Study On Mechanical Properties Of Buried Cracked Concrete Drainage Pipelines Under Multi-Factor Coupling

Concrete drainage pipe is the most widely used pipes in China.When concrete pipes fall into years of disrepair,numerous problems appear.As one of the most common problems of concrete pipelines,cracks impact on the deterioration of mechanical properties of pipelines,which cannot be ignored.On the basis of domestic and foreign scholars’ research on buried concrete drainage pipeline,this paper uses MpCCI software as a platform to transfer and exchange data,and carries out fluid-structure coupling calculation on the structural field model calculated by ABAQUS software(ground load-pipeline-soil interaction model)and the flow field model calculated by FLUENT software(pipeline-sewage interaction model).Moreover,the destructive test of single pipeline with pre-existing cracks and the field full-scale test of buried cracked concrete pipelines were carried out.The structural properties of cracked concrete pipelines with diseases and the mechanical properties of buried multi-field.coupling were studied and summarized by using the research methods of numerical simulation analysis and field prototype test.(1)By comparing and analyzing the field prototype test data with the numerical model calculation data,it is verified that the three-dimensional finite element numerical model established in this paper can well predict the stress distribution of the pipeline wall of the buried cracked concrete pipeline,and this method can be used to evaluate the mechanical properties of the buried concrete drainage pipeline under the coupling of multiple physical fields.(2)In the destructive test of concrete pipeline under external load,with the gradual increase of external load,the circumferential strain on the concrete pipeline also rises,and the change in strain versus load can be divided into three stages:the elastic stage,the elastic-plastic stage and the plastic-failure stage.Among them,the elastic-plastic phase occurs for a short time and is not transparently significant,which is due to the fact that concrete is a brittle material,that its compressive strength is far greater than its tensile strength,and that there is no significant plastic deformation stage.The length,depth,and location of the cracks greatly affect the bearing capacity of the concrete pipelines.The greater the length and the depth of the cracks are,the smaller the bearing capacity of the concrete pipeline becomes.When the crack is located either at the crown or at the invert,its influence on the bearing capacity of the pipeline is basically the same,and it is greater than when the crack is located at the springline.(3)Through the coupling calculation of the structural field model and the flow field model,it is found that under the condition of the same sewage flow rate in the pipeline,the maximum circumferential principal stress and radial displacement of the pipeline are most affected by the stacking load ratio traffic load.The vertical displacement curve of the pipeline is basically "high on both sides,low in the middle,V-shaped" under the action of stacking load and traffic load respectively,and the distribution curve is highly discontinuous at the bell-and-spigot joint due to the shape of the bell-and-spigot joint.When the position of load changes,the vertical displacement and stress distribution of buried pipeline also change,and the stress value at crack position is the maximum.(4)Under the action of fluid-solid coupling,the maximum principal stress at the crown,invert and springline is distributed along the longitudinal direction of the pipeline,which is not symmetrical about the longitudinal center line of the pipeline,and the height at the pipeline joint is discontinuous,which is caused by the asymmetric structure of the pipeline at the bell-and-spigot joint and the crack in the pipeline body.When the traffic load acts directly above the bell-and-spigot joint(J3),for the pipeline body,the stress distribution at the crown has a greater influence than that at the invert and springline,and the influence range on the pipeline is about the length of a pipeline.The crack has a great influence on the stress distribution of the pipeline.