Study On Stability Analysis Of Slopes With Embedded Pipelines And Calculation Methods For Their Mechanical Behaviours Under Rainfall And Earthquake

Long-distance oil and gas pipeline transportation in mountainous areas is an important type of energy supply line.Since pipelines are generally buried in slopes,landslide hazards induced by rainfall and earthquakes have adverse effects on the safe operation of pipelines.The stability of the slopes in which pipelines are embedded and pipeline mechanical analysis are one of the main concerns in practice.In this dissertation,the stability of slope body under rainfall infiltration and earthquake,the seismic dynamic response of slope body and pipeline,the force analysis method of pipeline,the mechanical behavior of pipeline and its influencing factors and the design method of material selection are systematically studied by using various methods such as limit equilibrium theory,elastic foundation beam theory and numerical simulation analysis,etc.The main research works and results are as follows:(1)The mechanism of slope pressure acting on the pipeline crossing the slope under rainfall infiltration conditions is revealed.With the continuous increase of rainfall duration and rainfall intensity,the rainwater inside the infiltrated slope body increases continuously,which makes the volume water content of the shallow surface layer of the slope body increase continuously,resulting in the increase of pore water pressure of the soil body and the decrease of matrix suction,causing the shear strength of the soil body to decrease;at the same time,the self-weight of the soil body increases,which,together with the effect of infiltration force,causes the pressure of the slope body on the back side of the pipe to increase continuously.(2)The mechanical analysis model of the pipe body is established,and the formulae for calculating the internal force and deformation of the pipeline are derived.Considering that the pipeline is subjected to lateral slope thrust action as trapezoidal load mode,the Winkler elastic foundation beam theory is used to establish the mechanical analysis model of the pipeline based on Euler-Bernoulli beam and Timoshenko beam model considering shear deformation,respectively,and the calculation method of pipeline deformation and internal force under the action of trapezoidal load are obtained.The case analysis shows that the overall trend of theoretical calculation and numerical simulation results are basically consistent,and the difference between the two is about 5.2%-22.7%and 0.9%-33.9%under storm and earthquake conditions,respectively.(3)The dynamic response characteristics of the pipeline body under seismic action are determined.The pipeline is always displaced with the movement of the surface in the earthquake,and the cumulative displacement at the post-earthquake moment is the largest,and the displacement polarity difference(the maximum and minimum difference deformation)of the pipeline is the largest,and the vertical seismic wave has an adverse effect on the displacement of the pipeline.The post-earthquake moment is also the most unfavorable moment for the pipeline.The bending moment,axial force,and shear force of the pipeline are generally small in the earthquake and post-earthquake,and the value is within 10~2(k N·m or k N);when the angle between the horizontal seismic wave excitation direction and the pipeline axis is small,the axial force of the pipeline in the earthquake and post-earthquake will increase significantly;the pipeline may have axial pull-off or crush damage mode and bending damage mode under the strong earthquake.The damage modes of axial pulling or crushing and bending may exist under strong earthquake.(4)The characteristics of the influence of each major factor on the internal force and deformation of the pipeline are analyzed.The effects of rainfall intensity,seismic dynamic strength,seismic impact coefficient,width of the pipe through the landslide,landslide thrust,and pipe cross-sectional dimensions on the internal forces and deformation of the pipe were analyzed by using the control variable method from three aspects,including external inducing factors,intrinsic slope conditions and geometric properties of the pipeline.The results show that with the increasing of rainfall intensity,horizontal seismic coefficient and ground vibration intensity,the maximum deflection value,displacement pole difference,maximum bending moment and shear value of the pipeline increase continuously;with the increasing of the width of the pipeline located in the landslide body,the deformation of the pipeline gradually becomes slower;with the increasing of the cross-sectional size of the pipeline,the maximum bending moment and shear value of the pipeline also increase,but the deflection of the pipeline gradually decreases.(5)The design method of pipeline selection is given.The maximum stress calculation formula of the pipe body,which is closely related to the landslide thrust load and the internal pressure of the pipe,is derived,and the strength requirements and economy of the pipe body are considered comprehensively,so that the pipeline can be designed for material selection.Case analysis shows that when the design landslide thrust is 20k N/m and 29k N/m,for the pipeline with cross-sectional size of 457mm(7.9mm)and 660mm(12.7mm),when the design internal pressure is 8MPa and 10MPa,it is appropriate to use X60 and X52 type steel,X70 and X65 type steel respectively.The research results of this paper in the stability analysis of slopes on which pipelines are embedded under rainfall infiltration conditions,the dynamic response characteristics of pipeline and slope under the action of earthquake,the method of pipeline force analysis and the characteristics of the main factors on the mechanical behavior of the pipe body,and the design method of pipeline material selection can provide guidance and reference for practical engineering,which has important theoretical significance and engineering application value.