Development of a capping material for an Engineered Landfill in Wet zone of Sri Lanka

Abstract

Capillary Barriers (CB) which consist of coarse sand overlain by a low permeable fine soil are low cost alternatives used in capping system for controlling the infiltration in a Landfill. In wet region, the durability of capping layer is questionable as due to high precipitation, capillary effect can reduce making the layer highly permeable. A potential solution is to alter the soil grains by mixing with a Hydrophobic Agent (HA) such as Oleic Acid (OA), so that the water repellent characteristics are introduced into the sand layer. In this study, the hydrophobicity (water repellency) of CBs containing coarse sand mixed with OA was investigated. Hydrophobicity was evaluated by measuring the time taken for a water droplet to penetrate the surface of a compacted sand sample which is identified as the Water Drop Penetration Time (WDPT). Initially, dry coarse sand particles were hydrophobized by mixing-in coating method with different OA contents. In addition, the effect of moisture content of coarse sand particles on its hydrophobicity was also studied. The results show that WDPT for dry samples increased sharply with increasing HA content and reached a peak value of 4080 s at 3gkg-1 of sand and thereafter decreased. Irrespective of the OA content, an increase in moisture content decreased the water repellency. However, this decrease is less significant for the optimum value of OA content of 3gkg-1 within the range of moisture content tested. The impact of the slope angle on the water repellancy was also investigated by increasing the slope upto 1V:3H. Results showed a decrease in water repellency when the slope angle was increased. It was observed that water drop was spreading due to the effect of weight acting along the slope and as a result the WDPT time decreased due to less surface tension.