In the Wenatchee Valley, it’s a common source of pride that Washington is the top producer of apples and pears in the nation. But with so much fruit coming off the trees at roughly the same time each year, have you ever wondered how crisp, crunchy apples and pears are available in the grocery store year-round? Or what enables people across the country—and around the globe—to recognize Washington as the source of the world’s best tree fruit varieties? Enter the technology of controlled atmosphere (CA) storage.
A quick background on tree fruit: as apples and pears ripen, they take in oxygen and release carbon dioxide. Years ago, researchers determined that by limiting oxygen, introducing a little nitrogen, and lowering the temperature, the ripening process can be slowed. To apply this concept at a scale large enough to support Washington’s apple and pear industries, packers build enormous warehouses capable of holding multiple-orchards-worth of fruit within special airtight, refrigerated rooms. This gives shippers the flexibility to releasing fruit incrementally throughout the year, and allows you and I to enjoy a crunchy Honeycrisp apple in the middle of February, months after it was picked.
Building a CA-storage warehouse involves three special considerations: they must be massive, they must be stable, and they must be built quickly. Once fruit is off the trees, it gets hauled in bins that can weigh upwards of 900 pounds when full. Moving these bins requires big equipment (like forklifts and semi-trucks) and efficient storage requires stacking them up to 12 high—that’s a lot of weight! To maintain precise control of the atmosphere within these buildings, the rooms must remain airtight. This means that the foundation and walls must not shift, settle, or crack. Finally, market demands for additional storage capacity often drives the need for new CA warehouses to be built on short notice, with expedited timelines.
To meet these rigorous requirements, CA-storage warehouses are typically constructed out of giant precast concrete walls supported by cast-in-place concrete foundations capable of supporting substantial floor loads—up to 1,000 pounds per square foot. Designing for this type of stability requires the expertise of a geotechnical engineer for understanding how soils beneath the building will behave when loaded. By studying the local geology, excavating test pits, and drilling cores, geotechnical engineers can specify how wide and stout the footings and floor slabs should be at a given site.
Aspect geotechnical engineers Nick Szot and Erik Andersen have guided the design of several CA-storage warehouse projects for industry leaders like Blue Bird, Gebbers Farms, McDougall and Sons, and Peshastin Hi-Up. Aspect is proud to be the tree-fruit industry’s local, responsive firm for geotechnical services in the Wenatchee Valley and central Washington, and for our role in bringing Northwest pride to homes across America and around the world.