b'There is a reduction in load capacity of 24% for Onemustuse Equation1b once again tothesamepileconfigurationinthesamesoil determinea piledesignwithsufficienthelicalwhen water is present at 10 feet below grade. plate area.Thisdemonstratesthatknowingthelevelof A H= P u /(q N q )the water table is critical to prepare a safe pile A H = 61,600/[(100 x 10 ft) + (60 x 15)] x 16design. A H= 2.03 ft 2Thismeans that anewpileconfigurationwith Thestandard helicalpile productthatwillincreased plate area sufficient to provide 61,600 provide a suitable helical plate area is a TAF-288lb capacity in the same soil but with a water table (10-12-14), with 2.26 ft 2of plate area.ten feet below grade.This example clearly illustrates that if subsurface water is not considered during the designingprocess, it is highly likely that the pile or anchor will be under designed and could fail.Mixed SoilsCohesive and Cohesionless SoilsWhen reviewing soil boring logs one often sees descriptions that combine the two soil types.One oftensees such terms as clayey sand or sandy clay in the soil descriptions on the soil boring log.Thesoilsengineersusetermstodescribesoilsthat contain both cohesive soil and granular soil Table 8 Mixed Soil Descriptionsinthesamples.Whenoneencounterssuch Soil Description Estimated Percentage Presentdescriptions in the soil report, the design analysisrequiresthatbothsoiltypesbeconsidered. trace 1% to 5%Equation1mustbeusedtodeterminethe slightly 6% to 15%ultimatecapacityorprojectedhelicalarea little 10% to 20%requirement.Thedesignermustassigna with 15% to 25%percentageofeachtypeofsoilpresentwhen silty orclayey 20% to 49%placing data into Equation 1. some 20% to 34%Table8providesguidanceforrelative very 35% to 49%percentages of each type of soil.Experience has Note: There is no national standard for soil descriptionshown that there is no national standard for these percentages reported by soil engineers.Listed above aresoildescriptions.Becauseofthis,Table8 thedescriptorsandmostcommonlyencounteredpercentages.For increased accuracy, or when workingprovidesthemosttypicalpercentages.Itis onacriticalproject,verifythedescriptivepercentagesalwaysagoodideatocheckwiththesoil with the project soil engineer.engineer to verify his or her soil type percentages Equation 1 is modified as shown to adjust to theon a specific soil boring log when working on a reported soil composition:critical project.Whenpreparingaloadcapacitydesignwhen P u= Helical Plate Area x (30% strength ofmixedsoilsarepresent,adjustfortheclay + 70% strength of sand)percentagesofcohesiveandcohesionlesssoils P u= A H(0.30 c N c+ 0.70 q N q )present in Equation 1.For example, assume that The result of the analysis will be a helical pilethe soils engineer described the soil on the site as capacity that is lower than if it was embedded inbeing clayey sand.Referring to Table 8 there only sand, but greater than if embedded only inis a range from 20% to 49% for the cohesive clay.claycomponentinthesample.Forthisillustration it is assumed that no additional data Keepinmindthatwhendealingwithis available from the soil engineer regarding the incompletedata,itiswisetoaddagreaterpercentagespresent.Avalueforthecohesive factorofsafetyortochoosethepercentageclaycomponentofthesoilisestimatedtobe usedforthecohesionlesssoilcomponentatabout 30% and the remaining 70% of the soil is the lower end of the range shown in Table 8.assumed to be sand:ECP Helical Torque Anchors Technical Service Manual2021 Earth Contact Products, L.L.C.2021-09 Chapter 1 - Page 21 All rights reserve'