A microseismic positioning method based on fiber grating acoustic emission sensing technology

Abstract

The application discloses a kind of microseismic positioning methods based on fiber grating acoustic emission sensing technology, comprising: (a) at least four monitoring points are selected in the underground mine to be measured, and a fiber grating acoustic emission sensor is arranged at each monitoring point, and four fiber gratings are equidistantly arranged on the fiber grating acoustic emission sensor;(b) the propagation velocity of acoustic emission signals on the path from all fiber grating acoustic emission sensors to the source is solved;(c) the coordinate data of each fiber grating acoustic emission sensor and the time data of receiving acoustic emission signals are processed to obtain corresponding data on the corresponding monitoring point;(d) the propagation velocity obtained by calculation, the coordinate data of monitoring point and the time data of receiving acoustic emission signals are substituted into the source calculation equation set to obtain the coordinates of the source.The application can accurately locate the source in the underground mine, can provide reliable technical guidance for taking targeted reinforcement and other measures, and ensure the safe production and mining of underground mine.

Description

Technical Field

[0001] This invention belongs to the field of microseismic source location technology, specifically relating to a microseismic location method based on fiber optic grating acoustic emission sensing technology. This method can use fiber optic grating acoustic emission sensing technology to locate the seismic source in underground mines with high accuracy. Background Technology

[0002] In recent years, with the continuous growth of the population and the rapid development of industry, the national demand for underground metal ores has been increasing, making underground metal mining a significant economic activity. As mine depth increases and mining difficulty rises, unstable geological environments bring higher safety risks to mineral resource extraction and production. Therefore, improving the accurate assessment of the mine geological environment and the ability to predict disasters is one of the urgent tasks for ensuring safe underground mine production. Precise seismic source location technology is a crucial foundation for mine disaster prediction, providing technical support for safe mine production in areas such as early warning, monitoring, and emergency response.

[0003] Because solid materials, under the influence of external forces (mechanical loads, temperature changes, etc.), will generate internal stress concentration areas. When this high-energy state transitions to a low-energy state, its strain energy is rapidly released in the form of elastic waves, i.e., acoustic emission occurs. Acoustic emission phenomena between 10Hz and 300Hz are called microseismic events, which are tiny signals indicating deformation or fracture within solid materials. Microseismic monitoring is a method of studying the mechanical behavior and dynamic processes of underground nonlinear materials by recording changes in microseismic signals. Based on acoustic emission and seismology, microseismic monitoring technology monitors and analyzes the occurrence of microseismic events during mining and production activities to assess their impact on the underground environment and engineering structures. This technology typically analyzes the location distribution of seismic sources and the source mechanism (shear fracture or tensile fracture) to predict whether an accident will occur. Therefore, the core of this technology lies in accurately determining the location of the seismic source to eliminate or mitigate the potential threats to the environment and safety posed by mining and production activities.

[0004] Acoustic emission signals carry a wealth of information about internal damage and failure of underground mining materials, enabling timely monitoring of crack location, nature, and propagation. This allows for precise early warning of damage location and extent, effectively preventing accidents. Therefore, accurate detection of acoustic emission signals is a crucial aspect of microseismic monitoring. Traditional acoustic emission signal measurement uses piezoelectric ceramic sensors, which suffer from electromagnetic interference and the inability to achieve real-time, long-term monitoring. Therefore, fiber optic grating acoustic emission sensors are increasingly used in mining operations to measure acoustic emission signals.

[0005] Fiber Bragg grating acoustic emission sensors are favored due to their advantages such as high sensitivity, small size, immunity to electromagnetic interference, and the ability to be located at a considerable distance from the electronic device. Especially when the sensing signal is wavelength modulated, the measurement signal is unaffected by fiber loss, connection loss, light source fluctuation, and detector aging; in contrast, traditional piezoelectric ceramic sensors struggle to achieve this. Furthermore, fiber Bragg grating acoustic emission sensors can combine multiple gratings within a single transmission fiber, and then use wavelength division multiplexing (WDM) technology to achieve distributed measurement. For multiple acoustic emission signals, data acquisition and processing based on this method can yield more accurate signal data.

[0006] However, current microseismic source location calculation methods based on fiber Bragg grating acoustic emission sensing technology have many limitations in underground mining applications. They suffer from significant errors, lack sufficient accuracy and stability, and thus cannot provide reliable technical guidance and predictions, impacting safe mining operations. The main reason for this is that the microseismic location calculation methods are overly simplified, leading to large calculation errors. Therefore, a new source location calculation method is urgently needed to improve its accuracy and reliability, providing more effective technical support for safe underground mining operations. Summary of the Invention

[0007] To address the aforementioned technical problem of significant errors in seismic source location, the present invention aims to provide a microseismic location method based on fiber optic grating acoustic emission sensing technology. This method can accurately locate seismic sources in underground mines, providing reliable technical guidance for targeted reinforcement and support measures, and ensuring safe production and mining in underground mines.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a micro-seismic localization method based on fiber optic grating acoustic emission sensing technology, comprising the following steps:

[0009] (a) Select at least four monitoring points in the underground mine to be tested, and deploy a fiber Bragg grating acoustic emission sensor at each monitoring point. Each fiber Bragg grating acoustic emission sensor is provided with four fiber Bragg gratings at equal intervals.

[0010] (b) Determine the propagation speed of the acoustic emission signal along the path from all fiber optic grating acoustic emission sensors to the seismic source;

[0011] (c) Process the coordinate data and the time data of the received acoustic emission signal of each fiber optic grating acoustic emission sensor to obtain the corresponding data at the corresponding monitoring point;

[0012] (d) Substitute the calculated propagation velocity, the coordinate data of the monitoring point, and the time data of the received acoustic emission signal into the source calculation equations to obtain the coordinates of the source.

[0013] Preferably, the fiber optic grating acoustic emission sensor described in step (a) is installed at the monitoring point in a vertical or horizontal manner.

[0014] Optionally, step (b) involves calculating the propagation speed of the acoustic emission signal along the path from all fiber Bragg grating acoustic emission sensors to the seismic source, including:

[0015] Select one of the monitoring points and denote it as P. A Monitoring point P A The deployed fiber Bragg grating acoustic emission sensor is denoted as A, and the spacing between the fiber Bragg gratings is l. The coordinates of the four fiber Bragg gratings on the fiber Bragg grating acoustic emission sensor A are denoted as (x, y, y). A1 y A1 , z A1 ), (x A2 y A2 , z A2 ), (x A3 y A3 , z A3 ), (x A4 y A4 , z A4 );

[0016] Assuming the vibration of the earthquake source q, the times at which the fiber optic grating acoustic emission sensor A receives the four acoustic signals are denoted as T. A1 T A2 T A3 T A4 The distances from fiber Bragg grating sensor A to the seismic source q are denoted as S. A1 S A2 S A S A4 ;

[0017] Assuming the coordinates of the earthquake source q are (x0, y0, z0) and the earthquake initiation time is T0, calculate the propagation speed V of the acoustic emission signal along the path from the fiber optic grating acoustic emission sensor A to the earthquake source q. A The system of equations is as follows:

[0018]

[0019] The time T of the four acoustic signals from fiber optic grating acoustic emission sensor A is... A2 T A3 T A4 With T A1 The time difference between them is denoted as Δt. a Δt b Δt c ,make

[0020]

[0021] Based on the time difference Δta Δt b Δt c The spacing l between the fiber grating and the fiber grating is obtained as follows:

[0022]

[0023]

[0024] The above system of equations can be solved as follows:

[0025]

[0026] Therefore, the unknown quantity is V. A t A , n, m, and the known quantity is Δt a Δt b Δt c 、l;

[0027] The propagation speed V of the acoustic emission signal along the path from the fiber Bragg grating acoustic emission sensor A to the earthquake source q can be calculated. A for:

[0028]

[0029] By analogy, the propagation speed V of the acoustic emission signal along the path from all fiber Bragg grating acoustic emission sensors i to the vibration source q can be obtained. i , i = A, B, C, ...

[0030] Optionally, the source calculation equations in step (d) are:

[0031]

[0032] In the formula: S i T represents the distance between each monitoring point and the epicenter. i V represents the time when acoustic emission signals are received at each monitoring point. i The propagation speed of the acoustic emission signal on the path from each fiber Bragg grating acoustic emission sensor to the monitoring point.

[0033] Optionally, the data from each monitoring point is processed as follows:

[0034]

[0035]

[0036]

[0037]

[0038] In the formula: x iIndicates monitoring point P i Represents the x-coordinate, y-coordinate i Indicates monitoring point P i Represents the y-axis coordinate, z i Indicates monitoring point P i The z-axis coordinate, T i Indicates monitoring point P i The time when the acoustic emission signal is received; j = 1, 2, 3, 4; i = A, B, C, ...

[0039] Compared with the prior art, the present invention has at least the following beneficial effects:

[0040] 1. The main difference between the microseismic location calculation method provided by this invention and traditional methods lies in its profound understanding of the differences in acoustic emission signal propagation speed caused by the underground mining medium. That is, the propagation speed of acoustic emission signals varies in different media. Based on this, a scientific and reasonable microseismic location algorithm is proposed. Existing traditional microseismic location techniques have not considered the influence of the medium on the propagation speed of acoustic emission signals. When dealing with acoustic emission propagation speed data, they all treat the underground mine as a homogeneous model, failing to distinguish the acoustic emission propagation speed on different paths. This results in large errors in source location and a lack of stability and accuracy. Therefore, using the microseismic location calculation method provided by this invention, the source location can be calculated more accurately, meeting the needs of practical engineering applications and possessing significant practical significance and scientific value.

[0041] 2. This invention provides a novel method for calculating the propagation velocity of acoustic emission signals along the path from the seismic source to the monitoring point. This method utilizes equally spaced gratings etched on the transmission optical fiber of the acoustic emission sensor. By measuring the time difference of acoustic emission signals received at different grating positions and combining this with the spacing between two gratings, the propagation velocity of acoustic emission along the path is finally obtained. This method has the advantages of simple solution process and high accuracy, and can provide strong support for microseismic monitoring and early warning.

[0042] 3. The earthquake source location calculation method provided by this invention only requires setting equally spaced gratings on the transmission optical fiber to achieve accurate measurement. The method is economical and practical, easy to operate, and convenient for data processing. It can provide reliable technical support for earthquake source location and underground disaster prediction, and has good promotion and application value. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 A simplified diagram illustrating a monitoring point arrangement method according to an embodiment of the present invention;

[0045] Figure 2 A schematic diagram of a fiber Bragg grating acoustic emission sensor provided in one embodiment of the present invention;

[0046] Figure 3 Monitoring point P provided in one embodiment of the present invention A A simplified calculation diagram of the fiber optic grating acoustic emission sensor A.

[0047] Figure label: P i —Location of monitoring point; S i —i - Distance of the monitoring point from the earthquake source; V i —The propagation speed of the acoustic emission signal along the i-path; T i —i—the moment when the acoustic emission signal is received at monitoring point i; q—the location of the seismic source;

[0048] 1—Transmission optical fiber; 2—Metal sheath; 3—Grate; 4—Polyvinyl chloride. Detailed Implementation

[0049] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0050] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0051] In the description of this invention, it should also be noted that the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on this application. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0052] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0053] Figure 1 The diagram illustrates a method for arranging monitoring points according to an embodiment of the present invention. The arrangement of monitoring points requires that monitoring stations be deployed at at least four different locations within the area to be monitored. In this embodiment, P is shown as the monitoring point. A P B P C P D There are a total of 4 monitoring points; point q is the location of the earthquake source; S A S B S C S D T is the distance between the epicenter and the monitoring point; A T B T C T D V represents the time when acoustic emission signals are received at the four monitoring points. A V B V C V D The propagation speed of the acoustic emission signal along the four paths.

[0054] Based on the time difference distance method and the Euclidean distance formula, the source equations can be solved as follows:

[0055]

[0056] In the system of equations, the time (T) at which the acoustic emission signal is received. A T B T C T DThe propagation speed of the acoustic emission signal in the underground mine is known, but it depends on the mining medium it passes through. Since the four paths traverse different media, their propagation speeds are not identical. Therefore, the unknowns in this system of equations include the propagation speed V of the acoustic emission signal along the four paths. A V B V C V D The initiation time T0 and the coordinates of the epicenter (x0, y0, z0).

[0057] Figure 2 The diagram illustrates a schematic of a fiber Bragg grating acoustic emission sensor according to an embodiment of the present invention. The fiber Bragg grating acoustic emission sensor is encapsulated in polyvinyl chloride (PVC) 4. This encapsulation method has advantages such as no distortion after curing; fatigue resistance; non-hygroscopicity; good corrosion resistance; and high electrical insulation under certain temperature and humidity conditions. A metal sleeve 2 is fitted onto the transmission optical fiber 1 of the fiber Bragg grating acoustic emission sensor, and equally spaced gratings 3 are arranged on the transmission optical fiber 1 to achieve distributed measurement. Based on the unknowns required to be solved in the above-mentioned source equations—the source coordinates and the propagation speed of the acoustic emission signal—at least four sets of equations are needed to solve them. Therefore, at least four equally spaced gratings are arranged on a single fiber Bragg grating acoustic emission sensor. In this embodiment, four equally spaced gratings 3 are arranged on a single fiber Bragg grating acoustic emission sensor.

[0058] Figure 3 The diagram illustrates a simplified calculation method for one monitoring point according to an embodiment of the present invention. In this embodiment, monitoring point P is used as an example. A Taking fiber Bragg grating acoustic emission sensor A as an example, with four fiber Bragg gratings on sensor A, distributed data can be measured due to the equally spaced gratings. After the vibration source q, the fiber Bragg grating acoustic emission sensor can obtain a total of four acoustic signals. The time for the sensor to receive the acoustic signals is denoted as T. A1 T A2 T A3 T A4 The distance between the grating and the seismic source is denoted as S. A1 S A2 S A3 S A4 It is obvious that S A1 ≠S A2 ≠S A3 ≠S A4 Due to the size of the fiber Bragg grating acoustic emission sensor compared to S... A1 S A2 S A3 S A4The medium is small enough that all four paths pass through the same underground mine, therefore they can be considered to have the same acoustic emission signal propagation speed V. A Therefore, the time T for receiving the sound signal can be determined. A1 T A2 T A3 T A4 There is a time difference, which can be expressed as:

[0059]

[0060] It should be emphasized that the fiber optic grating acoustic emission sensor must be arranged horizontally or vertically in underground mines. In this embodiment of the invention, a vertical arrangement is used as an example.

[0061] The coordinates of the four points on fiber optic grating acoustic emission sensor A are (x... A1 y A1 , z A1 ),(x A2 y A2 , z A2 ),(x A3 y A3 , z A3 ),(x A4 y A4 , z A4 Since the fiber Bragg grating acoustic emission sensor is vertically arranged and the transmission fiber is equipped with equally spaced gratings with a spacing of l, the following relationship can be obtained:

[0062]

[0063]

[0064] Assuming the coordinates of the earthquake source q are (x0, y0, z0) and the earthquake initiation time is T0, the source equations can be solved using the time difference distance method and the Euclidean distance formula:

[0065]

[0066] make

[0067] According to equations (2) and (4), we can obtain:

[0068]

[0069]

[0070] Therefore, the system of equations (5) can be transformed into:

[0071] In the above system of equations (9), the unknown is V.A , t A n, m, and the known quantity is Δt a , Δt b , Δt c , l.

[0072] System of equations (9) 2 We can obtain:

[0073]

[0074] Perform difference calculations on the above equations (10)(11)(12)(13) to eliminate the unknown quantity n.

[0075] Equations (11)-(10), (12)-(10), and (13)-(10) yield the following:

[0076]

[0077] By performing difference calculations on the above equations (14), (15), and (16) to eliminate the unknown quantity m, only the known quantity grating spacing l remains in the equation.

[0078] 2 × equation (14) - equation (15), 3 × equation (14) - equation (16), we can obtain:

[0079]

[0080] In equation (17):

[0081]

[0082] Substituting equation (19) into equation (18):

[0083]

[0084] That is, for monitoring point P A The time difference Δt between the acoustic signals received on the equally spaced l fiber optic grating acoustic emission sensors can be used as a basis. a Δt b Δt c Get S A Velocity V on the path A The specific expression is equation (20).

[0085] Similarly, using this method, the velocity V of the acoustic emission signal propagating in different media can be obtained. B V C V D Substituting this into equation (1), and combining the coordinate data and the time data of the received acoustic emission signal, the final source coordinates can be obtained.

[0086] It is important to emphasize that this embodiment sets up a total of 4 monitoring points. In order to solve for the acoustic emission propagation velocity from each monitoring point to the seismic source, the data to be monitored at each monitoring point is refined into 4 values, resulting in a total of 16 sets of data. Processing all the data separately would make the calculation process too complicated. Taking monitoring point P as an example... A For example, due to monitoring point P A The four sets of data can be grouped together and processed as a whole. By averaging the data, the monitoring point P can be obtained. A Representative values ​​for each of the above data:

[0087]

[0088] Where j = 1, 2, 3, 4, and x in the formula A Indicates monitoring point P A Represents the x-coordinate, y-coordinate A Indicates monitoring point P A Represents the y-axis coordinate, z A Indicates monitoring point P A The z-axis coordinate, T A Indicates monitoring point P A The time when the acoustic emission signal is received. The other monitoring points can be processed in the same way, combined with the acoustic emission signal propagation speed V from each monitoring point to the seismic source obtained from equation (20). i Thus, the V required to calculate the system of equations (1) can be obtained. i T i x i y i , z i ,(i=A,B,C,D).

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A microseismic localization method based on fiber optic grating acoustic emission sensing technology, characterized in that, Includes the following steps: (a) Select at least four monitoring points in the underground mine to be tested, and deploy a fiber Bragg grating acoustic emission sensor at each monitoring point. Each fiber Bragg grating acoustic emission sensor is provided with four fiber Bragg gratings at equal intervals. (b) Determine the propagation speed of the acoustic emission signal along the path from all fiber optic grating acoustic emission sensors to the seismic source; (c) Process the coordinate data and the time data of the received acoustic emission signal of each fiber optic grating acoustic emission sensor to obtain the corresponding data at the corresponding monitoring point; (d) Substitute the calculated propagation velocity, the coordinate data of the monitoring point, and the time data of the received acoustic emission signal into the source calculation equations to obtain the coordinates of the source; Step (b) involves determining the propagation speed of the acoustic emission signal along the path from all fiber Bragg grating acoustic emission sensors to the seismic source, including: Select one of the monitoring points and denote it as P. A Monitoring point P A The deployed fiber Bragg grating acoustic emission sensor is denoted as A, and the spacing between the fiber Bragg gratings is l. The coordinates of the four fiber Bragg gratings on the fiber Bragg grating acoustic emission sensor A are denoted as (x, y, y). A1 y A1 , z A1 ), (x A2 y A2 , z A2 ), (x A3 y A3 , z A3 ), (x A4 y A4 , z A4 ); Assuming the vibration of the earthquake source q, the times at which the fiber optic grating acoustic emission sensor A receives the four acoustic signals are denoted as T. A1 T A2 T A3 T A4 The distances from fiber Bragg grating sensor A to the seismic source q are denoted as S. A1 S A2 S A S A4 ; Assuming the coordinates of the earthquake source q are (x0, y0, z0) and the earthquake initiation time is T0, calculate the propagation speed V of the acoustic emission signal along the path from the fiber optic grating acoustic emission sensor A to the earthquake source q. A The system of equations is as follows: The time T of the four acoustic signals from fiber optic grating acoustic emission sensor A is... A2 T A3 T A4 With T A1 The time difference between them is denoted as Δt. a Δt b Δt c ,make Based on the time difference Δt a Δt b Δt c The spacing l between the fiber grating and the fiber grating is obtained as follows: The above system of equations can be solved as follows: Therefore, the unknown quantity is V. A t A , n, m, and the known quantity is Δt a Δt b Δt c 、l; The propagation speed V of the acoustic emission signal along the path from the fiber Bragg grating acoustic emission sensor A to the earthquake source q can be calculated. A for: By analogy, the propagation speed V of the acoustic emission signal along the path from all fiber Bragg grating acoustic emission sensors i to the vibration source q can be obtained. i , i = A, B, C, ...

2. The microseismic localization method based on fiber optic grating acoustic emission sensing technology according to claim 1, characterized in that, The fiber optic grating acoustic emission sensor described in step (a) is installed at the monitoring point in a vertical or horizontal manner.

3. The microseismic localization method based on fiber optic grating acoustic emission sensing technology according to claim 1, characterized in that, The source calculation equations described in step (d) are as follows: In the formula: S i T represents the distance between each monitoring point and the epicenter. i V represents the time when acoustic emission signals are received at each monitoring point. i The propagation speed of the acoustic emission signal on the path from each fiber Bragg grating acoustic emission sensor to the monitoring point.

4. The microseismic localization method based on fiber optic grating acoustic emission sensing technology according to claim 1, characterized in that, The data from each monitoring point are processed as follows: In the formula: x i Indicates monitoring point P i Represents the x-coordinate, y-coordinate i Indicates monitoring point P i Represents the y-axis coordinate, z i Indicates monitoring point P i The z-axis coordinate, T i Indicates monitoring point P i The time when the acoustic emission signal is received; j = 1, 2, 3, 4; i = A, B, C, ...

Images