Thomco Construction Inc. 6/14/2021

1 ' KRAZAN&ASSOCIATES,INC. KA Project No. 092-20006 DRAFT Geotechnical Engineering Investigation ' Everett Water Main"V" May 7,2020 Page No. 13 I CONCLUSIONS AND RECOMMENDATIONS General ' It is our opinion from a geotechnical standpoint, based on our subsurface investigation, that the project areas should be suitable for the proposed water main installation using conventional open trench and shoring methods. Existing Pavement: The pavement encountered throughout most of the project areas consisted of approximately 3 to 6 inches of asphalt. One of the soil boring locations, near the intersection of Olympic Boulevard and Seahurst Avenue, encountered 10 inches of Portland cement concrete underlying the asphalt pavement. It may be prudent to further explore the pavement section in the alignment of the planned water main replacement prior to the beginning of excavation for the project. Summary of Subsurface Conditions: The soils that underlie most of the project areas are interpreted to be native glacial soils, which typically have good strength with respect to soil bearing and overall stability and should provide suitable support for the planned water main. However, very loose to ' medium dense undocumented fill and stiff to hard clay and silt were encountered in some of our soil borings. For areas where the proposed new water main will traverse loose fill soils, it might be prudent to compact the bottom of the utility trench with appropriate equipment, such as a hoepack, prior to water pipe installation. Compaction of loose trench bottom soils should reduce the potential for future utility pipe subsidence. The clay and silt soils are interpreted to be ancient lacustrine (lake) deposits. The clay and silt soils ' should have moderate strength with respect to soil bearing and should provide adequate support for the planned water main. However,the clayey and silty soils are considered to be highly moisture sensitive and are not considered to be suitable for trench backfill. Imported granular materials should be considered for trench backfill for portions of this project where fine-grained soils are exposed. The silty sand with gravel soils may be suitable for use as trench backfill,but will depend on the moisture content of the soils at the time of utility construction. It is possible that layers of undocumented fill could be encountered overlying the native soils in some portions of the project areas. Caving of the excavation walls in the clayey and silty soils, as well as any loose to medium dense granular soil or fill, should be anticipated. The contractor should be prepared to shore the excavation walls or bench the excavation to a stable configuration. Groundwater: We observed groundwater seepage in soil boring B-4 at a depth of approximately 5.0 feet, and in soil boring B-7 at a depth of about 5.0 feet. Moist to wet conditions were encountered in Krazan&Associates,Inc. Offices Serving The Western United States 1