AIA 101 Agreement 08302024 - Laserfiche WebLink

Home Browse Search

June 13, 2023 HWA project No. 2022-188-21 4A.1 Bearing Capacity for Footings The proposed structures are located in areas in which the site explorations indicate the presence of 3 feet to 10 feet of very soft to stiff, potentially compressible, organic topsoil and fine-grained alluvial soils below the existing ground surface. These fine-grained alluvial soils will not be suitable for support of the proposed structures. We therefore recommend over -excavating these soils to expose underlying medium dense to dense Coarse -grained alluvial soils. For footings founded on the coarse -grained native materials, or properly compacted structural fill placed directly on undisturbed native coarse -grained soils, we recommend using a net allowable bearing capacity of 3,000 pounds per square foot (psf). For short-term wind and seismic loading conditions, this allowable bearing pressure may be increased by 33 percent to resist increased pressures on the edge of the foundation due to over -turning moments. Strip footings should have a minimum width of 18 inches, and column footings should have a minimum width of 24 inches. Footings should bear at least 2.5 feet below finished grade to be below the anticipated frost penetration depth of 24 inches at the site. 4.4.2 Lateral Resistance Wind, earthquakes, and unbalanced earth loads will subject the foundation system to lateral forces which will be resisted by sliding (base) resistance. The frictional force between the native coarse -grained soils or structural fill and mass concrete can be estimated as 50 percent of the normal force (a frictional coefficient of 0,5). The friction coefficient is an ultimate value, and we recommend applying a factor of safety of 1,5 with its use. 4.4.3 Settlement For footings placed on structural fill placed in accordance with these recommendations provided in Section 4.12,2, and having subgrades prepared as recommended in Section 4.12.1, the foundations would experience up to about'/z inch of differential settlement over 40 feet where structural fill depths below the footings are approximately equal. Where the thickness of structural fill below the footings varies, the differential settlement may be greater. For a difference of about 10 feet in fill depth, differential settlement should be taken as an additional '/z-inch and for a difference of about 20 feet of fill height, an additional 1 inch should be assumed. The largest potential for both overall settlement and differential settlement is due to inadequate preparation/cleaning of the subgrade, and improper backfill and compaction of structural fill, which is not accounted for in these estimations. A method to limit differential settlement of smaller buildings placed over structural fill, would be to cut the base of the excavation to be relatively level and the fill pad built up evenly across the building footprint. The depth of excavation needed for these structures would likely be determined during construction once the unsuitable soils have been completely excavated. 2022-188-21 KCTS — Final Geotechnical Report I () HWA GEOSCIENCES INC.