CN111175468B - Test method for pressure relief and anti-scour of water-wetted coal rock under true three-dimensional stress - Google Patents

Abstract

The invention discloses a pressure relief and anti-scour test method for water-injection-wetted coal rock under true three-dimensional stress, including sample preparation; installation of water injection pipes; installation of raw coal samples on a true triaxial test device; application of triaxial stress; Press; simulate roof pressure; replace raw coal samples, repeat steps 2 to 4; water injection test; repeat step 6, simulate roof pressure again; organize test data. The hexahedral raw coal sample with water injection holes on the front surface is selected for the test, and then the hexahedral sample is placed in a special true triaxial test test device, and the control of the stress loading mode during the pressure relief process and the simulation of the roof pressure are used skillfully. , to carry out an indoor simulation test method for pressure relief and anti-scour under true three-dimensional stress, which is used to study the mechanism of water injection to prevent rock burst under the action of primary stress in coal seams, and to provide a scientific basis for scientific selection of relevant process parameters.

Description

Test method for pressure relief and anti-scour of water-wetted coal rock under true three-dimensional stress

technical field

The invention belongs to the technical field of coal and rock laboratory tests, and particularly relates to a test method for pressure relief and anti-scour of water-injection-wetted coal rock under true three-dimensional stress.

Background technique

With the increase of mining depth and mining intensity of coal resources, dynamic disasters such as mine rock burst are increasingly intensifying, which seriously threatens the safety of coal mining. Statistical analysis shows that various types of mines have reports of rockburst, and all types of coal seams have experienced shocks. The geological structure ranges from simple to complex, the coal seam ranges from thin to thick, and the dip angle ranges from horizontal to steep, conglomerate. , sandstone, limestone, kerogen shale roof have experienced rock burst. Rockburst refers to the dynamic phenomenon of sudden and violent destruction of the rock mass around the well roadway or working face due to the instantaneous release of elastic deformation energy, often accompanied by coal and rock mass throwing, loud noises and gas waves. It is very destructive and is one of the major disasters in coal mines.

The method of coal seam water injection to prevent rock burst is simple and easy to implement, with low prevention and control costs and wide adaptability. Even for non-wet coal seams, only a small amount of wetting agent can be added, and it also has various effects of dust reduction, cooling and softening of coal seams. Coal seam water injection has been used in coal mines of the former Soviet Union to prevent rock bursts since the early 1950s. In various coal mining countries in the world, the method of water injection in coal seams has been widely used to prevent and control rock burst. In the early 1980s, my country successfully applied coal seam water injection in the prevention and control of rock burst in Longfeng Mine in Fushun. At present, coal seam water injection has been promoted in the prevention and control of rock burst across the country.

Although coal seam water injection has a long history to prevent rock burst, there are few reports about the mechanism of coal seam water injection to prevent rock burst and research on the selection of process parameters for coal seam water injection to prevent rock burst. There is no scientific basis for the selection of process parameters for coal seam water injection prevention and control of rock burst, and there is no basically a relatively complete method, which is still determined by engineering analogy and experience. The main reason for this situation is that there is no practical test device and innovative test method to support the pressure relief and anti-scour mechanism of water-wetting coal and rock.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide an indoor simulation test method for pressure relief and anti-scour of water-injection-wetted coal rock under true three-dimensional stress. Process parameters provide scientific basis.

To this end, the technical solution adopted in the present invention is: a water-injection-wetted coal rock pressure relief and anti-scour test method under true three-dimensional stress, comprising the following steps:

Step 1, sample preparation;

The raw coal block is cut into hexahedrons, and then processed by a grinder to make the end surface flatness within ±0.02mm, dried at 105±15° for 24±4 hours, and cooled to room temperature for use;

Step 2. Install the water injection pipe;

Use a drilling rig to drill a horizontal blind hole at the center of the front surface of the hexahedral raw coal sample as a water injection hole, select a water injection pipe with an outer diameter equal to the water injection hole diameter, and a length 8-12 mm smaller than the water injection hole depth, and evenly smear the outer wall of the water injection pipe. Silicone rubber, insert the water injection pipe into the water injection hole, seal the gap between the outer wall of the water injection pipe and the water injection hole through the silicone rubber, and then install a universal sealing joint at the water injection hole;

Step 3. The raw coal sample is installed on the true triaxial test device;

The true triaxial test device includes a main engine, a main engine support assembly, a slide rail, a slide rail support assembly and a servo oil cylinder. Six sets of the servo oil cylinders are arranged outside the main engine in the up and down, left and right, and front and rear directions. The lower part extends forward and backward, and is supported on the ground by the slide rail support assembly after passing through the main engine. The main engine includes a cast integral annular frame, and the front and rear sides of the integral annular frame have holes, and each opening position The outer side is equipped with a cover plate, the integral annular frame and the cover plate enclose the main casing, the inner cavity of the main machine is used to place the sample, and the upper, lower, left, right, front and rear sides of the sample are respectively equipped with sample pads There is a sample moving bracket that can move back and forth on the slide rail under the sample pad located on the lower side; the oil cylinder moving bracket that can move back and forth on the slide rail is arranged under the servo cylinders on the front and rear sides. The cover plate can move together with the servo cylinders on the corresponding side. The servo cylinders on the upper, lower, left, and right sides are fixed outside the corresponding sides of the overall annular frame. A load sensor is arranged at the center of the front end of the piston rod of the servo cylinder. A pressure head is installed after the front end passes through the main casing;

Put the sample into the cavity surrounded by six sample pads and install it through the quick-lock combination, and then seal it with the edge sealant at the joint of the sample pad to form a sample gasket, so as to seal the sample. Wherein; the edge sealant is applied by brushing liquid silicone rubber on the edge that needs to be sealed, and the sealing between the sample pads can be realized after the silicone rubber is cured;

First, install the sample gasket on the lower indenter, and then control the upper indenter to move down and install it with the universal sealing joint. At the same time, the upper indenter is attached to the upper surface of the sample gasket, and finally control the front, rear, left, and The right four indenters are moved to make the corresponding indenters fit to the corresponding surfaces of the sample gasket respectively;

Step 4. Apply triaxial stress;

Apply stress to the sample to a predetermined value through the front, back, left, right, upper and lower indenters;

Step 5, pressure relief;

Keep the stress loading mode of the upper indenter as constant force loading, convert the stress loading mode of the left, right, and front three indenters to constant stiffness loading, and convert the stress loading mode of the lower indenter to constant displacement loading, and then control the rear indenter. Retreat in the direction of unloading until the distance from the rear surface of the raw coal sample reaches 20±5mm;

Step 6, simulate the top plate to press;

Increase the pressure on the upper indenter at a constant loading rate until the raw coal sample fails, record the stress and displacement changes of each indenter, and calculate the energy evolution during the test;

Step 7: Replace the raw coal sample, and repeat steps 2 to 4;

Step 8, water injection test;

Through the water injection hole on the front surface of the raw coal sample, inject water into the interior of the raw coal sample at a predetermined water injection rate, and stop after reaching the predetermined water injection time;

Step 9. Repeat step 6 to simulate the top plate to press again;

Step 10. For other tests in the same group, replace the raw coal sample, change the hardness of the raw coal sample, or change the water injection rate, the triaxial pressure, and the pressure relief rate of the front indenter, and repeat steps 1 to 9;

Step 11: Arrange the test data. As a preference of the above solution, the hexahedral raw coal sample sample is a cube, and the sample size is 200mm×200mm×200mm.

Further preferably, the diameter of the water injection hole in the raw coal sample is 12mm and the hole depth is 105mm; the outer diameter of the water injection pipe is 12mm and the length is 95mm; the diameter of the semicircle at the bottom of the water injection hole is 10mm.

Beneficial effects of the present invention:

(1) The new true triaxial test device is adopted. Compared with the traditional cavity structure enclosed by the inner and outer frames, the main body of the test device is only provided with an integral annular frame formed by casting. The sample pad surrounds a sample gasket for accommodating the sample, thus omitting the separate pressure-resistant cavity formed between the traditional inner and outer layers, and the indenter directly touches the sample pad on the corresponding side after passing through the main casing On the block, it can free up more space to arrange an overall ring frame with a larger size and thickness, so that the cavity can withstand greater pressure and can meet the simulation test in a more complex environment;

(2) Since the inner frame is omitted, the servo cylinder directly exerts force on all sides of the sample, and does not need to pass through the pressure-resistant cavity. The dynamic seal needs to be considered when the servo cylinder passes through the pressure-resistant cavity, thus simplifying the structure and reducing the At the same time, because the traditional inner frame is thinner than the outer frame, the inner frame is prone to expansion and deformation when the pressure is high, which further affects the sealing between the inner frame and the servo cylinder;

(3) In this test device, the pressure head and the sample pad are designed separately, and the connection of the sample pad is coated with liquid silicone rubber and sealed after curing, so that the injected fluid will not penetrate into the external area;

(4) Holes are opened on the front and rear sides of the overall annular frame, and a cover plate is equipped on the outside of each opening position, which together form the main casing, which is more convenient for the installation of parts on the front side of the sample; The side opening is equipped with a cover plate, and the front parts need to be repaired or disassembled, and the sample needs to be moved out of the overall ring frame through the sample moving bracket, which is very troublesome;

(5) The hexahedral raw coal sample with water injection holes on the front surface is selected for the test, and then the hexahedral sample is placed in a special true triaxial test device, and the control of the stress loading mode during the pressure relief process and the simulated roof are cleverly used. It is used to study the mechanism of water injection to prevent rockburst in coal seam under the action of primary stress, and provide a scientific basis for scientific selection of relevant process parameters.

Description of drawings

FIG. 1 is a schematic structural diagram of the true triaxial test device used in the present invention (including two states of sample loading and taking out).

FIG. 2 is a left side view of the host and the host support assembly in FIG. 1 .

Figure 3 is a perspective view of a sample gasket surrounded by six sample spacers.

FIG. 4 is a front view of the cross-sectional state of FIG. 3 .

FIG. 5 is a plan view of the cross-sectional state of FIG. 3 .

Figure 6 shows the state after the edge sealing of the sample spacer is cured with silicone rubber.

Detailed ways

Below by embodiment and in conjunction with accompanying drawing, the present invention is further described:

A water-injection-wetted coal rock pressure relief and anti-scour test method under true three-dimensional stress, comprising the following steps:

Step 1, sample preparation;

The raw coal block is cut into hexahedrons, and then processed by a grinder to make the end surface flatness within ±0.02mm. After drying at a temperature of 105±15° for 24±4 hours, it is cooled to room temperature for use; the hexahedral raw coal sample is the most It is preferably a cube, and the size of the sample is 200mm×200mm×200mm.

Step 2. Install the water injection pipe;

As shown in Figure 5, a horizontal blind hole is drilled at the center of the front surface of the hexahedral raw coal sample as the water injection hole 15 with a drilling rig. The water pipe, and evenly smear silicone rubber on the outer wall of the water injection pipe, insert the water injection pipe into the water injection hole 15, seal the gap between the outer wall of the water injection pipe and the water injection hole 15 through the silicone rubber, and then install the universal sealing joint 16 at the mouth of the water injection hole 15. .

Preferably, the diameter of the water injection hole 15 in the raw coal sample is 12mm and the hole depth is 105mm; the outer diameter of the water injection pipe is 12mm and the length is 95mm.

Step 3. The raw coal sample is installed on the true triaxial test device;

As shown in Figure 1 - Figure 5, the true triaxial test device is mainly composed of main engine A, main engine support assembly B, slide rail C, slide rail support assembly D and servo cylinder E. The main engine A is supported on the ground by the main engine support component B, and the six sets of servo cylinders E are arranged outside the main engine A in the up and down, left and right, and front and rear directions (ie, three directions of XYZ). The slide rail C extends forward and backward under the host A, and the slide rail C passes through the host A and is supported on the ground by the slide rail support assembly D.

The integral annular frame 1 is formed by casting, and the front and rear sides of the integral annular frame 1 have holes, and a cover plate 2 is provided on the outside of each opening position. The integral annular frame 1 and the two cover plates 2 together form a main casing. At least two heating rods 17 are symmetrically installed on the upper and lower walls of the main casing at left and right intervals to heat the sample in the main casing when necessary. The inner cavity of the host is used to place the sample 3. The upper, lower, left, right, front and rear sides of the sample 3 are respectively equipped with sample pads 4, and a total of six sample pads 4 are required. A sample moving support 5 that can move back and forth on the slide rail C is provided below the sample spacer 4 located on the lower side.

The front and rear servo cylinders E are arranged outside the cover plate 2 on the corresponding side, and the front and rear servo cylinders E are provided with oil cylinder moving brackets 6 that can move back and forth on the slide rail C, and the cover plate 2 can follow the corresponding side. Servo cylinder E moves together. The servo cylinders E on the upper, lower, left and right sides are arranged outside the corresponding side of the overall annular frame.

A load sensor 8 is provided at the center position of the front end of the piston rod 7 of the servo oil cylinder E, and the load sensor 8 is preferably embedded. The front end of the load sensor 8 is provided with a pressure head 9, and the front end of the load sensor 8 is installed with the pressure head 9 after passing through the main casing. When loading the sample 3, the indenter 9 directly abuts the sample spacer 4 on the corresponding side. Before the test, install the sample pad 4 outside the sample 3, and then seal the joint of the sample pad 4. After the sealing is completed, place the sample 3 on the sample moving bracket 5, and place the sample The sample moving bracket 5 and the rear cylinder moving bracket 6 are sequentially pushed into the inner cavity of the main engine and fixed, so that all the indenters 9 directly touch the sample pads 4 on the corresponding side before the test is performed.

Put the sample into the cavity enclosed by the six sample pads 4 and install it through the quick lock 14, and then seal it with the edge sealant at the joint of the sample pad 4 to form a sample gasket. The sample 3 is sealed; the edge sealant is used to brush liquid silicone rubber on the edge to be sealed, and the sealing between the sample pads 4 can be achieved after the silicone rubber is cured (as shown in Figure 6). Pre-sealing is achieved after the silicone rubber is cured. During the test, the confining pressure of the inner cavity of the host makes the silicone rubber close to the sample, which can not only achieve the sealing between the adjacent surfaces of the sample pad 4, but also weaken the edges. boundary effects. Preferably, a cylinder displacement sensor 10 is arranged in the servo oil cylinder E, the servo oil cylinder E on the upper, lower, left and right sides is fixedly installed on the integral annular frame 1 through the end cover 11, and the front and rear servo oil cylinders E are fixedly installed on the integral annular frame 1 through the cover plate 2. On the frame 1, all the positions where the piston rods 7 pass through the main casing are provided with bushings to ensure the airtightness of the inner cavity of the main engine.

Preferably, in the XYZ direction outside the sealed cavity enclosed by the six sample spacers 4, the sample deformation and displacement sensors 12 are provided in pairs, and the sample deformation and displacement sensors 12 are installed on the sample through the displacement sensor extension rod 13. A pair of sample deformation and displacement sensors 12 in the same direction outside the edge of the cushion block 4 are arranged diagonally staggered, which can realize the measurement of unbalanced and uneven deformation under the condition of true triaxiality.

Preferably, it is also equipped with two sets of electro-hydraulic servo boosters, which provide confining pressure for the inner cavity of the host and water injection pressure or osmotic pressure for the sample, so that the confining pressure, water injection pressure or osmotic pressure can be controlled separately. Complete complex test conditions. The working pressure of the control high-pressure valve in the electro-hydraulic servo booster is greater than the maximum output pressure of the booster, in order to ensure high reliability and long service life.

Preferably, it is also equipped with an axial piston pump hydraulic source, and the hydraulic source has a high and low pressure switch, which is convenient for the smooth switching of high and low pressure during the test.

First put the sample into the sample gasket surrounded by six sample spacers 4, and then brush the liquid silicone rubber on the edges. After the silicone rubber is cured, push the sample into the sample through the sample moving bracket 5. In the inner cavity of the main engine, finally, the front and rear cover plates 2 are installed on the integral annular frame 1 through the cylinder moving bracket 6, and the sealing of the inner cavity of the main engine is ensured during installation, and then the test is started.

First, install the sample gasket on the lower indenter, and then control the upper indenter to move down and install it together with the universal sealing joint 16. At the same time, the upper indenter is attached to the upper surface of the sample gasket, and finally control the front, rear and left respectively. , Move the four right indenters to make the corresponding indenters fit to the corresponding surfaces of the sample gasket respectively.

Step 4. Apply triaxial stress;

Apply stress to the sample to a predetermined value through six indenters: front, rear, left, right, upper and lower.

Step 5, pressure relief;

Keep the stress loading mode of the upper indenter as constant force loading, convert the stress loading mode of the left, right, and front three indenters to constant stiffness loading, and convert the stress loading mode of the lower indenter to constant displacement loading, and then control the rear indenter. Back off in the direction of unloading until the distance from the rear surface of the raw coal sample reaches 20±5mm.

Step 6, simulate the top plate to press;

The pressure of the upper indenter was increased at a constant loading rate until the failure of the raw coal sample, the stress and displacement changes of each indenter were recorded, and the energy evolution during the test was calculated.

Step 7: Replace the raw coal sample and repeat steps 2 to 4.

Step 8, water injection test;

Through the water injection holes on the front surface of the raw coal sample, water is injected into the interior of the raw coal sample at a predetermined water injection rate, and the water injection is stopped when the predetermined water injection time is reached.

Step 9. Repeat step 6 to simulate the top plate to press again.

Step 10. For other tests in the same group, replace the raw coal sample, change the hardness of the raw coal sample, or change the water injection rate, triaxial pressure, and pressure relief rate of the front indenter, and repeat steps 1 to 9.

Step 11: Arrange the test data. The following table shows the recorded data during the test, in which the failure strength refers to the force of the upper indenter when the coal and rock specimens fail.

Claims (3)

1. A pressure relief and impact prevention test method for water injection wetting coal rock under true three-dimensional stress is characterized by comprising the following steps:

step one, sample preparation;

cutting a raw coal block into hexahedrons, processing the hexahedrons by a grinding machine to ensure that the flatness of the end surface of the hexahedron is within +/-0.02 mm, drying the hexahedron at the temperature of 105 +/-15 ℃ for 24 +/-4 hours, and cooling the hexahedron to normal temperature for later use;

step two, installing a water injection pipe;

drilling a horizontal blind hole at the central position of the front surface of a hexahedral raw coal sample by using a drilling machine to serve as a water injection hole (15), selecting a water injection pipe with the outer diameter equal to the diameter of the water injection hole (15) and the length 8-12 mm smaller than the depth of the water injection hole (15), uniformly coating silicon rubber on the outer wall of the water injection pipe, inserting the water injection pipe into the water injection hole (15), sealing a gap between the outer wall of the water injection pipe and the water injection hole (15) through the silicon rubber, and then installing a universal sealing joint (16) at the opening of the water injection hole (15);

step three, mounting the raw coal sample on a true triaxial test testing device;

the true triaxial test testing device comprises a host (A), a host supporting component (B), a slide rail (C), a slide rail supporting component (D) and servo oil cylinders (E), wherein six sets of servo oil cylinders (E) are arranged in the upper-lower, left-right and front-back directions outside the host (A), the slide rail (C) extends and is arranged in the front-back direction below the host (A) and passes through the host (A) and then is supported on the ground through the slide rail supporting component (D), the host (A) comprises a cast integral annular frame (1), holes are formed in the front side and the back side of the integral annular frame (1), a cover plate (2) is arranged outside each hole position, the integral annular frame (1) and the cover plate (2) enclose to form a host shell, an inner cavity of the host is used for placing a sample (3), and sample cushion blocks (4) are respectively arranged outside the upper side, the lower side, the left side, the right side, the front, a sample moving bracket (5) which can move back and forth on the slide rail (C) is arranged below the sample cushion block (4) positioned at the lower side; oil cylinder moving supports (6) capable of moving back and forth on a sliding rail (C) are arranged below the servo oil cylinders (E) on the front side and the rear side respectively, the cover plate (2) can move along with the servo oil cylinders (E) on the corresponding side, the servo oil cylinders (E) on the upper side, the lower side, the left side and the right side are fixedly arranged outside the corresponding side of the integral annular frame (1), a load sensor (8) is arranged in the middle position of the front end of a piston rod (7) of each servo oil cylinder (E), and a pressure head (9) is installed at the front end of each load sensor (8) after penetrating through the main machine shell;

placing a sample into a cavity surrounded by six sample cushion blocks (4), assembling and installing the sample through a quick lock (14), and then sealing the sample with a sealing adhesive at the edge of the joint of the sample cushion blocks (4) to form a sample sealing gasket, so that the sample (3) is sealed therein; the edge sealant is liquid silicon rubber and is coated on the edges to be sealed in a brushing mode, and the sealing between the sample cushion blocks (4) can be achieved after the silicon rubber is solidified;

firstly, a sample sealing gasket is arranged on a lower pressure head, then an upper pressure head is controlled to move downwards to be arranged with a universal sealing joint (16), meanwhile, the upper pressure head is attached to the upper surface of the sample sealing gasket, and finally, the front pressure head, the rear pressure head, the left pressure head and the right pressure head are respectively controlled to move, so that the corresponding pressure heads are respectively attached to the corresponding surfaces of the sample sealing gasket;

step four, applying triaxial stress;

applying stress to the sample to a preset value through the front, rear, left, right, upper and lower six pressure heads;

step five, releasing pressure;

keeping the stress loading mode of the upper pressure head to be constant force loading, converting the stress loading modes of the left pressure head, the right pressure head and the front pressure head into constant rigidity loading, converting the stress loading mode of the lower pressure head into constant displacement loading, and controlling the rear pressure head to retreat towards the force unloading direction until the distance from the rear surface of the raw coal sample reaches 20 +/-5 mm;

step six, simulating the coming pressure of the top plate;

increasing the pressure of the upper pressure head at a constant loading rate until the raw coal sample is damaged, recording the stress and displacement changes of each pressure head, and calculating the energy evolution condition in the test process;

step seven, replacing the raw coal sample, and repeating the step two to the step four;

step eight, water injection test;

injecting water into the raw coal sample at a preset water injection rate through a water injection hole on the front surface of the raw coal sample, and stopping after the preset water injection time is reached;

step nine, repeating the step six, and simulating the pressure of the top plate again;

step ten, replacing the raw coal sample, changing the hardness of the raw coal sample, or changing the water injection rate, the triaxial pressure and the front pressure head pressure relief rate, and repeating the steps from the first step to the ninth step;

and step eleven, finishing test data.

2. The pressure relief and impact prevention test method for water injection-wetted coal rocks under true three-dimensional stress according to claim 1, characterized by comprising the following steps: the hexahedral raw coal sample is a cube, and the sample size is 200mm × 200mm × 200 mm.

3. The pressure relief and impact prevention test method for water injection-wetted coal rocks under true three-dimensional stress as claimed in claim 2, characterized in that: the diameter of the water injection hole (15) in the raw coal sample is 12mm, and the depth of the hole is 105 mm; the outer diameter of the water injection pipe is 12mm, and the length of the water injection pipe is 95 mm.

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