DESCRIPTION: Two bridges were replaced on I-84 crossing the Sandy River near its confluence with the Columbia River. The Sandy River Bridges are 840-foot long, four‑span structures supported on 8-foot diameter drilled shafts at the interior bents and driven piles at the abutments.
SERVICE: Foundation Engineering completed a foundation investigation for the project. The work included site‑specific seismic and liquefaction hazard evaluations. Based on the findings, we designed stone columns to provide lateral spread mitigation at the west abutments.
To increase the drilled shaft resistance and reduce the required shaft length, the foundation design for the interior bents included post‑grouting of the drilled shaft tips. This innovative method has the potential to significantly reduce the cost of drilled shafts by utilizing more of the available end resistance. Shorter shafts meant a smaller crane and a smaller work-bridge could be used. This reduced the required number of temporary piles and the associated construction impacts to fish habitat.
Osterberg Cell (O-cell) test data from this project can be used to aid in calculating resistance in Portland area foundation soils and for shafts with post grouting. Therefore, future bridge projects will benefit from the testing performed on this project. Results of the testing and shaft construction were presented at the Deep Foundation Institute, Super Pile 2012.