Geotechnical Aspects of Deep Foundation Design and Construction at the SR520 Pontoon Casting Facility

This paper presents a case history of the geotechnical design and construction aspects of the deep foundations at the State Route 520 Pontoon Casting Facility (PCF) in Aberdeen, Washington. The Washington State Department of Transportation contracted Kiewit-General Joint-Venture to design and construct the PCF that will fabricate 33 concrete pontoons for use in the proposed SR 520 floating bridge in Seattle, Washington. The PCF basin is 940 feet long by 190 feet wide and 30 feet below the adjacent ground surface. The PCF floor is 10 feet below the adjacent Chehalis River level. This paper highlights the key geotechnical deep foundation aspects including: installation of 900 driven steel pipe piles, axial pile design methodology, performance of a dynamic pile testing program during design and construction, and unique pile construction aspects. Given the large quantities of excavation required to construct the basin and significant number of piles, on-time completion of these activities was critical to the successful construction of the PCF. Design of the PCF began in March 2010, basin excavation began in May 2011, and PCF construction was completed in December 2011. Pontoons are currently being constructed in the facility.