A method for recovering pillars between workings in gently inclined thin and medium thick ore bodies

Abstract

The application discloses a kind of gentle inclined thin and medium thick ore body stope inter-column recovery methods, comprising the following steps: S1, determine recovery unit and mining sequence;S2, mining engineering arrangement;S3, recovery unit advance pressure relief and pre-splitting;S4, mechanized continuous recovery, transportation and support;S5, after constructing filling retaining wall in the bottom of recovery unit, subsequent filling is carried out, bagged gravel filling recovery unit and ore roadway corner is used, and the ore roadway is expanded and brushed to the next adjacent recovery unit to carry out ore body advance pre-splitting and pressure relief, to prepare for the recovery of the next recovery unit;The method requires simple equipment, easy to operate, safe, efficient and economical, low ore loss and dilution, and can safely and effectively control the stability of stope surrounding rock and the occurrence of rock dynamic disaster during mining, and has broad application prospect.

Description

Technical Field

[0001] This invention relates to the field of underground mining technology, and in particular to a method for recovering pillars between stopes in gently dipping thin and medium-thick ore bodies. Background Technology

[0002] Mineral resources are a vital material foundation for national economic and social development, and their development and utilization are an essential requirement for modernization. However, the large-scale, high-intensity, and extensive overexploitation in recent decades has led to the gradual depletion of easily minable high-grade mineral resources, forcing underground mining to venture into complex and difficult-to-mine bodies such as deep ore bodies, soft and fractured ore bodies, and low-grade ore bodies. Given the limitations of existing mining technologies and equipment, how to safely, efficiently, and environmentally develop complex and difficult-to-mine bodies is one of the major bottlenecks currently facing mines.

[0003] Mining gently dipping thin and medium-thick ore bodies has always been a key focus and challenge in the mining industry. This is because the gentle dip angle (5°–30°) is unfavorable for the uphill operation of mining machinery. Currently, few rock-breaking equipment can break through slopes exceeding 25°, and steeper slopes hinder stope management and safe operations. Furthermore, the gentle dip angle also makes it difficult to throw blasted rock, and the broken ore from drill-and-blast methods is difficult to slide naturally into the stope floor structure, limiting the application of most mining methods. To create conditions for trackless equipment operation, pseudo-dipping methods are commonly used in the mining of gently dipping ore bodies. Ore blocks are generally divided into stops and pillars. Pillars include top and bottom pillars and inter-pillars between stops, providing crucial protection for the safe recovery of stops, but increasing ore loss. Currently, engineers often recover the top, bottom, and pillars of stops by designing new bottom structures, constructing artificial false bottoms and tops with reinforced concrete, and using post-mining secondary drill-and-blast methods, thereby significantly improving ore recovery rates.

[0004] However, there are few reports on technologies for recovering pillars in gently dipping ore bodies. The width of pillars within each block is generally 5-15m, resulting in a significant waste of mineral resources. Therefore, there is an urgent need to invent a method for recovering pillars in gently dipping ore bodies to achieve efficient development and utilization of mineral resources. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for recovering pillars between stopes in gently dipping thin and medium-thick ore bodies.

[0006] This invention provides a method for recovering pillars between stopes in gently dipping thin and medium-thick ore bodies. First, the mining units are divided according to the pillar size and rock mass stability to determine the mining sequence. Second, the cutting and mining works are arranged to create conditions for ventilation, pedestrian and transportation, and backfilling. Third, pre-splitting holes are drilled in the center of the mining unit and advanced pre-splitting is performed to concentrate stress relief and increase rock cutability. Next, a self-constructing base platform is used with a tunneling machine for continuous mechanical cutting and ore extraction. After ore is transported and extracted by a loader, hydraulic props, I-beams, and rubber airbags are used for temporary and permanent support. Finally, after the ore body of the mining unit is mined, a backfilling retaining wall is constructed at its bottom, and the mining backfilling system is used for subsequent backfilling of the mining unit.

[0007] The solution of the present invention is:

[0008] A method for recovering pillars between stopes in a gently dipping ore body includes the following steps:

[0009] S1. Determine the mining units and mining sequence.

[0010] Based on the spacing between ore blocks and the stability level of the rock mass, the inter-pillar is divided into several strips along the horizontal direction, with each strip serving as a mining unit. The mining sequence is as follows: one mining unit is pre-fracturing for future use, one mining unit is currently being mined, and one mining unit is backfilled after mining. The length of each mining unit is the inclined length of the inter-pillar (not exceeding 200m), the width of each mining unit is 4-8m, and the height of each mining unit is the thickness of the ore body. Each mining unit undergoes processes such as pre-decompression and pre-fracturing, mechanical mining and support, and subsequent backfilling.

[0011] S2, Mining and Cutting Engineering Layout

[0012] Based on the existing stage transport roadways and stage return air roadways of the ore block, a new through-vein is constructed that is perpendicularly connected to the stage return air roadways and leads to the inter-pillar, a bypass connecting the stage transport roadways and the ore extraction roadways for trackless transportation, pedestrians and ventilation, an ore extraction roadway connecting the mining unit stope and the bypass, and a ore chute connecting the ore extraction roadways and the stage transport roadways for storage and ore discharge, which leads to the mining unit and forms a production system for ventilation, pedestrian transportation, filling and compressed air power supply and drainage.

[0013] S3, Pre-stress relief and pre-fracking of the longwall mining unit

[0014] A pre-splitting hole with a diameter of 60–150 mm is drilled parallel to the dip surface of the ore body at the center of the mining unit section using a deep-hole drilling rig. Pre-splitting of the rock mass is then performed from the bottom of the hole to the opening using loosening blasting or hydraulic fracturing methods, either in a backward motion or from the opening to the bottom. This releases concentrated high stress in the ore body and increases its cutability. Simultaneously, the pre-splitting hole, connecting the stope and the cross-section, also serves as a ventilation guide in the stope.

[0015] S4, Mechanized continuous mining, transportation and support

[0016] Under the premise of pre-fracture and depressurization of the ore body in the mining unit, a tunneling machine is used to mechanically cut and continuously excavate the ore body in the mining unit, mining the full thickness in one pass. Based on the fallen broken ore, the tunneling machine uses the floor to level the ore and gradually construct triangular platforms. The ore unloaded at the tail of the tunneling machine is shoveled by a loader with a large climbing capacity to the ore pass in the ore extraction roadway, and then unloaded onto the belt conveyor in the stage transport roadway to be transported out of the stope. Subsequently, hydraulic props, I-beams, rubber airbags, and metal mesh are used to provide temporary and permanent support for the excavated surrounding rock.

[0017] S5, Subsequent backfilling of the mining unit

[0018] A backfill retaining wall of a certain thickness is constructed at the bottom of the mining unit. The backfilling system is used to introduce the backfilling pipe from the stage return airway through the cross-cutting vein to the upper part of the mining unit. The goaf is then backfilled according to a certain ratio and mass concentration. During the backfilling process, bagged crushed stone is used to fill the corners of the mining unit and the ore extraction roadway, and the ore extraction roadway is widened and scoured to connect to the next adjacent mining unit for pre-fracture and pressure relief of the ore body, in preparation for the mining of the next mining unit.

[0019] As a preferred technical solution, the width of the mining unit is based on the principle of dividing the width of the inter-pillar into integers, with a smaller value used when the surrounding rock is unstable and a larger value used when it is stable. The length of the mining unit is the inclined length of the inter-pillar, ≤200m, to prevent large deviations in the drilling of the pre-splitting holes.

[0020] As a preferred technical solution, the cross-section of the mining and cutting project is rectangular or three-centered arched. The cross-sectional dimensions and slope are designed to meet the requirements of trackless equipment operation, pedestrian passage, and drainage. The tunnel area is ≥15m². 2 The diameter of the ore pass is ≥1.0m.

[0021] As a preferred technical solution, the rock mass pre-splitting is carried out by micro-differential loosening blasting or hydraulic segmented fracturing, proceeding from the bottom of the hole to the opening in segments or from the opening to the bottom of the hole in segments.

[0022] As a preferred technical solution, the rock mass pre-fracturing is carried out using a hydraulic segmented fracturing method, either retreating segmentally from the bottom of the borehole to the orifice or advancing segmentally from the orifice to the bottom. The hydraulic segmented fracturing method employs a hydraulic fracturing system, the equipment of which includes a hydraulic drilling rig with an extendable drill rod, a high-flow-rate high-pressure water pump, and a pressure-resistant plugging device with a borehole diameter matching the pre-fracturing borehole. Fracturing is terminated when the water inflow from both sides of the stope and the water pressure of the high-flow-rate high-pressure water pump significantly decrease. The length of the pressure-resistant plugging device is 1–3 m; the maximum flow rate of the high-flow-rate high-pressure water pump is >200 m³ / h. 3 / min, maximum pump pressure >50MPa. The hydraulic segmented fracturing method enables precise control of crack propagation boundaries and reduces the concentration of cutting dust in the rock mass.

[0023] As a preferred technical solution, the tunneling machine is a cantilever tunneling machine with a cutting power of ≥160kW, which can sequentially cut the full thickness and the cutting section is rectangular; the triangular platform constructed by the shovel plate of the tunneling machine has a length of ≥3m and a slope of ≤18°, which can meet the needs of the tunneling machine's track movement.

[0024] As a preferred technical solution, the permanent support row spacing is 0.4–1.5 m. Each row of support structure consists of three hydraulic props with constant resistance characteristics connected by pins to form a rectangular structure. The hydraulic props are equipped with three-way valves for injection, constant resistance automatic drainage, and discharge. Behind each hydraulic prop, a metal mesh with a steel diameter of Φ6–10 mm and a mesh size of 100–150 mm is evenly installed, along with a disc-shaped rubber airbag with a diameter of 0.3–1.0 m and a thickness of 0.2–0.6 m. The rubber airbag is equipped with a pressure-reducing valve to maintain constant resistance characteristics under pressure deformation. The combined constant resistance effect of the hydraulic props and the rubber airbags ensures the permanent support structure remains in place. Permanent support has the function of preventing deformation under pressure and suppressing sudden energy release that could induce rock dynamic disasters; temporary support uses long strip-shaped I-beams for roof control, with the I-beams evenly spaced along the axis of the strip on the roadway roof, and bound to the hydraulic prop column of the permanent roof support by 2 to 5 sets of steel wire ropes or U-shaped clamps; the I-beams are of type 16 to 22, with a length of 3 to 5 meters and a quantity of 3 to 7; during ore cutting, the I-beams are moved forward manually and re-fixed to support the exposed roof; during permanent support, the I-beams are moved backward manually to create support space for the permanent support operation.

[0025] As a preferred technical solution, in the subsequent backfilling process, the ash-sand ratio of the backfill slurry is ≤1:8 and the mass concentration is ≥65%, ensuring that the backfill body has a certain self-stabilizing ability when the adjacent mining unit is exposed; the backfill retaining wall is made of reinforced concrete with a thickness of ≥20cm and a grade of C20 or above.

[0026] A method for recovering pillars in gently dipping thin and medium-thick ore bodies using the above-mentioned technical solution includes the following steps: S1. Determining the mining units and mining sequence: Based on the spacing between ore blocks and the stability level of the rock mass, the pillars are divided into several strips along the horizontal direction, with each strip serving as a mining unit. The mining sequence is as follows: one mining unit is pre-fracturing for future use, one mining unit is currently being mined, and one mining unit is backfilled after mining. The length of the mining unit is the inclined length of the pillar (not exceeding 200m), the width of the mining unit is 4-8m, and the height of the mining unit is the thickness of the ore body. Each mining unit undergoes processes such as pre-stressing and pre-fracturing, mechanical mining and support, and subsequent backfilling. S2. Layout of the mining and cutting engineering: Based on the existing stage transport roadways and stage return air roadways of the ore blocks. The project includes the construction of a new through-vein perpendicularly connected to the stage return airway and leading to the inter-pillar; a bypass connecting the stage transport roadway and the ore extraction roadway for trackless transport, pedestrians, and ventilation; an ore extraction roadway connecting the mining unit stope and the bypass; and a series of ore chute cutting works connecting the ore extraction roadway and the stage transport roadway for storage and ore discharge, leading to the mining unit and forming a production system for ventilation, pedestrian transport, backfilling, compressed air, power supply, and drainage. S3 involves pre-fracturing and decompression of the mining unit. A pre-fracturing hole with a diameter of 60-150 mm, parallel to the dip surface of the ore body, is drilled at the center of the mining unit cross-section using a deep-hole drilling rig. Pre-fracturing is performed from the bottom to the top of the hole using loosening blasting or hydraulic fracturing methods, either in a backward motion or from the top to the bottom, to release concentrated high stress in the ore body and increase its cutability. Simultaneously, the pre-fracturing hole connecting the stope and the through-vein also serves as a ventilation guide in the stope. S4. Mechanized continuous mining, transportation, and support: Under the premise of pre-fracture and depressurization of the ore body in the mining unit, a tunneling machine is used to mechanically cut and continuously excavate the ore body in the mining unit, mining the full thickness in one pass. Based on the fallen broken ore, the tunneling machine uses the floor to level the ground and gradually construct triangular platforms. The ore unloaded at the tail of the tunneling machine is shoveled by a loader with a large climbing ability to the ore pass in the ore passage, and then unloaded onto the belt conveyor in the stage transportation roadway to be transported out of the stope. Subsequently, hydraulic props, I-beams, rubber airbags, and metal mesh are used to provide temporary and permanent support for the excavated surrounding rock. S5. Subsequent backfilling of the mining unit: A backfilling retaining wall of a certain thickness is constructed at the bottom of the mining unit. The backfilling pipe is introduced into the upper part of the mining unit through the stage return airway using the mine backfilling system. The goaf is then backfilled according to a certain ratio and mass concentration. During the filling process, bagged crushed stone is used to fill the corners of the mining unit and the ore extraction roadway, and the ore extraction roadway is widened and brushed to the next adjacent mining unit for pre-splitting and depressurization of the ore body, in preparation for the mining of the next mining unit.

[0027] Advantages of this invention:

[0028] (1) The use of pre-decompression and pre-splitting methods disperses the concentrated stress of the ore body and improves the cutability of the ore body and the water content of the rock body. Through pre-splitting, the complete and hard rock body is transformed into a fractured rock body, making it possible for the tunneling machine to continuously mine ore. This subverts the traditional drilling and blasting method with its complex processes and multiple processes.

[0029] (2) The tunneling machine cuts the ore and the shovel loader unloads the ore, achieving parallel operation. The ore blocks cut by mechanical cutting are relatively small, which provides the prerequisite for the use of belt conveyors in the stage roadways and greatly improves the production and transportation efficiency of the mining area.

[0030] (3) The permanent support structure adopts the form of "rubber airbag + hydraulic prop + metal mesh", which has strong constant resistance characteristics and deformation capacity, and has significant effect on controlling deformation and buffering energy release in the surrounding rock of dynamic pressure roadways.

[0031] (4) The tunneling machine’s own shovel and tracks are used to construct a triangular working platform through flattening, which enables the tunneling machine to adapt to large-angle ore bodies and meet the safety requirements of climbing and cutting operations. Attached Figure Description

[0032] Figure 1 This is a front view of the mining method according to Embodiment 1 of the present invention;

[0033] Figure 2 This is a side view of the mining method AA according to Embodiment 1 of the present invention;

[0034] Figure 3 This is a side view of the mining method BB according to Embodiment 1 of the present invention;

[0035] Figure 4 This is a CC side view of the mining method of Embodiment 1 of the present invention;

[0036] Figure 5 This is a side view of the mining method DD according to Embodiment 1 of the present invention;

[0037] Figure 6 This is a top view of the mining method EE according to Embodiment 1 of the present invention;

[0038] Figure 7 This is a top view of the mining method FF according to Embodiment 1 of the present invention;

[0039] Figure 8 This is a cross-sectional view of the mining unit in Embodiment 1 of the present invention;

[0040] Figure 9 This is a structural diagram of the rubber airbag of Embodiment 1 of the present invention;

[0041] Among them, 1-stope; 2-reinforced concrete; 3-pillar; 4-stage haulage roadway; 5-stage return airway; 6-through vein; 7-bypass; 8-mining roadway; 9-ore chute; 10-mining unit; 11-ore; 12-tunneling machine; 13-filling body; 14-filling retaining wall; 15-bagged crushed stone; 16-pre-splitting hole; 17-crack; 18-incline; 19-triangular platform; 20-hydraulic prop; 21-three-way valve; 22-metal mesh; 23-rubber airbag; 24-pressure reducing valve; 25-I-beam. Detailed Implementation

[0042] This invention provides a method for recovering pillars between stopes in gently dipping thin and medium-thick ore bodies.

[0043] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0044] Example 1

[0045] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 and Figure 9 As shown; First, based on the dimensions of the pillars 3 between the pillars 1 and the stability of the surrounding rock, several mining units are divided along the strike of the pillars 3. The dimensions of mining units 10 (between 4-8m) are determined based on the principle of integer division and the direct proportionality of surrounding rock stability, forming a mining sequence of "one pre-fractured unit for standby, one currently being mined, and one post-mining backfill." Second, based on the existing preparatory works of the ore block, new mining and cutting works are constructed to serve the mining of the pillars 3. These include a through-cutting 6 perpendicularly connected to the stage return airway 5 and leading to the pillars 3; a bypass 7 connecting the stage transport roadway 4 and the ore extraction roadway 5 for trackless transport, pedestrians, and ventilation; an ore extraction roadway 8 connecting the mining unit 10 stope and bypass 7; and a series of mining and cutting works, including a ore pass 9 connecting the ore extraction roadway 8 and the stage transport roadway 4 for storage and ore discharge, leading to mining unit 10 and forming a production system serving the pillar mining. The area of ​​the aforementioned mining and cutting roadways is not less than 15m². 2 The diameter of the ore pass 9 shall not be less than 1.0m. Next, a pre-splitting hole 16, 60-150mm deep, penetrating the entire inter-pillar, is drilled in the center of the mining unit 10 to connect the mining unit 10 stope with the cross-cut 6. This hole serves as a pre-splitting mechanism for the ore body in the mining unit 10 and for stope ventilation. Rock mass pre-splitting is performed from the bottom of the hole to the opening using loosening blasting or hydraulic fracturing methods, either in a retreating manner or from the opening to the bottom, resulting in a uniformly distributed network of fractures 17 in the rock mass surrounding the pre-splitting hole 16. This aims to release concentrated high stress in the ore body and increase its cutability.

[0046] After the pre-splitting of the mining unit 10 is completed, the tunneling machine 12 is used to mechanically cut the ore body of the mining unit 10 and continuously cut the ore, mining the full thickness in one go. Based on the fallen broken ore 11, the tunneling machine 12 is used to level the bottom plate and gradually construct a triangular platform 19. The ore 11 unloaded from the tail of the tunneling machine 12 is shoveled by a loader with a large climbing ability to the ore pass 9 in the ore exit roadway 8, and then unloaded onto the belt conveyor in the stage transport roadway 5 to be transported out of the mining area.

[0047] Subsequently, hydraulic props 20, rubber airbags 23, and metal mesh 22 were used to permanently support the surrounding rock after excavation. The suspended roof after the strip cutting of the ore was temporarily supported by manually erecting I-beams 25.

[0048] Finally, after the mining of unit 10 is completed, a concrete backfill retaining wall 14 with a thickness of more than 20cm is constructed at its bottom. The backfilling pipeline is introduced into the upper part of unit 10 via the stage return airway 4 and the cross-cutting vein 6 using the mine backfilling system. The goaf is then backfilled according to a certain mix ratio and mass concentration. During the backfilling process, bagged crushed stone 15 is used to fill the corners of unit 10 and the ore extraction roadway 8, and the ore extraction roadway 8 is widened and extended to the next adjacent unit 10 for pre-splitting and depressurization of the ore body, in preparation for the mining of the next unit.

[0049] The steps of the present invention are described below with reference to an embodiment:

[0050] The ore body of a certain phosphate mine is a sedimentary type of phosphorite, with a P2O5 grade of 25%, a thickness of 4.0m, a dip angle of 25°, and a burial depth of 300-800m. It is a typical gently dipping ore body with moderate ore stability and simple geological conditions. The mine's central section is 40m high, with the preparatory works arranged outside the vein. The ore block is 50m long, with an 8m wide inter-pillar. A 5m thick concrete false bottom is constructed to replace the original pillars, and no top pillar is left. The mine employs a pseudo-dipping strip drilling and blasting method, with a strip width of 5m. The stope is filled with cement-sand ratio 1:8 and a mass concentration of 68% cementitious tailings. The stope production capacity is 200t / d, the stope recovery rate is 86%, and the dilution rate is 8%. The existing mining and cutting roadways all have a cross-sectional dimension of 5×4m. 2 The anchor mesh spraying process is used for support.

[0051] In view of the above conditions, the implementation steps of the method of the present invention are as follows:

[0052] (S1) Determine the mining unit and mining sequence: Based on the size of the inter-block pillar 3 and the stability level of the ore rock mass, the inter-block pillar 3 between the ore blocks is divided into two mining units 10 along the ore body strike, with each mining unit having a width of 4m; at the same time, the mining preparation sequence is determined according to the mining sequence of "one pre-fractured for standby, one currently being mined and one post-mining backfill".

[0053] (S2) Layout of mining and cutting works: Construct a series of new mining and cutting works (cross-sectional area not less than 15m²) 2 The production system is formed, specifically including the through vein 6 which is vertically connected to the stage return airway and leads to the inter-pillar 3; the bypass 7 which connects the stage transport roadway 4 and the ore extraction roadway 5 for trackless transportation, pedestrians and ventilation; the ore extraction roadway 8 which connects the mining unit 10 stope and the bypass 7; and the ore chute 9 (diameter not less than 1.0m) which connects the ore extraction roadway 8 and the stage transport roadway 4 for storage and ore discharge, creating conditions for ventilation of mining materials and ore, pedestrian transportation, ore extraction and backfilling, and power supply and drainage.

[0054] (S3) Pre-fracturing and stress relief in the mining unit: Using an XTDL-4 deep-hole drilling rig, a 90mm diameter pre-fracturing hole 16 parallel to the dip surface of the ore body is drilled at the center of the mining unit 10 section. A hydraulic fracturing system (ZF-A90 plugs, BZW200 / 31.5 water pumps, and a ZDY3500L hydraulic geological drilling rig with matching drill rods) is used to perform backward-moving, segment-by-segment pre-fracturing from the bottom of the hole to the opening, with a fracturing interval of 1.0m. This is to release the concentrated high stress in the ore body of mining unit 10 and increase the shearability and water content of the ore body. Through the hydraulic fracturing process, a uniformly distributed network of fractures 17 is formed in the rock mass of the strip section around the pre-fracturing hole 16. Simultaneously, the pre-fracturing hole 16, connecting the mining unit 10 stope and the cross-section 6, also serves as a ventilation guide in the stope.

[0055] (S4) Mechanized continuous mining, transportation, and support: After the pre-splitting is completed, an EBZ320 roadheader 12 is used to construct a triangular platform 19 with a length of not less than 3m and a slope of not more than 18° on the bottom plate using the leveling function. The roadheader 12 performs mechanical cutting on the triangular platform 19 to extract the ore in one pass, and the stripped ore 11 is unloaded at the tail of the roadheader 12. The AtlasCopco2 loader is used to transport the ore 11 from the mining unit 10 to the chute 9 next to the ore extraction roadway 8, and then unloads it onto the belt conveyor in the stage transport roadway 4 to be transported out of the mining area. After excavation, three hydraulic props 20, each equipped with a three-way valve 21, are connected to form a rectangular support structure with a row spacing of 1.0m. The hydraulic props have a lifting range of 3-6m and a diameter of 30cm. Behind each hydraulic prop 20 is a metal mesh 22 with a mesh opening of 100mm and a steel bar diameter of 6mm, and a rubber airbag 23 with a pressure reducing valve 24, a diameter of 0.5m, and a thickness of 0.3m. The pressure threshold of both the three-way valve 21 and the pressure reducing valve 24 is set to 40MPa. When the surrounding rock pressure exceeds 40MPa, the three-way valve 21 maintains constant resistance and deformation to reduce pressure by automatically releasing oil, while the pressure reducing valve 24 maintains constant resistance to adapt to large deformations of the surrounding rock by releasing air. The constant resistance function of both valves can also adapt to the sudden release of high elastic energy, effectively suppressing the occurrence of rock dynamic disasters. In addition, four 3.0m long No. 16 I-beams 25 are installed at intervals on the hydraulic props 20 on the roof, and are manually pushed to the face for temporary support of the unsupported roof.

[0056] (S5) Subsequent backfilling of the mining unit: After the first mining unit 10 is completed, a 0.3m thick C30 reinforced concrete backfilling retaining wall is constructed at its bottom. The backfilling pipeline is introduced into the upper part of the mining unit via the stage return airway 5 and the cross-cutting vein 6 using the mine backfilling system. Subsequent backfilling is carried out on the goaf according to the lime-sand ratio of 1:6 and the mass concentration of 68%. During the backfilling process, bagged crushed stone 15 is used to fill the corners of mining unit 10 and the ore extraction roadway 8, and the ore extraction roadway 8 is widened and connected to the next adjacent mining unit 10 for pre-splitting and depressurization of the ore body, in preparation for the mining of the next mining unit.

[0057] In this invention, pre-splitting increases the cutability of the ore body and the water content of the rock mass, creating favorable conditions for mechanized and efficient cutting of ore by tunneling machines and reducing dust pollution during cutting. The application of hydraulic supports with constant resistance characteristics, rubber airbags, and I-beams enables temporary and permanent supports to effectively control large deformations of the surrounding rock and sudden energy release without damage, providing an important reference for roadway and stope support under fractured and soft rock conditions. Through the application of this method, the stope production capacity reached 280 t / d, the recovery rate of the pillar ore body reached 94%, and the dilution rate was 3%.

[0058] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for recovering pillars between stopes in gently dipping thin and medium-thick ore bodies, characterized in that, Includes the following steps: S1. Determine the mining units and mining sequence. Based on the spacing between ore blocks and the stability level of the rock mass, the inter-pillar is divided into several strips along the horizontal direction. Each strip is used as a mining unit. The mining sequence is as follows: one mining unit is pre-fractured for future use, one mining unit is being mined, and one mining unit is backfilled after mining. The length of the mining unit is the inclined length of the inter-pillar, the width of the mining unit is 4 to 8 m, and the height of the mining unit is the thickness of the ore body. S2, Mining and Cutting Engineering Layout Based on the existing stage transport roadways and stage return air roadways of the ore block, a new through-passage is constructed that is perpendicularly connected to the stage return air roadway and leads to the inter-pillar. A bypass roadway connecting the stage transport roadway and the ore extraction roadway is provided for trackless transportation, pedestrians and ventilation. An ore extraction roadway connects the mining unit stope and the bypass roadway. A ore chute is constructed connecting the ore extraction roadway and the stage transport roadway for storage and ore discharge. The chute cutting project leads to the mining unit and forms a production system for ventilation, pedestrian transportation, filling and compressed air power supply and drainage. S3, Pre-stress relief and pre-fracking of the longwall mining unit Using a deep-hole drilling rig, a pre-splitting hole with a diameter of 60-150 mm is drilled in the center of the mining unit section, parallel to the inclined surface of the ore body. The rock mass is pre-splitting is carried out segment by segment inside the hole. S4, Mechanized continuous mining, transportation and support Under the premise of pre-fracture and depressurization of the ore body in the mining unit, a tunneling machine is used to mechanically cut the ore body in the mining unit continuously to extract the full thickness in one pass. Based on the crushed ore that has fallen, the tunneling machine is used to level the bottom plate and construct triangular platforms in stages. The ore unloaded at the tail of the tunneling machine is shoveled by a loader with a large climbing ability to the ore pass in the ore extraction roadway, and then unloaded onto the belt conveyor in the stage transport roadway to be transported out of the mining area. Subsequently, hydraulic props, I-beams, rubber airbags and metal mesh are used to provide temporary and permanent support for the excavated surrounding rock. S5, Subsequent backfilling of the mining unit A filling retaining wall of a certain thickness is constructed at the bottom of the mining unit. The filling pipeline is introduced into the upper part of the mining unit through the stage return air roadway using the mine filling system. The goaf is then filled according to a certain ratio and mass concentration. During the filling process, bagged crushed stone is used to fill the corners of the mining unit and the ore extraction roadway. The ore extraction roadway is then widened and extended to the next adjacent mining unit for pre-splitting and depressurization of the ore body, in preparation for the mining of the next mining unit.

2. The method for recovering pillars in gently dipping thin and medium-thick ore bodies as described in claim 1, characterized in that: The width of the mining unit is based on the principle of dividing the column width into integers, with a smaller value taken when the surrounding rock is unstable and a larger value taken when it is stable.

3. The method for recovering pillars in gently dipping thin and medium-thick ore bodies as described in claim 1, characterized in that: The cross-section of the mining and cutting project is rectangular or three-centered arch. The cross-sectional dimensions and slope are designed to meet the requirements of trackless equipment operation, pedestrian passage, and drainage. The tunnel area is ≥15m². 2 The diameter of the ore pass is ≥1.0m.

4. The method for recovering pillars in gently dipping thin and medium-thick ore bodies as described in claim 1, characterized in that: The rock mass pre-splitting is carried out by micro-differential loosening blasting or hydraulic segmented fracturing, either by retreating in segments from the bottom of the borehole to the opening or by advancing from the opening to the bottom of the borehole.

5. A method for recovering pillars in gently dipping thin and medium-thick ore bodies as described in claim 4, characterized in that: The rock mass pre-fracture is performed in stages from the bottom of the borehole to the borehole opening using hydraulic fracturing. The hydraulic fracturing system consists of a hydraulic drilling rig with an extendable drill rod, a high-flow-rate, high-pressure water pump, and a pressure-resistant plugging device with a borehole diameter matched to the pre-fractured hole. Fracturing is terminated when water inflow occurs on both sides of the stope and the water pressure of the high-flow-rate, high-pressure water pump drops significantly. The pressure-resistant plugging device has a length of 1–3 m, and the high-flow-rate, high-pressure water pump has a maximum flow rate >200 m³ / h. 3 / min, the maximum pump pressure of the high-flow-rate high-pressure water pump is >50MPa.

6. The method for recovering pillars in gently dipping thin and medium-thick ore bodies as described in claim 1, characterized in that: The tunneling machine is a cantilever tunneling machine with a cutting power of ≥160kW; the triangular platform constructed using the shovel plate of the tunneling machine has a length of ≥3m and a slope of ≤18°.

7. The method for recovering pillars in gently dipping thin and medium-thick ore bodies as described in claim 1, characterized in that: The permanent support is spaced 0.4–1.5 m apart. Each row of support structure consists of three hydraulic props with constant resistance characteristics connected by pins to form a rectangular structure. The hydraulic props are equipped with three-way valves for injection, automatic constant resistance drainage, and discharge. Behind each hydraulic prop, a metal mesh with reinforcing bars of Φ 6–10 mm diameter, a mesh size of 100–150 mm, a diameter of 0.3–1.0 m, and a thickness of 0.2–0.5 mm is evenly installed. A 0.6m disc-shaped rubber airbag is used, equipped with a pressure-reducing valve to maintain constant resistance under pressure deformation. Temporary support utilizes I-beams for roof control, with the I-beams evenly spaced along the axis of the strip on the roadway roof. They are secured to the hydraulic props of the permanent roof support using 2-5 sets of wire ropes or U-shaped clamps. The I-beams are of type 16-22, 3-5m in length, and 3-7 in number. During ore cutting, the I-beams are manually moved forward and re-secured to support the exposed roof. For permanent support, the I-beams are manually moved backward to create support space for the permanent support operation.

8. The method for recovering pillars in gently dipping thin and medium-thick ore bodies as described in claim 1, characterized in that: In the subsequent filling process, the mortar has a cement-sand ratio of ≤1:8 and a mass concentration of not less than 65%; the filling retaining wall is made of reinforced concrete with a thickness of ≥20cm and a grade of C20 or above.

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