Strain Analysis Of Buried Pipelines Crossing Active Normal Faults With The Non-Homogeneous Soil Medium

Active fault is one of main geological hazards faced by buried pipelines during its installation,and it is also considered as the primary threat to the integrity of pipeline system,which would cause tensile or compressive failure on pipes.It has been noticed that there are some differences between soil properties on each side of the fault plane,and the deformation of pipeline may be more serious in this case.However,the study focusing on the difference of the soil property has not been previously addressed by other researchers.In view of this,it is necessary to carry out the strain analysis of buried pipelines crossing active faults with the non-homogeneous soil medium,which can be referenced for the design of pipeline,and guarantee the safety of pipelines during its service.Based on the theory of elastoplastic model,an analytical method calculating the deformation and the axial strain of the buried pipeline subjected to normal faults with non-homogeneous soil medium was proposed.The interaction between the soil and pipe was simulated using nonlinear soil spring element,and the nonlinearity of material was also considered.The accuracy of the proposed method was demonstrated according to results of the finite element model.The finite element model of pipeline at normal fault crossing,of which the fault dip angle is no more than 90 degree,with non-homogeneous soil medium was established using a simulation software.Effects of the difference of the soil property on each side on the distribution of axial and bending strain of pipes were conducted in this paper.And results show that when the soil in the hanging wall was sand,the soil property of the footwall has little effect on the axial strain of the pipe;while the soil of the hanging wall turns into clay,the soil property of the footwall has a significant impact on the axial strain.Regressive equations of pipe's design strain were proposed based on a large number of finite element results.The strain prediction formula was optimized by the 1stOpt software,and then,the equations were obtained by using Levenberg-Marquardt algorithm based on the least square method.Equations were divided into two categories according to the fault dip angle.For the condition where the fault dip angle equals to 90 degree,the active fault is associated with other geological hazards,such as the mining-collapse and thawing-settlement,which takes the influence of mutation length into account especially,which makes the application of regressive equations more widely utilized.