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Predicting Scour of Bedrock in Wisconsin
| 题名： | Predicting Scour of Bedrock in Wisconsin |
| 作者： | Seo, J.; Torres, E.; Schaffer, W. |
| 关键词： | Self-consolidating concrete (SCC)##Prestressed concrete bridges##Geologic characterization##Bridge girders##Highway bridges##Shallow foundations##Degradable rock##Hydraulic modeling## |
| 摘要： | This research evaluates the scour potential of rocks supporting Wisconsin DOT bridge foundations. Ten highway bridges were selected for this study, of which seven are supported by shallow foundations, and five were built on sandstone in rivers/streams. The remaining bridges are supported by foundations on degradable granite, gneiss, and dolo-stone. The research study included modified slake durability tests on core and hand-picked rock specimens obtained from streams/river of seven bridge sites (10 bridge structures), field work that included site visits and geologic characterization of bedrocks, hydro-graphic bottom channel surveys, and hydraulic modeling and analysis to estimate scour depth of bedrocks on both the river bed and around bridge piers. Based on the analysis of the modified slake durability test results, the sandstone exhibited significant mass loss during the continuous abrasion test. The geotechnical scour numbers and the abrasion numbers were calculated for the investigated rock specimens, which provided higher values for the sandstone compared with the other investigated rock types. This indicates that under high stream powers such degradable rock (i.e., sandstone) is more susceptible to higher scour rates compared with the other investigated rock types. It should be noted that the scour is water-rock interaction phenomenon; while the effective stream powers applied to these specimens in the modified slake durability test are high, the bedrocks that support bridge foundations in a river may not be subjected to these extreme stream power values and therefore they may degrade/abrade at a slower rate. The hydraulic modeling and analysis presents the details of the rock scour prediction at each bridge site based on stream flow data collected/analyzed from gauge stations near the investigated project sites and the results of the modified slake durability tests. The hydraulic modeling and analysis on six bridge sites demonstrated that the estimated annual scour depths of the investigated rocks on both the river bed foundations and around bridge piers are typically small to negligible except for two bridge sites on the Wisconsin River and the Black River. When using continuous stream power without the threshold of a “channel-forming” condition, the 75-year scour depths at STH13-WR are estimated as 7.7 and 10.2 ft. on the river bed and around the bridge pier, respectively. These numbers likely over-predict scour considering the sediment deposition that covers the channel bed. Scour depths with flood frequency analysis are generally close to that of the cumulative stream power from daily flow series with “channel-forming” threshold conditions. |
| 总页数： | 181 |
| 报告类型： | 科技报告 |
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