Browsing by Author "Mielke, Sara"

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    Design Considerations for Embankment Protection During Road Overtopping Events
    (Minnesota Department of Transportation, 2017-06) Marr, Jeffrey D.G.; Hernick, Matthew; Gabrielson, Robert; Mielke, Sara
    This report describes the research conducted by the University of Minnesota and project partners on roadway embankment overtopping by flood water. Roadway overtopping is a major safety concern for Minnesota transportation managers because of the potential for rapid soil erosion and mass wasting resulting in partial or complete failure of the roadway embankment. This multi-year research study focused on various aspects of the roadway embankment overtopping. A robust literature survey was performed to identify research, reports and other published knowledge that would inform the project. A field- based research campaign was developed with the goal of collecting data on the hydraulics associated with full-scale overtopping events. Finally, a series of laboratory experiments were conducted at the St. Anthony Falls Laboratory, University of Minnesota to study the hydraulic and erosional processes associated with embankment overtopping and in particular study of three slope protection techniques under overtopping flow. The largest component of the research project was the laboratory hydraulic testing, which focused on bare soil (base case) and three slope protection technologies. A full- scale laboratory facility was constructed to carry out the testing. Three erosion protection techniques were examined including 1) armored sod, 2) turf reinforcement mat, and 3) flexible concrete geogrid mat. Overtopping depths of up to 1-ft were used to determine the failure point of the protection technique and soil on both the 4h:1V and 6V:1H slopes. The full project report details the testing of each protection technique as well as observations and findings made during the testing.
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    Matrix (Partially Grouted) Riprap Lab Flume Study
    (Center for Transportation Studies University of Minnesota, 2014-04) Marr, Jeffrey; Weaver, Rita R.; Mohseni, Omid; Taylor, Craig; Hilsendager, Jon; Mielke, Sara
    The Minnesota Department of Transportation (MnDOT) in conjunction with the Saint Anthony Falls Laboratory (SAFL) has conducted a research study on the use of matrix riprap, or partially grouted riprap, as a spill-through abutment countermeasure. Spill-through abutments at river bridges require a countermeasure to protect the abutment from erosion and scour and often riprap is used. However obtaining large enough stone to protect the abutment can significantly increase construction costs. Matrix riprap, or partially grouted riprap, is an option that will allow for smaller stone, that when partially grouted, will provide equivalent protection to larger sized riprap. This study focused on matrix riprap applied to bridge abutments and included a review of published literature; site visits and observation of matrix riprap installation; laboratory experiments to evaluate matrix riprap application/installation (e.g., non-hydraulic experiments looking at rock and grout placement); experiments to test matrix riprap on a prototype abutment within a flume (hydraulic flume experiments), and finally hydraulic experiments focused on quantifying matrix riprap strength (steep flume experiments). Study results showed that the shear strength of matrix riprap was determined to be more than three times greater than conventional riprap in a laboratory setting. Additional investigation should be completed to better understand the application and performance of the matrix riprap, however this study can be used to support the use of matrix riprap in place of larger stone or other bridge countermeasures.
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    Sediment Transport through Recessed Culverts: Laboratory Experiments
    (Minnesota Department of Transportation, 2015-03) Kozarek, Jessica; Mielke, Sara
    Recessed culverts are often installed in Minnesota to facilitate aquatic organism passage (AOP) by providing a natural streambed through the culvert. The least expensive option when installing a recessed culvert is to allow the culvert to fill in with sediment naturally over time; however, previous field studies suggest that in many cases, sediment fails to deposit within the culvert. The objective of this research was to understand the function of a culvert set below the streambed elevation under various sediment transport conditions. Laboratory experiments were designed to assess the performance of recessed culverts across a range of geomorphic characteristics representative of Minnesota streams. These experiments explored the functionality of a culvert that is prefilled with sediment representative of the stream as a part of the installation process against one that is empty after installation and assessed the potential for headcutting and downstream degradation. The experiments evaluated the need for artificial roughness installations within recessed culverts in high gradient streams. Three sets of experiments were conducted examining: 1) the effect of sediment grain size, slope, and flow hydrograph on sediment transport through a single recessed box culvert, 2) the effect of bed roughness structures on sediment stability in a single recessed box culvert in high-gradient streams, and 3) the effect of culvert offset and skew on sedimentation in multi-barrel culverts.