Hidden in the hillside

PHOTO: Atlas Technical Consultants

The American Society of Civil Engineers’ Southern Idaho Section has awarded the Whistle Pig Tank development Project of the Year in the less than $10 million category. The 2.65-million-gallon concrete tank provides vital water supply to South Ada County, Idaho residents and businesses, and is fully buried within a steep hillside to harmonize with its surroundings.

Developed in collaboration with Atlas Technical Consultants and engineering firm Keller Associates for water utility company Veolia, the Whistle Pig Tank project faced unique design challenges. The Atlas team successfully guided the tank’s construction into the hillside, performing specialized geotechnical investigations, calculating lateral earth pressures, designing foundations and pavements, and offering comprehensive construction recommendations.

“This [award] is a testament to the exceptional geotechnical capabilities of our Boise team,” says Atlas CEO Jacque Hinman. “We’re proud of their hard work and look forward to their continued innovation and success.”

The tank is a large, 120-ft. diameter, 35-ft. sidewall tank with 32 interior columns and a heavily reinforced concrete deck. Contractor JC Constructors had crews excavate nearly 20,000 cubic yards into the steep hillside site to place the base slab. Work progressed with 35-ft. high wall forms and taller column forms. Concrete suppliers were G & B Redi Mix and Idaho Materials and Construction.

Following subcontracted pre-stressing, JC Constructors installed a very extensive 370,000-ft.3 shoring system to support, form and place the heavy deck. The tank was then backfilled with up to 60-ft. plus fills with an extensive slope stability effort. Included in the fill effort was room for a new 800-ft. site access road across the very steep terrain. The project is now buried, the site is re-graded and re-seeded, and few will know it exists.

PHOTO: JC Constructors Inc.