Stability Of Steel Pipe-Jacking Under Complicated Environment In Construction Stage

The stability of large diameter steel pipe-jacking in construction stage is investigated through the theoretical derivation,numerical simulation and case study in the thesis.Finite strip method(FSM)based on the first-order shear deformation plate theory is proposed,which reveals the buckling characteristic of steel pipe-jacking considering the pipe-soil interaction and the effect of longitudinal stiffeners.Meanwhile the effects of annular stiffeners and orthogonal stiffeners have been analyzed by finite element method(FEM)as well as the stability of curved steel pipe-jacking.The control and remedial treatments combining with practical engineering are recommended.The main results can be summed up as following:(1)Finite strip method(FSM)is proposed to analyze buckling of cylindrical shells under axial compression based on the first-order shear deformation plate theory.The Pasternak elastic foundation model is introduced.The numerical solution by FSM of cylindrical shell embedded in the Pasternak elastic foundation is deduced based on energy method and Matlab program is built.Comparing the numerical solution in this thesis and the analytical solutions in the literature,the results is verified to be rational and reliable.(2)The stability analysis models of steel pipe-jacking under axis pressure are built with the pipe-soil interaction.The mechanism of pipe-soil interaction is clarified.The relationship between the geometric parameters of steel pipe-jacking,different parameters of elastic foundation and the critical axial buckling load are respectively summarized through parameter analysis.The result indicates the critical axial buckling loads increase in different degree as the coefficient of subgrade reaction(k)gradually increases in Winkler foundation,while the critical axial buckling loads increase in different degree as shear modulus(G)gradually increases in Pasternak foundation,which can simulate more complicated stratum conditions by considering the vertical compression and shear deformation at the same time.The load curve of super-large diameter and long steel pipe-jacking tends to be convergent when considering the effect of elastic foundation.The local buckling is prone to occur.FSM is still an important means of the analysis.(3)The stability analysis models of different stiffened steel pipe-jacking are built.The effect of the different cross sections and arrangement of longitudinal stiffeners on steel pipe-jacking is studied based on FSM,while the effect of annular stiffeners and orthogonal stiffeners has been analyzed based on FEM.It turned out that the U-beams have better bending torsional performance than T-beams as stiffeners.Results suggest that the annular stiffener interval to the pipe diameter Is/d<2 is used for large diameter steel pipe-jacking and orthogonal stiffeners is used for super-large diameter steel pipe-jacking with Is/d?1.Four longitudinal stiffeners are uniformly distributed.The orthogonal stiffener can significantly improve the stability of steel pipe-jacking under axial compression in construction stage.Its effectiveness is presented by practical engineering.(4)The stability analysis models of curved steel pipe-jacking are built.The relationship between the different radiuses of curvature and the stability of axial compressed steel pipe-jacking is revealed based on FEM.The effect of orthogonal stiffeners is discussed.It suggests the critical axial buckling loads significantly decrease as the radiuses of curvature decrease.The change of the radius of curvature has little influence for large diameter curved steel pipe-jacking under axis compression.But it has great influence for super-large diameter curved steel pipe-jacking.Considering orthogonal stiffeners,it has greater influence for large diameter curved steel pipe-jacking.Local and global buckling occur simultaneously in curved steel pipe-jacking with different diameters.The mixed buckling mode will gradually disappear as the radius of curvature increases.The results are in accordance with practical engineering.It can be effectively used for evaluate the risk of buckling of curved steel pipe-jacking.