Servo-controlled stiffness-variable static-dynamic loading test system for tunnel linings

Abstract

A servo-controlled stiffness-variable static-dynamic loading test system for tunnel linings, comprising a servo-controlled stiffness-variable test system. The servo-controlled stiffness-variable test system comprises a stiffness-variable test loading system, a monitoring system, a vibration platform (3), a hydraulic pump station, and a control system. By means of adjusting the stiffness-variable test loading system, the present application can simulate tests of tunnels with a plurality of stiffness ranges at different positions in the circumferential direction and in the axial direction under a compressed state according to test requirements, and can also simulate dynamic response characteristics of tunnels under the compressed state by means of the vibration platform (3), so as to more accurately meet indoor test requirements of tunnels under compression and earthquake conditions. During loading, data monitored by the monitoring system is fed back to the control system in real time; and on the basis of the monitoring data and a preset stiffness value, the control system adjusts the pressurization magnitude of the stiffness-variable test loading system in real time, thereby realizing high-precision motion control.

Description

A Servo-Controlled Static-Dynamic Loading Test System for Variable Stiffness Tunnel Lining Technical Field

[0001] This invention relates to the field of tunnel engineering testing equipment technology, and in particular to a servo-controlled variable stiffness tunnel lining static-dynamic loading test system. Background Technology

[0002] Traditional tunnel and underground engineering model tests typically utilize similar material model testing systems. First, the similarity ratio of the model is determined based on the requirements of the prototype and the indoor laboratory conditions. Materials such as quartz sand, gypsum, glycerin, and water are mixed and proportioned to separately cast the surrounding rock and lining models. This process is not only labor-intensive but also consumes a large amount of materials, making the tests relatively time-consuming and labor-intensive. Another approach is to use mechanical devices to pressurize the tunnel lining model. Multiple hydraulic loading devices are arranged along the circumferential direction of the lining to apply and control the load. This effectively reduces manual labor and material preparation, saving time and effort. However, because the loading stiffness in the mechanical pressurization system is a constant value, different levels of surrounding rock can only be characterized by changing springs with different stiffnesses, increasing the difficulty of the test process. Currently, mechanical pressurization devices are mostly used for studying the strength and deformation characteristics of two-dimensional tunnel models under static loads, lacking the design and development of corresponding three-dimensional devices for dynamic loads (seismic action). Located between two major seismic belts in the world—the Circum-Pacific Seismic Belt and the Eurasian Seismic Belt—my country experiences frequent and active seismic activity in the region. Nearly half of its land area is located in high-intensity seismic zones of intensity 7 or higher. The comprehensive and rapid development of my country's transportation engineering means that tunnel projects will inevitably be built in high-intensity areas. Therefore, it is essential to develop an experimental system that can simultaneously assess the evolution of tunnel mechanical properties under seismic loads. Summary of the Invention

[0003] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0004] In view of the problems existing in the above and / or existing tunnel similar material model test systems, the present invention is proposed.

[0005] Therefore, the technical problem to be solved by this invention is that traditional model tests require determining the similarity ratio of the model based on the requirements of the on-site prototype and indoor laboratory conditions, and using materials such as quartz sand, gypsum, glycerin and water to adjust the proportions and pour the surrounding rock and lining models separately. This not only involves a large workload and consumes a lot of materials, but also makes the test relatively time-consuming and labor-intensive. Secondly, the loading stiffness of the mechanical pressurization system is a constant value, and different levels of surrounding rock can only be characterized by changing springs with different stiffnesses, which increases the difficulty of the test process. Furthermore, currently, mechanical pressurization devices are mostly used for the study of strength and deformation characteristics of two-dimensional tunnel models under static loads, and there is a lack of design and development of corresponding three-dimensional devices under dynamic loads (seismic action).

[0006] To achieve the above objectives, the present invention provides the following technical solution: a servo-controlled variable stiffness tunnel lining static-dynamic loading test system, comprising a servo-controlled variable stiffness test system, which includes a variable stiffness test loading system, a monitoring system, a vibration platform, a hydraulic pump station, and a control system;

[0007] The variable stiffness test loading system includes a first reaction frame, a second reaction frame, a first support, a second support, a pressure head assembly, and a lining fixing base;

[0008] The first and second reaction frames are equipped with tunnel lining specimens. One end face of the first support is fixed to the first and second reaction frames by bolts, and the other end face of the first support is fixed to the vibration platform by bolts. One end face of the second support is fixed to the first and second reaction frames by bolts, and the other end face of the second support is fixed to the vibration platform by bolts.

[0009] There are four lining fixing bases. The tunnel lining specimen is placed on the lining fixing base, and the lining fixing base is located between the first support and the second support, and is fixedly connected to the first support and the second support by bolts.

[0010] The pressure head assembly consists of a servo electric cylinder, guide rods, a fixed flange, a pressure sensor, a displacement sensor, and an arc-shaped clamping plate. The servo electric cylinder is fixedly mounted on the fixed flange, and a guide rail is provided below the servo electric cylinder. The displacement sensor is mounted on the bottom end of the servo electric cylinder. There are two guide rods, which pass through the guide rail, the fixed flange, and the side of the displacement sensor. The bottom ends of the two guide rods are mounted on arc-shaped clamping plates, and the pressure sensor is fixedly mounted on the top of the arc-shaped clamping plates.

[0011] The vibration platform is divided into an upper platform, a middle platform, a lower platform, a servo cylinder, and fixed feet. The upper platform is mounted on top of the middle platform, the middle platform is mounted on top of the lower platform, the servo cylinder is installed on the upper platform and the middle platform, and the lower platform is fixed to the fixed feet.

[0012] As a further aspect of the present invention: the displacement sensor and the pressure sensor constitute a monitoring system.

[0013] As a further aspect of the present invention: the axial lengths of the first reaction frame and the second reaction frame are 1m respectively;

[0014] The axial lengths of the first and second supports are 2m each.

[0015] As a further embodiment of the present invention: the middle platform and the lower platform of the vibration platform are connected by a slide rail, and the middle platform generates X-axis movement under the action of the servo cylinder;

[0016] The upper platform and the middle platform are also connected by slide rails, and the upper platform generates Y-axis movement under the action of the servo cylinder.

[0017] The vibration frequency of the vibration platform is within 0-20Hz.

[0018] As a further aspect of the present invention: each of the first and second reaction frames is provided with nine mounting holes, and each mounting hole has a scale line on one side, with an annular spacing of 22.5° between the mounting holes;

[0019] Two pressure head assemblies are installed on each mounting hole of the first and second reaction frames. The fixed flange and guide rail cooperate to make the pressure head assembly slide linearly in the mounting hole.

[0020] As a further aspect of the present invention: the arc-shaped clamp is a detachable structure, and a rubber pad is fixedly connected to the inner surface of the arc-shaped clamp;

[0021] The arc-shaped clamp is made of metal, and the curvature of the arc-shaped clamp is consistent with the curvature of the corresponding part of the tunnel lining specimen.

[0022] As a further aspect of the present invention: the servo electric cylinder consists of a loading cylinder and a stiffness adjusting cylinder.

[0023] As a further aspect of the present invention: the first reaction frame and the second reaction frame are made of Q235 steel, which are welded from steel plates and square tubes, and then heat-treated and powder-coated after welding.

[0024] As a further aspect of the present invention: the servo electric cylinder of the pressure head assembly and the servo cylinder of the vibration platform are powered by a hydraulic pump station.

[0025] As a further aspect of the present invention: the data monitored by the displacement sensor and the pressure sensor are fed back to the control system in real time, and the control system adjusts the pressure of the stiffness regulating cylinder in real time according to the displacement monitored by the displacement sensor and the preset stiffness value.

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

[0027] 1. This servo-controlled variable stiffness tunnel lining static-dynamic loading test system can simulate tests of various stiffness ranges at different positions in the circumferential and axial directions of a tunnel under compression, by adjusting the variable stiffness loading system. It can also simulate the dynamic response characteristics of a tunnel under compression through a vibration system, thus accurately meeting the indoor testing requirements for tunnels under compression and seismic conditions. Furthermore, during loading, the pressure head assembly can be adjusted to simulate static-dynamic load tests on tunnel linings with cavities behind the tunnel, satisfying the mechanical performance testing requirements for damaged tunnels.

[0028] 2. This servo-controlled variable stiffness tunnel lining static-dynamic loading test system uses an electro-hydraulic servo system to achieve load control, resulting in low noise, energy saving, and environmental friendliness. It connects to PLC and other control systems to achieve high-precision motion control. Furthermore, this device uses a pressure head assembly to concentrate force instead of surrounding rock load, reducing the rock pouring process and achieving automated characterization of surrounding rock stiffness. It eliminates the need to replace springs of different stiffnesses, saving time and effort, and is easy to operate.

[0029] 3. This servo-controlled variable stiffness tunnel lining static-dynamic loading test system, through the design of a vibration platform, can be applied to the test of the deformation characteristics of tunnel lining under dynamic load. This device can simultaneously meet the performance test of tunnel lining under static-dynamic load, and can also realize the performance evaluation and damage evolution law study of damaged tunnel lining. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of 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. Wherein:

[0031] Figure 1 is a three-dimensional structural schematic diagram of a servo-controlled variable stiffness tunnel lining static-dynamic loading test system according to an embodiment of the present invention.

[0032] Figure 2 is a schematic diagram of the vibration platform in a servo-controlled variable stiffness tunnel lining static-dynamic loading test system according to an embodiment of the present invention.

[0033] Figure 3 is a three-dimensional structural schematic diagram of the first reaction frame in a servo-controlled variable stiffness tunnel lining static-dynamic loading test system according to an embodiment of the present invention.

[0034] Figure 4 is a three-dimensional structural schematic diagram of the pressure head assembly in a servo-controlled variable stiffness tunnel lining static-dynamic loading test system according to an embodiment of the present invention.

[0035] Figure 5 is a schematic diagram showing the division of the cross-section of the tunnel lining specimen of the present invention.

[0036] Figure 6 shows the variation of the yield strength of the tunnel lining specimen with the size of the void in the arch of the tunnel lining specimen under different loading stiffnesses according to the present invention.

[0037] Figure 7 is a schematic diagram showing the change of strain at the top of the tunnel lining specimen over time.

[0038] Figure 8 is a schematic diagram showing the variation of strain in the lining arch under different ground motion intensities according to the present invention.

[0039] In the figure: 1 - First reaction frame; 11 - Mounting hole; 2 - Second reaction frame; 3 - Vibration platform; 31 - Upper platform; 32 - Middle platform; 33 - Lower platform; 34 - Fixed foot; 4 - Pressure head assembly; 41 - Servo electric cylinder; 42 - Guide rod; 43 - Fixed flange; 44 - Pressure sensor; 46 - Displacement sensor; 45 - Arc-shaped clamp; 5 - First support; 6 - Lining fixing base; 7 - Tunnel lining specimen; 8 - Second support. Detailed Implementation

[0040] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0041] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0042] Secondly, the present invention will be described in detail with reference to the schematic diagrams. When describing the embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure will be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In addition, actual fabrication should include the three-dimensional spatial dimensions of length, width, and depth.

[0043] Furthermore, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that mutually excludes other embodiments.

[0044] Detailed Implementation

[0045] As shown in Figures 1-8, the servo-controlled variable stiffness tunnel static-dynamic loading test system provided by this invention patent is implemented as follows:

[0046] A servo-controlled variable stiffness tunnel lining static-dynamic loading test system, characterized in that: it includes a servo-controlled variable stiffness test system, which comprises a variable stiffness test loading system, a monitoring system, a vibration platform 3, a hydraulic pump station, and a control system;

[0047] The variable stiffness test loading system includes a first reaction frame 1, a second reaction frame 2, a first support 5, a second support 8, a pressure head assembly 4, and a lining fixing base 6. The axial lengths of the first reaction frame 1 and the second reaction frame 2 are 1m and 2m respectively, and the axial lengths of the first support 5 and the second support 8 are 2m respectively. Each of the first reaction frame 1 and the second reaction frame 2 has nine mounting holes 11, and each mounting hole 11 has a scale line on one side. The annular spacing of the mounting holes 11 is 22.5°. Two pressure head assemblies 4 are installed in each mounting hole 11 of the first reaction frame 1 and the second reaction frame 2. The fixing flange 43 and the guide rail cooperate to make the pressure head assembly 4 slide linearly in the mounting hole 11. The first reaction frame 1 and the second reaction frame 2 are made of Q235 steel, which is welded from steel plates and square tubes. After welding, the steel plates are heat-treated and powder-coated. The servo electric cylinder 41 of the pressure head assembly 4 and the servo cylinder of the vibration platform 3 are powered by a hydraulic pump station.

[0048] The first reaction frame 1 and the second reaction frame 2 contain tunnel lining specimens 7. The tunnel lining specimens 7 can be of various shapes, such as horseshoe or circular. The prototype of the lining model is made of reinforced C25 or C30 concrete. Such test models are cast according to the length and strength similarity ratio. There are two first supports 5 and two second supports 8. One end face of the first support 5 is fixed to the first reaction frame 1 and the second reaction frame 2 by bolts. The other end face of the first support 5 is fixed to the vibration platform 3 by bolts. One end face of the second support 8 is fixed to the first reaction frame 1 and the second reaction frame 2 by bolts. The other end face of the second support 8 is fixed to the vibration platform 3 by bolts.

[0049] There are four lining fixing bases 6. The tunnel lining specimen 7 is placed on the lining fixing base 6. The lining fixing base 6 is located between the first support 5 and the second support 8 and is fixedly connected to the first support 5 and the second support 8 by bolts.

[0050] The pressure head assembly 4 consists of a servo electric cylinder 41, a guide rod 42, a fixed flange 43, a pressure sensor 44, a displacement sensor 46, and an arc-shaped clamping plate 45. The arc-shaped clamping plate 45 is a detachable structure, and by replacing the arc-shaped clamping plate 45, the pressure requirements of tunnel lining models of different shapes can be met. A rubber pad is fixedly connected to the inner surface of the arc-shaped clamping plate 45 to increase anti-slip properties. The arc-shaped clamping plate 45 is made of metal, and its curvature is consistent with the curvature of the corresponding part of the tunnel lining specimen 7, thereby ensuring uniform stress on the tunnel lining specimen 7. The displacement sensor 46 and the pressure sensor 44 form a monitoring system, which are used to monitor the displacement and pressure magnitude of the tunnel lining specimen 7 during the test process, respectively. The data monitored by displacement sensor 46 and pressure sensor 44 are fed back to the control system in real time. The control system adjusts the pressure of stiffness adjustment cylinder in real time according to the displacement monitored by displacement sensor 46 and the preset stiffness value. Servo electric cylinder 41 is fixedly installed on fixed flange 43. A guide rail is provided below servo electric cylinder 41. Displacement sensor 46 is installed at the bottom of servo electric cylinder 41. There are two guide rods 42. The guide rods 42 can be used to limit the loading direction. The guide rods 42 pass through the guide rail, fixed flange 43 and the side of displacement sensor 46. Arc-shaped clamping plate 45 is installed at the bottom of the two guide rods 42. Pressure sensor 44 is fixedly installed above arc-shaped clamping plate 45. Servo electric cylinder 41 consists of loading cylinder and stiffness adjustment cylinder.

[0051] The vibration platform 3 is divided into an upper platform 31, a middle platform 32, a lower platform 33, a servo cylinder, and a fixed foot 34. The upper platform 31 is mounted above the middle platform 32, and the middle platform 32 is mounted above the lower platform 33. Servo cylinders are installed on the upper platform 31 and the middle platform 32. The lower platform 33 is fixed to the fixed foot 34, which is installed and fixed on a pre-poured concrete foundation. Since strong vibrations will be generated during the test, to prevent the entire machine from moving and the vibration platform 3 from interfering with the surrounding environment, the middle platform 32 and the lower platform 33 of the vibration platform 3 are connected by slide rails. The middle platform 32 moves along the X-axis under the action of the servo cylinder. The upper platform 31 is also connected to the middle platform 32 by slide rails. The upper platform 31 moves along the Y-axis under the action of the servo cylinder. Through the X and Y axis movements, the tunnel lining specimen 7 can achieve unidirectional movement along the X-axis, unidirectional movement along the Y-axis, or synchronous combined movement along the X and Y axes. The vibration frequency of the vibration platform 3 is within 0-20Hz.

[0052] Example 1

[0053] This embodiment relates to a static loading method for a tunnel lining test system. This method is based on a servo-controlled variable stiffness tunnel static-dynamic loading test system to meet the requirements of loading tests with different stiffnesses. Specifically, it includes the following steps:

[0054] First, based on the size of the test system and the provided load limit value, the geometric similarity ratio and strength similarity ratio of the tunnel lining specimen 7 are determined. The mass ratio of gypsum and water is adjusted according to the determined strength similarity ratio to pour the tunnel lining specimen 7 with the required strength. The poured tunnel lining specimen 7 is then cured. After curing, the tunnel lining specimen 7 is fixed on the lining fixing base 6. The number and pressure position of the pressure head assembly 4 are selected according to the test requirements. The initial position of the arc-shaped clamp 45 is adjusted. During static loading, the vibration platform 3 remains fixed and in a non-working state.

[0055] This example uses a tunnel lining with voids in the arch as an example, but the test system is not limited to void defects; it can also be used for linings with cracks, linings with reduced strength, etc. Figure 5 shows the cross-section of the tunnel lining specimen 7. The arc-shaped clamping plate 45 of the pressure head assembly 4 at the arch top is not in contact with the outer surface of the tunnel lining specimen 7, thus simulating voids behind the tunnel lining specimen 7. According to field research, stress concentration occurs near the voids in the lining. Therefore, the pressure of the pressure head assembly 4 at the arch shoulder of the tunnel lining specimen is selected as the yield strength evaluation index of the lining. After the tunnel lining specimen 7 is installed, the preset stiffness required for the test is set, and then the servo electric cylinder 41 begins to pressurize the lining through the arc-shaped clamping plate 45. After the tunnel lining specimen 7 is loaded, the displacement sensor 46 and the pressure sensor 44 transmit the data to the control system in real time. The control system adjusts the actual loading pressure of the stiffness regulating cylinder in real time based on the data fed back by the displacement sensor 46 and the preset stiffness. The pressure head assembly 4 continuously loads the specimen, ensuring that the loading stiffness meets the preset stiffness and remains constant, until the tunnel lining specimen 7 becomes unstable and fails, thus completing the loading test. The peak pressure of the pressure head assembly 4 at the arch shoulder is recorded as the yield strength of the tunnel lining specimen 7. During the test, a high-pixel camera is used to collect the deformation and crack evolution characteristics of key parts of the lining specimen. By adjusting different loading stiffnesses and loading multiple times, specimen loading tests can be carried out under different loading stiffnesses. Figure 6 shows the yield strength of the tunnel lining specimen 7 under different stiffnesses, i.e., under different surrounding rock grades, when the arch top contains cavities of different sizes. It can be seen that the yield strength of the lining increases significantly with the increase of the surrounding rock grade.

[0056] Example 2

[0057] This embodiment relates to a vibration loading method for a tunnel lining test system. This method, based on a servo-controlled variable stiffness tunnel static-dynamic loading test system, fulfills the requirements for loading tests under dynamic load conditions. Specifically, it includes the following steps:

[0058] Before applying the dynamic load, the tunnel lining specimen 7 is fixed on the lining fixing base 6. Strain gauges are attached to the inner surface of the tunnel lining specimen 7. The position of the arc-shaped clamp 45 of the pressure head assembly 4 is adjusted to fit against the outer surface of the tunnel lining specimen 7. Then, the actual loading pressure and stiffness value of the servo electric cylinder 41 are adjusted to the preset test values. This process can also be completed with reference to Example 1. During the application of the dynamic load, the seismic wave excitation signals with different vibration frequencies and intensities are input to the vibration platform 3 through the control system to achieve unidirectional movement along the X-axis, unidirectional movement along the Y-axis, or synchronous composite movement along the X and Y axes. The dynamic strain at the crown is recorded, as shown in Figure 7. Figure 8 shows the extreme values ​​of strain at the crown under different seismic wave intensities. It can be seen that the tensile and compressive strains increase significantly with the increase of seismic intensity, and the tunnel lining specimen 7 is severely damaged.

[0059] It is important to note that the constructions and arrangements of this application shown in several different exemplary embodiments are merely illustrative. Although only a few embodiments are described in detail in this disclosure, those who consult this disclosure will readily understand that many modifications are possible (e.g., changes in the size, dimensions, structure, shape, and proportions of various elements, as well as parameter values ​​(e.g., temperature, pressure, etc.), mounting arrangements, use of materials, color, orientation, etc.) without substantially departing from the novel teachings and advantages of the subject matter described in this application). For example, an element shown as integrally formed may be composed of multiple parts or elements, the position of elements may be inverted or otherwise altered, and the nature or number or position of discrete elements may be changed or altered. Therefore, all such modifications are intended to be included within the scope of the invention. The order or sequence of any process or method steps may be changed or rearranged according to alternative embodiments. In the claims, any "device plus function" clause is intended to cover the structure described herein that performs the function, and not only structurally equivalent but also equivalent in structure. Other substitutions, modifications, alterations, and omissions may be made in the design, operation, and arrangement of the exemplary embodiments without departing from the scope of the invention. Therefore, the present invention is not limited to the specific embodiments, but extends to various modifications that still fall within the scope of the appended claims.

[0060] Furthermore, in order to provide a concise description of exemplary embodiments, not all features of actual embodiments (i.e., those features that are not relevant to the currently considered best mode for carrying out the invention, or those features that are not relevant to implementing the invention) may be omitted.

[0061] It should be understood that numerous specific implementation decisions can be made during the development of any practical implementation, such as in any engineering or design project. Such development efforts may be complex and time-consuming, but for those skilled in the art who benefit from this disclosure, the development effort will be a routine work of design, manufacturing, and production without requiring much experimentation.

[0062] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A servo-controlled static-dynamic loading test system for variable stiffness tunnel lining, characterized in that: It includes a servo-controlled variable stiffness test system, which includes a variable stiffness test loading system, a monitoring system, a vibration platform (3), a hydraulic pump station, and a control system; The variable stiffness test loading system includes a first reaction frame (1), a second reaction frame (2), a first support (5), a second support (8), a pressure head assembly (4), and a lining fixing base (6); The first reaction frame (1) and the second reaction frame (2) are equipped with tunnel lining specimens (7). One end face of the first support (5) is fixed to the first reaction frame (1) and the second reaction frame (2) by bolts. The other end face of the first support (5) is fixed to the vibration platform (3) by bolts. One end face of the second support (8) is fixed to the first reaction frame (1) and the second reaction frame (2) by bolts. The other end face of the second support (8) is fixed to the vibration platform (3) by bolts. There are four lining fixing bases (6). The tunnel lining specimen (7) is placed on the lining fixing base (6). The lining fixing base (6) is located between the first support (5) and the second support (8) and is fixedly connected to the first support (5) and the second support (8) by bolts. The pressure head assembly (4) consists of a servo electric cylinder (41), guide rods (42), a fixed flange (43), a pressure sensor (44), a displacement sensor (46), and an arc-shaped clamping plate (45). The servo electric cylinder (41) is fixedly installed on the fixed flange (43). A guide rail is provided below the servo electric cylinder (41). The displacement sensor (46) is installed at the bottom of the servo electric cylinder (41). There are two guide rods (42). The guide rods (42) pass through the guide rail, the fixed flange (43), and the side of the displacement sensor (46). The arc-shaped clamping plate (45) is installed at the bottom of the two guide rods (42). The pressure sensor (44) is fixedly installed above the arc-shaped clamping plate (45). The vibration platform (3) is divided into an upper platform (31), a middle platform (32), a lower platform (33), a servo cylinder, and a fixed foot (34). The upper platform (31) is mounted on top of the middle platform (32), and the middle platform (32) is mounted on top of the lower platform (33). Servo cylinders are installed on the upper platform (31) and the middle platform (32). The lower platform (33) is fixed to the fixed foot (34). The middle platform (32) and the lower platform (33) of the vibration platform (3) are connected by slide rails. The middle platform (32) generates X-axis motion under the action of the servo cylinder. The upper platform (31) and the middle platform (32) are also connected by a slide rail. The upper platform (31) moves along the Y axis under the action of the servo cylinder. The vibration frequency of the vibration platform (3) is within 0-20Hz; The first reaction frame (1) and the second reaction frame (2) are each provided with nine mounting holes (11), and each mounting hole (11) has a scale line on one side. The annular spacing of the mounting holes (11) is 22.5°. Two pressure head assemblies (4) are installed on each mounting hole (11) of the first reaction frame (1) and the second reaction frame (2). The fixed flange (43) and the guide rail cooperate to make the pressure head assembly (4) slide linearly in the mounting hole (11). The data monitored by the displacement sensor (46) and pressure sensor (44) are fed back to the control system in real time. The control system adjusts the pressure of the stiffness regulating cylinder in real time according to the displacement monitored by the displacement sensor (46) and the preset stiffness value.

2. The servo-controlled variable stiffness tunnel lining static-dynamic loading test system as described in claim 1, characterized in that: The displacement sensor (46) and pressure sensor (44) together form a monitoring system.

3. The servo-controlled variable stiffness tunnel lining static-dynamic loading test system as described in claim 1, characterized in that: The axial lengths of the first reaction frame (1) and the second reaction frame (2) are 1m respectively; The axial lengths of the first support (5) and the second support (8) are 2m respectively.

4. The servo-controlled variable stiffness tunnel lining static-dynamic loading test system as described in claim 1, characterized in that: The arc-shaped clamp (45) is a detachable structure, and a rubber pad is fixedly connected to the inner surface of the arc-shaped clamp (45); The arc-shaped clamp (45) is made of metal, and the arc of the arc-shaped clamp (45) is consistent with the arc of the corresponding part of the tunnel lining specimen (7).

5. The servo-controlled variable stiffness tunnel lining static-dynamic loading test system as described in claim 1, characterized in that: The servo electric cylinder (41) consists of a loading cylinder and a stiffness adjustment cylinder.

6. The servo-controlled variable stiffness tunnel lining static-dynamic loading test system as described in claim 1, characterized in that: The first reaction frame (1) and the second reaction frame (2) are made of Q235 steel, and are made of steel plate and square tube welded together. After welding, they are heat treated and powder coated.

7. The servo-controlled variable stiffness tunnel lining static-dynamic loading test system as described in claim 1, characterized in that: The servo electric cylinder (41) of the pressure head assembly (4) and the servo cylinder of the vibration platform (3) are powered by a hydraulic pump station.

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