Development of dual capillary barrier system using recycled materials
Fakhrur Rozy Harnas
Date of Issue2015
School of Civil and Environmental Engineering
Residues and Resource Reclamation Centre
At the end of operation, a landfill should be covered in order to reduce water infiltration. A capillary barrier (CB) is a cover system that uses the contrast in hydraulic properties between fine and coarse-grained layers under unsaturated conditions to minimize downward water movement. The performance of a CB in the tropics is tied to its ability to remove water through lateral diversion. Therefore, increasing the lateral diversion capacity of a capillary barrier is an important research area. The use of recycled concrete (RC) and recycled asphalt pavement (RA) is widely accepted in civil engineering applications such as highway pavement construction. Since coarse-grained soil are most suitable for capillary barrier systems, RC and RA could be used as alternative materials for forming capillary barrier cover systems. However, the use of these materials in capillary barrier cover systems has never been investigated. The objectives of this study were to develop a modified capillary barrier system to reduce water infiltration into a landfill and to investigate the potential use of RC and RA as capillary barrier forming materials. The study consisted of laboratory experiments and numerical modelling. The laboratory experiments included an investigation of the properties of RC and RA followed by 1-D and 2-D infiltration experiments. Numerical modelling was conducted as preliminary guidance for the development of an experimental plan, and the results of the numerical modelling were then compared to the experimental data. The verified numerical model was subsequently used to perform a parametric study. This study proposes a modification to the conventional capillary barrier cover (single capillary barrier, SCB). The modified capillary barrier, termed a dual capillary barrier (DCB), consists of two stacks of capillary barriers. The experimental results showed that DCB has a considerably higher water storage than SCB, which leads to a higher lateral diversion capacity. The higher water storage of DCB was caused by higher volumetric water content at breakthrough caused by the thinner thicknesses of the fine-grained layers of DCB and the effect of layering. Both SCB and DCB can be constructed using combinations of RC or RA, as demonstrated in this study. The low water-entry value of coarse RA and the low residual volumetric water content of fine RA results in high storage that make fine and coarse RA ideal materials for the construction of SCB or DCB.