Determination of Surface and Thickness Characteristics of Textured Geomembranes Using Image Analysis

Image analysis was used to determine surface topography and thickness of textured geomembranes. Images of cross sections (specimen length × thickness) of geomembranes were obtained at 50× magnification using a digital optical microscope. Thickness was determined as the distance between the top and bottom surfaces along an entire cross section. For surface analysis, profiles of top and bottom surfaces were extracted from the cross section images. Amplitude, spatial, hybrid, and functional texture parameters were determined. Tests were conducted on eleven samples of HDPE and LLDPE geomembranes manufactured by co-extrusion and embossing at varying thicknesses. The geomembranes were classified into three texture categories: high, medium, and low. Anisotropy and directionality were observed for all samples to varying degrees between and within manufacturing directions, respectively. Statistical analysis of the results indicated that surface topography of geomembranes could be determined by analyzing one surface of five specimens with 50 mm length. Comparisons were made between image analysis and mechanical tests for core thickness and asperity height. Image analysis and mechanical measurements were significantly different. Recommendations were made for the redesign of the mechanical devices by sizing the components in relation to the size and spacing of geomembrane texture features

Analysis of Temperatures at a Municipal Solid Waste Landfill

A study is conducted to determine the thermal regime within and around a municipal solid waste landfill located in midwestern U.S.A. Spatial distributions of temperatures have been determined over time since 1999 within the waste mass, liner and cover systems, and surrounding subgrade. Seasonal variations, placement of waste, age of waste, depth and location of waste, and available moisture have significant effects on temperatures. Temperatures of wastes at shallow depths, bottom liner systems prior to waste placement, and final cover systems conform to seasonal temperature variations. Steady elevated temperatures are reached with respect to air and ground temperatures at central locations and at depth in the waste mass. Increasing trends are observed for temperatures in wastes and bottom liner systems in cells containing newly placed wastes. It is estimated that waste temperatures increased due to effects of leachate recirculation at portions of the facility. Subgrade temperatures at the perimeter of the landfill have not yet been significantly affected by the presence of the facility

Implications of variable waste placement conditions for MSW landfills

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

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

Temperature effects on the swelling and bentonite extrusion characteristics of GCLs

This investigation was conducted to evaluate effects of temperature on swelling and bentonite extrusion properties of GCLs. The swelling characteristics were determined using standardized test procedures and extrusion characteristics were determined using a new test method developed by the authors. Tests were conducted on a conventional medium-weight woven/nonwoven GCL. The range of test temperatures was 2 to 98°C (swelling tests) and -5 to 100°C (extrusion tests). The extrusion tests were conducted under stresses between 100 and 400 kPa and moisture contents between 50 and 150%. Temperature had significant effects on both swell and extrusion. The swell index ranged from 21 mL/2g at 2°C to 36.5 mL/2g at 98°C, with the largest increase occurring from 20 to 40°C. The amount of extrusion ranged from nearly 0 to 40.5 g/m2 with generally decreasing extrusion with temperature from 2 to 100°C. At a given temperature, extrusion increased with increasing stress and moisture content

Use of Post-Consumer Corrugated Fiberboard as Fine Aggregate Replacement in Controlled Low-Strength Materials

This study was conducted to investigate the use of post-con­sumer corrugated board in controlled low-strength material (CLSM) applica­tions. Corrugated fiberboard (termed corrugate), which constitutes a significant fraction of the municipal solid waste stream in the United States (approximately one third by weight), was used as a partial replacement for fine aggregate in CLSM at aggregate replacement ratios ranging from 0 % (i.e., control) to 6 %. The corrugate was fiberized (i.e., repulped) in a blender prior to being mixed with other constituents in the CLSM. The density, air con­tent, and flow consistency of the fresh CLSM were determined, and bleeding was qualitatively assessed. Also, the unconfined compressive strength was determined for the resulting mixtures at different test ages. As the corrugate content increased, air content and water demand increased, density and compressive strength decreased, and some mixtures exhibited excessive bleeding. Corrugated fiberboard was determined to be effective as a fine ag­gregate replacement to produce mixtures with 28-day compressive strengths within the range for excavatable CLSM

Desiccation and Cracking Behavior of Three Compacted Landfill Liner Soils

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 wet–dry cycles, the amount of cracking did not change significantly after the second cycle

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