b'The 2-7/8diameter shaftsizeselectedin 4. Installation Torque. Please remember that aDesign Example 1 must be changed to a stiffer largerdiametertubularshaft willpassthroughshaft to be able to successfully pass through the soil less efficiently due to friction with thetheveryweekupper soilstratawithout soil. Thiseffectofsoilfriction ondifferentbuckling. tubular shaft diameters was fully discussed at thebeginning of Chapter 4.A3-1/2inchdiametertubularshaftisableto As a result, when the design requires a change inoffer more shaft stiffness (also called Moment ofInertia) or resistance to buckling.Referring to shaftsize,theinstallationtorquerequirementTable 15 (previous page); notice the row labeled must be recalculated.The shaft friction is higher3-1/2 inch dia. x 0.300 presents a conservative for a largerdiametershaft;therefore,theSoilestimatedbucklingloadcapacityof78,000 Efficiency Factor (k) will be lower.pounds for this larger diameter shaft. Because A check of Table 1 in Chapter 4 shows that theveryweaksoilexistsnearthesurfaceinthis 3-1/2inchdiametershafthasarecommendedexample, the specified pile shaft diameter must efficiency factor, k = 8 as compared to k ofbe increased to prevent buckling of the pile shaft 9 fora2-7/8inchdiametershaftusedfortheas the pile passes through these weak soils. earlier design.3.TorqueAnchorSpecifications.TheTorque Anchor plate configuration remains as Equation 2 in Chapter 1 is used to calculate aoriginallydeterminedtosupportthestructural newinstallationtorquerequirementfortheload, but the shaft diameter must be increased to larger 3-1/2 inch diameter pile shaft.the 3-1/2 inch diameter, 0.300 inch wall tubular T = P u/ k, Where,shaft for increased buckling strength: P u= 60,000 lb TAF-350-84 08-10-12 Lead Section k = 8 (Table 12Chapter 1) TAE-350-84 Extension Section T = 60,000 lb / 8 ft -1= 7,500 ft-lb TAE-350-120 Extension Section T = 7,500 ft-lb, minimum TAB-350NC PileCapthat fitsover the3- End of Example 1B1/2 tubular shaft and has a 3/4 x 8 x 8bearing plate.Earth Contact Products highly recommends that a Registered Professional Engineer conduct theevaluation and design of Helical Torque Anchors where shaft buckling may occur due to theshaft being installed through weak soil or in cases where the shaft is fully exposed without lateralshaft support.Review of Results of Example 1 & 1BItisimportanttorememberthatbucklingisanissuewhenpileshaftspassthroughweaksoilsanywhere along the length of the shaft.The key is to watch SPT - N values at all soil depths.Soil strata that are weaker than N 5 blows per foot for solid square shaft installations and weakerthan N 4 blows per foot for tubular shafts could allow shaft buckling.When such weak soils arereported, please check the critical buckling load in Table 15 to select a shaft diameter suitable forsupport through the weak soil stratum.This could require a larger shaft diameter be used.Exposed Pile Shafts:When a pile shaft extends above the ground, (in the air or in water), this portionof the pile shaft has no lateral support; please refer to Graph 8 - Chapter 1.Here you can estimate thecritical buckling load for various shaft configurations relative to the amount of exposed shaft in the air orwater.(Unsupported column height)Technical Design AssistanceEarth Contact Products, LLC. has a knowledgeable staff that stands ready to help you with understanding howto prepare preliminary designs, installation procedures, load testing, and documentation of each placementwhen using ECP Torque Anchors.If you have questions or require engineering assistance in evaluating,designing, and/or specifying Earth Contact Products, please call us at 913 393-0007, Fax at 913 393-0008.ECP Technical Design ManualTorque Anchor Design Examples2021 Earth Contact Products, L.L.C.2021-09 Chapter 5Page 84 All rights reserved'