A longwall retreat mining method based on the theory of roof cutting and pressure relief

Abstract

A longwall retreat mining method based on the theory of roof cutting and pressure relief, that is, first, controlled blasting and slotting are carried out along the goaf to cut off the roof of the goaf and build a roof-supporting loose-rock dam with a certain width in situ to support the roof of the goaf. Then, as the blasting holes in the coal mining face are continuously detonated and the ore is transported out of the ore pile, a row of supports on the goaf side is gradually removed and supported near the ore body to be mined. In this way, when the pillars are turned over to the goaf and the suspension reaches a certain length, and it is difficult for the supports to overcome the rock burst pressure of the roof and the suspended roof is not tensioned over a large area, controlled blasting and slotting are carried out again to build a roof-supporting loose-rock dam to support the roof of the goaf. The present invention can extend the longwall retreat mining method to the mining of medium-thick and below (<10m) horizontal to gently inclined stratified non-coal mines, which can not only greatly improve the blasting mining efficiency but also solve the problem of rock burst in the working face.

Description

Technical Field

[0001] The present invention belongs to the technical field of mining, and particularly relates to a longwall retreat mining method based on the theory of roof cutting and pressure relief. Background Art

[0002] After the longwall retreat mining method for non-coal mines with horizontal to gently inclined seams is adopted, a large area of continuous gob areas are formed. When the roof is hard and thick overlying rock, the hanging gob areas that fail to collapse in time or still do not contact the roof over a large area after collapse will inevitably induce roof falls or roof rock bursts such as rib spalling of pillars and mine walls, resulting in the breakage of several rows of powered supports near the working face, seriously endangering mining safety. Therefore, in the past, the room-and-pillar blasting method was commonly used to mine hard ore bodies in such non-coal mines, and the mining efficiency was extremely low. The daily ore output in the stope was no more than 100 tons, and generally only reached 30 - 50 tons per day. Summary of the Invention

[0003] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a longwall retreat mining method based on the theory of roof cutting and pressure relief, integrating the theory of roof cutting and pressure relief and the longwall retreat mining method, so as to invent an efficient and safe mining method for the above-mentioned horizontal to gently inclined layered non-coal ore bodies. That is, control blasting cut grooves at a certain distance to release the roof pressure, and also use the pillar turning and support moving processes of the longwall retreat method to protect the safety of the working face, and economically and safely increase the daily output of mining such ore bodies to more than 280 - 340 tons.

[0004] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A longwall retreat mining method based on the theory of roof cutting and pressure relief, where the ore body is a horizontal to gently inclined layered non-coal mine. It is characterized in that first, control blasting cut grooves are made along the gob area to cut off the roof of the gob area, and a loose rock dam for roof contact is built in place to support the roof of the gob area. Then, as the blasting holes for ore drawing in the stope are continuously detonated and the ore pile is transported out, a row of powered supports on the side of the gob area is gradually removed and supported near the ore body to be mined (this process is called pillar turning in the longwall retreat mining method for coal mines). In this way, when the hanging length of the gob area reaches the point where the powered supports are difficult to overcome the roof rock burst and the roof is not tensioned over a large area, control blasting cut grooves are made again to release the pressure and build a loose rock dam for roof contact to support the roof of the gob area.

[0006] In one embodiment, the roof cutting height and dam building width of the loose rock dam for roof contact are designed according to the theory of roof cutting and pressure relief. The interval distance between two adjacent control blasting cut grooves for pressure relief, that is, the distance between two loose rock dams for roof contact plus the width of one dam building, is designed according to the overlying rock stress, roof tension situation and the supporting force of the powered supports in the longwall retreat mining, ensuring that the tensioned area of the roof is small and the overlying rock stress is less than or equal to the supporting force of the powered supports.

[0007] In one embodiment, the design formulas for the top cutting height and dam width of the top pine stone dam are:

[0008] Cutting height:

[0009] Dam width:

[0010] Where, L is the cutting height, i.e. the vertical depth of the borehole for cutting and top caving, in m; N is the vertical height of the goaf, i.e. the thickness of the ore body, in m; k is the loose coefficient, generally taken as 1.4; z is the rock acoustic impedance, in kg / (m 2 ·s), the value can be obtained by looking up the table; r e is the blasthole radius; S t is the uniaxial tensile strength of the top rock, in Pa; W is the dam width, in m; C is the resistance coefficient, determined by experiments, generally 1.1 to 1.27; ρ0 is the air density, in kg / m 3 , which was measured by downhole sampling and was 0.9; v is the air velocity, in m / s; f is the friction coefficient between loose rocks, and for safety and reliability, the minimum value is 0.25; γ is the bulk density of loose rocks, in N / m 3 .

[0011] In one embodiment, since the ore rock is hard and the hardness coefficient is greater than 8, it is currently not possible to use a coal mining machine to mine this type of ore body like coal mining, and blasting must be used. Taking into account the convenience of strong support frame movement and shoveling and transporting ore, ground pressure management and comprehensive support costs, generally about 3 to 4m deep blast holes are used to blast the ore body in rows to form an ore pile. The length of the working surface generally does not exceed 100m, and the thickness of the collapsed ore body is generally about 2 to 3m. Since the ore is loose after blasting and ore compensation space is required, taking into account the looseness coefficient, the initial ore drop generally has no more than 5 rows of blast holes symmetrically detonated on both sides, and then gradually increases to 10 rows, 15 rows, and 20 rows.

[0012] In one embodiment, under the protection of three rows of strong supports near the working surface, rock drilling is performed to form several rows of blastholes for dropping ore.

[0013] In one embodiment, when controlled blasting and grooving to release the roof, in order not to affect the production of ore falling and pillar turning, 4 rows of strong supports with a spacing of about 3 to 4 meters are specially arranged along the goaf to support the roof, and rock is drilled between these strong supports to control the blasting and grooving to release the roof blast holes. After charging and connecting the lines, the 2 middle rows of strong supports are removed, and then the blasting and grooving to release the roof is controlled to cut off the goaf roof and blast and pile loose stones on the spot to form a loose stone dam connecting the top. After the loose stone dam connecting the top is self-stabilized (about half a month), the strong supports on both sides of the rockfill dam are removed, which ensures both the construction safety of the controlled blasting and grooving to release the roof and the self-stability of the loose stone dam connecting the top.

[0014] In one embodiment, for the ore-drawing blast holes, when drilling to a depth of 3 - 4 m, rock drilling is carried out at an angle of approximately 75°, and when drilling to a depth of 3 m, rock drilling is carried out at an angle of approximately 45°. If the thickness of the ore body is 3 m, 3 rows of blast holes are drilled; when the thickness of the ore body increases to approximately 4 - 5 m, 4 rows of blast holes are drilled, and the spacing between the blast holes within a row is approximately 1 - 1.5 m.

[0015] In one embodiment, after the rock drilling of the ore-drawing blast holes is completed, blasting for ore drawing is carried out by retreating symmetrically from the two ore-drawing and transportation roadways towards the middle. The thickness of the ore body blasted at one time is 2 - 3 m; considering the fragmentation and swelling of the ore, only 5 rows can be blasted for the first time, 10 rows for the second time, and 15 - 20 rows for the third and fourth times.

[0016] In one embodiment, after 1 - 2 cycles of blasting for ore drawing and ore extraction are completed, the suspended span near the working face reaches 3 - 4 m. The third row of strong supports near the goaf side is removed, and support (turning columns) is carried out row by row to within 0.5 m of the ore body 1 to be mined, so as to timely support the roof and ensure the safety of rock drilling in the next cycle.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] The longwall retreat mining method is not suitable for mining horizontal to gently inclined ore bodies with hard and thick roofs. In the past, the room-and-pillar method was commonly used for blasting hard ore bodies in such non-coal mines, and the mining efficiency was extremely low. The daily ore output of the stope was no more than 100 tons, and generally only reached 30 - 50 tons per day.

[0019] The present invention integrates the theory of roof cutting and pressure relief and the longwall retreat mining method, and adopts the process of controlled blasting slotting for roof caving and dam building. It has a design system with strict dam building width and roof cutting construction height, and can also blast the loose rock at a certain interval to build a self-stable roof-connected loose rock dam. The blasting for roof cutting releases a certain amount of ground pressure, and the residual ground pressure can be transferred to the floor and cause uniform settlement of the roof by means of the self-stable roof-connected loose rock dam. Therefore, the application scope of the longwall retreat mining method is expanded, and it is extended to the mining field of hard ore bodies with medium thickness and below (<10 m) in thick overburden with horizontal to gently inclined hard roofs that were not suitable in the past. The daily output can be safely increased to more than 280 - 340 tons. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the projection drawing of the goaf floor of the present invention, and is also Figure 2 the view in the direction of Ⅳ-Ⅳ in

[0021] Figure 2 is the longitudinal projection drawing of the present invention, and is also Figure 1 the view in the direction of Ⅰ-Ⅰ in

[0022] Figure 3 is the longitudinal projection drawing of the present invention, and is also Figure 1 the view in the direction of ⅠⅠ-Ⅱ in

[0023] Figure 4 is the longitudinal projection view of the present invention and also the Figure 1 view in the direction of III-III in Specific Embodiments

[0024] The following describes in detail the embodiments of the present invention in conjunction with the accompanying drawings and embodiments.

[0025] The longwall retreat mining method is applicable to the roof of coal mines and the like that caving in and releasing ground pressure in a timely manner as the working face advances; sedimentary hard rock roofs such as deeply metamorphosed dolomite, whose uniaxial compressive and tensile strengths are at least 3 times higher than those of coal mine sandstone roofs, and the thickness is several times that of coal mine sandstone roofs. Under the influence of mining-induced ground pressure, it will neither cave in immediately with mining nor is it possible to cave in and connect to the roof, and it is easy to accumulate huge mining-induced ground pressure, thus impacting the working face mined by the longwall retreat mining method. In order to extend the longwall retreat mining method to the mining of medium-thick and below (<10m) horizontal to gently inclined stratified non-coal mines, while greatly improving the blasting mining efficiency and solving the problem of rock burst in the working face, integrating the longwall retreat mining method and the roof cutting and pressure relief theory, the present invention provides a longwall retreat mining method based on the roof cutting and pressure relief theory, integrating the roof cutting and pressure relief theory and the longwall retreat mining method, realizing efficient and safe mining of horizontal to gently inclined stratified non-coal ore bodies. That is, in the present invention, the ore body 1 is a horizontal to gently inclined stratified non-coal mine. The present invention first cuts the roof of the goaf by controlled blasting in the cut groove along the goaf and builds a capping loose rock dam with a certain width in place to support the roof of the goaf. Then, as the blasting holes for ore drawing in the blasting mining working face are continuously detonated and the ore is transported out of the ore pile, a row of supports on the goaf side is gradually removed and supported near the ore body to be mined. In this way, when the pillars are turned over to the goaf and the suspension reaches a certain length, the supports are difficult to overcome the roof rock burst, and when the suspended roof is not tensioned over a large area, similar controlled blasting cut groove and roof caving are carried out again to build a capping loose rock dam to support the roof of the goaf. The present invention also provides a design method for the cut groove depth, cut groove width, and the interval distance between two controlled blasting cut groove and roof caving operations.

[0026] Specifically, as shown in Figure 1 , Figure 2 , Figure 3 and Figure 4 , when the ore body 1 is mined to a certain suspended length, in order not to affect the production ore drawing and pillar turning, 4 rows of powerful supports 4 with a spacing of about 3 - 4m are specially arranged along the goaf 6 to support the roof, and controlled blasting cut groove and roof caving holes are drilled between these powerful supports 4. After charging and wiring, the middle 2 rows of powerful supports 4 are removed, and then the controlled blasting cut groove and roof caving are carried out to cut the roof of the goaf and build a capping loose rock dam by in-situ blasting. After the loose rock dam is self-stabilized (about half a month), the powerful supports 4 on both sides of the rockfill dam are removed to greatly release and transfer the roof ground pressure.

[0027] Near the working face, such asFigure 1 , Figure 2 Under the protection of the three rows of powerful supports 4 shown in the I-I section of Figure 2 , a rock drilling jumbo or a tunneling jumbo is used to drill rock in a certain direction (at an angle of about 75° when drilling holes about 3 - 4 m deep, and at an angle of about 45° when drilling holes about 3 m deep), forming several rows of ore-drawing blast holes 2 as shown in Figure 1 , Figure 3 the I-I to II section of Figure 3 , Figure 4 as shown in Figure 4 . If the thickness of the ore body is about 3 m, generally drill Figure 1 , Figure 3 the three rows of blast holes shown in the I-I to II section of Figure 3 ; Figure 4 as shown in Figure 4 . When the thickness of the ore body increases to about 4 - 5 m, according to blasting common sense, the number of rows of blast holes should be increased to 4 rows, and the spacing between blast holes in a row is generally about 1 - 1.5 m. If the width of the working face, that is, the distance between the two ore-drawing and transportation roadways 7, is 100 m, it takes about 1 day for 2 rock drilling jumbos or tunneling jumbos to drill these ore-drawing blast holes 2.

[0028] After the blast hole drilling is completed, according to the longwall retreat mining method, as shown in Figure 1 , Figure 2 the I-I section of Figure 2 , Figure 4 as shown in Figure 4 , the ore is blasted and mined by retreating symmetrically from the two ore-drawing and transportation roadways 7 towards the middle. The thickness of the ore body blasted and fallen at one time is about 2 - 3 m; considering the fragmentation and swelling of the ore, only 5 rows can be blasted for the first time, 10 rows can be blasted for the second time, and 15 - 20 rows can be blasted for the third and fourth times. If the longwall retreat working face is 100 m long, the ore can be blasted and mined by retreating and initiating the blast symmetrically from both sides towards the middle in the order of 5 rows, 10 rows, 15 rows, and 20 rows. In this way of ore mining, for a 100 - m long longwall retreat working face, with 2 load-haul-dump machines each equipped with several three-wheeled vehicles, it takes about 3 - 4 days to complete one cycle of blast ore mining and ore extraction.

[0029] After 1 - 2 cycles of blast ore mining and ore extraction are completed, the suspended span near the working face reaches about 3 - 4 m. It is necessary to timely remove the third row of powerful supports 4 close to the goaf side and timely support them row by row and line by line within 0.5 m near the ore body 1 to be mined, so as to timely support the roof and ensure the safety of rock drilling in the next cycle. In this way of turning columns and moving supports, it takes about 1 day of working time.

[0030] Therefore, when the thickness of the ore body blasted and fallen at one time is about 2 m, the average daily ore output of the stope can reach 280 - 340 tons. If the thickness of the ore body blasted and fallen at one time is about 3 m, the average daily ore output of the stope can reach 430 - 510 tons, greatly increasing the daily output of the traditional room-and-pillar method stope, which does not exceed 100 tons and is generally only 30 - 50 tons.

Claims

1. A longwall retreat mining method based on the theory of roof cutting and pressure relief, where the ore body (1) is a horizontally to gently inclined layered non-coal mine, and the hardness coefficient of the ore and rock is greater than 8. It is characterized in that, First, control the blasting to cut the top and release the roof along the goaf (6) to cut off the roof of the goaf, and build a loose-rock dam (5) in place to support the roof of the goaf. Then, as the ore-drawing blast holes (2) in the blasting working face are continuously detonated and the ore heap (3) is transported out, gradually remove a row of strong supports (4) on the goaf (6) side and support them near the ore body (1) to be mined. In this way, when the suspended length of the goaf (6) reaches a point where the strong supports (4) are difficult to overcome the roof rock burst pressure and the roof is not tensioned over a large area, control the blasting to cut the top and release the roof again to build a loose-rock dam (5) to support the roof of the goaf; When controlling the blasting to cut the top and release the roof, arrange 4 rows of strong supports (4) with a spacing of 3 - 4 m along the goaf (6) to support the roof, and drill rock holes for controlling the blasting to cut the top and release the roof between the strong supports (4). After charging and connecting the wires, remove the 2 middle rows of strong supports (4), and then control the blasting to cut the top and release the roof to cut off the roof of the goaf and build a loose-rock dam by in-situ blasting. After the loose-rock dam (5) stabilizes itself, remove the strong supports (4) on both sides of the rock-fill dam; The cutting height and dam-building width of the loose-rock dam (5) for roof cutting are designed based on the theory of roof cutting and pressure relief. The interval distance between two adjacent times of controlling the blasting to cut the top and release the roof, that is, the distance between two loose-rock dams (5) for roof cutting plus one dam-building width, is designed based on the overlying rock stress, the tension situation of the roof, and the supporting force of the strong supports (4) in longwall retreat mining to ensure that the tension area of the roof is not large and the overlying rock stress is less than or equal to the supporting force of the strong supports (4); The design formulas for the cutting height and dam-building width of the loose-rock dam (5) for roof cutting are as follows: Cutting height: Dam width: In the formula, L is the roof cutting height, that is, the vertical depth of the borehole for cutting the slot and caving the roof, with the unit of m; N is the vertical height of the goaf, that is, the thickness of the ore body, with the unit of m; k is the loose coefficient; z is the acoustic impedance of the rock, with the unit of kg / (m 2 ·s); r e is the radius of the blast hole; S t is the uniaxial tensile strength of the roof rock, with the unit of Pa; W is the dam building width, with the unit of m; C is the resistance coefficient; ρ0 is the air density, with the unit of kg / m 3 ; v is the air flow velocity, with the unit of m / s; f is the friction coefficient between loose rock blocks; γ is the bulk density of loose rock, with the unit of N / m 3 .

2. The longwall retreat mining method based on the theory of roof cutting and pressure relief according to claim 1, characterized in that, Taking into account the convenience of moving the strong supports, shoveling, transporting ore, ground pressure management, and the comprehensive support cost, use ore-drawing blast holes (2) with a depth of 3 - 4 m to blast the ore body in rows to form an ore heap (3). The length of the working face does not exceed 100 m, and the thickness of the caved ore body is 2 - 3 m. Considering the bulking factor, the number of symmetrically detonated ore-drawing blast holes (2) on both sides of the initial ore drawing does not exceed 5 rows, and then gradually increases to 10 rows, 15 rows, and 20 rows.

3. The longwall retreat mining method based on the theory of roof cutting and pressure relief according to claim 1, characterized in that, Under the protection of 3 rows of strong supports (4) near the working face, drill several rows of ore-drawing blast holes (2).

4. The longwall retreat mining method based on the theory of roof cutting and pressure relief according to claim 3, characterized in that, For the ore-drawing blast holes (2), when drilling to a depth of 3 - 4 m, drill the rock at a 75° angle, and when drilling to a depth of 3 m, drill the rock at a 45° angle; if the thickness of the ore body (1) is 3 m, drill 3 rows of blast holes; when the thickness of the ore body (1) increases to 4 - 5 m, drill 4 rows of blast holes, and the spacing between the blast holes in a row is 1 - 1.5 m.

5. The longwall retreat mining method based on the theory of roof cutting and pressure relief according to claim 4, characterized in that, After the ore-drawing blast holes (2) are drilled, blast the ore from the two ore-drawing and transportation roadways (7) symmetrically towards the middle and retreat. The thickness of the caved ore body at one time is 2 - 3 m; considering the swelling of the ore, only 5 rows can be blasted for the first time, 10 rows for the second time, and 15 - 20 rows for the third and fourth times.

6. The longwall retreat mining method based on the theory of roof cutting and pressure relief according to claim 5, characterized in that, After 1 - 2 cycles of blasting ore drawing and ore output are completed, the suspended span near the working face reaches 3 - 4 m. Remove the third row of strong supports (4) near the goaf side and support them in rows and columns within 0.5 m near the ore body (1) to be mined in order to timely support the roof and ensure the safety of drilling in the next cycle.

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