Numerical Simulation Research On Dynamic Response Of Buried Pipeline Under Blast Loads

Buried pipelines are widely used to transport water,minerals,crude oil,industrial gas,etc.They are regarded as an important part of the country’s economic development due to their large size and small impact on climate.In general,buried pipelines have few protective measures and small buried depth.As a sequence,it is easy to be disturbed by various external loads,which lead to different deformations or damage of the buried pipeline.In recent years,terrorist attacks and accidental explosions occur frequently in the world,and various pipelines closely related to strategic and economic interests have become the targets of terrorist organizations.With the acceleration of the urbanization process and dense distribution of urban pipe network systems,blasting construction is also easy to result in the damage of pipelines.In the present study,the dynamic response of conventional buried pipelines under blast loads is studied by numerical method.The influence degree and change rule of different influencing factors are also studied.Moreover,the grey relational grade of each influencing factor is analyzed by Grey theory.Then,the influence of pipeline connection mode（welding）on the dynamic response of pipeline is studied,and the influence of welding joint groove parameters is studied.Finally,the dynamic response law of defective pipeline reinforced by casing subjected to underground explosion is investegated by numerical simulation.The main conclusions are as follows:（1）In the simulation study of the dynamic response of buried polyethylene（PE）pipeline under blast loads,it is found that it is most affected by transverse vibration on the cross-section of the pipe facing the basting center,and the positions where the pipe is most affected by the axial vibration is on both sides of the cross-section of the pipe facing the basting center.The compression strain of the pipeline is more affected than that of the tension strain,and the pipeline is damaged by compression.The differences of the attenuation curve of peak vibration velocity are limited in the X-direction of four PE pipes with the same standard dimension ratio under different proportion distances.In the three-dimensional stress state at different cross-sections of the pipe,the three principal stress directions of the front and back surfaces of the PE pipe are the same,and the principal stress value decreases along the axis of the pipe.When the proportion distance is greater than 2 m·kg^-1/3,differences of peak pressure attenuation curves of the four PE pipes are less than 1 MPa,and the differences decrease gradually with the proportion distance increasing.Grey correlation grades of peak overpressure and maximum vibration velocity of the pipeline are also analyzed by Grey theory,and the descending order of grey correlation grade is as follows:blast charge,pipeline size,and explosive distance.（2）In the simulation study of dynamic response of buried pipeline near weld zone under blast loads,it is found that when the blast height is 60 cm,the pipe with weld reinforcement is greatly affected by stress concentration and that it yields earlier than the pipe without weld reinforcement.When the blast height is 60 cm and 85 cm,the ability of the pipe with weld reinforcement to resist deformation is significantly weaker than that of the pipe without weld reinforcement.The interaction between soil and pipe supports the explosion-back surface of the X70 pipe,which can effectively reduce the displacement of the explosion-back surface of the pipe.Under the same conditions,the vibration resistance performance of the pipe with weld reinforcement is weaker than that of the pipe without weld reinforcement.Moreover,compared with the weld form,blast height plays an important role in the maximum vibration velocity of the pipe near the weld zone.（3）In the simulation study of the effect of welding joint groove parameters on the dynamic response of buried welded X70 steel pipeline under blast loads,it is found that the effects of welding joint groove parameters on the dynamic response parameters（including vibration velocity,stress,strain,and displacement）of the welded pipeline are as follows:the influence of blast charge is the largest;weld reinforcement,root opening,and groove surface angle are the second.However,the influence of weld reinforcement is the greatest of the three factors（weld reinforcement,root opening,and groove surface angle）.The increase of weld reinforcement could result in an increase of maximum equivalent stress of the pipeline.The excessive value of the groove surface angle and root opening can give rise to a change in the circumferential stress of the pipe from tension to compression.The excessive value of the blunt edge high could result in the change of the circumferential stress from compression to tension.Welding joint groove parameters have been changed.The axial stress of the pipeline is mainly compressive stress,and the increase of the groove surface angle will increase the compressive stress.The axial strain of the pipe is mainly tensile strain,which varies with welding joint groove parameters.The axial tensile strain of the pipeline can be decreased by decreasing the groove surface angle.However,the increase of weld reinforcement and blunt edge high will increase the axial tensile strain of the pipeline.The vibration velocity and deformation of the front-blast surface of the pipe are always larger than that of the back-blast surface,and excessive values of the weld reinforcement can increase the deformation of the pipe.The changes in bevel face angle,weld residual height,and blunt edge height in different ranges have different effects on pipe vibration velocity and deformation,so the size of the weld seam should be reasonably optimized.（4）In the simulation study of the dynamic response of a defective pipeline reinforced by casing under underground blast loads,it is found that the influence of three factors（internal pressure of the pipeline,the wall thickness of the casing,and the defect location）on the maximum equivalent stress and the equivalent plastic strain of the pipeline is as follows:The influence of the defect location is the greatest,the internal pressure of the pipe is the second,and the influence of casing wall thickness is minimal.The influence degree of the three factors on the maximum vibration velocity of the pipeline is as follows:the wall thickness of the casing is the largest,the defect location is the second,the internal pressure of the pipeline is the smallest.The existence of the internal pressure of the pipeline can reduce the stress level of the pipeline.Meanwhile,the excessive internal pressure has a negative impact on the pipeline.The increase of pipe internal pressure and casing wall thickness can effectively prevent X70 steel pipe from being damaged by circumferential tension and compression,while an increase in the internal pressure reduces the effect of axial compression on the pipe.The increase of casing wall thickness in a range（0～17 mm）can reduce the axial tensile stress of the pipeline.The tensile or compressive stresses in the pipe are greatest when the defect is located on the front-blast surface of the pipe,and the transfer of the defect location of the back-blast surface can reduce the effect of the blast loads on the pipeline.The increase of pipeline internal pressure and the thickness of pipeline reinforcement can reduce the deformation of the pipeline.It is most unfavorable for the safety of the pipeline that the defect is located in the front-blast surface of the pipe,and the deformation of the pipeline decreases as the defect position moves back.As the thickness of the pipe reinforcement and the angle of the defect location vary,the maximum position of the pipeline to be affected by blasting vibrations is always the front-blast surface of the pipe.The vibration effect can be decreased by increasing the internal pressure of the pipeline and the wall thickness of the casing.