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

qt 3.8 SPREAD FOOTINGS We expect that major load-bearing elements of the 40-58 building structure will be supported by drilled shafts, as discussed above. However, it may be possible to support some of the building columns in the southwest portion of the building footprint—where very dense glacial till is present near the ground surface—on spread footings. (The potential for shallow foundation support at this location, and bearing capacity recommendations[as appropriate], will be evaluated in the draft version of this report) Lightly loaded structures, such as retaining walls, tunnel floors and utilidor floors, and the west and east building walls could be supported by shallow foundations such as isolated or continuous spread footings. Spread footings may be proportioned for an allowable bearing capacity of 4, 000 lbs per square foot (psf). This capacity is based upon settlement considerations and the presence of existing medium dense fill or future fill at these locations. The allowable bearing capacity recommended above may be increased by one-third for transient wind or seismic loads. During excavation of lightly loaded footings, loose existing fill subgrade soil will need to be overexcavated where exposed at the footing subgrade elevation to a depth of two feet below the footing subgrade and then replaced with structural backfill. If encountered during foundation excavation,wet or organic-rich soils would need deeper overexcavation and replacement with structural backfill. Structural backfill should be placed and compacted as described in Section 3.4. Where overexcavation and replacement with structural backfill is necessary,the plan extent of the structural fill layer should extend beyond the edge-of-footing a distance equivalent to the depth of the structural fill. Alternatively, controlled density fill (CDF) or lean concrete could be used as backfill, in which case the limits of the overexcavation do not need to extend beyond the width of the footing. During foundation excavation, loose material at an otherwise suitably dense bearing soil should either be properly recompacted or removed. All soil directly below footings should be compacted to at least 95 percent of maximum dry density (ASTM D1557) prior to placement of forms, reinforcing steel, and concrete. We understand that lateral column loads along the west and east sides of Building 40-58likely be resisted by the interior floor slab and a pavement apron. For other structures,passive earth pressures that develop against the sides of foundations, in conjunction with friction developed between the base of the footings and the supporting subgrade,can be used to resist lateral loads. For design purposes,the passive resistance of well-compacted fill placed against walls or the sides of foundations may be considered equivalent to a fluid with a density of 300 lbs per cubic ft. The recommended value includes a safety factor of about 1.5 and is based on the assumption that the ground surface adjacent to the structure is level in the direction of movement for a distance equal to or greater than twice the embedment depth. The recommended value also assumes drained conditions that will prevent the buildup of hydrostatic pressure 5/16/14 P:\1423\002\010\FileRm\R\Draft Bldg 40-58 Report\Bldg 40-58_draft rpt.dacx INTERIM DRAFT 3-7