United States Department of Transportation
i
Investigation of approach slab and its settlement for roads and bridges.
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2014
[PDF-4.96 MB]
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Abstract:Approach slabs serve as a transitional system between an approach road and a bridge. Settlement of bridge approach slabs and their
supporting backfill has been experienced by more than ten Departments of Transportation throughout the United States. According to
current Wyoming Department of Transportation inspection reports, bridge approach slab settlements occurred not only on existing
bridges but also on newly built bridges that were just opened to traffic. These settlements typically create voids ranging from 6-in to 12-
in between the base of the approach slab and the geotextile reinforced backfill. This research presents factors causing bridge approach
slab settlements and provides necessary design and construction recommendations. A comprehensive literature review pertaining to
approach slabs was performed to examine outcomes of research conducted by 12 states. The current specifications and standards on
bridge approach slabs of the corresponding states’ Departments of Transportation were also evaluated. A nationwide survey was
conducted to fill in the missing knowledge identified in the literature review. The results of the survey are categorized in three groups
based on the percentage of bridges experiencing approach slab settlements in that state. Results of the survey show that 46 percent of the
total 28 respondents are not satisfied with their current approach slab designs. The survey results revealed that the most common cause
of approach slab settlement is poor construction practices. The most important finding of the survey is that performing in-situ tests to
control backfill compaction reduces the amount of approach slab settlement. Using the lessons learned from the literature and the results
of the survey, potential amendments to current Wyoming Department of Transportation design and construction manuals are
recommended
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