3003 W CASINO RD BLDG 40-58 Geotech Report 2022-10-25

Prior to placement of any site fill, the exposed subgrade under all areas to be occupied by the floor slab, apron, or asphalt pavement should be compacted to a firm, dense, and unyielding condition. The compacted surface should then be proof rolled with a fully-loaded dump truck, large self-propelled vibrating roller,or equivalent piece of heavy equipment to identify possible loose or soft soil deposits. Proof rolling should be carefully observed by geotechnical personnel. Areas exhibiting appreciable deflection, pumping, weaving or other indications of poor subgrade that cannot be readily compacted should be overexcavated to firm soil. Overexcavated areas should be backfilled with compacted material,in accordance with subsequent recommendations for site fill. 3.2 FILL SELECTION AND REUSE OF SITE SOIL Apart from soils generated from stripping and grubbing in current landscape areas (such as between Bldgs. 40-83 and 40-84), and which will likely be unsuitable for re-use as fill, little cutting is expected as part of grading operations. However,minor cutting may occur in the southwest corner of the site,where existing grades are near the planned earthwork subgrade, and also in the autoclave area,where a lower local subgrade elevation is planned. Soils in these areas are likely to consist of either native glacial till, or existing fill originally derived from a glacial till source,respectively. These soils exhibit a high fines content and can be problematic for reuse as fill, although with proper moisture conditioning, placement, and compaction, they can perform well as fill. Successful reuse of these soils will generally depend upon both good practices employed by the earthwork contractor and favorable weather. However, if used,these materials use should be reserved for lower portions of the fill. Within a few feet of the final subgrade, only imported structural fill should be used for backfill. Only imported structural fill should be used for backfill behind walls. Several existing berm stockpiles are currently under investigation by the design team. The contents of the berms are being evaluated for potential re-use as general fill within the 40-58 footprint. The suitability of the stockpile contents for this purpose will be reported by technical memorandum at a later date. If practical for re-use, it is expected that these material sources would constitute a small fraction of the total fill volume required for the project grading requirements. For more uniform subgrade performance in proximity to the slab subgrade elevation, we recommend that non-granular or high fines content fill material be placed only where the top of the as-compacted surface for that material will be located four or more feet below the slab subgrade elevation. Within four feet of the slab subgrade elevation, only Select Borrow or Gravel Borrow conforming to the requirements presented in Section 9-03.14 of the 2014 Washington State Department of Transportation(WSDOT) Standard Specifications for Road, Bridge, and Municipal Construction(WSDOT 2014)should be used for site filling. 5/16/14 P:\1423\002\010\FileRm\R\Draft Bldg 40-58 Report\Bldg 40-58_draft rpt.docx INTERIM D RA F T 3-2