Evaluation and Design of Wicking Geotextile for Pavement Applications

Abstract

Geotextiles are often included in roadway structures as substituting drainage layers for gravel or sand drainage layers. When water infiltrates through pavements and enters base courses, it increases water content of base courses with fines, which leads to a decrease in base resilient modulus and accelerated development of deformation and eventually shortens the pavement structure service life. A geotextile allows free water to flow in the geotextile in its plane direction more easily than through its surrounding geomaterial. Thus, the geotextile placed at the interface between the base course and the subgrade shortens the drainage path and accelerates the drainage rate in a pavement structure. However, conventional geotextiles can only provide drainage for free water (i.e., water that flows under action of gravity). In unsaturated soils, suction (also called capillary force) between soil particles hold water and conventional geotextiles cannot provide drainage to capillary water within base courses. A new type of geotextile, wicking geotextile, was recently developed to remove water from soil via capillary action or suction. This wicking geotextile includes special deep-groove fibers in the cross-machine direction of the geotextile. The hydrophilic and hygroscopic deep-groove fibers can induce high capillary force to “wick” water out from unsaturated soil. Few case studies have shown the wicking geotextile could maintain or reduce the water content of the base course after compaction. However, the effectiveness of wicking geotextile depends on many factors’ which have not been fully evaluated. Currently, there is no design method or guideline available to incorporate the water content reduction benefit of the wicking geotextile. A series of laboratory tests, including demonstration tests, water removal tests, small box tests, and soil column tests, were conducted in this study to investigate the hydraulic characteristics of the wicking geotextile when in contact with free water and/or soil. Six large-scale cyclic plate loading tests with rainfall simulation were conducted to evaluate the effect of the wicking geotextile on the permanent deformations of base courses over weak subgrade. Based on the test results, the mechanisms of the wicking geotextile in removing water from base courses were investigated. The small box tests, the soil column tests, and the large-scale cyclic plate loading tests provided relationships between base course water content and drainage time. Design guidelines that incorporate the water content reduction benefit of the wicking geotextile were developed by modifying the 1993 AASHTO Pavement Design Guide and the Mechanistic-Empirical Pavement Design Guide.