Study On The Engineerining Characteristics Of Composite Foundation With CFG Piles-Gravel Piles

Combined composite foundation with two or more different types of pile gets fast development. It has the features of different composite foundations with one kind of pile, and brings them into full play to achieve the coordination of strength and deformation and the organic unity of economic and technology. So it has great advantages to be used in the engineering construction widely. Composite foundation with CFG piles-gravel piles not only has high bearing capacity but also has good drainability. It has a good processing effect to treat the soft ground and eliminate the liquefaction in the liquefied foundation. It was applied in both coastal areas and inland areas in China for good adaptability and economic benefits, social benefits.This thesis that built on the project of Xichang Yuechenglijing is based on the principle of composite foundation with one kind of pile, and proposes the design methods of composite foundation with different lengthes and diameters of CFG piles and gravel piles. It is on the ground of in situ test results and field monitoring results, and makes some analysis and discussion on working performance of this new type of composite foundation. The emphases of this paper are as the follows:(1)Simply summary and analysis the characteristics of the composite foundation with CFG piles and gravel piles, basic theory and the general situation of development, put forward the bearing capacity and settlement calculations theory of this kind composite foundation, make an inquiry into the advantages and disadvantages of each.(2)This paper analyzes p-s curve of load test and the ultimate shaft resistance test of CFG piles based on the deep plate loading test and pile shaft resistance test, in situ test, soil information and ground treatment design. It finds that there is negative skin friction on the CFG piles throughout the construction process through comparative analysis of the stress of the pile, stress of the top pile, soil stress, pile-soil stress ratio, and find that soil pressure of pile top, axial force of the CFG pile and pile-soil stress ratio also increase with the increase of the upper structure load.(3)The finite element software of Midas/GTS is used to simulate the settlement and axial force and pile-soil stress ratio of the composite foundation with CFG piles-gravel piles. According to comparing the measured results with the the results of numerical simulation, the result shows that the finite element analysis precision is able to meet the engineering requirements. On this basis, it studies the law of settlement and pile-soil stress ratio with the increase of the upper structure load. And it analyses the various factors on affecting the reciprocity of the pile and soil, and finds the more reasonable range of the factors of cushion and piles.(4)Using the finite element software Midas/GTS to discuss the engineering properties of the composite foundation with CFG piles-gravel piles for laying a foundation for the future damping characteristics study of the composite foundation with CFG piles-gravel piles.(5)According to the results of in situ field test and finite element numerical analysis, study the rationality of the formula for calculating the ultimate bearing capacity for the current specification.