Model test apparatus and test method for variable stiffness tunnel excavation and support process

Abstract

This invention discloses a model test device and method for the variable stiffness tunnel excavation and support process, relating to the field of tunnel support testing technology. It includes: a main frame, a model chamber, multiple monitoring and loading units distributed along a first direction, and multiple variable stiffness support excavation units distributed along the first direction. The model chamber is fixedly installed on the main frame and is used to hold rock mass material. One end of the monitoring and loading unit is connected to the top of the main frame, and the other end is used to apply a load force to the top of the rock mass material in the model chamber. The variable stiffness support excavation unit includes a support excavation column, friction plates, and a thruster. The top of the support excavation column is used to contact the bottom of the rock mass material. The support excavation column passes through the bottom of the main frame. The friction plates are used to contact the sidewalls of the support excavation column and can press against the support excavation column. The thruster is connected to the friction plates and can apply different loads to the friction plates, simulating the longitudinal changes in the stiffness of the support structure and the surrounding rock itself during tunnel excavation and support.

Description

Technical Field

[0001] This invention relates to the field of tunnel support testing technology, and in particular to a model test device and test method for the variable stiffness tunnel excavation and support process. Background Technology

[0002] With the large-scale construction of tunnels in my country, engineering geological conditions are becoming increasingly complex and diverse. Tunnel engineering activities conducted under complex stress environments such as ultra-deep burial, extremely high ground stress, and extremely fractured strata face the risk of engineering disasters such as tunnel surrounding rock instability and structural failure induced by large deformations of the surrounding rock. To ensure the safe and rapid construction of tunnels under complex strata and stress environments, research on the theory of synergistic design of tunnel surrounding rock support stiffness is extremely urgent and necessary. Indoor physical model tests of multifunctional variable stiffness excavation support systems are important means to analyze the synergistic effect of surrounding rock support stiffness and the influence of variable stiffness support on surrounding rock deformation. They also serve as an important verification and supplement to numerical calculations and mechanical analysis results in tunnel stiffness design theory research, playing a crucial role in the entire research process.

[0003] Currently available tunnel structure deformation and stress loading simulation test benches, such as the Shandong University surrounding rock support test bench, which studies the mechanical properties of low-grade surrounding rock after anchor bolt and cable reinforcement; the Wuhan University tunnel surrounding rock mechanical property simulation test bench, which studies the grouting characteristics and effects of weak surrounding rock under high ground stress; and the Wuhan Institute of Rock and Soil Mechanics deep tunnel dynamic load failure test bench, which studies the impact of dynamic load on tunnel safety under high ground stress; however, none of them can conduct research on the stiffness of the tunnel support structure system. Summary of the Invention

[0004] The purpose of this invention is to provide a model test device and test method for tunnel excavation and support process, so as to solve the problems existing in the prior art and to simulate the change of stiffness during tunnel excavation and support process.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] This invention provides a model test device for the variable stiffness tunnel excavation and support process, comprising: a main frame, a model chamber, multiple monitoring and loading units distributed along a first direction, and multiple variable stiffness support excavation units distributed along the first direction. The model chamber is fixedly installed on the main frame and is used to hold rock mass material. One end of each monitoring and loading unit is connected to the top of the main frame, and the other end is used to apply a load force to the top of the rock mass material in the model chamber. Each variable stiffness support excavation unit includes a support excavation column, a friction plate, and a thruster. The top of the support excavation column is used to contact the bottom of the rock mass material, and the support excavation column passes through the bottom of the main frame. The friction plate is used to contact the side wall of the support excavation column and can press against the support excavation column. The thruster is connected to the friction plate and can apply different loads to the friction plate.

[0007] Preferably, the system also includes a plurality of first settlement displacement gauges, with one first settlement displacement gauge fixedly connected to the bottom of each of the support excavation columns. The first settlement displacement gauges are used to monitor the vertical displacement of the support excavation columns.

[0008] Preferably, it also includes a thrust rod, one end of which is detachably connected to the friction plate, and the other end is fixedly connected to the output component of the thruster.

[0009] Preferably, the main frame includes frame pillars, two vertical connecting frames, a top reaction frame, and a bottom reaction frame. The two vertical connecting frames, the top reaction frame, and the bottom reaction frame are arranged in a ring. The frame pillars are located at the bottom of the bottom reaction frame. The model compartment is located between the top reaction frame and the bottom reaction frame, and its two ends are fixedly connected to the two vertical connecting frames respectively.

[0010] Preferably, the friction plate is semi-circular and the inner diameter of the friction plate is equal to the outer diameter of the support excavation column.

[0011] Preferably, the variable stiffness support excavation unit further includes an intelligent monitoring and control system, which is signal-connected to the thruster and used to control the magnitude of the force applied by the thruster to the thrust rod.

[0012] Preferably, the monitoring and loading unit includes a loading and monitoring cylinder, a thrust plate, and a second settling displacement gauge. The top of the loading and monitoring cylinder is fixedly connected to the top reaction frame, and the output component at the bottom of the loading and monitoring cylinder is fixedly connected to the thrust plate. The thrust plate is used to contact the rock mass material. A displacement gauge placement slot is provided in the middle of the loading and monitoring cylinder and the thrust plate. The second settling displacement gauge passes through the displacement gauge placement slot, and the bottom of the second settling displacement gauge is in contact with the rock mass material.

[0013] Preferably, it further includes an elastomer placement chamber and an elastomer, the elastomer placement chamber being disposed above the bottom reaction frame and used to place the elastomer, the elastomer being used to connect each of the support excavation columns to transmit the load between each of the support excavation columns in the longitudinal direction to simulate the longitudinal stress of the support structure.

[0014] The present invention also provides a test method for a model test device for the variable stiffness tunnel excavation and support process as described above, characterized by comprising the following steps:

[0015] S1: Set the stiffness of each variable stiffness support excavation unit to k∞, put rock material into the model chamber, and start the monitoring and loading unit to load until it is stable.

[0016] S2: Adjust the stiffness of the first variable stiffness support excavation unit along the first direction to k1, and the stiffness of the remaining variable stiffness support excavation units is k. ∞ The rock mass material is displaced to equilibrium, and the vertical displacement of all the support excavation columns and the load on the support excavation columns are recorded.

[0017] S3: Adjust the stiffness of the first variable stiffness support excavation unit along the first direction to k2, the stiffness of the second variable stiffness support excavation unit to k1, and the stiffness of the remaining variable stiffness support excavation units to k2. ∞ The rock mass material is displaced to equilibrium, and the vertical displacement of all the support excavation columns and the load on the support excavation columns are recorded.

[0018] S4: Adjust the stiffness of the first variable stiffness support excavation unit along the first direction to k3, the stiffness of the second variable stiffness support excavation unit to k2, the stiffness of the third variable stiffness support excavation unit to k1, and the stiffness of the remaining variable stiffness support excavation units to k. ∞ The rock mass material is displaced to equilibrium, and the vertical displacement of all the support excavation columns and the load on the support excavation columns are recorded.

[0019] S5: Adjust the stiffness of the first variable stiffness support excavation unit along the first direction to k4, the stiffness of the second variable stiffness support excavation unit to k3, the stiffness of the third variable stiffness support excavation unit to k2, the stiffness of the fourth variable stiffness support excavation unit to k1, and the stiffness of the remaining variable stiffness support excavation units to k. ∞ The rock mass material is displaced to equilibrium, and the vertical displacement of all the support excavation columns and the load on the support excavation columns are recorded.

[0020] S6: Adjust the stiffness of the first variable stiffness support excavation unit along the first direction to k4, the stiffness of the second variable stiffness support excavation unit to k4, the stiffness of the third variable stiffness support excavation unit to k3, the stiffness of the fourth variable stiffness support excavation unit to k2, the stiffness of the fifth variable stiffness support excavation unit to k1, and the stiffness of the remaining variable stiffness support excavation units to k. ∞ The rock mass material is displaced to equilibrium, and the vertical displacement of all the support excavation columns and the load on the support excavation columns are recorded.

[0021] S7: Repeat this process until the stiffness of the first variable stiffness support excavation unit along the first direction is adjusted to k4, the stiffness of the second variable stiffness support excavation unit is k4, the stiffness of the third variable stiffness support excavation unit is k4, the stiffness of the fourth variable stiffness support excavation unit is k4, the stiffness of the fifth variable stiffness support excavation unit is k3, the stiffness of the sixth variable stiffness support excavation unit is k2, the stiffness of the seventh variable stiffness support excavation unit is k1, the stiffness of the eighth variable stiffness support excavation unit is k∞, the stiffness of the ninth variable stiffness support excavation unit is k∞, and the stiffness of the tenth variable stiffness support excavation unit is k∞. Record the vertical displacement of all the support excavation columns and the load on the support excavation columns when the rock mass material shifts to equilibrium.

[0022] Where k ∞ k1 and k2 decrease progressively, corresponding to three stages of changes in the stiffness of the surrounding rock in front of the tunnel face, while k3 and k4 increase progressively, corresponding to two stages of support stiffness.

[0023] The present invention achieves the following technical effects compared to the prior art:

[0024] This invention provides a model test device and method for the variable stiffness tunnel excavation and support process. By placing rock mass material in a model chamber and applying loads to the rock mass material through a monitoring loading unit, the device simulates the in-situ stress experienced by the surrounding rock. Furthermore, by setting up multiple variable stiffness support excavation units to contact the rock mass material and provide support forces with different support stiffnesses, the invention simulates the longitudinal changes in the stiffness of the support structure and the surrounding rock itself during excavation and support. This allows for the simulation of the variable stiffness tunnel excavation and support process. This invention enables indoor simulation of the support action and surrounding rock deformation under a given tunnel support stiffness distribution, providing a more intuitive understanding. This invention demonstrates and showcases the longitudinal dynamic interaction between the tunnel support structure system and the surrounding rock, providing a teaching experiment platform for simulating the mechanical behavior of tunnel construction. It also provides an experimental foundation for scientific research on the root causes and evolution of tunnel surrounding rock deformation, the distribution of support stiffness required for support based on the deformation distribution of the surrounding rock, and the stiffness design theory of tunnel support systems aimed at controlling surrounding rock deformation. Furthermore, this invention provides an experimental platform for in-depth research on fundamental scientific issues in tunnel engineering, such as support structure system design theory and surrounding rock deformation control, and is of great significance for breakthroughs in key scientific issues and the construction and development of the discipline. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A schematic diagram of the structure of the model test device for the variable stiffness tunnel excavation and support process provided by the present invention;

[0027] Figure 2 A vertical cross-sectional view of the model test device for the variable stiffness tunnel excavation and support process provided by the present invention;

[0028] Figure 3 This is a top view of the variable stiffness support excavation unit in the model test device for the variable stiffness tunnel excavation and support process provided by the present invention.

[0029] In the diagram: 1. First settlement displacement gauge; 1-1. Second settlement displacement gauge; 2. Thrust plate; 3. Model chamber; 4. Variable stiffness support excavation unit; 5. Frame column; 6. Elastomer placement chamber; 7. Loading monitoring cylinder; 8. Displacement gauge placement slot; 9. Guide frame; 10. Top reaction frame; 11. Loading hole; 12. Support monitoring hole; 13. Bottom reaction frame; 4-1. Support excavation column; 4-2. Thrust rod; 4-3. Friction plate; 4-4. Thruster; 4-5. Intelligent monitoring and control system. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0031] The purpose of this invention is to provide a model test device and test method for tunnel excavation and support process, so as to solve the problems existing in the prior art and to simulate the change of stiffness during tunnel excavation and support process.

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Example 1

[0034] This embodiment provides a model test device for the variable stiffness tunnel excavation and support process, such as... Figures 1-3As shown, the system includes: a main frame, a model chamber 3, multiple monitoring and loading units distributed along a first direction, and multiple variable stiffness support excavation units 4 distributed along the first direction, which is the longitudinal excavation direction of the tunnel. The model chamber 3 is fixedly installed on the main frame and is used to hold rock mass material. One end of the monitoring and loading unit is connected to the top of the main frame, and the other end is used to apply a load to the top of the rock mass material in the model chamber 3 to simulate the in-situ stress experienced by the rock mass material in reality. The variable stiffness support excavation unit 4 includes a support excavation column 4-1, a friction... Friction plate 4-3 and thruster 4-4 are used to simulate the actual ground stress on the surrounding rock by placing rock material in model chamber 3 and applying loads to the rock material by monitoring the loading unit; multiple variable stiffness support excavation units are also used. The top of the support excavation column 4-1 is used to contact the bottom of the rock material. The support excavation column 4-1 passes through the bottom of the main frame. Friction plate 4-3 is used to contact the side wall of the support excavation column 4-1 and can tighten the support excavation column 4-1. The thruster 4-4 is connected to the friction plate 4-3 and can apply different loads to the friction plate 4-3. The model simulates the actual ground stress on the surrounding rock by placing rock material in model chamber 3 and applying loads to the rock material by monitoring the loading unit; and by setting multiple variable stiffness support excavation units. Yuan 4 simulates the longitudinal changes in the stiffness of the support structure and surrounding rock during excavation and support by providing support forces with different support stiffnesses in contact with rock materials. It can simulate the excavation and support process of variable stiffness tunnels. This invention can realize indoor simulation of support action and surrounding rock deformation under a given tunnel support stiffness distribution, intuitively demonstrating and showcasing the longitudinal dynamic interaction between the tunnel support structure system and the surrounding rock, and providing a teaching experiment platform for simulating the mechanical behavior of tunnel construction. This invention can provide an experimental basis for scientific research on the root causes and evolution of tunnel surrounding rock deformation, the distribution of support stiffness required for tunnel surrounding rock deformation distribution, and the stiffness design theory of tunnel support system with surrounding rock deformation control as the goal. This invention provides an experimental platform for in-depth research on fundamental scientific issues in tunnel engineering, such as support structure system design theory and surrounding rock deformation control, and is of great significance for breakthroughs in key scientific issues and the construction and development of the discipline. Furthermore, by using thruster 4-4 and friction plate 4-3, the excavation process can be simulated, avoiding the problems of difficulty in achieving stepless variable stiffness and large data errors encountered by the spring replacement method.

[0035] In a preferred embodiment, the model test device for the variable stiffness tunnel excavation and support process also includes multiple first settlement displacement gauges 1. Each support excavation column 4-1 is fixedly connected to a first settlement displacement gauge 1. The first settlement displacement gauge 1 is used to monitor the vertical displacement of the support excavation column 4-1. It has a simple structure and is convenient to display the vertical displacement of the support excavation column 4-1.

[0036] In a preferred embodiment, the variable stiffness support excavation unit 4 further includes a thrust rod 4-2, one end of which is detachably connected to the friction plate 4-3, and the other end is fixedly connected to the output component of the thruster 4-4, resulting in a simple structure.

[0037] In a preferred embodiment, the main frame includes frame pillars 5, two vertical connecting frames, a top reaction frame 10, and a bottom reaction frame 13. The two vertical connecting frames, the top reaction frame 10, and the bottom reaction frame 13 are arranged in a ring. The frame pillars 5 are located at the bottom of the bottom reaction frame 13. The model chamber 3 is located between the top reaction frame 10 and the bottom reaction frame 13 and its two ends are fixedly connected to the two vertical connecting frames respectively. The top reaction frame 10 is provided with a loading hole 11. The loading monitoring cylinder 7 passes through the loading hole 11 at the top of the reaction frame and is fixed to the top of the reaction frame. The bottom reaction frame 13 is provided with a support monitoring hole 12. The support excavation column 4-1 is located in the support monitoring hole 12 and the support monitoring hole 12 is provided with space for the support excavation column 4-1 to move downward. The guide frame 9 is installed at the top of the top reaction frame 10 and the bottom of the bottom reaction frame 13 to limit the horizontal displacement of the first settlement displacement gauge 1 and the second settlement displacement gauge 1-1.

[0038] In a preferred embodiment, the friction plate 4-3 is semi-annular and the inner diameter of the friction plate 4-3 is equal to the outer diameter of the support excavation column 4-1. The structure is simple and can provide the maximum friction coefficient.

[0039] In a preferred embodiment, the variable stiffness support excavation unit 4 further includes an intelligent monitoring and control system 4-5, which is signal-connected to the thruster 4-4 and is used to control the magnitude of the force applied by the thruster 4-4 to the thrust rod 4-2.

[0040] In a preferred embodiment, the monitoring and loading unit includes a loading and monitoring cylinder 7, a thrust plate 2, and a second settling displacement gauge 1-1. The top of the loading and monitoring cylinder 7 is fixedly connected to the top reaction frame 10, and the output component at the bottom of the loading and monitoring cylinder 7 is fixedly connected to the thrust plate 2. The thrust plate 2 is used to contact the rock mass material. A displacement gauge placement groove 8 is provided in the middle of the loading and monitoring cylinder 7 and the thrust plate 2. The second settling displacement gauge 1-1 passes through the displacement gauge placement groove 8, and the bottom of the second settling displacement gauge 1-1 is in contact with the rock mass material. The thruster 4-4 is arranged vertically within the space of the loading and monitoring cylinder 7.

[0041] In a preferred embodiment, the model test apparatus for the variable stiffness tunnel excavation and support process further includes an elastic body placement chamber 6 and an elastic body. The elastic body placement chamber 6 is disposed above the bottom reaction frame 13 and is used to place the elastic body. The elastic body is used to connect each support excavation column 4-1 to transfer the load between each support excavation column 4-1 in the longitudinal direction to simulate the longitudinal stress of the support structure.

[0042] Example 2

[0043] This embodiment also provides a test method using the model test device for the above-mentioned variable stiffness tunnel excavation and support process, including the following steps:

[0044] S1: Set the stiffness of each variable stiffness support excavation unit 4 to k∞, put rock material into the model chamber 3, and start the monitoring loading unit to load until it is stable.

[0045] S2: Adjust the stiffness of the first variable stiffness support excavation unit 4 along the first direction to k1, and the stiffness of the remaining variable stiffness support excavation units 4 is k. ∞ The rock mass material shifts to equilibrium, and the vertical displacement of all support excavation columns 4-1 and the load on support excavation columns 4-1 are recorded.

[0046] S3: Adjust the stiffness of the first variable stiffness support excavation unit 4 along the first direction to k2, the stiffness of the second variable stiffness support excavation unit 4 to k1, and the stiffness of the remaining variable stiffness support excavation units 4 to k2. ∞ The rock mass material shifts to equilibrium, and the vertical displacement of all support excavation columns 4-1 and the load on support excavation columns 4-1 are recorded.

[0047] S4: Adjust the stiffness of the first variable stiffness support excavation unit 4 along the first direction to k3, the stiffness of the second variable stiffness support excavation unit 4 to k2, the stiffness of the third variable stiffness support excavation unit 4 to k1, and the stiffness of the remaining variable stiffness support excavation units 4 to k. ∞ The rock mass material shifts to equilibrium, and the vertical displacement of all support excavation columns 4-1 and the load on support excavation columns 4-1 are recorded.

[0048] S5: Adjust the stiffness of the first variable stiffness support excavation unit 4 along the first direction to k4, the stiffness of the second variable stiffness support excavation unit 4 to k3, the stiffness of the third variable stiffness support excavation unit 4 to k2, the stiffness of the fourth variable stiffness support excavation unit 4 to k1, and the stiffness of the remaining variable stiffness support excavation units 4 to k. ∞ The rock mass material shifts to equilibrium, and the vertical displacement of all support excavation columns 4-1 and the load on support excavation columns 4-1 are recorded.

[0049] S6: Adjust the stiffness of the first variable stiffness support excavation unit 4 along the first direction to k4, the stiffness of the second variable stiffness support excavation unit 4 to k4, the stiffness of the third variable stiffness support excavation unit 4 to k3, the stiffness of the fourth variable stiffness support excavation unit 4 to k2, the stiffness of the fifth variable stiffness support excavation unit 4 to k1, and the stiffness of the remaining variable stiffness support excavation units 4 to k. ∞ The rock mass material shifts to equilibrium, and the vertical displacement of all support excavation columns 4-1 and the load on support excavation columns 4-1 are recorded.

[0050] S7: Repeat this process until the stiffness of the first variable stiffness support excavation unit 4 along the first direction is adjusted to k4, the stiffness of the second variable stiffness support excavation unit 4 is k4, the stiffness of the third variable stiffness support excavation unit 4 is k4, the stiffness of the fourth variable stiffness support excavation unit 4 is k4, the stiffness of the fifth variable stiffness support excavation unit 4 is k3, the stiffness of the sixth variable stiffness support excavation unit 4 is k2, the stiffness of the seventh variable stiffness support excavation unit 4 is k1, and the stiffness of the eighth variable stiffness support excavation unit 4 is k3. ∞ The stiffness of the ninth variable stiffness support excavation unit 4 is k. ∞ The stiffness of the tenth variable stiffness support excavation unit 4 is k. ∞ Record the vertical displacement of all support excavation columns 4-1 and the load on support excavation columns 4-1 when the rock mass material shifts to equilibrium.

[0051] Where k ∞ k1 and k2 decrease progressively, corresponding to three stages of changes in the stiffness of the surrounding rock in front of the tunnel face, while k3 and k4 increase progressively, corresponding to two stages of support stiffness.

[0052] By adjusting the load applied by the loading monitoring cylinder 7 and the stiffness of the variable stiffness support excavation unit 4, and analyzing the corresponding load, the load borne by the support excavation column 4-1, and the displacement values, the longitudinal spatial effect of the tunnel surrounding rock and the synergistic effect of variable stiffness support and surrounding rock can be revealed.

[0053] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A model test device for the variable stiffness tunnel excavation and support process, characterized in that: include: Main framework; The model compartment is fixedly installed on the main frame and is used to hold rock mass materials; Multiple monitoring and loading units distributed along a first direction, one end of each monitoring and loading unit being connected to the top of the main frame, and the other end being used to apply a load force to the top of the rock material in the model chamber; The system also includes multiple variable stiffness support excavation units distributed along a first direction. Each variable stiffness support excavation unit comprises a support excavation column, friction plates, and thrusters. The top of the support excavation column is used to contact the bottom of the rock mass material. The support excavation column passes through the bottom of the main frame. The friction plates are used to contact the sidewalls of the support excavation column and can press against the support excavation column. The thrusters are connected to the friction plates and can apply different loads to the friction plates. The system also includes multiple first settlement displacement gauges, one of which is fixedly connected to the bottom of each support excavation column. The first settlement displacement gauge is used to monitor the vertical displacement of the support excavation column; the main frame includes a frame support column, two vertical connecting frames, a top reaction frame and a bottom reaction frame; it also includes an elastic body placement chamber and an elastic body, the elastic body placement chamber is set above the bottom reaction frame and is used to place the elastic body, the elastic body is used to connect each of the support excavation columns in the longitudinal direction to transfer the load between each of the support excavation columns to simulate the longitudinal force of the support structure; the first direction is the longitudinal excavation direction of the tunnel.

2. The model test device for the variable stiffness tunnel excavation and support process according to claim 1, characterized in that: It also includes a thrust rod, one end of which is detachably connected to the friction plate, and the other end is fixedly connected to the output component of the thruster.

3. The model test device for the variable stiffness tunnel excavation and support process according to claim 2, characterized in that: The main frame includes frame pillars, two vertical connecting frames, a top reaction frame, and a bottom reaction frame. The two vertical connecting frames, the top reaction frame, and the bottom reaction frame are arranged in a ring. The frame pillars are located at the bottom of the bottom reaction frame. The model compartment is located between the top reaction frame and the bottom reaction frame, and its two ends are fixedly connected to the two vertical connecting frames respectively.

4. The model test device for the variable stiffness tunnel excavation and support process according to claim 3, characterized in that: The friction plate is semi-circular, and its inner diameter is equal to the outer diameter of the support excavation column.

5. The model test device for the variable stiffness tunnel excavation and support process according to claim 4, characterized in that: The variable stiffness support excavation unit also includes an intelligent monitoring and control system, which is connected to the thruster signal and is used to control the magnitude of the force applied by the thruster to the thrust rod.

6. The model test device for the variable stiffness tunnel excavation and support process according to claim 3, characterized in that: The monitoring and loading unit includes a loading and monitoring cylinder, a thrust plate, and a second settling displacement gauge. The top of the loading and monitoring cylinder is fixedly connected to the top reaction frame, and the output component at the bottom of the loading and monitoring cylinder is fixedly connected to the thrust plate. The thrust plate is used to contact the rock mass material. A displacement gauge placement slot is provided in the middle of the loading and monitoring cylinder and the thrust plate. The second settling displacement gauge passes through the displacement gauge placement slot, and the bottom of the second settling displacement gauge is in contact with the rock mass material.

7. A test method using a model test apparatus for the variable stiffness tunnel excavation and support process as described in any one of claims 1 to 6, characterized in that: Includes the following steps: S1: Set the stiffness of each variable stiffness support excavation unit to k. ∞ Rock material is placed in the model chamber, and the monitoring and loading unit is activated to load until it stabilizes. S2: Adjust the stiffness of the first variable stiffness support excavation unit along the first direction to k1, and the stiffness of the remaining variable stiffness support excavation units is k. ∞ The rock mass material is displaced to equilibrium, and the vertical displacement of all the support excavation columns and the load on the support excavation columns are recorded. S3: Adjust the stiffness of the first variable stiffness support excavation unit along the first direction to k2, the stiffness of the second variable stiffness support excavation unit to k1, and the stiffness of the remaining variable stiffness support excavation units to k2. ∞ The rock mass material is displaced to equilibrium, and the vertical displacement of all the support excavation columns and the load on the support excavation columns are recorded. S4: Adjust the stiffness of the first variable stiffness support excavation unit along the first direction to k3, the stiffness of the second variable stiffness support excavation unit to k2, the stiffness of the third variable stiffness support excavation unit to k1, and the stiffness of the remaining variable stiffness support excavation units to k. ∞ The rock mass material is displaced to equilibrium, and the vertical displacement of all the support excavation columns and the load on the support excavation columns are recorded. S5: Adjust the stiffness of the first variable stiffness support excavation unit along the first direction to k4, the stiffness of the second variable stiffness support excavation unit to k3, the stiffness of the third variable stiffness support excavation unit to k2, the stiffness of the fourth variable stiffness support excavation unit to k1, and the stiffness of the remaining variable stiffness support excavation units to k. ∞ The rock mass material is displaced to equilibrium, and the vertical displacement of all the support excavation columns and the load on the support excavation columns are recorded. S6: Adjust the stiffness of the first variable stiffness support excavation unit along the first direction to k4, the stiffness of the second variable stiffness support excavation unit to k4, the stiffness of the third variable stiffness support excavation unit to k3, the stiffness of the fourth variable stiffness support excavation unit to k2, the stiffness of the fifth variable stiffness support excavation unit to k1, and the stiffness of the remaining variable stiffness support excavation units to k. ∞ The rock mass material is displaced to equilibrium, and the vertical displacement of all the support excavation columns and the load on the support excavation columns are recorded. S7: This process is repeated until the stiffness of the first variable stiffness support excavation unit along the first direction is adjusted to k4, the stiffness of the second variable stiffness support excavation unit is k4, the stiffness of the third variable stiffness support excavation unit is k4, the stiffness of the fourth variable stiffness support excavation unit is k4, the stiffness of the fifth variable stiffness support excavation unit is k3, the stiffness of the sixth variable stiffness support excavation unit is k2, the stiffness of the seventh variable stiffness support excavation unit is k1, and the stiffness of the eighth variable stiffness support excavation unit is k3. ∞ The stiffness of the ninth variable stiffness support excavation unit is k. ∞ The stiffness of the tenth variable stiffness support excavation unit is k. ∞ And record the vertical displacement of all the support columns and the load on the support columns when the rock mass material shifts to equilibrium; where k ∞ k1 and k2 decrease progressively and correspond to the three stages of rock mass stiffness change in front of the tunnel face, while k3 and k4 increase progressively and correspond to the two stages of support stiffness.

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