Tunnel earthquake advanced detection method based on observation system optimization and angle domain reverse time migration imaging

Abstract

The invention discloses a tunnel earthquake advanced detection method based on observation system optimization and angle domain reverse time migration imaging, and the method specifically comprises the steps: 1, setting an observation system with the same shot-geophone point in a tunnel, and carrying out the collection of a tunnel earthquake record; 2, constructing a rectangular grid geologic model; 3, solving a tunnel seismic source seismic wave field; 4, solving a tunnel detector seismic wave field, and obtaining a tunnel reverse time migration imaging result; step 5, solving a Poynting vector # imgabs0 # of the seismic wave field of the tunnel seismic source and a Poynting vector # imgabs1 # of the seismic wave field of the tunnel detector; step 6, obtaining a tunnel seismic source seismic wave field and a tunnel detector seismic wave field of an angle domain; and step 7, obtaining a high-precision imaging result. According to the method, the imaging precision of tunnel advanced detection can be effectively improved, so that the front geological structure can be identified more accurately.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel advance geological detection, and in particular relates to a tunnel seismic advance detection method based on observation system optimization and angle domain reverse time migration imaging. Background Art

[0002] Tunnel geological exploration is a crucial step in underground engineering construction. By predicting adverse geological conditions ahead of the tunnel face, such as fault fracture zones, water-rich structures, and karst caves, and implementing preemptive measures, advanced geological exploration can effectively prevent disasters such as sudden water and mud inrush, tunnel collapse, and large deformation, thereby ensuring tunnel construction safety and reducing economic losses and casualties. After years of hard work, researchers at home and abroad have developed a variety of tunnel geological exploration methods, primarily including seismic wave, electromagnetic, resistivity, and infrared detection. Seismic wave methods, with their advantages of long detection range, excellent interface recognition, and high efficiency, have become one of the most important methods for advanced geological exploration. Commonly used tunnel seismic wave exploration methods include horizontal seismic profiling (HSP), tunnel reflection tomography (TRT), tunnel seismic prediction (TSP), and tunnel geological tomography (TST).

[0003] Unlike surface seismic exploration, tunnel seismic wave advance detection is limited by the confines of the tunnel, and the layout of the observation system can affect imaging quality. Observation systems can be primarily categorized into two types: linear and spatial. Linear systems, due to their lack of lateral offset, cannot fully capture spatial wavefield information. Spatial systems also have room for improvement in tunnel space utilization. Furthermore, the single-sidewall seismic source method primarily achieves single-sided illumination of the advance detection wavefield, resulting in poor imaging quality. The number of geophones also affects the intensity of the illumination energy. Optimizing the observation system can effectively improve imaging quality. However, due to factors such as tunnel shape and rock strata heterogeneity, seismic wave propagation in tunnels is significantly more complex than in surface environments. High-precision seismic data imaging technology is essential. Researchers have developed a variety of methods, including Kirchhoff integral migration imaging, reverse time migration based on vector wavefield decomposition, and reverse time migration imaging combined with Q-value compensation data. These methods can effectively improve tunnel advance detection accuracy to a certain extent, but applying traditional cross-correlation imaging conditions in tunnels can produce low-wavenumber interference, which can affect tunnel imaging quality.

[0004] Applying reverse time migration imaging to tunnels can effectively suppress the mirror artifacts found in traditional imaging methods. Angle-domain imaging is increasingly being used to address low-wavenumber interference in the imaging process, but the wave equation itself does not directly provide angle information. To further improve the accuracy of tunnel advance detection, it is necessary to utilize a tunnel seismic advance detection method based on observation system optimization and angle-domain reverse time migration imaging. Proper configuration of the observation system and the correct use of angle-domain methods are essential. Summary of the Invention

[0005] The purpose of the present invention is to provide a tunnel seismic advance detection method based on observation system optimization and angle domain reverse time migration imaging, which can effectively improve the imaging accuracy of tunnel advance detection and thus more accurately identify the geological structure ahead.

[0006] The technical solution adopted by the present invention is a tunnel seismic advance detection method based on observation system optimization and angle domain reverse time migration imaging, specifically: Step 1: Set up an observation system with the same point of blasting and inspection in the tunnel to collect tunnel seismic records. ; Step 2: Construct a rectangular grid geological model; Step 3: Given velocity model , the earthquake source propagates along the forward time axis to obtain the tunnel earthquake source seismic wave field ; Step 4: Obtain the seismic wave field of the tunnel geophone , and obtain the tunnel reverse time migration imaging results; Step 5: Obtain the Poynting vector of the tunnel source seismic wave field and the Poynting vector of the seismic wave field of the tunnel geophone ; Step 6: Obtain the tunnel source seismic wave field in the angle domain and tunnel geophone seismic wavefield ; Step 7: Obtain high-precision imaging results .

[0007] The present invention is also characterized in that: In step 1, the observation system for the same-point shot detection consists of multiple seismic sources and multiple geophones. The specific layout of the observation system for the same-point shot detection is as follows: starting from 15m-20m from the tunnel face, a geophone is set every 3m-5m on both sides of the tunnel wall. The number of geophones set on both sides of the tunnel wall is the same, and a seismic source is placed at the position corresponding to each geophone. At the same time, several seismic sources are evenly distributed on both sides of the tunnel wall. The position in the tunnel is The detector at time Tunnel seismic records were collected, including Represented as the location of the earthquake source in the tunnel.

[0008] Step 2 is as follows: Set the number of horizontal grid points of the rectangular grid geological model and the number of vertical grid points , and set the spatial sampling interval and time sampling interval of the forward simulation and maximum sampling time ; Among them, the spatial sampling interval includes the horizontal sampling interval and longitudinal sampling interval .

[0009] Step 3 is as follows: Step 3.1: Use numerical simulation techniques to construct a velocity model based on the distribution of the velocity inside the medium surrounding the tunnel. ; Step 3.2: Obtain the tunnel source seismic wave field according to the propagation law of the earthquake source along the forward time axis , The following acoustic wave equation is satisfied: (1) In formula (1), For The earthquake source at time The tunnel source seismic wave field, Indicates that it is located The source function at is the Laplace operator; Among them, the velocity model The acoustic wave equation (1) is applied as the medium velocity at the spatial position x of the tunnel.

[0010] Step 4 is as follows: Step 4.1: The earthquake records received by the geophone in the tunnel Extrapolate backward along time to obtain the seismic wave field of the tunnel geophone , the specific expression is as follows: (2) In formula (2), For The detector at time The seismic wave field of the tunnel geophone; Step 4.2: Use the high-order finite difference method on a regular grid to solve formula (1) and formula (2), and transform the tunnel source seismic wave field in formula (1) into and the tunnel geophone seismic wave field in formula (2) Combined with the Claerbout cross-correlation imaging formula, the tunnel reverse time migration imaging formula is obtained as follows: (3).

[0011] In step 5, the Poynting vector of the tunnel source seismic wave field and the Poynting vector of the seismic wave field of the tunnel geophone Calculated by the following formula: (4) (5) In formula (4), is the Poynting vector of the tunnel source seismic wave field The horizontal component of the direction, is the Poynting vector of the tunnel source seismic wave field The vertical component of the direction, represents the time differential of the tunnel source seismic wave field, is the spatial gradient of the seismic wave field of the tunnel source; In formula (5), is the Poynting vector of the tunnel source seismic wave field The horizontal component of the direction, is the Poynting vector of the tunnel source seismic wave field The vertical component of the direction, represents the time differential of the seismic wave field of the tunnel geophone, is the spatial gradient of the seismic wave field of the tunnel geophone. Step 6 is as follows: Step 6.1: Based on the Poynting vector of the tunnel source seismic wave field obtained in step 5 Get the propagation angle of the earthquake wave field at the source , the Poynting vector of the seismic wave field through the tunnel geophone Get the propagation angle of the seismic wave field of the geophone , specifically in the following forms: (6) (7) Based on equations (4) to (7), the propagation angle of each position in the wave field at each moment is calculated.

[0012] Step 6.2, Introducing the tunnel source seismic wave field The tunnel source seismic wave field in the angle domain is obtained , Introducing the tunnel geophone seismic wave field The tunnel geophone seismic wave field in the angle domain is obtained , satisfying the following form: (8) (9) In formula (8) is the propagation angle of the tunnel earthquake source wave field, in formula (9) is the propagation angle of the seismic wave field of the tunnel geophone.

[0013] Step 7 is as follows: Substituting equations (8) and (9) into the tunnel reverse time migration imaging formula (3), we get the imaging formula in the angle domain, which is as follows: (10) Indicates the wave field angle is The angle filter is as follows: (11) In formula (11), It is an angle threshold manually set according to different speed models.

[0014] The beneficial effects of the present invention are: (1) The method of the present invention optimizes the tunnel observation system, adjusts the arrangement of the source and the detector, and obtains the tunnel seismic record; secondly, the forward seismic wave field in the tunnel is obtained based on the forward simulation, and the reverse seismic wave field in the tunnel is obtained by reverse extrapolation along the time according to the tunnel seismic record; thirdly, the propagation angle of the tunnel source and the detector wave field is calculated using the Poynting vector, and the tunnel source and the detector wave field in the angle domain is obtained; finally, the cross-correlation imaging formula is used and the angle filter is introduced to obtain high-precision tunnel imaging results.

[0015] (2) Compared with the commonly used tunnel seismic advance detection method, the method of the present invention is suitable for imaging of large-angle structural models. The reasons why this method has the above advantages are: first, an observation system with simultaneous shot detection is designed, that is, the detector is set in front of the tunnel face and the seismic source is set at the tunnel face and the detector position. Because the observation system is optimized, the detector is close to the tunnel face, which effectively reduces the artifacts and symmetry illusions on both sides of the tunnel. The seismic source is arranged at the detector position, which effectively suppresses the illusion caused by the observation layout. The seismic source is arranged at the tunnel face to eliminate the artifacts between the tunnel face and the identified interface; second, because the angle domain reverse time migration imaging method based on the Poynting vector is used, the imaging result is decomposed into angles to suppress noise, reduce the interference of low-wavenumber signals, and improve the accuracy of advance detection imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flow chart of the tunnel seismic advance detection method based on observation system optimization and angle domain reverse time migration imaging of the present invention; Figure 2 The observation system optimized by the present invention is called the gun inspection same-point observation system; Figure 3 It is a multi-layered karst cave model used in the model calculation example of the present invention; Figure 4 This is the observation system 1 used for comparative study with the gun inspection co-point observation system in the model calculation example of the present invention; Figure 5 This is the observation system 2 used for comparative study with the gun inspection co-point observation system in the model calculation example of the present invention; Figure 6 This is the observation system 3 used for comparative study with the gun inspection co-point observation system in the model calculation example of the present invention; Figure 7 This is the observation system 4 used for comparative study with the gun inspection co-point observation system in the model calculation example of the present invention; Figure 8 This is the observation system 5 used for comparative study with the gun inspection co-point observation system in the model calculation example of the present invention; Figure 9 is the reverse time migration imaging result based on observation system 1 in the model example of the present invention; Figure 10 is the reverse time migration imaging result based on observation system 2 in the model example of the present invention; Figure 11 is the reverse time migration imaging result based on observation system 3 in the model example of the present invention; Figure 12 is the reverse time migration imaging result based on observation system 4 in the model example of the present invention; Figure 13 is the reverse time migration imaging result based on observation system 5 in the model calculation example of the present invention; Figure 14 This is the reverse time migration imaging result based on the shot inspection same-point observation system in the model calculation example of the present invention; Figure 15 This is the result of reverse time migration imaging in the angle domain based on the shot-check same-point observation system in the model example of the present invention. DETAILED DESCRIPTION

[0017] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] The present invention provides a tunnel earthquake advance detection method based on observation system optimization and angle domain reverse time migration imaging, such as Figure 1 As shown, please follow the steps below: Step 1: Set up an observation system with the same point of blasting and inspection in the tunnel to collect tunnel seismic records. ; In step 1, the observation system for the same-point shot detection consists of multiple seismic sources and multiple geophones. The specific layout of the observation system for the same-point shot detection is as follows: starting from 15m-20m from the tunnel face, a geophone is set every 3m-5m on both sides of the tunnel wall. The number of geophones set on both sides of the tunnel wall is the same, and a seismic source is placed at the position corresponding to each geophone. At the same time, several seismic sources are evenly distributed on both sides of the tunnel wall. The position in the tunnel is The detector at time Tunnel seismic records were collected, including Represented as the location of the earthquake source in the tunnel.

[0019] Step 2: Construct a rectangular grid geological model. Specifically, set the number of horizontal grid points of the rectangular grid geological model. and the number of vertical grid points , and set the spatial sampling interval and time sampling interval of the forward simulation and maximum sampling time ; Among them, the spatial sampling interval includes the horizontal sampling interval and longitudinal sampling interval ; Step 3: Given velocity model , the earthquake source propagates along the forward time axis to obtain the tunnel earthquake source seismic wave field ; Step 3 is as follows: Step 3.1: Use numerical simulation techniques to construct a velocity model based on the distribution of the velocity inside the medium surrounding the tunnel. ; Step 3.2: Obtain the tunnel source seismic wave field according to the propagation law of the earthquake source along the forward time axis , The following acoustic wave equation is satisfied: (1) In formula (1), For The earthquake source at time The tunnel source seismic wave field, Indicates that it is located The source function at is the Laplace operator; Among them, the velocity model The acoustic wave equation (1) is applied as the medium velocity at the spatial position x of the tunnel.

[0020] Step 4: Obtain the seismic wave field of the tunnel geophone , and obtain the tunnel reverse time migration imaging results; Step 4 is as follows: Step 4.1: The earthquake records received by the geophone in the tunnel Extrapolate backward along time to obtain the seismic wave field of the tunnel geophone , the specific expression is as follows: (2) In formula (2), For The detector at time The seismic wave field of the tunnel geophone; Step 4.2: Use the high-order finite difference method on a regular grid to solve formula (1) and formula (2), and transform the tunnel source seismic wave field in formula (1) into and the tunnel geophone seismic wave field in formula (2) Combined with the Claerbout cross-correlation imaging formula, the tunnel reverse time migration imaging formula is obtained as follows: (3) There will be low-wavenumber interference in the tunnel reverse time migration imaging results, and there will be insufficient imaging of large-angle structures, so the next step is to solve these problems.

[0021] Step 5: Obtain the Poynting vector of the tunnel source seismic wave field and the Poynting vector of the seismic wave field of the tunnel geophone ; In step 5, the Poynting vector of the tunnel source seismic wave field and the Poynting vector of the seismic wave field of the tunnel geophone Calculated by the following formula: (4) (5) In formula (4), is the Poynting vector of the tunnel source seismic wave field The horizontal component of the direction, is the Poynting vector of the tunnel source seismic wave field The vertical component of the direction, represents the time differential of the tunnel source seismic wave field, is the spatial gradient of the seismic wave field of the tunnel source; In formula (5), is the Poynting vector of the tunnel source seismic wave field The horizontal component of the direction, is the Poynting vector of the tunnel source seismic wave field The vertical component of the direction, represents the time differential of the seismic wave field of the tunnel geophone, is the spatial gradient of the seismic wave field of the tunnel geophone. Step 6: Calculate the propagation angle of the tunnel source seismic wave field and the propagation angle of the seismic wave field of the geophone , and obtain the tunnel source seismic wave field in the angle domain and tunnel geophone seismic wavefield ; Step 6 is as follows: Step 6.1: Based on the Poynting vector of the tunnel source seismic wave field obtained in step 5 Get the propagation angle of the earthquake wave field at the source , the Poynting vector of the seismic wave field through the tunnel geophone Get the propagation angle of the seismic wave field of the geophone , specifically in the following forms: (6) (7) Based on equations (4) to (7), the propagation angle of each position in the wave field at each moment is calculated.

[0022] Step 6.2, Introducing the tunnel source seismic wave field The tunnel source seismic wave field in the angle domain is obtained , Introducing the tunnel geophone seismic wave field The tunnel geophone seismic wave field in the angle domain is obtained , satisfying the following form: (8) (9) In formula (8) is the propagation angle of the tunnel earthquake source wave field, in formula (9) is the propagation angle of the seismic wave field of the tunnel geophone.

[0023] Step 7: Use the tunnel reverse time migration imaging formula (3) and introduce the angle filter to obtain , and obtain high-precision imaging results .

[0024] Step 7 is as follows: Substituting equations (8) and (9) into the tunnel reverse time migration imaging formula (3), we get the imaging formula in the angle domain, which is as follows: (10) Indicates the wave field angle is The angle filter is as follows: (11) In formula (11), It is an angle threshold manually set according to different speed models.

[0025] Example 1 Model Example The present invention first arranges the observation system of the same point of artillery inspection as follows Figure 2 As shown in the figure, the layout of the system is to set a seismic source at an interval of 2m on the tunnel face, with a total of 6 seismic sources evenly distributed; starting from 15m away from the tunnel face, a detector is set at an interval of 5m on both sides of the tunnel wall, and 3 detectors are set on each side of the tunnel wall, and a seismic source is arranged at the position corresponding to each detector; at the same time, starting from 65m away from the tunnel face, a seismic source is set at an interval of 2m on both sides of the tunnel wall, with a total of 48 seismic sources evenly distributed. The specific implementation process is applied to the multi-layered cave model as shown in the figure. Figure 3 As shown in the figure, the model was generated using MATLAB software based on the velocity distribution of the medium surrounding the tunnel. It consists of a 150×200 grid with a spatial grid spacing of 1 meter. The tunnel is located as the black rectangle in the figure, with a length of 80 meters and a width of 10 meters. During the migration imaging process, a Ricker wavelet with a frequency of 300 Hz was used as the source, with a time sampling interval of 0.1 ms and 5000 time sampling points.

[0026] In order to study the influence of observation layout on imaging accuracy, five different observation systems are set up. First, in order to analyze the influence of detector distance on imaging results, the following settings are set up: Figure 4 The layout of the observation system 1 shown in the figure is that the starting point is 79m away from the tunnel face, and a geophone is set every 5m on both sides of the tunnel wall. There are 3 geophones on each side of the tunnel wall. At the same time, the starting point is 65m away from the tunnel face, and a seismic source is set every 2m on both sides of the tunnel wall. A total of 48 seismic sources are evenly distributed. Figure 7 The observation system 4 shown in the figure takes the position 15m away from the tunnel face as the starting point, and sets a detector every 5m on both sides of the tunnel wall. There are 3 detectors on each side of the tunnel wall. The layout is the same as that of the observation system 1. 48 seismic sources are evenly arranged on both sides of the tunnel wall. Then, in order to analyze the influence of the presence or absence of seismic sources on the tunnel face on the imaging effect, the following is set up based on the observation system 1 and the observation system 4. Figure 5 The observation system 2 shown and Figure 8The observation system 5 shown in the figure has a seismic source set at an interval of 2m on the tunnel face, with a total of 6 seismic sources evenly arranged. Secondly, in order to analyze the influence of the presence or absence of seismic sources on the imaging effect at the same position of the geophone, the following is set on the basis of observation mode 2: Figure 6 The observation method 3 shown in the figure has an observation layout in which one source is arranged at the position corresponding to each geophone.

[0027] Reverse time migration is performed based on observation systems 1-5, such as Figure 9 The imaging results of observation system 1 show that the detector in this system is far away from the tunnel face, resulting in obvious artifacts in the red frame area and on both sides of the tunnel. In addition, the imaging accuracy of the area behind the oblique interface is low, and the cave and vertical interface are not clear enough. Figure 10 The imaging results of observation system 2, in which the seismic source is arranged at the tunnel face, weaken the false image between the tunnel face and the inclined interface, but the interference caused by the layout of the observation system is still significant; Figure 11 The imaging results of observation system 3 show that after the source is arranged at the position of the geophone, the false images caused by the observation layout are significantly reduced, but the imaging accuracy is still insufficient; Figure 12 Observing System 4 and Figure 13 The imaging results for observation system 5 show that placing the geophones closer to the tunnel face reduces artifacts on both sides of the tunnel, but artifacts in the red framed area and due to the observation layout remain significant. The reverse time migration imaging results based on these five observation systems exhibit significant interference and limited imaging accuracy. When the geophones are farther from the tunnel face, more artifacts appear on both sides of the tunnel. Without a seismic source at the tunnel face, artifacts also appear between the tunnel face and the identified interface. Furthermore, the observation system itself significantly interferes with the imaging results.

[0028] Figure 14 This is the angle-domain reverse time migration imaging result based on the shot inspection same-point observation system. It can be seen that the artifacts on both sides of the tunnel (the areas indicated by the red arrows) and the symmetry illusion are effectively reduced, the illusions caused by the observation layout are effectively suppressed, and the artifacts in front of the tunnel (the red elliptical area) are weakened. It can be seen that the observation system proposed in this invention effectively improves the accuracy of the imaging effect and removes some interference in the imaging results.

[0029] Figure 15 This is the angle-domain reverse time migration imaging result obtained using a shot-check collocated observation system, obtained through steps 1 through 7 of the proposed method. The angle threshold set in step 7 is 30° based on the multi-layered cave model. The imaging results show that this method significantly suppresses low-frequency noise in the imaging results, further improving imaging accuracy.

[0030] Based on the shot inspection and same-point observation system, the imaging accuracy is further improved by using the angle domain reverse time migration method based on the Poynting vector. The obtained imaging results verify the effectiveness of the proposed method.

[0031] Example 2 The tunnel seismic advance detection method based on observation system optimization and angle domain reverse time migration imaging is as follows: Step 1: Set up an observation system with the same point of blasting and inspection in the tunnel to collect tunnel seismic records. ; In step 1, the observation system for the same-point shot detection consists of multiple seismic sources and multiple geophones. The specific layout of the observation system for the same-point shot detection is as follows: starting from 15m-20m from the tunnel face, a geophone is set every 3m-5m on both sides of the tunnel wall. The number of geophones set on both sides of the tunnel wall is the same, and a seismic source is placed at the position corresponding to each geophone. At the same time, several seismic sources are evenly distributed on both sides of the tunnel wall. The position in the tunnel is The detector at time Tunnel seismic records were collected, including Represented as the location of the earthquake source in the tunnel.

[0032] Step 2: Construct a rectangular grid geological model; Step 3: Given velocity model , the earthquake source propagates along the forward time axis to obtain the tunnel earthquake source seismic wave field ; Step 4: Obtain the seismic wave field of the tunnel geophone , and obtain the tunnel reverse time migration imaging results; Step 5: Obtain the Poynting vector of the tunnel source seismic wave field and the Poynting vector of the seismic wave field of the tunnel geophone ; Step 6: Obtain the tunnel source seismic wave field in the angle domain and tunnel geophone seismic wavefield ; Step 7: Obtain high-precision imaging results .

[0033] Example 3 The tunnel seismic advance detection method based on observation system optimization and angle domain reverse time migration imaging is as follows: Step 1: Set up an observation system with the same point of blasting and inspection in the tunnel to collect tunnel seismic records. ; Step 2: Construct a rectangular grid geological model; Step 2 is as follows: Set the number of horizontal grid points of the rectangular grid geological model and the number of vertical grid points , and set the spatial sampling interval and time sampling interval of the forward simulation and maximum sampling time ; Among them, the spatial sampling interval includes the horizontal sampling interval and longitudinal sampling interval .

[0034] Step 3: Given velocity model , the earthquake source propagates along the forward time axis to obtain the tunnel earthquake source seismic wave field ; Step 4: Obtain the seismic wave field of the tunnel geophone , and obtain the tunnel reverse time migration imaging results; Step 5: Obtain the Poynting vector of the tunnel source seismic wave field and the Poynting vector of the seismic wave field of the tunnel geophone ; Step 6: Obtain the tunnel source seismic wave field in the angle domain and tunnel geophone seismic wavefield ; Step 7: Obtain high-precision imaging results .

[0035] Example 4 The tunnel seismic advance detection method based on observation system optimization and angle domain reverse time migration imaging is as follows: Step 1: Set up an observation system with the same point of blasting and inspection in the tunnel to collect tunnel seismic records. ; Step 2: Construct a rectangular grid geological model; Step 3: Given velocity model , the earthquake source propagates along the forward time axis to obtain the tunnel earthquake source seismic wave field ; Step 3 is as follows: Step 3.1: Use numerical simulation techniques to construct a velocity model based on the distribution of the velocity inside the medium surrounding the tunnel. ; Step 3.2: Obtain the tunnel source seismic wave field according to the propagation law of the earthquake source along the forward time axis , The following acoustic wave equation is satisfied: (1) In formula (1), For The earthquake source at time The tunnel source seismic wave field, Indicates that it is located The source function at is the Laplace operator; Among them, the velocity model The acoustic wave equation (1) is applied as the medium velocity at the spatial position x of the tunnel.

[0036] Step 4: Obtain the seismic wave field of the tunnel geophone , and obtain the tunnel reverse time migration imaging results; Step 5: Obtain the Poynting vector of the tunnel source seismic wave field and the Poynting vector of the seismic wave field of the tunnel geophone ; Step 6: Obtain the tunnel source seismic wave field in the angle domain and tunnel geophone seismic wavefield ; Step 7: Obtain high-precision imaging results .

[0037] Example 5 The tunnel seismic advance detection method based on observation system optimization and angle domain reverse time migration imaging is as follows: Step 1: Set up an observation system with the same point of blasting and inspection in the tunnel to collect tunnel seismic records. ; Step 2: Construct a rectangular grid geological model; Step 3: Given velocity model , the earthquake source propagates along the forward time axis to obtain the tunnel earthquake source seismic wave field ; Step 4: Obtain the seismic wave field of the tunnel geophone , and obtain the tunnel reverse time migration imaging results; Step 4 is as follows: Step 4.1: The earthquake records received by the geophone in the tunnel Extrapolate backward along time to obtain the seismic wave field of the tunnel geophone , the specific expression is as follows: (2) In formula (2), For The detector at time The seismic wave field of the tunnel geophone; Step 4.2: Use the high-order finite difference method on a regular grid to solve formula (1) and formula (2), and transform the tunnel source seismic wave field in formula (1) into and the tunnel geophone seismic wave field in formula (2) Combined with the Claerbout cross-correlation imaging formula, the tunnel reverse time migration imaging formula is obtained as follows: (3).

[0038] Step 5: Obtain the Poynting vector of the tunnel source seismic wave field and the Poynting vector of the seismic wave field of the tunnel geophone ; Step 6: Obtain the tunnel source seismic wave field in the angle domain and tunnel geophone seismic wavefield ; Step 7: Obtain high-precision imaging results .

[0039] Example 6 The tunnel seismic advance detection method based on observation system optimization and angle domain reverse time migration imaging is as follows: Step 1: Set up an observation system with the same point of blasting and inspection in the tunnel to collect tunnel seismic records. ; Step 2: Construct a rectangular grid geological model; Step 3: Given velocity model , the earthquake source propagates along the forward time axis to obtain the tunnel earthquake source seismic wave field ; Step 4: Obtain the seismic wave field of the tunnel geophone , and obtain the tunnel reverse time migration imaging results; Step 5: Obtain the Poynting vector of the tunnel source seismic wave field and the Poynting vector of the seismic wave field of the tunnel geophone ; In step 5, the Poynting vector of the tunnel source seismic wave field and the Poynting vector of the seismic wave field of the tunnel geophone Calculated by the following formula: (4) (5) In formula (4), is the Poynting vector of the tunnel source seismic wave field The horizontal component of the direction, is the Poynting vector of the tunnel source seismic wave field The vertical component of the direction, represents the time differential of the tunnel source seismic wave field, is the spatial gradient of the seismic wave field of the tunnel source; In formula (5), is the Poynting vector of the tunnel source seismic wave field The horizontal component of the direction, is the Poynting vector of the tunnel source seismic wave field The vertical component of the direction, represents the time differential of the seismic wave field of the tunnel geophone, is the spatial gradient of the seismic wave field of the tunnel geophone.

[0040] Step 6: Obtain the tunnel source seismic wave field in the angle domain and tunnel geophone seismic wavefield ; Step 7: Obtain high-precision imaging results .

Claims

1. A tunnel seismic advance detection method based on observation system optimization and angle domain reverse time migration imaging, characterized by: Specifically: Step 1: Set up an observation system with the same point of blasting and inspection in the tunnel to collect tunnel seismic records. ; Step 2: Construct a rectangular grid geological model; Step 3: Given velocity model , the earthquake source propagates along the forward time axis to obtain the tunnel earthquake source seismic wave field ; Step 4: Obtain the seismic wave field of the tunnel geophone , and obtain the tunnel reverse time migration imaging results; Step 5: Obtain the Poynting vector of the tunnel source seismic wave field and the Poynting vector of the seismic wave field of the tunnel geophone ; Step 6: Obtain the tunnel source seismic wave field in the angle domain and tunnel geophone seismic wavefield ; Step 7: Obtain high-precision imaging results .

2. The tunnel seismic advance detection method based on observation system optimization and angle domain reverse time migration imaging according to claim 1 is characterized in that: In step 1, the observation system for the same-point shot detection consists of multiple seismic sources and multiple geophones. The specific layout of the observation system for the same-point shot detection is as follows: starting from 15m-20m from the tunnel face, a geophone is set every 3m-5m on both sides of the tunnel wall. The number of geophones set on both sides of the tunnel wall is the same, and a seismic source is placed at the position corresponding to each geophone. At the same time, several seismic sources are evenly distributed on both sides of the tunnel wall. The position in the tunnel is The detector at time Tunnel seismic records were collected, including Represented as the location of the earthquake source in the tunnel.

3. The tunnel seismic advance detection method based on observation system optimization and angle domain reverse time migration imaging according to claim 1 is characterized in that: Step 2 is as follows: Set the number of horizontal grid points of the rectangular grid geological model and the number of vertical grid points , and set the spatial sampling interval and time sampling interval of the forward simulation and maximum sampling time ; Among them, the spatial sampling interval includes the horizontal sampling interval and longitudinal sampling interval .

4. The method for tunnel seismic advance detection based on observation system optimization and angle domain reverse time migration imaging according to claim 1, characterized in that: Step 3 is as follows: Step 3.1: Use numerical simulation techniques to construct a velocity model based on the distribution of the velocity inside the medium surrounding the tunnel. ; Step 3.2: Obtain the tunnel source seismic wave field according to the propagation law of the earthquake source along the forward time axis , The following acoustic wave equation is satisfied: (1) In formula (1), For The earthquake source at time The tunnel source seismic wave field, Indicates that it is located The source function at is the Laplace operator; Among them, the velocity model The acoustic wave equation (1) is applied as the medium velocity at the spatial position x of the tunnel.

5. The method for tunnel seismic advance detection based on observation system optimization and angle domain reverse time migration imaging according to claim 1, characterized in that: Step 4 is as follows: Step 4.1: The earthquake records received by the geophone in the tunnel Extrapolate backward along time to obtain the seismic wave field of the tunnel geophone , the specific expression is as follows: （2） In formula (2), For The detector at time The seismic wave field of the tunnel geophone; Step 4.2: Use the high-order finite difference method on a regular grid to solve formula (1) and formula (2), and transform the tunnel source seismic wave field in formula (1) into and the tunnel geophone seismic wave field in formula (2) Combined with the Claerbout cross-correlation imaging formula, the tunnel reverse time migration imaging formula is obtained as follows: （3）。 6. The method for tunnel seismic advance detection based on observation system optimization and angle domain reverse time migration imaging according to claim 1, characterized in that: In step 5, the Poynting vector of the tunnel source seismic wave field and the Poynting vector of the seismic wave field of the tunnel geophone Calculated by the following formula: （4） （5） In formula (4), is the Poynting vector of the tunnel source seismic wave field The horizontal component of the direction, is the Poynting vector of the tunnel source seismic wave field The vertical component of the direction, represents the time differential of the tunnel source seismic wave field, is the spatial gradient of the seismic wave field of the tunnel source; In formula (5), is the Poynting vector of the tunnel source seismic wave field The horizontal component of the direction, is the Poynting vector of the tunnel source seismic wave field The vertical component of the direction, represents the time differential of the seismic wave field of the tunnel geophone, is the spatial gradient of the seismic wave field of the tunnel geophone.

7. The method for tunnel seismic advance detection based on observation system optimization and angle domain reverse time migration imaging according to claim 1, characterized in that: Step 6 is as follows: Step 6.1: Based on the Poynting vector of the tunnel source seismic wave field obtained in step 5 Get the propagation angle of the earthquake wave field at the source , the Poynting vector of the seismic wave field through the tunnel geophone Get the propagation angle of the seismic wave field of the geophone , specifically in the following forms: （6） （7） Based on equations (4) to (7), the propagation angle of each position in the wave field at each moment is calculated; Step 6.2, Introducing the tunnel source seismic wave field The tunnel source seismic wave field in the angle domain is obtained , Introducing the tunnel geophone seismic wave field The tunnel geophone seismic wave field in the angle domain is obtained , satisfying the following form: （8） （9） In formula (8) is the propagation angle of the tunnel earthquake source wave field, in formula (9) is the propagation angle of the seismic wave field of the tunnel geophone.

8. The method for tunnel seismic advance detection based on observation system optimization and angle domain reverse time migration imaging according to claim 1, characterized in that: Step 7 is as follows: Substituting equations (8) and (9) into the tunnel reverse time migration imaging formula (3), we get the imaging formula in the angle domain, which is as follows: (10) Indicates the wave field angle is The angle filter is as follows: (11) In formula (11), It is an angle threshold manually set according to different speed models.

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