| When Gaoshiti-Moxi gas export pipeline go through the wetlands,we often encounters difficulties such as large machinery can not approach,pipes can not be transported,and hard to shape ditch.During the construction,the process is summed up:Surveying—Pavement construction—Cleaning-up operations—Strengthening operations—Piling-up pipes field construction—Arrangement of pipes—Welding paired pipes—Weld inspection—Mending weld defects—Installing counterweights—Immersed ditch—Assisting pipe stability—Cathodic protection—Backfilling-Landscape restoration.Immersed ditch technology is the key point of the construction process,also it is the hardest part.Immersed ditch technology is the pipe slumping to the bottom of the ditch by its own pressure and excavator’s side thrust rather than directly hanging the pipe to appropriate location.When the operation pipe is too long,it would be influenced by its own gravity,so it is easy to set more trench depth;when the operation pipe is too short,pipeline couldn’t be immersed;when the operation pipe is bend pipe,elbow force may exceed the limit.As a result,reasonable pipe length and excavation length are needed.For pipes in different conditions,such as horizontal straight pipe,horizontal bend pipe,sloping straight pipe,and sloping bend pipe,we simplify its mechanical model respectively.In the beam model,we list pipe stress analysis formula and the maximum deflection calculation formula depending on the force balance principle,torque balance principle and the deflection formulas.In the soil spring model,according to project experience,we determine the stiffness of soil spring,and through Birth&Death method,we simulate excavator removing the soil.We can get computer simulation results by ANSYS software.Based on beam model,we calculate the length of pipe.While based on soil spring model,we calculate the length of the excavation.Finally,we get guidance of the engineering project. |
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