Study On Bearing Capacity And Settlement Characteristics Of Soft Soil Foundation Reinforced By PHC Piles In High Speed Railway In Northern Anhui

At present,China’s high-speed railway is in a period of rapid development.The construction of high-speed railway is different from the traditional railway construction,and puts forward higher requirements for railway design,construction and post-construction settlement and foundation bearing capacity.For high-speed railways constructed in soft soil areas,due to the special engineering properties of soft soils,it is necessary to eliminate the bad characteristics of soft soils through reasonable ground treatment methods to meet the requirements of high-speed railway bearing capacity and post-construction settlement.Prestressed high-strength concrete pipe pile(PHC)is a precast concrete member developed on the basis of modern high performance concrete(HPC)and prestressing technology.It has high bearing capacity,good bending resistance,wide application range and sinking.The pile quality is reliable and many other advantages,and it is widely used in foundation treatment.After the PHC pile treatment,the bearing capacity of the composite foundation is obviously improved,and the settlement deformation of the foundation is also effectively controlled.Although the foundation technology of PHC pile reinforcement treatment has been widely used in practical engineering,its theoretical research still lags far behind engineering practice.This paper mainly relies on the foundation treatment project of Shang-He-Hang High-speed Railway Lumiao Station,and studies the bearing and settlement characteristics of soft soil foundation strengthened by PHC piles.The main work is as follow:(1)Through the reading of related literatures,the bearing capacity and settlement characteristics of PHC pile composite foundation are discussed on the basis of composite foundation theory,and the settlement calculation theory of PHC pile composite foundation is summarized.(2)A large number of indoor geotechnical tests were carried out on the foundation soil of the test section to obtain the physical and mechanical indexes of the foundation soil.The physical and mechanical properties of the foundation soil and the spatial distribution of each index are analyzed and analyzed.The basic engineering characteristics of the foundation soil are revealed to provide basis for engineering design and related numerical calculation.(3)Based on the field test of PHC piles,the load-settlement relationship curve of single-pile composite foundation is obtained by static load test,and the bearing capacity of single-pile composite foundation is determined.Through the static penetration test,the characteristic values of the penetration resistance and bearing capacity of the base soil layer are obtained,and the characteristic value of the ultimate bearing capacity of the PHC pile is estimated.Through standard test,the standard penetration hammer number of soil between pile and natural foundation is obtained,and the characteristic value of bearing capacity of PHC pile composite foundation is estimated by reference to relevant empirical formula.Through the foundation soil reinforcement test,the soil compaction coefficient and dry density of the two piles and the physical and mechanical indexes of the foundation soil before and after the foundation consolidation treatment were obtained.(4)The finite element calculation software MIDAS/GTS was used to establish the PHC single pile and group pile composite foundation model,and the numerical analysis of soft soil foundation was carried out by PHC pile reinforcement treatment.The settlement deformation and load transfer law of composite foundation with simulated vertical load are obtained.The settlement law of pile body and the distribution of axial force and lateral friction of pile body are obtained.The settlement characteristics and load transfer mechanism of PHC pile are analyzed.Finally,a single variable method is used to consider the effects of different applied loads,pile lengths,cushion thickness and cushion modulus on the bearing and settlement characteristics of PHC pile composite foundation,and reasonable design suggestions are proposed.