CN109918696B - Classification method and device for rock burst strength grade - Google Patents
Classification method and device for rock burst strength grade Download PDFInfo
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Abstract
The application discloses a classification method and a device for rock burst strength grade, wherein the classification method comprises the following steps: obtaining coal damage loss energy based on a coal damage constitutive model, and determining a first intensity level demarcation value of rock burst; determining a rock burst second intensity level demarcation value based on the coal body damage loss energy and the broken coal body first ejection energy; and determining a third intensity level demarcation value of the rock burst corresponding to the set surface wave level based on the energy relation between the total energy of the raw rock coal body and the set surface wave level.
Description
Technical Field
The present disclosure relates generally to the field of geologic hazard control technologies, and in particular, to a method and apparatus for classifying rock burst strength levels.
Background
Along with the increasing depth and intensity of coal mine exploitation, the frequency of occurrence of dynamic disasters of mines is increased, and for rock burst mines, the dynamic disasters of rock burst are important in the safety production of the mines. Rock burst is when the energy of coal rock reaches or exceeds the critical energy of rock burst, the accumulated elastic energy of coal rock is suddenly released to throw out the coal rock, and the underground equipment and the underground engineering space are damaged and even the underground staff are injured and killed along with strong sound. In addition, rock burst can also have an effect on other mine disasters. Because the rock burst generation mechanism is complex and is greatly influenced by geological conditions and mining conditions, the rock burst research is one of important subjects for ensuring the safe production of coal mines.
At present, the academic circles at home and abroad mainly have rigidity theory, strength theory and impact tendency theory on the research of rock burst generation mechanism, and as the research of the rock burst generation mechanism is deepened, three-criterion theory, shearing slip theory, three-factor theory, deformation instability theory and the like are further provided, so that the rock burst prevention and control and safety production of the coal mine are realized. (1) theory of stiffness: after the appearance of the pressure testing machine, petukhov, cook and Digest first find that rock burst can be described by dynamic destruction of a rock test piece on a flexible testing machine with smaller rigidity, and then put forward the theory of the impact earth pressure rigidity. After proposing energy theory, cook recognizes that rock burst is due to structural instability. Further experiments were performed using marble. Salaman, brady and Petukhov et al have also conducted extensive studies on the rock burst problem for a number of pillars. (2) theory of intensity: the theoretical view of strength is that when the load carried by the coal rock mass reaches its strength limit, the coal rock mass will begin to break. Classical theory of coal body clamping is proposed by bujohno. If the boundary between the coal body and the surrounding rock and the coal body reach the limit balance condition, the strength condition of rock burst is reached. But the rock burst is also equal to the coal rockThe sudden body failure is related to the fact that sometimes coal rock failure does not mean that rock burst must occur. (3) theory of impact propensity: impact trend theory states that: impact tendency K of coal rock mass E ≥K EC At this time, impact damage to the coal rock mass may occur. (4) three-criterion theory: the Leyusheng indicates that the strength criterion is a coal body destruction criterion and the energy criterion and impact tendency criterion are sudden destruction criteria, and it is proposed that the rock burst generation mechanism can be described by the strength criterion, the energy criterion and the impact tendency criterion, and that rock burst will occur when all three criteria are satisfied. (5) "three factor" theory: ji Qingxin et al consider rock burst generation to be affected by three factors, intrinsic factors of the coal rock mass, active source factors of mining engineering and structural factors. The theory of three factors of rock burst generation is proposed. (6) theory of deformation instability: zhang Mengtao the rock burst is considered to be a strain softening phenomenon of a coal rock mass after the coal rock mass enters the peak strength, a mathematical model is built based on a finite element method, and quantitative research is carried out on the rock burst.
In conclusion, students at home and abroad carry out analysis and demonstration on rock burst mechanism researches from different angles, and system description is also given for different geological power conditions, so that a lot of precious results and experiences are obtained.
At present, the analysis and research of the energy theory about the impact damage of coal rock mass are more, but most of the energy theory is researched from the same starting point, namely: the energy remaining after the coal-rock mass is destroyed provides energy for rock burst to occur. However, since the rock burst mechanism is complex, the impact factors on the rock burst are more, the generation rule and mechanism of the rock burst cannot be comprehensively disclosed in the prior art, and a scientific method for classifying the generated rock burst strength grade is not available.
Disclosure of Invention
In view of the above-described drawbacks or deficiencies of the prior art, it is desirable to provide a scientific classification scheme for impact ground pressure intensity levels.
In a first aspect, embodiments of the present application provide a method for classifying rock burst strength levels, including the steps of:
obtaining coal damage loss energy based on a coal damage constitutive model, and determining a first intensity level demarcation value of the impact ground pressure;
determining a rock burst second intensity level demarcation value based on the coal body damage loss energy and the broken coal body first ejection energy;
and determining a third intensity level demarcation value of the impact ground pressure corresponding to the set surface wave level based on the energy relation between the total energy of the raw rock coal body and the set surface wave level.
The corresponding coal body damage loss energy, the first coal body breaking and first coal body throwing energy and the coal body raw rock energy are expressed through corresponding energy densities, the total energy of the coal bodies in corresponding areas can be calculated according to different conditions, and the quantitative prediction of the occurrence intensity of rock burst can be realized.
The formula of the coal body damage constitutive model is as follows:
y is the damage energy consumption rate;
sigma is stress;
e is the elastic modulus;
d is a damage variable and represents the microcrack number in unit volume;
D E is the damage value at the time of complete fracture failure at position E;
D D is the damage value at the time of the complete fracture failure at the position D;
U D energy is consumed for coal rock mass damage.
And the damage variable in the coal body damage constitutive model is determined through the stress-strain test relation of the coal body in the mine. The method comprises the steps of establishing a coal rock mass damage constitutive model fitting curve, a damage variable curve relation and calculating the energy damaged by coal rock mass damage of a coal mine by using Matlab software. According to the close correlation of the development and evolution of microcracks of coal and rock mass and the development and distribution of internal damage, a coal and rock mass damage model is established, and the model can be considered as follows:
(1) The coal rock mass damage is performed in the direction of the stress main axis under the coupling of elasticity and damage, and is regarded as a main diagonal matrix of the damage tensor;
(2) The coal rock mass damage evolution should have a power function relation with stress or strain, and damage variables can be reflected by macroscopic physical quantities of internal tensile strain.
The throwing speed of the broken coal body corresponding to the first throwing energy of the broken coal body is 8-12m/s. The damage mechanics can obtain the energy lost when the coal body is damaged according to the lithology of the coal rock body; the throwing energy of the broken coal body corresponds to different throwing energy and impact size according to different speeds when the coal body is thrown, so that the strength of different rock burst can be predicted, the rock burst does not occur when the throwing speed v is less than or equal to 1m/s, and the rock burst has higher possibility when v is more than or equal to 10m/s. Typically, the ejection speed can be set to 8-12m/s to calculate the critical energy formula.
The total energy of the raw rock coal body is considered in modern structural stress fields, active fracture is divided by a geological region method, and the control effect on rock burst is judged and can be obtained through theoretical calculation. The impact ground pressure energy inoculation effect of modern structural stress is macroscopically analyzed, and the classification of the impact ground pressure intensity grade by using a geological power division method is proposed.
The original rock energy generated by the modern construction stress field comprises the energy under the dead weight stress field and the energy under the construction stress field,
energy W under self-weight stress field Z The method comprises the following steps:
wherein: e-elastic modulus, GPa;
poisson ratio of μ -cell;
average volume weight of gamma-overburden, KN/m 3 ；
The depth of the position of the H-unit body, m;
r-rock burst system scale radius, m.
Energy W under the structural stress field G The method comprises the following steps:
wherein: k (k) 1 -a maximum principal stress concentration coefficient;
k 2 -an intermediate principal stress concentration coefficient;
k 3 -a minimum principal stress concentration coefficient.
The deformation and stress change of the regional coal rock mass are the energy basis of the original rock under natural conditions, and the original rock energy mainly consists of two parts, namely the energy under the dead weight stress field and the energy under the structural stress field. The well Tian Gouzao and ground stress field patterns are also relatively complex due to the complex and variable well geological conditions. Therefore, the original rock stress value and distribution of the investigation region are analyzed and calculated according to the mining depth, fracture structure, roof lithology and the like, and the energy value and distribution are analyzed and calculated to divide a high energy region and a low energy region.
Determining the scale radius of the rock burst system based on the corresponding relation between the original rock energy generated by the modern construction stress place and the energy of the set surface wave magnitude; and determining the corresponding energy density as a third intensity level demarcation value based on the original rock energy and/or the surface wave magnitude energy and the rock burst system scale radius.
In a second aspect, embodiments of the present application provide a device for predicting mine rock burst strength, the device comprising:
the acquisition module is used for acquiring the coal body damage constitutive model, the broken coal body throwing energy, the total energy of the raw rock coal body and the set related parameters of the surface wave magnitude;
a calculation module for: and determining a first intensity level demarcation value of rock burst based on the coal body damage loss energy obtained by the coal body damage constitutive model, determining a second intensity level demarcation value of rock burst based on the coal body damage loss energy and the first ejection energy of the broken coal body, and determining a third intensity level demarcation value of rock burst equivalent to the set surface wave level based on the total energy of the raw rock coal body and the energy relation of the set surface wave level.
Based on the rock burst energy theory, the rock burst intensity level classification scheme provided by the embodiment of the application starts from the root of rock burst occurrence, researches the relation between rock burst and coal rock mass energy, and proposes that raw rock energy is main energy of rock burst occurrence, determines the intensity level of the rock burst, and does not take the residual energy after the coal rock mass is destroyed as the basis of the intensity level of rock burst occurrence. The method can comprehensively reveal the generation rule and mechanism of the rock burst, can more accurately classify the intensity level of the rock burst, can perform prospective work of rock burst prevention and control at the initial stage of mine construction, and can radically prevent and control the rock burst.
Drawings
Other features, objects and advantages of the present application will become more apparent upon reading of the detailed description of non-limiting embodiments, made with reference to the following drawings, in which:
FIG. 1 shows a schematic diagram of the change in elastic potential in front of a working surface in an embodiment of the present application;
fig. 2 shows a deformation failure stress-strain curve of a coal rock mass.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention.
It should be noted that the components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations without conflict. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
As described in the background art, at present, many studies are conducted on the analysis of the energy theory of the impact damage of coal rock mass, but most of these energy theories are studied from the same starting point, namely: the energy remaining after the coal-rock mass destruction provides energy for the impact ground pressure to occur. However, in the prior art, no related research on the relation between rock burst inoculation, development and energy in the process of occurrence is carried out, and in particular, the influence of the stress of the rock burst is not considered.
The theoretical research results of the application are as follows:
the mine does not have the regional geological power condition of the mine rock burst, and is mutually coupled with mining stress caused by mining activities, so that the stress is increased and energy is accumulated, the condition of the mine rock burst is achieved, and the mine rock burst is induced. In the dynamic balance process, the energy is concentrated near the coal wall, and when the energy value reaches the softening strength of the coal body, the coal body is softened and deformed, so that the concentrated energy is transferred to the deep part of the coal body, and the new energy balance is achieved. When the concentrated energy exceeds the damage dissipation energy of the coal body, the coal body is destroyed, and rock burst may occur.
In the stoping process of the working face, the energy gathering area is gradually pushed, so that coal and rock mass is broken, and energy is released. Definition of the product of a coal rock mass under the action of an initial ground stress fieldThe energy gathered is the energy of the original rock, U is used B A representation; the energy consumed by coal rock mass damage is U D The method comprises the steps of carrying out a first treatment on the surface of the Critical energy of rock burst occurrence is U L The method comprises the steps of carrying out a first treatment on the surface of the Under the exploitation condition, the total energy of pushing coal and rock mass along with working face is U T 。
In the working face extraction process, total energy U in coal rock mass T Is a variable that is constantly changing. Total energy U of coal and rock mass T The energy consumed by the damage to the coal rock mass is U D The difference is U T-D Its variation may present three possibilities:
(1) when U is T-D > 0, indicating that the accumulated energy in the coal rock body is more than the energy consumed by the damage of the coal rock body, U T-D The propulsion of the working surface is increased continuously;
(2) when U is T-D =0, indicating that the energy accumulated in the coal rock mass is equal to the energy consumed by the coal rock mass damage, and the accumulation and dissipation of energy are in an equilibrium state;
(3) when U is T-D < 0, indicating that the damage of coal rock mass consumes more energy than accumulated in the rock mass, U T-D And the pushing force is continuously reduced along with the pushing of the working surface.
Thus, the change in energy in the coal rock mass in front of the working face can be represented by the model shown in FIG. 1, where U T-D Is U (U) T (total energy of coal rock mass) U D (energy consumed by coal rock mass damage), U L Is the critical energy of the rock burst.
When U is T-D At > 0, this indicates that the accumulated energy in the coal rock is greater than the dissipated energy, and that the energy is in an increasing state. But only U T-D ＜U L No rock burst occurs. U (U) T-D -U L The greater the difference, the greater the risk. When U is T-D ＝U L If the energy is increased, rock burst occurs. If U T-D ＞U L Moreover, if the energy is released without timely taking the dangerous measure, the energy is further increased in the working face extraction process, so that rock burst is likely to occur.
When U is T-D When less than 0, the accumulated energy in the coal rock body is smaller than that of the coal rockEnergy dissipated in the body, coal and rock mass energy is gradually released, energy is continuously reduced, U T-D -U L The greater the difference, the less the risk, in which case no danger-relieving measures are taken and no rock burst risk occurs.
Grady and Kipp (1980) propose that the microcrack number N and strain epsilon per unit volume inside the rock mass satisfy the two-parameter (k and m) Weibull distribution rules under uniaxial tensile stress, as shown in formula (1).
According to the close correlation of the development and evolution of microcracks of coal and rock mass and the development and distribution of internal damage, a coal and rock mass damage model is established, and the model can be considered as follows:
(1) The coal rock mass damage is performed in the direction of the stress main axis under the coupling of elasticity and damage, and is regarded as a main diagonal matrix of the damage tensor;
(2) The coal rock mass damage evolution has a power function relation with stress or strain, and damage variables can be reflected by macroscopic physical quantities of internal tensile strain;
when a one-dimensional coal rock mass damage model is established, the following steps are assumed: the rock is in a state of uniaxial pressure,
the tensile strain causes internal microcrack propagation, and thus a relationship between the number of microcracks and the tensile strain is established, expressed by formula (2).
N＝∝mε n (2)
Wherein: n-microcrack number per unit volume;
epsilon-axial compressive strain, under the action of a single shaft, the tensile strain is equal to the compressive strain in value;
m, n-coal rock mass parameters.
The number of microcracks per unit volume is expressed by a damage variable D, and is expressed by a formula (3).
Wherein:
-an effective stress; sigma-stress.
Setting:
then:
and (7) a damaged coal rock mass constitutive relation formula.
E is the modulus of elasticity.
The evolution equation of the coal rock mass damage variable is shown as a formula (8).
Elastic strain energy release rate dPhi of damaged coal rock mass e And the damage energy consumption rate Y can be expressed as formula (9), formula (10).
And obtaining a damaged coal rock mass damage release rate formula (11) according to an effective stress concept and a strain equivalence principle.
For isotropic lesions, the lesion variable is a scalar.
Then:
setting:
the partial stress tensor is: s is S ij ＝σ-σ H I (14)
The Misses equivalent stress is equation (15).
Equation (16) is derived from equation (12).
Wherein: s is S t -a triaxial stress factor reflecting the effect of the triaxial stress ratio.
Wherein the method comprises the steps of
Under the stress of a single axis, the stress of the single axis,
defining damage equivalent stress as:
then:
the coal rock mass will continue to develop as the external load increases until the rock is fully broken, theoretically when d=1, the coal rock mass is considered to be fully broken, but many experiments show that when D<1, the material is completely destroyed, as shown in position E of FIG. 2, the damage value at the time of complete fracture destruction at position E is set to be D E The corresponding injury energy release rate is Y E The damage in the coal rock mass at the position D is rapidly increased, so that the strain softening is increased, the damage in the coal rock mass begins to be destroyed, and the energy consumed by the damage of the coal rock mass is expressed as a formula (21).
In the following examples, the energy consumed by damage of the coal body of the mountain in coal mine is calculated by a deduction formula, and stress-strain relation formulas before and after the peak value are fitted in sections by adopting origin9.0 software according to a stress-strain test curve of the coal body of the mountain in coal mine.
The relationship with D is established by the stress-strain curve as shown in the following equation.
According to the stress-strain curve, when the strain is 0.0117, the damage in the coal body is rapidly increased, the damage in the coal body is started to be destroyed, and when the strain is 0.014, the coal body is completely destroyed, so that the Matlab software is used for calculating that the damage loss energy of the coal body of the mountain stream coal mine is 1.45x10 according to the formula (23) 5 J/m 3 。
When rock burst occurs, on one hand, energy U consumed by coal body damage D On the other hand, the energy U is thrown out by the broken coal body F Coal body damage consumptionThe sum of the energy of (2) and the energy of the broken coal body thrown is defined as the critical energy of rock burst, U is used L The expression is calculated as formula (25). In general, the motion of an object takes the velocity of a particle as a measurement, and the average initial velocity (v) of the broken coal body thrown into free space determines the kinetic energy generated by the coal body. When v is less than or equal to 1m/s, rock burst does not occur, and when v is more than or equal to 10m/s, the rock burst has higher possibility. By the critical energy calculation formula (25), the energy density was 2.41×10 5 J/m 3 。
U L ＝U D +U F (25)
In the present application, the purpose of determining each demarcation value of the rock burst strength grade is to determine U T-D Comparing with each boundary value, when U T-D <When the first intensity level is a boundary value, the level is rock burst-free; when the first intensity level is divided into values<U T-D <When the second intensity level is a boundary value, the level is weak rock burst; when the second intensity level is divided into values<U T-D <When the third intensity level is a boundary value, the level is medium rock burst; u (U) T-D >And when the third intensity level is a boundary value, the level is high rock burst.
The classification method for rock burst strength grade provided by the embodiment of the application comprises the following steps:
obtaining coal damage loss energy based on a coal damage constitutive model, and determining a first intensity level demarcation value of the impact ground pressure;
determining a rock burst second intensity level demarcation value based on the coal body damage loss energy and the broken coal body first ejection energy;
and determining a third intensity level demarcation value of the impact ground pressure corresponding to the set surface wave level based on the energy relation between the total energy of the raw rock coal body and the set surface wave level.
The formula of the coal body damage constitutive model is as follows:
y is the damage energy consumption rate;
sigma is stress;
e is the elastic modulus;
d is a damage variable and represents the microcrack number in unit volume;
D E is the damage value at the time of complete fracture failure at position E;
D D is the damage value at the time of the complete fracture failure at the position D;
U D energy is consumed for coal rock mass damage.
The corresponding coal body damage loss energy, the first coal body throwing energy and the coal body raw rock energy are obtained through the corresponding energy density, the total coal body energy of the corresponding area can be calculated according to different conditions, and the quantitative prediction of the occurrence intensity of rock burst can be realized.
And the damage variable in the coal body damage constitutive model is determined through the stress-strain test relation of the coal body in the mine. The method comprises the steps of establishing a coal rock mass damage constitutive model fitting curve, a damage variable curve relation and calculating the energy damaged by coal rock mass damage of a coal mine by using Matlab software. According to the close correlation of the development and evolution of microcracks of coal and rock mass and the development and distribution of internal damage, a coal and rock mass damage model is established, and the model can be considered as follows:
(1) The coal rock mass damage is performed in the direction of the stress main axis under the coupling of elasticity and damage, and is regarded as a main diagonal matrix of the damage tensor;
(2) The coal rock mass damage evolution should have a power function relation with stress or strain, and damage variables can be reflected by macroscopic physical quantities of internal tensile strain.
The throwing speed of the broken coal body corresponding to the first throwing energy of the broken coal body is 8-12m/s. The damage mechanics can obtain the energy lost when the coal body is damaged according to the lithology of the coal rock body; the throwing energy of the broken coal body corresponds to different throwing energy and impact size according to different speeds when the coal body is thrown, so that the strength of different rock burst can be predicted, the rock burst does not occur when the throwing speed v is less than or equal to 1m/s, and the rock burst has higher possibility when v is more than or equal to 10m/s. Typically, the ejection speed can be set to 8-12m/s to calculate the critical energy formula.
The total energy of the raw rock coal body is considered in modern structural stress fields, active fracture is divided by a geological region method, and the control effect on rock burst is judged and can be obtained through theoretical calculation. The impact ground pressure energy inoculation effect of modern structural stress is macroscopically analyzed, and the classification of the impact ground pressure intensity grade by using a geological power division method is proposed.
The original rock energy generated by the modern construction stress field comprises the energy under the dead weight stress field and the energy under the construction stress field,
energy W under self-weight stress field Z The method comprises the following steps:
wherein: e-elastic modulus, GPa;
poisson ratio of μ -cell;
average volume weight of gamma-overburden, KN/m 3 ；
The depth of the position of the H-unit body, m;
r-rock burst system scale radius, m.
Energy W under the structural stress field G The method comprises the following steps:
wherein: k (k) 1 -maximum principal stressForce stress concentration coefficient;
k 2 -an intermediate principal stress concentration coefficient;
k 3 -a minimum principal stress concentration coefficient.
Determining the scale radius of the rock burst system based on the corresponding relation between the original rock energy generated by the modern construction stress place and the energy of the set surface wave magnitude; and determining the corresponding energy density as a third intensity level demarcation value based on the original rock energy and/or the surface wave magnitude energy and the rock burst system scale radius.
In a second aspect, embodiments of the present application provide a device for predicting mine rock burst strength, the device comprising:
the acquisition module is used for acquiring the coal body damage constitutive model, the broken coal body throwing energy, the total energy of the raw rock coal body and the set related parameters of the surface wave magnitude;
a calculation module for: and determining a first intensity level demarcation value of rock burst based on the coal body damage loss energy obtained by the coal body damage constitutive model, determining a second intensity level demarcation value of rock burst based on the coal body damage loss energy and the first ejection energy of the broken coal body, and determining a third intensity level demarcation value of rock burst equivalent to the set surface wave level based on the total energy of the raw rock coal body and the energy relation of the set surface wave level.
Example 1
1 region structural features and energy field features
1.1 coal field area Structure and mobility characteristics thereof
(1) Impact ground pressure energy source and coal rock mass damage energy research
Macroscopically analyzing the inoculation effect of geological structure, new structure movement and modern structure stress on the impact earth pressure energy, and evaluating the rock burst risk by using a geological power division method; the energy transfer and dissipation conditions of the coal rock mass during deformation and destruction are analyzed microscopically, and the critical energy density of rock burst is determined based on the characteristics of the formation of the rock burst phenomenon.
(2) Well Tian Gouzao motion and formation energy analysis
Based on the structural stress field, the energy field and the crust strain energy characteristics of the Beijing coal field, the control action of the structural form and the movement mode in the Jian well field on the rock burst is analyzed, the geological partitioning method is utilized to partition the movable fracture, the control action of the movable fracture on the rock burst is analyzed, the raw rock energy under the natural geological condition is calculated, the high energy region and the release region of the three-slot and two-slot coal bed are partitioned based on the critical energy density of the rock burst, the control action of the high energy region on the rock burst is analyzed, and then the relation between the raw rock energy and the pressure of the impact ground is established.
(3) Mining energy analysis under mining conditions
Based on the energy characteristics of the raw rock under natural conditions, FLAC3D numerical simulation software is applied to simulate exploitation of the working face of the energy accumulation area of the raw rock of the coal seam with three grooves and two grooves, the influence of exploitation activities on the energy distribution characteristics of the front part of the working face and the coal pillar area under exploitation conditions is analyzed, and rock burst strength is classified. Based on the front of working face, the energy distribution characteristics of coal pillar areas and the rock burst intensity classification, the relation between the coal rock mass energy and the rock burst intensity under the exploitation condition is established, and hierarchical control technical measures are adopted for areas with different rock burst intensities.
2 structural stress field and energy field characteristics
In recent years, by examining the problems of mountain coal mines, large table wells, long-ditch valley coal mines, and the like in the Beijing mining area, the results of the ground stress measurement and the energy value show that (table 3.1), the maximum principal stress azimuth in the Beijing mining area is north east-east, the maximum energy density is 3.25X105J/m 3, the minimum energy density is 0.44X105J/m 3, and the average energy density is 1.51X105J/m 3. Research shows that the construction movement has a great influence on the energy distribution of the Jingxi coal fields, the energy is different, and energy is accumulated in some areas and released in some areas due to the construction movement. According to the method, a large amount of ground stress measurement data in China are statistically analyzed through Zhao Dean, jing Feng and the like, the energy density is calculated according to the ground stress, a comparison graph of the Beijing-Xie-field energy density obtained according to the calculation and the national energy density is obtained, the Beijing-Xie-field energy density is higher than the national average level, particularly, the Beijing-Xie-field energy density is more obvious at the depth of burial of more than 700m, the Beijing-Xie-field energy density is unevenly distributed, the Beijing-Xie-field coal rock mass bears a stronger non-uniform energy environment, and accordingly, the Beijing-Xie-well field area is divided into energy areas.
3 well Tian Weizhi and construction overview
3.1 well field position and traffic
The Jian Jijing field is located in the western mountain area of Beijing, and belongs to the Beijing-Xie coal field, and the mining area spans the two areas of the mountain and the door sulcus.
3.2 coal-based stratum and roof-floor lithology
(1) Coal-based strata
The dwarfism coal-bearing stratum is a kiln slope group, and the maximum thickness can exceed 720m. The sedimentary lithology and lithofacies have large change and complex gyratory, and are composed of sandstone, siltstone, argillite, coal seam, conglomerate, tuff sandstone and the like.
(2) Coal seam roof and floor
Roof cracks and small faults of the coal bed in the well field develop, the roof is broken, the roof and the floor are uneven in lifting, and the requirement on support is high.
3.3 geologic formation characteristics of well fields
The wing of Beijing temple An Ling- chignon mountain is located in Jurassic well, jian and Jurassic well, and is located in the south of the Mirass Duan Nadong. A series of secondary fold structures are developed in the well field, and the main axis track positions are folds of NE 56-70 degrees, NE 40-45 degrees, NE 5-15 degrees, NE 15-30 degrees and NW 330-350 degrees. The well field fold structure plays an important role in controlling the accumulation of the impact ground pressure energy.
The energy of the raw rock in the wood-city coal mine well field is controlled by the geological structure, the influence of the geological structure formed by different types and different periods on the energy of the raw rock is different, the energy distribution conditions of the coal rock bodies at different positions of the same structure are also greatly different, and the analysis of the influence degree of the wood-city coal mine Tian Gouzao on the energy distribution of the raw rock is very important for calculating the energy distribution of the well field below.
Under the action of the construction movement, the end of the fault accumulates a great amount of elastic energy to provide a dynamic condition for the occurrence of impact ground pressure. When the area is disturbed by the mining work, the stress and accumulated elastic energy in the coal rock body are rapidly released, the coal body is destroyed, and under the action of energy expansion, the coal body is thrown to the mining space, and rock burst occurs. Statistical analysis of rock burst accidents of mountain stream coal mine shows that in 20 rock burst accidents of mountain stream coal mine occurring in nearly five years, almost all rock burst accidents are located near faults or affected by faults in a well field.
Through the analysis, the wood urban coal mine is controlled by the geological structures such as the buckling structure, the fracture structure, the structural compounding, the combination and the like, and the mine rock burst mostly occurs in the geological structure belt. The 3 rock burst is near the syncline of the cow canal, and the 17 rock burst is near the reverse fault of the north harbor canal and the co-deposited normal fault of the blind canal.
3.4 Beijing-Xie area break block division
The geosteering effort should follow a general to local principle by progressively narrowing the split range, analyzing the broken block configuration of the well Tian Chedu or less, establishing a link between the block configuration and the raw rock energy, which is calculated in the context of the broken block diagram of the well Tian Hua, and thus analyzing the field activity fracture is the basis for calculating the raw rock energy.
(1) I-stage broken block structure division
At 1: the construction of class I breaks was found on a 250 ten thousand scale map, with a total of 14.
(2) Level II block structure division
At 1:100 ten thousand scale topography of the ascertained class II fault block construction, a total of 40 active breaks were scored in the study area.
(3) III level block structure division
At 1: on 20 ten thousand topography, find out III level broken block structure with the coal mine of wooden city as the center, the III level fracture of dividing totally 12.
(4) IV-level broken block structure division
At 1: the grade IV block structure found on the 5 ten thousand scale topographic map total drawn 29 active breaks in the study area.
(5) V-stage block structure division
At 1: the v-level block structure found on the topography of 1 ten thousand proportions total 21 active breaks were scored in the study area.
4 natural condition zone of original rock energy
4.1 rule of stress distribution in well field
The study of stress fields is of significant importance for understanding the course of construction activities. The original rock energy distribution is estimated from the known fractures. The method of geosteering based on the plate theory is significantly representative in analyzing the energy of the raw rock. The internal relationship between the zone structure and the stress state of the rock mass is revealed by theoretical or numerical analysis, inversion, back calculation and simulation.
The method combines the actual area where the stress abnormality of the wood urban mountain stream coal mine occurs and the underground actual production technical conditions. And finally determining a ground stress test area to be positioned in a 3-groove surrounding rock area of a +450m horizontal 2-4 stone gate, wherein the +450m horizontal is provided with 3 field test points in total.
And carrying out ground stress test on the wood urban mountain stream coal mine to obtain the maximum main stress value, the middle main stress value, the minimum main stress value, the azimuth angle, the inclination angle and other junction parameters calculated by 3 ground stress measuring holes.
4.2 calculation and division of the stress of the original rock under natural conditions
(1) Roof lithology analysis and classification
And finally obtaining lithology distribution diagrams of roof plates of the three-slot and the two-slot coal seam of the mountain stream coal mine by analyzing and processing the drilling data of the mountain stream coal mine.
(2) Establishing a calculation model and meshing
And constructing a grid for modern structural movement of a mountain area of the mountain through the I-V-level block diagram, and selecting the V-level block diagram to form a model.
(3) Parameter definition
The parameters to be defined mainly include the following: ground stress, rock mass and fracture mechanics parameters, rock mass mechanics parameters, fracture geometry parameters, etc. The above parameters are obtained as a result of the ground stress test. Lithology distributions are determined from well Tian Zuankong data.
4.3 energy Density computation and energy zone graphical output
And (3) reversely calculating the energy density value according to the calculated stress data, and displaying the energy density in a contour diagram mode.
4.4 raw rock energy differentiation and impact analysis on rock burst
The energy region dividing principle under the natural geological condition divides a high energy region and a low energy region according to the critical energy density condition of rock burst occurrence and the comparison of the energy density of the original rock, wherein the region of the original rock with the energy density exceeding the critical energy density condition of the rock burst is the high energy region, and the low energy region is the low energy region according to the condition that the energy density of the non-impact ground pressure is smaller than the energy density of the original rock.
(1) Coal seam energy zone division
On the basis of rock mass energy density calculation, dividing the energy density of a roof of a three-slot coal seam of a mountain in a wood city into a high-energy area and a low-energy area. The 20 times rock burst is 12 times in a high-energy area, the horizontal maximum principal stress value is 27.5 MPa-31.5 MPa, and the energy density value is 1.67 multiplied by 10 5 J/m 3 ～2.77×10 5 J/m 3 The maximum principal stress value at the level of 1 time is 26 MPa, and the energy density value is 2.37X10 5 J/m 3 The maximum principal stress value at the level of 1 time is 25MPa, and the energy density value is 2.39X10 5 J/m 3 The maximum principal stress value at the level of 1 time is 24MPa, and the energy density value is 2.43 multiplied by 10 5 J/m 3 The maximum principal stress value at the level of 3 times is 23MPa, and the energy density value is 2.53 multiplied by 10 5 J/m 3 。
Mining energy analysis under 5 mining conditions
5.1 mining energy Density analysis in the Primary rock energy accumulation zone
5.1.1 three-groove Western five-wall model establishment
In order to comprehensively and systematically reflect the energy density distribution rule of the front part of a working face and the inside of a coal pillar of a five-wall stoping working face of a horizontal Siemens three-groove Siemens with the length, the width and the height of 375m, 300m and 203m respectively in the stoping process of a horizontal Siemens three-groove Siemens five-wall stoping working face of +250m, a FLAC3D large numerical simulation software is utilized to build a model by taking geological conditions and mining technical conditions as backgrounds.
And calculating the boundary conditions of the model, namely respectively applying constraint along the X axis and the Y axis on the boundaries at the two ends of the X axis and the Y axis, wherein the displacement of the X axis and the Y axis is zero, the top of the model is a free boundary, and the bottom boundary is fixed. The boundary load conditions of the calculation model are that gradient stress of 19.9MPa, 45.0MPa and 22.6MPa are respectively applied to the X-axis, Y-axis and Z-axis directions.
5.1.2 three-tank West five-wall mining energy density analysis
And calculating to obtain the energy density distribution of the three-groove western five-wall working surface during recovery for 30m, and specifically obtaining the maximum energy density and the minimum energy density. An energy density distribution curve along the working surface to the middle position, etc. The energy density peak value in the middle of the working surface is 5.48 multiplied by 10 5 J/m 3 The energy density peak is 5.3m from the coal wall of the working surface, belonging to the medium rock burst strength.
5.2 coal rock energy characteristics and rock burst strength relation
5.2.1 rock burst Strength Classification
(1) Without risk of rock burst
In the working face mining process, rock burst does not occur when the energy of the coal body is smaller than the energy consumed by coal body damage, and the coal body damage loss energy of the wood city is calculated to be 1.45 multiplied by 10 according to the coal body damage constitutive model 5 J/m 3 Thus, when the coal body is under mining conditions, the energy density is less than 1.45X10 5 J/m 3 Determined to be free of rock burst risk.
(2) Weak rock burst risk definition value determination
Coal or rock is thrown into the mined space according to the phenomenon description of weak rock burst, but the coal or rock is not very destructive, and the coal or rock is basically not damaged to brackets, machines and equipment; the surrounding rock generates vibration with loud sound; coal dust is generated, a large amount of gas can be gushed out in a gas coal bed, and the average initial speed v of throwing the crushed coal body into a free space is less than 10m/s. By calculation formula
Can obtain an energy density of 2.41 x 10 when the average initial velocity v=10m/s of the throwing 5 J/m 3 . Thus, when the coal body is under the exploitation condition, the energy density is 1.45 multiplied by 10 5 J/m 3 ～2.41×10 5 J/m 3 And between, is determined to be a weak rock burst hazard.
(3) Medium rock burst strength cutoff determination
According to the phenomenon description of medium rock burst, part of coal or rock is broken sharply, a large amount of broken coal is thrown into a mined space, and the average initial speed v of throwing broken coal bodies into a free space is more than or equal to 10m/s.
From the energy and magnitude relationship of the rock burst system, the magnitude M of the surface wave can be determined L When=2, the scale radius R of the rock burst system is calculated as:
the scale radius of the rock burst system is 1.83m, and the micro-vibration energy is 10 8 J, the energy density of the coal is calculated by equation 5.3. The actual situation of rock burst occurring in the east-west wall of three grooves of 5 th year 2008 of a mountain coal mine in the wood city is shown as follows, and the calculation formula (5.2) of the scale radius of the rock burst system is adopted, wherein sigma 1 ＝28.7MPa，σ 2 23.1MPa, σ3=15.9mpa, e=1828 MPa, μ=0.25, γ=40000 KN/m3, h=500, yielding a rock burst system scale radius of 1.83m, through microseismic energy of 10 8 J, the energy density of the coal is calculated to be 1.3X10 by the formula 5.3 6 J/m 3 。
Thus, when the coal body is under the exploitation condition, the energy density is 2.41 multiplied by 10 5 J/m 3 ～ 1.3×10 6 J/m 3 And, when determined to be a medium rock burst hazard.
R＝1.83m
(4) Determination of high rock burst strength limit
According to the description of the phenomenon of strong rock burst, most of coal or rock is broken sharply, a large amount of coal or rock is thrown into a mined space, and support breakage, equipment movement and surrounding rock vibration, and the surface wave vibration level M appear L Above level 2, with large sound, forming a large amount of coal dust and generating shock wave, and microseismic energy of 10 8 J is more than or equal to J. Thus, when the coal body is under mining conditions, the energy density is greater than 1.3X10 6 J/m3, a strong rock burst risk is determined.
Coal rock energy characteristics and rock burst strength relationship under mining conditions
The working face mining engineering activities cause the mechanical properties and occurrence state changes of surrounding rock and overlying strata, so that the stress balance in a natural state is destroyed, the stress state is redistributed, and a new balance state is achieved. Under the natural geological power condition, the mutual coupling action of the original rock energy and the mining energy caused by mining activity leads to the accumulation of energy, and the energy condition of mine rock burst is reached, so that the mine rock burst is induced.
The current engineering activities in the wood urban well field have entered the rock burst hazard intensity area. Under the allowable conditions of geology and engineering, regional and local danger-eliminating measures are selected to reduce the danger degree, so that the energy of the coal and rock mass in the high energy area is released to eliminate or reduce the danger degree. When the working face is mined, corresponding local detection measures are adopted, so that the dangerous degree of the mining activity area is reduced; and on the other hand, checking the effectiveness of the danger eliminating measures. And according to the corresponding local detection result, determining whether to continue mining engineering activities or whether to continue taking rock burst dangerous measures. The existing dangerous-relief measures adopted by the mountain stream coal mine include measures such as drilling and pressure relief, coal seam water injection, pressure relief blasting and the like.
The foregoing description is only of the preferred embodiments of the present application and is presented as a description of the principles of the technology being utilized. It will be appreciated by persons skilled in the art that the scope of the invention referred to in this application is not limited to the specific combinations of features described above, but it is intended to cover other embodiments in which any combination of features described above or equivalents thereof is possible without departing from the spirit of the invention. Such as the above-described features, are mutually replaced with the features disclosed in the present application (but not limited to the features having similar functions).
Claims (7)
1. A method of classifying rock burst strength levels, comprising the steps of:
obtaining coal damage loss energy based on a coal damage constitutive model, and determining a first intensity level demarcation value of rock burst;
determining a rock burst second intensity level demarcation value based on the coal body damage loss energy and the broken coal body first ejection energy;
determining a third intensity level demarcation value of rock burst corresponding to the set surface wave level based on the energy relation between the total energy of the raw rock coal body and the set surface wave level;
expressing the corresponding coal body damage loss energy, the first coal body breaking and first coal body throwing energy and the coal body raw rock energy through the corresponding energy density;
the formula of the coal body damage constitutive model is as follows:
y is the damage energy consumption rate;
sigma is stress;
e is the elastic modulus;
d is a damage variable and represents the microcrack number in unit volume;
D E is the damage value at the time of complete fracture failure at position E;
D D is the damage value at the time of the complete fracture failure at the position D;
U D energy is consumed for coal rock mass damage;
determining the scale radius of the rock burst system based on the corresponding relation between the original rock energy generated by the modern construction stress place and the energy of the set surface wave magnitude; and determining the corresponding energy density as a third intensity level demarcation value based on the original rock energy and/or the surface wave magnitude energy and the rock burst system scale radius.
2. The method of claim 1, wherein the damage variables in the coal damage constitutive model are determined by stress-strain test relation of coal in a mine.
3. The method for classifying rock burst strength levels as claimed in claim 2, wherein the first ejection energy of the crushed coal body corresponds to an ejection speed of the crushed coal body of 8-12m/s.
4. A method of classifying rock burst strength levels as claimed in claim 3, wherein the total energy of the raw rock coal body takes into account modern structural stress fields.
5. The method of claim 4, wherein the primary rock energy generated at the modern structural stress site comprises self-weight stress field energy and structural stress field energy.
6. The method of classifying rock burst strength levels as claimed in claim 5, wherein the energy W under the self-weight stress field Z The method comprises the following steps:
wherein: e-elastic modulus, GPa;
poisson ratio of μ -cell;
average volume weight of gamma-overburden, KN/m 3 ；
The depth of the position of the H-unit body, m;
r-the scale radius of the rock burst system, m;
energy W under the structural stress field G The method comprises the following steps:
wherein: k (k) 1 -a maximum principal stress concentration coefficient;
k 2 -an intermediate principal stress concentration coefficient;
k 3 -a minimum principal stress concentration coefficient.
7. A mine rock burst strength prediction apparatus, the apparatus comprising:
the acquisition module is used for acquiring the coal body damage constitutive model, the broken coal body throwing energy, the total energy of the raw rock coal body and the set related parameters of the surface wave magnitude;
a calculation module for: determining a first intensity level demarcation value of rock burst based on coal body damage loss energy obtained by the coal body damage constitutive model, determining a second intensity level demarcation value of rock burst based on the coal body damage loss energy and the first ejection energy of the broken coal body, and determining a third intensity level demarcation value of rock burst equivalent to the set surface wave magnitude based on the energy relation between the total energy of the raw rock coal body and the set surface wave magnitude;
expressing the corresponding coal body damage loss energy, the first coal body breaking and first coal body throwing energy and the coal body raw rock energy through the corresponding energy density;
the formula of the coal body damage constitutive model is as follows:
y is the damage energy consumption rate;
sigma is stress;
e is the elastic modulus;
d is a damage variable and represents the microcrack number in unit volume;
D E is the damage value at the time of complete fracture failure at position E;
D D is the damage value at the time of the complete fracture failure at the position D;
U D energy is consumed for coal rock mass damage;
determining the scale radius of the rock burst system based on the corresponding relation between the original rock energy generated by the modern construction stress place and the energy of the set surface wave magnitude; and determining the corresponding energy density as a third intensity level demarcation value based on the original rock energy and/or the surface wave magnitude energy and the rock burst system scale radius.
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