Evaluation of the Development of Capillary Barriers at the Interface between Fine-Grained Soils and Nonwoven Geotextiles

The objective of this paper is to assess the formation of capillary barriers on soils in contact with nonwoven geotextiles that have been placed with the primary function of acting as a separator between clay and gravel. This includes a comprehensive experimental program that involved a number of soil column infiltration tests conducted using a variety of material combinations to assess the hydraulic performance of interfaces between the unsaturated clay and the geotextile. Soil moisture was recorded using time domain reflectometers. The acrylic soil columns custom made for this study were comparatively small (20 cm diameter and 17 cm tall) in order to facilitate test setup and reduce total testing time. Eight column tests were conducted, which included four different nonwoven geotextiles selected to observe the geotextile characteristics that may affect the formation of a capillary barrier. The tests were all performed using the same configuration, soils, relative compaction, initial unsaturated water content, and inflow rate, in order to assess the impact of different geotextiles on the hydraulic performance. Based on data from the moisture sensors, all tests were found to show a clear formation of a capillary barrier, which resulted in additional moisture storage in the overlying fine-grained soil layer. The test results show that currently available standard nonwoven geotextiles will create a capillary barrier and restrict moisture flow into the underlying soil layer until the overlying fine-grained soil has become nearly saturated. The strength of the capillary barrier was found to be similar for the multiple standard polypropylene nonwoven geotextiles investigated in this study.