McCoy Road Pedestrian Bridge

Providing Better Alternatives

The original contract called for 15 helical piles to be installed at bridge’s timber boardwalk concrete abutments and at three timber pier locations. Helical piles are screwed into the earth, creating deep foundations even in the weak soil typically found in wetland environments. After careful consideration, it was proposed that four timber piles from the initial design be replaced with six helical pulldown micropiles. Helical pulldown micropiles have a much smaller diameter than standard helical piles, but use a sleeved top portion to better resist lateral loads.

Adjusting Installation Plans

The task of designing and installing the helical pulldown micropiles was not straightforward. The first design iteration used a 6-inch diameter top portion and a 15-degree batter to achieve additional lateral capacity.  This design worked flawlessly for the southern pier cap, but a buried Verizon line was in conflict with one of the battered piles for the northern pier cap.  The load requirement was satisfied by increasing the micropile casing to an 8-inch diameter sleeve and installing the piles plumb rather than battered.

Saving Time and Money

Thanks to the innovative use of helical micropiles, equipment that was already on site for the rest of the structure was able to be used throughout, avoiding the week-long mobilization and set-up of a crawler crane, driving leads, and a diesel pile hammer needed for timber piles. This streamlining allowed the project to be completed under budget on Contract Calendar Day 52, which was eight days sooner than what was promised to the Red Lion Chase community.