This code specifies the design and construction guidelines for foundations of overhead transmission line towers and poles. It emphasizes load determination, particularly the critical calculation of uplift resistance using the earth frustum method for various soil and rock classifications.
Code of practice for design and construction of foundations for transmission line towers and poles
Quick Reference Values
Factor of safety against uplift (Normal)1.5
Factor of safety against uplift (Broken wire)1.5
Angle of earth frustum for ordinary dry soil30 degrees
Angle of earth frustum for hard rock0 degrees
Unit weight of dry soil (Standard assumption)1440 kg/m3
Key Formulas
Uplift capacity (Tu) = Wc + We (where Wc is weight of concrete and We is weight of earth frustum)
Practical Notes
Uplift is often the governing criteria for transmission tower foundations, unlike standard building foundations where downward bearing pressure governs.
Using assumed conservative soil parameters instead of actual geotechnical investigation can lead to massively oversized pad and chimney foundations, increasing project costs.
Undercut foundations should only be proposed in stiff, cohesive soils that can remain stable without shoring during excavation.