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

Thc cvaluation of liyucfac[ion potential is a complex procedure and is dependent on numerous sit� parametcrs, including soil grain size, soil density, site geometry, static stresses, and the design ground accelcration. "fypically, the liqucfaction potential of a site is evaluated by comparing the cyclic shcar stress ratio (the ratio of the cyclic shear stress to the initial effective overburden stress) induced by an earthquake to the cyclic shear stress ratio required to cause liquefaction. lVe evaluated the earthquakc induced cyclic shear stress ratio at this site using an empirical relationship developed by researchers for this purpose. A design earthquake with a magnitude of G.5 and a peak horizontal acceleratian of 017e (27 percent of the acceleration due to graviry) was used for our analysis. "1'his analysis also assumes ; level ground surface. The cyclic shear stress ratio rcquired to cause liquefac[ion was estimated using an empirical procedure haszd on correlations from the cone penetration tests. This method re!ates the cyclic shear sVess ratio requir.d ro cause liquefaction to the cone tip and slecve resistance valucs. Estima[ed g�oun� settlement resulting from earthquake-induced liquefaction was analyzed using an empirical proccdi�re that relates setdement ro average SPT N-values, which we correlatcd fiom the CPT tip values. Tl�e results of our liquefaction analyses are discussed in the Garthquake Engineering section of this report CONCLUSIONS AND RECOMMENDATIONS GENERAL Based on dic results of ou; subsurface esploration program, it is our opinion that the proposed Concrete Nor'west Smith Island Batch Plant may be cunstructed satisfactorily as planned with respect to geotechnicalissues. Key geotechnicalissues forthe projectinclude: • The near-surface, native, on-site soils contain a high pereentage of fincs and are highly sensitivc to small changes in mo�sture content. Thesc soils are susceptible to disturbance from construction traffic. The native soils are wet and will be difticult, if not impossible, to compact tu thc recommcndcd compaction criteria. The r.ative soils should not be considered for reuse as structural �iil. • In the arcas oi the site where gre�ter than two feet of structural fill will be placed above existing site 6�ades, the existing topsoil may be left in place afrer mowing and removing surface grasses � and shrubs. We recommend placement of a geotextile FaUric over the subgrade prior to placement and compaction of imported s[ructural fill. • Imported fll consisting of common boaow will be suitable during periods of dry �veathec If cor.struction is performed during �vet weather, gravel borrow with Iess than 5 percent fines sho.ild bc uscd. • Scttlement will msult Irom the placement of fill and the loads associated with aggregate , stockpiles and proposed structures. We recommcnd that areas where non-pile suppoRed structures will Ue supportcd at grade be preluaded to pre-induce the majority of the an[icipated sctdcment. • l'he batch plant, concrete aggrega[c bins and other heavily loaded and/or settlement-sensitive structures should be supported on pilc founda[ions. Ne recommend 18-inch augercast piles extending a minimum of 40 feet belo�v final site grades. • Miscellaneous light'v ��adrd structures/equipment can Ue supported on shallow foundations provided the areas are preloaded. We recommcnd an allowable, soil bearing pressure of 2,500 pounds per squarc foot (ps� for founda[ions b�aring on a minimum 2-foot thiclmess of adcquately compacted structural till overlying a geotextile separa[or. I Fi(ei1'o.R9R7-OOJ-0O Paf�l'S GEOENGINEEN� I Ocmbcr I l, _'q�lb , :' _ ��Sy .`` �,I t, 1 _ , � ��\ �� , -- .. ._ '.1�r 1(� V� '�a�� ; " x� . � �� `- �� .}.��ti � � i� �F ''� � �A:,a. �1;';� __—_ -— `.�r�