Riprap is the most commonly employed countermeasure where bridge piers need to be protected against possible undermining by scour. An extensive review of available design techniques revealed a wide range of equations and proposed design procedures but no generally accepted method for riprap sizing and implementation. The aim of this study was to develop a design procedure for riprap protection at piers which can be used in most river environments. The failure mechanisms and stability of riprap layers around cylindrical and rectangular shaped piers were examined in a comprehensive experimental study. The study assessed the importance of various riprap, flow, sediment, and pier parameters. Parameters for investigation were determined by dimensional analysis and included riprap placement and arrangement. A riprap size prediction formula was developed based on an allowable maximum local scour depth of up to 20%. This equation has been incorporated in a design approach which was tested through a model study of the Hutt Estuary Bridge. The influence of various parameters on riprap stability are incorporated in the equation by way of adjustment factors. The adjustment factors, KY and KD, represent the effects of riprap placement and pier/sediment size ratio effects respectively. They were deemed the most important parameters in riprap layer performance and are therefore included in the riprap size prediction formula. Additional experiments using synthetic filters have shown their ability to eliminate local scour, however they are susceptible to failure under degrading bed conditions. Degrading bed conditions cause the riprap to subside as a layer with the downward movement of the surrounding bed. Subsidence allows the layer to withstand rapid short term degradation. However long term degradation will ultimately result in failure of the stone protection. A preliminary experimental study of the use of submerged vanes as a scour countermeasure was performed. Submerged vanes have been used previously in channel protection with much success. Results indicate that vanes with a length to height ratio greater than one can reduce the maximum local scour depth in live bed conditions by as much as 34%. Further testing is required to develop a complete design procedure.
| Identifer | oai:union.ndltd.org:ADTP/276280 |
| Date | January 1999 |
| Creators | Lauchlan, Christine Sandra |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Source | http://wwwlib.umi.com/dissertations/fullcit/9918629 |
| Rights | Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated., http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm, Copyright: The author |
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