ； piping ； reverse water flows

參考文獻

11 Bathia, S. K., and Smith, J. L., “Application of the Bubble Point Method to the Characterization of the Pore-Size Distribution of Geotextiles” Geotechnical Testing Journal, GTJODJ, Vol. 18, No. 1, March, 1995, pp.94-105.

12 Bathia, S. K., and Smith, J. L., “Application of the Bubble Point Method in the Characterization of the Pore-Size Distribution of Geotextiles” accepted for publication by Geotechnical Testing Journal, ASTM, 1994.

14 Canadian Geotechnical Society, Canadian Foundation Engineering Manual, 3rd Edition, Vancouver, B. C.

24 Fischer, G. R., Christopher, B. R., and Holtz, R. D., “Filter International Conference on Geotextiles, Geomambrances and Related Products, The Hague, 1990, pp.273-278.

28 Giroud, J. P., “Filter Criteria for Geotextiles”. Proceedings, 2nd International Conference on Geotextile, Las Vegas, 1982.