Types of ground Micropile Foundation for Transmission Line The logistical problems of installing large foundations, often in difficult ground conditions, must be taken into account when considering foundation design. This results in the need for the use of special, generally larger, foundations. Increasingly, transmission lines are routed through areas of poor ground conditions, often for reasons of amenity. 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. In the past, it was often acceptable to ‘over-design’ foundations to allow for uncertainties in the soil characteristics.
In ground of poor load-bearing capacity the dimensions of foundations become considerable. With tension towers, ultimate loads of 200 or 300 tonnes are often developed. 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. The foundation must be compatible with the soil and must not lose strength with age. The selected foundation design for a particular tower must provide an economical, reliable support for the life of the line. 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.Īccordingly, 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. Sunrise Powerlink Steel Cap Micropile Foundation (Patent Pending)
Usually, the limiting design load with transmission line foundations is the uplift load. 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.
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