Skip to main content
CalcStack

Helical Screw Pile Ultimate Axial Capacity Calculator

Helical screw piles and anchors provide rapid foundation support for solar farms, transmission towers, and underpinning works without spoils excavation.

Number of circular helical plates along the lead section (typically 1 to 4).

Mean diameter of the steel helix plates (typically 200 to 400 mm).

Cohesive shear strength of fine-grained soil stratum.

Internal friction angle for sand and granular bearing layer.

Bulk or submerged unit weight of overburden soil.

Total vertical embedment depth from grade to topmost helix plate.

Calculated Result
246.4 kN

Allowable Axial Compressive Capacity

Allowable Axial Capacity (Q_all, FS=2.0)

246.4 kN (55.4 kips)

Total Ultimate Axial Capacity (Q_ult)

492.8 kN

Frictional Overburden Bearing

454.6 kN

Cohesive End-Bearing Resistance

38.2 kN

Total Helical Plates Area

0.212 m² (3 plates @ 0.30m)

Calculation Breakdown

  1. Total Helix Bearing AreaA_total = n × (π × D_h² / 4) = 3 × [π × (0.3 m)² / 4] = 0.212 m²
  2. Individual Plate Bearing Capacity EvaluationQ_ult = Σ [ A_h × (c N_c + σ'_v N_q) ] = 38.2 kN (cohesive) + 454.6 kN (frictional) = 492.8 kN
  3. Allowable Geotechnical Working LoadQ_allow = Q_ult / FS = 492.8 kN / 2.0 = 246.4 kN

Helical Pile Axial Capacity (kN)

Interactive visualization based on your current inputs

Capacity (kN)
0.064127191255Cohesive ComponentFrictional ComponentTotal UltimateAllowable (FS=2)ComponentCapacity (kN)

What Is the Helical Screw Pile Ultimate Axial Capacity Calculator?

The Helical Screw Pile Ultimate Axial Capacity Calculator predicts compressive working and ultimate load resistance for deep screw foundations.

How Does the Helical Screw Pile Ultimate Axial Capacity Calculator Work?

It computes the projected surface area of all helical plates and mobilizes cohesive end-bearing and frictional overburden stress resistances.

Helical Screw Pile Ultimate Axial Capacity Calculator Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

Q_{ult} = \sum_{i=1}^n A_{h,i} \left( c N_c + \sigma'_v N_q \right), \quad Q_{allow} = \frac{Q_{ult}}{2.0}

Terzaghi / Meyerhof deep foundation plate bearing method summing load resistance across individual helical plates.

How to Use the Helical Screw Pile Ultimate Axial Capacity Calculator

  1. Select number of helical plates and average diameter.
  2. Enter soil shear strength parameters (cohesion and friction angle).
  3. Input overburden depth and unit weight.

Step-by-Step Example Calculation

Triple-Helix 300mm Pier in Silty Sand

Input Values:

numberOfHelices:3
averageHelixDiameterMm:300
soilCohesionKPa:20
soilFrictionAngleDeg:32
soilUnitWeightKNPerM3:18.5
helixEmbedmentDepthM:5
Worked Steps: Delivers 254.8 kN ultimate axial compressive capacity (127.4 kN allowable load at FS = 2.0).

Understanding Your Result

Allowable Axial Capacity: Safe structural working load with FS = 2.0.

Ultimate Capacity: Total geotechnical failure load.

Helix Area: Combined horizontal projected bearing footprint.

Factors That Affect the Result

  • Dense granular strata yield high N_q factors, rapidly multiplying capacity.
  • Deeper embedment increases effective overburden stress σ'_v.

When Should You Use This Calculator?

  • Utility-scale solar tracker posts, foundation underpinning, modular housing, and telecommunication tower guy wire anchors.

Assumptions & Limitations

  • Assumes individual plate failure mechanism without cylindrical shear slip between closely spaced plates.

Frequently Asked Questions

Calculation Accuracy & Reference Note

Conforms to ICC-ES AC358 and Canadian Foundation Engineering Manual guidelines.

Related Calculators

Explore more tools and calculators in Math Calculators

Soil Nail Wall Pullout & Tendon Sizing Calculator

Calculates ultimate and allowable pullout resistance along the grout-ground interface, steel tendon yield strength, and governing limit state per FHWA GEC 7.

Culvert Outlet Riprap Apron Erosion Protection Calculator (HEC-14)

Calculates median stone size (D₅₀), apron length, downstream width, and blanket thickness for culvert outlet scour protection per FHWA HEC-14.

Dry Extended Detention Basin Drawdown Orifice Calculator

Calculates the required release orifice diameter, average discharge rate, and drawdown velocity for stormwater dry extended detention basins.

Broad-Crested Rectangular Weir Discharge Calculator (ISO 3846)

Calculates open channel discharge capacity, critical depth, crest flow velocity, and discharge coefficient for broad-crested rectangular weirs.

SWMM Urban Catchment Peak Runoff & Infiltration Calculator

Calculates peak stormwater runoff, Horton infiltration abstraction, depression storage losses, and composite runoff coefficients for urban subcatchments.

Flexible Pavement 18-kip ESAL Traffic Loading Calculator (AASHTO)

Calculates 20/30-year cumulative 18-kip Equivalent Single Axle Loads (W₁₈), compound traffic growth factors, and AASHTO design lane classifications.