4920 24TH AVE W Geotech Report 2023-06-22

• GeoTest Services, Inc. October 8, 2021 2405 Hillside Lane, Everett,WA Project No. 21-0845 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, GeoTest 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 • Limiting the size and type of construction equipment used • Providing gravel 'working mats'over areas of prepared subgrade • Removing wet surficial soil prior to commencing fill placement each day • Sealing the exposed ground surface by rolling with a smooth drum compactor or rubber- tired roller at the end of each working day • Providing up-gradient perimeter ditches or low earthen berms and using temporary sumps to collect runoff and prevent water from ponding and damaging exposed subgrades Seismic Design Considerations The Pacific Northwest is seismically active, and the site could be subject to movement from a moderate or major earthquake. Consequently, moderate levels of seismic shaking should be accounted for during the design life of the project, and the proposed structure should be designed to resist earthquake loading using appropriate design methodology. For structures designed using the seismic design provisions of the 2018 International Building Code, the medium dense to dense Transitional Beds underlying the site is classified as Site Class D,according to ASCE 7-16.The structural engineer should select the appropriate design response spectrum based on Site Class D soil and the geographical location of the proposed construction. Foundation Support Foundation support for the proposed developments can be established via continuous or isolated spread footings founded on firm and unyielding, remedially compacted Transitional Beds, or on 11