5816 25TH AVE W Geotech Report 2025-06-25

Kierstein Residence Retaining Wall Everett Washington Geotechnical Engineering Report SIERRASCAPE WALL RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION Wall Design Associated Earth Sciences, Inc. (AESI) designed the planned SierraScape wall based on discussions with you and available subsurface information. We designed the SierraScape wall using the computer software program MSEW Version 3.0. We analyzed global stability of the wall using the software program Slope/W Version 8.16 by GeoSlope International. Soil parameters were derived based on the soils encountered in our borings, established correlations, prior laboratory testing, and previous experience in similar soils in the Puget Sound area. For seismic design we used a peak ground acceleration (PGA) of 0.652g. For global stability we used a PGA reduced by 50 percent. Our analysis indicates that that the wall will require geogrid (Tensar UX110OMSE or approved equivalent) having a length approximately equal to the total wall height. Calculations supporting the design of the wall are included in Appendix B at the end of this letter-report. Construction plan sheets G1 and G2 are presented separately from this report. Site Preparation Site preparation of the area for the new retaining wall should include removal of all organic debris, and any other deleterious material. Areas where looser native soils exist should be recompacted in place, or if this is not feasible due to either soil composition or moisture content, the loose soils should be removed and replaced as subsequently recommended for structural fill placement. In our opinion, stable construction slopes should be the responsibility of the contractor and should be determined during construction. For estimating purposes, we anticipate that temporary, unsupported cut slopes in the advance outwash may be made at a maximum slope of 1H:1V (Horizontal:Vertical). In existing fill soils or slide debris, we recommend temporary cut slopes inclined at 1.5H:1V. As is typical with earthwork operations, some sloughing and raveling may occur, especially if groundwater seepage is present in temporary cut slopes and inclinations may have to be adjusted in the field. In addition, WISHA/OSHA regulations should be followed at all times. Based on our observations, the on-site soils have a low to moderate percentage of fine-grained material making them slightly to moderately moisture-sensitive and subject to disturbance when wet. The contractor must use care during site preparation and excavation operations so that the underlying soils are not softened. If disturbance occurs, the softened soils should be removed and the area brought to grade with structural fill. Any exposed soils should also be protected with plastic sheeting during the winter months. July 1, 2022 ASSOCIATED EARTH SCIENCES,INC. SASlih-20180614EO01-002 Page 6