Study On Dynamic Response Law Of Buried Oil And Gas Pipeline Under Blasting Wave

With the expansion of domestic infrastructure construction scale and geographical area,blasting construction is more and more frequent in the area near the buried oil and gas pipeline.The influence of blasting shock and vibration effects on the operation safety of buried pipelines has become a hot issue in the field of pipeline engineering,tunnel engineering and blasting engineering.In order to eliminate the potential safety hazard of blasting operation on the surrounding underground pipelines,the precise determination of the distance to ensure the safety of the pipeline and the reasonable explosive dosage is very important for the design and safe construction of engineering blasting.The blasting criterion for buried pipeline in national and industry standards have not yet been clearly stipulated.The study of the dynamic response law of pipelines is the foundation of establishing blasting safety criterion,which has great engineering practical significance and scientific research value.In order to solve the problems of unclear response mechanism and disordered blasting safety standards of buried pipeline under the action of explosion wave,a series of prototype tests of oil and gas pipelines commonly used in materials(PE)and steel were designed and implemented by using strain,blasting vibration velocity and acceleration test system,supplemented by Piezoelectric Impedance Technology(PZT).Through the analysis of test data,finite element calculation and theoretical modeling,the response law of buried pipeline is systematically studied.The partition dynamic response mechanism of the pipelines under the action of blasting wave is expounded.The mechanical calculation models of circumferential and axial deformation of flexible pipe are established by semi empirical and semi theoretical method.The pipeline strength condition based on the distortion energy theory is established;the blasting safety standard of pipeline is proposed;the rationality of the ground particle velocity as the monitoring quantity of pipeline safety is clarified.The main study contents and conclusions are as follows:(1)By means of theoretical analysis and numerical calculation,the propagation and attenuation laws of blasting wave in different regions are discussed.According to the transmission theorem of spherical pack explosion in soil,the calculation formula of spherical wave front pressure attenuation and the three-dimensional stress state of soil element,the calculation formula of plastic zone limit of soil is derived based on Mohr Coulomb yield criterion.The case analysis shows that with the increase of water content in highly saturated soil,the influence range of plastic wave increases and the radius of the plastic zone of the soil increases.The explosion process of the spherical pack in cohesive soil is simulated by finite element method.The results show that the boundary pressure between the near and the middle fields of the blasting waves in the highly saturated soil is about 1?3 MPa,and the peak particle vibration is about 1?3 m/s.(2)The analysis of test data shows that the local impact of near-field blasting wave will cause large circumferential and axial strain of flexible pipe.When the scaled distance is small,the hoop strain may be greater than the axial strain.With the increase of the scaled distance,the axial strain is greater than the hoop strain.Through dimensional analysis and experimental verification;there is a power function attenuation relationship between peak strain and scaled distance.According to the spectrum analysis of strain and particle velocity,the centroid frequency of each motion parameter is between 10Hz and60Hz,which belongs to low frequency vibration.There is a strong linear correlation between the peak particle velocity of pipeline?the peak particle velocity of ground and the peak dynamic strain of the pipeline,which confirms the feasibility of using the peak ground particle velocity to characterize the pipeline vibration and strain level.(3)The natural frequency of circular vibration of pipeline is much higher than that of soil vibration,and the dynamic response characteristics of structure are not obvious,therefore the circular vibration can be simplified by quasi-static calculation.Based on the Iowa model,a practical mechanical calculation model of pipeline circumferential deformation is established.Based on the Winkler beam model and the Tension or compression pole model,the lateral and axial vibrations of the pipe-soil system are analyzed.Vibration differential equation of pipe-soil system is solved by the mode superposition method and the separation variable method.The calculation formulas of circumferential and axial strain are derived from the calculation model,and the calculation accuracy is acceptable after verification of test data.For flexible pipelines with the pipe-soil relative stiffness coefficient less than 0.3,Soil stiffness is the main factor to resist circumferential deformation.The response mechanism of axial and lateral vibration is more complicated.Under the test conditions,compared with the lateral soil spring stiffness,the bending stiffness has little effect on the lateral vibration,and the tensile stiffness of the pipeline and the axial soil spring coefficient have the same effect during the axial vibration.(4)According to the established pipeline strength conditions,the threshold value of the additional peak hoop stress(PHS)or peak axial stress(PAS)of the pipeline control point can be calculated.At the nominal working pressure,when the design factor of PE pipe is 2,the additional peak circumferential stress(PHS)or peak axial stress(PAS)at the critical point must be less than 19%MRS(minimum required strength).The steel pipe is10%?_s(the lower limit of material yield)when the design factor is 0.76.The proposed blasting safety criterion comprehensively considers the influence of pipeline type,pipeline material,buried condition,soil property and pipeline operation state on pipeline safety.By using the blasting safety criterion,the surface safety particle velocity threshold of underground pipeline blasting vibration can be obtained,which can guide the engineering blasting design and safety monitoring of adjacent buried pipeline.