Experimental Investigation of the Geosynthetic Capillary Barrier Effect in multi-layer Road Embankments

In road embankments containing soils or recycled materials with environmentally relevant constituents, geosynthetics, such as non-woven geotextiles and geosynthetic drainage mats can be installed as technical safeguards between the top-soil and the core to minimize percolation. Non-woven geotextiles possess a higher hydraulic conductivity than soil in the saturated zone and a lower hydraulic conductivity in the unsaturated zone, so the geosynthetics act as a capillary barrier layer. This study uses large-scale lysimeters to investigate the capillary barrier effect of non-woven geotextiles on the water balance of multi- layer road embankments. During seven irrigation-evaporation cycles, the soil suction and water content variation above and underneath the geosynthetics were monitored using Tensiometers and TDR sensors, respectively. Simultaneously, surface runoff, percolation, water storage, evaporation, and water drained along the geosynthetics layer were measured to evaluate the water balance of the embankments. As long as the precipitation rate is beneath a critical value a preferential runoff in the cover layer was observed, which leads to quasi-zero percolation and is, therefore, positive from the perspective of groundwater protection. At higher precipitation (above a critical value), the capillary break effect failed. Seepage water penetrated the geotextile, as the water pressure in the cover layer above the geotextile exceeded a critical value.