CN109085052B - Test method for the effect of roof strength on coal seam deformation under non-uniform load - Google Patents

Abstract

The invention discloses a test method for the influence of roof strength on coal seam deformation under the action of non-uniform load. The steps are as follows: making a test device, including a "concave"-shaped sealing cavity and a transparent box, and the notch part of the sealing cavity constitutes a test piece Placement cavity, the front pressure plate is equipped with a front pressure rod, the left, right and rear sides of the specimen placement cavity are equipped with side pressure plates, the head end of the side pressure plate is provided with a ventilation hole, the side pressure plate is equipped with a side pressure rod, and the upper backing plate is tightened front and rear. The upper pressure plate is arranged next to the ground, and the upper pressure plate is equipped with an upper pressure rod, and the end of the upper pressure rod adopts the structure of installing spherical balls between two plywood; preparation of pulverized coal; preparation of briquette specimens; installation of briquette specimens; Apply triaxial stress; apply gas pressure; carry out the test; for other tests in the same group, replace the upper backing plate with different surface roughness, and re-press the briquette specimen whose upper surface is consistent with the roughness of the lower surface of the upper backing plate; organize the test data . Therefore, the triaxial real simulation test of roof strength and coal seam deformation under non-uniform load is carried out.

Description

Test method for the effect of roof strength on coal seam deformation under non-uniform load

technical field

The invention belongs to the technical field of coal mine safety, and in particular relates to a test method for the influence of roof strength on coal seam deformation under the action of non-uniform load.

Background technique

In the process of coal mining and production, the excavation of the working face makes a local goaf formed underground, which destroys the original stress distribution state and stress balance of the stratum. The most direct threat in the process of roof deformation is rock burst or rock burst, which seriously affects the safety of coal mine resources in my country. Understanding the formation mechanism and disaster-causing mechanism of rock burst and improving the safety of coal production are important issues for relevant scientific researchers. Therefore, it is an important way to understand rock burst or rockburst by studying the key factor of roof deformation during the excavation process of the working face.

During the excavation process of the coal seam working face, the roof is not uniformly deformed, and the non-uniform stress distribution in the coal seam causes non-uniform stress distribution inside the coal seam, which affects the permeability characteristics of coal seam gas. At the same time, the non-uniform stress distribution of the coal seam in turn affects the roof. Deformation and stress state of hydraulic support. Therefore, conducting experiments on the effect of roof strength on coal seam deformation and permeability evolution under non-uniform loads can provide theoretical support and engineering guidance for roof support and in-depth disclosure of rock burst formation and disaster mechanisms and risk identification.

At present, domestic and foreign scholars have little research on the effect of roof strength on coal seam deformation and permeability under non-uniform load, and the only laboratory research also focuses on two-dimensional similarity simulation without considering the effect of gas pressure, and there is still no effective method. The experimental device and method are used to simulate the effect of roof strength on coal seam deformation and permeability evolution under the action of non-uniform load under true triaxial stress state, so as to study the effect of roof strength and various parameters on coal body deformation and permeability under true triaxial stress state. Impact.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a test method for the influence of roof strength on coal seam deformation under non-uniform load, which is used to study the influence of roof strength on coal and gas outburst under true triaxial stress state.

To this end, the technical solution adopted in the present invention is: a test method for the influence of roof strength on coal seam deformation under the action of non-uniform load, comprising the following steps:

Step 1, make a test device;

The test device includes a "concave" shaped sealed cavity, the notch of the sealed cavity faces forward, and a transparent box of the same height and width as the notch is arranged in front of the sealed cavity. The rear and top of the sealing cavity are open and just connected to the notch part, the transparent box and the sealing cavity share the same bottom plate, and a number of transparent materials are arranged right and left between the notch part of the sealing cavity and the transparent box. the front pressure plate, so that the notch part of the sealing cavity constitutes the test piece placement cavity;

Each of the front pressure plates is equipped with a front pressure rod, and the front pressure rod is connected to the corresponding front pressure plate through the transparent box from front to back. The tunneling speed of the working face; the left side, right side and rear side of the specimen placement cavity are respectively equipped with a side pressure plate, the head end of the side pressure plate is inserted into the corresponding side wall of the sealing cavity, and the head end is opened with a side pressure plate. The vent hole is used to connect the specimen placement cavity and the sealing cavity. Each side pressure plate is equipped with a side pressure rod, which passes through the sealing cavity from the outside to the inside and is connected to the end of the side pressure plate; the test piece placement cavity and the upper edge of the inner wall of the transparent box share the same upper backing plate, a number of upper pressing plates are arranged in front and back of the upper backing plate, each upper pressing plate is equipped with an upper pressing rod, and the end of the upper pressing rod adopts two plywoods The structure of installing spherical balls between them, the upper pressure rods corresponding to each upper pressure plate are independently controlled, and different loads are applied to reflect the uneven deformation of the coal seam roof under non-uniform loads;

The side wall of the sealed cavity is provided with a fluid inlet hole, and the side wall of the transparent box is provided with a fluid outlet hole;

Step 2: Prepare pulverized coal, crush and grind the raw coal to the required particle size range, sieve the pulverized coal through a vibrating screen and dry it for use;

Step 3: Preparation of the briquette test piece, mixing the pulverized coal according to the particle size ratio requirements, adding the pulverized coal binder in proportion, and stirring it evenly, and putting the pulverized coal into the mold and pressing it into a square block briquette test piece;

Step 4: Install the briquette test piece, put the pressed briquette test piece into the test piece placement cavity of the test device;

Step 5: Apply triaxial stress to the left, right and rear side pressure bars of the test device, as well as the front and upper pressure bars, so that the briquette specimen is constrained by the triaxial;

Step 6: Apply gas pressure, inject gas gas into the test device through the fluid inlet hole, and the gas gas enters the inside of the briquette specimen through the ventilation holes on the left, right and rear side pressure plates, so that a certain amount of gas is formed inside the briquette specimen. After the pressure and keep the gas injection pressure unchanged, go to the next step;

Step 7. Carry out the test, move the front pressure plate back from left to right or from right to left according to the set stress or displacement change rate in the direction away from the briquette specimen, and record the left, right, rear side pressure plate and upper pressure plate. Displacement at different positions, obtain coal seam deformation data, and record the change of gas flow rate of fluid outlet;

Step 8. For other tests in the same group, replace the top plate with different strengths, and repeat steps 4 to 7;

Step 9: Arrange the test data.

As a preference of the above scheme, in step 8, other tests in the same group are carried out by using the upper backing plates with uniaxial compressive strengths of 30Mpa, 50Mpa and 70Mpa respectively.

Further preferably, in step 3, the briquette test piece is a square block of 600mm×600mm×100mm, and correspondingly, in step 1, the test piece placement cavity is also a square cavity of 600mm×600mm×100mm.

Further preferably, in step 2, after the raw coal is crushed and ground, it is dried at 105-110° C. for 22-26 hours.

The beneficial effects of the invention are as follows: the stress applied to each pressure plate can truly simulate the stress state of the coal seam triaxial original rock, the gas source can be applied to simulate the gas pressure, the successive unloading of the front pressure plate can simulate the excavation process of the working face, and its unloading speed can simulate the working face. For the driving speed, the deformation amount of the briquette specimen can be obtained by obtaining the displacement change of each pressure rod, and the real-time visualization of coal and gas outburst can be realized through the transparent material. The test method for the effect of roof strength on coal seam deformation under distributed load provides theoretical support and engineering guidance for coal mine safety production.

Description of drawings

Figure 1 is a plan view of the test apparatus.

FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1 .

FIG. 3 is a cross-sectional view taken along the line B-B of FIG. 1 .

Figure 4 is a partial enlarged view of the end of the upper pressure plate.

The symbols in the figure are as follows: sealed cavity 1, transparent box 2, front pressure plate 3, front pressure rod 4, bottom plate 5, specimen placement cavity 6, side pressure plate 7, side pressure rod 8, upper backing plate 9, upper pressure plate 10, Upper pressure rod 11, fluid inlet hole 12, fluid outlet hole 13, first sealing ring 14a, second sealing ring 14b, third sealing ring 14c, fourth sealing gasket 14d, cover plate 15, bolt 16, briquette test piece 17.

Detailed ways

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

A test method for the influence of roof strength on coal seam deformation under the action of non-uniform load, comprising the following steps:

Step 1, make a test device.

1 to 3, the test device is mainly composed of a sealed cavity 1, a transparent box 2, a front pressure plate 3, a front pressure rod 4, a side pressure plate 7, a side pressure rod 8, an upper backing plate 9, an upper pressure plate 10, and an upper pressure plate. The pressure rod 11 is composed.

The sealing cavity 1 is in a "concave" shape as a whole, and the notch of the sealing cavity 1 faces forward.

A transparent box 2 having the same height and width as the notch is arranged in front of the sealed cavity 1 . The rear and top of the transparent box 2 are open and just connect with the notch. The transparent box 2 and the sealed cavity 1 share the same bottom plate 5, that is, the transparent box 2 only has left, right and front side walls. A number of front pressure plates 3 made of transparent material are arranged right and left between the notch part of the sealing cavity 1 and the transparent box 2, so that the notch part of the sealing cavity 1 constitutes a test piece placement cavity 6, and the test piece placement cavity 6 Used to place the briquette specimen 17.

Each front pressure plate 3 is equipped with a front pressure rod 4, and the front pressure rod 4 passes through the transparent box 2 from front to back and is connected to the corresponding front pressure plate 3, and the front pressure rod 4 corresponding to each front pressure plate 3 is independently controlled. And the tunneling speed of the working face is simulated by unloading in turn. Both the front pressing plate 3 and the transparent box 2 are made of transparent materials, and the tester can observe the crack propagation on the surface of the test piece during the test. Among the transparent materials, the ultra-high-strength and toughness transparent material Pam polycarbonate plate is the best, and its performance is better.

The left side, right side and rear side of the specimen placement chamber 6 are respectively equipped with a side pressure plate 7, the head end of the side pressure plate 7 is inserted into the corresponding side wall of the sealing cavity 1, and a ventilation hole is opened at the head end of the side pressure plate 7 7a is used to communicate the specimen placement cavity 6 and the sealing cavity 1 . Each side pressure plate 7 is respectively equipped with a side pressure rod 8, and the side pressure rod 8 is connected to the end of the side pressure plate 7 through the sealing cavity 1 from the outside to the inside. Preferably, the side pressure plate 7 adopts a structure in which vertical spacers are arranged in the rectangular outer frame, and the vertical spacers are just offset from the ventilation holes 7a, so that the fluid in the sealing cavity 1 can enter the specimen placement cavity through the ventilation holes 7a 6.

The specimen placement cavity 6 and the upper edge of the inner wall of the transparent box 2 share the same upper backing plate 9 , and a plurality of upper pressing plates 10 are arranged directly above and behind the upper backing plate 9 . Each upper pressing plate 10 is equipped with an upper pressing rod 11 , and the end of the upper pressing rod 11 adopts a structure in which spherical balls 11 b are installed between two clamping plates 11 a (as shown in FIG. 4 ). The rods 11 are independently controlled and apply different loads to reflect the uneven deformation of the coal seam roof under non-uniform loads. Since the upper pressure plate 10 is arranged in close proximity, an upper backing plate 9 is added to ensure the sealing of the specimen placement cavity 6 and simulate the coal seam roof and goaf.

A fluid inlet hole 12 is opened on the side wall of the sealed cavity 1, and fluid is introduced into the sealed cavity 1 through the fluid inlet hole 12; a fluid outlet hole 13 is opened on the side wall of the transparent box 2. During the test, the fluid passes through The fluid outlet hole 13 is discharged. Preferably, there are two fluid inlet holes 12, which are symmetrically arranged on the rear side wall of the sealing cavity 1;

In addition, the specimen placement cavity 6 is preferably a square cavity with the same length and width.

The bottom plate 5 and the cover plate 15 are fixed to the side wall of the sealing cavity 1 by bolts 16 . In order to ensure the tightness of the test device, a first sealing ring 14a can be arranged between the bottom plate 5 and the sealing cavity 1 and the specimen placement cavity 6; between the sealing cavity 1 and the side pressure rod 8, the sealing cavity 1 and the A second sealing ring 14b is arranged between the side pressure plates 7 ; a third sealing ring 14c is arranged between the sealing cavity 1 and the self-contained cover plate 15 ; Gasket 14d.

Preferably, the front pressure rod 4 and the front pressure plate 3 are connected by screw threads, and the side pressure rod 8 and the side pressure plate 7 are connected by screws, and other fixed connection methods can also be used.

Preferably, there are seven upper pressing plates 10 in total, and the upper pressing rods 11 corresponding to each upper pressing plate 10 are controlled by respective independent control parts to reflect the uneven deformation of the coal seam roof; there are six front pressing plates 3, and each front pressing plate 3. The corresponding front pressure bars 4 are respectively controlled by their independent control parts, and the driving speed of the working face is simulated by sequentially unloading.

Features of this test device:

1. The true triaxial stress can be applied from front, back, left and right and above, and the end of the upper platen adopts the structure of installing spherical balls between two plywood plates. By applying non-uniform loads, the non-uniform deformation of the top plate can be simulated realistically. .

2. The front pressure plate adopts a multi-piece combination structure, and the excavation process of the working face is simulated by gradually unloading; the upper pressure plate adopts a combination of multiple pieces and optimizes the end structure of the upper pressure rod, and the upper pressure plate is independently controlled to simulate the uneven load of the coal seam roof. Loading, the upper backing plate simulates the roof of the coal seam and the goaf; compared with the way of manual excavation, the actual working conditions are more realistically simulated, thereby improving the test accuracy.

3. There are ventilation holes on the back side of the test piece and the pressure plates on the left and right sides. The test piece can be inflated by the fluid inlet hole to achieve a certain gas pressure. There are no air supply holes at the bottom, front and upper part of the test piece. Thus, the actual working conditions can be more realistically reflected and the test accuracy can be improved.

4. The test device adopts a sealed structure, which can apply relevant gas pressure to reflect the real working conditions.

Step 2: Prepare pulverized coal, crush and grind the raw coal to the required particle size range, sieve the pulverized coal through a vibrating screen and dry it for use. Preferably, the raw coal is dried at 105-110°C for 22-26 hours after being crushed and ground.

Step 3: Preparation of the briquette test piece, mix the pulverized coal according to the particle size ratio requirements, add the pulverized coal binder in proportion and stir evenly, put the pulverized coal into the mold and press it into a square block briquette test piece.

Preferably, the briquette specimen is a square block of 600mm×600mm×100mm, and correspondingly, in step 1, the specimen placement cavity 6 is also a square cavity of 600mm×600mm×100mm.

Step 4: Installation of the briquette specimen, placing the pressed briquette specimen into the specimen placement cavity 6 of the test device.

Step 5: Apply triaxial stress to the left, right and rear side pressure rods 8, front pressure rod 4 and upper pressure rod 11 of the test device, so that the briquette test piece is subject to triaxial constraints.

Step 6: Apply gas pressure, inject gas gas into the test device through the fluid inlet hole 12, and the gas gas enters the inside of the briquette test piece through the ventilation holes 7a on the left, right, and rear side pressure plates 7, so that the inside of the briquette test piece is formed. After a certain gas pressure and keeping the gas injection pressure unchanged, go to the next step. When there are two fluid inlet holes 12 in total, gas is injected into the test device through the two fluid inlet holes 12 at the same time.

Step 7. Carry out the test, move the front pressure plate 3 backwards in turn from left to right or from right to left according to the set stress or displacement change rate in the direction away from the briquette specimen. The displacement of the upper platen 10 at different positions is obtained to obtain the coal seam deformation data, and the change of the gas flow rate of the fluid outlet hole 13 is recorded at the same time.

Step 8. For other tests in the same group, replace the upper backing plate 9 with different strengths, and repeat steps 4 to 7. It is better to use the top plate 9 with uniaxial compressive strengths of 30Mpa, 50Mpa and 70Mpa respectively to conduct other tests in the same group.

For example, pulverized coal with different particle sizes are mixed according to the mass ratio of less than 40 mesh: 40-60 mesh: 60-80 mesh: 80-100 mesh: greater than 100 mesh = 1:1:1:1:1, and add mass The ratio of 5% milk white glue is used as a binder to press the coal sample, and the repeated test is carried out according to the following table:

By repeating the test as shown in the table above, the relationship between roof strength and coal seam deformation under non-uniform load can be studied.

Claims (4)

1. A test method for testing influence of roof strength on coal seam deformation under the action of non-uniform load is characterized by comprising the following steps:

Step one, manufacturing a test device;

The test device comprises a concave-shaped seal cavity (1), a notch of the seal cavity (1) faces the front, a transparent box (2) which is equal in height and width to the notch is arranged in front of the seal cavity (1), the rear part and the top part of the transparent box (2) are both open and just connected with the notch, the transparent box (2) and the seal cavity (1) share the same bottom plate (5), and a plurality of front pressure plates (3) made of transparent materials are arranged between the notch of the seal cavity (1) and the transparent box (2) in a left-right close manner, so that the notch of the seal cavity (1) forms a test piece placing cavity (6);

Each front pressure plate (3) is provided with a front pressure rod (4), the front pressure rods (4) penetrate through the transparent box (2) from front to back to be connected with the corresponding front pressure plate (3), the front pressure rods (4) corresponding to each front pressure plate (3) are independently controlled, and the tunneling speed of a working face is simulated through sequential unloading; the left side, the right side and the rear side of the test piece placing cavity (6) are respectively provided with a side pressing plate (7), the head end of each side pressing plate (7) is inserted into the corresponding side wall of the sealed cavity (1), the head end is provided with an air hole (7a) for communicating the test piece placing cavity (6) with the sealed cavity (1), each side pressing plate (7) is respectively provided with a side pressing rod (8), and each side pressing rod (8) penetrates through the sealed cavity (1) from outside to inside to be connected with the tail end of each side pressing plate (7); the test piece placing cavity (6) and the upper edge of the inner wall of the transparent box (2) share the same upper base plate (9), a plurality of upper pressure plates (10) are arranged above the upper base plate (9) in a front-back adjacent mode, each upper pressure plate (10) is provided with an upper pressure rod (11), the end of each upper pressure rod (11) adopts a structure that a spherical ball (11b) is arranged between two clamping plates (11a), the upper pressure rods (11) corresponding to the upper pressure plates (10) are independently controlled, and different loads are applied to reflect the uneven deformation of the coal seam roof under the non-uniform load;

A fluid inlet hole (12) is formed in the side wall of the sealed cavity (1), and a fluid outlet hole (13) is formed in the side wall of the transparent box (2);

Step two, preparing coal powder, crushing and grinding raw coal to a required particle size range, screening the ground coal powder through a vibrating screen, and drying for later use;

Step three, preparing a briquette test piece, mixing coal powder according to the particle size ratio, adding a coal powder binder in proportion, stirring uniformly, and filling the coal powder into a mold to press the coal powder into a square briquette test piece;

Step four, mounting a molded coal test piece, and placing the pressed molded coal test piece into a test piece placing cavity (6) of the test device;

Applying triaxial stress, and applying stress to the left, right and rear side pressure rods (8), the front pressure rod (4) and the upper pressure rod (11) of the test device to make the briquette test piece be subjected to triaxial constraint;

Step six, applying gas pressure, injecting gas into the test device through the fluid inlet holes (12), and enabling the gas to enter the molded coal test piece through the air holes (7a) on the left side pressure plate, the right side pressure plate and the rear side pressure plate (7), so that a certain gas pressure is formed in the molded coal test piece, and the molded coal test piece enters the next step after the gas injection pressure is kept unchanged;

Seventhly, performing a test, namely sequentially withdrawing the front pressing plate (3) from left to right or from right to left in the direction away from the briquette test piece according to the set stress or displacement change rate, obtaining coal seam deformation data by recording the displacement of the left side pressing plate, the right side pressing plate, the rear side pressing plate (7) and the upper pressing plate (10) at different positions, and simultaneously recording the gas flow change of the fluid outlet hole (13);

Step eight, replacing the upper backing plate (9) with different strength in other tests in the same group, and repeating the steps four to seven;

And step nine, collating the test data.

2. The test method for the deformation of the coal seam influenced by the roof strength under the action of the non-uniform load according to claim 1, which is characterized in that: and step eight, performing the same group of other tests by adopting the upper backing plate (9) with the uniaxial compressive strength of 30Mpa, 50Mpa and 70Mpa respectively.

3. the test method for testing the influence of the roof strength on the coal seam deformation under the action of the non-uniform load is characterized in that in the third step, the briquette coal test piece is a square block with the size of 600mm multiplied by × 100mm, and correspondingly, in the first step, the test piece placing cavity (6) is a square cavity with the size of 600mm multiplied by × 100 mm.

4. The test method for the deformation of the coal seam influenced by the roof strength under the action of the non-uniform load according to claim 1, which is characterized in that: in the second step, the raw coal is dried for 22-26 hours at 105-110 ℃ after being crushed and ground.

Images