Fairview Ave. N. Bridge Replacement A joint effort between material supplier and equipment supplier breaks barriers and records and drives innovation in helical pile installation.
When there is no available technology to meet the project needs within environmental limits or criteria... When there is no design guide for the proposed solution ... When there is no precedent project or model specification to put in front of the governing body for approval of the solution... Marine Project. Noise Limitations. Vibration Limitations. A replacement for the Fairview Ave North Bridge was designed with 8’ Drilled Shafts into the bed of Lake Union in Seattle. A working platform would be necessary for the crane to install the shafts as designed. A temporary trestle structure with piles to provide the necessary service load at 500 kips per pile was designed. There could be no impact hammer used due to the environmental restrictions in place to protect Lake Union’s water mammals and fish. Additionally, vibration limits imposed
by adjacent structures also played into the limitations of installation options.
Working backwards, the potential solution, large diameter helical piles would need to be designed Pileworks, to support “We knew that the Magnoan ultimate large diameter axial load of lia, TX steel pile manufac- helical piles could 750 kips. The turer knew piles would be achieve tremendous that large installed to a capacities and diameter depth where helical piles the alluvial the means of could supply installation could sands were the bearing present and reduce a lot of capacity and would achieve exposure on a the vibration these loads. of installaproject like this.” With driven tion would be of Says Pileworks piles minimal, and course, the General Manager, blow counts noise relative to other would deMatt Fenwick. installation termine the would be greatly reduced. capacity of each pile. Determining the load capacity of helical piles is somewhat different. With helical piles the torsional resistance of the pile during advancement is measured by the torque exerted on the member via the drill head, torque data at pile toe creates a base line for an applied Kt value to be assigned, which is used to determine the axial load the pile has achieved. “We knew that large diameter helical piles could
achieve tremendous capacities and the means of installation could reduce a lot of exposure on a project like this.” Says Pileworks General manager, Matt Fenwick. “When designing helical pile in diameters over 12.75”, one of the crucial pieces of information that needs to be determined is what Kt could be expected to a 22” diameter pile shaft”. The helical pile industry has limited empirical information on large shafts and a fair bit of conservatism must be used when determining the theoretical performance. Applying a conservative Kt value, relying heavily on sub surface data, confirming the ability to place the pile toe into the denser strata are precursory steps used to determined that the performance of the pile could achieve the required design load.” Fenwick continued, “As for as a top drive rotary head capable of delivering over 350,000+ ft-lbs while resting on top of an 80’ section of pile, I don’t think a configuration of mast and rotary like this is readily available and combining existing equipment to do so will be necessary”. Then Fenwick recommended a drill motor manufactured by Eskridge in Kansas City capable of achieving the required 375,000 ft-lb of torque necessary to install these large diameter helicals.... Enter APE... At the time, APE had the
