CN111027787B - Real-time prediction method for inducing coal and gas outburst based on fault slip instability - Google Patents
Real-time prediction method for inducing coal and gas outburst based on fault slip instability Download PDFInfo
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Abstract
The invention discloses a real-time prediction method for inducing coal and gas outburst based on fault slippage instability, aiming at the high correlation between faults and outburst, applying tribology and speed state friction criteria, comprehensively considering factors such as fault occurrence shape, activation evolution characteristic influence, physical and mechanical characteristics of coal at a mining site, ground stress, gas migration characteristic and the like, describing the friction slippage state and the slippage instability characteristic in a fault area at the mining site under laboratory conditions, establishing a slippage instability criterion, and finally combining stress and gas dynamic data measured on site to realize the real-time prediction of the outburst. The method disclosed by the invention gives consideration to all parameter characteristics and fault structure activation slippage of the excavation site conditions, is suitable for real-time accurate prediction of local areas of the excavation site, and can play a certain theoretical guidance for coal and gas outburst prevention and control.
Description
Technical Field
The invention belongs to the fields of geology and coal mine gas disaster prevention and control, and particularly relates to a real-time prediction method for inducing coal and gas outburst based on fault slip instability.
Background
Coal and gas outburst is a phenomenon that coal and gas broken under the action of stress are suddenly sprayed to a mining space in large quantity. Coal and gas outburst has great destructiveness, seriously threatens the safety production of coal mines and the life safety of coal mine workers, and is a main factor for restricting the safety and high-efficiency production of the coal mines. China is one of the most serious countries in the world with coal and gas outburst, and in recent years, the coal mine outburst risk is increasing along with the deepening of mining depth and the increase of mining intensity. Therefore, it is an urgent technical problem to accurately realize the real-time prediction of coal and gas outburst.
According to research and investigation, the occurrence of coal and gas outburst is directly related to geological structures, particularly fault structures have a leading effect on the occurrence of the coal and gas outburst, for example, more than 85% of coal and gas outburst in Huainan mining areas are related to the fault structures. Therefore, it is an essential component for studying the dynamic phenomenon of mine outburst to investigate the process of fault structure activation slip instability under the influence of mining.
The fault structure is taken as an important factor influencing the outburst, a plurality of students develop research work on fault-induced coal and gas outburst prediction, and most of the students describe the outburst tendency under the action of stress distribution characteristics and gas occurrence migration characteristics based on gas geology and structure physics; however, these methods only perform qualitative and static feature descriptions on the tectonic geology and the gas geology, and these descriptions are based on macroscopic and overall analysis, which is difficult to be applied to the prominent real-time prediction of the local coal body region in front of the mining working face. The current real-time outburst prediction means generally adopted by the mining working face only considers field data such as ground stress, gas pressure and the like, and the influence on fault structure activation slippage is not described; therefore, an effective real-time prediction means suitable for fault structure induction prominence in the field is not available at present.
Therefore, it is important to realize real-time prediction of the induced outburst of the fault structure as a key point for researching coal and gas outburst. At present, the prediction aiming at fault structure induced protrusion is mostly based on macroscopic and qualitative prediction and fracture caused by the site condition of a mining working face; the existing field prediction means only considers local conditions and lacks the connection with fault structure activation slip characteristics, so that the realization of real-time and accurate prominent prediction of a mining working face field under the influence of the fault structure is difficult to realize. Therefore, it is necessary to overcome the existing technical defects, and it is important to design a prominent real-time prediction that can describe the fault dynamic activation mechanism and also consider the factors of site stress, gas pressure, coal and rock physical mechanics, etc.
Disclosure of Invention
The invention provides a real-time prediction method for inducing coal and gas outburst based on fault slippage instability, which aims to solve the problems in the current real-time prediction technical method for inducing coal and gas outburst to fault structure; the method simulates the activation sliding process of the fault of the coal rock containing gas through a test, and analyzes the friction coefficient of the sliding block under multiple factors and the evolution characteristics of sliding instability, thereby carrying out risk evaluation prediction on fault induced outburst based on the friction coefficient and the evolution characteristics.
The invention uses the related theories of fault tribology, speed-state friction law and the like, and considers that the process that the coal and rock slip body generates friction slip instability in the fault and fault area is highlighted, in the process, the separation belt generates slow sliding displacement along with the coal body due to the space difference of the shear strength, the separation belt reaching the shear strength is firstly damaged, and the local area generates instantaneous sliding; then, due to the redistribution of the physical structure of the slip body and the mechanical field, the new barrier band continues to prevent the slip tendency of the coal, and the slip body enters a locked state; with the redistribution of the landing stress and the gas action, the slip continues to generate slow friction slip behavior and continues the process, and if a new state of the barrier zone still cannot effectively lock the slip in the process, the slip instability, namely the coal and gas outburst, occurs.
The invention provides a real-time prediction method for inducing coal and gas outburst based on fault slip instability, which comprises the following steps:
s1: sampling:
firstly, acquiring a corresponding coal rock sample near a fault according to a geological data map of a mining area;
s2: preparing a coal/rock laboratory coal rock sample:
cutting a plurality of blocky coal/rock samples with uniform texture and 10 x 20cm surface size, processing coal/rock sample interfaces to reach set roughness, wrapping the coal samples by nylon adhesive tapes to expose slip surfaces, respectively placing the two blocky coal/rock samples in an experimental device, and sealing;
s3: preparation of the test:
placing the glass tube in a set constant-temperature environment, checking the air tightness, and then carrying out vacuum-pumping treatment;
s4: the test was carried out:
firstly, a predetermined normal stress sigma is applied to a coal rock sample 1 Then applying a predetermined gas pressure p 1 To the set value and maintaining the gas pressureKeeping the adsorption time constant, and fully adsorbing the coal sample for 24 hours; after full adsorption, the air outlet is opened and the data acquisition system is started, after the flow is stable, a speed step sliding test with the sliding speed of 1-10 mu m/s-1 mu m/s is carried out, and the shear stress tau measured at each moment is continuously monitored and recorded 1 And a sliding displacement;
s5: after a test period is finished, replacing the coal rock sample, changing the applied gas pressure and the normal stress again, continuing to perform the processes of S3 and S4 to obtain the friction coefficient under each given condition, and then obtaining the crustal stress and the gas pressure threshold parameter inducing outburst through the established slip instability criterion;
s6: and continuously collecting outburst risk parameters during the advancing process of the mining working face and comparing the outburst risk parameters with threshold parameters, so as to carry out outburst real-time prediction based on the outburst risk parameters.
In the geological related field, the experiment adopts simplified coal rock blocks to simulate fault friction slip as a conventional means, and the speed-state friction law obtained based on laboratory results is widely applied in field practice and has good applicability.
The specific requirements for obtaining the coal rock sample in the S1 are as follows: and obtaining a friction slip object in the region according to the position of a fault near a preset forward propulsion working face, performing coal-coal or coal-rock slip, and obtaining a coal/rock sample with the same physical and mechanical properties as the coal/rock sample so as to ensure that the block slip of the laboratory is as close to the field condition as possible.
The roughness setting in S2 is determined by analyzing the geometrical morphology characteristics of the actual fault, and specifically comprises the following steps: recording local geometric morphology characteristics of a fault plane according to a field survey and equipment detection method, then establishing a corresponding joint roughness model based on a self-similar fractal theory, and finally preparing a coal rock sample with corresponding joint roughness by using computer software and a 3D printer.
S2 the roughness preparation purpose is as follows: the similarity of the friction slip behavior characteristics of the friction slip block and the natural condition fault under the same condition is ensured as much as possible.
In S2, the coal sample is wrapped by the Ni Long Jiaodai and only the sliding surface of the coal sample is exposed, so that gas can flow from the friction sliding interface of the coal rock sample as far as possible, and the gas flow in a fracture layer is simulated.
In the S4, the value ranges of the preset normal stress and the preset gas pressure are estimated according to the field conditions, and the preset normal stress is determined by calculating the stress change of the fault slip surface under the excavation condition through the actual fault occurrence, the burial depth condition and the numerical simulation; and the preset gas pressure value range is estimated and determined according to the burial depth and the geological condition.
And S4, the estimation of the preset normal stress and the gas pressure can enable the stress and gas pressure values of the experimental conditions to be as close to the field conditions as possible and reduce the value range, so that the stress and gas pressure values under the same test times are finer, and the accuracy of the outburst prediction is improved.
The friction coefficient in S5 is calculated by the following formula:
in the formula of i Is the friction coefficient at a certain moment and is a constant; tau is i 、σ i 、p i Friction force, normal stress and gas pressure in the current state are respectively, and the unit is MPa;
the slip instability criterion and threshold in the S5 are obtained specifically as follows:
first, a change law of the friction coefficient after the change of the sliding speed is described:
in the formula v 0 And v is the speed before and after the change, unit um/s, respectively; μ is the coefficient of friction after the velocity change is v, μ 0 Is a velocity v before change 0 Coefficient of friction at steady state; theta is a state variable characterizing the contact area in front ofThe sliding history of (1), namely, the state variable of the previous moment has influence on the state variable of the next moment; a. b is an empirical constant associated with the experiment, D C Is the critical sliding distance, um, i.e. the sliding distance required during steady sliding at a certain speed to steady sliding at another speed;
and fitting according to the test and the formula to obtain corresponding values of a and b, considering that the outburst occurs when the slip instability occurs when a is less than b, and recording the gas pressure and the normal stress threshold value when the slip instability occurs.
It should be noted that: mu.s i Refers to the coefficient of friction at a certain time or at a certain displacement, which is related only to the effective positive stress and friction; and mu 0 Coefficient of friction before and after a change in velocity, respectively, where 0 It can be seen that the constant (coefficient of friction in steady state before speed change) is known, and μ is a function related to speed and friction history, which emphasizes that the coefficient of friction is affected by the friction history. Mu and mu 0 What is essentially described is the μ in different friction histories (i.e., different moments or displacements) under the influence of a change in velocity i The change rule of (2).
Regarding the action mechanism of the values of a and b for the slip instability, the instantaneous slip speed of the coal rock mass tends to infinity due to the slip instability, so that the reduction of the friction coefficient can generate the effect of promoting the slip when the speed is increased, and finally the slip instability is caused; the change of the friction coefficient in the process is directly related to a and b, and is further explained in conjunction with a schematic diagram. Through research and study, various national scholars consider that: the dimensionless parameters a and b can be used directly when the laboratory derived speed-state friction law is used on natural faults.
The danger parameters in the S6 comprise ground stress and gas pressure, and the normal stress of the fault slip surface is further calculated based on the ground stress parameters;
all parameters are obtained by means of ground stress test and gas drilling pressure measurement respectively.
The invention has the advantages that: aiming at the high correlation between faults and outburst, the friction principle of tribology and speed state is applied, the factors of fault occurrence shape and appearance, activation evolution characteristics, coal physical and mechanical characteristics, ground stress, gas migration characteristics and the like are comprehensively considered, the friction slip state and the slip instability characteristics in the fault area of the mining site are described under the laboratory condition, the slip instability criterion is established, and finally the outburst real-time prediction is realized by combining the stress and gas dynamic data measured on the site. The method disclosed by the invention gives consideration to all parameter characteristics and fault structure activation slippage of the excavation site conditions, is suitable for real-time accurate prediction of local areas of the excavation site, and can play a certain theoretical guidance for coal and gas outburst prevention and control.
Drawings
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings, in which:
fig. 1 is a flow chart provided by an embodiment of the present invention.
Fig. 2 is a schematic diagram of an experimental apparatus provided in an embodiment of the present invention.
Fig. 3 is a schematic diagram provided by an embodiment of the present invention.
FIGS. 4 and 5 are graphs illustrating examples of a friction coefficient-rate step test provided by an embodiment of the present invention, wherein FIG. 4 is an example of a slip instability occurring when a < b; FIG. 5 shows an example where a > b indicates that a stability slip occurs.
In fig. 2: 1-coal rock sample, 2-slip plane and 3-gas channel, wherein 301 is a gas inlet, and 302 is a gas outlet.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings; the preferred embodiments are merely illustrative of the present invention and are not intended to limit the scope of the present invention.
FIG. 1 is a flow chart provided by an embodiment of the present invention; FIG. 2 is a schematic diagram of an experimental apparatus provided in an embodiment of the present invention; FIG. 3 is a schematic diagram provided by an embodiment of the present invention; FIGS. 4 and 5 are graphs illustrating examples of a friction coefficient-rate step test provided by an embodiment of the present invention, wherein FIG. 4 is an example of a slip instability occurring when a < b; FIG. 5 shows an example where a > b indicates that a stability slip occurs. The invention provides a real-time prediction method for inducing coal and gas outburst based on fault slip instability, which comprises the following steps.
The method for predicting the tunnel driving process under the influence of the fault zone of a certain high gas mine in Shanxi needs the following processes, such as the following steps:
s1: sampling:
firstly, according to a geological data map of a certain mining area in Shanxi, corresponding coal and sandstone samples near a fault are obtained.
The specific sampling requirement of S1 is as follows: according to the fault position near the preset front propelling working surface, coal and sandstone samples with the same physical and mechanical properties are obtained through analysis.
S2: coal and sandstone sample laboratory coal and rock sample preparation.
A plurality of blocky coal and sandstone samples with uniform texture and 10 x 20cm surface size are cut, the coal and rock sample interfaces are all processed to reach the set roughness, the nylon adhesive tape is used for wrapping the coal samples and only exposing the sliding surfaces of the coal samples, so that gas only flows from the sliding interfaces, and then the two coal and rock samples are respectively arranged in an experimental device and are sealed.
The roughness setting in S2 is determined by analyzing the geometrical morphology characteristics of the actual fault, and specifically comprises the following steps: recording local geometric morphology characteristics of a fault plane according to a field survey and equipment detection method, then establishing a corresponding joint roughness model based on a self-similar fractal theory, and finally preparing a coal rock sample with corresponding joint roughness by using computer software and a 3D printer.
S3: preparation of the test:
and placing the glass substrate in a set constant-temperature environment, checking the airtightness, and then vacuumizing.
S4: the test was carried out with the schematic diagram of the test apparatus as shown in FIG. 2:
firstly, a predetermined normal stress sigma is applied to a coal rock sample 1 1 Then a predetermined gas pressure p is applied to the gas inlet 301 1 When the pressure reaches a set value, keeping the gas pressure unchanged, and fully adsorbing the coal sample 1 for 24 hours; after full adsorption, the gas outlet 302 is opened and the data acquisition system is started, after the flow is stable, a speed step length sliding test with the sliding speed of 1-10 mu m/s-1 mu m/s is carried out, and the shearing stress measured at each moment is continuously monitored and recordedForce τ 1 And a sliding displacement.
In the S4, the value ranges of the preset normal stress and the preset gas pressure are estimated according to the field conditions, and the preset normal stress is determined by calculating the stress change of the fault slip surface under the excavation condition through the actual fault occurrence, the burial depth condition and the numerical simulation; and the preset gas pressure value range is estimated and determined according to the burial depth and the geological condition. The preset normal stress and the gas pressure are refined by combining the value range obtained by field condition estimation, so that the prediction is more accurate.
Through calculation and analysis: the normal stress of the fault slip band is in the range of 6.0-10MPa, and the gas pressure is 2-3MPa; in the test, the preset normal stress is 6.0, 7.0, 8.0, 9.0 and 10.0MPa, and the gas pressure is 2.0, 2.3, 2.6 and 3.0MPa; and respectively carrying out 20 groups of experiments according to the preset values.
S5: and after a test period is finished, replacing the coal rock sample, changing the applied gas pressure and the normal stress again, continuing to perform the processes of S3 and S4 to obtain the friction coefficient under each given condition, and then obtaining the crustal stress and the gas pressure threshold parameter inducing the outburst through the established slip instability criterion.
The friction coefficient in S5 is calculated by the following formula:
in the formula of i Is the friction coefficient at a certain moment and is a constant; tau is i 、σ i 、p i The friction force, the normal stress and the gas pressure in the current state are respectively expressed in MPa.
The slip instability criterion and threshold in the S5 are obtained specifically as follows:
first, a change law of the friction coefficient after the change of the sliding speed is described:
in the formula v 0 And v is the speed before and after the change, unit um/s, respectively; μ is the coefficient of friction after the velocity change is v, μ 0 Is a velocity v before change 0 Coefficient of friction at steady state; theta is a state variable and is used for representing the sliding history before the contact surface, namely the state variable at the previous moment has influence on the state variable at the next moment; a. b is an empirical constant associated with the experiment, D C Is the critical sliding distance, um, that is, the sliding distance required during steady sliding at one speed to steady sliding at another speed.
And fitting according to the test and the formula to obtain corresponding values of a and b, considering that the outburst occurs when the slip instability occurs when a is less than b, and recording the gas pressure and the normal stress threshold value when the slip instability occurs.
About mu i Mu and mu 0 The relationship of (1), as shown in FIG. 3, μ i I.e. the coefficient of friction at a certain displacement, i.e. the curve of the coefficient of friction in the figure is mu during the whole slip i A set of (a); while mu 0 Then the velocity is v 1 Coefficient of friction at steady state, μ is velocity from v 1 The change being v 2 Followed by a coefficient of friction that varies with friction slip.
Corresponding a and b values can be obtained through fitting according to a test and the formula, and the instantaneous slip speed of the coal rock mass tends to infinity due to the slip instability, so that the reduction of the friction coefficient can generate the effect of promoting the slip when the speed is increased, and finally the slip instability is caused. The value of the schematic diagram such as 3,a and b determines the change rule of the friction coefficient after the speed is increased; wherein the value a plays a role in promoting friction stability, and the value b plays a role in promoting friction slip instability; based on this, when a < b, the friction coefficient is lowered, and at this time, the occurrence of slip destabilization is considered to be prominent.
The test has twenty groups of data, and is classified according to the values of a and b: an exemplary graph of the test results of a < b and a > b is shown in FIG. 4 and FIG. 5; FIG. 4 shows an example where a < b indicates that slip destabilization occurs, and FIG. 5 shows an example where a > b indicates that stability slip occurs.
As shown in FIG. 4, in order to further improve the reliability of the slip destabilization phenomenon that a < b occurs with the increase of the speed, the last speed value is set to 20.0um/s, and the rule that a < b occurs with the increase of the speed is still met.
And analyzing the test group in which a is less than b, namely the occurrence of the slip instability, recording the gas pressure and the normal stress threshold when the slip instability occurs, and finding that the condition that a is less than b occurs under the condition that the gas pressure is more than 2.6MPa and the normal stress is less than 7 MPa.
S6: and continuously collecting outburst risk parameters in the advancing process of the tunneling working face, and comparing the outburst risk parameters with threshold parameters, so as to carry out outburst real-time prediction based on the outburst risk parameters.
The danger parameters in the S6 comprise ground stress and gas pressure, and the normal stress of the fault slip surface is further calculated based on the ground stress parameters;
the parameters are respectively obtained by means of ground stress test, gas drilling pressure measurement and the like. .
In the ground stress test, the values and the stress directions of the vertical principal stress, the maximum horizontal principal stress and the minimum horizontal principal stress are respectively measured, and then the normal stress value of the fault slip surface can be calculated by combining the distance of the fault structure and the structural characteristics.
Comparing the actually measured normal stress value and gas pressure of the fault slip surface with threshold parameters, and considering that the fault slip surface has a prominent danger when the conditions that the gas pressure is more than 2.6MPa and the normal stress is less than 7MPa are met.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit of the corresponding technical solutions and scope of the present invention as defined in the appended claims.
Claims (6)
1. A real-time prediction method for inducing coal and gas outburst based on fault slip instability is characterized by comprising the following steps: the method comprises the following steps:
s1: sampling:
firstly, acquiring corresponding coal/rock samples near a fault according to a geological data map of a mining area;
s2: coal/rock laboratory coal/rock sample preparation:
cutting a plurality of blocky coal/rock samples with uniform texture and 10 x 20cm surface size, processing coal/rock sample interfaces to reach set roughness, wrapping the coal/rock samples by using nylon adhesive tapes to expose slip surfaces, and then respectively placing the two blocky coal/rock samples in an experimental device and sealing;
s3: preparation of the test:
placing the glass tube in a set constant-temperature environment, checking the air tightness, and then carrying out vacuum-pumping treatment;
s4: the test was carried out:
first of all, a predetermined normal stress sigma is applied to the coal/rock sample 1 Then applying a predetermined gas pressure p 1 When the pressure reaches a set value, keeping the gas pressure unchanged, and fully adsorbing the coal/rock sample for 24 hours; after full adsorption, the air outlet is opened and the data acquisition system is started, after the flow is stable, a speed step sliding test with the sliding speed of 1-10 mu m/s-1 mu m/s is carried out, and the shear stress tau measured at each moment is continuously monitored and recorded 1 And a sliding displacement;
s5: changing the coal/rock sample after a test period is finished, changing the applied gas pressure and the normal stress again, continuing to perform the processes of S3 and S4 to obtain the friction coefficient under each given condition, and then obtaining the crustal stress and the gas pressure threshold parameter inducing the outburst through the established slip instability criterion;
s6: and continuously collecting outburst risk parameters during the advancing process of the mining working face and comparing the outburst risk parameters with threshold parameters, so as to carry out outburst real-time prediction based on the outburst risk parameters.
2. The method for predicting coal and gas outburst in real time based on fault slip instability as claimed in claim 1, wherein: the specific requirements for obtaining the coal/rock sample in the S1 are as follows: and obtaining a friction slip object in the region according to the fault position near the preset forward propulsion working face, performing coal-coal or coal-rock slip, and obtaining a coal/rock sample with the same physical and mechanical properties as the coal/rock sample.
3. The method for predicting coal and gas outburst in real time based on fault slip instability as claimed in claim 1, wherein: the roughness setting in S2 is determined by the analysis of the geometric morphology features of the actual fault, and specifically comprises the following steps: recording local geometric features of the fault plane according to a field survey and equipment detection method, then establishing a corresponding joint roughness model based on a self-similar fractal theory, and finally preparing a coal/rock sample with corresponding joint roughness by using computer software and a 3D printer.
4. The method for predicting coal and gas outburst in real time based on fault slip instability as claimed in claim 1, wherein: in the S4, the value ranges of the preset normal stress and the preset gas pressure are estimated according to the field conditions, and the preset normal stress is determined by calculating the stress change of the fault slip surface under the excavation condition through the actual fault occurrence, the burial depth condition and the numerical simulation; and the preset gas pressure value range is estimated and determined according to the burial depth and the geological condition.
5. The method for predicting coal and gas outburst in real time based on fault slip instability as claimed in claim 1, wherein: the friction coefficient in S5 is calculated by the following formula:
in the formula of i Is the friction coefficient at a certain moment and is a constant; tau is i 、σ i 、p i Friction force, normal stress and gas pressure at corresponding moments are respectively expressed in MPa;
the slip instability criterion and threshold in the S5 are obtained specifically as follows:
first, a change law of the friction coefficient after the change of the sliding speed is described:
in the formula v 0 And v is the speed before and after the change, unit um/s, respectively; μ is the coefficient of friction after the velocity change is v, μ 0 Is a velocity v before change 0 Coefficient of friction at steady state; theta is a state variable and is used for representing the sliding history before the contact surface, namely the state variable at the previous moment has influence on the state variable at the next moment; a. b is an empirical constant associated with the experiment, D C Is the critical sliding distance, with unit um, that is, the sliding distance required from stable sliding at a certain speed to stable sliding at another speed;
and (3) obtaining corresponding values of a and b according to the test and the fitting of the formula, considering that the outburst occurs when the slip instability occurs when a is less than b, and recording the gas pressure and the normal stress threshold value when the slip instability occurs.
6. The method for predicting coal and gas outburst in real time based on fault slip instability as claimed in claim 1, wherein: the danger parameters in the S6 comprise ground stress and gas pressure, and the normal stress of the fault slip surface is further calculated based on the ground stress parameters;
all parameters are obtained by means of ground stress test and gas drilling pressure measurement respectively.
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