This investigation was conducted to evaluate experimental determination of specific gravity (Gs) of municipal solid waste (MSW). Water pycnometry, typically used for testing soils was adapted for testing MSW using a large flask with 2000 mL capacity and specimens with 100-350 g masses. Tests were conducted on manufactured waste samples prepared using US waste constituent components; fresh wastes obtained prior and subsequent to compaction at an MSW landfill; and wastes obtained from various depths at the same landfill. Factors that influence specific gravity were investigated including waste particle size, compaction, and combined decomposition and stress history. The measured average specific gravities were 1.377 and 1.530 for as-prepared/uncompacted and compacted manufactured wastes, respectively; 1.072 and 1.258 for uncompacted and compacted fresh wastes, respectively; and 2.201 for old wastes. The average organic content and degree of decomposition were 77.2% and 0%, respectively for fresh wastes and 22.8% and 88.3%, respectively for old wastes. The Gs increased with decreasing particle size, compaction, and increasing waste age. For fresh wastes, reductions in particle size and compaction caused occluded intraparticle pores to be exposed and waste particles to be deformed resulting in increases in specific gravity. For old wastes, the high Gs resulted from loss of biodegradable components that have low Gs as well as potential access to previously occluded pores and deformation of particles due to both degradation processes and applied mechanical stresses. The Gs was correlated to the degree of decomposition with a linear relationship. Unlike soils, the Gs for MSW was not unique, but varied in a landfill environment due both to physical/mechanical processes and biochemical processes. Specific gravity testing is recommended to be conducted not only using representative waste composition, but also using representative compaction, stress, and degradation states.

This investigation was conducted to evaluate the influence of waste placement practices on the engineering response of municipal solid waste (MSW) landfills. Waste placement conditions were varied by moisture addition to the wastes at the time of disposal. Tests were conducted at a California landfill in test plots (residential component of incoming wastes) and full-scale active face (all incoming wastes including residential, commercial, and self-delivered components). The short-term effects of moisture addition were assessed by investigating compaction characteristics and moisture distribution and the long-term effects by estimating settlement characteristics of the variably placed wastes. In addition, effects on engineering properties including hydraulic conductivity and shear strength, as well as economic aspects were investigated. The unit weight of the wastes increased with moisture addition to a maximum value and then decreased with further moisture addition. At the optimum moisture conditions, 68% more waste could be placed in the same landfill volume compared to the baseline conditions. Moisture addition raised the volumetric moisture content of the wastes to the range 33-42%, consistent with values at and above field capacity. Moisture transfer occurred between consecutive layers of compacted wastes and a moisture addition schedule of 2 days of as-received conditions and 1 day of moisture addition was recommended. Settlement of wastes was estimated to increase with moisture addition, with a 34% increase at optimum moisture compared to as-received conditions. Overall, moisture addition during compaction increased unit weight, the amount of incoming wastes disposed in a given landfill volume, biological activity potential, and predicted settlement. The combined effects have significant environmental and economic implications for landfill operations.

Effects of Waste Placement Practices on the Engineering Response of MunicipalSolid Waste Jason T. Cox An extensive laboratory and field investigation was conducted at Santa Maria Regional Landfill (SMRL) in Santa Maria, California to determine the effects of waste placement practices on the engineering response of municipal solid waste (MSW). Laboratory and field testing was used to determine the engineering properties and monitor field response of MSW.The specific gravity (G s ) of manufactured MSW (MMSW), fresh MSW (FMSW), and old MSW (OMSW) was determined experimentally using a modified version of standard soil testing procedures. Effects of particle size, compactive effort, and degradation on the specific gravity of waste were evaluated. Specific gravity of manufactured waste samples increased with decreasing particle size, with compaction, and with increased degradation. The average specific gravity of uncompacted MMSW samples was 1.333, 1.374, and 1.424 for coarse, medium, and fine particle sizes, respectively. Specific gravity of coarse, medium, and fine MMSW samples compacted at dry of optimum ( = 30%) was determined to be 1.497, 1.521, and 1.552, respectively and at wet of optimum ( = 90%) to be 1.500, 1.542, and 1.570, respectively. The compacted and uncompacted specific gravity of fresh MSW was lower than manufactured and old MSW. The average G s of uncompacted and compacted fresh MSW was 1.072 and 1.208, respectively whereas old MSW had G s of 2.201.v Additional physical and engineering properties of MSW were determined for fresh and old wastes. A total of 8 magnetic extensometer settlement arrays and 4 thermocouple arrays were installed in old wastes. The settlement and temperature data were collected for an approximate duration of 1 year. In addition, laboratory experiments were conducted to determine the particle size distribution, organic content, and moisture content of fresh waste sampled from the active face of the landfill and from old waste sampled from different depths.The particle size distribution of OMSW was comparable to a well-graded coarsegrained soil. The average baseline moisture content of incoming MSW at SMRL was 42.7% (dry-weight basis). The average moisture content of residential MSW, commercial MSW, and self-delivered MSW were determined to be 57.7, 46.3, and 12.0%, respectively. The organic content of fresh and old MSW was determined to be 77.2 and 23.5%, respectively. Temperature increased over time due to heat generation of the waste mass. The temperature increased on average 3 to 6°C between the initial and final day of measurements for wastes that were 0.3 to 9 years old.Fresh and old wastes at SMRL exhibited unique compression behavior. A majority of the waste was undergoing secondary compression characterized using a secondary compression ratio ( ′ ) ranging from 0.013 to 0.067 with an average of 0.030. In addition, the fresh and old wastes exhibited recompression behavior. Fresh waste lifts were determined to be slightly overconsolidated such that the self-weig...