Finite-element-based Nonlinear Analysis Of Bridge Piles In Steep Slopes

In order to speed up the construction and economic development of Western China,more and more highway and railway projects have been extended to mountains,which inevitably need to cross the complex topography such as frequent change of slope surface and great change of slope height.Then many roads often drive along the river banks or mountain slopes.The structure forms including halfway bridge and full viaduct are always adopted to cross rivers and valleys,which could reduce the project impacts on the engineering hydrogeological environment,but make many bridge pile foundations located in the high and steep slope.Considering complexity and particularity are reflected in such piles' analysis procedure about engineering environment,load type and bearing mechanism,the current theoretical and experimental researches all exist a number of shortcomings,while the current national and industry standards have not given specific design ideas.Error analysis may be caused if design theories of conventional pile foundations are blindly applied.Therefore,how to design the bridge piles in steep slope reasonably is one of the problems to be solved urgently in mountain road and bridge engineering.In view of this,theoretical researches has been carried in this paper on the bearing mechanism and engineering characteristics,the lateral thrust of the slope and the distribution law of the internal force displacement of the pile,which could further improve the design calculation theory of the bridge pile foundations in steep slope.First of all,the existing researches on bridge pile foundations in steep slope at home and abroad are summarized in this paper,and then the engineering environment and load characteristics of pile foundations are discussed.The influence of the steep slope effect on the engineering characteristics of the pile foundation are emphatically studied,its influencing scope included.Then bearing mechanisms and failure modes of pile foundations under axial load,lateral load and complex load are researched.Secondly,the strain wedge model used in the analysis of the transversely loaded piles is reasonably improved after considering the actual geotechnical conditions of the slope,which is applied to the analysis process of the rear slope of the steep pile foundation.Then calculation method of lateral thrust in three dimensional slope could be proposed,which is suitable for homogeneous soil slope and layered soil slope.Thirdly,based on the basic principle of the finite element method,the pile side friction and the lateral thrust of the slope are analyzed at first,combining with the bearing characteristics of steep slope pile foundation.Corresponding equivalent load vector representation method is obtained then.The "P-?" effect and the soil resistance around the pile are studied next,based on the virtual work principle and the p-y curve method,which could correct the traditional unit stiffness matrix.Then,the nonlinear analysis method of the bridge pile foundations in steep slope considering the "P-?" effect and the pile-of the pile foundation is proposed.Combining with two existing engineering examples,the rationality and superiority of this method are verified.Finally,based on an existing engineering example,the influence of the horizontal load level,the lateral thrust type and the horizontal and pile diameter on the internal force and deformation of the bridge pile foundations in steep slope are discussed.The results show that the increase of lateral load and axial load would increase the pile top deformation and maximum bending moment,while the effect of lateral load is stronger than that of axial load.The effect of the lateral thrust force on the displacement of the pile is stronger than that of thrust force distribution.The internal force and displacement of piles are obviously affected by pile diameter,and the displacement and bending moment of the pile are decreasing with the increase of pile diameter.