Edward Kavazanjian

Shear Strength of Municipal Solid Waste

A comprehensive large-scale laboratory testing program using direct shear (DS), triaxial (TX), and simple shear tests was performed on municipal solid waste (MSW) retrieved from a landfill in the San Francisco Bay area to develop insights about and a framework for interpretation of the shear strength of MSW. Stability analyses of MSW landfills require characterization of the shear strength of MSW. Although MSW is variable and a difficult material to test, its shear strength can be evaluated rationally to develop reasonable estimates. The effects of waste composition, fibrous particle orientation, confining stress, rate of loading, stress path, stress-strain compatibility, and unit weight on the shear strength of MSW were evaluated in the testing program described herein. The results of this testing program indicate that the DS test is appropriate to evaluate the shear strength of MSW along its weakest orientation (i.e., on a plane parallel to the preferred orientation of the larger fibrous particles within MSW). These laboratory results and the results of more than 100 large-scale laboratory tests from other studies indicate that the DS static shear strength of MSW is best characterized by a cohesion of 15 kPa and a friction angle of 36° at normal stress of 1 atm with the friction angle decreasing by 5° for every log cycle increase in normal stress. Other shearing modes that engage the fibrous materials within MSW (e.g., TX) produce higher friction angles. The dynamic shear strength of MSW can be estimated conservatively to be 20% greater than its static strength. These recommendations are based on tests of MSW with a moisture content below its field capacity; therefore, cyclic degradation due to pore pressure generation has not been considered in its development.

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.

Performance of Solid Waste Landfills in Earthquakes

Interpretation and analysis of observational data on the performance of solid waste landfills during earthquakes is the most reliable source of information on the seismic response of solid waste landfills. The data from several major California earthquakes indicate that the general performance of landfills during earthquakes is from good to excellent. None of the landfills on which observational data is available experienced major earthquake-induced damage. Recorded strong ground motion data indicate that amplification of both peak and spectral accelerations can occur at the top of a landfill. This, combined with the fact that only a limited number of landfills with geosynthetic liners and no landfill with a geosynthetic cover have been subjected to strong ground motions, indicate that attention to detail is warranted in the design of modern, geosynthetic-lined and/or covered landfills in areas of high seismicity.

Compositional effects on the dynamic properties of municipal solid waste

Large-scale cyclic simple shear tests were conducted on reconstituted specimens of municipal solid waste (MSW) collected from the Tri-Cities landfill in Fremont, California, USA. The influence of waste composition and compacted unit weight on the shear wave velocity, small-strain shear modulus, and strain-dependent shear modulus reduction and damping ratio curves of MSW was investigated in these tests. Modulus reduction and damping ratio curves were evaluated over a strain range of 0.01-3%. Specimens were reconstituted using 100%, 65%, and 35%, by weight, of the material that passed through a 20mm screen and four different levels of compaction effort. All specimens were consolidated under a normal stress of 75 kPa prior to testing. The test results show a very strong dependence of shear wave velocity and small strain shear modulus on unit weight. Unit weight also had an influence on modulus reduction and damping ratio. Waste composition had a very strong influence on damping and also influenced shear wave velocity, small strain shear modulus, and modulus reduction. The interrelationship between unit weight and waste composition made it difficult to separate out the effects of these parameters.

11th Peck Lecture: Predesign Geotechnical Investigation for the OII Superfund Site Landfill

AbstractThe predesign geotechnical investigation for closure of the Operating Industries, Inc. (OII) Superfund site landfill significantly advanced the state of the art for solid waste landfill engineering. Contributions to solid waste landfill engineering from the OII predesign geotechnical investigation include a solid waste classification system, a method for in situ measurement of waste unit weight, an enhanced understanding of the mechanical properties of solid waste, including unit weight, compressibility, shear strength, shear wave velocity, and equivalent linear shear modulus and equivalent viscous damping, and a methodology for seismic stability and deformation analysis of the waste mass. Many of the procedures and waste property relationships developed for the OII predesign geotechnical investigation remain the state of practice today for solid waste landfill engineering.

RMS acceleration hazard for San Francisco

Abstract The annual probability of exceeding levels of the root mean square acceleration (RMS a ) of strong ground shaking is evaluated for downtown San Francisco. Attenuation relationships for RMS a are developed for use in the seismic hazard analysis. A Bayesian seismic hazard analysis that incorporates the variability in seismicity parameters and the attenuation uncertainty is used.

Stiffness and Dilatancy Improvements in Uncemented Sands Treated through MICP

AbstractLaboratory testing shows that microbially induced carbonate precipitation (MICP) through microbial denitrification can improve the mechanical properties of a sand without inducing significant interparticle cementation. Consolidated isotropically undrained triaxial compression testing of Ottawa 20–30 sand treated with denitrifying microorganisms shows that, even at low carbonate contents and with no observed cementation, soil treated through MICP exhibits significantly improved stiffness and dilatant behavior. These improvements are also evident when the treated soil is dried, reconstituted, and retested, indicating that the stiffness and dilatant properties of the soil can be improved by MICP in the absence of interparticle cementation, particularly at low strains. However, these improvements may be reduced or eliminated when the soil is reconstituted and tested multiple times. These results indicate that small amounts of MICP can induce significant improvement in treated soils, potentially leadin...

Large scale centrifuge test of a geomembrane-lined landfill subject to waste settlement and seismic loading

A large scale centrifuge test of a geomembrane-lined landfill subject to waste settlement and seismic loading was conducted to help validate a numerical model for performance based design of geomembrane liner systems. The test was conducted using the 240g-ton centrifuge at the University of California at Davis under the U.S. National Science Foundation Network for Earthquake Engineering Simulation Research (NEESR) program. A 0.05mm thin film membrane was used to model the liner. The waste was modeled using a peat-sand mixture. The side slope membrane was underlain by lubricated low density polyethylene to maximize the difference between the interface shear strength on the top and bottom of the geomembrane and the induced tension in it. Instrumentation included thin film strain gages to monitor geomembrane strains and accelerometers to monitor seismic excitation. The model was subjected to an input design motion intended to simulate strong ground motion from the 1994 Hyogo-ken Nanbu earthquake. Results indicate that downdrag waste settlement and seismic loading together, and possibly each phenomenon individually, can induce potentially damaging tensile strains in geomembrane liners. The data collected from this test is publically available and can be used to validate numerical models for the performance of geomembrane liner systems.

Enzyme induced carbonate precipitation (eicp) columns for ground improvement

Columns of improved soil created by Enzyme Induced Carbonate Precipitation (EICP) offer the potential for non-disruptive, cost effective ground improvement for a variety of geotechnical purposes. EICP employs urease enzyme to precipitate CaCO3 from an aqueous solution of calcium chloride and urea to fill the soil pores (increasing dilatancy and reducing compressibility) and cement soil particles (increasing shear strength). EICP is similar to Microbially Induced Carbonate Precipitation (MICP) except that, instead of employing microbes to generate the urease enzyme, the enzyme is obtained from agricultural sources. A major advantage of agriculturally-derived urease compared to microbial urease is its small size and water solubility, which allows penetration through the pore throat of finer grained soils such as silts, whereas ureolytic MICP is essentially restricted to soils of fine to medium sized sand or larger. The small size of the enzyme can also mitigate the potential for bio-clogging due to carbonate precipitation and biofilm formation, both of which my limit the applicability of MICP. Bench top tests in the laboratory show that cemented columns of soil can be created by infusing a cementation solution through a perforated tube or pipe or by mix and compact methods. EICP columns can be installed in patterns similar to root piles (pali radicii) for slope stability, micro piles for foundation support, and stone columns or soil cement columns to support embankments and restrict lateral spreading in liquefiable soils. Furthermore, EICP piles could be installed under existing structures without causing heave or settlement, making them ideal for remediation of poor (e.g. liquefiable) foundation soils.

MIDP: Liquefaction mitigation via microbial denitrification as a two-stage process. I: Desaturation

AbstractThis paper focuses on desaturation due to the microbially mediated dissimilatory reduction of nitrogen, or denitrification, for mitigating the potential for earthquake-induced soil liquefac...