Seismic Analysis And Earthquake Disaster Scenario Construction Of Urban Underground Gas Pipelines

Earthquake emergency is an important means for disaster prevention and mitigation.Among the earthquake emergency process,an earthquake disaster scenario analysis method is utilized by the emergency management department.The idea of the method is to build an earthquake disaster response scenario and an earthquake disaster response task model.Based on the response model,one can compute emergency response requirements and optimize disaster prevention and emergency preparation.This article focuses on seismic analysis and earthquake disaster scenario construction of underground gas pipelines in cities.Our work includes the theoretical analysis,empirical analysis and dynamic finite element analysis of buried gas pipelines.We establish a workflow for stochastic ground motion prediction model,and apply to Hebei region for case study.In addition,we extend the work to gas system functional failure.The main research contents and results are as follows:1.The theoretical and empirical methods of pipeline seismic analysis are discussed.By taking into account the effect of Rayleigh wave on the underground pipeline,the seismic response calculation formula of underground pipeline under Rayleigh wave is derived.In the empirical model,the empirical formula of the seismic damage rate of the buried pipelines based on PGV is analyzed by statistical method.In addition,a comprehensive evaluation analysis method is proposed.This method is based on mutation series method,and is able to include various factors for seismic damage grade of buried gas pipelines.The results show that:（1）In the area of rich developed Rayleigh wave,such as sedimentary plain or basin,the axial strain generated by the surface wave is higher than that of shear wave.（2）The mutation series method can reduce the uncertainty in the calculation of seismic damage grade of buried gas pipelines,which is important for theorical study and real application.2.We conduct study on dynamic finite element analysis of buried continuous pipelines and segmented pipelines under ground motion.Based on the soil-pipeline contact finite element model,a finite element analysis model of buried pipeline is established.In order to eliminate error caused by cutting a finite-sized model from an infinite site model,the viscoelastic artificial boundary is used in the finite element model.Furthermore,by considering the nonlinearity of the segmented pipeline interface,a model of buried pipeline is established.Influences of the input direction of ground motion,pipe-soil interaction,pipe type,and interface structure on the seismic response of buried pipelines are investigated.The results show that:（1）Seismic response of buried pipelines is restrained by the surrounding soil.And the seismic response of the buried pipeline is affected by the direction of ground motion input.（2）A larger coefficient of friction between the pipe and soil,or softer the pipe material result in an increase of the seismic response of the pipe.（3）The joint will cause stress and strain discontinuous variation.The weaker the interface strength is,the more significant the discontinuity phenomenon is.In addition,seismic response analysis of buried pipelines under near-fault ground motion is investigated.To study the influence of different types of ground motion on seismic response of buried pipelines,we select 10 different ground motion records whose inputs include forward-directivity velocity pulse,fling-step velocity pulse,near fault no pulse ground motions,far fault zone velocity pulse ground motions and far field ground motions.Then we compare the effects of different types of ground motions on seismic response of buried pipelines.The results show that:（1）Compared with the ground motions with no velocity pulse,seismic response of buried pipelines will be amplified under ground motions with velocity pulse.（2）Furthermore,the major contributing factors are the PGV and PGD of velocity pulse,while the response is insensitive to PGA.（3）The influence of fling-step pulse is greater than forward-directivity pulse in Chi-Chi Earthquake.（4）Seismic response of buried pipeline will be amplified under the large-amplitude and long-period surface waves in the plain or basin.3.Based on the stochastic finite fault method of dynamic corner frequency,a comprehensive study of Hebei region is conducted using the model of ground motion prediction.So the detailed ground motion input is provided for the demonstration area.Taking Zhangjiakou as an example,we conduct research on the earthquake scenario analysis of urban underground gas pipelines.First of all,based on drilling data of 36 strong motion stations,this paper establishes the soil layer model of Class II and Class III site in Hebei and calculates the average site amplification factor.Then,the paper calculates the high-frequency attenuation model κ₀ and analyzes its distribution in Hebei.The corner frequency and stress drop of small and medium earthquakes in Hebei in recent years are analyzed.In addition,a method for establishing the slip distribution model of the asperities is proposed.Based on the parameters of ground motion prediction model in Hebei,the Xingtai earthquake and Zhangjiakou set earthquake are taken as examples.And comparative analysis of the asperity distribution and random distribution are done in the near-field strong ground motion simulation of Xingtai earthquake.In the ground motion simulation of Zhangjiakou set earthquake,combined effects of different local site amplification factors and high frequency attenuation models are analyzed.The results show that:（1）The local site amplification factor is regionally dependent.（2）The high-frequency attenuation model κ₀ is affected by factors such as elevation,site condition and terrain.In general,the increase of κ₀ correlates with increase of site hardness,evaluation,and degree of terrain relief.And the outputs from the plain area used average model are in good agreement with the actual data.（3）Compared with the random sliding distribution model,the proposed model yileds a better result in the near fault area.（4）The site amplification effect is the combined effect of local site amplification and high frequency attenuation,where the high frequency attenuation component controls the peak and inflection point.Furthermore,in the mountainous region scenario,the contribution from the terrain should also be considered.In summary,the ground motion prediction model established in this chapter is suitable for Hebei region.And we conduct research on the earthquake disaster scenario construction of urban underground gas pipelines.To understand the seismic hazard in line with local geological features and construct a ground motion field,we need to collect the gas pipeline data and the regional data.Based on PGA and PGV,the structure damage of underground gas pipelines are analyzed by empirical method and catastrophe series method.Then,based on the structure damage of underground gas pipelines and two-state failure criterion,we complete the functional failure analysis of gas pipelines.The results show that:（1）Compared with results based on seismic intensity,empirical method and catastrophe series method proposed in this paper produce better results.（2）Some measures should be utilized to ensure functionality of the gas supply,including the design of annular pipeline network,two or more gas transmission trunk.