Tunnel by digging is accepted as one of the most effective methods for river-crossing in pipeline constructions, especially for large river-crossing. Pipeline is often installed on a series of low supports in the tunnel underneath river. Generally, pipeline in tunnel experiences various loadings during service period due to operational and environmental conditions, such as operation pressure fluctuation, external temperature variation or support damage. Under these loadings, high stress and huge longitudinal force may be accumulated in pipe that may eventually result in pipeline elongation or bending. These kinds of deformation have been found in pipelines in some river crossing tunnels. To investigate the mechanical behavior of pipeline in tunnel crossing, finite element models (FEM) are produced to simulate pipeline operation condition and the maximum design operation condition. With FEM, stress distribution and deformation of pipeline are analyzed. The result shows that 1) axial elongation of pipeline from finite element analysis is in accordance with that of on-site measurement, 2) pipeline is analyzed to be safe under operation condition or the maximum design operation condition, 3) supports should be designed and constructed with enough strength to resist the force from pipeline deformation, and 4) some treatments are proposed to solve the problems of pipeline in tunnel crossing. Finally, a new type of support with vertical constrained damping is designed for stress and deformation relief of pipeline in tunnel crossing.

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