2416 61ST ST SE 2022-03-04 - Laserfiche WebLink

i 2416 61$t Street SE Limited Subsurface Exploration and Geotechnical Everett, Washington Assessment for Slab and Foundation Repair Vashon Advance Outwash Directly below the fill, all explorations encountered native soils consisting of loose to medium dense, moist, reddish brown to brown, sand and silty sand with trace to some gravel. We interpret these soils as Vashon advance outwash, where the lower-density soils encountered near the contact with the overlying fill represent a weathered horizon. Vashon advance outwash sediments were deposited by meltwater streams flowing from the base of the southward advancing glacial front during the Vashon Stade of the Fraser Glaciation. The advance outwash sediments extended beyond the maximum depth of our explorations (about 5 feet). GROUNDWATER CONDITIONS No groundwater seepage was encountered within the boreholes at the time of excavation. The fill soils below the kitchen floor slab appeared to be very moist to wet, likely due to water leakage from the cracked drain pipe located below the slab. It should be noted that the depth of occurrence of groundwater seepage may vary in response to changes in season, amount of precipitation,topography, and on-and off-site land use. GEOTECHNICAL ASSESSMENT AND REPAIR RECOMMENDATIONS The results of our shallow hand-auger borings indicate that the building is supported on existing fill soils underlain by advance outwash with a relatively thin weathered horizon near the contact with overlying fill. The loose state of the existing fill soils indicates that the material was not suitably compacted when initially placed. We assess that the cracks observed within the interior slabs and exterior footings could be due to long-term settlement of the existing fill soils and possibly the loose weathered horizon of the advance outwash soils. Roof runoff that is discharged from the downspouts onto the exterior grade adjacent to the building foundations may also be contributing to the observed distresses at the building exterior. Our recommendations for repair of the interior floor slabs and settlement mitigation of exterior footings are provided below. Kitchen Floor Slab Repair Since the floor slab within the kitchen is planned to be removed for plumbing repairs, we recommend that the existing fill soils below the slab also be removed to expose native advance outwash soils (about 2 to 3 feet below the slab) and replaced with crushed rock aggregate (5/8-inch minus crushed rock or equivalent). The exposed native soils should be recompacted with mechanical equipment, such as a vibratory plate compactor or jumping jack, to a firm and unyielding condition before placing the crushed rock. We recommend placing the crushed rock in thin lifts of approximately 6 inches, with each lift compacted to a firm and unyielding condition. We also recommend the floor slab be protected from dampness by an impervious moisture barrier at least 10 mils thick. The moisture barrier should be placed between the crushed rock material and the new concrete slab. October 26,2021 ASSOCIATED EARTH SCIENCES,INC. BD/Id-20210370E001-002 ge 5 /v/