Abstract:
Solving Variable Bedrock Challenges with Ductile Iron Piles
Bryan Plaskett, E.I.1, Kevin R. Johnson, Ph.D., P.E.2, Matt Caskey, P.E.3
Working in urban environments presents unique logistical challenges beyond those typically associated with traditional geotechnical design and construction. These challenges can include constrained sites with limited access and laydown area, vibration concerns for adjacent structures, and the need to complete work within limited schedules. When challenging geotechnical conditions like variable bedrock elevations are present, the need to balance performance requirements with logistical constraints become the driving factor when selecting deep foundation systems.
This paper focuses on the deep foundations used for a new elevated pedestrian bridge at a major health care facility in Tampa, Florida. The new bridge crosses a wide, busy, arterial street and was located in close proximity to an existing clinic building on one side and a new bed tower under construction on the other side. The project involved support for 13 new foundations subject to heavy compression, tension, and lateral forces. The geotechnical conditions consisted of locally-typical sands and clays over limestone bedrock that varied widely in strength and elevation. In addition to the technical design requirements, of particular importance to the owner, was the utilization of a deep foundation system that could offer low vibrations, rapid production, and clean installation to limit impacts on both properties and the public roadway that separated them.
This paper describes the use of Ductile Iron Piles on the project to meet the many design and construction challenges, while providing the benefit of cost and time savings compared with other piling systems. A staple in European construction for over 30 years, the low vibration, driven pile system offers the ability to work within restricted environments while delivering moderate to high capacities. The paper describes the unique project specific geotechnical and design conditions, describes Ductile Iron Pile design approaches, and focuses on how installation of the system addressed the unique logistical challenges. In addition, the implementation of robust full-scale load testing program to assess compression, uplift, and lateral design capacities is presented. This paper represents one of the few published references on the use of Ductile Iron Piles on projects in the United States and is of importance to designers and contractors on projects teams looking for value-added alternatives to traditional deep foundation construction approaches.
1Project Engineer, Earth Tech, LLC. 2620 Hunt Rd., Land O’ Lakes, FL 34638 bplaskett@earthtech.com
2Senior Engineer, Earth Tech, LLC. 2620 Hunt Rd., Land O’ Lakes, FL 34638 kjohnson@earthtech.com
3Director of Sales, DuroTerra, LLC. 639 Granite Street, Braintree, MA 02184. mcaskey@duroterra.com