Asymmetric high geo-stress tunnel rock burst micro-seismic sensor arrangement method

Abstract

An asymmetric high stress tunnel rock burst micro-seismic sensor arrangement method, relating to the technical field of tunnel engineering. On the basis of tunnel surrounding rock geological data, three-dimensional numerical simulation is carried out for asymmetric high stress tunnel stability on the basis of asymmetric in-situ rock geo-stress distribution and tunnel section geometric characteristics, and asymmetric high stress tunnel energy is calculated; the location of a rock burst risk area is determined; micro-seismic sensors are arranged in front of and behind a stress concentration area; the area at a high risk and nearby areas thereof are always incorporated in two micro-seismic sensor arrays arranged in front of and behind a tunnel face. The micro-seismic sensors work cooperatively and are staggered in space, the mounting and arrangement of the micro-seismic sensors changes forwards and backwards along with the stress concentration area, and the micro-seismic sensors always keep a certain distance range with the stress area. The tunnel stress concentration area and more nearby effective micro-crack source signals can be captured by the micro-seismic sensors, thereby improving the precision of locating a micro-seismic source and laying a foundation for accurate prediction and forecast of deep-buried hard rock tunnel disasters.

Description

A method for arranging microseismic sensors for rockburst in asymmetric high-in-situ stress tunnels Technical Field

[0001] The present invention relates to the technical field of tunnel engineering, and in particular to a method for arranging rockburst microseismic sensors in an asymmetric high-in-situ stress tunnel. Background Art

[0002] Deep tunnels are characterized by asymmetric high in-situ stresses, which can lead to stress concentrations in certain areas of the tunnel, making them critical for surrounding rock stability. Tunnel excavation produces intense stress adjustments, and the use of drilling and blasting methods can cause catastrophic accidents such as rockbursts, landslides, and falling blocks in these stress-concentrated areas, resulting in casualties, equipment damage, and project delays.

[0003] In high-stress tunnel sections, asymmetric stress distribution often occurs. The surrounding rock in the stress concentration area is prone to generate higher energy and rock burst, which is an important part for controlling tunnel stability.

[0004] As the tunnel is excavated, the tangential stress of the surrounding rock behind the tunnel face with high ground stress σ θ Gradually increases, radial stress σ r As the stress difference (σ1-σ3, σ2-σ3) decreases, the surrounding rock gradually enters an unfavorable stress state. To mitigate these risks, it is very important to monitor microseismic activities in these tunnels.

[0005] Microseismic monitoring technology is currently being widely used in safety monitoring projects such as mines, underground laboratories, slopes, and tunnels in many countries, achieving a series of research results. Microseismic monitoring technology uses microseismic sensors deployed at different locations in space to capture seismic wave information emitted by rock microfractures. This information is analyzed and processed to determine the time, location, magnitude, and energy release of the microseismic event. Based on this information, the internal stress state and damage status of the rock mass can be inferred, allowing for rock stability assessment and early warning.

[0006] Experience shows that a stress concentration zone forms in the surrounding rock perpendicular to the line of maximum principal stress in the tunnel cross section behind the face, making it a key location for rockburst microseismic monitoring. The application of microseismic monitoring technology in asymmetric high-in-situ stress tunnels faces many difficulties, including: 1) Traditional microseismic sensor placement methods generally adopt a geometrically symmetrical approach, which does not take into account the characteristics of the stress concentration zone in asymmetric high-in-situ stress tunnels. The monitoring location is often inconsistent with the vulnerable area of ​​the stress concentration zone, making it ineffective in assessing the stability of the surrounding rock; 2) The drilling location and depth of existing sensors do not take into account the stress concentration zone caused by asymmetric high-in-situ stress, making it ineffective for continuous monitoring of microseismic events; and 3) How to timely, efficiently, and accurately use microseismic monitoring technology to systematically monitor possible microfractures in the rock mass of asymmetric high-in-situ stress tunnels, evaluate the degree of surrounding rock damage, and identify potential unstable areas in advance, thereby correctly judging the surrounding rock stability. Currently, there is a lack of technical research in this area both domestically and internationally. Therefore, in order to address the issue of reasonable arrangement of monitoring points in the application of microseismic monitoring technology in the construction process of asymmetric high-ground stress tunnels, it is necessary to study the reasonable sensor layout method and establish a microseismic monitoring scheme that is compatible with the excavation process and tunneling speed, laying the foundation for the application of microseismic monitoring technology in the excavation process of asymmetric high-ground stress tunnels.

[0007] Summary of the Invention

[0008] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned existing technologies and provide a method for arranging microseismic sensors for rockbursts in asymmetric high-stress tunnels, thereby solving the problem that the microseismic monitoring sensor array is difficult to surround the stress concentration area and the rock mass nearby during tunnel excavation. This allows more effective microfracture source signals in the tunnel stress concentration area and its vicinity to be captured by the microseismic sensors, thereby improving the accuracy of microseismic source positioning and laying the foundation for accurate prediction and forecasting of disasters in deep-buried hard rock tunnels.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0010] A method for arranging microseismic sensors for rockburst in an asymmetric high-in-situ stress tunnel comprises the following steps:

[0011] Step S1: Based on the geological data of the tunnel surrounding rock, the asymmetric in-situ rock stress distribution and the geometric characteristics of the tunnel section, a three-dimensional numerical simulation of the stability of the asymmetric high-in-situ stress tunnel is performed, and the energy of the asymmetric high-in-situ stress tunnel is calculated. Combined with the construction information, the location of the stress concentration area behind the tunnel face of the asymmetric high-in-situ stress tunnel is determined;

[0012] Step S2: setting multiple boreholes from the tunnel wall to the surrounding rock in the stress concentration area behind the asymmetric high-in-situ stress tunnel face as microseismic monitoring holes, with the microseismic monitoring holes being spatially staggered.

[0013] Step S3: placing microseismic sensors at different radial depths in the borehole. The microseismic sensors are embedded in the rock mass on the inner wall of the tunnel through drilling. The embedding depth of the microseismic sensors must exceed the relaxation depth of the surrounding rock. The drilling depth must be greater than the microseismic sensor placement depth.

[0014] Step S4: N known microseismic sources are arranged in the tunnel space. The three-dimensional coordinates and the time of occurrence of the known microseismic sources are known. The positioning accuracy of the sensor arrangement scheme of step S3 is analyzed. When the positioning accuracy of the microseismic sources reaches a set threshold, the arrangement scheme of the microseismic sensors is determined, and grouting is injected into the borehole to ensure that the microseismic sensors are fixedly coupled to the rock mass. If the positioning accuracy of the microseismic sources does not reach the set threshold, the borehole position is fine-tuned and the microseismic sensors are re-placed until the positioning accuracy reaches the set threshold.

[0015] Step S5: When the stress concentration area passes through secondary support and the regional microseismic energy and activity gradually decrease, the next stress concentration area is determined according to step 1, and the microseismic sensors are rearranged according to steps 2 to 4 until the tunnel excavation is completed;

[0016] Step S6: During tunnel construction, a local area network is established between the microseismic monitoring center inside the tunnel and the microseismic monitoring project department outside the tunnel through the existing communication network. This allows monitoring personnel to timely collect and store microseismic activity at different depths within the stress concentration zone behind the tunnel face and analyze it. Based on the monitoring results, timely feedback on rock burst risks is provided.

[0017] Furthermore, in step S1, the specific method for calculating the energy of the asymmetric high ground stress tunnel is:

[0018] Tracking the unit energy process, the total energy of the rock mass in the principal stress space is specifically expressed as:

[0019] Where U is the total work done by the principal stress in the direction of the principal strain; σ i are the three principal stresses of the rock mass, ε i are the three principal strains of the rock mass, i=1, 2, 3.

[0020] Furthermore, the stress concentration zone is located in the tunnel surrounding rock behind the tunnel face in a direction perpendicular to the line connecting the maximum principal stress of the asymmetric high ground stress tunnel.

[0021] Furthermore, two monitoring sections are used before and after the stress concentration area, and four microseismic sensors are arranged in each monitoring section. The first row of microseismic sensors is 20 meters in front of the stress concentration area, and the second row of microseismic sensors is 20 meters behind the stress concentration area. Each microseismic sensor requires a drilling hole each time it is installed. The hole depth is 2 to 4 meters and the hole diameter is 75 mm.

[0022] Furthermore, microseismic sensors are installed at three locations: the surface, inward from the surface, and deep, to receive surrounding rock fracture information at different radial depths inside the surrounding rock.

[0023] Furthermore, the microseismic sensor uses a unidirectional velocity sensor and a three-directional velocity sensor to work together, with a measurable range of 7 to 2000 Hz to collect surrounding rock fracture information inside the surrounding rock.

[0024] Furthermore, three-way velocity sensors are preferentially arranged around the corners and inflection points of the tunnel in stress concentration areas, and one-way and three-way velocity sensors are arranged alternately in the remaining microseismic monitoring holes.

[0025] Furthermore, dedicated data processing software is used to calculate the source parameters of each microseismic event, including microseismic release energy, apparent volume, seismic moment, and moment magnitude; and the time evolution curve of typical microseismic characteristic parameters in the stress concentration area and the spatial distribution map of microseismic events are drawn to analyze the spatiotemporal evolution characteristics of microseismic activity in the stress concentration area.

[0026] The beneficial effects of adopting the above technical solution are as follows: the method for arranging microseismic sensors for rockburst in an asymmetric high-in-situ stress tunnel provided by the present invention is based on the geological data of the tunnel surrounding rock, the distribution of asymmetric original rock in-situ stress and the geometric characteristics of the tunnel section, and a three-dimensional numerical simulation of the stability of the asymmetric high-in-situ stress tunnel is performed. The energy of the asymmetric high-in-situ stress tunnel is also performed to determine the location of the rockburst risk area. The calculation fully utilizes the space provided by the tunnel excavation, and microseismic sensors are arranged in front of and behind the stress concentration area. The high-risk area and its adjacent areas are always included in the two groups of microseismic sensor arrays arranged in front of and behind the face of the tunnel, which is conducive to the collection of microfracture signals, ensures the accuracy of microseismic positioning, and lays the foundation for accurate prediction and forecasting of disasters. The microseismic sensors work together and are staggered in space, which is conducive to the microseismic sensors receiving signals and avoids the microseismic sensors being on the same plane and affecting the positioning of the microseismic source. The installation layout of the microseismic sensors moves forward and backward closely following the stress concentration area and always maintains a certain distance from the stress area to prevent damage to the microseismic sensors and lines caused by excavation blasting, rock destruction, etc., thereby ensuring the safety of the microseismic monitoring system installers. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a flow chart of a method for arranging microseismic sensors for rockburst in an asymmetric high-in-situ stress tunnel according to an embodiment of the present invention;

[0028] FIG2 is a diagram showing the arrangement of microseismic monitoring sensors for an asymmetric high-in-situ stress tunnel according to an embodiment of the present invention;

[0029] FIG3 is a schematic diagram showing a potential rock burst location perpendicular to a maximum principal stress line on a longitudinal section of an asymmetric high-in-situ stress tunnel provided by an embodiment of the present invention;

[0030] FIG4 is a cross-sectional projection diagram of the arrangement of microseismic monitoring sensors facing the tunnel face of an asymmetric high-in-situ stress tunnel provided by an embodiment of the present invention; wherein FIG4a is a schematic diagram of the boreholes arranged in front of the stress concentration area, and FIG4b is a schematic diagram of the boreholes arranged in the rear of the stress concentration area;

[0031] FIG5 is a distribution diagram of high-energy units around an asymmetric high-in-situ stress tunnel provided by an embodiment of the present invention;

[0032] FIG6 is a cross-sectional view of a method for arranging microseismic monitoring sensors behind an asymmetric high-in-situ stress tunnel face according to an embodiment of the present invention.

[0033] In the figure: 1. Tunnel; 2. Stress concentration area; 3. Potential rockburst location; 4. Microseismic signal; 5. Unexcavated tunnel; 6. Excavated tunnel. DETAILED DESCRIPTION

[0034] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0035] Existing microseismic monitoring methods do not take into account the stress concentration caused by asymmetric high ground stress in deep-buried tunnels. Excavation or other external disturbances can easily trigger the destruction and instability of the surrounding rock in this area. By determining the location of the stress concentration area after excavation through the direction of the principal stress in the cross section, and installing microseismic sensors, a method for arranging microseismic sensors during the construction of asymmetric high ground stress tunnels is provided. Based on the characteristics of asymmetric high ground stress tunnel excavation, a suitable sensor arrangement method is studied so that the sensor array always includes the stress concentration area and its nearby rock mass as much as possible, thereby improving the accuracy of microseismic source positioning and laying the foundation for accurate early warning and assessment of disasters. As shown in Figure 1, the method of this embodiment is described as follows.

[0036] Step S1: Based on the engineering geological conditions and underground structural characteristics of the asymmetric high-in-situ stress tunnel, a three-dimensional numerical simulation model of the stability of the cavern complex, including the main tunnel, through-guideway, and transverse passage, is established. Combined with construction monitoring information, the stress concentration zone behind the tunnel face of the asymmetric high-in-situ stress tunnel is located, as shown in Figure 2, and serves as the key area for microseismic sensor monitoring. The stress concentration zone is located in the tunnel surrounding rock behind the tunnel face, perpendicular to the line connecting the maximum principal stress experienced by the asymmetric high-in-situ stress tunnel, as shown in Figure 3.

[0037] Step S2: Perform energy calculations for asymmetric high-in-situ stress tunnels and further determine the monitoring area for microseismic sensors, as shown in Figure 4. Rock mass failure is a phenomenon in which a state loses equilibrium under energy drive. The stability of asymmetric high-in-situ stress tunnels in hard rock is directly related to the amount of strain energy stored in the rock mass after excavation. If the total strain energy exceeds the limit stored energy, the structure may lose equilibrium. By tracking the unit energy process, the total energy of the rock mass in the principal stress space can be specifically expressed as:

[0038] Where: U is the total work done by the principal stress in the direction of the principal strain; σ i (i=1, 2, 3) are the three principal stresses of the rock mass, σ1 is the asymmetric maximum principal stress; σ2 is the intermediate principal stress; σ3 is the minimum principal stress; ε i (i=1, 2, 3) are the three principal strains of the rock mass.

[0039] Step S3: Set multiple boreholes from the tunnel wall to the surrounding rock in the stress concentration area behind the asymmetric high ground stress tunnel face as microseismic monitoring holes. During tunnel blasting construction, as shown in Figure 2, set 1 20m in front of the stress concentration area. # , 2 # , 3 # , 4 # Four drill holes are arranged behind the stress concentration area of ​​the tunnel face. # , 6 # , 7 # , 8 # Four drill holes.

[0040] Step S4: Microseismic sensors are placed at different radial depths in the borehole. Each microseismic sensor is embedded in the tunnel's inner rock mass through drilling. The sensor embedment depth must exceed the surrounding rock relaxation depth to facilitate the sensor's reception of vibration signals. The borehole depth is greater than the sensor placement depth to prevent debris from accumulating at the bottom of the borehole, blocking the space for the microseismic sensor. Microseismic source positioning utilizes a combination of deep and shallow holes, alternating in placement, as shown in Figure 5, to avoid locating the source on the same plane, which could affect the microseismic source's location.

[0041] Microseismic sensors are placed at different radial depths of the borehole. There are four microseismic sensors in total, three of which are unidirectional microseismic sensors and one is a three-directional microseismic sensor. Different types of sensors can work together to facilitate the location of microseismic sources. Three-directional sensors are preferably placed around the corners and inflection points of the tunnel in stress concentration areas, and the basic arrangement of alternating unidirectional and three-directional sensors can be used in the remaining monitoring holes. In this embodiment, borehole 1 # , 2 # , 3 # , 5 # , 6 # , 8 #The middle is a unidirectional speed sensor, drill hole 4 # , 7 # The middle one is a three-way speed sensor.

[0042] Step S5: Arrange N known microseismic sources (with known three-dimensional coordinates and earthquake occurrence time) in the tunnel space, perform positioning accuracy analysis on the sensor arrangement scheme, and determine the optimal arrangement scheme for the microseismic sensors.

[0043] Assume that the rock mass P wave propagation velocity V and the arrival time error ξ obey the same normal distribution for the sensor, that is, V~N(u v ,σ v ),ξ~N(0,σ t ), after this influence, the time for the sensor to receive the microseismic source signal is:

[0044] Where t is the time when the sensor receives the microseismic source signal, t i represents the time of microseismic source, V represents the propagation velocity of elastic waves in the medium, ξ is the arrival time error, (x, y, z) represents the position coordinates of the sensor, and (x0, y0, z0) is the position coordinates of the microseismic source.

[0045] Based on the probability distribution characteristics of the P-wave propagation velocity V and the arrival time error ξ, the Monte-Carlo method is used to randomly generate M (generally greater than 1000) groups of samples (V, ξ). Substituting them into equation (1), the sensor reception time t of a certain microseismic source under the condition of the P-wave propagation velocity V can be obtained.

[0046] Based on the receiving time t, sensor position and P-wave propagation velocity V of all or part of the sensors (generally no less than 6), the microseismic source position (x′, y′, z′) and earthquake occurrence time t′ are inverted through optimization methods (simplex method, genetic algorithm, etc.) with the minimum cumulative arrival residual as the optimization function.

[0047] Formula (3) is used to determine the microseismic source positioning error. S represents the expected value of the positioning error. The smaller S is, the smaller the positioning error is and the better the positioning effect is.

[0048] The expected value of the positioning error of the same microseismic source under M groups of samples (V, ξ) is used as the positioning accuracy of the microseismic monitoring scheme for the microseismic source, and the expected value of the positioning accuracy of all microseismic sources is used as the evaluation index of the microseismic monitoring scheme, thereby determining the optimal monitoring scheme.

[0049] When the microseismic source positioning accuracy reaches the set threshold, the layout plan of the microseismic sensors is determined, and grouting is injected into the borehole to ensure that the microseismic sensors are fixedly coupled to the rock mass.

[0050] If the earthquake source location accuracy does not reach the set threshold, the drilling position is fine-tuned and the microseismic sensor is re-placed until the location accuracy reaches the set threshold.

[0051] Step S6: As the original stress concentration area is strengthened and the rock burst risk is reduced, the installation layout of the microseismic sensors always follows the changes in the stress concentration area and maintains a certain distance from the stress concentration area. The next stress concentration area is determined according to steps 1 and 2, and the microseismic sensors are rearranged according to steps 3 to 5 until the tunnel excavation is completed. This prevents rock damage to the microseismic sensors and lines, ensuring the safety of the microseismic monitoring system installers.

[0052] Step S7: During tunnel construction, a local area network (LAN) is established between the microseismic monitoring center inside the tunnel and the microseismic monitoring project department outside the tunnel using the existing communication network. This allows monitoring personnel to promptly collect and store microseismic activity at different depths within the stress concentration zone behind the tunnel face, analyze it, and provide timely feedback on rockburst risks based on the monitoring results. Using dedicated data processing software, the source parameters of each microseismic event, including microseismic release energy, apparent volume, seismic moment, and moment magnitude, are calculated. Furthermore, a time-dependent evolution curve of typical microseismic characteristic parameters (number of events and microseismic release energy) within the stress concentration zone is plotted, along with a spatial distribution diagram of microseismic events, to analyze the spatiotemporal evolution of microseismic activity within the stress concentration zone.

[0053] To date, there have been no reports on the arrangement of microseismic monitoring sensors for non-opposing high-ground stress tunnels. A reasonable arrangement of microseismic sensors can not only monitor more microseismic signals over a larger range, but also enable the positioning algorithm to quickly and accurately determine the source location and time of the earthquake, which is beneficial for risk early warning assessment of tunnel stress concentration areas.

[0054] In response to the above-mentioned problems, the present invention combines the characteristics of non-opposing high-ground stress tunnel projects and proposes a dispersed sensor arrangement method suitable for non-opposing high-ground stress tunnels: 1) fully utilizing the space provided by the tunnel excavation, arranging microseismic sensors in front and behind the stress concentration area, and always including the high-risk stress concentration area and its surrounding areas in the two groups of microseismic sensor arrays arranged in front and behind the stress concentration area, which is conducive to the collection of microfracture signals, ensures the accuracy of microseismic positioning, and lays the foundation for accurate prediction and forecasting of disasters; 2) different types of microseismic sensors work together and are staggered in space, which is conducive to the microseismic sensors receiving signals and avoids the microseismic sensors being on the same plane and affecting the microseismic source positioning; 3) the installation arrangement of the microseismic sensors moves forward and backward closely following the tunnel face and always maintains a certain distance range from the stress concentration area, preventing damage to the microseismic sensors and lines caused by face excavation blasting, rock destruction, etc., and ensuring the safety of the microseismic monitoring system installers.

[0055] Example 1

[0056] A tunnel project consists of a main tunnel and a through-guideway, with a spacing of 28m. The main tunnel has an elliptical cross-section, while the guideway has a horseshoe-shaped cross-section. Excavation was carried out using the full-section drilling and blasting method, and the surrounding rock relaxation depth of the tunnel was within 1.5m. A three-dimensional numerical simulation model of the stability of the cavern group, including the main tunnel, through-guideway, and cross-passage, was established for the tunnel. Combined with construction monitoring information, the stress concentration area behind the tunnel face in the asymmetric high-in-situ stress tunnel was determined and used as the key area for microseismic sensor monitoring. Considering the probability distribution characteristics of the rock mass longitudinal wave propagation velocity and the probability distribution characteristics of the arrival time error, the expected values ​​of the positioning errors of various preliminary schemes were calculated based on the Monte-Carlo random simulation method. Based on this, the positioning accuracy of each scheme was evaluated, and the optimal sensor layout scheme was finally determined. The corresponding sensors were buried in the monitoring holes. The microseismic sensor layout method is as follows:

[0057] 1) The maximum monitoring range of the microseismic sensors within the monitored tunnel rock mass is 150 meters. The first set of microseismic sensors is located behind the stress concentration zone of the tunnel face. Three of the sensors are unidirectional, and the other is a tridirectional sensor. Their natural frequency is 14 Hz, and their response range is 7 to 2000 Hz. These different sensor types work together to facilitate microseismic source location. The sensors are embedded in the tunnel rock mass via drilled holes. Grouting is injected into the boreholes to provide a secure coupling between the sensors and the rock mass. The placement depth is 2-3 meters, exceeding the depth of the surrounding rock relaxation, which facilitates the microseismic sensors' reception of vibration signals. The drillhole depth is greater than the sensor placement depth to prevent debris from accumulating at the bottom of the borehole, blocking the space for the sensors. Microseismic sensors within the same section are staggered by 2 meters in the tunnel axial direction to avoid being placed on the same plane, which could affect microseismic source location.

[0058] 2) The second group of microseismic sensors in front of the stress concentration area of ​​the tunnel face are arranged in the same way as above.

[0059] 3) When the stress concentration zone in the monitoring area is secondary supported and the rockburst risk is reduced, the first and second sets of microseismic sensors are moved horizontally to 20 meters behind and 20 meters in front of the next stress concentration zone, respectively, with the installation method remaining unchanged. The microseismic sensors are installed in close proximity to the stress concentration zone and maintain a certain distance from it, preventing damage to the microseismic sensors and wiring caused by rock failure and ensuring the safety of the microseismic monitoring system installers. Stability monitoring of the tunnel excavation was conducted, and a series of monitoring data was collected.

[0060] 4) As the stress concentration zone 2 of the tunnel changes, the above steps are repeated until the tunnel excavation is completed.

[0061] In this embodiment, three-way sensors are preferentially arranged at the corners, turning points or around key monitoring areas of the tunnel, and the basic arrangement of alternating one-way and three-way sensors can be adopted in the remaining monitoring holes.

[0062] The test results were promptly analyzed and processed. Figure 6 shows the test results from September 2nd to 3rd, 2022. Figure 6 shows the spatial distribution of microseismic signal 4, detected during excavation on September 2nd and 3rd, 2022. The sphere represents microseismic signal 4. The size of the sphere represents the energy released by the microfracture; larger spheres represent greater energy. During this period, two groups of microseismic sensors, positioned before and after the stress concentration zone, jointly detected microseismic signal 4 generated within the surrounding rock of the stress concentration zone. Figure 6 shows that microseismic signal 4 is concentrated near the stress concentration zone, consistent with the stress concentration characteristics of deep hard rock tunnels, indicating a high risk of rockburst in stress concentration zone 2. A minor rockburst occurred in the stress concentration zone where the microseismic signals were concentrated on September 4th, 2022, consistent with the monitoring results, demonstrating the accuracy of microseismic signal monitoring. The present invention makes full use of the space provided by the excavated tunnel, and always includes the stress concentration area 4 with a higher risk of damage and its surrounding areas in the two groups of microseismic sensor arrays arranged before and after the stress concentration area, which is conducive to the collection of microfracture signals 4, ensures the accuracy of microseismic source positioning, and better captures the microseismic signals 4 that are precursors to damage in the high-risk stress concentration area 2.

[0063] During the stability monitoring of the asymmetric high-ground stress tunnel by implementing the technical solution of the present invention, a total of 21 rock burst precursor microseismic signals of minor and above rock bursts in the stress concentration area and nearby tunnel sections were captured, accurately warning of the risks of excavating asymmetric high-ground stress tunnels. After the implementation of the technical solution of the present invention, the excavation of the asymmetric high-ground stress tunnel on site did not cause any casualties to the construction personnel, ensuring construction safety.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A method for arranging microseismic sensors for rock burst in an asymmetric high-in-situ stress tunnel, characterized by: The following steps are involved: Step S1: Based on the geological data of the tunnel surrounding rock, according to the asymmetric original rock ground stress distribution and the geometric characteristics of the tunnel section, a three-dimensional numerical simulation of the stability of the asymmetric high ground stress tunnel is performed, and the energy of the asymmetric high ground stress tunnel is calculated. Combined with the construction information, the position of the stress concentration area behind the tunnel face of the asymmetric high ground stress tunnel is determined; Step S2: multiple boreholes are set from the tunnel wall to the inside of the surrounding rock in the stress concentration area behind the asymmetric high-in-situ stress tunnel face as microseismic monitoring holes, and the microseismic monitoring holes are arranged in a staggered manner in space; Step S3: placing microseismic sensors at different radial depths of the borehole. The microseismic sensors are all buried in the rock mass on the inner wall of the tunnel through drilling. The buried depth of the microseismic sensors must exceed the relaxation depth of the surrounding rock. The drilling depth is greater than the arrangement depth of the microseismic sensors. Step S4: N known microseismic sources are arranged in the tunnel space. The three-dimensional coordinates and the time of occurrence of the known microseismic sources are known. The positioning accuracy of the sensor arrangement scheme of step S3 is analyzed. When the positioning accuracy of the microseismic sources reaches the set threshold, the arrangement scheme of the microseismic sensors is determined, and grouting is injected into the borehole to make the microseismic sensors fixedly coupled with the rock mass. If the positioning accuracy of the seismic sources does not reach the set threshold, the borehole position is fine-tuned and the microseismic sensors are re-placed until the positioning accuracy reaches the set threshold. Step S5: When the stress concentration area passes through the secondary support, the regional microseismic energy and activity gradually decrease, the next stress concentration area is determined according to step 1, and the microseismic sensors are rearranged according to steps 2 to 4 until the tunnel excavation is completed; Step S6: During the tunnel construction process, a local area network is established between the microseismic monitoring center in the tunnel and the microseismic monitoring project department outside the tunnel through the existing communication network, so that the monitoring personnel can timely collect and store the microseismic activities at different depths inside the stress concentration area behind the tunnel face and analyze them, and provide feedback on the rock burst risk in a timely manner based on the monitoring results.

2. The method for arranging microseismic sensors for rock burst in an asymmetric high-in-situ stress tunnel according to claim 1 is characterized by: In step S1, the specific method for calculating the energy of the asymmetric high stress tunnel is: Tracking the unit energy process, the total energy of the rock mass in the principal stress space is specifically expressed as: Where U is the total work done by the principal stress in the direction of the principal strain; σ i are the three principal stresses of the rock mass, ε i are the three principal strains of the rock mass, i=1, 2, 3.

3. The method for arranging microseismic sensors for rock burst in an asymmetric high-in-situ stress tunnel according to claim 1 is characterized by: The stress concentration zone is located at the tunnel surrounding rock in a direction perpendicular to the line of maximum principal stress of the asymmetric high stress tunnel behind the tunnel face.

4. The method for arranging microseismic sensors for rock burst in an asymmetric high-in-situ stress tunnel according to claim 1 is characterized by: Two monitoring sections are used before and after the stress concentration area, and four microseismic sensors are arranged in each monitoring section. The first row of microseismic sensors is 20m away from the stress concentration area, and the second row of microseismic sensors is 20m away from the stress concentration area. Each microseismic sensor requires a drilling hole each time it is installed. The hole depth is 2 to 4m and the hole diameter is 75mm.

5. The method for arranging microseismic sensors for rock burst in an asymmetric high-in-situ stress tunnel according to claim 4 is characterized by: Microseismic sensors are installed at three locations: the surface, inward from the surface, and deep in the layer, to receive surrounding rock fracture information at different radial depths inside the surrounding rock.

6. The method for arranging microseismic sensors for rock burst in an asymmetric high-in-situ stress tunnel according to claim 1 is characterized by: The microseismic sensor uses a one-way velocity sensor and a three-way velocity sensor to work together, with a measurable range of 7 to 2000 Hz to collect surrounding rock fracture information inside the surrounding rock.

7. The method for arranging microseismic sensors for rock burst in an asymmetric high-in-situ stress tunnel according to claim 6 is characterized by: Three-way velocity sensors are preferentially arranged around the corners and turning points of the tunnel in stress concentration areas, and single-way and three-way velocity sensors are arranged alternately in the remaining microseismic monitoring holes.

8. The method for arranging microseismic sensors for rock burst in an asymmetric high-in-situ stress tunnel according to claim 1 is characterized by: Using dedicated data processing software, the source parameters of each microseismic event are calculated, including microseismic release energy, apparent volume, seismic moment, and moment magnitude; The time evolution curves of typical microseismic characteristic parameters in the stress concentration area and the spatial distribution map of microseismic events are plotted to analyze the spatiotemporal evolution characteristics of microseismic activities in the stress concentration area.

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