An experimental device and experimental method for simulating tunnel stratum gas extraction

Abstract

The present invention relates to the technical field of experimental research on tunnel engineering, and in particular to an experimental device and an experimental method for simulating gas extraction from tunnel strata, comprising an experimental box, a tunnel model, geological simulation materials, a top loading component and an extraction component, wherein the tunnel model sealing sleeve is installed in a mounting hole, the inner side surface of the tunnel model is an excavation surface, a differential digital displacement meter, a strain type soil pressure box and a gas pressure sensor are arranged on the outer side surface of the tunnel model, a differential digital displacement meter and a resistance strain gauge are arranged on the excavation surface, the geological simulation materials include stratum simulation materials and coal series simulation materials, the top loading component includes a force transmission plate, a reaction frame, an air injection port and an air supply pump, and the extraction component includes a partition, an extraction pipe and an extraction pump, so as to simulate the working conditions of gas extraction from gas strata of different types of tunnels, thereby providing a theoretical basis and technical support for gas extraction from different types of gas tunnels in the future.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel engineering experimental research, and in particular to an experimental device and an experimental method for simulating tunnel stratum gas extraction. Background Art

[0002] In recent years, with the implementation of my country's strategy of building a strong transportation nation, railway and highway transportation in mountainous areas has developed rapidly, and the scale of tunnel construction has become larger and larger, accompanied by various complex adverse geological phenomena. Among them, gas disasters are common geological disasters in tunnel construction in mountainous areas in western my country in recent years. Gas is widely present in coal-bearing strata and various non-coal-bearing strata. At present, the most common prevention and control method for tunnel stratum gas disasters is to depressurize and drain stratum gas in strata suitable for gas extraction.

[0003] The specific implementation method of gas extraction is to arrange gas extraction boreholes at preset intervals on the tunnel excavation face suitable for gas extraction, and discharge gas from various strata, especially coal-bearing strata, out of the tunnel. During the gas extraction process, due to the continuous decrease in stratum gas pressure, under the dual effects of tunnel excavation disturbance and stratum gas pressure changes, the deformation and displacement of the stratum is difficult to avoid, affecting the stability of the excavation face, and in severe cases, causing collapse. Therefore, in the process of gas extraction from the stratum, it is very important to control the mechanism of the influence of stratum gas pressure relief extraction on the stability of the surrounding rock near the excavation face. If the stress-strain law of the surrounding rock near the excavation face can be mastered, it can provide a reliable theoretical basis and safety technical guidance for the safe construction of stratum gas extraction in similar gas tunnels.

[0004] At present, there are few studies on the influence mechanism of gas extraction effect on tunnel surrounding rock stability, and most of them are biased towards the study of extraction parameters. In contrast, the study of formation gas extraction effect through model experiments can better restore the actual situation of the influence of the extraction process on the tunnel surrounding rock to the greatest extent. However, since gas is a flammable and explosive gas, there is a certain risk, and improper operation will cause accidents. In the simulation system and experimental method for gas extraction and control to stabilize the tunnel excavation face, such as patent CN210533735U, the entire process of formation gas drilling and extraction is simulated, but there are some problems. For example, the use of real gas for model experiments places extremely high requirements on the explosion-proof and operation of the device; at the same time, patent CN210533735U does not distinguish between the types of gas formations, and uses an integrated formation simulation material, while tunnel gas formations are mainly divided into coal formations and non-coal formations, and there is a large difference in the gas occurrence state of the two. The gas occurrence state of coal formations is relatively stable, and the position of coal formations is relatively fixed; non-coal formation gas can be randomly distributed in the formation in front of the tunnel excavation face. Based on this, it is necessary to study an experimental device and experimental method for simulating tunnel formation gas extraction. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide an experimental device and experimental method for simulating tunnel stratum gas extraction, which effectively solves the problem that the existing experimental device model for simulating tunnel stratum gas extraction is different from the real stratum and the model is inaccurate.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present invention is: an experimental device for simulating tunnel stratum gas extraction, comprising an experimental box, a tunnel model, geological simulation materials, a top loading component and an extraction component; the upper part and the side of the experimental box are respectively provided with an open mouth and a mounting hole, the tunnel model is sealed and sleeved in the mounting hole, the inner side of the tunnel model is an excavation surface, a differential digital displacement meter, a strain type earth pressure box and a gas pressure sensor are arranged on the outer side of the tunnel model, a differential digital displacement meter and a resistance strain gauge are arranged on the excavation surface, a bracket supporting the inner end of the tunnel model is arranged in the experimental box, the geological simulation materials include stratum simulation materials and coal series simulation materials, the coal series simulation materials are arranged in a gauze to form a coal seam model, and the The coal seam model is arranged in front of the excavation face, and a plurality of extraction pipes are arranged between the gauze and the excavation face, and air holes are evenly distributed on the outer circumference of the extraction pipes, and the formation simulation material fills the gap between the coal series model and the tunnel model; the top loading assembly includes a force transmission plate, a reaction frame, an air injection port and an air supply pump, the force transmission plate is adapted to the open port, and the experimental box is closed by a sealing gasket, the rear side of the force transmission plate is installed on the reaction frame via a force cylinder, an air injection pipe is installed in the air injection port, and the air injection pipe is connected to the air supply pump via a valve, the extraction assembly includes a partition, an extraction pipe and an extraction pump, the partition is arranged in the tunnel model, and an extraction cavity is formed between the partition and the excavation face, the extraction pipe is sealed and mounted on the partition and the tunnel model, and the inner and outer ends of the extraction pipe are respectively connected to the extraction cavity and the extraction pump.

[0007] Furthermore, the tunnel model includes a main structure and an upper arc cover. The upper part of the main structure is provided with an opening, and the interior is a hollow model cavity. The partition extends into the main structure from the opening and divides the model cavity into a pumping cavity and a tunnel cavity. The upper arc cover is sealed and sleeved in the opening.

[0008] Furthermore, the main structure and the upper arc cover are cast with prefabricated formwork concrete, and the partition is an acrylic plate structure, which is adapted to the inner cavity of the main structure and is sealed to the upper arc cover and the main structure by sealant.

[0009] Furthermore, a plurality of air inlets are provided on the excavation surface, a plurality of connection ports are provided on the gauze, both ends of the extraction pipe are inserted into the air inlets and the connection ports, and penetrate into the extraction cavity and the coal-bearing simulation material, and air holes are provided at the front end and the outer side surface of the extraction pipe, and the air holes are covered with a filter screen, and the pore size of the filter screen is smaller than the particle size of the formation simulation material.

[0010] Furthermore, the force transmission plate includes a left force transmission plate, a right force transmission plate and a middle force transmission plate, wherein the middle force transmission plate corresponds to the coal-bearing simulation material, the left and right force transmission plates correspond to the formation simulation materials on the left and right sides respectively, and the outer sides of the left force transmission plate, the right force transmission plate and the middle force transmission plate are respectively fixed on the reaction frame through corresponding force cylinders.

[0011] Furthermore, the inner sides of the left and right force transfer plates are sealed through a middle sealing seat and a middle force transfer plate combination, and the middle sealing seat includes a U-shaped seat body, a partition plate and a sealing plate, and the sealing plate and the partition plate are respectively arranged on the upper and lower sides of the seat body, and the inner sides of the left and right force transfer plates are against the two sides of the sealing plate, and are provided with grooves corresponding to the clamping plates on both sides of the seat body, and a sealing gasket is arranged in the groove, and the clamping plate sealing sleeve is installed in the groove.

[0012] Furthermore, the air supply pump is connected to a pressure divider, and different outlets of the pressure divider are respectively connected to the air injection ports of the left force transmission plate, the right force transmission plate and the middle force transmission plate through corresponding pipelines.

[0013] Furthermore, a rotating shaft is rotatably arranged on the side wall of the experimental box, a driving handwheel is arranged at the outer end of the rotating shaft, a mounting seat is fixed at the inner end of the rotating shaft, the other side of the mounting seat is rotatably arranged on the experimental box, and the gauze is matched and mounted in the mounting seat.

[0014] An experimental method for simulating tunnel stratum gas extraction includes the following steps

[0015] Step 1: Process the tunnel model

[0016] The data line and the extraction pipe are sealed and put into the tunnel model through perforation, and the differential digital displacement meter, strain type earth pressure box and gas pressure sensor are arranged on the outside of the tunnel model, and the differential digital displacement meter and resistance strain gauge are arranged on the excavation surface, and then the tunnel model is placed in the experimental box;

[0017] Step 2: fix the separation gauze of the stratum simulation material in the experimental box at a certain angle; extend one end of a plurality of gas extraction pipes into and fix them on the excavation surface, and insert the other end into the gauze at a fixed angle;

[0018] Step 3: Place the two formation simulation materials in inflatable sealed bags respectively in advance, inject the carbon dioxide-nitrogen mixed gas into the two sealed bags, seal them after expansion, fully contact and mix the formation simulation materials with the simulated mixed gas, and leave them for 12 hours;

[0019] Step 4: Place the processed coal-series simulation material into the gauze, fill the other spaces of the experimental box with the formation simulation material, and install the force transfer plate on the upper part of the experimental box to seal the box;

[0020] Step 5: Open the gas injection valve and the gas supply pump to inject simulated gas into the experimental box to simulate the overburden pressure; after the pressure gauge stabilizes, turn off the booster pump and close each gas injection valve; open the gas extraction valve and the gas extraction pump to extract the gas in the formation simulation material of the experimental box;

[0021] Step 6: The data processing terminal records the real-time data monitored by the strain type earth pressure cell, displacement meter, strain gauge and gas pressure sensor, and dynamically displays it through the display terminal;

[0022] Furthermore, the simulated gas is a mixture of 45% carbon dioxide and 55% nitrogen.

[0023] The beneficial effects of the above technical solution are:

[0024] 1. The present invention adopts the method of pre-drilling and sets the extraction pipe in advance to reduce the gas pressure loss before the extraction experiment starts, and focuses on simulating the process of tunnel stratum gas extraction, so as to obtain the parameter changes of the influence of stratum gas pressure relief and extraction on the tunnel excavation face and surrounding rock, providing a theoretical basis and technical support for gas extraction in similar tunnel projects.

[0025] 2. The present invention uses a carbon dioxide-nitrogen mixture with a carbon dioxide volume fraction of 45% to simulate and replace real gas. It can not only truly simulate the changes in the morphological parameters of the formation caused by the pressure release of formation gas, but also greatly reduce the danger of using real gas for indoor experiments.

[0026] 3. The present invention uses two different formation simulation materials to simulate conventional formation surrounding rocks and common gas-containing coal-bearing formations. The inclination of the coal-bearing formations can be adjusted by flexibly adjusting the angle of the separation mesh, and the gas extraction conditions of the tunnel passing through the coal-bearing formations at different angles can be simulated.

[0027] 4. The present invention can simulate the gas extraction working conditions of two different typical gas tunnels passing through non-coal formations and coal formations respectively by flexibly installing and removing the gauze: use the gauze to separate two different formation simulation materials to simulate the gas extraction working conditions of the tunnel passing through the coal formation; after the experiment, take out the gauze, take out the coal formation formation simulation material, and only use conventional surrounding rock formation simulation material to fill the experimental box, repeat the experimental steps, and simulate the working conditions of gas extraction in non-coal formation tunnels.

[0028] 5. The present invention sets corresponding force transmission plates above the formation simulation material and the coal-bearing simulation material. The force transmission plates are sealed and combined with each other and can slide relatively, thereby providing corresponding overlying soil pressure on the corresponding simulation material. At the same time, the partition plate penetrates deep into the material, so that the gas injected by the gas injection pipe gathers and separates at the end, simulating the pressure difference caused by different porosities, which is more in line with the existing formation characteristics.

[0029] Therefore, in view of the characteristics of existing gas tunnels during stratum gas extraction construction and the deficiencies in the research on the influence of gas extraction effect on the stability of the surrounding rock in front of the extraction section, the present invention overcomes the deficiencies in the prior art and provides an experimental device and experimental method for simulating tunnel stratum gas extraction. The device can simulate the working conditions of gas extraction in gas strata of different types of tunnels by reasonably using gauze to separate different stratum simulation materials and stratum inclination angles, and obtain the influence mechanism of stratum pressure relief on the surrounding rock in front of the excavation face and the stability of tunnel support, thereby providing a theoretical basis and technical support for gas extraction in different types of gas tunnels in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a structural schematic diagram of the present invention;

[0031] Figure 2 It is a schematic diagram of the internal structure of the present invention;

[0032] Figure 3 This is a schematic diagram of the tunnel model.

[0033] Figure 4 It is a cross-sectional view of the internal structure of the present invention;

[0034] Figure 5 It is a schematic diagram of the structure of the extraction pipe;

[0035] Figure 6 is another structural schematic diagram of the force transmission plate;

[0036] Figure 7 Schematic diagram of the mounting results.

[0037] Figure numerals: 1-experimental box; 2-tunnel model; 3-external support structure; 4-excavation surface; 5-external sealing surface; 6-force cylinder; 7-force transmission plate; 8-stratum simulation material; 9-coal series simulation material; 10-pumping pipe; 11-differential digital displacement meter; 12-strain type earth pressure box; 13-gas pressure sensor; 14-resistance strain gauge; 15-gas injection port; 16-gas injection pipe; 17-pumping pipe; 18-pressure gauge; 19- Extraction valve; 20-data transmission port; 21-data transmission line; 22-inlet valve; 23-gauze; 24-bracket; 25-air supply pump; 26-extraction pump; 201-partition; 202-upper arc cover; 203-extraction interface; 204-main structure; 205-extraction pipe drilling hole; 1001-air vent; 1002-pipe mouth gauze, 27 is the seat body, 28 is the sealing plate, 29 is the partition plate, 30 is the driving hand wheel, and 32 is the mounting seat. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The schematic implementation modes of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention. The present invention is further described in detail below in conjunction with drawings and specific implementation modes.

[0039] Example 1. This example aims to provide an experimental device for simulating gas extraction from tunnel strata, which is mainly used to simulate the parameter changes on the tunnel surface during the gas extraction process from tunnel strata. The existing experimental simulation devices have limited structures, and there are differences between the simulated scenes and the real strata, and cannot truly reflect the changes in parameters such as force and displacement on the tunnel surface. Based on this, an experimental device for simulating gas extraction from tunnel strata is studied.

[0040] like Figure 1-4 An experimental device for simulating gas extraction from tunnel strata is shown, comprising an experimental box 1, a tunnel model 2, geological simulation materials, a top loading assembly and an extraction assembly; wherein the upper part and the side of the experimental box are respectively provided with an open opening and a mounting hole, the experimental box 1 is a box-like structure without a cover, and the stratum simulation material 8, the coal-bearing simulation material 9, the gauze 23, the extraction pipe 10 and the tunnel model 2 are all located in the experimental box.

[0041] The tunnel model 2 is sealed and sleeved in the mounting hole. The inner side of the tunnel model 2 is the excavation surface 4. The outer side of the tunnel model 2 is arranged with a differential digital displacement meter 11, a strain type earth pressure box 12 and a gas pressure sensor 13. The differential digital displacement meter 11 and a resistance type strain gauge 14 are arranged on the excavation surface 4. A bracket 24 supporting the inner end of the tunnel model is arranged in the experimental box 1. The outer side of the primary lining of the tunnel model 2 of this embodiment is arranged with a differential digital displacement meter 11, a strain type earth pressure box 12 and a gas pressure sensor 13; the edge of the tunnel excavation surface is arranged with a resistance type strain gauge 14, and a plurality of differential digital displacement meters 11 are arranged at the longitudinal center axis of the excavation surface; the differential digital displacement meter 11, the strain type earth pressure box 12, the gas pressure sensor 13 and the resistance type strain gauge 14 are all connected to the data transmission line 21 through the data transmission interface 20, and are connected to the external terminal. The gas pressure sensor 13 of this embodiment is arranged outside the primary lining of the tunnel model 2 and in the coal-bearing stratum formation simulation material.

[0042] In specific structures such as Figure 3In the figure, the tunnel model 2 includes a main structure 204 and an upper arc cover 202. The upper part of the main structure 204 is provided with an opening, and the interior thereof is a hollow model cavity. The partition 201 extends into the main structure 204 from the opening, and divides the model cavity into a pumping cavity and a tunnel cavity. The upper arc cover 202 is sealed and sleeved in the opening. The main structure 204 and the upper arc cover 202 are cast with prefabricated template concrete. The partition 201 is an acrylic plate structure. The partition 201 is adapted to the inner cavity of the main structure 204 and is sealed on the upper arc cover and the main structure by a sealant. After the assembly is completed, the tunnel model 2 of this embodiment is divided into two parts, the upper part has a semicircular cross section, and the lower part has a rectangular cross section, which are cast using concrete templates respectively. The external sealing surface 5 and the excavation surface 4 are cast in one piece, and the external sealing surface 5 is provided with holes for data transmission and gas pipelines, and the excavation surface end is provided with a pumping pipe drilling 205; a partition 201 is provided near one end of the excavation surface. After installing various monitoring devices, the tunnel model 2 is installed, fixed and bonded at the reserved hole position of the experimental box, and two brackets 24 are provided at the bottom for fixing the tunnel model 2. Except for the upper opening and the reserved tunnel lining model holes, the rest of the experimental box 2 of this embodiment is sealed.

[0043] like Figure 5 As shown in the figure, a plurality of air inlets are arranged on the excavation surface 4, a plurality of connection ports are arranged on the gauze, both ends of the extraction pipe 10 are inserted into the air inlets and the connection ports, and penetrate into the extraction cavity and the coal-bearing simulation material, and air holes 1001 are arranged at the front end and the outer side surface of the extraction pipe, and the air holes 1001 are covered with a filter screen, the aperture of the filter screen is smaller than the particle size of the formation simulation material, and a pipe mouth gauze 1002 is also arranged at the front end of the extraction pipe 10.

[0044] The geological simulation material includes a formation simulation material 8 and a coal-bearing simulation material 9. The coal-bearing simulation material 9 is arranged in a gauze to form a coal seam model. The coal seam model is arranged in front of the excavation face 4, and a plurality of extraction pipes 10 are arranged between the gauze 23 and the excavation face. Air holes are evenly distributed on the outer periphery of the extraction pipes. The formation simulation material fills the gap between the coal-bearing model and the tunnel model. The coal-bearing simulation material 9 adopts an environmentally friendly granular material with strong adsorption and has the property of physically adsorbing gas. A gas pressure sensor 13 is placed in the coal-bearing simulation material 9. The formation simulation material 8 adopts an environmentally friendly material with smaller particle size and poorer adsorption. The two simulation materials are separated by a gauze 23, and the separation gauze 23 is fixed to the experimental box by nail-free glue on all sides.

[0045] Air holes 1001 are provided around the body of the extraction pipe 10, and the aperture of the air holes is smaller than the particle diameter of the formation simulation material, so as to ensure that the gas in the surrounding rock can smoothly enter the gas extraction pipe under negative action, and prevent the formation simulation material from entering the gas extraction pipe. A pipe mouth mesh 1002 is provided at the pipe mouth; while simulating the extraction of coal-bearing stratum gas, the extraction pipe can also extract the adsorbed gas in the nearby conventional surrounding rock. The extraction pipe 10 is inserted into the coal-bearing stratum simulation material 9 at a certain angle and range, and the other end extends into the tunnel model 2 through the reserved borehole 205 on the tunnel excavation surface 4. The joints are coated with sealant, and the other end of the gas extraction pipe 10 is reserved for a short distance in the tunnel model 2.

[0046] The top loading assembly includes a force transmission plate 7, a reaction frame, an air injection port 15 and an air supply pump 25. The force transmission plate 7 is adapted to the open port and the test box is sealed by a sealing gasket. An air injection pipe 16 is installed in the air injection port 15, and the air injection pipe 16 is connected to the air supply pump 25 through a valve.

[0047] The extraction component includes a partition 23, an extraction pipe 17 and an extraction pump 26. The partition 23 is arranged in the tunnel model and forms an extraction cavity between the partition 23 and the excavation surface. The extraction pipe 177 is sealed and mounted on the partition and the tunnel model 2. The inner and outer ends of the extraction pipe are respectively connected to the extraction cavity and the extraction pump; a gas pressurizing air supply pump 25 and a gas extraction pump 26 are arranged outside the experimental box 1, and the gas pressurizing air supply pump 25 is connected to the gas injection port 15 through the gas injection pipe 16; the gas extraction pump 26 is connected to the sealing surface 5 outside the excavation surface through the extraction pipe 17, and pressure gauges 18 are arranged on the gas injection pipe 16 and the extraction pipe 17; a gas extraction valve 19 is arranged on the pipeline 17.

[0048] In the actual process of gas extraction from tunnel strata, as the gas pressure in the strata is gradually released, under the action of overlying stress, stress redistribution will occur in the surrounding rock near the excavation face, thereby affecting the stability of the tunnel surrounding rock, and the corresponding surrounding rock support also needs to be further adjusted.

[0049] In the scheme of this embodiment, a mixture of carbon dioxide with a volume fraction of 45% carbon dioxide and 55% nitrogen is used to replace the real gas. On the one hand, the mixture of carbon dioxide and nitrogen is a non-hazardous gas, which can greatly reduce the risk of accidents during the experiment; on the other hand, the mixture of carbon dioxide and nitrogen is widely used for gas displacement in coal mine formations and can be adsorbed in the formation. The use of a mixture of carbon dioxide and nitrogen can simulate the adsorption and release process of gas in the formation. In this technical solution, before the tunnel model is placed in the experimental box, a hole is drilled on the excavation surface, and the diameter of the drilled hole is slightly larger than the diameter of the extraction pipe. Then, the tunnel model is installed and fixed in the reserved hole position of the experimental box; the surrounding rock simulation material separation gauze is fixed in the experimental box at a certain angle to simulate the inclination angle of the coal-bearing strata; one end of a number of gas extraction pipes is fixed to the excavation surface, and the other end is inserted into the gauze at a fixed angle; two kinds of surrounding rock simulation materials are placed in inflatable closed bags in advance, and a carbon dioxide-nitrogen mixture is injected into the two closed bags, which are sealed after expansion, so that the surrounding rock simulation materials and the simulated mixed gas are fully contacted and mixed, and left for 12 hours; the two treated surrounding rock simulation materials are placed in the experimental box, the coal-bearing stratum surrounding rock simulation material is placed in the gauze, and the conventional surrounding rock simulation material fills the other spaces of the experimental box, and then the box is sealed; the gas injection valve is opened and the pressure pump is turned on to inject gas into the experimental A simulated mixed gas is injected into the box, and the overburden pressure is simulated by the top pressurizing device. After the pressure gauge stabilizes, the pressurizing pump is turned off and the gas injection valves are closed. The gas extraction pump is turned on and the extraction valves are opened to extract the gas in the surrounding rock inside the experimental box. During the extraction process, the gas pressure sensor transmits the gas pressure in the simulated material of the surrounding rock of the coal formation on the outer surface of the tunnel lining in real time. The strain type earth pressure box monitors the pressure change on the surface of the tunnel lining in real time. The differential digital displacement meter monitors the horizontal displacement data of the surrounding rock in front of the tunnel excavation face and the deformation of the surrounding rock on the lining surface in real time. The resistance strain gauge monitors the stress of the tunnel excavation face. The data acquisition terminal collects various data and displays the changes of various data in real time for the experimental personnel to analyze and study. The influence mechanism of simulated stratum gas extraction on the surrounding rock in front of the excavation face and the stability of the tunnel lining support can be analyzed, thereby providing a theoretical basis and technical support for the implementation of gas extraction in similar tunnel projects.

[0050] In the specific use of this embodiment, an experimental method for simulating tunnel stratum gas extraction includes the following steps:

[0051] Step 1: Process the tunnel model

[0052] The data line and the extraction pipe are sealed and put into the tunnel model through perforation, and the differential digital displacement meter, strain type earth pressure box and gas pressure sensor are arranged on the outside of the tunnel model, and the differential digital displacement meter and resistance strain gauge are arranged on the excavation surface, and then the tunnel model is placed in the experimental box;

[0053] Step 2: fix the separation gauze of the stratum simulation material in the experimental box at a certain angle; extend one end of a plurality of gas extraction pipes into and fix them on the excavation surface, and insert the other end into the gauze at a fixed angle;

[0054] Step 3: Place the two formation simulation materials in inflatable sealed bags respectively in advance, inject the carbon dioxide-nitrogen mixed gas into the two sealed bags, seal them after expansion, fully contact and mix the formation simulation materials with the simulated mixed gas, and leave them for 12 hours;

[0055] Step 4: Place the processed coal-series simulation material into the gauze, fill the other spaces of the experimental box with the formation simulation material, and install the force transfer plate on the upper part of the experimental box to seal the box;

[0056] Step 5: Open the gas injection valve and the gas supply pump, and inject simulated gas into the experimental box to simulate the overburden pressure. The simulated gas is a mixture of 45% carbon dioxide and 55% nitrogen. After the pressure gauge stabilizes, turn off the booster pump and each gas injection valve. Open the gas extraction valve and the gas extraction pump to extract the gas in the formation simulation material of the experimental box.

[0057] Step 6: The data processing terminal records the real-time data monitored by the strain type earth pressure cell, displacement meter, strain gauge and gas pressure sensor, and displays it dynamically through the display terminal.

[0058] Embodiment 2: This embodiment further illustrates the structure of the force transmission plate.

[0059] Due to the different geology and porosity of strata and coal seams, the actual overlying stratum pressures they bear are different. However, the existing simulation methods cannot simulate this situation. Based on this, it is necessary to study an experimental device and experimental method for simulating tunnel stratum gas extraction.

[0060] This embodiment is based on the above-mentioned problem. The effective stress in the formation is mainly the pore gas pressure and the overlying ground stress. Due to the difference between the coal seam and the bottom layer, the actual pore gas pressure and overlying ground stress to which the coal seam simulation material and the formation simulation material are subjected are different. In order to realize the pore gas pressure and overlying ground stress of different materials, the force transmission plate in this embodiment includes a left force transmission plate, a right force transmission plate and a middle force transmission plate, wherein the middle force transmission plate corresponds to the coal series simulation material, and the left and right force transmission plates correspond to the formation simulation materials on the left and right sides respectively. The outer sides of the left force transmission plate, the right force transmission plate and the middle force transmission plate are respectively fixed to the reaction frame via the corresponding force cylinders 6. In this embodiment, the reaction frame is fixed to the ground or other fixed structures via the external support structure 3.

[0061] In order to achieve a seal, Figure 6As shown in the figure, the inner sides of the left force transfer plate 71 and the right force transfer plate 73 are sealed by the middle sealing seat and the middle force transfer plate 72. The middle sealing seat includes a U-shaped seat body 27, a partition plate 29 and a sealing plate 28. The sealing plate 28 and the partition plate 29 are respectively arranged on the upper and lower sides of the seat body 27. The inner sides of the left force transfer plate 71 and the right force transfer plate 73 are against the two sides of the sealing plate, and are provided with card grooves corresponding to the card plates on both sides of the seat body. Sealing gaskets are arranged in the grooves, and the card plate sealing sleeves are installed in the card grooves. The air supply pump is connected to the pressure divider, and the different outlets of the pressure divider are respectively connected to the air injection ports of the left force transfer plate, the right force transfer plate and the middle force transfer plate through corresponding pipes. The two sides of the left force transfer plate and the right force transfer plate are also sealed on both sides of the experimental box by card installation.

[0062] This embodiment uses a force cylinder to provide overlying soil stress, and the force transmission plates are sealed and combined with each other. When the force cylinder provides power, the force transmission plates on both sides are buckled and connected with the middle force transmission plate through the middle sealing seat, and can slide relative to each other. The force transmission plates are in contact with the simulated materials, thereby providing corresponding overlying soil pressure on the corresponding simulated materials. At the same time, the partition plates penetrate into the material (lower than the force transmission plates), so that the gas injected by the gas injection pipe gathers and separates at the end, simulating the pressure difference caused by different porosities, which is more in line with the characteristics of the existing formation.

[0063] Embodiment 3, this embodiment further illustrates the fixing position of the gauze.

[0064] like Figure 7 As shown in the figure, a rotating shaft is rotatably arranged on the side wall of the experimental box 1, a driving hand wheel 30 is arranged at the outer end of the rotating shaft, a mounting seat 32 is fixed at the inner end of the rotating shaft, and the other side of the mounting seat 32 is rotatably arranged on the experimental box 1, and the gauze 23 is matched and mounted in the mounting seat 32.

[0065] In this embodiment, the experimental box 1 can simulate the coal-bearing stratum surrounding rock environment of the tunnel with different inclinations by adjusting the angle of the gauze 23; take out the gauze 23 and the internal stratum simulation material, and fill the internal space of the experimental box 1 with the processed conventional stratum simulation material 8. By repeating the operation experiment, the gas extraction condition in the tunnel non-coal-bearing stratum surrounding rock environment can be simulated.

Claims

1. An experimental device for simulating tunnel stratum gas extraction, characterized in that: It includes an experimental box, a tunnel model, geological simulation materials, a top loading component and an extraction component; the upper part and the side of the experimental box are respectively provided with an open mouth and a mounting hole, the tunnel model is sealed and sleeved in the mounting hole, the inner side of the tunnel model is an excavation surface, the outer side of the tunnel model is arranged with a differential digital displacement meter, a strain type soil pressure box and a gas pressure sensor, the excavation surface is arranged with a differential digital displacement meter and a resistive strain gauge, a bracket supporting the inner end of the tunnel model is arranged in the experimental box, the geological simulation materials include formation simulation materials and coal series simulation materials, the coal series simulation materials are arranged in a gauze to form a coal seam model, the coal seam model is arranged in front of the excavation surface, and a plurality of extraction pipes are arranged between the gauze and the excavation surface, and air holes are evenly distributed on the outer periphery of the extraction pipes, the formation simulation materials are filled in the coal series model and the tunnel model The gap between them; the top loading assembly includes a force transmission plate, a reaction frame, an air injection port and an air supply pump, the force transmission plate is adapted to the open port, and the experimental box is closed by a sealing gasket, the rear side of the force transmission plate is installed on the reaction frame via a force cylinder, and an air injection pipe is installed in the air injection port, and the air injection pipe is connected with the air supply pump via a valve, the extraction assembly includes a partition, an extraction pipe and an extraction pump, the partition is arranged in the tunnel model, and an extraction cavity is formed between the excavation surface, the extraction pipe is sealed and mounted on the partition and the tunnel model, and the inner and outer ends of the extraction pipe are respectively connected with the extraction cavity and the extraction pump; the force transmission plate includes a left force transmission plate, a right force transmission plate and a middle force transmission plate, wherein the middle force transmission plate corresponds to the coal series simulation material, the left and right force transmission plates correspond to the formation simulation materials on the left and right sides respectively, and the outer sides of the left force transmission plate, the right force transmission plate and the middle force transmission plate are respectively fixed on the reaction frame via corresponding force cylinders.

2. The experimental device for simulating tunnel stratum gas extraction according to claim 1 is characterized in that: The tunnel model includes a main structure and an upper arc cover. The upper part of the main structure is provided with an opening, and the interior is a hollow model cavity. The partition extends into the main structure from the opening and divides the model cavity into a pumping cavity and a tunnel cavity. The upper arc cover is sealed and sleeved in the opening.

3. The experimental device for simulating tunnel stratum gas extraction according to claim 2 is characterized in that: The main structure and the upper arc cover are cast by prefabricated template concrete, and the partition is an acrylic plate structure. The partition is adapted to the inner cavity of the main structure and is sealed on the upper arc cover and the main structure by a sealant.

4. The experimental device for simulating tunnel stratum gas extraction according to claim 1 is characterized in that: A plurality of air inlets are arranged on the excavation surface, a plurality of connection ports are arranged on the gauze, both ends of the extraction pipe are inserted into the air inlets and the connection ports, and penetrate into the extraction cavity and the coal-bearing simulation material, air holes are arranged on the front end and the outer side surface of the extraction pipe, and the air holes are covered with a filter screen, and the aperture of the filter screen is smaller than the particle size of the formation simulation material.

5. The experimental device for simulating tunnel stratum gas extraction according to claim 1 is characterized in that: The inner sides of the left and right force transfer plates are sealed through the middle sealing seat and the middle force transfer plate combination. The middle sealing seat includes a U-shaped seat body, a partition plate and a sealing plate. The sealing plate and the partition plate are respectively arranged on the upper and lower sides of the seat body. The inner sides of the left and right force transfer plates are against the two sides of the sealing plate, and are provided with grooves corresponding to the clamping plates on both sides of the seat body. A sealing gasket is arranged in the groove, and the clamping plate sealing sleeve is installed in the groove.

6. The experimental device for simulating tunnel stratum gas extraction according to claim 5 is characterized in that: The air supply pump is connected to the pressure divider, and different outlets of the pressure divider are respectively connected to the air injection ports of the left force transmission plate, the right force transmission plate and the middle force transmission plate through corresponding pipelines.

7. The experimental device for simulating tunnel stratum gas extraction according to claim 1 is characterized in that: A rotating shaft is rotatably arranged on the side wall of the experimental box, a driving hand wheel is arranged at the outer end of the rotating shaft, a mounting seat is fixed at the inner end of the rotating shaft, the other side of the mounting seat is rotatably arranged on the experimental box, and the gauze matching card is installed in the mounting seat.

8. An experimental method for simulating tunnel stratum gas extraction, using the experimental device for simulating tunnel stratum gas extraction according to claim 1, characterized in that: The following steps are included Step 1: Process the tunnel model The data line and the extraction pipe are sealed and put into the tunnel model through perforation, and the differential digital displacement meter, strain type earth pressure box and gas pressure sensor are arranged on the outside of the tunnel model, and the differential digital displacement meter and resistance strain gauge are arranged on the excavation surface, and then the tunnel model is placed in the experimental box; Step 2: fix the separation gauze of the stratum simulation material in the experimental box at a certain angle; extend one end of a plurality of gas extraction pipes into and fix them on the excavation surface, and insert the other end into the gauze at a fixed angle; Step 3: Place the two formation simulation materials in inflatable sealed bags respectively in advance, inject the carbon dioxide-nitrogen mixed gas into the two sealed bags, seal them after expansion, fully contact and mix the formation simulation materials with the simulated mixed gas, and leave them for 12 hours; Step 4: Place the processed coal-series simulation material into the gauze, fill the other spaces of the experimental box with the formation simulation material, and install the force transfer plate on the upper part of the experimental box to seal the box; Step 5: Open the gas injection valve and the gas supply pump to inject simulated gas into the experimental box to simulate the overburden pressure; after the pressure gauge stabilizes, turn off the booster pump and close each gas injection valve; open the gas extraction valve and the gas extraction pump to extract the gas in the formation simulation material of the experimental box; Step 6: The data processing terminal records the real-time data monitored by the strain type earth pressure cell, displacement meter, strain gauge and gas pressure sensor, and displays it dynamically through the display terminal.

9. The experimental method for simulating tunnel stratum gas extraction according to claim 8, characterized in that: The simulated gas is a mixture of 45% carbon dioxide and 55% nitrogen.

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