11831 AIRPORT RD WHOLE SITE FILE Geotech Report 2022-10-25

Allowable Soil Bearing Pressure (psf) Allowable Lateral Founded at a Founded at a Bearing Pressure Friction Angle Depth of Depth of 9 or Location (psf) (degrees) 6 feet more feet Airport Road and 112th Street SW 1,500 28 1,500 2,500 Airport Road and Kasch Park Road 1,500 30 1,500 2,500 Notes: 1 Based on our review of public information regarding the existing landfill perimeter and the proposed signal pole location,the foundation appears to be outside the landfill area.Similar to the station foundation preparation in this area,we recommend potholes be planned to locate either native soil or the landfill liner prior to drilling new foundations. 2 At the northeast corner of 132nd Street SE and 16th Avenue SE,peat was encountered from a depth of 9 to 12 feet.Therefore,at this corner we recommend that the signal pole foundation extend to a minimum depth of 15 feet below existing grade. Timber Strain Poles We understand that timber strain (span wire) poles will be used in the northwest and southwest corners of the intersection of SR 527 and 208th Street SE. In general, medium dense sand and gravels are anticipated in this area. The standard span wire design assumes a soil lateral bearing pressure of 2,000 psf and a friction angle of 32 degrees. In our opinion, these design parameters are appropriate for this intersection. Gravelly soils were encountered at the southwest intersection corner; it might be difficult to install poles in this area using open hole techniques. Luminaire Poles Luminaire poles are planned along Airport Road east of SR 99.The lateral bearing values presented above in Table 10 may also be used for design of the luminaire poles. The recommended values for this area along Airport road will result in using a Type B pole design. Construction Considerations We recommend that signal pole foundations have a minimum diameter of 3 feet and be installed using the WSDOT procedure. Concrete should be cast neat against excavation sides. The use of temporary casing, drilling mud or other types of procedures should be used, as necessary, to control sloughing of sidewalls. Slough should be removed from the bottom of the excavation prior to placement of concrete, as loose or disturbed soil in the excavation base could result in increased settlement. Structures that require relatively short shafts(less than 9 feet deep) may be formed and constructed in an open excavation provided seepage is not present and the excavation remains stable. The backfill placed around the foundation in the excavation must be compacted in accordance with the WSDOT Standard Specification M41-10, Section 2-09.3(1)E and as described in this report. Foundation construction should be in accordance with WSDOT Standard Specifications M41-10, Sections 8-20.3(2) and 8-20.3(4). Following the removal of the concrete forms (the forms may be left in place ONLY if corrugated metal pipe is used), compacted backfill should be placed around the shaft to provide containment. Controlled density fill may be used as an alternative for structural backfill. GEOENGINEERSri) April 14,2017 Page20 File No.2095-032-00