An experimental method for simulating the cracking failure behavior of hard rock slabs.

Abstract

This invention discloses an experimental method for simulating the cracking failure behavior of hard rock slabs. The method includes steps S1, preparing a sample; S2, installing a blasting device; S3, preparing experimental instruments; S4, setting experimental parameters; and S5, starting the experiment. This invention accurately reproduces the stress environment of the surrounding rock under the action of drilling and blasting excavation in tunnels, which is characterized by "loading and unloading + strong dynamic disturbance". It reflects the actual stress situation of the surrounding rock under the action of drilling and blasting excavation and provides a new experimental means for scientifically revealing the cracking failure mechanism of the surrounding rock slabs in hard rock tunnels.

Description

Technical Field

[0001] This invention relates to the field of rock mechanics experimental technology, and in particular to an experimental method for simulating the cracking and failure behavior of hard rock plates. Background Technology

[0002] In recent decades, large-scale, high-intensity, and extensive over-exploitation has led to the increasing depletion of shallow mineral resources. Underground mines have successively entered the stage of deep mining at depths of thousands of meters, with the maximum mining depth reaching 4350 meters. Deep resources are characterized by complex occurrences, with mining environments exhibiting high stress (>50 MPa), high ground temperature (>40℃), high karst water pressure (>10 MPa), and strong disturbances. This results in frequent and severe disasters such as roof falls, rock bursts, and rib collapses during mining operations, which are difficult to predict and effectively prevent. Compared to soft rock, hard rock is more brittle (σc / σt>10) and has higher energy storage (>105 J / m3), leading to a greater magnitude and frequency of roadway disasters induced by drilling and blasting activities in deep hard rock mines. Furthermore, in deep hard rock roadways, onion-skin-like plate cracks are frequently observed in the surrounding rock, eventually developing into V-shaped grooves. The plate cracking phenomenon commonly found in deep hard and brittle surrounding rock is not only related to the properties of hard rock and stress state, but also affected by the dynamic and static disturbances of excavation activities. However, its failure mechanism is unclear and the inducing cause is unknown, which seriously threatens the safety of tunnel construction and the stability of the surrounding rock.

[0003] The cracking failure of surrounding rock in tunnels is a "black box" problem, as its fracture evolution process is difficult to observe visually on-site. To scientifically reveal the cracking failure mechanism of hard rock, it is necessary to reconstruct the mechanical environment of the surrounding rock under excavation disturbance and conduct rock mechanics tests in the laboratory based on the stress state of the surrounding rock. The stress problem of the surrounding rock in deep hard rock tunnels is complex. During excavation, the stress changes at different locations in the surrounding rock vary, involving not only high-stress unloading but also stress concentration loading and strong dynamic disturbances generated or derived from drilling and blasting activities. In other words, the stress path of the surrounding rock in the tunnel is a combination of "loading and unloading + strong dynamic disturbance." Therefore, conducting rock mechanics tests under corresponding stress paths for hard rock is crucial to understanding the cracking failure mechanism. However, experimental methods for studying the cracking failure behavior of hard rock are currently lacking. Based on a true triaxial testing machine, the research team developed different models of true triaxial disturbance-induced mutation experimental systems for rocks. These systems mechanically apply dynamic and static loads to rock samples based on the principle of impact using additional servo cylinders and rigid connecting rods. However, the frequency and duration of the disturbance loads applied by the system differ fundamentally from the explosive stress waves in hard rock mining drilling and blasting operations, making it difficult to accurately reflect the impact of blasting dynamic loads on rock slab cracking. Patent publication number CN107807051A discloses an experimental device and method for simulating unloading during deep-buried tunnel blasting excavation. This method uses hydraulic jacks to load predetermined values ​​onto the top, left, and right sides of a three-dimensional similar material model, then drills multiple small holes on the front and back sides with explosives for blasting excavation. Clearly, this device cannot achieve simultaneous application of three-dimensional loads, which is inconsistent with the three-dimensional mechanical environment of on-site tunnel blasting excavation. Based on this, patent publication number CN107807051A pre-casts multiple blasting holes in the production of a three-dimensional similar model and uses hydraulic jacks to load the sample in five directions (X, Y, Z) to a constant value, achieving the purpose of simulating the blasting excavation and unloading of underground engineering under three-dimensional stress conditions. However, it does not provide detailed descriptions of the blasting materials and detonation methods, and it is difficult to guarantee the quality of the tunnel model. In addition, some patents have been published, such as patent publication numbers CN201810886382.0, CN201810069320.0 and patent applications 201610220535.9, 201610551010.3, 201610028031.7 and 201510228942.X, all of which have invented an excavation unloading / blasting pressure relief device. However, most of them use water pressure or mechanical loads to load and unload in the pre-cast holes of the sample to simulate tunnel excavation behavior. Clearly, the above patents are used to simulate excavation unloading, but they cannot achieve the experimental objective of demonstrating the local rock slab cracking failure behavior under excavation. Furthermore, the loading methods are insufficient to reflect the mechanical environment of rock slab cracking during loading and unloading. Therefore, there is an urgent need to invent an experimental method to simulate the cracking failure behavior of hard rock slabs. Summary of the Invention

[0004] This invention provides an experimental method for simulating the cracking and failure behavior of hard rock slabs to solve the aforementioned problems in the prior art.

[0005] The solution of the present invention is:

[0006] A test method for simulating the cracking failure behavior of hard rock slabs includes the following steps:

[0007] S1. Prepare the sample. Process and prepare a cubic hard rock sample of the required size. Apply a thin layer of lubricant to the six surfaces of the hard rock sample. Then, drill a circular blind hole of a certain depth vertically at the center of one of the surfaces of the hard rock sample.

[0008] S2. Install the blasting device and fabricate a thin-walled sleeve that matches the size of the circular blind hole of the hard rock sample. Apply Vaseline to the outer surface of the thin-walled sleeve and place it in the circular blind hole to ensure full coupling and contact between the thin-walled sleeve and the hole wall. Then, bind the detonating cord and electric detonator of the required design weight with tape and place them in the thin-walled sleeve of the circular blind hole of the hard rock sample. Seal the thin-walled sleeve with stemming material and leave the electric detonator lead exposed for connection to the detonator.

[0009] S3. Prepare experimental instruments, including a true triaxial rock test system, an acoustic emission system, and an acoustic emission sensor installation auxiliary device. Six acoustic emission sensor installation auxiliary devices that match the surface of the hard rock sample are respectively installed and fixed on the true triaxial testing machine in the true triaxial rock test system. The acoustic emission sensor of the acoustic emission system is placed in the acoustic emission sensor installation auxiliary device and connected to the acoustic emission instrument through an amplifier via a signal line.

[0010] S4. Set the experimental parameters. Place the hard rock sample between the acoustic emission sensor mounting auxiliary devices on the true triaxial testing machine. The axial direction of the blind hole of the hard rock sample is consistent with the designed unloading direction. Move each loading module of the true triaxial testing machine through the control station of the true triaxial testing machine so that the acoustic emission sensor mounting auxiliary devices make initial contact with the six surfaces of the hard rock sample. After the electric detonator lead passes through the corresponding acoustic emission sensor mounting auxiliary device, it is connected to the detonator. Then, set the true triaxial experimental parameters, loading and unloading stress paths, and emission monitoring parameters.

[0011] S5. Start the experiment. Load the hard rock sample with a three-dimensional servo displacement control method according to the stress state and stress path set in the experimental scheme. After the set stress state is reached, the stress in one direction of the hard rock sample is kept constant. The other direction is suddenly unloaded on both sides and the detonator is started to detonate and apply dynamic load immediately. The remaining direction is kept loaded until the hard rock sample is destroyed. The acoustic emission system starts and stops synchronously with the true triaxial rock test system.

[0012] S6. Analyze the test data. After the experiment is stopped, analyze the stress and deformation data obtained by the control station and extensometer of the true triaxial testing machine and the real-time acoustic wave signal collected by the acoustic emission system. Perform three-dimensional positioning and moment tensor calculation on the acoustic emission event to determine whether plate cracking has occurred. Restore the test system to its original state, adjust the initial stress parameters and detonating cord weight test parameters in the test, and conduct the next set of experiments until plate cracking is observed. Determine the stress conditions and characteristics of plate cracking.

[0013] As a preferred technical solution, the thin-walled sleeve is a metal thin-walled sleeve, the bottom of the thin-walled sleeve is closed, the wall thickness is 1-2 mm, and the diameter is 6-8 mm. The function of the metal thin-walled sleeve is to prevent the explosive force from causing explosive damage to the sample. The detonating cord and the electric detonator are bound by either tape or rope.

[0014] As a preferred technical solution, the Protodyakonov coefficient of the hard rock sample is ≥8, and the side length is 100-300mm; a circular blind hole with a diameter of 8-10mm is vertically drilled in the surface of the hard rock sample, and the depth of the circular blind hole is < half the side length of the hard rock sample; the lubricant is either petroleum jelly or grease, and the circular blind hole is drilled by either a hand-held electric drill or a high-pressure water jet device.

[0015] As a preferred technical solution, the acoustic emission sensor installation auxiliary device is placed between each loading module of the true triaxial testing machine and each surface of the hard rock sample. The acoustic emission sensor installation auxiliary device includes a retractable pad, a hollow long screw, a rubber pad, and a rectangular block. The block is composed of multiple levels of rectangular sub-pads that match different sample sizes, connected by interlocking. Each sub-pad has 4-8 pre-drilled circular through holes with internal threads for placing the acoustic emission sensor and the detonator lead wire. The acoustic emission sensor of the acoustic emission system is placed at the front end of the circular through holes. The rubber pad is a cylinder with a certain degree of elasticity, placed in the circular through holes of the retractable pad to transmit the acoustic emission sensor... Between the sensor and the hollow long screw, one end is a sleeve base for mounting the acoustic emission sensor. The depth of the sleeve base is less than the thickness of the acoustic emission sensor. A small hole is opened at the bottom of the sleeve base to the other end, serving as a channel for the signal line. The hollow screw is connected to the circular through hole of the retractable pad by threads. The flange is a cuboid welded to the outer edge of the retractable pad, with a circular flange hole at each corner. The bolt passes through the circular hole of the flange and the hollow gasket to thread the flange and fix it to the loading module. The function of the hollow gasket is to create space between the flange and the loading module, providing routing conditions for manually tightening the hollow long screw and the acoustic emission probe signal line.

[0016] As a preferred technical solution, the stress path is a stress path of loading / unloading and strong dynamic disturbance. The stress path of loading / unloading and strong dynamic disturbance includes a first stress path and a second stress path. The first stress path and the second stress path respectively include σ1 loading, σ2 constant, σ3 unloading, and σd application. In the triaxial servo displacement control loading of the hard rock sample, the three directions are X, Y and Z. σ1, σ2, σ3 and σd are the vertical Z-direction stress, horizontal Y-direction stress, horizontal X-direction stress and the blasting dynamic load applied to the hard rock sample by the true triaxial rock test system. The blasting dynamic load is applied when unloading in one direction after the triaxial stress of the hard rock sample is applied to the set initial stress state. For each stress path, a set of no-blasting conditions with zero detonating cord weight is set as a reference for the blasting dynamic load.

[0017] As a preferred technical solution, the acoustic emission system comprises an acoustic emission instrument, two preamplifiers, and an acoustic emission sensor.

[0018] As a preferred technical solution, the loading module includes a Z-direction loading module, an X-direction loading module, and a Y-direction loading module.

[0019] A test method for simulating the cracking failure behavior of hard rock slabs, employing the aforementioned technical solution, includes the following steps: S1, sample preparation: A cubic hard rock sample of the required size is prepared. A thin layer of lubricant is applied to the six surfaces of the hard rock sample. Then, a circular blind hole of a certain depth is drilled vertically at the center of one surface of the hard rock sample. S2, installation of a blasting device: A thin-walled sleeve matching the size of the circular blind hole in the hard rock sample is fabricated. Vaseline is applied to the outer surface of the thin-walled sleeve, which is then placed in the circular blind hole, ensuring full coupling contact between the thin-walled sleeve and the hole wall. Finally, the designed required detonating cord and electric detonator are bound together with tape and placed in the hard rock sample. S3. In the thin-walled sleeve of the circular blind hole of the rock sample, the thin-walled sleeve is sealed with stemming material, leaving the electric detonator lead exposed for connection to the detonator; S4. Prepare the experimental instruments, including a true triaxial rock test system, an acoustic emission system, and acoustic emission sensor installation auxiliary devices. Six acoustic emission sensor installation auxiliary devices, matched to the surface of the hard rock sample, are respectively installed and fixed on the true triaxial testing machine of the true triaxial rock test system. The acoustic emission sensor of the acoustic emission system is placed in the acoustic emission sensor installation auxiliary device and connected to the acoustic emission instrument via an amplifier and signal line; S5. Set the experimental parameters, place the hard rock sample on the acoustic emission sensor installation auxiliary device on the true triaxial testing machine. Between the auxiliary devices, the axial direction of the blind hole of the hard rock sample is aligned with the designed unloading direction. The loading modules of the true triaxial testing machine are moved by the control station of the true triaxial testing machine to make initial contact between the acoustic emission sensor installation auxiliary device and the six surfaces of the hard rock sample. The detonator lead passes through the corresponding acoustic emission sensor installation auxiliary device and is connected to the detonator. Then, the true triaxial experimental parameters, loading and unloading stress paths, and emission monitoring parameters are set. S5: Start the experiment. According to the stress state and stress path set in the experimental scheme, the hard rock sample is loaded using a three-dimensional servo displacement control method. After reaching the set stress state, the stress in one direction of the hard rock sample remains constant, while the other direction undergoes double-sided loading. Suddenly unload and start the detonator to blast, immediately apply dynamic load, and continue loading in the remaining direction until the hard rock sample fails; the acoustic emission system starts and stops synchronously with the true triaxial rock test system; S6, analyze the test data. After the experiment stops, analyze the stress and deformation data obtained by the control station of the true triaxial testing machine and the extensometer and the real-time acoustic wave signal collected by the acoustic emission system, perform three-dimensional positioning and moment tensor calculation of the acoustic emission event, and determine whether plate cracking failure has occurred; restore the test system to its original state, adjust the initial stress parameters and detonating cord weight test parameters in the test, and conduct the next set of experiments until plate cracking failure is observed, and determine the stress conditions and characteristics of plate cracking failure.

[0020] The beneficial effects of this invention are:

[0021] This invention provides an experimental method for simulating the cracking failure behavior of hard rock slabs. Based on all stress paths of the surrounding rock at different locations in a drill-and-blast excavation tunnel, a true triaxial rock test system, an acoustic emission system, and an acoustic emission sensor installation auxiliary device are used to apply static loads and unload cubic rocks in different directions. Then, at the moment of unloading, a blasting device is used to blast the pre-made holes on the unloading surface of the cubic sample. By detonating detonating cords of different weights, different dynamic loads of the blasting stress wave are reflected. This method realizes the indoor reproduction of the rock's "loading and unloading + strong dynamic disturbance" stress mode, providing a new approach for scientifically revealing the cracking failure behavior of rock slabs.

[0022] (1) The stress environment of the surrounding rock under the action of drilling and blasting in the tunnel was accurately restored. The stress state of the surrounding rock at different positions before and after the excavation was analyzed and two stress path evolution forms were summarized. By drilling a certain depth of circular blind hole on the unloading side of the hard rock sample to fill the detonating cord of different weights, a triaxial loading and unloading experiment was carried out using a true triaxial experimental system. When the hard rock sample was unloaded in one direction, the detonating cord was detonated simultaneously to simulate the dynamic load effect of blasting of different degrees. This truly reflects the actual stress situation of the surrounding rock under the action of drilling and blasting, and provides a new experimental means for scientifically revealing the failure mechanism of the surrounding rock plate crack in hard rock tunnels.

[0023] (2) The acoustic emission sensor installation auxiliary device of the invention can adapt to samples of different sizes by means of the telescopic pad. Multiple circular through holes are built in it to install multiple acoustic emission sensors, which creates favorable conditions for three-dimensional positioning of acoustic emission and safe routing of electric detonator leads. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the present invention;

[0025] Figure 2 This is a cross-sectional view of the structure of the present invention (AA).

[0026] Figure 3 This is a schematic diagram of the structure of a true triaxial test system for rocks;

[0027] Figure 4 A schematic diagram of the acoustic emission system structure and its installation.

[0028] Figure 5 Schematic diagram of the auxiliary device for installing an acoustic emission sensor;

[0029] Figure 6 A schematic diagram showing the placement of the acoustic emission sensor on the rock.

[0030] Figure 7 This is a schematic diagram of the structure and connection of the blasting device;

[0031] Figure 8This is a schematic diagram of the stress path in a plate crack test of a hard rock specimen; where (A) is the first path and (B) is the second path.

[0032] The components are as follows: 1-True triaxial rock testing machine; 2-True triaxial testing machine control station; 3-Acoustic emission system; 4-Acoustic emission sensor installation auxiliary device; 5-Hard rock sample; 6-Blasting device; 101-Crossbeam; 102-Base; 103-Column; 104-Pressure plate; 105-Z-direction loading module; 106-X-direction loading module; 107-Y-direction loading module; 108-Extensometer; 109-Data cable; 110-Threaded hole; 301-Acoustic emission instrument; 302-Amplifier; 303-Acoustic emission sensor; 304-Signal cable; 401-Retractable pad; 4 02-Circular through hole; 403-Rubber pad; 404-Hollow long screw; 405-Flange; 406-Flange hole; 407-Bolt; 408-Hollow pad; 40101-First pad; 40102-Second pad; 40103-Third pad; 40104-Reset hole; 40105-Self-locking button; 40106-Telescopic hole; 40301-Sleeve base; 40302-Lead wire hole; 501-Circular blind hole; 601-Thin-walled sleeve; 602-Detonating cord and electric detonator; 603-Sticker putty; 604-Electric detonator lead wire; 605-Initiator. Detailed Implementation

[0033] To overcome the above deficiencies, the present invention provides an experimental method for simulating the cracking and failure behavior of hard rock slabs to solve the problems in the background art.

[0034] A test method for simulating the cracking failure behavior of hard rock slabs includes the following steps:

[0035] S1. Prepare the sample. Process and prepare a cubic hard rock sample of the required size. Apply a thin layer of lubricant to the six surfaces of the hard rock sample. Then, drill a circular blind hole of a certain depth vertically at the center of one of the surfaces of the hard rock sample.

[0036] S2. Install the blasting device and fabricate a thin-walled sleeve that matches the size of the circular blind hole of the hard rock sample. Apply Vaseline to the outer surface of the thin-walled sleeve and place it in the circular blind hole to ensure full coupling and contact between the thin-walled sleeve and the hole wall. Then, bind the detonating cord and electric detonator of the required design weight with tape and place them in the thin-walled sleeve of the circular blind hole of the hard rock sample. Seal the thin-walled sleeve with stemming material and leave the electric detonator lead exposed for connection to the detonator.

[0037] S3. Prepare experimental instruments, including a true triaxial rock test system, an acoustic emission system, and an acoustic emission sensor installation auxiliary device. Six acoustic emission sensor installation auxiliary devices that match the surface of the hard rock sample are respectively installed and fixed on the true triaxial testing machine in the true triaxial rock test system. The acoustic emission sensor of the acoustic emission system is placed in the acoustic emission sensor installation auxiliary device and connected to the acoustic emission instrument through an amplifier via a signal line.

[0038] S4. Set the experimental parameters. Place the hard rock sample between the acoustic emission sensor mounting auxiliary devices on the true triaxial testing machine. The axial direction of the blind hole of the hard rock sample is consistent with the designed unloading direction. Move each loading module of the true triaxial testing machine through the control station of the true triaxial testing machine so that the acoustic emission sensor mounting auxiliary devices make initial contact with the six surfaces of the hard rock sample. After the electric detonator lead passes through the corresponding acoustic emission sensor mounting auxiliary device, it is connected to the detonator. Then, set the true triaxial experimental parameters, loading and unloading stress paths, and emission monitoring parameters.

[0039] S5. Start the experiment. Load the hard rock sample with a three-dimensional servo displacement control method according to the stress state and stress path set in the experimental scheme. After the set stress state is reached, the stress in one direction of the hard rock sample is kept constant. The other direction is suddenly unloaded on both sides and the detonator is started to detonate and apply dynamic load immediately. The remaining direction is kept loaded until the hard rock sample is destroyed. The acoustic emission system starts and stops synchronously with the true triaxial rock test system.

[0040] S6. Analyze the test data. After the experiment is stopped, analyze the stress and deformation data obtained by the control station and extensometer of the true triaxial testing machine and the real-time acoustic wave signal collected by the acoustic emission system. Perform three-dimensional positioning and moment tensor calculation on the acoustic emission event to determine whether plate cracking has occurred. Restore the test system to its original state, adjust the initial stress parameters and detonating cord weight test parameters in the test, and conduct the next set of experiments until plate cracking is observed. Determine the stress conditions and characteristics of plate cracking.

[0041] The thin-walled sleeve is a metal thin-walled sleeve with a closed bottom, a wall thickness of 1-2 mm, and a diameter of 6-8 mm. The function of the metal thin-walled sleeve is to prevent the explosive force from causing explosive damage to the sample. The detonating cord and the electric detonator are bound by either tape or rope.

[0042] The hard rock sample has a Protodyakonov coefficient ≥8 and a side length of 100–300 mm. A circular blind hole with a diameter of 8–10 mm is vertically drilled in the surface of the hard rock sample, and the depth of the circular blind hole is less than half the side length of the hard rock sample. The lubricant is either petroleum jelly or grease. The circular blind hole is drilled by either a hand-held electric drill or a high-pressure water jet device.

[0043] The acoustic emission sensor installation auxiliary device is placed between each loading module of the true triaxial testing machine and each surface of the hard rock sample. The device includes a retractable pad, a hollow long screw, a rubber pad, and a rectangular block. The rectangular block is composed of multiple levels of cuboid sub-pads that match different sample sizes, connected by interlocking. Each sub-pad has 4-8 pre-drilled circular through holes with internal threads for placing the acoustic emission sensor and the detonator lead wire. The acoustic emission sensor of the acoustic emission system is placed at the front end of the circular through holes. The rubber pad is a cylinder with a certain degree of elasticity, placed in the circular through holes of the retractable pad, connecting the acoustic emission sensor and the hollow... Between the long screws, one end is a sleeve base for mounting the acoustic emission sensor. The depth of the sleeve base is less than the thickness of the acoustic emission sensor. A small hole is opened at the bottom of the sleeve base to the other end, serving as a channel for the signal line. The hollow screw is connected to the circular through hole of the retractable pad by threads. The flange is a cuboid, welded to the outer edge of the retractable pad, with a circular flange hole at each corner. The bolts pass through the circular holes of the flange and the hollow pad to thread the flange and fix it to the loading module. The function of the hollow pad is to create space between the flange and the loading module, providing routing conditions for manually tightening the hollow long screw and the acoustic emission probe signal line.

[0044] The stress path is the stress path of loading / unloading and strong dynamic disturbance. The stress path of loading / unloading and strong dynamic disturbance includes a first stress path and a second stress path. The first stress path and the second stress path respectively include σ1 loading, σ2 constant, σ3 unloading, and σd application. The hard rock sample is loaded in a three-dimensional servo displacement control mode. The three dimensions are X, Y and Z. σ1, σ2, σ3 and σd are the vertical Z-axis stress, horizontal Y-axis stress, horizontal X-axis stress and the blasting dynamic load applied to the hard rock sample by the true triaxial rock test system. The blasting dynamic load is applied when unloading in one direction after the triaxial stress of the hard rock sample is applied to the set initial stress state. For each stress path, a set of no-blasting conditions with zero detonating cord weight is set as a reference for the blasting dynamic load.

[0045] The loading module includes a Z-direction loading module, an X-direction loading module, and a Y-direction loading module. The acoustic emission system consists of an acoustic emitter, two preamplifiers, and an acoustic emission sensor.

[0046] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0047] Example 1:

[0048] See Figure 1-8A test method for simulating the cracking failure behavior of hard rock slabs includes six steps: sample preparation, installation of blasting device, preparation of experimental instruments, setting of experimental parameters, start of experiment, and analysis of test data. The specific steps are as follows:

[0049] S1. Preparation of sample 5: A cubic hard rock sample 5 of a certain size is prepared. A thin layer of lubricant is applied to the six surfaces of the hard rock sample 5. Then, a circular blind hole 501 of a certain depth is drilled vertically at the center of any surface of the hard rock sample 5.

[0050] S2. Install the blasting device 6: Fabricate a thin-walled sleeve 601 that matches the size of the blind hole 501 of the sample. Apply Vaseline to the outer surface of the thin-walled sleeve and place it in the circular blind hole 501 to ensure that the thin-walled sleeve is fully coupled and in contact with the hole wall of the circular blind hole 501. Then, tie a certain weight of detonating cord and electric detonator 602 together and place it in the metal thin-walled sleeve 601 of the circular blind hole 501 of the hard rock sample 5. Use stemming putty 603 to seal the metal thin-walled sleeve 601 and leave the electric detonator lead wire 604 for connection to the detonator 605.

[0051] S3. Prepare experimental instruments: Prepare a true triaxial rock test system (true triaxial rock testing machine 1 and true triaxial testing machine control station 2), an acoustic emission system 3, and an acoustic emission sensor installation auxiliary device 4. Six acoustic emission sensor installation auxiliary devices 4 that match the sample surface are respectively installed and fixed on the true triaxial testing machine 1 in the true triaxial test system, and screwed to each loading module 105-107 and bearing plate 104. The acoustic emission sensor 303 of the acoustic emission system 3 is placed in the acoustic emission sensor installation auxiliary device 4 and connected to the acoustic emission instrument 301 through the signal line 304 and amplifier 302.

[0052] S4. Setting Experimental Parameters: Place the specimen 5 between the acoustic emission sensor mounting devices 4 on the true triaxial testing machine 1. The axial direction of the blind hole 501 on the specimen should be aligned with the designed unloading direction. Move the Z-direction loading module 105, X-direction loading module 106, and Y-direction loading module 107 of the true triaxial testing machine via the control station 2 to ensure that the acoustic emission sensor mounting auxiliary device 4 makes initial contact with the six surfaces of the hard rock specimen 5. The electric detonator lead 604 passes through the corresponding acoustic emission sensor mounting auxiliary device 4 and connects to the detonator 605. Then, set the true triaxial experimental parameters, loading / unloading stress paths, and acoustic emission monitoring parameters.

[0053] S5. Start-up Experiment: Based on the stress state set in the experimental scheme and the two "loading / unloading and dynamic disturbance" stress paths, the specimen is subjected to triaxial (X, Y, Z) servo loading. After reaching the set stress state, the stress in one direction of the specimen remains constant, while a sudden double-sided unloading is performed in the other direction, and the detonator 605 is activated to immediately apply dynamic load. Loading continues in the remaining direction until specimen 5 is destroyed. The acoustic emission system 3 starts and stops synchronously with the true triaxial rock experimental systems 1 and 2. The two "loading / unloading and dynamic disturbance" stress paths include the first path and the second path.

[0054] S6. Analyze Test Data: After the experiment is stopped, analyze the stress and deformation data obtained by the control station 2 of the true triaxial testing machine and the extensometer 108, as well as the real-time acoustic wave signals collected by multiple acoustic emission sensors 303 in the acoustic emission system 3. Perform three-dimensional localization and moment tensor calculation on the acoustic emission event to determine whether plate cracking failure has occurred. Restore the test instruments and equipment to their original state, adjust the initial stress parameters and experimental parameters such as the weight of the detonating cord, and conduct the next set of experiments until plate cracking failure is observed, and determine the stress conditions and characteristics of plate cracking failure.

[0055] See Figure 5 The Protodyakonov coefficient of the hard rock sample 5 is not less than 8, and the side length is 100-300 mm. A circular blind hole 501 with a diameter of 8-10 mm and a depth not exceeding half the side length of the sample is vertically drilled in the surface of the sample 5. The lubricant is petroleum jelly or grease, and the drilling tool is a hand-held electric drill or a high-pressure water jet device.

[0056] See Figure 7 The thin-walled sleeve 601 is closed at the bottom, made of metal, with a wall thickness of 1-2 mm and a diameter of 6-8 mm. The function of the metal sleeve is to prevent explosive damage to the sample from the explosive force. The detonating cord and electric detonator 602 are bound together with tape or rope, etc.

[0057] See Figure 1-3 The true triaxial testing system consists of a true triaxial testing machine 1 and a true triaxial testing machine control station 2 connected to it via a data cable 109. The true triaxial testing machine 1 mainly includes a crossbeam 101, a base 102, a column 103, a pressure plate 104, a Z-direction loading module 105, an X-direction loading module 106, a Y-direction loading module 107, an extensometer 108, and a data cable 109.

[0058] See Figure 4 The acoustic emission system 3 includes an acoustic emitter 301, an amplifier 302, an acoustic emission sensor 303, and a signal line 304. The acoustic emission signal generated by the cracking of the rock slab is picked up by the acoustic emission sensor 303, transmitted to the amplifier 302 via the signal line 304, and then transmitted to the acoustic emitter 301 for acquisition and processing.

[0059] See Figure 4-5 The acoustic emission sensor installation auxiliary device 4 is placed between each loading module of the true triaxial testing machine 1 and each surface of the cubic rock sample 5. The acoustic emission sensor installation auxiliary device 4 includes a retractable pad 401, a circular through hole 402, a rubber pad 403, a hollow long screw 404, a flange 405, a flange hole 406, a bolt 407, and a hollow pad column 408. There are also Z-direction loading modules 105, X-direction loading modules 106, and Y-direction loading modules 107.

[0060] Furthermore, the retractable pad 401 is a cuboid, composed of multiple levels of cuboid sub-pads that match samples of different sizes, connected by interlocking. Each sub-pad has 4 to 8 pre-made circular through holes 402 with internal threads, which can be used to place the acoustic emission sensor 303 and the detonator lead 604 for wiring. The acoustic emission sensor 303 of the acoustic emission system 3 is placed at the front end of the circular through hole 402. The rubber pad 402 is a cylinder with a certain elasticity, placed between the acoustic emission sensor 303 and the hollow long screw 404 in the circular through hole of the retractable pad. It serves two purposes: first, to install the acoustic emission sensor 303, and second, to act as a buffer element for transmitting the preload force of the hollow long screw 404. The hollow screw 404 is connected to the circular through hole 402 of the telescopic pad by threads; the flange 405 is a cuboid, welded to the outer edge of the telescopic pad 401, and a circular flange hole 406 is arranged at each of the four corners of the flange 405; the bolt 407 passes through the flange circular hole 406 and the hollow pad 408 to thread the flange 405 and fix it to each loading module 105-107 and the pressure plate 104. The function of the hollow pad 408 is to create space between the flange 405 and the loading module 105-107 / pressure plate 104, creating conditions for manually tightening the hollow long screw 404 and routing the signal line 304 of the acoustic emission sensor 303. Z-direction loading module 105, X-direction loading module 106 and Y-direction loading module 107;

[0061] See Figure 4-5 The retractable pad 401 is composed of three sub-pads of different sizes (first pad 40101, second pad 40102, and third pad 40103) connected by interlocking. Each sub-pad has 4 to 8 pre-drilled circular through holes 402. The sub-pads are connected by tenon joints between the outer ring pad's reset hole 40104 or telescopic hole 40106 and the inner ring sub-pad's self-locking button 40105, enabling the inner ring pad to expand and contract to match cubic hard rock samples 5 of different sizes. The reset hole 40104 or telescopic hole 40106 is a through hole with the same shape as the self-locking button 40105, and its shape can be circular or rectangular, etc. The reset hole 40104 or telescopic hole 40106 and the self-locking button 40105 can also appear symmetrically in pairs on the upper and lower surfaces of the sub-pads.

[0062] See Figure 8 The stress paths include two types: Stress Path I: σ1 loading, σ2 constant, σ3 unloading, σd applied; Stress Path II: σ1 unloading, σ2 constant, σ3 loading, σd applied. σ1, σ2, σ3, and σd represent the vertical Z-direction stress, horizontal Y-direction stress, horizontal X-direction stress, and the dynamic load applied in the unloading direction, respectively, applied to the specimen by the true triaxial testing system. The dynamic load is applied when unloading occurs in a certain direction after the triaxial stress of the specimen has reached the set initial stress state. Correspondingly, a set of no-explosion conditions with zero detonating cord weight is set as a reference for the dynamic load of each stress path.

[0063] Example 2

[0064] Specific applications are as follows:

[0065] In this design, the true triaxial rock testing machine 1 has external dimensions of 1200×1200×2000mm (length×width×height), a base 102 of 500×500×500mm, a crossbeam 101 of 1000×40×40mm (length×width×height), and a column 103 with a diameter of 10cm and a height of 0.8m. It includes a Z-direction loading module 105, an X-direction loading module 106, and a Y-direction loading module 107. The maximum load of each loading module (105~107) is 2000kN (error ±1%), with a displacement range of 200mm (error ±0.5%FS). Loading can be achieved through displacement control or force control. The extensometer 108 is an LVDT model with a range of 10cm and an accuracy of 0.01mm. Each loading module 105–107 and the bearing plate 104 has a disc diameter of 30–40 mm, and the pre-drilled threaded hole 110 has a diameter of 8–16 mm and a depth of 10–20 mm. The cubic hard rock sample 5 has dimensions of 150 × 150 × 150 mm.

[0066] The acoustic emission system 3 consists of a PCI-2 type acoustic emission instrument 301 manufactured by PAC (USA), two 2 / 4 / 6 preamplifiers 302 with a preamplifier gain of 40dB, and two PICO type piezoelectric ceramic acoustic emission sensors 303 with a center response frequency of 250kHz. In the acoustic emission sensor installation auxiliary device 4, the retractable pad 401 includes three sub-pads: the first pad 40101 has dimensions of 100×100×(50~100)mm (length, width, and thickness); the second pad 40102 has dimensions of 150×150×(50~100)mm (length, width, and thickness); and the third pad 40103 has dimensions of 200×200×(50~100)mm (length, width, and thickness). The first pad 40101 has a self-locking button 40105, and the second pad has a reset hole 40104. The mortise and tenon joint connects the self-locking button 40105 of the second pad (40102) to the telescopic hole 40106 of the third pad. The tenon joint allows the first and second sub-pads to extend as a whole, matching the surface dimensions of the cubic sample 5. Each sub-pad has four pre-drilled circular through holes 402 with full-length internal threads, each 12–15 mm in inner diameter. An internal rubber pad 403 has an outer diameter of 8–10 mm and a length of 5–8 cm. The sleeve base 40301 has a wall thickness of 2 mm and a depth of 3–5 mm. The lead wire hole 40302 has a diameter of 3–5 mm. The hollow screw 404 measures M12 × 20 mm × Φ6.2 mm, with a knurled head that can be manually rotated to connect with the internal threads of the circular through holes 402. A flange 405, 8–12 mm thick, is welded to the outer edge of the telescopic pad 401. The flange hole 406 has a diameter of 12 mm. The hollow pad column 408 has an inner diameter of 12–15 mm, an outer diameter of 30–40 mm, and a length of 5–10 cm. The bolt 407 is M10.

[0067] The cubic hard rock specimen 5 has dimensions of 150×150×150mm. The telescopic pad 401 of the acoustic emission sensor auxiliary mounting device 4 is adjusted to match the surface of the hard rock specimen 5. Four acoustic emission sensors 303 are placed in each acoustic emission sensor auxiliary mounting device 4. Four initial stress states are set: ①σ1=60MPa, σ2=50MPa, σ3=40MPa; ②σ1=60MPa, σ2=40MPa, σ3=30MPa; ③σ1=60MPa, σ2=30MPa, σ3=20MPa; ④σ1=60MPa, σ2=20MPa, σ3=10MPa. The cubic hard rock specimen 5 is first loaded to the initial stress state, and then loading and unloading are performed sequentially according to stress paths I and II. The loading rate is 2kN / s, and the unloading method is sudden unloading from both sides. After the instantaneous unloading is completed, the detonating cord and detonating cable 602 are immediately detonated to apply the blasting dynamic load. The weight of the detonating cord 602 inside the circular blind hole 501 of the sample was set at three levels: 0g, 3g, and 6g. It should be particularly noted that if no hard rock slab cracking is observed under the above experimental conditions, the experimental parameters (initial stress state, detonating cord weight) should be adjusted and the test repeated until the expected result is achieved.

[0068] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A test method for simulating the cracking failure behavior of hard rock slabs, characterized in that, Includes the following steps: S1. Prepare the sample. Process and prepare a cubic hard rock sample of the required size. Apply a thin layer of lubricant to the six surfaces of the hard rock sample. Then, drill a circular blind hole of a certain depth vertically at the center of one of the surfaces of the hard rock sample. S2. Install the blasting device and fabricate a thin-walled sleeve that matches the size of the circular blind hole of the hard rock sample. Apply Vaseline to the outer surface of the thin-walled sleeve and place it in the circular blind hole to ensure full coupling and contact between the thin-walled sleeve and the hole wall. Then, bind the detonating cord and electric detonator of the required design weight with tape and place them in the thin-walled sleeve of the circular blind hole of the hard rock sample. Seal the thin-walled sleeve with stemming material and leave the electric detonator lead exposed for connection to the detonator. S3. Prepare experimental instruments, including a true triaxial rock test system, an acoustic emission system, and an acoustic emission sensor installation auxiliary device. Six acoustic emission sensor installation auxiliary devices that match the surface of the hard rock sample are respectively installed and fixed on the true triaxial testing machine in the true triaxial rock test system. The acoustic emission sensor of the acoustic emission system is placed in the acoustic emission sensor installation auxiliary device and connected to the acoustic emission instrument through an amplifier via a signal line. S4. Set the experimental parameters. Place the hard rock sample between the acoustic emission sensor mounting auxiliary devices on the true triaxial testing machine. The axial direction of the blind hole of the hard rock sample is consistent with the designed unloading direction. Move each loading module of the true triaxial testing machine through the control station of the true triaxial testing machine so that the acoustic emission sensor mounting auxiliary devices make initial contact with the six surfaces of the hard rock sample. After the electric detonator lead passes through the corresponding acoustic emission sensor mounting auxiliary device, it is connected to the detonator. Then, set the true triaxial experimental parameters, loading and unloading stress paths, and emission monitoring parameters. S5. Start the experiment. Load the hard rock sample with a three-dimensional servo displacement control method according to the stress state and stress path set in the experimental scheme. After the set stress state is reached, the stress in one direction of the hard rock sample is kept constant. The other direction is suddenly unloaded on both sides and the detonator is started to detonate and apply dynamic load immediately. The remaining direction is kept loaded until the hard rock sample is destroyed. The acoustic emission system starts and stops synchronously with the true triaxial rock test system. S6. Analyze the test data. After the experiment is stopped, analyze the stress and deformation data obtained by the control station and extensometer of the true triaxial testing machine and the real-time acoustic wave signal collected by the acoustic emission system. Perform three-dimensional positioning and moment tensor calculation on the acoustic emission event to determine whether plate cracking has occurred. Restore the test system to its original state, adjust the initial stress parameters and detonating cord weight test parameters in the test, and conduct the next set of experiments until plate cracking is observed. Determine the stress conditions and characteristics of plate cracking.

2. The test method for simulating the cracking failure behavior of hard rock slabs as described in claim 1, characterized in that: The thin-walled sleeve is a metal thin-walled sleeve with a closed bottom, a wall thickness of 1-2 mm, and a diameter of 6-8 mm. The function of the metal thin-walled sleeve is to prevent the explosive force from causing explosive damage to the sample. The detonating cord and the electric detonator are bound by either tape or rope.

3. The test method for simulating the cracking failure behavior of hard rock slabs as described in claim 1, characterized in that: The hard rock sample has a Protodyakonov coefficient ≥8 and a side length of 100–300 mm. A circular blind hole with a diameter of 8–10 mm is vertically drilled in the surface of the hard rock sample, and the depth of the circular blind hole is less than half the side length of the hard rock sample. The lubricant is either petroleum jelly or grease. The circular blind hole is drilled by either a hand-held electric drill or a high-pressure water jet device.

4. The test method for simulating the cracking failure behavior of hard rock slabs as described in claim 1, characterized in that: The acoustic emission sensor installation auxiliary device is placed between each loading module of the true triaxial testing machine and each surface of the hard rock sample. The device includes a retractable pad, a hollow long screw, a rubber pad, and a rectangular flange. It is composed of multiple levels of rectangular sub-pads that match different sample sizes, connected by interlocking. Each sub-pad has 4-8 pre-drilled circular through holes with internal threads for placing the acoustic emission sensor and the detonator lead wire. The acoustic emission sensor of the acoustic emission system is placed at the front end of the circular through holes. The rubber pad is a cylinder with a certain degree of elasticity, placed in the circular through holes of the retractable pad, where the acoustic emission sensor and the... Between the hollow long screws, one end is a sleeve base for mounting the acoustic emission sensor. The depth of the sleeve base is less than the thickness of the acoustic emission sensor. A small hole is opened at the bottom of the sleeve base to the other end, serving as a channel for the signal line. The hollow long screws are connected to the circular through hole of the telescopic pad by threads. The flange is a cuboid, welded to the outer edge of the telescopic pad, with a circular flange hole at each corner. Bolts pass through the circular holes of the flange and the hollow pad to thread the flange and fix it to the loading module. The function of the hollow pad is to create space between the flange and the loading module, providing routing conditions for manually tightening the hollow long screws and the acoustic emission probe signal line.

5. The test method for simulating the cracking failure behavior of hard rock slabs as described in claim 1, characterized in that: The stress path is the stress path of loading / unloading and strong dynamic disturbance. The stress path of loading / unloading and strong dynamic disturbance includes a first stress path and a second stress path. The first stress path and the second stress path respectively include σ1 loading, σ2 constant, σ3 unloading, and σd application. The hard rock sample is loaded in a three-dimensional servo displacement control mode. The three dimensions are X, Y and Z. σ1, σ2, σ3 and σd are the vertical Z-axis stress, horizontal Y-axis stress, horizontal X-axis stress and the blasting dynamic load applied to the hard rock sample by the true triaxial rock test system. The blasting dynamic load is applied when unloading in one direction after the triaxial stress of the hard rock sample is applied to the set initial stress state. For each stress path, a set of no-blasting conditions with zero detonating cord weight is set as a reference for the blasting dynamic load.

6. The test method for simulating the cracking failure behavior of hard rock slabs as described in claim 1, characterized in that: The acoustic emission system comprises an acoustic emitter, two preamplifiers, and an acoustic emission sensor.

7. A test method for simulating the cracking failure behavior of hard rock slabs as described in claim 1 or 4, characterized in that: The loading module includes a Z-direction loading module, an X-direction loading module, and a Y-direction loading module.

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