CN113188870A - Testing and evaluating method for rock mechanical heterogeneity - Google Patents
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Abstract
The invention relates to a testing and evaluating method of rock mechanical heterogeneity, firstly selecting a stratum to be tested; secondly, drilling the stratum to be detected to obtain a rock core column; secondly, processing the core column to prepare a rock sample; secondly, carrying out region division on the rock sample; secondly, arranging a certain number of strain gauges on the rock sample, and recording data measured by the strain gauges under the splitting condition; and finally, calculating a mean value, a standard deviation and a variation coefficient according to the recorded data, and evaluating the mechanical heterogeneity of the rock according to the variation coefficient. The mechanical response anisotropism characteristic of the rock is obtained according to the deformation dispersion under the same stress condition; 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 mechanical heterogeneity characteristics of deep underground engineering rocks, and particularly relates to a test evaluation method of mechanical heterogeneity of rocks.
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 conventional rock mechanical heterogeneity evaluation method cannot deeply characterize the mechanical heterogeneity of materials in the rock, the invention aims to provide a rock mechanical heterogeneity test evaluation method 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 test evaluation method for rock mechanical heterogeneity, the method comprises the following steps:
s1, selecting a stratum to be tested;
s2, drilling the stratum to be tested to obtain a rock core column;
s3, processing the core column to obtain a rock sample;
s4, carrying out region division on the rock sample;
s5, arranging a certain number of strain gauges on the rock sample, and recording data measured by the strain gauges under the splitting condition;
and S6, calculating a mean value, a standard deviation and a variation coefficient according to the recorded data, and evaluating the mechanical heterogeneity of the rock according to the variation 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 stratum 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 perform region division on the disc-shaped rock sample, and mark out a test region and a stress concentration region.
In the aspect and any possible implementation manner described above, an implementation manner is further provided, in which a region within 10mm from the top and the bottom of the central axis of the disc-shaped rock sample is used as a stress concentration region, and other regions are divided into an experimental region.
The above aspect and any possible implementation manner further provide an implementation manner, a certain number of strain gauges with the specification of 5mm × 3mm are continuously arranged in the experimental area, and the distance between each strain gauge is 1-5 mm.
As to the above-mentioned aspect and any possible implementation manner, there is further provided an implementation manner, where the step S6 specifically is:
s61, performing a splitting experiment on the rock sample, recording strain values corresponding to the strain gauges, which are damaged by the cracks and pass through the central axis, immediately before the cracks break, and recording the number of the corresponding damaged strain gauges;
s62, obtaining the mean value and the standard deviation of the strain values under different stress conditions according to the strain values and the number of the strain sheets recorded in the step S61.
The above aspect and any possible implementation further provide an implementation, wherein the coefficient of variation is a product of a ratio and a percentage of the mean to the standard deviation.
The aspect and any possible implementation manner described above further provide an implementation manner, wherein the smaller the value of the coefficient of variation, the better the mechanical heterogeneity of the rock sample is evaluated to be; the larger the value of the coefficient of variation, the worse the mechanical heterogeneity of the rock sample is evaluated.
The above aspects and any possible implementation manner further provide an implementation manner, wherein when the coefficient of variation is less than or equal to 20%, the mechanical heterogeneity of the rock sample is evaluated as good; when the coefficient of variation is more than 20% and less than or equal to 50%, the mechanical heterogeneity of the rock sample is evaluated to be medium; and when the coefficient of variation is more than 50%, evaluating the mechanical heterogeneity of the rock sample 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 firstly, a stratum to be tested is selected; secondly, drilling the stratum to be detected to obtain a rock core column; secondly, processing the core column to prepare a rock sample; secondly, carrying out region division on the rock sample; secondly, arranging a certain number of strain gauges on the rock sample, and recording data measured by the strain gauges under the splitting condition; and finally, calculating a mean value, a standard deviation and a variation coefficient according to the recorded data, and evaluating the mechanical heterogeneity of the rock according to the variation coefficient. Obtaining mechanical response heterogeneity characteristics of the rock according to the dispersion of deformation under the same stress condition; the rock sample is convenient to manufacture, simple in calculation and high in practicability, and helps to quantitatively evaluate the internal heterogeneity of the rock, promote the evaluation and classification of the quality of the underground engineering surrounding rock and evaluate the dynamic disaster risk of the rock more effectively.
Drawings
Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:
FIG. 1 is a schematic flow chart of a method in an embodiment of the present invention;
FIGS. 2(a), 2(b) and 2(c) are graphs showing strain values generated by fracture strain gauges of three rock samples in the embodiment of the invention;
FIG. 3 is a schematic diagram showing the coefficient of variation of three rock samples according to an embodiment of the present invention;
FIG. 4 is a schematic illustration of the placement of strain gages on a rock sample in an embodiment of the invention;
FIG. 5 is a schematic representation of the contour of the transverse tensile stress in a rock sample in an embodiment of the invention.
Wherein the reference numerals are as follows:
1, a rock sample; 2 a linear load applying device; 3 a compressed clamping spring; 4, a side-proof sliding rod; 5 the pressure head can slide along the anti-side slide rod; 6 strain gauge.
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.
In order to better explain the invention, the variegated rock in a deep well construction area is taken as an experimental object, and the spatial variability variation trend of the disraption deformation of the variegated rock under different metamorphic degrees is researched.
The method is based on the principle that the transverse deformation of the prepared disc-shaped rock sample is in a tensioned state on a central axis except the top and the bottom of the rock sample under the splitting condition, and the tensile stress is equal, and is shown in figure 4. The linear load applying devices 2 and the compression clamping springs 3 are arranged in two, the upper end and the lower end of the disc-shaped rock sample 1 are correspondingly connected with the linear load applying devices 2 one by one, one ends of the two compression clamping springs 3 are connected with the rock sample 1, and the disc-shaped rock sample 1 is fixed through the two compression clamping springs 3 to prevent the disc-shaped rock sample 1 from toppling;
meanwhile, the two linear load applying devices 2 are connected with two pressure heads 5 which are arranged at the upper end and the lower end of the disc-shaped rock sample 1 and can slide along the side sliding rod in a one-to-one correspondence mode, the two pressure heads 5 which can slide along the side sliding rod bear pressure loads, the pressure loads are transmitted to the linear load applying devices 2, the two linear load applying devices 2 apply linear loads to the disc-shaped rock sample 1, the disc-shaped rock sample 1 is pressed, and the disc-shaped rock sample 1 is split along the central axis of the disc-shaped rock sample 1.
The other end of two pressurized clamping springs 3 is connected with two slide bars 4 of defending of setting up respectively in the discoid rock sample 1 left and right sides, and two slide bars 4 of defending of controlling also are used for fixed discoid rock sample 1, prevent that discoid rock sample 1 from taking place to empty, influence the experimental result.
The left and right slide bar 1, the upper and lower pressure head 5 which can slide along the slide bar and the two pressed clamping springs 3 are connected with each other; the load is applied along the central axis of the disc-shaped rock sample 1 and is simultaneously connected with the compressed clamping spring 3, so that the pressure head 5 which can slide along the lateral sliding rod is prevented from inclining.
And the strain gauge 6 is attached to the surface of the experimental area of the disc-shaped rock sample 1 by epoxy resin glue and used for monitoring the strain of the disc-shaped rock sample 1 under the action of load.
The invention provides a method for quantitatively evaluating the heterogeneity of a rock structure based on the spatial dispersion of the deformation of the central axis of the split rock, as shown in figure 1, and the method comprises the following steps:
s1, selecting a stratum to be tested;
s2, drilling the stratum to be tested to obtain a rock core column;
s3, processing the core column to obtain a rock sample;
s4, carrying out region division on the rock sample;
s5, arranging a certain number of strain gauges on the rock sample, and recording data measured by the strain gauges under the splitting condition;
and S6, calculating a mean value, a standard deviation and a variation coefficient according to the recorded data, and evaluating the mechanical heterogeneity of the rock according to the variation coefficient.
Specifically, the method for evaluating the rock heterogeneity is a split rock deformation dispersion coefficient method, and comprises the following steps:
1.1 selection and preparation of Standard samples
(1) Selecting a stratum: selecting a deep stratum to be tested as a region to be drilled and sampled;
(2) core drilling: the method comprises the steps of conducting vertical drilling coring on a 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 the stratum instead of the stratum with broken zones. 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 sample 1: 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 1 with the diameter of 50mm and the thickness of 25mm is preferably processed;
(4) according to the stress characteristics of the rock sample 1 under the splitting experiment, the rock sample 1 obtained in the step (3) is subjected to region division, and an experimental region and stress concentration are marked, wherein the reason for the region division is that the stress on the top and the bottom 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, and the mechanical heterogeneity difference of the rock sample can be evaluated only by observing the deformation difference of a small area of the experimental area under the condition of equal tensile force.
(5) Dividing areas within 10mm from the top and the bottom on the axial line of the rock sample 1 into stress concentration areas;
(6) dividing the area of the rock sample 1 on the axial line, which is apart from the top and the bottom by 10mm, into an experimental area, dividing the rock sample 1 into the experimental area and a stress concentration area, and arranging the strain gauge in the experimental area, thereby facilitating the analysis of the strain of the rock sample.
(7) The method adopts three disc-shaped rock samples 1, strain gauges which are 5.0(mm) × 3.0(mm) and have the same specification and the same number of N at the same position are continuously arranged at the central axis experiment area positions of the three disc-shaped rock samples 1 respectively, N is more than or equal to 1, the method adopts 7 strain gauges, the distance between each strain gauge is 2mm, a splitting experiment is adopted, the three rock samples 1 are loaded through a press machine, the three rock samples 1 are crushed from the middle part, the crushing result is that splitting cracks are generated at the central axis of the rock samples 1, and the strain value of the strain gauge 6 is recorded in real time in the loading process; in order to adequately measure the strain changes in a small area within the test zone of the rock sample, more strain values are obtained, so that strain gauges 6 of as small a size as possible are used in the test zone.
1.2 processing of Strain gage data
(1) Under the splitting experiment, the disc-shaped rock sample 1 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 mechanical heterogeneity of the rock mechanical characteristics can be reflected by the deformed heterogeneity.
(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 1 into two parts, the macrocrack penetrates through the strain gauge 6 arranged at the macrocrack, the strain gauge 6 is broken along with the macrocrack, the strain value of the strain gauge 6 becomes infinite after the strain gauge 6 is damaged, and data generated after the strain gauge is broken are not counted. For the strain gauge which is not passed by the split crack at the central axis of the rock sample 1, eliminating the strain value obtained by the strain gauge without considering, only counting the strain value generated by the strain gauge which is passed and damaged by the macrocrack in the beginning of the macrocrack, wherein a plurality of moments are set in the beginning of the macrocrack, and the strain value of the strain gauge 6 can be obtained at each moment;
(3) let the strain value of each strain gage 6 at each moment immediately before the macroscopic cracking be
The number of the damaged strain gauges is recorded as N, and then the mean value of the strain values under different stress levels can be obtained
I.e. all strain values
The sum obtained after addition is divided by N*Obtaining a mean value, and calculating a standard deviation according to the mean value:
1.3 quantitative characterization of rock heterogeneity
Further, the mechanical heterogeneity of the internal structure of the rock under the same stress condition leads to the incongruity of the transverse deformation on the axis of the rock sample 1. In order to quantitatively reflect the incongruity of deformation under the same loading level among different regions, a deformation space variation coefficient C is introducedV(ii) a By means of a splitting test, as shown in fig. 2(a), 2(b) and 2(c), an experimental area of three rock samples 1 under the same stress condition is used as a large area, a plurality of small areas are divided in the large area, strain gauges are respectively placed in each small area, the mechanical difference of the internal texture of the rock is reflected by the deformation difference among different small areas, and strain values measured at various moments before macroscopic cracking are reflected by strain 1, strain 2 and strain 3;
furthermore, the invention adopts the deformation space variation coefficient CVDescribing the dispersion of deformation distribution among different small areas of the experimental area of the rock sample 1 under the same stress condition, and calculating the dispersion in a mode of CVσ/mx 100%, which is the product of the ratio and percentage of the mean to the standard deviation;
this expression shows that the coefficient of variation CVThe smaller the value of (A), the closer the strain values measured by the strain gauge in the small area are, i.e. indirectly indicating the rock testThe mechanical heterogeneity of the whole large area of the experimental area of the sample 1 is good; and the coefficient of variation CVThe larger the value of (A) is, the larger the deformation difference between the textures of the constituent rock sample 1 is, the less the mechanical non-uniformity of the rock sample 1 is, and thus the less the mechanical non-uniformity of the rock in which the rock sample 1 is located is.
The mechanical anisotropies of the three rock samples shown in FIG. 3 are different, and the coefficient of variation C is determinedVDividing the rock samples with the mechanical heterogeneity of less than or equal to 20 percent into rock samples with low mechanical heterogeneity, and dividing the coefficient of variation CVMore than 20% and less than or equal to 50% of the samples are divided into rock samples with medium mechanical heterogeneity, and the coefficient of variation C is calculatedVMore than 50% of the samples are divided into rock samples with high mechanical heterogeneity.
Preferably, the strain gauge is adhered to the surface of the rock sample by 502 glue for the rock with smaller porosity, such as igneous rock, and is adhered to the surface of the rock sample by epoxy resin for the rock with larger porosity, such as sandstone, mudstone and the like;
example 1
The invention takes the gabbro rock in the deep well construction area as an example, and the method comprises the following steps:
a1: finding out the address structure of the stratum where the variegated gabbro is located in detail, selecting an evaluation area, and ensuring that the core has good representativeness;
a2: finding out the lithology, engineering characteristics and weathering degree of the metamorphic barite in detail, and evaluating the quality grade of the surrounding rock;
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: dividing the splitting disc rock sample obtained in the above steps into a test area and a stress concentration area on the surface of the rock sample, wherein the areas within 10mm from the top bottom of the splitting central axis of the disc rock sample are the stress concentration areas, and the areas outside 10mm from the top bottom of the central axis are the test areas, as shown in fig. 5;
a6: continuously arranging 3 strain gauges with the specification of 5.0(mm) × 3.0(mm) at the test area, wherein the distance between each strain gauge is 3mm, and adhering the strain gauges to the surface of the rock sample by adopting epoxy resin;
a7: in the process of loading the rock sample, stabilizing the rock sample by adopting a side-sliding prevention rod 4 and a pressure head 5 which can slide along the side-sliding prevention rod to prevent the rock sample from sideslipping or toppling over to influence the experimental result;
a8: in order to ensure the accuracy of the experimental data result, performing splitting experiments on 20 rock samples and obtaining deformation data of the rock samples;
a9: for the strain gauge which does not pass through the crack at the central axis of the rock sample, eliminating data obtained by the strain gauge, and only counting data corresponding to the strain gauge which passes through and is damaged by the crack;
a10: because the rock sample generates a splitting split seam during the damage, the data of the strain gauge has great discreteness, and therefore the deformation of the rock sample only calculates the data corresponding to each strain gauge of the rock sample before the damage;
a11: and dividing the rock sample into three conditions of good heterogeneous degree, medium heterogeneous degree and poor heterogeneous degree according to the strain result obtained by the splitting experiment and the rock variation coefficient. Dividing the rock samples with the coefficient of variation less than or equal to 20% into rock samples with good heterogeneity;
furthermore, the rock samples with the coefficient of variation larger than 20% and not larger than 50% are classified as rock samples with medium heterogeneity, and the rock samples with the coefficient of variation larger than 50% are classified as rock samples with poor heterogeneity.
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 (10)
1. A testing and evaluating method for rock mechanical heterogeneity is characterized by comprising the following steps:
s1, selecting a stratum to be tested;
s2, drilling the stratum to be tested to obtain a rock core column;
s3, processing the core column to obtain a rock sample;
s4, carrying out region division on the rock sample;
s5, arranging a certain number of strain gauges on the rock sample, and recording data measured by the strain gauges under the splitting condition;
and S6, calculating a mean value, a standard deviation and a variation coefficient according to the recorded data, and evaluating the mechanical heterogeneity of the rock according to the variation coefficient.
2. The test evaluation method according to claim 1, wherein the step S2 is specifically to perform vertical drilling coring on the 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 to divide the disc-shaped rock sample into regions, mark a test region and a stress concentration region.
5. The test evaluation method according to claim 4, wherein a region within 10mm from the top and bottom of the disk-shaped rock specimen on the central axis thereof is defined as a stress concentration region, and the other regions are defined as experimental regions.
6. The test and evaluation method according to claim 5, wherein a certain number of the strain gauges of 5mm x 3mm are arranged in series in the experimental area, and the distance between each strain gauge is 1-5 mm.
7. The test evaluation method according to claim 6, wherein the step S6 is specifically:
s61, performing a splitting experiment on the rock sample, recording strain values corresponding to the strain gauges, which are damaged by the cracks and pass through the central axis, immediately before the cracks break, and recording the number of the corresponding damaged strain gauges;
s62, obtaining the mean value and the standard deviation of the strain values under different stress conditions according to the strain values and the number of the strain sheets recorded in the step S61.
8. The test evaluation method according to claim 1, wherein the coefficient of variation is a product of a ratio and a percentage of the mean to the standard deviation.
9. The test evaluation method according to claim 1, wherein the smaller the value of the coefficient of variation, the better the mechanical heterogeneity of the rock sample is evaluated; the larger the value of the coefficient of variation, the worse the mechanical heterogeneity of the rock sample is evaluated.
10. The test evaluation method according to claim 9, wherein when the coefficient of variation is 20% or less, the mechanical heterogeneity of the rock sample is evaluated as good; when the coefficient of variation is more than 20% and less than or equal to 50%, the mechanical heterogeneity of the rock sample is evaluated to be medium; and when the coefficient of variation is more than 50%, evaluating the mechanical heterogeneity of the rock sample as poor.
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| CN114441214A (en) * | 2022-01-17 | 2022-05-06 | 合肥工业大学 | Heterogeneous degree evaluation method of rock particle structure |
| GB2612152A (en) * | 2021-10-25 | 2023-04-26 | Univ Tongji | Method and system for evaluating crack resistance of asphalt mixture under intermediate-temperature condition, and storage medium |
| CN117606937A (en) * | 2024-01-24 | 2024-02-27 | 北京科技大学 | Rock material energy storage capacity evaluation method and system in high stress state |
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| GB2612152B (en) * | 2021-10-25 | 2023-12-06 | Univ Tongji | Method and system for evaluating crack resistance of asphalt mixture under intermediate-temperature condition, and storage medium |
| CN114441214A (en) * | 2022-01-17 | 2022-05-06 | 合肥工业大学 | Heterogeneous degree evaluation method of rock particle structure |
| CN117606937A (en) * | 2024-01-24 | 2024-02-27 | 北京科技大学 | Rock material energy storage capacity evaluation method and system in high stress state |
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