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

Weather Consideraticns I'he on-site soils and common borrow contain a sufficient percentage of fines Isilt and fine organics) to bc highly moisture sensitive. When the moistum content of these soils is more than a fcw percent above the optimum moisWre content, these soils become unstable, operation of equipment on [hese soils will br difficult and will generate mud due to severe rutting and pumping, and it will be difficult or impossihle :o mcet the required compaction critena. Additionally, disturbance of near surface soils should be expzcted any time of the year where the native soils are exposed at thc ground surface, especially if ear.hwork is completed during periods of wet weadur. The wet wcather season generally begins in Octr.oer and continues through btay in the Puget Sound regian; however, periods of wet weather may occur during an} I' month of the ycar. It will be preferable [o schedule site preparation and earth�ao�k ac[ivitics during periods af dry weather whcn the soils �vill (1) be less susceptible io disturbance, (?)providc bettcr support for construction equipment, and (3) more likelv to meet the required compaction criteria. The optinmm carthwork period for these typP� of soils is typically June through September. If «ei weather caRhwork is unavoidable, as we understand for this project, we recommend that: � • Structural fill placed dunng the wet season or during periods of wet �ccather consist of gra��l borrow with Icss than � percent fines(material passing Uic U.S. No. 20U Sicve). � • The geotextile separator and overlying structural till should be placed as soon as possible after � subgrade is achieved to prevent soRening of the sub�,rade amas and to pro��de support for �� equipment. ' • The ground surface in and around the work area should he sloped so that surface wat:� directed ,way from the work area. The ground surface should be graded such that arcas of ponded water I do not develop. Mcasures should be taken by the contractar to prevent surFace ��ater from collecting in excavations and trenches. Mensures should F e implemented to mmove surface water from thc work arca. • Larth�vork activitics should nat take place during periods of hea�y precipitation. • Slopes with cxposcd soils should be covered with plastic shecting or similar mcans. • Measures should be takcn to prcvent omsite soils and s.oils to be used as till from becoming �vet or tmstable. Thcse mcasures may include the use of plastic sheeting, sumps ��ith pumps, and grading. The site soils should not be Icft un-compacted and exposed to moisture. Sealing the surticial soils b�' rolling with a smooth-drmn roller prior to periods of precipimtion will reduce the extent Ihat d soils become wet or unstable. • Construction and t�u[ traffic should bc restricted to specific areas of d�e site, preferably areas that are surfaced �vith materials not susceptible tu wet weather diswrbance. The contractor should keep eyuipment off as much af the site as possible and restrict access to as small of areas as possiblc. • Construction activities should be scheduled so that the length uf time that soils are left exposed to moisture is reduced to the e�tent practical. Temporary Slopes �Ve recommend temporary slopes constructed in fill placed to raise site grades and the native urganic silt soils be inclined no steeper than 1'/•_H:1 V, Flatter slopes may be necessary if seepage is present on the face of the cut slopcs or if localized slouch;ng occurs. In addition, vibrations from construction equipment can cause sloughing of temporary slopes and thus slopes may have to be flattened if soughing is observed. For temporary slopes at Qie site, we recommend that: � Filc No.N987-004-OU P45C 9 �iEOENGINEEPS� OctnGcr 1/,?006