Numerical Simulation Of Bridge Composite Foundation Based On Pile-soil Interaction

Bridge construction must ensure the overall stability of the foundation under the bridge.The relevant codes all put forward certain requirements on the bearing capacity and settlement of the foundation.In order to meet the corresponding requirements,foundation treatment is required.In this paper,combined with the actual working conditions,the composite foundation of cement mixing piles is selected.In order to make the design plan give full play to the bearing characteristics and settlement characteristics of the cement mixing pile and the soil around the pile,in-depth research is carried out to further optimize the design.This paper takes the Qinhe Bridge on the reconstruction project from Jiaozuo to Wenxian section of National Highway 207 as an example.Based on three research methods of field static load test,theoretical formula derivation and finite element numerical simulation,the vertical bearing capacity of cement mixing pile composite foundation is studied.,The main contents are as follows:(1)This paper summarizes and outlines the bearing principles of composite foundations,the current research status of composite foundations and pile-soil interaction,and considers three methods: field static load test,theoretical formula derivation and numerical simulation,which provides a solid theoretical basis for pile-soil interaction analysis.(2)The load transfer mechanism of composite foundation is introduced,the formula for calculating the settlement of composite foundation is derived,and a comparative analysis is made with the field test.The calculation results show that the settlement characteristic law corresponding to the formula recommended by the two specifications is consistent with the test results,and the calculation results of the Technical Specification for Construction Pile Foundation are more appropriate;the settlement characteristic law calculated by the derived analytical formula changes linearly with the increase of load,and gradually converges to the test value,and the error is relatively large.(3)Combined with the cement stirred pile composite foundation project of Qinhe Special Bridge,the finite element calculation results of single pile composite foundation were compared with the test results to determine the pile-soil interaction parameters in the finite element model,establish the corresponding finite element simulation analysis model,and conduct numerical analysis of the composite foundation with different pile lengths and different pile diameters.The analysis shows that with the increase of pile length,the settlement and load sharing ratio at the top of the pile both increase first and then decrease;the lateral frictional resistance at the top of the pile shows a gradually increasing trend,and the play of lateral friction resistance below the top of the pile is limited,and overall,the highest degree of lateral frictional resistance of the pile is exerted when the length of the pile is 10 m.With the increase of pile diameter,the bearing capacity of composite foundation is greatly improved,the load borne by the top of pile shows a gradually smaller trend,the lateral friction resistance at the top position of pile gradually increases,the lateral friction resistance of pile in the middle and upper part of pile shows a trend of first increase and then decrease,and the development degree of lateral friction resistance of pile in the middle and lower part gradually increases;overall,it seems that the larger the diameter of pile,the higher the development degree of lateral friction resistance.(4)Based on the pile-soil interaction parameters determined by monopile fitting,ABAQUS was used to numerically analyze the composite foundations of cement mixing pile groups with different pile spacing.The analysis shows that the settlement value of the top of the pile at different locations of the group pile is much larger than that of the single pile when the upper part is loaded at the same level,and the settlement of the pile at the middle location is the largest,the side pile is the second and the corner pile is the smallest.The settlement of the top of the pile increases gradually with the increase of the pile spacing,among which,the settlement of the end of the pile increases gradually and the compression of the pile body decreases gradually.The proportion of load sharing at the top of the pile in the group pile composite foundation decreases sharply with the increase of the pile spacing.Comparing the pile top stresses at different locations under the bearing platform,it is found that the corner pile is the largest,the side pile is the second largest and the central pile is the smallest.With the increase of pile spacing,the lateral friction resistance of the middle and upper part of the cement mixing pile increases and then decreases,and the degree of play of the lateral friction resistance of the middle and lower part of the pile shows a gradually increasing trend.