1205 50TH ST SW 2020-07-02 - Laserfiche WebLink

Geotechnical Engineering Evaluation NGA File No. 1033518 Larsen Property Garage May 8,2018 Everett,Washington Page 6 Our explorations indicated that the site was underlain by medium=dense to dense glacialtill soils at depth. These competent glacial soils should provide adequate,support for foundation,slab, and pavement loads. We,recommend that the structures,.within the site be designed utilizing shallow foundations. Footings should extend through any loosesurficial soil.and be keyed into the underlying competent native soils. These soils should be encountered roughly three to,four feet,below the existing ground surface withinthe proposed garage area with some potential localized areas of deeper loose soils in unexplored areas of,the site.. All grading operations and drainage improvements planned as part of this development should be planned and completed in a matter that enhances the stability site slopes and neighboring structures,not reduces it. Excavation spoils associated with the building excavations should not be stockpiled near the slope or be allowed to encroach on the.slope. Also,runoff generated within the site should be collected and routed into a permanent discharge system. Future vegetation management should be the subject of a specific evaluation and a.plan approved by the City of Everett. The slope_and neighboring retaining walls should be monitored on an ongoing basis, especially during the wet season, for any signs of instability, and corrective actions promptly taken should any signs of instability be observed. Lawn clipping and.any other household trash or debris should never be allowed to reach the slope. The soils encountered on this site are considered moisture-sensitive and will disturb easily when wet. To lessen the potential impacts of construction and to reduce cost overruns and delays, we recommend that construction take place during the drier summer months. If construction takes place during the rainy months, additional expenses and delays should be expected. Additional expenses could include the need for placing erosion control and temporary drainage measures to protect the slopes, the need for placing a blanket of rock spalls onexposed subgrades and construction traffic areas prior to placing structural fill, and the need for importing all-weather material for structural fill. Under no circumstances should water be allowed to flow over or concentrate on the site slopes, both during construction, and after construction has been completed. We recommend that stormwater runoff from the new roof and yard drains be collected and :tightiined to a suitable discharge point. We recommend that the stomiwater runoff from the existing residence be.investigated and tightlined to flow into an approved.system. The slopes should be protected from erosion. We recommend that all disturbed areas be. replanted with vegetation to re-establish vegetation cover as soon as possible. . Specific recommendations for erosion control are presented in the.. Erosion Control and Slope Protection Measures subsection of this report. NELSON GEOTECHNICAL ASSOCIATES,INC.