Soft rock tunnel buffer layer model test device and test method

Abstract

The invention discloses a soft rock tunnel buffer layer model test device and test method, and belongs to the technical field of geotechnical engineering.The soft rock tunnel buffer layer model test device comprises an outer box, and the outer box comprises a bottom plate, a top plate and four side plates which are fixedly connected; a first round steel sheet is arranged between the top plate and the bottom plate and is a cylindrical hollow steel sheet, the top end of the first round steel sheet is welded with the edge of the round hole of the top plate, and the bottom end is welded with the bottom plate; a simulation surrounding rock is arranged in the outer box; a second round steel sheet, a third round steel sheet and a fourth round steel sheet are arranged on the inner side of the first round steel sheet; a primary support is cast between the first round steel sheet and the second round steel sheet, and a secondary lining is cast between the third round steel sheet and the fourth round steel sheet; and a buffer layer is arranged between the primary support and the secondary lining. Real deformation of different buffer layer materials in a tunnel is simulated through the tunnel detection model, and the performance of the buffer layer materials can be detected under three different working conditions of radial yielding, annular yielding and simultaneous existence of the radial direction and the annular direction.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical engineering, and in particular relates to a soft rock tunnel buffer layer model test device and a test method. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] In recent years, it has been difficult for traditional composite lining structures to meet the long-term deformation characteristics of soft surrounding rock in tunnels. Studies have shown that the use of buffer energy-absorbing materials can achieve coordinated deformation with soft surrounding rock, and can achieve continuous deformation while ensuring strength, which is a hot topic in current research.

[0004] In order to solve the problem of tunnel deformation, the compression support system must not only meet the coordinated deformation of the tunnel surrounding rock and the support structure, but also have the characteristics of light weight, high specific energy absorption, low cost, and easy construction. However, the mechanical properties of the current buffer energy-absorbing materials, such as slag, ceramsite, polyurethane foam materials, etc., are difficult to meet the above requirements at the same time, and there are no relevant specifications for support parameters, and the construction process is extremely imperfect. Therefore, it is necessary to find a new buffer layer material to meet the corresponding requirements.

[0005] At present, there is a lack of understanding of the basic mechanical properties of buffer and energy-absorbing materials in tunnels and their compression-yielding mechanism, which has resulted in the inability to unify the parameter design and construction process of compression-yielding support, limiting the application of buffer and compression-yielding support technology in tunnels and underground projects.

[0006] The reasons are, on the one hand, the geological conditions of tunnel construction are complex, making it difficult to conduct tests on site, and field tests are often accompanied by disadvantages such as high cost, poor applicability and economy. Therefore, the performance of common buffer energy-absorbing materials is mostly tested through numerical simulation; on the other hand, the buffer energy-absorbing materials have not been studied under various working conditions; and finally, the preparation cycle of new buffer energy-absorbing materials is relatively long, such as fly ash geopolymers and other materials, and the raw material ratio during preparation will affect the various properties of the materials. Summary of the invention

[0007] In view of the above problems, the present invention provides a soft rock tunnel buffer layer model test device and test method, which can simulate the actual deformation of the buffer layer material in the tunnel through a tunnel detection model, and can design buffer layers of different thicknesses under three different working conditions of radial yielding, circumferential yielding and simultaneous existence of radial and circumferential directions, to test the mechanical and yielding properties of the buffer layer material.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] In a first aspect, a soft rock tunnel buffer layer model test device is provided, comprising an outer box, the outer box being fixedly arranged on a base, the outer box comprising a bottom plate, a top plate and four side plates which are fixedly connected;

[0010] The top plate and the bottom plate are of the same size and shape, except that a circular hole is provided at the center of the top plate;

[0011] A first round steel sheet is arranged between the top plate and the bottom plate. The first round steel sheet is a cylindrical hollow steel sheet. The top end of the first round steel sheet is welded to the edge of the circular hole of the top plate, and the bottom end is welded to the bottom plate.

[0012] Simulated surrounding rock is arranged in the outer box; the second round steel sheet, the third round steel sheet and the fourth round steel sheet are arranged on the inner side of the first round steel sheet; the space between the first round steel sheet and the second round steel sheet is used for casting and making the initial support, and the space between the third round steel sheet and the fourth round steel sheet is used for casting and making the secondary lining; a buffer layer is provided between the initial support and the secondary lining.

[0013] Preferably, a loading device is provided on each of the side plates, the output end of the loading device passes through the center of the side plate and is slidably connected thereto, and the output end is fixedly connected to the loading plate.

[0014] Preferably, the centers of the first round steel sheet, the second round steel sheet, the third round steel sheet and the fourth round steel sheet are all the same as the center of the bottom plate; the second round steel sheet, the third round steel sheet and the fourth round steel sheet all have multiple specifications, and the difference between each specification lies in the size of its diameter.

[0015] Preferably, the simulated surrounding rock is made by filling sand in an outer box or 3D printing lime sand.

[0016] Preferably, a buffer layer material is poured into the buffer layer;

[0017] Alternatively, multiple compressible units are evenly arranged in the buffer layer and then poured with ordinary concrete;

[0018] Alternatively, the buffer layer is divided into two layers, one layer is uniformly provided with a plurality of compressible units and then poured with ordinary concrete, and the other layer is poured with the buffer layer material.

[0019] Preferably, optical fiber sensors need to be placed on the buffer layer, simulated surrounding rock, secondary lining and compressible unit during the manufacturing process.

[0020] Preferably, after the buffer layer is manufactured, a strain gauge is pasted on the inner side of the fourth round steel sheet. The strain gauge is arranged at four pressurized positions. In each position, the strain gauge is arranged at 1 / 3 and 2 / 3 of the longitudinal position of the fourth round steel sheet. The strain gauge is connected to a static strain gauge.

[0021] In a second aspect, a test method of a soft rock tunnel buffer layer model test device is provided, using the above-mentioned soft rock tunnel buffer layer model test device, and the specific steps are as follows:

[0022] S1: According to the thickness requirement of the reserved buffer layer, select the corresponding second round steel sheet, the third round steel sheet, and the fourth round steel sheet, and place the three selected round steel sheets in the outer box;

[0023] S2, pouring initial support and secondary lining, followed by curing. After the curing is completed, the second and third round steel sheets are removed to reserve a buffer layer;

[0024] S3. Select appropriate buffer layer materials, cast and make the buffer layer, set optical fiber sensors in the buffer layer, and then perform maintenance; after the maintenance is completed, install strain gauges on the inner side of the fourth round steel sheet;

[0025] S4, controlling the loading devices on the four sides of the outer box to load simultaneously, and after the loading is completed, obtaining the deformation displacement of the buffer layer material and the strain of the fourth round steel sheet;

[0026] S5, replacing the buffer layer material in S3 with conventional concrete material to make a buffer layer, and remaining operations remain unchanged, obtaining the deformation displacement of the buffer layer made of conventional concrete material and the strain of the fourth circular steel sheet;

[0027] S6. Compare the test results of S4 and S5 to verify the protection and pressure-relieving effect of the buffer layer material on the secondary lining, so as to determine whether the deformation of the buffer layer and secondary lining meets the tunnel deformation requirements.

[0028] Preferably, in step S3, before pouring the buffer layer, the selected buffer layer material is first subjected to a strength test, specifically, the buffer layer material is subjected to a strength test through a uniaxial compression test to determine the feasibility of fly ash geopolymer as the buffer layer material;

[0029] Firstly, the buffer layer material test blocks are made according to the ratios of different raw materials, and then the test blocks with different ratios are subjected to uniaxial compression tests to obtain their mechanical property curves; finally, it is determined whether the mechanical property curves corresponding to the test blocks with each ratio have an obvious buffer yielding stage.

[0030] Preferably, in step S3, not only the radial pressure yielding condition test can be performed, but also the circumferential pressure yielding condition test or the circumferential pressure yielding and radial pressure yielding condition test can be performed.

[0031] Compared with the prior art, the present invention has the following advantages and positive effects:

[0032] The present invention designs a soft rock tunnel buffer layer model test device to simulate the actual deformation of different buffer layer materials in the tunnel, and can design buffer layers of different thicknesses under three different working conditions of radial yielding, circumferential yielding and simultaneous existence of radial and circumferential directions, and test the mechanical and yielding properties of different buffer layer materials; thereby testing the basic mechanical properties of the buffer layer material and its yielding mechanism, as well as the effects and performance under different yielding mechanisms.

[0033] The present invention performs strength tests on the selected buffer layer materials in advance, obtains mechanical property curves of test blocks of the buffer layer materials with various ratios, determines whether the buffer layer materials with the ratios have obvious buffering pressure-yielding stages, and determines whether the buffer layer materials with the ratios are feasible as buffer layer materials, thereby shortening the preparation cycle of the buffer layer materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0035] Figure 1 It is a front view of the tunnel detection model of embodiment 1 or 2 of the present invention;

[0036] Figure 2 is embodiment 1 or 2 of the present invention Figure 1 Middle AA section view;

[0037] Figure 3 is embodiment 1 or 2 of the present invention Figure 2 Enlarged view of point B in the middle;

[0038] Figure 4 Schematic diagram of the coexistence of radial pressure relief and annular pressure relief of the buffer layer of Embodiment 1 or 2 of the present invention;

[0039] Figure 5 is a flow chart of Embodiment 2 of the present invention;

[0040] Figure 6 is a schematic diagram of a mechanical property curve in Example 2 of the present invention;

[0041] In the figure:

[0042] 1. Outer box; 11. Bottom plate; 12. Top plate; 13. Side plate; 14. First round steel sheet; 15. Loading plate; 16. Second round steel sheet; 17. Third round steel sheet; 18. Fourth round steel sheet; 2. Base; 3. Loading device; 4. Simulated surrounding rock; 5. Initial support; 6. Secondary lining; 7. Buffer layer; 71. Compressible unit. DETAILED DESCRIPTION

[0043] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0044] The present invention is described in detail below in conjunction with the accompanying drawings.

[0045] Example 1

[0046] This embodiment discloses a soft rock tunnel buffer layer model test device, such as Figure 1 As shown, it includes an outer box 1. In this embodiment, the size of the outer box is 0.8m*0.8m*0.5m. The outer box 1 is set on the base 2. The outer box 1 includes a bottom plate 11, a top plate 12 and four side plates 13. The four edges of the bottom plate 11 are fixedly connected to the four side plates 13, and the four side plates 13 are fixedly connected. The top plate 12 is consistent with the bottom plate 11 in size and shape, and the difference is that a circular hole is provided at the center of the top plate 12; a first round steel sheet 14 is provided between the top plate 12 and the bottom plate 11, and the first round steel sheet 14 is a cylindrical hollow steel sheet, and the center of the first round steel sheet 14 is the same point as the center of the bottom plate 11; the top end of the first round steel sheet 14 is welded to the edge of the circular hole of the top plate 12, and the bottom end is welded to the bottom plate 11, thereby forming a closed box body.

[0047] like Figure 1 , Figure 2 As shown, a loading device 3 is disposed on each side plate 13, and four loading devices 3 are respectively disposed on the four side plates of the outer box 1. It can be understood that the loading device can be a servo electric cylinder, the output end of the servo electric cylinder passes through the center of the side plate 13 and is slidably connected thereto, and the output end is fixedly connected to the loading plate 15.

[0048] In this embodiment, simulated surrounding rock 4 is arranged in the outer box 1, and the simulated surrounding rock 4 is made by filling sand or 3D printed lime sand in the outer box 1; it can be understood that the simulated surrounding rock 4 is first filled in the outer box 1, and then the top plate 12 is closed. Filling the simulated surrounding rock 4 needs to be filled in steps, and optical fiber sensors are placed during the filling process to monitor the strain information inside it.

[0049] like Figure 2 , Figure 3 As shown, a second round steel sheet 16 , a third round steel sheet 17 , and a fourth round steel sheet 18 are also provided on the inner side of the first round steel sheet. It can be understood that the centers of the first round steel sheet 14 , the second round steel sheet 16 , the third round steel sheet 17 , and the fourth round steel sheet 18 are all the same as the center of the bottom plate 11 .

[0050] In this embodiment, the second round steel sheet 16, the third round steel sheet 17, and the fourth round steel sheet 18 all have a variety of specifications, and the difference between each specification lies in the size of its diameter.

[0051] like Figure 2 As shown, the second round steel sheet 16, the third round steel sheet 17, and the fourth round steel sheet 18 are placed inside the first round steel sheet and temporarily fixed; concrete is poured between the first round steel sheet 14, the second round steel sheet 16, and between the third round steel sheet 17 and the fourth round steel sheet 18 to make the initial support 5 and the secondary lining 6. According to the specification requirements, the strength of the concrete is not less than C20. After curing, the second round steel sheet 16 and the third round steel sheet are removed; the second round steel sheet 16 and the third round steel sheet 17 reserve a buffer layer 7. It should be noted that when making the secondary lining 6, it needs to be poured in steps, and a light sensor is placed during the pouring process to monitor the strain information inside it.

[0052] It is understandable that before pouring, the thickness of the second round steel sheet and the third round steel sheet are taken into account when reserving the buffer layer, and a release agent is applied to the corresponding round steel sheet to facilitate the removal of the corresponding round steel sheet after curing, so as to prevent the strength of the concrete from being destroyed due to the connection between the round steel sheet and the concrete when the round steel sheet is removed.

[0053] It can also be understood that by changing the different second round steel sheets 16, the third round steel sheets 17, and the fourth round steel sheets 18, the thickness of the initial support and the secondary lining can be changed, and the thickness of the buffer layer between the initial support and the secondary lining can also be changed. After the second round steel sheet and the third round steel sheet are removed, the buffer layer 7 is cast between the initial support and the secondary lining using the buffer layer material. It should be noted that optical fiber sensors need to be placed during the casting process of the buffer layer material, and the casting is divided into multiple steps. The optical fiber sensor is used to measure the internal strain information of the buffer layer material. In this embodiment, the strain information monitored by each optical fiber sensor is accurately obtained through the FOR-1 portable single-channel optical fiber signal reader.

[0054] According to the yielding mechanism, the yielding support is summarized into two categories: radial yielding and circumferential yielding. When only buffer layer material is arranged in the buffer layer 7, the radial yielding function is played.

[0055] A circumferential pressure relief device can be set in the buffer layer so that the buffer layer only plays the circumferential pressure relief function. In this embodiment, a compressible unit 71 is used as the circumferential pressure relief device. The specific operation is that before pouring the buffer layer 7, a compressible unit 71 is first set. The compressible unit 71 uses a compressible material, which is generally of two types, the first is a porous material, and the second is a high compressibility element. In this embodiment, a porous material is used to fill the compressible unit, and the porous material is EPS foam concrete; in the reserved space of the buffer layer, a blocking steel sheet is placed on both sides of the compression unit, and EPS foam concrete is poured between the blocking steel sheet, the initial support, and the secondary lining, and then cured. After the curing is completed, the blocking steel sheet is removed, and finally ordinary concrete is poured. It can be understood that the release agent is also applied to the blocking steel sheet; the number of compressible units 71 is multiple, and they are evenly arranged along the circumference of the buffer layer, and their function is to realize the circumferential pressure relief function. It can be understood that an optical fiber sensor is also placed when pouring EPS foam concrete.

[0056] In this embodiment, the buffer layer can also play the role of circumferential and radial pressure relief, and its specific operation is as follows: Figure 4 As shown, a third round steel sheet is placed between the initial support and the secondary lining. This third round steel sheet can divide the buffer layer into two layers; one layer is set with annular pressure relief, and the other layer is set with radial pressure relief; it can be understood that there is no requirement for the casting order of the two buffer layers.

[0057] After the buffer layer is poured, strain gauges are pasted on the inner side of the fourth round steel sheet 18. The strain gauges are set at the four pressurized positions. At each position, the strain gauges are set at the longitudinal 1 / 3 and 2 / 3 of the fourth round steel sheet 18, for a total of eight strain gauges. The strain gauges are connected to static strain gauges to measure the strain of the secondary lining.

[0058] It can be understood that by controlling the four loading devices to apply pressure at the same time, the simulated surrounding rock is subjected to uniform force on all four sides and squeezed inward at the same time. The squeezing force is evenly transmitted to the initial support through the first round steel sheet, and then to the buffer layer, and finally to the secondary lining.

[0059] Example 2

[0060] This embodiment discloses a test method for a soft rock tunnel buffer layer model test device, using a soft rock tunnel buffer layer model test device disclosed in Example 1.

[0061] like Figure 5 As shown, the specific steps are as follows:

[0062] S1: According to the thickness requirement of the reserved buffer layer, select the corresponding second round steel sheet, the third round steel sheet, and the fourth round steel sheet, and place the three selected round steel sheets in the outer box;

[0063] S2, pouring initial support and secondary lining, followed by curing. After the curing is completed, the second and third round steel sheets are removed to reserve a buffer layer;

[0064] S3. Select appropriate buffer layer materials, cast and make the buffer layer, set optical fiber sensors in the buffer layer, and then perform maintenance; after the maintenance is completed, install eight strain gauges on the fourth round steel sheet;

[0065] S4, controlling the loading devices on the four sides of the outer box to load simultaneously, and after the loading is completed, obtaining the deformation displacement of the buffer layer material and the strain of the fourth round steel sheet;

[0066] S5, replacing the buffer layer material in S3 with conventional concrete material to make a buffer layer, and remaining operations remain unchanged, obtaining the deformation displacement of the buffer layer made of conventional concrete material and the strain of the fourth circular steel sheet;

[0067] S6. Compare the test results of S4 and S5 to verify the protection and pressure-relieving effect of the buffer layer material on the secondary lining, so as to determine whether the deformation of the buffer layer and secondary lining meets the tunnel deformation requirements.

[0068] In step S3, a suitable buffer layer material is selected. In order to be close to the environmental protection theme, this embodiment uses fly ash geopolymer material. It can be understood that the buffer energy absorbing material can also be other materials, and its mechanical properties and pressure-yielding properties can be tested by the method of this embodiment.

[0069] In step S3, before pouring the buffer layer, it is necessary to perform a uniaxial compression test on the selected buffer layer material; in this embodiment, the fly ash geopolymer is subjected to a strength test. Specifically, the fly ash geopolymer test block is subjected to a strength test through a uniaxial compression test to determine the feasibility of using the fly ash geopolymer as a buffer layer material.

[0070] Specifically, firstly, fly ash geopolymer test blocks were prepared according to the ratio of different raw materials. In this embodiment, test blocks with liquid-to-solid ratios of 0.44 and 0.55 were prepared. The test block size was a standard cylindrical model with a diameter of 50 mm and a height of 100 mm. Subsequently, uniaxial compression tests were performed on different types of fly ash geopolymer test blocks to obtain their mechanical property curves, such as Figure 6 shown.

[0071] By comparing the obtained mechanical characteristic curve with the qualified curve, it is determined whether the mix ratio has an obvious buffering and pressure-releasing stage; having a buffering and pressure-releasing stage indicates that the material has a large deformation capacity, can absorb the deformation of the surrounding rock, protect the secondary lining, and can be used as a buffer and energy-absorbing material in tunnel engineering. Figure 6As shown in the figure, by comparing the stress-strain curves of the test blocks with liquid-to-solid ratios of 0.44 and 0.55, it is found that the buffering yielding stage of the curve of the test block with a liquid-to-solid ratio of 0.55 is more obvious, and the buffering yielding stage curve is flatter. Therefore, the fly ash geopolymer material with a liquid-to-solid ratio of 0.55 is selected as the buffer layer material.

[0072] Through uniaxial compression test, the qualified ratio of stress-strain curve of fly ash geopolymer specimen is obtained, and the buffer layer material is adjusted according to this ratio, and then poured in layers to ensure that it bears pressure evenly during loading after completion.

[0073] In step S3, not only radial pressure relief test can be performed, but also circumferential pressure relief or circumferential pressure relief and radial pressure relief coexistence test can be performed.

[0074] After verifying the feasibility of the fly ash geopolymer specimens, the mechanical properties test of the tunnel model can be carried out by casting fly ash geopolymer materials of different thicknesses to study the influence of different density and thickness conditions on the secondary lining, which can serve as a reference for the actual application of the material in tunnel engineering.

[0075] In addition to being able to conduct tunnel model tests on buffer layer materials of different material types to determine whether the materials meet the tunnel deformation requirements, the present invention can also set other devices suitable for circumferential pressure relief in the model to conduct mechanical property research. Moreover, since the model can be equipped with circumferential pressure relief devices and radial pressure relief materials at the same time, multiple groups of control tests can be carried out in the circumferential, radial and combination directions.

[0076] The tunnel model of the present invention is applied to the study of the mechanical properties of new buffer layer materials and annular pressure-yielding devices, mainly for studying the feasibility of new buffer layer materials and annular pressure-yielding devices in resisting tunnel deformation in actual application tunnels. It can clearly reflect the mechanical properties of different types of new buffer layer materials and annular pressure-yielding devices, and serve as a reference for these materials and devices in the actual application of tunnel engineering.

[0077] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A soft rock tunnel buffer layer model test device, characterized in that: It includes an outer box, which is fixedly arranged on the base, and includes a bottom plate, a top plate and four side plates that are fixedly connected; The top plate and the bottom plate are of the same size and shape, except that a circular hole is provided at the center of the top plate; A first round steel sheet is arranged between the top plate and the bottom plate. The first round steel sheet is a cylindrical hollow steel sheet. The top end of the first round steel sheet is welded to the edge of the circular hole of the top plate, and the bottom end is welded to the bottom plate. Simulated surrounding rock is arranged in the outer box; the second round steel sheet, the third round steel sheet and the fourth round steel sheet are arranged on the inner side of the first round steel sheet; the space between the first round steel sheet and the second round steel sheet is used for casting and making the initial support, and the space between the third round steel sheet and the fourth round steel sheet is used for casting and making the secondary lining; a buffer layer is provided between the initial support and the secondary lining.

2. A soft rock tunnel buffer layer model test device as claimed in claim 1, characterized in that: A loading device is arranged on each of the side plates, the output end of the loading device passes through the center of the side plate and is slidably connected thereto, and the output end is fixedly connected with the loading plate.

3. A soft rock tunnel buffer layer model test device as claimed in claim 1, characterized in that: The centers of the first round steel sheet, the second round steel sheet, the third round steel sheet and the fourth round steel sheet are all the same as the center of the bottom plate; the second round steel sheet, the third round steel sheet and the fourth round steel sheet all have multiple specifications, and the difference between each specification lies in the size of its diameter.

4. A soft rock tunnel buffer layer model test device as claimed in claim 1, characterized in that: The simulated surrounding rock is made by filling sand in an outer box or 3D printing lime sand.

5. A soft rock tunnel buffer layer model test device as claimed in claim 1, characterized in that: pouring a buffer layer material in the buffer layer; Alternatively, multiple compressible units are evenly arranged in the buffer layer and then poured with ordinary concrete; Alternatively, the buffer layer is divided into two layers, one layer is uniformly provided with a plurality of compressible units and then poured with ordinary concrete, and the other layer is poured with the buffer layer material.

6. A soft rock tunnel buffer layer model test device as claimed in claim 1, characterized in that: Optical fiber sensors need to be placed on the buffer layer, simulated surrounding rock, secondary lining and compressible unit during the manufacturing process.

7. A soft rock tunnel buffer layer model test device as claimed in claim 1, characterized in that: After the buffer layer is manufactured, a strain gauge is pasted on the inner side of the fourth round steel sheet. The strain gauge is arranged at four pressurized positions. In each position, the strain gauge is arranged at 1 / 3 and 2 / 3 of the longitudinal position of the fourth round steel sheet. The strain gauge is connected to a static strain gauge.

8. A test method for a soft rock tunnel buffer layer model test device, using a soft rock tunnel buffer layer model test device as claimed in any one of claims 1 to 7, characterized in that: The specific steps are as follows: S1: According to the thickness requirement of the reserved buffer layer, select the corresponding second round steel sheet, the third round steel sheet, and the fourth round steel sheet, and place the three selected round steel sheets in the outer box; S2, pouring initial support and secondary lining, followed by curing. After the curing is completed, the second and third round steel sheets are removed to reserve a buffer layer; S3. Select appropriate buffer layer materials, cast and make the buffer layer, set optical fiber sensors in the buffer layer, and then perform maintenance; after the maintenance is completed, install strain gauges on the inner side of the fourth round steel sheet; S4, controlling the loading devices on the four sides of the outer box to load simultaneously, and after the loading is completed, obtaining the deformation displacement of the buffer layer material and the strain of the fourth round steel sheet; S5, replacing the buffer layer material in S3 with conventional concrete material to make a buffer layer, and remaining operations remain unchanged, obtaining the deformation displacement of the buffer layer made of conventional concrete material and the strain of the fourth circular steel sheet; S6. Compare the test results of S4 and S5 to verify the protection and pressure-relieving effect of the buffer layer material on the secondary lining, so as to determine whether the deformation of the buffer layer and secondary lining meets the tunnel deformation requirements.

9. The test method of the soft rock tunnel buffer layer model test device according to claim 8, characterized in that: In the step S3, before pouring the buffer layer, the selected buffer layer material is first subjected to a strength test. Specifically, the buffer layer material is subjected to a strength test through a uniaxial compression test to determine the feasibility of fly ash geopolymer as a buffer layer material; Firstly, the buffer layer material test blocks are made according to the ratios of different raw materials, and then the test blocks with different ratios are subjected to uniaxial compression tests to obtain their mechanical property curves; finally, it is determined whether the mechanical property curves corresponding to the test blocks with each ratio have an obvious buffer yield stage.

10. A soft rock tunnel buffer layer model test device test method as claimed in claim 8, characterized in that: In step S3, not only radial pressure relief test can be performed, but also circumferential pressure relief or circumferential pressure relief and radial pressure relief coexisting test can be performed.

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