Thomco Construction Inc. 6/14/2021

I KRAZAN&ASSOCIATES,INC. KA Project No. 092-20006 DRAFT Geotechnical Engineering Investigation ' Everett Water Main"V" May 7,2020 Page No. 15 Pipe Support and Trench Backfill The Washington State Department of Transportation Standard Specifications for Road, Bridge, and Municipal Construction includes specifications for aggregates to be used for water mains in roadways. The foundation material specifications are found in 9-03.17. Specifications for gravel backfill for pipe zone bedding are found in 9-03.12(3). The pipe zone backfill and trench backfill material specifications are found in 9-03.19. Pipe support is available within the medium dense/stiff or firmer native soil on typical granular bedding (e.g., at least 6 inches below the bottom of the bells, couplings or joints of pipe). Local areas of deeper loose fill in the trench alignment may require the removal of soft/loose, unsuitable material and replacement with granular material (e.g., 3/4 inch crushed rock) to achieve a stable and nonyielding subgrade. Materials generated from the trench excavation will likely include soil containing greater than 5% passing a #200 sieve. These materials do not meet typical trench backfill specifications. Import material will likely be necessary for trench backfill within the road. Large cobbles and boulders may also be generated during excavation,and will need to be disposed of at appropriate locations. During wet weather conditions, subgrade stability problems and fill compaction difficulties may develop due to excess moisture, disturbance of sensitive soils and/or the presence of perched groundwater. Construction during the extended periods of wet weather could result in the need to remove wet disturbed soils if they cannot be suitably compacted due to elevated moisture contents. The on-site soils have significant silt content and are considered to be moisture sensitive, and can be easily disturbed when wet. If over-excavation is necessary, it should be confirmed through continuous monitoring and testing by a qualified geotechnical engineer or geologist. Soils that have become unstable may require drying to near their optimal moisture content before compaction is feasible. Selective drying may be accomplished by scarifying or windrowing surficial material during extended periods of dry, warm weather(typically during the summer months). If the soils cannot be dried back to a workable moisture condition,remedial measures may be required. General project site winterization should consist of the placement of aggregate base and the protection of exposed soils during construction. It should be understood that even if Best Management Practices (BMP's) for wintertime soil protection are implemented and followed there is a significant chance that moisture disturbed soil mitigation work will still be required. Any buried structures encountered during construction should be properly removed and backfilled. The resulting excavations should be backfilled with structural fill. Krazan&Associates,Inc. Offices Serving The Western United States