稳定化飞灰填埋场渗滤液产量预测

以南方某稳定化飞灰填埋场为研究对象，通过钻孔获取了新鲜、1、3、6和11个月等5个龄期的试样，并在实验室开展了颗粒分析、含水量、持水量等测试.不均匀系数Cu > 5，曲率系数Cc<1，属于级配不良土，容易形成优势流通道.含水量介于18.6%~46.4%之间，随埋深的增大而减小，随龄期的增长而增大.持水量介于15.0%~52.4%之间，随上覆应力的增大而减小，随龄期的增长而增大，由此建立了持水量计算模型.对于相同龄期和埋深的稳定化飞灰，其含水量要低于持水量2.6%~13.7%，这表明稳定化飞灰整体上未达到持水量状态，由此推测底部导排层收集到的渗滤液主要由雨水入渗后经过稳定化飞灰体内优势通道而进入导排层.在此基础上，建立了考虑填埋进程、降雨入渗量、优势流通道、稳定化飞灰产/吸水量等因素的填埋场渗滤液产量预测模型，并利用现场记录数据对模型进行了参数率定.模型分析结果表明，填埋场开始运营后的9个月内，渗滤液主要来源于降雨入渗量和运输车辆冲洗水量，分别占比约48%和52%.当稳定化飞灰体内优势流通道占总孔隙的比例从0%增至20%，导排层收集到的渗滤液量占渗滤液总收集量的比例从0增至34.1%.因此，建议对稳定化飞灰进行充分压实后再填埋，以减少优势流现象的发生，同时改用节水型车辆冲洗装置，最终降低渗滤液总产量.上述研究成果能够为我国类似稳定化飞灰填埋场中导排系统、调节池等的设计提供重要参考.

Prediction of leachate production from a stabilized MSWI fly ash landfill

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.