7505 SEAWAY BLVD Geotech Report 2022-10-25

November 11, 2016 HWA Project No. 2014-117-21 Structural backfill and compaction considerations are discussed in Sections 4.8.3 and 4.8.5, respectively. 4.3.2 Foundation Considerations We understand the bus shelters and maintenance facility will be supported by shallow foundations. We recommend all undocumented fill material be excavated from below the footings until native glacial soils are encountered. Footings should be founded in the native glacial soils, or in compacted structural fill constructed above the native glacial soils, depending on footing elevations. We recommend a maximum allowable bearing capacity of 3,000 psf be used for design of the footing foundations founded on weathered glacial till, non-weathered glacial till, or properly compacted structural fill. For short-term wind and seismic loading conditions, the allowable bearing pressure maybe increased by 1/3 (to 4,000 psf). We recommend minimum footing widths of 18 and 24 inches for strip and square footings,respectively. For development of lateral resistance to sliding, an allowable coefficient of friction of 0.5 may be assumed for spread and strip footings cast neat against properly prepared subgrade. For frost protection considerations, all footings should be buried at least 18 inches, measured from finished grade to footing base level. 4.4 PAVEMENT CONSIDERATIONS We understand the center island will be surrounded by a PCC pavement structure. We also understand that hot-mix asphalt(HMA)pavement sections will be constructed in the vicinity of the Seaway Boulevard and 75th Street SW entrances; where those alignments will be widened to accommodate construction of the transit center. It is our understanding that all pavement design is being performed by Perteet. Assuming the pavement sections are constructed on properly prepared subgrade soils or compacted structural fill a subgrade resilient modulus of 15,000 psi should be used for design of pavements. 4.4.1 Subgrade Preparation We recommend excavating all undocumented fill from below the footprint of the pavement structure and replacing with"Structural Backfill". The remnant HMA pavement section encountered at hand borings HH-1 and HH-2 should also be removed. The exposed subgrade should be thoroughly proof-rolled to identify poor subgrade areas after excavation. All organic material should be removed from beneath the entire footprint of the pavement areas. Loose or soft soil, defined as being penetrable more than 1 foot with a 1/2-inch diameter rod pushed in under a 150 lb load (T-probe pushed in by hand), should be removed and 2014-117 Final Geotechnical Report 9 HWA GEOSCIENCES INC.