4320 THOMSON AVE GEOTECHNICAL ENGINEERING REPORT Geotech Report 2023-08-10

GeoTest Services, Inc. March 17, 2022 4320 Thomson Avenue, Everett, WA Project No. 22-0285 -;, should be placed along the back and top of the drainage layer. We recommend that suitable imported structural fill be placed behind the drainage blanket and extend to the contact point with the native cut slope soils. Typical Modular -Block Wall Construction Recommendations Key elements in the construction of a stable wall include the following: • The proposed wall must be founded on suitably prepared flat and benched native soils as applicable. • The exposed subgrade surface should be observed by GeoTest personnel to confirm that the design assumptions are met. A minimum of 6 inches of crushed rock base must be placed and compacted beneath the wall footing or first row of blocks. All crushed rock base must be thoroughly compacted to a minimum 95 percent of the relative density based on Modified Proctor (ASTM D1557). • The base of all walls must be embedded a minimum of 8 inches below finished grades. • Drainage is essential for proper performance of the wall. Thus, GeoTest recommends that a perforated drainpipe be placed at the inside base of the wall. This drain should be surrounded in rock and wrapped with filter fabric. The purpose of this drain is to prevent a buildup of hydrostatic pressure behind the walls. All wall drainage should be discharged to a suitable outlet away from the wall locations. • For wall drainage backfill, the material should consist of free -draining 5/8" or 1-1/4" crushed rock with no fines. The drainage material should extend a minimum of 12 inches immediately behind the blocks and may fill the entire void between the blocks and soil cut/backfill. • Every effort should be made to minimize surface water infiltration during and after construction. All areas behind the wall should be sloped to direct water away from the wall. • The wall contractor is responsible for monitoring and maintaining safe excavation conditions. The wall construction and installation specifications given above are subject to modification. GeoTest should be given an opportunity to review the final wall drawings before they are submitted to the City of Everett. Temporary and Permanent Slopes The contractor is responsible for construction slope configurations and maintaining safe working conditions, including temporary excavation stability. All applicable local, state, and federal safety codes should be followed. All open cuts should be monitored during and after excavation for evidence of instability. If instability is detected, the contractor should flatten the side slopes or install temporary shoring. 12