Dimitrios Zekkos

Shear modulus and material damping of municipal solid waste based on large-scale cyclic triaxial testing

Representative dynamic properties of municipal solid waste (MSW) are required to perform reliable seismic analyses of MSW landfills. A comprehensive large-scale cyclic triaxial laboratory testing program was performed on MSW retrieved from a landfill in the San Francisco Bay area to evaluate the small-strain shear modulus, and strain-dependent normalized shear modulus reduction and material damping ratio relationships of MSW. The effects of waste composi- tion, confining stress, unit weight, time under confinement, and loading frequency on these dynamic properties were evaluated. The small-strain shear modulus depends primarily on waste composition, confining stress, unit weight, and time under confinement. The normalized shear modulus reduction and material damping curves for MSW depend on waste composition and confining stress. Based on the results of this study and a review of literature, strain-dependent shear modulus reduction and material damping relationships are recommended for use in landfill design.

Large-scale direct shear testing of municipal solid waste

Large direct shear testing (300 mm x 300 mm box) of municipal solid waste (MSW) collected from a landfill located in the San Francisco Bay area was performed to gain insight on the shear response of MSW. The study investigated the effects of waste composition, confining stress, unit weight, and loading rate on the stress-displacement response and shear strength of MSW. The amount and orientation of the fibrous waste materials in the MSW were found to play a critical role. The fibrous material had little effect on the MSWs strength when it was oriented parallel to the shear surface, as is typically the case when waste material is compressed vertically and then tested in a direct shear apparatus. Tests in which the fibrous material was oriented perpendicular to the horizontal shear surface produced significantly stronger MSW specimens. The test results indicate that confining stress and loading rate are also important factors. Based on 109 large-scale direct shear tests, the shear strength of MSW at low moisture contents is best characterized by cohesion=15 kPa, friction angle=36 degrees at a normal stress of 1 atmosphere, and a decrease in the friction angle of 5 degrees for every log-cycle increase in normal stress.

Physical Characterization of Municipal Solid Waste for Geotechnical Purposes

A procedure to characterize municipal solid waste (MSW) for geotechnical engineering purposes is developed based on experience with waste characterization and testing. Existing MSW classification systems are reviewed briefly, and the field and laboratory waste characterization programs of two important projects are presented. Findings on the influence of the wastes physical composition on its mechanical response from these projects and recent studies of MSW are integrated to develop a waste characterization procedure for efficient collection of the relevant information on landfill operation and waste physical characteristics that are most likely to affect the geotechnical properties of MSW. A phased approach to implementation of this procedure is proposed as a best practice for the physical characterization of MSW for geotechnical purposes. The scope of the phased procedure can be adjusted to optimize the effort required to collect relevant information on a project-specific basis. The procedure includes a systematic evaluation of the moisture and organic content of MSW, because they are important factors in the geotechnical characterization of MSW.

Drained response of municipal solid waste in large-scale triaxial shear testing

A comprehensive laboratory investigation was performed on municipal solid waste (MSW) from a landfill located in northern California using a large-scale triaxial (TX) apparatus. An improved, standardized waste specimen preparation method was developed and used to prepare 27 large-scale TX specimens (d=300 mm, h=600-630 mm). The effects of waste composition, confining stress, unit weight, loading rate, and stress path on the drained stress-strain response of MSW were investigated. Waste composition has a significant effect on its stress-strain response. The commonly observed upward curvature of the stress-strain response of specimens composed of larger-sized waste materials results from the fibrous constituents (primarily paper, plastic and wood) reinforcing the waste matrix. This effect is greatest when the MSW specimen is sheared across the long axis of the fibrous particles. Due to this significant strain hardening effect and wastes in situ stress state, a limiting strain failure criterion of 5% axial strain from the K(o) field consolidation state is judged to be most appropriate. Results from this test program and data from the literature indicate that the TX compression secant friction angle of MSW varies from 34° to 44°, with 39° as a best estimate, at a confining stress of one atmosphere (assuming c=0). The friction angle decreases as confining stress increases. The friction angles measured in this testing program are representative of failure surfaces that are oriented at an angle to the predominant orientation of the long axis of the fibrous waste particles. These friction angles are higher than those obtained in direct shear tests where shearing typically occurs parallel to the orientation of the fibrous waste particles.

Municipal solid waste as a reinforced soil: Investigation using synthetic waste

It is commonly accepted that the shear strength of Municipal Solid Waste (MSW) may be enhanced by the reinforcing effect of fibrous waste constituents. However, until recently no investigation has systematically evaluated the effects of the fibrous waste materials on the stress-strain-strength response of MSW. The present study is a continuation of a previous investigation conducted by the authors and aims at experimentally quantifying the effect of the fibrous materials on the stress-strainstrength response of MSW, as well as demonstrating the analogy of MSW to reinforced soil. Preliminary direct shear test results indicate that, similarly to tests performed on reinforced soils, the orientation of the fibrous materials with respect to the shear surface is critical and affects significantly the stress-displacement-strength response. In addition, the type of fibrous materials also affects the stress-displacementstrength response.

Liquefaction at Strong Motion Stations and in Urayasu City during the 2011 Tohoku-Oki Earthquake

The 2011 MW = 9.0 Tohoku-oki earthquake generated a large number of unique soil liquefaction case histories, including cases with strong ground motion recordings on liquefiable or potentially liquefiable soils. We have compiled a list of 22 strong motion stations (SMS) where surface evidence of liquefaction was observed and 16 SMS underlain by geologically recent sediments or fills where surface evidence of liquefaction was not observed. Pre-earthquake standard penetration test data and borehole shear wave velocity (Vs) profiles are available for some stations, but critical information, such as grain size distribution and fines plasticity, are often lacking. In the heavily damaged city of Urayasu, we performed post-earthquake cone penetration testing at seven SMS and Vs profiles, using surface wave methods at 28 additional locations to supplement existing geotechnical data. We describe the liquefaction effects in Urayasu, the available site characterization data, and our initial data interpretations.

Quantification of parameters influencing methane generation due to biodegradation of municipal solid waste in landfills and laboratory experiments

The energy conversion potential of municipal solid waste (MSW) disposed of in landfills remains largely untapped because of the slow and variable rate of biogas generation, delayed and inefficient biogas collection, leakage of biogas, and landfill practices and infrastructure that are not geared toward energy recovery. A database consisting of methane (CH4) generation data, the major constituent of biogas, from 49 laboratory experiments and field monitoring data from 57 landfills was developed. Three CH4 generation parameters, i.e., waste decay rate (k), CH4 generation potential (L0), and time until maximum CH4 generation rate (tmax), were calculated for each dataset using U.S. EPAs Landfill Gas Emission Model (LandGEM). Factors influencing the derived parameters in laboratory experiments and landfills were investigated using multi-linear regression analysis. Total weight of waste (W) was correlated with biodegradation conditions through a ranked classification scheme. k increased with increasing percentage of readily biodegradable waste (Br0 (%)) and waste temperature, and reduced with increasing W, an indicator of less favorable biodegradation conditions. The values of k obtained in the laboratory were commonly significantly higher than those in landfills and those recommended by LandGEM. The mean value of L0 was 98 and 88L CH4/kg waste for laboratory and field studies, respectively, but was significantly affected by waste composition with ranges from 10 to 300L CH4/kg. tmax increased with increasing percentage of biodegradable waste (B0) and W. The values of tmax in landfills were higher than those in laboratory experiments or those based on LandGEMs recommended parameters. Enhancing biodegradation conditions in landfill cells has a greater impact on improving k and tmax than increasing B0. Optimizing the B0 and Br0 values of landfilled waste increases L0 and reduces tmax.

Development of Model for Shear-Wave Velocity of Municipal Solid Waste

AbstractThe shear-wave velocity and associated small-strain shear modulus of municipal solid waste (MSW) are important engineering parameters in evaluating the seismic response of MSW landfills as well as in characterizing the waste material and its response to static loads. Semiempirical and empirical models for the shear-wave velocity are presented. The semiempirical model is a more comprehensive model that aims to separately capture the effect of waste density and confining stress on the shear-wave velocity of MSW. It is based on similar models for soils, and its mathematical expression is formulated using data generated from large-scale laboratory studies on reconstituted MSW. The empirical model has a simpler mathematical expression that is a function of depth only. The parameters of both models are derived by calibrating them against a total of 49 in situ shear-wave velocity profiles at 19 MSW landfills, i.e., 13 profiles from four landfills in Michigan generated as part of this study and 36 additio...

Archaeal community structure in leachate and solid waste is correlated to methane generation and volume reduction during biodegradation of municipal solid waste

Duplicate carefully-characterized municipal solid waste (MSW) specimens were reconstituted with waste constituents obtained from a MSW landfill and biodegraded in large-scale landfill simulators for about a year. Repeatability and relationships between changes in physical, chemical, and microbial characteristics taking place during the biodegradation process were evaluated. Parameters such as rate of change of soluble chemical oxygen demand in the leachate (rsCOD), rate of methane generation (rCH4), rate of specimen volume reduction (rVt), DNA concentration in the leachate, and archaeal community structures in the leachate and solid waste were monitored during operation. The DNA concentration in the leachate was correlated to rCH4 and rVt. The rCH4 was related to rsCOD and rVt when waste biodegradation was intensive. The structures of archaeal communities in the leachate and solid waste of both simulators were very similar and Methanobacteriaceae were the dominant archaeal family throughout the testing period. Monitoring the chemical and microbial characteristics of the leachate was informative of the biodegradation process and volume reduction in the simulators, suggesting that leachate monitoring could be informative of the extent of biodegradation in a full-scale landfill.

An experimental setup for simultaneous physical, geotechnical, and biochemical characterization of municipal solid waste undergoing biodegradation in the laboratory

Municipal solid waste (MSW) is biodegradable in landfills under anaerobic conditions. The biodegradation of MSW consists of physical and biochemical processes that affect the geotechnical characteristics of the waste. Laboratory landfill simulators that enable simultaneous characterization of these processes are presented. The simulator configuration, testing procedure, sampling methods, and measurement methods are described. The temporal phases of MSW biodegradation were studied using the experimental setup. Good repeatability of the measurements was demonstrated between duplicate simulators. In addition to data on biogas and leachate samples, a solid waste core sampling technique for retrieving disturbed solid waste samples for chemical and microbial analyses is presented. It was demonstrated that core sampling did not significantly affect simulator operation and measurements. The simulators and sampling methods presented in this study can be used to generate data that will be useful in the development and calibration of comprehensive models for MSW biodegradation in landfills.