DESCRIPTION: The Webb Diking District and the Army Corps of Engineers completed construction of a new pump station and tide gate on Webb District Road, near Woodson in Columbia County, Oregon. The project also included a new pump station, head gate through the dike and stabilization of the discharge pipe. Foundation Engineering, Inc. provided geotechnical engineering services including geotechnical exploration, laboratory testing, geotechnical analysis and design, and preparation of recommendations for design and construction of the pump station pile foundation support, seepage mitigation, walls, filter drain and sheet piles for temporary excavation support.
The project site is located in the Columbia River Lowland along Westport Slough. The site is underlain by alluvial soils consisting of loose to medium dense sand and very soft, organic silt.
SERVICES: Geotechnical exploration included one exploratory boring and a review of existing pump station plans and geologic maps. Geotechnical analysis included calculation of pile capacity and evaluation of hydrostatic and lateral earth pressures for a buried wall design and temporary sheet pile support. We also evaluated seismic response and liquefaction potential.
We provided construction-phase services including: pile driving observation, review of contractor submittals, and evaluation of dewatering and backfill material properties. The project was completed in 2008 and is the primary pump station for the Webb Diking District. Project challenges included dewatering during construction, seepage and dike stability, battered pile support and stabilization of excavations for the headgate construction.