A non-destructive testing method for the pre-splitting effect of roof cutting along the goaf.

Abstract

This invention discloses a non-destructive testing method for the pre-fracture effect of roof cutting in a goaf-retention tunnel. Multiple seismic detectors are arranged in a ring around the pre-fracture hole to collect waveform signals. Before the pre-fracture blasting is performed, a hammer-driven excitation source is activated, causing each seismic detector to collect the excitation signals from each source. Cross-correlation calculations and sequential superposition processing are then performed to obtain the cross-correlation superimposed signal of each seismic detector before the blasting. After the pre-fracture is performed, the hammering process is repeated to obtain the cross-correlation superimposed signal of each seismic detector after the blasting. The two signals are subtracted to obtain the signal of the cracks induced by the blasting. Then, based on this signal, a spatial grid of sensitive cores is established within a certain range around the pre-fracture hole, and the above signal is mapped onto the spatial grid based on energy, thereby obtaining a distribution map of crack development degree within the imaging area. Finally, the pre-fracture effect in each azimuth region of the pre-fracture hole is evaluated based on this map.

Description

Technical Field

[0001] This invention relates to a non-destructive testing method for the pre-splitting effect of roof cutting along the goaf, belonging to the technical field of roof cutting pre-splitting effect testing. Background Technology

[0002] Goaf retention is a technique that maintains and preserves the original mining roadways along the edge of the goaf after the coal face. It improves coal extraction rate, reduces roadway excavation rate, and alleviates the tension in mining and excavation succession, meeting the requirements of safe, green, and efficient coal mining development. It is an important development direction and technical support for scientific mining. Due to the influence of deep underground stress and mining disturbance, roadway supports are easily damaged and difficult to maintain their function, which is a problem that urgently needs to be solved in the process of goaf retention. Existing research shows that using pre-splitting blasting to cut the roof cantilever can reduce the length of the roof cantilever, alleviate the pressure on the roadway side supports, and ensure successful roadway retention.

[0003] The key to top-cutting pressure relief lies in the formation and propagation of cracks around the pre-splitting blasting holes. The degree of crack development directly determines the effectiveness of top-cutting pre-splitting. However, current methods for detecting the effectiveness of top-cutting pre-splitting require drilling exploratory boreholes around the pre-splitting area and then conducting subsequent evaluations. This is not only cumbersome but also requires destructive drilling on the pre-splitting area. Currently, there is no non-destructive testing and evaluation technology for top-cutting pre-splitting effects. Therefore, providing a new method that can non-destructively test and evaluate the effectiveness of top-cutting pre-splitting is a research direction in this industry. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a non-destructive testing method for the pre-splitting effect of roof cutting along the goaf. By combining a specific processing procedure of signal acquisition, processing, imaging and interpretation, the method obtains pre-splitting images of roof cutting through non-destructive testing and evaluates the pre-splitting effect of roof cutting.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a non-destructive testing method for the pre-splitting effect of roof cutting along the goaf, the specific steps of which are as follows:

[0006] Step 1: After selecting the location on the roof of the goaf-keeping roadway, construct the pre-splitting hole. After completion, arrange N seismic detectors on the roof of the goaf-keeping roadway around the pre-splitting hole. The N seismic detectors are arranged in a ring around the pre-splitting hole, and the spacing between two adjacent seismic detectors is the same. Then, connect each seismic detector to the seismograph to complete the deployment of the ring seismic wave observation system.

[0007] Step 2: Establish a seismic observation coordinate system for the pre-splitting borehole with the pre-splitting borehole as the origin, the X-axis along the direction of the goaf roadway as the X-axis, and the Y-axis along the radial direction of the goaf roadway as the Y-axis. Calculate the coordinates of each seismic detector in this coordinate system accordingly.

[0008] Step 3: Before the pre-splitting blasting, using hammering as the seismic source, multiple seismic waves are excited at the pre-splitting hole with the same force and equal intervals. Each seismic detector simultaneously collects the seismic wave data generated by each source and feeds it back to the seismograph for recording. After completion, the seismograph obtains the excitation signals from each source collected by each seismic detector. The excitation signals from each source collected by each seismic detector are cross-correlated and superimposed according to the excitation sequence of each source, thereby improving the signal-to-noise ratio and obtaining the maximum correlation signal. Finally, the cross-correlation superimposed signal M from each seismic detector is output. 前1 M 前2 ... M 前N The seismograph was disconnected from each seismic detector, and the top-cutting and pre-splitting blasting construction began inside the pre-splitting hole.

[0009] Step 4: After completing the pre-splitting blasting operation, reconnect N seismic detectors to the seismograph, and following the process in Step 3, finally obtain the cross-correlation superposition signal M from each seismic detector. 后1 M 后2 ... M 后N ;

[0010] Step 5: Subtract the cross-correlation superposition signal amplitude value obtained from each seismic detector in Step 4 from the cross-correlation superposition signal amplitude value obtained in Step 3, respectively, to obtain the signal formed by the crack induced by the blast, denoted as M1, M2, ..., M N ;

[0011] Step Six: Based on the signals M1, M2, ..., M8 obtained in Step Five, establish the crack scattering coma propagation density function in the signals acquired by each seismic source and each seismic detector. The specific calculation process is as follows:

[0012] Obtain the excitation location of each seismic source and the location of each seismic detector. Given the seismic wave propagation velocity v, calculate the crack scattering coma diffusion density function K(s1,s2,x0,t) at different spatial locations based on the different signal propagation times, i.e., the spatial distribution of the sensitive nuclei:

[0013]

[0014] In equation (1), K(s1,s2,x0,t) describes the probability that the wave train is emitted at point s1, passes through x0, and is received at position s2 after time t; p(s1,s2,t) represents the probability that the wave train travels from s1 to s2 after time t, specifically,

[0015]

[0016] In equation (2), |s1-s2| represents the distance between s1 and s2, and D is the scattering coefficient;

[0017] After calculation using the above formula, a spatial grid for the distribution of sensitive nuclei is established within a certain range around the pre-cracked hole.

[0018] Step 7: Using M1, M2, ..., M N Based on the energy of the mid-coil wave signal, and according to the time delay relationship of each coil wave signal, it is mapped into the corresponding sensitive distribution space grid to obtain the coil wave disturbance distribution imaging result of each coil wave signal;

[0019] Step 8: Superimpose the imaging results of the various tail wave disturbance distributions obtained in Step 7 to obtain the crack development degree distribution map within the spatial grid range of the sensitive core distribution. Then, delineate a certain range around the pre-cracked hole as the imaging area, and then obtain the crack development degree distribution map of the imaging area.

[0020] Step 9: Perform statistical analysis on the energy distribution within the imaging region and calculate its average value, denoted as E. 平均 Finally, the pre-cracking effect of the pre-cracking hole in each orientation is evaluated: if the energy of a certain orientation of the pre-cracking hole in the imaging area is greater than E... 平均 This determines that the area has many cracks and a good pre-cracking effect; conversely, it determines that the area has a poor pre-cracking effect; thus completing the evaluation of the pre-cracking effect in each area around the current pre-cracking hole.

[0021] Furthermore, in step one, there are eight seismic detectors, which are evenly distributed on a ring centered on the pre-fractured hole. The radius of the ring can be set as needed.

[0022] Furthermore, the specific process of performing cross-correlation and superposition calculations according to the excitation sequence of each seismic source in step three is as follows:

[0023] The cross-correlation calculation is performed in the order of excitation. Specifically, the record obtained by cross-correlation calculation of the signal obtained from the first excitation and the signal obtained from the second excitation is then cross-correlated with the signal obtained from the third excitation, and so on, until the signal obtained from the last excitation is cross-correlated.

[0024] The formula for calculating cross-correlation is:

[0025]

[0026] In the formula, x(n) and y(n) represent the seismic signals under different excitations participating in the cross-correlation, respectively, τ represents the time shift of y(n) relative to x(n), and N represents the length of the entire sampled signal participating in the cross-correlation.

[0027] Furthermore, the calculation of the wake signal energy in step seven adopts the absolute amplitude calculation method, that is, the absolute value of the amplitude of the corresponding signal is used.

[0028] Furthermore, in step six, a spatial grid for the distribution of sensitive nuclei is established in a 10m region centered on the pre-cracked hole, with the internal grid size set to 0.1m × 0.1m.

[0029] Furthermore, in step eight, the imaging area is defined as a 10m radius around the pre-cracked hole.

[0030] Furthermore, in step nine, the energy distribution within the imaging area is statistically analyzed and its variance D(M) is calculated. When evaluating the pre-cracking effect of the pre-cracking holes in the subsequent process, for different pre-cracking holes, the smaller the variance D(M), the more stable the pre-cracking effect is.

[0031] Since existing evaluation methods for roof cutting and pre-splitting effects are all destructive post-construction assessments, while current mine geophysical exploration technology has achieved non-destructive exploration in detecting concealed structures and water-bearing properties in mining faces, it cannot be directly used for evaluating roof cutting and pre-splitting effects. The inventors have developed the method of this invention, which has the following advantages compared to existing technologies:

[0032] 1. The present invention arranges multiple seismic detectors on the roof of the goaf-retention roadway. The multiple seismic detectors are arranged in a ring around the pre-splitting hole, and the spacing between two adjacent seismic detectors is the same, thus forming a ring seismic wave observation system. This arrangement can realize the acquisition of seismic tail wave signals of cracks in different directions of the pre-splitting hole, which can be used to evaluate the development of multi-directional cracks after the pre-splitting hole is blasted and pre-splitting.

[0033] 2. This invention first involves using a hammer to excite a seismic source before the pre-splitting blasting is performed. This causes each seismic detector to collect the excitation signals from each source, and performs cross-correlation calculations and sequential superposition processing to obtain the cross-correlation superposition signals of each seismic detector before the blasting. Then, after the pre-splitting blasting is performed, the hammering process is repeated to obtain the cross-correlation superposition signals of each seismic detector after the blasting. The two signals are subtracted to obtain the signal of the cracks induced by the blasting. Next, a spatial grid of sensitive core distribution is established within a certain range around the pre-splitting hole based on this signal, and the above signal is mapped into the spatial grid based on energy, thereby obtaining a distribution map of the crack development degree in the imaging area. Finally, the pre-splitting effect in each azimuth region of the pre-splitting hole is evaluated based on this map. Thus, this invention forms a non-destructive testing process for the pre-splitting effect of goaf-side roadway retention with roof cutting, which integrates signal acquisition, processing, imaging, and interpretation. This method is beneficial to improving the actual effect of goaf-side roadway retention and provides technical support for deep coal seam mining. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the layout of the ring seismic wave observation system in this invention;

[0035] Figure 2 yes Figure 1 A top view of the area surrounding the pre-splitting blast hole;

[0036] Figure 3 This is the signal and its envelope diagram formed by the crack induced by the explosion in this invention;

[0037] Figure 4 This is a spatial grid of sensitive nuclei and a distribution map of crack development in this invention. Detailed Implementation

[0038] The present invention will be further described below.

[0039] like Figure 1 As shown, the specific steps of this invention are as follows:

[0040] Step 1: After selecting the location on the roof of the goaf-retention roadway, construct pre-splitting holes. After completion, arrange eight seismic detectors at equal intervals on a 2m radius ring centered on the pre-splitting holes. Then, connect each seismic detector to a seismograph, thus completing the deployment of the ring seismic wave observation system. To ensure signal coupling, each seismic detector is fixed to the roof rock using long tail cones and grease fittings. Figure 2 As shown, the eight seismic detectors are numbered R1 to R8 in clockwise order;

[0041] Step 2: Establish a seismic observation coordinate system for the pre-splitting borehole, with the pre-splitting borehole as the origin (i.e., its coordinates X and Y are both 0), the direction of the goaf roadway as the X-axis, and the radial direction of the goaf roadway as the Y-axis. Calculate the coordinates of each seismic detector in this coordinate system; that is, the X-axis coordinates and Y-axis coordinates of R1 to R8 are X1, X2, ..., X8 and Y1, Y2, ..., Y8, respectively.

[0042] Step 3: Before the pre-splitting blasting, using hammer impact as the seismic source, 10 seismic waves are excited at equal intervals with the same force at the pre-splitting hole. Each seismic detector simultaneously collects the seismic wave data generated by each source and feeds it back to the seismograph for recording. The sampling frequency is 20kHz, the number of sampling points is 2048, and the sampling length is 100ms. After completion, the seismograph obtains the excitation signals from the 10 sources collected by each seismic detector. The excitation signals from the 10 sources collected by each seismic detector are cross-correlated and superimposed according to the excitation order of the 10 sources. The specific process is as follows:

[0043] The cross-correlation calculation is performed in the order of excitation sequence 1 to 10. Specifically, the record obtained by cross-correlation calculation of the signal obtained from the first excitation and the signal obtained from the second excitation is then cross-correlated with the signal obtained from the third excitation, and so on until the signal obtained from the tenth excitation is cross-correlated.

[0044] The formula for calculating cross-correlation is:

[0045]

[0046] In the formula, x(n) and y(n) represent the seismic signals under different excitations participating in the cross-correlation, respectively; τ represents the time shift of y(n) relative to x(n); and N represents the length of the entire sampled signal participating in the cross-correlation.

[0047] This improves the signal-to-noise ratio and obtains the maximum correlation signal, ultimately outputting the cross-correlation superposition signal M from each seismic detector. 前1 M 前2 ... M 前8 The seismograph was disconnected from each seismic detector, and the top-cutting and pre-splitting blasting construction began inside the pre-splitting hole.

[0048] Step 4: After completing the pre-splitting blasting operation, reconnect N seismic detectors to the seismograph, and following the process in Step 3, finally obtain the cross-correlation superposition signal M from each seismic detector. 后1 M 后2 ... M 后8 ;

[0049] Step 5: Subtract the cross-correlation superimposed signal amplitude value obtained in Step 3 from the cross-correlation superimposed signal amplitude value obtained in Step 4 for each seismic detector, such as... Figure 3 As shown, the signals formed by the cracks induced by the blast are obtained, denoted as M1, M2, ..., M8; for example: M1 = M 后1 -M 前1 M2 = M 后2 -M 前2 In the specific calculation, the amplitude value at each same sampling time is subtracted and the new amplitude value at this sampling time is output.

[0050] Step Six: Based on the signals M1, M2, ..., M8 obtained in Step Five, establish the crack scattering coma propagation density function in the signals acquired by each seismic source and each seismic detector. The specific calculation process is as follows:

[0051] Obtain the excitation location of each seismic source and the location of each seismic detector. Given the seismic wave propagation velocity v, calculate the crack scattering coma diffusion density function K(s1,s2,x0,t) at different spatial locations based on the different signal propagation times, i.e., the spatial distribution of the sensitive nuclei:

[0052]

[0053] In equation (1), K(s1,s2,x0,t) describes the probability that the wave train is emitted at point s1, passes through x0, and is received at position s2 after time t; p(s1,s2,t) represents the probability that the wave train travels from s1 to s2 after time t, specifically,

[0054]

[0055] In equation (2), |s1-s2| represents the distance between s1 and s2, and D is the scattering coefficient;

[0056] After calculation using the above formula, a spatial grid for the distribution of sensitive nuclei is established in a 10m area centered on the pre-cracked hole, with the internal grid size set to 0.1m × 0.1m.

[0057] Step 7: Using the wake signal energy in M1, M2, ..., M8 as a basis, this energy is calculated using the absolute amplitude calculation method, that is, using the absolute value of the amplitude of the corresponding signal. Then, based on the time delay relationship of each wake signal, it is mapped into the corresponding sensitive distribution spatial grid to obtain the wake disturbance distribution imaging result of each wake signal;

[0058] Step 8: Superimpose the imaging results of the various wake perturbation distributions obtained in Step 7, such as... Figure 4 As shown, this allows us to obtain a distribution map of crack development within the spatial grid range of the sensitive core distribution. Then, we define a 10m radius around the pre-cracked hole as the imaging area, and then obtain a distribution map of crack development within the imaging area.

[0059] Step 9: Perform statistical analysis on the energy distribution within the imaging region and calculate its average value, denoted as E. 平均 Finally, the pre-cracking effect of the pre-cracking hole in each orientation is evaluated: if the energy of a certain orientation of the pre-cracking hole in the imaging area is greater than E... 平均 This determines that the area has many cracks and a good pre-cracking effect; conversely, it determines that the area has a poor pre-cracking effect; thus completing the evaluation of the pre-cracking effect in each area around the current pre-cracking hole.

[0060] As an improvement of the present invention, in step nine, the energy distribution in the imaging area is statistically analyzed and its variance D(M) is calculated; when evaluating the pre-cracking effect of the pre-cracking hole in the subsequent process, for different pre-cracking holes, the smaller the variance D(M), the more stable the pre-cracking effect is, that is, the pre-cracking effect of each orientation of the pre-cracking hole is not much different, indicating that the pre-cracking is relatively uniform and stable.

[0061] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A non-destructive testing method for the pre-splitting effect of roof cutting along the goaf, specifically: Step 1: After selecting the location on the roof of the goaf-keeping roadway, construct the pre-splitting hole. After completion, arrange N seismic detectors on the roof of the goaf-keeping roadway around the pre-splitting hole. The N seismic detectors are arranged in a ring around the pre-splitting hole, and the spacing between two adjacent seismic detectors is the same. Then, connect each seismic detector to the seismograph to complete the deployment of the ring seismic wave observation system. Step 2: Establish a seismic observation coordinate system for the pre-splitting borehole with the pre-splitting borehole as the origin, the X-axis along the direction of the goaf roadway as the X-axis, and the Y-axis along the radial direction of the goaf roadway as the Y-axis. Calculate the coordinates of each seismic detector in this coordinate system accordingly. Step 3: Before the pre-splitting blasting, using hammering as the seismic source, multiple seismic waves are excited at the pre-splitting hole with the same force and equal intervals. Each seismic detector simultaneously collects the seismic wave data generated by each source and feeds it back to the seismograph for recording. After completion, the seismograph obtains the excitation signals from each source collected by each seismic detector. The excitation signals from each source collected by each seismic detector are cross-correlated and superimposed according to the excitation sequence of each source, thereby improving the signal-to-noise ratio and obtaining the maximum correlation signal. Finally, the cross-correlation superimposed signal M from each seismic detector is output. 前1 ... M 前N The seismograph was disconnected from each seismic detector, and the top-cutting and pre-splitting blasting construction began inside the pre-splitting hole. Step 4: After completing the pre-splitting blasting operation, reconnect N seismic detectors to the seismograph, and following the process in Step 3, finally obtain the cross-correlation superposition signal M from each seismic detector. 后1 ... M 后N ; Step 5: Subtract the respective cross-correlation superimposed signal amplitude values ​​obtained in Step 3 from the cross-correlation superimposed signal amplitude values ​​obtained in Step 4 to obtain the signals formed by the cracks induced by the blast, denoted as M1, ..., M2. N ; Step Six: Based on the signals M1, ..., M obtained in Step Five N Establish the crack scattering tail wave diffusion density function in the signals obtained from each earthquake source and each seismic detector, and establish a spatial grid for sensitive core distribution within a certain range around the pre-fractured hole; Step 7: Using M1, ..., M N Based on the energy of the mid-coil wave signal, and according to the time delay relationship of each coil wave signal, it is mapped into the corresponding sensitive core distribution space grid to obtain the coil wave disturbance distribution imaging result of each coil wave signal; Step 8: Superimpose the imaging results of the various tail wave disturbance distributions obtained in Step 7 to obtain the crack development degree distribution map within the spatial grid range of the sensitive core distribution. Then, delineate a certain range around the pre-cracked hole as the imaging area, and then obtain the crack development degree distribution map of the imaging area. Step 9: Perform statistical analysis on the energy distribution within the imaging region and calculate its average value, denoted as E. 平均 Finally, the pre-cracking effect of the pre-cracking hole in each orientation is evaluated: if the energy of a certain orientation of the pre-cracking hole in the imaging area is greater than E... 平均 This determines that the area has many cracks and a good pre-cracking effect; conversely, it determines that the area has a poor pre-cracking effect; thus completing the evaluation of the pre-cracking effect in each area around the current pre-cracking hole.

2. The non-destructive testing method for the pre-splitting effect of the goaf-keeping roadway cutting as described in claim 1, characterized in that, In step one, there are eight seismic detectors, which are evenly distributed on a ring centered on the pre-fractured hole.

3. The non-destructive testing method for the pre-splitting effect of the goaf-keeping roadway cutting as described in claim 1, characterized in that, The specific process of performing cross-correlation and superposition calculations according to the excitation sequence of each seismic source in step three is as follows: The cross-correlation calculation is performed in the order of excitation. Specifically, the record obtained by cross-correlation calculation of the signal obtained from the first excitation and the signal obtained from the second excitation is then cross-correlated with the signal obtained from the third excitation, and so on, until the signal obtained from the last excitation is cross-correlated. The formula for calculating cross-correlation is: In the formula, and These represent seismic signals under different excitations that participate in the cross-correlation. express Compared to The time shift, This represents the length of the entire sampled signal involved in the cross-correlation.

4. The non-destructive testing method for the pre-splitting effect of the goaf-keeping roadway cutting as described in claim 1, characterized in that, In step seven, the calculation of the wake signal energy adopts the absolute amplitude calculation method, that is, the absolute value of the amplitude of the corresponding signal is used.

5. The non-destructive testing method for the pre-splitting effect of the goaf-keeping roadway cutting as described in claim 1, characterized in that, In step six, a spatial grid for the distribution of sensitive nuclei is established in a 10m area centered on the pre-cracked hole, with the internal grid size set to 0.1m × 0.1m.

6. The non-destructive testing method for the pre-splitting effect of the goaf-keeping roadway cutting as described in claim 1, characterized in that, In step eight, the imaging area is defined as a 10m radius around the pre-cracked hole.

7. The non-destructive testing method for the pre-splitting effect of the goaf-keeping roadway cutting as described in claim 1, characterized in that, In step nine, the energy distribution within the imaging area is statistically analyzed and its variance D(M) is calculated. When evaluating the pre-cracking effect of the pre-cracking holes in the subsequent process, for different pre-cracking holes, the smaller the variance D(M), the more stable the pre-cracking effect is.

Images