These are notes that I am writing to help me learn our industrial history. They are my best understanding, but that does not mean they are a correct understanding.
Sunday, October 24, 2021
I-395 Miami Signature Bridge "The Fountain" and Midtown Exchange Rebuild
(Update: RoadTraffic-Technology article "Rising 325ft above the ground and spanning 650ft, the arch will be the world’s third-biggest precast concrete segmental arch." H&H has more photos.)
The above bridge over a park is part of a project that is rebuilding the Midtown exchange and adding lanes to the east/west route. It was estimated at $802m, but it is now up to $818m.
In addition to rebuilding the existing roads, the project will add some FL-386 express lanes between NW 17th Ave and the MacArthur Causeway and it will make a 30 acre "community activity space" under the east end of I-395. They make that community activity space by hanging the new I-394 roadbed from cables. 30% of the design competition for the bridge is that it looks pretty. (The 30 acre figure comes from a factsheet. miami.curbed-2017 provides a figure of 55 acres. RoadTraffic agrees with the 55-acre Heritage Trail figure.)
Before I dig into the Signature Bridge, I'll describe the FL-386 express lanes because it did not have a design controversy. A rendering makes it obvious that the express lanes are being built over the local lanes.
The winning design for the Signature Bridge was announced in May 2017, and it was by Archer Western - De Moya. Using a tunnel to have an open park in the museum area of Miami was quickly ruled out as too expensive.
Rendering by Archer Western - De Moya via miami.curbed-2017, this article has several more renderings of the proposed bridge.
Below was the runner-up design by Fluor-Astaldi-MCM. It lost by a half-point on a scale with 100 points. A 2013 settlement determined that aesthetics would determine 30% of the points. Originally, the aesthetics committee consisted of one FDOT member and four community representatives. But when the FDOT member dropped out, FDOT designated its technical committee of five FDOT staffers as the replacement voters. Thus FDOT changed the ratio of FDOT/community from 1/4 to 5/4. [ENR-Jul2017, I'm down to one free article. I don't know what the initial count was.]
The "spider legs" design was controversial because FDOT kept the selection process secret and rigged the voters on the aesthetics committee and because Archer Western De Moya was fired from a hospital project because of a two-year delay. [CommunityNewspapers]
The funding to rebuild the road without piers in the downtown area was identified in 1996. But some thought the money would be better spent on new rapid transit facilities. The idea of removing piers by using some arches was around since at least 2015. [MiamiTodayNews- Dec2015]
An article from May 2017 expected construction to start by December. Obviously that did not happen. Evidently the delay was caused by protests from Munilla Construction Management and Figg Bridge Group. But in Apr 2018, they dropped their protests. [TheRealDeal-2018, I didn't subscribe] I recognize Figg as the designers of the FIU Bridge that collapsed on 3/15/2018.
The pier that terminates all six arches is pushing foundation technology. First of all, it uses auger cast piles to support the foundations. It is one of the first times they have been used for a road bridge in the US. [wsp]
When early tests showed that the FDOT’s preferred foundation method of precast piles wouldn’t have enough load capacity, and that drilled shafts would take too long, they needed a new solution. The fact that Keller has successfully used auger cast piles for around 90 percent of high-rise towers in the area, achieving several world records along the way, helped convince the consulting engineers to meet with Keller and develop an auger cast pile design solution. That solution was then presented by Keller to FDOT and general contractor (Archer Western-de Moya joint venture), who green-lit the project....Over the next couple of years, Keller will work in phases to install more than 2,000 auger cast piles, with diameters of 30 and 36 inches, up to depths of 134ft. [keller]
Construction began on Oct 29, 2018 and was expected to be done in the fall of 2023. But by Nov 2019, they had already added a year to the schedule. One of the reasons for the delay was "instead of driven concrete piles, the foundation of the I-395 segmental and signature bridges will now be built with auger cast piles." [TheNextMiami]
For the Big Pour of the six-arch foundation pier, they used six miles of cooling pipes and seven large chillers. They had embedded wireless thermometers in the footing so that they could insure a uniform temperature during cooling. [wsp]
The central pier footing is 140' x 68' x 14' and required 5,200 cubic yards of 8,000 psi. The Big Pour used four pump trucks and started on Friday, Jul 23, 2021. After 33 hours, it was done Sunday morning. The rebar was so dense at the bottom of the footing that they had to use a special concrete mix so that it flowed correctly into the tiny spaces, just inches, in the dense rebar. [wsp] BASF Kaolin supplied 300 tons of MetaMax in one day during the Big Pour. [kaolin]
Attention has now turned to the 345 cast segments that will be needed to build the six arches. The rebar in these segments is tied even more thickly than in the footings. So they are using self-consolidating concrete. "Because of the elliptical shape of the arches, he said each segment will meet its neighboring segments at slightly different angles. That means the forms for all 345 segments must be adjusted to create the precise angle specified for each segment." [wsp]
In the meantime, they started work on the regular road on Jun 22, 2020. Walsh tweeted three photos of the placement of the first two segments.
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The Walsh Group posted Unique view from inside the installed precast segments that are part of the new Miami Signature Bridge.
The Walsh Group commented on their post And for context: Here’s an exterior view of installed precast segments.
About a year later, some of the new roadway is built and the piles for the other ends of two of the arches are done.
This is the post that taught me about the existence of this project. Has Walsh replaced Archer Western - De Moya, or are they a subcontractor? Neither, I think Archer Western is part of the Walsh Group.
The Walsh Group commented on their post Each segment will be a precast install. However, the final piece (in purple) will be poured in place.
One of four photos posted by The Walsh Group Jan 4, 2022: Plan the work; work the plan. Crews construct the center pier of Miami’s Signature Bridge. The center pier is the principle foundation for the bridge’s towering arches.
The Walsh Group posted four photos with the comment: "Over the tracks and under the bridge. Deck pour along I-95 Express Phase 3C. " [another concrete pump]
1:01 video @ 0:31 (source) Archer Western and the de Moya Group are utilizing its S.A.B.E.R. beam launcher to place 320 beams for the new double-decked section of the SR 836 / Dolphin Expressway in Miami. Each beam measures approximately 185 feet long and weighs 120 tons. What does S.A.B.E.R. mean?... Segment and Beam Erection Rig.
I did not find comparable renderings for the winning design. I wonder what the official name of that design was. I doubt it was "spider legs."
Auger cast piles are another name for CFA continuous flight auger. The drill stays in the hole-filling and supporting it. It is only withdrawn as concrete is pumped through it from the bottom.
Thanks for the information. Using "continuous flight auger" for a Google search resulted in several videos. It looks like such an effective way to do pilings that I'm surprised it has taken so long to be adopted in America. Hopefully, I'll be able to write some notes about it this week and change these notes to reference the new notes.
Auger cast piles are another name for CFA continuous flight auger. The drill stays in the hole-filling and supporting it. It is only withdrawn as concrete is pumped through it from the bottom.
ReplyDeleteThanks for the information. Using "continuous flight auger" for a Google search resulted in several videos. It looks like such an effective way to do pilings that I'm surprised it has taken so long to be adopted in America. Hopefully, I'll be able to write some notes about it this week and change these notes to reference the new notes.
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