Job Description: The Summit County Metroparks put out for bid the design of a bridge to extend the Ohio and Erie Canal Towpath Trail from just south of I-277/S.R. 224 to just north of the overpass. The design utilized helical screw piles to support a boardwalk that extends over the existing Ohio and Erie Canal. This layout was necessary to extend the trail around the large concrete columns for the highway overpass.
Analysis and Design: The structural engineer working for the Metroparks already determined the layout of the helical screw piles and required load capacities. The design of the pile, however, was left to the helical screw pile contractor. Specifications in the bid package instructed the pile designer to ignore the top five of soils for lateral support of the pile shaft. Therefore, we selected the 1-1/2" solid steel square shaft helical screw pile with a grout column (referred to as "pulldown" pile or HPM, Helical Pulldown Micropile). This is a patented system for increasing the lateral stiffness of the helical screw pile in very weak soils. To properly install a grout column in 4 to 5 feet of water, we chose to case the grout column with PVC. This configuration also tripled the corrosion protection of the helical screw pile.
Installation: 44 piles for compression loads of the bridge were installed to an average depth of 17 feet and 22 tiebacks for lateral loads at an average length of 15 feet. The piles were installed with a Bobcat 441 Mini-Excavator and 4,000 foot-pound drivehead. The piles were terminated with a U-shaped bracket to support the wood beams of the walkway. The brackets were bolted to the piles to resist any potential uplift on the boardwalk. The challenge in installing the piles was working in 4 to 5 feet of water in the canal.