A method for evaluating the timeliness of coal seam pressure relief drilling

Abstract

The present invention discloses a method for evaluating the timeliness of coal seam pressure relief drilling, comprising the following steps: S1, obtaining the seismic moment of the mine earthquake source, calculating the peak vibration velocity and dynamic load stress of the coal rock mass caused by the mine earthquake during its outward propagation; S2, determining the critical stress of coal body damage around the pressure relief drilling hole, calculating the particle vibration velocity threshold that causes coal body damage, and determining the damage range of mine earthquakes of different energy levels; S3, considering the cumulative damage effect of mine earthquake events in the mining area and introducing a drilling failure index to characterize the pressure relief effect of the pressure relief drilling hole; S4, obtaining the cumulative PPV that the pressure relief drilling hole endures during the pressure relief period, and calculating the effective pressure relief time of the pressure relief drilling hole for evaluating the timeliness of the pressure relief drilling hole. The present invention can evaluate the timeliness of the pressure relief drilling hole in real time, dynamically, and quickly, judge the pressure relief efficiency of the pressure relief drilling hole, determine the dangerous state of the pressure relief area, and make the pressure relief more targeted.

Description

Technical Field

[0001] The invention belongs to the technical field of safe mining of coal mines, and in particular relates to a method for evaluating the timeliness of coal seam pressure relief drilling effects. Background Art

[0002] As the mining depth of coal mines continues to increase, the tunnels are in a complex stress environment. Large deformations or rock bursts are prone to occur in stress anomaly areas, causing serious tunnel damage or casualties. Pressure relief drilling, as one of the most effective means of coal seam pressure relief, is widely used to relieve coal pressure in high-stress areas. By constructing large-diameter holes with a hole diameter greater than 100 mm within a certain range of the coal seam from the tunnel as pressure relief holes, coal powder is discharged, the strength of the coal body is destroyed, and the stress of the coal body around the tunnel is reduced, thereby achieving the purpose of pressure relief. However, with the continuous action of working face mining and mine vibration loads, the pressure relief holes will gradually be damaged and lose their pressure relief effect. When the pressure relief holes lose their pressure relief efficiency, the stress of the coal rock mass in the area returns to its original high stress state, especially in the impact danger zone, which seriously threatens the safe mining of the working face.

[0003] Evaluating the effectiveness of pressure relief boreholes has long been a challenge for safe coal mining. Currently, commonly used methods rely primarily on manual observation or empirical judgment. Some mines employ secondary hole expansion to determine whether the original pressure relief borehole is fully closed. However, manual observation inevitably leads to errors. For example, a collapse at the exit of a pressure relief borehole can cause the entire borehole to be considered ineffective, while deformation and damage deeper in the hole are difficult to observe. Furthermore, manual observation is time-consuming and labor-intensive, especially when observing large-scale pressure relief boreholes. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for evaluating the timeliness of the effect of coal seam pressure relief drilling, which can evaluate the timeliness of the effect of pressure relief drilling in real time, dynamically and quickly, judge the pressure relief efficiency of the pressure relief drilling, determine the dangerous state of the pressure relief area, and make the pressure relief more targeted.

[0005] To achieve the above object, the present invention provides a method for evaluating the timeliness of coal seam pressure relief drilling, comprising the following steps:

[0006] S1. Obtain the seismic moment of the mine earthquake source and calculate the peak vibration velocity and dynamic load stress of the coal and rock mass caused by the mine earthquake during its outward propagation;

[0007] S2. Determine the critical stress for coal failure around the pressure relief borehole, calculate the particle vibration velocity threshold that causes coal failure, and determine the damage range of mining tremors of different energy levels;

[0008] S3. Considering the cumulative damage effect of mine earthquake events in the stope and introducing the borehole failure index to characterize the pressure relief effect of the pressure relief borehole;

[0009] S4. Obtain the cumulative PPV experienced by the pressure relief borehole during the pressure relief period, and calculate the effective pressure relief time of the pressure relief borehole to evaluate the timeliness of the pressure relief borehole;

[0010] Calculating the seismic moment of the earthquake source using the characteristic parameters of the far-field vibration displacement spectrum of the mine earthquake event :

[0011] ;

[0012] Where, is the volume density of the propagation medium; is the P-wave or S-wave velocity; is the value of the low-frequency constant part in the far-field displacement spectrum, is the distance from the earthquake source to the signal receiving point, is a function that takes into account the emission directionality of the source volume wave;

[0013] When the source parameters are difficult to solve or the conditions for solving are not met, the source energy is used to estimate the earthquake moment and earthquake magnitude. and earthquake moment The relationship between them is as follows:

[0014] ;

[0015] earthquake energy E and earthquake magnitude The relationship is:

[0016] .

[0017] As a further solution of the present invention: the mine earthquake propagates outward in the form of vibration waves, and the peak vibration velocity of the particle is Distance from the earthquake source to the signal receiving point The relationship is as follows:

[0018] ;

[0019] Where, is a proportional constant related to the source intensity; is the earthquake source rupture radius; is the attenuation coefficient, which is related to the medium in which the vibration wave propagates;

[0020] Proportional constant c and attenuation coefficient It is obtained by fitting the c values ​​of multiple mine earthquake events with different energy levels.

[0021] As a further solution of the present invention: the calculation formula of the earthquake source rupture radius R is as follows: ;

[0022] Where, is the seismic moment, is the stress drop;

[0023] Or use the empirical formula to calculate: ;

[0024] Where, The magnitude of the earthquake.

[0025] As a further solution of the present invention: dynamic load stress caused by shock wave The calculation formula is as follows: ;

[0026] Where, is the volume density of the propagation medium, is the peak vibration velocity of the particle, and C is the P-wave or S-wave velocity.

[0027] As a further solution of the present invention: under the action of dynamic and static load stress, the coal body around the pressure relief borehole is most likely to undergo shear failure or tensile failure. The critical stress and particle vibration velocity threshold of the coal body around the pressure relief borehole are determined according to the maximum tensile stress criterion. for:

[0028] ;

[0029] Where, is the minimum principal stress, is the tensile strength of coal rock mass (tensile stress is negative), is the volume density of the propagation medium, and C is the P-wave or S-wave velocity.

[0030] As a further solution of the present invention, when the PPV of the coal body near the pressure relief borehole exceeds the critical value of its damage, the coal body is damaged. The cumulative PPV exceeding the threshold is used and dimensionless processing is used to express the borehole failure index, that is: ;

[0031] Where, is the pressure relief borehole failure index. The larger the value, the more serious the damage to the pressure relief borehole and the lower its pressure relief efficiency. is the PPV of coal and rock mass caused by the i-th shock wave; is the maximum cumulative particle vibration velocity when the pressure relief drilling fails completely, is the particle vibration velocity threshold, and N is the number of statistical mining earthquakes.

[0032] As a further solution of the present invention, the effective pressure relief time of the pressure relief drilling hole is calculated using the following formula: ;

[0033] Where, The effective decompression time of the decompression borehole; Date of initial drilling for the decompression borehole; The date when the pressure relief borehole loses its pressure relief effectiveness; the effective pressure relief time of the pressure relief borehole is used to evaluate the timeliness of the pressure relief borehole. When the borehole is within the effective pressure relief period, it is considered that the pressure relief area has a certain ability to resist dynamic loads.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention constructs a borehole failure index based on microseismic data during mining, counts the cumulative PPV of the mining area and the vicinity of the pressure relief borehole, and calculates the effective action time of the pressure relief borehole to evaluate the timeliness of the pressure relief borehole. The invention can evaluate the timeliness of the pressure relief borehole in real time, dynamically and quickly based on the data received by the remote microseismic monitoring system, judge the pressure relief efficiency of the pressure relief borehole, determine the dangerous state of the pressure relief area, and make the pressure relief more targeted.

[0036] The present invention simplifies the evaluation process and uses indicators with clear physical meaning. It can dynamically evaluate the pressure relief efficiency of pressure relief boreholes in coal seam tunnels in real time, significantly reducing the engineering workload of local monitoring methods. Furthermore, the present method can be programmed to automatically evaluate the pressure relief effectiveness of pressure relief boreholes, providing guidance for on-site pressure relief. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic flow chart of the present invention;

[0038] Figure 2 Schematic diagram of stress state near the pressure relief borehole and damage caused by mining earthquakes in the present invention;

[0039] Figure 3 The invention is the advanced mining earthquake distribution and large diameter pressure relief drilling arrangement of the working face;

[0040] Figure 4 It is the PPV attenuation test value of a mine earthquake and the theoretical fitting curve of the present invention;

[0041] Figure 5 This is the PPV three-dimensional effect diagram of the earthquake source energy of 1.0E+J in the present invention;

[0042] Figure 6 This is the cumulative PPV distribution cloud diagram of the working face of the present invention;

[0043] Figure 7 This is a distribution cloud diagram of the failure index of the pressure relief drilling of the present invention.

[0044] In the figure: Mohr-Coulomb refers to the Mohr-Coulomb Failure Criterion of rock failure. The formula represented by the curve is: , where is the shear stress, is the normal stress, is the internal friction angle, The cohesion of the material. DETAILED DESCRIPTION

[0045] The present invention will be further described below by way of examples.

[0046] like Figure 1 As shown, a method for evaluating the timeliness of coal seam pressure relief drilling includes the following steps:

[0047] S1. Obtain the seismic moment of the mine earthquake source and calculate the peak vibration velocity and dynamic load stress of the coal and rock mass caused by the mine earthquake during its outward propagation;

[0048] S2. Determine the critical stress for coal failure around the pressure relief borehole, calculate the particle vibration velocity threshold that causes coal failure, and determine the damage range of mining tremors of different energy levels;

[0049] S3. Considering the cumulative damage effect of mine earthquake events in the stope and introducing the borehole failure index to characterize the pressure relief effect of the pressure relief borehole;

[0050] S4. Obtain the cumulative PPV experienced by the pressure relief borehole during the pressure relief period, and calculate the effective pressure relief time of the pressure relief borehole to evaluate the timeliness of the pressure relief borehole.

[0051] Furthermore, the far-field vibration displacement spectrum characteristic parameters of the mine earthquake event are used to calculate the seismic moment of the earthquake source. :

[0052] ;

[0053] In formula (1), is the volume density of the propagation medium; is the P-wave or S-wave velocity; is the value of the low-frequency constant part in the far-field displacement spectrum, is the distance from the earthquake source to the signal receiving point, is a function that takes into account the emission directionality of the source volume wave;

[0054] When the source parameters are difficult to solve or the conditions for solving are not met, the source energy is used to estimate the earthquake moment and earthquake magnitude. and earthquake moment The relationship between them is as follows:

[0055] ;

[0056] earthquake energy E and earthquake magnitude The relationship is:

[0057] .

[0058] Furthermore, the mine earthquake propagates outward in the form of vibration waves. Considering the influence of the near-field source, the peak vibration velocity of the particle is Distance from the earthquake source to the signal receiving point The relationship is as follows:

[0059] ;

[0060] In formula (4), is a proportional constant related to the source intensity; is the earthquake source rupture radius; is the attenuation coefficient, which is related to the medium in which the vibration wave propagates.

[0061] Furthermore, the proportional constant c in equation (4) is related to the attenuation coefficient It is obtained by fitting the c values ​​of multiple mine earthquake events with different energy levels.

[0062] Mine earthquakes are coal-rock fractures caused by high stress. The energy released is related to the earthquake source fracture radius. Furthermore, the earthquake source fracture radius R is calculated as follows: ;

[0063] In formula (5), is the seismic moment, is the stress drop;

[0064] Or use the empirical formula to calculate: ;

[0065] In formula (6), The magnitude of the earthquake.

[0066] Furthermore, the dynamic load stress caused by the shock wave The calculation formula is as follows: ;

[0067] In formula (7), is the volume density of the propagation medium, is the peak vibration velocity of the particle, and C is the P-wave or S-wave velocity.

[0068] Furthermore, under the action of dynamic and static load stress, the coal body around the pressure relief borehole is most likely to undergo shear failure or tensile failure. The critical stress and particle vibration velocity threshold of the coal body around the pressure relief borehole are determined according to the maximum tensile stress criterion. for:

[0069] ;

[0070] In formula (8), is the minimum principal stress, is the tensile strength of coal rock mass (tensile stress is negative), is the volume density of the propagation medium, and C is the P-wave or S-wave velocity.

[0071] Furthermore, when the PPV of the coal body near the pressure relief borehole exceeds the critical value of its destruction, the coal body will be destroyed. The cumulative PPV exceeding the threshold is used and dimensionless processing is used to express the borehole failure index, that is: ;

[0072] In formula (9), is the pressure relief borehole failure index. The larger the value, the more serious the damage to the pressure relief borehole and the lower its pressure relief efficiency. is the PPV of coal and rock mass caused by the i-th shock wave; is the maximum cumulative particle vibration velocity when the pressure relief drilling fails completely, is the particle vibration velocity threshold, and N is the number of statistical mining earthquakes.

[0073] Use the drilling failure index to guide the project to determine whether it is necessary to construct a pressure relief drilling again:

[0074] when When the pressure relief drilling hole still has the pressure relief effect, it is considered that there is no need to take pressure relief measures temporarily; when When the pressure relief drilling is completed, it indicates that the original pressure relief drilling hole has failed. It is determined whether the pressure relief drilling hole needs to be constructed again based on the on-site conditions.

[0075] Furthermore, the following formula is used to calculate the effective pressure relief time of the pressure relief drilling hole: ;

[0076] In formula (10), The effective decompression time of the decompression borehole; Date of initial drilling for the decompression borehole; The date when the pressure relief borehole loses its pressure relief effectiveness; the effective pressure relief time of the pressure relief borehole is used to evaluate the timeliness of the pressure relief borehole. When the borehole is within the effective pressure relief period, it is considered that the pressure relief area has a certain ability to resist dynamic loads.

[0077] The present invention is mainly based on the damage effect of mining vibration load on coal and rock mass in the mining area. That is, combining the mining working face and the arrangement of pressure relief drilling holes, the pressure relief drilling index distribution cloud map is obtained by using the parameters of mining vibration events to quickly evaluate the pressure relief efficiency of drilling holes. Figure 2 and Figure 7 shown.

[0078] During the mining process, geological structures or unreasonable mining designs often lead to abnormal high stress in the mining tunnels, which makes underground mining face the threat of dynamic disasters such as rock burst, rock burst, and coal and gas outburst. Pressure relief drilling is a method of drilling pressure relief holes into the coal body in high stress areas to discharge coal powder to provide deformation space for the coal and rock bodies, thereby reducing stress concentration. It can effectively reduce the support stress and transfer its peak value to the depth, such as Figure 2 As shown in the figure. After the pressure relief borehole is constructed, the coal mass surrounding the pressure relief borehole transitions from a triaxial stress state to a biaxial stress state. In particular, the coal mass near the pressure relief borehole is damaged and fractured, resulting in lower mechanical strength. The pressure relief borehole is subjected to high static stress due to the supporting stress of the overburden. Furthermore, mining vibration loads generated by mining activities, coal rock fracturing, blasting, and hydraulic fracturing act on the coal mass near the pressure relief borehole, causing damage. These vibration loads propagate outward in the form of vibration waves. Failure occurs when the dynamic stress increment caused by the PPV of the coal mass near the pressure relief borehole exceeds its strength. The coal mass near the pressure relief borehole primarily fails in tension or shear. The critical stress for failure is calculated using the maximum tensile stress criterion or the Mohr-Coulomb criterion, thereby determining the particle vibration velocity threshold that causes failure in the coal mass near the pressure relief borehole. As mining vibration loads accumulate, the pressure relief borehole space is gradually filled with fractured coal, losing its pressure relief effect. The pressure relief efficiency of the pressure relief borehole is evaluated by calculating the cumulative PPV.

[0079] The following is an introduction based on a specific embodiment. The pressure relief drilling arrangement and microseismic parameters of a certain working face during the mining period from 2018 / 10 / 4 to 2018 / 10 / 30 are selected. Figure 3 The method of the present invention is used to evaluate the pressure relief performance of the pressure relief borehole, and the steps are as follows:

[0080] ① Formula (2) and formula (3) are used to calculate the seismic moment and magnitude of the microseismic events during the mining period from 2018 / 10 / 4 to 2018 / 10 / 30 in a certain working face in the embodiment. The seismic moment and magnitude corresponding to microseismic events of different energy levels are shown in Table 1.

[0081]

[0082] ② Using formula (4) and combining the field measurements of the peak vibration velocity of the particle point of different energy levels for fitting, the PPV attenuation coefficient is obtained to be 0.0025. The relationship between the proportional coefficient and the source energy is: The rupture radius of the earthquake source is calculated according to the empirical formula (6). The rupture radius and proportional coefficient c of the earthquake source for microseismic events of different energy levels are shown in Table 1. Figure 4 is the source energy The PPV field measurement value of a mine earthquake and the theoretical fitting curve show that the fitting effect is good, indicating that the fitting parameters are reasonably determined. When the proportional coefficient c and the attenuation coefficient Substituting into formula (4), we can draw the PPV distribution diagram as follows: Figure 5 shown.

[0083] ③ According to the dynamic load stress calculation formula (7) caused by mine earthquake and the maximum tensile stress failure criterion calculation formula (8), the particle vibration velocity threshold of coal body damage is determined, and the tensile strength of the coal body near the pressure relief borehole is taken as , coal density , longitudinal wave velocity , the calculated particle vibration velocity threshold is 0.037m / s.

[0084] ④ According to the PPV attenuation law of mine earthquake represented by formula (4), combined with the particle vibration velocity threshold of 0.037m / s for the damage effect of the coal body near the pressure relief borehole, the damage radius of different microseismic events is determined. The damage radius of representative events is shown in Table 1. A program is written to grid the study area, calculate the PPV distribution value of each microseismic event above the threshold, and accumulate them. The interpolation method is used to obtain the cumulative PPV distribution cloud map of the working face, as shown in the following figure: Figure 6 shown.

[0085] ⑤ The cumulative particle vibration velocity of the pressure relief drilling failure is determined by installing a borehole stress gauge in the secondary drilling or near the pressure relief drilling hole. Here, the value is 0.35 m / s. The drilling failure index is calculated using formula (9). For the area outside the pressure relief drilling hole, the coal body is in a triaxial stress state, and the damage caused by the mining vibration load is relatively small. Therefore, the failure index is multiplied by 0.1, and the data is smoothed using Gaussian filtering to obtain the drilling failure index distribution cloud map, as shown in the figure. Figure 7 As shown in Figure 1. For areas where the pressure relief borehole failure index is less than 1, it indicates that the protocol borehole in this area still has a certain pressure relief and anti-seismic performance, while in areas where the pressure relief borehole failure index is greater than 1, the pressure relief borehole has lost its pressure relief performance. Formula (10) can be used to calculate the effective pressure relief time of the pressure relief borehole.

[0086] The case analysis shows that the present invention uses the location and source energy parameters of microseismic events ( Figure 3 ), which can evaluate the timeliness of the pressure relief drilling in real time, dynamically and quickly, and judge the pressure relief efficiency of the pressure relief drilling ( Figure 7 This method is based on the damaging effect of mining vibration load on coal and rock mass. It has clear physical meaning and good evaluation effect. It can effectively guide the timely implementation of pressure relief measures on site and reduce the amount of manual drilling cuttings monitoring work.

Claims

1. A method for evaluating the timeliness of coal seam pressure relief drilling, characterized in that: The following steps are involved: S1. Obtain the seismic moment of the mine earthquake source and calculate the peak vibration velocity and dynamic load stress of the coal and rock mass caused by the mine earthquake during its outward propagation; S2. Determine the critical stress for coal failure around the pressure relief borehole, calculate the particle vibration velocity threshold that causes coal failure, and determine the damage range of mining tremors of different energy levels; S3. Considering the cumulative damage effect of mine earthquake events in the stope and introducing the borehole failure index to characterize the pressure relief effect of the pressure relief borehole; S4. Obtain the cumulative PPV experienced by the pressure relief borehole during the pressure relief period, and calculate the effective pressure relief time of the pressure relief borehole to evaluate the timeliness of the pressure relief borehole; Calculating the seismic moment of the earthquake source using the characteristic parameters of the far-field vibration displacement spectrum of the mine earthquake event : ； Where, is the volume density of the propagation medium; is the P-wave or S-wave velocity; is the value of the low-frequency constant part in the far-field displacement spectrum, is the distance from the earthquake source to the signal receiving point, is a function that takes into account the emission directionality of the source volume wave; When the source parameters are difficult to solve or the conditions for solving are not met, the source energy is used to estimate the earthquake moment and earthquake magnitude. and earthquake moment The relationship between them is as follows: ； earthquake energy E and earthquake magnitude The relationship is: 。 2. The method for evaluating the timeliness of coal seam pressure relief drilling according to claim 1, characterized in that: Mine earthquake propagates outward in the form of vibration waves, and its peak vibration velocity is Distance from the earthquake source to the signal receiving point The relationship is as follows: ； Where, is a proportional constant related to the source intensity; is the earthquake source rupture radius; is the attenuation coefficient, which is related to the medium in which the vibration wave propagates; proportionality constant and attenuation coefficient Through multiple mine earthquake events of different energy levels The value is fitted.

3. The method for evaluating the timeliness of coal seam pressure relief drilling according to claim 2, characterized in that: earthquake source rupture radius The calculation formula is as follows: ； Where, is the seismic moment, is the stress drop; Or use the empirical formula to calculate: ; Where, The magnitude of the earthquake.

4. The method for evaluating the timeliness of coal seam pressure relief drilling according to claim 1, characterized in that: Dynamic stress caused by shock waves The calculation formula is as follows: ； Where, is the volume density of the propagation medium, is the peak vibration velocity of the particle, and C is the P-wave or S-wave velocity.

5. The method for evaluating the timeliness of coal seam pressure relief drilling according to claim 1, characterized in that: The coal around the pressure relief borehole is most likely to undergo shear failure or tensile failure under dynamic and static load stress. The critical stress and particle vibration velocity threshold of the coal around the pressure relief borehole are determined based on the maximum tensile stress criterion. for: ； Where, is the minimum principal stress, is the tensile strength of coal rock mass, is the volume density of the propagation medium, and C is the P-wave or S-wave velocity.

6. The method for evaluating the timeliness of coal seam pressure relief drilling according to claim 1, characterized in that: When the PPV of the coal body near the pressure relief borehole exceeds the critical value of its destruction, the coal body will be destroyed. The cumulative PPV exceeding the threshold is used to express the borehole failure index through dimensionless processing, that is: ； Where, is the pressure relief borehole failure index. The larger the value, the more serious the damage to the pressure relief borehole and the lower its pressure relief efficiency. is the PPV of coal and rock mass caused by the i-th shock wave; is the maximum cumulative particle vibration velocity when the pressure relief drilling fails completely, is the particle vibration velocity threshold, and N is the number of statistical mining earthquakes.

7. The method for evaluating the timeliness of coal seam pressure relief drilling according to claim 1, characterized in that: The effective pressure relief time of the pressure relief drilling hole is calculated using the following formula: ; Where, The effective decompression time of the decompression borehole; Date of initial drilling for the decompression borehole; The date when the pressure relief borehole loses its pressure relief effectiveness; the effective pressure relief time of the pressure relief borehole is used to evaluate the timeliness of the pressure relief borehole. When the borehole is within the effective pressure relief period, it is considered that the pressure relief area has a certain ability to resist dynamic loads.

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