3620 36TH PL NE 2018-01-02 MF Import

liquefaction induced settlement. Because of the random nature of liquefaction, differential settlements m, y be on the same order as the total settlements. In addition to settlements, there is the possibility that lateral spreading of the soils could occur as a result of liquefaction. Lateral spreading involves lateral displacement of large, surficial blocks of non - liquefied soil, as well as the liquefied soil, as the underlying soil layer liquefies. Lateral spreading generally develops in areas where sloping ground is present or near a free face, such as a river or slough. If liquefaction were to occur within the sands at the site, we anticipate that there would be a moderate to high potential for lateral spreading to occur, characterized by movement of the soils towards the Snohomish River or Steamboat Slough. In general, the magnitude of lateral spread will decrease with increasing distance between the p int of interest and the Snohomish River or Steamboat Slough. During a design earthquake, lateral spread displacements along the existing north levee are estimated to be on the order of 5 feet. Similarly, during a design earthquake, lateral spread displacements near the compost system pads are estimated to be on the order of I foot. ' The design recommendations for the structural foundations presented above do not take into the account the effects of liquefaction and lateral spreading. Measures to mitigate the effects of lateral spreading include constructing a foundation system that will effective;y limit lateral spreading, or densifying/reinforcing the liquefiable soils. Remediation would most likely consist of densifying the sand deposits with methods such vibrocompaction or installing stone columns. These mitigation measures are typically very costly and not commonly accomplished for project , of this type. We recommend that Cedar Grove Composting be made aware of the risks associated with liquefaction and lateral spreading at this site. We can provide recommendations for mitigating the seismic hazard at the site upon request. 4.7.2 2000 IBC Seismic Design Information We reconanend the 2000 International Building code (IBC) parameters for Average Field Standard Penetration Resistance, Soil Profile Type, short period spectral response acceleration (Ss), I -second period spectral response acceleration (Sl), and Seismic Coefficients FAand Fv presented in Table 2. Table 2. Seismic Parameters 2000IBC Para mt.ter Soil Profile Type Ij- Recommended'Value', I E Short Period Spectral Response Acceleration, Ss (percent g) 124 1-Second Period Spectral Response Acceleration, SI (percent g) 10 Seismic Coefficient, F,j 0.9 Seismic Coefficient, F, 2.4 2 S) G e o lin g i jeers 20 File No. 10625-001-02/123003