Flagler Memorial Bridge Micropile Underpinning of Bascule Piers
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Project Objective

The aging Flagler Memorial Bridge suffered from detrimental settlement caused by vibratory installation of steel drilled shaft casings for a new, immediately adjacent bridge crossing.

Deformations of the existing bascule piers were so significant that the leaves would not properly align, forcing the Florida Department of Transportation (FDOT) to close the existing bridge, constructed in 1927, and plan for design and implementation of underpinning for stabilization.

Geosyntec’s Scope of Services

Working with Moretrench American Corporation, Geosyntec designed emergency foundation support . The design included explicitly considering the appropriate construction drilling means and methods for the difficult subsurface conditions and formulating engineering parameters accordingly. The site was underlain to great depth by alternating strata of loose to medium-dense fine sands and dense cemented sands. Voidaceous limerock was also found in the subsurface. Prior construction experience indicated the cemented sands degrade under the expected rotary duplex foundation drilling methods, and the limerock has the potential to cause grout loss.

Our micropile construction expertise allowed us to address appropriate design methods and parameters in anticipation of these difficult subsurface conditions. The final micropile design was greater than 90 ft long (50 ft cased length + 40 ft bond length) to develop adequate resistance in the variable subsurface conditions for static loading.

Geosyntec provided micropile axial and lateral design for the loading conditions designated by the owner and its consultants, developed an axial load testing program comprising two over-water compression load tests with unbraced lengths over 20 ft, and supplied field quality assurance, monitoring, and construction engineering during load testing. We developed an innovative analysis and construction method for bracing the test piles and limiting the potential for buckling under the planned verification test loads, which were further increased by FDOT.

Notable Accomplishments

Geosyntec’s micropile design, executed rapidly for this emergency contract, was successfully load tested, and production piles were installed as planned under difficult access and nighttime working conditions by our client. Our responsiveness during a rapid design process and practical assessments and solutions throughout the construction process contributed to the success and schedule of this emergency stabilization project for this historic bridge. Geosyntec also gained recognition by FDOT as a Specialty Engineer of Record for this project.

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Project Summary

  • Location: West Palm Beach, Florida
  • Client: Moretrench American Corporation
  • Project Practice Areas: Geotechnical
  • Type of Facility: Commercial Construction and Development
  • Services Provided: Micropile underpinning design, Construction sequencing, Load testing, Construction engineering
  • Type of Work: Geotechnical and Construction Engineering
  • Governing Regulation: State and local