Borehole type three-way multi-point coal and rock mass wireless stress meter and coal and rock mass stress monitoring method

Abstract

The present disclosure relates to the safety field of coal rock mass and underground engineering, and provides a drilling type three-way multi-point coal rock mass wireless stress meter and a coal rock mass stress monitoring method. The uniaxial stress monitoring unit of the stress meter comprises a polyvinylidene fluoride piezoelectric film, a wire, an upper protective layer and a lower protective layer arranged on the upper and lower surfaces of the polyvinylidene fluoride piezoelectric film. A plurality of skeletons comprise a main skeleton and a secondary skeleton, and the skeleton is tubular. A uniaxial stress monitoring unit arranged along the axial direction of the skeleton is embedded on the side of the main skeleton close to the cap. The main skeleton and the secondary skeleton are both embedded with at least two uniaxial stress monitoring units arranged along the radial direction of the skeleton and perpendicular to each other. The polyvinylidene fluoride piezoelectric film of the uniaxial stress monitoring unit arranged along the radial direction is coplanar with the outer wall of the skeleton. A signal processing module connected with the wire is arranged in the hollow pipe of each skeleton or adjacent skeleton, and the signal processing module is in wireless communication with an external device. The stress meter according to the present disclosure improves the accuracy of stress monitoring data.

Description

Technical Field

[0001] This disclosure relates to the safety fields of coal and rock mass and underground engineering, and in particular to a borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass and a method for monitoring stress in coal and rock mass. Background Technology

[0002] The mining of underground mineral resources, tunnel excavation, or other geological engineering projects all alter the stress distribution in the original coal and rock mass. Different underground projects have different requirements for service life and deformation during use. For example, the service life of mining roadways in coal mines is usually no more than 3 years, while the service life of central roadways is basically the same as that of the mine shaft. Similarly, for mining roadways, as long as production is not affected during the working face mining period, a certain amount of roadway deformation and convergence is allowed. However, tunnels and other projects have strict requirements for deformation. Therefore, it can be said that different underground projects have drastically different requirements for deformation and service life for different purposes. The factors affecting the deformation of underground projects, i.e., safety, can be mainly divided into three types: the mechanical characteristics of the rock strata where the underground project is located, the stress applied to the boundary of the underground project, and the artificial support measures. If the changes in stress applied to the boundary of the underground project can be monitored and perceived in a timely and long-term manner, appropriate measures can be taken to ensure the normal operation of the underground project and the health and safety of the workers.

[0003] Currently, borehole stress gauges or geophysical methods are commonly used to monitor the stress occurrence and evolution of surrounding rock at different depths from the surface of underground engineering projects. While existing geophysical methods, such as stress wave sensing, can achieve anomaly monitoring within a certain range, their waveform analysis cannot adequately address the differences in cavities, water, and stress anomalies within the monitored area. Borehole stress gauges typically come in various types, including hydraulic, vibrating wire, fiber optic grating, and hollow inclusion types. However, existing stress gauges all have certain shortcomings in practical applications, such as complex installation processes and limited data volume. To a certain extent, they cannot meet the current requirements for higher precision and richer stress monitoring data. Therefore, there is an urgent need to develop new borehole stress gauges to better monitor the stress state of rock masses in underground engineering projects. Summary of the Invention

[0004] This disclosure aims to at least partially address one of the technical problems in the related art.

[0005] Therefore, the first objective of this disclosure is to propose a borehole-type three-dimensional multi-point wireless stress meter for coal and rock mass to improve the accuracy of stress monitoring data.

[0006] The second objective of this disclosure is to propose a method for monitoring coal and rock mass stress based on a borehole-type three-dimensional multi-point wireless stress gauge.

[0007] To achieve the above objectives, the first aspect of this disclosure provides a borehole-type three-dimensional multi-point wireless stress meter for coal and rock mass, including multiple unidirectional stress monitoring units, multiple signal processing modules, multiple frames, and protective caps;

[0008] The uniaxial stress monitoring unit includes a polyvinylidene fluoride piezoelectric film, an upper protective layer and a lower protective layer respectively disposed on the upper and lower surfaces of the polyvinylidene fluoride piezoelectric film, and a wire connected to the polyvinylidene fluoride piezoelectric film.

[0009] The plurality of skeletons includes a main skeleton and a secondary skeleton. One end of the main skeleton is connected to the protective cap, and the other end of the main skeleton is connected to the secondary skeleton. The skeleton is tubular. The main skeleton has a uniaxial stress monitoring unit arranged along the skeleton axis and located in a hollow tube, and at least two uniaxial stress monitoring units arranged radially and perpendicularly to the skeleton, embedded on the side near the protective cap. The secondary skeleton has at least two uniaxial stress monitoring units arranged radially and perpendicularly to the skeleton, embedded on the side near the main skeleton. The polyvinylidene fluoride piezoelectric film of the radially arranged uniaxial stress monitoring unit is coplanar with the outer wall of the skeleton.

[0010] A signal processing module is arranged in one hollow pipe of an adjacent frame, or a signal processing module is arranged in each of two hollow pipes. The signal processing module is connected to the wires of all unidirectional stress monitoring units in the corresponding frame, and the signal processing module communicates wirelessly with external devices.

[0011] In one embodiment of this disclosure, the polyvinylidene fluoride piezoelectric film is elongated, and the length and width of the polyvinylidene fluoride piezoelectric film are both at least 100 times the thickness of the polyvinylidene fluoride piezoelectric film. The length and width of the upper protective layer and the lower protective layer are respectively greater than or equal to the length and width of the polyvinylidene fluoride piezoelectric film.

[0012] In one embodiment of this disclosure, the upper protective layer or the lower protective layer is formed by casting target concrete, the target concrete being obtained based on the materials and proportions determined by the basic physical and mechanical properties of rock samples from stress monitoring points of the coal and rock mass at the site.

[0013] In one embodiment of this disclosure, the surface of the polyvinylidene fluoride piezoelectric film is coated with a silicone layer.

[0014] In one embodiment of this disclosure, each frame has a slurry outlet hole on its outer wall, the slurry outlet hole connecting the hollow pipe inside the frame to the outer wall.

[0015] In one embodiment of this disclosure, the number of secondary skeletons is multiple, and the borehole-type three-dimensional multi-point coal and rock wireless stress gauge also includes a connector, through which each skeleton is connected.

[0016] In one embodiment of this disclosure, the signal processing module includes an analog-to-digital conversion circuit, a temperature compensation unit, and a wireless transmission unit. The analog-to-digital conversion circuit is used to convert the analog stress data collected by the unidirectional stress monitoring unit into digital stress data, and the wireless transmission unit is used to send the digital stress data to an external device.

[0017] To achieve the above objectives, a second aspect of this disclosure proposes a method for monitoring coal and rock mass stress based on a borehole-type three-dimensional multi-point wireless stress gauge, comprising:

[0018] The number of skeletons was determined based on multiple stress monitoring points in the boreholes of the coal and rock mass in the field.

[0019] Acquire a pre-fabricated uniaxial stress monitoring unit and multiple tubular skeletons, wherein the multiple skeletons include a main skeleton and a secondary skeleton;

[0020] After connecting one end of the main frame to the protective cap, place it in the borehole. On the side of the main frame near the protective cap, arrange a unidirectional stress monitoring unit located in the hollow pipe along the axial direction of the frame, arrange at least two unidirectional stress monitoring units perpendicular to each other along the radial direction of the frame, and arrange a signal processing module in the hollow pipe of the main frame.

[0021] After connecting the main frame and the secondary frame through the connector, at least two unidirectional stress monitoring units perpendicular to each other are arranged radially along the side of the secondary frame close to the main frame. A signal processing module is arranged in the hollow tube of the secondary frame. The polyvinylidene fluoride piezoelectric film of the radially arranged unidirectional stress monitoring unit is coplanar with the outer wall of the frame. After each signal processing module is arranged, the signal processing module is connected to the wires of all unidirectional stress monitoring units of the frame.

[0022] After all the skeleton arrangements are completed, the holes of the skeleton are sealed, and the hollow pipes inside the skeleton are grouted to allow the drilled three-dimensional multi-point coal and rock wireless stress gauge to be cast into the borehole.

[0023] Real-time monitoring of coal and rock mass stress information was achieved using a borehole-type three-dimensional multi-point wireless stress gauge.

[0024] In one embodiment of this disclosure, the manufacturing process of the unidirectional stress monitoring unit includes: configuring target concrete based on the physical and mechanical properties of rock samples from stress monitoring points in the field coal and rock mass; selecting a polyvinylidene fluoride piezoelectric film with a preset length and width, and using the target concrete to cast an upper protective layer and a lower protective layer with a length and width greater than or equal to the preset length and width on the upper and lower surfaces of the polyvinylidene fluoride piezoelectric film, thereby obtaining the unidirectional stress monitoring unit.

[0025] In one embodiment of this disclosure, after the uniaxial stress monitoring unit is fabricated, it is necessary to perform maintenance and uniaxial compression tests on the uniaxial stress monitoring unit.

[0026] In one or more embodiments of this disclosure, a borehole-type three-dimensional multi-point coal and rock mass wireless stress meter includes multiple unidirectional stress monitoring units, multiple signal processing modules, multiple frames, and a protective cap. Each unidirectional stress monitoring unit includes a polyvinylidene fluoride (PVDF) piezoelectric film, an upper protective layer and a lower protective layer respectively disposed on the upper and lower surfaces of the PVDF piezoelectric film, and a wire connected to the PVDF piezoelectric film. The multiple frames include a main frame and a secondary frame. One end of the main frame is connected to the protective cap, and the other end of the main frame is connected to the secondary frame. The frame is tubular, and a hollow tube is embedded in the side of the main frame near the protective cap, arranged axially along the frame. A uniaxial stress monitoring unit and at least two uniaxial stress monitoring units perpendicular to each other arranged radially along the skeleton are included. The secondary skeleton, near the main skeleton, has these uniaxial stress monitoring units embedded in its radially arranged form. The polyvinylidene fluoride piezoelectric film of the radially arranged uniaxial stress monitoring units is coplanar with the outer wall of the skeleton. A signal processing module is arranged in one hollow tube in adjacent skeletons, or two hollow tubes each house a signal processing module. The signal processing modules are connected to the wires of all uniaxial stress monitoring units in their respective skeletons, and communicate wirelessly with external devices. In this configuration, the polyvinylidene fluoride piezoelectric film is placed inside two protective layers to form a uniaxial stress monitoring unit. Different uniaxial stress monitoring units are arranged according to the purpose of triaxial stress monitoring to collect triaxial stress information. Simultaneously, multiple skeletons are used to obtain multi-point stress information, thereby improving the accuracy of the stress monitoring data.

[0027] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this disclosure. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the specific embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. The above and / or additional aspects and advantages of this disclosure will become apparent and readily understood from the following description of the embodiments in conjunction with the accompanying drawings, wherein:

[0029] Figure 1 This is a schematic diagram of the structure of a borehole-type three-dimensional multi-point wireless stress meter for coal and rock mass provided in an embodiment of the present disclosure;

[0030] Figure 2A perspective view of the unidirectional stress monitoring unit provided in the embodiments of this disclosure;

[0031] Figure 3 This is a schematic diagram of the main skeleton provided in an embodiment of the present disclosure;

[0032] Figure 4 This is a schematic diagram of the secondary skeleton provided in an embodiment of the present disclosure;

[0033] Figure 5 The main skeleton located inside the borehole along Figure 3 A schematic diagram of the cross-section along the dashed line A1-A2;

[0034] Figure 6 This is a schematic diagram of borehole azimuth coordinates provided in an embodiment of the present disclosure;

[0035] Figure 7 This is a block diagram of the signal processing module provided in an embodiment of this disclosure;

[0036] Figure 8 This is a flowchart illustrating a method for monitoring coal and rock mass stress based on a borehole-type three-dimensional multi-point wireless stress gauge, as provided in an embodiment of this disclosure. Detailed Implementation

[0037] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the embodiments of this disclosure as detailed in the appended claims.

[0038] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0039] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly and specifically defined. It should also be understood that the term "and / or" as used in this disclosure refers to and includes any or all possible combinations of one or more associated listed items.

[0040] Embodiments of this disclosure are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this disclosure, and should not be construed as limiting this disclosure.

[0041] This disclosure provides a borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass and a method for monitoring stress in coal and rock mass, with the main purpose of improving the accuracy of stress monitoring data. The borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass disclosed herein can be simply referred to as a stress gauge.

[0042] In the first embodiment, Figure 1 This is a schematic diagram of a borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass provided in an embodiment of this disclosure. Figure 1 As shown, the borehole-type three-dimensional multi-point coal and rock mass wireless stress meter 1 includes multiple unidirectional stress monitoring units 10, multiple skeletons 20, protective caps 30, and multiple signal processing modules 40.

[0043] In this embodiment, the unidirectional stress monitoring unit 10 is used to collect stress information in a single direction. There are multiple unidirectional stress monitoring units 10.

[0044] Figure 2 This is a perspective view of a unidirectional stress monitoring unit provided in an embodiment of this disclosure. In some embodiments, such as Figure 2 As shown, the unidirectional stress monitoring unit 10 includes a polyvinylidene fluoride piezoelectric film 11 (PVDF piezoelectric film), an upper protective layer 12 and a lower protective layer 13 respectively disposed on the upper and lower surfaces of the PVDF piezoelectric film, and a wire 14 connected to the PVDF piezoelectric film 11.

[0045] In this embodiment, the polyvinylidene fluoride piezoelectric film refers to a polyvinylidene fluoride (PVDF) film with piezoelectric effect after polarization.

[0046] In this embodiment, the polyvinylidene fluoride piezoelectric film generates an electrical signal based on the load it bears (i.e., stress). The electrical signal can be a voltage signal or a current signal.

[0047] In some embodiments, the electrical signal is a voltage signal, and the load (i.e., stress) borne by the polyvinylidene fluoride piezoelectric film and the output voltage signal typically exhibit a linear relationship, satisfying the following condition: In the formula, U represents the voltage signal output by the uniaxial stress monitoring unit. The value represents the equivalent piezoelectric coefficient of the uniaxial stress monitoring unit, and F represents the load borne by the uniaxial stress monitoring unit.

[0048] In some embodiments, the shape of the polyvinylidene fluoride piezoelectric film can be Figure 2 The square shape shown can also be circular or rectangular. However, the shape of the polyvinylidene fluoride piezoelectric film in the embodiments of this disclosure is not limited to these.

[0049] In this embodiment, the length, width, or diameter of the polyvinylidene fluoride (PVDF) piezoelectric film is much larger than its thickness. This "much larger" is 100 times or more, for example, 100 times, 150 times, 200 times, etc. In this case, only loads parallel to the direction of the PVDF piezoelectric film (i.e., parallel to the normal direction of the PVDF piezoelectric film) will cause an electrical signal to appear on the PVDF piezoelectric film, thereby obtaining unidirectional stress information.

[0050] In some embodiments, if the upper and lower surfaces of the polyvinylidene fluoride (PVDF) piezoelectric film are circular, the diameter of the PVDF piezoelectric film is at least 100 times the thickness of the PVDF piezoelectric film. If the upper and lower surfaces of the PVDF piezoelectric film are square or rectangular, the length and width of the PVDF piezoelectric film are both at least 100 times the thickness of the PVDF piezoelectric film.

[0051] In some embodiments, a silicone layer is coated on the surface of the polyvinylidene fluoride (PVDF) piezoelectric film. Specifically, a PVDF piezoelectric film of a preset length and width is selected, wires are soldered onto the PVDF piezoelectric film, and then a silicone layer of a preset thickness is uniformly coated or cast onto the surface of the PVDF piezoelectric film to waterproof and protect the PVDF piezoelectric film.

[0052] In some embodiments, the preset length is, for example, less than 1 cm, the preset width is, for example, less than 0.5 cm, and the preset thickness is, for example, no more than 0.5 cm.

[0053] In some embodiments, the silicone layer may be made of materials such as epoxy resin.

[0054] In this embodiment, the upper protective layer and the lower protective layer are used to protect the polyvinylidene fluoride piezoelectric film. The contact surface between the upper protective layer and the upper surface of the polyvinylidene fluoride piezoelectric film covers the upper surface of the polyvinylidene fluoride piezoelectric film, and the contact surface between the lower protective layer and the lower surface of the polyvinylidene fluoride piezoelectric film covers the lower surface of the polyvinylidene fluoride piezoelectric film.

[0055] In some embodiments, if the upper and lower protective layers are cylinders, then the diameters of both the upper and lower protective layers are greater than or equal to the diameter of the polyvinylidene fluoride piezoelectric film. If the upper and lower protective layers are cuboids, then the length and width of the upper and lower protective layers are respectively greater than or equal to the length and width of the polyvinylidene fluoride piezoelectric film.

[0056] In other embodiments, if the upper and lower protective layers are cylindrical and the polyvinylidene fluoride piezoelectric film is square or rectangular, then the diameters of the upper and lower protective layers are both greater than or equal to the diagonal length of the polyvinylidene fluoride piezoelectric film.

[0057] In some embodiments, if the length of the polyvinylidene fluoride piezoelectric film is less than 1 cm and the width is less than 0.5 cm, the upper protective layer and the lower protective layer can be, for example, cuboids with a length greater than or equal to 1 cm, a width greater than or equal to 0.5 cm, and a thickness of 0.5 cm.

[0058] In some embodiments, if the diameter of the polyvinylidene fluoride piezoelectric film is less than 1 cm, the upper protective layer and the lower protective layer may be, for example, cylinders with a diameter of 1 cm and a thickness of 1 cm.

[0059] In some embodiments, the dimensions (diameter or length and width) of the upper and lower protective layers can be determined by combining the dimensions of the polyvinylidene fluoride piezoelectric film, the diameter of the hollow tubes of the skeleton, and the borehole diameter.

[0060] In some embodiments, the upper or lower protective layer is formed by pouring target concrete, which is obtained based on the materials and proportions determined by the basic physical and mechanical properties of rock samples from stress monitoring points of the coal and rock mass in the field.

[0061] In some embodiments, after obtaining an upper protective layer or a lower protective layer, the upper protective layer or the lower protective layer can be arranged on the upper and lower surfaces of the electroceramic laminated with silicone to obtain a uniaxial stress monitoring unit.

[0062] In some embodiments, after the silicone layer, such as epoxy resin, on the surface of the polyvinylidene fluoride piezoelectric film has solidified, the polyvinylidene fluoride piezoelectric film is placed in the middle of a mold, with space left in the middle of the mold for the wires, and the target concrete is poured into the mold, thereby integrally forming an upper or lower protective layer on the upper and lower surfaces of the polyvinylidene fluoride piezoelectric film, thus obtaining a uniaxial stress monitoring unit.

[0063] In some embodiments, after the silicone layer, such as epoxy resin, on the surface of the polyvinylidene fluoride piezoelectric film has solidified, the polyvinylidene fluoride piezoelectric film is placed in the middle of a mold, leaving space for wires in the middle of the mold. A lower protective layer, such as a cylinder or cuboid, is first cast below the polyvinylidene fluoride piezoelectric film, and then an upper protective layer, such as a cylinder or cuboid, is cast above it, thereby obtaining a uniaxial stress monitoring unit.

[0064] In some embodiments, the uniaxial stress monitoring unit 10 can be cured before being placed on the frame, with different curing times for different materials. This allows the uniaxial stress monitoring unit to have the required strength.

[0065] In some embodiments, before placing the cured uniaxial stress monitoring unit 10 on the frame, a uniaxial compression test can be performed on the uniaxial stress monitoring unit 10 to obtain the compressive strength and equivalent piezoelectric coefficient of each uniaxial stress monitoring unit. Specifically, the uniaxial stress monitoring unit is placed on the experimental model for a uniaxial compression test to obtain the compressive strength of the uniaxial stress monitoring unit. A resistor with a set resistance value is connected in series in the circuit, and the wire is connected to a signal amplifier. The generated voltage / current is amplified and recorded using the signal amplifier. By analyzing the voltage / current output under different pressures, the equivalent piezoelectric coefficient of the uniaxial stress monitoring unit is obtained, thus achieving the calibration of the uniaxial stress monitoring unit. Based on the experiment, it is known that the equivalent piezoelectric coefficient is directly related to the polyvinylidene fluoride piezoelectric film, the material of the upper or lower protective layer, the casting material, etc., and is also directly related to the precision and fit of the processing.

[0066] In this embodiment, the frame 20 is used to support the uniaxial stress monitoring unit. There are multiple frames 20, which are connected sequentially, and multiple uniaxial stress monitoring units are arranged in each frame.

[0067] In this embodiment, the skeleton is tubular. The tubular shape can be, for example, a round tube or a square tube. The wall thickness of the skeleton is h (see...). Figure 5 In some embodiments, the frame may be, for example, an iron pipe or a PVC (Polyvinyl Chlorid) pipe.

[0068] In this embodiment, a plurality of through holes are provided on the outer wall of one end of the skeleton, each through hole being a hollow tube penetrating the outer wall and the skeleton. The axial direction of each through hole coincides with the radial direction of the skeleton. At least two of the plurality of through holes have axial directions perpendicular to each other. A uniaxial stress monitoring unit is arranged in each through hole. The upper surface of the polyvinylidene fluoride piezoelectric film of the uniaxial stress monitoring unit is coplanar with the outer wall of the skeleton surrounding the through hole.

[0069] In this embodiment, the multiple frames include a main frame and a secondary frame. One end of the main frame is connected to a protective cap, and the other end is connected to the secondary frame. A unidirectional stress monitoring unit, arranged axially within a hollow tube, and at least two other unidirectional stress monitoring units arranged radially and perpendicularly to the frame are embedded in the main frame near the protective cap. At least two other unidirectional stress monitoring units, arranged radially and perpendicularly to the frame, are embedded in the secondary frame near the main frame. The polyvinylidene fluoride piezoelectric film of the radially arranged unidirectional stress monitoring units is coplanar with the outer wall of the frame.

[0070] In this embodiment, a signal processing module is arranged in one hollow conduit of an adjacent skeleton, or a signal processing module is arranged in each of the two hollow conduits. In other words, a signal processing module is arranged in the hollow conduit of each skeleton, or adjacent skeletons share a signal processing module.

[0071] The signal processing module is connected to the wires of all unidirectional stress monitoring units in the corresponding frame, and the signal processing module communicates wirelessly with external devices. Specifically, when one signal processing module is arranged in the hollow pipe of each frame, the signal processing module is connected to the wires of all unidirectional stress monitoring units in that frame; when adjacent frames share a signal processing module, the signal processing module is connected to the wires of all unidirectional stress monitoring units in the two adjacent frames.

[0072] Figure 3 This is a schematic diagram of the main skeleton provided in an embodiment of this disclosure. Figure 4 This is a schematic diagram of the secondary skeleton provided in an embodiment of the present disclosure. Figure 5 The main skeleton located inside the borehole along Figure 3 A schematic diagram of the cross-section along the dashed line A1-A2. Figure 6 This is a schematic diagram of borehole azimuth coordinates provided in an embodiment of the present disclosure.

[0073] In some embodiments, such as Figure 1 , Figure 3 , Figure 5 and Figure 6 As shown, each skeleton is a circular tube, and the multiple skeletons 20 include a main skeleton 20A and a secondary skeleton 20B. One end of the main skeleton 20A is connected to the protective cap 30, and the other end of the main skeleton 20A is connected to the secondary skeleton 20B. Two unidirectional stress monitoring units 10 are embedded in the main skeleton 20A near the protective cap, arranged radially along the skeleton. The directions of the two unidirectional stress monitoring units are perpendicular to each other.

[0074] Figure 6 This is a partial cross-sectional view perpendicular to the depth direction of the tunnel; the borehole is located on the sidewall of the tunnel. Figure 6 The location, number, depth, and diameter of the boreholes shown are for illustrative purposes only. Taking XYZ three-dimensional coordinates as an example, where... Figure 6In this diagram, the Z-direction represents the drilling depth (i.e., the axial direction of the skeleton), while the X and Y directions are two mutually perpendicular directions in a plane perpendicular to the depth direction. For example, the X-direction is horizontal, and the Y-direction is vertical. The directions of the two unidirectional stress monitoring units are the X and Y directions, respectively.

[0075] In some embodiments, such as Figure 1 and Figure 3 As shown, a unidirectional stress monitoring unit is embedded in the hollow pipe 21, which is arranged along the axial direction (i.e., the Z direction) of the main frame 20A near the cap.

[0076] In some embodiments, to better acquire stress information, the hollow tubing of the skeleton at the uniaxial stress monitoring unit arranged along the skeleton axis can conform to the shape of the upper or lower protective layer of the uniaxial stress monitoring unit. For example, if the upper protective layer is square, the skeleton at the uniaxial stress monitoring unit arranged along the skeleton axis can have a square hollow tubing with a circular outer wall or a square hollow tubing with a square outer wall. If the upper protective layer is circular, the skeleton at the uniaxial stress monitoring unit arranged along the skeleton axis can have a circular hollow tubing with a circular outer wall or a circular hollow tubing with a square outer wall. The diameter or length and width of the hollow tubing are equal to the diameter or length and width of the upper or lower protective layer of the uniaxial stress monitoring unit (see [reference]). Figure 3 ).

[0077] In some embodiments, such as Figure 1 and Figure 3 As shown, a signal processing module 40A is arranged in the hollow pipe of the main frame 20A. The signal processing module 40A is connected to the wires of all unidirectional stress monitoring units in the main frame 20A and communicates wirelessly with external devices.

[0078] In some embodiments, such as Figure 1 and Figure 4 As shown, two uniaxial stress monitoring units 10 are embedded in the secondary frame 20B near the main frame, arranged radially along the frame. The arrangement of the two uniaxial stress monitoring units 10 in the secondary frame 20B is consistent with the arrangement of the two uniaxial stress monitoring units 10 in the main frame 20A.

[0079] In some embodiments, such as Figure 1 and Figure 4 As shown, a signal processing module 40B is arranged in the hollow pipe of the secondary frame 20B. The signal processing module 40B is connected to the wires of all unidirectional stress monitoring units in the secondary frame 20B, and the signal processing module 40B communicates wirelessly with external devices.

[0080] In some embodiments, such as Figure 1 , Figure 3 and Figure 4As shown, the wires of the unidirectional stress monitoring unit 10 arranged in each skeleton are located in the hollow tube of their respective skeleton and are connected to the signal processing module in the hollow tube of their respective skeleton.

[0081] In some embodiments, if there are many skeletons and the drilling is deep, the stress information collected by the unidirectional stress monitoring unit 10 in the skeleton far from the drilling can be wirelessly transmitted to the signal processing module in the adjacent skeleton or other skeletons within a certain distance through the signal processing module.

[0082] In some embodiments, such as Figure 1 , Figure 3 and Figure 4 As shown, each frame has a slurry outlet 22 on its outer wall, which connects the hollow pipe 21 inside the frame to the outer wall.

[0083] In some embodiments, the number of secondary skeletons is multiple. The number of secondary skeletons can be determined based on the location and number of stress monitoring points. This allows the monitoring needs of multiple stress monitoring points within a single borehole to be met.

[0084] In some embodiments, the frames of the stress gauge can be arranged according to the spacing between stress monitoring points, thereby enabling free adjustment of the length between two frames to meet actual needs.

[0085] In this embodiment, the cap 30 is used to better transmit axial (i.e., Z-direction) force and push the debris in the borehole to the bottom of the hole.

[0086] In this embodiment, the signal processing module 40 is used to receive stress information collected from the unidirectional stress monitoring unit, process the stress information, and then send it to an external device wirelessly.

[0087] In some embodiments, the signal processing module 40 includes an analog-to-digital conversion circuit and a wireless transmission unit. The analog-to-digital conversion circuit is used to convert the analog stress data collected by the unidirectional stress monitoring unit into digital stress data, and the wireless transmission unit is used to send the digital stress data to an external device.

[0088] Figure 7 This is a block diagram of a signal processing module provided in an embodiment of this disclosure.

[0089] Specifically, such as Figure 7As shown, the signal processing module 40 includes a signal conversion unit and a signal transmission unit. The signal conversion unit includes a temperature compensation unit, a signal amplification circuit, a signal filtering circuit, an analog-to-digital conversion circuit, and an energy module. The signal transmission unit includes a wireless signal acquisition unit, a storage unit, and a wireless transmission unit. The temperature compensation unit improves the accuracy of the obtained stress values ​​because the polyvinylidene fluoride piezoelectric film is highly sensitive to temperature. During concrete pouring, heat is released, and the temperature compensation unit eliminates the influence of temperature during pouring, thereby improving the accuracy of the obtained stress values.

[0090] When the unidirectional stress monitoring unit is subjected to an external load, it deforms and releases an electrical signal. This signal is analog stress data. The signal travels through a wire to the signal conversion unit, where it is processed sequentially by a temperature compensation unit, a signal amplification circuit, a signal filtering circuit, and an analog-to-digital conversion circuit to obtain digital stress data. This digital stress data then enters the signal transmission unit. The wireless signal acquisition unit acquires digital stress data from other skeletons, the storage unit stores the digital stress data, and the wireless transmission unit wirelessly transmits the digital stress data output from the wireless signal acquisition unit and the digital stress data from the signal conversion unit to external devices outside the borehole or to wireless signal acquisition units on other skeletons. The energy module provides power to the temperature compensation unit, signal amplification circuit, signal filtering circuit, analog-to-digital conversion circuit, wireless signal acquisition unit, storage unit, and wireless transmission unit. In this configuration, wireless transmission effectively avoids installation problems caused by excessive signal cables.

[0091] In some embodiments, the external device can be a dedicated data acquisition and analysis device. This dedicated data acquisition and analysis device is a multifunctional device integrating a wireless transmission device, a storage device, and a data acquisition device. It collects digital stress data from different boreholes and ultimately integrates and analyzes data from different measuring points within the borehole. In this case, the measurable electrical signal (i.e., stress information) transmitted under pressure from the polyvinylidene fluoride piezoelectric film is processed by a signal processing module and transmitted to the external device for subsequent analysis.

[0092] In some embodiments, external devices can be installed at the borehole opening. This facilitates display at the borehole opening while simultaneously transmitting data to the ground via a ring network.

[0093] In some embodiments, the borehole-type three-dimensional multi-point coal and rock wireless stress gauge also includes a connector, through which the frames are connected.

[0094] In some embodiments, to ensure the directionality of the force measured at the stress monitoring point, high installation requirements are placed, and a semi-rotary joint is used to achieve rapid connection between adjacent frames. Furthermore, to ensure that the stress gauge is aligned with the direction of the measured force, the connection is directly pushed horizontally after completion.

[0095] In some embodiments, such as Figure 1 , Figure 3 and Figure 4 As shown, a connector is provided at one end of the main frame 20A, through which the main frame 20A is connected to the secondary frame 20B. A first connector 51 and a second connector 52 are arranged at both ends of the secondary frame 20B. The secondary frame 20B is sequentially connected to other frames through the first connector 51 and the second connector 52.

[0096] In this embodiment, the borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass can be deployed inside a borehole excavated in underground engineering where the borehole diameter is larger than the outer circumference diameter of the skeleton. Additionally, as... Figure 5 As shown, concrete is arranged between the outer wall of the skeleton and the borehole wall. This allows the stress gauge to automatically couple according to the surrounding rock development, enhancing the adaptability of the stress gauge.

[0097] In the borehole-type three-dimensional multi-point wireless stress meter of coal and rock mass according to the embodiments of this disclosure, the borehole-type three-dimensional multi-point wireless stress meter of coal and rock mass includes multiple unidirectional stress monitoring units, multiple signal processing modules, multiple skeletons and protective caps; the unidirectional stress monitoring unit includes a polyvinylidene fluoride piezoelectric film, an upper protective layer and a lower protective layer respectively disposed on the upper and lower surfaces of the polyvinylidene fluoride piezoelectric film, and a wire connected to the polyvinylidene fluoride piezoelectric film; the multiple skeletons include a main skeleton and a secondary skeleton, one end of the main skeleton is connected to the protective cap, and the other end of the main skeleton is connected to the secondary skeleton. The skeleton is tubular, and the side of the main skeleton near the protective cap is embedded with a hollow core arranged along the skeleton axis. The system comprises a uniaxial stress monitoring unit within a conduit and at least two uniaxial stress monitoring units arranged radially and perpendicularly to the main frame. At least two uniaxial stress monitoring units arranged radially and perpendicularly to the main frame are embedded in the secondary frame. The polyvinylidene fluoride piezoelectric film of the radially arranged uniaxial stress monitoring units is coplanar with the outer wall of the frame. A signal processing module is arranged in one hollow conduit of adjacent frames, or one signal processing module is arranged in each of the two hollow conduits. The signal processing module is connected to the wires of all uniaxial stress monitoring units in the corresponding frame, and the signal processing module communicates wirelessly with external devices. In this configuration, the polyvinylidene fluoride piezoelectric film is placed inside two protective layers to form a uniaxial stress monitoring unit. Different uniaxial stress monitoring units are arranged according to the purpose of triaxial stress monitoring to collect triaxial stress information. Simultaneously, multiple frames are used to obtain multi-point stress information, thereby improving the accuracy of stress monitoring data. The stress gauge disclosed herein can be installed in boreholes within underground rock masses to achieve multi-point triaxial stress monitoring in a single borehole, and the borehole data (i.e., stress information) can be wirelessly acquired and transmitted via a signal processing module. The stress gauge disclosed herein has the advantages of abundant monitoring data, high accuracy, good sensitivity, no need for extensive signal line (i.e., wire) deployment, low cost, easy installation, portability, long-term monitoring, low power consumption, and stable power saving.

[0098] The following are embodiments of the method disclosed herein. For details not disclosed in the embodiments of the method disclosed herein, please refer to the stress gauge embodiments of the method disclosed herein. The method embodiments of the method disclosed herein propose a method for monitoring coal and rock mass stress based on a borehole-type three-dimensional multi-point wireless stress gauge. This method for monitoring coal and rock mass stress based on a borehole-type three-dimensional multi-point wireless stress gauge performs stress monitoring based on the stress gauge embodiments described above.

[0099] Figure 8 This is a schematic flowchart illustrating a method for monitoring coal and rock mass stress based on a borehole-type three-dimensional multi-point wireless stress gauge, as provided in an embodiment of this disclosure. Figure 8 As shown, the method for monitoring coal and rock mass stress based on a borehole-type three-dimensional multi-point wireless stress gauge includes the following steps:

[0100] Step S11: Determine the number of skeletons based on multiple stress monitoring points in the boreholes of the coal and rock mass on site.

[0101] Step S12: Obtain a pre-fabricated uniaxial stress monitoring unit and multiple tubular skeletons, wherein the multiple skeletons include a main skeleton and a secondary skeleton.

[0102] In step S12, the fabrication process of the uniaxial stress monitoring unit includes: configuring target concrete based on the physical and mechanical properties of rock samples from stress monitoring points of the coal and rock mass on site; selecting a pre-defined length and width of a polyvinylidene fluoride piezoelectric film; and using the target concrete to cast an upper protective layer and a lower protective layer with lengths and widths greater than or equal to the pre-defined lengths and widths on the upper and lower surfaces of the polyvinylidene fluoride piezoelectric film, thereby obtaining the uniaxial stress monitoring unit.

[0103] In some embodiments, the method for obtaining target concrete includes: sampling rock samples at stress monitoring points of the coal and rock mass in the field; testing the rock samples to obtain their basic physical and mechanical properties; determining the materials and mix proportions of experimental components based on the basic physical and mechanical properties of the rock samples; and obtaining target concrete based on the materials and mix proportions.

[0104] In some embodiments, sampling is performed at stress monitoring points in the on-site coal and rock mass to obtain rock samples, including: taking samples at stress monitoring points in the on-site coal and rock mass and then processing them into columnar rock samples of a preset size. The preset size may be, for example, 50mm × 100mm (diameter × height), and the number of columnar rock samples may be, for example, no less than 15 sets.

[0105] In some embodiments, testing rock samples to obtain their basic physical and mechanical properties includes: conducting physical and mechanical tests on the rock samples and measuring ultrasonic wave velocity, etc., to obtain the basic physical and mechanical properties of the rock samples.

[0106] In some embodiments, the material and proportion of the experimental fittings are determined based on the basic physical and mechanical properties of the rock sample, and the target concrete is obtained based on the material and proportion. This includes: determining the appropriate concrete filler strength, material and proportion based on the physical and mechanical properties of the obtained rock sample, thereby obtaining a fast-setting concrete with self-expanding properties that is as close as possible to the strength and mechanical properties of the rock sample. This fast-setting concrete is the target concrete.

[0107] In step S12, after the uniaxial stress monitoring unit is fabricated, it is necessary to perform curing and uniaxial compression tests on the uniaxial stress monitoring unit.

[0108] In step S12, the outer circumferential diameter of the multiple tubular skeletons is determined based on the borehole diameter of the boreholes drilled at the locations where stress monitoring is required in the underground engineering, and the borehole diameter is larger than the outer circumferential diameter of the skeleton.

[0109] Step S13: After connecting one end of the main frame to the protective cap, place it in the borehole. On the side of the main frame near the protective cap, arrange a unidirectional stress monitoring unit located in the hollow pipe along the axial direction of the frame, arrange at least two unidirectional stress monitoring units perpendicular to each other along the radial direction of the frame, and arrange a signal processing module in the hollow pipe of the main frame.

[0110] In step S13, the signal processing module in the hollow tube of the main frame is connected to the wires of all unidirectional stress monitoring units of the main frame.

[0111] Step S14: After connecting the main frame and the secondary frame through the connector, arrange at least two unidirectional stress monitoring units perpendicular to each other in the radial direction of the secondary frame near the main frame. Arrange a signal processing module in the hollow tube of the secondary frame. The polyvinylidene fluoride piezoelectric film of the radially arranged unidirectional stress monitoring unit is coplanar with the outer wall of the frame. After each signal processing module is arranged, connect the signal processing module to the wires of all unidirectional stress monitoring units in the frame.

[0112] In some embodiments, the number of secondary skeletons in step S14 can be multiple. Each time, a secondary skeleton is selected and connected to the previous skeleton until the connection is completed. Each secondary skeleton contains a signal processing module. Before connecting the secondary skeleton to the previous skeleton, the signal processing module of the previous skeleton needs to be connected to the wires of all unidirectional stress monitoring units of its skeleton.

[0113] Step S15: After completing the arrangement of all the skeletons, seal the holes at the skeleton openings and grout the hollow pipes inside the skeletons so that the borehole-type three-dimensional multi-point coal and rock wireless stress gauge is cast into the borehole.

[0114] In some embodiments, after all the skeleton arrangements are completed in step S15, when casting the borehole-type three-dimensional multi-point coal and rock wireless stress gauge, the borehole opening (i.e., the position of the skeleton closest to the borehole opening) can be sealed with an airbag or yellow mud. Then, high-pressure grouting is performed using a grouting material with self-expanding properties through the hollow pipe of the borehole-type three-dimensional multi-point coal and rock wireless stress gauge. The grouting material is, for example, self-compacting concrete, high-polymer quick-setting material, etc. In addition, before casting the borehole-type three-dimensional multi-point coal and rock wireless stress gauge, a venting pipe is left between the stress gauge and the borehole wall to facilitate venting. In this way, the entire borehole is grouted to achieve integral casting, thereby casting the entire stress gauge inside the borehole. After casting, the stress transmission inside the entire borehole is better, and the grout inside the borehole can seal the cracks in the borehole wall. The entire borehole plays a certain role in reinforcing the location of the stress monitoring point.

[0115] Step S16: Use a borehole-type three-dimensional multi-point wireless stress gauge to monitor the stress information of the coal and rock mass in real time.

[0116] In some embodiments, the stress information collected in real time by the uniaxial stress monitoring unit of the borehole-type triaxial multi-point coal and rock wireless stress gauge in step S16 is processed by the signal processing module and converted into a wireless signal and sent to an external device outside the borehole. The external device obtains the triaxial stress values ​​of the measuring points at different times and locations.

[0117] In some embodiments, the external device is also used to record stress information, such as voltage signals, reflected by the borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass, and to calculate stress values ​​based on the relationship between the voltage signals and the load values. The external device is also used to use the obtained stress values ​​as basic data to support the analysis of the stress environment, damage range, and damage degree of the surrounding rock.

[0118] It should be noted that the explanation of the above-mentioned embodiment of the borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass also applies to the coal and rock mass stress monitoring method of this embodiment, and will not be repeated here.

[0119] The sequence numbers of the embodiments disclosed above are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0120] In the coal and rock mass stress monitoring method based on a borehole-type three-dimensional multi-point wireless stress meter of this disclosure embodiment, the number of skeletons is determined based on multiple stress monitoring points in the borehole of the coal and rock mass in the field; a pre-fabricated unidirectional stress monitoring unit and multiple tubular skeletons are obtained, wherein the multiple skeletons include a main skeleton and a secondary skeleton; one end of the main skeleton is connected to the cap and placed in the borehole; on the side of the main skeleton near the cap, a unidirectional stress monitoring unit located in a hollow tube is arranged along the axial direction of the skeleton and at least two unidirectional stress monitoring units perpendicular to each other are arranged along the radial direction of the skeleton; a signal processing module is arranged in the hollow tube of the main skeleton; after connecting the main skeleton and the secondary skeleton through a connector, a signal processing module is arranged in the secondary skeleton. Near the main frame, at least two unidirectional stress monitoring units perpendicular to each other are arranged radially along the frame. A signal processing module is placed in the hollow tube of the secondary frame. The polyvinylidene fluoride piezoelectric film of the radially arranged unidirectional stress monitoring units is coplanar with the outer wall of the frame. After each signal processing module is placed, it is connected to the wires of all unidirectional stress monitoring units in the frame. After all frames are arranged, the holes in the frames are sealed, and the hollow tubes inside the frames are grouted to allow the borehole-type three-dimensional multi-point coal and rock wireless stress gauge to be cast into the borehole. The borehole-type three-dimensional multi-point coal and rock wireless stress gauge is used to monitor the stress information of the coal and rock mass in real time. In this case, by arranging stress gauges including multiple frames and unidirectional stress monitoring units in the borehole, and arranging different unidirectional stress monitoring units in the frame according to the purpose of three-dimensional stress monitoring, the measurable electrical signals transmitted by the pressure of the polyvinylidene fluoride piezoelectric film are transmitted through the signal processing module and used for subsequent analysis such as stress monitoring, thereby improving the accuracy of stress monitoring data. Furthermore, the unidirectional stress monitoring unit is based on the piezoelectric effect, consisting of a polyvinylidene fluoride (PVDF) piezoelectric film placed inside two protective layers with mechanical properties similar to those of the rock strata. The thickness of the PVDF piezoelectric film is much smaller than its diameter or length and width dimensions, ensuring that only loads parallel to the direction of the PVDF piezoelectric film will induce an electrical signal on it. This improves the accuracy and sensitivity of the PVDF piezoelectric film, thereby further enhancing the accuracy of stress monitoring data. In addition, the stress information is converted using a signal amplification circuit, temperature compensation unit, signal filtering circuit, and analog-to-digital conversion circuit built into the stress gauge. The data signal is then transmitted wirelessly, while a wireless signal acquisition unit collects stress information from other adjacent skeletons at a certain distance, completing a two-way acquisition and transmission function. Based on this, related research can be conducted.The method disclosed herein boasts advantages such as high precision, long-term monitoring, high sensitivity, stability, and energy saving. It enables wireless transmission and can function simultaneously as a signal acquisition and transmission device, facilitating efficient signal transmission and collaborative operation between different stress gauges. It allows for long-term monitoring with low power consumption, stability, energy saving, high sensitivity, low cost, and impact resistance. The single-point stress measuring instrument utilized can be miniaturized, resulting in smaller borehole diameters and enabling direct installation using anchor bolts and cables. It offers higher and more stable response frequency, bandwidth, and resolution to external loads. It can monitor and measure dynamic loads. It can automatically couple according to the surrounding rock development, exhibiting strong adaptability. It can be arranged in a multi-point array, further enriching the content of coal and rock mass stress monitoring. It can locally reinforce the strength of the surrounding rock in roadways. Concrete columns are used to achieve coordinated deformation and enhance resistance to external forces. It enables multi-point stress monitoring in three directions within a single borehole, generating abundant data.

[0121] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this disclosure can be achieved, and this disclosure does not impose any limitations herein.

[0122] The specific embodiments described above do not constitute a limitation on the scope of protection of this disclosure. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass, characterized in that, It includes multiple unidirectional stress monitoring units, multiple signal processing modules, multiple frames, and protective caps; The unidirectional stress monitoring unit includes a polyvinylidene fluoride piezoelectric film, an upper protective layer and a lower protective layer respectively disposed on the upper and lower surfaces of the polyvinylidene fluoride piezoelectric film, and a wire connected to the polyvinylidene fluoride piezoelectric film. The upper protective layer or the lower protective layer is formed by casting target concrete. The target concrete is obtained based on the materials and proportions determined by the basic physical and mechanical properties of the rock samples at the stress monitoring point of the coal and rock mass on site. The plurality of skeletons includes a main skeleton and a secondary skeleton. One end of the main skeleton is connected to the protective cap, and the other end of the main skeleton is connected to the secondary skeleton. The skeleton is tubular. The main skeleton has a uniaxial stress monitoring unit arranged along the skeleton axis and located in a hollow tube, and at least two uniaxial stress monitoring units arranged radially and perpendicularly to the skeleton, embedded on the side near the protective cap. The secondary skeleton has at least two uniaxial stress monitoring units arranged radially and perpendicularly to the skeleton, embedded on the side near the main skeleton. The polyvinylidene fluoride piezoelectric film of the radially arranged uniaxial stress monitoring unit is coplanar with the outer wall of the skeleton. A signal processing module is arranged in one hollow pipe of an adjacent frame, or a signal processing module is arranged in each of two hollow pipes. The signal processing module is connected to the wires of all unidirectional stress monitoring units in the corresponding frame, and the signal processing module communicates wirelessly with external devices.

2. The borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass according to claim 1, characterized in that, The polyvinylidene fluoride piezoelectric film is elongated, and the length and width of the polyvinylidene fluoride piezoelectric film are both at least 100 times the thickness of the polyvinylidene fluoride piezoelectric film. The length and width of the upper protective layer and the lower protective layer are respectively greater than or equal to the length and width of the polyvinylidene fluoride piezoelectric film.

3. The borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass according to claim 1, characterized in that, The surface of the polyvinylidene fluoride piezoelectric film is coated with a silicone layer.

4. The borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass according to claim 1, characterized in that, Each frame has a slurry outlet hole on its outer wall, which connects the hollow pipe inside the frame to the outer wall.

5. The borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass according to claim 1, characterized in that, The number of secondary skeletons is multiple, and the borehole-type three-dimensional multi-point coal and rock wireless stress gauge also includes a connector, through which each skeleton is connected.

6. The borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass according to claim 1, characterized in that, The signal processing module includes an analog-to-digital conversion circuit, a temperature compensation unit, and a wireless transmission unit. The analog-to-digital conversion circuit is used to convert the analog stress data collected by the unidirectional stress monitoring unit into digital stress data, and the wireless transmission unit is used to send the digital stress data to an external device.

7. A method for monitoring stress in coal and rock mass based on a borehole-type three-dimensional multi-point wireless stress gauge, characterized in that, The borehole-type three-dimensional multi-point wireless stress gauge for coal and rock mass according to any one of claims 1-6 comprises: The number of skeletons was determined based on multiple stress monitoring points in the boreholes of the coal and rock mass in the field. Acquire a pre-fabricated uniaxial stress monitoring unit and multiple tubular skeletons, wherein the multiple skeletons include a main skeleton and a secondary skeleton; After connecting one end of the main frame to the protective cap, place it in the borehole. On the side of the main frame near the protective cap, arrange a unidirectional stress monitoring unit located in the hollow pipe along the axial direction of the frame, arrange at least two unidirectional stress monitoring units perpendicular to each other along the radial direction of the frame, and arrange a signal processing module in the hollow pipe of the main frame. After connecting the main frame and the secondary frame through the connector, at least two unidirectional stress monitoring units perpendicular to each other are arranged radially along the side of the secondary frame close to the main frame. A signal processing module is arranged in the hollow tube of the secondary frame. The polyvinylidene fluoride piezoelectric film of the radially arranged unidirectional stress monitoring unit is coplanar with the outer wall of the frame. After each signal processing module is arranged, the signal processing module is connected to the wires of all unidirectional stress monitoring units of the frame. After all the skeleton arrangements are completed, the holes of the skeleton are sealed, and the hollow pipes inside the skeleton are grouted to allow the drilled three-dimensional multi-point coal and rock wireless stress gauge to be cast into the borehole. Real-time monitoring of coal and rock mass stress information was achieved using a borehole-type three-dimensional multi-point wireless stress gauge.

8. The method for monitoring coal and rock mass stress based on a borehole-type three-dimensional multi-point wireless stress gauge according to claim 7, characterized in that, The manufacturing process of the uniaxial stress monitoring unit includes: Target concrete was prepared based on the physical and mechanical properties of rock samples from stress monitoring points in the coal and rock mass. Select a polyvinylidene fluoride piezoelectric film with a preset length and width, and use the target concrete to pour on the upper and lower surfaces of the polyvinylidene fluoride piezoelectric film to form an upper protective layer and a lower protective layer with a length and width greater than or equal to the preset length and width, thereby obtaining a uniaxial stress monitoring unit.

9. The method for monitoring coal and rock mass stress based on a borehole-type three-dimensional multi-point wireless stress gauge according to claim 8, characterized in that, After the uniaxial stress monitoring unit is fabricated, it needs to be cured and subjected to uniaxial compression tests.

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