United States Department of Transportation
i
Advanced Methodology to Assess Riprap Rock Stability at Bridge Piers and Abutments
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2017-10-01
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[PDF-6.33 MB]
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OCLC Number:1038019569
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Abstract:The objectives of this research study were to: (1) assess whether detailed fluid structure interaction (FSI) modeling can inform evaluation of rock riprap movement for both the analysis of existing riprap aprons and for the design of new riprap aprons; and (2) develop recommendations for the design, installation, and monitoring of riprap aprons at bridge piers and abutments, where feasible. A new advanced computational methodology for assessing failure risk of geometrically complex riprap installations was developed for this study. The study demonstrated that detailed FSI modeling can inform evaluation of rock riprap movement for both the analysis of existing riprap aprons and for the design of new riprap aprons. The approach solved the FSI problem for the onset of rock riprap motion using weakly coupled computational fluid dynamics and computational structural mechanics software. The flow threshold for the onset of motion of riprap rocks was computed for a set of representative riprap rocks for both simplified laboratory and complex field conditions. Physical laboratory experiments were used to validate the numerical procedures. The FSI approach was also tested on a complex field case study of a riprap installation at a pier for a bridge over the Middle Fork of the Feather River. While the case study application was considered successful, the approach is limited by its high costs and limited availability. Therefore, good candidate applications for using FSI analysis to assess new or retrofit riprap installations would be those where the project cost is significant or the risks of failure are catastrophic. The study also identified recommendations for improving the design, installation, and monitoring of riprap apron installations at bridge piers and abutments, where feasible. These included: (1) verifying as-built conditions for assuring that the intended level of protection has been achieved, (2) inspecting for changes in stream morphology that may significantly change conditions from those anticipated at design, (3) recording the date of rock riprap installations and monitoring the performance of the installations after major floods, (4) applying sonar technologies for riprap monitoring, and (5) avoiding rock riprap installations for new bridge piers as they are not recommended by FHWA policy. The FSI numerical modeling approach has promise for supporting the design and evaluation of riprap installations for bridge abutments and piers. As computer capabilities increase and more detailed representations of rock riprap installations become more practical, the approach should continue to increase in its utility.
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