Test method and system for mechanical properties of tunnel structures with progressive degradation of primary support

Abstract

The present invention belongs to the field of tunnel engineering technology, specifically relating to a method and system for testing the mechanical properties of tunnel structures subjected to progressive degradation of primary supports. The method converts geometric similarity ratios based on operating conditions, configures surrounding rock similar materials, and combines similarity theory to determine similar materials and material parameters for support, thereby creating a temperature-controlled deteriorated tunnel structure support model. The present invention characterizes the degradation effect of the primary support structure by adjusting the temperature of the anchor mortar and primary support similar materials to alter their macroscopic mechanical properties, thereby simulating the progressive degradation process of the primary support structure. This method can demonstrate the load transfer mechanism and bearing characteristic evolution of soft rock tunnel structures under progressive degradation conditions of the primary support structure. Furthermore, it can systematically analyze the influence of various factors, such as the anchor degradation rate, anchor degradation location, surface primary support degradation rate, surface primary support degradation location, surface primary support inner surface roughness (smooth, moderate, rough), and secondary lining mechanics, on surrounding rock deformation, support structure deformation, and stress.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel engineering, and in particular relates to a method and system for testing the mechanical properties of a tunnel structure with progressive degradation of primary branches. Background Art

[0002] Tunnel structural failures are the result of long-term adverse interactions between support and surrounding rock. Essentially, they are changes in the structural system's stress conditions caused by variations in the support and surrounding rock conditions. While some soft rock tunnels can maintain short-term stability, as the tunnel ages, the surrounding rock load effects caused by rock rheology can disrupt this short-term stability and threaten tunnel operational safety. Soft rock tunnel support structures typically consist of primary support (a combination of anchor bolts, shotcrete, and steel frames) and secondary lining. Currently, deterioration of support structures in soft rock tunnels is widespread.

[0003] In the existing technology, since primary support is usually covered by permanent support during subsequent construction, its degradation issues have received relatively little attention. Furthermore, it is generally believed that the degradation of primary support has little impact on the entire project, resulting in insufficient recognition of its value. This has led to relatively little research on primary support degradation, with designs primarily focused on secondary lining degradation. For example, the invention patent application with publication number [CN115728216A] discloses an accelerated corrosion test device for lining structures. A corrosive liquid containing rust products is promptly discharged through a first pipe. The discharged corrosive liquid is then filtered through a filter box and returned to a corrosive liquid storage tank with a designed concentration. This prevents excessive rust products from accumulating in the corrosion tank and preventing them from adhering to the surface of the lining structure and embedding in rust cracks. This makes the environment in the corrosion tank more similar to the corrosion conditions in underground, especially underwater, corrosive environments. This allows for more accurate research on the corrosion degradation patterns of tunnel lining structures under these conditions, providing important support for accurately and scientifically evaluating the safety and reliability of tunnel lining structures throughout their life cycle.

[0004] However, degradation of initial support performance inevitably alters the mechanical state of the support structure in soft rock tunnels. For soft rock tunnels, where long-term load effects on the surrounding rock are significant, the coupling of primary support degradation and surrounding rock rheology complicates the long-term mechanical response of the support structure. During this dynamic adjustment process, the load distribution and functional evolution of the anchoring structure and surface primary support (shotcrete + steel frame)—as well as the coordinated load-bearing performance of the various support structures—all impact the long-term safety of the soft rock tunnel structure.

[0005] Therefore, it is urgent to develop a similarity model system and method for the soft rock tunnel support structure system that considers the primary support degradation process, in order to study the load transfer mechanism and collaborative bearing characteristics of the soft rock tunnel structure system under the action of primary support degradation and realize the scientific analysis and evaluation of the safety of the soft rock tunnel structure throughout its life cycle. Summary of the Invention

[0006] In order to address the problems of the relative lack of research on initial support degradation in the existing technology, the present invention proposes a test method and system for the mechanical properties of soft rock tunnel structures with progressive degradation of initial support. The method achieves the purpose of quantitative degradation of the initial support structure through temperature control, thereby providing technical support for further in-depth analysis of the impact of degradation of the anchor structure and surface initial support performance on the long-term coordinated bearing characteristics of the soft rock tunnel support structure system.

[0007] The present invention is implemented by adopting the following technical solutions: a test system for the mechanical properties of soft rock tunnel structures with progressive deterioration of initial support, comprising a model box, a tunnel support structure model, a deformation and strain testing device, a surrounding rock environment simulation component, a temperature control system, a monitoring system, and a servo loading control system, wherein the model box is fixed on a steel foundation base;

[0008] The tunnel support structure model is fixed in the middle of the model box, and the remaining space of the model box is filled with surrounding rock. The tunnel support structure model includes a primary support model and a secondary lining. The primary support model is composed of anchor rods and surface primary supports. Heating tapes connected to a temperature control system are attached to the surfaces of the anchor rods and the surface primary supports.

[0009] The deformation and strain testing device is installed on the tunnel support structure model to obtain the mechanical parameters of the tunnel structure during the test. The surrounding rock environment simulation component is connected to the servo loading control system to simulate the environmental pressure of the soil around the tunnel and apply the external load required for the simulation test. The temperature control system is used to control the temperature of the primary support model material to realize the quantitative degradation process simulation of the primary support model.

[0010] The core of this solution lies in how to simulate the gradual deterioration process of the initial support. By proposing to use resin materials to simulate the mortar material of the anchor rod and the shotcrete material of the surface primary support, heating tapes are attached to the surface of the anchor rod and the surface primary support. The heating tapes are connected to the temperature control system, and the anchor rod and the surface primary support are heated to achieve the gradual deterioration process of the macroscopic mechanical properties of the equivalent initial support.

[0011] Furthermore, the deformation and strain testing device includes a static strain collector, several grating displacement sensors, several strain gauges, several micro pressure gauges and a DIC system. The strain gauges and micro pressure gauges are connected to the static strain collector, and the DIC system and the static strain collector are connected to the monitoring system; the grating displacement sensor is set inside the tunnel support structure model and is in contact with the inner surface of the secondary lining. The strain gauge is fixed to the outside of the secondary lining and the primary support model, and several micro pressure gauges are fixed to the outside of the strain gauge.

[0012] Furthermore, the surrounding rock environment simulation component includes a reaction frame, a hydraulic pump, a jack displacement operator and a perforated steel pad. The pressure end of the surrounding rock environment simulation component acts on the top surface and both sides of the model box. The reaction frame is fixedly connected to the steel foundation base. The fixed end of the hydraulic pump is connected to the reaction frame. The movable end of the hydraulic pump is connected to the jack displacement operator and contacts the perforated steel pad. The perforated steel pad is arranged in contact with the surrounding rock. A pressure sensor is arranged between the jack displacement operator and the perforated steel pad. The hydraulic pump, the jack displacement operator and the pressure sensor are connected to the servo loading control system.

[0013] Furthermore, the surrounding rock is simulated by similar materials; the anchor rods are simulated by steel bars; the surface primary support is composed of shotcrete and steel arch frames, the shotcrete is simulated by resin materials, and the internal steel arch frames are simulated by iron sheets; the secondary lining is simulated by mixing gypsum and water in a certain proportion.

[0014] The present invention further provides a test method for a tunnel structure mechanical properties test system considering the gradual degradation of the primary branch, comprising the following steps:

[0015] Step S1: Calculate the geometric similarity ratio according to the working conditions, configure the surrounding rock similarity material, and determine the surrounding rock grade;

[0016] Step S2: Determine similar materials and their proportions for the anchor rods, surface primary support, and secondary lining using similarity theory; then, create a primary support model and secondary lining, lay a heating tape on the primary support model, and arrange deformation and strain testing devices on the surfaces of the anchor rods, surface primary support, and secondary lining;

[0017] Step S3: Filling the model box with surrounding rock-like materials in layers and batches, excavating a tunnel at a preset location, then constructing a tunnel support structure model at the tunnel location, and then connecting a servo loading control system, a static strain acquisition instrument, a monitoring system, and a temperature control system;

[0018] Step S4, experimental testing: The temperature of the primary support model is adjusted through the temperature control system to change the parameters of the anchor mortar and shotcrete, simulating the attenuation effect of the mechanical properties of the anchor mortar and the surface primary support. At the same time, different stress and surrounding rock load levels are simulated through the servo loading control system, and the structural deformation and strain data during the test are recorded. By analyzing the deformation and strain data, the mechanical response of the tunnel support structure model under the dual effects of temperature and load is studied.

[0019] Furthermore, in step S1, the surrounding rock similar material is prepared in the following manner:

[0020] First, based on the prototype parameters and similarity ratio of the surrounding rock, the mechanical parameters of the surrounding rock similar material were obtained with reference to density, deformation modulus, internal friction angle and cohesion; iron powder, barite powder and quartz sand were selected as aggregates of the soft rock similar material, and rosin alcohol and hydraulic oil were used as binders and adhesives, respectively; a proportioning test was carried out at room temperature, and the uniaxial compressive strength and triaxial compressive strength of the surrounding rock similar materials with different proportions were measured to obtain a reasonable proportion of aggregate, binder and adhesive, and the surrounding rock was prepared according to the proportion.

[0021] Furthermore, in step S2:

[0022] The specific determination of similar materials is as follows:

[0023] The similar material of the anchor rod is steel bar; the surface primary support is composed of shotcrete and steel arch frame. Resin material is used to simulate the shotcrete, and iron sheet is used to simulate the internal steel arch frame. The temperature of the resin material is controlled to change the macroscopic mechanical properties of the surface primary support, thereby characterizing the asymptotic degradation process of the surface primary support; the similar materials of the secondary lining are gypsum and water.

[0024] When implementing the tunnel support structure model, the following methods are used:

[0025] (1) To construct the secondary lining, first prefabricate the secondary lining mold, place the steel wire braid in the secondary lining mold, and then pour a mixture of gypsum and water in a certain proportion. After drying, remove the mold and bake the test piece. After the secondary lining is dried and solidified, apply a layer of waterproof varnish on its surface, stick a high-temperature foil strain gauge on the outside of the secondary lining, and arrange a micro pressure gauge on the outer surface.

[0026] (2) Construction of surface primary support, which includes shotcrete, steel mesh and steel arch frame. The steel arch frame is simulated by iron sheet. A certain thickness of resin material is evenly applied on the surface of the surrounding rock. Shotcrete is configured. Heating tape and high-temperature foil-type strain gauge are attached to the surface of the primary support. Micro pressure gauge is arranged on the surface. The roughness of the inner surface of the surface primary support is artificially set to characterize the different contact states between the surface primary support and the secondary lining.

[0027] (3) Anchor rods are installed. Drill holes according to the actual distribution of anchor rods, and steel bars are set in the holes around the temperature-controlled deteriorated tunnel support model. Resin is injected into the holes using a syringe to bond the steel bars. After applying resin material on the surface of the steel bars, a heating tape is attached, and a layer of resin material simulating anchor mortar is applied on the surface.

[0028] Furthermore, in step S3, after the tunnel support structure model is completed, the evenly mixed surrounding rock similar material is poured into the model box to a certain height, spread evenly, and compacted according to the specified compaction degree; then the tunnel support structure model is placed, and similar materials are filled again until it is filled to the top of the model box, and compacted according to the specified compaction degree, and covered with a perforated steel plate.

[0029] Furthermore, in step S4, when performing the test:

[0030] By adjusting the temperature of the heating belt through the temperature control system, the target temperature of the anchor structure and the surface primary support can be adjusted, the elastic modulus of the resin material can be changed, the physical and mechanical parameters of the material at different temperatures can be obtained, and the relationship between temperature and the degradation of the primary support structure performance can be established, thus achieving the purpose of quantitative degradation of the primary support structure.

[0031] Among them, while adjusting the temperature, a servo loading control system is used to perform slow graded loading to ensure that the test process is a quasi-static process, and the stress and strain of the primary support model and secondary lining during the loading process are recorded through the monitoring system; the loading level is determined, and the self-weight stress field is simulated according to the geometric similarity ratio. Combined with the stress state of similar materials in the surrounding rock, the collapse of the secondary lining is used as the termination condition of the test.

[0032] Compared with the prior art, the advantages and positive effects of the present invention are:

[0033] This scheme uses resin materials to simulate the anchor mortar and shotcrete in the soft rock tunnel support structure. By regulating the temperature and changing the parameters of the anchor mortar and surface primary support materials, the gradual deterioration process of the initial support structure is simulated. Factors such as the changes in the anchor body degradation rate, anchor body degradation location, surface primary support degradation rate, surface primary support degradation location, surface primary support inner surface roughness (smooth, moderate, rough), and secondary lining mechanical parameters are effectively simulated. The deformation and strain testing device installed in the tunnel model is used to record the stress response of the tunnel model, realizing a systematic analysis of the impact mechanism of the deterioration of the anchor structure and surface primary support performance on the long-term coordinated bearing characteristics of the soft rock tunnel support structure system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the test system according to an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the anchor support and heating belt arrangement structure according to an embodiment of the present invention;

[0036] Figure 3 This is a schematic diagram of the arrangement structure of the surface primary support and heating belt in an embodiment of the present invention;

[0037] Figure 4This is a schematic diagram of the installation position structure of the surface primary support strain gauge and the micro pressure gauge according to an embodiment of the present invention;

[0038] Figure 5 This is a schematic diagram of the installation position structure of the secondary lining strain gauge and the grating displacement sensor according to an embodiment of the present invention;

[0039] Among them, 1. Secondary lining; 2. Surface primary support; 3. Anchor rod; 4. Surrounding rock; 5. Hydraulic pump; 6. Reaction frame; 7. Model box; 8. Pressure sensor; 9. Servo loading control system; 10. Static strain collector; 11. Monitoring system; 12. Temperature control system; 13. Steel foundation base; 14. Perforated steel pad; 15. Jack loading device; 16. Resin material; 17. Rebar; 18. Steel arch frame; 19. Heating belt; 20. Strain gauge; 21. Micro pressure gauge; 22. Grating displacement sensor; 23. DIC system. DETAILED DESCRIPTION

[0040] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described below with reference to the accompanying drawings and embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0041] Example 1, as Figure 1 As described above, this embodiment proposes a tunnel structure mechanical properties test system for the gradual deterioration of primary support, including a model box 7, a tunnel support structure model, a deformation and strain testing device, a surrounding rock environment simulation component, a temperature control system 12 and a servo loading control system 9, wherein the model box 7 is arranged on a steel foundation base 13, and the surrounding rock environment simulation component is arranged on the periphery of the model box and is connected to the servo loading control system 9; the tunnel support structure model includes a secondary lining 1, a surface primary support 2 and an anchor rod 3, wherein the surface primary support 2 and the anchor rod 3 are simulated by a resin material and a steel bar 17 respectively; continue to refer to Figure 2-Figure 4 A heating belt 19 is pasted on the surface of the surface primary support 2, and a heating belt 19 is pasted on the surface of the anchor rod 3. The heating belt 19 is connected to the temperature control system 12. By changing the resin temperature, the mechanical parameters such as the elastic modulus of the resin material 16 of the surface primary support 2 and the anchoring mortar are changed, thereby achieving the conditions for quantitative degradation of the initial support structure.

[0042] Continue to refer Figure 1 The model box 7 is assembled by a steel frame and organic glass panels on all sides. The model box 7 is fixed on the steel foundation base 13. The tunnel support structure model is fixed in the middle of the model box 7. The remaining space of the model box 7 is filled with surrounding rock 4. The surrounding rock 4 is simulated with similar materials. The deformation and strain testing device is installed on the tunnel support structure model.

[0043] The pressure end of the surrounding rock environment simulation component acts on the top surface and both sides of the model box 7. Figure 1 The surrounding rock environment simulation component includes a reaction frame 6, a hydraulic pump 5, a jack loading device 15 (vertical and horizontal) and a perforated steel pad 14. The reaction frame 6 is fixedly connected to the steel foundation base 13. The fixed end of the hydraulic pump 5 is connected to the reaction frame 6. The movable end of the hydraulic pump 5 is connected to the jack loading device 15 and contacts the perforated steel pad 14. The perforated steel pad 14 is arranged in contact with the surrounding rock 4. A pressure sensor 8 is arranged between the jack loading device 15 and the perforated steel pad 14. The hydraulic pump 5, the jack loading device 15 and the pressure sensor 8 are electrically connected to the servo loading control system 9.

[0044] like Figure 5 As shown, the deformation and strain testing device includes a static strain collector 10, a plurality of strain gauges 20, a plurality of micro pressure gauges 21, a plurality of grating displacement sensors 22 and a DIC system 23 (three-dimensional full-field strain measurement and analysis system). The strain gauges 20, the micro pressure gauges 21 and the grating displacement sensors 22 are all connected to the static strain collector 10, and the DIC system 23 is connected to the static strain collector 10 and the monitoring system 11; the grating displacement sensor 22 is set on the inner side of the secondary lining 1, the strain gauges 20 are pasted on the inner and outer sides of the secondary lining 1 and the surface primary support 2, and the plurality of micro pressure gauges 21 are fixed on the inner sides of the secondary lining 1 and the surface primary support 2.

[0045] In this embodiment, micro-pressure gauges and high-temperature foil strain gauges are deployed to record the surrounding rock stress and the mechanical response of the support structure throughout the entire process. The tunnel structure deformation is acquired using a non-contact deformation measurement and analysis system. The system's high-definition measurement head enables image acquisition during the test, and the DIC system performs image calculations for analyzing the displacement, strain, velocity, and acceleration fields of the surrounding rock and support structure.

[0046] Example 2: Based on the experimental system described in Example 1, this example proposes a corresponding experimental method, including the following steps:

[0047] Step S1: Calculate the geometric similarity ratio according to the working conditions, configure the surrounding rock similarity material, and determine the surrounding rock grade;

[0048] Step S2: Determine similar materials and proportions for anchor rods, primary surface support, and secondary lining using similarity theory; then create a tunnel support structure model, and deploy deformation and strain testing devices on the support structure;

[0049] Step S3: Fill the model box with materials similar to the surrounding rock in layers and batches, excavate a tunnel at a preset location, and then construct a tunnel support structure model at the tunnel location. The tunnel support structure model includes anchor rods, surface primary support and secondary lining. During this process, it is necessary to ensure that the support structure is closely attached to the surrounding rock and that the contact integrity between each support is maintained. Then, connect the servo loading control system 9, static strain acquisition instrument 10, monitoring system 11 and temperature control system 12.

[0050] Step S4: Adjust the temperature of the anchor rods and the surface primary support through the temperature control system to change the parameters of the anchor mortar and shotcrete, simulate the attenuation effect of the mechanical properties of the anchor mortar and the surface primary support, and use the servo loading control system to simulate different ground stresses and surrounding rock load levels. Set graded loading until the support structure is destroyed, monitor the stress response of the temperature-controlled deteriorated tunnel support model under the simultaneous coupling of temperature and load through the deformation and strain testing device, and record the stress data and strain data.

[0051] Specifically, in step S1, the preparation of surrounding rock similar materials is specifically carried out in the following manner: first, based on the prototype parameters and similarity ratio of the surrounding rock, the mechanical parameters of the surrounding rock similar materials are obtained with reference to density, deformation modulus, internal friction angle and cohesion; iron powder, barite powder and quartz sand are selected as aggregates of soft rock similar materials, and rosin alcohol and hydraulic oil are selected as binders and adhesives respectively; a proportioning test is carried out at room temperature to obtain the proportion of aggregate, binder and adhesive, and the surrounding rock similar materials are prepared according to the proportion, and the surrounding rock similar materials are weighed and configured on a large scale according to the specified material proportions, and the materials are evenly stirred with a mixer; the uniaxial compressive strength and triaxial compressive strength of the surrounding rock similar materials with different proportions are carried out to obtain a reasonable proportion of aggregate, binder and adhesive, and the surrounding rock is prepared according to the proportion.

[0052] In step S2, the anchor rod 3 is simulated by the steel bar 17, and the anchoring mortar is composed of cement mortar. Considering that the resin material is easy to age under high temperature, the present embodiment uses a temperature-controllable resin material 16 to simulate the degradation of the anchoring mortar; in addition, the surface primary support 2 includes sprayed concrete and steel arch frame, and the sprayed concrete degradation is also simulated by a temperature-controlled deteriorated resin material, and the steel arch frame 18 is simulated by an iron sheet; the secondary lining 1 is composed of concrete, and its parameters include compressive strength and elastic modulus. In the present embodiment, similar materials for the secondary lining 1 are gypsum and water.

[0053] In addition, when constructing the tunnel support structure model inside the surrounding rock, the following methods are used:

[0054] (1) Apply anchor rods and similar materials: Drill holes at predetermined locations in the surrounding rock material according to the actual distribution of anchor rods, apply a certain thickness of resin material on the surface of the steel bar 17, and after the resin material solidifies and hardens, stick a high-temperature foil strain gauge on its surface, then wrap the anchor rod with a heating tape 19, and finally insert it into the pre-drilled anchor rod hole, such as Figure 2 ;

[0055] (2) Construction of primary surface support: The primary surface support includes shotcrete and steel arch frame, and the steel arch frame 18 is simulated by iron sheet. First, a layer of heating tape 19 is attached to the inner side of the surrounding rock in a circular manner, and then the resin material is applied in layers and in batches on the surface of the heating tape. When the resin material reaches a certain thickness, an iron sheet is placed inside it to simulate the steel arch frame 18, and then the resin material is applied in layers and in batches until the designed thickness is reached. Figure 3 As shown, high temperature foil type strain gauges 20 are attached to the inner and outer sides of the surface primary support, and micro pressure gauges 21 are arranged on the surface ( Figure 4 ), and artificially set the roughness of the inner surface of the surface primary support to characterize the different contact states between the surface primary support and the secondary lining;

[0056] (3) Construction of secondary lining 1: First, prefabricate the secondary lining mold, which consists of an inner mold and an outer mold; first, clean the outer surface of the inner mold and the inner surface of the outer mold of the secondary lining mold and apply a release agent. After assembly, place it on the mold base to complete the model support; place the steel wire braid in the prefabricated mold and then pour a mixture of gypsum and water in a certain proportion. After drying, remove the mold. After the secondary lining 2 solidifies and hardens, paste high-temperature foil strain gauges 20 on the inside and outside. Before the test, install a grating displacement sensor 22 on the inside of the secondary lining 2. Figure 5 As shown;

[0057] In this embodiment, tunnel excavation is performed within the surrounding rock, followed by anchor drilling at pre-set locations. A steel bar and resin material simulating an anchor is inserted into the hole (a high-temperature foil strain gauge and a heating tape are sequentially attached to the surface of the anchor). A heating tape is then circumferentially attached to the inner side of the surrounding rock. The resin material is then applied layer by layer to the surface of the heating tape. Iron sheets are installed to simulate a steel arch frame. High-temperature foil strain gauges and micro-pressure gauges are attached to the inner and outer sides of the surface primary support. Finally, a secondary lining is applied inside the surface primary support, with high-temperature foil strain gauges attached to the inner and outer sides of the secondary lining. A temperature control system is used to adjust the resin material temperature of the surface primary support and anchoring structure in stages, changing the resin material parameters and elastic modulus to simulate the deterioration of the anchor mortar and surface primary support. Deformation and strain testing equipment is then used to record the mechanical response of the tunnel support structure, simulating the gradual deterioration of the initial support structure. This effectively simulates the entire stress and damage process of the tunnel support structure under conditions of performance degradation of the primary support and anchoring structure in soft rock tunnels.

[0058] Finally, in step S4, during the test, the heating tape is connected to a temperature control system. The temperature of the heating tape is adjusted by the temperature control system to change the temperature of the resin material simulating the anchor structure and the surface primary support. This, in turn, changes the elastic modulus of the resin material, achieving a gradual degradation process for the anchor structure and the surface primary support. By conducting physical and mechanical tests on the resin material at different temperatures, a correlation between temperature and the degradation of the primary support structure can be established, achieving the goal of quantitatively determining the degradation of the primary support structure.

[0059] While adjusting the temperature, a cylinder pump was used to load the material in stages. The loading process was carried out slowly to ensure that the test process was a quasi-static process. The monitoring equipment was turned on to record the stress and strain of the surrounding rock and lining during the loading process. The loading level was determined, and the self-weight stress field was simulated according to the geometric similarity ratio. To better ensure the force transmission effect of similar materials, the test was set to about 10 levels each time, with each level increasing by 10%. The pressure was maintained for 3 to 5 minutes each time, based on the measured strain and pressure data. Combined with the stress state of the surrounding rock material, the secondary lining collapse was used as the test termination condition. The mechanical response of the tunnel support model under the combined coupling of temperature and load was realized, and the influence mechanism of the deterioration of the anchor structure and the surface primary support performance on the long-term coordinated bearing characteristics of the soft rock tunnel support structure system was deeply analyzed.

[0060] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any person skilled in the art may utilize the technical contents disclosed above to change or modify them into equivalent embodiments with equivalent changes for application in other fields. However, any simple modification, equivalent change, and modification of the above embodiments made in accordance with the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A test system for mechanical properties of tunnel structures with progressive degradation of primary support, characterized by: It includes a model box, a tunnel support structure model, a deformation and strain testing device, a surrounding rock environment simulation component, a temperature control system, a monitoring system and a servo loading control system. The model box is fixed on a steel foundation base. The tunnel support structure model is fixed in the middle of the model box, and the remaining space of the model box is filled with surrounding rock. The tunnel support structure model includes a primary support model and a secondary lining. The primary support model consists of anchor rods and surface primary supports; the anchor rods are simulated by steel bars, and the anchoring mortar is simulated by temperature-controlled resin materials; the surface primary supports are composed of sprayed concrete and steel arch frames, and the sprayed concrete is simulated by temperature-controlled resin materials, and the steel arch frames are simulated by iron sheets; the secondary lining is simulated by a mixture of gypsum and water in a certain proportion, and heating belts connected to the temperature control system are attached to the surfaces of the anchor rods and the surfaces of the surface primary supports; The deformation and strain testing device is installed on the tunnel support structure model to obtain the mechanical parameters of the tunnel structure during the test. The surrounding rock environment simulation component is connected to the servo loading control system to simulate the environmental pressure of the soil around the tunnel and apply the external load required for the simulation test. The temperature control system is used to control the temperature of the primary support model material to realize the quantitative degradation process simulation of the primary support model.

2. The tunnel structure mechanical properties testing system for primary branch progressive degradation according to claim 1 is characterized in that: The deformation and strain testing device includes a static strain acquisition instrument, a plurality of grating displacement sensors, a plurality of strain gauges, a plurality of micro pressure gauges and a DIC system. The strain gauges and the micro pressure gauges are connected to the static strain acquisition instrument, and the DIC system and the static strain acquisition instrument are connected to the monitoring system. The grating displacement sensor is set up inside the tunnel support structure model and is in contact with the inner surface of the secondary lining. The strain gauge is fixed to the inner and outer sides of the secondary lining and the primary support model, and the plurality of micro pressure gauges are fixed to the outer side of the strain gauge.

3. The tunnel structure mechanical properties testing system for primary branch progressive degradation according to claim 1 is characterized in that: The surrounding rock environment simulation component includes a reaction frame, a hydraulic pump, a jack displacement operator and a perforated steel pad. The pressure end of the surrounding rock environment simulation component acts on the top surface and both sides of the model box. The reaction frame is fixedly connected to the steel foundation base. The fixed end of the hydraulic pump is connected to the reaction frame. The movable end of the hydraulic pump is connected to the jack displacement operator and contacts the perforated steel pad. The perforated steel pad is arranged in contact with the surrounding rock. A pressure sensor is arranged between the jack displacement operator and the perforated steel pad. The hydraulic pump, the jack displacement operator and the pressure sensor are connected to the servo loading control system.

4. The test method of the tunnel structure mechanical properties test system for primary branch progressive degradation according to any one of claims 2-3 is characterized in that: The following steps are involved: Step S1: Calculate the geometric similarity ratio according to the working conditions, configure the surrounding rock similarity material, and determine the surrounding rock grade; Step S2: Determine similar materials and their proportions for the anchor rods, surface primary support, and secondary lining using similarity theory. Then, make a primary support model and secondary lining. Arrange a heating belt on the primary support model. Arrange deformation and strain testing devices on the surfaces of the anchor rods, surface primary support, and secondary lining. Step S3: Filling the model box with surrounding rock-like materials in layers and batches, excavating a tunnel at a preset location, then constructing a tunnel support structure model at the tunnel location, and then connecting a servo loading control system, a static strain acquisition instrument, a monitoring system, and a temperature control system; Step S4, experimental testing: The temperature of the primary support model is adjusted through the temperature control system to change the parameters of the anchor mortar and shotcrete, simulating the attenuation effect of the mechanical properties of the anchor mortar and the surface primary support. At the same time, different stress and surrounding rock load levels are simulated through the servo loading control system, and the structural deformation and strain data during the test are recorded. By analyzing the deformation and strain data, the mechanical response of the tunnel support structure model under the dual effects of temperature and load is studied.

5. The test method of the tunnel structure mechanical properties test system for primary support progressive degradation according to claim 4, characterized in that: In step S1, the surrounding rock similar material is prepared in the following manner: First, based on the prototype parameters and similarity ratio of the surrounding rock, the mechanical parameters of the surrounding rock similar material were obtained with reference to density, deformation modulus, internal friction angle and cohesion; iron powder, barite powder and quartz sand were selected as aggregates of the soft rock similar material, and rosin alcohol and hydraulic oil were used as binders and adhesives respectively; proportioning tests were carried out at room temperature, and uniaxial compressive strength tests and triaxial compressive strength tests were carried out on the surrounding rock similar materials with different proportions to obtain a reasonable proportion of aggregate, binder and adhesive, and the surrounding rock was prepared according to the proportion.

6. The test method of the tunnel structure mechanical properties test system for primary support progressive degradation according to claim 4, characterized in that: In step S2, the ratio of similar materials is determined through indoor material testing. The specific method for determining each similar material is as follows: Rebar is used as a similar material to anchor rods; the surface primary support is composed of shotcrete and a steel frame. Resin is used to simulate shotcrete, and iron sheets simulate the internal steel arch frame. The resin material is temperature-controlled to change the macroscopic mechanical properties of the surface primary support, thereby characterizing the asymptotic degradation process of the surface primary support. Similar materials for the secondary lining are gypsum and water.

7. The test method of the tunnel structure mechanical properties test system for primary branch progressive degradation according to claim 4, characterized in that: In step S2, when implementing the tunnel support structure model, the following methods are specifically adopted: (1) To construct the secondary lining, first prefabricate the secondary lining mold, place the steel wire braid in the secondary lining mold, and then pour a mixture of gypsum and water in a certain proportion. After drying, remove the mold and bake the test piece. After the secondary lining is dried and cured, apply a layer of waterproof varnish on its surface, stick a high-temperature foil strain gauge on the outside of the secondary lining, and arrange a micro pressure gauge on the outer surface. (2) Construction of surface primary support, which includes shotcrete, steel mesh and steel arch frame. The steel arch frame is simulated by iron sheet. A certain thickness of resin material is evenly applied on the surface of the surrounding rock. Shotcrete is configured. Heating tape and high-temperature foil-type strain gauge are attached to the surface of the primary support. Micro pressure gauge is arranged on the surface. The roughness of the inner surface of the surface primary support is artificially set to characterize the different contact states between the surface primary support and the secondary lining. (3) Anchor rods are installed. Drill holes according to the actual distribution of anchor rods, and steel bars are set in the holes around the temperature-controlled deteriorated tunnel support model. Resin is injected into the holes using a syringe to bond the steel bars. After applying resin material on the surface of the steel bars, a heating tape is attached, and a layer of resin material simulating anchor mortar is applied on the surface.

8. The test method of the tunnel structure mechanical properties test system for primary support progressive degradation according to claim 4, characterized in that: In step S3, after the tunnel support structure model is completed, the uniformly mixed surrounding rock similar material is poured into the model box to a certain height, spread evenly, and compacted according to the specified compaction degree; then the tunnel support structure model is placed, and similar material is filled again until it is filled to the top of the model box, and compacted according to the specified compaction degree, and covered with a perforated steel plate.

9. The test method of the tunnel structure mechanical properties test system for primary support progressive degradation according to claim 4, characterized in that: In step S4, when performing the test: By adjusting the temperature of the heating belt through the temperature control system, the target temperature of the anchor structure and the surface primary support can be adjusted, the elastic modulus of the resin material can be changed, the physical and mechanical parameters of the material at different temperatures can be obtained, and the relationship between temperature and the degradation of the primary support structure performance can be established, thus achieving the purpose of quantitative degradation of the primary support structure. Among them, while adjusting the temperature, a servo loading control system is used to perform slow graded loading to ensure that the test process is a quasi-static process, and the stress and strain of the primary support model and secondary lining during the loading process are recorded through the monitoring system; the loading level is determined, and the self-weight stress field is simulated according to the geometric similarity ratio. Combined with the stress state of similar materials in the surrounding rock, the collapse of the secondary lining is used as the termination condition of the test.

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