A device and method for indoor pull-out test of expansion-type anchor rod based on transparent rock mass

Abstract

This invention relates to an indoor pull-out testing device and method for expansion anchor bolts based on transparent rock mass, belonging to the field of geotechnical engineering and tunnel support technology. The testing device includes a confining pressure loading system, a transparent chamber, an anchor bolt pull-out system, and a non-contact strain monitoring system. The transparent chamber is filled with transparent rock mass with a matching refractive index, and pre-drilled channels are installed within the rock mass to accommodate the expansion anchor bolts to be tested. During the pull-out process, an industrial camera captures real-time images of the full-domain deformation of the rock mass and anchor bolt through the transparent chamber, and the evolution data of the strain field at the anchoring interface is obtained by combining digital image correlation technology. This invention achieves visualized monitoring of the entire anchoring process of expansion anchor bolts, avoids mechanical interference from anchor bolt expansion on sensors, can simulate complex stress environments, and provides an experimental platform for the study of anchoring mechanisms.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering and tunnel support technology, and particularly relates to an indoor pull-out test device and method for expansion anchor bolts based on transparent rock mass. Background Technology

[0002] Rock bolt support is a primary technical means of controlling rock mass stability in geotechnical engineering projects such as resource extraction, tunnel excavation, and hydraulic chambers. Its low cost and flexible support methods have led to its widespread application in various geotechnical engineering projects. The interface contact state between the rock bolt and the surrounding rock directly determines the support effect. For expansion bolts, the anchoring force mainly comes from friction or mechanical interlocking at the anchoring interface, and the anchoring effect is highly dependent on the contact quality between the expansion body and the surrounding rock and the interface evolution process.

[0003] Anchor pull-out tests are currently a standard method for evaluating the interaction performance between anchors and surrounding rock. However, anchor support is essentially a concealed engineering project, and neither field monitoring nor laboratory testing can directly observe the deformation and failure evolution of the anchor-rock interface during the test. Especially in expansion anchors, the anchoring force originates from the mechanical locking or friction between the expansion body and the surrounding rock, and processes such as interface slippage, compression, and localized failure directly affect the anchor's load-bearing capacity. The inability to achieve full-process visual monitoring will severely restrict a deeper understanding of its anchoring mechanism and performance optimization.

[0004] In recent years, some studies have attempted to monitor the deformation behavior of anchor bodies through visualization. CN116754367A discloses a visualized indoor pull-out test device and method for anchor bolts. The device uses multiple jacks, monitoring windows, and transparent loading plates within a rigid constraint frame, combined with stress and strain monitors, to achieve simultaneous monitoring of the anchored rock mass. However, the monitoring of this device is still limited to strain monitoring on the surface of the anchor body or in local areas of the bolt, making it difficult to reflect the true deformation evolution process at the anchoring agent-surrounding rock interface and within the surrounding rock. CN117949304A discloses a test device simulating the pull-out of deep constant-resistance anchor bolts, using several sets of radial measurement mechanisms to achieve a wider range of monitoring of the anchor bolt's constant resistance. However, this device also suffers from limited monitoring range and cannot fully reveal the anchoring mechanism of expansion anchor bolts.

[0005] In terms of interface deformation monitoring, CN114000502A and CN117782232A employ the method of adding a sleeve or sealing shell to the outside of the anchor bolt, and installing components such as angle sensors and infrared displacement sensors inside the sleeve to achieve monitoring and early warning of anchor bolt deformation. CN115265396A discloses an anchor bolt deformation monitoring structure based on cable sensing, which monitors the axial and bending deformation of the bolt interface through distributed Fabry-Perot strain sensors on a coaxial cable. However, the above methods are mainly applicable to bonded anchor bolts. During the installation of expansion anchor bolts, the sensors are easily interfered with by factors such as radial expansion compression and bending, and temperature rise during hydration reaction, leading to unstable signals or failures, making it difficult to continuously and reliably obtain anchor interface evolution data in actual tests.

[0006] In summary, existing technologies for testing the anchoring performance of expansion bolts have the following main drawbacks: First, it is difficult to conduct synchronous, full-process visual monitoring of the deformation at the anchoring interface and within the surrounding rock. Existing visualization methods are mostly limited to the surface of the anchor body or local areas of the bolt, failing to accurately reflect the deformation evolution process within the surrounding rock. Second, traditional contact sensors are susceptible to mechanical and thermal disturbances during the installation of expansion bolts, such as radial expansion compression, bending, and increased temperature due to hydration reactions, making it difficult to guarantee signal stability and data continuity, resulting in insufficient test reliability. Third, there is a lack of a comprehensive visual experimental platform capable of realistically reproducing different burial depths, geostress conditions, and rock mass structural features, making it difficult to systematically study the anchoring mechanism of expansion bolts under the coupled effects of multiple factors. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides an indoor pull-out testing device and method for expansion anchors based on transparent rock mass. This device and method enables synchronous and visual monitoring of the anchoring interface and the deformation field inside the surrounding rock throughout the entire process from installation to pull-out failure of the expansion anchor, avoids sensor contact interference, and can simulate complex stress environments and rock mass structural characteristics.

[0008] An indoor pull-out testing device for expansion-type anchor bolts based on transparent rock mass includes:

[0009] Rigidly constrained frame;

[0010] A confining pressure loading system, mounted on the rigid constraint frame, is used to apply controllable confining pressure to the transparent rock mass;

[0011] A transparent chamber is set inside the rigid constraint frame to accommodate the transparent rock mass; the transparent chamber has a light-transmitting area, and the transparent rock mass has pre-drilled installation holes along its length for installing the expansion bolts to be tested;

[0012] An anchor pull-out system, connected to the expansion anchor bolt to be tested, is used to apply an axial pull-out force to it;

[0013] The non-contact strain monitoring system includes an image acquisition device for real-time acquisition of deformation images of the transparent rock mass and the expansion anchor to be tested during the pull-out process through the light-transmitting area of ​​the transparent chamber.

[0014] The transparent rock mass is formed by mixing and solidifying solid transparent particles and liquid transparent cementitious agent. The refractive indices of the solid transparent particles and the liquid transparent cementitious agent are matched to eliminate light scattering at the particle-cement interface.

[0015] The confining pressure loading system includes a base, a rigid constraint frame disposed on the base, and multiple loading jacks disposed on each side of the outer periphery of the rigid constraint frame.

[0016] The transparent cabin includes a first limiting plate, a second limiting plate, and a transparent loading plate disposed between the first limiting plate and the second limiting plate. The first limiting plate and the second limiting plate are connected and fixed by limiting rods and nuts, forming a closed cabin together. The light-transmitting area includes the transparent loading plate and an observation window disposed on the first limiting plate.

[0017] The transparent rock mass contains simulated fractures embedded in a predetermined orientation, and the simulated fractures are colored flaky quartz or mica flakes.

[0018] The anchor bolt pulling system includes a reaction frame, a pulling jack, an extension rod, a load sensor, and a connector. The connector connects the expansion anchor bolt to be tested to the extension rod. The extension rod passes through the reaction frame, the pulling jack, and the load sensor in sequence and is axially limited by a fastening nut. The reaction frame is supported by a limiting frame, and a slide rail is provided at the bottom of the limiting frame.

[0019] The non-contact strain monitoring system also includes a shooting slide rail disposed on the opposite lateral sides of the rigid constraint frame. The image acquisition device is an industrial camera, which is mounted on the shooting slide rail and can slide along the slide rail.

[0020] An indoor pull-out test method for expansion anchor bolts based on transparent rock mass, using the aforementioned apparatus, includes the following steps:

[0021] Prepare transparent rock mass and reserve installation channels in the transparent rock mass;

[0022] The expansion anchor to be tested is installed in the installation hole;

[0023] A confining pressure is applied to the transparent rock mass to a preset value using a confining pressure loading system;

[0024] An axial pull-out force is applied to the expansion anchor bolt under test using an anchor bolt pull-out system;

[0025] Deformation images of the transparent rock mass and the expansion anchor to be tested were continuously acquired by a non-contact strain monitoring system, and the evolution data of the global strain field were obtained by analyzing the data using digital image correlation technology.

[0026] Record the pull-out force, displacement, and strain field changes during the pull-out process until the anchor rod is pulled out or breaks.

[0027] When preparing transparent rock masses, colored flaky quartz or mica sheets are embedded according to the preset occurrence to simulate fractures.

[0028] The expansion anchor to be tested is any one of self-expanding slotted pipe anchor, mechanical expansion anchor, or hydraulic expansion anchor; when using self-expanding slotted pipe anchor, immerse the self-expanding agent in water for 8 to 12 minutes before installation.

[0029] By independently controlling the output pressure of the loading jacks in each direction of the confining pressure loading system, bidirectional unequal confining pressure is applied to the transparent rock mass.

[0030] By employing the above technical solution, the present invention has at least the following beneficial effects:

[0031] This invention uses a refractive index matching technology between solid transparent particles and liquid transparent binder to prepare transparent rock mass. Combined with multi-angle industrial cameras arranged around and at the ends of the transparent chamber, it can capture real-time, non-contact, and full-domain visualization of the slippage of the anchor-surrounding rock interface, the initiation and propagation of internal cracks in the surrounding rock, and the evolution of the strain field of the expansion anchor throughout the entire process from installation, expansion anchoring to pull-out failure. This breaks through the technical limitation of traditional monitoring methods that can only observe surface deformation.

[0032] This invention employs a non-contact strain monitoring system that uses an industrial camera to capture images of transparent rock mass. This eliminates the need for any sensors to directly contact the anchor bolts or rock mass, fundamentally eliminating the risk of physical damage and thermal interference to the monitoring elements during the expansion installation process, and ensuring the continuity, stability, and reliability of the test data.

[0033] This invention designs a confining pressure loading system consisting of a rigid constraint frame and circumferentially independently controlled loading jacks. This system can apply bidirectional adjustable confining pressure to transparent rock masses, simulating geostress conditions under different burial depths and lateral pressure coefficients. Simultaneously, during the preparation of the transparent rock mass, colored flaky quartz or mica flakes with different attitudes, quantities, and spacings can be pre-set as simulated fractures to reproduce the characteristics of fractured rock masses with developed joints and fractures. This device provides a controllable and repeatable experimental platform for systematically studying the anchoring mechanism of expansion bolts under the coupled effects of multiple factors such as different confining pressures, rock mass masses, bolt types, and expansion sources.

[0034] This invention, through its pre-drilled installation holes, replaceable connectors, and flexible anchoring methods, is compatible with the installation and testing of various expansion anchors, including self-expanding slotted bolts, mechanical expansion anchors, and hydraulic expansion anchors, and has wide applicability.

[0035] The device of this invention has a compact structure and clearly defined collaborative operation among its various systems. The confining pressure loading system provides a controllable stress environment, the transparent chamber fixes and visualizes the rock mass, the anchor bolt pull-out system precisely applies loads and collects force and displacement data, and the non-contact monitoring system synchronously records the strain field across the entire domain. Furthermore, the testing method of this invention has clearly defined steps, forming a complete process from transparent rock mass preparation, anchor bolt installation, confining pressure loading to pull-out testing and data recording. It is easy to operate, provides intuitive test results, and facilitates multi-factor parallel comparative tests. Attached Figure Description

[0036] Figure 1 This is a cross-sectional schematic diagram of the indoor pull-out test device for expansion-type anchor bolts based on transparent rock mass according to the present invention;

[0037] Figure 2 This is a schematic diagram of the confining pressure loading system in the indoor pull-out test device for expansion-type anchor bolts based on transparent rock mass of the present invention;

[0038] Figure 3 This is a schematic diagram of the transparent chamber in the indoor pull-out test device for expansion-type anchor bolts based on transparent rock mass of the present invention;

[0039] Figure 4 This is a schematic diagram of the expansion anchor bolt to be tested in Embodiment 1 of the present invention;

[0040] In the picture:

[0041] 1. Base; 2. Rigid constraint frame; 3. Shooting slide rail; 4. Industrial camera; 5. Limiting rod; 6. Nut; 7. First limiting plate; 8. Second limiting plate; 9. Transparent loading plate; 10. Transparent rock mass; 11. Loading jack; 12. Expansion anchor bolt to be tested; 121. Pipe joint anchor bolt body; 122. Self-expanding agent; 123. Hollow cylinder; 124. Cover; 13. Tray; 14. Reaction frame; 15. Pull-out jack; 16. Extension rod; 17. Load sensor; 18. Flange; 19. Connector; 20. Limiting frame; 21. Fastening nut. Detailed Implementation

[0042] To better explain and facilitate understanding of the present invention, the technical solution and effects of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] Example 1

[0044] like Figures 1-3As shown, this embodiment provides an indoor pull-out testing device for expansion anchor bolts based on transparent rock mass, comprising four parts: a confining pressure loading system, a transparent chamber, an anchor bolt pull-out system, and a non-contact strain monitoring system. These parts work together to achieve full-process visual testing of the anchoring performance of expansion anchor bolts.

[0045] The confining pressure loading system serves as the external support and loading frame for the entire device, specifically comprising a base 1, a rigid constraint frame 2, and loading jacks 11. The rigid constraint frame 2 is made of high-strength alloy steel and is securely connected to the base 1 via fixing screws. Multiple loading jacks 11 are arranged in an array on the outer periphery of the base 1 and the rigid constraint frame 2, with the movable rod of each loading jack 11 extending towards the center of the rigid constraint frame 2. A limiting frame 20 is mounted on the base 1 via a slide rail; specifically, the bottom slide rail is located at the bottom of the limiting frame 20, allowing it to slide longitudinally to accommodate pull-out tests of anchor bolts of different lengths.

[0046] Furthermore, the transparent chamber is located inside the rigid constraint frame 2 to accommodate and fix the transparent rock mass 10. Specifically, the transparent chamber includes a limiting rod 5, a nut 6, a first limiting plate 7, a second limiting plate 8, a transparent loading plate 9, the transparent rock mass 10, the expandable anchor rod 12 to be tested, and a tray 13. The first limiting plate 7 and the second limiting plate 8 are connected and fixed by the limiting rod 5 and the nut 6. The transparent loading plate 9 is located between the first limiting plate 7 and the second limiting plate 8, together forming a closed chamber. The transparent rock mass 10 is filled inside the chamber, and the expandable anchor rod 12 to be tested passes through it. The second limiting plate 8 has a positioning channel, and the expandable anchor rod 12 to be tested is centrally inserted into this positioning channel. The front end of the expandable anchor rod 12 extends out of the outer side of the second limiting plate 8 and connects to the tray 13. The tray 13 is attached to the front surface of the second limiting plate 8 and is arranged opposite to the front end of the positioning channel. The outer side of the transparent loading plate 9 contacts the movable rod end of each of the loading jacks 11, so that when the loading jacks 11 apply pressure, the pressure is transmitted to the transparent rock mass 10 through the transparent loading plate 9, thereby achieving confining pressure loading on the transparent rock mass 10.

[0047] In this embodiment, the first limiting plate 7 and the second limiting plate 8 are made of high-strength alloy steel, with specific dimensions of 1000mm in length, 40mm in width, and 1000mm in height. The transparent loading plate 9 is a rectangular plate made of transparent tempered glass, with specific dimensions of 2000mm in length, 50mm in width, and 500mm in height. The sides of the transparent loading plate 9 are in contact with the opposite end faces of the first limiting plate 7 and the second limiting plate 8, respectively. The limiting rod 5 is an M40 fully threaded stud made of high-strength alloy steel, with a length of 2500mm. The nut 6 is made of high-strength alloy steel and has internal threads that mate with the limiting rod 5.

[0048] The transparent rock mass 10 is formed by mixing and solidifying solid transparent particles and a liquid transparent binder. The solid transparent particles can be fused silica sand or natural silica sand, and the liquid transparent binder can be mineral oil or epoxy resin. The refractive indices of the solid transparent particles and the liquid transparent binder are matched, thereby eliminating light scattering at the particle-binder interface and achieving a macroscopic transparency effect. Multiple sets of simulated fractures can be pre-set inside the transparent rock mass 10 according to experimental needs. These simulated fractures are made of high-temperature resistant colored flaky quartz or mica flakes, which are embedded according to a pre-set orientation during the preparation of the transparent rock mass 10. An installation channel is pre-reserved at the center of the transparent rock mass 10 along its length. This installation channel is formed by demolding after pre-embedding a cylindrical mold during the preparation of the transparent rock mass 10, and is used to install the expansion anchor 12 to be tested.

[0049] In this embodiment, the transparent rock mass 10 is prefabricated using silica sand and mineral oil according to a similarity ratio to the actual project, with specific dimensions of 2000mm in length, 500mm in width, and 500mm in height. Five sets of colored flaky quartz simulated fractures are pre-embedded within the transparent rock mass 10. A positioning channel is centrally located along the length of the transparent rock mass 10, and a 40mm diameter PVC plastic pipe is installed along the positioning channel. After casting, the pre-formed channel is demolded along the length of the transparent rock mass 10.

[0050] The anchor bolt pull-out system is used to apply a pull-out load to the expansion anchor bolt 12 under test. Specifically, it includes a reaction frame 14, a limiting frame 20, a connector 19, a pull-out jack 15, an extension rod 16, a flange 18, a load sensor 17, and a fastening nut 21. The side of the reaction frame 14 abuts against the limiting frame 20, which provides support. In this embodiment, the reaction frame 14 is made of high-strength alloy steel, specifically a hollow steel cylinder with a wall thickness of 10mm, open at the top and closed at the bottom with a 40mm diameter channel for the extension rod 16 to pass through. The internal space of the reaction frame 14 provides deformation space for the anchor bolt pull-out. One end of the connector 19 is connected to the expansion anchor bolt 12 under test, and the other end is connected to the extension rod 16. In this embodiment, the extension rod 16 is a left-hand threaded steel bar, specifically with a rod diameter of 20mm and a length of 1500mm. The extension rod 16 passes sequentially through the reaction frame 14, the pull-out jack 15, the load sensor 17, and the flange 18, and is axially limited by the fastening nut 21. When the piston end of the pull-out jack 15 slides, the fastening nut 21 drives the extension rod 16 and the connector 19 to move, thereby applying an axial pull-out force to the expansion anchor rod 12 under test. The load sensor 17 is used to monitor the pull-out force value borne by the anchor rod during the pull-out process in real time.

[0051] The non-contact strain monitoring system is used to acquire real-time deformation images of the transparent rock mass 10 and the expansion anchor 12 under test throughout the entire process. Specifically, it includes a camera slide rail 3 and an industrial camera 4. The camera slide rail 3 is positioned on the opposite lateral sides of the rigid constraint frame 2. The camera slide rail 3 has grooves and a mounting bracket for the industrial camera 4, allowing the industrial camera 4 to slide along the grooves. The industrial camera 4 is used to monitor the changes in the plane strain field of the expansion anchor 12 and the transparent rock mass 10. Furthermore, the first limiting plate 7 is also provided with an observation window, facilitating the industrial camera 4 to acquire digital images of the expansion anchor 12 under test at various deformation stages in real time.

[0052] Specifically, in this embodiment, the imaging slide rail 3 is set on the opposite lateral side of the rigid constraint frame 2 and arranged parallel to the length of the transparent rock mass 10. Each industrial camera 4 is respectively set on the base 1 on the left side of each imaging slide rail 3 and the first limiting plate 7, and is adjusted and aligned with the observation window of each lateral transparent loading plate 9 and the first limiting plate 7 to monitor the plane strain field changes of the anchor rod under test and the transparent rock mass.

[0053] During operation, the transparent rock mass 10 is housed within a transparent chamber, which is entirely placed within a rigid constraint frame 2. A loading jack 11 applies controllable confining pressure to the transparent rock mass 10 via a transparent loading plate 9 to simulate different geostress environments. The expansion bolt 12 to be tested is installed within a pre-drilled hole in the transparent rock mass 10. One end of the expansion bolt 12 is fixed to the second limiting plate 8 via a tray 13, and the other end is connected to the bolt pulling system via a connector 19. During the pulling process, the pulling force applied by the pulling jack 15 is transmitted to the expansion bolt 12 to be tested via an extension rod 16 and a connector 19. A load sensor 17 records the pulling force value in real time. Simultaneously, an industrial camera 4 continuously captures images of the transparent rock mass 10 and the expansion bolt 12 to be tested through observation windows on the transparent loading plate 9 and the first limiting plate 7. After processing using digital image correlation technology, the evolution data of the full-domain strain field within the anchoring interface and the surrounding rock can be obtained.

[0054] Based on the above-described device, this embodiment also provides an indoor pull-out test method for expansion anchors based on transparent rock mass. In this embodiment, the expansion anchor 12 to be tested is a self-expanding slotted pipe anchor, such as... Figure 4As shown, the self-expanding slotted anchor bolt includes an anchor bolt body 121, a self-expanding agent 122, a hollow cylinder 123, and caps 124. The anchor bolt body 121 is a C-shaped tube rolled from steel plate, with dimensions of 1800mm in length, 2mm in thickness, 10mm in longitudinal slot width, and 43mm in outer diameter. Its ends are tapered for easy installation. Inside the anchor bolt body 121 is a plastic container composed of the hollow cylinder 123 and caps 124. The hollow cylinder 123 has an outer diameter of 38mm, an inner diameter of 6mm, and a length of 150mm, with distributed permeable holes on its wall. The outer diameter of the caps 124 is 1mm smaller than the inner diameter of the hollow cylinder 123, and its thickness is 2mm. The plastic container contains a self-expanding agent 122, which is composed of 80% calcium oxide, 5% water-reducing agent, and 15% hardening material, with a filling density of 1.5 g / cm³.

[0055] The indoor pull-out test method specifically includes the following steps:

[0056] S1: Prepare transparent rock mass 10. Connect the first limiting plate 7 to the second limiting plate 8 through the limiting rod 5 and nut 6, adjust the position of the loading jack 11 and drive the transparent loading plate 9 to form a sample preparation space with an open top, closed sides and bottom.

[0057] S2: Determine the similar materials and proportions of the transparent rock mass 10, as well as the spatial location and number of prefabricated fractures.

[0058] S3: Prepare a transparent rock mass 10 with reserved channels. Install PVC plastic pipes along the positioning channels, and demold along the longitudinal direction of the transparent rock mass 10 after casting and fixing to form reserved channels.

[0059] During the pouring process, colored flake-shaped quartz simulates fractures are pre-embedded according to the preset orientation and spacing, including the dip angle and azimuth angle. In this embodiment, 5 sets are pre-embedded.

[0060] S4: Assemble the expandable anchor bolt 12 to be tested and fit the tray 13. Select the type and installation method of the expandable anchor bolt 12 to be tested. In this embodiment, a self-expanding slotted anchor bolt is used. Before installation, immerse the self-expanding agent 122, hollow cylinder 123, and cap 124 in water for 8 to 12 minutes. After the agent roll has fully absorbed water, insert it into the slotted anchor bolt body 121. Use an impact rock drilling device to insert the expandable anchor bolt 12 to be tested into the reserved channel in the transparent rock mass 10 and wait for the anchoring agent to expand and take effect. Alternatively, the expandable anchor bolt 12 to be tested can be directly placed into the reserved channel and expanded by injection using a high-pressure grouting pump.

[0061] S5: Adjust the position and angle of the industrial cameras 4 on the sides and top of the rigid constraint frame 2 according to the horizontal and vertical positions of the reserved channels. Slide the industrial cameras 4 on the opposite sides of the rigid constraint frame 2 on the shooting slide rail 3, aligning them with the center of each lateral transparent loading plate 9. Set the industrial cameras 4 with mounting brackets on the base 1 on the left side of the first limiting plate 7, aligning them with the center of the observation window of the first limiting plate 7. Begin recording the changes in the global strain field of the rock mass monitored by the non-contact full-field strain measurement system.

[0062] S6: Set confining pressure. Adjust the upper transparent loading plate 9 to be in close contact with the transparent rock mass 10, and seal the top opening. Load the anchored rock mass to the specified pressure using the loading jacks 11 arranged circumferentially on the rigid constraint frame 2.

[0063] S7: After the anchoring agent takes effect, select the connector 19 according to the form of the expansion anchor 12 to be tested, connect the clamping cavity of the connector 19 to the rod body between the tail of the anchor and the tray 13, and screw the extension rod 16 into the connector 19.

[0064] S8: Adjust the limit frame 20 to make the reaction frame 14 coaxially aligned with the expansion anchor rod 12 to be tested. Then, coaxially mount the extension rod 16 onto the reaction frame 14, the pull jack 15, the load sensor 17, and the flange 18 in sequence, and tighten them with the fastening nut 21.

[0065] S9: When the pull-out jack 15 is activated and the piston end slides, the extension rod 16 and the connector 19 are driven by the fastening nut 21, which in turn causes the expansion anchor rod 12 to be tested to move and deform within the reaction frame 14 under the action of axial pull-out force until the expansion anchor rod 12 to be tested is pulled out or breaks.

[0066] S10: Record the pull-out force, displacement, and global strain field changes of the expansion anchor 12 under test during the pull-out process.

[0067] S11: Repeat steps S1 to S10 to conduct multi-factor parallel tests on different types of expansion anchors 12 under different expansion source types, different surrounding rocks, and different rock mass qualities, so as to fully understand the anchoring mechanism of the expansion anchors 12 under test.

[0068] Example 2

[0069] The difference between this embodiment and Embodiment 1 lies in the specific form of the expansion anchor 12 to be tested. In this embodiment, the expansion anchor 12 to be tested is a hydraulic expansion anchor. Accordingly, the installation method of the expansion anchor 12 to be tested is as follows: after the hydraulic expansion anchor is placed into the reserved channel of the transparent rock mass 10, high-pressure water is injected into the anchor through a high-pressure grouting pump, causing the anchor body to expand radially and fit tightly against the hole wall, thereby achieving anchoring. Other device structures and testing methods are the same as in Embodiment 1.

[0070] Example 3

[0071] The difference between this embodiment and Embodiment 1 lies in the mix proportion of the transparent rock mass 10 and the setting of simulated fractures. To simulate surrounding rock conditions of different quality grades, the ratio of solid transparent particles to liquid transparent cement is adjusted in this embodiment to reduce the strength of the transparent rock mass 10 and simulate a soft rock environment. Simultaneously, 10 sets of colored flaky quartz simulated fractures with different occurrences are pre-set inside the transparent rock mass 10 to simulate fractured rock masses with developed joint fractures. Other device structures and testing methods are the same as in Embodiment 1.

[0072] Example 4

[0073] The difference between this embodiment and Embodiment 1 lies in the method of confining pressure loading. To simulate a deep, high-stress environment, in this embodiment, loading jacks 11 arranged circumferentially within a rigid constraint frame 2 are used to apply different confining pressure values ​​in the transverse, longitudinal, and vertical directions, placing the transparent rock mass 10 under a triaxial unequal pressure stress state to simulate the anchoring conditions under tectonic stress fields. Other device structures and testing methods are the same as in Embodiment 1.

Claims

1. An indoor pull-out testing device for expansion-type anchor bolts based on transparent rock mass, characterized in that, include: Rigidly constrained frame (2); A confining pressure loading system, set on the rigid constraint frame (2), is used to apply controllable confining pressure to the transparent rock mass; A transparent chamber is set inside the rigid constraint frame (2) to accommodate the transparent rock mass; the transparent chamber has a light-transmitting area, and the transparent rock mass has a reserved installation channel along its length for installing the expansion anchor to be tested; An anchor pull-out system, connected to the expansion anchor bolt to be tested, is used to apply an axial pull-out force to it; The non-contact strain monitoring system includes an image acquisition device for real-time acquisition of deformation images of the transparent rock mass and the expansion anchor to be tested during the pull-out process through the light-transmitting area of ​​the transparent chamber. The transparent rock mass is formed by mixing and solidifying solid transparent particles and liquid transparent cementitious agent. The refractive indices of the solid transparent particles and the liquid transparent cementitious agent are matched to eliminate light scattering at the particle-cement interface.

2. The indoor pull-out testing device for expansion-type anchor bolts based on transparent rock mass according to claim 1, characterized in that, The confining pressure loading system includes a base (1), a rigid constraint frame (2) is set on the base (1), and multiple loading jacks (11) are set on each side of the outer periphery of the rigid constraint frame (2).

3. The indoor pull-out testing device for expansion-type anchor bolts based on transparent rock mass according to claim 1, characterized in that, The transparent cabin includes a first limiting plate (7), a second limiting plate (8), and a transparent loading plate (9) disposed between the first limiting plate (7) and the second limiting plate (8). The first limiting plate (7) and the second limiting plate (8) are connected and fixed by a limiting rod (5) and a nut (6) to form a closed cabin. The light-transmitting area includes the transparent loading plate (9) and an observation window disposed on the first limiting plate (7).

4. The indoor pull-out testing device for expansion-type anchor bolts based on transparent rock mass according to claim 1, characterized in that, The transparent rock mass (10) has simulated fissures embedded inside according to a preset orientation. The simulated fissures are colored flaky quartz or mica flakes.

5. The indoor pull-out testing device for expansion-type anchor bolts based on transparent rock mass according to claim 1, characterized in that, The anchor bolt pulling system includes a reaction frame (14), a pulling jack (15), an extension rod (16), a load sensor (17), and a connector (19). The connector (19) connects the expansion anchor bolt (12) to be tested to the extension rod (16). The extension rod (16) passes through the reaction frame (14), the pulling jack (15), and the load sensor (17) in sequence and is axially limited by a fastening nut (21). The reaction frame (14) is supported by a limiting frame (20), and a slide rail is provided at the bottom of the limiting frame (20).

6. The indoor pull-out testing device for expansion-type anchor bolts based on transparent rock mass according to claim 1, characterized in that, The non-contact strain monitoring system also includes a shooting slide rail (3) set on the opposite side of the rigid constraint frame (2) in the lateral direction. The image acquisition device is an industrial camera (4). The industrial camera (4) is installed on the shooting slide rail (3) and can slide along the slide rail.

7. A method for indoor pull-out testing of expansion-type anchor bolts based on transparent rock mass, using the apparatus described in any one of claims 1 to 6, characterized in that, Includes the following steps: Prepare transparent rock mass and reserve installation channels in the transparent rock mass; The expansion anchor to be tested is installed in the installation hole; A confining pressure is applied to the transparent rock mass to a preset value using a confining pressure loading system; An axial pull-out force is applied to the expansion anchor bolt under test using an anchor bolt pull-out system; Deformation images of the transparent rock mass and the expansion anchor to be tested were continuously acquired by a non-contact strain monitoring system, and the evolution data of the global strain field were obtained by analyzing the data using digital image correlation technology. Record the pull-out force, displacement, and strain field changes during the pull-out process until the anchor rod is pulled out or breaks.

8. The indoor pull-out test method for expansion-type anchor bolts based on transparent rock mass according to claim 7, characterized in that, When preparing transparent rock masses, colored flaky quartz or mica sheets are embedded according to the preset occurrence to simulate fractures.

9. The indoor pull-out test method for expansion-type anchor bolts based on transparent rock mass according to claim 7, characterized in that, The expansion anchor to be tested is any one of self-expanding slotted pipe anchor, mechanical expansion anchor, or hydraulic expansion anchor; when using self-expanding slotted pipe anchor, immerse the self-expanding agent in water for 8 to 12 minutes before installation.

10. The indoor pull-out test method for expansion-type anchor bolts based on transparent rock mass according to claim 7, characterized in that, By independently controlling the output pressure of the loading jacks in each direction of the confining pressure loading system, bidirectional unequal confining pressure is applied to the transparent rock mass.

Images