COVER STORY Drilled Pier Foundations for Mercedes-Benz Stadium The new Mercedes-Benz Stadium (MBS), home of the Atlanta Falcons, is part of a new era of stadium construction in the U.S. These new-age stadiums are larger and have more amenities than their predecessors. Many of the MBS’s features, including its innovative retractable roof, result in extraordinary structural loads. The roof structure is supported by a series of mega columns that bear on eight large caps, six of which are supported by drilled piers. Each of the pier caps contains between 8 and 16 drilled piers that bear in the underlying bedrock. The design pier diameters are 6 and 6.5 ft (1.8 m and 1.9 m). Augercast piles were used to support two of the mega column caps. Drilled piers, augercast piles, aggregate piers and spread footings were used to support the more lightly loaded portions of the structure. The focus of this article is the construction aspects of the drilled pier foundations. Initially, a fairly extensive drilled pier load test program was performed. Load testing included a Statnamic compression test, two Osterberg Cell tests and two lateral tests. Production pier installation included over 3,800 linear ft (1,158.2 m) of earth excavation and over 1,350 linear ft (411.4 m) of hard rock excavation. The piers contain more than 6,600 cu yd (4,587.3 cu m) of concrete and 1,100 tons (998 12 • DEEP FOUNDATIONS • JULY/AUG 2016 Daniel C. Brahana, P.E., ABE Enterprises, Inc., and Jean Wehbe, P.E., Bauer-Pileco, Inc. AUTHORS tonnes) of reinforcing steel. Drilled pier installation took about 4.5 months. ABE Enterprises was the specialty foundation subcontractor and Bauer-Pileco was the equipment provider. Site and Subsurface Conditions The project site is in downtown Atlanta and was originally occupied by residential buildings. A portion of the site was later developed as a rail yard, and other areas contained light manufacturing, warehouses and other relatively light structures. For the past 15 to 20 years the site had been used for surface parking. Beneath a surficial layer of manmade fill, soil test borings at the site generally encountered residual soil, partially weathered rock and the parent bedrock. The bedrock at the site is highly variable, both in elevation and in hardness/quality. The depth to rock is Drilled Pier Diameter (ft) 5.5 6.0 6.5 Compressive Capacity (kips) 2,375 2,800-6,000 4,700-10,070 Drilled pier design capacities Tension Capacity (kips) 0 0-1,900 800-3,500 Lateral Capacity (kips) 20 20-450 20-525
