By Lt. Steven Becker, P.E., M.SAME, USCG
An 11-acre island located adjacent to Miami Beach, Fla., Coast Guard Base Miami Beach houses multiple staff commands and a small boat station, and supports the operations of eight ships. In total, more than 400 active duty, civilian, and contract personnel work onboard the base, enabling U.S. Coast Guard missions in southern Florida and the Caribbean. Access to the island is made possible by a single entry point: a one-lane roadway bridge.
The Base Miami Beach entrance bridge is 301-ft long, consisting of 11 bents at 32-ft typical spacing. Each bent comprises a 30-in by 30-in cast-in-place concrete cap, supported by four 18-in square pre-stressed concrete piles. The deck consists of 8-in-thick simply supported precast concrete planks that span between the caps. The bridge has a maximum allowable wheel load of 16,000-lb. The structure is more than 75 years old and owns an extensive repair history. The last two decades included a $200,000 deck replacement project in 2002 and a $600,000 above-water concrete spalling repair project in 2015.
In 2016, the Facility Engineering Department discovered signs of settlement along the northwest end of the bridge. A team of engineers investigated and confirmed that the first bent was actively settling. The cause was never determined with certainty, but it is suspected that waterfront bulkhead repairs executed at a neighboring facility using a vibratory hammer combined with inadequate pile depth contributed to the settlement.
Bridge loading restrictions were immediately put in place, and a two stage repair plan was developed. In the first stage, temporary crack repairs and leveling of the bridge deck had to be accomplished to ensure traffic could continue transiting on and off the base. A second, long-term solution, which involved arresting the settlement and replacing the pile cap and decking, would then need to be funded, designed, and executed. The first stage’s temporary repairs were completed within two years by injecting epoxy grout into the cracks at the settling bent and lifting the bridge decking until level. Grout was then applied to the void space.
Executing a major repair to the bridge’s entrance faced a host of complications, however. The bridge is only 22-ft wide, and except for brief interruptions, a traffic lane capable of accommodating 10-ft wide vehicular traffic had to be maintained throughout the project. Second, the Coast Guard lacked a real property interest to any laydown, staging, or construction work area at the head of the bridge. A real property agreement would be required before the project could even be sent out for bid. Third, construction on a neighboring ferry terminal and parking garage was scheduled to commence in 2019 and continue into 2020. The two major projects would likely be competing for the same laydown and work areas, making coordination between federal and commercial entities imperative.
As 2018 came to a close, funding was secured to execute a long-term bridge repair. A real property agreement was finalized between the State of Florida Department of Transportation, the City of Miami Beach, and the Coast Guard for use of the right-of-way as a construction staging area. Geotechnical surveys were completed and utilized to scope the project. It was decided that the existing piles would be left in place and four new 18-in square precast pre-stressed concrete piles would be placed 4-ft to the west of the existing bent number one and driven to 71-ft. Then, a new pile cap would be constructed, new first span deck planks would be laid, and post tensioning would be applied. Finally, the entire bridge would be milled and overlaid with new asphalt pavement. The end product would provide a stable support structure for the new bent number one and arrest any settlement, restoring the bridge to its original designed loading.
The project was awarded in late 2019 for $2.3 million, making it immediately apparent that the timing of the bridge construction efforts would directly conflict with neighboring ferry terminal construction. Construction work areas would be in short supply. Weekly stakeholder meetings were held by the construction project manager and attended by both base and contractor representatives. These meetings included review of the contractor’s two-week look ahead and critical path items. Due to the ongoing construction at the neighboring facility, the weekly meetings were later expanded to include the ferry terminal contractor as needed.
Base operations required continuous access through the entry bridge. As a result, all major work items had to be coordinated so the single lane would not be closed for more than 15 minutes. Any work item with a foreseeable closure of greater than 30 minutes had to be broken up to allow traffic to pass. Pile driving is an example of a task that had to be split up. Pauses were executed in-between pile driving steps, making the process less efficient but allowing for access on and off base. These pile driving bridge closures were limited to at most 45 minutes, which was detrimental to the project timeline.
The volume of temporary bridge closures along with the coordination complexity quickly proved to be a difficult and time-consuming practice for all parties involved.
A delicate balance was required between meeting the base’s operational needs for access while minimizing overtime or weekend work for the contractor, which would incur additional costs to the government. Looking back, if the contract had included provisions that provided for after-hours and weekend work, coordination efforts would have been far less contentious and more convenient to Coast Guard operations. Although overtime work provisions would have increased initial project costs, they would have been offset by avoiding complex coordination delays.
Further complications were encountered due to the unavailability of a suitable crane staging area. Since a 10-ft traffic lane had to be maintained throughout, the work was split into two phases. The first included driving two piles and replacing the cap and decking to the north, followed by a second phase to drive the two remaining piles and finish the cap and decking to the south. By the time construction progressed to the second phase in mid-2020, the neighboring ferry terminal construction was actively working in the only feasible crane staging area. Multiple coordination meetings eventually determined that the most advantageous solution to the government was to stop work on the bridge until the ferry terminal construction in the affected area was complete.
This stoppage resulted in almost two months of project delays that the government was responsible for. In hindsight, there are multiple avenues through which this delay could have been avoided. For one, construction could have commenced with Phase 2, the south half of the bridge, first. When construction initially began, the ferry terminal was not scheduled to start the conflicting work items until after the bridge project was complete. The construction team and stakeholders did not consider the possibility that a combination of project delays could result in both projects vying for the same staging/work area.
Had the phases been reversed, the conflict may have been avoided. Additionally, alternative pile driving methods could have been specified. Although more expensive, a barged crane would have been capable of driving the concrete piles and is readily available in the geographic area. Being able to execute pile driving from the water-side would have eliminated the need for a work area and simplified coordination and execution of the project overall to include limiting bridge closures. Admittedly, a barged crane would have been more susceptible to weather delays due to wind driven wave action, and would have required environmental review.
In the end, this complex structural repair project at Coast Guard Base Miami was completed in a relatively timely manner and with generally minimal modification costs. All parties worked collaboratively and within their given constraints to repair the bridge and restore it to its original capacity.
All the planning cannot prepare for the unexpected challenges encountered during construction. It is due to the collective actions of everyone involved in the project, and their can-do attitude and willingness to work together, that the repairs are now complete despite the challenges faced along the way.
Lt. Steven Becker, P.E., M.SAME, USCG, is Facility Engineer, Coast Guard Base Miami Beach, Fla.; firstname.lastname@example.org.
[This article first published in the May-June 2021 issue of The Military Engineer.]