Buckling Research On Pile Foundation Of Bridges In Thick Alluvium

This paper bases on the experiment, and uses the method of the 3-D contact model of finite element software ANSYS 7.1 to analyse and calculate the pile foundation, to calculate the critical buckling load of the pile foundation and then to make the optimized design on the load bearing weight of it.A single pile would have three kinds of destruction patterns when under the axial load, that is, the whole shearing destruction, the pricking destruction and the buckling destruction. As a pile foundation in the thick alluvium overcast, its intensity in holding load layer on the pile end is very large, and its length is long (the ratio of radius to length is great), and the soil around the pile is weak, the paper will calculate the circle buckling load around this character.First, this paper introduces us the dead load experimental test equipment, the increasing load method, and how to confirm the pile foundation's vertical bearing weight through this way. Then the paper researched how the load transmitted from the pile top to end by the mutual action of the pile and the soil. The axial bearing weight research of pile foundation has two ways to confirm, according to soil's bearing capability, or the material intensity of the pile body. In fact, the pile supporting capacity is the result of the mutual action of the pile and the soil. As the action of the pile and soil is complexity, the soil body is asymmetrical and discontinuous, the process of action is made more difficult. The research indicates that using the nonlinear function is more accurate to describe the load transmission process. This article mainly proposed three kinds of mathematical models: ideal elastic and plastic model, double curve model and index model. This paper introduced the establishing process of the index model primarily, through the mechanics, establishes the mathematical model that the pile body load weakened along with the depth, and shows that the process of the load transmitting is related with the rigidity ratio of the pile end and the soil around the pile, and the rigidity ratio of the pile and the soil, and the ratio of radius to length, etc.The paper uses the 3-D finite contact model of the pile and soil to simulate the contact condition, and has discussed separately the critical buckling load of the foundation under no soil body and having soil body. The result of calculation proves that the soil around the pile body can improve the buckling load a lot. At the same time, the quiet strength analysis to the pile foundation shows that the friction of the pile side is similar with the dead load test result. According to the research of the soil strength to the pile body, to get the function formula of the soil strength changed with the depth.The finite element buckling calculation and analysis indicates that the buckling destruction of the pile won't take place. Considering that the depth into rock and the critical buckling load is very large, to make the optimized design to this structure. First, discusses the critical depth into rock, on this basis, carries on the minimum pile radius and the optimized design of the depth into rock. The depth into rock calculation of the test pile indicates the optimized depth is 2.24 meters, it is smaller than the actual depth (11 meters).The paper finally carries on the summary to the research achievement. Generally speaking, using the finite element software ANSYS to carry on the simulation of the 3-D pile and soil action is feasible, but is also has some shortcomings, that is the computation convergence is difficult, and parameter determination must repeatedly trial calculate, which creates the massive repeatedly work.