Analysis On Corrosion Rule And Mechanical Properties Of Underground Circular Concrete Drainage Pipe

With the development of the national economy and people’s living standardsimproving, people requires of urban environment is higher than ever. Undergrounddrainage pipelines is one of the most important infrastructures to guarantee a cityoperation in normal, and it plays a significant role to urban environment and people’shealth. Underground drainage pipelines works in special environment, and its forced statealso very different. First of all, the underground drainage pipelines is a structure whichburied in some distance under the ground, in the homogeneous soil its ambient pressurearound the pipe close to uniform state, but when it buried in heterogeneous soil its stressstate became complexity. Secondly, sewage transferred by urban pipelines contains bothdomestic wastewater and domestic wastewater, which have much corrosive ions toconcrete. Under corrosion conditions, the mechanical properties of concrete is decreases,and because of the pipe wall becoming thinner, the stiffness of pipe is decreases, but therelative stiffness of pipeline soil have great influence on the distribution of soil pressaround the pipe. In many loading conditions, the concrete of pipes is easy to cracking orcrushing when it used for a long time, and then the pipeline will be damaged, and willhave a serious influence to the residential and living environment. The research isassociated to the sub-project of the national critical research on water pollution controland treatment science and technology (No.2008ZX07315-001). A systemic study on thecorrosion rule and mechanical behavior of underground drainage pipelines is executedthrough material collection, model test, and numerical simulations. It contains thefollowing parts:①The diffusion process of corrosion substance in pipe wall is calculated by usingthe Fick second law, exactitude of the numerical simulations is proved by compare withthe analytical result, to obtain the distribution of corrosion substance in pipe wall afterdifferent days corrosion by using finite element analysis method. The concentration ofcorrosion substance is reduced nonlinearly with the increase of depth, and the decreaserate is decrease with depth. Corrosion substance concentration is enhanced with thecontact time, but the decrease rate is lower.②The relationship of completely corrosion depth and corrosive time is carried outthrough small size pipeline models experience, then a loading test for undergroundpipeline is done. The strain change and soil pressure around the pipe which corroded for some time and buried in the soil through layout strain and micro soil pressure gauge.Cracks appeared first on the top of the pipe inner surface, and the maximal soil pressurearound the pipe appeared first on the top of the pipe.③A two-dimensional numerical model for the underground pipeline is made, andchose parameters according to the existing research results, then reducing the materialparameters of pipe wall according to the diffusion of corrosion substance. The mechanicalproperty of corrosive pipe wall is studied on the basis of the analysis of stress, strain, andsoil pressure around the pipeline. The pipe wall thickness becomes thinner after corrosion,the effective thickness becomes smaller, the stress neutral point moves outwards. Thefactor which influences mechanical properties is the effective thickness but not theresidual pipe wall thickness.④The corrosion rule and mechanical behavior changing of the different ratio ofthickness and radius as well as the different degree of fullness on pipe wall is studied bychanging its thickness and fullness, to provide a reference for pipeline design and furtherresearch. The anti-corrosion capacity of the pipe is enhanced with the ratio of thicknessand radius. The range of corrosion is influenced by fullness, so the mechanical propertyof the pipe is influenced. The stiffness of the pipe is decline after corrosion, and the soilpressure around the pipe will be redistribution. The relative stiffness between the tube andthe soil of the pipe that used for long period should be concerned.In this study, the numerical simulation results are agree with the analytical orexperimental result both corrosion and loading process, under the condition of permitsome errors on calculation and experiment, the three result has highly emulatingefficiency. Therefore, the theoretical study is reasonable and credible, and it can be alsoreference for design and research.