b'1b,theultimatebearing Table 7. Properties of Cohesionless Soilcapacity of the helical plate isdetermined.Theultimate Soil Density SPT Blow Friction Bearing Densitylb/ft 3capacity of a multi-plate helical Description Count N AngleCapacitypilemaybedeterminedby 0 Factor N qMoist Soil Submergedsummingthecapacitiesofall Very Loose 2 28 12 70100 45 - 62helical plates. 34 28 0 13A simpler method often used to Loose 57 29 0 141590115 52 - 65estimatetheultimatecapacity 810 30 0 1516ofamulti-platepile 1115 30 0 - 32 0 17 - 19configurationistodetermine 1619 32 0 - 33 0 2022thesoiloverburden,q,ata Medium 2023 33 0 - 34 0 2325110 130 68 - 90depthmidwaybetweenthe Dense 0 0upperhelicalplateandthe 2427 34 - 35 2629lowesthelicalplate,h mid . 2830 35 0 - 36 0 3032Thisvalueofqisusedto 3134 36 0 - 37 0 34 - 37estimatetheultimatecapacity 3538 37 0 - 38 0 3943of the pile configuration. Dense 3941 38 0 - 39 0 4548110140 80 - 97CohesionlessBearing 4245 39 0 - 40 0 5056Capacity Factor - N q : 4650 40 0 - 41 0 5968Zhangproposedtheultimate Very Dense 50 42 0 End Bearing 140+ 85compressioncapacityofthehelical screw pile in a thesis for the helical support product.theUniversityofAlbertain1999.Fromthiswork the dimensionless empirical value N qwas Illustrative Example:introduced.N qis related to the friction angle To illustrate the effect of the water table on theof the soil - , as estimated in Table 7. pilecapacity letusassumethat thejob siteWhendeterminingtheultimatecapacityfora contains25feetofcohesionlesssoilthatisTorque Anchor in cohesionless soils, Equation homogeneous,hasaconstantdensityof1001 may be simplified because granular soils have lb/ft 3and a constant Standard Penetration Test -no soil cohesion.Therefore c may be assumed N = 10 bpf that extends beyond the 25 feet.tobezero.Equation1whenusedfor Pleasenotethatsuchuniformsoilas thisiscohesionless soils can be modified as follows: seldom encountered.Equation 1b: Ultimate Capacity - Cohesionless The ultimate capacity of a TAF-288 8-10-12 pileSoil when no ground water is present is determinedP uor T u = A H(q N q ) or using Equation1b.FromTable7, A H foraA H= P uor T u /(q N q ) TAF-288 8-10-12 is 1.54 ft 2 .Where: P u = A H(q N q ) = 1.54 [(100 x 25 ft) x 16]P uor T u = Ult. Capacity of Torque Anchor- (lb) P u= 61,600 lb (Damp soil - no water Present)A H = Projected Helical Plate Area(s) (ft 2 ) Nowletsassumethatthewatertableisq = Soil Overburden Pressure from the surface toplate depth h(lb/ft 2 ) encountered at 10 feet below grade.N q= Bearing Capacity Factor for Granular Soil. P u= A H(q above WT + q below WT ) N qEffect of Water Table on Pile Capacity: P u= 1.54 [(100 x 10 ft) + (60 x 15)] x 16It cannot be emphasized enough that the buoyant P u= 1.54 [(1000) + (900)] x 16forceofwateronthesoiloverburdencan P u= 46,816 lb (Water Table at 10 feet)dramaticallychangetheloadcapacityofthe Notice the reduction in pile capacity when thehelicalpileoranchor. Calculatingsoil watertableispresentat10feetbelowgrade.overburdenforaspecificsiteusuallyentails Thisreductionincapacityiscausedbythedetermining the density of each stratum of soil buoyant force of the water.between the surface and the termination depth ofECP Helical Torque Anchors Technical Service Manual2021 Earth Contact Products, L.L.C.2021-09 Chapter 1 - Page 20 All rights reserve'