Staged room mining method for staged rock drilling and filling

Abstract

The invention discloses a staged room mining method for staged rock drilling and filling. The method comprises the following steps that S1, an ore body is divided into a plurality of stages; each stage is divided into a plurality of chambers, each chamber is divided into a plurality of segments, and each segment is internally provided with a plurality of segment units; permanent top columns and recoverable top columns are arranged at the tops of the stages; s2, a preparation mining project is arranged; s3, arranging a cutting project; s4, stoping the chambers according to a stage stoping sequence, and removing ore by adopting a shoveling machine; s5, after ore removal of the subsection units is completed, flexible retaining walls are built, then goaf filling is carried out, and S4 and S5 are circulated till all subsections of the stope room are stoped; s7, ore pillar recovery; compared with an existing sublevel rock drilling stage chamber subsequent filling method, on one hand, the number of reserved permanent jambs is reduced, and the recovery rate is increased; and on the other hand, the exposure time of the goaf is shortened, mining safety is guaranteed, caving of surrounding rocks on the two sides can be effectively prevented, and the mining dilution rate is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of mine mining, and particularly to a sublevel stoping and filling method for mining sublevel rooms with sectional rock drilling and filling. Background Art

[0002] The mining methods for metal mines mainly include three categories: open stoping method, filling method, and caving method. Compared with the open stoping method and the caving method, the filling method has obvious advantages in controlling ground pressure, increasing the recovery rate, reducing the dilution rate, treating goafs and solid wastes, etc. Therefore, the filling method has been widely applied in actual production.

[0003] The filling method for mining metal mines can be further divided into stratified (upward stratified and downward stratified) filling mining methods and subsequent filling mining methods. The stratified filling mining method has been widely applied in mines with high-value ore types, unstable surrounding rocks and ore rocks. It has the advantages of high recovery rate, low dilution rate, and favorable ground pressure control, etc. However, it has the disadvantages of frequent mining and filling cycles, small production capacity of the ore room, and unfavorable mechanized operation, etc. The subsequent filling mining method mainly refers to subsequent filling after the formation of goafs by the open stoping method. Among them, the sublevel stoping with sectional rock drilling and subsequent filling method is applicable to mines with stable surrounding rocks and ore rocks, and has the advantages of high production capacity of the ore room and favorable mechanized operation, etc. However, it has the disadvantages of low recovery rate, high dilution rate, and long exposure time of the goaf, etc. For the medium-thick and above steeply inclined ore bodies with general or relatively unstable surrounding rocks and ore rocks, there is no filling mining method that can simultaneously achieve high recovery rate, low dilution rate, large production capacity of the ore room, short exposure time of the goaf, and few mining and filling cycles. Therefore, it is difficult to achieve the safe, efficient, and economic development of resources. Summary of the Invention

[0004] In order to reduce the setting of permanent ore pillars, increase the recovery rate, reduce the dilution rate, while reducing the exposure time of the goaf and the frequency of mining and filling cycles, and improving the degree of mechanized operation and ensuring the production capacity of the ore room, the present application provides a sublevel stoping and filling method for mining sublevel rooms with sectional rock drilling and filling.

[0005] The present application provides a sublevel stoping and filling method for mining sublevel rooms with sectional rock drilling and filling, adopting the following technical solutions:

[0006] A sublevel stoping and filling method for mining sublevel rooms with sectional rock drilling and filling includes the following steps:

[0007] S1. The ore body is divided into multiple levels; within each level, multiple ore rooms are divided along the strike of the ore body, multiple sublevels are divided along the height direction within each ore room, and multiple sublevel units are divided along the strike of the ore body within each sublevel; a crown pillar is arranged at the top of the level, and the crown pillar includes a permanent crown pillar and a recoverable crown pillar;

[0008] S2. Arrange the development and preparatory works. The development and cutting works include the stage haulage roadway, stage return airway, district ramp, ore pass, sectional haulage roadway, stage crosscut, sectional crosscut, sectional drilling roadway, and stage return crosscut.

[0009] S3. Arrange the cutting works. The cutting works include: cutting level roadway and cutting return air and man shaft.

[0010] S4. Mine the ore room according to the stage mining sequence and use a load-haul-dump machine to draw out the ore.

[0011] S5. After the ore drawing of one sectional unit is completed, build a flexible retaining wall, and then carry out goaf filling. S4 and S5 are cycled until the mining of each section of the ore room is completed.

[0012] S6. Recover the ore pillars.

[0013] Optionally, in step S1, the length of the ore room is 40 - 80 m; the width of the ore room is the thickness of the ore body, 8 - 15 m; the stage height is 50 - 70 m, and the sectional height is 10 - 20 m.

[0014] Optionally, in step S1, the permanent crown pillar is located directly below the contact zone of the backfill of two sectional units, with a strike length of about 10 m, which is used to support the backfill of the upper stage and prevent its overall collapse.

[0015] Optionally, step S2 is specifically as follows: the stage haulage roadway is arranged in the footwall of the ore body; the stage return airway is transformed from the stage haulage roadway after the mining of the upper stage is completed;

[0016] Drive the district ramp from the stage haulage roadway to connect with each sectional haulage roadway. The district ramp serves as the main safety exit of the ore room; the sectional haulage roadway is arranged in the footwall of the ore body;

[0017] Drive an ore pass in the central position of the ore room to connect each sectional haulage roadway with the stage haulage roadway.

[0018] In the central position of the ore room, drive a stage crosscut from the stage haulage roadway to expose the ore body, and drive sectional crosscuts from each sectional haulage roadway to expose the ore body; drive sectional drilling roadways along the strike of the ore body from the stage crosscut and each sectional crosscut. The sectional drilling roadway is located near the contact surface of the footwall ore and rock in the ore body;

[0019] In the two-side positions of the ore room, drive stage return crosscuts from the stage return airway to connect with the cutting return air and man shaft.

[0020] Optionally, step S3 specifically involves driving cutting headings from each sublevel drilling heading to the ore-rock contact surface of the hanging wall of the orebody at both sides of the ore chamber; constructing cutting raises in each sublevel to connect the cutting headings and the stage return airway crosscut, and the cutting raises in each sublevel are connected vertically to form a cutting return airway and personnel access raise, which is located near the ore-rock contact surface of the hanging wall inside the orebody; an access ladder is installed in the cutting return airway and personnel access raise to serve as an emergency safety exit for the ore chamber.

[0021] Upward parallel medium-deep holes are drilled in the cutting heading, with the cutting return airway and personnel access raise as the free face, and a cutting slot is formed after blasting.

[0022] Optionally, in step S4, when adjacent ore chambers are mined simultaneously, the same sublevel is not mined simultaneously; the sublevels in the ore chamber are mined from bottom to top; within each sublevel, it is divided into two sublevel units along the strike of the orebody, that is, one sublevel unit is slightly smaller than the other, and the shorter sublevel unit is mined first within the sublevel, and then the other sublevel unit is mined.

[0023] Optionally, in step S4, the sublevel unit mining includes operations and work such as drilling, charging, blasting, ore drawing, and ventilation.

[0024] After the cutting slot is formed, mining is carried out from one side of the cutting slot towards the central position of the ore chamber. Upward fan-shaped medium-deep holes are drilled in the sublevel drilling heading, and ore caving is carried out with the cutting slot as the free face. 2 - 5 rows of blast holes are blasted each time to form an ore pile.

[0025] The caved ore is drawn by a LHD. The ore drawn from the first sublevel is loaded into the transport ore car after passing through the sublevel drilling heading and the stage crosscut; the ore drawn from other sublevels is loaded into the transport ore car after passing through the sublevel drilling heading, the sublevel crosscut, and the ore pass. When the mining of one sublevel unit is completed, the LHD enters the goaf for full ore drawing.

[0026] Optionally, in step S4, fresh air enters during sublevel mining from the stage transport roadway or the sublevel transport roadway, passes through the stage crosscut or the sublevel crosscut and the sublevel drilling heading to reach the sublevel drilling and blasting operation points, and the polluted air is discharged to the stage return airway through the cutting return airway and personnel access raise and the stage return airway crosscut; during the mining process, it is necessary to ensure smooth air flow in the sublevel drilling heading.

[0027] Optionally, in step S5, after the ore drawing of one sublevel unit is completed, a flexible retaining wall is built, which includes a roadway flexible retaining wall and a cutting slot flexible retaining wall; for the shorter sublevel unit, the flexible retaining wall is built in the sublevel drilling heading, and for the longer sublevel unit, the flexible retaining wall is built in the stage crosscut or the sublevel crosscut; the cutting slot flexible retaining wall is built on the side of the cutting return airway and personnel access raise in the ore chamber, and its height is the sublevel height.

[0028] After the flexible retaining wall is built, cut the return air pedestrian raise to connect the filling pipeline from the stage return airway and the stage return crosscut into the goaf for goaf filling; except for the uppermost section, the filling of other sections does not completely reach the roof to reserve the sectional drilling roadway for the extraction of the upper section.

[0029] During the hardening period of the filling body, carry out the mining and filling cycle of the next sectional unit, and so on until the mining of each section of the ore room is completed.

[0030] Optionally, in step S6, when the ore room is a low-grade ore body, the top pillar is not recovered; when the ore room is a high-grade ore body, the recoverable top pillar is recovered; when recovering the top pillar, drive a downward ramp and an in-vein drilling roadway from the stage return crosscut or the original stage crosscut roadway of the upper stage, drill upward fan-shaped holes in the drilling roadway, and recover the recoverable top pillar.

[0031] In summary, the present application includes the following beneficial technical effects:

[0032] This mining method divides the ore room into several sections vertically, and adopts sectional drilling, ore caving, ore drawing and filling; compared with the existing subsequent filling method of sectional drilling stage ore room, on the one hand, the setting of permanent ore pillars is reduced, and the recovery rate is improved; on the other hand, the exposure time of the goaf is reduced, which is beneficial to ensuring the safety of mining, and can also effectively prevent the caving of the surrounding rock on both sides, reducing the mining dilution rate. Compared with the existing stratified filling mining method, the frequency of the mining and filling cycle is greatly reduced, which is conducive to improving the degree of mechanized operation of the ore room and greatly improving the ore production capacity of the ore room. Description of the Drawings

[0033] Figure 1 is the schematic diagram of a sectional drilling and filling stage ore room mining method of the present application;

[0034] Figure 2 is Figure 1 the sectional view of A-A in

[0035] Figure 3 is Figure 1 the sectional view of B-B in

[0036] Description of the Reference Numerals:

[0037] 1, stage transportation roadway; 2, stage return airway; 3, mining area ramp; 4, ore pass; 5, sectional transportation roadway; 6, stage crosscut; 7, sectional crosscut; 8, sectional drilling roadway; 9, cutting level roadway; 10, cutting return air pedestrian raise; 11, stage return crosscut; 12, ore body; 13, recoverable top pillar; 14, permanent top pillar; 15, filling body; 16, medium-deep hole; 17, flexible retaining wall of roadway; 18, flexible retaining wall of cutting slot; 19, ore heap; 20, goaf; 21, sectional unit I; 22, sectional unit II. Detailed implementation mode

[0038] The following is a further detailed description of this application in conjunction with the attached Figures 1 - 3 drawings.

[0039] The embodiment of this application discloses a sublevel stoping method for sectional rock drilling and filling, which includes the following steps:

[0040] Division of stope structure

[0041] The stope is arranged along the strike of the ore body, with a strike length (L) of 40 - 80 m; the width (W) of the stope is the thickness of the ore body, 8 - 15 m; the stage height (H) is 50 - 70 m, and the sublevel height (T) is 10 - 20 m; within each sublevel, it is divided into two small sublevel units along the strike of the ore body; the height of the crown pillar (P) is 6 - 8 m, and the crown pillar is further divided into a recoverable crown pillar and a permanent crown pillar, without leaving intermediate pillars and sill pillars. The strike length (L) of the stope and the sublevel height (T) are determined according to the specific wall rock and ore-rock stability of the mine. When the stability is relatively poor, a smaller value is selected; when the stability is relatively good, a larger value is selected.

[0042] Development

[0043] The development engineering includes: stage haulage drift 1, stage return airway 2, district ramp 3, ore pass 4, sublevel haulage drift 5, stage crosscut 6, sublevel crosscut 7, sublevel drilling drift 8, stage return crosscut 11.

[0044] The stage haulage drift 1 is arranged in the footwall of the ore body, with a horizontal distance from the footwall of the ore body of about 15 m; the stage return airway 2 is transformed from the stage haulage drift after the stoping of the previous stage.

[0045] The district ramp 3 is driven from the stage haulage drift 1 to connect each sublevel haulage drift 5. The district ramp 3 serves as the main safety exit of the stope; the sublevel haulage drift 5 is arranged in the footwall of the ore body, with a horizontal distance from the footwall of the ore body of about 8 - 10 m.

[0046] An ore pass 4 is driven at the central position of the stope to connect each sublevel haulage drift 5 with the stage haulage drift 1.

[0047] At the central position of the stope, the stage crosscut 6 is driven from the stage haulage drift 1 to expose the ore body, and the sublevel crosscut 7 is driven from each sublevel haulage drift 5 to expose the ore body; the sublevel drilling drift 8 is driven along the strike of the ore body from the stage crosscut 6 and each sublevel crosscut 7. The sublevel drilling drift 8 is located near the contact surface of the footwall ore rock in the ore body;

[0048] At the two sides of the stope, the stage return crosscut 11 is driven from the stage return airway 2 to connect the cut-through return pedestrian raise 10.

[0049] Cutting

[0050] The cutting process includes: cutting the level heading 9 and the cutting return airway and manway raise 10.

[0051] At both sides of the ore room, the cutting level heading 9 is driven from each sublevel drilling drift 8 to the contact surface of the ore and rock in the hanging wall of the ore body; the cutting raise is constructed in each sublevel to connect the cutting level heading 9 and the stage return airway crosscut 11. The cutting raises in each sublevel are connected vertically to form the cutting return airway and manway raise 10, which is located near the contact surface of the ore and rock in the hanging wall of the ore body; a ladder way is installed in the cutting return airway and manway raise 10 as the emergency safety exit of the ore room.

[0052] Upward parallel medium-deep holes are drilled in the cutting level heading 9, with the cutting return airway and manway raise 10 as the free face, and a cutting slot is formed after blasting.

[0053] Stoping

[0054] The stoping sequence of ore rooms within a stage generally follows the stage stoping sequence. When adjacent ore rooms are stoped simultaneously, the same sublevel is not stoped at the same time; the sublevels within the ore room are stoped from bottom to top; within each sublevel, it is divided into two small sublevel units along the strike of the ore body, namely sublevel unit I 21 and sublevel unit II 22. In terms of the strike length, sublevel unit I 21 is slightly smaller than sublevel unit II 22. In the sublevel, sublevel unit I 21 is stoped first, and then sublevel unit II 22 is stoped.

[0055] The sublevel unit stoping includes operations and work such as drilling, charging, blasting, ore drawing, and ventilation.

[0056] After the cutting slot is formed, stoping is carried out from one side of the cutting slot towards the central position of the ore room. Upward fan-shaped medium-deep holes 16 are drilled in the sublevel drilling drift 8, and ore caving is carried out with the cutting slot as the free face. 2 - 5 rows of blast holes are blasted each time to form an ore heap 19.

[0057] The caved ore is drawn by a LHD. The ore drawn from the first sublevel is loaded into the transport ore car after passing through the sublevel drilling drift 8 and the stage crosscut 6; the ore drawn from other sublevels is loaded into the transport ore car after passing through the sublevel drilling drift 8, the sublevel crosscut 7, and the ore pass 4. A LHD with a remote control function is selected for ore drawing. When the stoping of a sublevel unit is completed, the LHD uses the remote control function to enter the goaf for comprehensive ore drawing.

[0058] When stoping in sublevels, fresh air enters from the stage haulage roadway 1 or the sublevel haulage roadway 5, passes through the stage crosscut 6 or the sublevel crosscut 7 + the sublevel drilling drift 8 to enter the sublevel drilling and blasting operation points, and the foul air is discharged to the stage return airway 2 through the cutting return airway and manway raise 10 and the stage return airway crosscut 11. During the stoping process, it is necessary to ensure the smooth flow of air in the sublevel drilling drift 8.

[0059] Filling

[0060] After the extraction of an ore-drawing section unit is completed, a flexible retaining wall is built, which includes a roadway flexible retaining wall 17 and a cut vertical slot flexible retaining wall 18. For the section unit I 21, the flexible retaining wall is built in the sectional drilling roadway 8, and for the section unit II 22, the flexible retaining wall is built in the level crosscut 6 or the sectional crosscut 7. The cut vertical slot flexible retaining wall 18 is built on the side of the cut return air and pedestrian raise 10 in the ore room, and its height is the section height. The purpose is to reserve a free space for the blasting of the corresponding section in the adjacent ore room during mining. If the corresponding section in the adjacent ore room has been mined and backfilled, this flexible retaining wall does not need to be built.

[0061] After the flexible retaining wall is built, using the cut return air and pedestrian raise 10, the filling pipeline is connected from the level return airway 2 and the access level return crosscut 11 to the goaf 20, and the goaf 20 is filled. Except for the topmost section, during the filling of other sections, the filling does not completely reach the roof, and the sectional drilling roadway 8 is reserved for the mining of the upper section.

[0062] During the hardening period of the filling body 15, the mining and filling cycle of the next section unit is carried out, and this cycle continues until the mining of each section in the ore room is completed.

[0063] Recovery of ore pillars

[0064] Only a crown pillar is left in the ore room to prevent the caving of the filling body 15 in the upper stage during mining.

[0065] The crown pillar is divided into a recoverable crown pillar 13 and a permanent crown pillar 14. The permanent crown pillar 14 is located directly below the contact zone of the filling bodies 15 of two section units, with a strike length of about 10 m, and is used to support the filling body 15 in the upper stage to prevent its overall caving.

[0066] When the ore body in the ore room is of low grade, the crown pillar is not recovered; when the ore body in the ore room is of high grade, the recoverable crown pillar 13 is recovered. When recovering the crown pillar, a downward ramp and an in-vein drilling roadway are driven from the level return crosscut 11 or the original level crosscut roadway in the upper stage. Upward fan-shaped holes are drilled in the drilling roadway to recover the recoverable crown pillar 13.

[0067] The above are all the preferred embodiments of this application, and the protection scope of this application is not limited accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of this application should be covered within the protection scope of this application.

Claims

1. A stage chamber mining method with segmented rock drilling and filling, characterized in that The steps include: S1. The ore body is divided into multiple stages; multiple mine rooms are divided along the ore body strike in each stage, multiple sections are divided along the height direction in each mine room, and multiple section units are divided along the ore body strike in each section; top pillars are arranged at the top of each stage, including permanent top pillars and recoverable top pillars; S2. Arrange the mining and cutting works, including the stage transport tunnel, stage return air tunnel, mining area ramp, chute, segmented transport tunnel, stage vein tunnel, segmented vein tunnel, segmented rock drilling tunnel, and stage return air vein tunnel; S3. Arrange the cutting works, which include: cutting the lanes and cutting the return air pedestrian skylights; S4. Mining the mine room in accordance with the phased mining sequence and using a remote excavator to mine the ore; S5: After the mining of a subdivision unit is completed, a flexible retaining wall is built, and then the goaf is filled. S4 and S5 are repeated until the mining of each subdivision in the mine room is completed; S6. Pillar recovery.

2. A stage chamber mining method of segmented rock drilling and filling according to claim 1, characterized in that: In step S1, the length of the mine room is 40 to 80 m; the width of the mine room is the thickness of the ore body, 8 to 15 m; the stage height is 50 to 70 m, and the segment height is 10 to 20 m.

3. A stage chamber mining method of segmented rock drilling and filling according to claim 2, characterized in that: In step S1, the permanent top column is located directly below the contact zone between the two segmented unit filling bodies, extending for about 10m, and is used to support the upper stage filling body to prevent it from falling off as a whole.

4. A stage chamber mining method of staged rock drilling and filling according to claim 3, characterized in that: Step S2 specifically includes: arranging the stage transport lane in the footwall of the ore body; the stage return air lane is transformed from the stage transport lane after the previous stage mining is completed; The mining area ramp is excavated from the stage transport lane to connect the various segment transport lanes. The mining area ramp serves as the main safe exit of the mine room; the segment transport lane is arranged in the footwall of the ore body; A chute is dug in the center of the mine to connect the various segmented transport tunnels and stage transport tunnels. In the center of the mine room, the ore body is exposed by excavating the stage vein tunnel from the stage transportation tunnel, and the ore body is exposed by excavating the segment vein tunnel from each segment transportation tunnel; the segment rock drilling tunnel is excavated along the ore body from the stage vein tunnel and each segment vein tunnel, and the segment rock drilling tunnel is located near the ore-rock contact surface of the lower wall of the ore body; On both sides of the mine room, the return air veins are penetrated from the stage return air tunnel excavation to connect and cut the return air pedestrian skylight.

5. A stage chamber mining method of staged rock drilling and filling according to claim 4, characterized in that: Step S3 specifically includes: at both sides of the mine room, cutting lanes are excavated from each segmented rock drilling lane to the ore-rock contact surface of the upper plate of the ore body; each segmented cutting skylight is constructed to connect the cutting lanes and the stage return air through veins, and each segmented cutting skylight is connected up and down to form a cutting return air pedestrian skylight, and the cutting return air pedestrian skylight is located near the ore-rock contact surface of the upper plate of the ore body; a ladder room is installed in the cutting return air pedestrian skylight as an emergency safety exit of the mine room; A medium-depth hole parallel to the top is drilled in the cutting tunnel, with the return air pedestrian skylight as the free surface, and a cutting vertical groove is formed after blasting.

6. A stage chamber mining method of staged rock drilling and filling according to claim 5, characterized in that: In step S4, when adjacent mining rooms are mined at the same time, the same segment is not mined at the same time; each segment in the mining room is mined from bottom to top; each segment is divided into two segment units along the strike of the ore body, that is, one of the segment units is slightly smaller than the other segment unit in the strike direction, and the shorter segment unit is mined first, and then the other segment unit is mined.

7. A stage chamber mining method of staged rock drilling and filling according to claim 6, characterized in that: In step S4, the subdivision unit recovery includes rock drilling, charging, blasting, mining and ventilation; After the cutting groove is formed, mining is carried out from one side of the cutting groove to the center of the mine room, and upward fan-shaped medium-deep holes are drilled in the segmented rock drilling tunnel. The cutting groove is used as the free surface for caving. Each time blasting, 2 to 5 rows of blast holes are blasted to form an ore pile. The collapsed ore is unloaded by a shovel. The first-stage ore is loaded into a transport car after passing through the segmented rock drilling tunnel and the staged vein tunnel; the other ore is loaded into a transport car after passing through the segmented rock drilling tunnel, the segmented vein tunnel and the chute. When the mining of a segment unit is completed, the shovel enters the goaf to carry out comprehensive ore unloading.

8. A stage chamber mining method of staged rock drilling and filling according to claim 7, characterized in that: Step S4, during segmented mining, fresh air enters from the stage transport tunnel or the segmented transport tunnel, enters the segmented rock drilling and blasting operation point through the stage vein tunnel or the segmented vein tunnel and the segmented rock drilling tunnel, and the polluted air is discharged to the stage return air tunnel through the cut return air pedestrian skylight and the stage return air vein tunnel; during the mining process, the air flow in the segmented rock drilling tunnel must be ensured to be unobstructed.

9. A stage chamber mining method of staged rock drilling and filling according to claim 8, characterized in that: In step S5, after the mining of a segmented unit is completed, a flexible retaining wall is built, and the flexible retaining wall includes a tunnel flexible retaining wall and a cutting vertical groove flexible retaining wall; for a shorter segmented unit, the flexible retaining wall is built in the segmented rock drilling lane, and for a longer segmented unit, the flexible retaining wall is built in the staged vein lane or the segmented vein lane; The flexible retaining wall of the cut vertical slot is built on the side of the cut return air pedestrian skylight of the mine room, and the height is segmented; After the flexible retaining wall is built, the filling pipeline is connected from the stage return air lane and the access stage return air through-vein to the goaf for filling the goaf; except for the top segment, the other segments are not completely connected to the top during filling, and the segmented rock drilling lane is reserved for the upper segment mining; During the hardening period of the filling body, the mining and filling cycle of the next segment unit is carried out, and this cycle is repeated until the mining of each segment of the mine is completed.

10. A stage chamber mining method of staged rock drilling and filling according to claim 9, characterized in that: In step S6, when the mine chamber is a low-grade ore body, the top pillar is not recovered; when the mine chamber is a high-grade ore body, the recyclable top pillar is recovered; when recovering the top pillar, the downward inclined ramp and the rock drilling lane in the vein are excavated from the stage return air through-vein or the original stage through-vein lane of the previous stage, and upward fan-shaped holes are drilled in the rock drilling lane to recover the recyclable top pillar.

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