Research On Tunnel Engineering Response And Damage Analysis Method Based On Active Fault Dislocation And Ground Motion

At least 495 active faults have been identified in mainland China.With the development of western China and the construction and development of the Sichuan-Tibet Railway,it has become an inevitable event to cross or cross active faults during route selection and design of tunnel projects.At present,the research on active fault detection and precise positioning has made great progress.Therefore,it is urgent to study and understand the hazard of active faults to tunnel engineering and the reaction behavior and catastrophic mechanism of tunnels under the action of faults.Starting from the geophysical change mechanism of the active fault itself,it is of high scientific value and engineering significance to carry out research on dislocation and earthquake resistance of cross-fault engineering.Aiming at the key scientific issues of cross-active fault tunnels,this paper has carried out research on the hazards of active faults and the disaster process and destruction mechanism of tunnels under the action of active fault dislocation and ground motion.Aiming at the characteristics of ground motion in the near-fault area,this paper proposes a reasonable selection method of near-site motion,and compares and analyzes the influence of different amplitude and periodic velocity pulses on the damage distribution of tunnel lining.An algorithm for identifying the strongest velocity pulse based on wavelet analysis is proposed in the article,and a statistical model of pulse peak value,period,magnitude and fault distance is established.At the same time,the dislocation distribution on the fault plane is discussed,and a new dislocation distribution mode considering the dislocation unevenness on the fault plane is proposed.The calculation errors caused by the layered structure of the soil,the dislocation distribution on the fault rupture surface and the dislocation input method are analyzed,and a refined fault dislocation input method is established.Finally,a study on the coupling input of dislocations and ground motions was carried out to explore the different destructive effects of the separate and coupled effects of dislocations and ground motions on the tunnel.The main research work is summarized as follows:(1)Based on the viscoelastic artificial boundary and equivalent nodal force method,a set of seismic plane wave input methods suitable for any incident angle are proposed.The research analyzes the accuracy and robustness of selecting the viscoelastic artificial boundary,and determines the reasonable viscoelastic boundary parameters.Furthermore,the input of seismic plane wave at any incident angle is established based on the principle of coordinate system conversion,which greatly simplifies the calculation method of equivalent effectiveness of boundary nodes.The MATLAB program is compiled for the secondary development of ABAQUS,and the accuracy of the input method in this paper is verified by a calculation example,which can provide theoretical support for the seismic analysis of near-fault engineering.(2)A reasonable selection method of near-field vibration is proposed,which fully considers the velocity pulse effect of near-field vibration and site characteristics.Using the mathematical model proposed by Mavroeidis,the influence of different amplitude and periodic velocity pulses on the damage distribution of the tunnel lining is compared and analyzed.(3)Based on wavelet analysis,an algorithm for identifying the strongest velocity pulse considering the three-directional components of seismic waves is proposed,and continuous wavelet transform is used for the three-directional orthogonal components to identify the direction of the velocity pulse with the largest energy.After considering the three-way components,the algorithm in this paper significantly expands the results of impulse classification.Especially for earthquakes with magnitude 7～8,the algorithm in this paper can more effectively identify impulse ground motion records.(4)A new dislocation distribution model based on the theory of bumps was discussed.Taking the Mw6.95 Loma Prieta earthquake in 1989 as an example,the rationality and accuracy of the bumps distribution model compared to the uniform distribution model was verified.(5)The Hankel transform and the Thomson-Haskell propagation algorithm are used to obtain the spatial deformation field of the layered soil.Based on the orthogonal normalization technology,the numerical stability problem is solved,and the fault dislocation input of the layered soil in any semi-infinite space is realized.The errors in the calculation of coseismic deformation field caused by the layered structure of the soil,the distribution of dislocations on the fault rupture surface,and the dislocation input method are explored.And a refined input method for fault dislocation resistance analysis is proposed.(6)Combining the viscoelastic artificial boundary and the equivalent nodal force input method,a new input method that converts the fault dislocation from a static process to a dynamic process is established.The accurate input of the coupling effect of fault dislocation and ground motion is realized.Starting from the rupture process of active faults,the different destructive effects of dislocations and ground motions in separate and coupled effects on tunnels are explored.The stress and damage distribution changes in typical locations of tunnel linings are compared.The results show that the coupling effect of dislocations and ground motions causes both the peak tensile damage and the peak compressive damage to increase.The tensile damage to the tunnel lining is more serious than the compression damage.The peak increase of tensile damage caused by the coupling of dislocation and ground motion is mainly concentrated on the arched shoulders and arched feet,which need to be paid attention to in seismic fortification.