CN111859702B - Method for judging rock burst dangerousness - Google Patents
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Abstract
The invention discloses a rock burst risk judging method, which is based on obtaining relevant parameters such as tensile strength, elastic modulus, crushing expansion coefficient of a coal seam roof rock and the like of a key layer rock through rock mechanical property test, and further comprises the following steps: calculating deflection of the key layer under the action of the overlying load, calculating the upper deflection limit when the key layer breaks, calculating the lower deflection limit when the key layer breaks, and establishing a rock burst risk judging model based on the deflection of the key layer. The invention establishes a method for judging the risk of rock burst, and judges the risk of the rock burst through calculating the deflection of a key layer.
Description
Technical Field
The invention relates to a rock burst risk judging method which is suitable for a production mine with rock burst threat.
Background
Along with the strategic western shift of coal mining planning in China, the coal mining depth is gradually increased, and the facing rock burst threat degree is also obviously enhanced. Underground rock burst of a coal mine becomes one of the major hidden trouble facing mine safety production, and domestic expert and scholars establish a three-factor mechanism, a strength weakening and impact reducing mechanism, a stress control theory, an impact starting theory, a disturbance response instability theory and the like to explain the occurrence mechanism of the rock burst, so that a series of rich research results are obtained. The method has been greatly developed in the aspect of rock burst prevention and control measures, but no method at present can fundamentally solve the problem of rock burst, and technologies such as early warning and distinguishing of the rock burst in coal mine production and the like are still to be further researched.
Disclosure of Invention
The invention aims to provide a rock burst risk judging method, which predicts the risk that rock burst is likely to occur in coal seam exploitation according to the relation between the deflection of a key layer, the mining thickness of a coal seam, the crushing expansion coefficient and the accumulated energy of the key layer, and is used for guiding underground rock burst prevention and control work and guaranteeing mine safety production.
In order to achieve the above purpose, the invention is realized by adopting the following technical scheme:
a rock burst risk judging method comprises the following steps:
1) Testing rock mechanical properties of the drilled rock core, and obtaining the tensile strength, the elastic modulus and the crushing expansion coefficient of the coal seam roof rock of the key layer rock;
2) Calculating deflection generated by the key layer under the action of the overlying load;
calculating the upper limit of deflection when the key layer is broken;
calculating the lower deflection limit when the key layer is broken;
3) And establishing a rock burst risk judging model based on the critical layer deflection, and judging the rock burst risk.
The invention is further improved in that in the step 2), the specific implementation method for calculating the deflection generated by the key layer under the action of the overlying load is as follows:
201 Determining a key layer position;
starting from the old top rock stratum, calculating the load of the nth layer rock stratum to the 1 st layer rock stratum, wherein the calculation formula is as follows;
wherein: q 1 | n -layer 1 loading of layer n, kN;
E 1 layer 1 modulus of elasticity, MPa;
h 1 、h i layer 1 and layer i thickness, m;
γ i i-th layer rock Dan Rongchong, kN/m 3 ；
If the layer n to layer 1 load is less than the layer n-1 to layer 1 load, then:
stiffness conditions: q 1 | n <q 1 | n-1 ；
The nth layer is a key layer, otherwise, the load of the n+1 layer to the nth layer is continuously calculated;
202 Calculating the span-drop distance of the old roof of the coal seam;
in different stages of working face propulsion, the boundary support forms before breaking of the old roof are different, and according to the support mode that one side is a goaf simply supported and the other three sides are fixedly supported, the old roof straddling distance is as follows:
wherein: a, an old roof span drop distance;
λ—the ratio of the working surface advance distance to the working surface length;
h, the thickness of the old roof;
δ s -tensile strength of the aged roof;
μ -poisson ratio;
203 Calculating a key layer falling distance;
according to the data observed in the production practice, the stratum collapse angle is 60 degrees, and the span-drop distance of the key layer, namely the stratum overhanging length La, is calculated according to the stratum collapse angle;
wherein: h is a c -distance between roof of coal seam to critical layer, m;
204 According to 201) calculating the static load q born by the key layer;
the dead load borne by the key layer is the gravity of the key layer per se plus the gravity of the rock mass between the key layer and the next hard rock layer above the key layer;
205 Calculating deflection generated by the key layer under the action of the overlying load;
the static load q born by the key layer is brought into a deflection calculation formula to obtain the deflection when the key layer is broken:
wherein: c-deflection coefficient;
q-the load to which the formation is subjected;
taking the smaller of the length and width dimensions of the mining-space strata;
e-modulus of elasticity;
h' -critical layer thickness;
μ -is poisson's ratio.
The invention is further improved in that in the step 2), the specific implementation method for calculating the deflection upper limit when the key layer is broken is as follows:
301 Calculating a spacing between the bottom of the key layer and the top of the cross-falling rock layer;
the thickness of the direct roof layer is Sigma h, taking the shadow thereof into considerationCoefficient of expansion on shatter P After that, the height of the pile after collapse is K P Σh, the height of the residual space that may be left between it and the old roof is:
Δ＝∑h+M c -K P ·∑h＝M c -∑h(K p -1)
wherein: Σh—direct top thickness;
M c -picking up;
K P taking the rock breaking expansion coefficient to be 1.1-1.4;
302 Combining the formulas of step 205) and step 301), calculating an expression when the spacing and deflection between the bottom of the key layer and the top of the cross-landing rock layer are equal;
303 Calculating an upper limit criterion for the key layer to generate fracture;
304 Judging according to 303) formula: when f<f kp When the key layer is broken, the key layer can be broken; when f is greater than or equal to f kp And the key layer is not broken.
The invention is further improved in that in the step 2), the specific implementation method for calculating the deflection lower limit when the key layer is broken is as follows:
401 Simplifying the stress of the key layer judged in the step 202) into a beam model with two ends fixedly supported;
402 Calculating bending moment M of roof strata and corner of bending sinking of roof strata
Wherein: q-the unit length converted load of the roof weight and overburden additional load, pa;
j-section moment of inertia of roof, m 4 ；
L a -the overhanging length of the top plate, m;
403 Calculating the accumulated bending elastic energy U of the key layer w ；
Wherein: m, bending moment of roof stratum, N.m;
-a corner of the roof strata bending sinking, rad;
404 Will 402) sum M inThe formula of (a) is brought into 303);
wherein: u (U) W -roof bending elastic energy, J;
q-unit load of overburden on key layer, pa;
L a -formation overhang length, m;
e-elastic modulus, pa;
j-stratum section moment of inertia, m 4 ；
405 Calculating moment of inertia of the key layer;
wherein: j-stratum section moment of inertia, m 4 ；
b, the width of the rectangular section of the key layer, m;
h' —the rectangular section height of the key layer, namely the thickness of the key layer, m;
406 Calculating the maximum deflection of the key layer;
wherein: la-length of beam, m;
j-stratum section moment of inertia, m 4 ；
q-unit load of overburden on key layer, pa;
e-elastic modulus, pa;
407 Combined formulas 406) and 404), the critical layer maximum deflection f) is derived U And its accumulated energy U w The relation between:
408 Calculating a critical deflection value of the critical layer to generate fracture;
409 Judging according to the formula 408): when f U <f, the key layer can be broken; when f U And when the temperature is not less than f, the key layer is not broken.
The invention is further improved in that the specific implementation method of the step 3) is as follows:
deflection f generated by a critical layer by energy accumulated by stress of the critical layer caused by coal seam mining u As a lower deflection limit for determining whether a high energy event has occurred; in addition, the maximum deflection of the key layer is limited by the falling space of the lower part, and the top plateThe volume of the broken rock layer expands to fill the lower goaf, so that the lower part of the key layer is supported, and the key layer lacks the breaking space and cannot generate a large energy event, thus the key layer deflection f which can be accommodated by the residual space of the lower part of the key layer Kp As an upper limit value of deflection for judging whether a large energy event occurs; accordingly, a criterion equation of occurrence of the large energy event is established:
f U ＜f＜f Kp
f U -lower deflection limit value, m, for critical layer fracture;
f, deflection generated by the key layer, m;
f Kp -upper limit value of deflection of critical layer breaking, m;
if f is satisfied U ＜f＜f Kp A large energy event may occur and the risk of rock burst is high; otherwise, no large energy event occurs, and the danger of rock burst is small.
The invention has at least the following beneficial technical effects:
the invention provides a method for judging the risk of rock burst, which is characterized in that a key layer in a bottom layer structure is found through analysis and calculation, a lower limit thickness value of the breaking of the key layer is calculated according to parameters such as a cross-falling expansion coefficient of a roof rock layer and the thickness of the key layer, the maximum elastic energy which can be gathered under the condition of the maximum deflection of the key layer is calculated, an upper limit thickness value of the breaking of the key layer is calculated, the actually measured thickness value of the key layer is compared with the upper limit thickness value and the lower limit thickness value of the key layer which are calculated theoretically, the possibility of occurrence of high energy time is judged, and the risk of rock burst is judged.
In summary, the rock burst risk judging method provided by the invention can judge the rock burst risk possibly occurring in coal mining, and has a guiding effect on the development of underground rock burst control work.
Drawings
FIG. 1 is a diagram of the steps in the practice of the present invention.
FIG. 2 is a schematic diagram showing the height of the residual space between the roof of the coal seam and the key layer after cross-shattering and expanding.
Fig. 3 is a schematic view of formation load calculation provided by the present invention.
Fig. 4 is a schematic diagram of calculating a critical layer drop distance according to an old top drop distance according to the present invention.
FIG. 5 is a schematic diagram of the calculation of the stress concentration elastic energy of the key layer provided by the invention.
Detailed Description
The invention is further described below with reference to the drawings and examples.
And judging the rock burst risk faced by the coal seam stoping according to the rock burst problem of a certain mine and related data.
As shown in fig. 1 to 4, the method for discriminating the rock burst risk provided by the invention comprises the following steps:
step 1: the coal seam impact tendency of the target mine is measured before stoping, so that the impact risk of the mine is shown, and the rock physical and mechanical parameters of the related rock sample are collected and tested in the stoping process;
step 2: calculating deflection generated by the key layer under the action of the overlying load;
(1) calculating and judging the position of the key layer;
(2) calculating the old roof falling distance;
(3) calculating a key layer falling distance;
(4) calculating the static load q born by the key layer;
(5) calculating deflection generated by the key layer under the action of the overlying load:
wherein: c-deflection coefficient;
q-the load to which the formation is subjected;
taking the smaller of the length and width dimensions of the mining-space strata;
e-modulus of elasticity;
h' -critical layer thickness;
μ -is poisson's ratio.
Step 3: calculating the upper limit of deflection when the key layer is broken;
(1) calculating the distance between the bottom of the key layer and the top of the straddling rock stratum;
(2) calculating the residual space height between the key layer and the old roof;
(3) calculating deflection when the distance and deflection between the bottom of the key layer and the top of the straddling rock stratum are equal;
wherein: Σh—direct top thickness;
bending moment of M-roof strata;
K P taking the rock breaking expansion coefficient to be 1.1-1.4;
(4) the calculated deflection is the upper deflection limit when the key layer breaks
Step 4: calculating the lower deflection limit when the key layer is broken;
(1) calculate M and
wherein: q-the unit length converted load of the roof weight and overburden additional load, pa; j-section moment of inertia of roof, m 4 ；
L a -the overhanging length of the top plate, m;
(2) calculating the accumulated bending elastic energy U of the key layer w ；
Wherein: u (U) W -roof bending elastic energy, J;
q-unit load of overburden on key layer, pa;
L a -formation overhang length, m;
e-elastic modulus, pa;
j-stratum section moment of inertia, m 4 ；
(3) Calculating a moment of inertia of the key layer;
wherein: j-stratum section moment of inertia, m 4 ；
b, the width of the rectangular section of the key layer, m;
h' —the rectangular section height of the key layer, namely the thickness of the key layer, m;
(4) calculating the maximum deflection of the key layer;
wherein: la-length of beam, m;
j-stratum section moment of inertia, m 4 ；
q-unit load of overburden on key layer, pa;
e-elastic modulus, pa;
(5) calculating a lower limit deflection value of the fracture generated by the key layer;
step 5: establishing a rock burst risk discrimination model based on critical layer deflection;
f U ＜f＜f Kp
if f is satisfied U ＜f＜f Kp A large energy event may occur and the risk of rock burst is high; otherwise, no large energy event occurs, and the danger of rock burst is small.
The foregoing is illustrative of the present invention and is not to be construed as limiting thereof, but rather, the present invention is to be construed as limited to the appended claims.
Claims (2)
1. The method for discriminating the rock burst risk is characterized by comprising the following steps of:
1) Testing rock mechanical properties of the drilled rock core, and obtaining the tensile strength, the elastic modulus and the crushing expansion coefficient of the coal seam roof rock of the key layer rock;
2) The deflection generated by the key layer under the action of the overlying load is calculated, and the specific implementation method is as follows:
201 Determining a key layer position;
starting from the old top rock stratum, calculating the load of the nth layer rock stratum to the 1 st layer rock stratum, wherein the calculation formula is as follows;
wherein: q 1 | n -layer 1 loading of layer n, kN;
E 1 layer 1 modulus of elasticity, MPa;
h 1 hi—layer 1 and i thickness, m;
γ i i-th layer rock Dan Rongchong, kN/m 3 ；
If the layer n to layer 1 load is less than the layer n-1 to layer 1 load, then:
stiffness conditions: q 1 | n <q 1 | n-1 ；
The nth layer is a key layer, otherwise, the load of the n+1 layer to the nth layer is continuously calculated;
202 Calculating the span-drop distance of the old roof of the coal seam;
in different stages of working face propulsion, the boundary support forms before breaking of the old roof are different, and according to the support mode that one side is a goaf simply supported and the other three sides are fixedly supported, the old roof straddling distance is as follows:
wherein: a, an old roof span drop distance;
λ—the ratio of the working surface advance distance to the working surface length;
h, the thickness of the old roof;
δ s -tensile strength of the aged roof;
μ -poisson ratio;
203 Calculating a key layer falling distance;
according to the data observed in the production practice, the stratum collapse angle is 60 degrees, and the span-drop distance of the key layer, namely the stratum overhanging length La, is calculated according to the stratum collapse angle;
wherein: h is a c -distance between roof of coal seam to critical layer, m;
204 According to 201) calculating the static load q born by the key layer;
the dead load borne by the key layer is the gravity of the key layer per se plus the gravity of the rock mass between the key layer and the next hard rock layer above the key layer;
205 Calculating deflection generated by the key layer under the action of the overlying load;
the static load q born by the key layer is brought into a deflection calculation formula to obtain the deflection when the key layer is broken:
wherein: c-deflection coefficient;
q-the load to which the formation is subjected;
taking the smaller of the length and width dimensions of the mining-space strata;
e-modulus of elasticity;
h' -critical layer thickness;
μ -poisson ratio;
the upper deflection limit when the key layer is broken is calculated, and the specific implementation method is as follows:
301 Calculating a spacing between the bottom of the key layer and the top of the cross-falling rock layer;
the collapse thickness of the direct roof stratum is Sigma h, and the influence of the direct roof stratum on the coefficient of crushing expansion K is considered P After that, the height of the pile after collapse is K P Σh, the height of the residual space that may be left between it and the old roof is:
Δ＝∑h+M c -K P ·∑h＝M c -∑h(K p -1)
wherein: Σh—direct top thickness;
M c -picking up;
K P taking the rock breaking expansion coefficient to be 1.1-1.4;
302 Combining the formulas of step 205) and step 301), calculating an expression when the spacing and deflection between the bottom of the key layer and the top of the cross-landing rock layer are equal;
303 Calculating an upper limit criterion for the key layer to generate fracture;
304 Judging according to 303) formula: when f<f kp When the key layer is broken, the key layer can be broken; when f is greater than or equal to f kp When the method is used, the key layer is not broken;
the lower deflection limit when the key layer is broken is calculated, and the specific implementation method is as follows:
401 Simplifying the stress of the key layer judged in the step 202) into a beam model with two ends fixedly supported;
402 Calculating bending moment M of roof strata and corner of bending sinking of roof strata
Wherein: q-the unit length converted load of the roof weight and overburden additional load, pa;
j-section moment of inertia of roof, m 4 ；
L a -the overhanging length of the top plate, m;
403 Calculating the accumulated bending elastic energy U of the key layer w ；
Wherein: m, bending moment of roof stratum, N.m;
-a corner of the roof strata bending sinking, rad;
404 Will 402) sum M inThe formula of (a) is brought into 303);
wherein: u (U) W -roof bending elastic energy, J;
q-unit load of overburden on key layer, pa;
L a -formation overhang length, m;
e-elastic modulus, pa;
j-stratum section moment of inertia, m 4 ；
405 Calculating moment of inertia of the key layer;
wherein: j-stratum section moment of inertia, m 4 ；
b, the width of the rectangular section of the key layer, m;
h' —the rectangular section height of the key layer, namely the thickness of the key layer, m;
406 Calculating the maximum deflection of the key layer;
wherein: la-length of beam, m;
j-stratum section moment of inertia, m 4 ；
q-unit load of overburden on key layer, pa;
e-elastic modulus, pa;
407 Combined formulas 406) and 404), the critical layer maximum deflection f) is derived U And its accumulated energy U w The relation between:
408 Calculating a critical deflection value of the critical layer to generate fracture;
409 Judging according to the formula 408): when f U <f, the key layer can be broken; when f U When the critical layer is not less than f, the critical layer is not broken;
3) And establishing a rock burst risk judging model based on the critical layer deflection, and judging the rock burst risk.
2. The method for discriminating the risk of rock burst according to claim 1 wherein the specific implementation method of step 3) is as follows:
deflection f generated by a critical layer by energy accumulated by stress of the critical layer caused by coal seam mining u As a lower deflection limit for determining whether a high energy event has occurred; in addition, the maximum deflection of the key layer is limited by the falling space of the lower part, the volume of the broken roof strata can expand to fill the lower goaf, so that the lower part of the key layer is supported, and a large energy event cannot be generated due to the lack of the broken space of the key layer, thus the deflection f of the key layer which can be accommodated by the residual space of the lower part of the key layer Kp As an upper limit value of deflection for judging whether a large energy event occurs; accordingly, a criterion equation of occurrence of the large energy event is established:
f U ＜f＜f Kp
f U -lower deflection limit value, m, for critical layer fracture;
f, deflection generated by the key layer, m;
f Kp -upper limit value of deflection of critical layer breaking, m;
if f is satisfied U ＜f＜f Kp A large energy event may occur and the risk of rock burst is high; otherwise, no large energy event occurs, and the danger of rock burst is small.
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| CN106934178A (en) * | 2017-04-07 | 2017-07-07 | 中国矿业大学 | A kind of island working face adopts preceding danger of burst Pre-Evaluation method |
| AU2020100227A4 (en) * | 2020-02-16 | 2020-03-26 | Xi'an University Of Science And Technology | Method for determining coal wall rib spalling of large mining-height fully-mechanized mining face of shallow coal seam |
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| AU2020100227A4 (en) * | 2020-02-16 | 2020-03-26 | Xi'an University Of Science And Technology | Method for determining coal wall rib spalling of large mining-height fully-mechanized mining face of shallow coal seam |
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| 强冲击大采高工作面关键层周期破断规律研究;赵雷;王俊峰;;陕西煤炭(03);全文 * |
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