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

We recommend that a representative from our firm be present during placement of the structural fill. Our representative will evaluate subgrade conditions prior to placing fill, perform in -place moisture density tests in the fill to evaluate if the work is being done in accordance with the compaction specifications, and advise on any modifications to procedure that may be appropriate for the prevailing conditions. 4.2.8 Weather Considerations The on -site soils and common borrow contain a sufficient percentage of fines (silt and clay) to be highly moisture sensitive. When the moisture content of these soils is more than a few percent above the optimum moisture content, these soils become unstable, operation of equipment on these soils will be difficult and will generate mud due to severe rutting and pumping, and it will be difficult or impossible to meet the required compaction criteria. Additionally, disturbance of near surface soils should be expected any time of the year where the native soils are near the ground surface, especially if earthwork is completed during periods of wet weather. The wet weather season generally begins in October and continues through May in the Puget Sound region; however, periods of wet weather may occur during any month of the year. It will be preferable to schedule site preparation and earthwork activities during periods of dry weather when the soils will (1) be less susceptible to disturbance, (2) provide better support for construction equipment, and (3) more likely to meet the required compaction criteria. We understand that earthwork for this project may commence in the wet months from February through May. The optimum earthwork period for these types of soils is typically June through September. If wet weather earthwork is unavoidable, as we understand for this project, we recommend that: • Structural fill placed during the wet season or during periods of wet weather consist of gravel borrow with less than 5 percent fines (material passing the U.S. No. 200 Sieve). • The geotextile separator and overlying structural fill should be placed as soon as possible after subgrade is achieved to prevent softening of the subgrade areas and to provide support for equipment. • The ground surface in and around the work area should be sloped so that surface water is directed away from the work area. The ground surface should be graded such that areas of ponded water do not develop. Measures should be taken by the contractor to prevent surface water iFom collecting in excavations and trenches. Measures should be implemented to remove surface water from the work area. • Earthwork activities should not take place during periods of heavy precipitation. • Slopes with exposed soils should be covered with plastic sheeting or similar means. • Measures should be taken to prevent on -site soils and soils to be used as fill from becoming wet or unstable. These measures may include the use of plastic sheeting, sumps with pumps, and grading. The site soils should not be left un-compacted and exposed to moisture. Sealing the surfrcial soils by rolling with a smooth -drum roller prior to periods of precipitation will reduce the extent that these soils become wet or unstable. • Construction and foot traffic should be restricted to specific areas of the site, preferably areas that are surfaced with materials not susceptible to wet weather disturbance. The contractor should keep equipment off as much of the site as possible and restrict access to as small of areas as possible. G e o En g i nc a rs 13 File No. 10625-001-02/123003