CN114544372A - Gas-containing coal triaxial testing machine with single hydraulic pump controlling constant-proportion loading and testing method - Google Patents

Abstract

The invention discloses a gas-containing coal triaxial testing machine with a single hydraulic pump controlling fixed-proportion loading and a testing method, and relates to the technical field of rock mechanics. The active loading device comprises a single hydraulic pump, a pressurizing shaft and a hydraulic oil cylinder. The driven loading device comprises an oil cylinder, a fixed-ratio pressure reducing valve, a pilot type two-way overflow valve, a hydraulic pipeline and a driven shaft. The pressure bearing shaft is a movable shaft, and the interior of the pressure bearing shaft contains oil liquid which is communicated with the driven loading device. And monitoring systems formed by sensors are respectively arranged on the three-way loading shaft and the test inner wall and used for monitoring rock data. The seepage device can inject gas such as gas and the like. According to the invention, the single hydraulic pump is used for pressurizing, the pressure bearing shaft transmits pressure to the driven loading system through oil to adjust, and the driven shaft is driven to load confining pressure, so that the test requirement of the coal sample on the three-dimensional stress loaded in a fixed proportion under the condition of containing gas is realized through the single hydraulic pump.

Description

Gas-containing coal triaxial testing machine with single hydraulic pump controlling constant-proportion loading and testing method

Technical Field

The invention relates to the technical field of rock mechanics, in particular to a gas-containing coal triaxial testing machine with a single hydraulic pump controlling constant-proportion loading and a testing method.

Background

Nowadays, underground works are increasingly developed under the background of development of various industrial equipments and increase of social demands. The mechanical property test of rock is taken as important research content in rock engineering, and is widely applied to the field of underground engineering such as mines, tunnels and the like, because the rock is in a three-way stress state under the ground, the true triaxial test of the rock is particularly important, and currently, a triaxial tester is mainly used for pressurizing rock samples with fixed shapes by different pressures so as to obtain related indexes. Ordinary triaxial testing machine simple and convenient has solved true triaxial loading problem, but its cost is higher, is provided with a plurality of hydraulic pumps, and the use step is comparatively loaded down with trivial details, can't satisfy the experiment of carrying out scaling loading three-dimensional stress to the rock under some special experimental conditions, and because there are gases such as a large amount of gas underground, the device can't provide true seepage flow state and scaling pressure control at present, need improve current true triaxial testing machine to this type of experiment.

Disclosure of Invention

The invention provides a gas-containing coal triaxial testing machine with a single hydraulic pump controlling constant-proportion loading and a testing method, aiming at solving the problems that the currently most commonly used true triaxial testing machine device has a complex adjusting process and is long in time and cannot provide a real seepage state and constant-proportion pressure adjustment under special requirements, and the specific technical scheme is as follows: a three-axis testing machine for coal containing gas with a single hydraulic pump controlling constant-proportion loading is characterized by comprising a supporting frame, a closed testing chamber, a driving loading device, a driven loading device, a gas injection and discharge device, a bearing shaft and a monitoring system; the active loading device comprises a vertical active pressurizing shaft, a hydraulic pump and a hydraulic oil cylinder, wherein the hydraulic pump is connected with the hydraulic oil cylinder, and the pressurizing shaft is connected with the hydraulic pump and arranged above the test chamber; the driven loading device comprises a transverse pressurizing shaft, a longitudinal pressurizing shaft, an oil cylinder, a hydraulic pipeline guide type two-way overflow valve and a proportional pressure reducing valve, the oil cylinder is fixed below the supporting frame, the transverse pressurizing shaft and the longitudinal pressurizing shaft are respectively arranged on the left side, the right side, the front side and the rear side of the testing chamber, and the hydraulic pipeline penetrates through the tabletop of the supporting frame to be connected with the oil cylinder and the driven pressurizing shaft; the monitoring system comprises a displacement sensor, a pressure sensor, a gas pressure sensor, an acoustic emission sensor and a three-dimensional digital speckle testing device; the pressure bearing shaft is arranged below the test chamber and connected with the lower oil cylinder; when the pressure applied to the pressure bearing shaft is increased or reduced, oil liquid transmits pressure to the driven shaft through the oil cylinder and the pipeline, and accordingly pressure change in a corresponding proportion is generated.

Preferably, the test chamber is subjected to sealing treatment, the sealing performance is good after the chamber window is closed, and the condition of no leakage of the introduced gas is avoided.

Preferably, a bearing plate is arranged on the bearing shaft, a groove hole with the same size as the sample is formed in the bearing plate, and the bearing plate is made of anti-skidding materials and is tightly attached to the bearing shaft without sliding.

Preferentially, the pressure bearing shaft is a large-radius moving shaft, the displacement caused by pressure bearing is small, a certain amount of oil is arranged in the pressure bearing shaft, and the oil is connected with the oil cylinder below the pressure bearing shaft.

Preferably, the pressure bearing shaft is connected with the lower oil cylinder through a pilot type two-way overflow valve, the rated pressure of the lower end of the pilot type two-way overflow valve is larger than that of the upper end of the pilot type two-way overflow valve, and the two-way overflow valve is characterized in that the two-way overflow valve is conducted after the rated value is reached, and the two-way overflow valve plays roles in stabilizing pressure and protecting safety.

Preferably, the hydraulic pipeline is a "Y" type oil pressure pipe, the two sides of the transverse pressurizing shaft are connected to an oil port on the left side of the oil cylinder below, the two sides of the longitudinal pressurizing shaft are connected to an oil port on the back side of the oil cylinder, and the oil cylinder is connected with the hydraulic pipeline through a control valve.

Preferably, the control valve is a proportional pressure reducing valve, and is characterized in that the output pressure and the input pressure are in a fixed proportion, and the oil pressure at the same height in the oil cylinder is equal, so that the output pressure of the two proportional pressure reducing valves can achieve the proportional effect, and the valve group and the specific value are selected according to the test requirements when leaving a factory.

Preferably, the gas injection and discharge device is connected with an external gas tank, and the type of the introduced seepage gas can be changed by replacing the external gas tank.

Preferentially, monitoring system includes displacement sensor, pressure sensor, gas pressure sensor, acoustic emission sensor and three-dimensional digital speckle testing arrangement, pressure sensor sets up in vertical initiative pressurization axle, displacement sensor sets up in vertical initiative pressurization axle, horizontal driven pressurization axle and bearing shaft, gas pressure sensor sets up by the seepage flow device, the aperture is seted up to each pressurization axle head, acoustic emission sensor arranges in the aperture of each pressurization axle head and fixes with the spring, connects the transmission through the wire for receive rock specimen acoustic emission signal, three-dimensional digital speckle testing arrangement sets up in the inner wall both sides, comprises two high-speed cameras, combines two mesh stereovision techniques to gather the speckle image of rock specimen deformation stage.

The invention also provides a three-axis test method for loading gas-containing coal in a fixed proportion by controlling the single hydraulic pump, which comprises the following steps:

the first step is as follows: the ink is sprayed on the surface of the rock sample to manufacture scattered spots, the scattered spots are placed in the middle of a slotted hole in the bearing plate to prevent the scattered spots from sliding, and the position of the bearing shaft is adjusted according to the size of the test piece, so that the bearing shaft can be aligned to the middle of the rock sample by the axes of the driven pressurizing shafts on two sides after the bearing shaft is reduced by a small distance under the action of pressure.

The second step is that: and closing the pressure control valve, manually adjusting the initial position of the driven shaft, enabling the pressure head to be tightly attached to the surface of the test piece, and enabling the acoustic emission sensor to be attached to the surface of the sample.

The third step: the fixed-ratio pressure reducing valve is opened, the hydraulic pump is adjusted, a small amount of initial load is applied to the driving shaft, the internal oil pressure of the pressure bearing shaft is increased until the internal oil pressure is larger than the rated pressure of the upper part of the pilot-operated two-way overflow valve, the overflow valve is connected, a small amount of oil is extruded into the oil cylinder below, the pressure is further transmitted to the driven shaft, the test piece is slightly tightened around the driven shaft, then the loading of the driving shaft is stopped, the pressure of the pressure bearing shaft is reduced at the moment, the oil pressure in the oil cylinder is larger than the pressure bearing shaft but does not reach the rated pressure of the lower end of the overflow valve, the overflow valve is not connected, and therefore the test piece is slightly tightened by the pressure in the driven loading system.

The fourth step: adjusting the pressure and the displacement sensor to return to zero, starting the three-dimensional digital speckle testing device, adjusting the shooting direction to be vertical to the sample, opening the seepage device, introducing seepage gas with preset concentration by monitoring the numerical value of the gas pressure sensor, gradually pressurizing the hydraulic pump after the gas completely permeates into the rock sample, performing a cyclic loading test until the rock sample is damaged, stopping loading, wherein the pressure in the oil cylinder is greater than the rated value of the lower end of the overflow valve, the overflow valve is switched on to release the pressure, the test piece is loosened by the driven shaft, the seepage device recovers the gas, and the test is finished.

The fifth step: the method comprises the steps of obtaining a numerical value or a curve for calculation according to a sensor, wherein the strain in the vertical direction is the difference between the displacement variation on a pressurizing shaft and the displacement variation on a bearing shaft, the strain in the horizontal direction is the sum of the displacement variations of a corresponding driven shaft, a main stress curve is obtained by the pressure sensor, transverse and longitudinal stress curves are obtained by multiplying the main stress curve by a fixed proportion, an acoustic emission sensor is used for receiving an acoustic emission signal of a rock sample, and a three-dimensional digital speckle testing device measures a three-dimensional deformation field of the sample by a digital image correlation method.

Compared with the prior art, the invention has the following technical effects:

the invention provides a gas-containing coal triaxial testing machine with single hydraulic pump controlled constant proportion loading and a testing method, which simulate the surrounding rock environment of a rock sample under special conditions, compared with the multi-hydraulic pump loading mode of the traditional triaxial testing machine, the testing machine cancels a hydraulic pump required in the confining pressure direction, and is changed into a single hydraulic pump for pressurization, a pressure bearing shaft bears a first main stress and performs small displacement downwards when increasing, and part of oil in the shaft is pressed into an oil cylinder through a two-way overflow valve between the oil cylinder and a lower oil cylinder, so that the pressure between the pressure bearing shaft and the oil cylinder is communicated, further the oil cylinder transmits the increased pressure to a transverse pressurizing shaft and a longitudinal pressurizing shaft through a connected hydraulic pipe respectively, the pressure ratio is automatically adjusted through a constant proportion reducing valve, thereby achieving the testing effect of only performing single-phase pressurization to ensure that the three-way stress ratio is constant, and greatly reducing the number of the hydraulic pumps, the production cost and the complexity are reduced, and because the pressure ratio is constant, all pressure curves can be obtained only by installing one pressure sensor on the driving shaft, the magnitude of the confining pressure does not need to be adjusted repeatedly, and the seepage device is additionally arranged in a closed testing chamber, so that the surrounding rock conditions under the condition of seepage gas such as underground gas are provided, the performance of the analysis material is better by the speckle images of various deformation stages acquired by the acoustic emission sensor and the three-dimensional digital speckle testing device, the testing process is simplified, the testing content is enriched, and the efficiency and the result reliability are improved.

Drawings

FIG. 1 is a subjective view of a coal-containing gas triaxial testing machine with a single hydraulic pump controlling a constant-ratio loading according to the present invention

FIG. 2 is a left side view of a gas-containing coal triaxial testing machine with single hydraulic pump controlling constant-proportion loading according to the present invention

FIG. 3 is a partial view showing an acoustic emission sensor according to the present invention

In the figure, 1-hydraulic pump; 2-actively pressurizing the shaft; 3-a hydraulic oil cylinder; 4-a transverse driven pressurized shaft; 5-a pressure bearing plate; 6-pressure bearing displacement sensor; 7-a pilot operated two-way overflow valve; 8-bottom oil cylinder; 9-a support frame; 10-horizontal axis hydraulic line; 11-horizontal axis proportional pressure reducing valve; 12-a bearing shaft; 13-driven shaft displacement sensor; 14-enclosing the test chamber; 15-pressure sensor and displacement sensor; 16-a longitudinal driven pressurized shaft; 17-vertical axis proportional pressure reducing valve; 18-longitudinal axis hydraulic line; 19-a three-dimensional digital speckle test device; 20-a gas pressure sensor; 21-gas injection and discharge device; 22-an acoustic emission sensor; 23-spring.

Detailed Description

In order to more clearly illustrate the technical solutions provided by the present invention, the following detailed description is given with reference to the accompanying drawings for clarity and completeness

The invention aims to provide a gas-containing coal triaxial testing machine with a single hydraulic pump controlling constant-proportion loading and a testing method, so as to solve the problems that the most commonly used true triaxial testing machine is complex in device and cannot perform a constant-proportion pressure test, and improve the testing efficiency.

A three-axis testing machine for coal containing gas with a single hydraulic pump controlling fixed-proportion loading specifically comprises a support frame 9, a closed testing chamber 14, a driving loading device, a driven loading device, a gas injection and discharge device 21, a pressure bearing shaft 12 and a monitoring system. The testing machine realizes the loading in the first main stress direction through the single hydraulic pump 1, and the pressure bearing shaft 12 communicates the pressure to the driven loading device and carries out the constant-ratio adjustment, thereby realizing the three-way constant-ratio pressurization through the one-way pressurization under special conditions; the active loading device is used for adjusting the first main stress on the rock sample, the seepage device provides different gas injection and discharge fields, and the detection system measures the stress and the strain in the loading process in real time.

The active loading device specifically comprises a hydraulic pump 1, a hydraulic oil cylinder 3 and an active pressurizing shaft 2, the hydraulic pump 1 is connected with the hydraulic oil cylinder 3 and the pressurizing shaft 2, the pressurizing shaft 2 penetrates through the upper part of the testing chamber 14 and is fixed, and the hydraulic pump 1 can apply load to a rock sample through the pressurizing shaft 2.

The bearing plate 12 is arranged below the test chamber 14 and penetrates through the desktop of the support frame 9, the bearing plate 5 can move up and down along a vertical shaft, the bearing plate 5 is placed above the bearing plate 12, a slotted hole is formed in the middle of the bearing plate 5, the bearing plate 5 is made of anti-skidding elastic materials, the bearing plate 5 deforms when bearing load, so that the bearing plate 12 is in close contact with the bearing plate to prevent sideslip, stress distribution is uniform, the bearing plate 12 is a large-radius rigid motion shaft, deformation or deformation quantity can be ignored when the bearing load is guaranteed, oil liquid is stored inside, the small displacement quantity generated under the action of large load is guaranteed, and therefore the influence of friction force generated between the rock sample and a driven shaft is reduced.

The driven loading device comprises a transverse pressurizing shaft 4, a longitudinal pressurizing shaft 16, a bottom oil cylinder 8, a hydraulic pipeline 10, a hydraulic pipeline 18, a transverse shaft proportional pressure reducing valve 11, a longitudinal shaft proportional pressure reducing valve 17 and a pilot type two-way overflow valve 7. The transverse pressurizing shafts 4 are disposed on the left and right sides of the test chamber 14, and the longitudinal pressurizing shafts 16 are disposed on the front and rear sides. The oil cylinder 8 is fixed below the supporting frame 9, and the left side and the rear side of the upper part of the oil cylinder 8 are open. An opening above the oil cylinder 8 is connected with the lower part of the pressure bearing shaft 12 through a pilot type two-way overflow valve 7, oil inside the oil cylinder 8 is communicated with oil inside the pressure bearing shaft 12 through the pilot type two-way overflow valve 7, the pilot type two-way overflow valve 7 is used for controlling the flow direction of the oil, the oil flows into the oil cylinder 8 from the pressure bearing shaft 12 during loading, and the oil flows out reversely during pressure unloading. The left opening of the oil cylinder 8 is communicated with the transverse pressurizing shaft 4 through a hydraulic pipeline 10, a proportional pressure reducing valve 11 is connected between the left opening of the oil cylinder 8 and the hydraulic pipeline 10, the back opening of the oil cylinder 8 is communicated with a longitudinal pressurizing shaft 16 through the hydraulic pipeline 10, and a proportional pressure reducing valve 17 is connected between the back opening of the oil cylinder 8 and a hydraulic pipeline 18. The fixed-ratio pressure reducing valve 11 and the fixed-ratio pressure reducing valve 17 are used for adjusting and generating fixed-ratio driven shaft pressure, and the output ratio of the pressure reducing valves is selected according to requirements when the pressure reducing valves are delivered out of a factory. When the pressure bearing shaft 12 is loaded, micro displacement is generated, internal part of oil is squeezed into the oil cylinder 8 through the pilot type two-way overflow valve 7 under the action of pressure, so that the pressure is communicated, the increased pressure is output to the driven pressurizing shaft 4 and the driven pressurizing shaft 16 in a fixed ratio through the adjustment of the fixed ratio pressure reducing valve 11 and the fixed ratio pressure reducing valve 17 after the internal pressure of the oil cylinder 8 is increased, and therefore the three-way stress borne by a rock sample is in a fixed ratio state.

The gas injection and discharge device 21 is arranged above the closed test chamber 14 and is connected with an external gas tank, the type of seepage gas can be changed by replacing the gas tank, and the injection and discharge device can perform pressurization and gas inflation and gas recovery actions.

The detection device comprises a pressure and displacement sensor 15, a pressure bearing displacement sensor 6, a driven shaft displacement sensor 13, a gas pressure sensor 20, an acoustic emission sensor 22 and a three-dimensional digital speckle testing device 19. The pressure and displacement sensor 15 is disposed on the active compression shaft 2 for monitoring the load and the strain in the first main stress direction. The pressure bearing displacement sensor 6 is arranged on the pressure bearing shaft 12 and used for monitoring the strain on the pressure bearing shaft. The transverse displacement sensor 13 is arranged on the driven pressurizing shaft 4 and used for monitoring the strain magnitude in the second main stress direction. The longitudinal displacement sensor 13 is arranged on the driven pressurizing shaft 16 and used for monitoring the strain magnitude in the third main stress direction. The gas pressure sensor 20 is disposed beside the seepage device 21 and is used for monitoring the seepage gas concentration and the internal gas pressure. The acoustic emission sensors 22 are arranged in small holes at the end heads of the pressurizing shafts, are fixed by the springs 3, are connected with the testing machine through conducting wires, and need to be tightly attached to the surface of a sample when in use, and are used for receiving acoustic emission signals when the rock sample deforms. The three-dimensional digital speckle testing device 19 is arranged on two sides of the inner wall and used for collecting speckle images of the sample at each deformation stage so as to measure a three-dimensional deformation field of the sample.

A single hydraulic pump control fixed proportion loading gas-containing coal triaxial testing machine test method comprises the following specific implementation mode:

adjusting the initial position of the bearing shaft in the first step: ink is sprayed on the surface of a rock sample to manufacture scattered spots, the scattered spots are placed in the middle of a slotted hole in the bearing plate 5, the bearing plate 5 is tightly attached to the bearing shaft 12 to prevent the bearing shaft 12 from sliding, and the initial positions of the bearing shaft 12 and the bearing plate 5 are adjusted according to the specific height of the tested rock sample, so that when the rock sample is loaded with an initial load by the driving shaft 2, the internal pressure of the bearing shaft 12 rises under the load effect, the bearing shaft 12 descends for a small distance, and the centers of the pressure heads of the driven shafts 4 and 16 on two sides can be aligned to the middle of the rock sample.

The second step is to adjust the initial position of the driven shaft: closing proportional pressure reducing valves 11 and 17 between the bottom oil cylinder 8 and the hydraulic pipelines 10 and 18 to temporarily keep the internal pressure of the hydraulic pipelines 10 and 18 unchanged, smearing proper vaseline on the surface of the acoustic emission sensor 22, manually adjusting the initial positions of the transverse driven shaft 4 and the longitudinal driven shaft 16 to enable pressure heads of the driven shafts 4 and 16 to be tightly attached to the surface of the test piece, and enabling the acoustic emission sensor 22 to be tightly attached to the surface of the test piece through the elastic force of a spring 23.

Thirdly, preloading initial confining pressure: opening the pressure control valves 11 and 17, adjusting the hydraulic pump 1, driving the driving shaft 2 to descend and contact the upper surface of the rock sample, continuously applying a small amount of initial load and transmitting the load to the lower pressure bearing shaft 12, increasing the pressure in the pressure bearing shaft 12 to compress the oil, conducting when the pressure exceeds the rated value of the upper end of the pilot-operated two-way overflow valve 7, extruding part of the oil into the oil cylinder 8, further transmitting the oil and the pressure in the oil cylinder 8 to the driven shafts 4 and 16 through the valves 14 and 17 and the hydraulic pipelines 10 and 18, so that the driven shafts 4 and 16 load the surface of the rock sample, stopping loading the driving shaft 2 when no obvious relative sliding between the surface of the rock and the driven shafts 4 and 16 is observed, reducing the pressure of the pressure bearing shaft 12, and ensuring that the pressure in the oil cylinder 8 is higher than the rated value of the lower end of the pilot-operated two-way overflow valve 7 and is not conducted reversely, the pressure prevailing inside the driven shaft remains unchanged, at which point the rock specimen assumes a slightly tightened state by the driven shaft 4 and the driven shaft 16 and no relative sliding occurs anymore.

Fourthly, starting a system zeroing test: adjusting the sensors 6, 13 and 15 to be zero values, starting the three-dimensional digital speckle testing device 19, adjusting the shooting direction to be vertical to the sample, opening the seepage device 21, introducing gas with preset concentration through monitoring the numerical value of the gas pressure sensor 20, gradually loading the hydraulic pump adjusting hydraulic pump 1 after the gas completely permeates into the rock sample, performing a cyclic loading test, continuously feeding oil into a driven loading system for constant-ratio pressurization after the load exceeds the initial pressure during preloading until the instability of the rock sample is destroyed, stopping loading, at the moment, the pressure in the oil cylinder 8 is greater than the rated value at the lower end of the overflow valve 7, conducting the overflow valve 7 for reverse pressure relief, loosening the test piece of a driven shaft, recovering seepage gas by the seepage device 21 to unload the internal air pressure, and finishing the test.

And fifthly, processing monitoring data: the computer is used for calculating according to the numerical value or curve monitored by the sensor, wherein the strain of the rock in the vertical direction is the difference between the displacement change quantity on the driving pressurizing shaft 2 and the displacement change quantity on the bearing shaft 12, the strain in the transverse direction and the longitudinal direction is the sum of the displacement change quantities of the corresponding driven shafts, the first main stress pressure numerical value is obtained by the pressure sensor 15, the transverse direction and the longitudinal direction stress curve are obtained by multiplying the vertical curve by a fixed proportion, the fixed proportion is the fixed proportion of the pressure in the three directions set by the valve when the testing machine leaves the factory according to the requirement, the acoustic emission sensor 22 receives the internal acoustic emission signals when the rock sample deforms, and the three-dimensional digital speckle testing device 19 collects the speckle images of each deformation stage of the sample.

The invention provides a gas-containing coal triaxial testing machine and a testing method for controlling proportional loading by a single hydraulic pump, which reduce the number of hydraulic pumps from a plurality of traditional triaxial testing machines into a single one, reduce the production cost and complexity, change the original three-way active pressurization into the mode of the single hydraulic pump active pressurization and the driven loading device controlled by a valve to carry out the driven proportional pressurization, thereby solving the problem that the currently used testing machine can not carry out the proportional loading of samples under special requirements, and needing no repeated confining pressure adjustment, and only one pressure sensor can obtain a three-way stress curve because the three-way pressure is constant in a fixed proportion, and a gas injection and discharge device is additionally arranged, thereby providing the real state that surrounding rocks are in gas injection and discharge places such as gas under the coal mine condition, and carrying out diversified analysis on the rock performance by an acoustic emission sensor and a three-dimensional digital speckle testing device, the accuracy and the practicability of the test are improved, and the test result can be conveniently popularized to underground roadways and other places.

The above-mentioned embodiments are only for convenience of description, and are not intended to limit the present invention in any way, and those skilled in the art will understand that the present invention can be modified or modified in some ways without departing from the scope of the present invention.

Claims (12)

1. A gas-containing coal triaxial testing machine with a single hydraulic pump controlling constant-proportion loading is characterized by comprising a supporting frame, a closed testing chamber, a driving loading device, a driven loading device, a gas injection and discharge device, a pressure bearing shaft and a monitoring system; the active loading device specifically comprises a hydraulic pump, a hydraulic oil cylinder and a vertical pressurizing shaft, the hydraulic pump is connected with the hydraulic oil cylinder and the pressurizing shaft, and the pressurizing shaft penetrates through the upper part of the test chamber and is fixed; the driven loading device comprises a transverse pressurizing shaft, a longitudinal pressurizing shaft, a bottom oil cylinder, a hydraulic pipeline, a fixed-ratio pressure reducing valve and a pilot-operated two-way overflow valve. The transverse pressurizing shafts are arranged on the left side and the right side of the testing chamber, and the longitudinal pressurizing shafts are arranged on the front side and the rear side. The oil cylinder is fixed below the supporting frame, and the upper part, the left side and the back side of the oil cylinder are provided with openings. An opening above the oil cylinder is connected with the lower part of the pressure bearing shaft, oil is communicated, an opening on the left side of the oil cylinder is communicated with the transverse pressurizing shaft through a hydraulic pipeline, and an opening on the back side of the oil cylinder is communicated with the longitudinal pressurizing shaft through a hydraulic pipeline; the monitoring system comprises a displacement sensor, a pressure sensor, a gas pressure sensor, an acoustic emission sensor and a three-dimensional digital speckle testing device; the bearing shaft is arranged below the test chamber, penetrates through the tabletop of the support frame, can move up and down along the vertical shaft and is connected with the lower oil cylinder; when the pressure applied to the pressure bearing shaft is increased or reduced, oil can transmit pressure to a driven shaft through the oil cylinder and the pipeline, and corresponding load changes are caused.

2. The gas-containing coal triaxial testing machine with the single hydraulic pump controlling the proportional loading according to claim 1, wherein the testing chamber is subjected to special sealing treatment, and no gas leakage is caused when a chamber window is closed.

3. The gas-containing coal triaxial testing machine with single hydraulic pump controlled proportional loading according to claim 1, wherein a pressure bearing plate is installed on the pressure bearing shaft, and the pressure bearing plate is tightly attached to the pressure bearing shaft.

4. The gas-containing coal triaxial testing machine with single hydraulic pump control and proportional loading according to claim 1, wherein a slot hole with the same size as the sample is formed in the bearing plate, and the bearing plate is made of an anti-skid material.

5. The three-axis testing machine for coal containing gas with a single hydraulic pump controlling the constant-proportion loading according to claim 1, wherein the pressure bearing shaft is a large-radius rigid moving shaft, the displacement caused by pressure bearing is small, a certain amount of oil is arranged in the pressure bearing shaft, and the oil is communicated with an oil cylinder below the pressure bearing shaft.

6. The three-axis testing machine for coal containing gas with a single hydraulic pump controlling the constant-proportion loading according to claim 1, wherein the pressure bearing shaft is connected with the lower oil cylinder through a two-way overflow valve, and the rated pressure of the lower end of the two-way overflow valve is larger than that of the upper end of the two-way overflow valve and is used for controlling the flowing direction of oil.

7. The gas-containing coal triaxial tester with single hydraulic pump controlled proportional loading according to claim 1, wherein the hydraulic pipeline is a Y-shaped oil hydraulic pipe, and the transverse pressurizing shaft and the longitudinal pressurizing shaft are both connected with the lower oil cylinder through oil passages.

8. The gas-containing coal triaxial testing machine with single hydraulic pump control and fixed-proportion loading according to claim 1, wherein the oil cylinder is connected with the hydraulic pipeline through a control valve, the control valve is a fixed-proportion pressure reducing valve and is used for outputting oil pressure according to a fixed proportion, and a valve group and a ratio are selected according to specific requirements when the gas-containing coal triaxial testing machine leaves a factory.

9. The gas-containing coal triaxial testing machine with single hydraulic pump control and proportional loading according to claim 1, wherein the detection system comprises a displacement sensor, a pressure sensor and a gas pressure sensor, the pressure sensor is arranged on a vertical driving pressurizing shaft, and the displacement sensor is arranged on the driving pressurizing shaft, a driven pressurizing shaft and a bearing shaft. The end heads of the pressurizing shafts are provided with small holes, the acoustic emission sensors are arranged in the small holes of the end heads of the pressurizing shafts and are connected and transmitted through wires, and the gas pressure sensor and the three-dimensional digital speckle testing device are arranged on the inner wall of the testing chamber.

10. The three-axis testing machine for coal containing gas with a single hydraulic pump for controlling the proportional loading according to claim 1, wherein the gas injection and discharge device is connected with an external gas tank, and the type of the injected gas can be changed by replacing the gas tank.

11. The gas-containing coal triaxial testing machine with the single hydraulic pump controlling the proportional loading according to claim 1, wherein the three-dimensional digital speckle testing device consists of two high-speed cameras, and is used for collecting speckle images of a rock sample deformation stage by combining a binocular stereo vision technology.

12. A three-axis test method of gas-containing coal with single hydraulic pump controlled constant-proportion loading, which utilizes the three-axis test machine of gas-containing coal with single hydraulic pump controlled constant-proportion loading of any one of claims 1 to 10,

the first step is as follows: the ink is sprayed on the surface of the rock sample to manufacture scattered spots, the scattered spots are placed in the middle of a slotted hole in the bearing plate to prevent the scattered spots from sliding, and the position of the bearing shaft is adjusted according to the size of the test piece, so that the bearing shaft can be aligned to the middle of the rock sample by the axes of the driven pressurizing shafts on two sides after the bearing shaft is reduced by a small distance under the action of pressure.

The second step is that: and closing the pressure control valve, manually adjusting the initial position of the driven shaft, enabling the pressure head to be tightly attached to the surface of the test piece, and enabling the acoustic emission sensor to be attached to the surface of the sample.

The third step: the fixed-ratio pressure reducing valve is opened, the hydraulic pump is adjusted, a small amount of initial load is applied to the driving shaft, the internal oil pressure of the pressure bearing shaft is increased until the internal oil pressure is larger than the rated pressure of the upper part of the pilot-operated two-way overflow valve, the overflow valve is connected, a small amount of oil is extruded into the oil cylinder below, the pressure is further transmitted to the driven shaft, the test piece is slightly tightened around the driven shaft, then the loading of the driving shaft is stopped, the pressure of the pressure bearing shaft is reduced at the moment, the oil pressure in the oil cylinder is larger than the pressure bearing shaft but does not reach the rated pressure of the lower end of the overflow valve, the overflow valve is not connected, and therefore the test piece is slightly tightened by the pressure in the driven loading system.

The fourth step: adjusting the pressure and the displacement sensor to return to zero, starting the three-dimensional digital speckle testing device, adjusting the shooting direction to be vertical to the sample, opening the gas injection and discharge device, introducing seepage gas with preset concentration by monitoring the numerical value of the gas pressure sensor, gradually pressurizing the hydraulic pump after the gas completely permeates the rock sample, performing a cyclic loading test until the rock sample is damaged, stopping loading, wherein the pressure in the oil cylinder is greater than the rated value of the lower end of the overflow valve, reversely conducting the overflow valve for pressure relief, loosening the test piece by the driven shaft, recovering the seepage gas, and finishing the test.

The fifth step: the method comprises the steps of obtaining a numerical value or a curve for calculation according to a sensor, wherein the strain in the vertical direction is the difference between the displacement variation on a pressurizing shaft and the displacement variation on a bearing shaft, the strain in the horizontal direction is the sum of the displacement variations of a corresponding driven shaft, a main stress curve is obtained by the pressure sensor, transverse and longitudinal stress curves are obtained by multiplying the main stress curve by a fixed proportion, an acoustic emission sensor is used for receiving an acoustic emission signal of a rock sample, and a three-dimensional digital speckle testing device measures a three-dimensional deformation field of the sample by a digital image correlation method.

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