Stability Research & Numeric Analysis Of The Oblique Inserting Iron Tower Foundation

The oblique inserting foundation of iron tower for electric power as a new type of foundation, is widely used in the design of transmission lines because it can bear the external force rationally and can save a large amount of materials . Yet, the design theory of this foundation is not perfect , neither is the application experience. At present, "Designing Techniques and Regulations for foundation of transmission lines" (SDGJ-84,1984)is still used to guide the design of iron tower foundation. For this technical criterion has not offered the relevant criterion to the design of the new-type foundation, most designs are based on the accumulation of experience, lack of certain theoretical support. Therefore, considering the deficiency of the existing regulation, this paper carries on a deep analysis and study in the stability of the new-type iron tower foundation under different combined loads. The detailed account is as follows:First, on the basis of existing theory and literatures, this paper chooses a proper three-dimensional sliding mode through a certain simplification and assumption. Then adopting the upper-bound method of limit analysis, the paper analyses the stability of this kind of foundation under the horizontal and compression forces and derives the formula of ground bearing capacity. Second, according to the theory of acting-on-together between the foundation and the ground, it analyses the influence on the foundation stability when the soil body around the foundation appears plasticity at a limit state. It in turn proposes a new appraisal method about stability of iron tower foundation when it is under the most disadvantageous loads ( uplift and horizontal forces). And using the upper-bound method of limit analysis similarly, it analyses the limit bearing capacity of soil in front of the pillar and gives the corresponding calculation formula .In addition, based on the theory of acting-on-together between the foundation and the ground, this paper, using the large-scale numeric analysis software FLAC-3D, sets up the actual models of the foundation. And through the displacement distributions and the developing plasticity zones of the ground, which are obtained from numeric calculation results under the different combined loads, it analyses the ground bearing capacity and the foundation stability of the iron tower.Finally, using the calculation formula of this paper, we analyses the stabilities of three kinds of typical foundations in the Nan Long project of circuit of 500 kilovolts designed by Electric Power Design and Consultation Limited Company of Sichuan Province. The results indicate the numeric analysis accords well with the results of calculation formula of the paper, and the foundations are stable under the design loads.