填埋场垃圾中优先流特征的染色示踪试验
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摘要
生活垃圾具有大孔隙特性,垃圾中水分运动常表现出优先流特征。针对垃圾组成复杂、难以切片的特点,设计了一种能方便地得到垃圾染色剖面的试验方法。使用填埋场不同深度处的垃圾样进行染色示踪试验,对染色后的垃圾柱分别进行水平切片和竖向切片。基于数字图像处理技术,研究了垃圾中优先流特征。垃圾中大孔隙多、基质少,染色模式与土中不同,基质部分的染色比例较高。试验所得的染色面积比和染色深度能反映出垃圾中优先流的明显程度,染色面积比与参与优先流的大孔隙比例有关,染色面积比越大,优先流越明显,而染色深度与基质流比例有关,上部垃圾中基质流比例越低,入渗深度越深。不同入渗强度的试验结果表明,入渗强度越大时垃圾中优先流程度越高;不同初始含水率的试验结果表明,初始含水率高的垃圾试样中优先流更明显;不同埋深垃圾试样的试验结果表明,浅层垃圾中更易产生优先流。竖向切片与水平向切片所得规律完全一致,试验方法在实现垃圾染色示踪和切片研究的同时,未改变垃圾中优先流原有规律,准确揭示了垃圾中优先流特征。
Municipal solid waste(MSW) is characterized by large pores, so preferential flow is a common flow pattern in MSW. As the complex composition of MSW and difficulty in sample sectioning are concerned, a test method is developed to make the sectioning easy. MSW samples corresponding to different depths of a landfill are used in the dye tracer test. The MSW columns are dyed and then sectioned in horizontal and vertical directions. Digital image processing technology is used to investigate the preferential flow pattern in MSW. There are many macropores and less matrix in MSW, and the dyeing pattern is different from that in soil. The proportion of dyeing matrix in MSW is higher than that in soil. The degree of preferential flow can be described by dyeing area ratio and the dyeing depth. The dyeing area ratio reflects the ratio of large pores involved preferential flow and is proportional to the degree of preferential flow. The dyeing depth is related with the matric flow ratio in upper part of the column. The lower the matric flow ratio, the deeper the dyeing depth will be. The dye tracer tests with different infiltration rates show that the degree of preferential flow in MSW increases with infiltration rate. The tests with different initial water contents show that preferential flow is more obvious in MSW with high initial water content. The tests with samples of different depths show preferential flow is more easily to happen in shallow MSW. The results of vertical section tests are consistent with that of horizontal sectioning tests, which show that the test method is applicable and has no influence on the preferential flow pattern in MSW.
Municipal solid waste(MSW) is characterized by large pores, so preferential flow is a common flow pattern in MSW. As the complex composition of MSW and difficulty in sample sectioning are concerned, a test method is developed to make the sectioning easy. MSW samples corresponding to different depths of a landfill are used in the dye tracer test. The MSW columns are dyed and then sectioned in horizontal and vertical directions. Digital image processing technology is used to investigate the preferential flow pattern in MSW. There are many macropores and less matrix in MSW, and the dyeing pattern is different from that in soil. The proportion of dyeing matrix in MSW is higher than that in soil. The degree of preferential flow can be described by dyeing area ratio and the dyeing depth. The dyeing area ratio reflects the ratio of large pores involved preferential flow and is proportional to the degree of preferential flow. The dyeing depth is related with the matric flow ratio in upper part of the column. The lower the matric flow ratio, the deeper the dyeing depth will be. The dye tracer tests with different infiltration rates show that the degree of preferential flow in MSW increases with infiltration rate. The tests with different initial water contents show that preferential flow is more obvious in MSW with high initial water content. The tests with samples of different depths show preferential flow is more easily to happen in shallow MSW. The results of vertical section tests are consistent with that of horizontal sectioning tests, which show that the test method is applicable and has no influence on the preferential flow pattern in MSW.
引文
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[3]詹良通,罗小勇,管仁秋,等.某垃圾填埋场污泥坑外涌及其引发下游堆体失稳机制[J].岩土工程学报,2013,35(7):1189-1196.ZHAN Liang-tong,LUO Xiao-yong,GUAN Ren-qiu,et al.The mechanism of the sludge dump in a landfill site and the instability of the downstream reactor[J].Chinese Journal of Geotechnical Engineering,2013,35(7):1189-1196.
[4]张文杰,陈云敏,邱战洪.垃圾土渗透性和持水性的试验研究[J].岩土力学,2009,30(11):3313-3317.ZHANG Wen-jie,CHEN Yun-min,QIU Zhan-hong.Experimental study on permeability and water holding capacity of waste soil[J].Rock and Soil Mechanics,2009,30(11):3313-3317.
[5]冯世进,张旭.考虑垃圾体沉降的生物反应器填埋场渗滤液回灌运移规律[J].岩土工程学报,2012,34(10):1836-1842FENG Shi-jin,ZHANG Xu.Leachate recirculation in bioreactor landfills considering settlement of municipal solid waste[J].Chinese Journal of Geotechnical Engineering,2012,34(10):1836-1842.
[6]ZHANG W J,ZHANG G G,CHEN Y M.Analyses on a high leachate mound in a landfill of municipal solid waste in China[J].Environmental Earth Sciences,2013,70(4):1747-1752.
[7]ROSQVIST N H,DOLLAR L H,FOURIE A B.Preferential flow in municipal solid waste and implications for long-term leachate quality:valuation of laboratory-scale experiments[J].Waste Management Research,2005,23:285-295.
[8]ROSQVIST H,DESTOUNI G.Solute transport through preferential pathways in municipal solid waste[J].Journal of Contaminant Hydrology,2000,46(1-2):39-60.
[9]张文杰,严宏罡,孙铖.城市生活垃圾中优先流规律的穿透试验研究[J].岩土工程学报,2018,40(7):1316-1321.ZHANG Wen-jie,YAN Hong-gang,SUN Cheng.Breakthrough test on preferential flow in municipal solid waste[J].Chinese Journal of Geotechnical Engineering,2018,40(7):1316-1321.
[10]FLURY M,FLUHLER H,JURY W A,et al.Susceptibility of soils to preferential flow of water:a field study[J].Water Resource Research,1994,30(7):1945-1954.
[11]李萼,王康,张仁铎,等.非均匀流动示踪试验及活动性流场模型的应用[J].土壤学报,2009,46(1):37-45.LI E,WANG Kang,ZHANG Ren-duo,et al.Tracer experiment and application of active region model for heterogeneous soil water flow[J].Acta Pedologica Sinica,2009,46(1):37-45.
[12]张财宝,刘目兴,王文德,等.三峡库区森林土壤优先流染色特征[J].水土保持学报,2012,26(2):80-84.ZHANG Cai-bao,LIU Mu-xing,WANG Wen-de,et al.Dyeing characteristic of preferential flow under forestland in the Three Gorges reservoir area[J].Journal of Soil and Water Conservation,2012,26(2):80-84.
[13]FELLNER J,BRUNNER P H.Modeling of leachate generation from MSW landfills by a 2-dimensional2-domain approach[J].Waste Management,2010,30:2084-2095.