Research On Safety Control Technology For The Complex Configuration River-crossing Pipeline With Coupled Multi-bodies In Its Immersion Construction

In practical engineering,due to the limitation of construction space on the river surface and navigation in the upstream,it is difficult to use large lifting and sinking equipment.Thus,the river-crossing pipelines are usually equipped with a specific immersion system consisting of multiple floating bodies(such as barges,airbags,and steel buoys)to ensure the security of immersion construction.Some special circumstances may occur in actual projects,such as limitations of the topography of the underwater foundation trench on the riverbed or specific navigation and construction needs.As a result,it may be necessary to design a river-crossing pipeline with an irregular curved crank shape.The immersion process of the above special river-crossing pipeline involves the problem of multi-body coupling(dozens or hundreds),irregular structural shape,the coordination of the overall arrangement of personnel and equipment,etc.In order to investigate the dynamic response laws of complex configuration river-crossing pipeline with multi-floating body coupling in the immersion process,and to ensure the safety of the actual engineering.This study takes a long-large-curved river-crossing pipeline project spanning yongjiang river and a U-shaped river-crossing pipeline project spanning youjiang river in South of China as the engineering background.The tension of suspension cables and mooring ropes,the dynamic responses and stress distribution of the complex configuration river-crossing pipeline are studied by numerical simulation and model test.And the influences of key parameters such as airbags deflate time,airbags deflate ways,lowering speed of the suspension cable and boundary conditions on the dynamic response of the immersion system are also discussed.The results are as follows:(1)Overall,the immersion process for the long-large-curved river-crossing pipeline is safe,stable,and controllable.In the final immersion stage,the tail end of the pipeline inclines upward,and the two steel buoys at the tail end of the pipeline are not completely submerged in the water.Therefore,lowering the height of each suspension cable is recommended for reasonable control according to the actual engineering situation.(2)In the immersion process for the long-large-curved river-crossing pipeline,there is taut–slack phenomenon in the suspension cables,and the largest maximum dynamic tensions occur in suspension cables 4–6.Thus,to avoid the taut–slack phenomenon,it is suggested that the dynamic tensions of all the suspension cables should be measured in real-time to make timely and flexible adjustments in the construction process.Meanwhile,it is recommended that the two 50 t barges with greater bearing capacities be removed from the two ends to the mid-span location of the pipeline.(3)The scheme comparison analysis results for the long-large-curved river-crossing pipeline in the immersion process show that each scheme has its own advantages and disadvantages under different airbags deflate ways,airbags deflate time and lowering speed of the suspension,and it is suggested to make comprehensive choice according to the actual engineering situation.(4)The immersion process for the U-shaped river-crossing pipeline generally is safe and reliable,the largest maximum dynamic tensions occur in suspension cables.The maximum stress value occurs at the mid-span of the pipeline,not at the maximum bending position the pipeline.But improper operation can easily lead to excessive cable tension.In the actual project,it is recommended that the airbags at the two ends of the pipeline are deflated firstly,the lowering speed of the suspension cables is coordinated with the deflate times of the airbags,and the lowering speed or initial lowering time point of the middle suspension cables is slightly slower than that of the two sides suspension cables.