Evaluation of paper mill sludges for use as landfill covers.

摘要

This study evaluated the geotechnical properties of seven paper sludges for use in landfill covers. Paper mill sludges are characterized by high water contents and organic contents. At the optimum moisture content, the paper sludges were unworkable. A high water content was desirable when designing a paper sludge landfill cover. The compressibilities of paper mill sludges are characterized by large reductions in void ratios and water contents. As the molding water content increases, the compressibility increases. As the organic content decreased, the compressibility decreased.; A high initial water content is desirable for the construction of a paper sludge cover to ensure a minimum permeability. As the organic content of paper sludge decreased, the permeability decreased. Paper sludges exhibited a decrease in permeability five times that for a typical clay over the same range in effective stresses. Initially, the sludge may not meet the regulatory requirement for permeability (often {dollar}1 times 10sp{lcub}-7{rcub}{dollar} cm/sec or less). However, the change in void ratio that results from the application of an overburden pressure (i.e., drainage layer and vegetative support layer) can reduce the permeability to an acceptable value in a relatively short period of time as shown by laboratory permeability tests conducted on insitu samples from two landfills.; Freezing and thawing cycling conducted on remolded paper sludge samples resulted in an increase in permeability of one to two orders of magnitude. Macrostructure analysis of the thin sections conducted by using back lighting and by using microscopy revealed details of ice structure in clays, but did not reveal the same ice structures in paper sludge. The high water content and organic content of paper sludge contributed to the lack of visible shrinkage cracks and ice lenses.; The depth of frost penetration at landfills that used paper sludge and clay as the hydraulic barrier was measured using a frost measurement system. From December, 1992 to January, 1995, no freezing occurred into the sludge layer. The high water content and the drainage and vegetation layer prevented the penetration of the freezing front. Freezing occurred into the clay layer, since it was unprotected from the freezing front.