A method for testing a circular tunnel mode through a non-uniform soil body

Abstract

The present application relates to a kind of circular tunnel modal test methods crossing non-uniform soil body, the non-uniform soil counterforce equivalent simulation device used includes, the cross section module group of multiple cross section modules, test piece and fixed frame and base track.The zero stiffness composite spring includes metal spiral spring, rubber, spring top end cover, spring fixed screw rod, spring bottom end cover, bottom screw rod, contact plate and displacement-shaft force sensor, steps are as follows: design data arrangement: determine the geometric parameters of circular tunnel, material parameters and soil parameters, determine test scale ratio and the geometric size and discrete length of structure model;Test piece processing;Strain gauge positioning installation;Soil spring parameter calculation;Zero stiffness composite spring debugging;Cross section module assembly;Cross section module group installation;Test piece installation;Sensor debugging;Loading and testing: data acquisition analysis.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of underground structure-soil interaction test, and particularly relates to a modal test method for a circular tunnel penetrating through non-uniform soil. BACKGROUND

[0002] Buried tubular structures are one of the most commonly used engineering structures in production and life, such as oil and gas pipelines, underground tunnels, and buried cables. During the design, construction, and operation of buried tubular structures, their interaction with soil needs to be considered. In particular, buried tubular structures are often elongated and large-span structures, and the soil along their length direction is not uniform, so the underground structure-soil interaction is no longer consistent. Currently, underground structure-soil interaction tests are mainly carried out in field soil sites and artificial soil sites, such as Chinese patent applications 2021103045131, 202123083348.6, and 2020113208802. Field soil site tests can obtain real data of underground structure-soil interaction, and are often considered as a test method that can provide relatively reliable results in engineering. However, original site soil test often needs to arrange related sensors during the construction stage, and later measurement operations can easily damage the field state of buried tubular structures, making field measurement difficult and the cost of test manpower and materials high. Artificial soil site tests effectively overcome the difficulties and shortcomings of original site soil tests, and can simulate various loading conditions in a laboratory environment, so they are widely used in engineering testing and scientific research. Artificial soil site tests need to use centrifuges and other equipment, and go through steps such as consolidation tests to prepare test soil, which has a large amount of work, a complex test process, and a long test cycle. Chinese patent application 202011382075.8 discloses a test device and determination method for simulating a pipeline penetrating through a strike-slip fault, which arranges pressure-bearing parts on both sides of the pipeline and connects the outer peripheral wall of the pipeline through the winding form of a flexible belt, for studying the stress of the pipeline penetrating through different fault displacements and the pipe-soil interaction. This patent can avoid the complex process of test soil preparation, but there is a difference between the loading method of the test model and the theoretical model, and it can only simulate the pipe-soil interaction in a single direction under fault displacement. Therefore, in view of the problems existing in the prior art, it is urgent to provide a buried tubular structure non-uniform soil reaction force equivalent simulation device and simulation method that are theoretically rigorous, simple in structure, and easy to operate. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a modal test method for a circular tunnel penetrating through non-uniform soil on the basis of providing a non-uniform soil reaction force equivalent simulation device. The device is used to simulate the force of the soil around the circular tunnel on its cross section, and to carry out a model test of the circular tunnel structure considering the non-uniform soil reaction force. The technical scheme is as follows:

[0004] The application discloses a mode test method for a circular tunnel crossing a non-uniform soil body, and an equivalent simulation device for a non-uniform soil reaction force.

[0005] The zero-stiffness composite spring 6 comprises a metal spiral spring 10, rubber 11, a spring top end cover 12, a spring fixing screw rod 13, a spring bottom end cover 14, a bottom screw rod 15, a contact plate 16 and a displacement-axial force sensor 18; the metal spiral spring 10 is embedded in the rubber 11; the rubber 11 is connected with the spring top end cover 12 at the top and connected with the spring bottom end cover 14 at the bottom, and the displacement-axial force sensor 18 is arranged in the axial direction of the zero-stiffness composite spring 6; the spring top end cover 12 of the zero-stiffness composite spring 6 is connected to the inner side of the cross-section frame 7 through the spring fixing screw rod 13; and the contact plate 16 is connected to the spring bottom end cover 14 through the bottom screw rod 15.

[0006] The cross-section module 1 comprises the zero-stiffness composite spring 6 and the cross-section frame 7; the cross-section frame 7 is fixedly connected to the base track 4; and the zero-stiffness composite spring 6 is distributed on the inner side of the cross-section frame 7 and fixedly connected with the cross-section frame 7.

[0007] The cross-section module group 5 composed of a plurality of cross-section modules 1 is used for simulating a region with the same soil body property; when a structure is distributed in a non-uniform soil body in the length direction, different cross-section module groups 5 are arranged to simulate non-uniform soil reaction forces.

[0008] The test piece 2 comprises at least one structure model 19, the structure models 19 are axially connected to form the test piece 2, and the test piece 2 is fixed on the base track 4 through the fixing frame.

[0009] The mode test method for the circular tunnel crossing the non-uniform soil body comprises the following steps.

[0010] Step one: design data arrangement: determining geometric parameters, material parameters and soil body parameters of the circular tunnel, determining a test scale ratio, geometric dimensions of the structure model and a discrete length;

[0011] Step two: test piece processing: processing the structure model according to the geometric parameters determined in step one;

[0012] Step three: strain gauge positioning and installation: marking boundary lines of structure discretization on the structure model according to the discrete length determined in step one, the middle section between the two boundary lines being a contact position of the zero-stiffness composite spring; at least six strain gauges are installed in the length direction to obtain the first six bending modes of the circular tunnel, and the contact positions of the zero-stiffness composite spring and the structure model are avoided;

[0013] Step four, soil spring parameter calculation: select the foundation model, consider the interaction between the tunnel and the soil, obtain the soil spring parameters corresponding to the structural geometric parameters and soil parameters, including the maximum soil reaction force per unit length and the relative displacement yield value; according to the test scale ratio and the discrete length, the maximum linear elastic compression load of the zero-stiffness composite spring is calculated as P0, and the corresponding maximum linear elastic compression deformation at this time is calculated as Δ0;

[0014] Step five, zero-stiffness composite spring 6 debugging: according to the calculation results of step four, the zero-stiffness composite spring 6 in each direction is debugged;

[0015] Step six, section module assembly: the zero-stiffness composite spring is installed on the spring fixing threaded hole of the section frame through the spring fixing threaded rod; the contact plate is installed on the bottom screw rod through the contact plate connecting screw rod;

[0016] Step seven, section module group assembly: according to the distribution of the soil in the length direction of the circular tunnel, the number of structural models and section module groups is determined, and the section module is fixed on the base track according to the model unit length;

[0017] Step eight, test piece installation;

[0018] Step nine, sensor debugging: connect the displacement-axial force sensor and the strain gauge to the data acquisition instrument, perform communication debugging, and complete zero adjustment and calibration;

[0019] Step ten, loading and testing: the exciter is used to excite the structural model, the excitation position and the excitation frequency are changed, and the structural model is repeatedly excited;

[0020] Step eleven, data acquisition and analysis: record the displacement-axial force data, strain data and excitation force data of the zero-stiffness composite spring in the exciter; analyze the recorded test data, the frequency and mode of the structural model.

[0021] Further, according to the size of the test piece, the feeding amount of the spring fixing screw rod 13 and the bottom screw rod 15 is adjusted to change the size of the area surrounded by the zero-stiffness composite spring 6 of the section module 1.

[0022] Further, the section frame 7 is a circular square section, and four zero-stiffness composite springs 6 are uniformly distributed inside one section frame 7.

[0023] Further, the base track 4 includes a H-shaped base 23 and a base fixing groove 24; the base fixing groove 24 is located on both sides of the H-shaped base 23 and can pass through the double-headed screw rod, which is used to connect and fix the bracket and the section module 1.

[0024] The present application has the following advantages due to the above technical scheme:

[0025] 1. The test device simulates the soil reaction force by using zero-stiffness composite springs, and does not need a field soil site and an artificial soil site. The parameters of the zero-stiffness composite springs can be adjusted to simulate soil bodies of different strengths, and a large scale test can be selected in the case of a small overall size of the device. The test device not only effectively saves test manpower and resources, but also improves test accuracy.

[0026] 2. The cross-section module follows the mechanical principle of a "buried tubular structure-spring" finite element model. The four zero-stiffness composite springs correspond to the nonlinear soil springs on the upper, lower, left and right sides of the structure unit cross-section in the finite element model. The load-displacement curve of each zero-stiffness composite spring meets the similarity theory with the load-displacement curve of the nonlinear soil spring in the authoritative design specification.

[0027] 3. The cross-section module group can be assembled into a test model of any length. The parameters of the zero-stiffness composite springs of each cross-section module group can be adjusted to simulate the uneven distribution of soil bodies in the length direction of the underground structure, which is difficult to achieve in the traditional artificial soil site test.

[0028] 4. The cross-section module allows the structure model to have relative displacement in any direction within the cross-section. The maximum relative displacement in the upper, lower, left and right directions is the smaller value of one-half the length of the contact plate and the maximum compression deformation of the zero-stiffness composite spring in the corresponding direction.

[0029] 5. The test device is designed in a modular manner. The zero-stiffness composite springs, cross-section modules, cross-section module groups and end fixing frames can be modified and replaced. The mechanical structure is simple, the manufacturing is economical and convenient, and the operation is simple. The test device is suitable for experimental research and teaching of the interaction between underground structures and soil bodies. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Overall view of the test device

[0031] Figure 2 Schematic view of the cross-section module

[0032] Figure 3 Schematic view of the zero-stiffness composite spring

[0033] Figure 4 Schematic view of the test piece

[0034] Figure 5 Schematic view of the end fixing frame

[0035] Figure 6 Schematic view of the base rail

[0036] Figure 7 Schematic view of the load-displacement curve of the zero-stiffness composite spring

[0037] Figure 8Schematic diagram of load-displacement curve of zero-stiffness composite spring

[0038] Figure 9 Schematic diagram of partially suspended buried pipeline

[0039] Figure 10 Schematic diagram of modal test of partially suspended buried pipeline

[0040] Figure 11 Schematic diagram of circular tunnel crossing non-uniform soil

[0041] Figure 12 Schematic diagram of modal test of circular tunnel crossing non-uniform soil

[0042] Explanation of figure reference: 1 - cross section module; 2 - test piece; 3 - end fixing frame; 4 - base track; 5 - cross section module group; 6 - zero-stiffness composite spring; 7 - cross section frame; 8 - base fixing hole; 9 - spring fixing threaded hole; 10 - metal coil spring; 11 - rubber; 12 - spring top end cover; 13 - spring fixing screw rod; 14 - spring bottom end cover; 15 - bottom screw rod; 16 - contact plate; 17 - contact plate connecting screw rod; 18 - displacement-axial force sensor; 19 - structural model; 20 - test piece flange plate; 21 - flange fixing hole; 22 - end flange frame; 23 - back-to-back base; 24 - base fixing groove DETAILED DESCRIPTION

[0043] In order to make the personnel in the technical field better understand the present application scheme, the technical scheme in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor should belong to the scope of protection of the present application.

[0044] It should be noted that the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, device, product or equipment containing a series of steps or units does not have to be limited to the clearly listed steps or units, but can include other steps or units not clearly listed or inherent to these processes, methods, products or equipment.

[0045] The test piece used in the equivalent simulation device for non-uniform soil reaction of buried tubular structure of the present application can be various buried tubular structures. The embodiments of the present application mainly involve two structures, one is a steel buried pipeline, and the other is a circular tunnel.

[0046] The buried tubular structure non-uniform soil reaction equivalent simulation device comprises a section module 1, a test piece 2, an end fixing frame 3, a base track 4 and a section module group 5.

[0047] The section module 1 comprises a zero-stiffness composite spring 6, a section frame 7, a bottom fixing hole 8 and a spring fixing threaded hole 9. According to the symmetry of the buried tubular structure, the section frame 7 is preferably a square section with rounded corners. The spring fixing threaded hole 9 is located at the center of the four sides of the section frame 7 and is used to install the zero-stiffness composite spring 6. The bottom fixing hole 8 is located at the symmetrical position of the bottom edge of the section frame 7 and can pass through a double-headed screw rod, which is used for the fixed connection of the section frame 7 and the base track 4.

[0048] The zero-stiffness composite spring 6 comprises a metal spiral spring 10, a rubber 11, a spring top end cover 12, a spring fixing screw rod 13, a spring bottom end cover 14, a bottom screw rod 15, a contact plate 16, a contact plate connecting screw rod 17 and a displacement-axial force sensor 18. Preferably, the zero-stiffness composite spring 6 adopts a straight cylinder type composite spring recommended in the literature (Zero-stiffness composite spring[J]. China University Technology Market, 1996(12): 5-6.), which has the characteristics of ordinary composite springs and a significant characteristic of having a large corresponding offset when having zero stiffness. When the maximum linear elastic compression deformation of the zero-stiffness composite spring 6 is Δ0, Δ1 is the maximum compression deformation allowed by the zero-stiffness of the zero-stiffness composite spring 6. When the axial action of the zero-stiffness composite spring 6 has a pressure load P (i.e. P < P0) or the compression deformation of the zero-stiffness composite spring is Δ < Δ0, the metal spiral spring 10 and the rubber 11 are compressed at the same time, and the P-Δ curve is linearly elastic. When the P value increases further (P0 < P or Δ0 < Δ < Δ1), the metal spiral spring 10 generates compression deformation and exhibits positive stiffness, the rubber 11 between the pitches of the metal spiral spring 10 changes from compression deformation to shear deformation and expands between the pitches, and the elastic modulus decreases to 1 / 3 of the original value and exhibits negative stiffness. The positive and negative stiffnesses are offset after being combined, and the zero-stiffness is exhibited. According to actual needs, the maximum compression deformation Δ1 entering the zero-stiffness should be greater than or equal to the maximum relative displacement that may occur between the underground structure and the soil. The P-Δ curve shape can be adjusted to meet the requirements of different types of soil. The nonlinear soil spring load displacement curve of the zero-stiffness composite spring 6 meets the similarity theory as specified in the standard SY / T0450-2004 "Anti-seismic design specification for oil (gas) steel pipelines" and ALA-2001 "Guidelines for the design of buried steel pipe", P0 corresponds to the maximum soil reaction on the structure discrete length, and Δ0 corresponds to the structure-soil relative displacement yield value.

[0049] Metallic coil spring 10 is embedded in rubber 11. Rubber 11 is in the shape of a circular ring, with its top connected to spring top end cap 12 and its bottom connected to spring bottom end cap 14. Inside the rubber 11 is installed displacement-axial force sensor 18. Preferably, the size of the area surrounded by the four zero stiffness composite springs 6 in the cross section module 1 can be changed by adjusting the feed amount of spring fixing screw rod 13 and bottom screw rod 15 according to the needs of the test pipe. Spring fixing screw rod 13 cooperates with spring fixing threaded hole 9 to connect zero stiffness composite spring 6 and cross section frame 7.

[0050] The bottom side plane of contact plate 16 is in contact with test pipe 2, and the center of the top side plane is welded with contact plate connecting screw rod 17. Contact plate connecting screw rod 17 is connected to bottom screw rod 15 through the threaded hole on the end face of bottom screw rod 15. Preferably, contact plate 16 is a flat plate, allowing test piece 2 to move in its contact plane, ensuring that contact plate 16 and test piece 2 only have pressure action when they are in contact. The length of contact plate 16 should be less than test piece 2, so that the four contact plates 16 in the cross section module 1 will not interfere with each other under the relative displacement of the structure-soil in any direction after installation. In the upper, lower, left and right directions in the cross section, the maximum value of the allowable relative displacement of the underground structure-soil is the smaller value of one-half of the length of the contact plate 16 and the maximum compression deformation Δ1 of the corresponding zero stiffness composite spring 6.

[0051] The working principle of cross section module 1 follows the mechanical principle of the "buried tubular structure-spring" finite element model. The finite element model often uses a nonlinear soil spring model to describe the force of the surrounding soil on the pipeline. The four zero stiffness composite springs 6 of the cross section module 1 correspond to the nonlinear soil springs on the nodes of the finite element structure unit or the midpoint of the structure unit, with directions respectively horizontal right, horizontal left, vertical up and vertical down, used to simulate the soil reaction force on a unit pipe length. According to the test measurement results published in the literature (Rofooei F R, Jalali H H, Attari N, et al. Parametric study of buried steel and high density polyethylene gas pipelines due to oblique-reverse faulting [J]. Canadian Journal of Civil Engineering, 2015, 42(3): 178-189.), when the structure and the soil have relative displacement, the force of the soil on the tension side of the structure can be ignored, and the soil reaction force only appears on the compression side of the structure. Therefore, zero stiffness composite spring 6 only works under axial compression load.

[0052] The test piece 2 includes a structural model 19, a test piece flange plate 20, and a flange fixing hole 21. The structural model 19 is a full-size or scaled model of a buried tubular structure. When the end boundary condition of the structural model 19 is completely fixed, the test piece flange plate 20 is welded at the end of the structural model 19, and the double-end screw rod is connected to the end fixing frame 3 through the flange fixing hole 21. Preferably, the flange fixing hole 21 is arranged in a circular array on the test piece flange plate with at least 8 holes to ensure the reliability of the connection. When the end boundary condition of the structural model 19 is simply supported, a circular flat plate of the same material, thickness, and outer diameter should be welded at the end of the structural model 19. The center of the flat plate is welded with a connecting rod, and then the flat plate is clamped with a foam vibration isolator. Preferably, the implementation of the simply supported boundary condition can refer to Chinese patent applications 2021103757600 and 2021103757757. When the end boundary condition of the structural model 19 is completely free, the end of the structural model 19 does not require additional connection treatment.

[0053] The end fixing frame 3 includes a base fixing hole 8, a flange fixing hole 21, and an end flange frame 22. The end flange frame 22 is an end flange plate with a bottom support. Preferably, the flange fixing hole 21 is arranged in a circular array on the end flange plate with at least 8 holes to ensure the reliability of the connection. The base fixing hole 8 is located at the symmetrical position of the two sides of the bottom support, and can pass through a double-end screw rod for fixed connection of the end fixing frame 3 and the base track 4.

[0054] The base track 4 includes a H-shaped base 23 and a base fixing groove 24. The base fixing groove 24 is located on both sides of the H-shaped base 23 and can pass through a double-end screw rod for fixed connection of the end fixing frame 3 and the cross-section module 1 with the base track 4. Preferably, the base fixing groove 24 can not only reduce the weight of the device, but also allow the end fixing frame 3 and the cross-section module 1 to be installed at any position of the base fixing groove 24.

[0055] The cross-section module group 5 includes a plurality of identical cross-section modules 1 for simulating areas with the same soil properties. When the soil along the structure length direction is non-uniform, different cross-section module groups 5 are set to simulate the non-uniform soil reaction force.

[0056] The circular tunnel is the main structure form of the urban underground transportation system. The non-uniform soil circular tunnel modal test is used to study the influence of the non-uniform soil along the way on the vibration characteristics of the circular tunnel. When the test piece adopts a circular pipeline structure model, the non-uniform soil circular tunnel modal test method is as follows:

[0057] Step one, design data collection. According to the project design data, the geometric parameters, material parameters and soil parameters of the circular tunnel are determined, including the outer diameter, wall thickness, lengths of buried sections 1, 2 and 3, elastic modulus, material yield stress, burial depth, soil cohesion, overburden effective unit weight, natural soil effective unit weight, natural soil total unit weight, static earth pressure coefficient and internal friction angle, etc. The test scale ratio and the geometric dimensions and discrete length of the structural model 19 are determined.

[0058] Step two, test piece 2 processing. The structural model 19 is processed according to the geometric dimensions determined in step one. The end boundary condition of the structural model 19 is completely free, and no additional connection treatment is required at the end.

[0059] Step three, strain gauge positioning and installation. According to the discrete length determined in step one, the structural discrete boundary lines are marked on the structural model 19, and the intermediate section between the two boundary lines is the contact position of the zero-stiffness composite spring 6. In order to obtain the first six bending modes of the circular tunnel, at least six strain gauges are installed in the length direction, and attention should be paid to avoiding the contact position of the zero-stiffness composite spring 6 and the structural model 19.

[0060] Step four, soil spring parameter calculation. A suitable foundation model (e.g. the most commonly used Winkler foundation model) is selected to consider the interaction between the tunnel and the soil (Selvadurai A P S. Elastic analysis of soil and foundation interaction [M]. Fan Wen Tian, Beijing: China Railway Press, 1984, 16-23.), and the soil spring parameters corresponding to the structural geometric parameters and soil parameters are obtained, including the maximum soil reaction per unit length and the relative displacement yield value; P0 and Δ0 of the zero-stiffness composite spring 6 are calculated according to the test scale ratio and the discrete length.

[0061] Step five, zero-stiffness composite spring 6 debugging. According to the calculation results of step four, the zero-stiffness composite spring 6 in each direction is debugged to make its P-Δ curve meet the similarity theory with the nonlinear soil spring load-displacement curve specified in the design specification.

[0062] Step six, cross-section module 1 assembly. The zero-stiffness composite spring 6 is installed on the spring fixing threaded hole 9 of the cross-section frame 7 through the spring fixing threaded rod 13; the contact plate 16 is installed on the bottom screw rod 15 through the contact plate connecting screw rod 17.

[0063] Step seven, cross-section module group 5 installation. The double-headed screw rod passes through the base fixing hole 8 and the base fixing slot 24, and the cross-section module 1 is fixed on the base track 4 according to the model unit length one by one. According to the distribution of the soil in the length direction of the circular tunnel, three cross-section module groups 5 need to be arranged in turn.

[0064] Step eight, test piece 2 installation. First, adjust the feed amount of spring fixing screw rod 13 and bottom screw rod 15 so that the square area surrounded by four zero-stiffness composite springs 6 in cross-section module 1 is slightly larger than the outer diameter of test piece 2. Then, pass test piece 2 through each cross-section module group 5. Install end fixing frame 3 on base rail 4 by passing double-end screw rod through base fixing hole 8 and base fixing slot 24. Finally, fine-tune the feed amount of spring fixing screw rod 13 and bottom screw rod 15 so that the contact plate 16 of zero-stiffness composite spring 6 is in contact with test piece 2. Except for the bottom zero-stiffness composite spring 6, the contact axial force of other zero-stiffness composite springs 6 is zero.

[0065] Step nine, sensor debugging. Connect displacement-axial force sensor 18 and strain gauge to data acquisition instrument, perform communication debugging, and complete zeroing and calibration.

[0066] Step ten, loading and testing. Use exciter to excite structural model 19. Change excitation position and excitation frequency to repeatedly excite structural model 19.

[0067] Step eleven, data acquisition and analysis. Record displacement-axial force data, strain data and excitation force data in exciter of zero-stiffness composite spring 6 by data acquisition instrument; analyze recorded test data, frequency and mode of structural model 19. Preferably, the strain data analysis method uses the method recommended in the literature (Trim AD, Braaten H, Lie H, et al. Experimental investigation of vortex-induced vibration of long marinerisers [J]. Journal of Fluids & Structures, 2005, 21(3):335-361).

[0068] Step twelve, device disassembly and storage. After the test is completed, sequentially disassemble end fixing frame 3, test piece 2, cross-section module group 5, cross-section module 1, zero-stiffness composite spring 6 and base rail 4, and arrange and store them.

[0069] The specific embodiments of the application are described in detail above with reference to the accompanying drawings, but the application is not limited to the above-described embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the application.

Claims

1. A modal test method for a circular tunnel traversing non-uniform soil, wherein the non-uniform soil reaction equivalent simulation device comprises a cross-section module group (5) consisting of multiple cross-section modules (1), a test specimen (2), a fixing frame, and a base track (4), wherein: The zero-stiffness composite spring (6) includes a metal helical spring (10), rubber (11), a spring top cap (12), a spring fixing screw (13), a spring bottom cap (14), a bottom screw (15), a contact plate (16), and a displacement-axial force sensor (18). The metal helical spring (10) is embedded in the rubber (11). The top of the rubber (11) is connected to the spring top cap (12), and the bottom is connected to the spring bottom cap (14). The displacement-axial force sensor (18) is arranged along the axial direction of the zero-stiffness composite spring (6). The spring top cap (12) of the zero-stiffness composite spring (6) is connected to the inside of the cross-section frame (7) through the spring fixing screw (13). The contact plate (16) is connected to the spring bottom cap (14) through the bottom screw (15). The cross-section module (1) includes a zero-stiffness composite spring (6) and a cross-section frame (7); the cross-section frame (7) is fixedly connected to the base track (4); the zero-stiffness composite spring (6) is distributed on the inner side of the cross-section frame (7) and fixedly connected to the cross-section frame (7); A section module group (5) consisting of multiple section modules (1) is used to simulate areas with the same soil properties; when the soil is non-uniformly distributed along the length of the structure, different section module groups (5) are set to simulate non-uniform soil reaction forces. The test piece (2) includes at least one structural model (19), and the test piece (2) is formed by axially connecting the structural models (19). The test piece (2) is fixed on the base rail (4) by a fixing frame. The modal test method for a circular tunnel traversing non-uniform soil includes the following steps: Step 1: Data Compilation: Determine the geometric parameters, material parameters, and soil parameters of the circular tunnel; determine the experimental scale ratio and the geometric dimensions and discrete lengths of the structural model. Step 2, Test Specimen Fabrication: Fabricate the structural model according to the geometric parameters determined in Step 1; Step 3: Strain gauge positioning and installation: Based on the discrete length determined in Step 1, mark the discrete boundary lines of the structure on the structural model. The intermediate section between the two boundary lines is the contact position of the zero-stiffness composite spring. To obtain the first 6 bending modes of the circular tunnel, install at least 6 strain gauges along the length direction, and take care to avoid the contact position between the zero-stiffness composite spring and the structural model. Step 4: Calculation of soil spring parameters: Using a foundation model, considering the interaction between the tunnel and the soil, the soil spring parameters corresponding to the structural geometric parameters and soil parameters are obtained, including the maximum soil reaction force per unit length and the relative displacement yield value. Based on the experimental scaling ratio and discrete length, the maximum linear elastic compressive load of the zero-stiffness composite spring is calculated to be P0, and the corresponding maximum linear elastic compressive deformation is: 0; Step 5: Zero-stiffness composite spring adjustment: Adjust the zero-stiffness composite springs in each direction according to the calculation results in Step 4; Step 6: Section module assembly: The zero-stiffness composite spring is installed on the spring fixing threaded hole of the section frame through the spring fixing screw rod; the contact plate is installed on the bottom screw rod through the contact plate connecting screw rod. Step 7: Section module assembly installation: Based on the soil distribution along the length of the circular tunnel, determine the number of structural models and section module assemblies, and fix each section module onto the base track one by one according to the unit length of the model; Step 8: Test specimen installation; Step 9, Sensor Debugging: Connect the displacement-axial force sensor and strain gauge to the data acquisition instrument, perform communication debugging, and complete zeroing and calibration; Step 10, Loading and Testing: Excite the structural model using a vibrator, changing the excitation position and frequency, and repeatedly excite the structural model. Step 11: Data Acquisition and Analysis: Record the displacement-axial force data, strain data, and excitation force data in the vibrator of the zero-stiffness composite spring; analyze the recorded test data to obtain the frequency and modes of the structural model.

2. The modal test method for a circular tunnel traversing non-uniform soil as described in claim 1, characterized in that, Based on the size of the test piece, the size of the area enclosed by the zero-stiffness composite spring (6) of the cross-section module (1) is changed by adjusting the feed amount of the spring fixing screw (13) and the bottom screw (15).

3. The modal test method for a circular tunnel traversing non-uniform soil as described in claim 1, characterized in that, The cross-section frame (7) is a rounded square cross-section, and four zero-stiffness composite springs (6) are evenly distributed inside the cross-section frame (7).

4. The modal test method for a circular tunnel traversing non-uniform soil as described in claim 1, characterized in that, The base track (4) includes a U-shaped base (23) and a base fixing groove (24); the base fixing groove (24) is located on both sides of the U-shaped base (23) and can pass through a double-headed screw rod for connecting the fixing frame and the section module (1).

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