Foundation Of Transmission Line Towers

ABSTRACT

Nigeria is one of the countries with large population and the electricity supply is need of this population creates requirements of a large transmission and distribution. In transmission line towers, the tower legs are usually set in concrete which generally provides good protection to the steel.

In transmission line towers, foundation plays an important role in safety and satisfactory performance of the structure as it transmits the load from structure to earth. In present study, a typical 220 KV double circuit transmission tower is considered, for designing the foundation manually with respect to loadings viz downward, uplift and side thrusts. A proposed site was considered situated on the banks of river analyzed and design the transmission tower in this work and on the basis of analysis results and soil investigation reports the three forces are validated in the designing of foundation manually.

In this paper, the tower foundation is designed manually and a methodology is obtained for designing the foundation as per conditions malleably

CHAPTER ONE

1.1                                                           INTRODUCTION

Foundations of any structure plays on important role in safety and satisfactory performance of the structure as it transmits the loads from structure to earth. The towers legs are usually set in concrete which generally provides good protection to the steel. Without having a sound and safe foundation, structure cannot perform the functions for which it has been designed. Therefore, the importance of foundation needs not to be over emphasized.

The sizes of transmission line tower are increasing because of the present day high, extra high and ultra-high voltage transmission, resulting in heavier loads and as such requiring bigger and heavier foundations. A large number of foundations are normally required in any transmission line project. Thus, the total cost of foundation in a transmission line project becomes quite substantial. Apart from the financial aspects, past records show those failures of tower foundations have also been responsible for collapse of towers. These failures have usually been associated with certain deficiencies either in the design which certainly depends on the types of loadings on the foundation or classification or construction of foundation. Many times, foundations cast are over safe because of inappropriate classification, resulting in wastage of resources. From engineering point of view, task of design and selection of most suitable type of tower foundation is challenging because of the variety of soil conditions encountered enroute the transmission line and remoteness of construction sites. The foundations in various types of soil have to be designed to suit the soil conditions of particular type.

1.2                                                OBJECTIVES OF THE STUDY

• To study the types of foundation as per the desired loadings on different types of soil
• To study the designed parameters and checks required for designing the transmission tower foundation.
• To designed the safe and durable foundation on the proposed site.
• Improved efficiency through extension of the planning horizon.
• Design, construct and maintain foundations to minimise lifecycle costs while meeting required levels of performance.
• Minimise cost of capital projects through long term resource planning of service providers.
• Minimise cost of works by packaging work into blocks of consecutive structures wherever possible.

1.3                                                   SCOPE OF THE STUDY

Foundation of any structure plays an important role in safety and satisfactory performance of the structure as it transmits mechanical loads of the electrical transmission system to earth. A transmission structure without having a sound and safe foundation, it cannot perform the functions for which it has been designed. The foundations in various types of soils have to be designed to suit the soil conditions of particular type. In addition to foundations of normal towers, there are situations where considering techno-economical aspect for special towers required or river crossing which may be located either on the bank of the river or in the mind stream or both, pile foundation may be provided.

1.4                                                 PURPOSE OF THE STUDY

Failures on transmission line towers are usually associated with extreme weather events. The purpose of this work is to design transmission towers that withstand severe climatic loading conditions, and to monitor and maintain them to ensure satisfactory performance.

1.5                                            SIGNIFICANCE OF THE STUDY

This study permits correct operation and maintenance of foundations is essential for the safe and reliable transport of electricity from generators to customers and distribution networks across public and private land.

1.6                  SOIL PARAMETERS FOR DESIGNING THE FOUNDATIONS

The following parameters are required.

• Limit bearing capacity of soil.
• Density of soil.
• Angle of earth frustum.

1.7                                     TYPES OF LOADS ON FOUNDATIONS

The foundations of towers are normally subjected to three types of forces. These are:

1. The compression or download thrust;
2. The tension or uplift;

• The lateral forces or side thrusts in both transverse and longitudinal