Effects of the structural properties of nonwoven geotextiles on their filtration behavior
Abstract
Nonwoven geotextiles have been introduced as viable alternatives to granular filters as early as 1970. They have been used as filters in several civil engineering applications, e.g., highway subdrains, dams, wick drains and landfills. In these applications, geotextiles are expected to filter soils with wide range of gradations. Meanwhile, they are subjected to structural changes due to loading and soil entrapment. The current filter criteria are purely empirical and do not account for important structural properties of geotextiles such as the overall pore size distribution, thickness, and porosity. Geotextile compressibility and the internal stability of the base soil are also neglected. Therefore, a rational approach need to be developed. The approach should consider important structural properties of the geotextile and soil. Intensive laboratory testing was performed to determine the micro-structural properties of 14 nonwoven geotextiles obtained from five manufacturers using mercury intrusion porosimetry and image analysis. The test methods were improved to suit geotextiles. The results indicated similar pore size distribution for geotextiles from the same manufacturer (group), however, significant differences in porosity, specific surface area, and surface porosity between different geotextile groups were obtained. A probabilistic model was developed based on the microstructural investigation. The model estimates the geotextile thickness needed to retain a stable soil, for a target reliability. It was based on the overall pore size distribution, porosity, and thickness of the geotextile. The model was extended to include the effects of compressibility on the retention ability of geotextiles. Model predictions were validated with data from laboratory tests. The effects of the microstructural properties of nonwoven geotextiles and the particle size distribution of gap graded soils on the long term performance was studied using data from the literature. It was concluded that for unstable soil/geotextile systems that the flux decay is not significantly influenced by either the soil gradation or the geotextile structure. Long term studies of field geotextile samples obtained from highway subdrains indicated that, the image analyzer can be a useful tool in understanding the factors and mechanisms influencing long term performance.
Degree
Ph.D.
Advisors
Lovell, Purdue University.
Subject Area
Civil engineering
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