Analysis Of The Working Mechanism Of Composite Foundation And The Buckling Load Of Rigid Pile

Long-short-pile composite foundation is a new type of foundation developed in China recently year .In this paper, firstly working mechanisms of long-pile, short-pile and cushion are analyzed under vertical load. Secondly the analysis model of load sharing character was set up according to coordinated act of long-pile, short-pile and cushion. With this model load transferring differential equation was made by adopting some supposes. Then the analytic solution of pile and soil foundation's load are derived and then, analyzing the influence of some parameters, such as the length and the elastic modulus of the long-pile and the short-pile, the elastic modulus and thickness of the cushion est, to pile and soil foundation's load share. Thirdly the formula of pile's duckling load was derived with Galgin method when the pile in the single uniform soil foundation and two pieces of soil foundation .The influences of coefficient of soil foundation, the proportion of the part pile in soil to the whole pile and the pile's the length to the buckling load .The findings of this paper are provided to true in some degree by comparing with other conclusion .The major conclusions of this paper are followed;(1)The share load of long-pile is raised when the elastic modulus and the length of long-pile and the elastic modulus of the cushion enlarge but reduced when the elastic modulus and the length of short-pile enlarge. But the patter of the short-pile and the soil foundation are contrary to the long-pile in the same conditions. So different measures can be adopted in design to achieve the same effect, but adapting the thickness and the elastic modulus of the cushion is the best one to adjust the load share.(2) When the elastic modulus of the short-pile is bigger, adapting the elastic modulus of the long-pile to adjust load share is better than that when the elastic modulus of the short-pile is smaller.(3) When the length of the long-pile is smaller, the influence of short-pile's length to load share is more outstanding than that the long-pile's length is larger. When the length of long-pile is bigger than 40m,the influence of the short-pile to load share is very weak.(4) When the coefficient of soil foundation enlarges, the buckling load raised also. When the proportion of the pile in soil to the whole is smaller than 0.1 or larger than 0.8, the influence of the coefficient of soil foundation to the buckling is veryweak, in other condition, the influence of the coefficient of soil foundation to the buckling is outstanding.(5) The buckling load of pile in long-short-pile composite foundation has some difference to that in single uniform soil foundation because of the influence of the short-pile. When the coefficient of soil foundation under the short-pile is something big, the influence of the short-pile to the long-pile's buckling load is very weak, on the contrary, it is strong.