Parameters affecting the development of capillary barriers due to conventional geotextiles

¹ Jacobs Engineering Group, Inc, Geotechnical Engineer, Portland, Oregon, USA
² University of Texas at Austin, Professor, Dept. of Civil, Architectural, and Environmental Engineering, Austin, Texas, USA

^* Corresponding author: marcelo.azevedo@jacobs.com

Abstract

The objective of this study is to assess the formation of capillary barriers on unsaturated soils in contact with geotextiles that have been placed with the primary function of acting as a separator between soil or drainage layers, including the geotextile component of a geocomposite. A comprehensive experimental program involving soil column infiltration tests was conducted using a variety of material combinations to assess the hydraulic performance of interfaces between unsaturated clay and geotextiles. Soil moisture was recorded using time domain reflectometers. Custom made acrylic soil columns were comparatively small (20 cm diameter and 33 cm tall) in order to facilitate test setup and reduce total testing time. Multiple column tests were conducted, which included woven and nonwoven geotextiles selected to identify which geotextile characteristics may affect the formation of a capillary barrier. Other tests were conducted to assess the effect of varying relative compaction and inflow rate on the hydraulic performance. Based on data from the moisture sensors, all tests were found to clearly show the formation of a capillary barrier, which resulted in additional moisture storage in the overlying finegrained soil layer. The test results show that currently available conventional geotextiles create a capillary barrier and restrict moisture flow into the underlying soil or drainage layer until the overlying fine-grained soil has become essentially saturated. This includes nonwoven geotextiles that are commonly used as the top layer in geocomposite drainage products or as separators between a soil layer and an underlying gravel drainage layer. The strength of the capillary barrier was found to be similar for the multiple conventional polypropylene geotextiles investigated in this study.