Application Of CFG Pile In Soft Soil Foundation Treatment Of High-speed Railway

At present,China’s high-speed railway is in the stage of rapid development,and the construction of high-speed railway has the characteristics of heavy tasks,long line mileage and large spanning area.The high-speed operation of high-speed railway requires high stability of its foundation,but China has a vast territory and widely distributed soft soil foundation,so many high-speed railway constructions are bound to appear in soft soil foundation areas.In view of this soft foundation,a large number of engineering examples adopt CFG pile composite foundation for reinforcement treatment.Compared with conventional bored piles,CFG pile composite foundation not only has the advantages of high strength,short construction period and high efficiency,but also uses fly ash in pile concrete preparation to avoid waste of resources and has higher engineering economy.However,many engineering practices show that the mechanical properties of composite foundation strengthened by CFG pile have not been fully developed,and its calculation theory still has some shortcomings.Therefore,aiming at the soft foundation treatment in the construction of high-speed railway,this paper takes the section DK69+420.77 ～DK72+571.30 of Weilai high-speed railway as the engineering background,and analyzes and studies the CFG pile reinforcement mechanism,calculation theory,field test and numerical simulation,etc.The main contents of this paper include the following aspects:(1)Summarize the research and development status of CFG pile in theory,test and numerical simulation at home and abroad,and summarize the main problems existing in CFG pile at present.This paper analyzes the bearing characteristics,strengthening mechanism,bearing capacity and settlement calculation methods of CFG pile,demonstrates the high efficiency of CFG pile in strengthening soft foundation,and summarizes the advantages and disadvantages of each calculation method in engineering application.(2)Combined with the actual project,the soft foundation reinforcement scheme is compared and selected,and the CFG pile reinforcement scheme is determined.According to engineering geology and theoretical calculation,the applicability of main parameters of CFG pile is designed.After the foundation is reinforced with this parameter,the static load test of single pile bearing capacity,low strain test of pile integrity and static load test of single pile composite foundation are carried out,and the test results are evaluated and analyzed.(3)The static load test of CFG pile composite foundation is simulated by MIDAS GTS NX finite element analysis software,and the settlement results of test and numerical simulation under different loads are compared and analyzed,which demonstrates the reasonable effectiveness of numerical simulation under this condition,and provides effective support for subsequent related research work.(4)Using MIDAS GTS NX finite element analysis software,a three-dimensional model of CFG pile strengthening soft foundation is established.Under the train cyclic load,the necessity and effectiveness of CFG pile treatment for soft foundation are demonstrated by simulation comparison before and after reinforcement.The main factors(pile arrangement,pile length,pile strength,pile diameter,pile spacing,cushion thickness)that affect the foundation reinforcement effect are studied by using the control variable method,and the influencing rules of each factor are analyzed.On this basis,the reinforcement parameters of CFG pile composite foundation are optimized by combining theoretical calculation.