Research Of Load Model And Mechanical Characteristics Of Bridge Piles In Granite Soil Slope

With the vigorous development of transportation infrastructure construction,a large number of roads and railways have expanded to mountainous areas.At this stage,most lines often use high-pier bridges to pass through mountainous valleys,which will make some bridge pile foundations directly set on the slopes,thus forming a relatively complex and interactive interaction consisting of the bridge superstructure,pile foundations and slopes.Compared with the conventional flat pile foundation,the bridge pile foundation on the slope not only has to bear the transverse axial load and bending moment transmitted from the upper part of the bridge to the pile top,but also may bear the lateral thrust generated by the deformation of the slope.It is more complicated and the bearing conditions are more unfavorable,and it is difficult to find its belonging in the ordinary pile foundation category.Therefore,studying the force characteristics of slope bridge pile foundations under complex loads has important engineering practical value.The thesis is based on the slope pile foundation project of the Yunmao Expressway Monolithic Bridge in Guangdong Province,combined with the research methods of on-site investigation,monitoring and numerical simulation.The study proved the force mode and state of the slope bridge pile foundation in actual engineering,studied the bearing deformation law and stability influence factors of the slope bridge pile foundation under complex load,and proposed the design analysis method of the bridge pile foundation under the condition of high and steep slope.The corresponding optimization design method is given,and the research results can provide a theoretical reference for the design and construction of slope bridge pile foundation under similar geological conditions.The main work and research results carried out in the paper are as follows:(1)Based on the results of field investigation and analysis of relevant engineering case data,the load characteristics and typical failure modes of slope bridge pile foundations are summarized.Under complex loads,the slope bridge pile foundation has the force characteristics of both active and passive piles.The asymmetric distribution of the pile side friction resistance within a certain depth below the pile top and the rock and soil on the downslope side of the pile can provide The weakening effect of the resistance of the foundation is the "slope effect" produced by the slope on the bearing of the pile foundation.Under the influence of "slope effect",the typical failure failure mode of pile foundation is more concentrated reflection under the complex load coupling action and is mainly divided into the following three categories: overall instability failure,pile strength failure failure,and structural displacement failure failure.(2)Carry out on-site monitoring test research of slope bridge pile foundation and prove the force mode and state of slope pile foundation in engineering practice:The thrust of the pile foundation against the upslope is approximately parabolic.The soil pressure on the downslope of the pile foundation may be distributed in a regular triangle or an inverted triangle due to the different deformation modes of the pile body.The side friction resistance provided by the rock and soil within 11 m below the top of the pile foundation on the side of the slope is extremely limited.The point of the maximum bending moment of the pile body under lateral load is located near the junction of the fully weathered layer.With the construction of the superstructure and the vertical load on the top of the pile increases,the bending moment of the pile body will continue to increase.The P-delat effect of the slope bridge pile foundation is significant.(3)The finite element software is used to carry out the analysis of the force characteristics and stability influencing factors of the granite-like soil slope bridge pile foundation under complex loads.Under the action of different load combinations,the bending moment of the single-pile on the slope shows a single-peak curve distribution that first increases and then decreases,and the double-pile has an approximate S-shaped distribution.The bending moment of the pile is most sensitive to the change of the horizontal load on the pile top.The bending moment of the pile body increases after the uniformly distributed load on the top of the slope is applied.The vertical load applied to the pile top as soon as possible has a positive effect on the pile foundation force under the combined load.The slope,the length of the piles in the rock and the thickness of the overburden are the significant factors affecting the stability of the double-pile foundation of slope bridges.In the P-H loading mode,the main feature is that the rock and soil mass on the downslope side of the pile foundation is laterally extruded in the form of passive blocks and the lateral deformation of the pile top is aggravated.In the H-P loading mode,the failure characteristics of the rock and soil at the bottom of the pile reaching the ultimate bearing capacity and the pile foundation piercing and sinking as a whole are dominant.In the P-H-D loading mode,the main characteristics are the instability deformation of the rock and soil on the upslope side of the pile foundation and the structural failure caused by the aggravated pile top deformation.(4)Through the numerical model test study of the vertical bearing of the slope pile foundation,the influence mechanism of the "slope effect" on the vertical bearing of the pile foundation is obtained:when the lack of soil on the side of the pile caused by the slope terrain weakens the lateral restraint of the pile,the limit value of the pile side friction is reduced,and the ultimate bearing capacity of the pile foundation decreases.A method for calculating the ultimate bearing capacity of slope pile foundations under the coupling influence of slope and rock(strongly weathered layer)pile length is proposed,which can provide a reference for related projects.(5)By simplifying the load-bearing model of the pile foundation of the high-steep slope bridge,an equivalent simplified analysis model of the high-steep slope bridge pile foundation is established.The internal force and deformation of pile foundations on steep slopes are calculated and checked by the analysis method of single-row and multi-row piles under lateral load.A comparison and selection analysis of design schemes was carried out based on engineering examples.The optimization design analysis method of steep slope pile foundation considering engineering safety and economy is put forward,which can provide reference for the design analysis of steep slope pile foundation under similar geological conditions.