Study On Pile Soil Interaction Mechanism Of Cement Soil Composite Pile With Concrete Core

Concrete core cement soil composite pile is a new pile type in recent years.It is a composite pile type formed by inserting a certain length of concrete core pile into cement soil mixing pile.The insertion of concrete core pile improves the section stiffness of the pile body.On the one hand,it extrudes the water and soil,making the cement soil soil interface bond more closely;On the other hand,the cement soil at the pile end is compacted.This gives full play to the material strength of concrete core pile,overcomes the problem of "effective pile length" of cement soil mixing pile,and gives full play to the side friction of cement soil soil interface pile.Because of this,composite pile has high cost performance and has been widely used.The research on composite pile has been more in-depth.There is a double-layer load transfer mechanism in composite pile,and cement soil plays an important role as the transition area of load transfer.However,in the current research,the Coulomb shear model is adopted for the middle interface of composite pile,and the influence of relative displacement on load transfer of composite pile is not considered.Moreover,the existing research is mostly limited to the dilatancy of cement soil under laboratory test,and there are few studies considering the dilatancy of cement soil in pile-soil interaction.Therefore,through experimental research,numerical simulation and statistical analysis,this paper studies the pile-soil interaction mechanism of composite pile,and discusses the main influencing factors of vertical bearing performance such as interface and size of composite pile;The multivariate adaptive spline model is established,the statistical modeling of the above influencing factors is carried out,and the importance and prediction formula of the influencing factors of the vertical bearing capacity of composite piles are obtained.The main research contents and conclusions of this paper include:Using the finite element software,based on FORTRAN language and clough Duncan hyperbolic model,the Interface subroutine is compiled and applied to the cement soil soil interface,which is compared with the Coulomb model.The results show that clough Duncan hyperbolic model can better reflect the process of interface shear and the influence of interface relative displacement on the vertical bearing performance of composite pile,and can show the shear dilatancy of cement soil,which is more in line with the reality,which is of great significance for the analysis of composite pile;Through the field static pressure test analysis of composite pile with pile length of17 m,the laws of Q-S curve and axial force curve are summarized.Combined with numerical simulation,the load transfer mechanism of composite pile is studied and analyzed.The research shows that there is a double-layer load transfer mechanism in the composite pile,and the existence of concrete cement soil interface and cement soil soil interface forms a strong medium weak load transfer structure.Such a load transfer structure not only gives full play to the material strength of rigid pile in composite pile;On the other hand,the side friction of composite pile is brought into full play;Through numerical simulation,the effects of core pile length,cement soil strength,cement soil thickness,concrete cement soil interface friction coefficient and cement soil shear expansion on the vertical bearing capacity of composite pile are studied.The results show that the cement soil under the core pile can provide high pile end resistance,so the bearing capacity of cement soil under the core pile is of great significance to the vertical bearing capacity of composite pile.Composite piles with different cement soil strength correspond to different stress modes.For low strength cement soil,composite pile shows the characteristics of friction pile,and when it reaches the limit value of vertical bearing capacity,it is often accompanied by the failure of cement soil soil interface;For high strength cement soil,composite pile shows the characteristics of end bearing friction pile,and when it reaches the limit value of vertical bearing capacity,it is often accompanied by the compression failure of soil under core pile;The multivariate adaptive spline model is established,the influence degree of each influencing factor is analyzed,and the prediction formula of vertical bearing capacity of composite pile is given.The results of statistical analysis show that the bearing capacity prediction formula can better predict the vertical ultimate bearing capacity of composite piles;The length of core pile has the greatest influence on the limit value of vertical bearing capacity of composite pile;The second is the radius of composite pile;The compressive stiffness of section plays a decisive role in the bearing capacity of composite pile.