b'capacity of the typical solid square shaft helical torsion measurements on the new placementproduct within a given soil stratum is ten times shall be averaged over three feet, but the anchorthe average shaft torsion measured over the final shall not be installed to the spin depth.three feet of installation.When estimating the anchors capacity, one must Due to larger friction between the soil andnot consider any torque readings on an anchor tubular shaft configurations, one cannot usewhen it is stalled or encountering obstructions; the ten to one relationship mentioned above toinstead average the readings three feet before the estimate ultimate capacity of tubular shafts.stall.Likewise the shaft torsion readings on an Amoredetaileddiscussionoftherelationshipanchor that spins upon encountering very dense between torque on the shaft and anchor capacitysoil cannot be used.When a tension anchor is presented in the next section.spins, it must be removed and repositioned.TheHelical Torque Anchor Design ConsiderationsProjectedAreasofHelicalPlates: When Table 10. Projected Areas* of Helicaldetermining the capacity of a screw pile in aTorque Anchor Platesgivensoil,knowledgeoftheprojectedtotalareaofthehelicalplatesisrequired.This Helical 6 8 10 12 14 16projected area is the summation of the areas of Plate Dia. Dia. Dia. Dia. Dia. Dia.the helical plates in contact with the soil less Shaft Projected Areaft 2the cross sectional area of the shaft.Table 10 1-1/2 Sq. 0.181 0.333 0.530 0.770 1.053 1.381providesprojectedareasinsquarefeetof 1-3/4 Sq. 0.175 0.328 0.524 0.764 1.048 1.375bearingareaforvariousplatediameterson 2 Sq. 0.168 0.321 0.518 0.758 1.041 1.396different shaft configurations.AllowableHelicalPlateCapacity: When 2-7/8 Dia 0.151 0.304 0.500 0.740 1.024 1.351conductingapreliminarydesign,onemust 3-1/2 Dia 0.130 0.282 0.478 0.719 1.002 1.329also be aware of the mechanical capacity of 4-1/2 Dia 0.086 0.239 0.435 0.675 0.959 1.286the helical plate and the shaft weld strength. * Projected area is the face area of the helical plate less the crossAveragecapacitiesofplatesaregivenin sectional area of the shaft.Table11.Actualcapacitiesaregenerally Important: When a 90 0spiral cut leading edge is specified, thehigher than shown for smaller diameter helical projectedareas listed in Table 10are reduced by approximately 20%.plates.Capacitiesarealsoslightlyhigherwhenthehelicesaremountedtolarger Table 11. Average Ultimate Mechanicaldiameter tubular shafts. Helical Plate CapacitiesDesigns using 12 to 14 diameter plates on 6 through 14 Diameter Platessquarebarshaftswillhaveultimate Helical Plate Average Ultimate Averagemechanical capacities that are slightly lower Thickness Load Service Loadthanshown inTable11.Thisvarianceis 3/8 40,000 lb 20,000 lbusuallynotaconcernexceptwhenasmall 1/2 50,000 lb 25,000 lbshaft is highly loaded with only a single or 16 Diameter Platedouble helix configuration. 1/2 40,000 lb 20,000 lbRelationships between Installation Torqueand Torque Anchor Capacity: shouldbeselectedwhendesigning.WhileEstimatingthecapacityofagivenscrewpile values for k have been reported from 2 to 20,based upon the installation torque has been used most projects will produce a value of k in the 6for many years. to14range. EarthContactProductssuggestsusing the values for k as shown in Table 12Unlessaloadtestisperformedonsiteto whenestimatingTorqueAnchorultimatedetermineaspecificvaluefortherelationship capacities.betweeninstallationshafttorsionandultimate It is important to understand that the value of kproduct capacity, commonly referred to as Soil isameasureoffrictionduringinstallationasEfficiencyFactor,k,aconservativevalue illustrated in Figure 2 on page 26 above.ThisECP Helical Torque Anchors Technical Service Manual2021 Earth Contact Products, L.L.C.2021-09 Chapter 1 - Page 27 All rights reserve'