CN109100247B - Coal-like rock ground stress K point testing method based on Kaiser effect - Google Patents
Coal-like rock ground stress K point testing method based on Kaiser effect Download PDFInfo
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Abstract
The invention discloses a coal-like rock ground stress K point testing method based on Kaiser effect, which replaces a coal-like test piece with an undisturbed low-strength concrete test piece to reduce the influence caused by primary occurrence stress. The method comprises the steps of simultaneously collecting acoustic emission signals by two resonant frequency sensors, comprehensively and preliminarily determining Kaiser effect points by using 2 representative acoustic emission time domain parameters, simultaneously detecting the accuracy of the Kaiser effect points according to the distribution characteristics of main frequencies of the Kaiser effect points, finally verifying the Kaiser effect points again from the aspect of multi-frequency band energy distribution characteristics, and establishing 3 methods for mutual evidence and improving the test accuracy.
Description
Technical Field
The invention relates to the field of ground stress testing, in particular to a coal-like rock ground stress K point testing method based on an acoustic emission Kaiser effect.
Background
The existing ground stress testing methods comprise a hydraulic fracturing method, a stress relieving method, a strain recovery method, a drilling caving method, an acoustic emission Kaiser effect method and the like, wherein the acoustic emission Kaiser effect method has the advantages of simplicity, intuition and easiness in mass testing, and can realize fine testing of ground stress. The key of the Kaiser effect measurement ground stress is the selection of K point, the selection mode is continuously innovated on the original parameter selection method, meanwhile, a great deal of research is carried out on the effectiveness of the K point, and certain results are obtained.
Whether the stress borne by the coal in the occurrence process affects the acoustic emission Kaiser effect is not clear, so that the accuracy of the test cannot be judged when the acoustic emission Kaiser effect is used for testing the ground stress. Therefore, the undisturbed (or force calculable) concrete test piece is adopted to replace coal for carrying out ground stress test research, and the test accuracy can be judged.
At present, most achievements mainly adopt a single resonant frequency sensor to carry out acoustic emission signal acquisition on the rock existing in the crust in the whole process of destruction, and a single parameter is adopted for analysis when K points are determined.
Disclosure of Invention
In order to solve the support of the defects of the prior art, the invention provides a coal-like rock ground stress K point testing method based on an acoustic emission Kaiser effect, which adopts the following technical scheme:
a coal-like rock ground stress K point testing method based on an acoustic emission Kaiser effect comprises the following steps:
carrying out a uniaxial compression test on the coal-like rock test piece, determining a load peak value of the uniaxial compression test, carrying out uniaxial compression circulation on the coal-like rock test piece in a load loading mode according to the load peak value until the coal-like rock test piece is loaded to be damaged, monitoring by an acoustic emission monitoring system in the experimental process, and collecting an acoustic emission signal generated by the acoustic emission monitoring system;
analyzing the absolute energy of the acoustic emission signals acquired by the acoustic emission signal acquisition device and the Kaiser effect characteristic of acoustic emission of ringing count in different circulation processes, simultaneously carrying out Fourier transform on the signals acquired by the acoustic emission signal acquisition device, and counting the dominant frequency values of the signals in different circulation processes;
establishing a preliminary basis for judging K points according to the acoustic emission Kaiser effect characteristics of the acoustic emission absolute energy and the ringing count and the main frequency values of signals in different circulation processes;
and carrying out wavelet packet three-layer decomposition on the waveform near the preliminarily determined K point in different cyclic loading processes, counting the energy ratio of each frequency band, analyzing the change condition of the energy ratio of each frequency band in different cyclic loading processes, counting the frequency bands with high energy ratios, analyzing the distribution characteristics of the energy at the K point, and determining the K point.
In the step of carrying out the uniaxial compression test on the coal-rock-like test piece, the coal-rock-like test piece is tested by replacing an undisturbed concrete test piece.
The manufacturing process of the concrete test piece comprises the following steps:
airing the river sand, screening by using a 80-mesh sieve, and measuring the density;
uniformly coating the periphery of the test mold with engine oil, and pouring cement, screened river sand and water into the test mold according to a ratio;
standing for one day in a normal temperature environment after the test mold is manufactured, and then numbering and demolding; and (3) after the mould is removed, soaking the concrete test piece in water, preserving the heat, controlling the water temperature to be 20 ℃, and curing for 28 days.
The acoustic emission signal acquisition device is a resonance frequency sensor R6 alpha and a resonance frequency sensor NANO 30.
In the experimental process, an acoustic emission monitoring system is used for carrying out acoustic emission monitoring on the concrete test piece, wherein the acoustic emission monitoring system is a PCI-II and Disp acoustic emission monitoring system which are connected to the concrete test piece; the R6 alpha resonance frequency sensor is used for sensing and acquiring acoustic emission signals generated by the Disp acoustic emission monitoring system, and the NANO30 resonance frequency sensor is used for sensing and acquiring acoustic emission signals generated by the PCI-II acoustic emission monitoring system.
In the process of carrying out a uniaxial cyclic loading experiment on the concrete sample, the control mode adopts load loading, the cycle times are 4, the load value of each cyclic loading is 20%, 40%, 60% and 80% of the peak load of the concrete sample, and the loading and unloading rates are 0.1kN/s until the concrete sample is loaded to be damaged.
Different from the prior art, the coal-like rock ground stress K point testing method based on the acoustic emission Kaiser effect provided by the invention utilizes an undisturbed low-strength concrete test piece to replace a coal-like test piece so as to reduce the influence generated by the primary occurrence stress. The method comprises the steps of simultaneously collecting acoustic emission signals by two resonant frequency sensors, comprehensively and preliminarily determining Kaiser effect points by using 2 representative acoustic emission time domain parameters, simultaneously detecting the accuracy of the Kaiser effect points according to the distribution characteristics of main frequencies of the Kaiser effect points, finally verifying the Kaiser effect points again from the aspect of multi-frequency band energy distribution characteristics, and establishing 3 methods for mutual evidence and improving the test accuracy.
Drawings
FIG. 1 is a schematic flow diagram of a coal-like rock ground stress K point testing method based on an acoustic emission Kaiser effect.
FIG. 2 is a cumulative ringing count-absolute energy-time curve collected by two resonant frequency sensors when the applied load is 40% of the peak load in the coal-like rock ground stress K-point test method based on the acoustic emission Kaiser effect.
FIG. 3 is a cumulative ringing count-absolute energy-time curve collected by two resonant frequency sensors when the applied load is 60% of the peak load in the coal-like rock ground stress K-point test method based on the acoustic emission Kaiser effect.
FIG. 4 is a cumulative ringing count-absolute energy-time curve collected by two resonant frequency sensors when the applied load is 80% of the peak load in the coal-like rock ground stress K-point test method based on the acoustic emission Kaiser effect.
FIG. 5 is a cumulative ringing count-absolute energy-time curve collected by two resonant frequency sensors when the applied load is 100% of the peak load in the coal-like rock ground stress K-point test method based on the acoustic emission Kaiser effect provided by the invention.
FIG. 6 is a logic schematic diagram of a coal-like rock ground stress K point testing method based on an acoustic emission Kaiser effect.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.
In the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention.
Referring to fig. 1 and 6, fig. 1 is a schematic flow diagram of a coal-like rock ground stress K-point testing method based on an acoustic emission Kaiser effect, and fig. 6 is a schematic logic diagram of the coal-like rock ground stress K-point testing method based on the acoustic emission Kaiser effect. The method comprises the following steps:
s110: carrying out uniaxial compression test on the coal-like rock test piece, determining a load peak value of the uniaxial compression test, carrying out uniaxial compression circulation on the coal-like rock test piece in a load loading mode according to the load peak value until the coal-like rock test piece is loaded to be damaged, monitoring through an acoustic emission monitoring system in the experimental process, and collecting an acoustic emission signal generated by the acoustic emission monitoring system.
S120: and analyzing the absolute energy of the acoustic emission signals acquired by the acoustic emission signal acquisition device and the Kaiser effect characteristic of acoustic emission of ringing count in different circulation processes, simultaneously carrying out Fourier transform on the signals acquired by the acoustic emission signal acquisition device, and counting the dominant frequency values of the signals in different circulation processes.
S130: and establishing a preliminary basis for judging the K point according to the acoustic emission Kaiser effect characteristics of the acoustic emission absolute energy and the ringing count and the main frequency values of signals in different circulation processes.
S140: and carrying out wavelet packet three-layer decomposition on the waveform near the preliminarily determined K point in different cyclic loading processes, counting the energy ratio of each frequency band, analyzing the change condition of the energy ratio of each frequency band in different cyclic loading processes, counting the frequency bands with high energy ratios, analyzing the distribution characteristics of the energy at the K point, and determining the K point.
Preferably, in the step of performing the uniaxial compression test on the coal-rock-like test piece, the coal-rock-like test piece is tested by replacing an undisturbed concrete test piece.
Preferably, the manufacturing process of the concrete test piece comprises the following steps:
airing the river sand, screening by using a 80-mesh sieve, and measuring the density;
uniformly coating the periphery of the test mold with engine oil, and pouring cement, screened river sand and water into the test mold according to a ratio;
standing for one day in a normal temperature environment after the test mold is manufactured, and then numbering and demolding; and (3) after the mould is removed, soaking the concrete test piece in water, preserving the heat, controlling the water temperature to be 20 ℃, and curing for 28 days.
Preferably, the acoustic emission signal acquisition device is a resonant frequency sensor of R6 α and NANO 30. Preferably, in the experimental process, an acoustic emission monitoring system is used for carrying out acoustic emission monitoring on the concrete test piece, wherein the acoustic emission monitoring system is a PCI-II (peripheral component interconnect-express) and Disp (Disp) acoustic emission monitoring system which are connected to the concrete test piece; the R6 alpha resonance frequency sensor is used for sensing and acquiring acoustic emission signals generated by the Disp acoustic emission monitoring system, and the NANO30 resonance frequency sensor is used for sensing and acquiring acoustic emission signals generated by the PCI-II acoustic emission monitoring system.
Preferably, in the process of carrying out the uniaxial cyclic loading experiment on the concrete sample, the control mode adopts load loading, the cyclic times are 4, the load value of each cyclic loading is 20%, 40%, 60% and 80% of the peak load of the concrete sample, and the loading and unloading rates are both 0.1kN/s until the concrete sample is loaded to be damaged.
Specifically, the preparation method comprises the following steps of preparing a mixture of 1: 4. concrete test pieces having dimensions of 50mm by 100 mm. According to the proposal of the international rock mechanics society on the size of the laboratory sample, the non-parallelism of the two end faces of the prepared test piece is less than 0.05mm, and the two ends of the prepared test piece are polished by a SPM-250 double-disc lapping machine so as to ensure the test requirement. And carrying out rock mechanical test on the test pieces by a press machine, measuring the peak load, wherein the test quantity is not less than 5, the average value of the peak values is obtained, and the peak load value is 36kN after uniaxial compression test is carried out on the test pieces in the same batch.
And (3) carrying out uniaxial cyclic loading on the concrete test piece, wherein the control mode adopts load loading, the cyclic times are 4, finally, the concrete test piece is loaded to be damaged, the peak load of each cyclic loading is 20%, 40%, 60% and 80% of the peak load of the test piece measured before, and the loading and unloading rates are all 0.1 kN/s. Starting the PCI-II and Disp acoustic emission monitoring systems all the time from the first loading to the completion of the whole loading to monitor the damage process, and acquiring acoustic emission signals by using two sensors of R6 alpha and NANO30 in the test piece damage process. The PCI-II acoustic emission system is connected with the NANO30 resonant frequency sensor, and the Disp acoustic emission system is connected with the R6 alpha resonant frequency sensor. Each resonant frequency sensor is 2 for a total of 4.
Under the condition of 40% peak load level (second cycle loading), the absolute energy of the acoustic emission is increased firstly and then enters a calm-like period, the phenomenon that the ringing count is slowly increased can be used as a K point judgment basis, the error is less than 10%, and the sharp increase point of the peak value point of the absolute energy of the acoustic emission and the accumulated ringing count curve can not be judged as a Kaiser point. As shown in fig. 2. A certain interference signal exists in front of a signal K point acquired by the NANO30, and the R6 alpha and the NANO30 are combined together, so that interference can be effectively eliminated, and the accuracy is improved.
Under the condition of a peak load 60% level (third cyclic loading), the distribution characteristics of signals collected by the R6 alpha and the NANO30 resonant frequency sensors are obviously different, and the K point can be accurately judged by combining the commonalities of the two. The absolute energy can be greatly increased and then decreased, and the phenomenon that the ringing count curve is increased is taken as the criterion of the K point. As shown in fig. 3.
Under the condition of 80% peak load level (fourth cycle loading), the characteristic that absolute energy is sharply increased to a peak value and then sharply reduced can be selected as the basis for judging the K point, and the error is less than 10%. As shown in fig. 4. The distribution characteristics of the ring count and the absolute energy of the signal acquired by R6 alpha and the signal acquired by NANO30 are different, and the frequency of the high-value point of the absolute energy of the signal acquired by R6 alpha is more. Compared with the third cycle, the K point is judged according to the rule that the K point and the K point are consistent.
Under the condition of 100% peak load level (final loading), the phenomenon that absolute energy obviously increases and reaches a first peak point and a ringing curve starts to increase is taken as a criterion to be judged as a Kaiser point, the error of the Kaiser point is less than 10%, but certain error exists when a signal collected by R6 alpha is used for judging the K point, so that the accuracy and the reliability of K point judgment can be improved by combining the two types of sensors. As shown in fig. 5.
In the whole loading process, acoustic emission dominant frequencies acquired by the R6 alpha resonance frequency sensor are mainly distributed in two intervals of about 35-40kHz and 100kHz, signals acquired by the NANO30 resonance frequency sensor are mainly concentrated in the interval of 225-250kHz, and meanwhile, the fact that a high-frequency sensor acquires more low dominant frequency signals at the initial loading stage and before damage can be found. Throughout the cyclic loading process, the main distribution intervals of the acoustic emission signals are all contained in the three intervals. In the first four-cycle loading stage, the main frequency of the acoustic emission signal gradually develops from low frequency to high frequency, and during final loading, the main frequency of the signal appears in large quantities at high frequency and low frequency. Meanwhile, points before the major frequency of the acoustic emission appears are judged as K points, the error is less than 10%, and the K points are basically consistent with the theoretical K points.
On the basis of the judgment of the K points, in order to analyze the relation between the K point signal frequency component difference and the K points in each cyclic loading stage, the wave form near the K point in each cyclic loading stage is subjected to wavelet packet decomposition, the energy ratio of each frequency band is counted, the change rule of the energy ratio of each frequency band under different load levels is analyzed, and the K points are judged according to the rule.
The judgment methods of the K points in the cyclic loading stages are consistent, namely the characteristic that the energy of adjacent frequency bands at the K points is higher or lower is used as the basis for judging the K points. Taking the loading to the destruction stage as an example, for the R6 alpha resonant frequency sensor, the frequency bands of sudden increase and sudden decrease of the energy ratio are 0-62.5 kHz and 62.5-125 kHz; for the NANO30 resonant frequency sensor, the energy accounts for 187.5-250 kHz and 250-312.5 kHz of sudden increase and sudden decrease.
Different from the prior art, the coal-like rock ground stress K point testing method based on the acoustic emission Kaiser effect provided by the invention utilizes an undisturbed low-strength concrete test piece to replace a coal-like test piece so as to reduce the influence generated by the primary occurrence stress. The method comprises the steps of simultaneously collecting acoustic emission signals by two resonant frequency sensors, comprehensively and preliminarily determining Kaiser effect points by using 2 representative acoustic emission time domain parameters, simultaneously detecting the accuracy of the Kaiser effect points according to the distribution characteristics of main frequencies of the Kaiser effect points, finally verifying the Kaiser effect points again from the aspect of multi-frequency band energy distribution characteristics, and establishing 3 methods for mutual evidence and improving the test accuracy.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (5)
1. A coal-like rock crustal stress K point test method based on Kaiser effect is characterized by comprising the following steps:
carrying out a uniaxial compression test on the coal-like rock test piece, determining a load peak value of the uniaxial compression test, carrying out uniaxial compression circulation on the coal-like rock test piece in a load loading mode according to the load peak value until the coal-like rock test piece is loaded to be damaged, monitoring by an acoustic emission monitoring system in the experimental process, and collecting an acoustic emission signal generated by the acoustic emission monitoring system;
analyzing the absolute energy of the acoustic emission signals acquired by the acoustic emission signal acquisition device and the Kaiser effect characteristic of acoustic emission of ringing count in different circulation processes, simultaneously carrying out Fourier transform on the signals acquired by the acoustic emission signal acquisition device, and counting the dominant frequency values of the signals in different circulation processes; the acoustic emission signal acquisition device is a resonance frequency sensor R6 alpha and a resonance frequency sensor NANO 30;
establishing a preliminary basis for judging K points according to the acoustic emission Kaiser effect characteristics of the acoustic emission absolute energy and the ringing count and the main frequency values of signals in different circulation processes;
and carrying out wavelet packet three-layer decomposition on the waveform near the preliminarily determined K point in different cyclic loading processes, counting the energy ratio of each frequency band, analyzing the change condition of the energy ratio of each frequency band in different cyclic loading processes, counting the frequency bands with high energy ratios, analyzing the distribution characteristics of the energy at the K point, and determining the K point.
2. The Kaiser effect-based coal-like rock ground stress K-point testing method according to claim 1, wherein in the step of performing the uniaxial compression test on the coal-like rock test piece, the coal-like rock test piece is tested by using an undisturbed concrete test piece instead.
3. The coal-like rock ground stress K point testing method based on the Kaiser effect as claimed in claim 2, wherein the manufacturing process steps of the concrete test piece include:
airing the river sand, screening by using a 80-mesh sieve, and measuring the density;
uniformly coating the periphery of the test mold with engine oil, and pouring cement, screened river sand and water into the test mold according to a ratio;
standing for one day in a normal temperature environment after the test mold is manufactured, and then numbering and demolding; and (3) after the mould is removed, soaking the concrete test piece in water, preserving the heat, controlling the water temperature to be 20 ℃, and curing for 28 days.
4. The coal-like rock ground stress K point testing method based on Kaiser effect of claim 1, wherein in the experimental process, an acoustic emission monitoring system is used to perform acoustic emission monitoring on the coal-like rock test piece, wherein the acoustic emission monitoring system is a PCI-II and Disp acoustic emission monitoring system, and the PCI-II and Disp acoustic emission monitoring systems are connected to the coal-like rock test piece; the R6 alpha resonance frequency sensor is used for sensing and acquiring acoustic emission signals generated by the Disp acoustic emission monitoring system, and the NANO30 resonance frequency sensor is used for sensing and acquiring acoustic emission signals generated by the PCI-II acoustic emission monitoring system.
5. The coal-like rock crustal stress K point testing method based on the Kaiser effect as claimed in claim 1, wherein in the process of conducting the uniaxial cyclic loading experiment on the coal-like rock specimen, the control mode adopts load loading, the cyclic times are 4, the load value loaded in each cycle is 20%, 40%, 60% and 80% of the peak load of the coal-like rock specimen, and the loading and unloading rates are 0.1kN/s until the coal-like rock specimen is loaded to be damaged.
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