| Summary: | 碩士 === 國立臺灣科技大學 === 營建工程系 === 101 === This study carried out a series of horizontal permeability tests to evaluate the permeability and drainage efficiency of low permeable soil with geosynthetic drainage system. The experimental variables include: number of drainage layers, with and without sand layer, and sand layer thickness. The objective of this study is to improve the drainage capacity of low permeable soil for the application of geosynthetic-reinforced soil (GRS) structures backfilled with in-situ soil, typically with low permeability, under typhoon and heavy rainfall conditions. Test results indicate that system short-term permeability is improved as number of drainage layer, and number and thickness of sand layer increase. However, the system permeability decreases as the applied normal pressure, simulating the overburden pressure within retaining structures, increases. The reason of decreasing trend is because the normal pressure would compress the thickness of soil and drainage layer, and meanwhile fine soil particles are likely forced to penetrate into drainage layer which results in the clogging of drainage layer. Regarding the long-term permeability, test results demonstrate that system long-term permeability decreases as time elapse increases and the sand layer thickness decreases. By calculating the degree of retention (DOR), the ratio of mass of soil retained in a geotextile to the mass of the pure geotextile, this study finds DOR decreases as sand layer thickness increases, which provides a strong experimental evidence that the sand layer can effectively improve system permeability by preventing the drainage layer from clogging in long-term. Last, the measured results were compared with the predicted results using theoretical equation for equivalent horizontal hydraulic conductivity of multi-layered soil. The comparison results indicate with absence of normal stress, the measured and predicted system permeability are in a good agreement. However, the theoretical equation was found to overestimate system permeability as normal stress increases.
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