Numerical Simulation On Covers With Capillary Barrier Effects

Cover systems of waste landfills are practical for controlling the intrusion of water into the waste disposal sites. Covers with capillary barrier effects (CCBEs) is an alternative earthen final covers (AEFCs), by adopting cheap materials. The research works in this paper are based on numerical simulation method. CCBEs are systems consisting of a fine-grained soil layer placed on a coarse-grained soil layer and take advantage of capillary barrier effects to controlling the intrusion of water. The numerical simulation used software Seep/w. On the basis of the traditional capillary barrier systems, there are several improved approaches on this system. By comparing the improved systems and the traditional capillary barrier systems, the evaluation on performance of the two kinds of systems can be obtained. The main research works and conclusions are as following:(1) According to numerical models established by Seep/w software under the Ross assumptions, the numerical solutions can be verified. The results of the diversion length and diversion capacity obtained from the Ross analytic solutions and from the numerical simulation solutions fitted well. There is a little deviation due to the assumptions of the Ross theory. The results show that numerical simulation can be used to study CCBEs.(2) Several numerical models are established to model different covering layer thickness, different materials, different slope angle, and different rainfall conditions. These models are used to finding the better materials, better covering layer thickness, better slope angle for CCBEs in different rainfall conditions. The results show that thicker soil layer can prolong the system failure time. When it is a small rainfall prolonged for a long time, larger slope angles are more useful for the CCBE system. When it is a heavy rainfall prolonged for a short time, larger slope angles have fewer effects on the system. Result also showed that the selecting of materials should be according to the local climate condition. If the hydraulic conductivity of the upper layers is bigger, the moisture retention layer would drain water more easily and the failure time would be lengthen under the small rainfall. If the hydraulic conductivity of the upper layers is smaller, the moisture retention layer would make precipitation become more surface runoff and the failure time would be lengthen under heavy rainfall.(3) This research proposed a multi-layer capillary barrier system. The multi-layer capillary barrier system is constituted of four or more soil layers. The single-deck CCBE system was put on other single-deck CCBE system. They work together to intrusion of water. This is to enhance performance of the CCBEs. According to comparison of multi-layer system and single-layer system, there were several results. In a small rainfall prolonged for a long time, multi-layer system is not always better than single-layer system. But in a heavy rainfall prolonged for a short time, multi-layer system is obvious better than single-layer system.