| In engineering construction,especially in the city,the increasing number of large buildings leads to the increasing area of the site required for the foundation pit,and the excavation depth of the foundation pit is getting deeper and deeper.This has higher and higher requirements for the supporting structure in the foundation pit.At present,a single supporting form is difficult to meet the design requirements of the project,and the composite supporting structure system,such as the supporting structure system composed of two or more supporting structures is a good choice currently.Through statistics and investigation,the supporting structure composed of three supporting forms of pile,anchor and brace has been practiced in a large number of deep foundation pit projects and has been successfully applied.For this more complex composite supporting structure system,because of its many influencing factors,and the level of theoretical research also lags behind the requirements of engineering practice,there is no more complete or mature design theory at present,so the theoretical calculation value of the deformation of the composite support ing structure system will differ greatly from the measured value.Based on what has said above,this paper introduces the application of pile-anchor-brace composite supporting structure in practical engineering,and understands the deformation of the support system at first.Secondly,on the basis of previous studies,starting from the overall deformation of the pile-anchor-brace,its working mechanism and deformation characteristics are expounded,and the maximum horizontal displacement formula of the pile top in the pile-anchor-brace composite structure is derived by using the minimum potential energy principle.Then,the stress of pile-anchor,pile-brace and pile-anchor-brace supporting system are analyzed,and the deformation coordination relationship between each system is obtained respectively.Finally,based on th e actual project,using PLAXIS 3D finite element software,the supporting effect of pile-anchor-brace composite structure is analyzed and studied.The specific research contents and conclusions are as follows:(1)The application of pile-anchor-brace composite supporting structure in deep foundation pit engineering is introduced.The corresponding data of the supporting system are obtained through field monitoring,and the deformation of the supporting structure in the system is discussed.It is considered that the practical application of the project is successful.It can not only provide reference for other similar projects,but also provide basis and guarantee for the subsequent theoretical study of the deformation characteristics of pile-anchor-brace composite supporting structure.(2)Through the analysis of the deformation characteristics of the pile-anchor-brace composite support structure system,the energy equations of the pile,anchor,brace,crown beam and other structures are obtained respectively.All the above energy equations are superimposed and summarized to make them the total energy of the system.Then,the maximum horizontal displacement of the pile top can be obtained by using the principle of minimum potential energy.At the same time,th e overall horizontal displacement curve of the pile-anchor-brace support system can be obtained by using the results.Finally,the rationality of the theoretical formula is verified by an example.(3)Based on the stress analysis of pile-anchor supporting structure system,and considering the influence of group anchor effect,the deformation coordination formula of pile-anchor supporting structure is obtained.At the same time,the calculation of anchor tension design value under pile-anchor deformation coordination is analyzed.According to the deformation coordination formula of pile-anchor,the deformation coordination formula of pile-brace supporting structure is obtained,and the stiffness coefficient of some types of support fulcrum is summarized and analyzed.The deformation coordination formula of pile-anchor-brace supporting structure is obtained by superimposing the deformation coordination conditions of pile-anchor and pile-brace.Finally,the theoretical formula is verified by the engineering example in this paper.(4)Combined with the actual project adopted in this paper,the finite element model is established by PLAXIS 3D numerical simulation software.Under the same excavation condition,the working characteristics of pile-anchor supporting structure,pile-brace supporting structure and pile-anchor supporting structure are systematically analyzed.It is found that the pile-brace supporting system has the most strict control over the deformation of foundation pit,the deformation control ability of pile-anchor supporting system is the worst,and the pile-anchor-brace supporting system is between the two. |
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