Testing method and device for simulating void ratio of fractured rock mass in goaf

Abstract

The invention discloses a void ratio testing method and device for simulating fractured rock mass in a goaf, and belongs to the technical field of void ratio determination. A charging bucket is used for charging and simulating the environmental change of the goaf; a top cover is installed at the upper end of the charging barrel, and a pressure guiding barrel is installed on the upper wall of the top cover and plays a role in transmitting pressure. The void ratio of the caving fractured rock mass in the goaf is tested in a laboratory, and meanwhile, a fractal dimension method is introduced in an experiment, so that the accuracy and scientificity of the method are ensured; by means of the equipment, the porosity value of the goaf caving rock mass when the goaf caving rock mass is just broken and collapsed can be obtained, and the porosity value of the goaf caving rock mass after the goaf caving rock mass is compacted by axial stress provided by an overlying rock layer can be detected; the compaction process after goaf collapse can be simulated; water is fed or discharged in the experiment process, and the water immersion and compaction process of the goaf can be simulated; after the experiment is finished, fractured rock masses can be conveniently taken out, and the characteristics are observed.

Description

Technical Field

[0001] The invention belongs to the technical field of void ratio determination, and in particular relates to a void ratio testing method and a device for simulating a broken rock mass in a goaf area. Background Art

[0002] The porosity is the percentage of the volume of voids between particles (the sum of open pores and interstitial volumes) in the total volume of natural accumulation of granular materials (such as sand and gravel). The size of the porosity reflects the degree of density of the mutual filling between the particles of the granular material. At present, most of the treatment methods for goafs are grouting treatment. In order to study the flow law and distribution of slurry in the goaf, it is necessary to conduct goaf grouting simulation experiments. The porosity of the rock mass inside the goaf is one of the key parameters that need to be considered in the design of goaf grouting simulation experiments.

[0003] There are many existing methods for testing porosity, including gas adsorption method, mercury intrusion method, organic dissolution method, scanning electron microscopy method, etc. These methods have a small testing range and poor operation convenience. Moreover, these methods can only test the porosity value under a certain situation, and cannot show the change of porosity of the collapsed rock mass in the goaf at different development stages of the goaf;

[0004] At the same time, the existing porosity testing equipment also has the following problems: the existing porosity detection device can only test the porosity value of the deposit when the deposit is freely deposited, and cannot detect the porosity value of the collapsed rock mass in the goaf after being compacted by the axial stress provided by the overlying rock strata; it cannot simulate the evolution of the porosity of the broken rock mass in the collapsed zone of the goaf during collapse and after compaction, and cannot simulate the compaction process after the collapse of the goaf, and it also cannot simulate the process of water immersion and compaction of the broken rock mass in the goaf after the pit is closed. Summary of the invention

[0005] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a method and device for testing the porosity of broken rock mass in a simulated goaf, which at least partially solves the above technical problems.

[0006] The technical solution adopted by the present invention is as follows: a method for testing the porosity of a simulated broken rock mass in a goaf, comprising the following steps:

[0007] (1) Determine the value of the axial stress exerted on the goaf by the deadweight of the overlying strata. The value of the axial stress is set as P. The calculation formula is:

[0008] P=ρgh

[0009] Where:

[0010] P is the overburden pressure, in MPa;

[0011] ρ is the average density of the overlying sediments, in kg / m 2 ;

[0012] g is the acceleration due to gravity, which is 9.8 m / s 2 ;

[0013] h is the vertical height of the overlying rock layer, in meters.

[0014] (2) The concept of fractal dimension D is introduced. By making the fractal dimension D of the rock block consistent with the fractal dimension of the collapsed rock mass in the goaf, it is ensured that the rock block used in the experiment has similar structure to the collapsed rock mass in the goaf, and the porosity evolution of the rock block in the indoor loading bucket is basically consistent with that of the collapsed rock mass in the goaf. The rock blocks used in the experiment are screened by different sieves, and there is a certain functional relationship between the mass of the sample under the sieve and the mass of the total sample:

[0015] ln[m1(d i ) / m t ]=(3-D)ln[d i / d max ]

[0016] Where:

[0017] m1(d i ) is the mass of the sample under the sieve, in kg;

[0018] m t is the total mass in kg;

[0019] D is the fractal dimension value, dimensionless;

[0020] d i is the mesh diameter, in mm;

[0021] d max is the maximum particle size in mm.

[0022] D max After the rock fragments screened by the diameter sieve are filled into the loading bucket, the mass of the rock fragments inside is set as m t , at this time the maximum diameter of the rock in the loading bucket is d max ; According to the above method, the weight required for samples with different particle sizes in the porosity simulation experiment is calculated;

[0023] (3) After the above calculation process is completed, the particles of different particle sizes screened out are mixed according to the above mass relationship, filled into the loading bucket, and weighed; the total mass of the loading bucket and the filler is weighed as M, and the void ratio γ0 before compaction is calculated. The calculation formula of the void ratio γ0 before compaction is:

[0024]

[0025] Where:

[0026] v 总 is the total volume of the barrel;

[0027] v 石 is the volume of the filler;

[0028] γ0 is the void ratio before compaction, dimensionless;

[0029] π is the ratio of the circumference of a circle, and its value is 3.14;

[0030] ρ is the average density of rock, in kg / m 2 ;

[0031] r is the radius of the barrel, in m;

[0032] h is the height of the barrel, in meters;

[0033] M is the total mass of the barrel and filler, in kg;

[0034] m0 is the mass of the barrel, in kg.

[0035] (4) After completing the above steps, place the loading barrel on the press; set the parameters of the press so that the pressure increases continuously during the compaction process and finally provides the axial stress of the above-mentioned calculated result P; during this process, record the displacement of the top cover of the loading barrel at different stresses, and draw a stress-displacement graph based on the data; after the axial stress reaches the maximum, the axial stress provided by the press remains unchanged; after the top cover of the loading barrel no longer displaces and maintains for a period of time, the pressurization can be suspended; during this process, record the displacement of the top cover of the loading barrel at different times and draw a displacement-time graph.

[0036] (5) Simulate the state of the broken rock mass in the goaf being completely filled with water underground: After the filler in the loading bucket is completely submerged in water and soaked for a period of time, the press is turned on and the stress of P is applied to simulate the process of water immersion and compaction. After the press is turned on, the position of the top cover of the loading bucket needs to be recorded at different times.

[0037] (6) Simulate the water immersion and compaction process of the broken rock mass in the goaf during the repeated rise and fall of the groundwater level: control the water inflow and outflow in the loading bucket, and alternate the water inflow and outflow to simulate the change of the groundwater level. Observe the water level in the loading bucket during the water discharge and water inflow process. After the water level is adjusted, turn on the press, and the press applies a stress of P to simulate the water immersion and compaction process. After the press is turned on, it is necessary to record the position of the top cover of the loading bucket at different times.

[0038] (7) Weigh the total mass M1 of the material barrel and the filler during immersion in step 5 and step 6 respectively, and then calculate the void ratio γ1 after compaction. The calculation formula of the void ratio γ1 after compaction is:

[0039]

[0040] Where:

[0041] m w is the mass of injected water, in kg;

[0042] m 吸 is the mass of water absorbed by the rock, in kg;

[0043] ρ w is the density of water, which is 1.0×10 3 kg / m 3 ;

[0044] v 总 is the total volume of the barrel, in m 3 ;

[0045] M1 is the total mass of the barrel, filler and water after immersion, in kg;

[0046] M is the total mass of the barrel and filler before soaking, in kg;

[0047] a is the water absorption rate of the rock, dimensionless;

[0048] m0 is the mass of the barrel, in kg;

[0049] π is the ratio of the circumference of a circle to its circumference, which is approximately 3.14;

[0050] r is the radius of the barrel, in m;

[0051] h is the height of the barrel, in meters;

[0052] x1 is the maximum displacement in m.

[0053] (8) After the experiment, the loading barrel was disassembled by using a disassembly device, and the crushed rock mass in the loading barrel was taken out to observe the shape of the crushed rock mass after repeated immersion and compaction.

[0054] Among them, the disassembly device includes a bracket and a hand-cranked hoist, the hand-cranked hoist is arranged at the upper end of the bracket, the bracket supports the hand-cranked hoist, a fixing rod is installed on the bottom wall of the bracket, and the slot is matched with the fixing rod. After the experiment, the loading barrel is placed on the bottom wall of the bracket, and the fixing rod on the bracket is stuck in the slot on the loading barrel to fix the barrel body for easy disassembly of the loading barrel. The hook on the hand-cranked hoist is hung on the lifting ear, which is convenient for lifting the top cover during disassembly.

[0055] The present invention also includes a device for simulating the porosity test of broken rock in a goaf, including a loading barrel for loading and simulating environmental changes in the goaf; a top cover is installed at the upper end of the loading barrel to provide a sealed experimental environment for the loading barrel, and a pressure-conducting barrel is installed on the upper wall of the top cover to transmit pressure.

[0056] Among them, the loading barrel includes a barrel body, and the side walls of the barrel body are respectively equipped with a liquid level gauge, a water outlet and a slot. The slot is matched with the disassembly device. The liquid level gauge can be used to observe the water level in the barrel body during the process of water filling and draining, so as to control the water level change of the barrel body; the slot cooperates with the disassembly device to fix the barrel body during the removal of the top cover after the experiment to prevent the barrel body from tilting or collapsing; the water outlet plays a role in controlling drainage in the experiment.

[0057] Furthermore, the upper wall of the top cover is provided with multiple water inlets to control the water inlet. The top cover is placed directly on the broken rock stored in the barrel body to provide pressure for the underlying rock. The upper wall of the top cover is provided with a groove, and the pressure-conducting barrel is placed in the groove. The groove can fix the pressure-conducting barrel. A lifting ear is provided in the center of the upper wall of the top cover to facilitate lifting the top cover with a hook during disassembly.

[0058] Preferably, the pressure-conducting barrel includes a pressure-conducting barrel cover and a pressure-conducting barrel body. The pressure-conducting barrel cover is arranged at the upper end of the pressure-conducting barrel body. The upper wall of the pressure-conducting barrel cover is provided with a mounting groove. The pressure-applying end of an external press is connected through the mounting groove to apply pressure to the pressure-conducting barrel, thereby facilitating the acquisition of axial stress. The side wall of the pressure-conducting barrel body is marked with scales to facilitate the observation of the displacement of the top cover during the experiment.

[0059] After adopting the above structure, the beneficial effects of the present invention are as follows:

[0060] (1) The porosity of collapsed rock mass in the goaf can be tested in the laboratory, which ensures the accuracy and effectiveness of the test results. The fractal method is introduced in the experiment to ensure the accuracy and scientificity of the test.

[0061] (2) This device can not only obtain the porosity value of the collapsed rock mass in the goaf when it is just broken and collapsed, but also detect the porosity value of the collapsed rock mass in the goaf after it is compacted by the axial stress provided by the overlying rock layer.

[0062] (3) It is compatible with the press to provide axial stress to the equipment and simulate the compaction process after the goaf collapses.

[0063] (4) During the experiment, water is added or discharged, and the water level in the barrel can be observed, which is convenient for controlling the water level in the barrel and simulating the process of water immersion and compaction of the goaf.

[0064] (5) The loading barrel is easy to disassemble, and the broken rock mass can be taken out after the experiment to observe its characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0066] Figure 1 This is a schematic diagram of the structure of a porosity testing device for simulating broken rock mass in a goaf area proposed by the present invention;

[0067] Figure 2 This is a schematic diagram of the structure of the charging barrel proposed by the present invention;

[0068] Figure 3 This is a schematic diagram of the structure of the charging barrel top cover proposed by the present invention;

[0069] Figure 4 This is a schematic diagram of the structure of the pressure-conducting barrel proposed by the present invention;

[0070] Figure 5 This is a schematic structural diagram of the disassembly device proposed in the present invention.

[0071] In the attached drawings: 1. charging barrel, 2. top cover, 3. pressure-conducting barrel, 4. disassembly device, 5. barrel body, 6. liquid level gauge, 7. water outlet, 8. slot, 9. water inlet, 10. lifting ear, 11. groove, 12. pressure-conducting barrel cover, 13. pressure-conducting barrel body, 14. bracket, 15. hand-cranked hoist, 16. fixing rod. DETAILED DESCRIPTION

[0072] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0073] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0074] like Figure 1-Figure 5 As shown, a method for testing the porosity of a simulated broken rock mass in a goaf includes the following steps:

[0075] (1) Before the experiment begins, the value of the overburden pressure in the goaf must be determined. In this method, the axial stress exerted on the goaf by the deadweight of the overburden strata is mainly considered. The formula for calculating the overburden stratum pressure is:

[0076] P=ρgh

[0077] Where:

[0078] P is the overburden pressure, in MPa;

[0079] ρ is the average density of the overlying sediments, in kg / m 2 ;

[0080] g is the acceleration due to gravity, which is 9.8 m / s 2 ;

[0081] h is the vertical height of the overlying rock layer, in meters.

[0082] (2) The concept of fractal dimension D is introduced to ensure that the rock blocks used in the experiment have similar structures to the collapsed rock mass in the goaf, so as to ensure that the porosity evolution of the rock blocks used in the indoor loading bucket 1 is basically consistent with the collapsed rock mass in the goaf. By making the fractal dimension D of the rock blocks used consistent with the fractal dimension of the collapsed rock mass in the goaf, the similarity between the rock blocks used in the experiment and the broken rock mass in the collapsed zone of the goaf is improved, thereby ensuring the accuracy and scientificity of the experiment; the fractal dimension of the collapsed rock mass in the goaf is selected based on experience. For example, in this experiment, the fractal dimension of the collapsed rock mass in the goaf is selected as 2.3 based on experience. The rock blocks used in the experiment are sieved by different sieves. There is a certain functional relationship between the mass of the sieved sample and the mass of the total sample:

[0083] ln[m1(d i ) / m t ]=(3-D)ln[d i / d max ]

[0084] Where:

[0085] m1(d i ) is the mass of the sample under the sieve, in kg;

[0086] m t is the total mass in kg;

[0087] D is the fractal dimension value, dimensionless;

[0088] d i is the mesh diameter, in mm;

[0089] d max is the maximum particle size in mm.

[0090] For example: the sieve hole diameters are 100mm, 50mm, 25mm, and 12.5mm;

[0091] After the rock fragments screened by the 100 mm diameter sieve are filled into the loading bucket 1, the mass of the rock fragments inside is set as m t At this time, the maximum diameter of the rock in the loading barrel 1 is d max 100mm;

[0092] Substituting di=50mm, 25mm, and 12.5mm into the above formula, we can obtain the mass of the sample under the sieve corresponding to different sieve hole diameters, which are a, b, and c respectively; the mass of the sample with a particle size less than 12.5mm is c, the mass of the sample with a particle size of 12.5-25mm is bc, the mass of the sample with a particle size of 25-50mm is ab, and the mass of the sample with a particle size of 50-100mm is m t -a; According to the above method, the weight required for samples with different particle sizes in the porosity simulation experiment can be calculated;

[0093] (3) After the above calculation process is completed, the particles of different particle sizes screened out are mixed according to the above mass relationship, filled into the loading barrel 1, and the loading barrel 1 is filled up, and weighed; the total mass of the barrel body 5 and the filler is weighed as M, and the void ratio γ0 before compaction can be calculated. The calculation formula of the void ratio γ0 before compaction is:

[0094]

[0095] Where:

[0096] v 总 is the total volume of the barrel;

[0097] v 石 is the volume of the filler;

[0098] γ0 is the void ratio before compaction, dimensionless;

[0099] π is the ratio of the circumference of a circle, and its value is 3.14;

[0100] ρ is the average density of rock, in kg / m 2 ;

[0101] r is the radius of the barrel, in m;

[0102] h is the height of the barrel, in meters;

[0103] M is the total mass of the barrel and filler, in kg;

[0104] m0 is the mass of the barrel, in kg.

[0105] (4) After completing the above steps, place the loading barrel 1 on the press, cover it with the top cover 2, and place the pressure-guiding barrel 3 on the top cover 2; set the parameters of the press so that the pressure increases continuously during the compaction process and finally provides the axial stress of the above-mentioned calculation result P; in this process, it is necessary to record the displacement of the top cover 2 at different stresses, and draw a stress-displacement graph based on the data; after the axial stress reaches the maximum (the above-mentioned calculation result P), the axial stress provided by the press remains unchanged; after the top cover 2 no longer displaces and maintains for a period of time, the pressurization can be suspended; in this process, it is necessary to record the displacement of the top cover 2 at different times and draw a displacement-time graph.

[0106] (5) Simulate the state of the broken rock mass in the goaf being completely filled with water underground: open the water inlet 9 on the top cover 2 to inject water, and observe the water level through the liquid level meter 6; after the filler is completely immersed in water, close the water inlet valve, close the valve of the liquid level meter 6 to soak for a period of time, open the press, apply the stress of P, simulate the process of immersion compaction, and record the position of the top cover 2 at different times after the press is opened.

[0107] (6) Simulate the process of water immersion and compaction of the broken rock mass in the goaf during the repeated rise and fall of the groundwater level: control the water level in the barrel 5 through the water inlet 9 and the water outlet 7, and alternately input and output water to simulate the change of the groundwater level. Observe the liquid level gauge 6 during the process of water discharge and water inlet, and observe the water level in the barrel 5. After the water level is adjusted, close the water inlet and outlet valves and the liquid level gauge 6 valve, and turn on the press. The press applies the stress P to simulate the process of water immersion and compaction; after the press is opened, it is necessary to record the position of the top cover 2 at different times.

[0108] (7) Weigh the total mass M1 of the barrel 5 and the filler during immersion in step 5 and step 6 respectively, and then calculate the void ratio γ1 after compaction. The calculation formula of the void ratio γ1 after compaction is:

[0109]

[0110] Where:

[0111] m w is the mass of injected water, in kg;

[0112] m 吸 is the mass of water absorbed by the rock, in kg;

[0113] ρ w is the density of water, which is 1.0×10 3 kg / m 3 ;

[0114] v 总is the total volume of the barrel, in m 3 ;

[0115] M1 is the total mass of the barrel, filler and water after immersion, in kg;

[0116] M is the total mass of the barrel and filler before soaking, in kg;

[0117] a is the water absorption rate of the rock, dimensionless;

[0118] m0 is the mass of the barrel, in kg;

[0119] π is the ratio of the circumference of a circle to its circumference, which is approximately 3.14;

[0120] r is the radius of the barrel, in m;

[0121] h is the height of the barrel, in meters;

[0122] x1 is the maximum displacement in m.

[0123] (8) After the experiment, the loading barrel 1 is transferred to the disassembly device 4, so that the fixing rod 16 on the disassembly device 4 is stuck in the slot 8 of the loading barrel 1 to achieve the function of fixing the barrel body 5. The top cover 2 is taken out by the hand-cranked hoist 15, and the broken rock mass therein is taken out to observe the shape of the broken rock mass after repeated immersion and compaction.

[0124] The disassembly device 4 includes a bracket 14 and a hand-cranked hoist 15, the hand-cranked hoist 15 is arranged at the upper end of the bracket 14, the bracket 14 supports the hand-cranked hoist 15, the bottom wall of the bracket 14 is installed with a fixing rod 16, the slot 8 is matched with the fixing rod 16, after the experiment, the charging barrel 1 is placed on the bottom wall of the bracket 14, the fixing rod 16 on the bracket 14 is stuck in the slot 8 on the charging barrel 1, and the barrel body is fixed to facilitate the disassembly of the charging barrel 1, and the hook on the hand-cranked hoist 15 is hung on the lifting ear 10, which is convenient for lifting the top cover 2 during disassembly.

[0125] The present invention also includes a device for simulating the porosity test of broken rock mass in a goaf, including a loading barrel 1 for loading and simulating environmental changes in the goaf; a top cover 2 is installed at the upper end of the loading barrel 1 to provide a sealed experimental environment for the loading barrel 1, and a pressure-conducting barrel 3 is installed on the upper wall of the top cover 2 to transmit pressure.

[0126] The loading barrel 1 includes a barrel body 5, and the side walls of the barrel body 5 are respectively installed with a liquid level gauge 6, a water outlet 7 and a slot 8. The slot 8 is matched with the disassembly device 4. The liquid level gauge 6 can be used to observe the water level in the barrel body 5 during the process of water inlet and outlet, so as to control the water level change of the barrel body 5; the slot 8 cooperates with the disassembly device 4 to fix the barrel body during the removal of the top cover 2 after the experiment is completed, so as to prevent the barrel body from tilting or collapsing; the water outlet 7 plays a role in controlling drainage in the experiment.

[0127] The upper wall of the top cover 2 is provided with multiple water inlets 9 to control the water inlet. The top cover 2 is placed directly on the broken rock stored in the barrel body 5 to provide pressure for the underlying rock. The upper wall of the top cover 2 is provided with a groove 11, and the pressure-conducting barrel 3 is placed in the groove 11. The groove 11 can fix the pressure-conducting barrel 3. A lifting ear 10 is provided in the center of the upper wall of the top cover 2 to facilitate lifting the top cover 2 with a hook when disassembling.

[0128] The pressure-conducting barrel 3 includes a pressure-conducting barrel cover 12 and a pressure-conducting barrel body 13. The pressure-conducting barrel cover 12 is arranged at the upper end of the pressure-conducting barrel body 13. The upper wall of the pressure-conducting barrel cover 12 is provided with a mounting groove. The pressure-applying end of the external press is connected through the mounting groove to apply pressure to the pressure-conducting barrel 3, thereby facilitating the acquisition of axial stress. The side wall of the pressure-conducting barrel body 13 is marked with scales to facilitate the observation of the displacement of the top cover 2 during the experiment.

[0129] Although the embodiments of the present invention have been shown and described, it is understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents. In short, if those skilled in the art are inspired by them and design structural modes and embodiments similar to the technical solution without creativity without departing from the purpose of the present invention, they shall all fall within the scope of protection of the present invention.

Claims

1. A method for testing the porosity of a broken rock mass in a simulated goaf area, comprising the following steps: (1) Determine the value of the axial stress exerted on the goaf by the deadweight of the overlying strata. The value of the axial stress is set as P. The calculation formula is: P=ρgh Where: P is the overburden pressure, in MPa; ρ is the average density of the overlying sediments, in kg / m 2 ; g is the acceleration due to gravity, which is 9.8 m / s 2 ; h is the vertical height of the overlying rock layer, in meters. (2) The concept of fractal dimension D is introduced. By making the fractal dimension D of the rock block consistent with the fractal dimension of the collapsed rock mass in the goaf, it is ensured that the rock block used in the experiment has similar structure to the collapsed rock mass in the goaf, and the porosity evolution of the rock block in the indoor loading bucket is basically consistent with that of the collapsed rock mass in the goaf. The rock blocks used in the experiment are screened by different sieves, and there is a certain functional relationship between the mass of the sample under the sieve and the mass of the total sample: ln[m1(d i ) / m t ]=(3-D)ln[d i / d max ] Where: m1(d i ) is the mass of the sample under the sieve, in kg; m t is the total mass in kg; D is the fractal dimension value, dimensionless; d i is the mesh diameter, in mm; d max is the maximum particle size in mm. D max After the rock fragments screened by the diameter sieve are filled into the loading bucket, the mass of the rock fragments inside is set as m t , at this time the maximum diameter of the rock in the loading bucket is d max ; According to the above method, the weight required for samples with different particle sizes in the porosity simulation experiment is calculated; (3) After the above calculation process is completed, the particles of different particle sizes screened out are mixed according to the above mass relationship, filled into the loading bucket, and weighed; the total mass of the loading bucket and the filler is weighed as M, and the void ratio γ0 before compaction is calculated. The calculation formula of the void ratio γ0 before compaction is: Where: v 总 is the total volume of the barrel; v 石 is the volume of the filler; γ0 is the void ratio before compaction, dimensionless; π is the ratio of a circle to a circle, and its value is 3.14; ρ is the average density of rock, in kg / m 2 ; r is the radius of the barrel, in m; h is the height of the barrel, in meters; M is the total mass of the barrel and filler, in kg; m0 is the mass of the barrel, in kg. (4) After completing the above steps, place the loading barrel on the press; set the parameters of the press so that the pressure increases continuously during the compaction process and finally provides the axial stress of the above-mentioned calculated result P; during this process, record the displacement of the top cover of the loading barrel at different stresses, and draw a stress-displacement graph based on the data; after the axial stress reaches the maximum, the axial stress provided by the press remains unchanged; after the top cover of the loading barrel no longer moves and maintains for a period of time, stop pressurizing; during this process, record the displacement of the top cover of the loading barrel at different times and draw a displacement-time graph; (5) Simulate the state of the broken rock mass in the goaf being completely filled with water underground: After the filler in the loading bucket is completely submerged in water, soak for a period of time, turn on the press, apply the stress P, and simulate the process of water immersion and compaction. After the press is turned on, the position of the top cover of the loading bucket needs to be recorded at different times; (6) Simulate the water immersion and compaction process of the broken rock mass in the goaf during the repeated rise and fall of the groundwater level: control the water inflow and outflow in the loading bucket, and alternate the water inflow and outflow to simulate the change of the groundwater level. Observe the water level in the loading bucket during the water discharge and water inflow process. After the water level is adjusted, open the press, and the press applies the stress of P to simulate the water immersion and compaction process; after the press is opened, it is necessary to record the position of the top cover of the loading bucket at different times; (7) Weigh the total mass M1 of the material barrel and the filler during immersion in step 5 and step 6 respectively, and calculate the void ratio γ1 after compaction. The calculation formula of the void ratio γ1 after compaction is: Where: m w is the mass of injected water, in kg; m 吸 is the mass of water absorbed by the rock, in kg; ρ w is the density of water, which is 1.0×10 3 kg / m 3 ; v 总 is the total volume of the barrel, in m 3 ; M1 is the total mass of the barrel, filler and water after immersion, in kg; M is the total mass of the barrel and filler before soaking, in kg; a is the water absorption rate of the rock, dimensionless; m0 is the mass of the barrel, in kg; π is the ratio of the circumference of a circle to its circumference, which is approximately 3.14; r is the radius of the barrel, in m; h is the height of the barrel, in meters; x1 is the maximum displacement in m. (8) After the experiment, the loading barrel was disassembled by using a disassembly device, and the crushed rock mass in the loading barrel was taken out to observe the shape of the crushed rock mass after repeated immersion and compaction.

2. The method for testing the porosity of the broken rock mass in the simulated goaf according to claim 1 is characterized in that: In step 8, the disassembly device includes a bracket and a hand-cranked hoist, the hand-cranked hoist is arranged at the upper end of the bracket, and a fixing rod is installed on the bottom wall of the bracket.

3. A device for testing the porosity of a simulated rock mass in a goaf, characterized in that: It includes a charging barrel for loading materials and simulating environmental changes in goaf areas; a top cover is installed on the upper end of the charging barrel to provide a sealed experimental environment for the charging barrel, and a pressure-conducting barrel is installed on the upper wall of the top cover to transmit pressure.

4. The device for testing the porosity of the broken rock mass in the simulated goaf according to claim 3 is characterized in that: The charging barrel comprises a barrel body, and the side walls of the barrel body are respectively equipped with a liquid level meter, a water outlet and a card slot.

5. The device for testing the porosity of the broken rock mass in the simulated goaf according to claim 4 is characterized in that: The upper wall of the top cover is provided with multiple water inlets, and the top cover is placed directly on the broken rock stored in the barrel body to provide pressure for the underlying rock. The upper wall of the top cover is provided with a groove, and the pressure-conducting barrel is placed in the groove. A lifting ear is provided in the center of the upper wall of the top cover.

6. The device for testing the porosity of the broken rock mass in the simulated goaf according to claim 4 is characterized in that: The pressure-conducting barrel includes a pressure-conducting barrel cover and a pressure-conducting barrel body. The pressure-conducting barrel cover is arranged on the upper end of the pressure-conducting barrel body. The upper wall of the pressure-conducting barrel cover is provided with a mounting groove. The pressure-applying end of an external press is connected through the mounting groove to apply pressure to the pressure-conducting barrel, thereby facilitating the acquisition of axial stress. The side wall of the pressure-conducting barrel body is marked with scales to facilitate the observation of the displacement of the top cover during the experiment.

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