Nazli Yesiller

Spatial and Temporal Temperature Distributions in Municipal Solid Waste Landfills

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 locations 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 temperature profiles were observed for winter waste placement. The highest heat gain and resulting high tem...

Experimental investigation of dynamic response of compacted clayey soils

A study was conducted to determine the dynamic properties of compacted clayey soils subjected to low amplitude vibration. A fast and simple ultrasonic pulse transmission method was used. Tests were conducted on three clayey soils with low to high plasticity compacted using standard and modified Proctor effort over a range of water contents. The samples were allowed to dry after compaction and P-wave velocity, S-wave velocity, Poissons ratio, and shear modulus were determined. The effects of soil type, compaction conditions, and degree of saturation on the dynamic response of the soils were investigated. The elastic wave velocities and the dynamic shear modulus increased as the soil plasticity decreased. The velocities and the modulus increased and the Poissons ratio decreased as the degree of saturation decreased due to drying. Generally, the velocities and moduli increased significantly at the early stages of drying with the changes becoming more gradual as drying progressed. Variations were high for soils compacted with low energy and high water content. The shear moduli of the soils were also estimated using a common empirical equation. Suction values obtained for the test soils in a different study were used as effective stresses in the estimation. The estimated shear moduli agreed well with the measured values.

Ultrasonic Pulse Velocity in Concrete Using Direct and Indirect Transmission

This research investigated the relationship between velocities of ultrasonic stress waves transmitted along direct and indirect paths. Tests were conducted on plain concrete slabs of dimensions 1000 x 1500 mm, with thickness of 250 mm. Direct ultrasonic wave transmission tests were conducted between top and bottom surfaces of the slabs and indirect tests were conducted along the slab surface. A test procedure, used to determine indirect wave velocities, was refined by defining the number and spacing of transducers. Comparisons were made between direct and indirect wave velocity measurements using statistical analysis. The statistical analysis revealed that direct and indirect wave velocities could be used interchangeably to evaluate properties of the concrete. The minimum number of test points required for a reliable estimate of indirect wave velocity was studied, and recommendations are provided.

Compaction Characteristics of Municipal Solid Waste

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 laboratory were γdmax-mod =5.2 kN/ m3 , wopt-mod =65% , γdmax-4×mod =6.0 kN/ m3 , and wopt-4×mod =56% ; in the field with effort were γdmax-low =5.7 kN/ m3 , wopt-low =70% ; γdmax-high =8.2 kN/ m3 , and wopt-high =73% ; ...

Analytical and Numerical Methodology for Modeling Temperatures in Landfills

Analytical and numerical approaches have been developed for modeling temperatures in municipal solid waste landfills. Steps for model formulation and details of boundary conditions are described. The formulation was based on a transient conductive heat transfer analysis. Conventional earth temperature theories were modified for landfill systems by incorporating heat generation functions representing biological decomposition of wastes. Finite element analysis was used for general modeling and parametric evaluations. Thermal properties of materials were determined using field observations and data reported in literature. The boundary conditions consisted of seasonal temperature cycles at the ground surface (established using near-surface field measurements) and constant temperatures at the far-field boundary (established using field measurements and maps of regional groundwater temperatures). For heat generation, first a step-function was developed to provide initial (aerobic) and residual (anaerobic) conditions. Second, an exponential growth- decay function was established; and third, the function was scaled for climatic conditions. 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.

Ultrasonic Testing for Compacted Clayey Soils

In this study, tests were conducted to investigate the use of ultrasonic methods to determine compaction characteristics of clayey soils. In particular, through-transmission test method was used to determine P-wave velocities in compacted clayey soils. Effects of soil type and compaction conditions on velocity were investigated. Tests were conducted on three soils that had low, medium, and high plasticity. Soils were prepared at water contents ranging from dry to wet of optimum using standard and modified compaction efforts. It was observed that velocity increased with increasing compactive effort and decreasing plasticity and clay content. Moreover, the variation of ultrasonic velocity with water content was similar to the variation of dry density with water content. Shapes of the water content versus velocity plots correlated well with the shapes of compaction plots. Access to two opposite surfaces of samples was required to perform through-transmission measurements. Additional tests were conducted to determine the feasibility of using surface-transmission with access required only to top surface of soils to measure velocity. Velocities that were similar to through-transmission velocities were obtained with surface measurements using correction factors. Through-transmission can be used in the laboratory; whereas surface-transmission can potentially be used in the field to determine ultrasonic velocity of compacted clayey soils. This method shows promise for determination of compaction properties of clayey soils in the field.

Waste heat generation: A comprehensive review

A comprehensive review of heat generation in various types of wastes and of the thermal regime of waste containment facilities is provided in this paper. Municipal solid waste (MSW), MSW incineration ash, and mining wastes were included in the analysis. Spatial and temporal variations of waste temperatures, thermal gradients, thermal properties of wastes, average temperature differentials, and heat generation values are provided. Heat generation was influenced by climatic conditions, mean annual earth temperatures, waste temperatures at the time of placement, cover conditions, and inherent heat generation potential of the specific wastes. Time to onset of heat generation varied between months and years, whereas timelines for overall duration of heat generation varied between years and decades. For MSW, measured waste temperatures were as high as 60-90°C and as low as -6°C. MSW incinerator ash temperatures varied between 5 and 87°C. Mining waste temperatures were in the range of -25 to 65°C. In the wastes analyzed, upward heat flow toward the surface was more prominent than downward heat flow toward the subsurface. Thermal gradients generally were higher for MSW and incinerator ash and lower for mining waste. Based on thermal properties, MSW had insulative qualities (low thermal conductivity), while mining wastes typically were relatively conductive (high thermal conductivity) with ash having intermediate qualities. Heat generation values ranged from -8.6 to 83.1MJ/m(3) and from 0.6 to 72.6MJ/m(3) for MSW and mining waste, respectively and was 72.6MJ/m(3) for ash waste. Conductive thermal losses were determined to range from 13 to 1111MJ/m(3)yr. The data and analysis provided in this review paper can be used in the investigation of heat generation and thermal regime of a wide range of wastes and waste containment facilities located in different climatic regions.

Determination of specific gravity of municipal solid waste

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.

Development of Numerical Model for Predicting Heat Generation and Temperatures in MSW Landfills

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.

Thermal Properties of High Water Content Materials

Thermal Properties of High Water Content Materials Abstract: Fundamental thermal properties of various high water content materials were determined using a number of thermal testing methods. Tests were conducted on peat soils, solid wastes, industrial sludge, and bentonite slurries. Thermal conductivity, heat capacity, and thermal diffusivity were determined. The thermal conductivity of the materials was determined using a needle probe method. The volumetric heat capacity of the materials was determined using a dual probe method. These values were used together to obtain thermal diffusivity. Analytical methods are also used to determine heat capacity and thermal diffusivity. The theory for determination of thermal parameters using the various methods is presented. Experimental methods were determined to be effective at measuring thermal properties of high water content materials. Thermal parameters are dependent on material composition and structure. Heat capacity and thermal diffusivity are greatly affected by water content because of the high heat capacity of water compared with air and solids. A comparison is made between experimental and analytical methods used to determine thermal parameters. Good agreement was observed between experimental and analytical methods. Results of thermal tests have applications in the prediction of heat transfer through soils, sludges, and wastes.