Model test device and method for researching tunnel face-advance-shotcrete-anchor support synergistic effect mechanism

Abstract

The invention discloses a model test device and method for researching a tunnel face-advance-shotcrete-anchor support synergistic effect mechanism, a model test system is mainly composed of the model test device, a simulation excavation device and a monitoring system, and corresponding test steps are given; the model test box is filled with a surrounding rock similar material, a soil pressure acquisition sensor, a primary support structure, a tunnel face support structure and an advance support structure are pre-buried in the surrounding rock similar material, and the anchoring layer is provided with a camera device and a light source outside the model test box. And the stress detection sensor, the soil pressure acquisition sensor and the camera device are connected with the computer.

Description

Technical Field

[0001] The invention relates to the research field of mountain tunnel engineering technology, and in particular to a model test device and a test method for studying the synergistic effect of tunnel face-advance-sprayed anchor support. Background Art

[0002] In the field of tunnel engineering, model test is an important research method to study the mechanical effects of tunnel excavation and the mechanical properties of support. In existing research, many scholars have used model test methods to study the mechanical effects of tunnel excavation, and the research results are relatively mature; at the same time, the research results of the mechanical properties of tunnel support using model test methods are also relatively mature, including the study of the mechanical properties of tunnel advance support, initial support and other support types.

[0003] However, existing research lacks the study on the synergistic effect of the tunnel face, advance support and initial support. There is no model test device that can intuitively analyze the synergistic effect among the three, and the corresponding test method has not yet been proposed.

[0004] The current status of testing on the tunnel face, advance support and initial support mechanism is mainly reflected in the following two aspects:

[0005] (1) The existing research on the mechanism of action of tunnel face and advance support mainly assumes that the initial support of the tunnel is a rigid body, and does not analyze its deformation and stress characteristics. The main reason is that the research in this area mainly focuses on the influence of tunnel face support and advance support on the stability of the tunnel face, and does not consider its influence on the rear support of the tunnel face (i.e., initial support);

[0006] (2) The existing research on the mechanical mechanism of initial tunnel support mainly assumes that it is a stress state under the action of two-dimensional plane strain, and does not take the stability of the tunnel face into consideration. In other words, it is impossible to study the effect of tunnel face support and advance support on initial support.

[0007] There are two main reasons for the above problems:

[0008] First, existing studies believe that there is no mutual influence between the three factors, which leads to the neglect of the study on the coordination effect of tunnel support;

[0009] Secondly, some researchers believe that there is a certain influence between the three, but due to the influence of experimental methods or equipment, and the technical difficulties that arise, it is difficult to study, and they assume that the coordinated influence is ignored.

[0010] Then, the difficulties of the testing technology are mainly manifested as follows:

[0011] (1) The existing technology of tunnel excavation unloading control device is mainly controlled separately, that is, when the tunnel face is unloaded, the surrounding rock behind the tunnel face is rigid support, and the influence of the tunnel face unloading on the initial support cannot be reflected; when the tunnel face is unloaded behind, it is assumed that it is not affected by the tunnel face, and thus the spatial effect of the tunnel face cannot be reflected;

[0012] (2) Tunnel support system. In the simulation of the existing support system, when studying the stability control of the tunnel face, it is assumed that the support behind the tunnel face is rigid, and its deformation and stress changes cannot be tested. Summary of the invention

[0013] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a model test device and a test method for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support. The model test system is mainly composed of a model test device, a simulated excavation device and a monitoring system, and corresponding test steps are given.

[0014] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0015] In the first aspect, the present invention provides a model test device for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support, comprising a model test box, a force-applying device arranged on the top of the model test box, the model test box is filled with surrounding rock-similar materials, and soil pressure acquisition sensors, initial support structures, face support structures, advance support structures, and anchoring layers are pre-buried in the surrounding rock-similar materials; wherein the initial support structure is a semi-arc support structure after longitudinal cutting along the axis direction of the tunnel, force detection sensors are arranged on the inner and outer sides of the support structure, and the side open end of the semi-arc support structure is close to the inner side of the tempered glass; the face support structure and the advance support structure are both simulated by plastic rods; the anchoring layer comprises metal wires, support plates, and springs; the metal wires are buried in the surrounding rock-similar materials for a set length and exposed for a set length, and then a certain preload force is applied through the support plates and springs; a camera device and a light source are arranged outside the model test box, and the force detection sensor, soil pressure acquisition sensor, and camera device are connected to a computer.

[0016] As a further technical solution, the initial support structure is composed of five plaster rings, and the stiffness of the first two plaster rings is 1 / 10 of that of the last three rings.

[0017] As a further technical solution, the outer surface of the gypsum ring is coated with epoxy resin and covered with a configured surrounding rock-similar material.

[0018] As a further technical solution, one of the surfaces of the model test box is transparent tempered glass.

[0019] As a further technical solution, the plastic rods of the face support structure use epoxy resin as a binder, and a layer of quartz sand with a particle size of 0.5 mm to 1.0 mm is bonded around the plastic rods.

[0020] In a second aspect, the present invention further provides a method for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support, comprising the following steps:

[0021] Step 1. Make a model test box, one of the surfaces of which is transparent tempered glass; in the model test box, the configured surrounding rock-like materials are layered and filled in the model box by density control method. When the initial support structure is filled to the position, the initial support structure is placed. The initial support structure is a semi-arc support structure after longitudinal cutting along the tunnel axis direction, and a force detection sensor is arranged on the support structure; the side open end of the semi-arc support structure is close to the inner side of the tempered glass; and the inner end face of the initial support structure is blocked by a plate to prevent the surrounding rock materials from flowing into the tunnel during the filling process; then continue to fill the surrounding rock-like materials, and place the face support structure, the advance support structure, and the anchoring layer at the set position during the filling process; when the surrounding rock materials are filled to bury the initial support structure, the uninflated airbag is inserted into the initial support structure, and the airbag is inflated. At this time, the air pressure should be small and fill the internal space of the initial support;

[0022] Step 2. Continue to fill the surrounding rock materials into the model test box in layers, observe the deformation of the initial support at all times, and continuously inflate the airbags. At the same time, during the filling process, install soil pressure collection sensors at the corresponding soil layer positions;

[0023] Step 3. After filling is completed, install a loading jack on the top of the model test box; connect the soil pressure acquisition sensor and the force detection sensor to the computer, and place a camera and a light source on the outside of the surface where the tempered glass of the model test box is located, and excavate after the data is stable;

[0024] Step 4. Deflate the airbags one by one, slowly withdraw them, remove the blocked plate, and turn on the strain collector to record data;

[0025] Step 5: After the data is stable, excavate in front of the face to set the simulated excavation footage, and record the data until the data is stable;

[0026] Step 6 Repeat steps 1 to 5 and repeat the test.

[0027] As a further technical solution, the tunnel face support structure and the advance support structure are both simulated by plastic rods.

[0028] As a further technical solution, the anchoring layer includes metal wire, a support plate, and a spring; the metal wire is buried in a set length of a material similar to the surrounding rock and exposed for a set length, and then a certain preload force is applied through the support plate and the spring.

[0029] As a further technical solution, during the surrounding rock displacement test, a camera was placed 1.5m outside the tempered glass surface to test the surrounding rock displacement during tunnel excavation unloading in a direction perpendicular to the tempered glass. After the test, PIVLAB was used to analyze the photos taken during the test to obtain the surrounding rock displacement field.

[0030] During the surrounding rock stress test, the soil pressure acquisition sensor is used to test the changes in the vertical stress field of the surrounding rock during the tunnel excavation and unloading process;

[0031] The spray support stress test is tested by force detection sensor.

[0032] The beneficial effects of the present invention are as follows:

[0033] The present invention proposes a method for pre-embedding a face support structure, an advance support structure, an anchoring layer and a force detection sensor while backfilling soil. In order to relieve the force of the initial support structure during the backfilling process, an uninflated airbag is inserted into the initial support structure and the airbag is inflated. At this time, the air pressure should be relatively small and the internal space of the initial support can be filled. In the process of filling the surrounding rock material into the model test box in layers, the deformation of the initial support is always observed and the airbag is continuously inflated. At the same time, during the backfilling process, a soil pressure collection sensor is installed at the corresponding soil layer position. When excavation is carried out after the data is stable, the airbag is deflated and slowly withdrawn. The backfilling method and the design of the unloading device overcome the defect that the existing model test device cannot be installed and tested for the deformation and force of the initial support. After the data is stable, set the simulated excavation advance in front of the face and record the data until the data is stable; this excavation method can be used to test the influence of excavation on the initial support deformation and force under different face stability states (the stability state of the face can be adjusted in real time through the face support and advance support), and realize the test of tunnel surrounding rock stress and initial support deformation force under different face stability states. Repeat the entire test steps, combine with the corresponding test plan, and change the parameters of the three support types through the control variable method to realize the test of surrounding rock stress and support deformation force under the coordinated influence of the three, and then explore the synergistic mechanism of tunnel face-advance-sprayed anchor support. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic diagram of a model test device of the present invention;

[0035] Figure 2 It is a schematic diagram of the process of the present invention;

[0036] Figure 3 It is a schematic diagram of applying prestress of the present invention;

[0037] FIG. 4( a ) and FIG. 4( b ) are schematic diagrams of the tunnel surrounding rock displacement field test process of the present invention;

[0038] Figures 5(a), 5(b), 5(c) and 5(d) are schematic diagrams of the arrangement of the earth pressure cell of the present invention;

[0039] Figure 6(a) and Figure 6(b) are schematic diagrams of the arrangement of the strain gauges for the sprayed support;

[0040] In the figure: 1. Model test box; 2. Jack; 3. Reaction frame; 4. High-definition digital camera; 5. Spotlight; 6. Static strain gauge; 7. Miniature soil pressure box; 8. Strain gauge; 9. Computer; 10. Airbag; 11. Initial support structure; 12. Face support structure; 13. Advanced support structure; 14. Anchor layer; 15. Gasket; 16. Fuse; 17. Spring. DETAILED DESCRIPTION

[0041] 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 in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0042] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless otherwise explicitly stated in the present invention, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "include" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof;

[0043] For the convenience of description, if the words "up", "down", "left" and "right" appear in the present invention, they only indicate that they are consistent with the up, down, left and right directions of the drawings themselves, and do not limit the structure. They are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0044] In order to solve the technical problems existing in the above-mentioned background technology, this embodiment provides a model test device and test method for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support. The model test system is mainly composed of a model test device, a simulated excavation device and a monitoring system, and the corresponding test steps are given. In the existing tunnel model tests, there are many studies on the independent analysis of the mechanical effects of tunnel excavation and the mechanical properties of the support structure, which are also relatively mature, but there are fewer studies on the coordinated support mechanical mechanism between tunnel face-advance-sprayed anchor support. For this reason, the present invention provides a model test device and test method for studying the tunnel face-advance-model test.

[0045] like Figure 1 As shown, the model test device for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support proposed in this embodiment mainly consists of a model test box 1, a jack 2, a reaction frame 3, a high-definition digital camera 4, a spotlight 5, a static strain gauge 6, a micro earth pressure box 7, a strain gauge 8, a computer 9, an initial support structure 10, a face support structure 11, an advance support structure 12, an anchoring layer 13 and the like. The model test box 1 is filled with surrounding rock-similar materials, and micro earth pressure boxes 7, initial support structures 10, face support structures 11, advance support structures 12, and anchoring layers 13 are pre-embedded in the surrounding rock-similar materials; wherein the initial support The protective structure 10 is a semi-arc support structure after longitudinal cutting along the axial direction of the tunnel. Force detection sensors are arranged on the inner and outer sides of the support structure, and the side open end of the semi-arc support structure is close to the inner side of the tempered glass; the face support structure 11 and the advance support structure 12 are simulated by plastic rods; the anchoring layer 13 includes a metal wire, a support plate, and a spring; the metal wire is buried in a material similar to the surrounding rock for a set length and exposed for a set length, and then a certain preload force is applied through the support plate and the spring; a camera device and a light source are arranged outside the model test box, and the force detection sensor, the soil pressure acquisition sensor, the camera device and the computer are connected.

[0046] In this embodiment, in order to facilitate the observation and recording of the instability process of the face during the test, only a 1 / 2 tunnel model is made; wherein, the model test box 1 is used to simulate tunnel excavation unloading, the spotlight 5 is used to provide a stable light source, the high-definition digital camera 4 is used to test the surrounding rock displacement field, the micro-earth pressure box 7 is used to test the surrounding rock stress field, and the strain gauge 8 is used to test the spray layer support stress. The clearance size of the model test box 1 is 1.5×1m×2.5m (length×width×height), the frame is welded with 10mm thick angle steel, there is no cover plate on the top surface, a 15mm thick tempered glass plate is set on the front, and the remaining surfaces are all surrounded by 10mm thick steel plates, and stiffening plates are set around to improve the overall rigidity of the model box. In order to facilitate the quantitative control of tunnel excavation unloading and footage during the test, this embodiment uses an "air bag" to simulate the excavation and unloading state of the tunnel.

[0047] The model test proposed in the present invention mainly studies the mutual influence between the heading face, advance support and shotcrete support during tunnel excavation, which belongs to the problem of three-dimensional space mechanics. If the actual tunnel engineering excavation process is used for simulation test, the model test operation is complicated, and many influencing factors cannot be controlled, and it is difficult to ensure the validity of the test results. Therefore, this model test simulates a certain state in the tunnel excavation process, and analyzes the surrounding rock stress and support structure force under the excavation state. Although relevant simplifications were made in the simulation process, the model test effect can be better reflected.

[0048] The method of prefabricated and embedded initial support disclosed in this embodiment realizes the test of the impact of face excavation on the initial support behind the face. At the same time, during the excavation process, the existence of the face is also retained, which realizes the test of the change in the initial support force of the tunnel under the action of changing the face support and advance support, thereby realizing the study of the coordination effect of the three supports.

[0049] The main steps of the model test are as follows:

[0050] Step 1. Make a model test box, one of the surfaces of which is transparent tempered glass; in the model test box, the configured surrounding rock-like materials are layered and filled in the model box by density control method. When the initial support structure is filled to the position, the initial support structure is placed. The initial support structure is a semi-arc support structure after longitudinal cutting along the tunnel axis direction, and a force detection sensor is arranged on the support structure; the side open end of the semi-arc support structure is close to the inner side of the tempered glass; and the inner end face of the initial support structure is blocked by a plate to prevent the surrounding rock materials from flowing into the tunnel during the filling process; then continue to fill the surrounding rock-like materials, and place the face support structure, the advance support structure, and the anchoring layer at the set position during the filling process; when the surrounding rock materials are filled to bury the initial support structure, the uninflated airbag is inserted into the initial support structure, and the airbag is inflated. At this time, the air pressure should be small and fill the internal space of the initial support;

[0051] Step 2. Continue to fill the surrounding rock materials into the model test box in layers, observe the deformation of the initial support at all times, and continuously inflate the airbags. At the same time, during the filling process, install soil pressure collection sensors at the corresponding soil layer positions;

[0052] Step 3. After filling is completed, install a loading jack on the top of the model test box; connect the soil pressure acquisition sensor and the force detection sensor to the computer, and place a camera and a light source on the outside of the surface where the tempered glass of the model test box is located, and excavate after the data is stable;

[0053] Step 4. Deflate the airbags one by one, slowly withdraw them, remove the blocked plate, and turn on the strain collector to record data;

[0054] Step 5: After the data is stable, excavate in front of the face to set the simulated excavation footage, and record the data until the data is stable;

[0055] Step 6 Repeat steps 1 to 5 and repeat the test.

[0056] The preparation of specific relevant test materials is as follows:

[0057] ① Determination of tunnel and surrounding rock materials

[0058] In this experiment, the geometric similarity ratio C l =30 and bulk density similarity ratio C γ =1 is the basic similarity ratio, and the strain similarity ratio C is determined according to the similarity theory. ε , Poisson's ratio C ν , similarity ratio of friction angle C φ , stress similarity ratio C σ , elastic modulus similarity ratio C E , cohesion similarity ratio C c, displacement similarity ratio C δ , as shown in Table 1.

[0059] Table 1 Similarity ratio of model test

[0060] variable <![CDATA[C l ]]> <![CDATA[C γ ]]> <![CDATA[C ε ]]> <![CDATA[C ν ]]> <![CDATA[C φ ]]> <![CDATA[C σ ]]> <![CDATA[C E ]]> <![CDATA[C c ]]> <![CDATA[C δ ]]> Similarity ratio 30 1 1 1 1 30 30 30 30

[0061] The tunnel section of the model test adopts a single-hole double-track high-speed railway tunnel section, with a section height of 12.5m, a section span of 15m, and a section area of ​​about 152m. 2 The geometric similarity ratio is 30, so the model tunnel section height is 42cm and the span is 50cm. The tunnel shape and the corresponding similarity ratio can be adjusted according to the actual project conditions.

[0062] With reference to TB 10003-2016 Railway Tunnel Design Code, V-grade soft and broken surrounding rock was selected as the prototype material. Three raw materials, barite, quartz sand and vaseline, were used. Through indoor proportioning tests, the proportion of similar surrounding rock materials was preliminarily determined to be barite: quartz sand: vaseline = 12:8:0.6, which met the test requirements, as shown in Table 2. Other surrounding rock grade materials can be used as a reference.

[0063] Table 2 Physical and mechanical parameters of surrounding rock materials

[0064]

[0065] ②Support material production

[0066] a. Similar materials to face anchor bolts - face support

[0067] Related studies have shown that the stress state of anchor rods in homogeneous strata is mainly tensile, so the prototype anchor rod material and similar anchor rod materials must meet similar tensile stiffness, that is:

[0068]

[0069] In the formula, E 原型 is the elastic modulus of the prototype material (MPa); A 原型 is the cross-sectional area of ​​the prototype material (m 2 );E 相似 is the elastic modulus of similar materials (MPa); A 相似 is the cross-sectional area of ​​similar materials (m 2 ).

[0070] The parameters of the face anchor are shown in Table 3. ABS plastic rods with a diameter of 4 mm are used to simulate the glass fiber anchor rods with a diameter of 22 mm in actual engineering. The actual tensile stiffness similarity ratio is 27500, which meets the test requirements.

[0071] Table 3. Material parameters of face anchor bolts

[0072] Anchor type Material Elastic modulus(GPa) Diameter(mm) Prototype anchor Fiberglass 40 20 Model anchor ABS plastic 2.2 4

[0073] In order to simulate the interaction between the surrounding rock and the anchor, epoxy resin is used as a binder to bond a layer of quartz sand with a particle size of 0.5 mm to 1.0 mm around the anchor.

[0074] b. Similar materials for advanced pipe roof - advanced support

[0075] Related research shows that the stress state of the advanced pipe shed in homogeneous strata is mainly bending, so the prototype pipe shed material and the model pipe shed material must meet similar bending stiffness, that is:

[0076]

[0077] In the formula, I 原型 is the moment of inertia of the prototype material (m 4 );I 相似 is the moment of inertia of similar materials (m 4 ).

[0078] ABS plastic pipes with an outer diameter of 6 mm and a wall thickness of 1.5 mm are used to simulate the advanced pipe rack with an outer diameter of 180 mm and a wall thickness of 6 mm in actual engineering. The parameters of the advanced pipe rack are shown in Table 4. The actual bending stiffness similarity ratio is 24900000, which meets the test requirements.

[0079] Table 4 Advanced pipe shed material parameters

[0080] Pipe Roof Type Material Elastic modulus(GPa) Outer diameter(mm) Wall thickness(mm) Prototype pipe shed Q235 Steel 210 180 6 Model pipe shed ABS plastic 2.2 6 1.5

[0081] c. Prestressed anchor similar materials - anchoring layer

[0082] Referring to relevant research results, 15A fuses are used for simulation of prestressed anchor support materials. The embedded length of the 15A fuse is 7cm, plus the exposed length of 3cm, the length of each 15A fuse is 10cm. The test uses a 4mmX4mmX2mm square aluminum plate to simulate the anchor gasket. A spring with a wire diameter of 1mm, a middle diameter of 4.5mm, a length of 10mm, and a stiffness coefficient of 0.85kN / m is used to apply preload. The preload value is set to 5~10N, the spring compression amount is 5~10mm, and the preload is applied by bending the fuse to support the tray, such as Figure 3 shown.

[0083] d. Shotcrete similar materials - sprayed layer

[0084] Composite lining is generally composed of initial support, waterproof layer and secondary lining. Among them, initial support is an important support component to ensure the stability of the tunnel after excavation, which is generally composed of shotcrete, anchor rods, steel mesh, steel frame, etc. In order to simplify the test process, this model test ignores components such as steel mesh and steel frame, and directly uses gypsum layer to simulate the spray layer support. Since the model test of the present invention is a certain state of the tunnel construction process, some sections are in the completed state, so the initial support is simulated by the pre-embedded method. In order to simulate the bonding performance between the initial support and the surrounding rock, after the initial support is completed, it is coated with epoxy resin and covered with a similar material to the surrounding rock. The size of the spray layer support and related mechanical parameters are shown in Table 5.

[0085] Table 5 Shotcrete support dimensions and mechanical parameters

[0086]

[0087] The test plan corresponding to the above system is as follows: it mainly includes three test contents: surrounding rock stress, surrounding rock displacement, and shotcrete support stress.

[0088] a. Surrounding rock displacement test plan

[0089] The surrounding rock displacement test system consists of a digital camera, two spotlights, PIV post-processing software PIVLAB and a computer. As shown in Figure 4(a) and Figure 4(b), the camera is placed 1.5m outside the tempered glass surface, and the surrounding rock displacement during tunnel excavation unloading is tested in the direction perpendicular to the tempered glass. After the test, PIVLAB is used to analyze the photos taken during the test to obtain the surrounding rock displacement field.

[0090] b. Surrounding rock stress test plan

[0091] The surrounding rock stress test system consists of three parts: earth pressure boxes, static strain gauges, and computers. As shown in Figure 5(a), Figure 5(b), Figure 5(c), and Figure 5(d), 38 earth pressure boxes were buried in the surrounding rock to test the changes in the vertical stress field of the surrounding rock during the unloading process of tunnel excavation.

[0092] c. Shotcrete support stress test scheme

[0093] During the test, in order to monitor the force of the sprayed layer support after excavation, the sprayed layer support structure was pre-buried in the tunnel. During the filling period, in order to ensure that the initial support structure was not damaged, air bags were used for simulated support. The sprayed layer support was assembled with five gypsum rings with a width of 10 mm, that is, the sprayed layer support was set to a length of 50 cm, of which the gypsum stiffness of the first two rings was 1 / 10 of that of the last three rings (considering the age characteristics of the shotcrete). The initial support was also monitored for force, and the measurement point layout is shown in Figure 6(a) and Figure 6(b). Three measurement points were set on each ring, and strain gauges were attached to the inside and outside.

[0094] This embodiment uses a self-designed model box and adopts the control variable method to carry out tunnel longitudinal surrounding rock stability tests under different support measures (face support, advance support, shotcrete support and coordinated reinforcement). Furthermore, according to the evolution characteristics of the tunnel longitudinal surrounding rock displacement field and stress field, the longitudinal stress transfer mechanism and support mechanism of the surrounding rock under different support effects are revealed. As shown in Table 6, this embodiment proposes to test 30 working conditions, and under the condition of a burial depth of 5m (the actual burial depth corresponding to 5m is 150m), 6 excavation advances are considered (the actual excavation advance corresponding to 5cm~30cm is 1.5m~9m). Among them, working conditions 1 to 6 use spraying support measures to study the longitudinal instability mechanism of the tunnel face, excavation advance section and support section under different excavation advances. Working conditions 7 to 30 use face support, advance support and shotcrete support measures to study the synergistic mechanism of tunnel face-advance-shotcrete support.

[0095] Table 1 Model test conditions

[0096]

[0097]

[0098] In response to the current situation where the mechanical effects of existing tunnel excavation and the mechanical mechanism of the coordinated action of various support components are unclear, this invention proposes a model test device and test method that can be used to study the coordinated action mechanism of tunnel face-advance-sprayed anchor support; it provides technical support for the design of tunnel engineering support structures and enriches the relevant theories of refined design of tunnel engineering support structures.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A model test device for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support, characterized in that: It comprises a model test box, a force applying device is arranged on the top of the model test box, the model test box is filled with surrounding rock-similar materials, and soil pressure collection sensors, initial support structures, face support structures, advance support structures, and anchoring layers are pre-buried in the surrounding rock-similar materials; wherein the initial support structure is a semi-arc support structure after longitudinal cutting along the tunnel axis direction, force detection sensors are arranged on the inner and outer sides of the support structure, and the side open end of the semi-arc support structure is in close contact with the inner side of the tempered glass; The tunnel face support structure and the advance support structure are both simulated by plastic rods; the anchoring layer includes metal wires, support plates, and springs; the metal wires are buried in a set length of a material similar to the surrounding rock and exposed to a set length, and then a certain preload is applied through the support plates and springs; a camera device and a light source are arranged outside the model test box, and the force detection sensor, the soil pressure acquisition sensor, the camera device, and the computer are connected.

2. The model test device for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support as claimed in claim 1, characterized in that: The initial support structure is composed of five plaster rings, and the stiffness of the first two plaster rings is 1 / 10 of that of the last three rings.

3. The method for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support according to claim 2, characterized in that: The outer surface of the gypsum ring is coated with epoxy resin and covered with a configured surrounding rock-similar material.

4. The method for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support according to claim 1, characterized in that: One of the surfaces of the model test box is transparent tempered glass.

5. The method for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support according to claim 1, characterized in that: The plastic rod of the face support structure adopts epoxy resin as a binder, and a layer of quartz sand with a particle size of 0.5mm to 1.0mm is bonded around the plastic rod.

6. A method for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support, characterized in that: The following steps are involved: Step 1. Make a model test box, one of the surfaces of which is transparent tempered glass; in the model test box, the configured surrounding rock-like materials are layered and filled in the model box by density control method. When the initial support structure is filled to the position, the initial support structure is placed. The initial support structure is a semi-arc support structure after longitudinal cutting along the tunnel axis direction, and a force detection sensor is arranged on the support structure; the side open end of the semi-arc support structure is close to the inner side of the tempered glass; and the inner end face of the initial support structure is blocked by a plate to prevent the surrounding rock materials from flowing into the tunnel during the filling process; then continue to fill the surrounding rock-like materials, and place the face support structure, the advance support structure, and the anchoring layer at the set position during the filling process; when the surrounding rock materials are filled to bury the initial support structure, the uninflated airbag is inserted into the initial support structure, and the airbag is inflated. At this time, the air pressure should be small and fill the internal space of the initial support; Step 2. Continue to fill the surrounding rock materials into the model test box in layers, observe the deformation of the initial support at all times, and continuously inflate the airbags. At the same time, during the filling process, install soil pressure collection sensors at the corresponding soil layer positions; Step 3. After filling is completed, install a loading jack on the top of the model test box; connect the soil pressure acquisition sensor and the force detection sensor to the computer, and place a camera and a light source on the outside of the surface where the tempered glass of the model test box is located, and excavate after the data is stable; Step 4. Deflate the airbags one by one, slowly withdraw them, remove the blocked plate, and turn on the strain collector to record data; Step 5: After the data is stable, excavate in front of the face to set the simulated excavation footage, and record the data until the data is stable; Step 6 Repeat steps 1 to 5 and repeat the test.

7. The method for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support according to claim 6, characterized in that: The tunnel face support structure and the advance support structure are both simulated by plastic rods.

8. The method for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support according to claim 6, characterized in that: The anchoring layer comprises a metal wire, a supporting plate and a spring. The metal wire is buried in a material similar to the surrounding rock by a set length and exposed by a set length. Then a certain pre-tightening force is applied through the supporting plate and the spring.

9. The method for studying the synergistic mechanism of tunnel face-advance-sprayed anchor support according to claim 6, characterized in that: During the surrounding rock displacement test, the camera was placed 1.5m outside the tempered glass surface, and the surrounding rock displacement during tunnel excavation unloading was tested in a direction perpendicular to the tempered glass. After the test, the photos taken during the test were analyzed to obtain the surrounding rock displacement field. During the surrounding rock stress test, the soil pressure acquisition sensor is used to test the changes in the vertical stress field of the surrounding rock during the tunnel excavation and unloading process; The spray support stress test is tested by force detection sensor.

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