5001 23RD AVE W Geotech Report 2022-10-25

other equivalent systems to mitigate and/or improve bearing capacity of existing footings and/or to level existing footings. It should be noted the helical piers should be provided and installed by the specialty contractor who is certified in the installation of the proprietary pier product. It should also be noted that foundation engineering or structural design of the proposed mitigation measures was beyond our scope of services. • Effective and average angle of internal friction for overburden soils, 0'-10' = 28 degrees • Effective and average angle of internal friction for overburden soils, 10'-20' = 34 degrees • Average unit weight of overburden soils = 110 pcf • Soil classification for power-installed screw anchors (PISA) = 3/4 • Bearing capacity factors: Nc = 50; Nq = 35; Ny = 35 • Horizontal modulus of subgrade reaction up to 6.0 feet = 75 pci • Horizontal modulus of subgrade reaction below 2.5 feet = 200 pci • Minimum Anchor Depth: In general, helix should be placed at least 20.0 feet below the ground surface. All anchor depths must be noted and confirmed in the field by a geotechnical engineer/geologist from our office. These anchor depths should be used only for planning purposes. Actual anchor depths may vary from location to location. We strongly recommend that AGS reviews and approves the structural design and plans for this project to assure that the helical piers have been properly designed for settlement or heave mitigation purposes. We strongly recommend that AGS should be present at the site during the installation of helical piers to assure that helical piers are installed through and beyond any unknown muck deposits and made to have bearing on the Vashon drift materials. • Minimum Torque: 4,000 to 6,000 foot-pounds or refusal to ensure that the helix(bearing plate) is embedded into the underlying dense to very dense glacial till. Torque criteria may be confirmed or revised in the field by a geotechnical engineer from our office. • Helix: Use a single minimum 12"-18" helix lead section located at least 20 feet below the ground surface. Other helices combinations providing same design capacities may be used after AGS's review and approval. Helix depth may be modified depending upon refusal or muck deposits (if any) encountered during installation. • Shaft: Use minimum 2 7/8" diameter Stabil-Loc or equivalent pier. No water infiltration should be allowed along the shaft. It is important that no slack or looseness exists in the connections between rod sections in the helical pier system. • Pier Location and Spacing: As per the foundation plan/details provided by the project structural engineer. Project No: 0314-WA19 August 07,2019 Page No:8 of 12