Value Engineering County Bridge Replacement

Foundation designs in a bid-build business environment can be challenging as so much depends on the capabilities of the selected contractor.  Owners and governing agencies must be open to value engineering (VE) alternatives.  This paper presents a case history where a foundation VE design was prepared for a county bridge replacement. The existing structure was a two-lane, simply-supported, truss bridge approximately 270 ft long and 30 ft wide.  The new bridge is a three-lane, two-span, continuous steel plate girder bridge approximately 250 ft long and 49 ft wide.  The new bridge was to be founded on two end abutments and one center pier by a total of 173 micropiles. Due to the number of micropiles and the time requirement to install a single micropile, an alternative design was proposed utilizing driven steel piles for support of the abutments and rock-socketed drilled shafts for the center pier. Replacing the micropiles with the proposed alternative was intended to reduce overall construction time and cost. Shallow bedrock and soil scour presented unique challenges for the bridge foundation and required an in-depth investigation to determine the required depth of foundation elements to achieve pile toe fixity. It was determined the sand layer thickness was not sufficient in some places to provide fixity to the VE driven piles and therefore the east abutment had to remain the original micropile design.  Substitution of driven pile and rock-socketed drilled shafts in the other areas still resulted in both time and cost savings.  This case history shows how engineers, contractors, owners, and governing officials can collaborate collectively to develop effective foundation solutions. Keywords: micropile, driven pile, drilled shaft, abutment, center pier