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Home / Technical Articles / Design of Overhead Transmission Line Foundation

Tower foundation

The foundation is the name given to the system which transfers to the ground the various steady state (dead) and variable (live) loads developed by the transmission tower and conductors.

Design of Overhead Transmission Line Foundation
Design of Overhead Transmission Line Foundation

Foundations may be variously subjected to compressive or bearing forces, uplift and shear forces, either singly or as a result of any combination of two or three of the forces.

Usually, the limiting design load with transmission line foundations is the uplift load.

Sunrise caps foundation of transmission tower
Sunrise Powerlink Steel Cap Micropile Foundation (Patent Pending)

In this respect, there is a major difference between the design of foundations for transmission lines compared to the design of foundations for most normal civil engineering structures.

Accordingly, the amount of literature describing design techniques for overhead line foundations is relatively small compared to the literature available for more traditional civil engineering foundation design practice.

The selected foundation design for a particular tower must provide an economical, reliable support for the life of the line. The foundation must be compatible with the soil and must not lose strength with age.

With the progressive increase in transmission system voltages there has been a related increase in foundation sizes and it is worth noting that with a typical quad conductor 500 kV line, single leg uplift and ultimate compression loads of 70 or 80 tonnes are usual for suspension towers.

With tension towers, ultimate loads of 200 or 300 tonnes are often developed.

In ground of poor load-bearing capacity the dimensions of foundations become considerable.

In the past, it was often acceptable to ‘over-design’ foundations to allow for uncertainties in the soil characteristics. With the large sizes of foundations for EHV and UHV transmission it is obvious that significant economies can be made in producing foundation designs to exactly match the soil conditions.

Increasingly, transmission lines are routed through areas of poor ground conditions, often for reasons of amenity. This results in the need for the use of special, generally larger, foundations.

The logistical problems of installing large foundations, often in difficult ground conditions, must be taken into account when considering foundation design.

Types of ground

Micropile Foundation for Transmission Line
Micropile Foundation for Transmission Line

The ground in which the foundations are installed can vary from igneous, sedimentary or metamorphic rock, noncohesive soils, sand or gravel to cohesive soil, usually clays. Equally, soils with a high organic content, for example peat, can also prevail. Composite soils will also be found, and examples of these are sandy gravels and silty sand or sandy peat.

Fundamental to the proper design of foundations is an accurate series of soil tests to determine the range of soil types for which the foundation designs will be required. It is good practice to carry out soil tests at a rate of 1 in 5 tower sites.

This is generally sufficient to enable an accurate forecast of the range of soil types to be established.

It should be pointed out, however, that with large towers having 15 or 20 m square bases, occasionally each of the four legs of a tower may be founded in four different types of ground.

Types of foundation

There are seven basic types of tower foundations:

  1. Steel grillage
  2. Concrete spread footing
  3. Concrete auger or caisson
  4. Pile foundation
  5. Rock foundation
  6. Raft foundation
  7. Novel foundations.

Foundation calculations

There are a number of methods of calculation of foundation uplift and bearing capacity. For the purposes of this article, however, we will confine ourselves to a simple approach which must be treated with care. Nevertheless, the methods indicated will give reasonably accurate results for the relatively shallow foundations which are normally employed with transmission line towers.

A shallow foundation is usually defined as one in which the breadth of the pad is greater than the setting depth.

It is usual to calculate the uplift capacity of a foundation as being equal to the mass of soil contained in the frustum developed between the base of the foundation pad and the soil surface.

The angle of the face of the frustum to the vertical is usually designated @ and will vary from 35° to 40° in rock, to 25° in good homogeneous hard clay to zero in saturated noncohesive ground. The soil density will vary from just over 2000 kg/m3 for homogeneous rock to about 1600 kg/m3 for soil with normal moisture content to about 800 or 900 kg/m3 in the case of ground subjected to water uplift.

Methods of calculation of uplift capacity are shown below.

Undercut Pyramid Foundation

Undercut pyramid foundation calculation
Undercut pyramid foundation calculation

Concrete Auger Foundation

Concrete auger foundation calculation
Concrete auger foundation calculation

Resource: High voltage engineering and testing – Hugh M. Ryan (Buy this book at Amazon)

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More Information

Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


    Oct 12, 2022


  2. Daryl
    Jan 11, 2021

    I am looking to see what the number of cubic metres was used in some of the examples above?

  3. svgk Rao
    Sep 05, 2020

    to optimum design of Transmission line towers and foundations

    • svgk Rao
      Oct 13, 2020

      would like to improve my skills for optimum design of transmission line towers and foundations.

  4. Cheema A Razzaq
    Jun 01, 2019

    Designing and esp these foundations vs soil conditions, is possible by group of design engineers working as a joint enterprise. Each tower is a project. So i believe in sharing of knowledge n experience.

  5. Aqeed
    Apr 27, 2019

    can I get any manual or book for foundation dosing of transmission lines towers?
    is there any software for designing?


  6. Zaw Min Oo
    Dec 04, 2018

    What are the relevant IEC/IEEE standards for transmission tower foundation Designing, If IEC / IEEE standards are not there for transmission tower foundation Designing, what are word accepted standards for that?And I would like to know how to calculate foundation design?

  7. kishore C.palo
    Feb 02, 2015

    pl send the manual of design with detail calculation

    • Namrata powar
      Jul 11, 2021

      Please send me the design problems of tower foundation which will improve my technical skill.

  8. Samer AL-lahham
    Dec 21, 2014


  9. Petrus
    Jun 17, 2014

    is concrete blinding of C15 necessary before a structural foundation of a 330kv transmission line foundation

  10. husain
    May 25, 2014

    hiits been days i am searching for step by step method /guide/training/course for electrical design but in vein … kindly help me out …. plz text on my email anyone who own this web ………… i am [email protected]

  11. rala
    May 08, 2014

    What are the relevant IEC/IEEE standards for transmission tower foundation Designing, If IEC / IEEE standards are not there for transmission tower foundation Designing, what are worl accepted standards for that?

  12. tabokhadra
    Sep 25, 2012

    Thanks for you

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