Small soil column investigation of soil-geotextile capillary barrier systems
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Geotextiles are often incorporated in engineered structures—including landfill liners and covers, earthen dams, retaining walls, and roads—to perform the separation, filtration, and/or drainage functions. Under unsaturated conditions typical of such structures, a capillary break may form at the interface between soil and geotextile. If the break is unplanned, the resulting build-up of moisture may be detrimental to the structure. Conversely, properly designed geotextile capillary barriers have the potential for many positive applications. Design information, including a complete framework for analysis and an accepted laboratory characterization approach, is lacking. The primary objectives of this study were to investigate geotextile capillary barrier performance with a simple laboratory model and propose a framework for complete analysis of a geotextile capillary barrier life cycle. Soil columns were designed to allow the formation and breakthrough of a geotextile capillary barrier to be observed. Materials used in the columns were obtained from a capillary barrier system currently under construction at the Rocky Mountain Arsenal in Denver, CO. Hydraulic characterization of the soil and geotextile were performed in the lab. Eleven column tests were completed for this study—soil compaction and applied flow rate were varied to investigate their effect on capillary barrier response. Analysis was approached within a proposed framework covering each stage of a capillary barrier life cycle. While there was considerable scatter in the test results, important insight was gained. The geotextile capillary barrier performed consistently. Conditions near the interface at breakthrough were similar between tests, regardless of soil compaction or applied flow rate, and were predicted adequately with the laboratory characterization. Storage capacity of the capillary barrier decreased with increasing relative compaction. A framework for analysis, from which the entire capillary barrier response may be modeled, was developed. Application of this model allowed for identification of weaknesses and recommendations for future work.