A true triaxial seepage test system and test method

Abstract

The present invention discloses a true triaxial seepage test system, which includes a pressure chamber and a true triaxial loading unit. A specimen is placed in the pressure chamber, and the true triaxial loading unit is used to load the specimen. The first loading component can apply a lateral load to the specimen by using a first pressure rod and a first pressure head to deform the specimen. The second loading component can apply a liquid load in the front-rear direction to the specimen by using a liquid pressurizing device. The third loading component can apply a load in the vertical axial direction to the specimen by using a second pressure rod and a second pressure head to deform the specimen. Gas channels are provided in both the base and the second pressure head, and the gas channels can communicate with the specimen. A gas control unit can perform vacuum pumping or gas filling operations on the specimen through the gas channels to facilitate the smooth progress of the test. The present invention also provides a true triaxial seepage test method, which uses the above-mentioned true triaxial seepage test system and combines different loading methods to simulate the actual seepage conditions of coal seams on site.

Description

Technical Field

[0001] The invention relates to the technical field of seepage test equipment and peripheral supporting facilities thereof, and in particular to a true triaxial seepage test system and a test method. Background Art

[0002] my country is a country with abundant coal resources. Most of the mineable coal seams are high-gas and low-permeability coal seams. The coal seams are accompanied by complex gas migration processes and are often in a true triaxial stress state. During the mine production process, the mining project destroys the balance of the original rock stress field and the original gas pressure, and a new stress distribution and gas flow will be formed in the rock mass around the mining. The permeability of the coal body is an important indicator for evaluating the difficulty of fluid flow in the coal body, and it is also a key parameter for gas dynamic disaster prevention and gas extraction rate. Therefore, studying the displacement seepage law under the real stress state of the coal body has a certain guiding significance for revealing the evolution law of the permeability of the coal seam.

[0003] In recent years, in order to study the seepage characteristics of coal seam gas, domestic and foreign researchers have developed a lot of related equipment and conducted relevant experimental research. However, the existing experimental equipment has certain defects and deficiencies in experimental functions and experimental conditions:

[0004] 1. The influencing factors of the seepage test considered by the existing experimental devices are relatively simple, and no device comprehensively considers temperature, pressure, deformation, initial stress, limit conditions, etc. Therefore, the experiments conducted cannot realistically simulate the actual coal seam seepage conditions on site.

[0005] 2. At present, the existing experimental devices mostly use liquid to load the left and right pressure, which limits σ2=σ3 and cannot simulate the real stress state. The pressure loading system of the experimental device that can meet the true triaxial loading is difficult to assemble and is not easy to replace, and cannot meet the diversity of loading methods.

[0006] 3. The existing experimental devices mostly use the drainage method to measure gas flow, but it cannot eliminate the errors caused by factors such as gas leakage and inaccurate readings, and the measurement process is cumbersome.

[0007] Therefore, how to change the current situation in which the seepage test device in the prior art cannot simulate the actual coal seam seepage conditions on site has become an urgent problem to be solved by those skilled in the art. Summary of the invention

[0008] The purpose of the present invention is to provide a true triaxial seepage test system and test method to solve the problems existing in the above-mentioned prior art, so that the test can better simulate the actual coal seam seepage conditions on site and provide convenient conditions for coal permeability research.

[0009] To achieve the above object, the present invention provides the following solution: The present invention provides a true triaxial seepage test system, comprising:

[0010] A pressure chamber, which is a closed container capable of accommodating a sample;

[0011] A true triaxial loading unit, the true triaxial loading unit comprises a first loading assembly, a second loading assembly and a third loading assembly, the first loading assembly can apply a load to the sample along the X-axis, the second loading assembly can apply a load to the sample along the Y-axis, and the third loading assembly can apply a load to the sample along the Z-axis, the X-axis is perpendicular to the Y-axis, and the Z-axis is perpendicular to the plane where the X-axis and the Y-axis are located; the first loading assembly comprises a first pressure head and a first pressure rod, the first pressure head can be pressed against the sample, one end of the first pressure rod is connected to the first pressure head, the other end of the first pressure rod is slidably connected to the pressure chamber and extends out of the pressure chamber, the reciprocating sliding direction of the first pressure rod is parallel to the X-axis, the number of the first pressure head and the first pressure rod are both two groups, and the two groups of the first pressure heads and the first pressure rods are symmetrically arranged with the center line of the sample as the axis; the second loading assembly comprises a liquid pressurizing device and a constant temperature assembly, The liquid pressurizing device can pressurize the liquid, the liquid pressurizing device is connected to the pressure chamber, the thermostatic component is connected to the liquid pressurizing device, and the thermostatic component can control the temperature of the working liquid; the third loading component includes a second pressure head, a second pressure rod and a base, the base and the second pressure head cooperate to fix the sample, a gas channel is arranged in the second pressure head and the base, one end of the gas channel is connected to the sample, the other end of the gas channel is connected to a gas control unit, the gas control unit can evacuate the sample and inflate the sample, the second pressure rod is connected to the second pressure head, the second pressure rod is slidably connected to the pressure chamber, the reciprocating sliding direction of the second pressure rod is parallel to the Z axis, and the end of the second pressure rod away from the second pressure head extends out of the pressure chamber; sealing elements are arranged between the first pressure rod and the pressure chamber and between the second pressure rod and the pressure chamber;

[0012] A testing unit, wherein the testing unit can monitor the deformation of the sample, the testing unit can also monitor the loading state of the true triaxial loading unit, and the testing unit can also monitor the working state of the gas control unit.

[0013] Preferably, the pressure chamber includes a main chamber, a cover and a buckle plate, the cover is detachably connected to the main chamber, a sealing element is arranged between the cover and the main chamber, the buckle plate is threadedly connected to the cover, transparent organic glass is arranged between the cover and the buckle plate, and the transparent organic glass is arranged facing the sample.

[0014] Preferably, the true triaxial loading unit further comprises a limit assembly, which is detachably connected to the first loading assembly and the third loading assembly, and the limit assembly can fix the relative positions of the first pressure rod and the second pressure rod and the pressure chamber, so that the first loading assembly and the third loading assembly maintain a certain loading state;

[0015] The limiting assembly includes a limiting plate, a limiting screw and a fixing rod, one end of the fixing rod is detachably connected to the pressure chamber, the other end of the fixing rod is connected to the limiting plate, the limiting screw passes through the limiting plate and abuts against the first pressure rod or the second pressure rod, and the limiting screw is threadedly connected to the limiting plate.

[0016] Preferably, the first pressure rod and the second pressure rod have a limiting groove at one end facing the limiting screw, and the limiting groove is a spherical groove. The limiting screw has a contact head adapted to the limiting groove, and the contact head is rotatably arranged in the limiting groove; the first pressure rod and the second pressure rod both have a flange at one end facing the limiting screw, and the first pressure rod and the second pressure rod can be connected to the test unit flange.

[0017] Preferably, the liquid pressurizing device includes a boosting pump and a boosting water tank, the boosting pump is connected to the boosting water tank, the constant temperature component includes a heater, the boosting pump can also be connected to an external water source, the boosting pump is connected to the water inlet of the pressure chamber through the heater, the boosting pump can pressurize the working liquid, the heater can heat the working liquid, and the drain outlet of the pressure chamber is connected to the boosting water tank.

[0018] Preferably, the gas control unit comprises a vacuum pump, a high-pressure gas storage bottle and a filter, the vacuum pump is connected to the filter, and the high-pressure gas storage bottle and the filter are connected to the gas channel via a connecting pipeline;

[0019] The filter is also connected to a vacuum sensor, which is connected to a vacuum digital display. The high-pressure gas cylinder is connected to a pressure reducing valve and a flow meter. The outlet end of the pressure reducing valve is connected to the inlet end of the flow meter, and the outlet end of the flow meter is connected to the external environment. A control valve is arranged between the connecting pipeline and the gas channel.

[0020] Preferably, the test unit comprises a deformation test assembly, the deformation test assembly comprises a resistive strain gauge and a strain acquisition instrument, the resistive strain gauge is connected to the strain acquisition instrument, the resistive strain gauge is arranged on the side elevation of the sample parallel to the X-axis, the number of the resistive strain gauges is two, one of the resistive strain gauges is parallel to the X-axis, and the other of the resistive strain gauges is parallel to the Z-axis;

[0021] The test unit further includes a temperature sensor connected to the pressure chamber, and the temperature sensor is capable of monitoring the temperature of the working fluid in the pressure chamber.

[0022] Preferably, the first loading assembly can be connected to a pressure cylinder. When the first loading assembly is connected to the pressure cylinder, the piston end of the pressure cylinder is connected to the first pressure rod, and a load sensor is also arranged between the piston end of the pressure cylinder and the first pressure rod.

[0023] Preferably, the first pressure rod is plug-connected with the first pressure head, the first pressure rod has a plug-in slot, the first pressure head has a plug-in block adapted to the plug-in slot, and the plug-in block is in a "convex" shape;

[0024] The base is slidably connected to the bottom of the pressure chamber. The bottom of the pressure chamber has a slide groove, which is a dovetail groove. The base is slidably arranged in the slide groove.

[0025] The present invention also provides a true triaxial seepage test method, using the above-mentioned true triaxial seepage test system, setting the sample in the pressure chamber, fixing the sample using the base, the second pressure rod and the second pressure head, applying load to the sample and deforming the sample through the first loading assembly and the third loading assembly, applying liquid load using the second loading assembly, and evacuating or inflating the sample using the gas control unit to change the working state of the true triaxial loading unit to simulate actual coal seam seepage conditions, and monitoring the test state of the sample using the test unit.

[0026] Compared with the prior art, the present invention has achieved the following technical effects: the true triaxial seepage test system of the present invention places the sample in the pressure chamber, and uses the true triaxial loading unit to load the sample. The first loading component can use the first pressure rod and the first pressure head to apply a lateral load to the sample and deform the sample. The second loading component can use the liquid pressurizing device to apply a front-to-back liquid load to the sample. The third loading component can use the second pressure rod and the second pressure head to apply a vertical axial load to the sample and deform the sample. Gas channels are set in the base and the second pressure head, and the gas channel can be connected to the sample. The gas control unit can vacuum or inflate the sample through the gas channel, which is convenient for the smooth progress of the test. The present invention also provides a true triaxial seepage test method, using the above-mentioned true triaxial seepage test system.

[0027] The present invention utilizes a true triaxial loading unit and adopts a combination of different loading methods, so as to better simulate the actual coal seam seepage conditions on site, and can more realistically reflect the seepage law of the coal body under the actual stress state. By changing the test conditions for testing, it can reflect the influence of different conditions on the seepage process and dynamic evolution characteristics of the coal body. The true triaxial seepage test system of the present invention is flexible and maneuverable, and provides convenient research conditions for in-depth research. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 It is a structural schematic diagram of the true triaxial seepage test system of the present invention;

[0030] Figure 2 It is a schematic front view of a pressure chamber of a true triaxial seepage test system of the present invention;

[0031] Figure 3 It is a side view schematic diagram of the pressure chamber of the true triaxial seepage test system of the present invention;

[0032] Figure 4 It is a top view schematic diagram of the pressure chamber of the true triaxial seepage test system of the present invention;

[0033] Figure 5 It is a schematic diagram of a pressure chamber of the true triaxial seepage test system of the present invention when performing a unidirectional limit test;

[0034] Figure 6 It is a schematic diagram of a pressure chamber of a true triaxial seepage test system of the present invention performing a bidirectional limit test;

[0035] Figure 7 It is a structural schematic diagram of a fixing rod of a true triaxial seepage test system of the present invention;

[0036] Figure 8 It is a structural schematic diagram of the first compression rod of the true triaxial seepage test system of the present invention.

[0037] Among them, 1 is a pressure chamber, 101 is a main chamber, 102 is a cover, 103 is a buckle plate, 104 is a transparent organic glass, 2 is a first pressure rod, 3 is a first pressure head, 4 is a second pressure rod, 5 is a second pressure head, 6 is a limit assembly, 601 is a limit plate, 602 is a limit screw, 603 is a fixing rod, 7 is a limit groove, 8 is a booster pump, 9 is a booster water tank, 10 is a heater, 11 is a temperature sensor, 12 is a vacuum pump, 13 is a high-pressure gas cylinder, 14 is a filter, 15 is a vacuum sensor, 16 is a vacuum digital display, 17 is a digital pressure gauge, 18 is a flow meter, 19 is a pressure cylinder, 20 is a load sensor, 21 is a water inlet, 22 is a drain, 23 is a buffer tank, 24 is a manual pump, 25 is a base, 26 is a sealing assembly, 27 is a heat shrink tube, and 28 is a sample. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] The purpose of the present invention is to provide a true triaxial seepage test system and test method to solve the problems existing in the above-mentioned prior art, so that the test can better simulate the actual coal seam seepage conditions on site and provide convenient conditions for coal permeability research.

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Please refer to Figure 1-8 ,in, Figure 1 is a structural schematic diagram of the true triaxial seepage test system of the present invention, Figure 2 is a schematic diagram of the front view of the pressure chamber of the true triaxial seepage test system of the present invention, Figure 3 is a side view schematic diagram of the pressure chamber of the true triaxial seepage test system of the present invention, Figure 4 Schematic diagram of a top view of a pressure chamber of the true triaxial seepage test system of the present invention, Figure 5This is a schematic diagram of a pressure chamber of the true triaxial seepage test system of the present invention performing a unidirectional limit test. Figure 6 This is a schematic diagram of a pressure chamber of a true triaxial seepage test system of the present invention performing a bidirectional limit test. Figure 7 is a schematic structural diagram of a fixing rod of a true triaxial seepage test system of the present invention, Figure 8 It is a structural schematic diagram of the first compression rod of the true triaxial seepage test system of the present invention.

[0042] The present invention provides a true triaxial seepage test system, comprising:

[0043] The pressure chamber 1 is a sealed container and can contain a sample 28 .

[0044] A true triaxial loading unit, the true triaxial loading unit includes a first loading component, a second loading component and a third loading component, the first loading component can apply a load to the sample 28 along the X-axis, the second loading component can apply a load to the sample 28 along the Y-axis, and the third loading component can apply a load to the sample 28 along the Z-axis, the X-axis is perpendicular to the Y-axis, and the Z-axis is perpendicular to the plane where the X-axis and the Y-axis are located; the first loading component includes a first pressure head 3 and a first pressure rod 2, the first pressure head 3 can be against the sample 28, one end of the first pressure rod 2 is connected to the first pressure head 3, the other end of the first pressure rod 2 is slidably connected to the pressure chamber 1 and extends out of the pressure chamber 1, the reciprocating sliding direction of the first pressure rod 2 is parallel to the X-axis, the number of the first pressure head 3 and the first pressure rod 2 are both two groups, and the two groups of the first pressure head 3 and the first pressure rod 2 are symmetrically arranged with the center line of the sample 28 as the axis; the second loading component includes a liquid pressurizing device and a constant temperature component, the liquid pressurizing device can pressurize the liquid , the liquid pressurizing device is connected to the pressure chamber 1, the thermostatic component is connected to the liquid pressurizing device, and the thermostatic component can control the temperature of the working liquid; the third loading component includes a second pressure head 5, a second pressure rod 4 and a base 25, the base 25 and the second pressure head 5 cooperate to fix the sample 28, and a gas channel is arranged in the second pressure head 5 and the base 25, one end of the gas channel is connected to the sample 28, and the other end of the gas channel is connected to the gas control unit, and the gas control unit can evacuate the sample 28 and inflate the sample 28, the second pressure rod 4 is connected to the second pressure head 5, and the second pressure rod 4 is slidably connected to the pressure chamber 1, the reciprocating sliding direction of the second pressure rod 4 is parallel to the Z axis, and the end of the second pressure rod 4 away from the second pressure head 5 extends out of the pressure chamber 1; sealing elements are arranged between the first pressure rod 2 and the pressure chamber 1 and between the second pressure rod 4 and the pressure chamber 1; the sealing element is a sealing assembly 26, which plays a guiding role while sealing.

[0045] The test unit can monitor the deformation of the sample 28, the test unit can also monitor the loading state of the true triaxial loading unit, and the test unit can also monitor the working state of the gas control unit.

[0046] The true triaxial seepage test system of the present invention places the sample 28 in the pressure chamber 1, and uses the true triaxial loading unit to load the sample 28. The first loading component can use the first pressure rod 2 and the first pressure head 3 to apply a lateral load to the sample 28 and deform the sample 28. The second loading component can use the liquid pressurizing device to apply a front-to-back liquid load to the sample 28. The third loading component can use the second pressure rod 4 and the second pressure head 5 to apply a vertical axial load to the sample 28 and deform the sample 28. Gas channels are set in the base 25 and the second pressure head 5. The gas channel can be connected to the sample 28. The gas control unit can vacuum or inflate the sample 28 through the gas channel to facilitate the smooth progress of the test. The present invention utilizes a true triaxial loading unit and adopts a combination of different loading methods, so as to better simulate the actual on-site coal seam seepage conditions, and can more realistically reflect the seepage law of the coal body under the actual stress state. By changing the test conditions for testing, it can reflect the influence of different conditions on the seepage process and dynamic evolution characteristics of the deformation of the coal body. The true triaxial seepage test system of the present invention is flexible and provides convenient research conditions for in-depth research. It should be explained here that in this specific implementation, the X-axis is horizontal, the Y-axis is the front-to-back direction, and the Z-axis is the vertical direction. The "horizontal" here is equivalent to the figure in the specification. Figure 1 The left and right direction of the medium pressure chamber 1, "front and back" is equivalent to the figure in the specification Figure 1 The medium pressure chamber 1 is perpendicular to the direction of the paper surface.

[0047] In this specific embodiment, the pressure chamber 1 includes a main chamber 101, a cover 102 and a gusset plate 103. The cover 102 is detachably connected to the main chamber 101, which is convenient for replacing the sample 28 for testing. A sealing element is arranged between the cover 102 and the main chamber 101 to ensure the sealing of the pressure chamber 1. The gusset plate 103 is threadedly connected to the cover 102 for easy disassembly and assembly. A transparent organic glass 104 is arranged between the cover 102 and the gusset plate 103. The transparent organic glass 104 is arranged directly opposite to the sample 28, realizing the visualization of the pressure chamber 1. The deformation and seepage process of the sample 28 during the test can be observed by using the transparent organic glass 104. It should be noted here that when conducting the test, a heat shrink tube 27 needs to be installed on the outside of the sample 28. In order to facilitate observation, a transparent heat shrink tube 27 is selected to be installed on the outside of the sample 28.

[0048] Specifically, the true triaxial loading unit also includes a limit assembly 6, which is detachably connected to the first loading assembly and the third loading assembly. The limit assembly 6 can fix the relative positions of the first pressure rod 2 and the second pressure rod 4 and the pressure chamber 1, so that the first loading assembly and the third loading assembly maintain a certain loading state, which is convenient for simulating the seepage process of the sample 28 under certain restrictive conditions.

[0049] Among them, the limit assembly 6 includes a limit plate 601, a limit screw 602 and a fixed rod 603, one end of the fixed rod 603 is detachably connected to the pressure chamber 1, and the other end of the fixed rod 603 is connected to the limit plate 601, the limit screw 602 passes through the limit plate 601 and abuts against the first pressure rod 2 or the second pressure rod 4, the limit screw 602 is threadedly connected to the limit plate 601, and by rotating the limit screw 602, the limit screw 602 can be used to push the first pressure rod 2 or the second pressure rod 4 to move, and then the first pressure head 3 or the second pressure head 5 can be used to apply a certain load to the sample 28, and the fixed rod 603 fixes the distance between the limit plate 601 and the pressure chamber 1, so that the limit screw 602 cooperates with the limit plate 601 to keep the load in a certain state. When it is necessary to keep the load in a certain direction at a certain loading pressure, the limit assembly 6 can be connected to the first loading assembly or the third loading assembly, thereby playing a limiting role and improving the simulation comprehensiveness of the test system. In this specific embodiment, both ends of the fixing rod 603 have external threads, and the two ends of the fixing rod 603 are respectively threadedly connected to the limiting plate 601 and the pressure chamber 1, which is convenient for disassembly and assembly, and the connection is tight, which greatly facilitates the operation of the test personnel.

[0050] It should be emphasized here that the first pressure rod 2 and the second pressure rod 4 have a limiting groove 7 at one end facing the limiting screw 602, and the limiting groove 7 is a spherical groove. The limiting screw 602 has a contact head adapted to the limiting groove 7, and the contact head is rotatably arranged in the limiting groove 7. The first pressure rod 2 and the limiting screw 602 as well as the second pressure rod 4 and the limiting screw 602 adopt a spherical abutment method, which effectively avoids the bias of the first pressure head 3 and the second pressure head 5, so that the test results can better reflect the actual stress change of the sample 28; the first pressure rod 2 and the second pressure rod 4 have a flange at one end facing the limiting screw 602, and the first pressure rod 2 and the second pressure rod 4 can be connected to the flange of the test unit to improve the convenience of disassembly and assembly operations.

[0051] More specifically, the liquid pressurizing device includes a booster pump 8 and a booster water tank 9, the booster pump 8 is connected to the booster water tank 9, the thermostatic assembly includes a heater 10, the booster pump 8 can also be connected to an external water source, the booster pump 8 is connected to the water inlet 21 of the pressure chamber 1 through the heater 10, the booster pump 8 can pressurize the working liquid, the heater 10 can heat the working liquid, and the drain port 22 of the pressure chamber 1 is connected to the booster water tank 9. The booster pump 8 pressurizes the water and inputs it into the pressure chamber 1 through the water inlet 21, applying pressure in the front and rear directions to the sample 28. After the test is completed, the water is stored in the booster water tank 9. The heater 10 in the thermostatic assembly can heat the water to keep the temperature of the water in the pressure chamber 1 constant or change the temperature of the working liquid in the pressure chamber 1 to simulate the stress state of the coal sample in various environments. The test unit also includes a temperature sensor 11, which is connected to the pressure chamber 1. The temperature sensor 11 can monitor the temperature of the working liquid in the pressure chamber 1 to improve the controllability of the test system.

[0052] Correspondingly, the gas control unit includes a vacuum pump 12, a high-pressure gas storage bottle 13 and a filter 14. The vacuum pump 12 is connected to the filter 14. The high-pressure gas storage bottle 13 and the filter 14 are connected to the gas channel via a connecting pipe. The filter 14 is also connected to a vacuum sensor 15. The vacuum sensor 15 is connected to a vacuum digital display 16. The high-pressure gas storage bottle 13 is connected to a pressure reducing valve and a flow meter 18. A control valve is provided between the connecting pipe and the gas channel. The vacuum pump 12 can evacuate the sample 28 to ensure that the gas and moisture in the coal sample are completely evacuated. At the same time, the vacuum sensor 15 is used to monitor the vacuum state. The vacuum digital display 16 facilitates the reading operation of the test personnel. The filter 14 is provided between the vacuum pump 12 and the pressure chamber 1 to ensure that the vacuum pump 12 can work smoothly. During the test, the gas control unit can use the high-pressure gas bottle 13 to inflate the sample 28. A digital pressure gauge 17 and a flow meter 18 are set on the connecting pipeline. The outlet end of the pressure reducing valve is connected to the inlet end of the flow meter 18, and the outlet end of the flow meter 18 is connected to the atmosphere. After the coal sample reaches adsorption equilibrium, subsequent test steps are carried out.

[0053] At the same time, the test unit includes a deformation test component, and the deformation test component includes a resistive strain gauge and a strain collector. The resistive strain gauge is connected to the strain collector. The resistive strain gauge is arranged on the side elevation of the sample 28 parallel to the X-axis. There are two resistive strain gauges, one of which is parallel to the X-axis, and the other is parallel to the Z-axis, respectively monitoring the lateral and axial deformations of the sample 28. The strain collector can collect deformation data of the sample 28. It should be explained here that the resistive strain gauge does not contact the first pressure head 3 and the second pressure head 5. The resistive strain gauge is arranged on the side elevation of the sample 28, and the resistive strain gauge is located on the side elevation of the sample 28 away from the transparent organic glass 104. The resistive strain gauge can monitor the deformation data of the sample 28, and the operator can use the transparent organic glass 104 to observe the macroscopic state changes of the sample 28 during the test.

[0054] In addition, the first loading assembly can be connected to the pressure cylinder 19. When the first loading assembly is connected to the pressure cylinder 19, the piston end of the pressure cylinder 19 is connected to the first pressure rod 2. A load sensor 20 is also arranged between the piston end of the pressure cylinder 19 and the first pressure rod 2. When the first loading assembly is loaded, the pressure cylinder 19 can be used to drive the first pressure rod 2 to move to ensure the stability of loading. The load sensor 20 can monitor the loading pressure value.

[0055] It should also be noted that the first pressure rod 2 is plug-connected with the first pressure head 3, the first pressure rod 2 has a plug-in slot, the first pressure head 3 has a plug-in block adapted to the plug-in slot, and the axial cross-section of the plug-in block is a "convex" shape; the plug-in connection is convenient for assembly and disassembly, and the vertical displacement of the first pressure head 3 is avoided. In actual operation, the first pressure head 3 can also be replaced according to the test requirements, thereby improving the flexibility, adaptability and maintenance convenience of the system.

[0056] In other specific embodiments of the present invention, the base 25 is slidably connected to the bottom of the pressure chamber 1. The bottom of the pressure chamber 1 has a slide groove, which is a dovetail groove. The base 25 is slidably arranged in the slide groove, which facilitates the installation and positioning of the base 25, avoids axial displacement of the base 25, improves the stability of the base 25, and facilitates the adjustment of the horizontal position of the base 25.

[0057] The present invention also provides a true triaxial seepage test method. Using the true triaxial seepage test system mentioned above, the true triaxial seepage test method of the present invention is further explained below through specific embodiments.

[0058] During the true triaxial seepage test under unidirectional limiting conditions, both sides of the first loading assembly are connected to the limiting assembly 6. The method for testing the permeability of coal rock includes the following steps, wherein, in order to ensure the sealing of the heat shrink tube 27 during the test, the gas pressure must be less than the confining pressure.

[0059] (1) Preparation of sample 28. Sample 28 was processed into a rectangular parallelepiped sample 28 by a CNC wire cutting machine. The height direction of sample 28 was parallel to the bedding direction of the coal body. A resistance strain gauge was pasted on the back of the coal sample at an angle of 90° in both the horizontal and vertical directions.

[0060] (2) Install the coal sample. Take the base 25 out of the pressure chamber 1, place the coal sample on the base 25, put a heat shrink tube 27 longer than the coal sample on the coal sample, extend the wiring of the resistance strain gauge from the bottom of the heat shrink tube 27, and place the second pressure head 5 on the coal sample. Use a hair dryer to evenly heat and press the heat shrink tube 27 to ensure that the heat shrink tube 27 is in close contact with the side of the coal sample, and then use metal hoops to respectively clamp the upper and lower ends of the sample 28 where the heat shrink tube 27 overlaps with the base 25 and the second pressure head 5.

[0061] (3) Installation. Place the installed second pressure head 5, coal sample and base 25 into the pressure chamber 1 along the dovetail groove at the bottom of the pressure chamber 1, connect the gas inlet pipe and the gas outlet pipe, and connect the resistance strain gauge to the data transmission wiring; fix the cover 102 to the front end of the pressure chamber 1 with bolts, then place the transparent organic glass 104 in the groove of the cover 102, and then cover the buckle plate 103 and fix it with bolts; install the second pressure rod 4, the left first pressure rod 2, the right first pressure rod 2 and the sealing assembly 26.

[0062] (4) Constant temperature. Connect the drain port 22, booster pump 8, heater 10 and water inlet 21 pipelines, open the valves of the exhaust port and the water inlet 21, add water from the booster water tank 9 into the pressure chamber 1 through the water inlet 21, close the exhaust port valve when the water submerges the temperature sensor 11, turn on the heater 10, and set the test temperature.

[0063] (5) Seepage test during the full stress-strain process.

[0064] a. Vacuuming. Confirm that the valve of the exhaust port is closed, check the air tightness of the device container, open the vacuum pipeline valve, and use the vacuum pump 12 to degas to ensure that the gas and moisture in the coal sample are completely extracted.

[0065] b. Apply confining pressure. Place the pressure chamber 1 on the servo press, rotate the right limit screw 602 to make the coal sample produce a certain initial deformation, use the manual pump 24 to apply pressure in the left and right directions, and monitor and read the data through the load sensor 20; set the pressure value, start the booster pump 8, pressurize the water in the pressure chamber 1 and apply pressure in the front and back directions, and keep the confining pressure unchanged during the test. The manual pump 24 is connected to the buffer tank 23 to achieve the purpose of uniform loading.

[0066] c. Inflation. Open the high-pressure gas storage bottle 13, open the valve of the air inlet, maintain a constant pressure, and inflate the coal sample. When the coal sample reaches adsorption equilibrium, that is, when the pressure reading at the air inlet is stable, open the valve of the exhaust port, and start applying axial pressure after the gas flow and pressure are stable for 30 minutes.

[0067] d. Axial pressure loading. Turn on the press, set the pressure loading speed, use the servo press to push the second pressure rod 4 to continuously apply axial pressure to the coal sample, observe the deformation of the coal sample during the test through the transparent organic glass 104, and use the computer to collect relevant test data. The test ends when the coal sample is destroyed.

[0068] (6) Seepage tests under different stress and gas pressure conditions.

[0069] a. Vacuuming. Confirm that the valve of the exhaust port is closed, check the air tightness of the device container, open the vacuum pipeline valve, and use the vacuum pump 12 to degas to ensure that the gas and moisture in the coal sample are completely extracted.

[0070] b. Apply confining pressure. Place the pressure chamber 1 on the servo press, rotate the right limit screw 602 to make the coal sample produce a certain initial deformation, use the manual pump 24 to apply pressure in the left and right directions, and monitor and read the data through the load sensor 20; set the pressure value, start the booster pump 8, pressurize the water in the pressure chamber 1 and apply pressure in the front and back directions, and keep the confining pressure unchanged during the test.

[0071] c. Seepage test under different stress conditions. Open the high-pressure gas storage bottle 13, open the valve of the air inlet, maintain a constant pressure, and inflate the coal sample. When the coal sample reaches adsorption equilibrium, that is, when the pressure indication number of the air inlet is stable, open the valve of the exhaust port, and start to apply axial pressure after the gas flow and pressure are stable for 30 minutes; open the press, apply axial pressure to the coal sample and keep the pressure constant. After the gas flow and pressure at the outlet are stable, use a step-by-step pressurization method to continuously increase the system axial pressure, and conduct seepage tests under different stress conditions. Observe the deformation of the coal sample during the test through the transparent organic glass 104, and collect relevant test data with a computer.

[0072] d. Seepage test under different gas pressure conditions. Open the press, set the pressure value, use the servo press to push the second pressure rod 4 to apply axial pressure to the system, and keep the axial pressure and confining pressure unchanged during the test after the pressure stabilizes; open the high-pressure gas storage bottle 13, keep the pressure constant, and inflate the coal sample. When the coal sample reaches adsorption equilibrium, that is, when the pressure indication number at the air inlet is stable, open the valve at the exhaust port. When the coal sample reaches adsorption equilibrium at each pressure point and the gas flow at the exhaust port is stable, the gas pressure is continuously increased by step-by-step pressurization to conduct seepage tests under different gas pressure conditions, and the deformation of the coal sample during the test is observed through the transparent organic glass 104, and the relevant test data are collected by computer.

[0073] (7) Seepage test under unidirectional confined conditions.

[0074] a. Installation of one-way limit device. Remove the pressure cylinder 19 on the left side of the pressure chamber 1, install the limit assembly 6 on the left side of the pressure chamber 1, and fix it with nuts. Rotate the limit screws 602 on the left and right sides successively to make the coal sample deform to a certain extent.

[0075] b. One-way limited seepage test under different stress conditions. Open the high-pressure gas storage bottle 13, open the valve of the air inlet, maintain a constant pressure, and inflate the coal sample. When the coal sample reaches adsorption equilibrium, that is, when the pressure indication number of the air inlet is stable, open the valve of the exhaust port, and start to apply axial pressure after the gas flow and pressure are stable for 30 minutes; open the press, apply axial pressure to the coal sample and keep the pressure constant. After the gas flow and pressure at the outlet are stable, use a step-by-step pressurization method to continuously increase the system axial pressure, and conduct one-way limited seepage tests under different stress conditions. Observe the deformation of the coal sample during the test through the transparent organic glass 104, and collect relevant test data with a computer.

[0076] c. One-way limited seepage test under different gas pressure conditions. Open the press, set the pressure value to apply axial pressure to the system, and keep the axial pressure and the position of the limit screw 602 unchanged during the test after the pressure stabilizes; open the high-pressure gas storage bottle 13, keep the pressure constant, and fill the coal sample with gas. When the coal sample reaches adsorption equilibrium, that is, when the pressure indication number at the air inlet is stable, open the valve of the exhaust port. When the coal sample reaches adsorption equilibrium at each pressure point and the gas flow at the exhaust port is stable, the gas pressure is continuously increased by step-by-step pressurization to conduct seepage tests under different gas pressure conditions, and the deformation of the coal sample during the test is observed through the transparent organic glass 104, and the relevant test data are collected by computer.

[0077] (8) Seepage test under bidirectional confinement conditions.

[0078] a. Installation of the two-way limit device. Based on the seepage test system under the one-way limit condition, install the fixing rod 603 on the top screw hole of the pressure chamber 1, install the limiting plate 601 of the limiting assembly 6 on the fixing rod 603, and fix it with a nut, and rotate the limiting screw 602 in the left, right and top directions successively to make the coal sample deform to a certain extent.

[0079] b. Bidirectional limited seepage test under different gas pressure conditions. Keep the position of the limited screw 602 unchanged during the test, open the high-pressure gas storage bottle 13, keep the pressure constant, and fill the coal sample with gas. When the coal sample reaches adsorption equilibrium, that is, when the pressure indication number at the air inlet is stable, open the valve of the exhaust port. When the coal sample reaches adsorption equilibrium at each pressure point and the gas flow at the exhaust port is stable, the gas pressure is continuously increased by step-by-step pressurization to conduct seepage tests under different gas pressure conditions. The deformation of the coal sample during the test is observed through the transparent organic glass 104, and the relevant test data are collected by computer.

[0080] (9) End of the test. The water in the pressure chamber 1 is stored in the booster water tank 9, the cover 102 is removed, the coal sample is taken out, and the test is ended.

[0081] The present invention comprehensively reflects the influence of temperature, pressure, deformation, initial stress and limiting conditions on the seepage process of coal body and the dynamic evolution characteristics of deformation. It can carry out tests under the influence of single factor and under the coupling of multiple factors, and better solves the problem of true triaxial loading. The tests carried out can better simulate the actual coal seam seepage conditions on site, and can more truly reflect the seepage law of coal body under the real stress state. Moreover, the true triaxial seepage test system of the present invention realizes the diversity of loading methods and has a wide range of adaptability.

[0082] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A true triaxial seepage test system, characterized in that, it includes: A pressure chamber, which is a closed container and can accommodate a specimen therein; A true triaxial loading unit, which includes a first loading component, a second loading component and a third loading component. The first loading component can apply a load to the specimen along the X-axis, the second loading component can apply a load to the specimen along the Y-axis, and the third loading component can apply a load to the specimen along the Z-axis. The X-axis is perpendicular to the Y-axis, and the Z-axis is perpendicular to the plane where the X-axis and the Y-axis are located. The first loading component includes a first pressure head and a first pressure rod. The first pressure head can abut against the specimen. One end of the first pressure rod is connected to the first pressure head, and the other end of the first pressure rod is slidably connected to the pressure chamber and extends out of the pressure chamber. The reciprocating sliding direction of the first pressure rod is parallel to the X-axis. The number of the first pressure heads and the first pressure rods is two groups, and the two groups of the first pressure heads and the first pressure rods are symmetrically arranged with the midline of the specimen as the axis. The second loading component includes a liquid pressurizing device and a constant temperature component. The liquid pressurizing device can pressurize the liquid. The liquid pressurizing device is connected to the pressure chamber, and the constant temperature component is connected to the liquid pressurizing device. The constant temperature component can control the temperature of the working liquid. The third loading component includes a second pressure head, a second pressure rod and a base. The base and the second pressure head cooperate to fix the specimen. Gas channels are provided in both the second pressure head and the base. One end of the gas channel is connected to the specimen, and the other end of the gas channel is connected to a gas control unit. The gas control unit can evacuate the specimen and fill the specimen with gas. The second pressure rod is connected to the second pressure head, and the second pressure rod is slidably connected to the pressure chamber. The reciprocating sliding direction of the second pressure rod is parallel to the Z-axis, and the end of the second pressure rod away from the second pressure head extends out of the pressure chamber. Sealing elements are provided between the first pressure rod and the pressure chamber and between the second pressure rod and the pressure chamber; A testing unit, which can monitor the deformation of the specimen, and can also monitor the loading state of the true triaxial loading unit and the working state of the gas control unit.

2. The true triaxial seepage test system according to claim 1, characterized in that: The pressure chamber includes a main chamber, a lid and a buckle plate. The lid is detachably connected to the main chamber. A sealing element is provided between the lid and the main chamber. The buckle plate is threadedly connected to the lid. A transparent organic glass is provided between the lid and the buckle plate. The transparent organic glass is arranged opposite to the specimen.

3. The true triaxial seepage test system according to claim 1, characterized in that: The true triaxial loading unit further includes a limiting component, which is detachably connected to the first loading component and the third loading component. The limiting component can fix the relative positions of the first pressing rod and the second pressing rod with respect to the pressure chamber, so that the first loading component and the third loading component maintain a certain loading state; The limiting component includes a limiting plate, a limiting screw rod, and a fixing rod. One end of the fixing rod is detachably connected to the pressure chamber, and the other end of the fixing rod is connected to the limiting plate. The limiting screw rod passes through the limiting plate and abuts against the first pressing rod or the second pressing rod. The limiting screw rod is threadedly connected to the limiting plate.

4. The true triaxial seepage test system according to claim 3, characterized in that: One ends of the first pressing rod and the second pressing rod facing the limiting screw rod are provided with limiting grooves, the limiting grooves are spherical grooves, the limiting screw rod has a contact head adapted to the limiting grooves, and the contact head is rotatably arranged in the limiting grooves; One ends of the first pressing rod and the second pressing rod facing the limiting screw rod are both provided with flange plates, and the first pressing rod and the second pressing rod can both be flange-connected to the test unit.

5. The true triaxial seepage test system according to claim 1, characterized in that: The liquid pressurizing device includes a booster pump and a pressurized water tank. The booster pump is communicated with the pressurized water tank. The constant temperature component includes a heater. The booster pump can also be communicated with an external water source. The booster pump is communicated with the water inlet of the pressure chamber through the heater. The booster pump can pressurize the working liquid, the heater can heat the working liquid, and the drain outlet of the pressure chamber is communicated with the pressurized water tank.

6. The true triaxial seepage test system according to claim 1, characterized in that: The gas control unit includes a vacuum pump, a high-pressure gas storage cylinder, and a filter. The vacuum pump is connected to the filter. The high-pressure gas storage cylinder and the filter are connected to the gas channel through a communication pipeline; The filter is further connected with a vacuum degree sensor, the vacuum degree sensor is connected with a vacuum degree digital display meter, the high-pressure gas storage cylinder is connected with a pressure reducing valve and a flow meter. The outlet end of the pressure reducing valve is connected to the inlet end of the flow meter, and the outlet end of the flow meter is communicated with the external environment. A control valve is arranged between the communication pipeline and the gas channel.

7. The true triaxial seepage test system according to claim 1, characterized in that: The test unit includes a deformation test component. The deformation test component includes a resistive strain gauge and a strain collector. The resistive strain gauge is connected to the strain collector. The resistive strain gauge is arranged on the side vertical surface of the specimen parallel to the X-axis. The number of the resistive strain gauges is two. The direction of one resistive strain gauge is parallel to the X-axis, and the direction of the other resistive strain gauge is parallel to the Z-axis; The test unit further includes a temperature sensor, which is connected to the pressure chamber and can monitor the temperature of the working liquid in the pressure chamber.

8. The true triaxial seepage test system according to claim 1, characterized in that: The first loading component can be connected to the pressure cylinder. When the first loading component is connected to the pressure cylinder, the piston end of the pressure cylinder is connected to the first pressure rod, and a load cell is further arranged between the piston end of the pressure cylinder and the first pressure rod.

9. The true triaxial seepage test system according to claim 1, characterized in that: The first pressure rod is connected to the first pressure head in a plug-in manner. The first pressure rod has a plug-in groove, and the first pressure head has a plug-in block adapted to the plug-in groove. The plug-in block is in a "convex" shape. The base is slidably connected to the bottom of the pressure chamber. The bottom of the pressure chamber has a chute, and the chute is a dovetail chute. The base is slidably arranged in the chute.

10. A true triaxial seepage test method, using the true triaxial seepage test system according to any one of claims 1-9, characterized in that: The specimen is arranged in the pressure chamber, and the specimen is fixed by using the base, the second pressure rod and the second pressure head. Loads are applied to the specimen through the first loading component and the third loading component to cause the specimen to deform. Liquid loads are applied by using the second loading component. The specimen is evacuated or inflated by using the gas control unit to change the working state of the true triaxial loading unit so as to simulate the actual coal seam seepage conditions, and the test state of the specimen is monitored by using the test unit.

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