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

p inches of compacted CSBC. For factory roads, the asphalt pavement thickness may be reduced to 3 inches. All pavement section subgrade soils should be stripped, compacted, and proof-rolled as described in Section 3.1. 3.11 BELOW-GRADE RETAINING WALLS The magnitude of lateral earth pressures that develop against below-grade walls will depend upon the inclination of any adjacent slopes, type of backfill, degree of wall restraint, method of backfill placement, degree of backfill compaction, drainage provisions, magnitude and location of any adjacent surcharge loads,and the degree to which the wall can yield laterally during or after placement of backfill. When a wall is restrained against lateral movement or tilting, the soil pressure exerted is the at-rest soil pressure. Such wall restraint may develop if a rigid structural network is constructed prior to backfilling or if the wall is inherently stiff or is otherwise restrained from rotation. We expect this to be the case for the north building wall,which will consist of an integral foundation wall and retaining supporting up to 9 ft of soil within the building footprint, and around the perimeter of the autoclave area. A rigid wall condition can be expected along the wall of the proposed pedestrian tunnel and the utilidor,where either a top strut is present or a moment is carried from the wall into the floor slab. This may also be the case for some or all of the walls of the tunnel entrance stairwells. In contrast, active soil pressure will be exerted on a subsurface structure or wall if its top is allowed to rotate or yield a distance of approximately 0.002 times its height or greater. The structural designer may evaluate whether this amount of deflection is permissible and likely; otherwise,the walls should be designed for at-rest pressures. Along the west and east sides of the fill pads, we expect that these minor rotations would be acceptable; at these locations, a mechanically stabilized earth wall may be a cost-effective retaining wall option. If this option is pursued, we recommend that one of the pre-approved wall designs contained in WSDOT's Geotechnical Design Manual(WSDOT 2012)be selected for site-specific design and construction. Nonyielding (restrained at the top) walls with level backfill under drained conditions should be designed for an equivalent fluid density of 56 pounds per cubic foot (pcf) for at-rest conditions. Non- restrained (yielding) walls with level backfill under drained conditions should be designed for an equivalent fluid density of 35 pcf for active soil conditions. These equivalent fluid densities assume well- drained wall backfill and the absence of hydrostatic pressure on the back of the wall. The above recommendations regarding active and at-rest earth pressures assume that the backfill placed against the below-grade walls will consist of properly compacted structural backfill as discussed in Section 3.2 and conforming to Gravel Backfill for Walls as specified in Sections 9-03.12(2) of the 2014 WSDOT Standard Specifications, compacted in accordance the recommendations in Section 3.4 of this report. 5/16/14 P:\1423\002\010\FileRm\R\Draft Bldg 40-58 Report\Bldg 40-58_draft rpt.docx INTERIM DRAFT 3-10