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

Subsurface Exploration, Geologic Hazards, and Proposed James Monroe Elementary School Replacement Revised Geotechnical Engineering Report Everett, Washington Design Recommendations ' and that construction uc ' n conforms to the recommendations contained in this report.ort. Such p inspections may be required by the governing municipality. Perimeter footing drains should be ' provided, as discussed under the "Drainage Considerations" section of this report. 11.1 Drainage Considerations ' Foundations should be provided with foundation drains. Drains should consist of rigid, perforated, polyvinyl chloride (PVC) pipe surrounded by washed pea gravel. The drains ' should be constructed with sufficient gradient to allow gravity discharge away from the proposed buildings. Roof and surface runoff should not discharge into the footing drain system, but should be handled by a separate, rigid, tightline drain. In planning, exterior ' grades adjacent to walls should be sloped downward away from the proposed structures to achieve surface drainage. The site has the potential to experience a perched ground water layer within the existing fill and weathered lodgement till, above the underlying lodgement till. These conditions have the potential to result in poor drainage conditions where site grades will slope towards pavement ' edges or building areas, since surface water and perched seepage might be directed towards these structures. If site grades will slope toward pavement edges or structures, it would be appropriate to include cutoff drains in project plans. We should be allowed to offer situation-specific recommendations for these drains once a grading plan has been finalized. For planning purposes, cutoff drains should be located outside of the building perimeter(s) and pavement edges, and should extend to depths sufficient to achieve a minimum 1 foot of ' penetration into the underlying lodgement till. The cutoff drains should be at least 18 inches wide, should be graded to drain by gravity to a suitable discharge location, and should be provided with a perforated pipe surrounded by washed drain rock. 12.0 FLOOR SUPPORT Floor slabs can be supported on suitable native sediments, or on structural fill placed above suitable native sediments. Floor slabs should be cast atop a minimum of 4 inches of clean, ' washed, crushed rock or pea gravel to act as a capillary break. Areas of subgrade that are disturbed (loosened) during construction should be compacted to a non-yielding condition prior to placement of capillary break material. Floor slabs should also be protected from dampness by an impervious moisture barrier at least 10 mils thick. The moisture barrier should be placed between the capillary break material and the concrete slab. 13.0 FOUNDATION WALLS ' All backfill behind foundation walls or around foundation units should be placed as per our recommendations for structural fill and as described in this section of the report. Horizontally October 5, 2009 ASSOCIATED EARTH SCIENCES, INC. owGied-KE090312A3-Projects120090312IKE%WP Page 17 1