CN111460666B - Rock burst risk prediction method for typical rock burst mine - Google Patents

Abstract

The invention relates to a rock burst risk prediction method for a typical rock burst mine, which comprises the following steps: (1) Collecting target mine data, testing physical and mechanical parameters, establishing a coal-rock power system model, and judging a typical rock burst mine by constructing a geological power environment system of the mine; (2) determining an energy characteristic of the coal-rock power system; (3) calculating the total energy and the basic energy of the coal-rock power system; (4) Calculating the energy released by the coal-rock power system, and deducing and calculating the critical depth of a typical rock burst mine by combining the result obtained in the step three; (5) The rock burst risk of a typical rock burst mine is predicted by critical depth. The step (2) reflects the energy characteristics by using the energy density. The method can quantitatively judge the critical depth of rock burst, so that the rock burst risk of a typical rock burst mine can be accurately predicted, and compared with actual monitoring, the accuracy is verified, and the method can provide a basis for effective prevention and control of the rock burst of a coal mine.

Description

A method for predicting rock burst hazard in a typical rock burst mine

Technical Field

The invention belongs to the technical field of coal mining, and in particular relates to a method for predicting rock burst hazard of a typical rock burst mine.

Background Art

Rock burst is a serious and destructive mine dynamic disaster, which poses a great threat to coal mine production safety and personnel life safety. A mine with rock burst coal seams is a rock burst mine. If the mine begins to experience rock burst after reaching a certain mining depth, this depth is called the critical depth of the rock burst mine. If the mining depth reaches this depth, there will be a risk of rock burst if mining continues. The critical depth value varies with different geological conditions. The overall trend is that the risk of rock burst increases with the increase of mining depth. For different rock burst mines, quantitative judgment of the critical depth of rock burst is particularly important for predicting the risk of rock burst, which can be effectively prevented and controlled. However, there is no consensus on the concept of deep mines and the critical depth issue, which brings inconvenience to the discussion of geological disasters encountered in deep mining. At present, most of the research results are based on depth intervals, and there is little quantitative research on the critical depth of typical rock burst mines. Therefore, there is a lack of quantitative judgment for the prediction of rock burst risk in typical rock burst mines.

Summary of the invention

In view of the deficiencies in the prior art, the present invention provides a method for predicting the rock burst hazard of a typical rock burst mine, thereby quantitatively determining the critical depth of rock burst occurrence and accurately predicting the rock burst hazard of a typical rock burst mine.

The technical solution of the present invention:

A method for predicting rock burst hazard of a typical rock burst mine comprises the following steps:

Step 1: Collect target mine data, test physical and mechanical parameters, and establish a coal-rock dynamic system model to determine typical rock burst mines by building a geological dynamic environment system for the mine;

Step 2: Determine the energy characteristics of the coal-rock power system;

Step 3: Calculate the total energy and basic energy of the coal-rock power system;

Step 4: Calculate the energy released by the coal-rock power system, and derive the critical depth of a typical rock burst mine based on the results obtained in step 3;

Step 5: Predict the rock burst hazard of typical rock burst mines by critical depth.

The method for constructing a mine geological dynamic environment system to determine a typical rock burst mine in step 1 specifically comprises the following steps:

(1) Construct a geodynamic environment evaluation system consisting of eight factors: the geomorphological conditions of the target mine's structural depression, the vertical movement conditions of the fault block structure, the horizontal movement conditions of the fault block structure, the influence range of the fault structure, the tectonic stress, the coal seam mining depth, the overlying hard rock conditions, and the rock burst judgment criteria of the area and the adjacent areas;

(2) The evaluation index values _ai in the geological dynamic environment evaluation index system are divided into four levels, and each evaluation index is judged one by one according to the degree of influence of each evaluation index on the mine geological dynamic environment. The evaluation index _ai with no influence on the mine geological dynamic environment is 0, the evaluation index _ai with weak influence is 1, the evaluation index _ai with medium influence is 2, and the evaluation index _ai with strong influence is 3; specifically:

① Geomorphic characteristics of the well field structural depression:

Where, C—contrast intensity of structural depression;

△h—the difference between the highest and lowest elevations of the structural depression, km;

△l—width of structural depression, km;

A, B—weight coefficients; mountainous landform: A=0.25, B=0.75, hilly landform: A=0.5, B=0.5, plain landform: A=0.75, B=0.25;

When C≥0.75, the evaluation index _a1 is 3; when 0.5≤C0.75, the evaluation index _a1 is 2; when 0.25≤C＜0.5, the evaluation index a1 is ₁ ; when C＜0.25, the evaluation index _a1 is 0;

②Conditions for vertical movement of fault-block structures:

The vertical movement speed of the fault block in the target mine is V ₁ . When the vertical movement speed V ₁ ≥8mm/yr, the evaluation index a ₂ is 3; when the vertical movement speed V ₁ ＞5mm/yr, the evaluation index a ₂ is 2; when the vertical movement speed V ₁ ＜-3mm/yr, the evaluation index a ₂ is 1; when the vertical movement speed -3mm/yr≤V ₁ ≤5mm/yr, the evaluation index a ₂ is 0;

③Conditions for horizontal movement of fault block structures:

The vertical movement speed of the fault block in the target mine is V ₂ . When the horizontal movement speed V ₂ >10 mm/yr, the evaluation index a ₃ is 3; when the vertical movement speed is 5 mm/yr≤V ₂ ≤10 mm/yr, the evaluation index a ₃ is 2; when the vertical movement speed is 2 mm/yr≤V ₂ ＜5 mm/yr, the evaluation index a ₃ is 1; when the vertical movement speed V ₂ ＜2 mm/yr, the evaluation index a ₃ is 0;

④Conditions of the influence range of fault structure

b＝±(K·10h)

Where: b is the width of the influence range of the fault structure, km. When the boundary of the influence range of the fault is outside the boundary of the well field, b takes a positive value; when the boundary of the influence range of the fault crosses into the boundary of the well field, b takes a negative value.

K—activity coefficient (K=1, 2, 3), when the fault activity is strong, K=3, when the fault activity is medium, K=2, when the fault activity is weak, K=1;

h—vertical height of the fracture, m;

When b≤0.5, the evaluation index _a4 is 3, when 0.5＜b≤2, the evaluation index _a4 is 2, when 2＜b≤5, the evaluation index _a4 is 1, and when b＞5, the evaluation index _a4 is 0;

⑤ Tectonic stress conditions

The evaluation index of tectonic stress on rock burst danger is expressed by stress concentration coefficient K. When K>2, the evaluation index _a5 is 3; when 1.2＜K≤2, the evaluation index _a5 is 2; when 0.8＜K≤1.2, the evaluation index _a5 is 1; when K≤0.8, the evaluation index _a5 is 0;

⑥ Mining depth conditions

When the mining depth h＞800m, the evaluation index a6 _is 3, when 600m＜h≤800m, the evaluation index _a6 is 2, when 400m＜h≤600m, the evaluation index _a6 is 1, and when the mining depth h≤400m, the evaluation index _a6 is 0;

⑦ Overlying hard rock conditions

The distance between the overlying hard and thick rock layer and the coal seam is d. When the distance between the overlying hard and thick rock layer and the coal seam is d≤20m, the evaluation index _a7 is 3; when the distance between the overlying hard and thick rock layer and the coal seam is 20m＜d≤50m, the evaluation index _a7 is 2; when the distance between the overlying hard and thick rock layer and the coal seam is 50m＜d≤100m, the evaluation index _a7 is 1; when the distance between the overlying hard and thick rock layer and the coal seam is d＞100m, the evaluation index _a7 is 0;

⑧ Evaluation of the criteria for this area and neighboring areas

The number of rock bursts in the same coal seam in this area and the adjacent areas is n. When n≥3, the evaluation index _a8 is 3; when 2≤n＜3, the evaluation index _a8 is 2; when n＝1, the evaluation index _a8 is 1; when n＝0, the evaluation index _a8 is 0;

(3) Add the values of each evaluation index a _i obtained in step (2) to obtain a comprehensive evaluation index

(4) Normalize the comprehensive evaluation index in step (3) to obtain the comprehensive evaluation index value of the target mine geological dynamic environment

(5) The target mine is classified into types according to the comprehensive evaluation index value N of the geological dynamic environment of the target mine in step (4), specifically: when 0.5＜N≤1, the target mine is defined as a typical rock burst mine, wherein when 0.5＜N≤0.75, the target mine is a geological dynamic environment with moderate rock burst, and when 0.75＜N≤1, the target mine is a geological dynamic environment with strong rock burst; when 0.25＜N≤0.5, the target mine is defined as an atypical rock burst mine, and the target mine is a geological dynamic environment with weak rock burst; when 0≤N≤0.25, the target mine is defined as a non-rock burst mine, and the target mine is a geological dynamic environment with no rock burst.

The data and parameters in step one include stress concentration factor, released energy of the coal-rock dynamic system monitored by the microseismic monitoring system, Poisson's ratio, elastic modulus, bulk density of the coal-rock mass, burial depth of the coal-rock mass, tensile strength, and compressive strength.

In step 2, the energy density of the coal-rock power system is used to reflect the energy characteristics, specifically:

(1) Energy characteristics of coal-rock dynamic system under self-weight stress field

Where: E _Z is the energy density of the coal-rock dynamic system under the self-weight stress field, J/m ³ , μ is Poisson's ratio; E is the elastic modulus, Pa; γ is the bulk density of the coal-rock mass, N/m ³ ; H is the burial depth of the coal-rock mass, m;

(2) Energy characteristics of coal-rock dynamic system under tectonic stress field

Where: _EG is the energy density of the coal-rock dynamic system under tectonic stress field, J/ ^m3 ; μ is Poisson's ratio; E is the elastic modulus, Pa; γ is the bulk density of the coal-rock mass, N/ ^m3 ; H is the burial depth of the coal-rock mass, m; _k1 , _k2 , _k3 are stress concentration coefficients.

The energy of the coal-rock power system in step 3 is:

(1) Energy of coal-rock dynamic system under self-weight stress field conditions

(2) Energy of coal-rock dynamic system under tectonic stress field conditions

The energy released by the coal-rock power system in step 4 is:

Where: v ₀ is the average initial velocity of the crushed coal-rock mass, m/s; ρ is the average density of the coal-rock mass thrown out after crushing, kg/m ³ ; σ _c is the uniaxial compressive strength of the coal mass, MPa;

Combined with the calculation results of step 3, the critical depth of a typical rock burst mine is deduced as:

The risk of rock burst is predicted based on the critical depth. When the mining depth reaches the critical depth, continued mining will lead to the risk of rock burst.

The beneficial effects of the present invention are as follows: due to different inducing causes, impact manifestation forms and degrees of impact in impact mines are different, and the degree of danger is also different. If it is defined as "impact mine" in general and indiscriminately, it will bring more difficulties to prevention, control and management work. Rock burst mines are divided into two types: "typical rock burst mines" and "atypical rock burst mines", the critical depth of typical rock burst mines is quantitatively calculated, the danger of rock burst is accurately predicted, and effective prevention and control of rock burst in coal mines is achieved. The present invention collects target mine data, tests physical and mechanical parameters, establishes a coal-rock power system model, and determines a typical rock burst mine by constructing a geological dynamic environment system of the mine. The energy characteristics of the coal-rock power system under the self-weight stress field and the tectonic stress field are analyzed for typical rock burst mines, and the corresponding calculation methods are determined respectively to calculate the energy of the coal-rock power system. On this basis, the critical depth of the typical rock burst mine is derived and calculated, the relationship between the energy evolution of the coal-rock power system and the manifestation of rock burst power is determined, and the accuracy is verified. The method can quantitatively calculate the critical depth of the typical rock burst mine, thereby accurately predicting the danger of rock burst, that is, when the mining depth reaches the critical depth, rock burst begins to occur, and mining should be stopped or effective prevention and control measures should be taken. The present invention can provide a basis for the effective prevention and control of rock burst in coal mines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of a method for predicting rock burst hazard in a typical rock burst mine;

FIG2 is a schematic diagram of a model showing the relationship between the coal-rock power system and rock burst pressure in the present invention;

FIG3 is a schematic diagram of a three-dimensional model of a coal-rock power system in the present invention;

FIG4 is a schematic diagram of energy sources of the coal-rock power system of the present invention;

FIG5 is a line graph showing the calculation results of the critical depth of rock burst at the fully mechanized caving face of a certain mine A01 provided in an embodiment of the present invention;

Among them, 1 is the power core area, 2 is the destruction area, 3 is the damage area, and 4 is the impact area.

DETAILED DESCRIPTION

In order to better explain the present invention and facilitate understanding, the technical solutions and effects of the present invention are described in detail below through specific implementation modes in conjunction with the accompanying drawings.

As shown in FIG1 , a method for predicting rock burst hazard of a typical rock burst mine specifically includes the following steps:

Step 1: Collect target mine data, test physical and mechanical parameters, and establish a coal-rock dynamic system model. Determine typical rock burst mines by constructing the geological dynamic environment system of the mine; the coal and rock mass that provide energy for rock burst and are affected constitute the "coal-rock dynamic system". Under different geological dynamic environments and mining conditions, the coal and rock mass accumulate and release energy in different forms, and rock burst characteristics are different. Under natural geological conditions, the coal-rock dynamic system is in a state of equilibrium; under the disturbance of mining activities, the stress of the coal and rock mass increases and energy accumulates. When it exceeds the strength limit of the coal and rock mass, it causes the system structure to become unstable, energy is released, and rock burst may occur. In order to describe the relationship between the coal-rock dynamic system and rock burst, a "coal-rock dynamic system and rock burst relationship model" is constructed, as shown in Figure 2. According to the characteristics of energy accumulation degree and influence range, the coal-rock dynamic system can be divided into "dynamic core area", "destruction area", "damage area" and "influence area", namely the four areas of dynamic core area 1, destruction area 2, damage area 3 and influence area 4 shown in Figure 2. The energy of the coal-rock dynamic system is concentrated in the "dynamic core area". The "dynamic core area" of the coal-rock dynamic system is the power source for rock burst. The three-dimensional model of the coal-rock dynamic system is shown in Figure 3, which is the dynamic core area 1, destruction area 2, damage area 3 and influence area 4 from the center to the outside. When rock burst occurs, the energy released by the coal-rock dynamic system is provided by the "dynamic core area", and the total energy of the coal-rock dynamic system is composed of basic energy and released energy. The radius of the "dynamic core area" is shown in the following formula:

Where R is the radius of the "dynamic core area" of the coal-rock dynamic system, m; _k1 , _k2 , and _k3 are stress concentration coefficients. _k1 is the ratio of the maximum principal stress to the vertical stress; _k2 is the ratio of the intermediate stress to the vertical stress; _k3 is the ratio of the minimum principal stress to the vertical stress; △U is the released energy of the coal-rock dynamic system monitored by the microseismic monitoring system, J. μ is Poisson's ratio; E is the elastic modulus, Pa; γ is the bulk density of the coal-rock mass, N/ ^m3 ; H is the burial depth of the coal-rock mass, m.

According to the geological dynamic environment assessment method, rock burst mines can be divided into two categories: typical rock burst mines and atypical rock burst mines. The occurrence of rock burst is the result of the combined effect of the geological dynamic environment and mining disturbance, and is also a dynamic process of energy accumulation and release of the coal-rock dynamic system. When the energy accumulated in the coal-rock dynamic system can support the occurrence of rock burst, the mine that will experience rock burst under the induction of mining activities is a typical rock burst mine; when the energy accumulated in the coal-rock dynamic system cannot support the occurrence of rock burst, other engineering conditions are needed to supplement the energy, and the mine that may experience rock burst only under the induction of mining activities is an atypical rock burst mine.

The method for determining a typical rock burst mine by constructing a geological dynamic environment evaluation system specifically includes the following steps:

(1) Construct a geodynamic environment evaluation system consisting of eight factors: the geomorphological conditions of the target mine's structural depression, the vertical movement conditions of the fault block structure, the horizontal movement conditions of the fault block structure, the influence range of the fault structure, the tectonic stress, the coal seam mining depth, the overlying hard rock conditions, and the rock burst judgment criteria of the area and the adjacent areas;

(2) The evaluation index values _ai in the geological dynamic environment evaluation index system are divided into four levels, and each evaluation index is judged one by one according to the degree of influence of each evaluation index on the mine geological dynamic environment. The evaluation index _ai with no influence on the mine geological dynamic environment is 0, the evaluation index _ai with weak influence is 1, the evaluation index _ai with medium influence is 2, and the evaluation index _ai with strong influence is 3; specifically:

① Geomorphic characteristics of the well field structural depression:

Where, C—contrast intensity of structural depression;

△h—the difference between the highest and lowest elevations of the structural depression, km;

△l—width of structural depression, km;

A, B—weight coefficients; mountainous landform: A=0.25, B=0.75, hilly landform: A=0.5, B=0.5, plain landform: A=0.75, B=0.25;

When C≥0.75, the evaluation index _a1 is 3; when 0.5≤C0.75, the evaluation index _a1 is 2; when 0.25≤C＜0.5, the evaluation index a1 is ₁ ; when C＜0.25, the evaluation index _a1 is 0;

②Conditions for vertical movement of fault-block structures:

The vertical movement speed of the fault block in the target mine is V ₁ . When the vertical movement speed V ₁ ≥8mm/yr, the evaluation index a ₂ is 3; when the vertical movement speed V ₁ ＞5mm/yr, the evaluation index a ₂ is 2; when the vertical movement speed V ₁ ＜-3mm/yr, the evaluation index a ₂ is 1; when the vertical movement speed -3mm/yr≤V ₁ ≤5mm/yr, the evaluation index a ₂ is 0;

③Conditions for horizontal movement of fault block structures:

The vertical movement speed of the fault block in the target mine is V ₂ . When the horizontal movement speed V ₂ >10 mm/yr, the evaluation index a ₃ is 3; when the vertical movement speed is 5 mm/yr≤V ₂ ≤10 mm/yr, the evaluation index a ₃ is 2; when the vertical movement speed is 2 mm/yr≤V ₂ ＜5 mm/yr, the evaluation index a ₃ is 1; when the vertical movement speed V ₂ ＜2 mm/yr, the evaluation index a ₃ is 0;

④Conditions of the influence range of fault structure

b＝±(K·10h)

Where: b is the width of the influence range of the fault structure, km. When the boundary of the influence range of the fault is outside the boundary of the well field, b takes a positive value; when the boundary of the influence range of the fault crosses into the boundary of the well field, b takes a negative value.

K—activity coefficient (K=1, 2, 3), when the fault activity is strong, K=3, when the fault activity is medium, K=2, when the fault activity is weak, K=1;

h—vertical height of the fracture, m;

When b≤0.5, the evaluation index _a4 is 3, when 0.5＜b≤2, the evaluation index _a4 is 2, when 2＜b≤5, the evaluation index _a4 is 1, and when b＞5, the evaluation index _a4 is 0;

⑤ Tectonic stress conditions

The evaluation index of tectonic stress on rock burst danger is expressed by stress concentration coefficient K. When K>2, the evaluation index _a5 is 3; when 1.2＜K≤2, the evaluation index _a5 is 2; when 0.8＜K≤1.2, the evaluation index _a5 is 1; when K≤0.8, the evaluation index _a5 is 0;

⑥ Mining depth conditions

When the mining depth h＞800m, the evaluation index a6 _is 3, when 600m＜h≤800m, the evaluation index _a6 is 2, when 400m＜h≤600m, the evaluation index _a6 is 1, and when the mining depth h≤400m, the evaluation index _a6 is 0;

⑦ Overlying hard rock conditions

The distance between the overlying hard and thick rock layer and the coal seam is d. When the distance between the overlying hard and thick rock layer and the coal seam is d≤20m, the evaluation index _a7 is 3; when the distance between the overlying hard and thick rock layer and the coal seam is 20m＜d≤50m, the evaluation index _a7 is 2; when the distance between the overlying hard and thick rock layer and the coal seam is 50m＜d≤100m, the evaluation index _a7 is 1; when the distance between the overlying hard and thick rock layer and the coal seam is d＞100m, the evaluation index _a7 is 0;

⑧ Evaluation of the criteria for this area and neighboring areas

The number of rock bursts in the same coal seam in this area and the adjacent areas is n. When n≥3, the evaluation index _a8 is 3; when 2≤n＜3, the evaluation index _a8 is 2; when n＝1, the evaluation index _a8 is 1; when n＝0, the evaluation index _a8 is 0;

(3) Add the values of each evaluation index a _i obtained in step (2) to obtain a comprehensive evaluation index

(4) Normalize the comprehensive evaluation index in step (3) to obtain the comprehensive evaluation index value of the target mine geological dynamic environment

(5) The target mine is classified into types according to the comprehensive evaluation index value N of the geological dynamic environment of the target mine in step (4), specifically: when 0.5＜N≤1, the target mine is defined as a typical rock burst mine, wherein when 0.5＜N≤0.75, the target mine is a geological dynamic environment with moderate rock burst, and when 0.75＜N≤1, the target mine is a geological dynamic environment with strong rock burst; when 0.25＜N≤0.5, the target mine is defined as an atypical rock burst mine, and the target mine is a geological dynamic environment with weak rock burst; when 0≤N≤0.25, the target mine is defined as a non-rock burst mine, and the target mine is a geological dynamic environment with no rock burst.

Step 2: Determine the energy characteristics of the coal-rock dynamic system for typical rock burst mines; in the coal-rock dynamic system, the energy factor plays a controlling role in the occurrence of rock burst and affects the stability of the entire coal-rock dynamic system. The energy of the coal-rock dynamic system mainly comes from two aspects: one is the natural geological dynamic conditions, mainly tectonic stress (including self-weight stress); the other is the mining engineering effect, that is, mining stress. The coal-rock dynamic system is in the geotectonic environment and modern stress field, and has the dynamic conditions for energy accumulation. Through mining and other engineering activities, the system's stress is superimposed and energy accumulates. When the accumulated energy exceeds the strength limit of the coal-rock mass, the system structure becomes unstable. When the energy release is greater than 10 ⁴ J to 10 ⁶ J, rock burst and other mine dynamic disasters occur, as shown in Figure 4. It can be said that without tectonic movement, there is no geological dynamic environment for rock burst to occur, there is no formation of the coal-rock dynamic system, and there is no energy condition for the occurrence of rock burst.

The total energy of the coal-rock dynamic system is composed of the energy under the self-weight stress field, the energy under the tectonic stress field and the energy under the mining stress field, as shown in the following formula:

U＝U _Z + _UG + _UC (2)

Where: U is the total energy of the coal-rock dynamic system, J; U _Z is the energy of the coal-rock dynamic system under the deadweight stress field, J; _UG is the energy of the coal-rock dynamic system under the tectonic stress field, J; _UC is the energy of the coal-rock dynamic system under the mining stress field, J.

The total energy of the coal-rock dynamic system includes basic energy and released energy. In order to facilitate comparative analysis and calculation, the energy density of the coal-rock dynamic system is used to reflect the energy characteristics. The energy density of a typical rock burst mine mainly comes from the tectonic stress field. Under the conditions of the tectonic stress field, the energy accumulated in the coal-rock dynamic system can already support the occurrence of rock burst. At this time, the contribution of mining engineering activities to the occurrence of rock burst only considers its inducing effect. Therefore, the critical depth of a typical rock burst mine is studied under the conditions of the tectonic stress field. Since the stress value obtained by the geostress measurement includes the stress under the self-weight stress field, the energy calculated under the tectonic stress field also includes the energy of the self-weight stress field. The energy of the coal-rock dynamic system under the self-weight stress field is the basic energy, and the energy of the coal-rock dynamic system under the tectonic stress field is defined as the total energy.

The energy of the coal-rock power system is calculated by integrating the energy density with the volume of the "power core area". From formula (1), it can be seen that the energy released by the coal-rock power system is different, the radius of the "power core area" is different, and then the volume is different. The unified calculation formula for the energy density of the coal-rock power system is shown in formula (3):

Where, Eε is the energy density of the coal-rock dynamic system, J/m ³ ; σ ₁ and σ ₃ are lateral stresses, MPa; σ ₂ is the self-weight stress, MPa.

(1) Energy characteristics of coal-rock dynamic system under self-weight stress field

Under the self-weight stress field, the stress value is related to the burial depth and bulk density. Taking the unit volume of coal rock as the research object, the energy density under the self-weight stress field is expressed as shown in formula (4). It can be seen from formula (4) that under the self-weight stress field, according to the Kinnick hypothesis, the energy of the coal rock dynamic system only considers the influence of the self-weight stress, and the lateral stress is numerically equal to the product of the self-weight stress and the lateral pressure coefficient. The energy accumulated in the coal rock dynamic system increases with the increase of mining depth. In this study, the energy of the coal rock dynamic system under the self-weight stress field is defined as the basic energy of the coal rock dynamic system.

Where E _Z is the energy density of the coal-rock dynamic system under the self-weight stress field, J/m ³ .

(2) Energy characteristics of coal-rock dynamic system under tectonic stress field

Under the condition of tectonic stress field, the energy of coal-rock dynamic system comes from tectonic stress field. The energy accumulated in coal-rock mass is related to triaxial stress σ ₁ , σ ₂ , σ _3. Taking unit volume of coal-rock mass as the research object, its energy density can be derived from formula (3) and further from formula (5) to (7), as shown in formula (8). It can be seen from formula (8) that under the condition of tectonic stress field, the energy accumulated in coal-rock dynamic system increases with the increase of tectonic stress.

σ ₁ ＝k ₁ γH (5)

σ ₂ = k ₂ γH (6)

σ ₃ = k ₃ γH (7)

Where _EG is the energy density of the coal-rock dynamic system under tectonic stress field, J/m ³ .

Step 3: Calculate the total energy and basic energy of the coal-rock power system

The coal-rock dynamic system is divided into four areas: "dynamic core area", "destruction area", "damage area" and "influence area". Only when the mining project enters the "dynamic core area", "destruction area" and "damage area", will there be the danger of rock burst with different degrees and forms of damage. When the mining project enters the "influence area", the dynamic manifestation is mainly in the form of "coal cannon"; when the mining project enters the "damage area", the dynamic manifestation is mainly in the form of "pressing out, pouring out" and so on; when the mining project enters the "destruction area", the dynamic manifestation is "rock burst"; when the mining project enters the "dynamic core area", it will produce "strong rock burst". Therefore, for a typical rock burst mine, the energy of its coal-rock dynamic system is obtained by integrating the energy density under each stress field over the volume of the "dynamic core area".

(1) Energy of coal-rock dynamic system under self-weight stress field conditions

The energy of the coal-rock power system under the condition of self-weight stress field is the volume integral of the energy density shown in formula (4), and the calculation method is shown in the following formula (10):

The calculation results are shown in formula (11), which is the basic energy of the coal-rock dynamic system under the tectonic stress field:

(2) Energy of coal-rock dynamic system under tectonic stress field conditions

The energy of the coal-rock dynamic system under tectonic stress field conditions is the volume integral of the energy density shown in formula (9), and the calculation method is shown in formula (12):

The calculation results are shown in formula (13), which is the total energy of the coal-rock dynamic system under the tectonic stress field:

Due to the interaction between structural fault blocks and the difference in rock mechanical properties, high stress areas, stress gradient areas and low stress areas will naturally form within the well field. In the high stress area, the elastic energy accumulated by the rock mass under higher stress is significantly increased compared with the normal stress area. Some rock masses have reached the critical transition from steady state to unsteady state, which is most likely to cause tunnel damage; in the stress gradient area, the stress and deformation modulus have increased significantly, the brittleness of the rock increases, the destructive strength decreases, and it is easy to form geological structures, which are easy to cause tunnel damage under the action of tectonic stress; the rock located in the low stress area has a small degree of change in characteristics, is not easy to produce energy accumulation, and has the lowest risk of tunnel damage. In general, when the stress concentration coefficient K>1.2, the corresponding range of the principal stress contour line is the high stress area; when K<0.8, the corresponding range of the principal stress contour line is the low stress area; the stress gradient area is usually located between the normal stress area and the high stress area. The system energy located in different stress areas can be calculated using the corresponding stress value and stress concentration coefficient.

Step 4: Calculate the energy released by the coal-rock dynamic system. Combined with the results obtained in step 3, deduce and calculate the critical depth of a typical rock burst mine, and determine the relationship between the energy evolution of the coal-rock dynamic system and the manifestation of rock burst dynamics: the energy released by the coal-rock dynamic system is equal to the difference between the total energy and the basic energy, and the intensity of rock burst manifestation is positively correlated with the energy released by the coal-rock dynamic system. Studies have shown that the initial velocity of the broken coal-rock mass thrown into free space is an important indicator of whether rock burst occurs. When the initial velocity is less than 1m/s, rock burst is unlikely to occur; when the initial velocity is greater than 10m/s, the possibility of rock burst is higher. When rock burst occurs, the required energy must satisfy both the energy consumed by the unit coal-rock mass to be broken and the minimum kinetic energy required for the coal-rock mass to accumulate for rock burst. When the elastic energy accumulated by the unit coal-rock mass exceeds the sum of the two, rock burst may occur. Therefore, when rock burst occurs, the energy density calculation result of the energy released by the coal-rock dynamic system can be expressed by formula (15), and the calculation result of the energy released by the coal-rock dynamic system can be expressed by formula (16):

Where, _Emin is the energy density of the energy released by the coal-rock dynamic system when rock burst occurs, J/ ^m3 ; _v0 is the average initial velocity of the crushed coal-rock mass, m/s; ρ is the average density of the coal-rock mass thrown out after crushing, kg/ ^m3 ; _σc is the uniaxial compressive strength of the coal mass, MPa. When rock burst occurs, the energy released by the coal-rock dynamic system can be expressed by the following formula:

Where _US is the energy released by the coal-rock dynamic system when rock burst occurs, J.

When rock burst occurs in a typical rock burst mine, the released energy is the difference between the tectonic stress field energy and the basic energy, that is:

U _G -U _Z =U _S =△U (17)

Substituting into equations (11), (13), and (16), the H value is defined as H _min , which is the critical depth of a typical rock burst mine:

Step 5: Predict the rock burst hazard of typical rock burst mines through critical depth: Predict the rock burst hazard based on the critical depth. When the mining depth reaches the critical depth, there will be a risk of rock burst if mining continues. Mining should be stopped immediately or effective prevention and control measures should be taken.

The rock burst hazard prediction method of a typical rock burst mine is applied in a typical rock burst mine to verify the accuracy of the method:

Firstly, the geodynamic environment of rock burst in the mine field is analyzed and evaluated from eight factors, including the geomorphological characteristics of the structural depression of a mine, the vertical movement conditions of the fault block structure, the horizontal movement conditions of the fault block structure, the influence range of the fault structure, the structural stress conditions, the mining depth conditions, the overlying hard rock conditions, and the evaluation of the criteria of the area and the neighboring areas. A geodynamic environment evaluation system is constructed to judge the typical rock burst mine:

(1) Geomorphic characteristics of the structural depression in the well field

After calculation, the contrast intensity of the structural depression in the well field is 0.62, and the evaluation index is 2, which is a medium-risk level.

(2) Conditions for vertical movement of block structures

According to the relative relationship between the mine's geographical location and the internal uplift movement of the North China Plate, the mine is located in the Ji-Liao uplift area, with an uplift speed of 3 mm/a. It is located in the uplift fault block belt of the Ji-Liao uplift area and the Xia Liaohe downlift area, that is, the area of intense relative movement of the fault blocks. The relative movement of the two fault blocks is 2.5 mm/a, indicating that the vertical movement rate of the mine is 5.5 mm/a. According to the geological dynamic environment evaluation index, the mine has an evaluation index of 2, which is a medium-risk level.

(3) Conditions for horizontal movement of block structures

The blocks in the area where the mine is located mainly move in vertical up and down motion, and the horizontal movement rate is 0. According to the geological dynamic environment evaluation indicators, the mine is in a stable area of horizontal block movement, the evaluation index is 0, and there is no danger.

(4) Conditions of the influence range of fault structure

According to the observation data of Hunhe Fault, the average rate of the upper wall of the fault from 1962 to 1982 was 1.0mm/a, and the historical earthquake magnitude was 4. Taking comprehensive consideration, the Hunhe Fault was judged to be a weakly active fault, and K = 1 was taken. The maximum drop of the F1 fault in the mine is about 1200m, so its affected width is:

b＝K·10h＝1×10×1200＝12000m

The F1 fault is located within the mining area. Therefore, based on the influence range of the fault structure, the mine evaluation index is 3, which is a highly dangerous level.

(5) Tectonic stress conditions

Combined with the measured data of ground stress in this mine, the mining depth of the mine is above 400m, the maximum principal stress _σ1 = 34.95MPa, the vertical principal stress _σv = 21.80MPa, and the ratio of the maximum horizontal stress to the vertical stress is 1.60, which is between 1.2 and 2. Therefore, according to the structural stress conditions, the evaluation index of the mine is 2, which is of medium risk.

(6) Mining depth conditions

The current mining depth of the mine is greater than 830m. Therefore, based on the mining depth conditions, the mine evaluation index is 3, which is a highly dangerous level.

(7) Overlying hard rock conditions

The roof rock layers of the mine are all soft shale layers, which is equivalent to the hard rock layers being more than 100m away from the coal seams. Therefore, based on the conditions of the overlying hard rock layers, the mine evaluation index is 0, which means there is no danger.

(8) Evaluation of the criteria for this area and neighboring areas

Both of the two adjacent mines of this mine have experienced rock bursts, and the number of such incidents in history is more than five times. Therefore, according to the evaluation results of this area and neighboring areas, the evaluation index of this mine is 3, which is a highly dangerous level.

In summary, judging by comprehensive indicators, the comprehensive evaluation index of this rock burst mine is 0.625, which is greater than 0.5 and falls within the range of typical rock burst mines.

The test results of the physical and mechanical parameters of coal and rock in the above-mentioned typical rock burst mines are shown in Table 1. The source depths of 20 rock bursts from January 2011 to November 2013 were selected, and the total energy, basic energy and released energy of the coal and rock dynamic system were calculated for each rock burst, as shown in Table 2.

Table 1 Summary of test results of physical and mechanical properties of coal and rock mass in a coal mine

Table 2 Calculation results of energy released by the coal-rock dynamic system of some rock bursts in a coal mine

The A01 fully mechanized caving working face of the mine is located at the -830m level, with a ground elevation of +89.1m to +95.4m, an underground elevation of -748.2m to -833.5m, a working face strike length of 603m, an inclined length of 163.5m, and a coal thickness of 11.8m. From June 23, 2014 to January 29, 2015, the working face experienced 58 rock bursts and mine shocks (energy above 16 ⁶ J), with a focal depth of -584m to -874m and an average elevation of -804.93m. According to the ground stress measurement results, the _k1 value of the working face is 1.97, the _k2 value is 1.00, and the _k3 value is 0.79. According to the calculation method shown in formula (18), the critical depth of rock burst in the working face is -754.54 m above sea level. Among the 58 sets of data shown in Figure 5, 54 sets of data are below the calculated critical depth, which shows that the method provided by the present invention can accurately predict the rock burst hazard of typical rock burst mines.

Claims (3)

1. A rock burst risk prediction method for a typical rock burst mine is characterized by comprising the following steps of: the method comprises the following steps:

step one: collecting target mine data, testing physical and mechanical parameters, establishing a coal-rock power system model, and judging a typical rock burst mine by constructing a geological power environment system of the mine;

step two: determining energy characteristics of a coal-rock power system;

step three: calculating the total energy and the basic energy of the coal-rock power system;

step four: calculating the energy released by the coal-rock power system, and deducing and calculating the critical depth of a typical rock burst mine by combining the result obtained in the step three;

step five: predicting rock burst dangers of a typical rock burst mine through critical depth;

the data and parameters in the first step comprise stress concentration coefficients, release energy of a coal-rock power system monitored by a microseismic monitoring system, poisson ratio, elastic modulus, volume weight of a coal-rock mass, burial depth of the coal-rock mass, tensile strength and compressive strength;

in the second step, the energy density of the coal-rock power system is used for reflecting the energy characteristics, and the method specifically comprises the following steps:

(1) Energy characteristics of coal-rock power system under dead weight stress field

Wherein: e (E) _Z Is the energy density, J/m of a coal-rock power system under a dead weight stress field ³ μ is poisson's ratio; e is elastic modulus, pa; gamma is the volume weight of the coal rock mass, N/m ³ The method comprises the steps of carrying out a first treatment on the surface of the H is the burial depth of the coal rock mass, m;

(2) Energy characteristics of coal-rock power system under construction stress field

Wherein: e (E) _G To construct the energy density, J/m, of a coal-rock power system under a stress field ³ The method comprises the steps of carrying out a first treatment on the surface of the μ is poisson's ratio; e is elastic modulus, pa; gamma is the volume weight of the coal rock mass, N/m ³ The method comprises the steps of carrying out a first treatment on the surface of the H is the burial depth of the coal rock mass, m; k (k) ₁ 、k ₂ 、k ₃ Is the stress concentration coefficient;

the energy of the coal-rock power system in the third step is respectively as follows:

(1) Energy of coal-rock power system under dead weight stress field condition

(2) Construction of energy of coal-rock power system under stress field condition

In the fourth step, the energy released by the coal rock power system is as follows:

wherein: v ₀ The average initial speed of throwing out for breaking the coal rock mass is m/s; ρ is the average density of the coal rock mass thrown out after crushing, kg/m ³ ；σ _c The uniaxial compressive strength of the coal body is MPa;

when rock burst begins to occur in a typical rock burst mine, the released energy is the difference between the energy of a structural stress field and the energy of a foundation, namely:

U _G -U _Z ＝U _S ＝ΔU

and (3) deriving the critical depth of the typical rock burst mine by combining the calculation result of the step (III) as follows:

2. a method of rock burst risk prediction for a typical rock burst mine as claimed in claim 1, wherein: the method for judging the typical rock burst mine by constructing the geological power environment system of the mine in the first step specifically comprises the following steps:

(1) Constructing a geological power environment evaluation system consisting of eight factors, namely a structural concave landform condition, a vertical movement condition of a broken block structure, a horizontal movement condition of the broken block structure, an influence range of the broken block structure, structural stress, coal seam mining depth, an overlying hard rock stratum condition, a local zone and an adjacent zone rock burst criterion condition of a target mine;

(2) Each evaluation index value a in the geological dynamic environment evaluation index system _i Dividing into four grades, judging the influence degree of each evaluation index on the geological power environment of the mine one by one, and evaluating the index a without influence on the geological power environment of the mine _i An evaluation index of 0, a when the influence degree is weak _i An evaluation index of 1, a at the time of moderate influence _i An evaluation index of 2, a when having a strong influence _i An evaluation index of 3; the method comprises the following steps:

(1) well Tian Gouzao concave geomorphic features:

wherein C is the contrast intensity of the structure depression;

Δh—constructing the difference between the highest and lowest elevations of the pit, km;

Δl—the width of the structural pit, km;

A. b is a weight coefficient; mountain land topography: a=0.25, b=0.75, hilly land: a=0.5, b=0.5, plain land appearance: a=0.75, b=0.25;

when C is not less than 0.75, the evaluation index a ₁ 3; when 0.5.ltoreq.C0.75, the index a is evaluated ₁ Is 2; when C is more than or equal to 0.25 and less than 0.5, the index a is evaluated ₁ 1 is shown in the specification; when C < 0.25, the index a is evaluated ₁ Is 0;

(2) vertical motion condition of broken block structure:

the vertical movement speed of the broken block of the target mine is V ₁ When the vertical movement rate V ₁ When the ratio is not less than 8mm/yr, the index a is evaluated ₂ 3; when the vertical movement velocity V ₁ Evaluation index a at > 5mm/yr ₂ Is 2; when the vertical movement velocity V ₁ When the ratio is < -3mm/yr, the index a is evaluated ₂ 1 is shown in the specification; when the vertical movement speed is-3 mm/yr is less than or equal to V ₁ When the density is less than or equal to 5mm/yr, the evaluation index is equal to or less thanNumber a ₂ Is 0;

(3) horizontal movement condition of broken block structure:

the vertical movement speed of the broken block of the target mine is V ₂ When the horizontal movement velocity V ₂ Evaluation index a at > 10mm/yr ₃ 3; when the vertical movement speed is 5mm/yr is less than or equal to V ₂ When the density is less than or equal to 10mm/yr, the index a is evaluated ₃ Is 2; when the vertical movement speed is 2mm/yr is less than or equal to V ₂ Evaluation index a when < 5mm/yr ₃ 1 is shown in the specification; when the vertical movement velocity V ₂ Evaluation index a when < 2mm/yr ₃ Is 0;

(4) fracture structure influence range condition

b＝±(K·10h)

Wherein: b-width of the fracture structure influence range, km, b takes a positive value when the fracture influence range boundary is outside the well field boundary, and b takes a negative value when the fracture influence range boundary straddles the inside of the well field boundary;

k-mobility coefficients (k=1, 2, 3), k=3 when the break mobility is strong, k=2 when the break mobility is medium, and k=1 when the break mobility is weak;

h-breaking vertical drop, m;

when b.ltoreq.0.5, the index a is evaluated ₄ When b is more than 0.5 and less than or equal to 2, the index a is evaluated ₄ 2, when 2 < b.ltoreq.5, the index a is evaluated ₄ 1, when b > 5, the index a is evaluated ₄ Is 0;

(5) structural stress conditions

The structural stress versus rock burst risk evaluation index is represented by a stress concentration coefficient K, and when K is more than 2, the evaluation index a ₅ 3, when K is more than 1.2 and less than or equal to 2, the index a is evaluated ₅ When K is more than 0.8 and less than or equal to 1.2, the index a is evaluated ₅ 1, when K is less than or equal to 0.8, the evaluation index a ₅ Is 0;

(6) depth of extraction conditions

When the mining depth h is more than 800m, the evaluation index a ₆ 3, when 600m < h is less than or equal to 800m, the index a is evaluated ₆ 2, when 400m < h.ltoreq.600m, the index a is evaluated ₆ 1, when the mining depth h is less than or equal to 400m, the evaluation index a ₆ Is 0;

(7) overburden hard formation conditions

The distance d between the hard-covered thick rock stratum and the coal seam is less than or equal to 20m, and the index a is evaluated ₇ 3; when the distance d between the hard-covered thick rock stratum and the coal seam is more than 20m and less than or equal to 50m, evaluating the index a ₇ Is 2; when the distance d between the hard-covered thick rock stratum and the coal seam is more than 50m and less than or equal to 100m, evaluating the index a ₇ 1 is shown in the specification; when the distance d between the hard-covered thick rock stratum and the coal seam is more than 100m, the index a is evaluated ₇ Is 0;

(8) evaluation of local and neighbor criteria

The occurrence frequency of rock burst of the same coal seam in the region and the adjacent region is n, and when n is more than or equal to 3, the index a is evaluated ₈ 3, when 2.ltoreq.n < 3, the index a is evaluated ₈ 2, when n=1, the evaluation index a ₈ 1, when n=0, the evaluation index a ₈ Is 0;

(3) Obtaining each evaluation index value a obtained in the step (2) _i Adding to obtain comprehensive evaluation index

(4) Normalizing the comprehensive evaluation index in the step (3) to obtain a comprehensive evaluation index value of the geological dynamic environment of the target mine

(5) Dividing the types of the target mine according to the comprehensive evaluation index value N of the geological power environment of the target mine in the step (4), wherein the method specifically comprises the following steps: defining the target mine as a typical rock burst mine when N is more than 0.5 and less than or equal to 1, wherein when N is more than 0.5 and less than or equal to 0.75, the target mine is a geological power environment with medium rock burst, and when N is more than 0.75 and less than or equal to 1, the target mine is a geological power environment with strong rock burst; when N is more than 0.25 and less than or equal to 0.5, defining a target mine as an atypical rock burst mine, wherein the target mine is a geological power environment with weak rock burst; when N is more than or equal to 0 and less than or equal to 0.25, the target mine is defined as a rock burst-free mine, and the target mine is a geological power environment with the rock burst-free mine.

3. A method of rock burst risk prediction for a typical rock burst mine as claimed in claim 1, wherein: the rock burst risk is predicted based on the critical depth, and when the depth of production reaches the critical depth, continued production will risk the rock burst to occur.

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