222 W CASINO RD Geotech Report 2022-10-25

GeoTest Services, Inc. May 3, 2019 Mukilteo School District 19-0194 OMIIINImwa Reuse of On-Site Soil Due to excessive silt contents and observed variability of the on-site soils, these soils are not recommended for use as structural fill due to the difficulties associated with moisture conditioning. GTS recommends any reuse of the native or previously placed fill soils be limited to landscape and other non- structural areas. Import Structural Fill GTS recommends that imported structural fill consist of clean,well-graded sandy gravel,gravelly sand,or other approved naturally occurring granular material (pit run) or a well-graded crushed rock. We recommend structural fill for dry weather construction meet Washington State Department of Transportation (WSDOT) Standard Specification 9-03.14(2) for "Select Borrow" with the added requirement that 100 percent pass a 4-inch-square sieve.Soil containing more than about 5 percent fines (that portion passing the U.S. No. 200 sieve) cannot consistently be compacted to a dense, non-yielding condition when the water content is greater than optimum. Accordingly, GTS recommends that imported structural fill for wet weather construction meet WSDOT Standard Specification 9-03.14(1) for "Gravel Borrow" with the added requirement that no more that 5 percent pass the U.S. No. 200 sieve. Due to wet weather or wet site conditions, soil moisture contents could be high enough that it may be very difficult to compact even 'clean' imported select granular fill to a firm and unyielding condition.Soils with over-optimum moisture contents should be scarified and dried back to more suitable moisture contents during periods of dry weather or removed and replaced with fill soils at a more suitable range of moisture contents. Backfill and Compaction Structural fill should be placed in horizontal lifts. The structural fill lift must measure 8 to 10 inches in loose thickness and be thoroughly compacted. All structural fill placed under load bearing areas should be compacted to at least 95 percent of the maximum dry density, as determined using test method ASTM D1557. The top of the compacted structural fill should extend outside all foundations and other structural improvements a minimum distance equal to the thickness of the fill. We recommend that compaction be tested after placement of each lift in the fill pad. Wet Weather Earthwork Fine grained native soils are particularly susceptible to degradation during wet weather. As a result, it may be difficult to control the moisture content of site soils during the wet season. If construction takes place during wet weather, GTS recommends that structural fill consist of imported, clean, well-graded sand or sand and gravel as described above. If fill is to be placed or earthwork is to be performed in wet conditions,the contractor may reduce soil disturbance by: • Limiting the size of areas that are stripped of topsoil and left exposed • Accomplishing earthwork in small sections • Limiting construction traffic over unprotected soil • Sloping excavated surfaces to promote runoff 5