CN115950746A - Roadway protection method for gob-side entry retaining of multiple coal seams in real ground stress environment - Google Patents
Roadway protection method for gob-side entry retaining of multiple coal seams in real ground stress environment Download PDFInfo
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Abstract
The invention discloses a roadway protection method for multi-coal-seam gob-side entry retaining in a real ground stress environment, which comprises the following steps: step one, sample preparation; step two, preparing a multi-field coupling coal rock mass dynamic disaster prevention and control technology simulation system for installation; thirdly, applying true triaxial prestress; step four, applying true triaxial mining induced stress, changing the stress value of the No. 4 loading device in the Z direction to 6, 8 and 10MPa, unloading until the coal seam roof is damaged, and keeping sigma after the damage z4 The method is unchanged, so that the roadway protection effect of gob-side entry retaining of the goaf is simulated; step five, starting the high-speed camera; visually monitoring and recording the whole loading process; step six, performing other tests in the same group; step seven, ending the test; the tunnel protection effect simulation of the large-size multi-coal-seam gob-side entry retaining can be carried out, and the simulation process is more real and reliable.
Description
Technical Field
The invention belongs to the technical field of coal seam mining simulation tests, and particularly relates to a roadway protection method for multi-coal seam gob-side entry retaining in a real ground stress environment.
Background
The existing multi-coal-seam gob-side entry retaining simulation test method mainly has the following problems: (1) The size of the adopted model is small, the simulation of the multi-coal-seam gob-side entry retaining has certain spatial limitation, and the real entry protection scene of the multi-coal-seam gob-side entry retaining in the real ground stress environment cannot be accurately simulated; and (2) visual monitoring cannot be realized in the simulation process.
Disclosure of Invention
The invention aims to provide the method for protecting the multi-coal-bed gob-side entry retaining in the real ground stress environment, so that the simulation of the lane protecting effect of the large-size multi-coal-bed gob-side entry retaining can be carried out, the simulation process is more real and reliable, and the visual monitoring of the simulation process can be realized.
Therefore, the technical scheme adopted by the invention is as follows: a roadway protection method for multi-coal-seam gob-side entry retaining in a real ground stress environment comprises the following steps:
step one, sample preparation;
preparing a coal sample, namely selecting 2 blocks of raw coal, and respectively cutting and grinding the raw coal into a cuboid test piece simulated coal bed with the thickness of 140mm multiplied by 400mm multiplied by 1000mm, wherein the flatness of the end surface of the cuboid test piece simulated coal bed is controlled within +/-0.05 mm;
preparing sandstone: selecting 3 sandstones, cutting and grinding the sandstones into cuboid test pieces of 40mm multiplied by 400mm multiplied by 1000mm to simulate a top-bottom plate rock stratum and a middle rock stratum, and controlling the flatness of end surfaces of the sandstone test pieces within +/-0.05 mm;
firstly, placing sandstone simulating a bottom layer into the bottom of a test piece box body, uniformly coating a high-strength epoxy resin adhesive on the upper surface of the sandstone simulating bottom layer, further uniformly coating a high-strength epoxy resin adhesive on the upper surface and the lower surface of a raw coal sample respectively, then placing the raw coal sample into the test piece box and compacting and attaching the raw coal sample to the sandstone simulating bottom plate, then placing a middle rock stratum and an upper coal seam, wherein the upper surface and the lower surface of the middle rock stratum are uniformly coated with the high-strength epoxy resin adhesive, and finally placing the sandstone simulating a top plate layer into the test piece box;
hoisting the box body of the test piece box to a transfer frame;
step two, preparing a multi-field coupling coal rock mass dynamic disaster prevention and control technology simulation system for installation;
the multi-field coupling coal rock mass dynamic disaster prevention and control technology simulation system comprises a main body model and a transfer frame; the main model has a true triaxial simulation experiment function and comprises a true triaxial loading system and a test piece box in the first step, wherein the test piece box and the shell of the main model are both made of high-strength transparent glass, and a high-speed camera is arranged outside the main model; an independent hydraulic loading device is arranged in the X direction for pressurization, and the maximum loading pressure is 5000kN; y, Z is pressurized by 4 groups of independent hydraulic loading devices in two directions, the maximum loading pressure of a single group of hydraulic loading devices is 3000kN, each group of hydraulic loading devices can be independently controlled, loading of different acting forces in the length direction of 1000mm is realized, and the triaxial stress state of an underground reservoir can be simulated more really;
sending the test piece box into a true triaxial loading system through a transfer frame, and enabling the stress loading cushion block of the test piece box body to correspond to the pressure heads in the true triaxial loading system one by one;
step three, applying true triaxial prestress;
according to the actually measured ground stress of the stratum, the true triaxial loading system is utilized to apply the ground stress to the simulated stratum, in the process of loading the stress, the pressure head is moved firstly, the pressure head is made to be in contact with the loading cushion block, and certain prestress is applied to achieve sigma x ＝σ y ＝σ z Loading Z, Y, X stress in three directions one by one in a step-type mode to reach a preset ground stress value;
step four, applying true triaxial mining induced stress;
loading force in the Z direction, selecting displacement loading control or stress loading control for loading, changing the stress values of No. 4Z direction loading devices to 6, 8 and 10MPa, and unloading until the coal seam roof is damaged and keeping sigma after the damage z4 The method is unchanged, so that the roadway protection effect of gob-side entry retaining of the goaf is simulated;
step five, starting the high-speed camera;
visually monitoring the whole loading process, and recording the roadway protection process of gob-side roadway retaining in the gob;
step six, performing other tests in the same group;
replacing sandstone materials, or changing true triaxial stress and stress loading rate, and repeating the steps from the first step to the fifth step;
step seven, ending the test;
after the test is finished, the force load is unloaded to zero, then the hydraulic system is switched to low pressure, the test piece is unloaded, the computer and the controller are closed, the power supply is cut off, and the test is finished.
Preferably, the main body model comprises a main body high-pressure cavity module and a test piece box, wherein a shell of the main body high-pressure cavity module is of a high-pressure closed pressure bin structure of an excircle and an inner circle, which are defined by a circular ring, a left circular end cover and a right circular end cover in combination with bolts, a front cushion block, a rear cushion block, an upper cushion block and a lower cushion block are respectively arranged on the front side, the rear side and the upper side of the inner wall of the circular ring, a rectangular cavity is defined by the front cushion block, the rear cushion block, the upper cushion block and the lower cushion block to be just suitable for placing the test piece box, an axial hydraulic cylinder is arranged on the left circular end cover in a penetrating manner, a seepage channel is arranged in the middle of the right circular end cover in a penetrating manner, wire harness pipeline leading-out holes are respectively arranged on the left circular end cover and the right circular end cover in a penetrating manner, a row of lifters are arranged in grooves at intervals on the left side and the right side of the top of the lower cushion block, and the lifters can protrude out of the lower cushion block and can also sink into the lower cushion block;
the test piece box is a rectangular test piece accommodating cavity formed by combining a left side plate, a bottom plate, a top plate, a right side plate, a front side plate and a rear side plate and surrounded by bolts, the axis of the rectangular test piece accommodating cavity is collinear with the axis of the high-pressure closed pressure bin, a left pressing plate is installed on the left side of the rectangular test piece accommodating cavity, a plurality of upper pressing plates are sequentially installed on the left and right sides of the top, a plurality of front pressing plates are sequentially installed on the left and right sides of the front part, an axial hydraulic cylinder can penetrate through the left side plate and is connected with the left pressing plate, each upper pressing plate is connected with a top hydraulic cylinder through an upper cushion block penetrating through the top plate, each front pressing plate is connected with a lateral hydraulic cylinder through a side cushion block penetrating through the front side plate, a plurality of heating pipes and temperature control probes are installed on the upper pressing plate, the front pressing plate, the bottom plate, the rear side plate and the right side plate, a row of rollers are installed at intervals on the bottom of the test piece box through a lining plate, and when the test piece box is pushed into the high-pressure cavity module of the main body, a lifter is supported below the rollers;
the anti-channeling plate is arranged right above the bottom plate and corresponds to the upper pressure plate in a one-to-one mode, a central air inlet hole and a plurality of annular grooves surrounding the central air inlet hole are formed in the anti-channeling plate, all the annular grooves are communicated with the central air inlet hole through communication grooves distributed in a divergent mode, the air inlet pipe transversely penetrates through the side wall of the test piece box and is connected to the bottom of the central air inlet hole, a ventilating partition plate is arranged above the anti-channeling plate, filter plates are arranged at the left end and the right end of the test piece, and sealing gaskets are arranged above, below, on the upper portion, below, behind and behind the test piece.
Preferably, only one axial hydraulic cylinder is used, and the maximum loading pressure is 5000kN; four groups of top hydraulic cylinders and four groups of lateral hydraulic cylinders are provided, each group of hydraulic cylinders is provided with two hydraulic loading systems connected in parallel for pressurization, one hydraulic loading system is a static load loading system, the other hydraulic loading system is a dynamic load loading system, the maximum loading pressure of a single group of hydraulic loading devices is 3000kN, each group of hydraulic loading systems independently controls one pressing plate and is arranged in the left and right middle of the corresponding pressing plate, and the axial hydraulic cylinders, the top hydraulic cylinders and the lateral hydraulic cylinders can all carry out loading of dynamic and static loads.
More preferably, the annular grooves are rectangular or circular and are distributed at equal intervals.
Preferably, the device further comprises a main body frame for supporting the main body model, wherein the main body frame is of a rectangular frame structure, the left end and the right end of the main body model extend out of the main body frame, a transfer slide rail is arranged on the right side of the main body frame and extends to the position right below the main body high-pressure cavity module, and the width of the transfer slide rail is smaller than the internal space width of the main body frame; the test piece box lifting transfer frame and the right round end cover transfer frame are arranged on the transfer slide rail in a sliding mode, can perform lifting movement and are used for supporting the test piece box; the right round end cover transfer frame top is the arc and is used for holding up right round end cover, just in time enables test piece case level to push in main part high-pressure chamber module after test piece case lift transfer frame rises, and test piece case lift transfer frame descends the back top and is less than the bottom of main part high-pressure chamber module to in the below of sliding in main part high-pressure chamber module, make right round end cover transfer frame can slide left and carry out the installation of right round end cover to the settlement position.
Preferably, each lifter adopts a double-support structure which is arranged at intervals in the front-back direction and symmetrically, each lifter adopts independent hydraulic drive, and all the lifters move in a synchronous lifting mode.
The invention has the beneficial effects that: the tunnel protection effect simulation of the large-size multi-coal-seam gob-side entry retaining can be carried out, the simulation process is more real and reliable, and the visual monitoring of the whole simulation process can be realized.
Drawings
FIG. 1 is a schematic diagram of the steps of the present invention.
FIG. 2 is a schematic diagram of a main model of a multi-field coupling coal rock mass dynamic disaster prevention and control technology simulation system.
Fig. 3 is an inner left side view of fig. 2.
Fig. 4 is a schematic structural view of the test piece box.
Fig. 5 is an inner left side view of fig. 4.
FIG. 6 is a simplified diagram of the arrangement of the heating tube, the temperature control probe and the ultrasonic probe.
Fig. 7 is a simplified illustration of a blow-by prevention plate.
Fig. 8 is a state before the test piece box is loaded into the main body high pressure chamber module.
Detailed Description
The invention is further illustrated by the following examples in combination with the accompanying drawings:
as shown in fig. 1, a method for protecting a multi-coal-seam gob-side entry retaining in a real ground stress environment includes the following steps:
step one, sample preparation;
preparing a coal sample, namely selecting 2 blocks of raw coal, and respectively cutting and grinding the raw coal into a cuboid test piece simulated coal bed with the thickness of 140mm multiplied by 400mm multiplied by 1000mm, wherein the flatness of the end surface of the cuboid test piece simulated coal bed is controlled within +/-0.05 mm;
preparing sandstone: selecting 3 sandstones, cutting and polishing the sandstones to form a cuboid test piece of 40mm multiplied by 400mm multiplied by 1000mm to simulate a top-bottom plate rock stratum and a middle rock stratum, and controlling the flatness of the end surfaces within +/-0.05 mm;
firstly, placing sandstone simulating a bottom layer into the bottom of a test piece box body, uniformly coating a high-strength epoxy resin adhesive on the upper surface of the sandstone simulating bottom layer, further uniformly coating a high-strength epoxy resin adhesive on the upper surface and the lower surface of a raw coal sample respectively, then placing the raw coal sample into the test piece box and compacting and attaching the raw coal sample to the sandstone simulating bottom plate, then placing a middle rock stratum and an upper coal seam, wherein the upper surface and the lower surface of the middle rock stratum are uniformly coated with the high-strength epoxy resin adhesive, and finally placing the sandstone simulating a top plate layer into the test piece box;
hoisting the box body of the test piece box to a transfer frame;
step two, preparing a multi-field coupling coal rock mass dynamic disaster prevention and control technology simulation system for installation;
the multi-field coupling coal rock mass dynamic disaster prevention and control technology simulation system comprises a main body model and a transfer frame; the main body model has a true triaxial simulation experiment function and comprises a true triaxial loading system and a test piece box in the first step, the test piece box and the shell of the main body model are both made of high-strength transparent glass, and a high-speed camera is arranged outside the main body model; an independent hydraulic loading device is arranged in the X direction for pressurization, and the maximum loading pressure is 5000kN; 5363 each of the two directions of Y, Z is provided with 4 groups of independent hydraulic loading devices for pressurization, the maximum loading pressure of a single group of hydraulic loading devices is 3000kN, each group of hydraulic loading devices can be independently controlled, the loading of different acting forces in the length direction of 1000mm can be realized, and the triaxial stress state of the underground reservoir can be simulated more truly;
sending the test piece box into a true triaxial loading system through a transfer frame, and enabling the stress loading cushion block of the test piece box body to correspond to the pressure heads in the true triaxial loading system one by one;
step three, applying true triaxial prestress;
according to the measured formation ground stress, a true triaxial loading system is utilized to apply ground stress to the simulated formation, in the process of loading the stress, a pressure head is moved firstly, the pressure head is made to be in contact with a loading cushion block, and certain prestress is applied to achieve sigma x ＝σ y ＝σ z Loading Z, Y, X stress in three directions one by one in a step-type mode to reach a preset ground stress value;
step four, applying true triaxial mining induced stress;
loading force in Z direction, selecting displacement loading control or stress loading control for loading, changing stress values of No. 4 loading devices in Z direction to 6, 8 and 10MPa, unloading until coal seam roof is damaged, and keeping sigma after damage z4 The method is unchanged, so that the roadway protection effect of gob-side entry retaining of the goaf is simulated;
step five, starting the high-speed camera;
visually monitoring the whole loading process, and recording the roadway protection process of gob-side roadway retaining in the gob;
step six, performing other tests in the same group;
replacing sandstone materials, or changing true triaxial stress and stress loading rate, and repeating the steps from the first step to the fifth step;
step seven, ending the test;
after the test is finished, the force load is unloaded to zero, then the hydraulic system is switched to low pressure, the test piece is unloaded, the computer and the controller are closed, the power supply is cut off, and the test is finished.
As shown in fig. 2-3, the main model of the multi-field coupling coal-rock mass dynamic disaster prevention and control technology simulation system mainly comprises a main high-pressure cavity module and a test piece box.
The shell 1 of the main body high-pressure cavity module is a high-pressure closed pressure chamber structure with an outer circle and an inner circle, which are formed by combining a circular ring 3, a left circular end cover 4, a right circular end cover 5 and bolts. The front cushion block 2, the rear cushion block 9, the upper cushion block 10 and the lower cushion block 11 are respectively arranged on the front, the rear, the upper and the lower parts of the inner wall of the circular ring 3. A rectangular cavity is defined by the front cushion block 2, the rear cushion block 9, the upper cushion block 10 and the lower cushion block 11 and is just used for placing a test piece box.
An axial hydraulic cylinder 6 is arranged on the left round end cover 4 in a penetrating mode, and a seepage channel is arranged in the middle of the right round end cover 5 in a penetrating mode.
The left round end cover 4 and the right round end cover 5 are respectively provided with a wire harness pipeline leading-out hole 7 in a penetrating mode, the top of the lower cushion block 11 is provided with a row of lifters 8 at intervals in a left-right mode, and the lifters 8 can protrude out of the lower cushion block 11 and can also sink into the lower cushion block 11. Each lifter 8 adopts a double-wheel structure which is arranged at intervals and symmetrically in the front and the back, so that front and back double support are realized, and the stress is balanced and stable. Each lifter 8 is driven by independent hydraulic pressure, and all the lifters 8 are controlled by a control system to move synchronously.
As shown in fig. 2-5, the test piece box is a rectangular test piece accommodating cavity formed by combining a left side plate 12, a bottom plate 13, a top plate 14, a right side plate 15, a front side plate 23 and a rear side plate 24 and bolts, and the rectangular test piece accommodating cavity is collinear with the axial lead of the high-pressure closed pressure bin, so that the rectangular test piece is arranged in the main model in the middle. A left pressing plate 16 is installed on the left side of the rectangular test piece accommodating cavity, a plurality of upper pressing plates 17 are installed on the left and right of the top of the rectangular test piece accommodating cavity in sequence, and a plurality of front pressing plates 18 are installed on the left and right of the front of the rectangular test piece accommodating cavity in sequence. The axial hydraulic cylinder 6 can penetrate through the left side plate 12 to be connected with the left pressing plate 16, each upper pressing plate 17 is connected with the top hydraulic cylinder 20 through an upper cushion block 19 which penetrates through the top plate 14, the top hydraulic cylinder 20 is provided with a hydraulic piston 20a, the upper cushion block 19 acts through the hydraulic piston 20a, and then the upper pressing plate 17 applies load to the rectangular test piece. Each front press plate 18 is connected to a lateral hydraulic cylinder 22 by means of a lateral spacer 21 mounted through a front side plate 23, the lateral hydraulic cylinder 22 also carrying a hydraulic piston, the lateral spacer 21 being acted upon by the hydraulic piston, and the front press plate 18 then applying a load to the rectangular test piece.
Referring to fig. 2-6, the upper press plate 17, the front press plate 18, the bottom plate 13, and the rear side plate 24 are provided with a plurality of heating pipes 27 and temperature control probes 28, and the upper press plate 17, the front press plate 18, the left press plate 16, the bottom plate 13, the rear side plate 24, and the right side plate 15 are provided with a plurality of ultrasonic probes 29. A row of rollers 26 are mounted on the bottom of the test piece box at left and right intervals through a lining plate 25, and when the test piece box is pushed into the main body high pressure chamber module, the lifter 8 is supported below the rollers 26.
Preferably, a high-frequency vibrator is mounted on the cavity of the axial hydraulic cylinder 6, and under the action of a high-pressure air source, high-speed vibration is generated, and high-frequency vibration force can be transmitted to the test piece rightwards through the corresponding hydraulic cavity, the hydraulic piston and the left pressing plate 16.
A flow-channeling preventing plate 30 corresponding to the upper pressure plate 17 one by one is disposed right above the bottom plate 13, as shown in fig. 7, a central air inlet 30a and a plurality of annular grooves 30b surrounding the central air inlet 30a are disposed on the flow-channeling preventing plate 30, and all the annular grooves 30b are communicated with the central air inlet 30a through communication grooves 30c distributed in a divergent manner, and an air inlet pipe transversely penetrates through the rear side wall of the test piece box and is connected to the bottom of the central air inlet 30 a. The annular grooves 30b are rectangular or circular and are equally spaced.
The air inlet pipe transversely penetrates through the rear side wall of the test piece box and is connected to the bottom of the central air inlet hole 30a, the air-permeable partition plate 31 is installed above the anti-channeling plate 30, the filter plates 32 are installed at the left end and the right end of the test piece, and the sealing gaskets 33 are installed above, below, in the front and at the back of the test piece.
The inner cavity of the test piece box can be provided with a rectangular test piece with the length of 1000 multiplied by the width of 400 multiplied by the height of 400mm, and the internal pressure resistance of the main body high-pressure cavity module is 10MPa.
Only one axial hydraulic cylinder 6 is arranged, and the maximum loading pressure is 5000kN; four groups of top hydraulic cylinders 20 and side hydraulic cylinders 22 are provided, each group of hydraulic cylinders is provided with two hydraulic loading systems connected in parallel for pressurization, one of the hydraulic loading systems is a static load loading system, the other hydraulic loading system is a dynamic load loading system, the maximum loading pressure of a single group of hydraulic loading devices is 3000kN, each group of hydraulic loading systems independently controls one pressing plate and is arranged in the left-right center of the corresponding pressing plate, and the axial hydraulic cylinders 6, the top hydraulic cylinders 20 and the side hydraulic cylinders 22 can all load dynamic and static loads.
As shown in fig. 8, the multi-field coupling coal rock mass dynamic disaster prevention and control technology simulation system includes a main body model, a main body frame 37 for supporting the main body model, a transfer slide rail 36, a test piece box lifting transfer frame 34, and a right circular end cap transfer frame 35. The test piece box lifting transfer rack 34 and the right round end cap transfer rack 35 are collectively referred to as a transfer rack.
The main body frame 37 is used for supporting the main body model, the main body frame 37 is of a rectangular frame structure, and the left end and the right end of the main body model are extended out of the main body frame 37. The right side of main part frame 37 is provided with transports slide rail 36, and transports slide rail 36 and extend to under the main part high pressure chamber module, and the width of transporting slide rail 36 is less than the interior empty width of main part frame 37. The transfer slide rail 36 is provided with a test piece box lifting transfer frame 34 and a right circular end cover transfer frame 35 in a sliding manner, and the test piece box lifting transfer frame 34 can move up and down and is used for supporting the test piece box. The frame 35 top is used for holding up right round end cap 5 for right round end cap 35 top is the arc, just in time enables test piece case level to push in the main part high-pressure chamber module after test piece case lift transport frame 34 rises, and test piece case lift transport frame 34 descends the back top and is less than the bottom of main part high-pressure chamber module, so that test piece case lift transport frame slips into the below of main part high-pressure chamber module, thereby makes right round end cap transport frame 35 can slide left and carry out the installation of right round end cap 5 to the settlement position.
The main characteristics of the main body model are as follows:
(1) The shell of the main body high-pressure cavity module is a high-pressure closed pressure bin which is surrounded by a circular ring, a left circular end cover and a right circular end cover and a bolt, and has an outer circle and an inner circle, and the structure of the high-pressure closed pressure bin is completely different from that of a traditional pressure bin which is surrounded by six plates and has an outer square and an inner square; meanwhile, as the test piece box is rectangular, in order to meet the installation of the test piece box, the front, the rear, the upper and the lower special-shaped cushion blocks are creatively and respectively installed on the front, the rear, the upper and the lower parts of the inner wall of the high-pressure closed pressure bin, and a rectangular cavity which is just used for placing the test piece box is enclosed by the front, the rear, the upper and the lower cushion blocks, so that a test piece box installation environment in the inner side of the excircle is formed, the internal pressure resistance is stronger, the sealing capability is better, the internal pressure resistance which can be provided can reach 10MPa, and a better test environment is provided for a roadway protection simulation test of a plurality of gob-side entry retaining roads in a real ground stress environment;
(2) The left and right spaced grooves on the top of the lower cushion block are provided with a row of lifters capable of protruding or sinking into the lower cushion block, and the bottom of the test piece box is provided with a row of rollers at left and right spaced intervals through the lining plate;
(3) The upper pressing plate, the front pressing plate, the bottom plate and the rear side plate are provided with a plurality of heating pipes and temperature control probes through holes, the upper pressing plate, the front pressing plate, the left pressing plate, the bottom plate, the rear side plate and the right side plate are provided with a plurality of ultrasonic probes through holes, and a fractured rock mass seepage test under the condition of three-dimensional stress-seepage-temperature multi-field coupling can be carried out; and combine the anti-channeling board that sets up directly over the bottom plate, the top of anti-channeling board is installed and is breathed freely the baffle, installs the filter at both ends about the test piece, installs sealed the pad around the upper and lower of test piece, can prevent the cross flow, can guarantee again that the gas permeability is good to possess and filter and sealed multiple effect.
The parameters of the mining stress in the specific test scheme are set as follows:
Claims (6)
1. a roadway protection method for multi-coal-seam gob-side entry retaining in a real ground stress environment is characterized by comprising the following steps:
step one, sample preparation;
preparing a coal sample, namely selecting 2 blocks of raw coal, and respectively cutting and grinding the raw coal into a cuboid test piece simulated coal bed with the thickness of 140mm multiplied by 400mm multiplied by 1000mm, wherein the flatness of the end surface of the cuboid test piece simulated coal bed is controlled within +/-0.05 mm;
preparing sandstone: selecting 3 sandstones, cutting and polishing the sandstones to form a cuboid test piece of 40mm multiplied by 400mm multiplied by 1000mm to simulate a top-bottom plate rock stratum and a middle rock stratum, and controlling the flatness of the end surfaces within +/-0.05 mm;
firstly, placing sandstone simulating a bottom layer into the bottom of a box body of a test piece, uniformly coating a high-strength epoxy resin adhesive on the upper surface of the sandstone simulating bottom layer, further uniformly coating a high-strength epoxy resin adhesive on the upper surface and the lower surface of a raw coal sample respectively, then placing the raw coal sample into the test piece box and compacting and jointing the raw coal sample with the sandstone simulating bottom plate, then placing a middle rock stratum and an upper coal seam, wherein the upper surface and the lower surface of the middle rock stratum are uniformly coated with the high-strength epoxy resin adhesive, and finally placing the sandstone simulating a top plate layer into the test piece box;
hoisting the test piece box body to a transfer frame;
step two, preparing a multi-field coupling coal rock mass dynamic disaster prevention and control technology simulation system for installation;
the multi-field coupling coal rock mass dynamic disaster prevention and control technology simulation system comprises a main body model and a transfer frame; the main model has a true triaxial simulation experiment function and comprises a true triaxial loading system and a test piece box in the first step, wherein the test piece box and the shell of the main model are both made of high-strength transparent glass, and a high-speed camera is arranged outside the main model; an independent hydraulic loading device is arranged in the X direction for pressurization, and the maximum loading pressure is 5000kN; y, Z is pressurized by 4 groups of independent hydraulic loading devices in two directions, the maximum loading pressure of a single group of hydraulic loading devices is 3000kN, each group of hydraulic loading devices can be independently controlled, loading of different acting forces in the length direction of 1000mm is realized, and the triaxial stress state of an underground reservoir can be simulated more truly;
sending the test piece box into a true triaxial loading system through a transfer frame, and enabling the stress loading cushion block of the test piece box body to correspond to the pressure heads in the true triaxial loading system one by one;
step three, applying true triaxial prestress;
according to the measured formation ground stress, a true triaxial loading system is utilized to apply ground stress to the simulated formation, in the process of loading the stress, a pressure head is moved firstly, the pressure head is made to be in contact with a loading cushion block, and certain prestress is applied to achieve sigma x ＝σ y ＝σ z Loading Z, Y, X stress in three directions one by one in a step-type mode to reach a preset ground stress value;
step four, applying true triaxial mining induced stress;
loading force in Z direction, selecting displacement loading control or stress loading control for loading, changing stress values of No. 4 loading devices in Z direction to 6, 8 and 10MPa, unloading until coal seam roof is damaged, and keeping sigma after damage z4 The method is unchanged, so that the roadway protection effect of gob-side entry retaining of the goaf is simulated;
step five, starting the high-speed camera;
visually monitoring the whole loading process, and recording the roadway protection process of gob-side entry retaining in the goaf;
step six, performing other tests in the same group;
replacing sandstone materials, or changing true triaxial stress and stress loading rate, and repeating the steps from the first step to the fifth step;
step seven, ending the test;
after the test is finished, the force load is unloaded to zero, then the hydraulic system is switched to low pressure, the test piece is unloaded, the computer and the controller are closed, the power supply is cut off, and the test is finished.
2. The roadway protection method for the gob-side entry retaining of the multiple coal seams in the real ground stress environment according to claim 1, is characterized in that: the main body model comprises a main body high-pressure cavity module and a test piece box, wherein a shell (1) of the main body high-pressure cavity module is of a high-pressure closed pressure bin structure of an outer circle and an inner circle which are formed by combining a circular ring (3), a left circular end cover (4) and a right circular end cover (5) with bolts, a front cushion block (2), a rear cushion block (9), an upper cushion block (10) and a lower cushion block (11) are respectively arranged on the front side, the rear side, the upper side and the lower side of the inner wall of the circular ring (3), a rectangular cavity is formed by the front cushion block (2), the rear cushion block (9), the upper cushion block (10) and the lower cushion block (11) in a surrounding mode and is just right for the test piece box to be placed in, an axial hydraulic cylinder (6) is arranged on the left circular end cover (4) in a penetrating mode, a seepage channel is arranged in the middle of the right circular end cover (5) in a penetrating mode, a wire harness pipeline lead-out hole (7) is respectively arranged on the left circular end cover (4) and the right circular end cover (11) in a groove is arranged at intervals left and right, a row of lifters (8) can protrude out, and the outer cushion block (11) can sink into the lower cushion block;
the test piece box is a rectangular test piece accommodating cavity formed by combining a left side plate (12), a bottom plate (13), a top plate (14), a right side plate (15), a front side plate (23) and a rear side plate (24) and being surrounded by bolts, the axis of the rectangular test piece accommodating cavity is collinear with the axis of the high-pressure closed pressure bin, a left pressure plate (16) is arranged on the left side of the rectangular test piece accommodating cavity, a plurality of upper pressure plates (17) are sequentially arranged on the left and right sides of the top, a plurality of front pressure plates (18) are sequentially arranged on the left and right sides of the front part, the axial hydraulic cylinder (6) can penetrate through the left side plate (12) to be connected with the left pressure plate (16), each upper pressure plate (17) is connected with a top hydraulic cylinder (20) through an upper cushion block (19) penetrating through the top plate (14), each front pressing plate (18) is connected with a lateral hydraulic cylinder (22) through a lateral cushion block (21) which is arranged on a front side plate (23) in a penetrating way, a plurality of heating pipes (27) and temperature control probes (28) are arranged on the upper pressing plate (17), the front pressing plate (18), the bottom plate (13) and the rear side plate (24) in a hole-forming way, a plurality of ultrasonic probes (29) are arranged on the upper pressing plate (17), the front pressing plate (18), the left pressing plate (16), the bottom plate (13), the rear side plate (24) and the right side plate (15) in a hole-forming way, a row of rollers (26) are arranged at the bottom of the test piece box at left and right intervals through a lining plate (25), when the test piece box is pushed into the main body high-pressure cavity module, the lifter (8) is supported below the roller (26);
the anti-channeling plate is characterized in that an anti-channeling plate (30) which corresponds to the upper pressing plate (17) in a one-to-one mode is arranged right above the bottom plate (13), a central air inlet hole (30 a) and a plurality of annular grooves (30 b) surrounding the central air inlet hole (30 a) are formed in the anti-channeling plate (30), all the annular grooves (30 b) are communicated with the central air inlet hole (30 a) through communication grooves (30 c) distributed in a divergent mode, an air inlet pipe transversely penetrates through the side wall of a test piece box to be connected into the bottom of the central air inlet hole (30 a), a ventilating partition plate (31) is installed above the anti-channeling plate (30), filter plates (32) are installed at the left end and the right end of the test piece, and sealing gaskets (33) are installed on the upper portion, the lower portion, the front portion and the rear portion of the test piece.
3. The roadway protection method for the gob-side entry retaining of the multiple coal seams in the real ground stress environment according to claim 2, characterized by comprising the following steps: only one axial hydraulic cylinder (6) is arranged, and the maximum loading pressure is 5000kN; four groups of top hydraulic cylinders (20) and lateral hydraulic cylinders (22) are arranged, each group of hydraulic cylinders is provided with two hydraulic loading systems connected in parallel for pressurization, one hydraulic loading system is a static load loading system, the other hydraulic loading system is a dynamic load loading system, the maximum loading pressure of a single group of hydraulic loading devices is 3000kN, each group of hydraulic loading systems independently controls one pressing plate and is arranged in the middle of the left side and the right side of the corresponding pressing plate, and the axial hydraulic cylinders (6), the top hydraulic cylinders (20) and the lateral hydraulic cylinders (22) can all load dynamic and static loads.
4. The roadway protection method for gob-side entry retaining of multiple coal seams in a true geostress environment according to claim 2, characterized by comprising the following steps: the annular grooves (30 b) are rectangular or circular and are distributed at equal intervals.
5. The roadway protection method for gob-side entry retaining of multiple coal seams in a true geostress environment according to claim 2, characterized by comprising the following steps: the high-pressure cavity module is characterized by further comprising a main body frame (37) used for supporting the main body model, the main body frame (37) is of a rectangular frame structure, the left end and the right end of the main body model extend out of the main body frame (37), a transfer slide rail (36) is arranged on the right side of the main body frame (37), the transfer slide rail (36) extends to the position right below the main body high-pressure cavity module, and the width of the transfer slide rail (36) is smaller than the inner hollow width of the main body frame (37); a test piece box lifting and transferring frame (34) and a right circular end cover transferring frame (35) are slidably mounted on the transferring slide rail (36), and the test piece box lifting and transferring frame (34) can perform lifting movement and is used for supporting the test piece box; right side circle end cap transports frame (35) top is the arc and is used for holding up right side circle end cap (5), just in time enables test piece case level and pushes in main part high-pressure chamber module after test piece case lift transports frame (34) rises, and test piece case lift transports frame (34) decline back top is less than the bottom of main part high-pressure chamber module, so that slide in the below of main part high-pressure chamber module, make right side circle end cap transport frame (35) can slide left to the settlement position and carry out the installation of right side circle end cap (5).
6. The roadway protection method for gob-side entry retaining of multiple coal seams in a true geostress environment according to claim 2, characterized by comprising the following steps: each lifter (8) adopts a double-support structure which is arranged at intervals in the front and at the back and symmetrically, each lifter (8) adopts independent hydraulic drive, and all the lifters (8) move up and down synchronously.
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