Experimental and statistical evaluation of compressibility of fresh and landfilled municipal solid waste under elevated moisture contents

Abstract

An investigation of the variability associated with primary and secondary compression indices of municipal solid waste (MSW) is conducted in the present study. A controlled laboratory experimental program was conducted to quantify the compressibility of fresh MSW and landfilled MSW (subjected to leachate recirculation for a year in the field) under different elevated moisture content conditions. Several series of one-dimensional compressibility experiments were conducted on fresh and landfilled waste samples under the field moisture content of 44% (by dry weight) and three elevated moisture contents of 60, 80 and 100% (by dry weight). The compression of waste samples was measured at different elapsed time periods under incremental normal stresses of 48, 96, 192, 383, and 766 kPa. The modified compression indices (or compression ratios) were calculated based on the measured compression versus stress data. Long term secondary compression behavior was determined by performing long term compression tests on fresh and landfilled waste samples under normal stress of 383 kPa. The steep slope is not evident on the vertical stress – strain plot for the 44% moisture content sample, potentially owing to breakdown of micro-fabric and mini-fabric of fresh waste and rearrangement of the particles. It is observed from the present study that the magnitudes of modified primary compression index for fresh MSW exhibited no specific correlation with an increase in moisture content from 44 to 100% owing to variations in the initial composition of fresh MSW, small scale laboratory testing, and rate of biodegradation of MSW. For a constant vertical stress, the landfilled waste compressed less than the fresh waste at initial and elevated sample moisture contents owing to reduction of organic content in the degraded waste. Based on the compilation of compression indices from several published studies, the average values of mean, standard deviation and coefficient of variation for modified primary compression and secondary compression indices are computed. Overall, this study demonstrated that the long term compression characteristics can highly vary depending on the waste composition, moisture content, and biodegradation. From the statistical analysis, it is determined that the variability associated with secondary compression index is significantly higher than the primary compression index , which may be attributed to significant differences in the biodegradable content of waste and associated extent and rate of biodegradation of waste.