Analysis Of Flow-induced Vibration Characteristics Of Pipeline Through Dike And Study On Seepage And Stability Of Dike

As an important part of the water diversion project,the flow-induced vibration of the pipeline poses a certain threat to the safety performance of the original dike.Vibration will cause the soil of the dike to loosen,and then form a seepage channel,which is easy to cause seepage failure and instability failure of the dike,and even cause engineering accidents and economic losses when it is serious.and at this stage,the research on a series of problems caused by the dike pipeline is not enough.Therefore,carrying out the analysis of the vibration characteristics and seepage characteristics of the dike-crossing project and exploring the stability of the dike under the action of multi-factors have important engineering practical significance for the optimal design,safe operation and stability evaluation of the new structure of dike-crossing pipeline.In this paper,taking a pipe-piercing dike in Guangdong Province as the research object,firstly,the theoretical study of pipe-soil-flow coupling,the inversion of flow-induced vibration load and the analysis of pipeline vibration characteristics are carried out,and then the numerical simulation method is adopted.in this paper,the influence of pipe-crossing position and flowinduced vibration on dike seepage is studied,and the corresponding anti-seepage measures are put forward according to the most unfavorable working conditions.Finally,the indirect coupling method is used to study the influence of seepage and flow-induced vibration on the stability of dike,and the dynamic response law of through-pipe dike under extreme seismic load is explored.The main research contents and conclusions are as follows:(1)Study on the mechanism of pipe-soil-flow coupling vibration in dike-crossing pipeline.The mechanism of fluid-solid coupling and the theory of pipe-soil interaction are summarized,which lays a theoretical foundation for the pipe-soil-fluid coupling analysis of the dike-crossing project.for the dike-crossing project,the interaction between fluid-solid coupling and pipe-soil interaction is considered.the microelements of soil,fluid and pipeline are analyzed respectively,and finally the pipe-soil-fluid coupling vibration equation is established,and the case simulation is carried out by using the simply supported pipeline model.The relationship between the natural frequency of the structure and fluid velocity and pipe parameters is analyzed.(2)Study on flow-induced vibration characteristics of pipeline passing through embankment.A variety of pipe crossing models were developed using numerical simulation methods and self-vibration frequency analysis was carried out on the dike crossing pipes.The natural frequency range of the pipeline through the dike is located in 0.72Hz-1.02 Hz.The flowinduced vibration load is inverted according to the field measured vibration response,and the flow-induced vibration characteristics of the dike are analyzed according to the inverse load.The results show that the most complex position of flow-induced vibration is the midpoint of the pipeline in the embankment,where the environmental excitation is complex,the peak value of the main frequency is more,the vibration form is more complex,and the frequency range of flow-induced vibration is mainly between 15Hz-30 Hz,which provides a reference basis for follow-up vibration reduction and vibration control research.(3)Study on the influence of pipeline flow-induced vibration on dike seepage and optimal design of anti-seepage measures.The disturbance range of the flow-induced vibration load on the soil around the pipe is calculated,and the effect of flow-induced vibrational loads on the seepage field of the embankment was also investigated in the context of flow-induced vibrational disturbances.The results show that the maximum disturbance range of the middle piercing condition is 0.3D(D is pipe diameter)and that of the upper piercing condition is 1.1D.Under the action of flow-induced vibration load,the permeability coefficient of the soil around the pipe increases and the infiltration line of the embankment through the pipe is significantly elevated.and the pipe penetration leads to the expansion of the seepage area on the downstream slope of the dike,and it is concluded that the working condition of pipe piercing in the middle is the most unfavorable working condition.According to the most unfavorable working condition of pipe piercing,the layout,size and quantity of anti-seepage measures such as outer concrete and cutoff ring are optimized.the optimal arrangement of pipe outer concrete is the whole arrangement in the dike,and the optimal interval of its thickness(the distance from sidewall to pipe wall)is 0.3D-0.4D,the optimal interval of the thickness of cutoff ring is 0.6D-0.75 D,and the number of cutoff ring is 4 or more.(4)Study on the influence of seepage and seepage-flow-induced vibration coupling on dike stability and seismic response analysis.Considering the effect of seepage,the finite element dynamic strength reduction method is used to analyze the dynamic stability of throughpipe dike,using the indirect coupling method to realize the multi-load coupling of infiltration force-flow-excited vibration,analyzing the influence of seepage and flow-excited vibration on the slope stability,and also carrying out the dynamic response analysis of the embankment through the pipe under the seismic load.The results show that the seepage action leads to a10.3% reduction in the safety factor of the embankment slope,and the safety factor is reduced by 15%,5.4% and 16.5% respectively due to the upper,middle and lower piercing positions of the dike.The coupling effect of flow-induced vibration leads to a decrease of 23.9%,36.5%and 36.8%,respectively,indicating that flow-induced vibration has the most significant effect on slope stability.The safety factor of dike decreases with the increase of the magnitude of flow-induced vibration and the disturbance range of flow-induced vibration to soil.Due to the seismic load,the maximum displacement of the through-pipe dike appears at the top of the dike,the maximum displacement at the top of the embankment is 0.018 m.The maximum values of the first and third principal stresses in the pipe are 77 MPa and 78 MPa respectively.The calculation results show that the midpoint of the pipeline in the embankment is greatly affected by the seismic load,which should be paid more attention to in the seismic design of the dikecrossing project.