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 preparation incurs initial costs; however, by limiting damage to moisture-sensitive site soils, later costly repairs are reduced or eliminated. In our experience, overall costs are lower if moisture-sensitive soils in construction areas are protected rather than repaired after construction is complete. Foundation subgrades may require protection from foot and equipment traffic, and ponding of runoff during wet weather conditions. Typically, compacted crushed rock or a lean-mix concrete mat placed over a properly prepared subgrade provides adequate subgrade protection. Foundation concrete should be placed and excavations backfilled as soon as possible to protect the bearing grade. 6.5 Proof-Rolling and Subgrade Compaction Following the recommended site stripping procedures and required excavation to grade, the stripped subgrade within the building and any new pavement areas should be proof-rolled with heavy rubber-tired construction equipment, such as a fully-loaded, tandem-axle dump truck. Proof-rolling should be performed prior to structural fill placement or foundation excavation. The proof-roll should be monitored by the geotechnical engineer so that any soft or yielding subgrade soils can be identified. Any soft/loose, yielding soils should be removed to a stable subgrade. The subgrade should then be scarified, adjusted in moisture content, and recompacted to the required density. Proof-rolling should only be attempted if soil moisture contents are at or near optimum moisture content. Proof-rolling of wet subgrades could result in further degradation. Low areas and excavations may then be raised to the planned finished grade with compacted structural fill. Subgrade preparation and selection, placement, and compaction of structural fill should be performed under engineering-controlled conditions in accordance with the project specifications. 6.6 Overexcavation/Stabilization Construction during extended wet weather periods could create the need to overexcavate exposed soils if they become disturbed and cannot be recompacted due to elevated moisture content and/or weather conditions. During dry weather periods, soft/wet soils, which may need to be overexcavated, may be encountered in some portions of the site. If overexcavation is necessary, it should be confirmed through continuous observation and testing by Associated Earth Sciences, Inc. (AESI). Soils that have become unstable may require remedial measures in the form of one or more of the following: 1. Drying and recompaction. Selective drying may be accomplished by scarifying or windrowing surficial material during extended periods of dry and warm weather. 2. Removal of affected soils to expose a suitable bearing subgrade and replacement with compacted structural fill. March 28,2019;Revised April 16,2019 ASSOCIATED EARTH SCIENCES,INC. SGB/Id-190104E001-3-Projects\20190104\KE\WP ( I'age ��