2514 51ST ST SW Geotech Report 2022-10-25

June 23, 2017 G-4400 Underpinning Evaluation Page 3 2514- 51'Street SW,Everett SEISMICITY Based on the site geology and the soils encountered by probing,the site is seismically classified as Site Class C, in accordance with the International Building Code and ASCE Chapter 20. The site is gently sloped,appears stable and there is negligible risk for a deep seated slide to occur. The potential is negligible for liquefaction and/or lateral spreading to occur based on the geology,the dense soils encountered at a depth of 7 feet and a lack of groundwater. No known faults intersect the subject property and the risk of surface rupture, as a result of a large magnitude seismic event, is interpreted to be very low. No geotechnical seismic mitigation measures are recommended as part of the underpinning. CONCLUSIONS AND RECOMMENDATIONS Based on our findings, we recommend portions of the east and north basement walls be underpinned to stabilize the foundation and mitigate additional settlement. We understand the client is planning to lift and relevel the foundation with the push piers. FOUNDATION UNDERPINNING The foundation may be underpinned from the interior or the exterior side of the basement using push pier consisting of 3-inch diameter steel pipe. The piers consist of a starter tube(bottom section of the pier) and additional tubes are added as the pier is advanced. A steel bracket assembly is placed under the foundation wall and used to transfer the building load from the building foundation to the push pier. PIER ALLOWABLE DESIGN CAPACITY&SPACING The allowable capacity of 3-inch diameter push pier is 50 percent of the measured installation force logged during installation, but no greater than 16,500 lbs per pier,provided the pier is installed in conformance with the manufactures instructions. We recommend an allowable design load of 13,500 lbs per pier. GEO Group Northwest,Inc.