Mechanical Characteristics Of Steel Pipe-jacking With Large Diameter In Complex Enviornment

The steel pipe-jacking has been widely applied in the construction of water supplyand sewage pipeline for its sealing performance, high capacity of inner pressure and lessenvironment impacts. The development trend of the steel pipe-jacking is larger diameter,longer distance and more complex underground condition in the construction field.Remarkable developments have been achived in the construction technology andequipments of steel pipe-jacking, but the theoretical research is obviously lagged to theengineering practice. With the increasing of the diameter and length of pipes, themechanical characteristics of deep-burried steel pipe-jacking in complex underground hasbecome new challenges, including the pipe’s internal force and deformation behavior, thejacking force and its control methods, and the stability of the large diameter pipe. Theseproblems also affect the thickness optimization and construction of pipelines. Based on thenumerical analysis and model tests, the earth pressure, the friction of the pipe-soilinterface, the behavior of curve pipe-jacking, and the stability characters of the steelpipe-jacking are studied. The main contents and conclusions are listed as fellow:(1) The pipe-soil interaction behavior during the process of steel pipe-jacking issimulated by the2D finite element method to study the deformation and earth pressuredistribution of jacked steel pipes. The analysis indicates that steel pipe was horizontalstretched and vertical compressed for the high diameter-thickness ratio and smallerring-stiffness. Such the deformation can be about2~3‰of diameter, which would causeredistribution of the earth pressure. The soil arch effect is reduced by the rebound ofunderlying soil because of the little weight of steel pipes, which caused that the verticalearth pressure at the crown of pipe is larger than the theoretical value and the differencebetween vertical earth pressure and subgrade reaction became less. The horizontalstretching induced lateral soil resistance. Therefore, the distribution of earth pressurebecomes more even and this effect becomes more significant when the ratio of burieddepth and diameter is larger.(2) A whole pipe jacking modeling system is designed by considering theover-cutting effect of the drivage machine and slurry pipe-jacking to investigate the thepipe-soil friction behavior and the efficiency of slurry.The jointed pipes with different sizeare adopted to simulate the over-cutting effect, and the test system includes three parts,pipe-jacking, jacking, grouting and measuring parts. The soil arch and unloading effects caused by the gap of over-cutting reduced the pipe-soil friction. The results of tests showthat the friction coefficient of the pipe-soil interface is less than experience value.Grouting slurry can obviously reduce the frictional resistance during pipe jacking, whichcan be decreased by the different slurries to10~40%of the normal friction without slurry.The premise of reduction effect is the form of mud screen. The amount of slurry groutingin sand which can form mud screen is3~4times of volume of gap.(3) Mechanics characteristic and minimum curvature radius(R) of normal steel pipeand steel pipe with spigot-socket joint in curve pipe-jacking, are studied with numbericalmethod. Results show that normal pipe isn’t suitable for curve pipe-jacking with smallradius. The minimum curvature radius is mainly decided by the length and diameter ofpipe. When the length diameter ratio (L/D) is larger than30, R=80L is recommented, andR=2400D is recommented when L/D is less than30. The steel pipe with spigot-and-socketjoint should be adopted in the curve pipe-jacking with small radius.Its curvature radius isthe ratio of single pipe length and deflection angle. Deflection angle is mainly controlledby the size of spigot-socket joint, including thickness of wood gasket, inner-outerclearance and joint length.(4) Stability of steel pipe-jacking under pipe-soil interactionis studied by beingsimplified as the buckling analysis of steel pipes. Elasto-plastic analysis is proceeded withthe initial imperfection which archived by elastic buckling model analysis. Correctness ofnumberical analysis is proved by comparing the results of uniform axial load andconfining pressure with the theoretical values. With this method, the steel pipe stabilityunder partical axial load and combined load is studied. Under the frictionand confiningpressure, its bucling model is similar to that under confining pressurewhen is small, andsimilar to the model under axial pressurewhen is large.Under the combined loads offriction, confining pressure and jacking force, the ultimate jacking force of bucklingincrease with confining pressure when the pressure is small, but the ultimate jacking forcedecresed sharply when the confining pressure is close to the buckling value.(5) Based on forementioned methods and results, the deformation and stability ofsteel pipe jacking are studied with an actual case pipe-jacking in the complex environment.Deformation of pipe under high earth and water pressure and reasons of buckling accidentare investigated. Then the treatments to deal with the accident are presented and evaluatedby the methods presented in this study. Suggestions about curvature radius and relay wellare given. The discussion and conclusion of the analysis in this case can providereferences for the design and construction of similar projects.