CN113203627B - Method for testing and evaluating mechanical heterogeneity of rock based on acoustic emission - Google Patents
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Abstract
The invention relates to a rock mechanics heterogeneity test evaluation method based on acoustic emission, which comprises the following steps of firstly, selecting a complete stratum to be tested; secondly, drilling a complete stratum to be detected to obtain a rock core column; secondly, processing the core column to prepare a rock sample; secondly, arranging acoustic emission sensors on two sides of the rock sample; and secondly, recording data measured by the acoustic emission sensor in the splitting experiment process, counting the number of acoustic emission signal events according to the recorded data, calculating the total number of acoustic emission events, the fracture component ratio coefficient of the rock sample and the heterogeneous coefficient of the rock, and evaluating the mechanical heterogeneous degree of the rock by using the heterogeneous coefficient of the rock. According to the mechanical response heterogeneity characteristic of the rock, the mechanical response heterogeneity characteristic of the rock is obtained according to the heterogeneity coefficient; the rock sample is convenient to manufacture, simple to calculate and high in practicability, quantitative evaluation of the heterogeneity inside the rock is facilitated, and evaluation and classification of the quality of the underground engineering surrounding rock are promoted.
Description
Technical Field
The invention belongs to the field of testing of rock mechanical heterogeneity characteristics of deep underground engineering, and particularly relates to a rock mechanical heterogeneity testing and evaluating method based on acoustic emission.
Background
The heterogeneity is an important index for evaluating the strength, deformation and self-energy storage capacity of the rock material, and particularly has different requirements on the heterogeneity of the rock material under different engineering background conditions in the field of deep underground engineering. For example, the requirement of underground impact protection engineering on rock materials is high strength but the cascading of damage is outstanding, which requires the heterogeneity of the rock materials to be outstanding, thereby avoiding the surrounding rock from appearing a rock burst dynamic damage form.
The evaluation of rock heterogeneity at home and abroad mainly comprises a rock core observation method, an X-CT scanning method, a logging identification method, a cast body slice method and the like. In the methods, microscopic components are adopted to analyze the homogeneity degree of the rock, mechanical heterogeneity caused by the difference of the texture of the rock is not considered, and the mechanical heterogeneity of rock materials has more remarkable influence on the macroscopic properties of the underground engineering surrounding rock in essence.
Therefore, the existing method is not comprehensive in evaluating the heterogeneity of the rock, and the existing heterogeneous evaluation method of the rock material, such as a scanning electron microscope method, is more of the visual heterogeneous characteristics of the microstructure of the rock, but does not deeply characterize the mechanical heterogeneity of the rock. However, the mechanical heterogeneity of rock is a major factor affecting the mechanical response of the rock in a particular project.
Disclosure of Invention
Aiming at the problem that the mechanical heterogeneity of materials in rocks cannot be deeply represented by the conventional rock heterogeneity evaluation method, the invention aims to provide a rock mechanical heterogeneity test evaluation method based on acoustic emission, which is used for solving the problems in the prior art.
The above technical object of the present invention will be achieved by the following technical solutions.
A rock mechanics heterogeneity test evaluation method based on acoustic emission comprises the following steps:
s1, selecting a complete stratum to be tested;
s2, drilling the complete stratum to be detected to obtain a rock core column;
s3, processing the core column to obtain a rock sample;
s4, arranging acoustic emission sensors on two sides of the rock sample;
s5, recording data measured by the acoustic emission sensor in the splitting experiment process, counting the number of acoustic emission signal events according to the recorded data, calculating the total number of acoustic emission events according to the number of acoustic emission signal events, and calculating the ratio coefficient of the total number of acoustic emission events to the fracture component of the rock sample;
s6, calculating a heterogeneous coefficient of the rock according to the fracture component proportion coefficient of the rock sample;
and S7, evaluating the mechanical heterogeneity of the rock according to the heterogeneous coefficient.
The above aspect and any possible implementation manner further provide an implementation manner, and the step S2 is specifically to perform vertical drilling coring on the complete formation to be tested, and continuously take 3 to 10 rock core columns with the length of 20 to 30 cm.
In the above aspect and any possible implementation manner, a further implementation manner is provided, in which in step S3, specifically, all the core pillars are processed to obtain the disc-shaped rock sample with a diameter of 25 to 75mm and a thickness of 10 to 40 mm.
The above-mentioned aspect and any possible implementation manner further provide an implementation manner, and the step S4 is specifically to arrange one acoustic emission sensor on each of two sides of the disk-shaped rock sample for monitoring an acoustic emission signal of the rock sample.
The above aspect and any possible implementation further provide an implementation in which the resonant frequencies of the two acoustic emission sensors are 60kHz and 150kHz, respectively.
The above aspects and any possible implementations further provide an implementation in which vaseline glue is applied to the interface between the acoustic emission sensor and the rock sample.
As to the above-mentioned aspect and any possible implementation manner, there is further provided an implementation manner, where the step S5 specifically is:
s51, performing a splitting experiment on the rock sample, wherein the rock sample is damaged along the central axis of the rock sample along the change of stress, so that an acoustic emission signal is generated, and data measured by an acoustic emission sensor is recorded;
s52, counting the number of acoustic emission signal events at different time intervals according to the data measured by the acoustic emission sensor recorded in the step S51;
s53, calculating the total number of acoustic emission events and fracture component ratio coefficients of the rock sample at different time intervals according to the number of acoustic emission signal events at different time intervals obtained in the step S52;
and S54, calculating the heterogeneous rock coefficient according to the fracture component proportion coefficient of the rock sample calculated in the step S53.
The above aspect and any possible implementation further provide an implementation in which the fracture component proportion coefficient of the rock sample is a ratio of the number of acoustic emission signal events at the different time intervals to the total number of acoustic emission events.
The above aspects and any possible implementations further provide an implementation where the rock heterogeneous coefficient is a standard deviation of a fracture component fraction coefficient of the rock sample.
The above aspects and any possible implementations further provide an implementation in which, when 0< the rock heterogeneous coefficient is less than or equal to 5, the mechanical heterogeneous degree of the rock is evaluated as good;
when the rock heterogeneous coefficient is less than or equal to 15 < 5 >, the mechanical heterogeneous degree of the rock is evaluated to be medium;
when the rock heterogeneity coefficient is greater than 15, the mechanical heterogeneity of the rock is evaluated as poor.
The invention has the beneficial technical effects
The embodiment provided by the invention is used for evaluating the mechanical heterogeneity of rock, and relates to a rock mechanical heterogeneity test evaluation method based on acoustic emission, wherein firstly, a complete stratum to be tested is selected; secondly, drilling the complete stratum to be detected to obtain a rock core column; secondly, processing the core column to prepare a rock sample; secondly, arranging acoustic emission sensors on two sides of the rock sample; secondly, recording data measured by the acoustic emission sensor in the splitting experiment process, counting the number of acoustic emission signal events according to the recorded data, and calculating the total number of acoustic emission events and the percentage coefficient of fracture components of the rock sample according to the number of acoustic emission signal events; and finally, calculating the heterogeneous coefficient of the rock by the fracture component proportion coefficient, and evaluating the mechanical heterogeneous degree of the rock by using the heterogeneous coefficient of the rock. The mechanical response heterogeneity characteristic of the rock is obtained according to the heterogeneity coefficient under the splitting condition, the rock sample is convenient to manufacture, simple to calculate and high in practicability, the heterogeneity inside the rock is favorably and quantitatively evaluated, and the quality evaluation and classification of the underground engineering surrounding rock are promoted.
Drawings
Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:
FIG. 1 is a schematic view of an acoustic emission sensor arrangement on a rock sample in an embodiment of the invention;
FIG. 2 is a schematic representation of a contour line of transverse tensile stress in a rock sample in an embodiment of the invention;
FIG. 3 is a graphical representation of the fractional fracture component coefficient of a rock sample of three rock samples in an example of the invention;
FIG. 4 is a schematic diagram of the evaluation method steps in the example of the present invention.
Wherein the reference numerals are as follows:
1, a rock sample; 2 a linear load applying device; 3, an acoustic emission sensor; 4, a side-proof sliding rod; 5 the pressure head can slide along the anti-side slide rod; 6 are compressed to clamp the spring.
Detailed Description
In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following detailed description is made with reference to the accompanying drawings and specific examples, but the embodiments of the present invention are not limited thereto.
The invention provides an evaluation method based on the principle that tensile stress on a central axis is equal except the top and the bottom of a prepared disc-shaped rock sample under the splitting condition, as shown in figure 2.
In order to better illustrate the invention, granite is taken as an experimental object, and the change trend of the proportion coefficient of the cracking component of a rock sample of the granite under 3 different metamorphic degrees is researched.
As shown in fig. 4, a method for testing and evaluating the mechanical heterogeneity of rock based on acoustic emission includes the following steps:
(1) selecting a complete stratum to be tested;
(2) drilling the complete stratum to be detected to obtain a rock core column;
(3) processing the core column to prepare a rock sample;
(4) arranging acoustic emission sensors on both sides of the rock sample;
(5) recording data measured by the acoustic emission sensor in the splitting experiment process, counting the number of acoustic emission signal events according to the recorded data, and calculating the total number of acoustic emission events and the fracture component ratio coefficient of the rock sample according to the number of acoustic emission signal events;
(6) calculating the heterogeneous coefficient of the rock according to the fracture component proportion coefficient of the rock sample;
(7) evaluating the mechanical heterogeneity of said rock from its heterogeneity coefficients.
The specific process is as follows:
1.1 selection and preparation of rock samples
(1) Selecting a stratum: selecting a complete stratum to be tested at the deep part as an area to be drilled and sampled;
(2) core drilling: the method comprises the steps of conducting vertical drilling coring on a complete stratum to be tested and to be evaluated for mechanical heterogeneity, continuously taking 3-10 rock core columns with the length of 10-50 cm, preferably, continuously taking 5 rock core columns with the length of 20-30 cm, enabling the sampling distance of each rock core column of the same stratum not to exceed 50cm, and enabling the stratum with the rock core columns to be a complete stratum rather than a fractured zone stratum. Sampling intervals of no more than 50cm are provided to ensure that the core pillars being sampled are from the same formation.
(3) Preparation of rock samples: and (3) processing the core pillars obtained in the step (2), and uniformly processing according to rock mechanical test standards to obtain the disc-shaped rock sample with the diameter of 25-75 mm and the thickness of 10-40 mm. In the invention, the disc-shaped rock sample with the diameter of 50mm and the thickness of 25mm is preferably processed;
(4) according to the stress characteristics of the rock sample under the splitting experiment, the stress on the top and the bottom of the rock is concentrated, and the stress change gradient is large. The central axis is far away from the top and bottom areas, the tensile stress is almost equal, under the condition of equal tension, the components near the central axis of the rock are gradually and sequentially cracked from weak phase to strong phase, so that the proportion coefficient of the cracked components of the rock sample is calculated, the heterogeneous coefficient of the rock is further calculated, and the mechanical heterogeneous degree of the rock is further evaluated by adopting the heterogeneous coefficient of the rock;
(5) the invention adopts three disc-shaped rock samples, as shown in figure 1, the upper end and the lower end of each rock sample 1 are connected with a linear load applying device 2, and a pressure clamping spring 6 is adopted to fix the rock sample 1 for preventing the rock sample from toppling; the linear load applying device 2 is also connected to a ram 5 slidable along the anti-sideslip bar for applying a linear load to the rock sample to stress the rock sample and to fracture the rock sample along the central axis. And (3) sticking acoustic emission sensors 3 to two sides of the rock sample by adopting Vaseline glue, and monitoring acoustic emission signals of strong and weak phase destruction of the rock sample under the action of load. The anti-side slide rod 4 is connected with the pressure head 5 capable of sliding along the anti-side slide rod and the compression clamping spring 6, the arrangement enables the load to be applied along the central axis position of the rock sample 1, and the compression head 5 capable of sliding along the anti-side slide rod is prevented from inclining by the compression clamping spring 6. The pressure head 5 which can slide along the slide rod is applied with pressure load, and transmits the pressure load to the linear load applying device 2, and the linear load applying device 2 applies the pressure load to the rock sample 1. In order to increase the frequency receiving range of the acoustic emission signals, the resonant frequencies of the two acoustic emission sensors are respectively 60kHz and 150 kHz; loading three rock samples by a press machine, crushing the three rock samples from the middle part, wherein the crushing result is that the central axis of the rock sample generates a splitting crack, and recording the generated acoustic emission signal in real time in the loading process;
1.2 quantitative characterization of rock heterogeneity
(1) Under the splitting experiment, the disc-shaped rock sample is transversely loaded to be tensile stress, the tensile stress of the area far away from the top and the bottom on the central axis is approximately equal, and the characteristic can be seen from a tensile stress contour map. Under the condition of equal tensile stress, the strength items in the rock are successively destroyed, and the mechanical heterogeneity of the mechanical characteristics of the rock can be reflected by calculating the heterogeneous coefficient of the rock;
(2) the three rock samples are finally cracked, the form is that a macrocrack is generated at the center of the splitting axis, the macrocrack divides the rock sample into two parts, and after the sample is cracked, an acoustic emission signal becomes infinite and has great discreteness, so that data generated after the sample is cracked are not counted;
(3) the mechanical heterogeneity of the internal structure of the rock under the same stress condition leads to different time for the strong and weak phase destruction at the central axis of the rock sample, thereby leading to different proportion coefficients of the fracture components of the rock sample, further leading to different heterogeneous coefficients of the rock, and leading in the proportion coefficient f of the fracture components in order to quantitatively reflect the incongruity of the deformation under the same load level among different regionsiAnd rock heterogeneous coefficient fv；
(4) The time elapsed from the start of the loading of the rock sample to the beginning of the macroscopic destruction is denoted t, and the time t is divided into 10 time interval equal parts on average, denoted t1,t2,t3,…,t10Wherein 0< t1≤0.1，0.1＜t2≤0.2，0.2＜t3≤0.3，…，0.9＜t10Less than or equal to 1.0, counting the number N of acoustic emission events of the rock sample in each time interval1，N2，N3，…，N10Calculating the total acoustic emission event number sigma N of the rock sample immediately before the macroscopic cracking1+N2+…+N10The fracture component fraction f of rock samples defining different time intervalsi＝NiV Σ N, where i is 1, 2, 3, …, 10 respectively, defining the average value of the fracture component fraction of the rock sample as m ═ Σ fi/10, where ∑ fi＝f1+f2+…+f10Defining the heterogeneous coefficient of rock
The standard deviation of the fracture component ratio coefficient of the rock sample is obtained, the change trend of the fracture component ratio coefficient of the rock sample along with the loading process is counted, and the rock heterogeneous coefficient can be calculated, so that the distribution state of the strong and weak components in the rock can be distinguished, and the mechanical heterogeneous degree of the rock is evaluated;
from the calculation result of step (4)Knowing the heterogeneous coefficient f of the rockvThe smaller the value, the better the mechanical heterogeneity of the rock sample is evaluated; said rock heterogeneous coefficient fvThe larger the value, the worse the mechanical heterogeneity of the rock sample is evaluated, as shown in fig. 3.
Example 1
The method is applied to granite experimental objects in deep well construction areas, and comprises the following steps:
a1: the geological structure of the stratum where the granite is located is found out in detail, an evaluation area is selected, and the rock core is guaranteed to have good representativeness;
a2: the lithology, engineering characteristics and weathering degree of the granite are found out in detail, and the quality grade of the surrounding rock is evaluated;
a3: carrying out vertical drilling coring on a stratum to be evaluated for homogeneity, continuously taking 5 core columns with the length of 20-30 cm, and keeping the sampling distance of each core column of the same stratum from exceeding 50 cm;
a4: processing the core pillars obtained in the above steps into disc rock samples with the diameter of 50mm and the thickness of 25mm in a unified manner, thereby obtaining a plurality of split disc-shaped rock samples;
a5: respectively arranging an acoustic emission sensor on each of two sides of the split disc rock sample obtained in the step for monitoring an acoustic emission signal of the rock sample, as shown in fig. 1;
a6: in order to increase the receiving range of the acoustic emission signals, the resonant frequencies of the two acoustic emission sensors are respectively 60kHz and 150kHz, and the generation of the acoustic emission signals is monitored;
a7: in the process of loading the rock sample, stabilizing the rock sample by adopting a side-slipping prevention rod and an anti-dumping device to prevent the rock sample from sideslipping or dumping to influence the experimental result;
a8: vaseline glue is coated on the contact surface of the acoustic emission sensor and the rock sample, so that the coupling effect of the acoustic emission sensor and the rock sample is improved;
a9: after the rock sample is loaded and broken, the acoustic emission signal becomes infinite, so that the acoustic emission signal data generated after the rock sample is broken are not counted;
a10: the rock sample generates a splitting and splitting seam during the damage, so that the acoustic emission data has great discreteness, and the acoustic emission data of the rock sample only counts the corresponding data monitored by the acoustic emission sensor immediately before the damage;
a11: dividing the rock sample into three conditions of good heterogeneity, medium heterogeneity and heterogeneity difference according to the acoustic emission monitoring result obtained by the splitting experiment and the calculated heterogeneous coefficient of the rock;
further, when the rock heterogeneous coefficient is 0< and is less than or equal to 5, the mechanical heterogeneous degree of the rock is evaluated to be good; when the rock heterogeneous coefficient is less than or equal to 15 < 5 >, the mechanical heterogeneous degree of the rock is evaluated to be medium; when the rock heterogeneity coefficient is greater than 15, the mechanical heterogeneity of the rock is evaluated as poor. FIG. 3 shows three different mechanical anisotropies according to the fracture component ratio coefficient of the rock sample after the method provided by the invention is used for carrying out test evaluation on three rock samples.
Furthermore, the differences among the rock textures of the rocks with the low rock heterogeneous coefficients are small, so that the fracture component proportion coefficient of the rock sample is in a low level, and the rock mechanical heterogeneous degree is always in a low level. The heterogeneity of the rock texture is increased, so that the fracture component proportion coefficient of the rock sample is at a higher level, and the mechanical heterogeneity of the rock is also at a higher level.
The foregoing description shows and describes several preferred embodiments of the invention, but as aforementioned, it is to be understood that the invention is not limited to the forms disclosed herein, but is not to be construed as excluding other embodiments and is capable of use in various other combinations, modifications, and environments and is capable of changes within the scope of the inventive concept as expressed herein, commensurate with the above teachings, or the skill or knowledge of the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (7)
1. A testing and evaluating method for rock mechanical heterogeneity based on acoustic emission is characterized by comprising the following steps:
s1, selecting a complete stratum to be tested;
s2, drilling the complete stratum to be detected to obtain a rock core column;
s3, processing the core column to obtain a rock sample;
s4, arranging acoustic emission sensors on two sides of the rock sample;
s5, recording data measured by the acoustic emission sensor in the splitting experiment process, counting the number of acoustic emission signal events according to the recorded data, and calculating the total number of acoustic emission events and the percentage coefficient of fracture components of the rock sample according to the number of acoustic emission signal events;
s6, calculating a heterogeneous coefficient of the rock according to the fracture component proportion coefficient of the rock sample;
s7, evaluating the mechanical heterogeneity of the rock according to the heterogeneity coefficient of the rock;
the step S5 specifically includes:
s51, performing a splitting experiment on the rock sample, wherein the rock sample is damaged along the central axis of the rock sample along the change of stress, so that an acoustic emission signal is generated, and data measured by an acoustic emission sensor is recorded;
s52, counting the number of acoustic emission signal events at different time intervals according to the data measured by the acoustic emission sensor recorded in the step S51;
s53, calculating the total number of acoustic emission events and fracture component ratio coefficients of the rock sample at different time intervals according to the number of acoustic emission signal events at different time intervals obtained in the step S52;
s54, calculating a rock heterogeneous coefficient according to the fracture component proportion coefficient of the rock sample calculated in the step S53;
the fracture component proportion coefficient of the rock sample is the ratio of the number of acoustic emission signal events at the different time intervals to the total number of acoustic emission events;
and the rock heterogeneous coefficient is the standard deviation of the fracture component proportion coefficient of the rock sample.
2. The test evaluation method according to claim 1, wherein the step S2 is specifically to perform vertical drilling coring on the complete stratum to be tested, and 3-10 rock core columns with the length of 20-30 cm are continuously taken.
3. The test and evaluation method according to claim 1, wherein the step S3 is to process all the core pillars to obtain the disk-shaped rock sample having a diameter of 25 to 75mm and a thickness of 10 to 40 mm.
4. The test evaluation method according to claim 3, wherein the step S4 is specifically to arrange an acoustic emission sensor on each side of the disc-shaped rock sample for monitoring the acoustic emission signal of the rock sample.
5. The test evaluation method according to claim 4, wherein the resonance frequencies of the two acoustic emission sensors are 60kHz and 150kHz, respectively.
6. The test evaluation method of claim 5, wherein petrolatum gel is applied to the interface of the acoustic emission sensor and the rock sample.
7. The test evaluation method according to claim 1,
when the rock heterogeneous coefficient is more than 0 and less than or equal to 5, the mechanical heterogeneous degree of the rock is evaluated to be good;
when the rock heterogeneous coefficient is less than or equal to 15 < 5 >, the mechanical heterogeneous degree of the rock is evaluated to be medium;
when the rock heterogeneity coefficient is greater than 15, the mechanical heterogeneity of the rock is evaluated as poor.
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| CN109580399A (en) * | 2018-12-27 | 2019-04-05 | 深圳大学 | Middle low strain dynamic rate sound integration test system |
| CN110987674B (en) * | 2019-12-23 | 2022-12-13 | 神华神东煤炭集团有限责任公司 | Crustal stress testing method based on core Kaiser effect |
| CN112444564B (en) * | 2020-11-17 | 2022-01-04 | 大连理工大学 | Rock fracture early warning method based on acoustic emission signal statistical analysis |
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