3313 OAKES AVE 2020-07-14 - Laserfiche WebLink

GeoTest Services,Inc. December 9,2016 3313 Oakes Avenue,Everett,WA Job No.16-0659 Groundwater For the purposes of this report, observed groundwater seepage represents either the existing surface of a groundwater table or the surface of perched seepage. The groundwater table is referred to as the atmospheric pressure surface that coincides with the top of the zone of saturation and is the surface that dictates the development design recommendations in this report. Perched seepage is referred to as a saturated zone that develops where a restrictive surface (i.e. dense, fine grained soils) limits the vertical, downward migration of near-surface water. This surface should be considered when determining methods of earthwork construction but is not used to dictate development design. However, if perched seepage at the subject property is ponded above a restrictive surface and no groundwater table exists, then the perched seepage dictates development design recommendations herein. No groundwater seepage was encountered in the test pit explorations. We expect that groundwater representative of infiltrated water slowed by low permeability, dense to very dense soil could be found perched atop the impervious till soils encountered approximately 1 to 6 feet BGS during the wetter winter months, and potentially in pockets within the till soils. Thus, proper drainage measures should be incorporated into the development plan,which are elaborated in a subsequent section of this report. CONCLUSIONS AND RECOMMENDATIONS Based upon an evaluation of the data collected during this investigation, it is our opinion that subsurface conditions at the site are suitable for the proposed development, provided the recommendations contained herein are incorporated into the project design. The test pits excavated for this project encountered native, loose to medium-dense, weathered till soils within 3 feet of existing grade, which then became unweathered and dense to very dense with depth. It is our opinion that the proposed buildings can be supported on conventional foundations bearing on these competent native soils, or on compacted structural fill placed atop these soils. Dense, unweathered till encountered at depth is unlikely to require much preparation. However, if foundations will be supported on the near-surface weathered till, the surface should be compacted to a firm and unyielding condition. Further recommendations regarding the placement and compaction of structural fill can be found in a subsequent section of this report. Remnants of the old house foundation were encountered in TP-3 (northeast portion of the proposed western building). Based on the proposed final grades for the new building, it will be necessary to remove all old foundation elements and loose fill or deleterious material from the proposed building footprint. The depth of fill tends to increase to the east towards the eastern property line. Cuts of up to 7 feet are expected to reach the planned excavation bottom for the proposed western building. Along the southern property line is a short retaining wall that runs the entire length of the property. Adjacent to the proposed western building, it appears that the footing of the retaining wall is within 1 foot of existing grade. The proposed building will be set back approximately 5 feet from the southern property line at its closest point. Assuming a 1H: 1V temporary cut slope, there does not appear to be adequate space for an adequate cut slope for the excavation without the use of Page 4 of 17