Large-scale model experiment method for visually measuring whole stress migration process of underground engineering

Abstract

The invention relates to a large-scale model experiment method for visually measuring the whole stress migration process of underground engineering. The method is suitable for the geotechnical engineering field. According to the technical scheme, the method comprises the steps that protolith samples at corresponding positions of underground engineering are obtained, and mechanical properties of the protolith samples are measured; based on the mechanical properties of the protolith sample, preparing a similar material capable of reproducing the mechanical properties of the protolith sample, and pouring the model sample by using the similar material; based on an initial crustal stress field of an underground engineering field in-situ test, applying a three-way load to the model sample, and excavating the model sample; obtaining internal stress and strain information of the model sample, global strain and stress information of the model sample, fracture and energy characteristics of the model sample and fracture information of an excavation area of the model sample in the excavation process; based on internal stress and strain information, global strain and stress information, fracture and energy characteristics and fracture information of an excavation area of the model sample in the excavation process, the whole stress migration process of the excavation-affected area in the model sample is monitored.

Description

Technical Field

[0001] The present invention relates to a large-scale model experimental method for visually measuring the whole process of stress migration in underground engineering, and is applicable to the field of geotechnical engineering. Background Art

[0002] With the sustained development of the national economy, my country's rigid demands for energy, resources, water conservancy and hydropower, transportation and environment are increasing, prompting the construction of mining shafts, water conservancy tunnels, hydropower caverns, highway and railway tunnels to continuously move from the surface to the underground space. The study of surrounding rock stability control is the primary problem facing the safe construction of underground projects, and the instability of surrounding rock is a direct reflection of the fact that the bearing capacity of the surrounding rock mass is insufficient to match the stress adjustment process. Therefore, it is urgent to deeply understand the stress adjustment characteristics of the surrounding rock and the mechanical response behavior of the surrounding rock under the corresponding stress state. Stress migration is a review of the entire process of secondary stress evolution of the surrounding rock, including the initiation, strengthening and transfer characteristics of the stress concentration zone. Intuitively measuring the entire process of stress migration is the prerequisite for recognizing the stability of the surrounding rock.

[0003] Physical model experiment is one of the important experimental methods to study the stability of surrounding rock of underground engineering. Based on similarity theory, similar materials that can reproduce the mechanical properties of original rock of underground engineering are configured, and then large-scale physical model specimens are prepared. Large-scale physical model experimental system is used to apply boundary loads and use machine or manual excavation to study the stability behavior of surrounding rock.

[0004] In such experiments, the most important thing is to monitor the whole process of stress migration in the surrounding rock affected by excavation. Only systematic and effective monitoring can more directly reveal the complex response law of the surrounding rock stress field under the combined effect of stress and excavation. However, the existing physical model experimental methods mainly measure the overall deformation, strength and failure characteristics of the surrounding rock, and cannot effectively monitor the whole process of stress migration in the surrounding rock affected by excavation. Summary of the invention

[0005] The technical problem to be solved by the present invention is: in view of the above-mentioned existing problems, a large-scale model experimental method for visually measuring the entire process of stress migration in underground engineering is provided.

[0006] The technical solution adopted by the present invention is: a large-scale model experimental method for visually measuring the entire process of stress migration in underground engineering, characterized in that:

[0007] Obtain original rock samples from the corresponding locations of underground projects and measure the mechanical properties of the original rock samples;

[0008] Based on the mechanical properties of the original rock sample, similar materials that can reproduce the mechanical properties of the original rock sample are configured, and the model sample is cast using the similar materials;

[0009] Based on the initial geostress field of the in-situ test of the underground engineering site, three-dimensional loads are applied to the model specimens, and the model specimens are excavated;

[0010] During the excavation process, the internal stress and strain information of the model specimen, the global strain and stress information of the model specimen, the fracture and energy characteristics of the model specimen, and the fracture information of the excavation area of ​​the model specimen are obtained;

[0011] Based on the internal stress and strain information of the model specimen during excavation, the global strain and stress information, the fracture and energy characteristics, and the fracture information of the excavation area, the entire process of stress migration in the excavation-affected area within the model specimen is monitored.

[0012] The mechanical properties of the original rock sample include elastic modulus, Poisson's ratio, cohesion, internal friction angle, uniaxial tensile strength, uniaxial compressive strength and post-peak brittleness.

[0013] The method of configuring similar materials capable of reproducing the mechanical properties of the original rock sample based on the mechanical properties of the original rock sample includes:

[0014] The selected materials of said similar materials include quartz sand, barite powder, gypsum, cement and water;

[0015] The mass ratio of quartz sand, barite powder, high-strength gypsum to cement and water were selected as influencing factors, and a variety of different proportions were obtained through orthogonal experimental design method.

[0016] Based on each mix ratio scheme, cast a model sample with the same size as the original rock sample;

[0017] Obtain the mechanical properties of the model specimens of each mix ratio scheme, and establish a quantitative relationship between the characteristic quantity of the mechanical properties and the selected material mix ratio scheme;

[0018] Based on the quantitative relationship between the characteristic quantities of mechanical properties and the selected material proportioning scheme, and the mechanical properties of the original rock samples, the proportioning scheme of similar materials is determined.

[0019] The method of obtaining the internal stress and strain information of the model specimen includes:

[0020] A pressure cell is embedded in the model sample to obtain internal stress information of the model sample through the pressure cell;

[0021] A fiber grating sensor is embedded in the model sample, and the internal strain information of the model sample is obtained through the fiber grating sensor.

[0022] The pressure box and the fiber Bragg grating sensor are arranged in the stress concentration area of ​​the model sample, and the stress concentration area is predetermined by numerical simulation analysis; the pressure box and the fiber Bragg grating sensor are arranged in layers, and each layer is arranged in a fan shape.

[0023] The obtaining of global strain and stress information of the model specimen includes:

[0024] Digital speckles are arranged on the surface of the model sample, and global strain and stress information of the model sample is obtained through the digital speckles.

[0025] The method of arranging digital speckles on the surface of the model sample includes: leveling the surface of the model sample, making a digital speckle white background, and making digital speckle black dots.

[0026] The model specimen fracture and energy characteristics include:

[0027] An acoustic emission probe is arranged on the surface of the model sample, and the fracture and energy characteristics of the model sample are obtained through the acoustic emission probe.

[0028] The method of obtaining fracture information of the excavation area of ​​the model specimen includes:

[0029] Following the excavation progress, an endoscope is gradually placed inside the model specimen to obtain the fracture information of the excavation area of ​​the model specimen.

[0030] The whole process of stress migration in the excavation-affected area of ​​the monitoring model specimen includes:

[0031] Determine the stress, strain or rupture information of the model specimen before it finally becomes unstable, and convert it into stress, deformation and damage information that can be easily measured on the engineering site, so as to serve as precursor warning information of surrounding rock instability in underground engineering.

[0032] The beneficial effects of the present invention are as follows: the present invention uses digital speckle and fiber Bragg grating sensor for strain monitoring, digital speckle and pressure box for stress monitoring, digital speckle, acoustic emission and endoscope for rupture monitoring, and ensures the integrity of monitoring data while verifying the monitoring results with each other (mutual verification does not involve algorithms, that is, direct comparison of monitoring results). Different monitoring means are used for joint monitoring, and then the monitoring results are compared. If the monitoring results differ greatly, the monitoring means are recalibrated and the experiment is carried out again. If the monitoring results differ within the allowable error, the experiment is carried out normally and the experimental results are analyzed. The credibility and accuracy of the monitoring results are ensured.

[0033] The digital speckle pattern in the present invention can visualize the evolution process of the global stress field on the surface of the model specimen, including the initiation, expansion and transfer of the stress concentration area, and the synergistic relationship between stress migration and rupture; the digital speckle pattern is completed in the form of plaster repair, sandpaper leveling, spray paint priming and pen painting, which can simultaneously ensure the dual requirements of digital speckle analysis accuracy and computer post-processing memory in large-scale physical model experiments.

[0034] The present invention can adapt to different scenarios of underground engineering and improve the applicability of experimental results by changing the size, material ratio, cavern morphology, loading stress boundary, and excavation speed of the model specimen. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of loading and excavation of the model specimen in the embodiment.

[0036] Figure 2 It is a schematic diagram of the layered installation monitoring means in the embodiment.

[0037] Figure 3 Schematic diagram of the fiber Bragg grating sensor and the pressure box in the embodiment.

[0038] Figure 4 Schematic diagram of digital speckle in the embodiment.

[0039] Figure 5 The figures are the indoor test results of the original rock samples in the examples; (a) is the marble sample after the test; (b) is the uniaxial and conventional triaxial test curves of the marble sample.

[0040] Figure 6 The uniaxial compression test and Brazilian splitting test of the model sample in the embodiment; wherein, (a) is the cast model sample, (b) is the uniaxial compression test, and (c) is the Brazilian splitting test.

[0041] Figure 7 This is a uniaxial compression test of the model sample prepared according to the final material ratio in the example.

[0042] Figure 8 The model sample cast in the embodiment and the arrangement of related monitoring equipment.

[0043] Fig. 9 This is a diagram showing an example of simulated excavation of a model specimen in the embodiment.

[0044] Fig.10 Typical results of acoustic emission and digital speckle monitoring of model specimens; (a) is the acoustic emission monitoring result; (b) is the digital speckle monitoring result.

[0045] 1. Model specimen; 2. Acoustic emission probe; 3. Endoscope; 4. Fiber Bragg grating sensor; 5. Pressure cell; 6. Digital speckle; 7. Cavern; 8. Layered position of monitoring means; 9. Tunnel; 10. Stress concentration area of ​​excavated tunnel; 11. Fracture point obtained by acoustic emission positioning. DETAILED DESCRIPTION

[0046] This embodiment is a large-scale model experimental method for visually measuring the entire process of stress migration in underground engineering, which specifically includes the following steps:

[0047] S1. Obtain the original rock samples at the corresponding locations of the underground project and measure the mechanical properties of the original rock samples.

[0048] In this embodiment, standard-sized original rock samples of underground engineering are obtained through sampling, on-site packaging, long-distance transportation and indoor sample preparation in the underground engineering research area; Brazilian splitting, uniaxial compression and conventional triaxial compression tests are carried out on the standard-sized original rock samples to obtain the deformation, strength and failure information of the original rock, and determine the physical properties of the original rock, as well as the pre-peak and post-peak mechanical properties.

[0049] In this case, non-destructive sampling should be adopted for in-situ sampling of underground engineering sites to avoid damage to rock samples during the core sampling process. The standard size of the original rock sample is a cylinder with a diameter of 50 mm and a height of 100 mm. The physical properties of the original rock mainly include density and porosity; the mechanical properties of the original rock mainly include elastic modulus, Poisson's ratio, cohesion, internal friction angle, uniaxial tensile strength, uniaxial compressive strength and post-peak brittleness.

[0050] S2. Based on the mechanical properties of the original rock sample, configure similar materials that can reproduce the mechanical properties of the original rock sample, and use the similar materials to cast the model sample.

[0051] In this embodiment, the similar material is a mixture of quartz sand, barite powder, gypsum, cement and water. The ratio of gypsum to cement can change the brittleness and strength of the model specimen. In order to better visualize the entire process of stress migration, similar materials with high strength and high brittleness characteristics can be configured.

[0052] In this embodiment, similar materials that can reproduce the mechanical properties of the original rock are configured, including:

[0053] The mass ratio of quartz sand, barite powder, high-strength gypsum to cement and water were selected as influencing factors, and a variety of different proportions were obtained through orthogonal experimental design method.

[0054] Based on each mix ratio scheme, cast a model sample with the same size as the original rock sample;

[0055] Obtain the mechanical properties of the model specimens of each mix ratio scheme, and establish a quantitative relationship between the characteristic quantity of the mechanical properties and the selected material mix ratio scheme;

[0056] Based on the quantitative relationship between the characteristic quantities of mechanical properties and the selected material proportioning scheme, and the mechanical properties of the original rock samples, the proportioning scheme of similar materials is determined.

[0057] According to the determined component material types and proportions required for casting the model sample, weighing, mixing, casting, vibrating, molding, demolding, and curing are carried out in sequence. During the casting process, pressure boxes and fiber grating sensors are buried in layers. After curing, acoustic emission probes are set on the surface of the model sample and digital speckles are produced (see Figure 1 , 4).

[0058] In this example, the pressure box and the fiber Bragg grating sensor are arranged in the stress concentration area of ​​the model specimen. The stress concentration area can be predetermined by numerical simulation analysis; the pressure box and the fiber Bragg grating sensor are arranged in layers, the number of layers is not less than 3, and the layered position of each layer monitoring means is arranged in a fan-shaped arrangement (the stress concentration area during the experimental loading process is fan-shaped). The pressure box and the fiber Bragg grating sensor (see Figure 2 , 3 ).

[0059] In this embodiment, four schemes are selected, namely, coating the sample surface with cement + coating with speckle with a marker, coating the sample surface with cement + spraying with paint, filling holes on the sample surface with plaster + coating with speckle with a marker, and filling holes on the sample surface with plaster + spraying with paint. The integrity and continuity of the digital speckle monitoring image on the sample surface during the test under different schemes are compared. The final preferred scheme in this example is filling holes on the sample surface with plaster + coating with speckle with a marker.

[0060] The method for producing digital speckle on the surface of the model sample in this embodiment is specifically as follows:

[0061] Smoothing the surface of the model specimen: holes are inevitable on the surface of the model specimen after curing. Use plaster to fill these holes. After the plaster solidifies, use fine sandpaper to smooth the surface of the model specimen;

[0062] To make a digital speckle white background: spray a thin layer of white paint on the flattened surface of the model sample;

[0063] Make digital speckle black spots: Use a marker pen to evenly apply black speckles on the surface of the model sample after spraying the white base layer.

[0064] After the plaster filling and marker pen painting on the sample surface were completed, high-strength transparent glass was added between the sample surface and the loading plate to prevent the digital speckle from being incomplete due to partial chipping on the sample surface.

[0065] S3. Based on the initial geostress field of the in-situ test of the underground engineering site, the true triaxial load is applied to the model sample to the corresponding set value using the force control mode, the load is stabilized, and the model sample is excavated by machine excavation or manual drilling to form a cave on the model sample.

[0066] In this example, true triaxial loads are applied to the model specimen, including:

[0067] Hydrostatic pressure loading: The maximum principal stress, intermediate principal stress and minimum principal stress are loaded simultaneously at the same loading rate until the stress reaches the preset minimum principal stress level;

[0068] Biaxial loading: Keep the minimum principal stress unchanged, and load the maximum principal stress and the intermediate principal stress at the same loading rate until the stress reaches the preset intermediate principal stress level;

[0069] Uniaxial loading: Keep the minimum principal stress and intermediate principal stress unchanged, and load the maximum principal stress until the stress reaches the preset maximum principal stress level.

[0070] In this embodiment, the excavation of the model sample includes: maintaining the preset maximum principal stress, intermediate principal stress and minimum principal stress levels, excavating at the preset position of the model sample by drilling or manual drilling, and controlling the excavation depth at each time to 20mm to 50mm until the model sample is excavated through.

[0071] S4. During the excavation process, always pay attention to the fracture morphology of the model sample and stop the experiment according to the experimental requirements. The global strain and stress information of the model sample is obtained through digital speckle, the internal strain information of the model sample is obtained through the fiber grating sensor embedded inside the model sample, the internal stress information of the model sample is obtained through the pressure box inside the model sample, and the fracture and energy characteristics of the model sample are obtained through the acoustic emission probe on the surface of the model sample. Following the excavation progress, the endoscope is continuously placed inside the model sample, and the fracture information of the model sample is obtained through the digital endoscope placed in the excavation area of ​​the model sample.

[0072] S5. Based on the internal stress and strain information of the model specimen during the excavation process, the global strain and stress information, the fracture and energy characteristics, the fracture information of the excavation area, etc., the whole process of stress migration in the area affected by the excavation in the model specimen is monitored.

[0073] The model specimen is excavated under a certain true triaxial stress state, and digital speckle, pressure box, fiber Bragg grating sensor, acoustic emission and endoscope monitoring are carried out simultaneously, so as to truly simulate the ground stress state of underground engineering and the surrounding rock excavation process, obtain the stress, strain, fracture and acoustic emission information inside the surrounding rock, judge the stability of the surrounding rock, study the influence of the surrounding rock redistribution stress field on the degree of surrounding rock fracture, analyze the surrounding rock stress transfer process, characteristics and laws, determine the precursor information of surrounding rock instability, provide guidance for disaster warning and safety protection of underground engineering, and make the experimental method more widely used.

[0074] The following is a specific example:

[0075] S1. Based on the second phase of an underground laboratory project, the original marble samples with sizes of Φ50mm×100mm and Φ50mm×25mm were obtained through drilling sampling in the laboratory research area, on-site packaging, remote transportation and indoor sample preparation. Brazilian splitting (Φ50mm×25mm), uniaxial compression and conventional triaxial compression tests (Φ50mm×100mm) of the original marble samples were carried out using a high-rigidity servo testing machine. The stress-strain curves of the marble samples and the photos of sample failure were measured to obtain the uniaxial compressive strength, tensile strength, and post-peak brittleness (post-peak brittleness is determined by the magnitude and rate of post-peak stress drop) of the original marble. Figure 5 shown.

[0076] S2. Four influencing factors, namely quartz sand, barite powder, mass ratio of high-strength gypsum to cement and water, were selected. Five orthogonal levels were set for each factor. Twenty-five different proportioning schemes were obtained through the orthogonal experimental design method. Model samples with the same size as the original marble rock samples were cast through a series of processes including weighing, mixing, vibration, molding, core drilling, and cutting.

[0077] The Brazilian splitting (Φ50mm×25mm), uniaxial compression and conventional triaxial compression tests (Φ50mm×100mm) of the model specimens were carried out using a high-rigidity servo testing machine to obtain information such as Young's modulus, Poisson's ratio, uniaxial compressive strength, tensile strength, and post-peak brittleness of the model specimens under different ratio schemes. Figure 6 shown.

[0078] The quantitative relationships between characteristic quantities such as Young's modulus, Poisson's ratio, uniaxial compressive strength, tensile strength, post-peak brittleness and the selected material proportioning scheme were established using regression analysis methods.

[0079] According to the determined physical and mechanical properties of the original marble and the selected similarity ratio (where the similarity ratio of Young's modulus, Poisson's ratio and post-peak brittleness is 1:1, and the similarity ratio of uniaxial compressive strength and tensile strength is 1:5), similar materials and their proportions that can reproduce the mechanical properties of the original marble are determined. The final optimal proportioning scheme in this embodiment is: the mass ratios of quartz sand, barite powder, high-strength gypsum: cement, and water are 30%, 30%, 18% (2.5:1), and 22%.

[0080] According to the final material ratio, a model sample with the same size as the original marble sample is prepared, and Brazilian splitting, uniaxial compression and conventional triaxial compression tests are carried out to verify the final material ratio scheme, such as Figure 7 shown.

[0081] Taking into account the loading box space and loading capacity of the large physical model test machine, the size of the model specimen is determined to be 310mm×310mm×310mm. According to the final mix ratio scheme determined above, the model specimen is cast in sequence through weighing, mixing, pouring, vibrating, molding, demoulding, curing, and pre-embedding of monitoring equipment (except digital speckle and acoustic emission). After the model specimen is cured, digital speckle is made on the surface of the model specimen by applying cement, filling holes with plaster, and filling with markers. After the digital speckle of the model specimen is made, an acoustic emission probe is installed at a preset position on the surface of the model specimen, such as Figure 8 shown.

[0082] S3. After all monitoring instruments are connected and all equipment is debugged successfully, the experiment begins. Loading of large physical model test machines, digital speckle, pressure box, fiber Bragg grating sensor, acoustic emission and endoscope monitoring should be carried out simultaneously. According to the initial geostress field and the selected similarity ratio of the on-site in-situ test of the China Jinping Underground Laboratory Phase II project, the force control mode is used to apply true triaxial loads to the calibrated initial geostress field to stabilize the load; the model specimen is excavated by machine excavation, such as Fig. 9 shown.

[0083] S4. During the excavation process, always pay attention to the fracture morphology of the model specimen and stop the experiment according to the experimental requirements. During the excavation process, obtain the internal stress and strain information of the model specimen, the global strain and stress information of the model specimen, the fracture and energy characteristics of the model specimen, and the fracture information of the excavation area of ​​the model specimen.

[0084] S5. After the load was applied, the surrounding rock remained stable as a whole. With the continuous progress of tunnel excavation, both acoustic emission and strain monitoring began to change. With the continuous application of tunnel excavation, the number of ringing, energy and event of acoustic emission began to increase suddenly. The number of rupture events in the stress concentration zone of the excavated tunnel accumulated more and more. The surface and shallow surrounding rock of the excavated tunnel began to peel off and fall off. Finally, the whole specimen collapsed. The results of digital speckle image processing later found that the progressive failure process of the model specimen was controlled by the formation, expansion and transfer process of the stress concentration zone, such as Fig.10 shown.

Claims

1. A large-scale model experimental method for visually measuring the entire process of stress migration in underground engineering, characterized by: Obtain original rock samples from the corresponding locations of underground projects and measure the mechanical properties of the original rock samples; Based on the mechanical properties of the original rock sample, similar materials that can reproduce the mechanical properties of the original rock sample are configured, and the model sample is cast using similar materials; Based on the initial geostress field of the in-situ test of the underground engineering site, three-dimensional loads are applied to the model specimens, and the model specimens are excavated; During the excavation process, the internal stress and strain information of the model specimen, the global strain and stress information of the model specimen, the fracture and energy characteristics of the model specimen, and the fracture information of the excavation area of ​​the model specimen are obtained; Based on the internal stress and strain information of the model specimen during excavation, the global strain and stress information, the fracture and energy characteristics, and the fracture information of the excavation area, the entire process of stress migration in the excavation-affected area within the model specimen is monitored.

2. The large-scale model experimental method for visually measuring the entire process of stress migration in underground engineering according to claim 1 is characterized in that: The mechanical properties of the original rock sample include elastic modulus, Poisson's ratio, cohesion, internal friction angle, uniaxial tensile strength, uniaxial compressive strength and post-peak brittleness.

3. The large-scale model experimental method for visually measuring the entire process of stress migration in underground engineering according to claim 1 is characterized in that: The method of configuring similar materials capable of reproducing the mechanical properties of the original rock sample based on the mechanical properties of the original rock sample includes: The selected materials of said similar materials include quartz sand, barite powder, gypsum, cement and water; The mass ratio of quartz sand, barite powder, high-strength gypsum to cement and water were selected as influencing factors, and a variety of different proportions were obtained through orthogonal experimental design method. Based on each mix ratio scheme, cast a model sample with the same size as the original rock sample; Obtain the mechanical properties of the model specimens of each mix ratio scheme, and establish a quantitative relationship between the characteristic quantity of the mechanical properties and the selected material mix ratio scheme; Based on the quantitative relationship between the characteristic quantities of mechanical properties and the selected material proportioning scheme, and the mechanical properties of the original rock samples, the proportioning scheme of similar materials is determined.

4. The large-scale model experimental method for visually measuring the entire process of stress migration in underground engineering according to claim 1 is characterized in that: The method of obtaining the internal stress and strain information of the model specimen includes: A pressure cell is embedded in the model sample to obtain internal stress information of the model sample through the pressure cell; A fiber grating sensor is embedded in the model sample, and the internal strain information of the model sample is obtained through the fiber grating sensor.

5. The large-scale model experimental method for visually measuring the entire process of stress migration in underground engineering according to claim 4 is characterized in that: The internal stress and strain information of the model sample is obtained, and the pressure box and the fiber grating sensor are arranged in the stress concentration area of ​​the model sample, and the stress concentration area is predetermined by numerical simulation analysis; the pressure box and the fiber grating sensor are arranged in layers, and each layer is arranged in a fan shape.

6. The large-scale model experimental method for visually measuring the entire process of stress migration in underground engineering according to claim 1 is characterized in that: The obtaining of global strain and stress information of the model specimen includes: Digital speckles are arranged on the surface of the model sample, and global strain and stress information of the model sample is obtained through the digital speckles.

7. The large-scale model experimental method for visually measuring the entire process of stress migration in underground engineering according to claim 6 is characterized in that: The method of arranging digital speckles on the surface of the model sample includes: leveling the surface of the model sample, making a digital speckle white background, and making digital speckle black dots.

8. The large-scale model experimental method for visually measuring the entire process of stress migration in underground engineering according to claim 1 is characterized in that: The model specimen fracture and energy characteristics include: An acoustic emission probe is arranged on the surface of the model sample, and the fracture and energy characteristics of the model sample are obtained through the acoustic emission probe.

9. The large-scale model experimental method for visually measuring the entire process of stress migration in underground engineering according to claim 1 is characterized in that: The method of obtaining fracture information of the excavation area of ​​the model specimen includes: Following the excavation progress, an endoscope is gradually placed inside the model specimen to obtain the fracture information of the excavation area of ​​the model specimen.

10. The large-scale model experimental method for visually measuring the entire process of stress migration in underground engineering according to claim 1 is characterized in that: The whole process of stress migration in the excavation-affected area of ​​the monitoring model specimen includes: Determine the stress, strain or rupture information of the model specimen before it finally becomes unstable, and convert it into stress, deformation and damage information that can be easily measured on the engineering site, so as to serve as precursor warning information of surrounding rock instability in underground engineering.

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