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

of hydros[atic pressurc behind the walls, as discussed beiow. Should any wall be tbunded in the ;oils located bzlow existing site grades, wc recommend that �vc be consulted to pro��ide dcsien recomerendations for lateral carth pressures. Positive drainage should be provided behind any permanent com�entional cast-in-placc subsurface ��alls by ptacing a rninimum 2-foot widc zone of bRavel backtill ibr walis immcdiately adjacent to the walls. Gravel backfill E'or walls should conform to Section 9-03.12(2) of the 2006 WSDOT Standard Specifications. The gravcl backtill for walls zone should extend from the base of the ��al� to within 1 foot of the finished eround surface behind the wall. The top I-foot of fill should consist of relativcly impermeable soil to prevent infiltration of surface walr.r into tne wall drainage zone. Wecp holes at about 8-foot centers at the base of the wall should be installed to drain �vatcr irom c.eterior walls. Altematively, a perforated drainpipe m�y he emi�edded at the basc of the �vall in the eravel backfill for walls to remove water[hat collects in this zone. PAVEMENT SUBGRADE PREPARATION Ncw pav�ment sections must be installcd ovcr a dcnsc and unyiclding subgradc Structural lill placed to estaUlish subgrude elevation in pavement areas should be compacted to at least 90 percent, exccpt the upper 24 inches of thc subgrade, which should be compacted to a minimum of)5 percent of its maximum dry density, as dctermincd using test method ASTM D 1»7. Prior to the placement of Uase course materials, the exposed subbRad� should bc proof rolled. Proof rolling should be accomplished with a , loadcd dump truck, large sclf-propclled vibrating roller, or equivalent piece of equipmcnt. The purpose of diis effort is to identily possible loose or sott soil and recompact disturbed areas of subgraJe. Proof rolling should be carefully observed Uy qualified gcotechnical pers�nnel. .4reas exhibiting significant detlection, pumping, or saturated soils that cannot be readily compac��.d should be overexcavated to firni soil. Overexcavat�d areas should be backfilled with compacted b�ranular fill. During periods of wet weather, proof rolling could damage die exposed subgrade. Under thesc conditions, yualiticd �;colechnical personncl should obscn�e subgrade cunditions to determine if proof rolling is leasible. DRAINAGE CONSIDERi�TION� We tecommend that all surlaces be sloped tu drain a��ay IFom the proposed structcrcs. Pacement surfaces and op�n sp:uc areas slwu�d bc slopcd such that tiu surface �catcr is collectcd and routed tu suitable discharge points. Based on the soil condition� ub;cr��d in thc explorutions, ��e anticip:�te th:�t uround��ater in tomporar}� shalloa• cxcavations can Uc controllcd by pumping thc �vatcr from ihallo�v sumps. 7�he cuntractor �huuld have the responsibility to detennine�vhat dewatenng measures are necdcd. EARTHQUAKE ENGINEERiNG Liquefaction and Laferal Spreading Potential Liquefaction refers to the condition where vibration or shaking of the eround, usually t�om eaRhquake forces, results in the development of excess pore pressures in saturated soils with subsequent ;oss of strength in thc deposit of soil so�ffected. In generai, soils that are susceptible to liquefaction include very loose to medium dense, cican to silty sands that are below the water table. Filc Nu.d987-00�-IlU Pn(�C I7 �iEOENGIMEER� OcmGc� 11.?00G