4730 COLBY AVE YMCA Geotech Report 2025-04-14

Subsurface Exploration, Geologic Hazard,and Snohomish County YMCA Geotechnical Engineering Report Everett, Washington Design Recommendations III. DESIGN RECOMMENDATIONS 8.0 INTRODUCTION Our explorations indicate that, from a geotechnical engineering standpoint, the proposed project is feasible provided the recommendations contained herein are properly followed. A portion of the site is underlain by existing fill, which necessitates full removal under areas of new foundations. Observed fill thicknesses near the proposed building ranged from 0.5 to 4.5 feet. The following report sections provide additional recommendations regarding site preparation, grading,foundations, floor support, and drainage. 9.0 SITE PREPARATION Existing structures, paving, buried utilities, vegetation, topsoil, and any other deleterious materials should be removed where they are located below planned construction areas. All disturbed soils resulting from demolition activities should be removed to expose underlying undisturbed native sediments and replaced with structural fill, as needed. All excavations below final grade made for demolition activities should be backfilled, as needed, with structural fill. Erosion and surface water control should be established around the clearing limits to satisfy local requirements. Once demolition has been completed, existing fill should be addressed.The observed thickness of existing fill ranged approximately 0.5 to 4.5 feet near the proposed new building. We recommend that existing fill below new foundation and slabs-on-grade areas, if encountered, be removed and replaced with structural fill. Below planned on-site paving, existing fill should be exposed, proof-rolled, and compacted to 95 percent of the modified Proctor maximum dry density. If a firm and unyielding condition is achieved, no further remedial preparation would be needed. If yielding conditions are encountered, existing fill would be partially removed and replaced with imported structural fill. The depth of replacement of the existing fill below paving should be determined at the time of construction when field conditions are known. 9.1 Temporary Cut Slopes In our opinion, stable construction slopes should be the responsibility of the contractor and should be determined during construction. For estimating purposes, however, temporary, unsupported cut slopes can be planned at 1.5H:1V (Horizontal:Vertical) in unsaturated existing fill sediments and Vashon advance outwash sediments. Temporary slopes of 1H:1V can be February26,2018 ASSOCIATED EARTH SCIENCES,INC. AWR/ms-170671E001-2-Projects1201706711KEIWP Page 10