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Spring Field Review Site 5
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Spring Field Review Site 5
Description:B-2938 - CARTERET-ONSLOW COUNTIES
LOCATION: Bridge #49 - SR1101 over the White Oak River
ITEM(S) OF INTEREST: A 2300-foot long Type II and Type IV prestressed concrete girder bridge. Several unique elements including 24" composite piles, 24" Dia. metallized pipe piles, closed drainage system, unarmored evazote joints with elastomeric headers.
Observations and Points of Discussion:
The existing bridge is relatively short with a causeway over the surrounding wetlands.
There were questions regarding the length of the replacement bridge, foundation types and size, and the span arrangements.
The site geometry especially at the bridge landing, where there is a roadway intersection and some businesses, presented a
significant challenge in providing sufficient under-clearance for the navigable waterway.
- Deeper girders would have required raising the grade, but it would have been difficult to tie back in to the approaches.
- Predicted scour resulted in waterline footings on piles.
- Relatively shallow layer of hard material resulted in A-frame interior bents
- There were several other concerns that were raised, but each discipline had cogent reasons for the resulting layout and design of the structure.
It was suggested that use of FB-Pier on projects with numerous challenges, such as this one, might allow the Department to design interior bents that are a lot less imposing.
Therefore on long coastal projects with waterline footings and lateral stability concerns the Department should consider alternate analysis approaches.
There were still questions as to who throws the flag for alternative analyses.
The group was in agreement that project schedules should not drive engineering decisions / designs.
FHWA inquired if this was a suitable location for jetting piles.
- It was noted that jetting is most suitable for Divisions 1 & 2 (coastal counties).
- Problems encountered when jetting for the Virginia Dare Bridge (Manteo) have been unduly generalized for all sites.
- However, the Department is still pursuing jetting. A Special Provision, which specifies limits on containment for the contractor, is currently being developed. This will provide a starting point.
- The Department has proposed to perform jetting demonstrations/tests, which will be the basis for new jetting models for the certain/various soil types.
- Regulatory Agencies don't qualify zones in which jetting is not acceptable. In general they view jetting favorably, but they want to know how jetting will be implemented.
- FHWA recommends making jetting a priority.
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NC DOT
NC DOH
NC GOV
