value of Gaylord’s project is reported to be near $900 million, with the adjoining National Harbor Development, launched by D.C. metro developer The Peterson Companies, at nearly the same value. Gaylord Entertainment of Nashville, the project owner, required a tight construction schedule and a firm opening date in spring 2008. The first project task was install- ing the foundations for the new 18-storey hotel containing 2,000 guestrooms.
The preliminary geotechnical designs suggested that both auger cast-in-place piles and drilled shafts (caissons) be used. Driven precast concrete piles were considered an “alterna- tive,” but one that was believed to be more expensive than auger cast-in-place piles or caissons. Engineering Consulting Services, Ltd. (ECS), the Washington metro area’s largest geo- technical consultant, believed that driven, precast concrete piles would be the least costly deep foundation alternative if the geotechnical design capacities could be increased from the preliminary assessments derived by others. ECS was hired by Gaylord Entertainment to demonstrate that driven precast concrete piles were more cost efficient and less risky than other deep foundations previously considered. Fourteen-inch square, prestressed, precast concrete piles with compression capacities of up to 150 tons each were ultimately chosen to support the hotel. Superior cost and schedule considerations, coupled with a high degree of design certainty — every driven pile is a tested pile — resulted in the choice of driven precast concrete piles for the hotel project.
Preliminaryprecastconcretepilecapacitiesweredetermined to be on the order of 100 tons per pile. To make driven, precast piles more attractive from a cost perspective, the capacities needed to be increased toward the upper levels of allowable stress limits permitted by the International Building Code (IBC). For the same sized piles originally considered, 14-inch square precast concrete, the capacity estimates were increased to 150 tons per pile, a 50 percent increase from the original
estimates. Even higher capacities were feasible, but pile driv- ing times and lengths were limiting factors. Pile capacities in this range were previously thought to be too aggressive in the D.C. metro area considering the variability of the underlying soil deposits. However, a comprehensive test pile program con- firmed that individual pile capacities in excess of 150 tons were possible with reasonable embedments into the bearing soils. Proving the higher range of capacities was key to the decision to utilize driven, precast concrete piles for this project.
Schedule was also an important consideration. Because higher capacity piles were considered, fewer were needed as compared to say auger, cast-in-place piles. Fewer piles result- ed in smaller pile caps, which also improved the schedule. Overall, preconstruction assessments determined that driven, precast concrete piles would be faster to construct than other deep foundation types, including drilled shafts. The positive schedule impacts of driven piles were a definitive cost-savings measure.
The positive impacts of efficiently designed, driven, pre- cast concrete piles for Gaylord National spilled over onto the neighboring National Harbor Development, which began con- struction about one year after the start of Gaylord National, by regional developer The Peterson Companies. The entire National Harbor development cost is estimated at $2 billion. Several of the adjoining larger hotel or mixed-use structures (the Westin or Wyndham Resorts, for example), were also sup- ported on driven, precast concrete piles, designed as efficiently as the project schedule would permit. Considering the con- struction dollars involved, all serious deep foundation alter- natives were considered for the entire National Harbor development. Cost and predictability were key reasons precast concrete piles were chosen and why other deep foundation alternatives were not selected.
National Harbor Development shown on the left, and Gaylord National (not pictured) is to the right.
Q2 • 2008