Design The Foundations of Transmission Towers

Foundation Design Definition

The foundation design for transmission towers involves creating stable bases using RCC, designed to withstand various loads and soil conditions.

Different Soil Types

Transmission tower foundations must adapt to different soil types like black cotton soil, fissured rock, and sandy soil, each requiring unique construction methods.

Dry Fissured Rock

Foundations in dry fissured rock need special considerations like undercuts and anchor bars for stability.

Stability Factors

Ensuring stability against sliding, overturning, and buoyancy is crucial, with specific safety factors for normal and short circuit conditions.

Protective Measures

Additional protection for foundations is necessary in aggressive soils to prevent damage and ensure longevity.

Design of Foundation of Transmission Towers in Different Soils

• All foundation shall be of RCC. The design and construction of RCC structures shall be carried out as per IS:456 and minimum grade of concrete shall be M-20.

• Limit state method of design shall be adopted.

• Cold twisted deformed bars as per IS:1786 or TMT bars shall be used as reinforcement.

• Foundations shall be designed for the critical loading combination of the steel structure and or equipment and/or superstructure.

• Protection should be provided to foundations when needed, especially for aggressive soils like alkaline soil, black cotton soil, or any soil harmful to concrete foundations.

• All structures must be checked for stability against sliding and overturning during construction and operation under various load combinations.

• When checking for overturning, consider the weight of the soil above the footing, but do not include the inverted frustum of the earth on the foundation.

• Base slab of any underground enclosure shall also be designed for maximum ground water table. Minimum factor of safety of 1.5 against bouncy shall be ensured.

• Tower and equipment foundations must have a safety factor of 2.2 for normal conditions and 1.65 for short circuit conditions to prevent sliding, overturning, and pullout.