5131 DOGWOOD DR 2016-08-31 - Laserfiche WebLink

August 12, 2015 G-3945 Geotechnical Evaluation & Underpinning Engineering Page 3 5131 Dogwood Drive, Everett Depth of Underpinning Piers Based on the soil conditions encountered, the piers should extend to a minimum depth of 6 feet below the bottom of the footing. The six piers that were installed extended to a depth of 7 feet, based on review of the pier logs and discussions with the underpinning contractor. SEISMICITY Based on the site geology and the presence of dense soils, the site is seismically classified as Site Class c, in accordance with the International Building Code(IBC) and ASCE Chapter 20. No geotechnical seismic mitigation measures are recommended as part of the foundation underpinning. CONCLUSIONS AND RECOMMENDATIONS The purpose of underpinning is to stabilize the foundation to prevent additional settlement and to attempt to relevel the foundation. The homeowner should be aware that the foundation lifting process may result in an improvement in the level of the house, however the house may not be perfectly level. The foundation underpinning and lifting process may create cosmetic cracks in the walls/ceiling of the home, racking of door jams and windows affecting their operation, and cracks may form in the concrete foundation. Some repairs should be anticipated. FOUNDATION UNDERPINNING The underpinning piers being installed by Innovative Foundation Solutions are Model PPB-300 steel piers manufactured by Earth Contact Products. The pier system consists of a starter tube and additional tubes which are added as the pier is advanced. The tubes measure 3.5 feet in length. A steel bracket assembly is placed under the foundation to transfer the building load from the building foundation to the push pier. Based on the product technical design manual, the pier tubes have a outside diameter of 2.875 inches (3 inch pier) and a wall thickness of 0.165 inches. The manufacturer specifies a maximum proof load of 51,000 lbs for the PPB-300 steel pier system, which is equivalent to a maximum design/service load capacity of 25,500 lbs per pier. For this project we recommend the push piers have an allowable design capacity of 50 percent of the logged pier installation force, but no greater than 12,000 pounds, provided the pier GEO Group Northwest,Inc.