DESCRIPTION: Umatilla Electrical Cooperative planned improvements at Coyote Springs Substation in Boardman, Oregon. Improvements included new and replacement transformers, pull-off structures, bus supports, and a new entrance road. A geotechnical investigation was completed for the project by another firm. That study indicated the presence of shallow bedrock. Differing site conditions were noted just prior to construction.
SERVICE: Foundation Engineering provided geotechnical exploration, laboratory testing, geotechnical analysis and design, and recommendations for design and construction of electrical structures and new mechanical buildings. Within three days, an emergency site investigation was completed to confirm a utility pole foundation condition that included shallow bedrock, which was misinterpreted by another party.
Project challenges for substation structures included long-term potential for dry fine-grained sand and silt soil settlement due to water induced soil-collapse or “hydrocompaction”. Foundation Engineering worked with the project team to develop cost-efficient substation foundation options including settlement tolerant adjustable supports that allowed for future structure re-leveling. Our local experience in the area also correctly interpreted utility pole subsurface conditions consisting of alluvial soil with boulders instead of shallow bedrock, thus eliminating potential contractor claims during construction and expensive project litigation.
Geotechnical analysis for replacement electrical structures were completed including calculation of shallow spread footing bearing capacity, estimated soil settlements, and axial and lateral capacity for augercast utility pole foundation. Recommendations for design and construction of mat foundation, spread footing and slab-on-grade were provided.