The design of foundation for the power transmission line tower is generally controlled by its uplift, compressive and horizontal bearing capacity to the wind load. In the present paper, the practical design formula are proposed based on the mechanical properties obtained from some proto-type field tests. They can evalaute the ultimate bearing capacities and the load-deformation relationships for the three direction loads. The reliability-based design method which wind loads and soil parameters are estimate as random variables is also shown using the developed bearing capacity formulas. Two kinds of probability of failure are considered. One is the probability which the load acting on the foundation will exceed the ultimate bearing capacity, the other is the probability which the deformation of foundation will exceed the allowable displacement for the stability of super structure. the optimization of the caisson type pile is carried out using the actual cost function. The optimum results are compared the results of the conventional design method.
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