Tests were conducted to investigate desiccation cracking of three compacted liner soils obtained from local landfills in southeast Michigan. The soils had low plasticity with varying fines content. Large-scale samples of the soils were subjected to wetting and drying cycles. Surficial dimensions of cracks and suction in the soils were monitored. Surficial dimensions of cracks were quantified using the crack intensity factor (CIF), which is the ratio of the surface area of cracks to the total surface area of a soil. All of the soils were subjected to a compaction-dry cycle (i.e. soils were allowed to dry after compaction) and a subsequent wet-dry cycle. An additional sample of one of the soils was subjected to a compaction-dry cycle and three wet-dry cycles. The maximum CIF obtained in the tests was 7% and suctions exceeding 6000 kPa were recorded. It was observed that cracking was affected by the fines content of the soils. In general, high suctions, rapid increases in suctions, and high amount of cracking were observed in soils with high fines content, with less cracking observed in soil with low fines content. In addition, it was observed that cracking increased significantly due to addition of moisture to the soils. The CIF for wet-dry cycles were significantly greater than the CIF for compaction-dry cycles. Subsequent to moisture addition to the soils, critical suctions that caused a significant change in CIF during the drying cycles were <1000 kPa for all the soils. In the test with multiple wet-dry cycles, the amount of cracking did not change significantly after the second cycle.

A laboratory investigation on a scaled model of a landfill liner was conducted to provide data regarding the occurrence and extent of desiccation cracking of prototype liners. The crack intensity factor, CIF, was introduced as a descriptor of the extent of surficial cracking. CIF is defmed as the ratio of the surface crack area A, to the total surface area of the clay liner, At. A computer aided image analysis program was used to determine CII' values from scanned photographs of the desiccation process. The variation of the CII' was related to duration of drying and measured soil moisture suctions.The soil of this investigation experienced significant cracking, with crack widths approaching 10 mm in the first drying cycle and penetration through the entire 16 cm thickness. Crack propagation was limited to a very intense period of the desiccation process.Nearly 90 percent of the crack development occurred during a 19hour time period, although the total duration of the desiccation cycle was approximately 170 hours. The soil moisture suction changed by only 2 bars during the period of rapid crack growth, although it changed by more than 40 bars during the period of reduced growth.

This study was conducted to investigate thermal aspects of municipal solid waste landfills as a function of operational conditions and climatic region. Spatial and temporal distributions of waste temperatures were determined at four landfills located in North America �Michigan, New Mexico, Alaska, and British Columbia�. Temperatures of wastes at shallow depths �extending to 6 to 8 m depth� and near the edges of a cell �within approximately 20 m� conformed to seasonal temperature variations, whereas steady elevated temperatures �23 to 57°C� with respect to air and ground temperatures were reached at depth and at central locations. Waste temperatures decreased from the elevated levels near the base of landfills, yet remained higher than ground temperatures. Thermal gradients in the range of approximately −30 to +22°C / m with average absolute values typically less than 5°C / m were measured within the wastes. Heat content �HC� of wastes was determined as the difference between measured waste mass temperatures and unheated baseline waste temperatures at equivalent depths. Peak HC values ranged from 12.5 to 47.8°C day/ day. The peak HCs were directly correlated with waste placement rates and initial waste temperatures, and they occurred at a specific average precipitation �2.3 mm/ day� beyond which further precipitation did not contribute to heat generation. HC was determined to conform to exponential growth and decay curve relationships as a function of climatic and operational conditions. Heat generation was determined based on HC using 1D heat transfer analysis. The heat generation values ranged from 23 to 77 MJ/ m 3 without losses and were significantly higher than biochemical prediction models, yet lower than values from incineration analyses. Overall, the highest values for temperatures, gradients, HC, and heat generation were observed in Michigan, followed by British Columbia, Alaska, and New Mexico. Integrated analysis of temperature and gas composition data indicated that temperature increases and HC values were greater during anaerobic decomposition than aerobic decomposition. Sustained high temperatures and heat generation occurred in wastes under anaerobic conditions.

Long-term spatial and temporal variations in temperatures have been investigated in covers, wastes, and liners at four municipal solid waste landfills located in different climatic regions: Alaska, British Columbia, Michigan, and New Mexico. Temperatures were measured in wastes with a broad range of ages from newly placed to old �up to 40 years�. The characteristic shape of waste temperature versus depth relationships consisted of a convex temperature profile with maximum temperatures observed at central loca tions within the middle third fraction of the depth of the waste mass. Lower temperatures were observed above and below this central zone, with seasonal fluctuations occurring near the surface and steady and elevated values �above mean annual earth temperature� near the base of the landfills. Heat gain and long-term temperatures were directly affected by placement temperatures. Sustained concave tem perature profiles were observed for winter waste placement. The highest heat gain and resulting high temperatures were observed in Michigan followed by British Columbia, New Mexico, and Alaska. The high heat gain in Michigan was attributed to coupled precipitation/moisture content and waste density. The time-averaged waste temperature ranges were 0. 9-33.0, 14.4-49.2, 14.8-55.6, and 20.5-33.6°C in Alaska, British Columbia, Michigan, and New Mexico, respectively. Temperature increases occurred rapidly �over multiple years� in British Columbia and then dissipated for tens of years. Longer periods of temperature increase were observed at the other sites. Temperatures, temperature increases, and heat gain were higher during anaerobic decomposition of wastes than aerobic decomposition. A parametric study indicated that use of insulating materials over covers decreased temperature variations compared to uninsulated conditions for prevention of frost penetration or desiccation and for optimum methane oxidation. Overall, thermal regime of landfills is controlled by climatic and operational conditions.

Tests were conducted to determine the variation of water content and pore water suction for compacted clayey soils. The soils had varying amounts of clay fraction with plasticities ranging from low to high plasticity. The unsaturated soil behavior was investigated for six conditions, covering a range of compactive efforts and water contents. The experimental data were fit to four commonly used models for the water content-pore water suction relationship. Each model provided a satisfactory fit to the experimental data. However, the individual parameters obtained from the curve fits varied significantly between models. The soil water characteristic curves �SWCCs� were more sensitive to changes in compaction effort than changes in compaction water content. At similar water contents, the pore water suction increased with increasing compaction effort for each compaction condition and soil type. For all compaction conditions, the lowest plasticity soils retained the smallest water content and the highest plasticity soils retained the highest water content at a specified suction. In addition, SWCCs for soils compacted in the laboratory and in the field were similar.

A numerical modeling approach has been developed for predicting temperatures in municipal solid waste landfills. Model formulation and details of boundary conditions are described. Model performance was evaluated using field data from a landfill in Michigan, USA. The numerical approach was based on finite element analysis incorporating transient conductive heat transfer. Heat generation functions representing decomposition of wastes were empirically developed and incorporated to the formulation. Thermal properties of materials were determined using experimental testing, field observations, and data reported in literature. The boundary conditions consisted of seasonal temperature cycles at the ground surface and constant temperatures at the far-field boundary. Heat generation functions were developed sequentially using varying degrees of conceptual complexity in modeling. First a step-function was developed to represent initial (aerobic) and residual (anaerobic) conditions. Second, an exponential growth-decay function was established. Third, the function was scaled for temperature dependency. Finally, an energy-expended function was developed to simulate heat generation with waste age as a function of temperature. Results are presented and compared to field data for the temperature-dependent growth-decay functions. The formulations developed can be used for prediction of temperatures within various components of landfill systems (liner, waste mass, cover, and surrounding subgrade), determination of frost depths, and determination of heat gain due to decomposition of wastes.

The effects of placement practices on decomposition of wastes were investigated at Anchorage Regional Landfill (Anchorage, Alaska) since 2002. Temperatures and gas concentrations of wastes placed at various seasons were monitored. Wastes were placed at sub-freezing temperatures during cold seasons. Waste temperatures generally increased upon placement.High variation was observed in waste temperatures near the surface whereas steady temperatures were obtained at depth. High maximum stable temperatures resulted from warm placement conditions. Steady temperatures between approximately -1 to +35°C were observed. The central portion of a frozen waste band (with a total initial thickness of 7 m at placement, currently between depths of approximately 8 m to 15 m) remains frozen 2 years after placement. Both the top and bottom regions of the frozen waste band have thawed. Heat Content (HC) varied between -8.2 (for 2-year-old waste at a depth of 11.9 m in frozen wastes) to +25.9°C-day/day (for 13-year-old waste at a depth of 32 m for waste placed in summer). The measured frost depths in waste ranged from 0.7 to 1.3 m and were less than that for native soil at the landfill site. Instantaneous thermal gradients ranged from -73 to +60°C/m. Gas concentrations were similar to air at the time of waste placement. Anaerobic decomposition conditions and onset of landfill gas production started within 3 to 4 years of placement for wastes placed during warm seasons. Virtually no decomposition or gas generation were observed in the frozen wastes. A 1-D numerical model was used to investigate distribution of temperatures for placement at varying temperatures and for varying lift thicknesses. It is recommended to minimize frozen lift thicknesses to obtain higher temperatures.

Compaction characteristics of municipal solid waste �MSW� were determined in the laboratory and in the field as a function of moisture content, compactive effort, and seasonal effects. Laboratory tests were conducted on manufactured wastes using modified and 4X modified efforts. Field tests were conducted at a MSW landfill in Michigan on incoming wastes without modifications to size, shape, or composition, using typical operational compaction equipment and procedures. Field tests generally included higher efforts and resulted in higher unit weights at higher water contents than the laboratory tests. Moisture addition to wastes in the field was more effective in winter than in summer due to dry initial conditions and potential thawing and softening of wastes. The measured parameters in the 3 3 laboratory were � dmax-mod = 5.2 kN/ m , w opt-mod = 65%, � dmax-4�mod = 6.0 kN/ m , and w opt-4�mod = 56%; in the field with effort were 3 3� dmax-low = 5.7 kN/ m , w opt-low = 70%; � dmax-high = 8.2 kN/ m , and w opt-high = 73%; and in the field with season were � dmax-cold 3 = 8.2 kN/ m , w cold = 79.5%, � dmax-warm = 6.1 kN/ m 3 , and w warm = 70.5%. Soil compaction theory was reasonably applicable to wastes with the exception that the G s of waste solids increased with compactive effort resulting in steep degree of saturation curves and low change in w opt between efforts. Moisture addition to wastes during compaction increased the workability, the unit weight, and the amount of incoming wastes disposed, and reduced the compaction time. The combined effects have significant environmental and economic impli cations for landfill operations.