Multi Circle Composite Tube For Super Large Diameter Deep Foundation Pit Study On Mechanical Properties Of Frozen Wall

In order to meet the needs of national economic development for underground space,large-scale deep and large foundation pit construction projects will appear in the future,especially when large-diameter excavation in the topsoil layer requires freezing and reinforcement methods to improve the ground around the excavation area.At present,domestic and foreign researches on frozen walls have started early and many research results have been obtained,but they are mainly concentrated in coal mine construction projects.In municipal engineering,the diameter of the foundation pit is large.According to the frozen wall design theory in coal mine construction engineering,a continuous thicker frozen wall is required,which is difficult to achieve in urban construction with dense buildings.It is proposed to use a multi-circle thin-walled combined cylindrical frozen wall structure to optimize the freezing design,that is,the frozen wall structure contains a circle of unfrozen soil to meet the requirements of engineering construction,while meeting the needs of economic rationality and environmental control.Compared with the continuous freezing wall structure,the strength and stability of the multi-circle composite cylinder freezing wall structure are theoretical and technical problems that need to be studied and solved urgently.In this thesis,theoretical analysis,numerical simulation,large-scale physical simulation test and other comprehensive research methods are used to study the mechanical characteristics of multi circle thin-walled composite tube frozen wall of super large diameter deep foundation pit.The research content considers the engineering conditions of super large diameter deep foundation pit and the engineering characteristics of multi circle thin-walled composite tube frozen wall,and obtains the mechanical characteristics of super large diameter deep foundation pit frozen wall formed by multi circle freezing.The thesis constructs a theoretical calculation model of the frost heave force generated by the freezing process around the circular hole under the plane strain model,and proposes a variable model of the fixed point of the freezing circle displacement,and realizes the gradual formation process of the thin-walled frozen wall frost heave through iterative calculation.The stress and displacement caused by frost heave and excavation of the frozen wall are obtained,and calculation examples are provided,which provide a useful reference for the design of the frozen wall of the multi-ring combined cylinder.Using the research function of the temperature-stress field sequence coupling of ANSYS finite element analysis software,the plane strain model of frozen soil and unfrozen soil and the axisymmetric vertical excavation model are established to study the force law of the frozen wall of the multi-circle composite cylinder.In this thesis,the mechanical characteristics of single-circle,two-circle,and three-circle composite cylinder freezing wall are studied respectively,and the influence of the geometric characteristics of the composite cylinder freezing wall on the stress and deformation of the freezing wall is discussed.Self-designed and developed a multi-circle thin-wall composite cylinder freezing wall simulation test system,which can simulate the temperature field of the multi-circle thin-wall composite cylinder freezing wall,the overall deformation law of the freezing wall and the freezing wall stress law after excavation.The simulation test is carried out in accordance with the construction mechanics characteristics of freezing engineering,soil consolidation-pressurized freezing-excavation and other processes.The temperature field distribution characteristics of the multi-circle frozen wall of the super large diameter deep foundation pit and the mechanical influence law of the frozen wall obtained by the research can provide a theoretical basis for the construction of the super large diameter deep foundation pit.It has certain theoretical and engineering practical significance,important economic value and social value.This thesis has 106 pictures,43 tables and 123 references.