9900 19TH AVE SE Geotech Report 2018-01-02 MF Import

Geotechnical Engineering Report Home Base Warehouse - Everett July 31, 1997 NCA File No. 213497 Page 6 I unweathered till, the subgrade should be compacted to a non -yielding condition using a steel drum vibratory compactor. The subgrade should be observed for indication of disturbance of the lower soils. j If the subgrade shows signs of disturbance, we should be retained to provide recommendations for repair or potertially alternate construction techniques. Disturbance to the exposed subgrade with heavy I equipm ;ntshould be avoided. The on -site soils are moisture sensitive and will disturb easily when wet. Increased earthwork costs should be expected if the earthwork is attempted during the wet time of year. These extra costs are associated with schedule delays, importing rock spalls for roads, traffic and staging areas, and potentially removing wet soils from the site and importing clean, granular fill material. The thickness of the spalls and the actual site grading techniques should be based on soil conditions at the time that the site is developed and the performance under heavy equipment. We recommend assuming a minimum thickness of 1 foot of spalls in traffic areas for estimating wet season construction costs. Cut and Fill Slopes The construction of the detention vault located in the southwest comer of the site will require a temporary excavation up to about 30 feet deep. Unsupported temporary slopes should be sloped at an inclination no steeper than 1.5 Horizontal to 1 Vertical (1.5H:IV) for the loose to medium dense soils and 0.5H:1V for dense till. These slopes should be protected from rain by well secured plastic sheeting. If ground water or seepage is encountered, we should be retained to comment on the stability of the slopes in the excavation. The above cut slope angles should be considered preliminary in nature. The contractor is ultimately responsible for the stability of the cut slopes, as he is continuously at the site and can observe the performance on a daily basis. All state and federal standards should be followed with respect to cut slopes and workman safety. The excavation may extend off the southwest side of the site to maintain the recommended temporary slope angles. Construction easements that allow access onto adjacent property may be needed to allow the use of the temporary cut slopes. If slopes meeting these geometries cannot be constructed and ieasements cannot be obtained, temporary shoring may be necessary. Recommendations for temporary / shoring are beyond the scope of this report. If shoring is needed, we should be retained to provide our geotechnical recommendations. NELSON-COwRETTE &ASSOCIATES, INC.