Study On Floatation Response Of Buried Pipeline Induced By Soil Liquefaction

The seismic hazards show that the soil liquefaction is one of the main reasons that buried pipelines are damaged. During an earthquake, the buried pipelines in liquefied soil suffer the action of floatation force induced by soil liquefaction in addition to the vibration due to the seismic wave. Sometimes this floatation makes the pipelines come out of the earth's surface and get damaged.In this paper, the floatation response of buried pipeline induced by soil liquefaction is studied numerically. The damage phenomenon of pipelines and the main influence factors in the earthquake are introduced briefly, and current state of research on the buried pipelines in soil liquefaction is discussed. To study the floatation response of buried pipelines in liquefied soil, the beam model based on the beam theory on elastic foundation is used for the pipelines buried in non-liquefaction and liquefaction area. The formulae are deduced for the floatation response of buried pipelines due to the soil liquefaction on the basis of Virtual Work, considering the effects of nonlinear soil constraint and nonlinear force of floatation. The nonlinear increment element iteration method through equivalent linearization is set up and the validity of the method and procedure is verified using a simple beam theoretical result. Some problems are discussed such as how to choose adequate parameters and how to deal with boundary condition. Based on the method, the floatation response of buried pipeline in uniform liquefied soil is studied and the effects of the initial deformation, the length of liquefied area, and the axial force on the pipeline are considered. Moreover the floatation response of buried pipeline in three kinds of heterogeneous liquefied soil is studied considering these effects also. Some calculation results are given.The study get some conclusions: the floatation displacement and the bending strain will increase with the axial force acting on the pipelines; the initial deformation has little effect on the floatation response of buried pipeline; the length of liquefied area influenced the floatation response of buried pipelines obviously, and the floatation displacement and the bending strain increase with the length of liquefied area; the spring stiffness of liquefied soil affects the floatation response of buried pipeline obviously and the floatation response will be increased when the spring stiffness of liquefied area reduces; when the length of liquefied area is smaller than 40 meters, the floatation response of buried pipelines is very small. To a long liquefied area, the treatment of the soil in the middle part of the area will reduce the length of the liquefied area, and can reduce the floatation displacement and bending strain of the buried pipelines greatly.Finally the summary is made and some problems needs further study in the future are discussed.