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

June 23, 2017. G-4400 Underpinning Evaluation Page 4 2514- 51"Street SW,Everett A maximum pier spacing of 5.5 feet was calculated for the east wall and a maximum pier spacing of 4.4 feet was calculated for the north wall based on the dead and live loads of the structure and using an allowable pier capacity of 13,500 lbs. The windows in the structure concentrate building loads at the northeast building corner. Building loads are also concentrated between the main entry doorway and window on the north wall. To support the concentrated loads,two piers are recommended at the northeast corner and three piers are recommended between the door and window on the north wall. Bending and shear capacity of the foundation were checked for the worst case condition and found to be acceptable for up to a 5.4 foot unsupported foundation section. The pier spacing,bending and shear calculations, are included in Appendix A. Because the house is to be lifted, we recommend a maximum spacing of 4 feet, except under the north window where foundation loads are concentrated at the ends of the windows and up to a 5.4 foot spacing is acceptable. PIER INSTALLATION DESCRIPTION The push piers are advanced into the soil with a hydraulic pump and cylinder combination using the structure as the reaction force. The hydraulic pressure is monitored with a calibrated pressure gauge during installation. When the tip of the pier reaches suitable bearing strata the hydraulic force on the pier is gradually increased to 200 percent of the design load or until movement of the design frame occurs (the foundation begins to lift). PIER LOAD TESTING&INSPECTION Installation of approximately 8 piers is anticipated. An ASTM quick test(load test)is recommended on one pier. Geotechnical inspection is recommended during pier installation and load testing to verify proper embedment to the bearing strata and to verify the pier capacities are achieved in accordance with the design. GEO Group Northwest,Inc.