9205 4TH AVE W 2025-12-03 - Laserfiche WebLink

July 2, 2008 Duplex Buildings L&A Job No. 8A067 Page 7 Erosion Hazard The fill, topsoil and weathered soils mantling site are of low to moderate resistance against erosion, while the underlying fresh till and advance outwash soils are of moderately high resistance against erosion. The weaker surficial soils, if mantling steep slopes or cuts devoid of vegetation, can be eroded easily. The site, however, is very gently sloped, which would make the potential for erosion hazard of the site minimal. To further mitigate the erosion hazard, the exposed unpaved ground of the site resulted from construction activities should be re -vegetated and landscaped as soon as possible. The re -vegetated areas should be covered with clear plastic sheets, as required, to protect them against erosion by storm runoff until the vegetation is fully established. Concentrated stormwater should not be discharged uncontrolled onto the ground within the site. Storm runoff over impervious surfaces, such as roofs or paved driveway, should be captured with underground drain line systems tied to roof downspouts and by catch basins installed in paved driveway. Water collected in these underground drain line systems should be tightlined to discharge into a nearby storm inlet or into suitable onsite stormwater disposal facilities, such as rain gardens or distribution trenches with vegetated flowpaths. Seismic Hazard The Puget Sound region is in an active seismic zone. The site is underlain at shallow depth by very -dense fresh till and/or dense advance outwash soils of very -high to high shear strength. Also, the site is very gently sloped and there is a lack of presence of a continuous, extensive, static groundwater table at shallow depth under the site. Therefore, the potential for seismic hazards, such as landslides, liquefaction, lateral soil spreading, to occur on the site should be minimal. The proposed duplex buildings should, however, be designed for seismic forces induced by strong earthquakes. Based on the soil conditions encountered by the test pits, it is our opinion that Seismic Use Group I and Site Class D should be used in the seismic design of the triplex building in accordance with the 2003 International Building Code (IBC). LIU & ASSOCIATES, INC.