Three-dimensional Numerical Simulation Study To The Seismic Advanced Prediction

The surrounding rocks in front of the tunnel are complicated and changeable.In the process of excavation,there are often bad geological conditions such as surge water,rock burst and quicksand,which seriously affect the construction progress,endanger personnel safety.Seismic reflection wave method is one of the common methods of geological advance prediction of tunnel.It is used to collect reflected signals,conduct wave field separation,reverse the potential geological hazards and guide the excavation of the tunnel.Therefore,three-dimensional numerical simulation is used to study the data of different attitude(vertical strata,steeply dipping strata and slanted strata)and different components by means of three-dimensional wave field snapshot,seismic record data,wave field separation.The research is as follows(1)Based on the wave field snapshots,The propagation rule and energy distribution characteristics of seismic waves are studied.Firstly,different component wave field snapshots are drew.Secondly,seismic wave types in different energy groups are identified.Thirdly,the reflection and transmission characteristics of seismic waves are observed.Finally,we compare the energy distribution characteristics of different components in the space.Based on seismograms,the rule of reflected waves travel time in different yields are studied.Firstly,we extract three component seismograms and know the types of seismic waves.Secondly,the travel time is recorded.Thirdly,Based on direct wave velocity,we calculate the distance between the source and wave impedance interface.Finally,the regulars about travel time or distance with the change of attitude are analyzed.(2)Based on seismograms,the rule of reflected wave apparent velocity in different yields are studied.Firstly,knowing arrange parameters of observation system and formula about time-distance curve of the reflected wave,we can calculate 24 discrete time-distance(t,x)points.Secondly,using least squares method,we can calculate the correlation coefficient and apparent velocity of reflected wave.Finally,based on apparent velocity in seismograms,we can conclude the change rule about correlation coefficient or apparent velocity with the change of attitude.Based on seismograms,the rule of reflected wave the amplitude ratio in different yields are studied.Firstly,the amplitude peak of the first detector in the seismograms is extracted.The amplitude peak ratio(Z/X and Y/X)of the reflected wave is plotted in two-dimensional or three-dimensional coordinates.Finally,the regulars about the amplitude ratio with the change of attitude are analyzed.(3)Based on the wave field separation,it is compared ?—p transformation and F-k transform.At the same time,it is analyzed the effect of wave field separation about seismograms of different occurrence.After ?—p transformation and F-k transform it is observed the distribution of reflected signals and selected filter window of rectangle or sector in order to separate the transverse waves and shear waves.Finally,it is evaluated the signal feature.(4)Based on the engineering data,it is studied simulation results and inversion conclusions.In the context of actual engineering,the whole process of data collecting and data processing is described.It is compared signal to noise ratio between the different components and studied the characteristics of wave field separation.We observe similarity of inversion results in the same range after two advanced prediction.It is generalized formula of average relative error which is evaluating the accuracy of the inversion results.Through the above research,the main results are as follows:(1)After vertical excitation energy at the tunnel face,the energy of X component longitudinal wave and Y and Z component transverse wave is mainly concentrated in front of the tunnel face.Therefore,in the three-component seismic recording signal,the X component data is often used to analyze the reflection of longitudinal wave in front of the tunnel face,while the Y and Z component data are commonly used to study in front of the reflection of shear wave.(2)When the stratum is tilted,The reflected wave from conventional tunnel short arrangement observation system collected is almost a linear relationship,which can apply the way of linear wave field separation to accomplish the wave field separation.However,the extracted reflection wave has the error of decrease in time and increase in apparent speed.For vertical and steeply dipping strata,the error can be ignored.In the case of low dipping formation,the error can result in the misjudgment trap of reflected longitudinal and transverse waves.The changes in the attitude of stratum will affect the amplitude ratio of the reflected waves(Z/X ? Y/X).When the local layer slows down,the amplitude ratio of the reflected longitudinal wave increases or the amplitude ratio of the reflected shear wave decreases.The change of angle has a great influence on the Z/X ratio and the change of inclination has a big impact on the Y/X ratio..(3)According to the energy group information,The commonly used linear wave field separation method(?—p ? F-K)can be used to complete wave field separation of reflected longitudinal and transverse waves.According to the energy group and the time information,?—p transform can recognize reflected wave,which is advantageous to the prediction or interpretation of the kinematic characteristics of the wave field.However,it can not.retain original amplitude,which is not apply to forecast or explain the dynamic characteristics of the wave field.The F-K method is mainly separated by wave field according to the apparent velocity value of the energy group.After the separation,the data is retained with the original frequency and wave number information,which is advantageous to the prediction or interpretation of the dynamic characteristics of the wave field.Because of lacking information about time,It is difficult to identify reflected waves directly.The fan-shaped filter area is mixed with various kinds of signals in the fan-angle filtering area with low frequency and low wave number,and the separation is difficult.(4)Numerical simulation and engineering application are shown.Because of the strong energy and low speed characteristics of the transverse wave,In the forecast,average relative error value about shear wave velocity,compressional wave velocity and poisson's ratio successively increase and the reliability of inversion results successively decreases.