Centrifuge Modeling On Uplift Behaviour Of Shallow Buried Pipe In Inclined Sand

Pipelines are the artery of modern industries and urban life,widely used in lifeline engineerings such as water supply,electricity supply,natural gas transportation line and communication cables.According to a large number of disaster surveys,the damage probability of the underground pipelines in inclined groud is far greater than that in the horizontal ground.However,most of the existing studies focused on the interaction of soil-pipe have been established on the premise that the pipeline is buried in horizontal ground.There are few discussions on the pipe buried in inclined ground.At present,the existing research is not enough to really understand the deformation characteristics of the pipeline and the soil in inclined gournd,and can not really reveal the deformation mode and failure mechanism of buried pipeline.Based on these,theoretical analysis and centrifuge tests were carried out to study the pipe-soil interaction when pipe buried in non-liquefaction and liquefaction inclined site:(1)The pullout capacity and the deformation mode of soil around pipe in non-liquefaction inclind ground is studied in this paper.An analytical expression for computing the failure plane angles and the soil resistance to pipeline upheaval bucking in inclined ground is proposed,and verified by the theotetical formula proposed by other researchers and the centrifuge test conducted in our study.(2)The dynamic response characteristics of pipe and soil in inclined liquefied soil is investigated.The force condition and the deformation mode are aslo acquired.The mechanical model for calculating the force around pipe during liquefaction is established and verified by the centrifuge test results.Based on these,the failure mechanism of pipeline buried in inclined liquefaction ground is revealed.The main research works and conclusions are as follows:1 Combine the centrifuge model tests of pipe buried in non-liquefaction site,the soil failure mechanism and the characteristic of soil resistance around pipeline is investigated.It turns out that a pipeline buried in sloping ground has an asymmetrically inclined slip surface pattern.The two failure surfaces both rotate in the downhill direction.The soil resistance when pipeline uplifting in sloping ground is smaller compare to horizontal ground.The failure planes rate of rotation and the reduction of soil resistance increases with increasing ground slope ? for a given pipeline buried ratio H/D,and decreases with increasing H/D for a given slope angle.2 This study has produced an analytical expression for computing the failure plane angles and the soil resistance to pipeline upheaval bucking in sloping ground,based on the Rankine earth pressure theory and the M-C law.The correction and the reasonability of this formula in our paper is verified by the theotetical formula proposed by other researchers and the centrifuge test conducted in our study,which can well reflect the characteristics of the soil deformation mode and soil resistance around pipeline buried in inclined ground.3 Based on the dynamic centrifuge model tests of horizontal ground with buried pipe,the deformation behavior of shallow buried pipe in liquefied field was investigated.It turns out that the horizontal displacement of pipe in liquefied ground is very small.The main failure form of the pipeline is vertical floating.The deeper the buried depth and the bigger the vibration amplitude is,the pipeline floating damage is more likely to occur.When pipe is floating,the soil around the pipeline gradually flowed around the pipe within a heart shaped region,and the deformation range of the soil is greater than that due to external forces for the same buried depth.The uplifting behavior of a pipe was highly dependent on the buildup of excess pore pressure.The floating of the pipeline are the combination effects of multiple forces.Based on these results,the vertical deformation mechanism of the pipeline in liquefaction ground is analyzed,and the mechanical model of the pipeline in the liquefaction process is established,which is verified by the centrifuge test results.4 Three dynamic centrifuge model tests are conducted to investigate the deformation behavior of shallow buried pipe in inclined liquefied field.In the sloping field,the vertical floating and lateral deformation of the pipeline will both happened in inclined liquefied ground.During the process of vibration,the soil around the pipe flow in a circular shaped,which is obviously different from the horizontal liquefaction ground,and is different from the inclined ground with no structures.After the vibration,the soil around pipe showing the characteristics of the static condtion.The vertical floating and lateral deformation of the pipeline are the combination effects of multiple forces.And is highly dependent on the buildup of excess pore pressure.During seismic vibration,excess pore pressure generates,and soil around the pipeline gradually flow,which causes both the variation of effective weight of overlying soil and supporting force of soil underlying the pipeline,as well as the shear resistance from shear planes that varies with the degree of liquefaction.As a result,the equilibrium of pipeline during shaking is broken,the pipe consequently in an unstable conditon.According to these,the deformation mechanism of the pipeline in the inclined liquefaction ground is analyzed,and mechanical model of the pipeline in the liquefaction process is established.The model can reveal the floating deformation behavior of the pipeline buried in inclined liquefaction site.