Laboratory evaluation of capillary rise in silty sands with geotextile

Capillary rise of water in soil from a groundwater table is commonly observed in soils with fines. The capillary rise increases moisture in subgrade and base course with fines, thus affecting roadway performance. Fines content controls the level of capillary rise and geotextile may affect this level. Limited research has quantitatively evaluated capillary rise in unsaturated soils considering the influence of soil fines content and geotextiles. This paper presents a laboratory study evaluating capillary rise in silty sands with varying fines contents and the effects of wicking and non-wicking geotextiles. Soil columns consisting of upper and lower boxes were placed in a water tub to allow capillary rise, and volumetric moisture contents were monitored using moisture sensors over a 14-day period. At the end of each test, gravimetric moisture contents were measured to establish their relationship with the volumetric moisture contents. The test results indicate that capillary rise increased with the fines content. Existing methods were found to either under- or overestimate capillary rise in sands with fines. Non-wicking geotextiles acted as capillary barriers, restricting upward moisture migration above the interface, whereas wicking geotextiles were less effective in limiting upward capillary movement but enhanced horizontal drainage. Soil Water Characteristics Curves (SWCCs) and relative Hydraulic Conductivity Functions (HCFs) were also estimated and compared with the literature-based Geotextile Water Characteristics Curves (GWCCs). Analysis indicated that the non-wicking geotextile created a hydraulic discontinuity that reduced and delayed upward capillary water movement, particularly in soils with higher fines contents.