CN112434418B - Method for estimating kinetic energy of impact caused by mining - Google Patents
Method for estimating kinetic energy of impact caused by mining Download PDFInfo
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Abstract
The invention discloses a method for estimating impact kinetic energy caused by mining, which comprises the steps of firstly calculating the kinetic energy in a coal body when different mining footage is obtained, obtaining an approximate linear relation between the kinetic energy of different plastic zone widths and the required mining footage when different levels of kinetic energy are formed according to the calculation result, further obtaining the relation between a critical footage L and the plastic zone width, obtaining the corresponding critical footage of a medium to be detected under a certain plastic zone width according to the relation, and comparing the estimated mining footage with the obtained critical footage to judge whether the kinetic energy is generated. The invention can provide basis for determining a reasonable footage range for coal mine stope face mining, thereby effectively avoiding rock burst caused by kinetic energy generated by the change of coal bed supporting pressure and improving the safety of coal mine production.
Description
Technical Field
The invention belongs to the technical field of coal mining, and particularly relates to a method for evaluating the danger of rock burst by calculating the kinetic energy in a coal body induced by the change of supporting pressure caused by the mining of a coal mining working face.
Background
In the process of coal mine stope face mining and roadway tunneling, due to the release of deformation energy, the coal rock mass around a mine roadway and a stope generates sharp and violent dynamic destruction characteristics, namely, impact on rock burst, so that casualties are caused and must be prevented and controlled.
In the aspect of the induction mechanism, more research is focused on the level of overall release of strain energy, and it is considered that accumulation of sufficient unstable energy is a necessary condition for occurrence, development and maintenance of sudden disasters. From the storage and release angle of seismic energy, when a certain volume of coal rock mass is mined, local stress concentration is inevitably caused, meanwhile, elastic strain energy is stored in the coal rock mass, and when the coal rock mass is damaged or impacted, the stored energy is released. On the technical level, researchers visually find out a shocking ground pressure nucleation area and a space-time evolution law of an energy density cloud later by adopting a microseismic accumulated energy density cloud picture, and define a shocking ground pressure potential danger area in advance. In the process of mining the coal mining working face, the supporting pressure acting on the coal bed continuously migrates to the front of the coal body, so that the aggregation deformation energy of the coal body in the range of the supporting pressure is changed, and a part of the deformation energy is released to promote the plastic deformation and damage of the coal body, namely the coal body is dissipated in a working mode and is a root cause of the breakage of the coal body; the other part is converted into kinetic energy which is the root of coal body power instability and induces rock burst. However, according to the change of the coal bed supporting pressure, the size of the kinetic energy of the coal bed stope face under different mining footings is directly determined, so that whether the danger of rock burst exists is judged, and the research on the aspect does not see the report of similar research at home and abroad at present.
Chinese patent application No. 2018113008391 discloses a rock burst initiation energy threshold determining method and a rock burst predicting method, which determine rock burst initiation energy according to indoor experiments, and establish the relationship between elastic strain energy accumulated by unit coal bodies and rock burst initiation energy threshold, thereby carrying out early warning on rock burst. The technology comprehensively considers the strength and deformation characteristics of the coal rock mass, can better reflect the distribution state of the energy value of the mined coal rock mass, and has certain applicability to predicting rock burst. However, the supporting pressure of the coal seam is changed continuously in different coal seams and different mining depths, the corresponding mining footage is changed accordingly, and the change of the coal body kinetic energy in the supporting pressure influence range cannot be determined according to the indoor test. A method for effectively estimating kinetic energy generated by bearing pressure change is provided by adopting a mechanical analysis method, and the method is very important.
Disclosure of Invention
The invention aims to provide a method for estimating the impact kinetic energy caused by mining according to the change of the bearing pressure of a coal seam.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for estimating kinetic energy of mining-induced impacts, comprising the steps of:
firstly, determining the original rock stress of a coal seam to be mined as gamma H;
wherein: gamma is the volume weight of overburden, and is typically 25000N/m 3 ；
H is the thickness of the overburden in m.
Second, calculate different mining footage as Δ Kinetic energy in coal body at l time
Respectively smaller and larger than the plastic region width R according to the mining footage Delal p The analysis is carried out, and the specific steps are as follows:
1. when the mining footage delta l is less than or equal to R p The kinetic energy contained in a unit working face length is determined according to the formula (1):
in the formula:
k c is the stress concentration coefficient;
k is the rigidity of the coal body to be measured, and the elastic modulus of the coal body to be taken under the unit working face length is unit Pa;
Δ l is the mining footage of the working face of the coal seam to be measured, and the unit is m;
R p the width of the plastic zone of the coal bed to be measured is unit m.
Because the mechanical condition for generating the dynamic energy is that the increased supporting pressure after the coal seam is pushed for one footage under the unit working face length of the coal seam is necessarily greater than zero, based on the increased supporting pressure, delta l is required>0.8R p Since Δ l is lower than 0.8R p When the pressure is reduced, the rock burst can not occur, and l is not calculated to be lower than 0.8R p Kinetic energy in the coal body.
2. When the mining footage Deltal>R p The kinetic energy contained in the unit working face length is calculated according to the formulas (2) and (3)
In the formula:
ΔF 2 the bearing pressure is increased after a footage is pushed for the length of the working surface of the coal seam unit, and the unit is N.
Calculating the widths R of different plastic zones according to the formula p Next, the kinetic energy at the advancing length Δ l is mined.
Thirdly, setting the minimum kinetic energy E capable of inducing the coal seam to be mined to generate rock burst c I.e. the rock burst pressure kinetic constant threshold value, and according to the calculation result of the second step obtaining the widths R of different plastic zones p The mining footage required for forming different levels of kinetic energy is determined by the plastic zone width R p The horizontal coordinate and the mining footage delta l are vertical coordinates to obtain the widths R of different plastic zones p The approximate linear relationship between the formation of the different levels of kinetic energy and the desired production footage, i.e. each level of kinetic energy corresponds to an approximate line from which the minimum kinetic energy E is found when the kinetic energy is the minimum c The corresponding straight line reflects the critical footage L c And R p In relation to (1), i.e. L c ＝F(R p )；
Fourthly, determining the width R of the plastic zone of the coal body to be mined p According to the critical footage L obtained in the third step c And R p Obtaining the critical footage L of the coal body to be mined c Judging the width R of the coal body to be mined in the plastic zone p According to the set mining footage Δ Mining whether kinetic energy is generated or not; when judging, the set mining footage of the coal body to be detected Δ L and its critical footage L c Comparing, if the set mining footage Δ L exceeds the critical footage L c And judging that kinetic energy is generated, and making corresponding adjustment to prevent the generation of larger kinetic energy in the mining process from inducing rock burst.
The invention has the positive effects that:
in the coal mining process, even if the same mining working face is adopted, the supporting pressure of the coal bed can be changed, the mining footage needs to be adjusted at any time to adapt to the change of the supporting pressure, the mining footage cannot be adjusted at will, the mining footage is too small, the mining efficiency is too low, the mining footage is too large, and potential safety hazards exist, so that the maximum implementation of the propelling speed under the condition of ensuring safety is particularly important. The method calculates the width of a plastic zone in front of a working face to be R according to the change of the supporting pressure acted on the coal bed caused by the mining of the stope face p The mining footage is Δ l, the kinetic energy in the coal body is large or small; by estimating the magnitude of the kinetic energy, a basis can be provided for determining a reasonable footage range for the coal mine stope face mining, so that rock burst caused by the kinetic energy generated by the change of the coal bed supporting pressure can be effectively avoided, and the safety of coal mine production is improved.
Drawings
FIG. 1 shows that the mining footage Deltal is smaller than the plastic region width R p A model diagram of the time coal body supporting pressure analysis;
FIGS. 2a-2c show different R values at a buried depth of 800m p 、Δl(0.8R p <Δl≤R p ) Graph of kinetic energy change of coal body, wherein R is shown in figure 2a p The kinetic energy of the coal body changes when the distance is 6-10m, and R is shown in FIG. 2b p The kinetic energy of the coal body varies from 11 to 15m, and R is shown in FIG. 2c p The change situation of the kinetic energy of the coal body when the coal body is 16-20 m;
FIG. 3 shows that the advancing length Δ l is larger than the plastic region width R p A model diagram of the time coal body supporting pressure analysis;
FIG. 4 shows different R at a buried depth of 800m p 、Δl(Δl>R p ) A coal body kinetic energy change diagram; wherein FIG. 4a shows R p The kinetic energy of the coal body changes when the distance is 6-10m, and R is shown in FIG. 4b p The kinetic energy of the coal mass at 11-15m, and R is shown in FIG. 4c p The change situation of the kinetic energy of the coal body when the coal body is 16-20 m;
FIG. 5 shows different R at a buried depth of 800m p Forming a footage map of the kinetic energy of different levels;
fig. 6 is a schematic block diagram of the kinetic energy generation process of the present invention.
Detailed Description
The method of the invention is further described below in terms of a specific implementation of a stope face at a certain depth of burial.
Different coal beds, different mining depths and widths R of plastic zones of the coal beds p Will be different. In order to analyze the widths R of different plastic regions p Under the condition of different footage deltal, the kinetic energy and the change rule thereof in the influence range of the supporting pressure are taken as examples, the embodiment takes a stope face with the burial depth of 800m as an example, namely the dead weight stress is gamma H which is 20MPa, the elastic modulus K of a coal body is 2.0GPa, the width of a plastic zone of the stope face is set to be 6-20m, and the rock burst is predicted by the method shown in figure 6, and the specific method is as follows:
the first step is as follows: is calculated at R p Under the condition of 6-20m, the kinetic energy of the coal body in the influence range of the supporting pressure is divided into two cases during calculation:
case 1: the length of the ruler is delta l less than the width R of the plastic zone p
For the convenience of calculation, the support pressure distribution is linearized. As shown in fig. 1, the mining footage is Δ l, which is less than the plastic region width R p . The distance from the maximum bearing pressure to the original rock stress area is R e The stress of the original rock is gamma H, and the peak value of the supporting pressure is k c γ H, wherein k c For the stress concentration coefficient, 2.5 may be generally adopted.
Then the mining advances Δ Before L, the coal body supporting pressure distribution is shown as a dotted line above the coal body in fig. 1, and then the coal body with the length L is stressed as follows:
mining advance Δ After L, the coal body supporting pressure distribution is shown as the solid line above the coal body in fig. 1, and then the coal body with the length L is stressed as follows:
then Δ F 1 Comprises the following steps:
thus, the mechanical condition for generating kinetic energy is obtained as Δ F 1 Must be greater than zero, then it is obtained by equation (6):
when k is c When 2.5 is taken, there is Δ l>0.8R p 。
The kinetic energy contained per working face length in this case is then:
obtaining R according to equation (8) p Under the condition of 6-20m, calculating the change condition of the kinetic energy in the influence range of the supporting pressure, and calculating the current footage to be 0.8R p ＜Δl≤R p The generated kinetic energy is plotted with the mining footage as abscissa and the kinetic energy as ordinate, and curves corresponding to different plastic zone widths are shown in fig. 2a-2 c. From the same curve it can be seen that: under the condition that the width of the plastic zone is constant, the larger the advancing length is, the larger the generated kinetic energy is, so that the limit of the propelling speed is an engineering requirement for preventing and controlling the impact dynamic disaster. Comparing different curves, it can be seen that when the ruler is advanced for a certain time, the larger the width of the plastic area is, the smaller the kinetic energy is generated.
Case 2: the length of the feed bar is delta l larger than the width R of the plastic zone p
As shown in FIG. 3, when the buried depth is shallow, or the coal body strength is high, the plastic failure area of the coal seam under the action of the supporting pressure is small, and the length Δ l is larger than the width R of the plastic area p The situation (2).
Then the mining advances Δ Before L, the coal body supporting pressure distribution is shown as a dotted line above the coal body in fig. 3, and then the coal body with the length L is stressed as follows:
mining advance Δ After L, the coal body supporting pressure distribution is shown as the solid line above the coal body in fig. 3, and then the coal body with the length L is stressed as follows:
then Δ F 2 Comprises the following steps:
to facilitate analysis, take R e ＝3R p ，k c 2.5, then Δ F 2 Conversion to:
the kinetic energy contained per unit length of working surface in this case is then:
obtaining R according to equation (13) p Under the condition of 6-20m, calculating the change condition of the kinetic energy in the influence range of the supporting pressure when the advancing ruler delta l is larger than the width R of the plastic zone p Kinetic energy is generated. Similarly, the footage is taken as the abscissa and the kinetic energy is taken as the ordinate, and curves corresponding to different plastic zone widths are drawn as shown in fig. 4a to 4c, and it can be seen from the graphs that for different plastic zone widths, the kinetic energy of the system tends to increase along with the increase of the footage, but the increase of the kinetic energy shows the phenomenon of separation after the "approximate synchronization" is performed. When the plastic region R is as shown in FIG. 4a p Approximately synchronizing before the footage delta l is less than or equal to 20m when the footage is 6-10 m;when the plastic region R is shown in FIG. 4b p Approximately synchronizing before the footage delta l is less than or equal to 32m when the footage is 11-15 m; when plastic region R shown in FIG. 4c p Approximately synchronous before the footage delta l is less than or equal to 45m when the footage is 16-20 m. This shows that when the advancing footage exceeds the plastic zone, the internal stress adjustment and kinetic energy conversion of the supporting pressure zone are mainly controlled by the elastic zone of the coal body, and once strong kinetic energy is formed, or the coal body has extremely strong capability of bearing the kinetic energy and cannot be damaged; or the coal body is damaged by strong elasticity and brittleness, and strong dynamic pressure impact is formed.
Calculating the widths R of different plastic zones according to the formula p Next, the kinetic energy generated when the footage is Δ l.
The second step is that: setting the minimum kinetic energy capable of inducing the coal seam to be measured to generate rock burst as E c Is 10 5 J, namely the rock burst pressure kinetic energy constant threshold value, and obtaining the plastic zone width R according to the calculation result of the first step p Form 10 under 6-20m 4 J、10 5 J、10 6 J and 10 7 J mining footage required by four different levels of kinetic energy, and the footage is respectively determined by the plastic zone width R p The abscissa and the ordinate are the mining footage, and the widths R of different plastic zones shown in FIG. 5 are obtained p The approximate linear relationship between the formation of different levels of kinetic energy and the desired production footage, from which the minimum kinetic energy E is found c Namely 10 5 The straight line corresponding to the time J, i.e. the straight line a shown in fig. 5, the relation between the mining footage corresponding to the straight line a and the plastic zone width is the critical footage L c And R p The relationship of (1), namely:
L c ＝0.8089R p +0.8506
where 0.8089 is the slope of the line a and 0.8506 is the intercept of the line a.
As can be seen in fig. 5, for a given kinetic energy level, the larger the plastic zone, the larger the footage that needs to be achieved, in a linearly increasing relationship. Alternatively, a small approach length can produce high kinetic energy for a small plastic region. The larger the extraction footage, the greater the kinetic energy developed at a constant plastic zone. Therefore, when the range of the coal plastic zone is small, the mining propulsion speed is limited and the size of the kinetic energy is reduced by comprehensively considering the buried depth, the coal strength and the like; and the width of a plastic failure area is artificially increased by means of loosening blasting and the like to form a protective structure for blocking kinetic energy.
The third step: actually measuring to obtain the plastic region width R of the coal body p And according to the critical footage L obtained in the second step c And R p Obtaining the critical footage L by the relation of c Judging that it has a width R in the plastic region p Then, according to the mining footage estimated and set in advance Δ And l, mining, judging the magnitude of generated kinetic energy, and estimating the danger degree of the rock burst. When judging, see the specific R p Whether the mining footage exceeds the critical footage L c If it is less than the critical footage L c The mining is safe; if the mining footage exceeds the critical footage L c If a certain risk of rock burst exists, the advancing speed of mining is limited, kinetic energy is reduced, or the width of a plastic failure area is artificially increased by means of drilling pressure relief, hydraulic fracturing, loosening blasting and the like, so that a protective structure for blocking the kinetic energy is formed. This fully verifies the reliability and scientificity of the method.
It is to be understood that the above description is not intended to limit the present invention, and the present invention is not limited to the above examples, and those skilled in the art may make modifications, alterations, additions or substitutions within the spirit and scope of the present invention.
Claims (1)
1. A method of estimating mining induced impact kinetic energy, comprising the steps of:
firstly, determining the original rock stress of a coal seam to be mined as gamma H
Wherein: gamma is the volume weight of overburden, unit N/m 3 ；
H is the thickness of the overburden, in m;
secondly, calculating the kinetic energy in the coal body when the different mining footage is delta l
Respectively smaller according to the mining footage delta lAt and above the plastic region width R p The method comprises the following specific steps:
1. when the mining footage delta l is less than or equal to R p The kinetic energy contained in a unit working face length is determined according to the formula (1):
in the formula:
k c is the stress concentration coefficient;
k is the rigidity of the coal body to be measured, and the elastic modulus of the coal body to be taken under the unit working face length is unit Pa;
delta l is the mining footage of the working face of the coal bed to be measured, and the unit is m;
R p the width of the plastic zone of the coal bed to be measured is unit m;
2. when the mining footage Deltal>R p The kinetic energy contained in the unit working face length is calculated according to the formulas (2) and (3)
In the formula:
ΔF 2 the bearing pressure increased after advancing a footage for the length of the unit working face of the coal seam is unit N;
calculating the widths R of different plastic zones according to the formula p Next, exploiting the kinetic energy when the footage is delta l;
thirdly, setting the minimum kinetic energy E capable of inducing the coal seam to be mined to generate rock burst c I.e. the rock burst pressure kinetic constant threshold value, and according to the calculation result of the second step obtaining the widths R of different plastic zones p The mining footage required for forming different levels of kinetic energy is determined by the plastic zone width R p For lying onMarking and mining footage delta l is a vertical coordinate to obtain widths R of different plastic zones p The approximate linear relationship between the formation of the different levels of kinetic energy and the desired production footage, i.e. each level of kinetic energy corresponds to an approximate line from which the minimum kinetic energy E is found when the kinetic energy is the minimum c The corresponding straight line reflects the critical footage L c And R p In relation to (1), i.e. L c ＝F(R p )；
Fourthly, determining the width R of the plastic zone of the coal body to be mined p According to the critical footage L obtained in the third step c And R p Obtaining the critical footage L of the coal body to be mined c Judging the width R of the coal body to be mined in the plastic zone p Then, mining according to a set mining footage delta l to determine whether kinetic energy is generated or not; when judging, the set mining footage delta L of the coal body to be detected and the critical footage L thereof are set c Comparing, if the set mining footage Delal exceeds the critical footage L c And judging that kinetic energy is generated, and making corresponding adjustment to prevent the generation of larger kinetic energy in the mining process from inducing rock burst.
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