Water retention characteristics and pore size distribution of landfilled municipal solid waste

The soil-water characteristic curve (SWCC) is usually used to describe the relation between water content and matric suction, and to some extent the pore distribution. However, the data at low matric suction are difficult to achieve by using the pressure plate extractor because of the macropore characteristic of municipal solid waste. The SWCCs corresponding to small pores are measured by the pressure plate extractor, and those corresponding to large pores are determined by means of the water breakthrough curves, in which the Poiseuille equation and Young-Laplace equation are used to calculate the pore radius. Based on the dual-porosity feature of landfilled waste, a SWCC equation is proposed by modifying the Van Genuchten equation. The pore-size distribution of landfilled waste is investigated. The results show that the modified equation can describe the water retention characteristics and the features of pores of landfilled waste very well. The saturated and residual water content of the municipal solid waste is high. The field capacity of shallow, middle and deep waste is 38.5%, 42.2% and 46.8%, respectively, corresponding to a matric suction range of 3~8 kPa. As the depth and age increase, the effective water content interval and specific yield decrease. Taking the matric suction of 1 kPa as the limit, the pores in waste can be devided into macropores and micropores. The probability density function of pore radius is bimodal. As the depth and age increase, the amount of macropores and their radiis decrease, at the same time, the amount of micropores increases and the average pore size becomes smaller.