The new, 1.2-million-sq-ft U.S. Coast Guard headquarters in Washington, D.C., is set on a hillside that overlooks the Potomac and Anacostia rivers. Given the sprawling building footprint over the site's steep, 160-ft vertical elevation change, 1.6 million cu yards of soils were excavated, which required 300,000 sq ft of timber lagging and 1,500 soldier piles.
Post-award, geotechnical analysis of the soils determined the existing marine clay would not support the originally designed foundation system. A revised foundations plan called for 1,500 caissons, measuring up to eight feet wide and 100 ft deep. Clark Concrete poured 250,000 cu yd of concrete.