Force Response Of Buried Pipelines Under Surface Loading To Ground Loss Induced Non-uniform Bedding Support

With the rapid development of China’s economy and the continuous advancement of urbanization,the number of underground pipelines is growing rapidly,pipeline engineering is widely used in national production and life,and occupies an important position.Due to pipeline corrosion,uneven settlement of soil and rupture of adjacent pipelines,underground pipelines will lead to soil erosion and mechanical characteristics change around pipelines,resulting in the formation of soil erosion area between the pipe body and soil,thus reducing the safety of pipelines.In addition,due to precipitation,human activities and other reasons,the overburden of the pipeline will also change,which will change the original stress balance of the pipeline.These factors are likely to cause pipeline damage,inconvenience to production and life,resulting in economic losses.In this paper,the influence of soil loss under the overburden on the stressed deformation of the pipeline is studied.Theoretical analysis,numerical simulation and model test are combined to study the stress deformation of the pipeline under the overburden.The main research methods are as follows:Based on the Boussinesq’s point load solution and the Winkler-based elastic foundation beam theory,the separation zone of the soil around the pipe and pipe is divided into the separation zone of pipe and soil and the semi-separation zone of pipe and soil.,and the pipe-soil coupling model is constructed,and the displacement,shear force and bending moment equations of the pipeline are obtained.Based on ABAQUS numerical simulation method and combined with pipeline engineering cases,the finite element model of pipe-soil coupling was established to verify the accuracy of the pipeline deformation equation,and the influence of the overburden of the pipeline and the degree of soil erosion on the variation law of pipeline stress was also explored.According to the test requirements,the pipe-soil test model box is used to study the influence of soil loss under the pipeline under the action of overburden load on the pipeline,and the strain variation law of the pipeline under the action of overburden load and soil loss is explored The influence of buried depth,pipe diameter,pipe material and soil type on the mechanical characteristics of pipeline is studied.The results show that:(1)Based on the stress and deformation state of buried pipeline,the theoretical model of pipe-soil coupling is established.The stress and deformation of pipeline are divided into pipe soil separation area and pipe soil semi-separation area.The stress deformation formula of pipeline is deduced by using Boussinesq’s point load solution and the Winkler-based elastic foundation beam theory,and the vertical displacement,bending moment and shear force of pipeline are calculated.(2)Through ABAQUS numerical simulation,based on the example of pipe soil coupling,the change trend of vertical displacement,shear force and bending moment of pipeline is basically consistent with the theoretical calculation result.The relative error between the numerical simulation of vertical displacement and the theoretical result is 2.02%,the relative error of shear force is 14.67%,and the relative error of bending moment is 2.03%.When the overlying load of buried pipeline is changed,the stress and deformation degree of pipeline with overlying load is 9.41%～32.38% larger than that without overburden load,and the stress deformation degree of pipeline with soil loss is 61.63% ～ 90.64% greater than that without soil loss.Considering the overburden load and soil loss,the deformation degree of buried pipeline is soil loss with overburden load>soil loss without overburden load>no soil loss with overburden load.(3)Based on the model test of pipe soil coupling,the stress variation law of pipeline under three conditions of overburden load without soil loss,soil loss without overburden load and soil loss with overburden load is studied.The results show that the strain of the top and bottom tubes varies from-435.4～-434.4με,and the strain ranges from-435.4～-464.4με,respectively.Through Gauss Amp equation,the data of strain measuring points at 0.4～1.5m of pipeline under three working conditions are fitted.It is found that the strain variation trend of pipeline under test condition is basically consistent with that of numerical simulation,and the test strain value is slightly smaller than that of numerical simulation,which reveals the strain variation law of pipeline.(4)By changing the pipe material,soil density and elastic modulus,overlying surface load and buried depth of pipeline,the influence of different parameters on the stress and deformation of pipeline and the length of pipe soil separation zone is explored.The results show that with the increase of pipeline strength,the length of pipe soil separation zone also increases with the increase of pipeline strength,with the variation range of 0.38～0.48 m,the deformation degree of the pipeline is polyethylene pipe>polyvinyl chloride pipe>steel plastic composite water supply pipe;with the increase of soil strength,the length of pipe soil separation zone decreases,and the variation range is 0.39～0.34 m.The deformation degree of pipeline is sand>clay>gravel soil;with the increase of the overlying surface load,the length of the pipe soil separation zone remains 0.38 m,and the deformation degree of the pipeline is 20 k Pa>15 k Pa>10k Pa;with the increase of the buried depth of the pipeline,the length of the pipe soil separation zone remains 0.38 m,and the deformation degree of the pipeline is 0.3m>0.4m>0.5m.