Hard rock medium state determination method

Abstract

This invention provides a method for determining the state of a hard rock stratum, comprising the following steps: preparing a standard sample of the hard rock stratum and obtaining initial microscopic characterization parameters of the sample in its intact state through microfocus CT scanning; subjecting the standard sample to multi-gradient irradiation treatment with a set microwave power for a set duration, and obtaining the microscopic characterization parameters of the sample under the irradiation gradient through microfocus CT scanning; conducting a uniaxial compression mechanical test on the sample after completing full-gradient microwave irradiation and CT scanning to obtain the macroscopic mechanical parameters of the sample; assigning weights to the single-factor transformation factors corresponding to each microscopic characterization parameter according to the correlation coefficient; calculating the medium state transformation factor by weighted average; identifying the hard rock stratum medium state corresponding to the sample; and evaluating the degree of medium state transformation. This invention simultaneously considers the influence of multiple dimensions such as fracture development scale, spatial structure complexity, and extension characteristics on the rock mass medium state.

Description

Technical Field

[0001] This invention relates to the field of rock mass condition evaluation technology, specifically to a method for determining the condition of hard rock strata. Background Technology

[0002] In my country, over 50% of coal reserves are located in deep strata. During the excavation of deep coal seam roadways, the sandstone, granite, and other hard rock strata form the main components of the roadway roof and floor due to the influence of the coal-bearing sedimentary environment and geological structure. The coupling effect of the high-stress environment at depth and the hard rock strata easily leads to severe wear of tunnel boring machine cutters and machine vibration, significantly reducing roadway excavation efficiency, increasing construction costs, and seriously restricting safe and efficient coal mine production. At the same time, the hard rock strata have small rebound deformation after unloading during excavation, making them prone to accumulating high stress and triggering dynamic disasters, threatening the safety of underground operations.

[0003] To address the aforementioned issues, pre-fracture treatment of hard rock surrounding tunnels is typically required in engineering projects. Currently, commonly used fracturing methods for hard rock tunnels in coal mines include drill-and-blast, hydraulic fracturing, and microwave irradiation. Among these, microwaves, as high-frequency electromagnetic waves, offer advantages such as selective heating, rapid temperature rise, and instantaneous controllability. They can create a significant temperature gradient within the hard rock through irradiation, inducing thermal stress and generating thermal cracks. Compared to drill-and-blast and hydraulic fracturing, the degree of fracture development can be artificially controlled, adapting to different engineering requirements. The essence of microwave-induced fracturing of hard rock is to alter the medium state of the rock mass by pre-creating and expanding the fracture network, gradually transforming the originally continuous rock mass into a quasi-continuous or discontinuous body. This aligns with the engineering requirements for stress relief and dynamic disaster prevention in tunnel surrounding rock, where stress relief is necessary to reduce the risk of dynamic disasters when high stress accumulates in the surrounding rock.

[0004] In the process of microwave-induced fracturing to regulate the state of rock mass media, accurately identifying the state of the media and evaluating the degree of transformation between the states of coal and rock media are crucial. The macroscopic mechanical properties of rock mass media (such as strength and elastic modulus) are directly related to the microscopic geometric structure of its internal defects (such as pore morphology, fracture connectivity, and fracture development scale). Currently, the media state evaluation indicators used in the industry are mostly based on single parameters defined by wave velocity and porosity. Single-parameter evaluation has significant drawbacks: on the one hand, single parameters are easily affected by the test environment and sample properties, which can lead to large errors in the evaluation results; on the other hand, single parameters are not sensitive enough to the continuous transformation process of hard rock media states, and cannot fully reflect the impact of fracture development scale and spatial structure on the mechanical properties of rock mass, making it difficult to accurately quantify the degree of transformation of media states and providing precise quantitative basis for roadway decompression design and dynamic disaster prevention. Summary of the Invention

[0005] The present invention proposes a method for determining the state of hard rock strata, which can at least solve one of the technical problems in the background art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for determining the state of a hard rock stratum includes the following steps: S1. Prepare standard samples of hard rock layers, dry the standard samples, test their initial longitudinal wave velocity, and obtain the initial microscopic characterization parameters of the samples in their intact state by microfocus CT scanning. S2. The standard sample is subjected to graded irradiation treatment with multiple gradient durations using the set microwave power. After each irradiation is completed, the surface temperature of the sample is tested. After the sample cools naturally to room temperature, the longitudinal wave velocity under the corresponding irradiation gradient is tested, and the microscopic characterization parameters of the sample under the irradiation gradient are obtained by micro-focus CT scanning. S3. After the specimens have undergone full-gradient microwave irradiation and CT scanning, a uniaxial compression mechanical test is performed to obtain the macroscopic mechanical parameters of the specimens. S4. Based on the microscopic characterization parameters and macroscopic mechanical parameters obtained in steps S1 to S3, perform a fitting analysis on the correlation between each microscopic characterization parameter and the macroscopic mechanical parameter, and assign the weight of the single-factor transformation factor corresponding to each microscopic characterization parameter according to the correlation coefficient. S5. Based on the single-factor transformation factors corresponding to each microscopic characterization parameter and their assigned weights, the medium state transformation factor is calculated using a weighted average. ; S6. Based on the preset medium state conversion factor The numerical range of the sample is used to determine the transformation state of the hard rock medium corresponding to the sample, providing a quantitative basis for the decompression design and dynamic disaster prevention of the surrounding rock in deep tunnels.

[0007] As a preferred embodiment of the method for determining the state of hard rock strata in this invention, in step S1, the standard sample is a cylindrical granite sample with a diameter of 50 mm and a height of 100 mm; the drying treatment is carried out by oven drying, the drying temperature is set to 105℃, the drying time is 24 h, and after drying, the sample is allowed to cool to room temperature before subsequent testing.

[0008] As a preferred embodiment of the method for determining the state of hard rock strata in this invention, in step S2, a multi-mode cavity industrial microwave system with a frequency of 2.45 GHz and a rated power of 0-6 kW is used for irradiation treatment. The constant irradiation power is set to 6 kW, and the irradiation duration gradient is set to 1 min, 2 min, 3 min, 4 min, and 5 min, for a total of 5 gradients. An infrared thermal imaging camera is used to test the surface temperature of the sample after irradiation.

[0009] As a preferred embodiment of the method for determining the state of hard rock strata described in this invention, the microscopic characterization parameters include fracture rate and fracture fractal dimension, and can be supplemented with fracture volume. Fracture volume is the total volume occupied by all fractures within the coal and rock in three-dimensional space, and is a direct indicator for quantifying damage. In CT scans, fracture volume is the sum of the volumes of all voxels marked as fractures, and its calculation formula is:

[0010] in: Indicates the fracture volume. ; It is the number of slit voxels; , , It represents the size of a voxel in three directions.

[0011] In a preferred embodiment of the method for determining the state of hard rock strata described in this invention, the fracture rate is the proportion of fractures per unit volume of the sample, calculated using the following formula:

[0012] in The fracture volume is expressed in units of 1. , Total volume of the sample, in units of The fractal dimension of the fracture is calculated using the box counting method, and the calculation formula is as follows:

[0013] in, The required side length to cover the crack is... The number of boxes.

[0014] As a preferred embodiment of the method for determining the state of hard rock media described in this invention, in step three, the uniaxial compression mechanics test adopts a rock mechanics servo test system, the loading method is displacement-controlled loading, and the loading rate is set to 0.002 mm / s; the macroscopic mechanical parameters include at least uniaxial compressive strength and elastic modulus.

[0015] As a preferred embodiment of the method for determining the state of hard rock media described in this invention, in step four, the Pearson correlation coefficients of each microscopic characterization parameter and macroscopic mechanical parameter are fitted using the nonlinear least squares method. After normalizing the correlation coefficients, the weights of the corresponding single-factor transformation factors are obtained, and the sum of the weights of all single-factor transformation factors is 1.

[0016] As a preferred embodiment of the method for determining the state of hard rock strata described in this invention, the medium state transformation factor is: The calculation formula is:

[0017] Among them, I Vf This represents the conversion factor based on the fracture volume definition; I φ This represents the conversion factor defined based on the crack ratio; I D This represents the transformation factor defined based on the fractal dimension. I This is based on multiple parameters, including fracture volume, fracture ratio, and fractal dimension. , , Indicates the weight of each conversion factor. + + =1.

[0018] In a preferred embodiment of the method for determining the state of hard rock media according to the present invention, the single-factor conversion factor is the ratio of the microscopic characterization parameter of the sample under the current irradiation state to the microscopic characterization parameter under the initial state; wherein:

[0019]

[0020]

[0021] In the formula: V fm , φ m , D m These represent the final state's fracture volume, fracture ratio, and fractal dimension, respectively.

[0022] As a preferred embodiment of the method for determining the state of hard rock strata media according to the present invention, in step S6, the media transformation state is divided into three levels: continuous media, quasi-continuous media, and discontinuous media; when When the value is ≤ the first preset threshold, it is determined to be a continuous medium, and fracturing and depressurization treatment is required for the corresponding engineering scenario; when the first preset threshold is < When the value is ≤ the second preset threshold, it is determined to be a quasi-continuous medium, and the corresponding engineering scenario requires further depressurization to a certain extent; when When the second preset threshold is reached, it is determined to be a discontinuous medium, and dynamic disaster prevention and control are required for the corresponding engineering scenario.

[0023] The beneficial effects of this invention are: This invention adopts an evaluation system that integrates multiple microscopic characterization parameters, which breaks through the limitations of existing single-parameter evaluation. It simultaneously considers the influence of multiple dimensions such as fracture development scale, spatial structure complexity, and extension characteristics on the state of rock mass medium, which greatly reduces the evaluation error caused by test interference and makes the evaluation results more comprehensive and accurate. This invention assigns weights based on the correlation between microscopic parameters and macroscopic mechanical parameters. The weighting system is scientific and reasonable, making the comprehensive evaluation index more sensitive to the continuous transformation process of hard rock media state. It can accurately capture the gradual transformation characteristics of rock media during microwave fracturing. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the overall process logic of the method for determining the state of hard rock media according to the present invention.

[0025] Figure 2 This is a graph showing the mechanical parameters of the method for determining the state of hard rock media according to the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0027] like Figures 1-2 As shown, a method for determining the state of a hard rock stratum is provided, comprising the following steps: S1. Prepare standard samples of hard rock layers. After drying the standard samples, test their initial longitudinal wave velocity and obtain the initial microscopic characterization parameters of the samples in their intact state by microfocus CT scanning. S2. The standard sample is subjected to graded irradiation treatment with multiple gradient durations using the set microwave power. After each irradiation is completed, the surface temperature of the sample is tested. After the sample cools naturally to room temperature, the longitudinal wave velocity under the corresponding irradiation gradient is tested, and the microscopic characterization parameters of the sample under the irradiation gradient are obtained by micro-focus CT scanning. S3. After the specimens have undergone full-gradient microwave irradiation and CT scanning, a uniaxial compression mechanical test is performed to obtain the macroscopic mechanical parameters of the specimens. S4. Based on the microscopic characterization parameters and macroscopic mechanical parameters obtained in steps S1 to S3, perform a fitting analysis on the correlation between each microscopic characterization parameter and the macroscopic mechanical parameter, and assign the weight of the single-factor transformation factor corresponding to each microscopic characterization parameter according to the correlation coefficient. S5. Based on the single-factor transformation factors corresponding to each microscopic characterization parameter and their assigned weights, the medium state transformation factor is calculated using a weighted average. ; S6. Based on the preset media attribute comprehensive conversion factor The numerical range of the sample is used to determine the transformation state of the hard rock medium corresponding to the sample, providing a quantitative basis for the decompression design and dynamic disaster prevention of the surrounding rock in deep tunnels.

[0028] In step S1, the standard sample is a cylindrical granite sample with a diameter of 50 mm and a height of 100 mm. The drying treatment is carried out by oven drying, the drying temperature is set to 105℃, the drying time is 24 hours, and after drying, the sample is allowed to cool to room temperature before subsequent tests are carried out.

[0029] Furthermore, in step S2, a multi-mode cavity industrial microwave system with a frequency of 2.45 GHz and a rated power of 0-6 kW is used for irradiation treatment. The constant irradiation power is set to 6 kW, and the irradiation duration gradient is set to 1 min, 2 min, 3 min, 4 min, and 5 min for a total of 5 gradients. An infrared thermal imaging camera is used to test the surface temperature of the sample after irradiation.

[0030] Among them, the microscopic characterization parameters include fracture rate and fracture fractal dimension, and can also be used to supplement fracture volume; Determining the state of the medium based on the I value provides a basis for the design of support and pressure relief for the surrounding rock of the tunnel.

[0031] Fracture volume is the total volume occupied by all fractures within coal and rock in three-dimensional space. It is a direct indicator for quantifying damage. In CT scans, fracture volume is the sum of the volumes of all voxels marked as fractures, and its calculation formula is:

[0032] in: Indicates the fracture volume. ; It is the number of slit voxels; , , It represents the size of a voxel in three directions.

[0033] The crack ratio is the proportion of the volume occupied by cracks per unit volume of the sample, and is calculated using the following formula:

[0034] in The fracture volume is expressed in units of 1. , Total volume of the sample, in units of The fractal dimension of the fracture is calculated using the box counting method, and the formula is as follows:

[0035] in, The required side length to cover the crack is... The number of boxes.

[0036] Furthermore, in step three, the uniaxial compression mechanics test adopts a rock mechanics servo test system, the loading method is displacement-controlled loading, and the loading rate is set to 0.002 mm / s; the macroscopic mechanical parameters include at least uniaxial compressive strength and elastic modulus.

[0037] In step four, the Pearson correlation coefficients of each microscopic characterization parameter and macroscopic mechanical parameter are fitted using the nonlinear least squares method. After normalizing the correlation coefficients, the weights of the corresponding single-factor transformation factors are obtained, and the sum of the weights of all single-factor transformation factors is 1.

[0038] Specifically, the medium state transformation factor The calculation formula is:

[0039] Among them, I Vf This represents the conversion factor based on the fracture volume definition; I φ This represents the conversion factor defined based on the crack ratio; I D This represents the transformation factor defined based on the fractal dimension. I This is based on multiple parameters, including fracture volume, fracture ratio, and fractal dimension. , , Indicates the weight of each conversion factor. + + =1.

[0040] Furthermore, the single-factor conversion factor is the ratio of the mesoscopic characterization parameter of the sample under the current irradiation state to the mesoscopic characterization parameter under the initial state; where:

[0041]

[0042]

[0043] In the formula: V fm , φ m , D m These represent the final state's fracture volume, fracture ratio, and fractal dimension, respectively.

[0044] In step S6, the medium conversion state is divided into three levels: continuous medium, quasi-continuous medium, and discontinuous medium; when When the value is ≤ the first preset threshold, it is determined to be a continuous medium, and fracturing and depressurization treatment is required for the corresponding engineering scenario; when the first preset threshold is < When the value is ≤ the second preset threshold, it is determined to be a quasi-continuous medium, and the corresponding engineering scenario requires further depressurization to a certain extent; when When the second preset threshold is reached, it is determined to be a discontinuous medium, and dynamic disaster prevention and control are required for the corresponding engineering scenario.

[0045] To achieve the above objectives, specific examples of the present invention are as follows: The test involved cylindrical granite specimens, measuring 50mm × 100mm (diameter × height). The equipment included a multi-cavity industrial microwave system, a microfocus CT scanning system, and an MTS-816 rock mechanics testing system. The industrial microwave system operated at a frequency of 2.45GHz with a power range of 0-6kW. Internally, it consisted of six microwave generators, refractory bricks, a control panel, and a sealed metal cavity. The rock mechanics testing system comprised a loading system, a control system, and a measurement system. The loading system included a hydraulic source, a load frame, actuators, and servo valves; the measurement system consisted of a frame force and displacement sensor, a force sensor, an extensometer, and displacement sensors; the control system consisted of a feedback control system, a data acquisition unit, and a computer. The entire process was computer-controlled, enabling automatic data acquisition and processing for the rock acoustic wave testing instrument.

[0046] After the experiment, the collected data were processed and the mechanical parameters of the irradiated granite were analyzed. Based on the processed CT microscopic data and mechanical parameters, a relationship curve was plotted as follows: Figure 2 As shown, the correlation coefficients between each microscopic parameter and the mechanical parameter were analyzed using an exponential function fitting method, and the weights of each conversion factor were assigned based on the magnitude of the correlation coefficients. Specific parameter information is shown in the table below. Table 1 shows the microscopic parameters obtained after CT scan processing.

[0047] Table 2 shows the mechanical properties after microwave irradiation.

[0048] Based on the above microscopic parameters and mechanical property parameters, each conversion factor was calculated. Since the conversion factors at 0 min and 5 min are fixed values ​​(0 for 0 min and 1 for 5 min), the following table is omitted:

[0049] The relationship between CT micro-parameters and peak stress was fitted using an exponential function, and the result follows the formula ExpDec1. The fitting results are as follows:

[0050] Based on the aforementioned correlation-based weighting method, the weights of the conversion factors are calculated as follows:

[0051] ω 1 = 0.34 ω 2 = 0.34 ω 3 = 0.32; Calculate the total conversion factor per minute using the formula:

[0052] Based on the calculated I value, the medium state is classified:

[0053] This invention adopts an evaluation system that integrates multiple microscopic characterization parameters, which breaks through the limitations of existing single-parameter evaluation. It simultaneously considers the influence of multiple dimensions such as fracture development scale, spatial structure complexity, and extension characteristics on the state of rock mass medium, which greatly reduces the evaluation error caused by test interference and makes the evaluation results more comprehensive and accurate. This invention assigns weights based on the correlation between microscopic parameters and macroscopic mechanical parameters. The weighting system is scientific and reasonable, making the comprehensive evaluation index more sensitive to the continuous transformation process of hard rock media state. It can accurately capture the gradual transformation characteristics of rock media during microwave fracturing.

[0054] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0055] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0056] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the state of a hard rock stratum, characterized in that, Includes the following steps: S1. Prepare standard samples of hard rock layers, dry the standard samples, test their initial longitudinal wave velocity, and obtain the initial microscopic characterization parameters of the samples in their intact state by microfocus CT scanning. S2. The standard sample is subjected to graded irradiation treatment with multiple gradient durations using the set microwave power. After each irradiation is completed, the surface temperature of the sample is tested. After the sample cools naturally to room temperature, the longitudinal wave velocity under the corresponding irradiation gradient is tested, and the microscopic characterization parameters of the sample under the irradiation gradient are obtained by micro-focus CT scanning. S3. After the specimens have undergone full-gradient microwave irradiation and CT scanning, a uniaxial compression mechanical test is performed to obtain the macroscopic mechanical parameters of the specimens. S4. Based on the microscopic characterization parameters and macroscopic mechanical parameters obtained in steps S1 to S3, perform a fitting analysis on the correlation between each microscopic characterization parameter and the macroscopic mechanical parameter, and assign the weight of the single-factor transformation factor corresponding to each microscopic characterization parameter according to the correlation coefficient. S5. Based on the single-factor transformation factors corresponding to each microscopic characterization parameter and their assigned weights, the medium state transformation factor is calculated using a weighted average. ; S6. Based on the preset medium state conversion factor The numerical range is used to determine the transformation state of the hard rock medium corresponding to the sample, providing a quantitative basis for stress relief and disaster prevention of the surrounding rock in deep tunnels.

2. The method for determining the state of hard rock strata according to claim 1, characterized in that: In step S1, the standard sample is a cylindrical granite sample with a diameter of 50 mm and a height of 100 mm. The drying treatment is carried out by oven drying, the drying temperature is set to 105℃, the drying time is 24 hours, and after drying, the sample is allowed to cool to room temperature before subsequent tests are carried out.

3. The method for determining the state of hard rock strata according to claim 1, characterized in that: In step S2, a multi-mode cavity industrial microwave system with a frequency of 2.45 GHz and a rated power of 0-6 kW is used for irradiation treatment. The constant irradiation power is set to 6 kW, and the irradiation duration gradient is set to 1 min, 2 min, 3 min, 4 min, and 5 min for a total of 5 gradients. An infrared thermal imaging camera is used to test the surface temperature of the sample after irradiation.

4. The method for determining the state of hard rock strata according to claim 1, characterized in that: The microscopic characterization parameters include fracture rate and fracture fractal dimension, and can be supplemented with fracture volume. Fracture volume is the total volume occupied by all fractures inside the coal and rock in three-dimensional space, and is a direct indicator for quantifying damage. In CT scans, fracture volume is the sum of the volumes of all voxels marked as fractures, and its calculation formula is as follows: in: Indicates the fracture volume. ; It is the number of slit voxels; , , It represents the size of a voxel in three directions.

5. The method for determining the state of hard rock strata according to claim 4, characterized in that: The crack rate is the proportion of the volume occupied by cracks per unit volume of the sample, and is calculated using the following formula: in The fracture volume is expressed in units of 1. , The total volume of the sample is expressed in units of 1000 liters. The fractal dimension of the fracture is calculated using the box counting method, and the calculation formula is as follows: in, The required side length to cover the crack is... The number of boxes.

6. The method for determining the state of hard rock strata according to claim 1, characterized in that: In step three, the uniaxial compression mechanics test uses a rock mechanics servo test system, the loading method is displacement-controlled loading, and the loading rate is set to 0.002 mm / s; the macroscopic mechanical parameters include at least uniaxial compressive strength and elastic modulus.

7. The method for determining the state of hard rock strata according to claim 1, characterized in that: In step four, the Pearson correlation coefficients of each microscopic characterization parameter and macroscopic mechanical parameter are fitted using the nonlinear least squares method. After normalizing the correlation coefficients, the weights of the corresponding single-factor transformation factors are obtained, and the sum of the weights of all single-factor transformation factors is 1.

8. The method for determining the state of hard rock strata according to claim 1, characterized in that: Medium state transformation factor The calculation formula is: Among them, I Vf This represents the conversion factor based on the fracture volume definition; I φ This represents the conversion factor defined based on the crack ratio; I D This represents the transformation factor defined based on the fractal dimension. I This is based on multiple parameters, including fracture volume, fracture ratio, and fractal dimension. , , Indicates the weight of each conversion factor. + + =1.

9. The method for determining the state of hard rock strata according to claim 8, characterized in that: The single-factor conversion factor is the ratio of the mesoscopic characterization parameter of the sample under the current irradiation state to the mesoscopic characterization parameter under the initial state; where: In the formula: V fm , φ m , D m These represent the final state's fracture volume, fracture ratio, and fractal dimension, respectively.

10. The method for determining the state of hard rock strata according to claim 1, characterized in that: In step S6, the medium conversion state is divided into three levels: continuous medium, quasi-continuous medium, and discontinuous medium; when When the value is ≤ the first preset threshold, it is determined to be a continuous medium, and fracturing and depressurization treatment is required for the corresponding engineering scenario; when the first preset threshold is < When the value is ≤ the second preset threshold, it is determined to be a quasi-continuous medium, and the corresponding engineering scenario requires further depressurization to a certain extent; when When the second preset threshold is reached, it is determined to be a discontinuous medium, and dynamic disaster prevention and control are required for the corresponding engineering scenario.

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