Tunnel micro-seismic enhanced positioning method and system based on DAS and blasting active source signal

Abstract

The invention discloses a tunnel micro-seismic enhanced positioning method and system based on a DAS and a blasting active source signal. The method comprises the steps that firstly, optical fibers are arranged on the surface of a tunnel wall and in a drill hole; blasting the tunnel face to generate a blasting active source signal with known time and space; then, a blasting active source signal is collected through a DAS system, and P wave arrival time of each monitoring point on the optical fiber is recorded; establishing and optimizing a wave velocity field partition model according to the spatio-temporal information of the blasting active source signal and P wave arrival time of each monitoring point on the optical fiber; and when a micro-seismic event occurs in the surrounding rock, the optimized wave velocity field partition model and P wave arrival time measured at each monitoring point on the optical fiber are utilized, a geometric algorithm is combined to invert and position the micro-seismic event, and a positioning result is output. The system comprises a signal acquisition system, an optical fiber network and a DAS system. The method has the advantages that the wave velocity field model is optimized and dynamically updated by using the tunnel face blasting signal, and the distributed sensing is performed by using the DAS system, so that the capability of monitoring and evaluating the micro-seismic event of the tunnel is remarkably enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of microseismic monitoring, and in particular to a tunnel microseismic enhanced positioning method and system based on DAS and blasting active source signals. Background Art

[0002] Before macroscopic failure, a rock mass usually generates many small microfractures, namely microseismic events. These microfractures will release elastic waves, and the elastic waves can radiate outward along the medium; the elastic wave information can be received by sensors installed within the effective range, and then the time, location, and nature of the microfractures in the rock mass can be obtained through the inversion method. According to the size, concentration degree, and fracture density of the microfractures, the development trend of the macroscopic fracture of the rock mass can be inferred. In engineering, the arrival time difference of elastic waves is often monitored by multiple monitoring stations, and then the microseismic source location is inversely calculated by combining the velocity model and geometric algorithm. The positioning principle is as Figure 1 shown.

[0003] Generally, the factors affecting the microseismic source positioning accuracy are: the accuracy of the velocity model, the arrival time picking error, and the sensor (monitoring station) layout scheme. For the velocity model, in the actual construction process, it is often assumed that the rock mass is an isotropic homogeneous medium, and a single fixed velocity model is used for inversion calculation; however, in reality, the rock mass is usually an anisotropic inhomogeneous medium, and using a single velocity model is likely to cause large errors. Moreover, the vibration and shock waves generated by each round of blasting may cause varying degrees of damage to the tunnel surrounding rock, and the rock mass wave velocity field may also change accordingly, thus affecting the microseismic positioning accuracy. Therefore, it is necessary to establish and calibrate the wave velocity field model in zones based on geological exploration and on-site inversion data in real time. However, due to the complexity of traditional active source devices and poor compatibility with the environment, it is difficult to achieve dynamic update of the wave velocity field, that is, recalibrate the wave velocity field after each round of blasting, which will seriously delay the construction period and increase the project cost. For the sensor layout scheme, currently, it is common to arrange multiple (at least four) geophones in boreholes on the tunnel wall at different positions to form a spatial geometric distribution. However, as point sensors, the layout density of geophones is limited by cost and construction conditions, and it is impossible to achieve full-range, high-density, distributed sensing of the tunnel. Especially in areas with complex geological structures, a sparse sensor network is likely to generate microseismic positioning blind spots and thus cause engineering safety problems. Therefore, there is an urgent need for a method to solve the current microseismic monitoring technical problems and improve the microseismic source positioning accuracy. And the factors affecting the arrival time picking error usually include: source characteristics, waveform overlap, environmental noise, sensor layout scheme, instrument error, and signal processing method, etc.

[0004] After retrieval, articles on optimizing the microseismic source location of coalbed methane hydraulic fracturing using distributed fiber optic acoustic sensing technology in the prior art have been published. It uses distributed fiber-optic acoustic sensing (DAS) technology to permanently arrange optical fibers outside the casing of coalbed methane reservoir wells. Based on waveform travel time information and a source constraint mapping algorithm, it conducts real-time monitoring of micro-vibrations during the process of coalbed hydraulic fracturing. However, this method has not been applied in the field of tunnel drilling and blasting. The main reasons are the differences in application scenarios and objectives, optical fiber layout methods, data processing and positioning algorithms, technical difficulties, etc. between the two. It is necessary to improve and innovate this method in combination with the characteristics of tunnel construction and the principle of fiber optic sensing. Summary of the Invention

[0005] To address the deficiencies of the above existing monitoring technologies, the present invention proposes a method and system for enhancing the location of tunnel microseisms based on DAS and blasting active source signals.

[0006] To achieve the above objectives, the technical solutions adopted by the present invention are as follows:

[0007] On the one hand, a method for enhancing the location of tunnel microseisms based on DAS and blasting active source signals is provided, which includes the following steps:

[0008] S1. Longitudinal optical fibers, transverse optical fibers, and helically wound optical fibers are respectively arranged on the tunnel wall surface and inside the tunnel boreholes, and the longitudinal optical fibers, transverse optical fibers, and helically wound optical fibers are connected to the DAS system.

[0009] S2. The face is blasted to generate a blasting active source signal with known space-time, and the blasting time point at the face and the coordinate positions of the blast holes are recorded.

[0010] S3. The DAS system is used to collect the blasting active source signal, and the arrival times of the P-waves at each monitoring point on the longitudinal optical fibers, transverse optical fibers, and helically wound optical fibers are recorded.

[0011] S4. Based on the space-time information of the blasting active source signal and the arrival times of the P-waves at each monitoring point on the longitudinal optical fibers, transverse optical fibers, and helically wound optical fibers, a wave velocity field zoning model is established and optimized.

[0012] S5. When a microseismic event occurs in the surrounding rock near the tunnel, the DAS system is used to collect the P-wave signal of the microseismic event, and the arrival times of the P-waves at each monitoring point on the longitudinal optical fibers, transverse optical fibers, and helically wound optical fibers at different positions of the tunnel are recorded.

[0013] S6. Using the optimized wave velocity field zoning model and the arrival times of P-waves measured at each monitoring point on the longitudinal optical fibers, transverse optical fibers, and helically wound optical fibers at different positions of the tunnel in step S5, inversely locate the microseismic events by combining geometric algorithms and output the location results.

[0014] Furthermore, the specific steps of step S1 are as follows:

[0015] First, longitudinally arranged optical fibers are successively laid on the tunnel wall surface along the circumferential direction of the tunnel, transversely arranged optical fibers are laid on the tunnel wall surface along the length direction of the tunnel, and helically wound optical fibers are laid in the tunnel boreholes. Then, the longitudinally arranged optical fibers, transversely arranged optical fibers, and helically wound optical fibers are connected to the DAS system together; among them, the numbers of the longitudinally arranged optical fibers, transversely arranged optical fibers, and helically wound optical fibers are all several, and several longitudinally arranged optical fibers and several transversely arranged optical fibers form an orthogonal high-density monitoring optical fiber network on the tunnel wall surface.

[0016] Furthermore, the specific steps of step S2 are as follows:

[0017] First, trigger circuit wires are arranged in the face holes of the tunnel face, then the two ends of the trigger circuit wires are connected to the signal acquisition system, and then the tunnel face is blasted to generate a blasting active source signal with known time and space, and the blasting time point of the tunnel face and the coordinate positions of the holes are recorded through the signal acquisition system.

[0018] Furthermore, the specific steps of step S3 are as follows:

[0019] First, the blasting active source signal generated by the tunnel face blasting is received through the longitudinally arranged optical fibers, transversely arranged optical fibers on the tunnel wall surface, and helically wound optical fibers in the tunnel boreholes, then transmitted to the DAS system, and then the arrival times of P-waves at each monitoring point on the longitudinally arranged optical fibers, transversely arranged optical fibers, and helically wound optical fibers at different positions of the tunnel are recorded through the DAS system.

[0020] Furthermore, the specific steps of step S4 are as follows:

[0021] S401. Establish an initial wave velocity field zoning model, and the established initial wave velocity field zoning model is specifically as follows:

[0022] (1)

[0023] Among them, is the initial wave velocity field; is the initial wave velocity value of the th wave velocity zone, with the unit of m / s; is the indicator function of the th wave velocity zone; N is the total number of wave velocity zones;

[0024] S402. Establish a wave velocity - travel - time residual objective function, and the established wave velocity - travel - time residual objective function is specifically as follows:

[0025] (2)

[0026] Wherein, is the weight factor of the th DAS optical fiber channel, , is the signal - to - noise ratio; is the theoretical travel - time of the th DAS optical fiber channel, and its value varies with changing, , is the ray path from the blasting active source to the th DAS optical fiber channel, is the indicator function of the th wave - velocity partition; is the arrival time of the first - arrival wave of the th DAS optical fiber channel, i = 1, 2, …, M, where M is the number of DAS optical fiber channels; is the regularization coefficient, and its value ranges from 0.1 to 1.0; is the wave - velocity value of the th wave - velocity partition; is the wave - velocity value of the th wave - velocity partition in the previous iteration; N is the total number of wave - velocity partitions;

[0027] S403. According to Fermat's principle, correct the ray path through the following formula (3);

[0028] (3)

[0029] Wherein, is the travel - time gradient, which characterizes the wave - front propagation direction; is the spatial change rate of the ray path from the blasting active source to the th DAS optical fiber channel; is the wave - velocity at a certain point in the rock mass to be measured;

[0030] S404. Solve the objective function based on the conjugate - gradient method, update the partition wave - velocity, and the updated wave - velocity is specifically calculated through the following formula (4):

[0031] (4)

[0032] Wherein, is the wave - velocity of the th wave - velocity partition after update; is the wave - velocity of the th wave - velocity partition before update; is the step factor; is the partial derivative of the objective function with respect to the wave velocity, is the Jacobian matrix; is the wave velocity value of the

[0033] Furthermore, the specific steps of step S6 are as follows:

[0034] S601. Establish a positioning objective function, and the established positioning objective function is specifically as follows:

[0035] (5)

[0036] where is the weight factor of the th DAS optical fiber channel, , is the signal-to-noise ratio; is the arrival time of the first arrival wave of the th DAS optical fiber channel, i = 1, 2,..., M, and M is the number of DAS optical fiber channels; is the occurrence time of the microseismic event; is the ray path from the microseismic event source to the th DAS optical fiber channel; is the wave velocity at a certain point in the rock mass to be measured;

[0037] S602. Use the iterative least squares method to solve the source location of the microseismic event and the occurrence time of the microseismic event. The solution formula for the source location of the microseismic event is specifically as follows:

[0038] (6)

[0039] where is the source parameter vector of the microseismic event in the th iteration; is the source parameter vector of the microseismic event in the th iteration, , is the spatial coordinate of the source of the microseismic event in the th iteration, is the occurrence time of the microseismic event; is the matrix transpose symbol; is the Jacobian matrix, , , , ; is the weight diagonal matrix, and the constituent elements are ; is the damping factor, and the value range is 0.01 to 0.1; is the identity matrix; is the residual vector, and its components are , is the arrival time of the first arrival wave at the -th DAS optical fiber channel, where i = 1, 2, …, M, and M is the number of DAS optical fiber channels; is the travel time of the first arrival wave at the -th DAS optical fiber channel, ; is the ray path from the microseismic event source to the -th DAS optical fiber channel; is the wave velocity at a certain point in the rock mass to be measured;

[0040] S603. Output the microseismic event source location result to obtain the location where the microseismic event occurs.

[0041] Furthermore, the several transverse optical fibers include some transverse optical fibers arranged at an interval D1 in the low-risk area of the tunnel and some transverse optical fibers arranged at an interval D2 in the high-risk area of the tunnel, where D1 ranges from 5 to 8 m; D2 ranges from 2 to 3 m;

[0042] All the several longitudinal optical fibers cover the surface of the tunnel wall in a straight line segment, and all the several transverse optical fibers cover the entire cross-section of the tunnel wall in a U shape;

[0043] The spiral-wound optical fiber is wound around the inner wall of the tunnel borehole with a preset pitch H and a preset angle θ; where H ranges from 20 to 30 cm, and θ is 60° with respect to the axis of the borehole.

[0044] Furthermore, the DAS system includes a laser, a first coupler, an optical modulator, an optical isolator, a waveform generator, a circulator, a second coupler, a photodetector, an analog-to-digital converter, and a processor; the laser is connected to the first coupler, the first coupler is respectively connected to the optical modulator and the second coupler, the optical modulator is respectively connected to the waveform generator and the optical isolator, the optical isolator is connected to the circulator, the circulator is respectively connected to the optical fiber to be measured and the second coupler, the second coupler is connected to the photodetector, the photodetector is connected to the analog-to-digital converter, and the analog-to-digital converter is connected to the processor.

[0045] On the other hand, a microseismic enhanced positioning system based on DAS and blasting active source signals is provided, including:

[0046] A signal acquisition system for recording the blasting time point of the tunnel face and the coordinate positions of the blast holes;

[0047] An optical fiber network, composed of longitudinal optical fibers, transverse optical fibers on the surface of the tunnel wall, and helically wound optical fibers in the boreholes, is used to receive the blasting active source signals generated during the face blasting, record the arrival times of P-waves at each monitoring point on the longitudinal optical fibers, transverse optical fibers, and helically wound optical fibers, and transmit the blasting active source signals and the arrival times of P-waves to the DAS system;

[0048] A DAS system is used to collect the blasting active source signals generated during the face blasting and record the arrival times of P-waves at each monitoring point on the longitudinal optical fibers, transverse optical fibers, and helically wound optical fibers in the optical fiber network.

[0049] Compared with the prior art, the advantages of the present invention are as follows:

[0050] (1) Compared with the traditional method of using seismic wave signals generated by hammering or the like as the active source to calibrate the wave velocity field, the present invention uses the seismic wave signals generated by face blasting as the active source signals to calibrate the wave velocity field, and the active source signals have large amplitudes, small attenuation, and long durations.

[0051] (2) During the tunnel drilling and blasting process, by improving the optical fiber layout scheme and using DAS instead of traditional point sensors, and using the known space-time blasting active source signals generated by face blasting to replace the traditional artificial seismic source signals to calibrate the wave velocity field, not only can the optimization (zoning establishment) and dynamic update of the wave velocity field model be realized with fewer processes, but also the full-range, wide-azimuth, and high-density distributed sensing of tunnel microseismic signals can be realized through the optimized sensor layout scheme, achieving the combination of high-density data of DAS and dynamic calibration of active source signals.

[0052] (3) Compared with traditional geophones, optical fibers have the advantages of anti-electromagnetic interference, high temperature and high pressure resistance, and permanent use after one-time installation, can provide richer information for microseismic positioning, and significantly enhance the monitoring and evaluation capabilities of tunnel microseismic events.

[0053] The innovation points of the present invention are as follows:

[0054] (1) Establish the wave velocity field in zones and use the acoustic wave signals generated by tunnel face blasting as the active source signals to dynamically update the wave velocity field. Compared with the traditional methods, either the wave velocity field is not established in zones, that is, it is defaulted that the wave velocity field in the monitoring area is the same, or a static wave velocity field model is used, both of which will lead to distortion of source parameters and a decrease in positioning accuracy. The microseismic source positioning method provided by the present invention can largely solve the above problems and significantly improve the positioning accuracy of microseismic sources;

[0055] (2) Using DAS technology for distributed sensing, that is, full-area sensing. Only one optical fiber is needed to achieve full-area, high-precision, and distributed sensing. Compared with traditional geophones, the present invention can greatly reduce the microseismic positioning blind area, ensure construction safety, and has lower costs and better cost performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the technical solutions in this embodiment, the following will briefly introduce the drawings required for the description of the embodiment. Obviously, the following described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0057] Figure 1 is the schematic diagram of microseismic positioning principle of traditional geophones (monitoring stations);

[0058] Figure 2 is the flowchart of the microseismic enhanced positioning method based on DAS and blasting active source signals of the present invention;

[0059] Figure 3 is the schematic plan view of optical fiber arrangement;

[0060] Figure 4 is the schematic three-dimensional view of optical fiber arrangement;

[0061] Figure 5 is the schematic diagram of spiral-wound optical fiber arrangement in tunnel drilling;

[0062] Figure 6 is the schematic diagram of DAS system structure;

[0063] DESCRIPTION OF REFERENCE NUMERALS: 100, longitudinal optical fiber; 200, transverse optical fiber; 300, spiral-wound optical fiber; 400, DAS system; 401, laser; 402, first coupler; 403, optical modulator; 404, optical isolator; 405, waveform generator; 406, circulator; 407, second coupler; 408, photodetector; 409, analog-to-digital converter; 410, processor. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0064] In order to make the technical means, creative features, achieved purposes, and effects of the present invention easy to understand, the following further elaborates how the present invention is implemented in combination with the drawings and specific embodiments.

[0065] Embodiment 1: Refer to Figure 2 The embodiment of the present invention provides a tunnel microseismic enhanced positioning method based on DAS and blasting active source signals, including the following steps:

[0066] S1. Fiber Optic Cable Deployment: First, longitudinally deploy longitudinal optical fibers 100 along the circumferential direction of the tunnel wall on the surface of the tunnel wall, transversely deploy transverse optical fibers 200 along the length direction of the tunnel on the surface of the tunnel wall, and deploy spiral-wound optical fibers 300 in the tunnel boreholes. Then, connect the longitudinal optical fibers 100, transverse optical fibers 200, and spiral-wound optical fibers 300 to the DAS system 400. Among them, the number of longitudinal optical fibers 100, transverse optical fibers 200, and spiral-wound optical fibers 300 are all several. And several longitudinal optical fibers 100 and several transverse optical fibers 200 form an orthogonal high-density monitoring optical fiber network on the surface of the tunnel wall. Refer to Figure 3 and Figure 4 as shown;

[0067] S2. Face Blasting to Generate Blasting Active Source Signals with Known Space-Time: First, arrange the trigger circuit wires in the face blast holes, then connect the two ends of the trigger circuit wires to the signal acquisition system. Subsequently, conduct face blasting to generate blasting active source signals with known space-time, and record the face blasting time point and the blast hole coordinate positions through the signal acquisition system. Among them, "time" refers to the detonation moment, and "space" refers to the spatial coordinates;

[0068] S3. Collect Blasting Active Source Signals through the DAS System 400 and Record the Arrival Times of P-Waves at Each Monitoring Point on the Optical Fiber: Receive the blasting active source signals generated by face blasting through the longitudinal optical fibers 100, transverse optical fibers 200 on the surface of the tunnel wall, and the spiral-wound optical fibers 300 in the tunnel boreholes, and transmit them to the DAS system 400. At the same time, record the arrival times of P-waves at each monitoring point on the longitudinal optical fibers 100, transverse optical fibers 200, and spiral-wound optical fibers 300 at different positions in the tunnel through the DAS system 400;

[0069] S4. Establish and Optimize the Wave Velocity Field Zoning Model Based on the Space-Time Information of the Blasting Active Source Signals and the Arrival Times of P-Waves at Each Monitoring Point on the Optical Fiber: Combine the geological exploration data, construct a wave velocity calibration objective function according to the space-time information of the blasting active source signals and the arrival times of P-waves at each monitoring point on the longitudinal optical fibers 100, transverse optical fibers 200, and spiral-wound optical fibers 300 at different positions in the tunnel, and use the bending method to correct the ray paths to achieve the construction and dynamic update of the wave velocity field zoning;

[0070] S5. Collect P-Wave Signals of Microseismic Events through the DAS System: When a microseismic event occurs in the surrounding rock near the tunnel, collect the P-wave signals of the microseismic event through the DAS system 400, and record the arrival times of P-waves at each monitoring point on the longitudinal optical fibers 100, transverse optical fibers 200, and spiral-wound optical fibers 300 at different positions in the tunnel;

[0071] S6. Using the optimized wave velocity field zoning model and the arrival times of P-waves measured at each monitoring point on the optical fiber, combined with the geometric algorithm to inversely locate the microseismic event and output the location result: Using the optimized wave velocity field zoning model and the arrival times of P-waves measured at each monitoring point on the longitudinal optical fiber 100, transverse optical fiber 200, and helically wound optical fiber 300 at different positions in the tunnel, construct a location objective function, and use the bending method to correct the ray path, iteratively solve the source parameters of the microseismic event, and then output the source location result of the microseismic event to obtain the location where the microseismic event occurs.

[0072] Specifically, in the embodiment of the present invention, refer to Figure 3 , several transverse optical fibers 200 include a part of the transverse optical fibers 200 arranged at intervals D1 in the low-risk area of the tunnel and a part of the transverse optical fibers arranged at intervals D2 in the high-risk area of the tunnel. The value of D1 is 5 - 8m, and the value of D2 is 2 - 3m. Among them, the low-risk area of the tunnel refers to the end far from the tunnel face, and the high-risk area of the tunnel refers to the end close to the tunnel face. The purpose of such a setting is to improve the monitoring accuracy of the key area (i.e., the high-risk area) while saving resources.

[0073] Specifically, in the embodiment of the present invention, refer to Figure 3 and Figure 4 , several longitudinal optical fibers 100 are all covered on the surface of the tunnel wall in a straight-line segment manner, and several transverse optical fibers 200 are all covered on the entire cross-section of the tunnel wall in a U-shaped manner.

[0074] Specifically, in the embodiment of the present invention, refer to Figure 5 , the helically wound optical fiber 300 is wound around the inner wall of the tunnel borehole with a preset pitch H and a preset angle θ; among them, the preset pitch H takes a value of 20 - 30 cm, and the preset angle θ takes a value of 60° with respect to the borehole axis. It should be noted here that: the buried depth of the helically wound optical fiber 300 needs to exceed the surrounding rock relaxation depth, and the role of the helically wound optical fiber 300 is to enhance the sensitivity to radially incident waves. In Figure 5 is a dashed line represents the borehole axis; point and point represent the two ends of the helically wound optical fiber; represents the borehole radius.

[0075] Specifically, in the embodiment of the present invention, the inside of the tunnel borehole is filled with a flexible encapsulation material, such as polyurethane foam, polyethylene foam, rubber, silica gel, epoxy resin, bentonite, fiber-reinforced composite material, cement-based flexible material, and polymer gel.

[0076] Specifically, in the embodiment of the present invention, the signal acquisition system is a prior art, and for details, refer to the signal acquisition system disclosed in the patent document with the publication number CN103217703A.

[0077] Specifically, in the embodiments of the present invention, refer to Figure 6 , the DAS system 400 includes a laser 401, a first coupler 402, an optical modulator 403, an optical isolator 404, a waveform generator 405, a circulator 406, a second coupler 407, a photodetector 408, an analog-to-digital converter 409, and a processor 410; wherein, the laser 401 is connected to the first coupler 402, the first coupler 402 is respectively connected to the optical modulator 403 and the second coupler 407, the optical modulator 403 is respectively connected to the waveform generator 404 and the optical isolator 405, the optical isolator 405 is connected to the circulator 406, the circulator 406 is respectively connected to the optical fiber to be measured and the second coupler 407, the second coupler 407 is connected to the photodetector 408, the electrical detector 408 is connected to the analog-to-digital converter 409, and the analog-to-digital converter 409 is connected to the processor 410.

[0078] The working principle of the DAS system 400 is as follows: The laser 401 emits laser light, which is divided into two paths by the first coupler 402. One path combines the linear frequency-swept pulse signal generated by the arbitrary waveform generator 405, is modulated to the detection light by the optical modulator 403, and then is emitted into the optical fiber to be measured through the optical isolator 404 and the circulator 406; the other path serves as the local reference light. The Rayleigh backscattered light generated by the detection light returning from the optical fiber to be measured will be superimposed together, and is beat with the local reference light and converted into an electrical signal. The electrical signal is converted into a digital signal by the analog-to-digital converter 409 and sent to the processor 410 for processing, and vibration data is obtained after demodulation.

[0079] More specifically, in the embodiments of the present invention, the optical modulator 403 can perform both optical frequency and optical intensity modulation, and is preferably an integrated optical modulator, a micro-ring resonator modulator, or an acousto-optic modulator based on lithium niobate (LiNbO3).

[0080] More specifically, in the embodiments of the present invention, the function of the optical isolator 404 is to only allow light to propagate unidirectionally and prevent the reflected light from returning to the laser 401.

[0081] More specifically, in the embodiments of the present invention, the waveform generator 405 is an arbitrary waveform generator.

[0082] Specifically, in the embodiments of the present invention, the optical fiber to be measured in the DAS system 400 is the longitudinal optical fiber 100, the transverse optical fiber 200, and the helically wound optical fiber 300 in the present invention.

[0083] Specifically, in the embodiments of the present invention, step S4, the specific steps are as follows:

[0084] S401. Establish an initial wave velocity field partition model, and the established initial wave velocity field partition model is specifically as follows:

[0085] (1)

[0086] Wherein, is the initial wave velocity field; is the initial wave velocity value of the th wave velocity partition (assigned based on geological exploration data), with the unit of m / s; is the indicator function of the th wave velocity partition; N is the total number of wave velocity partitions; if a certain point in the rock mass to be measured (i.e., a certain point in the wave velocity field partition model) belongs to the th wave velocity partition, then is 1, otherwise it is 0; the function of this formula (1) can be simply understood as: dividing the rock mass space of a large area of rock mass to be measured into several regions with different wave velocities, and then measuring the wave velocity fields of the rock masses in these several regions respectively to solve the error problem caused by the traditional unified wave velocity field (i.e., the whole rock mass adopts a unique wave velocity field model);

[0087] S402. Establish a wave velocity - travel - time residual objective function, and the established wave velocity - travel - time residual objective function is specifically as follows:

[0088] (2)

[0089] Wherein, is the weight factor of the th DAS optical fiber channel, , is the signal - to - noise ratio; is the theoretical travel time of the th DAS optical fiber channel, and its value changes with changing, , is the ray path from the blasting active source to the th DAS optical fiber channel, is the indicator function of the th wave velocity partition; is the arrival time of the first - arrival wave of the th DAS optical fiber channel, i = 1, 2,..., M, and M is the number of DAS optical fiber channels; is the regularization coefficient, with a value range of 0.1~1.0; is the wave velocity value of the th wave velocity partition; is the wave velocity value of the th wave velocity partition in the previous iteration, also called the prior wave velocity value, and its value is an iterative process. In the first iteration, takes the value of , and in the second iteration, takes the value of ,..., at the th iteration the value is ; N is the total number of wave velocity partitions;

[0090] S403. According to Fermat's principle, the ray path is corrected by the following formula (3);

[0091] (3)

[0092] where is the travel-time gradient, representing the propagation direction of the wavefront; is the spatial change rate of the ray path from the blasting active source to the th DAS optical fiber channel; is the wave velocity at a certain point in the rock mass to be measured;

[0093] S404. Solve the objective function based on the conjugate gradient method, update the partition wave velocity, and the updated wave velocity is specifically calculated by the following formula (4):

[0094] (4)

[0095] where is the wave velocity of the th wave velocity partition after update; is the wave velocity of the th wave velocity partition before update; is the step size factor, used to control the convergence speed; is the partial derivative of the objective function with respect to the wave velocity, calculated by the conjugate gradient method; is the Jacobian matrix; is the wave velocity value of the th wave velocity partition.

[0096] Through the above steps S401~S404, the dynamic partition update of the wave velocity field can be realized, providing a high-precision wave velocity field model for microseismic source location.

[0097] Specifically, in the embodiment of the present invention, step S6 is specifically as follows:

[0098] S601. Establish a positioning objective function, and the established positioning objective function is specifically as follows:

[0099] (5)

[0100] where is the weight factor of the th DAS optical fiber channel, , is the signal-to-noise ratio; is the arrival time of the first arrival wave of the th DAS fiber optic channel, i = 1, 2, …, M, where M is the number of DAS fiber optic channels; is the occurrence time of the microseismic event; is the ray path from the microseismic event source to the th DAS fiber optic channel; is the wave velocity at a certain point in the rock mass to be measured;

[0101] S602. The iterative least squares method is used to solve the microseismic event source location and the microseismic event occurrence time. The specific formula for solving the microseismic event source location is as follows:

[0102] (6)

[0103] where is the microseismic event source parameter vector at the th iteration; is the microseismic event source parameter vector at the th iteration, , is the spatial coordinate of the microseismic event source at the th iteration, is the occurrence time of the microseismic event; is the matrix transpose symbol; is the Jacobian matrix, , , , ; is the weight diagonal matrix, and its elements are ; is the damping factor, and its value ranges from 0.01 to 0.1; is the identity matrix; is the residual vector, and its elements are , is the arrival time of the first arrival wave of the th DAS fiber optic channel, i = 1, 2, …, M, where M is the number of DAS fiber optic channels; is the travel time of the first arrival wave of the th DAS fiber optic channel, ; is the ray path from the microseismic event source to the th DAS fiber optic channel; is the wave velocity at a certain point in the rock mass to be measured;

[0104] S603. Output the microseismic event source location result to obtain the microseismic event occurrence location.

[0105] Through the above steps S601 - S603, the accurate positioning of the microseismic event source can be achieved.

[0106] It should be noted here that the objective functions established in the above steps S402 and S601 in the mathematical models of wave velocity field calibration and microseismic positioning aim to minimize the difference between the observed data and the theoretical prediction through optimization algorithms, with the purpose of infinitely reducing the error to approach the true value.

[0107] Embodiment 2: The embodiment of the present invention provides a microseismic enhanced positioning system based on DAS and blasting active source signals, including:

[0108] A signal acquisition system for recording the blasting time point of the heading face and the coordinate positions of the blast holes;

[0109] An optical fiber network composed of longitudinal optical fibers 100, transverse optical fibers 200 on the tunnel wall surface, and helically wound optical fibers 300 in the drill holes, which is used to receive the blasting active source signals generated during the heading face blasting, and record the arrival times of P - waves at each monitoring point on the longitudinal optical fibers 100, transverse optical fibers 200, and helically wound optical fibers 300, and transmit the blasting active source signals and the arrival times of P - waves to the DAS system 400;

[0110] The DAS system 400 is used to collect the blasting active source signals generated during the heading face blasting and record the arrival times of P - waves at each monitoring point on the longitudinal optical fibers 100, transverse optical fibers 200, and helically wound optical fibers 300 in the optical fiber network.

[0111] Finally, it is stated that the above - mentioned are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A tunnel microseismic enhanced positioning method based on DAS and blasting active source signals, characterized in that It includes the following steps: S1. Longitudinal optical fibers (100), transverse optical fibers (200), and helically wound optical fibers (300) are respectively arranged on the surface of the tunnel wall and in the tunnel boreholes, and the longitudinal optical fibers (100), transverse optical fibers (200), and helically wound optical fibers (300) are connected to the DAS system (400); S2. The tunnel face is blasted to generate a blasting active source signal with known space-time, and the blasting time point of the tunnel face and the coordinate positions of the blast holes are recorded; S3. The blasting active source signal is collected by the DAS system (400), and the arrival times of P-waves at each monitoring point on the longitudinal optical fibers (100), transverse optical fibers (200), and helically wound optical fibers (300) are recorded; S4. Based on the space-time information of the blasting active source signal and the arrival times of P-waves at each monitoring point on the longitudinal optical fibers (100), transverse optical fibers (200), and helically wound optical fibers (300), a wave velocity field zoning model is established and optimized; S5. When a microseismic event occurs in the surrounding rock near the tunnel, the P-wave signal of the microseismic event is collected by the DAS system (400), and the arrival times of P-waves at each monitoring point on the longitudinal optical fibers (100), transverse optical fibers (200), and helically wound optical fibers (300) at different positions of the tunnel are recorded; S6. Using the optimized wave velocity field zoning model and the arrival times of P-waves measured at each monitoring point on the longitudinal optical fibers (100), transverse optical fibers (200), and helically wound optical fibers (300) at different positions of the tunnel in step S5, the microseismic event is inversely located by combining geometric algorithms, and the location result is output.

2. The tunnel microseismic enhanced positioning method based on DAS and blasting active source signals according to claim 1, wherein, For the step S1, the specific steps are as follows: First, the longitudinal optical fibers (100) are sequentially arranged along the circumferential direction of the tunnel wall on the surface of the tunnel wall, the transverse optical fibers (200) are arranged along the length direction of the tunnel wall on the surface of the tunnel wall, and the helically wound optical fibers (300) are arranged in the tunnel boreholes. Then, the longitudinal optical fibers (100), transverse optical fibers (200), and helically wound optical fibers (300) are connected to the DAS system (400); among them, the numbers of the longitudinal optical fibers (100), transverse optical fibers (200), and helically wound optical fibers (300) are all several, and several longitudinal optical fibers (100) and several transverse optical fibers (200) form an orthogonal high-density monitoring optical fiber network on the surface of the tunnel wall.

3. The tunnel microseismic enhanced positioning method based on DAS and blasting active source signals according to claim 1, wherein For the step S2, the specific steps are as follows: [[ID= 4. The tunnel microseismic enhanced positioning method based on DAS and blasting active source signals according to claim 1, wherein, ​ ​ 5. The tunnel microseismic enhanced positioning method based on DAS and blasting active source signals according to claim 1, wherein The specific steps of step S4 are as follows: S401. Establish an initial wave velocity field partition model, and the specific initial wave velocity field partition model is as follows: （1） Among them, is the initial wave velocity field; is the initial wave velocity value of the th wave velocity partition, with the unit of m / s; is the indicator function of the th wave velocity partition; N is the total number of wave velocity partitions; S402. Establish a wave velocity - travel time residual objective function, and the specific wave velocity - travel time residual objective function is as follows: （2） Among them, is the weight factor of the th DAS optical fiber channel, , is the signal-to-noise ratio of the signal; is the theoretical travel time of the th DAS optical fiber channel, and its value changes with changing, , is the ray path from the blasting active source to the th DAS optical fiber channel, is the indicator function of the th wave velocity partition; is the arrival time of the first arrival wave of the th DAS optical fiber channel, i = 1, 2,..., M, where M is the number of DAS optical fiber channels; is the regularization coefficient, and its value ranges from 0.1 to 1.0; is the wave velocity value of the th wave velocity partition; is the wave velocity value of the th wave velocity partition in the previous iteration; N is the total number of wave velocity partitions; S403. According to Fermat's principle, correct the ray path through the following formula (3); （3） Among them, is the travel-time gradient, representing the propagation direction of the wavefront; is the spatial change rate of the ray path from the blasting active source to the th DAS optical fiber channel; is the wave velocity at a certain point in the rock mass to be measured; S404. Solve the objective function based on the conjugate gradient method to update the partition wave velocity, and the updated wave velocity is specifically calculated through the following formula (4): （4） Among them, is the wave velocity of the th wave velocity partition after update; is the wave velocity of the th wave velocity partition before update; is the step factor; is the partial derivative of the objective function with respect to the wave velocity, is the Jacobian matrix, is the wave velocity value of the th wave velocity partition.

6. The tunnel microseismic enhanced positioning method based on DAS and blasting active source signals according to claim 1, wherein The specific steps of step S6 are as follows: S601. Establish a positioning objective function, and the specific positioning objective function is as follows: （5） Among them, is the weight factor of the th DAS fiber optic channel, , is the signal-to-noise ratio of the signal; is the arrival time of the first arrival wave of the th DAS fiber optic channel, i = 1, 2, …, M, where M is the number of DAS fiber optic channels; is the occurrence time of the microseismic event; is the ray path from the microseismic event source to the th DAS fiber optic channel; is the wave velocity at a certain point in the rock mass to be measured; S602. Use the iterative least - squares method to solve the source location and occurrence time of the microseismic event. The formula for solving the source location of the microseismic event is specifically as follows: （6） wherein, is the vector of microseismic event source parameters for the -th iteration; is the vector of microseismic event source parameters for the -th iteration, , is the spatial coordinate of the microseismic event source for the -th iteration, is the occurrence time of the microseismic event; is the matrix transpose symbol; is the Jacobian matrix, , , , ; is the weight diagonal matrix, and its constituent elements are ; is the damping factor, and its value ranges from 0.01 to 0.1; is the identity matrix; is the residual vector, and its constituent elements are , is the arrival time of the first arrival wave of the -th DAS optical fiber channel, i = 1, 2, …, M, where M is the number of DAS optical fiber channels; is the travel time of the first arrival wave of the -th DAS optical fiber channel, ; is the ray path from the microseismic event source to the -th DAS optical fiber channel; is the wave velocity at a certain point in the rock mass to be measured; S603. Output the source location result of the microseismic event to obtain the occurrence location of the microseismic event.

7. The tunnel microseismic enhanced positioning method based on DAS and blasting active source signals according to claim 2, wherein The several transverse optical fibers (200) include part of the transverse optical fibers (200) arranged at an interval D1 in the low - risk area of the tunnel and part of the transverse optical fibers arranged at an interval D2 in the high - risk area of the tunnel. Among them, the value of D1 is 5 - 8 m; the value of D2 is 2 - 3 m; The several longitudinal optical fibers (100) are all covered on the surface of the tunnel wall in a straight - line segment manner, and the several transverse optical fibers (200) are all covered on the full cross - section of the tunnel wall in a U - shaped manner; The spiral - wound optical fiber (300) is wound around the inner wall of the tunnel borehole with a preset pitch H and a preset angle θ; where H takes a value of 20 - 30 cm, and θ takes a value of 60° with respect to the borehole axis.

8. The tunnel microseismic enhanced positioning method based on DAS and blasting active source signals according to claim 1, wherein The DAS system (400) includes a laser (401), a first coupler (402), an optical modulator (403), an optical isolator (404), a waveform generator (405), a circulator (406), a second coupler (407), a photodetector (408), an analog - to - digital converter (409), and a processor (410); the laser (401) is connected to the first coupler (402), the first coupler (402) is respectively connected to the optical modulator (403) and the second coupler (407), the optical modulator (403) is respectively connected to the waveform generator (404) and the optical isolator (405), the optical isolator (405) is connected to the circulator (406), the circulator (406) is respectively connected to the optical fiber to be measured and the second coupler (407), the second coupler (407) is connected to the photodetector (408), the photodetector (408) is connected to the analog - to - digital converter (409), and the analog - to - digital converter (409) is connected to the processor (410).

9. A microseismic enhanced positioning system based on DAS and blasting active source signals, characterized in that, Including: A signal acquisition system for recording the blast time point of the heading face and the coordinate positions of the blast holes; The optical fiber network is composed of longitudinal optical fibers (100), transverse optical fibers (200) on the surface of the tunnel wall, and helically wound optical fibers (300) in the borehole, and is used to receive the blasting active source signals generated during the face blasting, and record the arrival times of P-waves through the monitoring points on the longitudinal optical fibers (100), transverse optical fibers (200), and helically wound optical fibers (300), and transmit the blasting active source signals and the arrival times of P-waves to the DAS system (400); The DAS system (400) is used to collect the blasting active source signals generated during the face blasting and record the arrival times of P-waves at the monitoring points on the longitudinal optical fibers (100), transverse optical fibers (200), and helically wound optical fibers (300) in the optical fiber network.

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