Safe and efficient combined mining method for thick and low-grade ore body near surface under the condition of broken ore rock

Abstract

The application provides a safe and efficient combined mining method for near-surface thick and low-grade ore body under the condition of broken ore rock, and belongs to the field of mine exploitation. First, the thickness of the isolation layer is determined through theoretical analysis and numerical simulation; a downward large-diameter deep hole subsequent filling method is used in the first-step stope, horizontal and vertical anchor hole drilling is carried out on the top of the stope, and the vertical anchor hole is connected with the surface; a segmented medium-deep hole subsequent filling mining method is used in the second-step stope, a downward anchor hole is drilled to the ore body boundary on the surface above the stope; after the anchor hole is injected with cement mortar, the anchor cable is connected and prestressed, and a combined anchor cable support system is formed; the first-step stope is filled immediately after mining; after the filling body reaches the predetermined strength, the second-step stope is mined and filled. Through the application of the combined support structure and the mining process, the near-surface thick and low-grade ore body resources can be safely and efficiently mined, the underground resources can be fully utilized, and the sustainable and high-quality development of the mining enterprises can be ensured.

Description

Technical Field

[0001] This invention relates to the field of mining technology, specifically to a safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions. Background Technology

[0002] For underground mining, the extraction of thick, low-grade ore bodies near the surface under fractured rock conditions currently faces severe technical and economic challenges. Given the prohibition of surface subsidence, most mines, due to their complex geological conditions and high mining difficulty, opt for the downward approach method with pre-support, which effectively ensures production safety; if production costs exceed the value of the ore, mining is simply not undertaken. However, the downward approach method with pre-support has high direct production costs and low efficiency, making it difficult to generate economic benefits; while directly abandoning this portion of ore resources would result in significant resource waste and is detrimental to the sustainable and stable development of mining enterprises.

[0003] In view of this, it is necessary to design a safe and efficient joint mining method for thick, low-grade ore bodies near the surface under fractured ore conditions to solve the above problems. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a safe and efficient joint mining method for thick, low-grade ore bodies near the surface under fractured ore conditions, aiming to solve the technical problems of high difficulty, high safety risk and low economic benefits in mining thick, low-grade ore bodies near the surface under fractured ore conditions.

[0005] This application provides a safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions, including the following steps: S1. Based on the ore body occurrence conditions, the thickness of the isolation layer is determined by combining theoretical analysis and numerical simulation. S2. The near-surface ore body is divided into mining areas, and a two-step mining method is adopted: the first-step mining area adopts the downward large-diameter deep hole subsequent backfilling mining method, and the second-step mining area adopts the segmented medium-deep hole subsequent backfilling mining method. S3. Construct a rock drilling chamber at the top of the first-step mining area, and construct horizontal and vertical anchor cable holes at the top of the rock drilling chamber, with the vertical anchor cable holes connected to the ground surface; Construct downward anchor cable holes to the upper boundary of the ore body at the surface location above the two-step mining area; After the anchor cables are placed, cement mortar is injected into all the anchor cable holes. The anchor cables exposed at the holes are connected in series and prestressed to form a combined anchor cable support system. S4. In the first-step mining operation, blasting is carried out through large-diameter blast holes to extract ore, and subsequent backfilling is carried out immediately after the ore is extracted. S5. After the backfill material in the first-step stope reaches the predetermined strength, the second-step stope construction will proceed with blasting and ore extraction through the upward fan-shaped holes, followed by subsequent backfilling.

[0006] As a further improvement of this application, in step S3, the diameter of the anchor cable hole is 80~100mm, and the row spacing and hole spacing of the anchor cable holes are 1~2m.

[0007] As a further improvement of this application, the anchor cable is a steel wire rope with a diameter of 20~25mm, the exposed length of the anchor cable outside the anchor cable hole is greater than 0.3m, and the strength grade of the cement mortar is not lower than M2.5.

[0008] As a further improvement of this application, in step S4, the diameter of the downward large-diameter blast hole is 110~130mm, the row spacing of the blast holes is 2.7~3.0m, and the hole spacing is 2.5~3.0m; the side holes of the row face are parallel to the side wall of the mining area, and the other blast holes on the row face are evenly distributed.

[0009] As a further improvement of this application, the downward large-diameter borehole charging adopts an axially uncoupled charging structure, the air gap length of the side holes is greater than the air gap length of the middle holes, and the charging sections and air gap sections of adjacent boreholes in the same row are staggered.

[0010] As a further improvement of this application, the bottom plugging length of the through hole in the charge structure is 1.2~1.5m, of which the sand filling length is greater than 1.0m.

[0011] As a further improvement to this application, for blast holes where the bottom of the hole does not penetrate the lower mining and cutting works, explosives are directly loaded.

[0012] As a further improvement of this application, in step S5, the diameter of the upward fan-shaped hole is 70~90mm, the hole spacing is 1.8~2.0m, and the hole bottom distance is 2.0~2.2m.

[0013] As a further improvement to this application, the strength of the first-step mining site filling body is ≥2MPa.

[0014] As a further improvement to this application, the strength of the two-step mining site filling body is ≥1MPa.

[0015] The beneficial effects of this application are as follows: This application provides a safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions. For such ore bodies, a two-step mining approach is adopted. First, the thickness of the isolation layer is determined through theoretical analysis and numerical simulation. In the first-step stope, a downward large-diameter deep-hole post-filling method is used, with horizontal and vertical anchor cable holes drilled in the top rock chamber, the vertical anchor cable holes connecting to the surface. In the second-step stope, a segmented medium-deep-hole post-filling mining method is used, with downward anchor cable holes drilled to the ore body boundary on the surface above. After the anchor cables are placed, cement mortar is injected into all anchor cable holes, and the anchor cables at the hole openings are connected in series and prestressed to form a combined anchor cable support system. Backfilling is immediately carried out after blasting and ore extraction in the first-step stope. After the backfill reaches a predetermined strength, upward fan-shaped hole blasting and ore extraction are carried out in the second-step stope, followed by backfilling. This application utilizes a combined structure of grouting long anchor cables (horizontal and vertical) to reinforce near-surface fractured ore, creating a more stable roof environment in the lower stope and effectively preventing roof collapse and surface subsidence. By combining the downward large-diameter deep-hole post-filling mining method and the segmented medium-deep-hole post-filling mining method, the amount of mining and cutting work can be effectively reduced while ensuring the stability of the oreable body's roof, thus decreasing mining and cutting costs. Simultaneously, the optimized charge structure during large-diameter deep-hole mining further reduces the impact of blasting disturbance on the stope sidewalls and ensures that the detonation energy generated by the explosives is evenly distributed across the blasting surface. This reduces explosive consumption per unit and ensures uniform blasting block size, facilitating ore extraction operations.

[0016] The safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions comprehensively considers the application of near-surface fractured ore support structures, mining methods for oreable bodies, and supporting mining technologies. It can safely and efficiently extract these thick, low-grade ore body resources, fully utilize underground resources, and ensure the continuous high-quality development of mining enterprises.

[0017] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0019] Figure 1 This is a schematic diagram of the stope structure for the combined mining method in the embodiments of this application; Figure 2 for Figure 1 Schematic diagram of the mining area structure in the middle II-II direction; Figure 3 for Figure 1 Schematic diagram of the mining area structure in the middle III-III direction; Figure 4 This is a diagram showing the arrangement of large-diameter boreholes facing downwards in Embodiment 1 of this application; Figure 5 This is a schematic diagram of the downward large-diameter borehole charging in Embodiment 1 of this application; Explanation of reference numerals in the attached diagram: 1. Intermediate transport roadway; 2. Mine pass; 3. Mine pass connecting roadway; 4. Mine collection trench; 5. Mine exit access road; 6. First-stage stope backfill; 7. Upward fan-shaped borehole; 8. Horizontal grouting long anchor cable; 9. Vertical grouting long anchor cable; 10. Bottom pillar; 11. Rock drilling chamber; 12. Connecting steel wire rope; 13. Downward large-diameter blast hole; 131. First blast hole; 132. Second blast hole; 133. Third blast hole; 134. Fourth blast hole; 135. Fifth blast hole; 136. Sixth blast hole; 137. Seventh blast hole; 138. Eighth blast hole; 14. Detonating cord and detonating wire; 15. Digital electronic detonator; 16. Sand filling section at the borehole opening; 17. Thin iron wire; 18. Air gap section; 19. Charging section; 20. Sand filling section at the bottom of the borehole; 21. Borehole plug. Detailed Implementation

[0020] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0024] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0025] Underground mining faces a dilemma when the ore is fractured, near the surface, and collapse is not allowed: the downward approach method with advanced support can ensure safety, but it is costly, inefficient, and has poor economic benefits, making it difficult to mine low-grade ore bodies; while abandoning the mine directly would result in a huge waste of resources, which is not only inconsistent with resource recovery policies, but also hinders the sustainable development of the mine.

[0026] To address the technical challenges of mining thick, low-grade ore bodies near the surface under fractured rock conditions, including high difficulty, high safety risks, and low economic benefits, this application provides a safe and efficient combined mining method for such bodies. By applying a combined support structure and mining technology, this method can safely and efficiently extract these thick, low-grade ore body resources, fully utilize underground resources, and ensure the sustainable and high-quality development of mining enterprises.

[0027] Please refer to Figure 1 This application provides a safe and efficient joint mining method for thick, low-grade ore bodies near the surface under fractured ore conditions, including the following steps: S1. Based on the ore body occurrence conditions, a safe and reasonable isolation layer thickness is determined by combining theoretical analysis and numerical simulation. S2. The near-surface ore body is divided into mining areas, and a two-step mining method is adopted: the first-step mining area adopts the downward large-diameter deep hole subsequent backfilling mining method, and the second-step mining area adopts the segmented medium-deep hole subsequent backfilling mining method. S3. Construct a rock drilling chamber 11 at the top of the first-step mining area, and construct horizontal and vertical anchor cable holes at the top of the rock drilling chamber 11, with the vertical anchor cable holes connected to the ground surface; Construct downward anchor cable holes to the upper boundary of the ore body at the surface location above the two-step mining area; After the anchor cables are placed, cement mortar is injected into all the anchor cable holes. The anchor cables exposed at the holes are connected in series and prestressed to form a combined anchor cable support system. S4. In the first-step mining operation, blasting is carried out to extract ore through the large-diameter blast hole 13, and subsequent backfilling is carried out immediately after the ore is extracted. S5. After the backfill body 6 of the first-step stope reaches the predetermined strength, the second-step stope construction will carry out blasting and ore extraction through the upward fan-shaped holes 7, and then carry out subsequent backfilling.

[0028] In the technical solution of this application embodiment, when mining near-surface ore bodies, a certain thickness of isolation layer needs to be left if surface collapse is not allowed. The thickness of the isolation layer is determined by a combination of theoretical analysis and numerical simulation. The theoretical analysis mainly employs six methods: KB Rubeneit formula, thickness-to-span ratio method, load transfer intersection line method, mechanics of materials method, simplified beam theory of structural mechanics, and Protodyakonov theory method. The calculation results of this method are mainly related to the width and height of the stope, with the strongest correlation to the stope width. Based on the theoretical calculation results and combined with the actual occurrence of near-surface ore bodies, a certain safety factor is considered when leaving the isolation layer thickness. The theoretical calculation results can be appropriately amplified, and numerical simulation calculations are performed using FLAC3D. The optimal isolation layer thickness parameters are determined by considering the stress field, displacement field, plastic zone distribution, and equivalent safety factor. The combined anchor cable system actively reinforces the surrounding rock, followed by passive bearing through backfilling, providing dual protection and effectively controlling the risk of collapse of the broken roof. Phased mining and timely backfilling ensure that workers operate under relatively stable backfill or pillars, significantly reducing operational risks. This safe and efficient mining method transforms thick, low-grade ore bodies that were previously too risky and costly to mine economically into valuable assets, greatly improving resource utilization.

[0029] Furthermore, in some embodiments, in step S3, the diameter of the anchor cable hole is 80~100mm, and the row spacing and hole spacing of the anchor cable holes are 1~2m.

[0030] In the technical solution of this application embodiment, in order to ensure that the anchor cable can effectively transfer the tensile force to the surrounding grout (cement mortar), the hole diameter needs to have sufficient clearance; too small a hole diameter will result in insufficient friction between the anchor cable and the grout, or the grout will be too thin, resulting in poor strength and durability. Typically, the row spacing and hole spacing of the anchor cable holes are set to be equal or similar, forming a square or rectangular arrangement, which can make the support stress field distribution more uniform and the stress distribution more reasonable.

[0031] Furthermore, in some embodiments, the anchor cable is a steel wire rope with a diameter of 20~25mm, the exposed length of the anchor cable at the anchor cable hole opening is greater than 0.3m, and the strength grade of the cement mortar is not lower than M2.5.

[0032] In the technical solution of this application embodiment, the wire rope is a flexible structure made of multiple strands of steel wire twisted together. Compared with steel strand (although also made of twisted steel wire, its structure is more compact) or steel bars, the wire rope has higher toughness and ductility. The diameter range of the wire rope provides sufficient cross-sectional area and tensile strength to ensure that a single anchor cable can withstand a certain amount of tension and effectively transfer it to the grouting body and surrounding rock. If it is too thin, the strength will be insufficient, and if it is too thick, the cost will increase and the drilling difficulty will increase. The exposed anchor cable ensures that the anchor cables can be reliably connected and tensioned to form an overall support force. M2.5 refers to the standard value of the cubic compressive strength of the mortar being 2.5MPa. The core function of the cement mortar is to fill the gap between the anchor cable and the borehole wall and to bond the anchor cable to the surrounding broken rock mass into a whole. M2.5 mortar can provide sufficient gripping force to ensure that the anchor cable will not slip out of the hole when it is tightened.

[0033] Furthermore, in some embodiments, in step S4, the diameter of the downward large-diameter blast hole 13 is 110~130mm, the blast hole row spacing is 2.7~3.0m, and the hole spacing is 2.5~3.0m; the row face side holes are parallel to the sidewall of the mining area, and the other blast holes on the row face are evenly distributed.

[0034] In the technical solution of this application embodiment, for thick ore bodies, large-diameter blast holes can achieve a hole layout with large resistance lines and large hole spacing, significantly reducing the total number of blast holes, thereby greatly reducing drilling costs, increasing the amount of ore per blast, and improving mining efficiency; the combination of hole spacing and row spacing forms a dense hole network, taking into account both crushing effect and construction convenience, effectively controlling the block rate, and creating conditions for subsequent ore extraction operations; the fine hole layout (parallel side holes, uniform internal structure) maximizes the protection of the stability of the isolation layer and sidewalls, providing a guarantee for the safety of the entire mining system.

[0035] Furthermore, in some embodiments, the downward large-diameter borehole 13 is loaded with an axially uncoupled loading structure, the air gap length of the side holes is greater than the air gap length of the middle holes, and the loading sections 19 and air gap sections 18 of adjacent boreholes in the same row are staggered.

[0036] In the technical solution of this application embodiment, different strategies are adopted for different locations. The charging positions of adjacent blast holes are staggered, which realizes the optimized superposition of stress waves. While improving the crushing effect, it effectively suppresses blasting vibration, optimizes energy transfer, and achieves a perfect balance between efficient crushing and surrounding rock protection. This ensures that after the first-step mining area is blasted with large-diameter deep holes downwards, it can not only successfully extract ore, but also provide a cavity with a regular shape and stable surrounding rock for subsequent filling, thereby ensuring the safety and efficiency of the entire combined mining method.

[0037] Furthermore, in some embodiments, the bottom plugging length of the through hole in the charging structure is 1.2~1.5m, of which the sand filling length is greater than 1.0m. For blast holes whose bottoms do not penetrate the lower mining and cutting works, charging is performed directly.

[0038] In the technical solution of this application embodiment, the through hole is a blast hole that drills through the entire ore body to reach the lower mining and cutting works. Through reasonable plugging design, the blasting energy is ensured to be used efficiently, thereby obtaining a good crushing effect. For blast holes that do not penetrate the lower mining and cutting works at the bottom, the complicated process of plugging a long section from the bottom of the hole is eliminated, the charging process is simplified, and the operation efficiency is improved.

[0039] Furthermore, in some embodiments, in step S5, the diameter of the upward fan-shaped hole 7 is 70~90mm, the hole spacing is 1.8~2.0m, and the hole bottom distance is 2.0~2.2m.

[0040] In the technical solution of this application embodiment, the blasting range is effectively controlled by fan-shaped hole arrangement, reducing dilution and loss; the blasting energy of medium-diameter holes is relatively concentrated, which can effectively crush the ore, and at the same time, it will not generate excessive blasting vibration due to excessive energy concentration, and the disturbance to the surrounding filling body and rock mass is small.

[0041] Furthermore, in some embodiments, the strength of the first-step stope backfill body 6 is ≥2MPa; the strength of the second-step stope backfill body is ≥1MPa.

[0042] In the technical solution of this application embodiment, the appropriate strength of the backfill body ensures good compactness and low permeability, which can effectively prevent surface water and loose material from seeping downhole and protect the underground working environment. After the first-step mining is completed, backfilling is carried out immediately. The strength of the backfill body needs to reach more than 2MPa to ensure that the backfill body has good self-support and homogeneity. When the second-step mining is carried out, it is surrounded by the high-strength backfill body of the first step, which has formed a stable support frame. Its safety risk is low. Therefore, the strength requirement can be appropriately reduced, and it only needs to be able to solidify on its own.

[0043] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific technologies or conditions are not specified in the embodiments, they shall be performed in accordance with the technologies or conditions described in the literature in this field or in accordance with the product manual.

[0044] Example 1 This embodiment provides a safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions, such as... Figures 1 to 3 As shown, it includes the following steps: S1. Based on the ore body occurrence conditions, the thickness of the isolation layer is determined by combining theoretical analysis and numerical simulation. The ore body has a strike length of 100m, a horizontal thickness of 25m, and a height of 35m. The thickness of the isolation layer is closely related to the width of the stope. Considering the safety and economy of ore body mining, and taking into account the selection of mine structure parameters under most similar mining conditions, the stope width is set at 10m and the stope height is within 35m. The isolation layer thickness calculated by comprehensively considering different rock mass conditions is mostly below 12.5m. Considering that the vertical thickness of the surrounding rock in this case is 15m, the thickness of the isolation layer is set at 15m. S2. The near-surface ore body is divided into mining areas, and a two-step mining method is adopted: the first-step mining area adopts the downward large-diameter deep hole subsequent backfilling mining method, and the second-step mining area adopts the segmented medium-deep hole subsequent backfilling mining method. In the footwall of the ore body, a mid-section transport roadway 1 is excavated for transportation, ventilation, and pedestrian access. A bottom connecting roadway 3 is excavated to connect to the ore pass 2. An ore extraction roadway 5 is excavated and a ore collection trench 4 is constructed. The ore collection trench 4 is used to collect the blasted ore and transport it to the ore pass 2 through the ore extraction equipment. A bottom pillar 10 of a certain height is retained at the lowest part of the stope to ensure structural stability. S3. Construct drilling chamber 11 at the top of the first-stage mining area, forming it through advanced support construction. Construct horizontal anchor cable holes and vertical anchor cable holes penetrating the ground surface at the top of drilling chamber 11. Using two adjacent drilling chambers 11 in the first-stage mining area as construction points, construct downward anchor cable holes to the upper boundary of the ore body at the ground surface location above the second-stage mining area. Construct 10m long anchor cable holes 5m outside the ore body boundary. The anchor cable hole diameter is 90mm, and the row spacing and hole spacing of the anchor cable holes are both 1.5m. The anchor cables are made of 22mm diameter steel wire rope. The exposed length of the rope outside the hole is greater than 0.3m. After the anchor cable is placed, cement mortar is injected into the anchor cable hole. The strength grade can reach M2.5. The cement mortar can seep into the rock mass around the anchor cable hole through the cracks, which can improve the rock mass fracture and crack development to a certain extent and improve its overall strength. A 12mm diameter series steel wire rope 12 is selected to wind and connect the anchor cables exposed at the hole. The ends of the series steel wire rope 12 can be fastened with special steel wire rope buckles. After completing the above process steps, prestress is applied to the anchor cables exposed at the hole. The combined reinforcement project of horizontal grouting long anchor cable 8 and vertical grouting long anchor cable 9 can enhance the stability of the near-surface fractured surrounding rock, make the top area of ​​the mining area a whole, and provide a more stable roof environment when the lower mining area is mined, which can effectively prevent the roof from collapsing and causing surface subsidence. S4. In the first-step mining operation, blasting is carried out in the large-diameter blast hole 13 to extract ore. After the ore is extracted, subsequent backfilling is carried out immediately. The strength of the backfill body reaches more than 2MPa, so that the self-support and homogeneity of the backfill body are both good. like Figure 4 As shown, in this embodiment, the downward-facing large-diameter blast holes 13 include a first blast hole 131, a second blast hole 132, a third blast hole 133, a fourth blast hole 134, a fifth blast hole 135, a sixth blast hole 136, a seventh blast hole 137, and an eighth blast hole 138. The blast hole diameter is 120mm. The side holes (first blast hole 131 and eighth blast hole 138) are parallel to the sidewall of the stope, making the sidewall shape more regular after blasting. The other blast holes are evenly distributed on the sidewall, resulting in better rock-breaking effect from the blasting detonation energy, reducing the proportion of large blocks, minimizing the construction of large-angle, large-diameter blast holes, and helping to improve the accuracy of blast hole construction. The blast hole row spacing is 2.7~3.0m, and the hole spacing is 2.5~3.0m. The bottom plugging length of the through hole is 1.2~1.5m, and the length of the sand-filled section 20 at the bottom of the hole is greater than 1.0m. ~1.2m; For boreholes whose bottom does not penetrate the lower mining section (Borehole 134 and Borough 135), sand filling is not required at the bottom; charge can be applied directly. Individual boreholes adopt an axially decoupled charging structure, with the charging section 19 and air gap section 18 arranged alternately within the borehole. The structures of boreholes at the stope boundary and intermediate boreholes differ, with longer air gaps in the side boreholes. This measure helps reduce the disturbance to the sidewalls caused by stope blasting. The shorter air gaps in the intermediate boreholes effectively balance the detonation capacity of a single stope blast, contributing to better blast block size and facilitating ore extraction. The alternating arrangement of the charging section 19 and air gap section 18 in adjacent large-diameter boreholes in the same row prevents them from being fixed at the same height, further reducing the blast block rate. Specifically, such as Figure 5As shown, the borehole charging structure includes a detonating cord and fuse 14, a digital electronic detonator 15, a sand-filling section at the borehole opening 16, a thin iron wire 17, an air gap section 18, a charging section 19, a sand-filling section at the bottom of the borehole 20, and a plug 21. The sand-filling section 16 at the borehole opening is 1.5~2.0m long, and the sand-filling section 20 at the bottom of the borehole is 1.0~1.2m long. The first borehole 131 and the eighth borehole 138 use the same charging structure, with the air gap section 18 being 1.5m long and the charging section 19 being 3.0m long. kg; the second borehole 132 and the seventh borehole 137 use the same charging structure, with an air gap section 18 of 1.0m, a bottom charging section 19 of 2.5m and a charge of 15kg, and the remaining charging sections 19 of 3.0m and a charge of 18kg; the third borehole 133 and the sixth borehole 136 use the same charging structure, with an air gap section 18 of 1.0m, a bottom charging section 19 of 4.0m and a charge of 24kg, and the remaining charging sections 19 of 3.0m and a charge of 18kg.

[0045] S5. After the backfill body 6 of the first-step stope reaches the predetermined strength, the second-step stope construction uses upward fan-shaped holes 7 for blasting to extract ore. After the ore is extracted, subsequent backfilling is carried out. This method can effectively ensure the stope's production capacity, reduce the amount of mining and cutting work, and reduce the input of direct production costs. Specifically, the diameter of the upward fan-shaped holes 7 is 80mm, the spacing between the holes is 1.8~2.0m, and the distance between the bottom of the holes is 2.0~2.2m.

[0046] The safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions provided in this application has the following significant advantages over the traditional down-entry backfilling mining method: 1. Reduce the cutting ratio and save on cutting work: In the near-surface thick and broken ore body area with a strike length of 100m, a horizontal thickness of 25m and a height of 35m, compared with the conventional down-entry backfilling mining method, the overall cutting ratio of the mining area is reduced from 8.7m / kt to 3.8m / kt. 2. Significantly improved production efficiency: Compared with conventional down-entry backfill mining, the overall production capacity of the mining area has increased from an estimated 800 t / d to approximately 1600 t / d; 3. Significantly reduced mining costs: Compared with conventional down-entry backfilling mining, the direct mining costs (preparation, support, drilling, blasting, ore extraction, and backfilling) are reduced from 260 yuan / t to 150 yuan / t, resulting in a significant reduction in mining costs; 4. Reduced proportion of large pieces after blasting: Optimization of the charge structure during large-diameter deep-hole mining can make the blasting energy evenly distributed within the discharge face, reducing the proportion of large pieces from the conventional 20% to less than 5%.

[0047] Mining thick, low-grade ore bodies near the surface under fractured rock conditions is difficult and carries high safety risks. Using only the downward-facing backfilling mining method is unlikely to generate economic benefits and may even result in losses. This application utilizes a combined structure of grouting long anchor cables (horizontal grouting long anchor cable 8 and vertical grouting long anchor cable 9) to reinforce the fractured rock near the surface, creating a more stable roof environment in the lower stope and effectively preventing roof collapse and surface subsidence. By combining the downward large-diameter deep-hole backfilling mining method with the segmented medium-deep-hole backfilling mining method, the amount of cutting work can be effectively reduced while ensuring the stability of the ore body's roof, thus reducing the investment in cutting operations. Simultaneously, the optimized charge structure during large-diameter deep-hole mining further reduces the impact of blasting disturbance on the stope sidewalls and ensures that the detonation energy generated by the explosives is evenly distributed across the blasting surface. This reduces explosive consumption per unit and ensures uniform blasting block size, facilitating ore extraction operations.

[0048] The safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions comprehensively considers the application of near-surface fractured ore support structures, mining methods for oreable bodies, and supporting mining technologies. It can safely and efficiently extract these thick, low-grade ore body resources, fully utilize underground resources, and ensure the continuous high-quality development of mining enterprises.

[0049] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions, characterized in that, Includes the following steps: S1. Based on the ore body occurrence conditions, the thickness of the isolation layer is determined by combining theoretical analysis and numerical simulation. S2. The near-surface ore body is divided into mining areas, and a two-step mining method is adopted: the first-step mining area adopts the downward large-diameter deep hole subsequent backfilling mining method, and the second-step mining area adopts the segmented medium-deep hole subsequent backfilling mining method. S3. Construct a rock drilling chamber at the top of the first-step mining area, and construct horizontal and vertical anchor cable holes at the top of the rock drilling chamber, with the vertical anchor cable holes communicating with the ground surface; the diameter of the anchor cable holes is 80~100mm, and the row spacing and hole spacing of the anchor cable holes are 1~2m; Construct downward anchor cable holes to the upper boundary of the ore body at the surface location above the two-step mining area; After the anchor cables are placed, cement mortar is injected into all the anchor cable holes. The anchor cables exposed at the holes are connected in series and prestressed to form a combined anchor cable support system. S4. In the first-step mining operation, blasting is carried out using large-diameter boreholes to extract ore, followed by immediate backfilling. The diameter of the large-diameter boreholes is 110-130mm, the borehole row spacing is 2.7-3.0m, and the hole spacing is 2.5-3.0m. The side holes on the row face are parallel to the sidewalls of the mining area, and the other boreholes on the row face are evenly distributed. The downward large-diameter borehole charging adopts an axially uncoupled charging structure, the air gap length of the side holes is greater than the air gap length of the middle holes, and the charging sections and air gap sections of adjacent boreholes in the same row are staggered. S5. After the backfill material in the first-step stope reaches the predetermined strength, the second-step stope construction will proceed with blasting and ore extraction through the upward fan-shaped holes, followed by subsequent backfilling.

2. The safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions as described in claim 1, characterized in that, The anchor cable is a steel wire rope with a diameter of 20~25mm, the exposed length of the anchor cable at the anchor cable hole is greater than 0.3m, and the strength grade of the cement mortar is not lower than M2.

5.

3. The safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions as described in claim 1, characterized in that, The length of the plugging at the bottom of the through hole in the charge structure is 1.2~1.5m, of which the length of the sand filling is greater than 1.0m.

4. The safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions as described in claim 1, characterized in that, For blast holes where the bottom has not been penetrated to the lower mining and cutting works, explosives are loaded directly.

5. The safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions as described in claim 1, characterized in that, In step S5, the diameter of the upward fan-shaped hole is 70~90mm, the hole spacing is 1.8~2.0m, and the hole bottom distance is 2.0~2.2m.

6. The safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions as described in claim 1, characterized in that, The strength of the backfill material in the first step of the mining area is ≥2MPa.

7. The safe and efficient combined mining method for thick, low-grade ore bodies near the surface under fractured ore conditions as described in claim 1, characterized in that, The strength of the filling material in the two-step mining area is ≥1MPa.

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