518 51ST ST SW 2023-06-23 - Laserfiche WebLink

• • April 6,2021 Page 6 of 7 Limited Geotechnical Evaluation The static compression load capacity of a Helical Pier® is the sum of all individual helix capacities below liquefiable soils and in bearing layer. Individual helix static compression capacity is the result of the projected area of the helix,and its bearing pressure. It is recommended that the piers penetrate into relatively dense native soils a minimum of 7 feet, or until refusal whichever is shallower. The bearing layer will be at variable depths below the existing ground surface due to previously natural slope conditions (anticipated to be io to 20 feet). Increased capacity can be obtained with increased penetration, and additional helical flights on the lead section. Helical Pier® installation should be monitored to verify installation torque, and proper embedment into the presumed bearing layer. The Helical Pier®lengths may need to be modified during construction if it is determined that the depth to the bearing layer varies. Helical Pier® anchors are well suited to field adjustments as length can be varied by merely adding or deleting extension sections(shafts)during installation. Monitoring installation torque in the field is used to estimate the anchor compression capacity, and also as a quality control during anchor installation, provided that the anchor is bearing in dense or hard soils. Dependent on the pile size and the equipment used to install the anchors,an empirical factor is multiplied by the average torque over the final 3 feet of installation to estimate ultimate capacity. Allowable Helical Pier Compression Capacity Pa may be estimated from the following equation provided that the pier is in the recommended bearing soils: Pa=Kt x T/FoS, Where T is the applied torque, Kt is the empirical ratio factor. The following industry standards apply to shafts with blades spaced along the shaft at 2.5 to 3.5 times the average blade diameter on-center and meeting the manufacturer's specifications. 1.5"and 1.75"Square Shafts - Kt=9 ft-i 2.875"O.D.Round Shafts - Kt=9 ft-i 3.0"O.D.Round Shafts - Kt=8 ft-i 3.5"O.D.Round Shafts - Kt=7 ft-i Proof testing of at least twenty percent of the helical piers in six (6) equal increments up to 150 percent of the design load, if required by the permitting authority. Each load increment up to the 15o percent of design load should be held for five(5)minutes and the vertical strain monitored.If the total strain between 1 and 5 minutes is less than o.04 inches, the helical pier may be considered acceptable.If the recorded strain exceeds o.04 inches,the helical pier should either be deepened and retested or abandoned and a new helical pier shall be installed and tested. Closure The information presented herein is based upon professional interpretation utilizing standard practices and a degree of conservatism deemed proper for this project. We emphasize that this report is valid for this project as outlined above and for the current site conditions and should not be used for any other site. Sincerely, www.cobaltgeo.com (206)331-1097