1907 W MUKILTEO BLVD 2021-11-15 - Laserfiche WebLink

' Pearson Property Slope Stabilization NGA File No 945216 1907 West Mukilteo Boulevard February 19,2016 a„,, Everett,Washington Page 4 The soils were visually classified in general accordance with the Unified Soil Classification System presented in Figure 4. The logs of our borings are attached to this report and presented as Figures 5 and 6. We present a brief summary of the subsurface conditions in the following paragraph. For a detailed description of the subsurface conditions,the boring logs should be reviewed. In Boring B-1, we encountered approximately 5.0 feet of very loose, red-brown fine to medium sand with gravel and organics that we interpreted as undocumented fill soils. Underlying the undocumented fill in Boring B-1 and the ground surface in Boring B-2, we encountered medium dense to very dense, fine to medium sand with varying amounts of silt and gravel that we interpreted to be native advance outwash deposits. Both of our borings were terminated within the native advance outwash deposits at depths of 31.5 and 25.3 feet,respectively. Hydrologic Conditions We did not encounter groundwater seepage in our explorations. However, we anticipate that a perched water condition will likely occur within the undocumented fill and silty soils encountered within our explorations. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of underlying, less permeable soils. Perched water does not represent a regional groundwater "table" within the upper soil horizons. Perched water tends to vary spatially and is dependent upon the amount of precipitation. We would expect the amount of perched water to decrease during drier times of the year and increase during wetter periods. For this site,perched water seepage was observed on the slope below the residence. Also, we expect the slope to indicate some seepage even during the dry period of the year. SENSITIVE AREA EVALUATION Seismic Hazard We reviewed the 2012 International Building Code (IBC). Since mostly medium dense or better native glacial soils are interpreted to underlie the site at depth,the site conditions best fit the IBC description for Soil Class D for native soils. Hazards associated with seismic activity include liquefaction potential and amplification of ground motion. Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit beneath the groundwater table. It is our opinion that the competent glacial deposits interpreted to underlie the site have a low potential for liquefaction or amplification of ground motion. NELSON GEOTECHNICAL ASSOCIATES,INC.