Recently, the necessity of constructing a large-scale offshore waste landfill in the city's port area is increasing instead of construction of new waste landfill inland. Due to the development of society and the intermittent occurrence of disasters induced by earthquakes and typhoons, the amount of waste generation tends to increase every year. In the case of South Korea, there is no big problem of landfill capacity at the final disposal site at present; however, new site development of the final waste landfill is still a matter of concern because of the resident’s complaints and NIMBY problem. In such a social atmosphere, it is considered as an alternative solution to build a final waste landfill at offshore. While there are no construction examples of offshore waste landfill in South Korea yet, and it is actually not provided the standards for construction of liner systems such as bottom layer and vertical barrier wall.
Therefore, in this study, the parametric analysis was conducted to evaluate the optimum geotechnical performance of barrier system to prevent leakage of contaminants at the offshore waste landfill by considering seepage, advection, and dispersion. Based on overseas landfill cases, a double steel-pile and rubble mound types of revetment structures were selected as the offshore waste landfill. The analysis was conducted under steady and unsteady flows on the basic liners, bottom layer and vertical barrier wall.
First, in case of steady flow, the parametric analysis was conducted to evaluate optimum geotechnical performance of barrier system on thickness and hydraulic conductivity of bottom layer both double sheet-pile and rubble mound types of revetments structures. In addition, the thickness, hydraulic conductivity, and embedment depth of double steel-pile structure were investigated to evaluate the performance of vertical barrier wall. For the rubble mound type of revetment, the parametric analysis was conducted on the length of HDPE sheet and the hydraulic conductivity of rubble mound type back-fill layer for revetment structure. Based on the study results, the minimum criteria is proposed which indicate optimal performance of barrier system on the both revetment structures.
Then, the parametric analysis was performed under unsteady flow condition considering tidal fluctuation where the offshore environment waste landfill is constructed. The result was compared to the ones obtained from the steady flow condition. Moreover, the analysis was performed considering the water level fluctuation inside the landfill at the time of actual landfill management and the results were compared to the preceding results.
Based on the outcomes of this study, the results obtained from the steady flow condition (where the water level in the landfill is set higher than the sea level) is much conservative comparing to the cases where the tidal fluctuation and water level is inside the landfill. Therefore, in general conditions, it is proper to consider the steady flow condition due to seepage, advection, and dispersion in the analysis of the leakage of contaminants at offshore waste landfill.