b'Table 3. Symbols Used In This Chapter Design Criteria Tieback installation angle from horizontal TheBearingCapacityofaTorqueAnchor A Projected area of helical plateft 2 (P w ) can be defined as the load which can bec Undrained shear strength of the soillb/ft 2 sustainedbytheTorqueAnchorwithoutd x Helical plate diameter ft producingobjectionablesettlement,eitherd largest Diameter of Largest Helical Plate initiallyorprogressively,whichresultsinCritical DepthThe distance from ground damage to the structure or interferes with theD cr surface to the shallowest helical tieback use of the structure.plate. (D cr= 6 x d largest ) BearingCapacityisdependantuponmany Dry Density Of The Soillb/ft 3 factors: Internal Friction Angle of SoilKind Of Soil,FS Factor Of Safety (Generally FS = 2)Soil Properties,H Height of soil against wall or basement - ftSurface and/or Ground Waterh Vertical depth from surface to helical plate Conditions,Vertical depth from the ground surface to aTorqueAnchorConfiguration(Shafth mid point midway between the lowest and Size&Type,HelixDiameter(s),andhighest helical platesft Number Of Helices),Empirical factor relating ultimate capacityDepth to Bearing,k of a pile or tieback to the installationtorqueft -1(k = P uor T u/ T)Installation Angle, Torque Anchor Spacing,Torque conversion factor that is used toK determine torque motor output fromInstallation Torque,pressure differential across motorType of Loading - Tension,L Total product length required by the design Compression, Alternating Loads, etc.L 0 Minimum required horizontal embedment ThedesignofHelical TorqueAnchorsusesDistance to achieve the minimumrequired classical geotechnical theory and analysis alongL 15 embedment length, L 0at 15 0Installation withempiricalrelationshipsthathavebeenAngle developed from extensive field load testing.InStandard Penetration Test (SPT) Results. ordertoprepareanengineeringdesign,N = Number of blows with a 140 lb hammer geotechnicalinformationisrequiredfromtheN to penetrate the soil a distance of one foot. sitealongwithstructuralloadrequirements(Note: N may be given directly or in 3segments.Always add the last two segment including a factor of safety - FS.counts to get N4/5/7 is N = 12.) The most accurate design requires knowledgeN c Bearing capacity factor for clay soil from soil testing using the Standard PenetrationN q Bearing capacity factor for granular soil Test (SPT) standardized to ASTM D1586 pluspH Measure of acidity or alkalinity laboratoryevaluationsofthesoilstrength,P Foundation or Wall Loadlb/Lineal ft which is usually given as soil cohesionc,P u Ultimate pile or anchor capacity*lb. soil density, and granular friction angle P w Working or design loadlb. p Pressure differential measured across a Soils will vary from site to site and may varytorque motor p =p in - p out - psi frompointtopointonsomesites.Eachq Soil overburden pressure (lb/ft 2 ) analysis must use data relevant to the project atS Helical Plate Embedment for Tension - ft hand as each project has different parameters.T Installation or Output Torqueft-lb EachdesignrequiresspecificinformationT u Ultimate Tension Capacitylb involvingthestructureandsoilT w Working Tension Loadlb characteristicsatthesite.Eachdesignw Distributed load along foundationlb/lin.ft. should involve geotechnical and engineeringX Product Spacing - ft input.* Unfactored Limit, use as nominal, P uvalue per design codesECP Helical Torque Anchors Technical Service Manual2021 Earth Contact Products, L.L.C.2021-09 Chapter 1 - Page 16 All rights reserved'