Item(s) of Interest: This overpass is located near a subdivision. The Division Office is concerned about driving piles adjacent to the nearby slab-on-grade houses. Evaluated a variety of foundation types for the end bents to avoid the potential liability of vibration-induced damage. The site has a high rock line, and therefore auger cast piles were initially considered, but were considered too expensive. Next auger/driven piles (where the piles would be driven after auguring a short distance), but it was deemed still too risky.
Noisewall on bridge.
Observations and Points of Discussion:
Single span bridge at a site with unusual situation due to neighborhood involvement.
Rockline 10 – 15 ft. below the roadway.
Original design included 9 ft. tall piles supporting the end bent cap.
Roadway approach fill has been in place for several months.
Division requested an alternate design. Auger cast piles were considered.
The Department does not have much experience with them, and hence there was too much risk associated with their use at this site.
The revised design includes 8ft of reinforced select material supporting the end bent on a spread footing.
The Geotechnical Engineering Unit (GEU) will monitor any vibration and movement in the end bent for about a year.
Stress gauges buried in the embankment will record data at each stage of construction. GEU anticipates stresses will dissipate over time.
Vibration from grading operation may be comparable to pile driving.
Monitoring ground stresses and movement in the embankment will assist the Department in determining if the embankment on future projects could be built once. Currently, embankments are built up and the soil is allowed to consolidate during the waiting period. Then a portion of the embankment is excavated for construction of the end bent and placement of the reinforced approach fill.
Noise walls on bridge will be included at this site.
Silt fences failed near roadway.
Would a 3-sided culvert on footings be a good option at this site?
Lighting in culvert would be a maintenance concern, and also possible graffiti problems.
Buried structures, especially prefabricated structures, have no well established method for rating.
NC DOT
NC DOH
NC GOV
