1001 N BROADWAY 2020 EVCC 2025-10-03

and to at least 95 percent of the MDD beyond 5 feet of the walls. The upper 2 feet of fill below floor slab subgrade should also be compacted to at least 95 percent of the MDD. The contractor should keep all heavy construction equipment away from the top of retaining walls a distance equal to half the height of the wall, or at least 5 feet, whichever is greater. 3. Structural fill in new pavement and hardscape areas, including utility trench backfill, should be compacted to at least 90 percent of the MDD, except that the upper 2 feet of fill below final subgrade should be compacted to at feast 95 percent of the MDD, see Figure 4, Compaction Criteria for Trench Backfill. 4. Structural fill placed as crushed rock base course below pavements should be compacted to 95 percent of the MDD. 5. Non-structural fill, such as fill placed in landscape areas,should be compacted to at least 90 percent of the MDD. 4.6.6.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 muddy and unstable, operation of equipment on these soils will be difficult and it will be difficult or impossible to meet the required compaction criteria. Additionally, disturbance of near-surface soils should be expected if earthwork is completed during periods of wet weather. 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 and (2) provide better support for construction equipment. The wet weather season in the Puget Sound region generally begins in October and continues through May; however, periods of wet weather may occur during any month of the year. The optimum earthwork period for these types of soils is typically June through September. if wet weather earthwork is unavoidable, we recommend the following: Structural fill placed during the wet season or during periods of wet weather should consist of imported gravel borrow with less than 5 percent fines (material passing the U.S. No. 200 sieve). Its The ground surface in and around the work area should be sloped so that surface water is directed away from the work area. im The ground surface should be graded such that areas of ponded water do not develop. The contractor should take measures to prevent surface water from collecting in excavations and trenches. 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 uncompacted and exposed to moisture. Sealing the surficial soils by rolling with a smooth-drum roller prior to periods of precipitation will reduce the extent to which these soils become wet or unstable. GWENGINEERS Y Jul 22,2fIi9 Pa e 13 File No.5836-011-00