A method for detecting remaining coal thickness in tunnels based on elastic waves

Abstract

The present invention discloses a method for detecting the remaining coal thickness in a tunnel based on elastic waves. The method first determines the wave velocity of the elastic wave in the coal seam to be detected, then arranges a circular observation system, and sequentially excites the elastic wave at each excitation point, so that a three-component geophone obtains the arrival time of the direct wave and the reflected wave of the elastic wave after the excitation at each excitation point, respectively, thereby obtaining the time consumed by the elastic wave after the excitation at each excitation point to travel back and forth to the coal seam. Then, the average time consumed is calculated, and a threshold is set to determine whether the calculated average time consumed meets the requirement. After the requirement is met, the remaining coal seam thickness at the current position is calculated. The present invention only needs to arrange one three-component geophone during the detection process at each position, and does not need to arrange other additional equipment, so that the installation is convenient. When performing the detection, the elastic wave is sequentially excited at each set excitation point to complete the detection process, so that the present invention can quickly and accurately detect the remaining coal seam thickness, thereby strengthening the coal resource management, improving the recovery rate and ensuring the coal quality of the coal mine.

Description

Technical Field

[0001] The invention relates to a method for detecting remaining coal thickness in a tunnel based on elastic waves, and belongs to the technical field of coal seam monitoring. Background Art

[0002] Coal seam thickness is a key control factor for coal mine production and safety. Coal seam tunnel excavation and working face production are directly controlled by coal seam thickness. During the excavation process, the thickness of the remaining bottom coal and top coal is closely related to the excavation speed, roof management, support effectiveness and safe excavation efficiency; the cutting height of the drum and cutting head during the excavation process still depends on the experience of the workers. Due to the lack of understanding of the specific situation of the remaining coal seam thickness, excess thickness of top and bottom coal is often reserved, resulting in too low recovery rate and reduced economic efficiency; to avoid leaving too much top and bottom coal, the height of the drum and cutting head needs to be increased to a certain extent, which will cause the pick to cut the rock, accelerate the wear of the pick, and shorten the life of the pick; at the same time, the gangue produced by cutting will also fall with the coal blocks, and be transported after mixing, increasing the cost of coal washing in the later stage. Therefore, the top coal thickness of the top coal caving working face is a key parameter for the control of the mining process; the current remaining coal thickness detection method mainly relies on drilling means, that is, drilling coal exploration holes into the top and bottom plates of the coal seam, and judging the coal thickness by manually sensing the reaction force of the top and bottom rock layers or the color of the returned coal rock powder during the drilling process of the electric (wind) drill. This method is difficult to control the inclination of the coal exploration borehole, which is prone to human errors in its detection accuracy. Although drilling to detect coal thickness is relatively accurate and reliable, it is time-consuming and labor-intensive and cannot keep up with the advancement speed of the working face. Therefore, how to provide a new detection method that is easy to install and deploy, can quickly and accurately detect the remaining coal seam thickness, and provide data guidance for strengthening coal resource management, improving recovery rate, ensuring coal quality, and determining a reasonable mining ratio in coal mines is one of the research directions of this industry. Summary of the invention

[0003] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for detecting the remaining coal thickness in the tunnel based on elastic waves. Only one three-component detector is required, which is easy to install and deploy, so that it can quickly and accurately detect the remaining coal seam thickness, thereby strengthening coal resource management, improving recovery rate and ensuring coal quality in coal mines, and ultimately providing data guidance for determining a reasonable mining ratio.

[0004] In order to achieve the above purpose, the technical solution adopted by the present invention is: a method for detecting the remaining coal thickness in a tunnel based on elastic waves, the specific steps are as follows:

[0005] A. Calibrate the wave velocity of elastic waves in coal seams: first determine the coal seam to be monitored, arrange two three-component geophones on the surface of the coal seam wall, and select an excitation point on the surface of the coal seam to excite elastic waves. The two three-component geophones receive the elastic waves transmitted in the coal seam respectively, and the time received by the two three-component geophones, the excitation point and the distance between the two three-component sensors are calculated comprehensively to determine the wave velocity V of the elastic wave in the current coal seam;

[0006] B. Layout of circular observation system: Select a location in the current coal seam, lay out a three-component geophone, and lay out multiple excitation points on the surface of the coal seam. Each excitation point is distributed on a circle with the location of the three-component geophone as the center and a radius of R, thus completing the layout of the circular observation system;

[0007] C. Collect elastic wave data with circular observation system: Elastic waves are excited at each excitation point in turn, and after each excitation point is excited, the three-component geophones collect elastic wave three-component data;

[0008] D. Filtering the elastic wave data: Selecting the elastic wave data of the component corresponding to the thickness direction of the coal seam to be detected from the collected three-component elastic wave data, performing low-pass filtering on the selected elastic wave data, and finally filtering out the low-frequency elastic waves that pass through the coal seam to the top of the rock layer, and saving the filtered data;

[0009] E. Determine the remaining coal seam thickness:

[0010] ① Obtain the selected elastic wave data. The time t1 recorded by the first wave peak after each excitation point is the arrival time of the direct wave at the excitation point. The time t2 recorded by the second wave peak is the arrival time of the reflected wave when the elastic wave encounters the top plate of the rock layer. The time taken for the elastic wave to travel to and from the coal seam is T = t2-t1. Thus, the time taken for the elastic wave to travel to and from the coal seam at each excitation point is obtained, where Tn is n = 1, 2, 3…n. The principle of this calculation is that the interval between the three-component geophone and each excitation point is 1m, which can be ignored relative to the thickness of the coal seam. Therefore, each The time recorded when the three-component geophone receives the first wave peak after the excitation point is excited is the time when the elastic wave directly reaches the sensor after the excitation of the excitation point is completed, that is, t1. After the elastic wave is generated, it diffuses to the surrounding area. When it encounters the rock layer on the top plate upward, the wave impedance changes and the reflection condition is met, so that the elastic wave is reflected and reaches the three-component geophone (recorded by the second wave peak). The time is t2. By calculating t2-t1, the time difference between the elastic wave just arriving at the three-component geophone and reflecting back after reaching the top plate of the rock layer is obtained; finally, the time it takes for the elastic wave to travel to and from the coal seam is determined.

[0011] ② Obtain the average time taken for elastic waves to travel back and forth between coal seams. The specific formula is:

[0012]

[0013] ③Set threshold a, then calculate the average time The corresponding variance If A≤a, the current is the time taken for the elastic wave to travel back and forth between the coal seams, and then proceed to step ④; if A>a, then determine The maximum value in the i Delete, and then recalculate the new Then calculate the corresponding variance A, and repeat this process until A≤a, and finally determine the current The time taken for the elastic wave to travel back and forth between the coal seams, and then proceed to step ④;

[0014] ④ Remaining coal seam thickness at the three-component geophone location Thus, the remaining coal thickness detection process at the current position is completed;

[0015] F. Continuously detect the remaining coal seam thickness at different positions: select multiple positions along the mining direction of the working face, and repeat steps B to E respectively, so as to determine the remaining coal seam thickness at different positions along the mining direction of the working face.

[0016] Further, the step A specifically comprises:

[0017] (1) First, select a roof position of a coal seam with a known thickness in the coal seam to be monitored, and fix two three-component geophones in the coal seam. The distance between the two three-component geophones is d;

[0018] (2) An excitation point is determined on one side of the two three-component geophones and on the line connecting the two three-component geophones. A small hammer is used to strike the edge of the top plate anchor cable tray to excite elastic waves. The excitation point is located at a distance d1 from the first three-component geophone and at a distance d2 from the second three-component geophone.

[0019] (3) Two three-component geophones receive the excited elastic waves in real time, wherein the time when the excited elastic waves propagate in the coal seam and arrive at the first three-component geophone is t1, and the time when the waves arrive at the second three-component geophone is t2;

[0020] (4) Assume that the propagation speed of the elastic wave between the excitation point and the first three-component geophone is v1, the propagation speed of the elastic wave between the excitation point and the second three-component geophone is v2, and the propagation speed of the elastic wave between the two three-component geophones is v3. The propagation speed of the excited elastic wave in the coal seam is Thereby determining the wave velocity V of the elastic wave in the current coal seam.

[0021] Furthermore, in step B, R is 1m, and each excitation point divides the circular ring equally.

[0022] Furthermore, there are five excitation points, namely excitation points 1 to 5, wherein the position of excitation point 1 coincides with the position of excitation point 5, and a small hammer is used to excite elastic waves at excitation points 1 to 5 in a clockwise direction.

[0023] Furthermore, the frequency of the low-pass filter in step D is 150 Hz.

[0024] Compared with the prior art, the present invention first determines the wave velocity of the elastic wave in the coal seam to be detected, and then arranges a circular observation system, which is composed of a three-component geophone and multiple excitation points, and the excitation points are distributed on a circular trajectory with the geophone as the center and a certain radius. Through the circular observation system, elastic waves are excited at each excitation point in turn, so that the three-component geophone obtains the arrival time of the direct wave and the reflected wave of the elastic wave after the excitation of each excitation point, thereby obtaining the time taken for the elastic wave after the excitation of each excitation point to travel back and forth to the coal seam, and then the average time is calculated, and a threshold is set to determine whether the calculated average time meets the requirements. After the requirement is met, the remaining coal seam thickness at the current position is calculated; in the process of detecting each position, the present invention only needs to deploy a three-component detector, and no other additional equipment is required, so that the installation is convenient, and the elastic wave is excited by hammering, which is also a common method in mines. No additional equipment is required. When detecting, the elastic wave is excited in turn at each set excitation point to complete the detection process, so that the present invention can quickly and accurately detect the remaining coal seam thickness, thereby strengthening the coal resource management of coal mines, improving the recovery rate and ensuring the coal quality, and finally providing data guidance for determining a reasonable mining ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the layout of the observation system in the present invention;

[0026] Figure 2 Schematic diagram of the present invention using an observation system to detect the remaining coal seam thickness;

[0027] Figure 3 It is a schematic diagram of calculating the remaining coal seam thickness after obtaining elastic wave data according to the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described below.

[0029] Embodiment: The specific steps of the present invention are:

[0030] A. Calibrate the velocity of elastic waves in coal seams: First determine the coal seam to be monitored, arrange two three-component geophones on the surface of the coal seam wall, and select an excitation point on the surface of the coal seam to excite elastic waves. The two three-component geophones receive the elastic waves transmitted in the coal seam respectively, and the time received by the two three-component geophones, the excitation point and the distance between the two three-component sensors are calculated comprehensively to determine the velocity V of the elastic wave in the current coal seam, which is:

[0031] (1) First, select a roof position of a coal seam with a known thickness in the coal seam to be monitored, and fix two three-component geophones in the coal seam. The distance between the two three-component geophones is d;

[0032] (2) An excitation point is determined on one side of the two three-component geophones and on the line connecting the two three-component geophones. A small hammer is used to strike the edge of the top plate anchor cable tray to excite elastic waves. The excitation point is located at a distance d1 from the first three-component geophone and at a distance d2 from the second three-component geophone.

[0033] (3) Two three-component geophones receive the excited elastic waves in real time, wherein the time when the excited elastic waves propagate in the coal seam and arrive at the first three-component geophone is t1, and the time when the waves arrive at the second three-component geophone is t2;

[0034] (4) Assume that the propagation speed of the elastic wave between the excitation point and the first three-component geophone is v1, the propagation speed of the elastic wave between the excitation point and the second three-component geophone is v2, and the propagation speed of the elastic wave between the two three-component geophones is v3. The propagation speed of the excited elastic wave in the coal seam is Thereby determining the wave velocity V of the elastic wave in the current coal seam.

[0035] B. Layout of circular observation system: Select a position in the current coal seam, lay out a three-component geophone, and lay out 5 excitation points on the surface of the coal seam, namely excitation points 1 to 5, where the position of excitation point 1 coincides with the position of excitation point 5, and excitation points 1 to 5 are distributed on a circle with a radius of 1m and the position of the three-component geophone as the center, and excitation points 1 to 4 divide the circle equally, such as Figure 1 As shown, the layout of the circular observation system is completed;

[0036] C. Collect elastic wave data with circular observation system: Use a small hammer to excite elastic waves at excitation points 1 to 5 every 90° in clockwise direction. After each excitation point is excited, the three-component geophone collects elastic wave three-component data;

[0037] D. Filtering the elastic wave data: Select the elastic wave data of the component corresponding to the thickness direction of the coal seam to be detected from the collected three-component elastic wave data, perform a 150 Hz low-pass filter on the selected elastic wave data, and finally filter out the low-frequency elastic waves that pass through the coal seam to the top of the rock layer, and save the filtered data;

[0038] E. Determine the remaining coal seam thickness:

[0039] ① Obtain the filtered elastic wave data, such as Figure 3 As shown, the time t1 recorded by the first wave crest after each excitation point is excited is the arrival time of the direct wave at the excitation point, and the time t2 recorded by the second wave crest is the arrival time of the reflected wave when the elastic wave encounters the top plate of the rock formation. The time taken for the elastic wave to travel back and forth to the coal seam is T=t2-t1; thus, the time taken for the elastic wave to travel back and forth to the coal seam at each excitation point is obtained, Tn, n=1,2,3…n; the principle of this calculation is: the position interval between the three-component detector and each excitation point is 1m, which can be ignored relative to the thickness of the coal seam. Therefore, the time recorded by the three-component detector receiving the first wave crest after each excitation point is excited is the time when the elastic wave directly reaches the sensor after the excitation of the excitation point is completed, that is, t1. After the elastic wave is generated, it diffuses to the surroundings. When it encounters the rock formation on the top plate upward, the wave impedance changes and reaches the reflection condition, so that the time when the elastic wave is reflected and reaches the three-component detector (recorded by the second wave crest) is t2. By calculating t2-t1, the time difference between the elastic wave just beginning to arrive at the three-component detector and the time reflected back after reaching the top plate of the rock formation is obtained; finally, the time taken for the elastic wave to travel back and forth to the coal seam is determined.

[0040] ② Obtain the average time taken for elastic waves to travel back and forth between coal seams. The specific formula is:

[0041]

[0042] ③Set threshold a, then calculate the average time The corresponding variance If A≤a, the current is the time taken for the elastic wave to travel back and forth between the coal seams, and then proceed to step ④; if A>a, then determine The maximum value in the i Delete, and then recalculate the new Then calculate the corresponding variance A, and repeat this process until A≤a, and finally determine the current The time taken for the elastic wave to travel back and forth between the coal seams, and then proceed to step ④;

[0043] ④ Remaining coal seam thickness at the three-component geophone location Thus, the remaining coal thickness detection process at the current position is completed;

[0044] F. Continuously detect the remaining coal seam thickness at different locations: e.g. Figure 2 As shown, multiple positions are selected along the mining direction of the working face, and steps B to E are repeated respectively, so that the remaining coal seam thickness at different positions along the mining direction of the working face can be determined.

[0045] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for detecting remaining coal thickness in a tunnel based on elastic waves, characterized in that: The specific steps are: A. Calibrate the wave velocity of elastic waves in coal seams: first determine the coal seam to be monitored, arrange two three-component geophones on the surface of the coal seam wall, and select an excitation point on the surface of the coal seam to excite elastic waves. The two three-component geophones receive the elastic waves transmitted in the coal seam respectively, and the time received by the two three-component geophones, the excitation point and the distance between the two three-component sensors are calculated comprehensively to determine the wave velocity V of the elastic wave in the current coal seam; B. Layout of circular observation system: Select a location in the current coal seam, lay out a three-component geophone, and lay out multiple excitation points on the surface of the coal seam. Each excitation point is distributed on a circle with the location of the three-component geophone as the center and a radius of R, thus completing the layout of the circular observation system; C. Collect elastic wave data with circular observation system: Elastic waves are excited at each excitation point in turn, and after each excitation point is excited, the three-component geophones collect elastic wave three-component data; D. Filtering the elastic wave data: Selecting the elastic wave data of the component corresponding to the thickness direction of the coal seam to be detected from the collected three-component elastic wave data, performing low-pass filtering on the selected elastic wave data, and finally filtering out the low-frequency elastic waves that pass through the coal seam to the top of the rock layer, and saving the filtered data; E. Determine the remaining coal seam thickness: ① Obtain the selected elastic wave data. The time t1 recorded by the first wave peak after each excitation point is the arrival time of the direct wave at the excitation point. The time t2 recorded by the second wave peak is the arrival time of the reflected wave when the elastic wave encounters the top plate of the rock layer. The time taken for the elastic wave to travel back and forth to the coal seam is T = t2-t1. Thus, the time taken for the elastic wave to travel back and forth to the coal seam at each excitation point is obtained, where Tn is n = 1, 2, 3…n. ② Obtain the average time taken for elastic waves to travel back and forth between coal seams. The specific formula is: ③Set threshold a, then calculate the average time The corresponding variance If A≤a, the current is the time taken for the elastic wave to travel back and forth between the coal seams, and then proceed to step ④; if A>a, then determine The maximum value in the i Delete, and then recalculate the new Then calculate the corresponding variance A, and repeat this process until A≤a, and finally determine the current The time taken for the elastic wave to travel back and forth between the coal seams, and then proceed to step ④; ④ Remaining coal seam thickness at the three-component geophone location Thus, the remaining coal thickness detection process at the current position is completed; F. Continuously detect the remaining coal seam thickness at different positions: select multiple positions along the mining direction of the working face, and repeat steps B to E respectively, so as to determine the remaining coal seam thickness at different positions along the mining direction of the working face.

2. The method for detecting remaining coal thickness in a tunnel based on elastic waves according to claim 1 is characterized in that: The specific steps in step A are: (1) First, select a roof position of a coal seam with a known thickness in the coal seam to be monitored, and fix two three-component geophones in the coal seam. The distance between the two three-component geophones is d; (2) An excitation point is determined on one side of the two three-component geophones and on the line connecting the two three-component geophones. A small hammer is used to strike the edge of the top plate anchor cable tray to excite elastic waves. The excitation point is located at a distance d1 from the first three-component geophone and at a distance d2 from the second three-component geophone. (3) Two three-component geophones receive the excited elastic waves in real time, wherein the time when the excited elastic waves propagate in the coal seam and arrive at the first three-component geophone is t1, and the time when the waves arrive at the second three-component geophone is t2; (4) Assume that the propagation speed of the elastic wave between the excitation point and the first three-component geophone is v1, the propagation speed of the elastic wave between the excitation point and the second three-component geophone is v2, and the propagation speed of the elastic wave between the two three-component geophones is v3. The propagation speed of the excited elastic wave in the coal seam is Thereby determining the wave velocity V of the elastic wave in the current coal seam.

3. The method for detecting remaining coal thickness in a tunnel based on elastic waves according to claim 1 is characterized in that: In step B, R is 1 m, and each excitation point divides the circular ring equally.

4. The method for detecting remaining coal thickness in a tunnel based on elastic waves according to claim 3 is characterized in that: There are five excitation points in total, namely excitation points 1 to 5, wherein the position of excitation point 1 coincides with the position of excitation point 5, and a small hammer is used to excite elastic waves at excitation points 1 to 5 in a clockwise direction.

5. The method for detecting remaining coal thickness in a tunnel based on elastic waves according to claim 1, characterized in that: The frequency of the low-pass filter in step D is 150 Hz.

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