A false roof type safe mining construction method suitable for soft rock stratum metal deposit

Abstract

The application provides a false roof type safe mining construction method suitable for soft rock stratum metal deposit, which comprises the following steps: S1, determining the mining sequence between each middle section ore block and the cutting sequence of the preparation; S2, using a non-explosive method to mine in the stope, cutting the rock mass in the stope and mining out; S3, filling immediately after the end of the mining of each stope, the stope filling comprises a lower bearing layer and an upper roof contact layer. The application is particularly suitable for the ore body with soft characteristics by the non-explosive method, the disturbance and damage to the ore body are small, the filling is performed by the high-strength bearing layer and the low-strength roof contact layer, the stability of the false roof is better after the filling, and a large amount of wood is not needed for support; the safe mining is realized under the unsafe condition, and the safety is higher in general.

Description

Technical Field

[0001] This invention relates to the field of mining construction technology, and in particular to a method for safe longwall mining of metal deposits with false roofs suitable for soft rock formations. Background Technology

[0002] Due to the extremely soft ore body, the original design employed the tunnel caving method for mining. Underground mining operations, including excavation, slag removal, and ore extraction, were all carried out manually using shovels, pneumatic picks, and wheelbarrows. This method involved high labor intensity and low production efficiency. Generally, blasting was not used; ore extraction relied on the natural caving of the ore after the supports were removed. Therefore, the mining boundary could not be controlled. Furthermore, the ore elliptic was poorly developed, making it easy for ore directly above the mining area to cavitate, while ore on the sides of the mining area was less likely to cavitate, resulting in losses. Overburden strata were also easily mixed into the mining area, leading to ore dilution.

[0003] All underground mining and cutting roadways require dense timber support with a support spacing of less than 30cm. The timber is not easy to recycle after use, resulting in high support costs. All personnel underground must work in densely supported roadways, and the timber supports need to be destroyed during mining. Therefore, safety is poor during roadway excavation, mining collapse, and ore extraction. According to the "Safety Regulations for Metal and Non-metallic Mines" (GB16432-2020), the "Standards for Judging Major Accident Hazards in Metal and Non-metallic Mines," and the requirements for hidden disaster investigation, timber and other flammable materials should not be used for permanent support underground. Therefore, the use of large quantities of timber support in mines does not comply with current regulations and policy requirements. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for safe mining of metal deposits with false roofs, suitable for use in soft rock formations. This invention eliminates the need for extensive timber support, resulting in higher mining efficiency and greater safety.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0006] A method for safe mining of metal deposits in soft rock formations using a false roof method includes the following steps: S1, determining the mining sequence and cutting sequence between intermediate ore blocks; S2, mining in the stope using a non-blasting method, cutting the rock mass and extracting ore; S3, immediately filling the stope after mining is completed, the stope filling includes a lower bearing layer and an upper connecting layer, wherein the filling strength of the bearing layer is not less than 4 MPa, and the filling strength of the ordinary layer is not less than 1.5 MPa.

[0007] Preferably, in step S1, the mining sequence between the ore blocks in each middle section adopts a mining sequence from both ends to the middle.

[0008] Preferably, the cutting sequence in step S1 is: mining area ramp → segmented roadway → layered connecting roadway → cutting vein → mining area.

[0009] Preferably, the non-blasting method in step S2 is carried out using a milling machine. The milling machine includes a milling and cutting section, a traveling section, and a shovel transport section. The milling and cutting section uses a cutting head and cutting teeth to break the rock, causing the rock mass to be subjected to compression, tension, and shearing.

[0010] A milling machine is a mechanized equipment capable of cutting rock, loading and transporting, spraying dust, and self-propelled movement. It can replace processes such as rock drilling, blasting, ventilation, loading, and slag removal in the drill-and-blast method. It has advantages such as continuous mining, no blasting damage, controllable over-excavation, reduced support, and improved working environment. The milling machine can also replace the milling head with a breaker hammer, slag rake, etc., to meet the needs of different mining technologies. The biggest feature of the milling machine's rock breaking technology is that there is no blasting vibration, resulting in less damage to the surrounding rock.

[0011] Preferably, the length of each mining area is 20m-30m, and the size of the mining area is 2.5m x 2.5m.

[0012] Preferably, in step S3, the bearing layer is filled with cemented filling grout with a cement-sand ratio of 1:4 (strength not less than 4MPa), and the top layer is filled with cemented filling grout with a cement-sand ratio of 1:8 (strength not less than 1.5MPa).

[0013] Preferably, the height of the supporting layer is 1.3m and the height of the top layer is 1.2m.

[0014] Preferably, after each stope is completed, the bottom slab is cleaned immediately, and a steel mesh is laid on the bottom slab. The steel mesh includes main bars, secondary bars and hanging bars. The hanging bars are hung up, and the main bars and secondary bars are connected together by the hanging bars, maintaining a height of 0.3m from the bottom slab of the filling stope. The main bars are on top and the secondary bars are on the bottom. The intersection of the main bars and secondary bars is tied with wire or welded.

[0015] Preferably, a filling retaining wall is constructed before the stope is filled. A wooden board, brick or reinforced concrete partition wall is built at the intersection of the stope and the layer road as a filling retaining wall. The retaining wall must be sealed to the surrounding area. Drainage holes are reserved at the bottom of the filling retaining wall as drainage channels during stope filling.

[0016] Preferably, before backfilling each stope, a 20-30cm layer of crushed ore is placed on the bottom plate, maintaining an inclination angle of 1°.

[0017] The beneficial effects of this invention are as follows:

[0018] Compared with existing technologies, non-blasting methods are particularly suitable for soft ore bodies, causing less disturbance and damage to the ore body. By filling with a high-strength bearing layer and a low-strength connecting layer, the stability of the false roof after filling is better, and there is no need to use a large amount of timber for support. Safe mining can be achieved under unsafe conditions, and the overall safety is higher. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the mining area structure of the present invention (h1+h2 height is the height of an independent mining area; h3+h4 height is the height of an independent mining area).

[0020] Figure 2 This is a three-dimensional structural diagram of the present invention.

[0021] Figure 3 For the present invention Figure 2 Schematic diagram of the II-II section structure.

[0022] Figure 4 For the present invention Figure 3 Schematic diagram of the III-III sectional view.

[0023] In the diagram: 1. Inclined ramp; 2. Inclined ramp connecting roadway; 3. Segmented horizontal roadway; 4. Layered connecting roadway; 5. Intermediate transport roadway; 6. Passage; 7. Return air filling shaft; 8. High-strength filling; 9. Ordinary filling; 10. Approach under mining; 11. Cutting vein; 12. Connecting to the top layer (low-strength filling body); 13. Bearing layer (high-strength filling body); 14. Stope sidewall (ore body or filling body); 15. Stope. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] When the surrounding rocks of this ore body and its top and bottom plates are breccia and weathered rock groups, most of the rocks are loose and have extremely poor stability. The structural surfaces are well-developed, and the tunnels are prone to deformation. Support measures must be taken during production to ensure production safety. In summary, the engineering geological conditions of the mine are of a complex type.

[0026] Due to the extremely soft ore body, the original design employed the tunnel caving method for mining. Underground mining operations, including excavation, slag removal, and ore extraction, were all carried out manually using shovels, pneumatic picks, and wheelbarrows. This method involved high labor intensity and low production efficiency. Generally, blasting was not used; ore extraction relied on the natural caving of the ore after the supports were removed. Therefore, the mining boundary could not be controlled. Furthermore, the ore elliptic was poorly developed, making it easy for ore directly above the mining area to cavitate, while ore on the sides of the mining area was less likely to cavitate, resulting in losses. Overburden strata were also easily mixed into the mining area, leading to ore dilution.

[0027] All underground mining and cutting roadways require dense timber support with a support spacing of less than 30cm. The timber is not easy to recycle after use, resulting in high support costs. All personnel underground must work in densely supported roadways, and the timber supports need to be destroyed during mining. Therefore, safety is poor during roadway excavation, mining collapse, and ore extraction. According to the "Safety Regulations for Metal and Non-metallic Mines" (GB16432-2020), the "Standards for Judging Major Accident Hazards in Metal and Non-metallic Mines," and the requirements for hidden disaster investigation, timber and other flammable materials should not be used for permanent support underground. Therefore, the use of large quantities of timber support in mines does not comply with current regulations and policy requirements.

[0028] The dip angle of the main ore body is 30-55°, and the height of the middle section should not be too large. The height of the middle section of the existing mine is 20-30m, so the height of the middle section in this study is 20-30mm. When the dip angle of the ore body is large, it is 30m, and when the dip angle of the ore body is small, it is 20m. The mining area is arranged along the strike direction, and the designed production capacity is 40,000 tons per year.

[0029] The technical features of this method are: 1. It is designed for the soft characteristics and conditions of the ore body, eliminating the need for blasting (non-blasting mining), thus reducing disturbance and damage to the ore body; 2. It allows for small mining size, with conventional mining sizes exceeding 3×4m; 3. After mining is completed, a steel mesh is laid on the bottom plate, and the stability of the false roof is improved after backfilling; it enables safe mining under unsafe conditions, resulting in higher overall safety.

[0030] 1) Layout of ore blocks

[0031] The ore blocks are arranged along the strike, with a length of 40-60m and a width equal to the width of the ore body, averaging 6-8m. The height of each section is 10m. The first mining section is 2x2m, and the normal mining section is (2.5x2.5mm~3x3m). Each section is responsible for mining 3-4 layers. The mining sequence between ore blocks in each section follows the mining sequence from both ends to the middle.

[0032] 2) Layout of mining and cutting engineering

[0033] The mining and cutting works mainly include the stope ramp, ramp connecting roadway, segmented level roadway, layered connecting roadway, cutting vein, ore pass, and backfilling return air shaft. Except for the cutting vein, which is located inside the ore body, all other mining and cutting works are arranged in the footwall of the ore body. The various segmented roadways are connected by the stope ramp, and the layered connecting roadways are excavated from the segmented roadways to the ore body. The backfilling return air shaft serves as an emergency safety exit for the stope.

[0034] The cutting sequence is as follows: mining area ramp → segmented roadway → layered connecting roadway → cutting vein → mining area.

[0035] 3) Mining and ore extraction

[0036] Due to the low hardness of the ore body, non-blasting methods were adopted for the mining of this ore body. The design for ore mining used non-blasting milling machines. Most of the preparatory work was arranged in the footwall of the ore body, where the rock was relatively hard and suitable for drilling and blasting.

[0037] The biggest advantage of milling machine rock breaking technology is that it eliminates blasting vibrations and minimizes damage to the surrounding rock. A milling machine mainly consists of three functional parts: a milling and cutting section, a traveling section, and a shovel transport section. The milling and cutting section uses a cutting head and cutting teeth to break the rock. As the cutting teeth rotate, they penetrate the rock mass, causing compression, tension, and shearing. When the rock's strength is exceeded, the rock mass is destroyed. The damage to the surrounding rock caused by mechanical rock breaking is negligible compared to blasting methods. The traveling section can be tracked or wheeled, both driven by electro-hydraulic systems, and is primarily responsible for the milling machine's movement. This design selects a tracked type.

[0038] The shovel plate transport unit is mainly responsible for muck removal, similar in principle to a muck rake. It uses a milling head to push the rock onto the shovel plate, and then a self-contained belt conveyor transports it to the rear of the milling machine for loading. This achieves all the functions of a muck rake. Therefore, the milling machine is a mechanized equipment capable of cutting rock, loading and transporting, dust suppression spraying, and self-propelled operation. It can replace drilling, blasting, ventilation, loading, and muck removal processes in the drill-and-blast method, offering advantages such as continuous mining, no blasting damage, controllable over-excavation, reduced support requirements, and improved working environment. The milling head can also be replaced with a hydraulic breaker or muck rake head to meet the needs of different mining technologies.

[0039] When the mining area is arranged along the strike of the ore body, the layered connecting roadway is excavated from the segmented roadway to the center of the mining area, and the cross vein is cut until the hanging wall of the ore body. Then, mining is carried out by dividing the mining area along the strike of the ore body. The length of each mining area is 20-30m, and the size of the mining area is 2.5x2.5m. When the stopes are arranged perpendicular to the ore body strike, the layered connecting roads are excavated from the segmented roadways towards the center of the panel stopes, cutting along the vein and the boundary of the footwall ore body. Then, mining is carried out in the form of horizontal stopes perpendicular to the ore body strike. The length of each stope is equal to the ore body thickness, and the stope dimensions are 2.5 x 2.5 m. It is designed that two stopes are mined simultaneously in one panel (excluding backfill stopes). The selection of the mining stopes adopts the method of mining two at a time, and the two sides of the mining stopes are either ore body or solidified backfill, which is conducive to the stability of the stopes. When a stope is mined out, backfilling operations are carried out immediately. When all mining stops in one layer are mined out, mining begins in the next layer. When the ore body thickness is greater than 10 m, the mining stops of the upper and lower layers need to be arranged vertically and alternately. When the ore body thickness is less than 10 m, the mining stops of the upper and lower layers need to be arranged in a diamond pattern and alternately.

[0040] 4) Filling

[0041] After each stope is mined, it needs to be backfilled immediately. The stope backfilling is divided into two parts: high-strength backfilling of the lower bearing layer (bearing layer) and backfilling of the upper ordinary layer (connecting to the top layer). The strength of the high-strength backfilling of the lower bearing layer shall not be less than 4MPa, and the strength of the ordinary layer backfilling shall not be less than 1.5MPa. The cemented backfilling method is used to backfill the stopes after mining. The lower part of the stope (1.2m high) is backfilled with cemented backfilling slurry with a cement-sand ratio of 1:4 (strength not less than 4MPa), and the upper part (1.3m high) is backfilled with cemented backfilling slurry with a cement-sand ratio of 1:8 (strength not less than 1.5MPa). (Mining proceeds from top to bottom. The bottom of the upper layer is filled with a steel mesh, which then becomes the top of the next layer. Therefore, when the total height is 2.5m, the lower 1.2m is filled with high-strength material to form the top of the next layer, ensuring good safety. The upper 1.3m is filled with low-strength material, which has no impact on the next layer, ensuring filling quality while saving costs.) See appendix below. Figure 1 Among them, h1=1.2m, h2=1.3m, h3=1.2m, h4=1.3m.

[0042] After each stope is completed, the bottom slab is immediately cleaned, and a steel mesh is laid on the bottom slab. The steel mesh includes main bars, secondary bars, and hanging bars. The main bars have a diameter of φ12mm and a spacing of 600mm; the secondary bars have a diameter of φ10mm and a spacing of 300mm; and the hanging bars have a diameter of φ10mm and a spacing of 1200mm. The hanging bars are then hung to connect the main bars and secondary bars together, maintaining a height of 0.3m from the bottom slab of the filling stope. The main bars are on top, and the secondary bars are on the bottom. The intersections of the main and secondary bars are tied or welded with 24# iron wire. In the first-step backfilling stope, the main bars and secondary bars extend 0.2~0.3m beyond the adjacent stope side to connect with the steel mesh of the adjacent stope. At the same time, a filling retaining wall is constructed, leaving drainage holes, and then filling is carried out.

[0043] Before backfilling the stope, a backfilling retaining wall needs to be constructed. At the intersection of the stope and the stratification roadway, a wooden board, brick or reinforced concrete partition wall should be built as a backfilling retaining wall. The backfilling retaining wall must be firm and reliable, and the retaining wall must be sealed to the surrounding area to prevent water and backfilling slurry from seeping in. Drainage holes should be reserved at the bottom of the backfilling retaining wall as drainage channels during stope backfilling.

[0044] Recommendation: Before backfilling each stope, a 20-30cm layer of crushed ore should be placed on the bottom plate, with a 1° inclination angle, to facilitate the subsequent backfilling and roof connection. If it is not possible to ensure that the backfilling stope has a certain angle, then an artificial backfilling trench needs to be constructed. The purpose is to ensure that the backfilling pipeline can be installed at the highest point of the backfilling area when the next layer is backfilled, so as to ensure the backfilling and roof connection rate.

[0045] 5) Ventilation

[0046] Fresh air enters from the intermediate transport roadways, then flows along the ramps into the segmented horizontal roadways. Local ventilation is used in the area from the segmented horizontal roadways to the working face of the mining area. Stale air is discharged from the backfilling return air shaft to the upper and middle section return air roadways, and finally discharged to the surface from the return air shaft.

[0047] 6) Roof management

[0048] Because non-blasting mining is used, the impact on roof and side stability is minimal. Since the roof is an artificial false roof, its stability is good and it generally does not require support. However, if the roof filling quality does not meet design requirements, steel arch frames or shotcrete and anchor mesh support are necessary. Due to the soft ore body, ore collapses may occur on both sides of the stope during mining. Therefore, the focus of roof management in this mining method is on stopes where the sidewalls are composed of primary ore bodies. Because the roof is relatively stable, the sidewalls can be supported using anchor mesh beams + steel supports. In highly fractured areas, advanced anchor bolts can be used for sidewall support.

[0049] 7) Side slope management (side slope support plan)

[0050] The mine's working roof is an artificial false roof with good stability. The main support targets are the loose and weak ore bodies on both sides of the working area. Domestically and internationally, the common support method for soft soil roadways is anchor mesh + steel arch support. Considering the mine's engineering geological conditions, mining methods, and actual production conditions, the design adopts steel support + anchor mesh beam support.

[0051] The support equipment is a wet concrete spraying machine, specifically an HSPM-12-10-22 model. This equipment is ideal for concrete construction in confined spaces in mines: the spraying volume is continuously adjustable (stepless speed control); it can be equipped with trackless tires for easy movement and simple maintenance; it has high pumping pressure and a long conveying and spraying distance; it has low rebound rate, which can be reduced to below 10% during wet spraying; it is a customized model and can also be used as a concrete mixer, making it a multi-purpose machine.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for safe longwall mining using a false roof in soft rock formations of metal deposits, characterized in that, Includes the following steps: S1. Determine the mining sequence and the cutting sequence between the intermediate ore blocks; S2. Non-blasting methods are used for mining within the stope to cut the rock mass and extract ore. S3. After each stope is completed, backfilling shall be carried out immediately. Stope backfilling includes the lower bearing layer and the upper connecting layer. The backfilling strength of the bearing layer shall not be less than 4MPa, and the backfilling strength of the connecting layer shall not be less than 1.5MPa. Before backfilling the mining area, a backfilling retaining wall is constructed. A wooden board, brick or reinforced concrete partition wall is built at the intersection of the mining area and the layer road as a backfilling retaining wall. The retaining wall must be sealed to the surrounding area. Drainage holes are reserved at the bottom of the backfilling retaining wall as drainage channels during mining area backfilling. Before backfilling each stope, a 20-30cm layer of crushed ore is placed on the floor, maintaining a 1° inclination angle.

2. The method for safe mining of metal deposits with false roofs in soft rock formations according to claim 1, characterized in that, In step S1, the mining sequence between the ore blocks in each middle section adopts the mining sequence from both ends to the middle.

3. The method for safe mining of metal deposits with false roofs in soft rock formations according to claim 1, characterized in that, The cutting sequence in step S1 is as follows: mining area ramp → segmented roadway → layered connecting roadway → cutting vein → mining area.

4. The method for safe mining of metal deposits with false roofs in soft rock formations according to claim 1, characterized in that, In step S2, the non-blasting method is carried out using a milling machine. The milling machine includes a milling and cutting section, a traveling section, and a shovel transport section. The milling and cutting section uses a cutting head and cutting teeth to break the rock, causing the rock mass to undergo compression, tension, and shearing.

5. The method for safe mining of metal deposits with false roofs in soft rock formations according to claim 1, characterized in that, Each stope is 20m-30m long and measures 2.5m x 2.5m.

6. The method for safe mining of metal deposits with false roofs in soft rock formations according to claim 1, characterized in that, In step S3, the bearing layer is filled with cemented filling grout with a cement-sand ratio of 1:4 and a strength of not less than 4MPa; the top layer is filled with cemented filling grout with a cement-sand ratio of 1:8 and a strength of not less than 1.5MPa.

7. The method for safe mining of metal deposits with false roofs in soft rock formations according to claim 6, characterized in that, The height of the supporting layer is 1.3m, and the height of the top layer is 1.2m.

8. The method for safe mining of metal deposits with false roofs in soft rock formations according to claim 1, characterized in that, After each stope is completed, the bottom slab is immediately cleaned and a steel mesh is laid on it. The steel mesh includes main bars, secondary bars, and hanging bars. The hanging bars are then hung to connect the main bars and secondary bars together, maintaining a height of 0.3m from the bottom slab of the filling stope. The main bars are on top and the secondary bars are on the bottom. The intersections of the main and secondary bars are tied with wire or welded.

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