Hiroshan Hettiarachchi

Compressibility and shear strength of municipal solid waste under short-term leachate recirculation operations

This paper describes a comprehensive laboratory study performed to investigate the compressibility and shear strength properties of 1.5-year-old municipal solid waste (MSW) exhumed from a landfill cell where low amounts of leachate were recirculated. The study results are compared with results from a previous study on fresh MSW collected from the same landfill and data from previous studies with known MSW age to assess the variation in properties due to degradation. Laboratory testing was conducted on shredded landfilled and fresh MSW that consisted of similar particle-size distribution, with maximum particle size less than 40 mm and approximately 80% of the waste consisting of particles ranging from 10 to 20 mm. Standard Proctor, compressibility, direct shear, and triaxial consolidated undrained (CU) shear tests were conducted in general accordance with the American Society of Testing and Materials Standard Procedures. These tests were conducted with samples at an in-situ moisture content of 44% (dry weight basis) as well as elevated moisture contents of 60, 80 and 100% (dry weight basis). Standard Proctor compaction tests yielded a maximum dry density of 600 kg/m3 at 77% optimum moisture content for landfilled MSW compared to the 420 kg/m3 maximum dry density at 70% optimum moisture content for fresh MSW. Compression ratio values for landfilled MSW varied in a close range of 0.19—0.24 with a slight increasing trend with increase in moisture content; however, for fresh waste they were in the close range of 0.24—0.33 with no definitive correlation with moisture content. Based on direct shear tests, drained cohesion and friction angle were varied in the range of 12—64 kPa and 31—35° for landfilled MSW and 31—64 kPa and 26—30° for fresh MSW. Neither cohesion nor friction angle demonstrated any correlation with the moisture content. Based on triaxial CU tests, the average total strength parameters (TSP) were found to be 39 kPa and 12° for landfilled MSW and 32 kPa and 12° for fresh MSW, while effective strength parameters (ESP) were 34 kPa and 23° for landfilled MSW and 32 kPa and 16° for fresh MSW. This study was limited to small-scale laboratory testing using MSW samples with the specimen size relative to the maximum particle size in the range of 1.6 to 2.6; therefore, large-scale laboratory and field studies are recommended to systematically assess the influence of composition, particle size distribution and specimen size on the geotechnical properties of MSW.

Geotechnical properties of municipal solid waste at different phases of biodegradation

This paper presents the results of laboratory investigation conducted to determine the variation of geotechnical properties of synthetic municipal solid waste (MSW) at different phases of degradation. Synthetic MSW samples were prepared based on the composition of MSW generated in the United States and were degraded in bioreactors with leachate recirculation. Degradation of the synthetic MSW was quantified based on the gas composition and organic content, and the samples exhumed from the bioreactor cells at different phases of degradation were tested for the geotechnical properties. Hydraulic conductivity, compressibility and shear strength of initial and degraded synthetic MSW were all determined at constant initial moisture content of 50% on wet weight basis. Hydraulic conductivity of synthetic MSW was reduced by two orders of magnitude due to degradation. Compression ratio was reduced from 0.34 for initial fresh waste to 0.15 for the mostly degraded waste. Direct shear tests showed that the fresh and degraded synthetic MSW exhibited continuous strength gain with increase in horizontal deformation, with the cohesion increased from 1 kPa for fresh MSW to 16-40 kPa for degraded MSW and the friction angle decreased from 35° for fresh MSW to 28° for degraded MSW. During the triaxial tests under CU condition, the total strength parameters, cohesion and friction angle, were found to vary from 21 to 57 kPa and 1° to 9°, respectively, while the effective strength parameters, cohesion and friction angle varied from 18 to 56 kPa and from 1° to 11°, respectively. Similar to direct shear test results, as the waste degrades an increase in cohesion and slight decrease in friction angle was observed. Decreased friction angle and increased cohesion with increased degradation is believed to be due to the highly cohesive nature of the synthetic MSW. Variation of synthetic MSW properties from this study also suggests that significant changes in geotechnical properties of MSW can occur due to enhanced degradation induced by leachate recirculation.

Effects of gas and moisture on modeling of bioreactor landfill settlement.

This manuscript describes a model that can predict settlement at variable moisture and pressure conditions as encountered in bioreactor landfills. In this model mechanical compression of municipal solid waste (MSW) was accounted with the help of laboratory compression tests. To model biodegradation-induced settlement, biodegradation of MSW was assumed to obey a first order decay equation. Richards equation was used to model moisture transport in the waste mass and mass balance was used to link settlement with gas pressure. The functionality of the numerical formulation was examined using a hypothetical bioreactor landfill. Four scenarios were analyzed to demonstrate how the proposed model can be used to analyze the settlement behavior of bioreactor landfills as well as dry landfills. The model predicted higher strains when moisture and gas pressures were incorporated into the settlement process. Results also indicated that the prediction capability of a MSW settlement model can be improved by coupling the settlement mechanisms with the generation and dissipation of gas pressure and the moisture distribution. The model is also able to predict landfill density values, and the predicted MSW wet density after 25 years agreed reasonably with those reported in literature.

Geotechnical properties of synthetic municipal solid waste

Abstract This paper presents the results of laboratory investigation performed to determine the geotechnical properties of synthetic municipal solid waste (SMSW) simulating typical composition of municipal solid waste (MSW) generated in the United States. Initial characterization of SMSW was performed through the determination of particle size distribution, moisture content, and organic content. Hydraulic conductivity, compression ratio, and shear strength were studied for their variation and significance through replicate testing. Hydraulic conductivity ranged between 1.2 × 10-5 to 7.62 × 10-8 cm/s which is lower than that of field MSW, mainly due to the use of low-permeable glacial till soil to represent inert fraction of SMSW. Compression ratio ranged between 0.16 and 0.31 which is within the range reported for fresh MSW. Drained direct shear tests resulted in cohesion 16-19 kPa and friction angle 27-29°; these results are within the range reported in the literature for fresh MSW. Based on the results from triaxial consolidated undrained (CU) shear tests, SMSW exhibited cohesive behavior with 22 kPa cohesion and 7° friction angle as the total stress parameters. This study showed that the compressibility and direct shear behavior of SMSW tested during this research were similar to fresh MSW, but hydraulic conductivity and triaxial CU shear strength were different. Replicate testing and statistical analyses demonstrated that the test results did not vary significantly hence repeatability was assured.

Geotechnical Properties of Municipal Solid Waste Subjected to Leachate Recirculation

This paper compares the geotechnical properties of fresh municipal solid waste (MSW) to landfilled MSW obtained from a bioreactor landfill. Fresh MSW samples were collected from the working face of Orchard Hills Landfill. Landfilled MSW (15-19 months old, subjected to intermittent very low flow leachate recirculation for a year) samples were recovered from a borehole located near a multi- level horizontal leachate recirculation system in the same landfill. Laboratory testing was performed on shredded samples to determine the variation in in-situ moisture content, organic content, biochemical methane potential (BMP), specific gravity, density, hydraulic conductivity, compressibility, and shear strength properties of fresh as well as landfilled MSW. In-situ dry gravimetric moisture content of fresh MSW was around 44% and landfilled MSW varied between 21-43%. Organic content of the fresh MSW was 76% whereas degradation and presence of other components in landfilled MSW resulted in organic content between 62-68%. Due to the presence of finer particles, reconstituted dry density of landfilled MSW was 601-712 kg/m 3 whereas fresh waste was 515 kg/m 3 . For confining pressure greater than 69 kPa, both fresh and landfilled waste possessed similar hydraulic conductivity. Compressibility test results showed higher strains for fresh MSW than for the landfilled, with compression index of 0.28 for fresh and 0.22 for landfilled MSW. Based on direct shear testing, shear strength properties for fresh MSW were: c�=47 kPa and ��=29 0

Environmental Resource Management and the Nexus Approach

This book elaborates how water, soil, and waste may be managed in a nexus and how this approach may help combat global change. In addition to providing a brief account on nexus thinking and how it may help us tackle issues important to the world community such as food security, the book presents the environmental resource perspective of three main aspects of global change: climate change, urbanization, and population growth. Taking as its point of departure the thematic discussions of the Dresden Nexus Conference (DNC 2015) held in March 2015, the book presents the perspectives of a number of thought leaders on how the nexus approach could contribute to sustainable environmental resource management. The first chapter provides an introduction to the issues and consent of the book. Chapters 2 and 3 focus on climate change adaptation. Chapters 4 and 5 discuss the role of urbanization as a main driver of global change. The last two chapters of the book present ideas on how the nexus approach may be used to cope with population growth and increased demand for resources.

Operation of a Landfill Bioreactor in a Cold Climate: Early Results and Lessons Learned

AbstractThis manuscript presents a detailed discussion of the challenges faced and lessons learned during the initial phase of operation of the Calgary Biocell. The Calgary Biocell is a full-scale pilot project that has been implemented to acquire data and demonstrate the applicability of the biocell concept under severe winter conditions. The biocell concept involves operating a waste cell in three phases: first as an anaerobic bioreactor to recover biogas and produce energy, second as an aerobic bioreactor or an in-ground composter, and finally mined to recover processed waste and land for reuse. The Calgary Biocell has been in operation in its first phase, as an anaerobic bioreactor, for over the past five years. The cell was equipped with sensors to gather performance data during anaerobic and aerobic bioreactor operation. The settlement, moisture content, pressure, and temperature sensors provided early data, but failed after several months of cell operation. Regular monitoring and repairs were perfo...

Estimating Shear Strength Properties of Soils Using SPT Blow Counts: An Energy Balance Approach

The subsurface exploration of a site is often the aspect of a project that gets overlooked during the design process. Many clients will get standard soil borings, but do not want to pay for a full laboratory analysis. Lack of data forces the designer to estimate important engineering properties of the soil. Very often the Standard Penetration Test (SPT) blow counts are used to estimate the shear strength properties of soil in foundation designs. Few correlations are widely used. However, no clear explanation is found to justify the selection most of these mathematical equations. This manuscript describes a new approach to estimate the shear strength parameters based on the SPT blow counts. In this method, the standard penetration test is treated analogous to driving a miniature pipe pile. The energy input to the soil is used to correlate the SPT blow count to the shear strength parameters of the soil at the depth of testing. Soil boring records from few different sites were analyzed and a statistical analysis revealed that the proposed method can provide a better estimation than the widely used existing correlations.

Managing Water, Soil, and Waste in the Context of Global Change

This is an introductory chapter to the book. It provides the background and brief discussion on how and why resource management efficiency should be improved and how the proposed nexus approach may help. It provides a definition to the nexus approach applied to the water-soil-waste context. It also discusses how the negative impacts from some global change aspects can be overcome with nexus thinking.

An Investigation on Erodibility and Geotechnical Characteristics of Fine Grained Fluvial Soils from Lower Michigan

Scour and erosion potential of a soil are closely related to each other. Similarities or differences between them have not been defined fully and the terms are often used interchangeably or in association with one another. Erodibility is a property of soil that describes erosion potential. Therefore, a proper understanding of erodibility should help predict scour more accurately. In the past, researchers have looked into erosion of soils with the ultimate objective of understanding the erodibility with respect to the standard geotechnical properties. Most research has shown the difficulties associated with correlating erodibility to any one or more soil properties. The research described in this paper is mainly focused on the relationship between erodibility and dry unit weight of soil with varying fractions of fines. Soils tested using laboratory Jet Erosion Test (JET) indicated that the logarithm of erodibility makes a linear inverse relationship with the dry unit weight. In situ JETs confirmed the range of erodibilities established by the laboratory JETs. The best correlations between erodibility and dry unit weight appeared within a single category of soil as classified by the Unified Soil Classification System. In addition, it was also determined that the logarithm of erodibility is inversely related to the angle of internal friction of the fluvial soils tested during this investigation.