3210 36TH PL NE 2018-01-02 MF Import

The results of our analyses indicate that several zones in ihe loose to medium dense sandy soils encountered in the explorations below th� organic silt have a moderate potential for liqucfaction during a design carthquake event, and a low to moderate potential during an event with a lower level of ground shaking. The organic silt and silt deposits located above the sand have a low potential for liquefaction � during a design eaRhquake(a magnitude G.5 earthquake with a PGA of 0.27g). I Our analyses indicate that settlements caused by liquefaction of the saturated loose to medium dense sand � layers at this site during a design carthyuake could be on the order of 1 to 3 inches. Foundations for the I planned structums will be cunstructed ovcr tl�e liquefiable suils and will therefore be prone to liqueiaction induced settlement. Because of thc random nature of liquefaction, differential settlements may be on thc same order as the total setdements. However, surface expression of the differential szttlement may Uc reduced duc to the anticipated fill placement above existing site grades. In addition to setdements, there is the possibility that lateral spreading of the soils could occur as a resuk of liquclaction. I.ateral spreading involves la[eral displacemcnt of largc, surficial blocks of non-liquefied soil, as well as the liquefied soil, as the underlying soil layer liquefes. Lateral spreading generally Idevclops in areas whcre sloping ground is present or near a free face, such as a river or slough. It liquefaction were to occur within Ihe sands at the site, we anticipa[c that [here �eould be a modcratc � potential for lateral spreading to occur, characterizcd by movement of thc soils to��ards the Snohomish i Ri��er or Steamboat Slough. In general, the magnitude of latcral spmad will decrease with increasing distance behveen the point of interest and Ihe Snohomish Itiver or Steamboat Slaugh. During a design earthquake, lateral spread displaccments across the site are estimated to be on die order of 0.� to 1.5 feet. I . . , The design recommendations for the structural foundations presented abo�e do not take into the account the e[fects of liquefaction and laieral sprcading. Measures to mitigate the eCfects of' lateral spreading includc constructing a foundation systcm that will effectively limit lateral spreading, or densifying/minforcing the Gquefiable soils. Remediation would most likely consist of densifying the sand deposits with methods such vibrocompaction or installing stone c�lumns. These mitigation measures are typic.Ily very cosdy and not common;y accomplished for projccts of this rype. We recommend that Concrete Nor'nest be made aware of d�c risks associated with liquefaction and I lateral spreading a[ this site. We can provic(c recommendations for mitigating the seismic harard at die � site upon reyuest. 2003 IBC Seismic Design Information We rccommend the 2003 Intemational Building code (IBC) parameters be used for project d�sign. Based on our interpretation oi the conditions encounrered during our field subsurface borings, test pits, and C['T explorations, we conclude the project si.e is classified as Site Class �, as defined in the 2003 [BC. The design parameters for the 2003 IBC are summarized in Table 3. The Site Class, short penod spectral response accelrration (SS), I-second period spectral response acceleration (SI), and Seismic Coefficients F,� and r�prescnted in Tablc 3. Fi(c No.8937-001-00 Page 18 �iEOENGINEEfl� Oc�oGcr!/,?006