Calculating Capacity

  • Individual Bearing method
    • This method assumes a bearing failure of the soil supporting each helix
    • Bearing capacity varies as a function of the soils angle of internal friction and the soil density description
    • Capacity is determined by calculating the ultimate bearing resistance of the soil at each helix and multiplying it times the projected area of the helix. The total capacity of a multi-helix system is then the sum of the individual capacities.
  • Torque correlation method
    • This method makes use of the empirically-derived relationship between installed capacity and the torsion resistance encountered during installation.
    • The empirical torque is related to friction during installation. It is not a unique number and it varies from 3 to 20 depending on the shaft size and shape, soil properties and numbers of helix plates and their sizes.