Coal Mine Rock Burst and Water Disaster Collaborative Early Warning Method Based on Acoustic Wave Detection

Abstract

The present invention discloses a collaborative early warning method for mine rock burst and water disaster based on acoustic wave detection, including: Step 1, determining the main water-bearing strata horizons, regions with strong water richness, and strata with rock burst proneness during coal seam mining; Step 2, using the "key stratum" theory to calculate the development height of the water-conducting fissure zone after coal seam mining and the key strata of rock burst; Step 3, dividing the sedimentary facies of the main aquifers and strata with rock proneness; Step 4, carrying out "static + dynamic" data statistics and monitoring of coal seam mining; Step 5, establishing a coupling risk assessment system for mine rock burst and water inrush based on the results obtained in Step 4; Step 6, constructing a coupling risk assessment model for mine rock burst and water inrush based on the fuzzy variable weight method on the basis of the coupling risk assessment system for mine rock burst and water inrush established in Step 5; Step 7, verifying and correcting the risk assessment model established in Step 6.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal mine safety, and particularly relates to a method for collaborative early warning of mine rock burst and water disaster based on acoustic wave detection. Background Art

[0002] With the acceleration of the westward shift of China's energy strategy, the development intensity of shallow-buried coal resources in the west has gradually increased. In recent years, the development of coal resources has gradually transitioned to deep parts. The spatial occurrence characteristics of coal seams and the safe, green and efficient mining technologies are different from those of shallow-buried coal seams. The sedimentary environment, rock mechanical characteristics, and hydrogeological conditions of the aquifers above the coal seam roof are becoming more and more complex. Mine rock burst disasters occur frequently, and the actual water inflow of the mine is far from the predicted water inflow during the exploration stage. According to incomplete statistics, the water inflow per ton of coal exceeds 3m 3 . The disaster accidents not only threaten the lives of miners but also cause significant economic losses. The rock mechanical properties, pore-throat distribution and its connectivity of the sandstone above the coal seam roof, and the development height of the water-conducting fissure zone after coal seam mining are the key core research objects for the prevention and control of rock burst and water inrush disasters during coal seam mining. Therefore, carrying out collaborative early warning of rock burst and water disaster during coal seam mining has important practical significance and great social significance for disaster prevention and control.

[0003] At present, the methods for evaluating the risk of water inrush from the mine roof mainly include the "three maps - double prediction" method and the improved "three maps - double prediction" method. Among them, the three maps in the "three maps - double prediction" method include the water-richness zoning map of the water-bearing layer filling the coal seam roof, the safety zoning map of roof caving and cracking, and the comprehensive zoning map of roof water inrush conditions. The improved "three maps - double prediction" method uses the analytic hierarchy process, grey theory, neural network algorithm, etc. to fuse multi-source information. The methods for evaluating impact risk include static evaluation at the macroscopic level and dynamic evaluation methods based on real-time monitoring data. Among them, the static evaluation methods include the comprehensive index method, the impact ground pressure possibility index diagnosis method, etc., and the dynamic evaluation methods include the microseismic method, the ground sound method, the stress method, the vibration CT detection method, the electromagnetic radiation method, etc. The existing risk evaluation methods have the following problems:

[0004] (1) In the "three maps - double prediction" method for evaluating the risk of water inrush from the roof, the water-richness zoning map of the roof does not consider the influence of the complex sedimentary environment in deep mines, and the safety zoning map of roof caving and cracking does not consider the situation where the development height of the water-conducting fissure zone during coal seam mining in deep mines completely communicates with the main aquifers above the coal seam, resulting in the inability to compile the safety zoning map of roof caving and cracking and affecting the accuracy of the evaluation of the risk of water inrush from the roof.

[0005] (2) For the microseismic method of mine rock burst risk assessment, it is the microwave signal emitted by rock mass fracture, which is a regional monitoring method that only monitors rock mass failure and cannot give early warnings for major events. For the geophone method, the signal is uploaded to the surface in the form of current, and the signal has poor anti-interference ability. For the stress method, it can only monitor stress increments, which belongs to static point data monitoring, and the coal and rock stress state is not a sufficient condition for the occurrence of rock bursts, so the warning purpose cannot be achieved. For the seismic CT detection method, one roadway needs to be excited and another roadway needs to receive, which is suitable for the detection of large-scale areas such as working faces, but cannot detect the driving face. For the electromagnetic radiation method, it monitors and predicts rock bursts according to the electromagnetic radiation intensity of surrounding rocks. However, due to the electromagnetic radiation of large underground equipment often interfering greatly with monitoring data, its accuracy cannot meet the requirements of rock burst warning.

[0006] (3) Due to the differences in sedimentary environment, geological conditions, hydrogeological conditions, mining geological conditions, rock mechanical properties, etc. in different regions, there are many factors affecting rock bursts and roof water inrushes, and the influencing mechanism is complex. Using only methods such as the analytic hierarchy process and entropy weight method to determine the weights of risk assessment indicators may have the risk of mutual cancellation between indicators.

[0007] (4) At present, the risk assessment methods for rock bursts and water hazards are all isolated methods for assessing the risk of rock burst disasters or water hazards, and no coupling warning method for the two has been proposed. Summary of the Invention

[0008] The purpose of the present invention is to provide a collaborative warning method for mine rock bursts and water hazards based on acoustic wave detection to judge the risks of rock bursts and water hazards of coal seam rocks.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is: a collaborative warning method for mine rock bursts and water hazards based on acoustic wave detection, which is specifically implemented according to the following steps:

[0010] Specifically implemented according to the following steps:

[0011] Step 1, determine the main water-bearing layer positions of coal seam mining, regions with strong water-richness, and rock layers with burst proneness;

[0012] Step 2, use the "key stratum" theory to calculate the development height of the water-conducting fissure zone after coal seam mining of the key stratum of rock bursts;

[0013] Step 3, divide sedimentary facies according to the regional sedimentary background, lithology, and logging information. On the basis of mastering the regional sedimentary evolution history, divide the sedimentary facies of the main aquifers and rock layers with rock proneness according to sedimentary facies division marks, petrological marks, paleontological marks, logging facies marks, etc.

[0014] Step 4: Conduct "static + dynamic" data statistics and monitoring for coal seam mining, where: static data statistics and monitoring include obtaining static geological information such as acoustic detection, thickness of the main aquifer, sand ratio, development height of the water-conducting fissure zone, water-richness, and sedimentary facies; dynamic data statistics and monitoring include microseismic monitoring, vibration CT monitoring, stress monitoring, ground noise monitoring, and dynamic geological information of mine water inflow;

[0015] Step 5: Establish a coupling risk assessment system for mine rock burst and water inrush based on the results obtained in Step 4;

[0016] Step 6: Based on the coupling risk assessment system for mine rock burst and water inrush established in Step 5, construct a coupling risk assessment model for mine rock burst and water inrush based on the fuzzy variable weight method;

[0017] Step 7: Verify and correct the risk assessment model established in Step 6.

[0018] As a preferred technical solution of the present invention, in the said Step 1, collect geological, hydrogeological, logging, and rock mechanical property data during the coal resource exploration stage, including hydrogeological borehole columns, hydrogeological pumping test results, geological exploration reports, supplementary hydrogeological exploration reports, geophysical exploration reports, and impact tendency identification reports. Determine the main aquifers affecting coal seam mining according to the division of aquiclude / aquifer and its main hydrogeological characteristics, and the development of the water-conducting fissure zone during coal seam mining; Determine the areas with strong water-richness according to hydrogeological characteristics, logging, and geophysical exploration interpretation results; Determine the rock strata with impact tendency by referring to relevant content in the impact tendency identification report.

[0019] As a preferred technical solution of the present invention, in the said Step 1, the main aquifers meet the following conditions: relatively large thickness; relatively large specific capacity of the borehole; after coal seam mining, the development height of the water-conducting fissure zone communicates with the main aquifer in part or all areas.

[0020] As a preferred technical solution of the present invention, in the said Step 1, the areas with strong water-richness meet the following conditions: in the determined main aquifers; the comprehensive display in the logging curve shows relatively large rock grain size and relatively small resistivity; the geophysical exploration report interprets water-rich abnormal areas.

[0021] As a preferred technical solution of the present invention, in the said Step 2, the determination of the key strata for rock burst is as follows:

[0022] Step 2.1: Determine the position of the hard rock strata in the overlying strata from bottom to top;

[0023] Assume that the first layer of rock stratum is a hard rock stratum, and the rock strata from the first layer to the m-th layer deform coordinately with it, while the (m + 1)-th layer of rock stratum does not deform coordinately with it. Then the (m + 1)-th layer of rock stratum is the second hard rock stratum. Since the rock strata from the first layer to the m-th layer deform coordinately, the curvature of each rock stratum is the same, and each rock stratum forms a combined beam. According to the principle of the combined beam, the load acting on the first layer of hard rock stratum can be derived as follows:

[0024]

[0025] In the formula, q1(x) m is the load formed by the m-th layer of rock stratum on the first layer of hard rock stratum; h i , γ i , E i are respectively the thickness, unit weight, and elastic modulus of the i-th rock stratum (i = 1, 2,..., m). Considering that the load formed by the (m + 1)-th layer on the first layer of hard rock stratum is:

[0026]

[0027] Since the (m + 1)-th layer is a hard rock stratum, its deflection is less than that of the lower rock strata, and the rock strata above the (m + 1)-th layer no longer require the lower rock strata to bear the load it bears. Then there must be:

[0028] q1(x) m+1 <q1(x) m (3)

[0029] Substitute equations (1) and (2) into equation (3) and simplify to obtain:

[0030]

[0031] Equation (4) is the formula for determining the position of the hard rock stratum. Specifically, when discriminating, start from the first layer of rock stratum above the coal seam and calculate layer by layer upwards. When

[0032] and

[0033] satisfy equation (4), then stop calculating upwards. At this time, from the first layer of rock stratum upwards, the m-th layer of rock stratum is the first layer of hard rock stratum. Starting from the first layer of hard rock stratum, determine the position of the second layer of hard rock stratum according to the above method, and so on, until the uppermost layer of hard rock stratum (assumed to be the n-th layer of hard rock stratum) is determined. By discriminating the position of the hard rock stratum, the position of the hard rock stratum in the overlying strata and the soft rock stratum group it controls are obtained.

[0034] Step 2.2, calculate the breaking distance of each hard rock stratum;

[0035] According to the mechanical model of a fixed-end beam and the analysis of the theory of materials mechanics, the normal stress at any point in the beam is:

[0036]

[0037] Wherein, M is the bending moment of the section where any point is located (KN·m); y is the distance between any point and the neutral axis of the section (m); h is the thickness of the rock beam (m);

[0038] It can be known from the analysis of the fixed-end beam that the maximum bending moment of the fixed-end beam occurs at both ends of the beam; that is:

[0039]

[0040] The corresponding maximum tensile stress is:

[0041]

[0042] When σ max = σ t , the rock beam fractures, and its limit span is obtained from Equation (7) as:

[0043]

[0044] Step 2.3, compare the breaking distances of each hard rock layer according to the following principle to determine the position of the key layer of rock burst;

[0045] If the k-th hard rock layer is the key layer, its breaking distance should be less than the breaking distances of all the hard rock layers above it, that is, it satisfies

[0046]

[0047] If the breaking distance L k of the k-th hard rock layer is greater than the breaking distance of the (k + 1)-th hard rock layer above it, then the load borne by the (k + 1)-th hard rock layer is added to the k-th hard rock layer, and the breaking distance of the k-th hard rock layer is recalculated;

[0048] Start from the bottommost hard rock layer and judge layer by layer upward whether L k < L k+1 holds. When L k > L k+1 , recalculate the breaking distance of the k-th hard rock layer.

[0049] As a preferred technical solution of the present invention, in the said Step 2, the determination method of the development height of the water-conducting fissure zone is as follows:

[0050] Step 2.4, calculate the free space height below the key layer and the soft rock layer;

[0051] Calculate the free space height below the key layer according to Equation (10);

[0052]

[0053] where, Δ i is the height of the free space under the i-th layer of rock stratum; M is the thickness of the coal seam mined; h j is the thickness of the j-th layer of rock stratum; k j is the residual swelling coefficient of the j-th layer of rock.

[0054] Step 2.5, calculation of the height of the water-conducting fissure zone;

[0055] When the working face advances to the distance where it can generate the maximum tension, the maximum deflection of the rock stratum is:

[0056]

[0057] At this time, if the maximum deflection of the soft rock stratum is greater than the height of the free space below it, due to the limitation of the free space, the soft rock stratum will remain in a plastic state without breaking, and the water-conducting fissure zone will no longer develop upward; thus, there is:

[0058] ω i,max > Δ i (12)

[0059] On the contrary, when the maximum deflection of the soft rock stratum is less than the height of the free space below it, it will break and conduct water, thus there is:

[0060] ω i,max < Δ i (13)

[0061] The beneficial effects of the present invention are: (1) A method for collaborative early warning of mine rock burst and water disaster based on acoustic wave detection according to the present invention first introduces acoustic wave detection technology to monitor the overpressure zone and water-rich abnormal zone of the roof overlying strata in coal seam mining, and at the same time provides technical data for early warning of mine rock burst and water inrush disasters, improving the accuracy of disaster early warning, reducing disaster accidents, and reducing the cost of disaster prevention and control; (2) A method for collaborative early warning of mine rock burst and water disaster based on acoustic wave detection according to the present invention uses microseismic monitoring data for both monitoring of large energy events of rock burst and monitoring of the development height of the water-conducting fissure zone in coal seam mining, and fuses dynamic monitoring and static monitoring data, providing comprehensive basic theoretical data for the establishment of a disaster early warning index system; (3) A method for collaborative early warning of mine rock burst and water disaster based on acoustic wave detection according to the present invention uses the fuzzy variable weight method to avoid the risk of mutual cancellation of the evaluation indexes of rock burst and water inrush hazards; (4) A method for collaborative early warning of mine rock burst and water disaster based on acoustic wave detection according to the present invention couples the early warning of two disasters, mine rock burst and water inrush, and has a powerful function compared with the previous single (rock burst or water inrush) disaster early warning in mines. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 is the flow chart of the present invention;

[0063] Figure 2 Schematic diagram of overpressure zone detected by acoustic wave

[0064] Figure 3 Schematic cross-section of overpressure zone detected by acoustic wave and water-rich anomaly area

[0065] Figure 4 Mine rock burst and water disaster coupling risk assessment system

[0066] In the figure: 1 is the coal seam; 2 is the drill site; 3 is the main hole of the directional drill; 4 is the branch hole of the directional drill; 5 and 7 are water-rich anomaly areas; 6 is the main aquifer / hard rock with impact tendency Specific implementation mode

[0067] The technical solutions of the present invention will be further described in detail below with reference to the attached drawings and specific embodiments

[0068] As Figure 1 shown, a mine rock burst and water disaster collaborative early warning method based on acoustic wave detection includes the following steps

[0069] Step 1: Determine the main aquifer horizons for coal seam mining, areas with strong water richness, and rock strata with impact tendency

[0070] Collect geological, hydrogeological, logging, and rock mechanical property data during the coal resource exploration stage, including hydrogeological borehole columns (including logging curves), hydrogeological borehole pumping test results, geological exploration reports, hydrogeological supplementary exploration reports, geophysical exploration reports, impact tendency identification reports, etc. Determine the main aquifers affecting coal seam mining based on the division of aquifers (confining beds) and their main hydrogeological characteristics, the development of water-conducting fissure zones during coal seam mining, etc. Determine areas with strong water richness based on hydrogeological characteristics, logging, and geophysical exploration interpretation results, and determine rock strata with impact tendency by referring to relevant content in the impact tendency identification report

[0071] The main aquifers meet the following conditions: (1) The main aquifers have a large thickness; (2) The unit water inflow of the boreholes in the main aquifers is large; (3) The development height of the water-conducting fissure zone after coal seam mining partially or completely communicates with the main aquifers

[0072] Areas with strong water richness meet the following conditions: (1) In the determined main aquifers; (2) The logging curves comprehensively show larger rock particle sizes and smaller resistivity; (3) Water-rich anomaly areas are interpreted in the geophysical exploration report

[0073] Step 2: Use the "key stratum" theory to calculate the key strata of rock burst and the development height of the water-conducting fissure zone after coal seam mining, and determine the development height of the water-conducting fissure zone by combining numerical simulation, physical simulation, on-site measurement and other means

[0074] The determination of the key strata for rock bursts is as follows:

[0075] Step 2.1: Determine the positions of the hard rock strata in the overlying strata from bottom to top. Assume that the first rock stratum is a hard rock stratum, and the rock strata from the first to the m-th stratum deform coordinately with it, while the (m + 1)-th rock stratum does not deform coordinately with it. Then the (m + 1)-th rock stratum is the second hard rock stratum. Since the rock strata from the first to the m-th stratum deform coordinately, the curvature of each rock stratum is the same, and each rock stratum forms a combined beam. According to the principle of the combined beam, the load acting on the first hard rock stratum can be derived as:

[0076]

[0077] In the formula, q1(x) m is the load formed by the m-th rock stratum on the first hard rock stratum; h i , γ i , E i are respectively the thickness, unit weight, and elastic modulus of the i-th rock stratum (i = 1, 2,..., m). Considering the load formed by the (m + 1)-th rock stratum on the first hard rock stratum is:

[0078]

[0079] Since the (m + 1)-th rock stratum is a hard rock stratum, its deflection is less than that of the underlying rock strata, and the rock strata above the (m + 1)-th stratum no longer require the underlying rock strata to bear the load it bears. Then there must be:

[0080] q1(x) m+1 <q1(x) m (3)

[0081] Substitute equations (1) and (2) into equation (3) and simplify to obtain:

[0082]

[0083] Equation (4) is the formula for determining the position of the hard rock stratum. During specific determination, start calculating layer by layer from the first rock stratum above the coal seam upwards. When

[0084] and

[0085] satisfy equation (4), stop calculating upwards. At this time, from the first rock stratum upwards, the m-th rock stratum is the first hard rock stratum. Starting from the first hard rock stratum, determine the position of the second hard rock stratum according to the above method, and so on, until the topmost hard rock stratum (assumed to be the n-th hard rock stratum) is determined. By discriminating the positions of the hard rock strata, the positions of the hard rock strata in the overlying strata and the soft rock strata groups they control are obtained.

[0086] Step 2.2: Calculate the breaking distances of each hard rock stratum.

[0087] According to the mechanical model of a fixed-end beam and the analysis of the theory of mechanics of materials, the normal stress at any point within the beam is:

[0088]

[0089] Where M is the bending moment (KN·m) of the cross-section where any point is located; y is the distance (m) from any point to the neutral axis of the cross-section; h is the thickness (m) of the rock beam.

[0090] From the analysis of the fixed-end beam, it can be seen that the maximum bending moment of the fixed-end beam occurs at both ends of the beam. That is:

[0091]

[0092] The corresponding maximum tensile stress is:

[0093]

[0094] When σ max = σ t , the rock beam fractures, and from Equation (7), its limit span (breaking distance) is:

[0095]

[0096] Where h k is the thickness (m) of the k-th hard rock layer; σ k is the tensile strength (MPa) of the k-th hard rock layer; q k is the load (kN / m 2 ) borne by the k-th hard rock layer.

[0097] From Equation (1), it can be seen that q k can be determined by the following formula:

[0098]

[0099] Where the subscript k represents the k-th hard rock layer; the subscript j represents the layer number of the soft rock layer group controlled by the k-th hard rock layer; m k is the number of soft rock layers controlled by the k-th hard rock layer; E k,j , h k,j , γ k,j are the elastic modulus, layer thickness, and unit weight of the j-th layer in the soft rock layer group controlled by the k-th hard rock layer respectively.

[0100] When j = 0, it is the mechanical parameter of the hard rock layer. For example, E 1,0 , h 1,0 , γ 1,0 are the elastic modulus, thickness, and unit weight of the first hard rock layer respectively, and E 1,1 , h 1,1 , γ1,1 They are respectively the elastic modulus, thickness and unit weight of the first soft rock layer in the soft rock layer group controlled by the first hard rock layer.

[0101] Since the elastic modulus of the surface soil layer can be regarded as 0, assuming the thickness of the surface soil layer is H and the unit weight is γ, the load on the nth hard rock layer, which is the uppermost hard rock layer, can be calculated by the following formula:

[0102]

[0103] Step 2.3, compare the breaking distances of each hard rock layer according to the following principles to determine the position of the key layer:

[0104] ① If the kth hard rock layer is the key layer, its breaking distance should be less than the breaking distances of all the hard rock layers above it, that is, it should satisfy

[0105]

[0106] ② If the breaking distance L of the kth hard rock layer k is greater than the breaking distance of the (k + 1)th hard rock layer above it, then add the load borne by the (k + 1)th hard rock layer to the kth hard rock layer and recalculate the breaking distance of the kth hard rock layer.

[0107] ③ Start from the bottommost hard rock layer and judge layer by layer upwards whether L k <L k+1 holds. When L k >L k+1 [[ID=3 to 32]]

[0108] The determination of the development height of the water-conducting fissure zone is as follows:

[0109] On the basis of judging the key layer, by calculating the free space height below the key layer and the soft rock layer, judging the maximum deflection of the soft rock layer and its free space height below, and judging the development height of the water-conducting fissure zone, and combining means such as numerical simulation, physical simulation, and on-site measurement, the development height of the water-conducting fissure zone can be determined more accurately.

[0110] Step 2.4, calculate the free space height below the key layer and the soft rock layer:

[0111] Assume that only the rock strata within the water-conducting fissure zone produce dilation. Due to the dilation of the rock, the free space will continuously shrink. When the working face advances to a certain extent, the overlying rock strata sink and contact the caved gangue and are gradually compacted. Eventually, the dilation of the caved gangue tends to the residual dilation coefficient. Generally, it is considered that only the rock strata within the caving zone and the fissure zone produce dilation, and there is no volume change in the subsidence zone above it. Calculate the free space height below the key layer by formula (12).

[0112]

[0113] In the formula, Δ i is the free space height under the i-th layer of rock stratum; M is the coal seam mining thickness; h j is the thickness of the j-th layer of rock stratum; k j is the residual swelling coefficient of the j-th layer of rock.

[0114] Step 2.5, Calculation of the height of the water-conducting fracture zone:

[0115] It is generally considered that hard rock strata (here mainly referring to key strata) do not have bendability, while soft rock strata have bendability. When the working face length is long enough and there is a free space height under the hard rock strata, the hard rock strata will fracture along the bedding plane and conduct water; otherwise, the hard rock strata will not break. For soft rock strata, due to their bendability, only plastic changes may occur, and water will not be conducted in this case. Whether the plastic changes can develop into rock stratum fractures depends on whether the free space height under the soft rock strata is greater than the settlement value (maximum deflection) allowed to maintain the plastic state. Specific judgment formulas are given below.

[0116] When the working face advances to the distance where it can generate the maximum tension, the maximum deflection of the rock stratum is:

[0117]

[0118] At this time, if the maximum deflection of the soft rock strata is greater than the free space height under it, due to the limitation of the free space, the soft rock strata will maintain the plastic state and will not be damaged, and the water-conducting fracture zone will not develop upward from this point. Thus, there is:

[0119]

[0120] Conversely, when the maximum deflection of the soft rock strata is less than the free space height under it, fracture and water conduction will occur. Thus, there is:

[0121]

[0122] Step 3: Divide sedimentary facies according to the regional sedimentary background, lithology, and logging data.

[0123] On the basis of mastering the regional sedimentary evolution history, divide the sedimentary facies of the main aquifers and the rock strata 6 with rock tendency according to sedimentary facies division markers such as petrological markers, paleontological markers, and logging facies markers.

[0124] The petrological indicators mainly include color, rock type and its combination, texture, and structure. Log facies analysis mainly relies on the information hidden in the natural gamma ray, spontaneous potential and their curves, and combines parameters such as acoustic travel time, triple lateral resistivity, and short-spacing gamma ray to comprehensively analyze the grain size change trend, heterogeneity, and rhythm of the sedimentary layer, so as to indirectly judge the hydrodynamic conditions and sedimentary environment. Different sedimentary environments often have different log curve morphological characteristics, and the log curve morphological characteristics of different sedimentary environments are composed of several basic types combined.

[0125] Step 4: Conduct "static + dynamic" data statistics and monitoring for coal seam mining.

[0126] In the area with strong water-richness of the rock strata with impact tendency overlying Coal Seam 1, an underground directional drill is constructed. The acoustic detection technology is used to explore the overpressure zone and the area with increased porosity. Among them, the main hole 3 of the directional drill is constructed to the first layer with strong water-richness and impact tendency above the coal seam 5, and the branch hole 4 is continuously constructed to the second layer with strong water-richness and impact tendency 7.

[0127] Basic principle of acoustic detection: Under normal circumstances, as the burial depth increases, the compaction degree of the mudstone formation increases, the fluid in the pores is excluded and reduced, and the acoustic velocity of the formation gradually increases. In some special structures and sedimentary environments, due to rapid subsidence and low compaction degree, some mudstone layers contain too much pore water. At this time, the pressure of the mudstone pore water will not only be the hydrostatic pressure, but also bear a part of the overlying formation pressure. This pressure will be transmitted to the underlying reservoir, forming an overpressure reservoir. Predicting overpressure reservoirs is of great significance for both drilling engineering and geological research. The acoustic velocity of the formation can reflect the compaction degree and porosity change of the formation. Therefore, the overpressure zone can be found by using acoustic velocity logging. Under normal circumstances, the change trend of the mudstone acoustic velocity is to increase with the increase of depth. When an overpressure formation appears, the velocity change will deviate from the normal trend, as Figure 2 shown. In different regions, the overpressure amplitude can often be estimated according to the deviation degree between the measured time difference value and the normal time difference value based on experience.

[0128] Stress and ground noise monitoring points are arranged in the coal seam mining face to carry out surrounding rock stress and high-frequency, low-energy vibrations. The stress monitoring points are arranged in argillaceous siltstone, mudstone, and siltstone with a vertical height of 3 - 8 m from the roof of the working face; the ground noise monitoring points are arranged within the influence range of the working face. The ground noise probes must ensure that they can receive the ground noise signals in the monitoring area, and there should be no geological fracture zones that interfere with the propagation of elastic waves between the installation points and the monitoring area. There are at least 2 ground noise probes in each monitoring area. The distance between the probes and the working face is determined according to the length of the working face, generally 20 - 200 m. When the working face conditions permit, the probes should be as far away from the noise source as possible.

[0129] An advanced microseismic monitoring system is adopted to monitor the low-frequency vibrations of the coal seam roof below 200 Hz. The microseismic monitoring system consists of sensors, a data acquisition system, a communication device, a time synchronization device, a server, and data processing and interpretation software. Monitoring stations are arranged on the ground and underground respectively, ensuring that at least 4 geophones can receive the vibration information in this area. The distance between geophones is determined according to the size of the working face. Generally, the smaller the distance, the higher the positioning accuracy. The geophones are arranged in a spatial three-dimensional form with a certain drop in the vertical direction. By monitoring the location, energy magnitude, etc. of the vibrations through the microseismic system, on the one hand, it provides a basis for the analysis of the risk of rock bursts, and on the other hand, it provides a basis for determining the development height of the water-conducting fissure zone in the coal seam.

[0130] The vibration CT monitoring system monitors the vibration waves of the working face and consists of a ground wireless or an optical terminal on the ground, an underground monitoring sub-station, and a seismic sensor. A blasting point is arranged in the roadway on one side of the working face or an artificial seismic source is used to artificially excite the seismic source, and seismic sensors are arranged in the roadway on the other side to receive the seismic waves. According to the distance between the two and the travel time of the seismic waves received by the seismic sensors, the seismic wave velocity distribution within the working face range is inversely calculated, and the positive correlation between the wave velocity and the stress is determined, thereby dividing the high-impact risk area.

[0131] The monitoring data of the mine water inflow is mainly obtained by methods such as the buoy method, the weir measurement method, the volumetric method, and observing the water sump water level.

[0132] Step 5: Establish a coupling risk assessment system for mine rock bursts and water inrusions. According to the main control factors affecting rock bursts and water inrusions, establish Figure 4 A risk assessment system integrating indicators such as static monitoring, dynamic monitoring, and geological information.

[0133] Step 6: Construct a coupling risk assessment model for mine rock bursts and water inrusions based on the fuzzy variable weight method. To avoid the mutual cancellation between the indicators affecting rock bursts and water inrusions and the masking of important indicators by generally important indicators, the present invention proposes the fuzzy variable weight method to determine the weights of each indicator, highlighting the role of important indicators in the risk assessment as much as possible, improving the accuracy of the risk assessment model. After determining the weights of each evaluation indicator, the geographical information composite overlay method is used to overlay each indicator to complete the risk early warning.

[0134] Step 7: Verify and correct the risk assessment model using the magnitude of mine water inrush, past cases of rock bursts, etc. Collect data such as the mine water inrush volume in the area, data on rock burst accidents in similar geological and mining conditions in the area or surrounding areas, and the unit water inrush of boreholes. Further verify and correct the risk assessment model, determine the warning thresholds for each indicator, and apply the corrected risk assessment model to the early warning of the coupling disaster of rock burst and water inrush in the unmined area. The risk assessment model is optimized and adjusted at any time according to the changes in monitoring data and geological exploration degree, providing technical support for the prevention and control of mine rock bursts and water disasters, and ensuring the safe and efficient mining of the mine.

[0135] Application example:

[0136] A certain coal mine is mining the No. 3 coal seam with a thickness of 6 m and a burial depth of 610 m. It belongs to a nearly horizontal coal seam. The overlying strata of the coal seam include the Yan'an Formation, Zhiluo Formation, and Anding Formation sandstone aquifers. The impact tendency report shows that the bottom of the Zhiluo Formation aquifer in the roof of the coal seam has impact tendency. Currently, the 12301 working face is being mined, with a strike length of 300 m and a dip length of 1500 m. The following steps are used to construct a collaborative early warning model for mine rock bursts and water disasters to scientifically guide the safe coal mining of other working faces with similar conditions in this mine.

[0137] Step 1: Determine the main aquifers 6 for coal seam 1 mining, the strata 6 with impact tendency, and the areas 5, 7 with relatively strong water-richness. Collect geological, hydrogeological, logging, and rock mechanical property data during the coal resource exploration stage, including hydrogeological borehole columns (including logging curves), pumping test results of hydrogeological boreholes, geological exploration reports, supplementary hydrogeological exploration reports, geophysical exploration reports, impact tendency identification reports, etc. Determine the main aquifers 6 affecting coal seam mining based on the division of aquifers (confining beds) and their main hydrogeological characteristics, and the development of water-conducting fissure zones during coal seam mining. Determine the areas 5, 7 with relatively strong water-richness based on hydrogeological characteristics, logging, and geophysical exploration interpretation results. The strata with impact tendency are the Zhiluo Formation aquifer 6 in the roof of the No. 3 coal seam, and the impact tendency index is 120 kJ, which is a strongly impact-tending stratum.

[0138] The main aquifers meet the following conditions: (1) The thickness of the Yan'an Formation aquifer in the roof of the coal seam is 80 - 120 m, the thickness of the Zhiluo Formation aquifer is 180 - 200 m, the thickness of the Anding Formation aquifer is 50 - 80 m, and the thickness of the Zhiluo Formation aquifer is the largest; (2) The unit water inrush of the pumping test boreholes in the Zhiluo Formation aquifer is 0.5 - 1.3 L / (s·m), which is larger than the unit water inrush of the boreholes in the Yan'an Formation and Anding Formation aquifers; (3) The fracture-to-mining ratio during coal seam mining is 28 (empirical value), and the development height of the water-conducting fissure zone is 140 m, and all areas communicate with the main aquifer 6.

[0139] The areas with strong water-richness meet the following conditions: (1) in the determined main aquifer 6; (2) in the logging curves, the integrated display shows that the rock grain sizes in areas 5 and 7 are larger and the resistivity is smaller; (3) in the geophysical exploration report, the water-rich anomaly areas 5 and 7 are interpreted.

[0140] Step 2: Using the "key stratum" theory, calculate that the height of the water-conducting fissure zone developed after the mining of the coal seam with the key stratum of rock burst 6 is 122.3 m. Combining numerical simulation, physical simulation, on-site measurement and other means, determine that the height of the water-conducting fissure zone developed is 131.2 m. Combining with Step 1, determine that 6 is the main stratum for rock burst and water inrush disasters.

[0141] Step 3: Divide sedimentary facies according to the regional sedimentary background, lithology and logging data. On the basis of mastering the regional sedimentary evolution history, divide the sedimentary facies of the main aquifer and the rock-stratified rock 6 according to the sedimentary facies division markers such as petrological markers, paleontological markers and logging facies markers. According to the division standard, divide the sedimentary facies of 6 into braided river, meandering river, flood plain and other sedimentary facies, among which 5 and 7 belong to the braided river sedimentary facies.

[0142] Step 4: Carry out the "static + dynamic" data statistics and monitoring of coal seam mining. Monitor rock burst, the height of the water-conducting fissure zone developed, water-richness, etc. in the 12301 working face of the coal seam 1 mining face.

[0143] Construct an underground directional drill in the area 6 with strong water-richness of the rock strata with rock burst tendency above the coal seam 1 mining. Use acoustic wave detection technology to detect the overpressure zone and the area 5 and 7 with increased porosity. Among them, the main hole 3 of the directional drill is constructed to the first layer with strong water-richness of the rock strata with rock burst tendency above the coal seam, and the branch hole 4 is continuously constructed to the second layer with strong water-richness of the rock strata with rock burst tendency 7.

[0144] Layout stress and ground noise monitoring points in the coal seam mining face, and carry out surrounding rock stress, high-frequency and low-energy vibrations. The stress monitoring points are arranged in the siltstone with a vertical height of 6 m from the roof of the 12301 working face, and the spacing of the stress monitoring points is 100 m; the ground noise monitoring points are arranged in the 12301 working face and staggered with the positions of the stress monitoring points. 9 ground noise probes are arranged in each of the two roadways in the monitoring area, and the spacing is 150 m.

[0145] Adopt an advanced microseismic monitoring system to monitor the low-frequency vibrations less than 200 Hz of the coal seam roof. Layout monitoring stations on the ground and underground respectively. Set 18 geophones to receive the vibration information of this area. The spacing of the geophones is determined according to the size of the working face, generally 100 m. The geophones are arranged in a spatial three-dimensional form, with a certain drop in the vertical direction, and the drop is 20 m. Through the microseismic system, monitor the location, energy size, etc. of the vibration occurrence, and determine that the dangerous strata of rock burst and the communication range of the height of the water-conducting fissure zone developed mainly concentrate on 5 of layer 6.

[0146] The vibration CT monitoring system monitors the vibration waves of the working face. An artificial seismic source is arranged in the roadway on one side of the working face, and seismic sensors are arranged in the roadway on the other side to receive seismic waves. The spacing between the seismic sensors is 50 m, and the seismic wave velocity distribution is inverted to divide the high impact hazard area.

[0147] The monitoring data of the mine water inflow is mainly obtained by observing the water level of the sump. When mining approaches near Area 5, the mine water inflow increases significantly.

[0148] Step 5: Establish a coupling risk assessment system for rock bursts and water inrusions in the mine. According to the main control factors affecting rock bursts and water inrusions, establish Figure 4 A risk assessment system that integrates indicators such as static monitoring, dynamic monitoring, and geological information.

[0149] Step 3: Construct a coupling risk assessment model for rock bursts and water inrusions in the mine based on the fuzzy variable weight method. The weights of each evaluation index determined according to the fuzzy variable weight method are: acoustic wave detection weight 0.15, stress monitoring weight 0.03, ground noise monitoring weight 0.05, thickness of the main aquifer weight 0.13, sand ratio of the main aquifer 0.02, development height of the water-conducting fissure zone weight 0.12, water-richness weight 0.14, sedimentary facies weight 0.12, microseismic monitoring weight 0.16, vibration CT monitoring weight 0.05, mine water inflow monitoring 0.03. Use the geographical information composite overlay method to fuse and overlay each evaluation index according to the above weights to complete the coupling risk assessment zoning map of rock bursts and water inrusions in the mine.

[0150] Step 7: Use the size of the mine water inflow, past cases of rock bursts, etc. to verify and correct the risk assessment model. According to the mine water inflow in the area, the data of rock burst accidents that occurred in mines with similar geological and mining conditions around, the unit water inflow of boreholes, and other data, further verify and correct the risk assessment model, and determine the warning thresholds for each index. Apply the determined risk assessment model to the early warning of the coupling disaster of rock bursts and water inrusions in the 12302 working face of this mine. The risk assessment model is optimized and adjusted at any time according to the changes in monitoring data and geological exploration degree, and the application effect is good.

Claims

1. A collaborative early warning method for mine rock bursts and water hazards based on acoustic wave detection, characterized in that, The implementation is specifically carried out according to the following steps: Step 1: Determine the main water-bearing strata horizons, regions with strong water-richness, and strata with rock burst proneness in coal seam mining; Step 2: Use the "key stratum" theory to calculate the development height of the water-conducting fissure zone after coal seam mining and the key strata of rock burst; Step 3: Divide sedimentary facies based on the regional sedimentary background, lithology, and logging information. On the basis of mastering the regional sedimentary evolution history, divide the sedimentary facies of the main aquifers and strata with rock proneness according to sedimentary facies division markers, petrological markers, paleontological markers, and logging facies markers; Step 4: Conduct "static + dynamic" data statistics and monitoring for coal seam mining, where: static data statistics and monitoring include obtaining static geological information such as acoustic detection, thickness of the main aquifers, sand-to-ground ratio, development height of the water-conducting fissure zone, water-richness, and sedimentary facies; dynamic data statistics and monitoring include microseismic monitoring, vibration CT monitoring, stress monitoring, rock noise monitoring, and dynamic geological information of mine water inflow; Step 5: Establish a coupling risk assessment system for rock burst and water inrush in the mine according to the results obtained in Step 4; Step 6: Based on the coupling risk assessment system for rock burst and water inrush in the mine established in Step 5, construct a coupling risk assessment model for rock burst and water inrush in the mine based on the fuzzy variable weight method; Step 7: Verify and correct the risk assessment model established in Step 6.

2. The method for collaborative early warning of mine rock burst and water disaster based on acoustic wave detection according to claim 1, characterized in that In the above Step 1, collect geological, hydrogeological, logging, and rock mechanical property data during the coal resource exploration stage, including hydrogeological borehole columns, hydrogeological pumping test results, geological exploration reports, supplementary hydrogeological exploration reports, geophysical exploration reports, and rock burst proneness identification reports. Determine the main aquifers affecting coal seam mining according to the division of aquifers / confining beds and their main hydrogeological characteristics, and the development of the water-conducting fissure zone during coal seam mining; determine the regions with strong water-richness according to hydrogeological characteristics, logging, and geophysical exploration interpretation results; determine the strata with rock burst proneness by referring to relevant content in the rock burst proneness identification report.

3. The method for collaborative early warning of mine rock burst and water disaster based on acoustic wave detection according to claim 1, wherein In the above Step 1, the main aquifers meet the following conditions: relatively large thickness; relatively large specific capacity of boreholes; the development height of the water-conducting fissure zone after coal seam mining partially or completely communicates with the main aquifers.

4. The method for collaborative early warning of mine rock burst and water disaster based on acoustic wave detection according to claim 1, wherein In the above Step 1, the regions with strong water-richness meet the following conditions: within the already determined main aquifers; the logging curves comprehensively show relatively large rock grain size and relatively small resistivity; water-rich abnormal areas are interpreted in the geophysical exploration report.

5. The method for collaborative early warning of mine rock burst and water disaster based on acoustic wave detection according to claim 1, wherein In the above Step 2, the determination of the key strata of rock burst is as follows: Step 2.1: Determine the positions of hard strata in the overlying strata from bottom to top; Assume that the first layer of strata is a hard stratum, and the strata from it to the m-th layer deform coordinately with it, while the (m + 1)-th layer does not deform coordinately with it, then the (m + 1)-th layer is the second hard stratum; since the strata from the first layer to the m-th layer deform coordinately, the curvatures of each layer are the same, and each layer forms a combined beam. According to the principle of the combined beam, the load acting on the first hard stratum can be derived as: （1） In the formula, is the load formed by the m -th layer of rock strata on the first layer of hard rock strata; h i , γ i 、E i are respectively the thickness, unit weight, and elastic modulus of the i rock strata, where i= 1, 2, …, m; Considering that the m load formed by the +1 layer on the first layer of hard rock formation is: （2） Since the m +(1) layer is a hard rock layer, and its deflection is less than that of the lower rock layer. For the rock layers above the m +(1) layer, it is no longer necessary for the lower rock layer to bear the load it bears. Therefore, it is inevitable that: （3） Substitute formulas (1) and (2) into formula (3) and simplify to obtain: （4） Formula (4) is the formula for discriminating the position of the hard stratum; specifically, when discriminating, start calculating layer by layer from the first layer of strata above the coal seam upwards. When and When the condition of Equation (4) is satisfied, the upward calculation will no longer be performed; at this time, starting from the first layer of rock formation and moving upward, the m-th layer of rock formation is the first layer of hard rock formation; starting from the first layer of hard rock formation, the position of the second layer of hard rock formation is determined by the above method, and so on, until the uppermost layer of hard rock formation is determined, which is set as the n-th layer of hard rock formation; by discriminating the position of the hard rock formation, the position of the hard rock formation in the overlying strata and the soft rock formation group it controls are obtained. Step 2.2: Calculate the breaking distance of each hard rock formation. According to the mechanical model of a fixed-end beam and the analysis of material mechanics theory, the normal stress at any point in the beam is: （5） In the formula, M is the bending moment of the cross-section where any point is located, with the unit of KN•m; y is the distance between any point and the neutral axis of the cross-section, with the unit of m; h is the thickness of the rock beam, with the unit of m; From the analysis of the fixed-end beam, it can be seen that the maximum bending moment of the fixed-end beam occurs at both ends of the beam; that is: （6） The corresponding maximum tensile stress is: （7） When occurs, the rock beam fractures, and its limit span can be obtained from Equation (7) as follows: （8） Step 2.3: Compare the breaking distances of each hard rock formation according to the following principles to determine the position of the key strata for rock burst. The k breaking distance of the hard rock stratum of the th layer should be less than that of all the overlying hard rock strata if it is a key stratum, that is, it should satisfy （9） If the breaking distance of the k hard rock layer L k is greater than the breaking distance of the hard rock layer above it, then the load borne by the k+1 hard rock layer k+1 is added to the k hard rock layer, and the breaking distance of the k hard rock layer is recalculated; Judge layer by layer from the bottommost hard rock layer upwards Whether it holds. When recalculate the break distance of the k layer of hard rock.

6. The method for collaborative early warning of mine rock bursts and water hazards based on acoustic wave detection according to claim 1, wherein In Step 2, the determination method of the development height of the water-conducting fissure zone is as follows: Step 2.4: Calculate the free space height below the key strata and soft rock formations. Calculate the free space height below the key strata by Equation (10). （10） In the formula, is the height of the free space under the i -th layer of rock strata; M is the thickness of the coal seam mined; h j is the thickness of the j -th layer of rock strata; k j is the residual swelling coefficient of the j -th layer of rock; Step 2.5: Calculate the height of the water-conducting fissure zone. When the working face advances to the distance at which it can generate the maximum tension, the maximum deflection of the rock formation is: （11） At this time, if the maximum deflection of the soft rock formation is greater than the free space height below it, due to the limitation of the free space, the soft rock formation will remain in a plastic state and will not be damaged, and the water-conducting fissure zone will no longer develop upward; thus, there is: （12） On the contrary, when the maximum deflection of the soft rock formation is less than the free space height below it, it will break and conduct water, so there is: （13）。

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