Soil - geotextile filter system is influenced by cyclic flows while changing in loads and fine contents
Date Issued
2006
Date
2006
Author(s)
Hsieh, En-Tzu
DOI
zh-TW
Abstract
地工織物常應用於週期性水流(bi-directional flow)作用的區域，然而傳統試驗方法雖能進行單向度的滲流試驗，但是對於雙向週期性水流則無法進行模擬；如水力坡降比試驗，對於有週期性水流作用的影響進行評估，於理論上並不適用。為了探討雙向週期水流作用下，覆土壓力及細料含量對土壤-地工織物過濾行為之影響，本研究研發一台可模擬雙向週期水流的試驗儀器-即雙向週期水流試驗儀。試樣由沈泥細料與砂土調配混合，分別調配之沈泥重量百分比為0% 、 10% 及 20% 三種，而軸向壓力分別為模擬覆土深度約為 3.5m (σ = 70 kPa)及7.0m (σ = 140 kPa)二種；週期水流速率則分別模擬一週期為600秒、300秒、150秒、75秒四種流速。
由試驗結果得到以下結論：(1)有摻入細料的試體發生管湧，原因是軸向載重 σ = 70 kPa 不足以束制土壤的移動，造成土壤的流失進而形成管湧；(2)織物之開孔徑尺寸雖符合地工織物於雙向水流狀況下之阻留準則，但由試驗結果發現，試體有發生管湧現象，原因與土壤條件、軸向壓力及水流速率有密切的關聯；(3)當軸向壓力為140 kPa 時，細料含量20% 者，試體中的砂土與細料緊密接觸，在軸向壓力140 kPa束制下不易被淘洗流出。
Geotextile is often used as a filter material in the area subject to cyclic flows such as seashore or river banks. Conventional permeability tests can generate uni-directional flow or bi-directional flow, but are unable to simulate cyclic flows, and therefore unsuitable for testing a soil-geotextile filter system under cyclic flow conditions. In this research, an apparatus which can simulate bi-directional cyclic flow conditions is developed for testing soil sample with geotextile. The soil samples are composed of sand mixing with various silt contents： 0, 10, and 20% by weight. Two axial pressures simulating the depths at 3.5m (70 kPa) and 7.0m (140 kPa) are applied on the samples. Four kinds of cyclic flow periods are 600, 300, 150 , and 75 seconds per cycle.
The results from the tests are: (1) Piping occurs in the samples having fine content under axial pressure 70 kPa. The axial load may not be large enough to confine soils and limit their movement; (2) Though the geotexitle used satisfies the retention criteria under bi-directional flow, it still results in piping. The causes are related to soil condition, axial load, and the period of cyclic flow； (3) When the axial pressure is 140 kPa, the sample with 20% silt content does not have piping phenomenon.. It seems that sand and silt are packed well so that soil is difficult to be washed out
Subjects
週期性水流
地工織物
雙向週期水流試驗儀
bi-directional flow
geotextile
bi-directional flow apparatus
Type
thesis
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