Tunnel structure mechanical property test method and system aiming at gradual deterioration of primary support

Abstract

The invention belongs to the technical field of tunnel engineering, and particularly relates to a tunnel structure mechanical property test method and system for initial support asymptotically deteriorated. And according to a working condition conversion geometric similarity ratio, configuring a surrounding rock similar material, determining a supporting similar material and material parameters in combination with a similarity theory, and manufacturing a temperature control degradation tunnel structure supporting model. By adjusting the temperature of the anchoring mortar and the initial support similar material to change the macromechanical properties, the degradation effect of the initial support structure is represented, the asymptotic degradation process of the initial support structure is simulated, the load transfer mechanism and the bearing characteristic evolution rule of a soft rock tunnel structure system under the asymptotic degradation condition of the initial support structure can be realized, and the construction efficiency is improved. And the influence degrees of various factors such as anchor body degradation rate, anchor body degradation position, surface layer primary support degradation rate, surface layer primary support degradation position, surface layer primary support inner surface roughness (smoothness, moderation and roughness), secondary lining mechanics and the like on surrounding rock deformation and support structure deformation and stress can be systematically analyzed.

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 mechanical properties of tunnel structures with progressive degradation of primary branches. Background Art

[0002] Tunnel structural diseases are the result of long-term adverse effects between support and surrounding rock. Their essence is the change in the stress conditions of the structural system caused by changes in the state of support and surrounding rock. For soft rock tunnel projects, although some tunnels can maintain their short-term stability, as the service life of the tunnel increases, the surrounding rock load effect caused by rock rheology will break this short-term stability and threaten the safety of tunnel operation. The support structure of soft rock tunnels is generally composed of initial support (anchor rods, shotcrete and steel frame combined support) and secondary lining. At present, the deterioration of the support structure of soft rock tunnels is relatively widespread.

[0003] In the prior art, since the initial support is usually covered by the permanent support in the subsequent construction, the attention paid to its degradation problem is relatively low. In addition, it is generally believed that the degradation of the initial support has little impact on the entire project. Therefore, the value of its research is not fully recognized, resulting in relatively few studies on the degradation of the initial support, and the design is mainly for the degradation of the secondary lining. For example, the invention patent with the application publication number [CN115728216A] discloses an accelerated corrosion test device for lining structures, which timely discharges the corrosive liquid containing rust products through the first pipeline, and the discharged corrosive liquid is filtered through the filter box and then returned to the designed concentration corrosive liquid storage tank to avoid excessive rust products in the corrosion tank and the rust products adhering to the surface of the lining structure and embedding in the rust cracks, so that the environment in the corrosion tank is closer to the corrosion situation in the underground, especially the underwater erosion environment, so as to more accurately study the corrosion degradation law of the tunnel lining structure under this condition, and provide important support for accurately and scientifically evaluating the safety and reliability performance of the tunnel lining structure during the entire life cycle.

[0004] But in fact, the degradation of initial support performance will inevitably change the mechanical state of the soft rock tunnel support structure system. For soft rock tunnel projects with significant long-term load effects on surrounding rocks, the coupling effect of initial support degradation and surrounding rock rheology will make the long-term mechanical response of the support structure system complicated. In this dynamic adjustment process, how the load of the anchor structure, surface initial support (sprayed concrete + steel frame) is distributed, how the function evolves, and how the various support structures play a synergistic role in bearing, all of these issues affect the long-term safety of the soft rock tunnel structure system.

[0005] Therefore, it is urgent to develop a similar model system and method for the soft rock tunnel support structure system considering the initial 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 initial support degradation, and to achieve 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 solve the problems of relative scarcity of research on initial support degradation in the prior art, the present invention proposes a test method and system for the mechanical properties of soft rock tunnel structures with asymptotic degradation of initial support, and achieves the purpose of quantitative degradation of the initial support structure by 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 collaborative bearing characteristics of the soft rock tunnel support structure system.

[0007] The present invention is implemented by adopting the following technical scheme: a test system for mechanical properties of soft rock tunnel structures with gradual deterioration of initial support, comprising a model box, a tunnel support structure model, a deformation and strain test 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; The tunnel support structure model is fixed in the middle of the model box, and the rest of the 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. A heating belt connected to a temperature control system is pasted on the surface of the anchor rods and the surface 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 soil environment pressure 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 achieve quantitative degradation process simulation of the primary support model.

[0008] The core of this scheme is how to realize the simulation of the asymptotic deterioration process of the initial support. It proposes to use resin materials to simulate the mortar materials of the anchor rods and the shotcrete materials of the surface initial support, and stick heating belts on the surfaces of the anchor rods and the surface initial support. The heating belts are connected to the temperature control system, and the anchor rods and the surface initial support are heated to achieve the asymptotic degradation process of the macroscopic mechanical properties of the equivalent initial support.

[0009] Furthermore, the deformation and strain testing device includes a static strain collector, 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 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 the plurality of micro pressure gauges are fixed to the outside of the strain gauge.

[0010] 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-applying 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.

[0011] 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 gypsum and water mixed in a certain proportion.

[0012] The present invention further proposes a test method for a tunnel structure mechanical property test system considering the asymptotic degradation of the primary branch, comprising the following steps: Step S1, converting the geometric similarity ratio according to the working conditions, configuring the surrounding rock similar materials, and determining the surrounding rock grade; Step S2, combining similarity theory to determine similar materials and proportions of anchor rods, surface primary support and secondary lining; then making a primary support model and secondary lining, laying a heating belt on the primary support model, and arranging deformation and strain testing devices on the surfaces of anchor rods, surface primary support and secondary lining; Step S3, filling the model box with similar materials of surrounding rocks in layers and batches, excavating a tunnel at a preset position, then constructing a tunnel support structure model at the tunnel position, and then connecting a servo loading control system, a static strain collector, a monitoring system and a temperature control system; Step S4, experimental test: adjust the temperature of the primary support model 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 simulate different stress and surrounding rock load levels through the servo loading control system, record the structural deformation and strain data during the test, and study the mechanical response of the tunnel support structure model under the dual effects of temperature and load by analyzing the deformation and strain data.

[0013] Furthermore, in step S1, the surrounding rock similar material is prepared in the following manner: Firstly, based on the prototype parameters and similarity ratio of the surrounding rock, the mechanical parameters of the surrounding rock similar materials with reference to density, deformation modulus, internal friction angle and cohesion were obtained; iron powder, barite powder and quartz sand were selected as aggregates of soft rock similar materials, and rosin alcohol and hydraulic oil were used as binders and adhesives respectively; proportioning tests were carried out at room temperature, and the uniaxial compressive strength and triaxial compressive strength of surrounding rock similar materials with different proportions were carried out to obtain a reasonable proportion of aggregate, binder and adhesive, and the surrounding rock was prepared according to the proportion.

[0014] Furthermore, in step S2: The similar materials are determined as follows: 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.

[0015] When implementing the tunnel support structure model, the following methods are used: (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, paste a high-temperature foil strain gauge on the outside of the secondary lining, and arrange a micro pressure gauge on the outer surface; (2) Construct the 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 gauges are 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 set steel bars in the drill holes around the temperature-controlled deteriorated tunnel support model. Resin is injected into the drill 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.

[0016] 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 in, 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 pad.

[0017] Furthermore, in step S4, when performing the test: The temperature of the heating belt is adjusted through the temperature control system to adjust the target temperature of the anchoring structure and the surface primary support, change the elastic modulus of the resin material, obtain the physical and mechanical parameters of the material at different temperatures, establish the relationship between temperature and the performance degradation of the primary support structure, and achieve the purpose of quantitative degradation of the initial 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.

[0018] Compared with the prior art, the advantages and positive effects of the present invention are: This scheme uses resin materials to simulate the anchor mortar and shotcrete in the soft rock tunnel support structure, and then simulates the asymptotic deterioration process of the initial support structure by adjusting the temperature and changing the parameters of the anchor mortar and the surface primary support materials. It effectively simulates the changes in the anchor body degradation rate, anchor body degradation position, surface primary support degradation rate, surface primary support degradation position, surface primary support inner surface roughness (smooth, moderate, rough) and secondary lining mechanical parameters. The deformation and strain testing device installed in the tunnel model is used to record the stress response of the tunnel model, so as to systematically analyze the influence mechanism of the degradation 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of a test system according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the anchor support and heating belt arrangement structure according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the arrangement structure of the surface primary support and the heating belt in an embodiment of the present invention; Figure 4 This is a schematic diagram of the installation position structure of the surface primary support strain gauge and the micro pressure gauge in an embodiment of the present invention; 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; Among them, 1. Secondary lining; 2. Primary support of the surface layer; 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

[0020] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and therefore, the present invention is not limited to the specific embodiments disclosed below.

[0021] Embodiment 1, as Figure 1 As described above, this embodiment proposes a mechanical property test system for a tunnel structure with asymptotic degradation of primary support, including a model box 7, a tunnel support structure model, a deformation and strain test 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 anchor mortar are changed, thereby achieving the conditions for quantitative degradation of the initial support structure.

[0022] Continue to refer Figure 1 The model box 7 is assembled by a steel frame and organic glass plates on all sides. The model box 7 is fixed on a 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 test device is installed on the tunnel support structure model.

[0023] The pressure end of the surrounding rock environment simulation component acts on the top surface and both sides of the model box 7. Figure 1The 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.

[0024] 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 side of the secondary lining 1 and the surface primary support 2.

[0025] In this embodiment, micro pressure gauges and high-temperature foil strain gauges are arranged to record the surrounding rock stress and the mechanical response of the support structure throughout the process; the tunnel structure deformation is obtained by a non-contact deformation measurement and analysis system. The high-definition measuring head of the system can realize image acquisition during the test process, and the DIC system can complete the calculation of the image for analyzing the displacement field, strain field, velocity field and acceleration field of the surrounding rock and the support structure.

[0026] Example 2, based on the experimental system described in Example 1, this example proposes a corresponding experimental method, including the following steps: Step S1, converting the geometric similarity ratio according to the working conditions, configuring the surrounding rock similar materials, and determining the surrounding rock grade; Step S2, determine similar materials and proportions of anchor rods, surface primary support and secondary lining in combination with similarity theory; then make a tunnel support structure model, and arrange deformation and strain testing devices on the support structure; Step S3, fill the model box with similar materials of surrounding rock in layers and batches, excavate the tunnel at the preset position, and then construct the tunnel support structure model at the tunnel position. The tunnel support structure model includes anchor rods, surface primary support and secondary lining. In this process, it is necessary to ensure that the support structure is in close contact with the surrounding rock and the contact integrity between each support. Then connect the servo loading control system 9, static strain collector 10, monitoring system 11 and temperature control system 12.

[0027] Step S4, adjusting the temperature of the anchor rod and the surface primary support through the temperature control system to change the parameters of the anchor mortar and the shotcrete, simulating the attenuation effect of the mechanical properties of the anchor mortar and the surface primary support, and using the servo loading control system to simulate different ground stresses and surrounding rock load levels, setting graded loading until the support structure is destroyed, monitoring 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 recording the stress data and strain data.

[0028] 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 with reference to density, deformation modulus, internal friction angle and cohesion are obtained; 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 aggregates, binders and adhesives, and surrounding rock similar materials are prepared according to the proportions, and surrounding rock similar materials are weighed and configured on a large scale according to the specified proportions of the materials, and the materials are uniformly stirred with a mixer; the uniaxial compressive strength and triaxial compressive strength of surrounding rock similar materials with different proportions are carried out to obtain a reasonable proportion of aggregates, binders and adhesives, and surrounding rock is prepared according to the proportions.

[0029] In step S2, the anchor rod 3 is simulated by the steel bar 17, and the anchor mortar is composed of cement mortar. Considering that the resin material is easy to age under high temperature, the temperature-controllable resin material 16 is used in this embodiment to simulate the degradation of the anchor mortar; in addition, the surface primary support 2 includes shotcrete and steel arch frame, and the temperature-controlled deteriorated resin material is also used to simulate the degradation of shotcrete, and the iron sheet simulates the steel arch frame 18; the secondary lining 1 is composed of concrete, and its parameters include compressive strength and elastic modulus. The similar materials of the secondary lining 1 in this embodiment are gypsum and water.

[0030] In addition, when constructing the tunnel support structure model inside the surrounding rock, the following methods are specifically adopted: (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, paste 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 ; (2) Construction of surface primary support: The surface primary support includes shotcrete and steel arch frame, and the steel arch frame 18 is simulated by iron sheet. First, a layer of heating belt 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 belt. 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 3As shown, high temperature foil-type strain gauges 20 are pasted on the inner and outer sides of the surface primary support, and a micro pressure gauge 21 is arranged on the surface ( Figure 4 ), and by artificially setting the roughness of the inner surface of the surface primary support, the different contact states between the surface primary support and the secondary lining are characterized; (3) Construction of secondary lining 1: First, prefabricate the secondary lining mold, which consists of an inner mold and an outer mold. First, wipe the outer surface of the inner mold and the inner surface of the outer mold of the secondary lining mold clean 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 the high-temperature foil strain gauge 20 on the inside and outside. Before the test, install the grating displacement sensor 22 on the inside of the secondary lining 2. Figure 5 As shown; In this embodiment, tunnel excavation is carried out inside the surrounding rock, and then anchor holes are drilled at preset positions, and steel bars + resin materials simulating anchors are inserted into the holes (high-temperature foil strain gauges and heating belts are sequentially pasted on the surface of the anchors), and then heating belts are circumferentially pasted on the inner side of the surrounding rock, and then resin materials are applied layer by layer and in batches on the surface of the heating belts, iron sheets are installed to simulate steel arch frames, and high-temperature foil strain gauges and micro pressure gauges are pasted on the inner and outer sides of the surface primary support; finally, secondary lining is applied on the inner side of the surface primary support, and high-temperature foil strain gauges are pasted on the inner and outer sides of the secondary lining. The temperature control system is used to adjust the resin material temperature of the surface primary support and anchoring structure in stages, change the resin material parameters and elastic modulus, and simulate the deterioration effect of the anchoring mortar and the surface primary support; and the deformation and strain test device is used to record the mechanical response of the tunnel support structure, so as to simulate the asymptotic deterioration process of the initial support structure, and effectively simulate the whole process of stress and destruction of the tunnel support structure under the condition of performance degradation of the primary support and anchoring structure of the soft rock tunnel.

[0031] Finally, in step S4, when conducting the test: connect the heating belt to the temperature control system, and adjust the temperature of the heating belt through the temperature control system to change the temperature of the resin material simulating the anchoring structure and the surface primary support, thereby changing the elastic modulus of the resin material to achieve the gradual degradation process of the anchoring structure and the surface primary support. Among them, by conducting physical and mechanical tests on resin materials at different temperatures, the relationship between temperature and the degradation of the performance of the primary support structure can be established, so as to achieve the purpose of quantitative degradation of the initial support structure.

[0032] While adjusting the temperature, use a cylinder pump to load in stages, and proceed slowly during the loading process to ensure that the test process is a quasi-static process. Turn on the monitoring equipment to record the stress and strain of the surrounding rock and lining during the loading process. Determine the loading level, simulate the self-weight stress field according to the geometric similarity ratio, and set the test to about 10 levels each time to better ensure the force transmission effect of similar materials, increase each level by 10%, and stabilize the pressure 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 is used as the termination condition of the test. Realize the mechanical response of the tunnel support model under the joint coupling of temperature and load, and deeply analyze the influence mechanism of the anchor structure and the degradation of the surface initial support performance on the long-term collaborative bearing characteristics of the soft rock tunnel support structure system.

[0033] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A test system for mechanical properties of tunnel structures with progressive degradation of primary branches, characterized by: It includes a model box, a tunnel support structure model, a deformation and strain test 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 rest of the 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. A heating belt connected to a temperature control system is pasted on the surface of the anchor rods and the surface 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 soil environment pressure 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 achieve quantitative degradation process simulation of the primary support model.

2. The tunnel structure mechanical properties test system considering the asymptotic degradation of the primary branch according to claim 1 is characterized in that: The deformation and strain testing device includes a static strain collector, 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 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 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 test system considering the asymptotic degradation of the primary branch 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 tunnel structure mechanical properties test system considering the asymptotic degradation of the primary branch according to claim 1 is characterized in that: 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 a mixture of gypsum and water in a certain proportion.

5. The test method of the tunnel structure mechanical characteristics test system considering the asymptotic degradation of the primary branch according to any one of claims 2 to 4 is characterized in that: The following steps are involved: Step S1, converting the geometric similarity ratio according to the working conditions, configuring the surrounding rock similar materials, and determining the surrounding rock grade; Step S2, combining similarity theory to determine similar materials and proportions of anchor rods, surface primary support and secondary lining, then making a primary support model and secondary lining, laying a heating belt on the primary support model, and arranging deformation and strain testing devices on the surfaces of anchor rods, surface primary support and secondary lining; Step S3, filling the model box with similar materials of surrounding rocks in layers and batches, excavating a tunnel at a preset position, then constructing a tunnel support structure model at the tunnel position, and then connecting a servo loading control system, a static strain collector, a monitoring system and a temperature control system; Step S4, experimental test: adjust the temperature of the primary support model 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 simulate different stress and surrounding rock load levels through the servo loading control system, record the structural deformation and strain data during the test, and study the mechanical response of the tunnel support structure model under the dual effects of temperature and load by analyzing the deformation and strain data.

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

7. The test method of the tunnel structure mechanical characteristics test system considering the asymptotic degradation of the primary branch according to claim 5 is characterized by: In step S2, the ratio of similar materials is determined through indoor material testing, and the specific method for determining each similar material is as follows: The similar material of anchor rod is steel bar; the surface primary support is composed of shotcrete and steel frame, resin material is used to simulate shotcrete, iron sheet is used to simulate the internal steel arch frame, and the macroscopic mechanical properties of the surface primary support are changed by controlling the temperature of the resin material, so as to characterize the asymptotic deterioration process of the surface primary support; Similar materials for secondary lining are gypsum and water.

8. The test method of the tunnel structure mechanical characteristics test system considering the asymptotic degradation of the primary branch according to claim 5 is characterized by: In step S2, when realizing the tunnel support structure model, the following method is 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, paste a high-temperature foil strain gauge on the outside of the secondary lining, and arrange a micro pressure gauge on the outer surface; (2) Construct the 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 gauges are 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 set steel bars in the drill holes around the temperature-controlled deteriorated tunnel support model. Resin is injected into the drill 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.

9. The test method of the tunnel structure mechanical characteristics test system considering the asymptotic degradation of the primary branch according to claim 5 is characterized by: 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 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 pad.

10. The test method of the tunnel structure mechanical characteristics test system considering the asymptotic degradation of the primary branch according to claim 5 is characterized by: In step S4, when performing the test: The temperature of the heating belt is adjusted through the temperature control system to adjust the target temperature of the anchoring structure and the surface primary support, change the elastic modulus of the resin material, obtain the physical and mechanical parameters of the material at different temperatures, establish the relationship between temperature and the performance degradation of the primary support structure, and achieve the purpose of quantitative degradation of the initial 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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