This award is an outcome of the NSF 09-524 program solicitation ''George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Research (NEESR)" competition and includes the University of Michigan (lead institution), California State University in Los Angeles (subaward) and Geosyntec Consultants (subaward). This project will utilize the NEES equipment site at the University of Texas at Austin.
The increasing amounts of municipal solid waste (MSW) generated every year are, in their majority, landfilled. Modern (since the 1990s) MSW landfills are environmentally sensitive, sophisticated facilities and are similar in size to large dams. Recent U.S. earthquakes (e.g. 1994 Northridge Earthquake) highlighted the potential seismic vulnerability of MSW landfills. Excessive movement during shaking may damage the landfill?s containment or cover system or cause stability failures. The impact of such failures on the environment can be devastating. The use of accurate and representative dynamic properties of Municipal Solid Waste is a requirement to reliable seismic engineering analyses and design, but our understanding of the dynamic properties of MSW is rudimentary and lacking.
The intellectual merit of this project is in evaluating, for the first time, the in-situ nonlinear dynamic properties of MSW using the T-Rex mobile shaker available at NEES@UT. The mobile shaker is a truck mounted, high capacity shaker that can induce significant cyclic strains in the waste material. Accelerometers are used to record the accelerations of the waste mass at depths in the vicinity of the shaker and derive the dynamic properties of the waste material. Testing using T-Rex will be performed at four locations, at four carefully selected MSW landfills (one in Texas and three in areas of high seismicity in California) with emphasis on documenting the variability of MSW and capture factors such as effect of age, degradation and moisture content. Subsequently, test pits will be excavated and waste material will be collected and tested in large-scale laboratory testing facilities at the University of Michigan and smaller scale testing facilities at California State University in Los Angeles. The laboratory tests will allow the investigators to study the various factors (e.g. confining stress, density, composition) that affect the dynamic properties of waste and compare the results with the field testing. Numerical analyses will be performed to evaluate the seismic behavior of landfills and provide recommendations for use in seismic design. This investigation has the potential to transform seismic engineering practice in landfill design by providing a new methodology for field testing of solid waste, validating the applicability of large-scale laboratory testing of MSW, generating much needed field and laboratory data, and developing recommended methodologies for the performance of seismic analyses of MSW landfills.
The broader impact of this project is the safer, more reliable, designs of Municipal Solid Waste landfills in seismic regions. The project will also be integrating research and education by actively involving undergraduate and high school students in research and mentoring activities. Outreach to a broader population of high school students and the community is planned during a demonstration and learning event at a landfill site. The research proposed will provide the basis for at least one Ph.D. dissertation (at U-M) and will promote collaboration between primarily research and primarily teaching institutions. A comprehensive plan for broad data and research results dissemination to the technical community is also outlined. Data from this project will be archived and made available to the public through the NEES data repository. This award is part of the National Earthquake Hazards Reduction Program (NEHRP).
Modern Municipal Solid Waste (MSW) landfills are environmentally sensitive, sophisticated, engineered facilities that are similar in size to large dams. Recent U.S. earthquakes (e.g. 1994 Northridge Earthquake) highlighted the seismic vulnerability of MSW landfills. Excessive movement during shaking may damage the landfill’s containment or cover system and cause stability failures. The impact of such failures on the environment can be devastating. Municipal Solid Waste Landfills need to perform well during future earthquakes. Landfill failures can have adverse effects on the environment and public health and their repair is costly. The findings of this study will allow engineers to more reliably assess the expected seismic response of landfills during future major earthquakes. The field testing executed as part of this study has generated an unprecedented dataset that is critical in understanding the seismic response of MSW landfills. Researchers from the University of Michigan (lead institution), California State in Los Angeles and Geosyntec Consultants, using large mobile shakers, known as Tri-axial mobile shaker (T-Rex) and Thumper, available through the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Facility of the University of Texas, have been able, for the first time, to generate field data on the dynamic properties of MSW not just at small strains, but at larger strains, similar to those that are expected during a major earthquake. The research team was able to shake the waste at large strains and observe how the stiffness of the material reduces with increasing strain. Similarly to soils, MSW loses some of its stiffness as the shaking increases, however, the data collected indicates that this reduction in stiffness with increasing strain is generally not as high as that observed for most soils. The dataset on the in-situ dynamic properties of MSW generated by this study is unprecedented. All previous research efforts have focused on assessing the dynamic properties of MSW either numerically or in the laboratory. The results from the numerical studies have been conflicting, whereas the results in the laboratory are always on reconstituted specimens of MSW that may not be large enough, and thus representative, of the field behavior of MSW. These uncertainties are eliminated through the executed field testing program. In addition to the field testing, samples of MSW were sent for large-size testing at the laboratory for further characterization using a unique shearing device developed at the University of Michigan. Direct comparisons were made between laboratory test results and field test results. Unique laboratory tests allowed the research team to assess additional critical seismic properties of MSW, providing key guidance to engineers with regards to the strength of the material during earthquakes. Numerical analyses were also executed using as input the data on the MSW seismic properties generated in this study, and thousands of seismic records. The results of the analyses are seismic design procedures, recommendations and design charts that can be used in engineering practice. The results from this study has also shed light to previously unquantified aspects of the nature of MSW. A critical one is the quantification of the impact of waste variability within a landfill, as well as nationwide on the seismic behavior of landfills. In addition to the research components of this project, a total of three PhD students, one Master students, and 11 undergraduate students were trained and mentored through this research project. Outreach videos were developed and research results were promoted through scientific publications in research journals and conferences.
