Located at the base of Eero Saarinen’s iconic Arch, this LEED Gold, $108.9-million project renovated and expanded the half-century-old subterranean museum and visitor center and added a new west entrance.

The largest public-private partnership investment ever in a national park, the project team sought to expand and improve the visitor’s center and connect the park via a walking path to St. Louis’ Old Courthouse, which had been cut off by a highway. It also had to be built without shutting down the Arch, which gets nearly 3 million visitors a year.

The entrance to the expanded museum allows visitors to enter the building at ground level. A gentle slope takes them through the 46,000-sq-ft addition to the museum, which explores the role of St. Louis in westward expansion.

One of the National Park Service’s requirements was that the below-grade expansion structure had to comply with Saarinen’s original berm height design. The tallest wall rises 41 ft, but most above-ground walls on the sloping entrance range from 25 ft to 35 ft tall. All of the walls slope inward from the park and had to be matched during concrete placement for final positions. Instead of using natural fill, project contractor McCarthy used lightweight geofoam to create the sloping grade that links the land bridge to the visitor center and then the Arch.

In 2015, two Mississippi River floods washed away the east slope of the center’s site and part of the site of a former parking garage that was demolished for the park reconfiguration. That forced a later opening.

Ryan Freeman, former vice president of operations at McCarthy, says, “We had to be able to construct the new museum and renovate the old museum while interacting with visitors and having hundreds of dump trucks coming into and out of the site every day.” Freeman adds, “We excavated 300,000 cu yd of material to dig down to the foundation wall of the existing museum.”

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