9909 2ND AVE W 2018-08-01 - Laserfiche WebLink

December 1'3,2006 Project No. T-G001 4.3 Seismic Review of City of Everett Ordinance No. 2909-06, Section 8, as well as City of Everett Liquefaction (Seismic) Hazard— Critical Areas Map 4 and Liquefaction Susceptibility Map of Snohomish County, Washington (Stephen P. Palmer et al, September 2004) indicate the site does not lie within a mapped seismic/liquefaction hazard area. Liquefaction is a phenomenon where there is a reduction or complete loss of soil strength due to an increase in water pressure induced by vibrations. Liquefaction main:y affects geologicallly recent deposits of loose, fine- grained sands that are below the groundwater table. Due to the relatively high shear strength exhibited by the till- like soils, the risk of soil liquefaction, soil failure, or settlements occurring at the site as a result of ground shaking during an earthquake is negligible. 2003 IBC Seismic Soil Site Class Based on the results of our investigation and the local geology, the 2003 International Building Code (IBC) indicates that Soil Site Class"C"should be used in structural design. 5.0 DISCUSSION AND PRELIMINARY RECOM 4'IENDATIONS 5.1 General Based on our study, in our opinion, there are no geotechnical constraints that would preclude development, as planned. The structures can be supported on conventional spread footings bearing on competent native soils or on structural fill placed above these native soils. Floor slabs and pavements can be similarly supported. Organic soils were found to depths ranging from six inches to three feet (Test Pit ). Due to the loose, organic nature of these soils, they will be unsuitable for support of structures and pavements. In building and paved areas, the organic soils will need to be removed to expose native bearing soil subgrades and replaced with compacted structural fill. Some of the near-surface silty sands and silts at the site contain a sufficient amount of fines (silt-and clay-sized particles) that will make them difficult to compact as structural fill when too wet. Accordingly, the ability to use the soils from site excavations as structural fill will depend on their moisture content and the prevailing weather conditions at the time of construction. If grading activities will take place during the winter season, the owner si ouid be prepared to import free-draining granular material for use as structural 511 and backfill. Detailed recommendations regarding these issues and other geotechnical design considerations are provided in the following sections of this report. These recommendations should be incorporated into the final design drawings and construction specifications. Page No. 4