Effect Of Soil Site Condition On The Deformation Response Of Pressure Pipelines Crossing Fault

The oil and gas pipeline,water supply pipeline,heat supply pipe and other pressure pipelines are important lifeline engineering.In this paper,the influence of ground condition on the deformation responses of pressure pipelines under fault movement has been studied.Based on the improved shell finite element model,the effects of different site soil and trench backfill soil have been discussed.The main results are as following:(1)Compared with the nonlinear contact model,the soil spring model for the pipe-soil interaction is widely used in the finite element analysis because of its simple caiculation method and clear physical mechanism.In addition to the pipe's diameter and depth,the soil density(?_s),cohesion(c),internal friction angle(?)and pipe-soil friction coefficient(?)affect the pipe-soil interaction.These four soil parameters are not completely independent and have a certain correlation.The finite element analysis result shows that the strain response of the pipeline in the hard clay site is much larger than that in the soft clay site.(2)In order to study the influence of the trench and backfill sand soil,the transverse soil spring model recommended by the seismic code has been improved.With the theoretical model of failure mechanism of the soil around shallow-buried pipeline,the effectiveness of the backfilled loose sand used for the seismic resistance measures of the pipeline through active faults is improved.But the effectiveness of anti-seismic measure will be gradually failed with the gradual compaction of backfilled loose sand,and the deformation response of the pipeline will gradually approach the pipeline deformation responses without seismic measures.(3)The influence of trench width on the deformation response of the fault pipeline has also been studied.The results show that the trench slope(A)is the main factor affecting the strain response of the pipe,the slope of the trench should be less than tan(45°-?/2),and the surface width of the trench should be greater than the horizontal displacement of the fault.(4)The shell finite element model of the pipeline under the action of the fault is improved to consider the inner pressure.The effect of inner pressure on the axial compressive strain of the pipe is greater than the tensile strain.In other words,when the strain response of the pipeline under fault movement is dominated by tensile strain,the effect of inner pressure can be ignored.This result is consistent with the views of Newmark et al.However,when the strain response of the pipeline is dominated by compressive strain,the effect of internal pressure cannot be ignored.The allowable compressive strain of pipelines may increases with the inner pressure if the strain-based design is adopted for pipelines crossing fault.