城市生活垃圾中优先流规律的穿透试验研究

Breakthrough tests on preferential flow in municipal solid waste

城市生活垃圾具有大孔隙特性,优先流是垃圾中水分运动的重要形式,目前垃圾中优先流基本规律尚不明确,优先流数值分析时相关参数的选取尚缺乏依据。通过垃圾柱穿透试验研究城市生活垃圾中的优先流,以Cl-为示踪剂,进行了不同埋深和龄期试样、不同高度试样和不同入渗强度的穿透试验,得到溶质穿透曲线,运用对数正态分布模型和双峰概率密度模型拟合试验结果,定量分析了垃圾中优先流规律。结果表明,通过大孔隙运移的溶液占比在55%~70%之间,垃圾中优先流现象明显。随着垃圾的埋深和龄期增加,参与溶质运移的孔隙比例增加,但通过大孔隙运移的比例减少,优先流程度降低;试样高度增加,参与溶质运移的孔隙比例增加,但其内部大孔隙贯通性变差,通过大孔隙运移占比减小,优先流程度降低;入渗强度增大,参与溶质运移的大孔隙占比增加,优先流程度增大。双峰概率密度模型比对数正态分布模型能更好地描述垃圾中溶质运移的优先流规律,同时为使用两域模型进行垃圾水分运移分析时的参数取值提供了依据。

The municipal solid waste（MSW） is characterized by large pores, so the water flow in MSW often takes the form of preferential flow. The fundamental rules of the preferential flow in MSW has not been revealed thoroughly at present, and parameters in numerical analysis still need to be studied further. The solute breakthrough tests are carried out by using Cl-as a tracer to investigate the preferential flow in MSW. The influences of depth and age, sample heights and infiltration rates on the preferential flow are considered. The regression analysis is performed using the log-normal probability distribution model and bimodal probability density model. The results show that 55% to 70% of the total solute is transported through large pores, indicating that the preferential flow is obvious in MSW. The proportion of pores that participates in solute movement increases as the depth and ages increase, but the proportion of solute movement through large pores decreases, such that the degree of preferential flow decreases. As heights of the MSW sample increase, the connectivity of large pores in MSW decreases and the proportion of solute movement through large pores decreases, so the degree of preferential flow decreases. As the infiltration rate increases, the proportion of solute movement through large pores increases and the degree of preferential flow increases. The bimodal probability density model is more suitable than the log-normal probability distribution model to characterize the preferential flow in MSW. The analysis helps to determine the parameters in two-domain model in analysis of water movement in MSW.