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Route 52 Causeway Bridge Geotechnical and Hydrologic Design


  1. Eric Dean,
  2. Quiana Finley,
  3. Mark Mankbadi (Team Leader),
  4.  Leslie Salsbury

Advisors: V. Krstic, M. Horst

The Route 52 Causeway reconstruction project in Ocean City, New Jersey involved the replacement of the existing two-mile long crossing connecting the cities of Ocean City and Somers Point across the Great Egg Harbor Bay. The NJDOT split the project into two contracts; Contract A and Contract B. Contract B includes the replacement of the two bascule-type bridges, along with their appurtenant embankments, with two high-rise structures constructed 100 feet offset from the existing bridge alignment through the use of staged construction. This project was limited to the geotechnical and hydrologic design of the two approach embankments and main-span piers; piers 6, 7, 69, 70 and 71. A subsurface soil analysis was done using the provided borings revealing six primary soil strata including three cohesive strata and three granular strata. A secondary peat stratum was found interbedded within the upper soil stratum found along the Ocean City portion of the project. Embankment analysis of the Somers Point end revealed a settlement of 2.65 inches at the abutment with a 90% primary consolidation time of 81 days. The embankment analysis of the Ocean City end had a total settlement of 2.43 inches at the abutment with a 90% primary consolidation time of 124 days.  The two approach embankments will be retained using Mechanically Stabilized Earth walls with heights varying between 14-20 feet with reinforcement lengths varying between 13 to 16 feet. A global stability analysis of the embankments revealed a factor of safety below 1.5 for the Ocean City approach embankment. Due to the highly compressible soils at the Ocean City approach, the use of 24 inch Vibro-Concrete Columns (VCC), spaced at 7 feet, were recommended to reduce settlement and increase global stability. From STA 176+57 to STA 178+15 and further down the embankment from STA 178+15 to STA 179+00, the proposed depth of the column was 30 feet and 15 feet, respectively. Primary analyses of the foundations for piers 6, 7, 69, 70, and 71 included axial capacity, lateral capacity and driveability. The use of 16, 30 inch, prestressed concrete square piles were recommended for the pier foundations with a varying estimated tip elevation between -80 and -130ft. A scour analysis was performed on the bridge structure to ensure stability during extreme storm events. The hydrologic assessment of the watershed gave 100 year and 500 year storm discharges of 8600 and 19800 cubic feet per second. These flow rates yielded maximum scour depths of 8.6 and 12.03 feet, for the 100 and 500 year design storms, respectively.

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