A tunnel model indoor test bench and method for simulating rock mass unloading deformation and active and passive collaborative support

Abstract

This invention belongs to the field of tunnel and underground engineering structural safety testing technology, specifically relating to an indoor test bench and method for simulating rock mass unloading deformation and active-passive coordinated support in a tunnel model. The test bench includes a reaction bearing frame, multiple radial loading components arranged circumferentially along the reaction bearing frame, and a bottom support component. The radial loading components can independently set and maintain their loading displacement or equivalent load, and can perform zoned unloading / unloading and reloading according to a preset zone sequence to simulate the unloading deformation path and stress redistribution of the surrounding rock caused by tunnel excavation. This invention enables controllable indoor reproduction of the entire process of surrounding rock unloading path—active support sequence—passive lining failure, providing a test platform for support optimization.

Description

Technical Field

[0001] This invention relates to an indoor test bench and method for simulating rock mass unloading deformation and active-passive coordinated support in tunnel models, belonging to the technical field of tunnel and underground engineering structure safety testing. Background Technology

[0002] The long-term safety of tunnel engineering depends on the synergistic bearing capacity of the surrounding rock-support-lining system. In actual engineering, tunnel excavation will cause stress release and redistribution in the surrounding rock. During the unloading and reloading process, the surrounding rock undergoes convergent deformation, relaxation, and local failure. At the same time, active supports such as anchor bolts and cables actively constrain the deformation of the surrounding rock and reconstruct the stress path through prestressing. The lining structure, as a passive load-bearing body, gradually enters a nonlinear response under the combined influence of surrounding rock pressure and support action, and may become unstable and fail. Therefore, studying the bearing mechanism and failure process under the coupled conditions of "surrounding rock unloading path - active support sequence - passive lining bearing capacity" is of great significance for revealing the tunnel disaster mechanism, determining the ultimate bearing capacity, and optimizing the parameters of active and passive supports.

[0003] Existing indoor tunnel model loading test devices mainly rely on applying external pressure. Although they can achieve full-circumference or multi-point loading, they generally have the following shortcomings: 1. Insufficient simulation capability of unloading path: Most devices focus on monotonic loading, making it difficult to realize the zonal unloading, reloading and spatiotemporal evolution control corresponding to excavation disturbance, resulting in difficulty in reproducing the stress release-redistribution process of surrounding rock; 2. The simulation of equivalent stiffness of surrounding rock is not flexible: Some devices have high loading rigidity, making it difficult to physically adjust the deformation resistance of surrounding rock and compare the differences in failure modes under different surrounding rock stiffness conditions. 3. Insufficient testing of active and passive support coordination: Existing devices often treat support as an additional condition, making it difficult to apply and lock the active support prestress and to synchronously couple it with the zonal unloading-reloading path. As a result, it is difficult to quantitatively evaluate the effect of support on the improvement of ultimate bearing capacity and the change of failure mode under the same path conditions.

[0004] 4. Insufficient data acquisition and interpretability throughout the destructive process: Destructive tests require synchronous and continuous multi-point load and displacement data to identify the bearing stage and failure threshold. Traditional force sensing methods are prone to impact overload or data loss at the moment of failure, and are difficult to correspond to the unloading-reloading path. Summary of the Invention

[0005] The purpose of this invention is to provide an indoor test bench and method for simulating rock mass unloading deformation and active-passive coordinated support in tunnel models. This invention is a comprehensive simulation test bench and method that can achieve the following indoor features: adjustable equivalent stiffness of surrounding rock, controllable unloading-reloading path, coordinated coupling of active support and passive lining, and reliable acquisition and interpretation of data throughout the entire process.

[0006] The technical solution provided by this invention to solve the above-mentioned technical problems is: an indoor test bench for simulating rock mass unloading deformation and active-passive coordinated support, comprising: It includes a reaction force bearing frame, a plurality of radial loading components arranged circumferentially along the reaction force bearing frame, and a bottom support component; The radial loading component can independently set and maintain its loading displacement or equivalent load, and can perform partitioned unloading / unloading and reloading according to a preset partition sequence to simulate the unloading deformation path and stress redistribution of the surrounding rock caused by tunnel excavation.

[0007] A further technical solution is that the reaction force bearing frame includes a base plate and a circular frame disposed on the base plate.

[0008] A further technical solution is that the radial loading assembly includes a guide constraint rod and a hollow screw rod with external threads, a small pad, a spring, and a large pad connected in sequence; the annular frame is radially provided with a loading threaded hole that matches the hollow screw rod, the hollow screw rod is installed in the loading threaded hole, one end of the hollow screw rod located in the annular frame is connected in sequence to the small pad, the spring, and the large pad, and the other end is provided with a loading nut; the guide constraint rod passes through the hollow screw rod, and one end passes through the small pad and the spring and is connected to the large pad.

[0009] A further technical solution is that the bottom support includes a support block, a support spring, and a support pad connected in sequence, with the support block fixed inside the lower part of the annular frame.

[0010] A further technical solution is that the annular frame is provided with several anchoring interface holes in the radial direction for installing anchoring support simulation units and applying prestress, so as to realize the coordinated force of active support and passive lining.

[0011] A further technical solution is that the test bench also includes a test data acquisition unit, which is used to monitor the spring compression of each loading channel and calculate the load based on the calibrated stiffness, and output load-displacement curves to characterize the bearing stage and failure process.

[0012] An indoor testing method for simulating rock mass unloading deformation and active-passive coordinated support in a tunnel model includes the following steps: S1. Working condition mapping and zone path setting: Based on the geological conditions and excavation procedures of the target tunnel project, determine the spatial distribution of surrounding rock pressure and map it to the initial loading value of each loading channel. At the same time, set the loading channel zones corresponding to the excavation sections and the zone unloading / unloading and reloading paths. S2. Model Installation and Boundary Construction: Install the tunnel lining model inside the reaction bearing frame. Place the bottom of the model on the bottom support component. Adjust the large pads of each radial loading component to fit the outer surface of the lining. Select a replaceable spring that matches the equivalent stiffness of the target surrounding rock. S3. Initial stress field loading: Synchronous loading or group loading is performed on each loading channel according to the differentiated initial loading value to establish the initial surrounding rock stress state and record the reference load-displacement data. S4. Surrounding rock unloading deformation simulation: Implement graded load reduction or unloading on the corresponding partition loading channel according to the preset partition sequence, and maintain or adjust the load on the non-unloading partition loading channel to simulate stress redistribution, and record the load-displacement response of the unloading section. S5. Active support application and dynamic adjustment: Based on the set support timing, simulated anchor bolts or anchor cables are installed. Externally, the prestress loading spring is compressed by rotating the locking nut. Combined with the real-time monitoring data of the micro tension sensor, the target prestress value is applied and locked. S6. Reload to failure: Apply graded loading to the loading channel according to the set reloading strategy until the lining structure cracks, yields or becomes unstable and fails, and obtain a complete load-displacement curve; S7. Curve Feature Extraction and Support Enhancement Evaluation: Feature parameters are extracted from the load-displacement curve, and the unsupported and supported conditions are compared under the same path. Based on the extracted feature parameters, the bearing capacity enhancement rate and ductility coefficient are calculated, and the influence of active support on the failure mode of passive lining is divided into brittle dominant mode, elastic-plastic transition mode and ductile synergistic mode, thereby quantifying the enhancement effect of active support.

[0013] A further technical solution is that the characteristic parameters include yield point, peak ultimate bearing capacity, and post-peak residual bearing capacity.

[0014] A further technical solution is that the calculation formulas for the bearing capacity improvement rate and ductility coefficient in step S7 are as follows:

[0015] In the formula: To improve the load-bearing capacity;

[0016] In the formula: It is the ductility coefficient; This is the convergence displacement at the ultimate failure point; This represents the convergence displacement at yield.

[0017] A further technical solution is that, in step S7, when the load-bearing capacity increase rate... And ductility coefficient When it is less than 15%, it is the brittle-dominated mode; the corresponding situation is: the active support prestress is too small or the timing of application is too late; the characteristic manifestation is: the threshold for the initial appearance of lining cracks is not significantly improved, the failure process is rapid, and it presents sudden brittle failure with local crushing or tensile cracking, and the active support only plays a weak delaying role. when And ductility coefficient Between 15% and 40%, it is an elastoplastic transition mode, which corresponds to the following: active support parameters are within the normal and reasonable range; characteristic features: the initial appearance time of cracks is significantly delayed, the failure mode changes from a single local brittle fracture to elastoplastic failure with multiple cracks developing in a dispersed manner, and the residual bearing capacity is preserved. when And ductility coefficient When it is greater than 40%, it is a ductile synergistic mode; the corresponding situation is: the active support has high stiffness and the prestress is applied in a timely manner; the characteristics are: the active support and the lining form a highly synergistic load-bearing system, the lining does not become unstable as a whole after a large convergence deformation, and the failure mode is completely transformed into ductile failure with obvious yield plateau, which greatly improves the safety reserve of the support system.

[0018] The present invention has the following beneficial effects: 1. Through multi-channel loading and partitioned unloading and reloading control, it is possible to simulate the unloading deformation path and stress redistribution process of surrounding rock caused by tunnel excavation indoors; 2. The equivalent stiffness of the surrounding rock can be adjusted by using replaceable springs, which facilitates the comparison of lining failure mechanisms under different surrounding rock conditions; 3. By introducing anchor bolts / cables through anchoring interfaces and applying prestress, a synergistic test of active support and passive lining load-bearing capacity can be achieved, which can quantify the support efficiency and changes in failure modes. 4. By using the data acquisition method of "deformation monitoring - stiffness back-calculation of load", the risk of data loss caused by the failure of force sensors at the moment of failure can be reduced, and complete load-displacement history data can be obtained. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure; Figure 2 This is a detailed partial structural diagram of a single radially loaded component. Detailed Implementation

[0020] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can also refer to a mechanical connection. The terms "fully through," "fully open," and "fully transparent" are equivalent to each other. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0024] like Figure 1 and Figure 2 As shown, the present invention discloses an indoor test bench for simulating rock mass unloading deformation and active-passive coordinated support in a tunnel model. Specifically, it includes a reaction bearing frame 8, a radial loading component, a bottom support component, an anchoring support simulation unit, and a test data acquisition unit. The radial loading component is arranged circumferentially along the reaction bearing frame 8 and is used to apply independently controllable radial loads to the tunnel model lining structure. Each loading channel supports synchronous loading, group loading, and zoned unloading and reloading to simulate the unloading deformation path of the surrounding rock. The anchoring support simulation unit is installed on the reaction bearing frame 8 and is used to install simulated anchor bolts or cables and apply prestress to achieve coordinated force distribution between active support and passive lining. The bottom support component is located at the bottom of the reaction bearing frame 8 and is used to simulate foundation settlement or changes in bottom elastic resistance. The test data acquisition unit monitors the spring compression of each loading channel and calculates the load based on the calibrated stiffness, outputting a load-displacement curve to characterize the bearing stage and failure process. The reaction bearing frame 8 forms the rigid outer skeleton of the test bench, used to enclose and position the tunnel model. Its specific structure is as follows: Figure 1 As shown, it includes a base plate and a circular frame set on the base plate; like Figure 2 As shown, the radial loading assembly includes a guide constraint rod 2 and a hollow screw rod 3 with external threads, a small pad 4, a spring 5, and a large pad 6 connected in sequence. The annular frame is radially provided with a loading threaded hole 10 that matches the hollow screw rod 3. The hollow screw rod 3 is installed in the loading threaded hole 10. One end of the hollow screw rod 3 located in the annular frame is connected in sequence to the small pad 4, the spring 5, and the large pad 6. The other end is fixedly provided with a loading nut 1. That is, rotating the loading nut 1 will drive the hollow screw rod 3 to rotate, thereby adjusting the screwing depth of the hollow screw rod 3 in the loading threaded hole 10. The guide constraint rod 2 passes through the hollow screw rod 3, and one end passes through the small pad 4 and the spring 5 and is connected to the large pad 6.

[0025] The large pad 6 has a positioning structure on the side facing the spring 5 to accommodate the end of the spring; the diameter of the central through hole of the small pad 4 is larger than the diameter of the guide constraint rod 2 but smaller than the outer diameter of the spring 5.

[0026] The rotating loading nut 1 drives the hollow screw 3 to axially feed the spring 5, generating a load. The stiffness of the spring 5 is used to simulate the equivalent compressive stiffness of the surrounding rock. Simultaneously, the test data acquisition unit measures and monitors the compressive deformation of each spring 5 synchronously (specifically, using a high-precision displacement sensor (such as a wire displacement gauge or LVDT) to measure the distance difference between the bottom surface of the small pad 4 and the top surface of the large pad 6), and based on... = × ,in For pressure, Let be the spring constant. This represents the deformation of the spring. The channel load is calculated inversely to generate the channel load-displacement curve and the total load-convergence curve, which are used to identify the elastic stage, the plastic development stage, the peak ultimate bearing capacity, and the post-peak residual bearing capacity stage.

[0027] Spring 5 is a replaceable high-strength helical spring. By replacing springs with different stiffness coefficients, the equivalent stiffness of the surrounding rock can be changed, thereby enabling comparative tests on different surrounding rock conditions and their unloading-reloading response differences.

[0028] In this embodiment, the loading nut 1 can be set to two, which are used to precisely control the loading displacement and realize the loading / unloading state locking.

[0029] like Figure 1As shown, each loading module on the reaction bearing frame 8 is provided with an anchoring interface hole 7 for installing the anchoring support simulation unit, so as to realize the coupling test of the active support and the stress process of the lining structure.

[0030] The anchoring support simulation unit includes a simulated anchor rod or cable, a miniature tension sensor connected in series with the simulated anchor rod or cable, a prestressed loading spring, and a locking nut. The simulated anchor rod or cable passes through the anchoring interface hole 7 on the reaction bearing frame 8 into the reserved channel, and then passes through the miniature tension sensor and the prestressed loading spring in sequence before being fastened by the locking nut. It is used to apply and lock the prestress by rotating the locking nut to compress the prestressed loading spring. The miniature tension sensor monitors and feeds back the prestress value in real time, so as to realize the precise quantitative application and dynamic adjustment of the active support force. This allows the active support force to remain constant or be adjusted according to a set law during the zonal unloading / unloading and reloading process, so as to realize the coordinated stress and comparative test between the active support and the lining structure as a passive load-bearing body. In this embodiment, as Figure 1 As shown, the bottom support assembly includes a support block 9, a support spring, and a support pad connected in sequence. The support block 9 is fixed inside the lower part of the annular frame. The bottom of the tunnel model is placed on the bottom support assembly to simulate settlement, bottom bulging, or bottom resistance degradation. The bottom support assembly can be replaced to change the bottom boundary conditions.

[0031] The test bench in this embodiment can: 1) establish the initial stress state of the surrounding rock through multi-channel radial loading indoors; 2) control the unloading and stress redistribution of the surrounding rock caused by tunnel excavation through zoned unloading and reloading; 3) achieve controllable participation of active support by introducing anchor bolts / anchor cables through anchoring interfaces; 4) load the lining structure as a passive support bearing until instability and failure, and obtain complete load-displacement and failure evolution data, which can be used for support parameter optimization and mechanism research.

[0032] The specific process of using the aforementioned test bench in this invention is as follows: Before the test, based on the tunnel engineering design conditions, numerical simulation is used to calculate the distribution of surrounding rock pressure in the tunnel arch, walls, and bottom. Based on this, a differentiated loading scheme is formulated. By adjusting the feed amount of each loading nut 1, each loading channel applies a non-uniform radial load to the lining corresponding to the actual working conditions, thereby restoring the true surrounding rock stress field. Through this differentiated loading, the asymmetric ground pressure action experienced by the tunnel under different geological conditions and burial depths can be simulated, thus more realistically reproducing the squeezing effect of the surrounding rock on the lining. S1. Working condition mapping and zone path setting: Based on the geological conditions and excavation procedures of the target tunnel project, determine the spatial distribution of surrounding rock pressure and map it to the initial loading value of each loading channel. At the same time, set the loading channel zones corresponding to the excavation sections and the zone unloading / unloading and reloading paths. S2. Model Installation and Boundary Construction: Install the tunnel lining model inside the reaction bearing frame 8, place the bottom of the model on the bottom support component, adjust the large pads 6 of each radial loading component to fit the outer surface of the lining, and select a replaceable spring that matches the equivalent stiffness of the target surrounding rock. S3. Initial stress field loading: Synchronous loading or group loading is performed on each loading channel according to the differentiated initial loading value to establish the initial surrounding rock stress state and record the reference load-displacement data. S4. Surrounding rock unloading deformation simulation: Implement graded load reduction or unloading on the corresponding partition loading channel according to the preset partition sequence, and maintain or adjust the load on the non-unloading partition loading channel to simulate stress redistribution, and record the load-displacement response of the unloading section. S5. Active support application and dynamic adjustment: Based on the set support timing, simulated anchor bolts or anchor cables are installed. Externally, the prestress loading spring is compressed by rotating the locking nut. Combined with the real-time monitoring data of the micro tension sensor, the target prestress value is applied and locked. S6. Reload to failure: Apply graded loading to the loading channel according to the set reloading strategy until the lining structure cracks, yields or becomes unstable and fails, and obtain a complete load-displacement curve; S7. Curve Feature Extraction and Support Enhancement Evaluation: Extract feature parameters (yield point, peak ultimate bearing capacity, and residual bearing capacity after the peak) from the load-displacement curve, and compare unsupported and supported conditions under the same path; calculate the bearing capacity enhancement rate based on the extracted feature parameters. With ductility coefficient Furthermore, the impact of active support on the failure mode of passive lining is divided into brittle-dominant mode (inefficient impact), elastoplastic transition mode (medium-efficacy impact), and ductile-synergistic mode (efficient impact), thereby quantifying the synergistic effect of active support. When the load-bearing capacity increase rate And ductility coefficient When it is less than 15%, it is the brittle-dominated mode; the corresponding situation is: the active support prestress is too small or the timing of application is too late; the characteristic manifestation is: the threshold for the initial appearance of lining cracks is not significantly improved, the failure process is rapid, and it presents sudden brittle failure with local crushing or tensile cracking, and the active support only plays a weak delaying role. when And ductility coefficient Between 15% and 40%, it is an elastoplastic transition mode, which corresponds to the following: active support parameters are within the normal and reasonable range; characteristic features: the initial appearance time of cracks is significantly delayed, the failure mode changes from a single local brittle fracture to elastoplastic failure with multiple cracks developing in a dispersed manner, and the residual bearing capacity is preserved. when And ductility coefficient When it is greater than 40%, it is a ductile synergistic mode; the corresponding situation is: the active support has high stiffness and the prestress is applied in time; the characteristic is that the active support and the lining form a highly synergistic load-bearing system. The lining does not become unstable as a whole after a large convergence deformation. The failure mode is completely transformed into ductile failure with obvious yield plateau, which greatly improves the safety reserve of the support system. The formulas for calculating the bearing capacity improvement rate and the ductility coefficient are as follows:

[0033] In the formula: To improve the load-bearing capacity;

[0034] In the formula: It is the ductility coefficient; This is the convergence displacement at the ultimate failure point; This represents the convergence displacement at yield.

[0035] The above description is not intended to limit the present invention in any way. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An indoor test bench for simulating rock mass unloading deformation and active-passive coordinated support, characterized in that, It includes a reaction bearing frame (8), multiple radial loading components arranged circumferentially along the reaction bearing frame (8), and a bottom support component; The radial loading component can independently set and maintain its loading displacement or equivalent load, and can perform partitioned unloading / unloading and reloading according to a preset partition sequence to simulate the unloading deformation path and stress redistribution of the surrounding rock caused by tunnel excavation.

2. The indoor test bench for simulating rock mass unloading deformation and active-passive coordinated support of a tunnel model according to claim 1, characterized in that, The reaction force bearing frame (8) includes a base plate and a circular frame set on the base plate.

3. The indoor test bench for simulating rock mass unloading deformation and active-passive coordinated support of a tunnel model according to claim 2, characterized in that, The radial loading assembly includes a guide constraint rod (2) and a hollow screw rod (3) with external threads, a small pad (4), a spring (5), and a large pad (6) connected in sequence. The annular frame is provided with a loading threaded hole (10) that matches the hollow screw rod (3) in the radial direction. The hollow screw rod (3) is installed in the loading threaded hole (10). One end of the hollow screw rod (3) located in the annular frame is connected to the small pad (4), the spring (5), and the large pad (6) in sequence, and the other end is provided with a loading nut (1). The guide constraint rod (2) passes through the hollow screw rod (3). One end passes through the small pad (4) and the spring (5) and is connected to the large pad (6).

4. The indoor test bench for simulating rock mass unloading deformation and active-passive coordinated support of a tunnel model according to claim 2, characterized in that, The bottom support includes a support block (9), a support spring, and a support pad connected in sequence. The support block (9) is fixed inside the lower part of the annular frame.

5. The indoor test bench for simulating rock mass unloading deformation and active-passive coordinated support of a tunnel model according to claim 2, characterized in that, The circular frame is provided with several anchoring interface holes (7) in the radial direction for installing the anchoring support simulation unit and applying prestress, so as to realize the coordinated force of active support and passive lining.

6. The indoor test bench for simulating rock mass unloading deformation and active-passive coordinated support as described in claim 3, characterized in that, The test bench also includes a test data acquisition unit, which monitors the spring compression of each loading channel and calculates the load based on the calibrated stiffness, outputting load-displacement curves to characterize the bearing stage and failure process.

7. A method for indoor testing of a tunnel model simulating rock mass unloading deformation and active-passive coordinated support, characterized in that, The method is tested using an indoor test bench for simulating rock mass unloading deformation and active-passive coordinated support as described in any one of claims 1-6. Includes the following steps: S1. Working condition mapping and zone path setting: Based on the geological conditions and excavation procedures of the target tunnel project, determine the spatial distribution of surrounding rock pressure and map it to the initial loading value of each loading channel. At the same time, set the loading channel zones corresponding to the excavation sections and the zone unloading / unloading and reloading paths. S2, Model Installation and Boundary Construction: Install the tunnel lining model in the reaction bearing frame (8), place the bottom of the model on the bottom support component, adjust the large pads (6) of each radial loading component to fit with the outer surface of the lining, and select a replaceable spring that matches the equivalent stiffness of the target surrounding rock. S3. Initial stress field loading: Synchronous loading or group loading is performed on each loading channel according to the differentiated initial loading value to establish the initial surrounding rock stress state and record the reference load-displacement data. S4. Surrounding rock unloading deformation simulation: Implement graded load reduction or unloading on the corresponding partition loading channel according to the preset partition sequence, and maintain or adjust the load on the non-unloading partition loading channel to simulate stress redistribution, and record the load-displacement response of the unloading section. S5. Active support application and dynamic adjustment: Based on the set support timing, simulated anchor bolts or anchor cables are installed. Externally, the prestress loading spring is compressed by rotating the locking nut. Combined with the real-time monitoring data of the micro tension sensor, the target prestress value is applied and locked. S6. Reload to failure: Apply graded loading to the loading channel according to the set reloading strategy until the lining structure cracks, yields or becomes unstable and fails, and obtain a complete load-displacement curve; S7. Curve Feature Extraction and Support Enhancement Evaluation: Feature parameters are extracted from the load-displacement curve, and the unsupported and supported conditions are compared under the same path. Based on the extracted feature parameters, the bearing capacity enhancement rate and ductility coefficient are calculated, and the influence of active support on the failure mode of passive lining is divided into brittle dominant mode, elastic-plastic transition mode and ductile synergistic mode, thereby quantifying the enhancement effect of active support.

8. The indoor testing method for simulating rock mass unloading deformation and active-passive coordinated support of a tunnel model according to claim 7, characterized in that, The characteristic parameters include yield point, peak ultimate bearing capacity, and post-peak residual bearing capacity.

9. The indoor testing method for simulating rock mass unloading deformation and active-passive coordinated support of a tunnel model according to claim 8, characterized in that, The formulas for calculating the bearing capacity improvement rate and ductility coefficient in step S7 are as follows: In the formula: To improve the load-bearing capacity; In the formula: It is the ductility coefficient; This is the convergence displacement at the ultimate failure point; This represents the convergence displacement at yield.

10. The indoor testing method for simulating rock mass unloading deformation and active-passive coordinated support of a tunnel model according to claim 9, characterized in that, In step S7, when the bearing capacity increase rate And ductility coefficient When it is less than 15%, the brittleness-dominated mode is observed. The corresponding situations are: insufficient prestress in active support or application too late; Characteristic manifestations: The initial threshold of lining cracks does not increase significantly, the failure process is rapid, and it presents as sudden brittle failure with local crushing or tensile cracking. Active support only plays a weak role in delaying the failure. when And ductility coefficient Between 15% and 40%, it is an elastoplastic transition mode, which corresponds to the following: active support parameters are within the normal and reasonable range; characteristic features: the initial appearance time of cracks is significantly delayed, the failure mode changes from a single local brittle fracture to elastoplastic failure with multiple cracks developing in a dispersed manner, and the residual bearing capacity is preserved. when And ductility coefficient When it is greater than 40%, it is a ductile synergistic mode; the corresponding situation is: the active support has high stiffness and the prestress is applied in a timely manner; the characteristics are: the active support and the lining form a highly synergistic load-bearing system, the lining does not become unstable as a whole after a large convergence deformation, and the failure mode is completely transformed into ductile failure with obvious yield plateau, which greatly improves the safety reserve of the support system.

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