Study On Mechanical Characteristics And Deformation Properties Of Flexible Buried Pipes Under Static And Dynamic Loads

In recent years,the pipeline transportation industry has developed vigorously all over the world,and the laying length of buried pipelines has been increasing year by year.Underground pipelines have become an indispensable part to ensure the normal operation of people’s daily life.However,with the diversification and complication of underground pipe network,more and more attentions have been paid to the potential safety problems caused by pipelines such as oil,gas and water pipelines.Due to the goods that buried pipelines transport are normally inflammable and explosive dangerous things or toxic and harmful pollutants.Once the accident occurs,not only will lead to huge economic losses and great environmental damage,but also most likely to cause casualties,and the consequences are tremendously serious.Therefore,it is of great significance to study the physical and mechanical characteristics of buried pipes so as to provide a theoretical reference for pipeline design and later protection works.In this paper,first of all,based on the laboratory tests the mechanical characteristics of buried pipe were studied.It was found that the settlements of the soil above the buried pipe are relatively uniform under static loading,before the damage,the pipe is deformed in an oval shape,the mechanical properties of the inner and outer sides of the pipe wall are opposite to those of pulling and pressing,the soil arching effect of the pipe roof is obvious.Then,the numerical simulation of static load tests were carried out by finite element software,by this way,the feasibility of the numerical analysis method was verified and the stress and strain distribution characteristics of buried pipes were explored.Next,the influence of the width of the bearing plate,the loading position and the initial deformation of the pipe on the mechanical properties and deformation characteristics of the buried pipe were further analyzed.The results showed that when the loading range is enlarged,the overall bearing capacity is improved linearly,and the influence on buried pipe is also more apparent;the farther the loading position is from the pipe,the smaller the influence is;on the whole,the initial deformation of the pipe has no obvious influence on the performance of the buried pipe.Finally,carry out model tests,study the performance of buried pipe under dynamic cyclic loading,and comprehensively analyze the influences of pipe depth,pipe wall thickness,pipe outer diameter,pipe material,load,loading frequency,loading angle and cycle times on the overall performance of buried pipes.The results showed that under the cyclic loading,the optimum buried depth of pipes is 4D(D is the outer diameter of pipe);the thicker the pipe wall is,the stronger the anti deformation ability of the pipe is;pipes with the same material and nominal pressure,the bigger the outer diameter is,the thicker the pipe wall is,and the harder it is to deform,meanwhile,polypropylene(PP)pipe has better deformability resistance than high-density polyethylene(HDPE)pipe;when the number of cycles is the same,increasing load level or decreasing loading frequency has more significant influence on buried pipes;the influence of symmetrical loading on the top of buried pipe is greater than that under asymmetric loading;compared with the static loading,the settlements of the soil above the pipe showed the characteristics that the settlement of shallow soil is large and of deep soil is small.