Abstract：The construction of stabilized municipal solid waste incineration (MSWI) fly ash landfill has just started in China, hence the corresponding design standards have not been proposed yet. The prediction of leachate production is significantly important for the stabilized fly ash landfills, because it can guide the capacity design of leachate drainage and collection system (LDCS) and leachate storage tank. In this paper, samples were taken from a stabilized MSWI fly ash landfill in Nanjing, China, which involved the filling ages of 0, 1, 3, 6 and 11months. The laboratory study involved the measurements of particle size distribution, moisture content, moisture retention capacity. The uniformity and curvature coefficients were obtained as > 5 and <1, respectively. Hence, the stabilized fly ash was classified as poorly graded soil, indicating that a preferential flow was likely to occur in the fly ash body. The moisture content and moisture retention capacity were obtained in the ranges of 18.6%~46.4% and 15.0%~52.4%, respectively, and both decreased with the filling depth (or overburden stress) and increased with filling age. Based on the test results, a mathematical model was proposed for the prediction of moisture retention capacity. It was found that the moisture content was 2.6%~13.7% lower than the moisture retention capacity at a given filling depth and age. This result indicated that the fly ash at sites has not reached the state of moisture retention capacity as a whole. Then, it was inferred that the leachate collected in the LDCS was probably from the rainfall that infiltrated downward through the macro void in the stabilized fly ash pile, in a way which was called preferential flow. On the above basis, a method was proposed for the prediction of leachate production for the stabilized fly ash landfills, in which the landfill process, rainfall infiltration, preferential flow and moisture absorption property of fly ash were considered. The model parameters were calibrated by using the filed investigating data. The calculated results indicated that the leachate was mainly produced from the rainfall infiltration and waste water for transport vehicles cleaning, accounting for about 48% and 52%, respectively. The results also indicated that the ratio of leachate produced from the preferential flow to the total amount was 34.1% when the volumetric ratio of the macro void to the total void was 20%. Therefore, it is suggested that the stabilized fly ash should be fully compacted in order to reduce the macro void, and the water saving system is also recommended for vehicle cleaning, in order to reduce the total leachate production. This work can provide guidance for the design of LDCS and leachate storage tank of stabilized MSWI fly ash landfills in China.
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