More than 20 years in the making, the California Trail doubles the size of the Oakland Zoo from 45 acres to roughly 100 acres. The $72-million project includes 26 structures on 22 acres of land and features California animal species in natural habitats.

Selected for their historical significance to California and for their status in the wild, the California Trail includes American buffalo, bears, mountain lions, jaguars and bald eagles. Open-air gondolas transport passengers 650 ft above sea level. The visitor center houses a restaurant and observation deck.

To support the restaurant, the contractor used post-tensioned beams in lieu of a conventional concrete deck, which saved time and money and afforded a more constructible solution, says Colby Powell, vice president of Overaa Construction. “High-bay shoring had to be brought in to span over the gondola machine to allow concrete placement. By using a post-tension solution, the thickness and weight of the floor above could be minimized. This also saved cost by reducing total concrete used.”

Overaa also used mechanically stabilized earth (MSE) retaining walls in lieu of cast-in-place concrete for many of the walls, some of which were 30 ft tall. “At the zoo, many of the interconnecting paths and roadways went through or near vegetation that was to be preserved,” says Powell. “The MSE walls had minimal impact to the surrounding areas and saved costs by eliminating forming operations.”

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