A gob-side entry precise roof cutting method based on rock stratum geological while-drilling detection

Abstract

The application discloses a kind of along empty roadway precision roof cutting methods based on strata geology while drilling detection, belong to coal mine intelligent mining field. Including steps: S1, the drilling parameter measuring instrument installed on drilling rig is used to collect drilling rig operating parameter;S2, the parameter collected in S1 is used to establish strata strength identification model based on comprehensive index, to determine roof strata lithology and rock sequence distribution;S3, the calculation model of the distribution range of advance support pressure in front of coal mining face is established, to judge along empty roadway roof cutting range;S4, along empty roadway roof cutting horizon is determined using roof cutting height calculation equation and strata lithology distribution;S5, drilling angle is corrected in real time using inclination sensor monitoring result.This application reaches according to roadway trend roof strata geological conditions by the real-time operation data of drilling rig, determines along empty roadway roof cutting range and roof cutting horizon, thereby dynamically adjusts roof cutting parameter, and drilling angle is corrected in real time, realizes the purpose that roof cutting effect is consistent with design result.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of intelligent mining of coal mines, in particular, relates to a kind of along empty roadway precision roof cutting method based on rock stratum geology drilling detection. BACKGROUND

[0002] The recoverable coal resources in the central and eastern mining areas of China are decreasing, and the coal pillars left between the coal mining faces cause great waste of resources and are prone to cause disasters such as rock burst, empty area fire and gas accumulation. One of the effective ways to solve the above problems is the roof cutting and pressure releasing along empty roadway technology, which is of great significance to improving the coal recovery rate and alleviating the downward pressure of the coal economy and the sustainable development of the mining industry.

[0003] The along empty roadway technology is to pre-split the roof of the roadway in front of the coal mining face, and the pre-split roof collapses under the action of mine pressure. After the collapsed roof is treated using gangue blocking support, temporary support and air leakage prevention technology, the roadway can be preserved for the next working face. The core link of the along empty roadway technology is roof cutting and pressure releasing. The traditional method uses a single roof cutting parameter for the entire along empty roadway based on the roof rock stratum geological information of the local area, which cannot dynamically adjust the roof cutting parameter according to the roof rock stratum geological conditions along the roadway, resulting in problems such as unreasonable roof cutting horizon and timing, high stress concentration degree of the roadway and large deformation amplitude of the surrounding rock.

[0004] In addition, anchor rod drills are commonly used for pre-split hole construction on site. However, due to the lack of effective monitoring means, the inclination angles of the pre-split holes often deviate from the designed angles to different degrees during pre-split hole construction, causing the pre-split holes not to be in the same plane, which seriously affects the blasting pre-splitting effect. SUMMARY

[0005] To solve the problems of the traditional roof cutting and pressure releasing method, such as the inability to dynamically adjust the roof cutting parameter according to the roof rock stratum geological conditions along the roadway, resulting in problems such as unreasonable roof cutting horizon and timing, high stress concentration degree of the roadway and large deformation amplitude of the surrounding rock, and the inclination angles of the pre-split holes often deviating from the designed angles to different degrees during pre-split hole construction, causing the pre-split holes not to be in the same plane, which seriously affects the blasting pre-splitting effect, the present application provides an along empty roadway precision roof cutting method based on rock stratum geology drilling detection, comprising the steps of:

[0006] S1: installing a drilling parameter measuring instrument on a single anchor rod drill used for roof cutting construction along the empty roadway, drilling the roof along the empty roadway using the drill, and collecting the drilling operation parameters such as thrust, torque, speed, displacement, vibration and inclination angle in real time through the drilling parameter measuring instrument;

[0007] S2: Calculate two comprehensive indexes of SEM and RDA using the collected drilling rig operation parameters; establish a rock strength identification model based on the comprehensive indexes by a multiple linear regression method; determine the lithology and rock sequence distribution of the roof rock stratum using the rock strength identification result and the drilling displacement;

[0008] S3: Establish a calculation model of the advanced abutment pressure distribution range in front of the coal mining face in combination with the buried depth, height, mining height of the coal mining face, and the roof lithology and rock sequence distribution;

[0009] S4: Bring the rock stratum lithology, rock sequence and thickness into a roof cutting height calculation equation to obtain the roof cutting height at the drilling position;

[0010] S5: On the basis of dynamically identifying the roof rock stratum lithology and rock sequence by the while-drilling detection technology, design different roof cutting drilling spacing according to the rock stratum distribution, and when the roof cutting hole is drilled along the gob roadway, the drilling angle is corrected in real time by using the monitoring result of the inclination sensor to finally obtain the blasting hole.

[0011] Further, in step S1, the device used includes a single anchor rod drilling rig, a while-drilling parameter measuring instrument, a signal wireless transmitting module, a signal wireless receiving module, a multi-channel data acquisition module, a data storage display terminal, a drill rod and a drill bit; the inside of the while-drilling parameter measuring instrument is installed with thrust, torque, rotating speed, displacement and inclination sensors, the lower end is connected with the single anchor rod drilling rig by using an outer hexagonal shaft, and the upper end is connected with a B19 hexagonal drill rod.

[0012] Further, the drilling rig operation parameters collected by each sensor first enter the signal wireless transmitting module, and then are transmitted to the multi-channel data acquisition module after being received by the signal wireless receiving module, and the multi-channel data acquisition module is connected with the data storage display terminal for storage and display.

[0013] Further, in step S2, the while-drilling parameters such as thrust, torque, rotating speed, drilling speed and vibration collected can be used to calculate two comprehensive indexes of the modulation specific energy SEM and the rock drillability index RDA by the following formulas:

[0014]

[0015] The multiple linear regression model for predicting the rock stratum strength by using the SEM and RDA can be expressed as:

[0016] Rc=k1xSEM+k2xRDA.

[0017] Further, in step S3, the calculation model of the advanced abutment pressure distribution range in front of the coal mining face is:

[0018]

[0019] Further, in step S4, the cutting height calculation formula is:

[0020]

[0021] Further, in step S5, the cutting method adopts blasting cutting, and according to different lithology, the blasting hole spacing is designed as: ① for hard roof, the spacing is 500 mm; ② for soft rock roof, the spacing is 550 mm; and ③ for broken roof, the spacing is 600 mm.

[0022] Further, in step S5, the design of the blasting hole angle β is: ① when H c ≤1m, β=20°; ② when 1m<H c ≤3m, β=15°; and ③ when 3m<H c ≤4.5m, β=10°.

[0023] Further, in step S5, a plurality of blasting holes with the same inclination angle form a splitting crack at the blasting position, the splitting cracks of each blasting hole are connected to form a planar regular structural weak surface, and the roof strata are cut off and caved along the structural weak surface under the action of the advanced support pressure of the working face.

[0024] In summary, the present application has the following beneficial effects compared with the prior art:

[0025] The present application obtains the parameters of the drilling machine during operation through the drilling parameter measuring instrument installed on the single anchor rod drilling machine used for the roof cutting construction along the gob roadway. The roof strata lithology and rock sequence distribution are determined by using the parameters of the drilling machine during operation. Then, combined with the information such as the buried depth, height, mining height of the coal mining face, and the roof lithology and rock sequence distribution, a calculation model of the advanced support pressure distribution range in front of the coal mining face is established, so as to take the advanced support pressure distribution range as the roof cutting area of the gob roadway, so as to realize the accurate drilling judgment of the roof cutting range of the gob roadway. The parameters such as the rock strata lithology, rock sequence and thickness are brought into the roof cutting height calculation equation, so as to realize the accurate drilling judgment of the roof cutting horizon of the gob roadway. The inclination sensor monitoring result is used to correct the drilling angle in real time, so as to ensure that each roof cutting hole is on a straight line to the greatest extent, so as to ensure the cutting effect.

[0026] The present application provides an accurate roof cutting method of the gob roadway based on the rock strata geological drilling detection, which realizes the purpose of accurately judging the roof cutting range and the roof cutting horizon of the gob roadway by using the real-time operation data of the drilling machine to dynamically adjust the roof cutting parameters according to the roof strata geological conditions along the roadway, and the drilling angle is corrected in real time by using the inclination sensor monitoring result, so as to ensure that the cutting effect is consistent with the design result in the construction process. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:

[0028] Figure 1 Flow chart of the method for precise roof cutting of gob-side entry based on stratum geology while drilling detection;

[0029] Figure 2 Overall structure diagram of the device for drilling detection;

[0030] Figure 3 Flow chart of drilling parameter acquisition and transmission;

[0031] Figure 4 Data curve acquired;

[0032] Figure 5 Relationship curve between SEM and RDA and stratum strength;

[0033] Figure 6 Flow chart of the multiple linear regression model;

[0034] Figure 7 Schematic diagram of the cutting height of the composite roof.

[0035] Among them, the above-mentioned drawings include the following reference signs:

[0036] 1, single anchor rod drilling machine; 2, drilling parameter measuring instrument; 3, signal wireless transmission module; 4, signal wireless receiving module; 5, multi-channel data acquisition module; 6, data storage display terminal; 7, B19 hexagonal drill rod; 8, roof stratum. DETAILED DESCRIPTION

[0037] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0038] It should be noted that the terms used herein are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form can also include the plural form unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in the specification, there is a feature, step, operation, device, component and / or combination thereof.

[0039] The relative arrangement of parts and steps, numerical expressions, and numerical values set forth in the examples herein are not intended to limit the scope of the application unless specifically so stated. It is to be understood that the drawings shown in the various figures are not drawn to scale and that elements of the various figures are shown as examples and not necessarily to scale. Techniques, methods, and devices known to those of ordinary skill in the relevant art can not be discussed in detail, but should be considered as part of the description of the application. In all examples shown and discussed herein, any specific value should be interpreted as merely an example and not a limitation. Thus, other examples of the example embodiments can have different values. It is noted that like numbers and letters refer to like elements throughout the several views of the drawings, and that the use of or reference to certain terms in various places of the specification are not intended to exclude those terms from the scope of the application, but rather to clarify the description of the application.

[0040] Referring to Figure 1 As shown, the application provides a precise roof cutting method for gob roadway based on rock stratum geological drilling detection, comprising the steps of:

[0041] S1: Install the rock stratum geological information intelligent drilling detection equipment on the drilling machine used for blasting pre-splitting hole construction, use the drilling machine to carry out roadway roof stratum 8 strength drilling experiment, and collect drilling machine operation parameters such as thrust, torque, speed, vibration and inclination in real time, to provide original data for establishing a rock stratum strength drilling identification model suitable for the on-site geological conditions.

[0042] As shown in Figure 2 The device used includes a single anchor rod drilling machine 1, a drilling parameter measuring instrument 2, a signal wireless transmission module 3, a signal wireless receiving module 4, a multi-channel data acquisition module 5, a data storage display terminal 6, and a B19 hexagonal drill rod 7. The drilling parameter measuring instrument 2 is internally installed with thrust, torque, speed, displacement and inclination sensors, the lower end of the drilling parameter measuring instrument 2 is connected with the single anchor rod drilling machine 1 using an outer hexagonal shaft, and the upper end is connected with the B19 hexagonal drill rod 7. The drilling machine operation parameters collected by each sensor first enter the signal wireless transmission module 3, and then are transmitted to the multi-channel data acquisition module 5 after being received by the signal wireless receiving module 4. The multi-channel data acquisition module 5 is connected with the data storage display terminal 6 for storage and display. The drilling parameter acquisition and transmission process in step S1 is as shown in Figure 3 .

[0043] During the experiment, first, the while-drilling parameter measuring instrument 2 is debugged to ensure that data acquisition and transmission are correct, then the outer hexagonal shaft at the lower end of the while-drilling parameter measuring instrument is inserted into the drilling machine drill rod interface position, and the while-drilling parameter measuring instrument is fixed with the single-anchor rod drilling machine 1. The B19 hexagonal drill rod 7 is installed on the upper end of the while-drilling parameter measuring instrument, the data acquisition device switch is turned on, and finally the water source and the gas source are connected to drill the roof rock stratum 8, and the while-drilling parameter measuring instrument 2 is used to collect drilling machine operation data such as thrust, torque, rotating speed, displacement, inclination and vibration in real time during drilling. The data curve collected through step S1 is as shown in Figure 4 S2: as shown in Figure 5 and Figure 6 , the two comprehensive indexes of SEM and RDA are calculated using the drilling machine operation parameters (thrust, torque, rotating speed, drilling speed and vibration) collected on site; through the multiple linear regression method, the rock stratum strength identification model based on the comprehensive indexes is established; the lithology and rock sequence distribution in the roof rock stratum 8 are determined using the rock stratum strength identification result and the drilling displacement.

[0044] (1) Modulation Energy Ratio (SEM)

[0045] The mutual information and statistical analysis methods are used to study the identification effect of the modulation energy ratio on the coal and rock boundary, and the results show that the modulation energy ratio (SEM) can distinguish the coal and non-coal rock strata with significant consistency. The modulation energy ratio SEM is expressed by the following formula:

[0046]

[0047] In the formula, the logarithmic function helps to amplify the weak signal in SEM and sharpen the difference characteristics of different lithologies. w is used to enhance the weak signal in the drilling energy ratio sequence, and c specifies the transition point of the logic function, which has the physical meaning of the characteristic point of the SEM curve when the lithology changes, and the value is 0.65. In this paper, a is fixed as 2, and the value controls the transition interval of the SEM curve when the lithology changes. In addition, the constant k a and C are 1000 and 2 respectively.

[0048] (2) Rock Drilling Index (RDA)

[0049] Dimensional analysis can be used to determine the specific functional relationship between various variables that interact with each other and express it as a simple mathematical or physical model. In this invention, the while-drilling parameters include thrust, torque, rotating speed, drilling speed and vibration, and since there is an obvious functional relationship between rock strength and while-drilling parameters, it is assumed that the functional relationship between the while-drilling parameters and the rock strength is:

[0050] f(F,v,T,ω,g)=0

[0051] According to the π theorem, three basic dimension groups M, L and T are selected to form dimension formulas of six dimension variables, and then three dimensionless quantities (π1, π2 and π3) are formed based on the dimension analysis theory to represent the relationship between the while-drilling parameters and the rock strength. Each dimensionless quantity can be expressed as:

[0052]

[0053] Since π1, π2 and π3 are independent of each other, there is π3 = λπ1 α π2 β where λ, α and β are important parameters for controlling the function relationship between the rock strength and the while-drilling parameters, and in this paper, λ = 0.01, u and t are respectively 2 and -0.5. The present application uses the rock drillability index to reflect the rock strength, and the relationship between the RDA and the while-drilling parameters can be expressed as:

[0054] RDA = λv u+2t ω u / F 3-u-t T u+t-2 .

[0055] (3) Rock strength multivariate linear regression model

[0056] For a group of data, the independent variables are x i (i = 1…m), the dependent variable is y, ε is a nonlinear error, and the regression coefficient is a i (i = 0…m), and the function relationship between the independent variables and the dependent variable can be expressed by a multivariate regression equation as:

[0057] y = a0 + a1x1 + … + a m x m + ε

[0058] Finally, the multivariate linear regression model for predicting the rock strength by using the SEM and the RDA can be expressed as:

[0059] R c = k1 × SEM + k2 × RDA.

[0060] S3: Combined with the information of the buried depth, height, mining height, roof lithology and rock sequence distribution of the coal mining face, a calculation model of the advanced abutment pressure distribution range in front of the coal mining face is established, so that the advanced abutment pressure distribution range is taken as the advanced cutting roof area of the gob-side entry, so as to realize the accurate while-drilling judgment of the cutting roof range of the gob-side entry.

[0061] For example Figure 7As shown, according to the rock sequence and distribution of rock sequence, the cutting position should be arranged at the interface of rock or thin and soft rock as much as possible, and the weak surface such as soft roof layer, lithology layering surface and the like is used as the cutting seam interface, which can facilitate the roof collapse after cutting seam, and on the basis of meeting the cutting height, if thick and hard rock layer is encountered, the cutting height should be additionally increased. In addition, on the basis of fully considering the rock distribution, the roof cutting height design must meet the requirements that the rock mass within the cutting range can effectively fill the goaf within a certain range of the roadway, and then the broken rock bank can play a necessary supporting role on the overburden strata of the goaf, and slow down the subsidence and rotation deformation of the overburden strata. On the basis of mastering the lithology, thickness and dilatancy coefficient of the roof rock stratum 8, the cutting height is calculated in detail according to the following method. Assuming that there are m layers of rock strata within the cutting range, the cutting height should meet the following formula:

[0062]

[0063] In the formula, H F is the cutting height, m; H c is the coal seam thickness, m; K P is the average dilatancy coefficient of rock stratum, usually 1.3-1.5.

[0064] S4: The rock lithology, rock sequence and thickness and other parameters are brought into the cutting height calculation equation to obtain the reasonable cutting height of the drilling position. On the basis of meeting the cutting height, the cutting terminal is arranged at the rock interface or soft rock position as much as possible, and the cutting height should be increased for thick and hard rock, and finally the precise judgment of the cutting position along the goaf roadway is realized.

[0065] The intersection point of the limit equilibrium zone and the elastic zone is the stress peak value, and the distance from the peak value of the advanced abutment pressure to the coal wall is:

[0066]

[0067] In the formula, m is the mining height of the coal seam, m; f is the friction factor between coal seams; C is the cohesion of coal, MPa; σ is the vertical stress, MPa; is the internal friction angle of coal, °; K is the stress concentration coefficient; γ is the average unit weight of the overburden strata of the working face, 25 kN / m3; H is the buried depth of the working face coal seam, m.

[0068] The intersection point of the elastic zone and the original rock stress zone can be approximately taken as the original rock stress, and the width of the elastic zone is:

[0069]

[0070] β is the reciprocal of the lateral pressure coefficient.

[0071] The influence range of the advanced abutment pressure is:

[0072] x = x0+ x1

[0073] In the calculation model of the range of the advanced support pressure, the lithology and the sequence distribution of the roof rock stratum 8 along the roadway can be more accurately measured by using the while-drilling detection technology, so that the vertical stress of the roadway can be more accurately solved, and the calculation of the range of the advanced support pressure can be more accurate.

[0074] S5: On the basis of dynamically and accurately distinguishing the lithology and the sequence of the roof rock stratum 8 by using the while-drilling detection technology, different roof-cutting borehole spacings are designed according to the rock stratum distribution. When the roof-cutting holes are drilled along the goaf roadway, the drilling angle is corrected in real time by using the monitoring result of the inclination sensor, so that each roof-cutting hole is ensured to be on a straight line to the greatest extent, and the roof-cutting effect is ensured.

[0075] The roof-cutting method adopts blasting roof-cutting. According to different lithology, the blasting hole spacing can be designed as follows: ① for hard roof, the spacing is 500 mm; ② for soft rock roof, the spacing is 550 mm; and ③ for broken roof, the spacing is 600 mm. The design of the blasting hole angle β is as follows: ① when H c ≤ 1 m, β = 20°; ② when 1 m < H c ≤ 3 m, β = 15°; and ③ when 3 m < H c ≤ 4.5 m, β = 10°. The split cracks are formed at the blasting position by a plurality of blasting holes with the same inclination, the split cracks of each blasting hole are connected to form a planar regular structural weak surface, and the roof rock stratum 8 is cut off and caved along the structural weak surface under the action of the advanced support pressure of the working face.

[0076] The anchor rod drilling machine is generally used for pre-splitting hole construction in the field. However, due to the lack of effective monitoring means, the inclination of each pre-splitting hole often deviates from the designed angle to different degrees during the pre-splitting hole construction, so that each pre-splitting hole is not in the same plane, and the blasting pre-splitting effect is seriously affected. The while-drilling detection technology can be used to monitor the pre-splitting hole construction angle in real time, and the drilling angle is corrected in time when the construction angle deviates from the designed angle by more than 2°, so that each pre-splitting hole can be ensured to be in the same plane.

[0077] Table 1 Application effect evaluation of the accurate roof-cutting method of the goaf roadway based on the rock stratum geology while drilling

[0078]

[0079]

[0080] The preferred embodiments of the present application have been described above, but the present application is not limited to the above. Various modifications and changes can be made by those skilled in the art based on the spirit and principles of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for precise roof cutting along the gob roadway based on rock stratum geological while drilling detection, characterized in that, Specifically comprising the following steps: S1: installing a while-drilling parameter measuring instrument (2) on a single anchor rod drilling machine (1) used for the roof cutting construction of the roadway along the goaf, drilling the roof rock stratum (8) of the roadway along the goaf by the drilling machine, and collecting drilling machine operation parameters in real time by the while-drilling parameter measuring instrument (2); the drilling machine operation parameters include thrust, torque, rotating speed, displacement, inclination angle and vibration; S2: calculating two comprehensive indexes of SEM and RDA by using the collected drilling machine operation parameters, establishing a rock stratum strength identification model based on the comprehensive indexes by a multiple linear regression method, and determining the lithology and rock sequence distribution of the roof rock stratum (8) by using the rock stratum strength identification result and drilling displacement; The modulation specific energy SEM and the rock drillability index RDA are represented by the following formulas: ； In the formula, c represents the conversion point of the logic function, and the physical meaning thereof corresponds to the characteristic turning position of the SEM curve when the lithology changes; The multiple linear regression model Rc for predicting the rock stratum strength by using the SEM and RDA can be represented as follows: Rc=k1×SEM+k2×RDA S3: combining the buried depth, height, mining height, roof lithology and rock sequence distribution information of the coal mining face to establish a calculation model of the advanced abutment pressure distribution range in front of the coal mining face; The calculation model of the advanced abutment pressure distribution range in front of the coal mining face is as follows: ； In the formula, m is the mining height of the coal seam, m; f is the interlayer friction factor of the coal seam; C is the cohesion of the coal body, MPa; σ is the vertical stress, MPa; φ is the internal friction angle of the coal body, °; K is the stress concentration coefficient; γ is the average unit weight of the overburden strata above the coal mining face, 25 kN / m3; H is the buried depth of the coal seam of the coal mining face, m; and β is the reciprocal of the lateral pressure coefficient; S4: bringing the rock stratum lithology, rock sequence and rock stratum thickness into a roof cutting height calculation equation to obtain the roof cutting height at the drilling position; Cutting height H 𝐹 The calculation formula is: ； wherein: H 𝑐 is the thickness of the coal seam, m; K 𝑃 is the average dilatancy coefficient of the rock formation; S5: on the basis of dynamically identifying the lithology and rock sequence of the roof rock stratum (8) by using the while-drilling detection technology, designing different roof cutting drilling spacings according to the rock stratum distribution; when cutting holes are drilled in the roof of the roadway along the goaf, the drilling angle is corrected in real time by using the monitoring result of the inclination angle sensor, and finally the cutting hole is obtained.

2. The method according to claim 1, wherein, In step S1, the device used includes a single anchor rod drilling machine (1), a while-drilling parameter measuring instrument (2), a signal wireless transmitting module (3), a signal wireless receiving module (4), a multi-channel data acquisition module (5), a data storage and display terminal (6) and a B19 hexagonal drill rod (7); the while-drilling parameter measuring instrument (2) is internally provided with thrust, torque, rotating speed, displacement, vibration and inclination angle sensors, the lower end is connected with the single anchor rod drilling machine (1) by using an external hexagonal shaft, and the upper end is connected with the B19 hexagonal drill rod (7).

3. The method according to claim 2, wherein, The drilling machine operation parameters collected by the sensors first enter the signal wireless transmitting module (3), are then received by the signal wireless receiving module (4) and are transmitted to the multi-channel data acquisition module (5), which is connected with the data storage and display terminal (6) for storage and display.

4. The method according to claim 1, wherein, In step S5, the roof cutting method is blasting cutting, and the blasting hole spacing is designed according to different lithologies as follows: ① hard roof, spacing of 500 mm; ② soft rock roof, spacing of 550 mm; and ③ broken roof, spacing of 600 mm.

5. The method according to claim 1, wherein, In step S5, the blast hole angle β is designed as follows: ① when H c ≤1m, β=20°; ② when 1m<H c ≤3m, β=15°; ③ when 3m<H c ≤4.5m, β=10°.

6. The method of claim 1, wherein, In step S5, the plurality of blasting holes with the same dip angle form the splitting cracks at the blasting position, the splitting cracks of each blasting hole are connected to form a plane regular structural weak surface, and the roof rock stratum (8) is cut off and caved along the structural weak surface under the action of the working face advance support pressure.

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