Crushed weakly cemented soft rock crustal stress measurement method based on Kaiser effect

Abstract

The invention relates to the technical field of pressure measurement, and discloses a crushed weakly cemented soft rock crustal stress measurement method based on a Kaiser effect. According to the method, based on the ultrasonic reflection principle, an ultrasonic probe is injected into a rock block in a drilling mode, ultrasonic detection is started, echo signals generated when ultrasonic waves enter the rock block and then are reflected in the rock block are recorded, m groups of received echo signals are processed by receiving the echo signals which are continuously reflected, the principal stress direction of the rock block is determined, and the rock block is determined. After the principal stress direction of the rock block is determined, the principal stress of the rock block is determined through the Kaiser effect, and meanwhile the three-direction principal stress of the rock block is determined based on the elastic mechanics theory; and after the three-dimensional principal stress of the rock is determined, the crustal stress measurement result of the crushed weakly cemented soft rock is calculated through the data estimation model, so that the crustal stress measurement efficiency of the crushed weakly cemented soft rock is improved.

Description

Technical Field

[0001] The invention relates to the technical field of pressure measurement, and in particular to a method for measuring ground stress of broken weakly cemented soft rocks based on the Kaiser effect. Background Art

[0002] The traditional Kaiser effect-based method for measuring geostress requires that the rock blocks be transported back to the laboratory, and it is not possible to conduct acoustic emission experiments on site. It is also time-consuming and labor-intensive to process the rock blocks into standard-sized specimens. In addition, the traditional method of using water to clean the excavated holes during the coring process in the borehole core stress relief method may cause the broken weakly cemented soft rock to disintegrate into mud, thereby affecting the coring. Therefore, the use of traditional acoustic emission experiments and borehole core stress relief methods in measuring geostress in broken weakly cemented soft rocks has obvious shortcomings.

[0003] There is an existing open patent application CN109374409A. This invention drills holes and classifies each hole according to wave velocity; at the same time, prepares expansive cement slurry, and places and fixes pressure sensors in each drilled hole; then obtains the tensile strength of the surrounding rock without the influence of geostress and the critical crushing pressure of the surrounding rock under the influence of geostress; calculates the minimum horizontal principal stress perpendicular to the fracture surface based on the obtained rock tensile strength and rock critical crushing pressure, but because only the minimum horizontal principal stress perpendicular to the fracture surface is measured, the accuracy is insufficient and has certain limitations. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the shortcomings of the prior art, the present invention provides a method for measuring the ground stress of broken weakly cemented soft rock based on the Kaiser effect, which has the advantages of accuracy and high efficiency, and solves the obvious shortcomings of traditional acoustic emission experiments and drilling casing stress relief methods.

[0006] (II) Technical solution

[0007] In order to solve the technical problems that the above-mentioned traditional acoustic emission experiment and drilling casing stress relief method have obvious shortcomings, the present invention provides the following technical solutions:

[0008] The present invention discloses a method for measuring ground stress of broken weakly cemented soft rock based on Kaiser effect, which specifically comprises the following steps:

[0009] S1. Based on the ultrasonic reflection principle, n ultrasonic probes are injected into the rock through drilling;

[0010] S2, start ultrasonic testing, and record the echo signal when the ultrasonic wave enters the rock block and then reflects inside the rock block;

[0011] S3, by receiving the continuously reflected echo signals, processing the received m groups of echo signals, and determining the principal stress direction of the rock block;

[0012] S31, performing noise reduction processing on the received echo signal to obtain a processed echo signal;

[0013] S32, based on the processed echo signal, calculating the echo signal wave velocity according to the difference between the horizontal coordinates of the echo signals of adjacent periods;

[0014] S33, determining the principal stress direction of the rock block based on the calculated echo signal velocity;

[0015] S4. After determining the principal stress direction of the rock block, the principal stress magnitude of the rock block is determined by the Kaiser effect, and at the same time, the principal stress magnitudes of the three directions of the rock block are determined based on the theory of elastic mechanics;

[0016] S5. After determining the magnitude of the three-dimensional principal stress of the rock block, the ground stress measurement results of the broken weakly cemented soft rock are calculated through the data estimation model.

[0017] The present invention uses an ultrasonic reflection principle to inject an ultrasonic probe into a rock block through a drilling method, and simultaneously enables ultrasonic detection, records echo signals when the ultrasonic wave is reflected inside the rock block after entering the rock block, processes m groups of received echo signals by receiving continuously reflected echo signals, and determines the principal stress direction of the rock block. After the principal stress direction of the rock block is determined, the principal stress magnitude of the rock block is determined through the Kaiser effect, and at the same time, the magnitude of the three-dimensional principal stress of the rock block is determined based on the theory of elastic mechanics; after the magnitude of the three-dimensional principal stress of the rock block is determined, the ground stress measurement result of the broken weakly cemented soft rock is calculated through a data estimation model, thereby improving the efficiency of the ground stress measurement of the broken weakly cemented soft rock.

[0018] Preferably, the step of performing noise reduction processing on the received echo signal to obtain the processed echo signal comprises the following steps:

[0019] Assuming the number of continuously reflected echo signals received is Z, the formula for average denoising of the reflected echo signals is as follows:

[0020]

[0021] in, is the reflected echo signal after mean denoising, g l is the lth received reflected echo signal; f is the ideal noise-free echo signal, m l is the noise of the lth received reflected echo signal;

[0022] The reflected echo signal after mean denoising is decomposed by constructing a Laplace pyramid;

[0023] The reflected echo signal after mean denoising is sampled for shear wave and longitudinal wave respectively, and then the sampled reflected echo signal is convolved using a Gaussian window function. Repeating the above operation repeatedly can form a series of tower layers with gradually decreasing resolution and low-pass filtering. Repeating the above process repeatedly can obtain a series of reflected echo signals. This step is the construction process of the Laplace pyramid.

[0024] Through the constructed Laplace pyramid, the reflected echo signals at the corresponding levels are fused to obtain the synthetic signal F(x);

[0025] The synthetic signal F(x) is filtered and denoised, and the formula used for filtering and denoising is:

[0026]

[0027] Where W represents the total number of filtering times; represents the i-th guided filtering;

[0028] Set the filtered and denoised composite signal to be the processed echo signal.

[0029] Preferably, the step of calculating the echo signal wave velocity based on the difference between the horizontal coordinates of the echo signals of adjacent periods based on the processed echo signal comprises the following steps:

[0030] When ultrasonic waves propagate in an ideal material, the propagation velocity of the longitudinal wave is expressed as:

[0031]

[0032] The propagation speed of shear waves is expressed as:

[0033]

[0034] The ratio of the propagation speed of shear waves to that of longitudinal waves is:

[0035]

[0036] Where E represents the elastic properties of the medium, ρ represents the density of the medium, σ represents the Poisson's ratio, and C s represents the propagation speed of longitudinal waves, C j represents the propagation speed of shear waves;

[0037] During the ultrasonic transmission process, the ultrasonic probe will receive two types of ultrasonic waves, transverse waves and longitudinal waves. According to the ratio of the propagation speeds of transverse waves to longitudinal waves in the same medium, the sound wave with a slower propagation speed is selected to extend the ultrasonic propagation time and improve the accuracy of extracting the corresponding time difference of adjacent echo signals.

[0038] Preferably, determining the principal stress direction of the rock block based on the calculated echo signal velocity comprises the following steps:

[0039] The echo signal velocities calculated by ultrasonic probes at multiple angles are compared, and the angle with the fastest echo signal velocity is set as the principal stress direction of the rock block.

[0040] The present invention performs noise reduction processing on the received echo signal to obtain a processed echo signal, and based on the processed echo signal, calculates the echo signal wave velocity according to the difference between the horizontal coordinates of adjacent period echo signals, and at the same time determines the principal stress direction of the rock block based on the calculated echo signal wave velocity, thereby ensuring the accuracy of ground stress measurement.

[0041] Preferably, after determining the principal stress direction of the rock block, determining the principal stress magnitude of the rock block by Kaiser effect, and determining the magnitude of the three-dimensional principal stress of the rock block based on the theory of elastic mechanics includes the following steps:

[0042] S41. Determine the magnitude of the principal stress in the direction of the principal stress of the rock block by using the Kaiser effect;

[0043] S42. Determine the magnitude of the three principal stresses in the rock block.

[0044] Preferably, determining the magnitude of the principal stress in the principal stress direction of the rock block by using the Kaiser effect comprises the following steps:

[0045]

[0046] Among them, α H represents the maximum principal stress of the rock block, α h represents the minimum principal stress of the rock block, α KH ,α Kh It represents the maximum Kaiser point stress and the minimum Kaiser point stress in the principal stress direction of the rock block, p represents the pore pressure, and β represents the effective stress coefficient.

[0047] Preferably, determining the magnitude of the three-dimensional principal stress of the rock block comprises the following steps:

[0048] The maximum principal stress of the rock block is set as the maximum horizontal principal stress, and the minimum principal stress of the rock block is set as the minimum horizontal principal stress. The vertical principal stress is calculated based on the maximum horizontal principal stress and the minimum horizontal principal stress.

[0049] The vertical principal stress calculation formula is as follows:

[0050]

[0051] Among them, α t Indicates the tensile strength of rock, k x represents the maximum horizontal principal stress direction coefficient, ky represents the minimum horizontal principal stress direction coefficient, k z represents the perpendicular principal stress direction coefficient, Represents the ratio of rock block radius to thickness, α z is the vertical principal stress.

[0052] The present invention determines the magnitude of the principal stress in the principal stress direction of the rock block through the Kaiser effect, and simultaneously calculates and determines the magnitude of the three-dimensional principal stress of the rock block based on the determined principal stress in the principal stress direction of the rock block, thereby improving the reliability of the calculation of the ground stress.

[0053] Preferably, after determining the magnitude of the three-dimensional principal stress of the rock block, calculating the ground stress measurement result of the broken weakly cemented soft rock by using a data estimation model comprises the following steps:

[0054] S51, constructing a data estimation model;

[0055] The three-dimensional principal stress of the rock block is set to be the ground stress of the broken weakly cemented soft rock;

[0056]

[0057] Among them, Q represents the data estimation model;

[0058] Collect the historically measured three-dimensional principal stress magnitudes of rock blocks and the corresponding rock fragmentation degree images;

[0059] Input the three-dimensional principal stress magnitudes of the rock block corresponding to the image of the degree of crushing into the data estimation model, and record the output data of the rock block;

[0060] S52, inputting the three-dimensional principal stress of the rock block measured in real time into the constructed data estimation model to determine the current degree of rock fragmentation.

[0061] The present invention constructs a data prediction model, collects historically measured three-dimensional principal stress magnitudes of rock blocks and corresponding rock fragmentation degree images, inputs the three-dimensional principal stress magnitudes of the rock blocks corresponding to the fragmentation degree images into the data prediction model, and performs analysis, thereby improving the efficiency of ground stress measurement and fragmentation degree analysis.

[0062] Preferably, based on the ultrasonic reflection principle, injecting n ultrasonic probes into the rock block by drilling comprises the following steps:

[0063] Place an ultrasonic probe at the center of the circular bottom surface of the rock block, and place an ultrasonic probe every 90 degrees on the non-circular surface;

[0064] Record the n ultrasound probes placed and number the n ultrasound probes n 1 ,n 2 ,...,n n , and save it to the database.

[0065] Preferably, the enabling of ultrasonic detection and recording of echo signals when ultrasonic waves enter the rock block and then reflect inside the rock block comprises the following steps:

[0066] For the n placed ultrasonic probes, the initial ultrasonic frequency, intensity and period of the n ultrasonic probes are set;

[0067] Based on the saved numbers, the ultrasound waves received by each ultrasound probe are recorded step by step.

[0068] (III) Beneficial effects

[0069] Compared with the prior art, the present invention provides a method for measuring ground stress of broken weakly cemented soft rock based on Kaiser effect, which has the following beneficial effects:

[0070] 1. The invention uses the ultrasonic reflection principle to inject an ultrasonic probe into a rock block through drilling, and simultaneously activates ultrasonic detection to record the echo signal when the ultrasonic wave is reflected inside the rock block after entering the rock block. By receiving the continuously reflected echo signals, the received m groups of echo signals are processed, and the principal stress direction of the rock block is determined. After the principal stress direction of the rock block is determined, the principal stress magnitude of the rock block is determined by the Kaiser effect, and at the same time, the magnitude of the three-dimensional principal stress of the rock block is determined based on the theory of elastic mechanics. After determining the magnitude of the three-dimensional principal stress of the rock block, the ground stress measurement result of the broken weakly cemented soft rock is calculated by a data estimation model, thereby improving the efficiency of the ground stress measurement of the broken weakly cemented soft rock.

[0071] 2. The invention performs noise reduction processing on the received echo signal to obtain a processed echo signal, and based on the processed echo signal, calculates the echo signal wave velocity according to the difference between the horizontal coordinates of the echo signals of adjacent periods, and at the same time determines the principal stress direction of the rock block based on the calculated echo signal wave velocity, thereby ensuring the accuracy of the ground stress measurement.

[0072] 3. The invention determines the magnitude of the principal stress in the principal stress direction of the rock block through the Kaiser effect, and at the same time calculates and determines the magnitude of the three-dimensional principal stress of the rock block based on the determined magnitude of the principal stress in the principal stress direction of the rock block, thereby improving the reliability of the calculation of ground stress.

[0073] 4. The invention constructs a data estimation model, collects the historically measured three-dimensional principal stress magnitudes of rock blocks, and the corresponding rock fragmentation degree images, inputs the three-dimensional principal stress magnitudes of the rock blocks corresponding to the fragmentation degree images into the data estimation model, and performs analysis, thereby improving the efficiency of ground stress measurement and fragmentation degree analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 It is a schematic diagram of the structural process of measuring ground stress of broken weakly cemented soft rock according to the present invention. DETAILED DESCRIPTION

[0075] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0076] Example 1

[0077] See also Figure 1 This embodiment discloses a method for measuring ground stress of broken weakly cemented soft rock based on Kaiser effect, which specifically includes the following steps:

[0078] S1. Based on the ultrasonic reflection principle, n ultrasonic probes are injected into the rock through drilling;

[0079] S2, start ultrasonic testing, and record the echo signal when the ultrasonic wave enters the rock block and then reflects inside the rock block;

[0080] S3, by receiving the continuously reflected echo signals, processing the received m groups of echo signals, and determining the principal stress direction of the rock block;

[0081] S31, performing noise reduction processing on the received echo signal to obtain a processed echo signal;

[0082] S32, based on the processed echo signal, calculating the echo signal wave velocity according to the difference between the horizontal coordinates of the echo signals of adjacent periods;

[0083] S33, determining the principal stress direction of the rock block based on the calculated echo signal velocity;

[0084] S4. After determining the principal stress direction of the rock block, the principal stress magnitude of the rock block is determined by the Kaiser effect, and at the same time, the principal stress magnitudes of the three directions of the rock block are determined based on the theory of elastic mechanics;

[0085] S5. After determining the magnitude of the three-dimensional principal stress of the rock block, the ground stress measurement results of the broken weakly cemented soft rock are calculated through the data estimation model;

[0086] For further information, see Figure 1 Based on the ultrasonic reflection principle, n ultrasonic probes are injected into the rock through drilling, which includes the following steps:

[0087] Place an ultrasonic probe at the center of the circular bottom surface of the rock block, and place an ultrasonic probe every 90 degrees on the non-circular surface;

[0088] Record the n ultrasound probes placed and number the n ultrasound probes n 1 ,n 2 ,...,n n , and save it to the database;

[0089] For further information, see Figure 1 , start ultrasonic testing, and record the echo signal when the ultrasonic wave enters the rock and then reflects inside the rock, including the following steps:

[0090] For the n placed ultrasonic probes, the initial ultrasonic frequency, intensity and period of the n ultrasonic probes are set;

[0091] Further, based on the saved serial numbers, the ultrasonic waves received by each ultrasonic probe are recorded step by step;

[0092] For further information, see Figure 1 , by receiving the continuously reflected echo signals, processing the received m groups of echo signals, and determining the principal stress direction of the rock block includes the following steps:

[0093] S31, performing noise reduction processing on the received echo signal to obtain a processed echo signal;

[0094] Assuming the number of continuously reflected echo signals received is Z, the formula for average denoising of the reflected echo signals is as follows:

[0095]

[0096] in, is the reflected echo signal after mean denoising, g l is the lth received reflected echo signal; f is the ideal noise-free echo signal, m l is the noise of the lth received reflected echo signal;

[0097] The reflected echo signal after mean denoising is decomposed by constructing a Laplace pyramid;

[0098] The reflected echo signal after mean denoising is sampled for shear wave and longitudinal wave respectively, and then the sampled reflected echo signal is convolved using a Gaussian window function. Repeating the above operation repeatedly can form a series of tower layers with gradually decreasing resolution and low-pass filtering. Repeating the above process repeatedly can obtain a series of reflected echo signals. This step is the construction process of the Laplace pyramid.

[0099] Through the constructed Laplace pyramid, the reflected echo signals at the corresponding levels are fused to obtain the synthetic signal F(x);

[0100] The synthetic signal F(x) is filtered and denoised, and the formula used for filtering and denoising is:

[0101]

[0102] Where W represents the total number of filtering times; represents the i-th guided filtering;

[0103] Set the filtered and denoised synthetic signal as the processed echo signal;

[0104] S32, based on the processed echo signal, calculating the echo signal wave velocity according to the difference between the horizontal coordinates of the echo signals of adjacent periods;

[0105] When ultrasonic waves propagate in an ideal material, the propagation velocity of the longitudinal wave is expressed as:

[0106]

[0107] The propagation speed of shear waves is expressed as:

[0108]

[0109] The ratio of the propagation speed of shear waves to that of longitudinal waves is:

[0110]

[0111] Where E represents the elastic properties of the medium, ρ represents the density of the medium, σ represents the Poisson's ratio, and C s represents the propagation speed of longitudinal waves, C j represents the propagation speed of shear waves;

[0112] Furthermore, during the ultrasonic transmission process, the ultrasonic probe will receive two types of ultrasonic waves, namely, transverse waves and longitudinal waves. According to the ratio of the propagation speeds of transverse waves to longitudinal waves in the same medium, the sound wave with a slower propagation speed is selected to extend the ultrasonic propagation time and improve the accuracy of extracting the corresponding time difference of adjacent echo signals.

[0113] S33, determining the principal stress direction of the rock block based on the calculated echo signal velocity;

[0114] Compare the echo signal wave velocities calculated by ultrasonic probes at multiple angles, and set the angle with the fastest echo signal wave velocity as the principal stress direction of the rock block;

[0115] For further information, see Figure 1 After determining the principal stress direction of the rock block, the principal stress magnitude of the rock block is determined by the Kaiser effect. At the same time, based on the theory of elastic mechanics, determining the magnitude of the three-dimensional principal stress of the rock block includes the following steps:

[0116] S41. Determine the magnitude of the principal stress in the direction of the principal stress of the rock block by using the Kaiser effect;

[0117]

[0118] Among them, α H represents the maximum principal stress of the rock block, α h represents the minimum principal stress of the rock block, α KH ,α Kh represents the maximum Kaiser point stress and the minimum Kaiser point stress in the principal stress direction of the rock block, p represents the pore pressure, and β represents the effective stress coefficient;

[0119] S42, determine the magnitude of the three principal stresses of the rock block;

[0120] The maximum principal stress of the rock block is set as the maximum horizontal principal stress, and the minimum principal stress of the rock block is set as the minimum horizontal principal stress. The vertical principal stress is calculated based on the maximum horizontal principal stress and the minimum horizontal principal stress.

[0121] The vertical principal stress calculation formula is as follows:

[0122]

[0123] Among them, α t Indicates the tensile strength of rock, k x represents the maximum horizontal principal stress direction coefficient, k y represents the minimum horizontal principal stress direction coefficient, k z represents the perpendicular principal stress direction coefficient, Represents the ratio of rock block radius to thickness, α z is the vertical principal stress;

[0124] For further information, see Figure 1 After determining the three-dimensional principal stress of the rock block, the following steps are included to calculate the ground stress measurement results of the broken weakly cemented soft rock through the data estimation model:

[0125] S51, constructing a data estimation model;

[0126] The three-dimensional principal stress of the rock block is set to be the ground stress of the broken weakly cemented soft rock;

[0127]

[0128] Among them, Q represents the data estimation model;

[0129] Collect the historically measured three-dimensional principal stress magnitudes of rock blocks and the corresponding rock fragmentation degree images;

[0130] Input the three-dimensional principal stress magnitudes of the rock block corresponding to the image of the degree of crushing into the data estimation model, and record the output data of the rock block;

[0131] S52, inputting the three-dimensional principal stress of the rock block measured in real time into the constructed data estimation model to determine the current degree of rock fragmentation.

[0132] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for measuring ground stress of broken weakly cemented soft rock based on Kaiser effect, characterized in that: The following steps are involved: S1. Based on the ultrasonic reflection principle, n ultrasonic probes are injected into the rock through drilling; S2, start ultrasonic testing, and record the echo signal when the ultrasonic wave enters the rock block and then reflects inside the rock block; S3, by receiving the continuously reflected echo signals, processing the received m groups of echo signals, and determining the principal stress direction of the rock block; S31, performing noise reduction processing on the received echo signal to obtain a processed echo signal; S32, based on the processed echo signal, calculating the echo signal wave velocity according to the difference between the horizontal coordinates of the echo signals of adjacent periods; S33, determining the principal stress direction of the rock block based on the calculated echo signal velocity; S4. After determining the principal stress direction of the rock block, the principal stress magnitude of the rock block is determined by the Kaiser effect, and at the same time, the principal stress magnitudes of the three directions of the rock block are determined based on the theory of elastic mechanics; S5. After determining the magnitude of the three-dimensional principal stress of the rock block, the ground stress measurement results of the broken weakly cemented soft rock are calculated through the data estimation model.

2. The method for measuring ground stress of broken weakly cemented soft rock based on Kaiser effect according to claim 1 is characterized in that: The step of performing noise reduction processing on the received echo signal to obtain the processed echo signal comprises the following steps: Assuming the number of continuously reflected echo signals received is Z, the formula for average denoising of the reflected echo signals is as follows: in, is the reflected echo signal after mean denoising, g l is the lth received reflected echo signal; f is the ideal noise-free echo signal, m l is the noise of the lth received reflected echo signal; The reflected echo signal after mean denoising is decomposed by constructing a Laplace pyramid; The reflected echo signal after mean denoising is sampled for shear wave and longitudinal wave respectively, and then the sampled reflected echo signal is convolved using a Gaussian window function. Repeating the above operation repeatedly can form a series of tower layers with gradually decreasing resolution and low-pass filtering. Repeating the above process repeatedly can obtain a series of reflected echo signals. This step is the construction process of the Laplace pyramid. Through the constructed Laplace pyramid, the reflected echo signals at the corresponding levels are fused to obtain the synthetic signal F(x); The synthetic signal F(x) is filtered and denoised, and the formula used for filtering and denoising is: Where W represents the total number of filtering times; represents the i-th guided filtering; Set the filtered and denoised composite signal to be the processed echo signal.

3. The method for measuring ground stress of broken weakly cemented soft rock based on Kaiser effect according to claim 1 is characterized in that: The step of calculating the echo signal wave velocity based on the processed echo signal according to the difference between the horizontal coordinates of the echo signals of adjacent periods comprises the following steps: When ultrasonic waves propagate in an ideal material, the propagation velocity of the longitudinal wave is expressed as: The propagation speed of shear waves is expressed as: The ratio of the propagation speed of shear waves to that of longitudinal waves is: Where E represents the elastic properties of the medium, ρ represents the density of the medium, σ represents the Poisson's ratio, and C s represents the propagation speed of longitudinal waves, C j represents the propagation speed of shear waves; During the ultrasonic transmission process, the ultrasonic probe will receive two types of ultrasonic waves, transverse waves and longitudinal waves. According to the ratio of the propagation speeds of transverse waves to longitudinal waves in the same medium, the sound wave with a slower propagation speed is selected to extend the ultrasonic propagation time and improve the accuracy of extracting the corresponding time difference of adjacent echo signals.

4. The method for measuring ground stress of broken weakly cemented soft rock based on Kaiser effect according to claim 1 is characterized in that: Determining the principal stress direction of the rock block based on the calculated echo signal velocity comprises the following steps: The echo signal velocities calculated by ultrasonic probes at multiple angles are compared, and the angle with the fastest echo signal velocity is set as the principal stress direction of the rock block.

5. The method for measuring ground stress of broken weakly cemented soft rock based on Kaiser effect according to claim 1 is characterized in that: After the principal stress direction of the rock block is determined, the principal stress magnitude of the rock block is determined by the Kaiser effect. At the same time, based on the theory of elastic mechanics, the magnitude of the three-dimensional principal stress of the rock block is determined, which includes the following steps: S41. Determine the magnitude of the principal stress in the direction of the principal stress of the rock block by using the Kaiser effect; S42. Determine the magnitude of the three principal stresses in the rock block.

6. The method for measuring ground stress of broken weakly cemented soft rock based on Kaiser effect according to claim 5 is characterized in that: Determining the magnitude of the principal stress in the principal stress direction of the rock block by using the Kaiser effect comprises the following steps: Among them, α H represents the maximum principal stress of the rock block, α h represents the minimum principal stress of the rock block, α KH ,α Kh It represents the maximum Kaiser point stress and the minimum Kaiser point stress in the principal stress direction of the rock block, p represents the pore pressure, and β represents the effective stress coefficient.

7. The method for measuring ground stress of broken weakly cemented soft rock based on Kaiser effect according to claim 5 is characterized in that: Determining the magnitude of the three-dimensional principal stress of the rock block comprises the following steps: The maximum principal stress of the rock block is set as the maximum horizontal principal stress, and the minimum principal stress of the rock block is set as the minimum horizontal principal stress. The vertical principal stress is calculated based on the maximum horizontal principal stress and the minimum horizontal principal stress. The vertical principal stress calculation formula is as follows: Among them, α t Indicates the tensile strength of rock, k x represents the maximum horizontal principal stress direction coefficient, k y represents the minimum horizontal principal stress direction coefficient, k z represents the perpendicular principal stress direction coefficient, Represents the ratio of rock radius to thickness, α z is the vertical principal stress.

8. The method for measuring ground stress of broken weakly cemented soft rock based on Kaiser effect according to claim 1, characterized in that: After determining the magnitude of the three-dimensional principal stress of the rock block, calculating the ground stress measurement result of the broken weakly cemented soft rock through the data estimation model includes the following steps: S51, constructing a data estimation model; The three-dimensional principal stress of the rock block is set to be the ground stress of the broken weakly cemented soft rock; Among them, Q represents the data estimation model; Collect the historically measured three-dimensional principal stress magnitudes of rock blocks and the corresponding rock fragmentation degree images; Input the three-dimensional principal stress magnitudes of the rock block corresponding to the image of the degree of crushing into the data estimation model, and record the output data of the rock block; S52, inputting the three-dimensional principal stress of the rock block measured in real time into the constructed data estimation model to determine the current degree of rock fragmentation.

9. The method for measuring ground stress of broken weakly cemented soft rock based on Kaiser effect according to claim 1, characterized in that: Based on the ultrasonic reflection principle, injecting n ultrasonic probes into the rock block by drilling includes the following steps: Place an ultrasonic probe at the center of the circular bottom surface of the rock block, and place an ultrasonic probe every 90 degrees on the non-circular surface; Record the n ultrasonic probes placed and number them n1, n2, ..., n n , and save it to the database.

10. The method for measuring ground stress of broken weakly cemented soft rock based on Kaiser effect according to claim 1, characterized in that: The method of activating ultrasonic detection and recording the echo signal when the ultrasonic wave enters the rock block and then reflects inside the rock block comprises the following steps: For the n placed ultrasonic probes, the initial ultrasonic frequency, intensity and period of the n ultrasonic probes are set; based on the saved numbers, the ultrasonic waves received by each ultrasonic probe are recorded step by step.

Images