Countermeasures to Protect Bridge Abutments from Scour (2007) / Chapter Skim
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68 6.1 Introduction This chapter presents observations and data from sets of brief, preliminary laboratory experiments conducted to evaluate scour countermeasures for protecting abutments. The experiments were carried out using small-scale replicas of a simple abutment form: a wing-wall abutment extending at a depth into a cohesionless bed of a rectangular channel.
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flow partially. Also, placing and positioning blocks around an abutment would seem relatively practicable, even in flowing water.
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6.3.2 Observations The experiments showed that single large individual armor units, or ensembles of blocks (or such units as dolos and tetrapods) , alone, are of limited effectiveness as a scour countermeasure.
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abutment. The large blocks, acting as exposed large elements, produced locally increased flow velocities and turbulence, such that bed sediment readily scoured from around the blocks.
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72 Table 6-2. Local scour depths at wing-wall abutment with geobag.
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maximum deepest point of scour, dsB. The values for these two locations were 0.40dsA0 and 0.27dsA0, respectively.
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scour reduction was 100 percent (dsA 0)
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6.6 Influence of Wing-Wall Angle A series of experiments was conducted in which the wingwall angle was varied. No additional scour countermeasure was used in these experiments.
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76 Figure 6-11. Experiment with a large geobag placed around the wing-wall abutment.
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77 Figure 6-13. Influence of wall angle on scour depth at a wing-wall abutment.
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78 6.8 Summary of Findings from Preliminary Experiments The results from the preliminary experiments led to the following findings in answer to the questions posed at the outset of this chapter. The findings are of significance for the more detailed sets of experiments that were conducted subsequently for the project: • Large concrete blocks placed around an abutment are insufficiently effective as a scour countermeasure for reducing scour depth at an abutment.
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