Avaliação em laboratório do comportamento de barreira capilar com utilização de diferentes tipos de geotêxteis

Abstract

Evapotranspirative capillary barrier coverage is a technology successfully employed in semiarid and arid climates and in locations with high evaporation rates. They are used as final cover of solid waste and mining tailings, with the function of flow control, basal water percolation and gas flow, in unsaturated medium. These coverings consider the permeability contrast of their constituents, a soil overlaps a thicker soil, replacing the thicker soil with a nonwoven geotextile (NGT) has been giving the capillary barrier system an improvement in its performance. The present thesis simulated and evaluated capillary barriers in the laboratory associated to NGTs, through wet-drying tests in soil columns monitored by humidity, temperature and pressure sensors. Three different capillary barrier configurations were made, two with geotextiles of different brands, composition, thickness and weight, and one with fine gravel. The capillary layer of all the barriers was the residual sandy soil with clay. The water retention characteristic curves (WRCCs) of the residual soil were determined, one part by the hanging column test and the other by the filter paper test. The NGT WRCCs were obtained by hanging column test. The WRCCs had their adjustments as proposed by Fredlund and Xing (1994) and from them were estimated the hydraulic conductivity functions according to Van Genuchten 1980 e Mualem (1976) model, which made possible the graphic determination of the critical suctions. The soil column tests associated with the geotextiles presented similar results and provided higher water retention in the middle portion of the capillary layer than the soil column without geotextile, which gave higher moisture content in the basal portion of the capillary layer when compared to other barriers. The NGTs presented WRCCs with pronounced hysteresis. The desorption and adsorption curves occurred for suction values lower than 5 kPa. The residual soil presented WRCCs with hysteresis less pronounced than NGTs and residual suction in the thousands of kPa. The research trials considered drying and wetting trajectory, which allows the evaluation of the most critical trajectory for a work involving these materials.