909 51ST PL SW Geotech Report 2022-10-25

Geotechncial Engineering Evaluation Garcia Property Additions Everett, Washington NGA Project No. 1040218 June 22, 2018 Page 11 Fill Placement: Following subgrade preparation, placement of structural fill may proceed. All filling should be accomplished in uniform lifts up to eight inches thick. Each lift should be spread evenly and be thoroughly compacted prior to placement of subsequent lifts. All structural fill underlying building areas and pavement subgrade should be compacted to a minimum of 95 percent of its maximum dry density. Maximum dry density, in this report, refers to that density as determined by the ASTM D-1557 Compaction Test procedure. The moisture content of the soils to be compacted should be within about two percent of optimum so that a readily compactable condition exists. It may be necessary to over -excavate and remove wet soils in cases where drying to a compactable condition is not feasible. All compaction should be accomplished by equipment of a type and size sufficient to attain the desired degree of compaction. Slab -on -Grade Slabs -on -grade should be supported on subgrade soils prepared as described in the Site Preparation and Grading subsection of this report. We recommend that all floor slabs be underlain by at least six inches of free -draining gravel with less than three percent by weight of the material passing Sieve #200 for use as a capillary break. We recommend that the capillary break be hydraulically connected to the footing drain system to allow free drainage from under the slab. A suitable vapor barrier, such as heavy plastic sheeting (6-mil minimum), should be placed over the capillary break material. An additional 2-inch-thick moist sand layer may be used to cover the vapor barrier. This sand layer is optional, and is intended to be used to protect the vapor barrier membrane and to aid in curing the concrete. Pavements Pavement subgrade preparation and structural filling where required, should be completed as recommended in the Site Preparation and Grading and Structural Fill subsections of this report. The pavement subgrade should be proof -rolled with a heavy, rubber -tired piece of equipment, to identify soft or yielding areas that require repair. The pavement section should be underlain by a minimum of six inches of clean granular pit run or crushed rock. We should be retained to observe the proof -rolling and recommend subgrade repairs prior to placement of the asphalt or hard surfaces. Site Drainage Surface Drainage: Stormwater handling plans were not developed at the time this report was prepared. We should be retained to evaluate drainage plans. If possible, final site grades should allow for drainage away from the top of the slopes and away from the planned residence. We suggest that the finished ground be sloped at a minimum gradient of three percent for a distance of at least 10 feet away from the building and top of the slopes. All runoff generated on this site, including roof downspouts, yard and footing drains, and hard surfaces, should be collected and routed into a permanent discharge system at the bottom of the slope or to the street. Under no circumstances should water be allowed to flow uncontrolled over the slopes. NELSON GEOTECHNICAL ASSOCIATES, INC.