Anchoring stress spatial diffusion visualization experiment method

Abstract

The invention discloses an anchoring stress spatial diffusion visualization experiment method which specifically comprises the following steps: firstly, preparing a coal-rock mass model with a three-dimensional structure and carrying out anchoring treatment, then carrying out internal stress freezing on the anchored coal-rock mass model, and then slicing in parallel to the end surface of the coal-rock mass model at equal intervals by taking the axis of an anchor rod as a center; selecting one slice body to carry out a photoelastic experiment, obtaining a grating image in the coal rock mass model, firstly processing the grating image to determine a phase principal value of three-dimensional information on the surface of an object, then adopting three-frequency heterodyne phase solution to obtain a continuous phase, and obtaining stress field information in the slice body; and finally, a plurality of slice bodies are processed respectively, and the anchoring stress space diffusion range of the whole coal and rock mass model is obtained. The method can visually display the spatial diffusion rule of the anchoring stress, has the advantages of simplicity in operation, high model optical sensitivity, good transparency and the like, and provides basic data for the design of a coal mine underground roadway support structure.

Description

Technical Field

[0001] This invention relates to anchor stress diffusion technology, belonging to the field of simulation experimental methods, and specifically to a visualization experimental method for spatial diffusion of anchor stress. Background Technology

[0002] During tunnel excavation, in order to effectively control the deformation of the surrounding rock and improve its stability, it is necessary to anchor the surrounding rock. However, anchoring will cause stress changes inside the surrounding rock, and the diffusion of stress will be affected by various factors such as changes in soil properties and increases in load. Clarifying the diffusion law of stress inside the anchor body can help personnel to accurately understand the interaction mechanism between the anchor body and the soil, thereby optimizing the anchor design, reducing the amount of materials used and the difficulty of construction, reducing costs and improving support efficiency. Due to the complex environment of underground coal mines, the main research methods for the spatial diffusion of stress in anchor bodies are: 1. Numerical simulation; for example, using the finite element method, which divides the continuum into finite elements and approximates the solution of the entire continuum by solving the equations of these elements; numerical simulation mainly relies on simulation, but it is difficult to simulate and capture the microscopic behavior of the slippage at the anchor interface during dynamic loading; 2. Field monitoring; for example, installing strain gauges and fiber optic sensors on the surface of the anchor bolt and surrounding rock to infer the internal stress distribution through surface data, but the sensor deployment density is low and the connection is complex, making it impossible to cover the entire anchor body. The data noise is high due to regional and underground environmental interference (such as vibration and humidity); 3. Experimental physical simulation; The anchor bolt is fixed in the coal and rock mass model, and strain gauges and pressure sensors are used to measure the anchor bolt tension or the surface stress of the anchor body. This method can flexibly and intuitively provide personnel with the stress parameters of the anchor bolt, but it still has the following shortcomings: The data mainly relies on sensors, and can only obtain the axial tension and surface stress of the anchor bolt. It is impossible to observe the internal three-dimensional stress field distribution, especially the spatial diffusion evolution path of the anchor stress of the anchor body is not clear enough, and it is difficult to determine the spatial diffusion mechanism of the anchor bolt anchor stress. Summary of the Invention

[0003] The purpose of this invention is to provide a visualization experimental method for the spatial diffusion of anchorage stress, which can intuitively display the spatial diffusion law of anchorage stress. It has the advantages of simple operation, high model optical sensitivity, and good transparency, and provides basic data for the design of support structures in underground coal mine roadways.

[0004] To achieve the above objectives, this paper presents a visualization experimental method for the spatial diffusion of anchorage stress, which specifically includes the following steps: S1, using epoxy resin and curing agent as raw materials, prepares a three-dimensional coal and rock mass model; S2, anchor the coal and rock mass model from step S1 to obtain the anchored coal and rock mass model. S3, freeze the internal stress of the anchored coal and rock mass model; S4. Slowly cool the stress-frozen coal and rock mass model to room temperature and remove it. Cut the coal and rock mass model into equal-interval slices with the anchor bolt axis as the center and both sides parallel to the end face of the coal and rock mass model, until the anchor bolt drilling position, and obtain n slices. S5. Select one slice from step S4 for photoelastic experiment to obtain the photoelastic fringe pattern inside the coal and rock mass model, and process the fringe pattern to obtain the stress field information inside the slice. S6, perform step S5 on each of the n slices to obtain the spatial diffusion range of anchoring stress in the entire coal and rock mass model.

[0005] In some examples of the present invention, in step S5, the formula for calculating the phase principal value of the fringe pattern is as follows: in, , , , When the grating phase is 0, , , The light intensity distribution function at that time; Introducing three different frequencies The three types of gratings have corresponding principal phase values ​​of , respectively. , and ; Based on the principle of tri-frequency heterodyne and and and By performing phase superposition, a phase function with a lower frequency is obtained. and At this time, the frequency corresponding to the phase function is , ; Then the phase function and Phase superposition yields a phase with only one period across the entire field. At this time, the frequency of the phase function is Finally by Reverse calculation , and The continuous phases are used to obtain the spatial diffusion range of anchorage stress under different preload forces.

[0006] In some examples of the present invention, in step S5, the apparatus matched for the photoelastic experiment includes: a light source arranged laterally on the experimental table, a spatial light modulator for adjusting the phase of the grating, a positioning component for fixing the slice, and a camera for acquiring the grating image. The cross-section of the slice is perpendicular to the line connecting the light source to the camera, and the camera transmits the raster image to the analysis unit.

[0007] In some examples of the present invention, in step S2, anchoring agent is placed in the anchoring interface reserved on the coal and rock mass model, and anchor rods are inserted and pre-tightening force is applied to form an anchoring structure. When anchoring the coal and rock mass model, the anchor rod located on the outside of the coal and rock mass model is fitted with a pair of washers and a nut that is threaded and connected to the anchor rod from bottom to top; One of the gaskets has a compressed elastic element between it.

[0008] In some examples of the present invention, in step S3, the anchored coal and rock mass model is placed in a high-temperature chamber, heated to 120°C at a heating rate of 1°C / min to 3°C / min, maintained for a period of time, and then cooled to room temperature at a cooling rate of ≤2°C / min to obtain a stress-frozen coal and rock mass model.

[0009] In some examples of the present invention, the anchored coal and rock mass model is first heated to 80°C at 3°C / min, then heated to 120°C at 1°C / min, and held at 120°C for 20 minutes to freeze the internal stress. Then it is slowly cooled down. During the cooling process, it can be cooled down to 80°C at 0.5°C / min, then cooled down to room temperature at 2°C / min, and finally a stress-frozen coal and rock mass model is obtained.

[0010] In some examples of the present invention, in step S1, E51 epoxy resin and anhydride curing agent are mixed at a mass percentage of 100:90 to obtain a mixture of epoxy resin and curing agent. First, add 2% plasticizer and 6% diluent to the mixture and stir at low speed. Then add 0.2% defoamer and stir at medium speed. Pour the whole mixture into a vacuum tank, evacuate to -0.1MPa, and keep it for 15-20 minutes until no bubbles escape. Once completed, the model is imported into a mold to create a three-dimensional coal and rock mass model.

[0011] In some examples of the present invention, the anhydride curing agent is methylhexahydrophthalic anhydride and the plasticizer is dibutyl phthalate; The diluent is propylene oxide butyl ether, and the defoamer is BYK-A530.

[0012] In some examples of the present invention, the mold is made of aluminum alloy and has a split upper and lower mold structure, with the mold surface located at the geometric center of the model.

[0013] Compared with existing technologies, this new method for visualizing the spatial diffusion of anchoring stress first establishes a transparent coal-rock mass model that conforms to the characteristics of coal-rock mass, applies a corresponding pre-tightening force to the model for anchoring, freezes the internal stress of the anchored coal-rock mass model, and then slices the coal-rock mass model at equal intervals. The photoelastic fringe pattern of the slices is obtained through photoelastic experiments, and the stress field information inside the model is obtained by using the phase shift method and the three-frequency heterodyne calculation. Thus, the spatial diffusion range of anchoring stress of the entire coal-rock mass model is obtained. The overall method has the advantages of simple operation, high model optical sensitivity, and good transparency, providing basic data for the design of support structures in underground coal mine roadways. The coal and rock mass model prepared using epoxy resin and curing agent has high transparency and high degree of reproduction, making the experimental results more accurate. In addition, two shims are placed between the nut and the coal and rock mass model to maintain a constant preload during the heating process. The elastic element can absorb displacement changes to achieve a constant preload. Furthermore, rotating the nut and pressing the elastic element with the shims allows for adjustment of different preloads, which facilitates the subsequent acquisition of the spatial diffusion range of anchoring stress of the coal and rock mass model under different preloads. Attached Figure Description

[0014] Figure 1 This is a flowchart illustrating the present invention; Figure 2 This is a schematic diagram of the anchor bolt anchoring structure in the coal and rock mass model of this invention; Figure 3 This is a schematic diagram of the present invention, in which slices are made sequentially towards the anchor rod axis with a thickness of 3mm; Figure 4 This is the stress-freezing temperature curve of the coal and rock mass model in step S3 of this invention; Figure 5 This is a front view of the device used in the photoelastic experiment of this invention; Figure 6 These are spatial diffusion diagrams of anchoring stress for slices numbered 1, 7, and 15 in embodiments of the present invention. In the diagram: 1. Coal and rock mass model, 2. Anchoring agent, 3. Anchor bolt, 4. Nut, 5. Washer; 6. Elastic component, 7. Light source, 8. Spatial light modulator, 9. Slice, 10. Camera, 11. Analysis component. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The same reference numerals in the drawings represent the same components. It should be noted that the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0016] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms “first,” “second,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, “an” or “a” and similar terms do not necessarily indicate a quantity limitation. Terms such as “comprising” or “including” mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships; these relative positional relationships may change accordingly when the absolute position of the described object changes.

[0017] like Figures 1 to 3 As shown, this method for visualizing the spatial diffusion of anchoring stress includes the following steps: S1, a three-dimensional coal and rock mass model 1 was prepared using epoxy resin and curing agent as raw materials; S2, anchor the coal and rock mass model 1 from step S1 to obtain the anchored coal and rock mass model 1. S3, freeze the internal stress of the anchored coal and rock mass model 1; S4. Slowly cool the stress-frozen coal and rock mass model 1 to room temperature and take it out. Cut the coal and rock mass model 1 into equal-interval slices with the anchor bolt 3 axis as the center and both sides parallel to the end face of the coal and rock mass model 1 until the anchor bolt 3 drilling position, and obtain n slices 9. S5. Select one slice 9 from step S4 to conduct a photoelastic experiment, obtain the photoelastic fringe pattern inside the coal and rock mass model 1, and process the fringe pattern to obtain the stress field information inside the slice 9. S6, perform step S5 on each of the n slices 9 to obtain the spatial diffusion range of anchoring stress in the entire coal and rock mass model 1.

[0018] Specifically, in step S1, the coal and rock mass model 1 is modeled and made using 3D software. It is a rectangular transparent structure to facilitate subsequent uniform slicing and photoelastic experiments. The anchoring of the coal and rock mass model 1 is mainly achieved by pre-tightening the anchor rods 3, thereby obtaining the anchored coal and rock mass model 1. In step S4, the stress-frozen coal and rock mass model 1 is sliced. The thickness of the slice 9 is determined according to the experimental requirements, such as 2-5 mm. In step S5, the slice 9 is placed in the photoelastic experimental device. The photoelastic fringe pattern inside the model is obtained by using the four-step phase-shifting method. The phase-shifting method is to acquire multiple frames of fringe images with a certain phase shift to calculate the initial phase value containing the three-dimensional information of the surface of the object being measured. By changing the phase of the grating, four different fringe patterns are obtained. Finally, the light intensity equation of the fringe pattern is combined to determine the initial phase value of the three-dimensional information of the object surface, so as to intuitively understand the distribution of anchoring stress.

[0019] In some examples of the present invention, in step S5, the formula for calculating the phase principal value of the stripe pattern (raster image) is as follows: in, , , , When the grating phase is 0, , , The light intensity distribution function at that time; Introducing three different frequencies The three types of gratings have corresponding principal phase values ​​of , respectively. , and ; Based on the principle of tri-frequency heterodyne and and and By performing phase superposition, a phase function with a lower frequency is obtained. and At this time, the frequency corresponding to the phase function is , ; Then the phase function and Phase superposition yields a phase with only one period across the entire field. At this time, the frequency of the phase function is Finally by Reverse calculation , and The continuous phase of the anchorage stress is used to obtain the spatial diffusion range of anchorage stress under different preloads; Specifically, the corresponding light intensity distribution function is obtained by changing the phase of the grating, i.e. When the grating phase is 0 When the grating phase is hour, When the grating phase is hour, When the grating phase is hour, Finally, by combining the above equations, the principal phase value of the raster image is obtained. The calculation formula; The formula for calculating the light intensity distribution function is: in, The average gray level of the image; For grayscale modulation of the image, The raster phase of the image; As explained above, the phase principal value of the raster image calculated above... It is unique within a phase period, but because there are multiple grating fringes throughout the measurement space, The phases are distributed in a sawtooth pattern, and phase expansion must be performed on the principal phase values ​​of the spatial points to obtain continuous absolute phase values. Therefore, a three-frequency heterodyne phase demodulation method is used to obtain continuous phase; Introducing three different frequencies The gratings, the three gratings corresponding to the principal phase values ​​are respectively , and ; Based on the principle of tri-frequency heterodyne and and and By performing phase superposition, a phase function with a lower frequency is obtained. and At this time, the frequency corresponding to the phase function is , ; in, frequency The calculation formula can be: Similarly, we can obtain , The calculation method; The heterodyne principle can be used to expand the relative phase values ​​of points in space, when the phase function... and Phase superposition yields a phase with only one period across the entire field. The frequency of this phase function is The value must be equal to 1; Finally, according to the formula: Depend on Reverse calculation , and The continuous phase of the anchorage stress is used to obtain the spatial diffusion range of anchorage stress under different preloads; in, ; This represents the ratio of the number of periods in the projected image.

[0020] In some examples of the present invention, such as Figure 5 As shown, in step S5, the apparatus matched for the photoelastic experiment includes a light source 7 arranged horizontally on the experimental table, a spatial light modulator 8 for adjusting the phase of the grating, a positioning component for fixing the slice 9, and a camera 10 for acquiring the grating image. The cross section of slice 9 is perpendicular to the line connecting light source 7 to camera 10, and camera 10 transmits the raster image to analysis unit 11; Specifically, a stable light source 7 is used. The light source 7 illuminates the slice 9 by changing the phase of different gratings through an SLM spatial light modulator 8. The image is then captured by a CCD camera 10 and imported into the analysis unit 11. Analysis component 11 can be a computer, which analyzes the light intensity distribution of camera 10 at different grating phases, i.e., the four interference fringes. , , , It can also perform phase principal values ​​of raster images and heterodyne phase decomposition calculations on slice 9, making it convenient to obtain stress field information inside the model.

[0021] In some examples of the present invention, such as Figure 2 As shown, in step S2, anchoring agent 2 is placed in the anchoring interface reserved on the coal and rock mass model 1, and anchor rod 3 is inserted and pre-tightened force is applied to form an anchoring structure. When anchoring the coal and rock mass model 1, the anchor rod 3 located on the outside of the coal and rock mass model 1 is fitted with a pair of washers 5 and a nut 4 that is threaded to the anchor rod 3 from bottom to top; Among them, a compressed elastic element 6 is provided between a pair of gaskets 5; Specifically, two washers 5 are placed between the nut 4 and the coal and rock mass model 1 to maintain a constant preload during the heating process. The elastic element 6 can be a low-stiffness cylindrical spring, which can absorb displacement changes and achieve a constant preload. Rotate nut 4 to press elastic element 6 through washer 5 to achieve different pre-tightening force adjustment, which facilitates subsequent acquisition of the spatial diffusion range of anchoring stress of coal and rock mass model 1 under different pre-tightening forces. The length change of the specimen under temperature change (ΔT) is as follows: in, It is the coefficient of thermal expansion of the material. It is the initial length of the specimen; The deformation of elastic element 6 is as follows: Where K is the stiffness of the elastic element and F is the preload force; The deformation of the elastic element 6 is made to completely compensate for the thermal expansion displacement, that is: The change in preload at this time for: Therefore, selecting a suitable low-stiffness elastic element can eliminate thermal expansion displacement and maintain a constant preload. In this example, assuming the applied preload is 100N, the thermal expansion displacement of the specimen in this embodiment is calculated as follows: The formula for calculating length change under temperature change (ΔT) in, The coefficient of linear expansion of E51 epoxy resin (take the median value of 50 × 10⁻⁶). −6 / ℃); This is the effective length in the direction of thermal expansion, for example, 100mm; ΔT represents the temperature change, such as rising from room temperature of 25℃ to 120℃, i.e., ΔT = 95℃; therefore ; When F = 100N, then ; When the stiffness of the elastic element 6 is too high, the stiffness of a single elastic element 6 can be reduced by using parallel elastic elements 6. In this embodiment, four elastic elements 6 are connected in parallel, so the stiffness of each elastic element 6 is... In some examples of the present invention, such as Figure 4As shown, in step S3, the anchored coal and rock mass model 1 is placed in a high-temperature chamber, first heated to 120°C at a heating rate of 1°C / min to 3°C / min, and maintained for a period of time, and then cooled to room temperature at a cooling rate of ≤2°C / min to obtain the stress-frozen coal and rock mass model 1. Specifically, such as Figure 4 As shown, the pre-stressed anchor body is placed in a high-temperature chamber and slowly heated to 120°C according to the corresponding freezing curve. The heating rate can be 3°C / min to 80°C, then 1°C / min to 120°C, and the temperature is maintained at 120°C for 20 minutes to freeze the internal stress. Then the temperature is slowly reduced. During the cooling process, the temperature can be reduced to 80°C at 0.5°C / min, then to room temperature at 2°C / min, and finally the stress-frozen coal and rock mass model 1 is obtained.

[0022] In some examples of the present invention, in step S1, E51 epoxy resin and anhydride curing agent are mixed at a mass percentage of 100:90 to obtain a mixture of epoxy resin and curing agent. First, add 2% plasticizer and 6% diluent to the mixture and stir at low speed. Then add 0.2% defoamer and stir at medium speed. Pour the whole mixture into a vacuum tank, evacuate to -0.1MPa, and keep it for 15-20 minutes until no bubbles escape. After completion, the model is imported into a mold with a split upper and lower structure to prepare a three-dimensional coal and rock mass model 1. Furthermore, the anhydride curing agent is methylhexahydrophthalic anhydride, and the plasticizer is dibutyl phthalate; The diluent is propylene oxide butyl ether, and the defoamer is BYK-A530; Specifically, the anhydride curing agent can be methylhexahydrophthalic anhydride; the plasticizer dibutyl phthalate is used to reduce brittleness and improve flexibility; the diluent propylene oxide butyl ether is used to reduce viscosity and improve casting fluidity. In the actual preparation process, after adding plasticizer and diluent, it is necessary to stir at low speed for 5 minutes, then add defoamer and stir at medium speed for 2 minutes. Pour the mixture into a vacuum tank, evacuate to -0.1MPa, and maintain for 15-20 minutes until no bubbles escape. The mold can be made of aluminum alloy (6061-T6), which has the advantages of high temperature resistance, uniform heat conduction and easy processing. It adopts the upper and lower mold split method, which is divided into upper mold (with gate) and lower mold (with venting groove) along the height direction of the model. The parting surface is located at the geometric center of the model. Conical positioning pin holes are set at the four corners to ensure the mold closing accuracy. Positioning holes are reserved at the three holes of the pre-embedded anchor rod on the side wall, and stainless steel positioning pins are inserted. The gap between the positioning pin and the mold hole is filled with high temperature sealant. Example S1 can use 3D modeling software such as AutoCAD and Solidworks to design a 3D model of coal and rock mass with 3 holes for 70mm anchor bolts. The overall size of the model is a square structure of 100×100×100mm, and an aluminum alloy mold of the same size can be made. Epoxy resin and curing agent are mixed in a certain proportion and injected into a prepared aluminum alloy mold to create a transparent coal and rock mass model 1; the specific operation method is as follows: Use E51 epoxy resin and anhydride curing agent (methylhexahydrophthalic anhydride) in a mass ratio of E51:curing agent = 100:90. Add 2% of plasticizer dibutyl phthalate to reduce brittleness and improve flexibility. Add 6% of diluent propylene oxide butyl ether to reduce viscosity and improve casting fluidity. After adding plasticizer and diluent, stir at low speed for 5 minutes. Then add 0.2% of defoamer BYK-A530 and stir at medium speed for 2 minutes. Pour the mixture into a vacuum tank, evacuate to -0.1MPa, and maintain for 15-20 minutes until no bubbles escape. The aluminum alloy (6061-T6) mold adopts an upper and lower parting method. The parting surface is located at the geometric center of the model. The net size of the inner cavity is 100×100×100mm. Φ8mm tapered positioning pin holes are set at the four corners to ensure the mold closing accuracy. The side wall has three pre-embedded anchor rod channels. For example, a positioning hole with a diameter of 4.1mm is reserved. A stainless steel positioning pin with a diameter of 4mm and a length of 80mm is inserted, with an embedding depth of 70mm and a 10mm margin for fixing the external baffle bolt. The gap between the positioning pin and the mold hole is filled with high-temperature sealant. Align the upper and lower molds with tapered positioning pins, tighten the bolts, pour the degassed resin into the pouring funnel, mainly by gravity pouring, and control the flow rate at 3-5 mm / s. When the resin reaches the overflow tank, stop pouring, remove the pouring funnel, and then seal the pouring port with resin preheated to 60°C. Transfer the mold as a whole to an oven preheated to 80°C and process it according to the step curing procedure: (1) Initial curing: 80°C constant temperature for 2 hours (heating rate 1°C / min); (2) Stress freezing: heat to 110°C constant temperature for 6 hours (heating rate 2°C / min); (3) Cooling: slow cooling to below 40°C at a rate of ≤2°C / min. Remove the positioning pin baffle, gently tap the exposed end of the pin to loosen it, then unscrew it. Loosen the mold closing bolts, and use a nylon pry bar to separate the upper and lower molds along the parting surface. Polish and clean the surface of the coal and rock model 1, and then perform quality inspections, including dimensional inspection (side length error ≤ ±0.1mm, hole depth 70±0.2mm), optical inspection (no stress stripe distortion or hazy defects observed under polarized light), and mechanical inspection (testing the model's elastic modulus, with an error of ≤10% compared to the original coal and rock model). S2, Anchor the obtained coal and rock mass model 1. Anchoring agent 2 can be placed in the reserved anchoring interface, and anchor rod 3 can be inserted and pre-tightened to form an anchoring structure, thus obtaining the anchored coal and rock mass model 1. During the anchoring process, a pair of washers 5 and an elastic body can be added between the nut 4 and the coal and rock mass model 1 to achieve a constant preload. S3, after the pre-tightening force has been applied, the anchor bodies are placed in a high-temperature chamber and the temperature is slowly raised to 120°C according to the freezing curve. The anchor stress distribution is frozen and recorded. Then the temperature is slowly lowered back to room temperature and the model is taken out. S4, as Figure 3 As shown, the coal and rock mass model 1 after stress freezing is sliced ​​along the axis parallel to the anchor rod 3. The thickness of the slice 9 is 3mm, that is, continuous slices are made every 3mm starting from the left edge. 15 slices are cut on both sides of the anchor rod 3 until the drilling position of the anchor rod 3, and the slices are numbered 1-30 in sequence. S5, the light source 7 illuminates the slice 9 by changing the different grating phases through the SLM spatial light modulator 8, and then the CCD camera 10 captures the image and imports it into the computer. Three grating patterns with period numbers of 70, 60, and 59 were selected. The phase calculation method was verified using a structured light measurement system consisting of a DLP projector and a CCD camera 10 (the DLP projector parameters are InFcousLP70+, effective resolution is 1280×1024), with an overall baseline length of 400mm and a measurement distance of 1200mm. Correspondingly, the frequencies of the three gratings , , The corresponding principal phase values ​​are respectively , and The connection phase is obtained by phase deconstructing the three-frequency heterodyne phase. In this example, slice 9, numbered 1, 7, and 15, is selected, and the corresponding experimental results are compared. Figure 6 As shown, the variation in the spatial diffusion range of anchoring stress can be clearly seen. Among them, the diffusion radius of slice 9 (number 15) is the largest, followed by slice 7, and the smallest is slice 1. That is, the closer to the anchor rod 3, the greater the diffusion range of anchoring stress.

[0023] The foregoing description, with reference to preferred embodiments, details an exemplary implementation of the visualization experimental method for spatial diffusion of anchoring stress proposed in this invention. However, those skilled in the art will understand that various modifications and alterations can be made to the above specific embodiments without departing from the concept of this invention, and various combinations can be made to the various technical features and structures proposed in this invention without exceeding the protection scope of this invention, which is determined by the appended claims.

Claims

1. A method for visualizing anchoring stress space diffusion experiments, characterized in that, Specifically comprising the following steps: S1, preparing a three-dimensional coal rock mass model (1) with epoxy resin and curing agent as raw materials; S2, anchoring the coal rock mass model (1) in step S1 to obtain an anchored coal rock mass model (1); S3, freezing the internal stress of the anchored coal rock mass model (1); S4, slowly cooling the stress frozen coal rock mass model (1) to room temperature and taking it out, and slicing the coal rock mass model (1) with the anchor rod (3) axis as the center and both sides parallel to the end face of the coal rock mass model (1) at equal intervals until the anchor rod (3) drilling position, obtaining n slice bodies (9); S5, selecting one slice body (9) in step S4 for photoelastic experiment, taking the photoelasticity fringe pattern inside the coal rock mass model (1), and processing the fringe pattern to obtain the stress field information inside the slice body (9); S6, performing step S5 on n slice bodies (9) to obtain the anchoring stress space diffusion range of the entire coal rock mass model (1).

2. The anchoring stress space diffusion visualization experiment method according to claim 1, wherein in step S5, the phase principal value of the fringe pattern is calculated according to the following formula:

3. The anchoring stress space diffusion visualization experiment method according to claim 1, wherein in step S5, the device matched by the photoelastic experiment comprises: a light source (7) arranged transversely on the experimental table, a spatial light modulator (8) for adjusting the grating phase, a positioning component for fixing the slice body (9), and a camera (10) for acquiring the grating image; wherein, , , , are the light intensity distribution functions when the grating phase is 0, , , , Introducing three different frequencies The three types of gratings have corresponding principal phase values ​​of , respectively. , and ; According to the three-frequency heterodyne principle, the phase functions and are superimposed with each other, and a phase function with a lower frequency is obtained and correspondingly. The frequency corresponding to the phase function is and at this time. The frequency corresponding to the phase function is , . The phase function is calculated by and phase superposition, the phase of only one cycle in the full field range is obtained , at this time the frequency of the phase function is ; finally, the continuous phase of , , and is calculated by reverse calculation, and the spatial diffusion range of anchoring stress under different pretension is obtained.​ The cross section of the slice body (9) is perpendicular to the line connecting the light source (7) to the camera (10), and the camera (10) transmits the grating image to the analysis component (11).

4. The anchoring stress space diffusion visualization experiment method according to any one of claims 1 to 3, wherein in step S2, the anchoring agent (2) is placed in the reserved anchoring interface of the coal rock mass model (1), and the anchor rod (3) is inserted and a pre-tightening force is applied to form an anchoring structure; When the coal rock mass model (1) is anchored, the anchor rod (3) located outside the coal rock mass model (1) is sequentially sleeved with a pair of spacers (5) and a nut (4) connected with the anchor rod (3) by threads from bottom to top; Wherein, a pair of spacers (5) are provided with an elastic element (6) subjected to compression.

5. The anchoring stress space diffusion visualization experiment method according to any one of claims 1 to 3, wherein in step S3, the anchored coal rock mass model (1) is placed in a high temperature box, first heated to 120℃ at a heating rate of 1℃ / min to 3℃ / min, and then cooled to room temperature at a cooling rate of ≤2℃ / min, to obtain the stress frozen coal rock mass model (1).

6. The anchoring stress space diffusion visualization experiment method according to claim 5, wherein ​ ​ ​ ​ The coal rock body model (1) after anchoring is first heated to 80℃ at 3℃ / min, then heated to 120℃ at 1℃ / min, and kept at 120℃ for 20 minutes to freeze the internal stress, and then slowly cooled down, during the cooling process, first cooled to 80℃ at 0.5℃ / min, then cooled to room temperature at 2℃ / min, finally obtaining the coal rock body model (1) with stress frozen.

7. The anchoring stress spatial diffusion visualization experimental method according to any one of claims 1 to 3, characterized in that, In step S1, the E51 epoxy resin and the anhydride curing agent are mixed in a mass percentage of 100:90 to obtain a mixture of the epoxy resin and the curing agent; First, 2% of a plasticizer and 6% of a diluent are added to the mixture and stirred at low speed, then 0.2% of a defoaming agent is added and stirred at medium speed, and then the whole mixture is poured into a vacuum tank and vacuumized to -0.1MPa for 15-20 minutes until no bubbles escape; After completion, it is introduced into a mold to prepare a coal rock body model (1) with a three-dimensional structure.

8. The anchoring stress spatial diffusion visualization experimental method according to claim 7, characterized in that, The anhydride curing agent is methylhexahydrophthalic anhydride, and the plasticizer is dibutyl phthalate; The diluent is propylene oxide butyl ether, and the defoaming agent is BYK-A530.

9. The anchoring stress spatial diffusion visualization experimental method according to claim 7, characterized in that, The mold is made of aluminum alloy, and has an upper and lower split structure, with the profile located at the geometric center of the model.

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