| The construction industry keeps up with the pace of the times and continues to flourish.In recent years,a series of "high and difficult " infrastructure projects such as high-rise buildings,cross-sea bridges,and subsea tunnels have emerged,which has brought challenges to the bearing capacity of pile foundations.Therefore,pile foundation engineering is constantly innovating,and new pile foundations with the advantages of good bearing capacity,less materials,strong adaptability,convenient construction and high economy emerge in endlessly.The performance of pressure-cast-in-situ pile with spray-expanded frustum is undoubtedly the representative of the new pile foundation.Because pressure-cast-in-situ pile with sprayexpanded frustum has not been published for a long time,there are few studies on the bearing characteristics of the single pile of the pile type,and there are no scholars involved in the study of the bearing characteristics of the pile groups.It is urgent to carry out the research on the bearing characteristics of the single pile and the pile groups of pressure-cast-in-situ pile with spray-expanded frustum,analyze the load transfer mechanism of the single pile body,establish the calculation method of the single pile settlement,and then consider the interaction of the pile group,analyze the bearing characteristics of the pile group,and establish the calculation method of the pile groups settlement.In this paper,field test,numerical simulation and theoretical analysis are used to study the vertical bearing characteristics and deformation mechanism of pressure-cast-in-situ pile groups with spray-expanded frustum.The main work and achievements are as follows:(1)The field static load test of single pile under pressure grouting of pressure-cast-in-situ pile groups with spray-expanded frustum is carried out.The variation rules of pile side friction resistance,pile axial force and pile end resistance of three single piles are analyzed.The ultimate bearing capacity of single pile is determined by combining the load-settlement curve of pile top.Combined with Rayleigh distribution and DSC theory,the preliminary expression of load transfer model of pile side,expanding body and pile end which can reflect the progressive failure characteristics of pile-soil is given by fitting.(2)Using the pile and soil layer data provided by the field test,a numerical model of single pile with reasonable model parameters is established,and the rationality of the numerical model is verified by comparing with the static load test results.The numerical model of two piles is established to analyze the influence of different diameter and spacing of double cone expansion body on the bearing characteristics of two piles.The numerical model of four piles is established to analyze the influence of the double cone expansion body on the bearing characteristics of four piles under the condition of staggered distribution,and to provide reference for the theoretical analysis of pile group in the fifth chapter.(3)Based on the load transfer model of pile side,expanding body and pile end considering Rayleigh distribution and DSC theory obtained from field static load test,the parameter significance of each model is further clarified through theoretical analysis and the parameter determination method is given.Through case verification and parameter analysis,the correctness of the load transfer model and the influence law of each parameter are verified.Combined with the load transfer method,the settlement method of single pile under pressure grouting of jet expansion cone is established,and the rationality of the method is verified by a case.(4)Based on the calculation method of single pile settlement,considering the effect of pile group,the influence of double cone expansion body is analyzed.The calculation method of single pile settlement is extended to pile group by load transfer method.The rationality of the calculation method of pile group settlement is verified by two cases of two piles and four piles. |
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