Hayward Baker Inc. recently completed micropile installation for the rehabilitation of the Merchant RR Bridge across the Mississippi River in St. Louis, Missouri.

The Merchant RR Bridge has been in continuous service since its construction in 1890. In order to extend its life for another century, the Terminal RR Association has begun major rehabilitation and reconstruction of the East and West approach spans. The reconstruction effort includes replacing existing trusses with new steel spans supported on new deep foundations.

The piers for typical new bridge construction are usually supported on driven piles or deep drilled shafts. On this project, because the foundation work had to be performed beneath the existing structure where available head room was less than 30 feet, an alternate foundation system was proposed by HBI.

Working closely with Terminal RR Association, and their structural engineer, Modjeski & Masters, Hayward Baker provided a micropile foundation system in lieu of drilled shafts.

HBI’s design included approximately 150 micropiles drilled and socketed 5 feet into solid bedrock. The micropiles were designed to carry 325 kips and were tested to 650 kips.

As of November 10, 2004, all foundation work on the site is complete and superstructure repairs and modifications are under way. The micropile alternate shaved several weeks off the schedule and saved significant costs for the owner.