1502 WALL ST IMAGINE CHILDRENS MUSEUM Geotech Report 2022-10-25

Imagine Children's Museum Building Addition Revised Geotechnical Engineering Report Everett, Washington Design Recommendations 3. Mechanical stabilization with a coarse crushed aggregate compacted into the subgrade, possibly in conjunction with a geotextile. 6.7 Temporary and Permanent 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, we anticipate that temporary, unsupported cut slopes in the lodgement till can be made at a maximum slope of 0.75H:1V (Horizontal:Vertical) or flatter. Temporary, unsupported cut slopes in compacted structural fill, if needed, should be limited to 1.5H:1V or flatter. As is typical with earthwork operations, some sloughing and raveling may occur, and cut slopes may have to-be adjusted in the field. If groundwater seepage is encountered in cut slopes, or if surface water is not routed away from temporary cut slope faces, flatter slopes will be required. In addition, WISHA/OSHA regulations should be followed at all times. Permanent cut and structural fill slopes that are not intended to be exposed to surface water should be designed at inclinations of 2H:1V or flatter. Slopes that are intended to be exposed to surface water are not expected for this project, but should be designed at inclinations of 3H:1V or flatter. All permanent cut or fill slopes should be compacted to at least 95 percent of the modified Proctor maximum dry density, as determined by ASTM D-1557, and the slopes should be protected from erosion by sheet plastic until vegetation cover can be established during favorable weather. 6.8 Frozen Subgrades If earthwork takes place during freezing conditions, all exposed subgrades should be allowed to thaw and then be recompacted prior to placing subsequent lifts of structural fill or foundation components. Alternatively, the frozen material could be stripped from the subgrade to reveal unfrozen soil prior to placing subsequent lifts of fill or foundation components. The frozen soil should not be reused as structural fill until allowed to thaw and adjusted to the proper moisture content,which may not be possible during winter months. 7.0 STRUCTURAL FILL Structural fill may be necessary to establish desired grades. All references to structural fill in this report refer to subgrade preparation, fill type, placement, and compaction of materials as discussed in this section. If a percentage of compaction is specified under another section of this report, the value given in that section should be used. After stripping, planned excavation, and any required overexcavation have been performed to the satisfaction of the geotechnical engineer/engineering geologist, the upper 12 inches of exposed ground should be recompacted to 90 percent of the modified Proctor maximum density using ASTM D-1557 as the standard. If the subgrade contains too much moisture, adequate recompaction may be difficult or impossible to obtain and should probably not be March 28,2019;Revised April 16,2019 ASSOCIATED EARTH SCIENCES,INC. SGB/ld-190104E001-3-Projects120190104WE\WP Page. 6 45 j