DESCRIPTION: Cowlitz County Department of Public Works completed construction of a ±16‑foot diameter structural plate arch culvert with wing walls on Clark Creek Road in Cowlitz County, Washington. The project was completed in 2012 and currently provides a 28‑foot wide crossing of Clark Creek.
SERVICE: Foundation Engineering provided geotechnical engineering services including geotechnical exploration, laboratory testing, geotechnical analysis and design, preparation of recommendations for design and construction of the arch culvert supported on spread footings, and wing walls supporting slopes at the inlet and outlet.
Geotechnical exploration included 2 exploration borings and mapping of rock outcrops adjacent to the proposed culvert. Geotechnical analysis included calculation of bearing resistance for spread footings on weak rock and earth pressure for the culvert and wing walls. Project challenges included estimating rock elevation for footing depths with limited rock exposures and subsurface information.
Foundation Engineering also provided construction phase services to verify the foundation conditions and provide adjustments to the footing depth if needed to accommodate the sloping rock surface.