Consolidation Mechanism And Settlement Prediction Analysis Of CFG Pile Composite Foundation In Xiamen-zhangzhou Area

Compared with the engineering practice experience of CFG pile composite foundation,the theoretical foundation of CFG pile composite foundation is relatively backward.Relying on the related research topics of the construction control of cast-in-situ box girders in deep silt stratum and the first phase of Zhangzhou section of National Highway 319,this paper studies the settlement and control of deep silt and soft soil composite foundation in Zhangzhou area of Xiamen.Based on the study of physical and mechanical properties of muddy soft soil,field foundation settlement observation test,mechanism analysis and model establishment of consolidation settlement of CFG pile composite foundation,Flac3D numerical modeling analysis and applicability analysis of deep muddy soft soil composite foundation,the settlement mechanism analysis and control research of composite foundation in deep muddy stratum are carried out,focusing on consolidation mechanism of CFG pile composite foundation.Research is carried out with settlement prediction and analysis.The main conclusions are as follows:1.On the basis of studying the mechanical properties of silt soft soil in Xiamen-Zhangzhou area,considering the particularity of pile-forming materials of CFG pile composite foundation and relying on the construction process on site,the assumption of impermeability of CFG pile body is put forward,the one-dimensional consolidation equation of CFG pile composite foundation is established,and the analytical solution of the equation is given.2.Based on the process of establishing one-dimensional consolidation equation of CFG pile composite foundation,the three-dimensional consolidation equation of CFG pile composite foundation is deduced theoretically,and the consolidation equation of CFG pile composite foundation is established.Under the condition of axisymmetry,the boundary conditions of the equation are used to prove theoretically that the consolidation of CFG pile composite foundation only occurs in the vertical direction under the condition of impervious pile body.3.Based on the one-dimensional consolidation equation of CFG pile composite foundation,the consolidation equation of double-layer foundation of CFG pile composite foundation is established.The analytical solution of consolidation equation of double-layer foundation of CFG pile composite foundation is given.Combined with the special value method and the control variable method,the consolidation time-degree function of one-dimensional double-layer CFG pile composite foundation is obtained.4.Combining with field settlement observation,the applicability analysis of composite foundation of silt and soft soil is carried out.It is pointed out that the compacted sand pile is not suitable for the treatment of the foundation of silt and soft soil with large thickness,and the cement mixing pile in deep silt stratum is relatively suitable for CFG pile composite foundation.5.The numerical analysis models of CFG piles and cement mixing piles for deep silt soft soil composite foundation treatment with different strip foundations are established.The calculation results show that the CFG pile soft foundation treatment technology has better technical advantages in silt soft soil layer,especially in deep silt soft soil layer(silt layer thickness>4?6m).6.Based on the one-dimensional consolidation equation theory of CFG pile composite foundation,the settlement prediction model of CFG pile composite foundation is established,and the correctness and practicability of the model are verified by the field settlement monitoring data.