5117 27TH AVE W 2025-05-29 - Laserfiche WebLink

• December 20,2021 Page 3 of 4 Limited Geotechnical Evaluation 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.o"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 eight equal increments up to 200 percent of the design load,if required by the permitting authority. Each load increment up to the 200 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. Driven Piles We understand that 2-7/8 inch piles may be used to support portions of the structure. These piles will likely be advanced using a double-cylinder hydraulic system. Piles should be advanced until working pressures are achieved that provide the specific minimum capacities with a factor of safety of at least 2. Work will be halted if the structure experiences uplift flexure. The working pressure for a 3.5 inch cylinder bore is 2,50o pounds per square inch (psi),and 2,000 psi for a 4 inch diameter cylinder bore. The required pile length in order to develop the recommended pile capacity is expected to vary depending on the depth of dense to very dense soils below the residence. We estimate pile lengths of 7 to 15 feet below foundation grades,with a likely average of about io feet. A total of 3 percent of the piles (one pile minimum) should be load tested to verify the design capacities.All load tests shall be performed in accordance with the procedure outlined in ASTM be 2 times the designload. Load testingmayneed to be Dii . The maximum test loadshall 43 terminated if additional lifting of the structure occurs. A representative of the geotechnical engineer shall provide full time observation of pile installation and testing to verify the driving refusal criteria if required by the permitting authority. www.cobaltgeo.com (206)331-1o97 3IB