Marr, Jeffrey D. G.

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.

The goal of this project was to develop a series of steel pipe service-life maps for the state of Minnesota. The California Method 643 is utilized to estimate steel pipe service life at locations throughout the state. Over 560 soil resistivity and pH samples were collected statewide during summer 2014 along embankments of state-trunk and county highways. Concurrent observations of soil texture, surrounding landscape, roadway type, and water presence were also made; water pH and conductivity measures were made where applicable. Data verification efforts to build confidence in field-measured soil pH and soil resistivity included comparing data to other available datasets including geology, soil pH, electrical conductivity, and soil texture, as well as observations available from district and county engineers. Field-measured soil pH data, with some exceptions in Districts 2 and 6, generally aligned with the available STATSGO soil pH data, indicating that this layer could reasonably be used in service-life calculations as it has greater resolution than provided by field data. In the absence of a statewide soil resistivity or electrical conductivity map, field-classified soil textures and the statewide STATSGO soil texture map were used to estimate soil resistivity values. Calculations of service life using the above data were completed for 18-, 16-, 14-, 12-, 10- and 8-gage galvanized and aluminized steel pipe across Minnesota. These maps were then compiled into a zone map and table that presents the 90th percentile service-life estimate for various gages and types of steel pipe. Caveats and limitations to this analysis are also discussed.

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.

Bridge scour is the removal of sediment around bridge foundations and can result in the failure of the bridge. Scour monitoring is performed to identify unacceptable scour on bridges considered to be scour critical and determine when scour reaches elevations that could cause potential bridge failure. Two types of monitoring are available: portable monitoring and fixed monitoring. Prior to this project, MnDOT was only using portable monitoring devices, which requires the deployment of personnel to make physical measurements of scour depths. For some scour critical bridges, especially during high-water events, fixed instrumentation capable of continuous scour monitoring was preferred, but MnDOT lacked the experience or expertise to install this type of equipment. This project installed fixed monitoring equipment at two bridge sites and monitored them for three years to determine the effectiveness and reliability of fixed scour monitoring deployments. Several device options were installed to allow MnDOT to analyze the installation and performance of different types of sensors. Both systems operated for the three years with some outages due to various causes but overall performance was acceptable. The outages were mostly related to power issues and communication issues. Valuable lessons were learned through the deployment, which may be applied to future installations. The deployment executed in this project has provided the confidence to deploy other fixed scour monitoring equipment at key bridges around the state of Minnesota. In addition, the data collected during deployment of the scour monitoring equipment has been stored and provides insight into scour processes. This data can be used by other research groups for design or research purposes.

Culvert pipe material selection has traditionally been a relatively simple task involving metal or concrete pipe. In recent years, the addition of coated metal and plastic pipe has led the federal government to implement a rule requiring the consideration of alternative pipe materials. The current MnDOT Drainage Manual provides limited guidance on the selection of pipe material. The manual is lacking detailed information on the influence of environmental conditions on pipe durability in Minnesota. It is necessary to provide updated, accurate information on pipe material and durability for factors directly related to Minnesota. To reach this goal, the availability and suitability of existing data, as well as the practices associated with predicting pipe life spans must be evaluated. This report is the result of the initial feasibility study for a larger project(s) to update the MnDOT Drainage Manual. The goal for this report is to identify knowledge gaps, produce a research plan that will guide future research, and draw any pipe materials conclusions possible using the data available.

In Minnesota there is not a standard culvert design used at road crossings to improve aquatic organism or fish passage. The design process for fish passage in Minnesota is currently based on the knowledge and experience of local county, state and DNR personnel. The design methodology attempts to maintain the natural stream dimensions, pattern and profile through the culvert crossing. If designed properly aquatic organisms and fish that can make it upstream to the culvert should be able to pass through the culvert. This research was conducted to better understand the hydraulic conditions related to the practice of recessing culverts and other fish passage design elements over a range of landscapes in Minnesota. The design elements analyzed included bankfull width, slope, channel materials, side barrels and recessed culverts. Nineteen culvert sites were survey around the state. The main criterion used to evaluate performance of the culverts was the presence or absence of adequate sediment in the recessed culvert barrel. Six of the fourteen sites with recessed barrels had no sediment accumulation. A likely reason that these culverts lack sediment was increased velocities due to improper sizing relative to bankfull channel width and the accumulation of sediment in the side barrels. Wider Rosgen "C" type channels also correlated with performance issues related to culvert design.

Bridge failure or loss of structural integrity can result from scour of riverbed sediment near bridge abutments or piers during high-flow events in rivers. In the past 20 years, several methods of monitoring bridge scour have been developed spanning a range of measurement approaches, complexities, costs, robustness, and measurement resolutions. This project brings together the expertise of Minnesota Department of Transportation (Mn/DOT) bridge engineers and researchers, university hydraulic and electrical engineers, field staff, and inspectors to take the first steps toward development of robust scour monitoring for Minnesota river bridges. The team worked with Mn/DOT engineers to identify variables of scour critical bridges that affect the application of scour monitoring technology. The research team will used this information to develop a Scour Monitoring Decision Framework (SMDF) that will aid Mn/DOT in selecting the best technologies for specific sites. The final component of the project will involve testing the SMDF on five bridges in a case-study type demonstration; work plans for two of the sites were developed for demonstration of deployed instrumentation.