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

TABLE 3.ANTICIPATED SOIL CONDITIONS AT STATION WALLS Location Cut/Fill Anticipated Foundation Soil Conditions NE corner of SR 527 and 220th Street SE Fill Fill SW corner of SR 527 and 180th Street SE Fill Fill on north end, glacial till on south end NE corner of SR 527 and 180th Street SE Cut Fill or glacial till SW corner of SR 527 and 164th Street SE Fill Fill or recessional sand and gravel NE corner of SR 527 and 164th Street SE Cut Gravel(fill?) Dumas Road and 132nd Street SE Fill Fill overlying glacial till SE corner of 128th Street SW and 3rd Avenue SE Fill Glacial till? NW corner of 128th Street SW and 3rd Avenue SE Fill Glacial till? Airport Road and 100th Street SE Fill Fill, located above an existing wall Airport Road and Kasch Park Road Fill Fill Foundation Support and Subgrade Preparation Fill Areas The density of the existing fill encountered in our explorations was primarily loose to medium dense, with occasional dense zones. We recommend that the upper 18 inches of the exposed existing fill be re-compacted to a minimum of 95 percent of the MDD in accordance with ASTM D 1557. All loosened or disturbed subgrade soils should be removed prior to forming the foundations. If the on-site soils cannot be compacted to the minimum criteria of 95 percent, excavation and replacement with material meeting the requirements for structural fill presented in the "Earthwork"section of this report will be necessary. Dumas and 132nd Street SE For the station wall at Dumas and 132nd Street SE, it is unclear whether the landfill extends this far to the east. However, our exploration at the base of the rockery encountered similar soils as those encountered in the nearby 1991 test pit, where landfill debris was not observed. We recommend that the foundation area be carefully potholed during construction through the upper fill to expose either the native glacial till or the landfill liner. If native soil conditions are encountered and the area is outside the liner, the wall for this station should be founded on the recompacted native soil or on structural fill overlying native soil. If the liner is encountered, lightweight fill and other subgrade preparation recommendations (e.g. using geotextiles or geogrid)should be developed based on the depth to the liner,thickness of new fill, and other factors. If the liner is encountered, we recommend we be retained to review these conditions during construction and provide appropriate fill placement and foundation support alternatives. Native Soil Walls can be supported directly on dense native sand or glacial till provided all loosened or soils disturbed during excavating are removed prior to forming the foundations. Design Parameters Wall footings should be founded a minimum of 18 inches below the lowest adjacent grade.We recommend that the front of the wall footings have a minimum setback of 3 feet from the face of existing slopes. This setback distance assumes that disturbed slopes are either recompacted or rebuilt with structural fill, as discussed in the "Earthwork"section of this report, and that the slope inclination is 2H:1V or flatter. GEOENGINEERS April 14,2017 Page 12 File No.2095-032-00