| The water diversion pipeline project from the Hanjiang to the Weihe river is also known as the "South to North Water Transfer" project in Shaanxi Province.This project is of significant strategic significance in fundamentally alleviating the industrial water use and urban development problems in the Guanzhong region.The water diversion pipeline project from Hanjiang to the Weihe river is located at the intersection of the Qinghai-Tibet seismic region,the North China seismic region,and the South China seismic region,which faces high seismic risks.Under the action of seismic loads,the seismic subsidence of more than 20 cm appear in the loess foundation of the Hanjiang to Weihe river water diversion pipeline is a large probability event.Moreover,the inertial forces generated during the earthquake process can also generate large additional stresses on the pipeline,posing a serious threat to the safe operation of the project,leading to huge economic losses.Therefore,the Sangzhen loess foundation and the underlying horizontal pipeline,as well as the Tianjiayao loess foundation and the underlying bent pipeline are selected as the research objects.The indoor dynamic triaxial deformation tests are conducted to study the dynamic deformation characteristics of the loess and light weight soil on the foundation of the water diversion pipeline from the Hanjiang to the Weihe river.The pipeline-soil interaction model and the pipeline-light weight soil damping layer-soil interaction model are established using the finite element software Abaqus.Deeply explore the influence of different earthquake intensities,water content,and buried depth of pipeline on seismic subsidence of loess foundation and the influence of seismic subsidence on the stress of underground water pipelines,while the seismic response of water pipelines with light weight soil damping layers at different EPS particle volume ratios and thicknesses is analyzed.This study can provide important technical support for the optimal engineering design and ensuring the safety of the Hanjiang to the Weihe river diversion pipeline project.The specific content and results are as follows:(1)As the peak acceleration of earthquakes increases,the maximum seismic subsidence,foundation maximum seismic subsidence,and maximum subsidence difference of horizontal and bent pipelines gradually increase,but their increasing rate gradually decreases.A small seismic subsidence difference can also lead to larger additional stress in the two types of pipelines,and as the seismic subsidence difference gradually increases,the maximum Mises stress on the pipeline also gradually increases.(2)The increase of water content in the loess foundation will lead to a exponential increase of the maximum seismic subsidence,foundation maximum seismic subsidence,and maximum subsidence difference.When the water content of the loess foundation is 30%,the maximum Mises stress of the horizontal pipeline is 319.98 MPa,and the maximum Mises stress of the bent pipeline is 330.09 MPa,which are close to the yield strength of the pipelines.Therefore,in practical engineering,attention should be paid to the increase of the water content in the foundation caused by pipeline leakage.(3)As the increase of pipelines burial depth,the effect of seismic subsidence on horizontal and bent pipelines gradually decreases.The maximum Mises stress on the pipelines presents a trend of first decreasing and then increasing.However,whether after or before the occurrence of seismic subsidence,the maximum Mises stress on shallow buried horizontal pipelines and bent pipelines is the smallest,so shallow burial is recommended for both types of pipelines.Meanwhile,both horizontal and bent pipelines have the ability to resist seismic subsidence,and when pipelines are shallowly buried,the surface ground seismic subsidence is smaller.(4)As the volume ratio of EPS particles in light weight soil increases,the Mises stress and acceleration on horizontal and bent pipelines gradually decrease,and the displacement gradually increases,but it is still smaller than the displacement without damping layer.In addition,when the volume ratio of EPS particles in light weight soil increases from 30% to40%,the maximum Mises stress on the pipeline does not decrease significantly.However,when the volume ratio of EPS particles is 40%,it will greatly increase the actual construction difficulty and cost.Therefore,it is recommended that the volume ratio of EPS particles in light weight soil for both horizontal and bent pipelines be 30%.As the thickness of the light weight soil damping layer increases,the acceleration and displacement on horizontal and bent pipelines gradually decrease,but are still smaller than the displacement without damping layer.The stress shows a phenomenon of first decreasing and then increasing,so there is the most reasonable thickness of the light weight soil damping layer.(5)The EPS particles volume ratio and thickness of the light weight soil damping layer do not change the spectral characteristics of the stress,displacement,and acceleration time history curves of horizontal and bent pipes,but only change their amplitude.Compared to the peak pulse time of seismic waves,the peak stress of horizontal pipeline has a hysteresis of about 0.12 s,and the peak stress of bent pipeline has a hysteresis of about 0.60 s.The peak displacement of horizontal pipelines and bent pipelines have an advance of 0.28 s,while the peak acceleration has neither hysteresis nor advance.After the seismic peak value pulse,similar seismic wave pulses will cause different stress responses in the pipelines.(6)When seismic subsidence occurs,the seismic subsidence amount,seismic subsidence distribution,maximum Mises stress and stress distribution of horizontal and bent pipeline foundations are different.The distribution of seismic subsidence in horizontal pipeline foundation is basically symmetrical,while there is no obvious symmetry in seismic subsidence in bent pipeline foundation.The maximum Mises stress on horizontal pipeline is distributed in the middle of the pipeline,while the maximum Mises stress on bent pipeline is distributed at the lower bent point of the pipeline.Under the same working condition,the foundation seismic subsidence of horizontal pipeline is larger than that of bent pipeline,while the Mises stress of horizontal pipeline is smaller than that of bent pipeline.The main reasons for the difference in stress between the two are the difference in pipeline loads and the phenomenon of stress concentration.(7)During the earthquake,the stress distribution of horizontal pipeline is independent of the spectral characteristics of the earthquake.The maximum Mises stress is mainly distributed in the middle of the pipeline,while the stress distribution of bent pipeline is related to the spectral characteristics of the earthquake.At the peak pulse time of the earthquake,the maximum Mises stress on the pipeline is distributed at the upper bent point of the pipeline,while at the lower pulse time of the earthquake,the maximum Mises stress on the pipeline is distributed at the lower bent point of the pipeline.When the volume ratio of EPS particles in the light weight soil damping layer is 30%,the optimal thickness of the horizontal pipeline damping layer is 60 cm,while the optimal thickness of the bent pipeline damping layer is 50 cm,which should be paid attention to in practical engineering. |
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