Hard roof cutting method for protective layer mining
Technical Field
The invention belongs to the technical field of mining engineering mine pressure control and roof cutting pressure relief, and particularly relates to a forced roof cutting method for blasting a large-area exposed hard roof in a goaf by arranging bidirectional drill holes in roadways on two sides of a working face into the hard roof and placing special blasting cartridges in the drill holes.
Background
After stoping of the working face, the top plate is periodically collapsed under the action of mine pressure to form a working face goaf. However, a hard top plate with high strength, large thickness, strong integrity, no joint crack development and difficult natural collapse in a short period exists on the coal seam, so that the top plate of the goaf cannot fall along with the top plate of the working face to form a long-distance suspended roof state.
The long-distance suspended ceiling is easy to cause large steps of initial pressure and periodic pressure, dynamic pressure impact is generated during pressure, the support is damaged, and the typical impact of the top plate can cause the cylinder body of the upright post of the high-tonnage hydraulic support to explode; if the suspended roof falls, the generated strong storm can destroy and blow down the working face equipment, and casualties are caused. Particularly for the mining of a protective layer, the permeability coefficient of a coal seam is easily reduced because a large-area hard top plate is suspended without collapsing, so that coal gas is accumulated, the gas pressure is increased and exceeds the standard, and great difficulty is brought to the mining of the protective layer.
In order to solve the above problems, technical measures such as dismantling anchor cable nets and softening top plates by high-pressure water injection are generally adopted. But has the following disadvantages: firstly, an anchor cable net removing and adding process increases the cost; secondly, the roof plate still has the problem of long-distance suspended ceiling after the anchor is withdrawn; thirdly, high-pressure water injection has requirements on lithology, and the effect is not obvious on sandstone, conglomerate and other roof rocks which are not easily softened by water; fourthly, the collapse size of the top plate is not easy to control by high-pressure water injection; high pressure water is easy to mud cracks and joints to block the release of gas.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a simple and feasible top cutting method which is easy to control and has good top cutting effect and can blast a hard top plate by reasonably arranging drill holes, so as to solve the problems of complicated working procedures, high production cost, unobvious effect, difficulty in control, long-distance suspended top formation and the like in the process of implementing technical measures such as anchor cable net disassembly, high-pressure water injection and the like.
The invention provides a hard roof cutting method for mining a protective layer, which comprises the following operation steps:
step 1, calculating an initial pressure step and a periodic pressure step;
L1-first pressure step, m;
h is the thickness of the old roof rock stratum, m;
Rt-old top ultimate tensile strength, MPa;
q-load applied to the old roof, KN/m2;
L2=(0.25~0.5)L1
L2-periodic incoming pressure step, m;
step 2, setting a top cutting operation position;
in order to ensure that the blasting and roof cutting effects are obvious, respectively arranging a drill site for roof cutting operation in two crossroads on a stope face at a distance 2 times of the initial pressure step distance from a cutting hole, setting the arranged drill sites as a first group, and setting the distance between each group of drill sites and the previous group of drill sites to be 2-3 times of the periodic pressure step distance;
step 3, setting drilling parameters;
3 drill holes are arranged in each drill site, namely an end cutting hole, an old top cutting hole and a block size control hole, wherein the hole pitch of the 3 drill holes is 1m, the 3 drill holes are arranged in an equilateral triangle, and the hole diameters are 60-75 mm;
wherein, the horizontal corner of the end cutting hole is 75 degrees, the elevation angle is 55 degrees, and the hole depth is 20 m; the horizontal corner of the old top cutting hole is 45 degrees, the elevation angle is 20 degrees to 27 degrees, and the hole depth is 45m to 60 m; the horizontal rotation angle of the block degree control hole is 0 degree, the elevation angle is 10 degrees to 15 degrees, and the hole depth is 60m to 85 m;
step 4, drilling construction and charging;
constructing in a drilling field according to the drilling parameters in the step 3, removing broken slag in the drilling hole by adopting a compressed air slag removal mode, immediately probing the hole by using a hole probing pipe after the blast hole construction is finished, verifying the hole depth, and immediately charging after the hole inspection is finished and is qualified in order to prevent hole collapse; wherein, the charge mode is: the blasting powder tube special for coal mine gas drainage is adopted for charging, the diameter of a charged powder bag is 32-45 mm, the length of the charged powder bag in an end cutting hole is 15m, the length of the charged powder bag in an old top cutting hole is 30-45 m, and the length of the charged powder bag in a block degree control hole is 42-60 m;
step 5, hole sealing;
after drilling construction and charging, hole sealing operation is carried out; the hole sealing material is quick-setting expansion and non-shrinkage cement slurry, the hole sealing length of the end cutting hole is 5m, the hole sealing length of the old top cutting hole is 15m, and the hole sealing length of the block control hole is 18 m-25 m;
step 6, carrying out blasting and top cutting operation;
after hole sealing operation is finished, detonating a group of drill holes every 10 days, before detonating, sequentially checking a detonating network, checking line connection, detonating after detecting that the safety detonating standard is met, and spraying with wind and water during blasting, scouring rock slopes after blasting and opening a water curtain;
step 7, checking the effect of the top cutting operation;
monitoring and observing the stress and shrinkage of the hydraulic support on the top-cutting working surface to obtain the mine pressure display characteristic and the roof pressure coming law; and the influence of the top cutting operation on the mining of the protective layer is obtained by comparing and analyzing the gas content, the gas pressure of the coal body, the extraction concentration change and the change of the gas exhaust amount before and after the top cutting of blasting.
The hard roof topping method for overburden mining comprises the following steps:
in the step 6, the group of drill holes comprises 6 drill holes; from step 2, dividing the drill sites into groups, wherein each group comprises 2 drill sites, and then arranging 3 drill holes for each drill site in step 3, so that one group of drill holes comprises 6 drill holes; in addition, because the explosive connecting line is in a series connection mode between holes, the sequential inspection detonating circuit in the step is to inspect the detonating circuit along the series lead.
The invention has the following advantages:
according to the geological conditions of the working surface of the hard top plate, the blasting and roof cutting positions are calculated theoretically, drilling parameters are determined, and drilling construction, charging and hole sealing are started; performing staged blasting topping according to a theoretical result; and finally, checking the top cutting effect. The invention takes the classical plate structure theory and the elastic foundation beam theory as the basis, combines the actual roof condition, adopts the blasting roof cutting method, shortens the length of the suspended roof, effectively controls the roof caving step, and has strong operability, low cost, high roof cutting speed and good effect. Especially for the mining of a protective layer, the blasting roof cutting technology can enable a coal rock body to generate new cracks, expand the cracks and even penetrate the cracks, increase the crushing degree of the coal rock body, greatly promote the release and the circulation of gas, improve the air permeability of the protected layer, further improve the pre-pumping rate of an extraction drill hole, release the gas stress in advance, and effectively prevent and treat coal and gas outburst and rock burst.
Drawings
FIG. 1 is a front truncated borehole plan view of a working surface.
FIG. 2 is a front truncated borehole profile view of the working face.
FIG. 3 is a schematic view of a borehole placement within a drill site; in the figure 123, 3 different drilling sites are shown.
FIG. 4 is a schematic diagram of hole filling and sealing.
Detailed Description
The process of the present invention will be further illustrated with reference to examples.
The mining depth of a working face of a certain ore protective layer is 1100m, the trend is as long as 572m, the trend is as long as 150m, and a trend long-wall total caving coal mining method and a retreat type stoping method are selected. The mining face support adopts a hydraulic support to control a top plate, the maximum top control distance is 5.14m, and the minimum top control distance is 4.54 m. According to geological drilling data, the thickness of the coal seam is 1.0m, the inclination angle of the coal seam is 6 degrees, and the coal seam belongs to a thin coal seam. The direct roof is 0-6 m of sandy mudstone, the old roof is 9m of medium-grain sandstone, and the roof belongs to a hard roof. There are problems in that: when mining by a caving coal mining method, the hard top plate can be suspended in a large area in a goaf without caving, dynamic pressure impact is generated during pressure application, and the support is easy to damage; because the large-area roof is hung without caving, a large amount of gas is accumulated in a goaf, the gas concentration is seriously overrun, and the mine production is seriously damaged.
A hard roof cutting method for mining a protective layer comprises the following specific operation steps:
step 1, calculating the initial pressure step and the periodic pressure step of the protective layer working surface;
the old top is medium sandstone with a thickness of 9.0m, and the ultimate tensile strength R of the medium sandstone is obtained through laboratory testst6.5MPa, and the load q of the overlying coal seam on the old top is 3.6 multiplied by 10 according to a coal seam histogram5From this, the step L of the first coming pressure of the old crown is obtained1Is 54m, the periodic pressure step L2The maximum is 27 m.
Step 2, setting a top cutting operation position;
two crossroads on a stope face are respectively provided with a drill site for top cutting operation at a position which is 2 times of the initial pressure step distance from a cutting hole, namely 108m, the arranged drill sites are set as a first group, the distance between each group of drill sites and the previous group of drill sites is 70m, namely about 2.6 times of the period pressure step distance, and the specific arrangement is shown in figure 1.
Step 3, setting drilling parameters;
3 drill holes are distributed in each drill site, namely an end cutting hole, an old top cutting hole and a block size control hole, as shown in figure 3, the hole spacing of the 3 drill holes is 1m and are distributed in an equilateral triangle, the diameter of the upper air inlet lane drill hole is 60mm, and the diameter of the lower air inlet lane drill hole is 75 mm;
as shown in fig. 1 and 2, the horizontal corner of the end cutting hole is set to be 75 degrees, the elevation angle of the upper air inlet lane is set to be 55 degrees, the hole depth is set to be 20m, the elevation angle of the lower air inlet lane is set to be 55 degrees, and the hole depth is set to be 20 m; the horizontal corner of the old top cutting hole is 45 degrees, the elevation angle of the upper air inlet lane is 20 degrees, the hole depth is 45m, the elevation angle of the lower air inlet lane is 27 degrees, and the hole depth is 60 m; the horizontal rotation angle of the block degree control hole is 0 degree, the elevation angle of the upper air inlet lane is 10 degrees, the hole depth is 60m, the elevation angle of the lower air inlet lane is 15 degrees, and the hole depth is 85 m.
Step 4, drilling construction and charging;
and (4) constructing in the drilling field according to the drilling parameters in the step (3), and removing slag in the drilled hole by adopting a compressed air slag removal mode so as to ensure that the subsequent hole exploring tube and the medicine tube can be smoothly transferred. After the blast hole construction is finished, immediately probing the hole by using a hole probing pipe, and verifying the depth of the hole, wherein the hole is verified to be finished and qualified;
wherein, the charge mode is: the explosive charging of the blasting explosive tube special for coal mine gas drainage is adopted, the diameter of the explosive charge loaded in the upper air inlet lane is 32mm, and the diameter of the explosive charge loaded in the lower air inlet lane is 45 mm. The length of the medicine bag filled in the end cutting hole is 15m, the length of the medicine bag filled in the upper air inlet lane old top cutting hole is 30m, the length of the medicine bag filled in the lower air inlet lane old top cutting hole is 45m, the length of the medicine bag filled in the upper air inlet lane block size control hole is 42m, and the length of the medicine bag filled in the lower air inlet lane block size control hole is 60 m.
Step 5, hole sealing;
after drilling construction and charging, hole sealing operation is carried out as shown in fig. 4; the hole sealing material is quick-setting expansion and non-shrinkage cement paste, and the length of the end cutting hole is 5 m; the sealing length of the old top cut-off hole is 15 m; the hole sealing length of the upper air inlet roadway block-size control hole is 18m, and the hole sealing length of the lower air inlet roadway block-size control hole is 25 m.
Step 6, blasting and top cutting operation;
and after hole sealing operation is finished, detonating a group of drill holes every 10 days, before detonating, sequentially checking a detonating network, checking line connection, detonating after detecting that the safety detonating standard is met, and spraying by using wind and water, scouring rock walls after blasting and opening a water curtain during blasting.
Step 7, monitoring and observing stress and shrinkage of the hydraulic support on the opposite-roof-cutting working surface; and comparing and analyzing parameters such as coal gas pressure, extraction concentration change and the like before and after blasting and roof cutting.
The results show that roof collapse is characterized by: when the working face is mined to the position of 52m, the middle part of the bracket begins to collapse sporadically. And (4) the mining face is pushed to 58m, the first group of top cutting holes are blasted, and most of hard top plates collapse after blasting. The maximum pressure of the bracket is 26MPa, and the step distance of the pressure of the old top in the first time can be inferred to be 55m, which is basically consistent with the theoretical calculation. The working face is pushed to 83m, and the comprehensive collapse occurs: most of the stent collapsed to the forced caving area. From the above roof collapse process, it can be known that: the initial pressure step pitch should be 55m, and the periodic pressure step pitch should be 20 m-30 m. In the process of collapse, the pressure of the support is not obvious, generally between 26 and 27MPa, and is within a normal controllable range.
Gas ginsengThe number variation is characterized by: before and after the blasting of the return airway, the average pumping concentration in the range of 30m before and after the blasting position is increased from 6.5 percent to 57 percent, the average pumping negative pressure is reduced from 236mmHg to 230mmHg, and the average differential pressure is increased by 0.2mmH2O, average daily allowance from 641m3Is raised to 742m3(ii) a The average pumping concentration in the range of 30m before and after the blasting position of the air inlet roadway is increased from 18 percent to 38.8 percent, the average pumping negative pressure is reduced from 235mmHg to 210mmHg, and the average pressure difference is reduced by 0.4mmH2O, average daily drainage is 984m3Rise to 1251m3。
In conclusion, the roof caving step is effectively controlled by the protective layer hard roof mining roof cutting method, and the method is strong in operability, high in roof cutting speed and remarkable in effect. Meanwhile, the coal body cracks are enlarged and even run through the cracks, the breaking degree of the coal rock body is increased, the gas release and circulation are greatly promoted, the air permeability of a protected layer is improved, the pre-pumping rate of the extraction drill hole is further improved, and a good effect is achieved.