Study On Bearing Characteristics Of Conical Column Foundation Of Transmission Towers In Permafrost Region

With the deepening of China’s Western Development strategy,constructing transmission lines across the permafrost regions is increasing,and the problems of permafrost engineering are unavoidable.In terms of the transmission line engineering through permafrost geology,the tower foundation decides its success or failure.The difficulty of the tower foundation is to guarantee the stability of the frozen soil foundation.The frozen soil has a large effect on the frost heave,and it has obvious frost heave damage on the construction.The tower foundation can produce large tangential heave force in frozen soil,and exert freeze-pulling effect on the foundation,thus affecting the stability of foundation.For this reason,the predecessor designs a new foundation which can eliminate the tangential heave force fully or partly by its own cross-section form,and that is cone pillar foundation.This article takes the Golmud to Lhasa ±400 kV DC transmission line project as the background,and based on the ABAQUS finite element analysis software,the finite element analysis model of the cone pillar foundation of transmission tower and the surrounding frozen soil are established,and the bearing capacity of the cone column foundation in permafrost region is researched.Firstly,the finite element model of freezing and thawing of the permafrost activity layer is based on the establishment of conical column base and its improved type.This paper studies the bearing capacity and failure mode of the cone column foundation in the frozen soil area under vertical pulling load,and discusses the influence of different basic types,different expansion plate’s diameter and different base height factors on the uplift bearing capacity of the foundation.Then,by establishing a three-dimensional finite element model based on cone-column,the paper studied the influence of the pulling performance on the conical column,which is based on the joining of horizontal loads.The displacement of conical column base on vertical uplift load and the simultaneous action of uplift load and horizontal load is analyzed by means of stepwise loading.The reduction coefficient of horizontal force can be recommended for 0.85~0.9 in the process of checking the stability of the frozen Soil foundation,and the ratio of the horizontal force to the uplift force between the 0.15~0.4 is obtained.Finally,the finite element model of conical column foundation in vertical downward pressure loads is established.This paper studies the pressure bearing capacity and its failure mode of the Cone Column Foundation subjected to vertical downward pressure on the frozen soil region,and analyzes the influence of different base surface area and different base height on the compressive bearing capacity of the conical column.The cone-pillar foundation is a kind of pole foundation specially applied in frozen soilregion,and it has less experience in the construction of transmission line engineering,which is relatively insufficient in theoretical computation.In the present article,the numerical simulation method is used to study the bearing features of the bottom and lower pressure of Cone-column foundation,which provides some theoretical basis for the design and calculation of cone pillar foundation in permafrost region,and provides some reference for the related designers.