A test method and analysis method for frost heave expansion of fractures in a closed transparent rock mass

Abstract

The present invention provides a test method and an analysis method for the frost heave expansion of internal fissures in a transparent rock mass under saturated and enclosed conditions. By designing a visual test device for the frost heave expansion of internal fissures in a transparent rock under enclosed conditions, the whole process of the frost heave expansion of internal cracks in the rock is quantitatively reconstructed, realizing the real-time three-dimensional reconstruction of the spatio-temporal evolution of internal fissure frost heave, and overcoming the deficiency in the previous studies that the description of frost heave fissures is only qualitative. In addition, an analysis method for the frost heave of internal fissures in a transparent rock mass under enclosed conditions is provided, and a new criterion for the initiation and expansion of internal fissure frost heave is obtained. The criterion is based on real and quantitative test results. Compared with the criterion derived from the previous traditional analysis methods, it has higher accuracy and can reflect the real frost heave failure mechanism of rock masses. The new criterion of the present invention, combined with numerical algorithms, is applied to the catastrophe prediction of rock mechanics engineering in cold regions, and can more accurately predict the disasters of rock mechanics engineering in cold regions.

Description

Technical Field

[0001] The present invention relates to the technical field of hydraulic rock mechanics, and particularly relates to a test method and an analysis method for freeze-thaw expansion of internal fissures in a transparent rock mass under enclosure. Background Art

[0002] Due to the opaque property of the rock mass, the evolution of internal fissures therein is a typical "black box" problem, being "invisible, inaccessible, and intangible". Just because the internal fissures of the rock mass are invisible, it is difficult to quantitatively describe their spatial distribution patterns. Traditional analysis methods equivalent the rock to a continuous medium and deduce a series of rock constitutive equations and failure criteria on this basis. This treatment method has insufficient representativeness for rock mechanics, resulting in difficulty in predicting the accurate failure locations in rock engineering using traditional analysis methods. Therefore, the chain problem of "rock is opaque → fissure distribution law is not quantitative → freeze-thaw mechanism criterion is unclear → prediction is inaccurate" has severely restricted the design and construction levels of hydraulic rock mechanics projects in cold regions.

[0003] With the proposal of the concepts of "transparent physical model" and "digital core", the technology of deducing the transparency inside the rock provides the possibility for quantitatively revealing the freeze-thaw fracture mechanics mechanism of fissured rock masses. However, currently, the evolution process of internal fissures in the rock in the "transparent physical model" is mostly described qualitatively, and it is difficult to quantitatively describe their spatial distribution patterns, resulting in the characteristics of "no comparison and large simplification" in the criterion research, which is also the root cause of the "inaccurate prediction" of the criterion; the high-resolution CT imaging technology can reconstruct the spatial distribution of fissures inside the opaque rock mass in three dimensions, but its size effect is obvious, and it is easily affected by subjectivity during the reconstruction process, resulting in low reconstruction accuracy. At the same time, it cannot reveal the three-dimensional spatial freeze-thaw evolution process of the fissures. In addition, the "threshold" of the research is relatively high, making it difficult to be popularized to ordinary scientific research workers and traditional design and construction units. Summary of the Invention

[0004] Aiming at the technical problem that the prior art cannot quantitatively describe the freeze-thaw evolution and distribution pattern of saturated fissures inside the rock, the present invention provides a test method for freeze-thaw cracking of internal fissures in a transparent rock mass under enclosure, which has the characteristics of quantification and real-time performance; the present invention also provides an analysis method for freeze-thaw of internal fissures in a transparent rock mass under enclosure.

[0005] To achieve the above object, the technical solution of the present invention is: a transparent rock mass enclosed internal crack frost heave expansion test device, which is characterized by comprising a 3D printed transparent rock mass specimen, a freezing test chamber, a camera equipment group, a pressure monitoring system and a temperature monitoring system. The temperature monitoring system and the pressure monitoring system are connected to a computer processing system. The interior of the 3D printed transparent rock mass specimen contains three-dimensional internal cracks and a pre-channel for placing a 3D printed closed tube. The bottom of the pre-channel communicates with the three-dimensional internal cracks and extends to the top of the 3D printed transparent rock mass specimen. The outer wall of the 3D printed closed tube is in closed contact with the inner wall of the pre-channel. The interior of the 3D printed closed tube is provided with a wire channel through which a wire passes and a water passage. The pressure monitoring system is connected to a pressure sensor in the three-dimensional internal cracks through the wire. The temperature monitoring system is connected to a temperature sensor installed on the surface of the 3D printed transparent rock mass specimen.

[0006] Further, the camera equipment group consists of 4 groups of binocular cameras, which are symmetrically installed around the 3D printed specimen.

[0007] Further, the side wall material of the freezing test chamber is high-strength transparent tempered glass.

[0008] Further, the pressure sensor is in the shape of a thin film, and its size is adapted to the size of the pre-channel. The center of the thin film pressure sensor is at the same point as the center of the three-dimensional internal cracks, and the spatial position angle between the thin film pressure sensor and the three-dimensional internal cracks is the same.

[0009] Further, the wire channel is arranged in the center of the 3D printed closed tube. The length of the 3D printed closed tube is greater than the length of the pre-channel. The outer side of the 3D printed closed tube is marked with length scale lines. The wire section coated with epoxy resin is between the bottom end of the wire channel and the thin film pressure sensor. The descending scale value of the 3D printed closed tube entering the pre-channel is the difference between the distance from the top of the 3D printed transparent rock mass specimen to the center of the three-dimensional internal cracks and the vertical distance from the bottom end of the wire channel to the center of the thin film pressure sensor.

[0010] Further, the 3D printed transparent rock mass specimen and the 3D printed closed tube are made of the same 3D printing material, which is a modified transparent resin. The components of the modified transparent resin include one or more of acrylate prepolymer, organoantimony compound, and propylene carbonate.

[0011] A method for testing the frost heave expansion of enclosed internal cracks in a transparent rock mass, using the above-mentioned transparent rock mass enclosed internal crack frost heave expansion test device, the steps include:

[0012] (1) Specimen preparation: Inject water into the three-dimensional internal crack through the pre-pipeline, place the 3D printed closed tube in the pre-pipeline and seal it. After preparing the 3D printed transparent rock mass specimen, place it in a freezing test chamber with a vacuum internal environment;

[0013] (2) Specimen freeze-thaw treatment: Turn on the freezing test chamber. The set freeze-thaw cycle temperature for the test is -20 to 20 °C, and the freezing and melting durations are both 6 hours, that is, 12 hours is one freeze-thaw cycle period;

[0014] (3) After taking out the 3D printed specimen that has completed one freeze-thaw cycle from the freezing test chamber, place it at the center point of the square formed by the camera equipment group. Use the binocular camera group to obtain the three-dimensional spatial quantitative distribution law of the freeze-thaw expansion of the three-dimensional internal crack through the built three-dimensional binocular stereo vision perception system. The three-dimensional spatial quantitative distribution law includes the critical deflection angle θ of the freeze-thaw expansion e ;

[0015] (4) If the crack does not expand and penetrate the specimen, add water to the water pipeline through a dropper to fill the three-dimensional internal crack with water, and then repeat steps (2) to (4) until the test ends.

[0016] Furthermore, the three-dimensional binocular stereo vision perception system includes determining the three-dimensional spatial point coordinates of each pixel point on the crack surface, forming a spatial point cloud to fit into the crack surface, and reconstructing the spatial morphology of the freeze-thaw of the three-dimensional internal crack.

[0017] An analysis method for the freeze-thaw expansion of a closed internal crack in a transparent rock mass, characterized by including the steps:

[0018] Step 1. Weight coefficient: Calculate the I-II-III type stress intensity factors K Ⅰ 、K Ⅱ 、K Ⅲ of the freeze-thaw of the three-dimensional internal crack based on the M integral. Initially determine the weight coefficients η' I 、η' II 、η' III of the stress intensity factors by analyzing the proportions of the I, II, and III type stress intensity factors. The weight coefficient determination formula is as follows:

[0019]

[0020] Where: K I 、K II 、K III are respectively the stress intensity factors at the front edge of the three-dimensional internal crack calculated by the M integral, and l is the path around the three-dimensional internal crack for one week; are respectively the integrals of K I 、K II 、K III along the path l of the three-dimensional internal crack;

[0021] Step 2. Calculation of the critical deflection angle of internal cracks in three dimensions: Select the improved maximum energy release rate criterion as the criterion for the frost heaving expansion of internal cracks in three dimensions. The direction angle at which G(θ) reaches the maximum is the critical deflection angle θ of internal cracks in three dimensions, and the expression is as follows:

[0022]

[0023] In the formula, θ is the critical deflection angle of frost heaving of internal cracks in three dimensions, G(θ) is the strain energy release rate, and η I , η II , η III are the weight coefficients of the stress intensity factors of types I, II, and III respectively, and K I r (θ), K II r (θ), and K III r (θ) are the stress intensity components corresponding to the fracture types of types I, II, and III respectively;

[0024] Step 3. Adjust the weight coefficients: Compare the critical deflection angle θ calculated in Step 2 with the critical deflection angle θ e obtained by the above-mentioned frost heaving expansion test method of internal cracks in the transparent rock mass; if θ = θ e , then the weight coefficients η I = η' I , η II = η' II , η III = η' III ; if θ ≠ θ e , adjust η' I , η' II , η' III , and use the expression in Step 2 to calculate to make θ = θ e , so as to obtain the weight coefficients η I =

[0025] η' I , η II = η' II , η III = η' III , thereby obtaining a new criterion for the frost heaving expansion of internal cracks in three dimensions in the improved form.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] (1) A quantitative transparent test method for the frost heave evolution of fractures in rocks and its supporting analysis method are established, solving the key scientific problems in traditional cold region rock mechanics engineering, such as "rocks are opaque → the law of fracture distribution is not quantitative → the criterion for frost heave mechanism is unclear → prediction is inaccurate".

[0028] (2) The 3D printed transparent rock mass specimen designed in the present invention is provided with pre-pipes and 3D printed closed pipes fitted with the pre-pipes, facilitating the connection and installation of the device; the pressure sensor wires penetrate through the conductive channels and are placed inside the three-dimensional internal fractures, and can be fixed by the 3D printed closed pipes through resin sealing at the top, so that the fixed position of the pressure sensor does not shift, ensuring the stability and accuracy of the obtained pressure values; the designed water supply pipes meet the requirement of repeatedly filling water inside the three-dimensional internal fractures during the test process.

[0029] (3) The present invention uses an improved transparent resin material as the 3D printing material, which is similar to the properties of rocks and can better reflect the mechanical properties of rocks; at the same time, its transparency can also provide convenient conditions for observing the frost heave evolution of internal fractures; the combination of the transparent material and the stereo vision reconstruction technology breaks through and realizes the real-time three-dimensional reconstruction of the spatio-temporal evolution of internal fracture frost heave, overcoming the deficiency that the description of frost heave fractures in previous studies was qualitative (such as expressions like "wing-shaped cracks" and "anti-wing cracks" in previous literature), making the distribution pattern of the frost heave expansion of internal fractures in the rock mass fully quantitative, so that the analysis "has evidence to rely on".

[0030] (4) The analysis method of the present invention obtains the weight coefficients of the stress intensity factors of types I, II, and III, as well as a new criterion for the initiation and propagation of internal fracture frost heave. The criterion is based on real and quantitative test results and has higher accuracy compared to the criteria derived from previous traditional analysis methods, and can reflect the real frost heave failure mechanism of rock masses; combining the new criterion of the present invention with numerical algorithms and applying it to the disaster prediction of cold region rock mechanics engineering can more accurately predict the disasters of cold region rock mechanics engineering, overcoming the deficiency that traditional views believe that numerical simulation "predicts inaccurately". Description of the Drawings

[0031] Figure 1 It is a structural schematic diagram of the device of the present invention;

[0032] Figure 2 It is a structural schematic diagram of the 3D printed transparent rock mass specimen of the present invention;

[0033] Figure 3 It is an arrangement diagram of the binocular camera group of the present invention;

[0034] Figure 4 It is a flow chart of the modification scheme of the 3D printing material of the present invention;

[0035] Figure 5This is the process diagram for building the three-dimensional binocular stereo vision perception system of the present invention;

[0036] Among them: 1 is a freezing test chamber, 2 is a high-strength transparent toughened glass, 3 is a pressure sensor, 4 is a 3D printed transparent rock mass specimen, 5 is a three-dimensional internal crack, 6 is a temperature sensor, 7 is a temperature monitoring system, 8 is a pressure monitoring system, 9 is a computer processing system, 10 is a pre-channel, 11 is a wire, 12 is a 3D printed closed tube, 13 is a water supply pipe, 14 is a dropper, and 15 is a binocular camera. Specific implementation manner

[0037] The following further elaborates in detail on a method for testing and analyzing the frost heave cracking of internal cracks in a saturated closed transparent rock mass of the present invention in combination with the accompanying drawings and embodiments.

[0038] The test device for the frost heave expansion test of internal cracks in the closed transparent rock mass of the present invention is as Figure 1 shown. The test device includes a freezing test chamber 1. Preferably, the side wall material of the freezing test chamber 1 is a high-strength transparent toughened glass 2 to achieve visualization.

[0039] The test device further includes a 3D printed transparent rock mass specimen 4, a camera device group, a temperature monitoring system 7, and a pressure monitoring system 8; the temperature monitoring system 7 and the pressure monitoring system 8 are connected to a computer processing system 9 to achieve the visualization of temperature data and pressure data.

[0040] As Figure 2 shown, the inside of the 3D printed transparent rock mass specimen contains a three-dimensional internal crack 5 and a pre-channel 10 for placing a 3D printed closed tube 12. The bottom of the pre-channel 10 is connected to the three-dimensional internal crack 5 and extends to the top of the 3D printed transparent rock mass specimen 4. The outer wall of the 3D printed closed tube 12 is in sealed contact with the inner wall of the pre-channel 10. A wire channel and a water supply pipe 13 through which a wire 11 passes are provided inside the 3D printed closed tube 12. The test device further includes a dropper 14 for injecting water into the three-dimensional internal crack 5 from the water supply pipe 13 during the test.

[0041] The pressure monitoring system 8 is connected to a pressure sensor 3 inside the three-dimensional internal crack 5 through the wire 11. The temperature monitoring system 7 is connected to a temperature sensor 6 installed on the surface of the 3D printed transparent rock mass specimen. The temperature sensor 6 collects the ambient temperature and transmits it to the temperature monitoring system to achieve the processing of temperature data. The pressure sensor 3 collects the frost heave pressure data of the internal crack and transmits it to the pressure monitoring system to achieve the processing of the frost heave pressure data.

[0042] As Figure 3 shown, the camera device group is 4 groups of binocular cameras 15, which are symmetrically installed around the 3D printed specimen.

[0043] Preferably, the pressure sensor is in the shape of a thin film, and its size is adapted to the size of the pre-channel. The center of the thin film pressure sensor is at the same point as the center of the three-dimensional internal crack, and the spatial position angle between the thin film pressure sensor and the three-dimensional internal crack is the same. In the present invention, the center of the designed thin film pressure sensor is positioned at the center of the three-dimensional internal crack to ensure the accuracy of the data collected by the pressure sensor.

[0044] As a preferred solution, the wire channel is arranged at the center of the 3D printed closed tube. The length of the 3D printed closed tube is greater than the length of the pre-channel. The outer side of the 3D printed closed tube is marked with length scales. The wire segment between the bottom end of the wire channel extending to the thin film pressure sensor is coated with epoxy resin. By curing the wire segment with epoxy resin, the spatial position angle of the thin film pressure sensor is made consistent with that of the three-dimensional internal crack. The epoxy resin curing can keep the wire segment in an unchanged position during the test and at the same time realize the central positioning of the thin film pressure sensor. The descending scale value of the 3D printed closed tube entering the pre-channel is the difference between the distance from the top of the 3D printed transparent rock mass specimen to the center of the three-dimensional internal crack and the vertical distance from the bottom end of the wire channel to the center of the thin film pressure sensor. The distance a between the top of the 3D printed transparent rock mass specimen and the center of the three-dimensional internal crack can be calculated according to the model size, and the vertical distance b between the bottom end of the wire channel and the center of the thin film pressure sensor can be measured. When the 3D printed closed tube is lowered into the pre-channel to the scale position of a - b, the connection between the 3D printed closed tube and the pre-pipe is fixed with epoxy resin to complete the central positioning of the thin film pressure sensor.

[0045] In order to reduce visual incoordination, in the present invention, the 3D printing photosensitive resin material used for the 3D printed transparent rock mass specimen is the same as that of the 3D printed closed tube.

[0046] Due to the disadvantages that the existing 3D printing transparent resin materials have relatively soft mechanical properties and there are large differences in key mechanical parameters such as elastic modulus, Poisson's ratio, peak strength, and brittleness degree from real rocks, the present invention conducts a modification study on the 3D printing transparent resin materials, and the method flow is as Figure 4As shown, the steps include: first, using a nuclear magnetic resonance spectrometer (such as model AVANCE III HD400M), a field emission scanning electron microscope system (such as model ZEISS Gemini SEM 300), and an X-ray single crystal diffractometer (such as model SMART APEX II) to determine the chemical composition of the UTR8100 model 3D printing photosensitive resin; second, analyzing the chemical properties of the key components of the 3D printing transparent resin material and screening chemical additives to improve the mechanical properties of the transparent resin; third, designing a modification test plan for the 3D printing photosensitive resin. Table 1 shows the influencing factors for the modification of the 3D printing photosensitive resin material, and Table 2 shows the orthogonal test plan. The influencing factors include different additive ratio schemes, heat treatment at different high temperature peaks, curing treatment under different ultraviolet light irradiations, and freezing treatment at different low temperature peaks; fourth, using a universal testing machine to test the mechanical properties of the improved transparent resin specimens under the orthogonal test plan, and selecting the improved transparent resin that meets the test conditions as the 3D printing material.

[0047] Table 1 Influencing factors for the modification of the 3D printing photosensitive resin material

[0048]

[0049] Table 2 Orthogonal test plan (4 factors and 4 levels)

[0050]

[0051] Perform a sensitivity analysis on the mechanical properties of the 3D printing materials under different influencing factors, so as to obtain a modification plan with mechanical properties closest to the mechanical properties of rock for use in the closed internal crack frost heave cracking test of the present invention. The 3D printing material of the present invention is a modified transparent resin, and the components of the modified transparent resin include one or more of acrylate prepolymer, organoantimony compound, and propylene carbonate.

[0052] The present invention provides a method for testing the frost heave expansion of closed internal cracks in a transparent rock mass. Using the above-mentioned test device for the frost heave expansion of closed internal cracks in a transparent rock mass, the steps include:

[0053] (1) Specimen preparation: Inject water into the three-dimensional internal cracks through the pre-pipeline, place the 3D printing closed tube in the pre-pipeline and seal it. After completing the preparation of the 3D printing transparent rock mass specimen, place it in a freezing test chamber with a vacuum internal environment;

[0054] (2) Specimen freeze-thaw treatment: Turn on the freezing test chamber. The set freeze-thaw cycle temperature of the test is -20 to 20 °C, and the freezing and melting durations are both 6 h, that is, 12 h is a freeze-thaw cycle period;

[0055] (3) After taking out the 3D printed specimen that has completed a freeze-thaw cycle from the freezing test chamber, place it at the center point of the square formed by the camera equipment group. Use the binocular camera group to obtain the three-dimensional quantitative distribution law of the three-dimensional crack frost heave expansion through the built three-dimensional binocular stereo vision perception system. The three-dimensional quantitative distribution law includes the critical deflection angle θ of frost heave expansion e ;

[0056] (4) If the crack does not expand through the specimen, fill the three-dimensional internal crack with water by adding water to the water pipeline through a dropper, and then repeat steps (2) to (4) until the test ends.

[0057] The specific method for building the three-dimensional binocular stereo vision perception system of the present invention is as shown in the method flow Figure 5 shown, where 15 is the calibration board, including four steps:

[0058] S1. Binocular calibration: First, calibrate the camera parameters of the binocular camera. The calibration method is intended to use the Zhang Zhengyou calibration method. The calibration formulas for the internal and external parameters of the camera are as follows:

[0059]

[0060] In the formula: s is the scalar coefficient; represents the pixel coordinates of the imaging point in the pixel coordinate system; f is the lens focal length of the camera; dx, dy are the horizontal and vertical physical sizes in pixel units; (u0, v0) represents the origin of the pixel image coordinate system; k1, k2, k3 represent the radial distortion parameters; p1, p2 represent the tangential distortion parameters; M2 = [R, T] is the external parameter matrix, R is the unit orthogonal matrix, T is the three-dimensional translation vector; Xp is the world coordinate vector;

[0061] S2. Stereo matching: On the basis of camera parameter calibration, determine the corresponding relationship of pixel points between the left and right cameras, calculate the disparity, and use the semi-global stereo matching algorithm (SGM) for stereo matching of images. The energy function for judging the similarity between the matching pixel points of the left and right camera images is intended to use the following formula:

[0062]

[0063] In the formula: D represents the disparity map; E(D) represents the energy function corresponding to the disparity map; p, q are pixel points; C(p, Dp) represents the matching cost function; Dp is the disparity corresponding to point p; Dq is the disparity corresponding to point q; T is the decision function, which is judged as 0 or 1 according to whether the formula holds;

[0064] S3. Refractive index determination: Considering the different refractive indices of air and 3D printing materials, the light path refracts at the interface between air and 3D printing materials. The relationship between the incident angle α and the refraction angle β is:

[0065]

[0066] Where: η1 is the refractive index of air, η2 is the refractive index of the 3D printing material, α is the incident angle, and β is the refraction angle;

[0067] S4. Fracture reconstruction: Finally, considering the three-dimensional spatial point position relationship of the internal fracture frost heave expansion considering the refraction effect, determine the three-dimensional spatial point coordinates of each pixel point on the fracture surface, form a spatial point cloud, and finally import it into 3D software such as Catia to fit the point cloud into the fracture surface, thus completing the three-dimensional reconstruction of the internal fracture.

[0068] The present invention also provides an analysis method for the frost heave expansion of internal fractures in a transparent rock mass, including the steps:

[0069] Step 1. Initial determination of weight coefficients: Based on the M integral, calculate the I-II-III type stress intensity factors K Ⅰ 、K Ⅱ 、K Ⅲ at the front edge of the three-dimensional fracture under frost heave. By analyzing the proportion of the I, II, and III type stress intensity factors, preliminarily determine the weight coefficients η' I 、η' II 、η' III of the stress intensity factors. The formula for determining the weight coefficients is as follows:

[0070]

[0071] Where: K I 、K II 、K III are the stress intensity factors at the front edge of the three-dimensional internal fracture calculated by the M integral, and l is the path around the three-dimensional internal fracture for one week; are the integrals of K I 、K II 、K III along the path l of the three-dimensional internal fracture;

[0072] Step 2. Calculation of the critical deflection angle: Select the improved maximum energy release rate criterion as the criterion for the frost heave expansion of the three-dimensional internal fracture. The direction angle at which the strain energy release rate G(θ) reaches the maximum is the critical deflection angle θ of the frost heave expansion of the three-dimensional internal fracture. The expression is as follows:

[0073]

[0074]

[0075] In the formula, θ is the critical deflection angle of the frost heave of the three-dimensional internal fracture, G(θ) is the strain energy release rate, η I 、η II 、ηIII The weight coefficients of the stress intensity factors of types I, II, and III are K I r (θ), K II r (θ), K III r (θ) are the stress intensity components corresponding to the fracture types of types I, II, and III respectively;

[0076] Substitute the K I , K II , K III calculated in the first step into Equation (9), and take the derivative through Equation (8). The direction angle at which the strain energy release rate G(θ) reaches the maximum is the critical deflection angle θ of the internal disaster-bearing catastrophe.

[0077] Step 3: Adjust the weight coefficients: Compare the critical deflection angle θ calculated in the second step with the critical deflection angle θ e obtained by the above-mentioned method of the frost heave expansion test of internal cracks in transparent rock mass; if θ = θ e , then the weight coefficient η I of the stress intensity factor corresponding to the analysis method is η' I , η II = η' II , η III = η' III ; if θ ≠ θ e , adjust η' I , η' II , η' III , and use the expression in the second step to calculate to make θ = θ e , so as to obtain the weight coefficient η I of the stress intensity factor corresponding to the analysis method = η' I , η II = η' II , η III = η' III , thus obtaining a new criterion for the frost heave expansion of three-dimensional internal cracks in the improved form.

[0078] The above is for the convenience of ordinary technical personnel in this technical field to understand and apply the present invention. Those skilled in the art can obviously make various modifications to these embodiments easily and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the embodiments here, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A test method for freeze-thaw expansion of fractures in a closed transparent rock mass, characterized in that the steps Including: (1) Specimen preparation: Inject water into the three-dimensional internal crack through the pre-pipeline, place the 3D printed closed tube in the pre-pipeline and seal it. After preparing the 3D printed transparent rock mass specimen, place it in a freezing test chamber with a vacuum internal environment. (2) Specimen freeze-thaw treatment: Turn on the freezing test chamber. The set freeze-thaw cycle temperature for the test is -20 to 20 °C, and the freezing and melting durations are both 6 h, that is, 12 h is a freeze-thaw cycle period. (3) After taking out the 3D printed specimen that has completed one freeze-thaw cycle from the freezing test chamber, place it at the center point of the square formed by the camera equipment group. Use the binocular camera group to obtain the three-dimensional quantitative distribution law of the internal crack frost heave expansion in three-dimensional space through the established three-dimensional binocular stereo vision perception system. The three-dimensional quantitative distribution law includes the critical deflection angle θ of frost heave expansion e ; (4) If the crack does not expand through the specimen, add water to the water-passing pipeline through a dropper to fill the three-dimensional internal crack with water, and then repeat steps (2) to (4) until the test ends. This method also includes an analysis method for the freeze-thaw expansion of the internal crack in the transparent rock mass, and the specific steps are as follows: Step 1. Weight coefficient: Calculate the stress intensity factors K Ⅰ , K Ⅱ , K Ⅲ of the I-II-III type of internal crack frost heaving based on the M integral. Initially determine the weight coefficient η' I , η' II , η' III of the stress intensity factors by analyzing the proportion of the I, II, and III type stress intensity factors. The formula for determining the weight coefficient is as follows: Where: K I , K II , K III are respectively the stress intensity factors at the front edge of the three-dimensional internal crack obtained by M integral, and l is the path around the three-dimensional internal crack for one week; are respectively the integrals of K I , K II , K III along the path l of the three-dimensional internal crack; Step 2: Calculation of the critical deflection angle of the three-dimensional internal crack: Select the improved maximum energy release rate criterion as the criterion for the freeze-thaw expansion of the three-dimensional internal crack. The direction angle at which G(θ) reaches the maximum is the critical deflection angle θ of the three-dimensional internal crack, and the expression is as follows: where θ is the critical deflection angle of internal crack frost heave in three dimensions, G(θ) is the strain energy release rate, η I , η II , η III are the weight coefficients of the stress intensity factors of modes I, II, and III, respectively, and K I r (θ), K II r (θ), and K III r (θ) are the stress intensity components corresponding to the fracture types of modes I, II, and III, respectively; Step 3. Adjust the weight coefficients: Compare the critical deflection angle θ obtained in Step 2 with the critical deflection angle θ in Step (3); if θ = θ e , then the weight coefficient η e of the stress intensity factor corresponding to the analysis method is η I = η' I , η II = η' II , η III = η' III ; if θ ≠ θ e , adjust η' I , η' II , η' III , and use the expression in Step 2 to calculate to make θ = θ e , so as to obtain the weight coefficient η I of the stress intensity factor corresponding to the analysis method is η I , η II = η' II , η III = η' III , thereby obtaining a new criterion for the frost heaving expansion of three-dimensional internal cracks in the improved form.

2. The method for testing the frost heaving expansion of fractures in a transparent rock mass enclosure according to claim 1, characterized in that, The three-dimensional binocular stereo vision perception system includes determining the three-dimensional space point coordinates of each pixel point on the crack surface, forming a spatial point cloud to fit into the crack surface, and reconstructing the spatial morphology of the freeze-thaw expansion of the three-dimensional internal crack.

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