7505 SEAWAY BLVD Geotech Report 2022-10-25

November 11, 2016 HWA Project No. 2014-117-21 4. CONCLUSIONS AND RECOMMENDATIONS 4.1 GENERAL The soil conditions at the project site are conducive to construction of the proposed transit center. The native weathered and non-weathered glacial till soils will provide adequate bearing capacity for the anticipated lightly-loaded structures associated with construction of the transit center. These native soils will also provide adequate support for pavement sections required to accommodate heavy bus loading. We understand a significant amount, if not all, of the fill mound on the eastern half of the property will be excavated in preparation for construction of the transit facility. This fill material may be suitable for reuse in non-structural applications;provided it is properly moisture conditioned and free of deleterious material. The high fines content of the onsite soils is such that all earthwork should be completed during the dry summer months. In periods of wet weather,the native soils and the onsite fill will deteriorate quickly under construction traffic and will likely be unworkable. Building footings should be founded on the dense native glacial till, or on structural backfill placed above the till. Footings should be designed for an allowable bearing capacity of 3,000 pounds per square foot(psf). The soils are conducive to construction of a retaining wall on the south side of the property. A 3-foot wide flat area should be maintained in front of the wall to provide access for future maintenance. We understand that six new cantilever traffic signals are proposed near the entrance to the transit facility and PUD entrance to facilitate access from these facilities onto 75th Street SW. Our explorations indicate the presence of loose undocumented fill extending to a depth of 15 feet below the ground surface at BH-5. These loose soils will not provide adequate lateral bearing pressures to permit use of the WSDOT Standard Plans signal pole foundations designs. Therefore, non-standard signal pole foundation design will be required for all Signal Poles 4 and 5. Additionally,two of the proposed signal poles to be constructed on the north side of 75th Street will be located near the crest of an existing steep slope. The foundations of these signal poles will need to be modified to account for the presence of the steep slope. We understand a buried detention vault will be used to collect and convey stormwater from the site. The detention vault is approximately 43 feet wide by 252 feet long and 10 feet in depth. The top of the vault will be 5 to 7 feet below ground surface. We recommend an allowable bearing capacity of 5,000 psf for the vault, as it will be founded in native, unweathered till. 2014-117 Final Geotechnical Report 6 HWA GEOSCIENCES INC.