Milton Madison Replacement Bridge
Milton Madison Replacement Bridge
A bridge born in 1929, as the Great Depression began, was reborn eight decades later as a result of the Great Recession. Funded in part by a $20 million TIGER (Transportation Investment Generating Economic Recovery) grant from the American Recovery and Reinvestment Act of 2009, the Milton Madison replacement bridge carries 4 lanes of US 421 between Milton, KY and Madison, IN. Originally constructed as a 2-lane, 20 ft. wide through truss bridge having only 16.8 ft. clearance, by 2009 the original bridge had a sufficiency rating of 6.5 out of 100, it was functionally obsolete and structurally deficient, and it was posted to prohibit trucks over 15 tons. Yet the Milton Madison Bridge is the only crossing of the Ohio River in a 72-mile stretch, from Louisville, KY, to Vevay, IN, making it a critical link in the local community’s transportation infrastructure.
By agreement between the Indiana Department of Transportation (INDOT) and the Kentucky Transportation Cabinet (KTC), INDOT managed this evenly cost-shared project and selected the design-build contracting method. This proved a wise choice when the winning bid by Walsh Construction Company (La Porte, IN) came in 20% below estimate, at $103 million. Walsh’s design-build partners included Burgess & Niple Engineers (Columbus, OH; overall designer), Buckland and Taylor Ltd. (N. Vancouver, BC; truss/superstructure) and H. C. Nutting (Cincinnati, OH; geotechnical). A significant part of the cost reduction was the Walsh team’s innovative design and unique construction method which strengthened, widened and reused the existing reinforced concrete piers, prefabricated the new truss in sections on barges, then assembled the new bridge on temporary steel piers placed immediately adjacent to each old pier. Traffic was relocated to the new span, in its temporary location, while the old bridge was razed. Then, during a brief bridge closure, the 2,428 ft. long, 30 million lb. new truss was slid 55 ft. horizontally from the temporary supports onto its permanent home atop the rehabilitated piers.
RECo played a crucial role in this design-build project by providing cost-effective permanent and temporary abutment structures for the onshore end bents in both Indiana and Kentucky. The permanent abutments comprise, in plan, a rectangular, U-shaped Reinforced Earth retained fill wrapped around the bridge seat, which is supported on a single row of piles. The Reinforced Earth walls have 5 ft. x 10 ft. precast concrete facing panels (with an ashlar stone architectural finish) and the granular backfill behind the panels is reinforced by RECo’s standard 50 mm x 4 mm hot dip galvanized steel reinforcing strips and ladder reinforcements. To prevent the reinforcements from interfering with the piles supporting the end bent, special design details in RECo’s shop drawings specified how to properly position and splay the reinforcements (up to a maximum of 15° away from the perpendicular, except where custom-designed for >15°) as they were installed along the abutment face wall and along the first +/- 5 ft. of each wing wall. A small Reinforced Earth panel-faced wall also supported a pedestrian access ramp leading to the Indiana end of new bridge (Figure 1).
Reinforced Earth walls can tolerate both total and differential settlement because these structures are compacted soil with a facing of discrete precast concrete panels having joints that allow adjacent panels to move relative to each other. Every project should include a settlement analysis, however, and at the Milton Madison Bridge the estimated total settlements at the wall faces ranged from slightly under 1 in. to just over 5 in. – well within the Reinforced Earth wall total settlement tolerance range. Of greater interest was the estimated differential settlement determined along the face of the wall. Typically a differential settlement ratio of 1:100 (equivalent to 1% or 1 ft. in 100 ft.) is considered of no consequence; the analysis at Milton Madison predicted differential settlement ratios of 1:300 or less – clearly of no concern for the stability of these walls.
The Ohio River is well known for its floods, so the walls, which are located within the 100-year flood plain, had to be designed for the river’s random but unavoidable cycle of saturation and drawdown. A Reinforced Earth wall is always constructed using granular backfill, but typically the MSE wall backfill specification sets upper, intermediate and lower limits, allowing the contractor to choose from a wide range of materials that fit within those limits – see “Typical INDOT MSE Backfill Gradation,” left side of Table 1. Some backfills that meet the “Typical” requirements could be inappropriate for the rapid drawdown condition at Milton Madison however. Therefore, to assure the high porosity necessary to handle rapid drawdown, MSE backfill below the 100-year flood elevation was required to be Indiana No. 8 Coarse Aggregate, having the completely free-draining characteristics shown in the right side of the table. Evidence of the expected flooding is seen in Figure 2 by the horizontal line of brown staining on the wall panels below the abutment coping.
As mentioned above, the new span carried traffic in a temporary location, so temporary approach roadways were also required. RECo supplied its TerraTrel® wire faced MSE wall system, with ladder reinforcing strips, to retain the temporary approach fills immediately behind the temporary end bents, while additional TerraTrel wire walls kept the temporary approach roadway embankment from encroaching on neighboring properties.
It is said that good things come in small packages. On the Milton Madison bridge replacement project, small Reinforced Earth walls played a big role in both the temporary and the permanent phases of the project.