Self-dewatering capillary barrier system (SDCBS) using preheated air flow method

M. Salah, Jules-Ange Infante, Rozalina Dimitrova

In the proceedings of: GeoOttawa 2017: 70th Canadian Geotechnical Conference; 12th joint with IAH-CNC

Session: Unsaturated Soils I

ABSTRACT: This Paper presents the results of experimental tests aimed at studying the impact of preheated airflow on the evaporation rate and removal of moisture from a soil mass. It is envisaged to provide an engineering solution to the percolation of water through capillary barrier systems, in addition to accelerating soil-water storage recovery. The preheated air generated from a simulated heating box was passed into the soil mass using a perforated pipe, and sensors were used to monitor the impact of the preheated air flow on the soil properties. The results obtained were compared with non-preheated air flow process in terms of volumetric water content, and matric suction over a short period. The results using preheated airflow indicated a significant decrease in volumetric water content and increase in matric suction.

RÉSUMÉ: Cet article présente les résultats d'essais expérimentaux visant à étudier l'impact du flux d'air préchauffé sur le taux d'évaporation et l'élimination de l'humidité d'une masse de sol. L'étude vise à fournir une solution au problème de percolation à travers les systèmes de barrière capillaires, en plus d'accélérer l'élimination de l'eau de la couche de stockage. L'air préchauffé, généré à partir d'un boîtier de chauffage, passe dans la masse de sol à l'aide d'un tuyau perforé, et des capteurs ont été utilisés pour mesurer l'impact du flux d'air préchauffé sur les propriétés du sol. Les résultats obtenus ont été comparés au processus d'écoulement d'air non préchauffé en termes de teneur en eau volumique et de suction matricielle sur une courte période. Les résultats utilisant le flux d'air préchauffé ont indiqué une diminution significative de la teneur en eau volumétrique et une augmentation de la suction matricielle. 1 INTRODUCTION The capillary barrier system is an engineering solution suitable for various civil engineering structures such as road embankments, and landfill covers. They are generally formed of a coarse-grained core layer, which is maintained in an unsaturated condition, and is covered by a layer of fine-grained soil. The Capillary barrier system is used to prevent water to infiltrate into the underlaying layers of the structure. The system can be utilized for numerous purposes in geotechnical engineering and in the environmental engineering (e.g., landfill cover) (Yang et al. 2004; Krisdani et al. 2005; Rahardjo et al. 2009; Bussiere et al. 2000; Khire et al. 2000; Tidwell et al. 2003). 2 MECHANISM OF THE SYSTEM The difference in hydraulic conductivity between the coarse-grained soil layer and the fine-grained soil layer provides the basis of the system function. . The difference of the matric suction between the two layers prevents water to infiltrate the coarse layer until the degree of saturation of the fine-grained layer is high enough that its matric suction is reduced to a value comparable to the coarse layers. Fine-grained layer therefore serves as a water storage layer. The permeability for the fine layer is higher than the coarse layer, which allows the alternating layers to function as an effective barrier (Krisdani et al. 2005; Yang et al. 2004; Rahardjo et al. 2009; Khire et al. 2000; Bussiere et al. 2003) Considerations in the design of capillary barriers include the grain size distribution of the different layers (fine, and coarse) which have a significant effect on the SWCC and therefore on the hydraulic properties such as soil permeability and the volumetric water content of the interface between those two materials (Yang et al. 2004; Rahardjo et al. 2009). Figure 1.a and 1.b show two SWCCs which provide the relationship between the volumetric water content as well as the coefficient of permeability in term of matric suction. 3 PROBLEM DEFINITION Continuous infiltration in a capillary barrier system due to precipitation results in an increase in the volumetric water content as well as the permeability of the fine soil layer. With time, the infiltration will proceed to the fine-coarse interface layer and eventually, the matric suction for the coarse soil layer starts decreasing. When the matric suction equals the water entry value, the permeability of the coarse layer will start increasing rapidly, exceeding the system. This will ensure a fast rate of matric suction recovery in the fine soil layer. This will cause a breakthrough through the coarse layer which may lead to percolation in the underlying layers, and rendering the barrier non-functional (Rahardjo et al. 2009; Wilson et al. 1995; Bussiere et al. 2003). The purpose of the current work is to investigate the use of an evaporation process that may be used to provide water removal from the coarse-grained soil layer in case of a breakthrough so that the capillary barrier may remain functional. 4 THE PROPOSED APPROACH The recovery of soil-water storage potential is one of the important variables which should be considered during the

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