Abstract: 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.

Key words: municipal solid waste (MSW), dye tracer test, MSW section, preferential flow