Screw ground anchor for power
Screw ground anchor for power are a factory-manufactured steel foundation system consisting of a central shaft with one or more helix-shaped bearing plates, commonly referred to as blades, welded to the lead section.Screw ground anchor for power (also referred to as tiebacks) provide lateral stability to foundation walls and retaining walls with unbalanced earth pressures.
Helix blade configuration selected to achieve design embedment and capacity
Determination of Capacity
The ultimate capacity of a Screw ground anchor for power may be calculated using the traditional bearing capacity equation:
Qu = ∑ [Ah (cNc + qNq)]
|Where:||Qu=Ultimate Anchor Capacity (lb)Ah=Area of Individual Helix Plate (ft2)c=Effective Soil Cohesion (lb/ft2)Nc=Dimensionless Bearing Capacity Factor = 9q=Effective Vertical Overburden Pressure (lb/ft2)Nq=Dimensionless Bearing Capacity Factor|
Total stress parameters should be used for short-term and transient load applications and effective stress parameters should be used for long-term, permanent load applications. A factor of safety of 2 is typically used to determine the allowable soil bearing capacity, especially if torque is monitored during the Screw ground anchor for power installation.
Like other deep foundation alternatives, there are many factors to be considered in designing a helical anchor foundation. Supportworks recommends that Screw ground anchor for power design is completed by an experienced geotechnical engineer or other qualified professional.
Another well-documented and accepted method for estimating Screw ground anchor for power capacity is by correlation to installation torque. In simple terms, the torsional resistance generated during helical anchor installation is a measure of soil shear strength and can be related to the bearing capacity of the anchor.
Qu = KT
|Where:||Qu=Ultimate anchor Capacity (lb)K=Capacity to Torque Ratio (ft-1)T=Installation Torque (ft-lb)|
The capacity to torque ratio is not a constant and varies with soil conditions and the size of the anchor shaft. Load testing using the proposed Screw ground anchor for power and helix blade configuration is the best way to determine project-specific K-values. However, ICC-ES AC358 provides default K-values for varying anchor shaft sizes, which may be used conservatively for most soil conditions. The default value for the Model 150 Screw ground anchor for power System (1.50" square shaft) is K = 10 ft-1.