2514 51ST ST SW Geotech Report 2022-10-25

June 23,2017 0-4400 Underpinning Evaluation Page 2 2514- 51'Street SW,Everett ago and the crack size has not increased. The foundation stem wall is approximately 3.8 feet in height, measured from the top of the basement concrete floor slab. The bottom of the footing is anticipated to be 4.5 feet below the top of the stem wall. The exterior ground surface at the northeast corner is approximately 1.8 feet below the top of the stem wall. SUBSURFACE CONDITIONS Geology According to the area geologic maps,the site is mapped as Advanced Outwash(Qva)deposits, described as mostly clean,gray,pebbly sand with increasing amounts of gravel higher in the section and fine grained sand and some silt common in the lower section. The advance outwash was deposited by meltwater flowing from the advancing front of the glacier during the Fraser glaciation period that ended some 12,000 years ago. Subsurface Investigation The subsurface soil conditions were investigated by hand augering a boring on the east side of the house, approximately located as illustrated on the Site Plan,Plate 2. Loose sand with silt with some gravel was encountered to a depth of about 2.5 feet where gravel refusal was encountered. The soils were probed with an extendable 1/2-inch diameter steel probing rod and dense soil was encountered at a depth of 7 feet below the ground surface(approximately 4.3 feet below the foundation footing). No groundwater was encountered. DEPTH OF UNDERPINNING PIERS Based on the soil conditions encountered in the boring, the piers should extend through the loose soils and embed into the denser soil encountered approximately 4.3 feet below the foundation footing. The pier depths may decrease up-gradient to the south and west based on the site topography. The actual depth of the piers may be more or less depending on the soil substrata encountered. 1 Minard J.P., 1982,"Distribution and Description of Geologic Units in the Mukilteo Quadrangle, Washington,"Dept.Of the Interior,U. S.Geological Survey,Map MF-1438,Scale 1:24,000. GEO Group Northwest,Inc.