5131 DOGWOOD DR 2016-08-31 - Laserfiche WebLink

August 12, 2015 G-3945 Geotechnical Evaluation&Underpinning Engineering Page 5 5131 Dogwood Drive, Everett PIER INSTALLATION DESCRIPTION The push pier is 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 and the tube installation pressures recorded. 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). INSPECTION We recommend the final pier depths and the recorded pier installation pressures be reviewed by the geotechnical engineer to verify proper embedment to the bearing strata and to verify acceptable pier capacities are achieved. EVALUATION OF PIERS PREVIOUSLY INSTALLED The six piers that were previously installed, and their spacing, are illustrated on the Foundation Sketch, Plate 2. The pier spacings are less than 6.3 feet, except for the pier spacing between pier #4 and pier#5 which has a pier spacing of 7.3 feet. We recommend pier#4 be reinstalled so it is located at the midpoint between piers #3 and #5. This will create a pier spacing of 5.875 feet(±) between piers #3 and#4, and between piers #4 and#5. The unsupported foundation section between the pier brackets will be approximately 5.1 feet. The pier logs of the six piers previously installed were reviewed and encountered suitable bearing strata at a depth of 7 feet, measured from the top of the pier tube. Installation pressures between 1800 psi and 2,600 psi were recorded at the time of installation. Using the hydraulic conversion factor of 9.62 lbs/psi, the pier installation pressures have equivalent pier load capacities of between 17,316 lbs and 25,012 lbs and equivalent pier working load capacities of between 8,658 lbs and 12,506 lbs. The pier depths and equivalent load capacities of the six piers installed are acceptable, with the exception of pier#4 which we recommend reinstalling to satisfy the max. pier spacing and max. span requirements. GEO Group Northwest, Inc.