Coal rock damage stress threshold determination method

Abstract

The invention provides a coal rock damage stress threshold determination method. According to the method, an acoustic emission technology is adopted to continuously monitor the coal rock micro-fracture expansion process, and changes near a stress threshold are captured. According to the acoustic emission data node determination method based on derivative analysis, errors caused by manual node position judgment are avoided, a node result is more objective and reliable, and scientific processing of data is achieved. A coal rock damage stress threshold value database is established, the coal rock damage stress threshold value is quickly searched in combination with an interpolation algorithm, and quick acquisition of a stress threshold value result is realized.

Description

Technical Field

[0001] The present invention relates to the field of underground engineering safety technology, and in particular to a method for determining a coal rock damage stress threshold. Background Art

[0002] In the process of underground resource development and underground space utilization, with the continuous increase in mining depth, the stability of coal and rock has become increasingly prominent. During the implementation of underground projects, blasting and excavation operations will inevitably cause changes in the stress state of the surrounding coal and rock, and the coal and rock are in multiple complex mechanical environments. The change in stress state has a profound and complex impact on the threshold of coal and rock. Stress changes can act on coal and rock in various ways, such as loading, unloading or dynamic stress processes. With the increase of stress, the internal structure of coal and rock gradually changes, resulting in changes in its bearing capacity and deformation characteristics. At the same time, the long-term effect of stress may also induce the rheological behavior of coal and rock, further affecting its threshold. The reduction or unloading of stress may cause the threshold of coal and rock to recover or adjust to varying degrees. In summary, stress changes have an important impact on the changes in the stress threshold of coal and rock damage.

[0003] In the field of deep underground engineering in my country, coal rock stability assessment is an important means to ensure the safety of underground engineering. Changes in the coal rock damage stress threshold will bring great difficulties and instability to the coal rock stability assessment. Therefore, determining the coal rock damage stress threshold has become an important technology for assessing coal rock stability and achieving the safety of deep underground engineering. Relevant research results show that the coal rock fracture evolution process can be divided into the initial crack closure stage, elastic stage, crack stable extension stage and crack unstable extension stage based on closure stress, crack initiation stress, damage stress and peak stress. The threshold points in each stage represent the nodes of coal rock damage development and change. Determining the coal rock damage stress threshold can understand in advance under what stress state the coal rock begins to be damaged, thereby predicting the potential dangers that may be faced in underground resource development and underground space utilization.

[0004] However, the existing coal rock stress threshold determination method usually has low sensitivity in identifying stress thresholds. The macroscopic damage of coal rock can only be found after the stress reaches a certain threshold. It is difficult to detect the occurrence of damage in the early stage, and there are certain errors in the acquisition of damage stress. In addition, the International Association of Rock Mechanics has not yet given a recommended method for determining coal rock stress thresholds. At the same time, the research results of coal rock damage stress thresholds are scattered, and it is difficult to fully obtain and systematically integrate data, so it is impossible to fully utilize the coal rock damage stress threshold in practical applications.

[0005] Therefore, it is of great significance to provide a method for determining the stress threshold of coal rock damage. Summary of the invention

[0006] The purpose of the present invention is to provide a method for determining a coal rock damage stress threshold value to solve the problems existing in the prior art.

[0007] The technical solution adopted to achieve the purpose of the present invention is as follows: a method for determining a coal rock damage stress threshold comprises the following steps:

[0008] 1) Prepare the target coal rock into a coal rock sample.

[0009] 2) The coal-rock samples were subjected to a loading test, a cyclic loading and unloading compression test, a shear test, and a tensile test. During the experiment, an acoustic emission sensor was used to continuously collect the acoustic emission signals generated by the damage and rupture of the coal-rock samples to monitor the expansion and slip process of the coal-rock microcracks.

[0010] 3) According to the axial stress and acoustic emission ringing cumulative number data of coal and rock samples, the acoustic emission ringing cumulative number-axial stress initial curve is drawn.

[0011] 4) Perform a preliminary visual inspection of the acoustic emission ringing cumulative number-axial stress initial curve to determine the curve form, which includes the S-shaped Boltzmann curve, exponential growth curve and double S-shaped curve.

[0012] 5) Fit the acoustic emission ringing cumulative number-axial stress initial curve. Based on derivative analysis, the acoustic emission data node is determined as the damage stress threshold.

[0013] 6) Prepare different types of coal and rock samples, repeat steps 2) to 5), and obtain the damage stress thresholds of various types of coal and rock under different mechanical conditions. Use the interpolation algorithm to build a coal and rock damage stress threshold database.

[0014] 7) According to the actual working conditions and coal-rock conditions on site, the actual working stress conditions and coal-rock types are input into the database to obtain the damage stress threshold of the coal-rock on site under the corresponding working conditions.

[0015] Furthermore, in step 1), the large rock sample is processed into a cylindrical original rock sample with a size of 50×100 mm by cutting, grinding and polishing.

[0016] Further, when the curve conforms to the S-shaped Boltzmann curve form, step 5 specifically includes the following sub-steps:

[0017] A5.1) The initial curve is further fitted into an S-shaped Boltzmann curve.

[0018] A5.2) Let N be the cumulative number of acoustic emission, σ be the axial stress, and the data point sequence be (σ1, N1), (σ2, N2), … (σn, Nn). The slope at a certain point (σi, Ni) is Second Derivative Set the second derivative of the curve to zero Find the inflection point of the stable growth phase of the curve (x 0 -d x ln(2), ) and the inflection point of the destruction stage (x 0 +d x ln(2), ).

[0019] A5.3) After determining the positions of the two inflection points, draw the tangent lines at the two inflection points and find the intersection point of the two tangent lines (dσ+σ 0 , ), which is the damage stress threshold of coal rock.

[0020] Further, step A5.1) specifically includes the following sub-steps:

[0021] A5.1.1) Import the data into Origin software.

[0022] A5.1.2) Use nonlinear curve fitting in Origin software and select the Boltzmann function model.

[0023] A5.1.3) According to the data range and physical meaning, the fitting parameter A 1 , A 2 、x 0 and d x Set reasonable initial values ​​and constraints.

[0024] A5.1.4) Check the goodness of fit R in the fit report 2 If R 2 ≤0.95, then adjust A 1 , A 2 、x 0 and d x The value of R 2 Meets the requirements.

[0025] Furthermore, when the curve conforms to the form of an exponential growth curve, step 5 specifically includes the following sub-steps:

[0026] B5.1) The initial curve is further fitted into an exponential growth curve.

[0027] B5.2) Assume that the cumulative number of acoustic emission is N, the axial stress is σ, and the data point sequence is (σ 1 , N 1 ), (σ 2 , N 2 ), …(σ n , N n ), any point (σ i , N i ) is

[0028] B5.3) When a point k i =90%·k max , it is confirmed that the horizontal axis of this point is the damage stress threshold.

[0029] Further, step B5.1) specifically includes the following sub-steps:

[0030] B5.1.1) Import the data into Origin software.

[0031] B5.1.2) Use nonlinear curve fitting in Origin software and select the ExpDecay2 function model.

[0032] B5.1.3) Set reasonable initial values ​​for the fitting parameters A and k based on the data range and physical meaning.

[0033] B5.1.4) Check the goodness of fit R in the fit report 2 If R 2 ≤0.95, then adjust the values ​​of A and k until R 2 Meets the requirements.

[0034] Further, when the curve conforms to the double S-shaped curve form, step 5 specifically includes the following sub-steps:

[0035] C5.1) The initial curve is further fitted into a double S-shaped curve.

[0036] C5.2) Assume that the cumulative number of acoustic emission is N, the axial stress is σ, and the data point sequence is (σ 1 , N 1 ), (σ 2 , N 2 ), …(σ n , N n ). Any point (σ i , N i ) is The second-order derivative is

[0037] C5.3) The last set of points where the second-order derivative of the second segment of the curve is zero is the last inflection point, and the horizontal coordinate of this point is confirmed to be the damage stress threshold.

[0038] Further, step C5.1) specifically includes the following sub-steps:

[0039] C5.1.1) Import the data into Origin software.

[0040] C5.1.2) Use Open Dialog in Origin software and use New Function to define the custom function y=A1 / (1+exp(-(x-x01) / dx1))+A2 / (1+exp(-(x-x02) / dx2)).

[0041] C5.1.3) According to the data range and physical meaning, the fitting parameter A 1 , A 2 、x 01 、x 02 、dx 1 and dx 2 Set reasonable initial values.

[0042] C5.1.4) Check the goodness of fit R in the fit report 2 If R 2 ≤0.95, then adjust A 1 , A 2 、x 01 、x 02 、dx 1 and dx 2 The value of R 2 Meets the requirements.

[0043] The technical effects of the present invention are unquestionable:

[0044] A. Aiming at the problem that it is difficult to determine the stress threshold of coal rock damage, the advantages of acoustic emission being sensitive to tiny damage and having high accuracy in numerical fitting are fully combined to more clearly identify effective information related to coal rock damage and concisely characterize the characteristics of coal rock damage, thereby accurately obtaining the stress threshold of coal rock damage and providing support for ensuring the safety of deep underground engineering;

[0045] B. Aiming at the problem that the stress threshold of coal rock is affected by the type of coal rock and loading conditions, the interpolation algorithm is effectively used to construct a damage stress threshold database of various types of coal rock under different mechanical conditions, which can quickly find the damage stress threshold of coal rock according to actual working conditions and environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Flow chart of the method for determining the damage stress threshold of coal rock.

[0047] Figure 2 Schematic diagram of the acoustic emission probe layout. DETAILED DESCRIPTION

[0048] The present invention is further described below in conjunction with the embodiments, but it should not be understood that the above subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the art, which should all be included in the protection scope of the present invention.

[0049] Embodiment 1:

[0050] See also Figure 1 This embodiment provides a method for determining a coal rock damage stress threshold, comprising the following steps:

[0051] 1) Prepare the target coal rock into a coal rock sample.

[0052] 2) Compression, shear and tensile tests are performed on the coal and rock samples respectively. Compression, shear and tensile tests all include a single loading compression test and a cyclic loading and unloading test, and the experiments contain different stress paths. During the experiment, an acoustic emission sensor is used to continuously collect the acoustic emission signals generated by the damage and rupture of the coal and rock samples to monitor the expansion and slip process of the coal and rock microcracks. The acoustic emission sensor is attached to the surface of the fixed pressure head or the surface of the coal and rock sample.

[0053] 3) According to the axial stress and acoustic emission ringing cumulative number data of coal and rock samples, the acoustic emission ringing cumulative number-axial stress initial curve is drawn.

[0054] 4) Perform a preliminary visual inspection of the acoustic emission ringing cumulative number-axial stress initial curve to determine the curve form, which includes the S-shaped Boltzmann curve, exponential growth curve and double S-shaped curve.

[0055] 5) Fit the acoustic emission ringing cumulative number-axial stress initial curve. Based on derivative analysis, the acoustic emission data node is determined as the damage stress threshold.

[0056] 6) Prepare different types of coal and rock samples, repeat steps 2) to 5), and obtain the damage stress thresholds of various types of coal and rock under different mechanical conditions. Use the interpolation algorithm to build a coal and rock damage stress threshold database.

[0057] 7) According to the actual working conditions and coal-rock conditions on site, the actual working stress conditions and coal-rock types are input into the database to obtain the damage stress threshold of the coal-rock on site under the corresponding working conditions.

[0058] This embodiment provides a clear and systematic method to conveniently and accurately determine the stress threshold of coal rock, which has extremely important practical significance for engineering construction, design, construction and stability evaluation.

[0059] Embodiment 2:

[0060] The main contents of this embodiment are the same as those of embodiment 1, wherein in step 1), the large rock sample is processed into a cylindrical original rock sample with a size of 50×100 mm by cutting, grinding and polishing. The acoustic emission sensor is arranged at the following positions: Figure 2 The numbers in the figure represent the acoustic emission probe numbers.

[0061] Embodiment 3:

[0062] The main contents of this embodiment are the same as those of Embodiment 1 or 2, wherein when the curve conforms to the form of an S-shaped Boltzmann curve, step 5 specifically includes the following sub-steps:

[0063] A5.1) further fitting the initial curve into an S-shaped Boltzmann curve. Step A5.1) specifically includes the following sub-steps:

[0064] A5.1.1) Import the data into Origin software.

[0065] A5.1.2) Use nonlinear curve fitting in Origin software and select the Boltzmann function model.

[0066] A5.1.3) According to the data range and physical meaning, the fitting parameter A 1 , A 2 、x 0 and d x Set reasonable initial values ​​and constraints.

[0067] A5.1.4) Check the goodness of fit R in the fit report 2 If R 2 ≤0.95, then adjust A 1 , A 2 、x 0 and d x The value of R 2 Meets the requirements.

[0068] A5.2) Let N be the cumulative number of acoustic emission, σ be the axial stress, and the data point sequence be (σ1, N1), (σ2, N2), … (σn, Nn). The slope at a certain point (σi, Ni) is Second Derivative Set the second derivative of the curve to zero Find the inflection point of the stable growth phase of the curve (x 0 -d x ln(2), ) and the inflection point of the destruction stage (x 0 +d x ln(2), ).

[0069] A5.3) After determining the positions of the two inflection points, draw the tangent lines at the two inflection points and find the intersection point of the two tangent lines (dσ+σ 0 , ), which is the damage stress threshold of coal rock.

[0070] When the curve conforms to the exponential growth curve form, step 5 specifically includes the following sub-steps:

[0071] B5.1) further fitting the initial curve into an exponential growth curve. Step B5.1) specifically includes the following sub-steps:

[0072] B5.1.1) Import the data into Origin software.

[0073] B5.1.2) Use nonlinear curve fitting in Origin software and select the ExpDecay2 function model.

[0074] B5.1.3) Set reasonable initial values ​​for the fitting parameters A and k based on the data range and physical meaning.

[0075] B5.1.4) Check the goodness of fit R in the fit report 2 If R 2 ≤0.95, then adjust the values ​​of A and k until R 2 Meets the requirements.

[0076] B5.2) Assume that the cumulative number of acoustic emission is N, the axial stress is σ, and the data point sequence is (σ 1 , N 1 ), (σ 2 , N 2 ), …(σ n , N n ), any point (σ i , N i ) is

[0077] B5.3) When a point k i =90%·k max When , confirm that the horizontal coordinate of the point is the damage stress threshold. When the curve conforms to the double S-shaped curve form, step 5 specifically includes the following sub-steps:

[0078] C5.1) further fitting the initial curve into a double S-shaped curve. Step C5.1) specifically includes the following sub-steps:

[0079] C5.1.1) Import the data into Origin software.

[0080] C5.1.2) Use Open Dialog in Origin software and use New Function to define the custom function y=A1 / (1+exp(-(x-x01) / dx1))+A2 / (1+exp(-(x-x02) / dx2)).

[0081] C5.1.3) According to the data range and physical meaning, the fitting parameter A 1 , A 2 、x 01 、x 02 、dx 1 and dx 2 Set reasonable initial values.

[0082] C5.1.4) Check the goodness of fit R in the fit report 2 If R 2 ≤0.95, then adjust A 1 , A 2 、x 01 、x 02 、dx 1 and dx 2 The value of R 2 Meets the requirements.

[0083] C5.2) Assume that the cumulative number of acoustic emission is N, the axial stress is σ, and the data point sequence is (σ 1 , N 1 ), (σ 2 , N 2 ), …(σ n , N n ). Any point (σ i , N i ) is The second-order derivative is

[0084] C5.3) The last set of points where the second-order derivative of the second segment of the curve is zero is the last inflection point, and the horizontal coordinate of this point is confirmed to be the damage stress threshold.

[0085] This embodiment uses acoustic emission technology to continuously monitor the expansion and sliding process of coal and rock microcracks, capture changes near the stress threshold, and make up for the limited information provided by traditional methods (such as destructive test methods, stress-strain curves, etc.). A method for determining acoustic emission data nodes based on derivative analysis is proposed to avoid the errors caused by artificial determination of node positions, make node results more objective and reliable, and realize scientific processing of data. A coal and rock damage stress threshold database is established, and the coal and rock damage stress threshold is quickly found in combination with an interpolation algorithm, realizing the rapid acquisition of stress threshold results.

[0086] Embodiment 4:

[0087] The main contents of this embodiment are the same as those of embodiment 3, wherein in step A5.1.3), A 1 It can be initially set to the maximum value of the accumulated acoustic emission value, A 2 It can be initially set to the minimum value of the acoustic emission accumulation number, x 0 It can be initially set to the middle value of the stress data, d x Can be initially set to a small positive number or set to At the same time, parameter constraints can be set according to actual conditions, such as A 1 >A 2 , d x >0, etc., to ensure the rationality of the fitting results.

[0088] In step B5.1.3), A is set to the maximum value of the accumulated number of acoustic emission ringings, and k is set to 0.1 to 1.

[0089] In step C5.1.3), A 1 , A 2 The initial value is set to half of the maximum value of the acoustic emission ringing cumulative number data, x 01 、x 02 The initial value is set as the growth center point of the two stages, dx 1 and dx 2 Set to 5 or some other small value.

Claims

1. A method for determining a coal rock damage stress threshold, characterized in that: The following steps are involved: 1) preparing the target coal rock into a coal rock sample; 2) Compression, shear and tensile tests were performed on the coal and rock samples respectively; during the experiment, acoustic emission sensors were used to continuously collect acoustic emission signals generated by damage and rupture of the coal and rock samples to monitor the expansion process of microcracks in the coal and rock; 3) According to the axial stress and acoustic emission ringing cumulative number data of the coal and rock samples, draw the acoustic emission ringing cumulative number-axial stress initial curve; 4) Perform a preliminary visual inspection of the acoustic emission ringing cumulative number-axial stress initial curve to determine the curve form; the curve forms include S-shaped Boltzmann curve, exponential growth curve and double S-shaped curve; 5) Fitting the acoustic emission ringing cumulative number-axial stress initial curve; determining the acoustic emission data node as the damage stress threshold based on derivative analysis; 6) Prepare different types of coal and rock samples, repeat steps 2) to 5), and obtain the damage stress thresholds of various types of coal and rock under different mechanical conditions; and construct a coal and rock damage stress threshold database through an interpolation algorithm; 7) According to the actual working conditions and coal-rock conditions on site, the actual working stress conditions and coal-rock types are input into the database to obtain the damage stress threshold of the coal-rock on site under the corresponding working conditions.

2. A method for determining a coal rock damage stress threshold according to claim 1, characterized in that: In step 1), the large rock sample is processed into a cylindrical original rock sample with a size of 50×100 mm by cutting, grinding and polishing.

3. A method for determining a coal rock damage stress threshold according to claim 1, characterized in that: In step 2), the compression, shear and tensile tests all include a single loading compression test and a cyclic loading and unloading test, and the experiments include different stress paths.

4. A method for determining a coal rock damage stress threshold according to claim 1, characterized in that: When the curve conforms to the S-shaped Boltzmann curve form, step 5 specifically includes the following sub-steps: A5.1) further fitting the initial curve into an S-shaped Boltzmann curve; A5.2) Let N be the cumulative number of acoustic emission, σ be the axial stress, and the data point sequence be (σ1, N1), (σ2, N2), … (σn, Nn). The slope at a certain point (σi, Ni) is Second Derivative Set the second derivative of the curve to zero Find the inflection point of the stable growth phase of the curve Inflection point of destruction phase A5.3) After determining the positions of the two inflection points, draw the tangent lines at the two inflection points and find the intersection of the two tangent lines. That is the stress threshold of coal rock damage.

5. A method for determining a coal rock damage stress threshold according to claim 4, characterized in that: Step A5.1) specifically includes the following sub-steps: A5.1.1) Import the data into Origin software; A5.1.2) Use nonlinear curve fitting in Origin software and select the Boltzmann function model; A5.1.3) According to the data range and physical meaning, the fitting parameters A1, A2, x0 and d x Set reasonable initial values ​​and constraints; A5.1.4) Check the goodness of fit R in the fit report 2 If R 2 ≤0.95, then adjust A1, A2, x0 and d x The value of R 2 Meets the requirements.

6. A method for determining a coal rock damage stress threshold according to claim 1, characterized in that: When the curve conforms to the exponential growth curve form, step 5 specifically includes the following sub-steps: B5.1) further fitting the initial curve into an exponential growth curve; B5.2) Assume that the cumulative number of acoustic emission is N, the axial stress is σ, and the data point sequence is (σ1, N1), (σ2, N2), … (σ n , N n ), any point (σ i , N i ) is B5.3) When a point k i =90%·k max , it is confirmed that the horizontal axis of this point is the damage stress threshold.

7. A method for determining a coal rock damage stress threshold according to claim 6, characterized in that: Step B5.1) specifically includes the following sub-steps: B5.1.1) Import the data into Origin software; B5.1.2) Use nonlinear curve fitting in Origin software and select the ExpDecay2 function model; B5.1.3) Set reasonable initial values ​​for fitting parameters A and k according to the data range and physical meaning; B5.1.4) Check the goodness of fit R in the fit report 2 If R 2 ≤0.95, then adjust the values ​​of A and k until R 2 Meets the requirements.

8. A method for determining a coal rock damage stress threshold according to claim 1, characterized in that: When the curve conforms to the double S-shaped curve form, step 5 specifically includes the following sub-steps: C5.1) further fitting the initial curve into a double S-shaped curve; C5.2) Assume that the cumulative number of acoustic emission is N, the axial stress is σ, and the data point sequence is (σ1, N1), (σ2, N2), … (σ n , N n ); any point (σ i , N i ) is The second-order derivative is C5.3) The last set of points where the second-order derivative of the second segment of the curve is zero is the last inflection point, and the horizontal coordinate of this point is confirmed to be the damage stress threshold.

9. A method for determining a coal rock damage stress threshold according to claim 8, characterized in that: Step C5.1) specifically includes the following sub-steps: C5.1.1) Import the data into Origin software; C5.1.2) Use Open Dialog in Origin software and use New Function to define the custom function y=A1 / (1+exp(-(x-x01) / dx1))+A2 / (1+exp(-(x-x02) / dx2)); C5.1.3) According to the data range and physical meaning, the fitting parameters A1, A2, x 01 、x 02 , dx1 and dx2 set reasonable initial values; C5.1.4) Check the goodness of fit R in the fit report 2 If R 2 ≤0.95, then adjust A1, A2, x 01 、x 02 , dx1 and dx2 values, until R 2 Meets the requirements.

Images