Keller’s US business Hayward Baker has been called in to help contractors working on the regeneration of the area around St Louis Gateway Arch in Missouri.
McCarthy, the contractors working on the project, came across problems when adding a mechanical suite below a new museum to house electronics, heating and ventilation, and other utilities.
“The only place to do it was beneath the museum, one basement level below the ground,” explains Hayward Baker director Jeff Hill. “The contractor thought they could excavate all of it in rock, but the ground turned out to be soft clays and soils. It quickly became a pressing issue.”
Hayward Baker designed a solution to install 12 micropiles to support three significant column foundations and around 200 wall feet of drilled micropile beam and lagging to allow for the deep excavations below the existing museum basement slab. The foundation and retention elements were varying lengths due to the karstic limestone.
“We faced difficult drilling conditions on a tight-access site, encountered layers of hard rock, then voids, clay fill voids and highly weathered rock,” said Hayward Baker’s St Louis office director Greg Terri
“Micropiles are generally used for a vertical load, but we had to design them for earth retention as well. It all came down to good solid design and a lot of planning with the engineer so we could get the equipment in there. We didn’t exactly know what we were going to find, so we had a couple of drilling methods ready to go.
“When excavating to install the micropile pile caps that were to tie into the existing columns, we encountered H-piles at some locations. However their extent, condition and capacity could not be verified. That probably meant we didn’t need all of the micropiles, but on projects beneath a National Monument on a critical schedule there can be no room for error” Terri added.
The team successfully completed the job in around four weeks.
“It’s great for Hayward Baker to work on these national projects,” Hill said. “There’s a patriotic aspect but also they’re just really interesting from an engineering point of view. There’s nothing else like the Gateway Arch in the world; it’s a completely unique structure and a masterpiece of structural engineering and architecture. You really feel like you’re getting into a bit of history with every pile you drill. It was a privilege to work on it.”