Ronald Reagan National Airport – The Challenge
At Ronald Reagan National Airport, JES provided a deep foundation support solution using helical piles. A new JetBridge for “Gate 8” of the JetBlue Airways “Terminal A” was on a fast-track construction schedule when JES was contacted by the contractor, who needed immediate assistance with the design and installation of Helical Piles, which were part of the overall foundation support system. The JetBridge is a telescoping and pivoting walkway supported by a single steel column, and due to the varying orientation of the JetBridge itself, there can be extremely high overturning loads imposed on a relatively small concrete foundation.
A soil test boring performed for the project indicated approximately 10 feet of old ﬁll, overlying a strata of apparently original ground containing organic matter.
The near surface soils and underlying organic strata were not acceptable for direct support of the concrete foundation, which necessitated the need for deep foundation support. Considering the airport was originally constructed in the 1950’s, there was concern regarding subsurface soil contamination. Therefore, the deep foundation system needed to limit the amount of soil disturbance. Additionally, the deep foundation system needed to be installed with minimal vibrations due to the proximity of the existing terminal structure, and the installing equipment needed to be mobile and compact due to the airport’s ongoing ﬂight operations.
Ronald Reagan National Airport – The Solution
The design structural engineer determined that helical piles were the most appropriate deep foundation system for the support of the concrete foundation.
The helical pile system was recommended because of its relative ease of installation, portable installation equipment, adaptability, and long term stability. Installation does not generate spoils or vibration, which addressed the concern of contaminated soil and close proximity of existing structures. The helical piles required to meet structural speciﬁcations were designed by the JES engineering team, and consisted of hollow round shaft piles with 3.50” outside diameter, 0.313” wall thickness, and ASTM A572 Grade 50 x 3/8-inch thick helix blades.
The piles were designed to provide 55 kips axial capacity and 46 kips of tension capacity. The torque required to achieve the design capacities was 15,714 ft-lbs.
The helical pile components were hot-dipped galvanized in accordance with ASTM A123 [Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products]. The helix configuration require to provide the designed axial and tension capacities consisted of 10″ -12″ -14″ helices.
Ronald Reagan National Airport – Project Summary
JES installed 8 Helical Piles. The installed pile lengths varied from 22-45 feet, with a typical depth of 33 feet. The piles were installed using an Eskridge Model 75-71 (20K) hydraulic drive motor. During pile installation a “Pro-Dig C440 Torque Transducer” was used to determine the actual torque applied to each pile, which then was used to verify that the piles were capable of supporting the design work loads.
It is noted that the original foundation plan called for 6 piles. However, based on discussion with the project structural engineer, 2 additional piles were added to ensure that adequate compressive and tension capacities were available.
New construction steel brackets (caps) were bolted to the top of the pile shafts and were embedded in the concrete foundation. To ensure proper bolt-hole alignment, JES ﬁeld crew used a “Magna-Drill” attached to an engineered guide system. Special anchor rods were welded to the tops of the standard steel pile cap as per the structural engineers design requirement.
JES Project Engineer: David E. Stinnette, PE
Architect: John N. Bratichak Architects
Structural Engineer: Johnson, Mirmiran & Thompson, Inc.
Geotechnical Engineer: Thomas L. Brown Associates, P.C.
General Contractor: J & J Construction