10901 27TH AVE SE Geotech Report 2025-07-29

I I Subsurface Exploration, Geologic Hazards, and Proposed James Monroe Elenterttaly.School Replacement Revised Geotechnical Engineering Report Everett, Washington Design Recommendations ofpit run sand andgravel is recommended. If subgrade conditions are soft and silty, a g Y geotextile separation fabric, such as Mirafi 500x or approved equivalent, should be used ' between the subgrade and the new fill. For building pads where floor slabs and foundation construction will be completed in the winter, a similar working surface should be used, composed of at least 6 inches of pit run sand and gravel or crushed rock. Construction of working surfaces from advancing fill pads could be used to avoid directly exposing the subgrade soils to vehicular traffic. 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 surface. 9.3 Proof-Rolling and Subgrade Compaction Following the recommended demolition, site stripping, and planned excavation, the stripped subgrade within the building 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 or areas of remaining existing fill can be identified. Any soft/loose, yielding soils or existing fill 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. 9.4 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. Even 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 October.5, 2009 ASSOCIATED EARTH SCIENCES, INC. DWG/!d-KE09031213-ProjecIs120090312IKE•I WP Page 13 1