A combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes

Abstract

This invention discloses a combined dewatering and drainage method for impermeable water in the upper layer of open-pit mine slopes. The combined dewatering and drainage system is constructed using inclined drainage holes (1), vertical drainage holes (2), and drainage ditches (3). Sleeves are installed in the inclined drainage holes (1) and vertical drainage holes (2) within the depth of the fracture zone. Rigid permeable pipes extend through the sleeves into the inclined drainage holes (1) and vertical drainage holes (2). Water-stop plugs are installed in the annular gap between the rigid permeable pipes and the drainage hole walls of the inclined drainage holes (1) and vertical drainage holes (2). Multiple permeable holes are formed on the rigid permeable pipes below the water-stop plug in the vertical drainage hole (2) and on the rigid permeable pipes within the water-stop plug in the inclined drainage hole (1). This invention reduces water pressure near the impermeable layer through continuous gravity drainage, reduces dewatering costs, avoids the erosive effect of water flow on slope fractures, and improves the overall stability of open-pit mine slopes.

Description

Technical Field

[0001] This invention belongs to the field of mine slope management, and particularly relates to a combined dewatering and drainage method for the upper layer of water retention on non-coal open-pit mine slopes. It can be widely used in the management of slopes in ferrous, non-ferrous, and non-metallic open-pit mines. Background Technology

[0002] 90% of mine slope instability is related to surface water and groundwater activity, mostly due to improper drainage and water diversion methods. Most open-pit mines must take effective waterproofing and drainage measures throughout the entire production period, and even during the infrastructure construction phase, to ensure the safe, normal, and orderly production of the open-pit mine.

[0003] Groundwater in open-pit mine slopes is often a major or contributing factor to instability. When an impermeable layer exists within the slope, and the more permeable rock mass lies deep within, a drop in the main groundwater level leads to the formation of a perched area, increasing pore water pressure and reducing the slope's stability. While mature drainage methods exist for perched water in foundation pits, such as the active extraction of perched water using a collection pipe as described in patent CN114855813B, this drainage structure does not consider the significant height of open-pit mine slopes and the long-term replenishment of perched water by rainfall. Extracting rainwater significantly increases drainage costs. Therefore, guiding perched water to deeper, more permeable rock masses or draining it from the slope via gravity precipitation can effectively remove perched water while reducing drainage costs.

[0004] Gravity-based dewatering is a common drainage measure for mine slopes, mainly including drainage holes, collection wells, and drainage tunnels. Single drainage methods are inefficient in complex groundwater environments; therefore, multi-stage drainage systems are often used for combined dewatering, such as the slope drainage structure with patent number CN204898695U. This structure, combining drainage holes and tunnels, can lower the groundwater level on the slope. However, it does not consider the surface fissures caused by excavation unloading and blasting. When groundwater seeps into these fissures, they pose a risk of softening and collapse. Therefore, to ensure safe mine production, a drainage method that can simultaneously lower the groundwater level and ensure the stability of the surface fissures on the slope is urgently needed. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned problems in existing technologies by providing a combined dewatering and drainage method for the upper layer of perched water on open-pit mine slopes. This method can significantly reduce water pressure near the aquitard, reduce dewatering costs, and avoid the impact of water flow on slope fissures. As a result, it effectively reduces the risk of collapse in the surface fissure zone of the slope and significantly improves the overall stability of open-pit mine slopes.

[0006] To achieve the above-mentioned objectives of this invention, the present invention provides a combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes, employing the following technical solution:

[0007] The application scenario of this invention is as follows: An upper layer of an open-pit mine bench slope contains a fracture zone, an impermeable layer exists within the slope, an upper water-retaining zone forms above the impermeable layer, and below the impermeable layer is a relatively permeable rock mass / bedrock. To achieve effective precipitation and drainage, this invention employs a combination of inclined drainage holes, vertical drainage holes, and drainage ditches to form a combined precipitation and drainage system. The inclined drainage holes are arranged in two rows: one row, from the outside in and inclined upwards, is located in a row of inclined boreholes above the impermeable layer within the open-pit mine bench slope; the other row, from the outside in and inclined upwards, is located in a row of inclined boreholes above the toe of the open-pit mine bench slope. The inclined drainage holes penetrate the fracture zone from the slope surface of the open-pit mine bench slope into the rear bedrock. The vertical drainage holes are arranged in three rows: two rows are located in two rows of vertical boreholes on the top surface of the open-pit mine bench slope, and the other row is located in the exposed rock mass / bedrock. In a row of vertical boreholes on the slope platform of the mine bench, vertical drainage holes pass through the upper water-retaining zone and the aquitard layer from top to bottom, and extend into the more permeable rock / bedrock below the aquitard layer. Two drainage ditches are mentioned: one is located on the top surface of the open-pit mine bench surrounding the uppermost row of vertical drainage holes, and the other is located at the toe of the slope of the open-pit mine bench where the inclined drainage holes are located. The inclined and vertical drainage holes are fitted with casings within the fracture zone depth. Rigid permeable pipes extend through the casings into the inclined and vertical drainage holes. Water-stop plugs are installed in the annular gap between the rigid permeable pipes and the drainage hole walls of the inclined and vertical drainage holes. Multiple permeable holes are formed on the rigid permeable pipes below the water-stop plugs in the vertical drainage holes and on the rigid permeable pipes within the water-stop plugs in the inclined drainage holes. The permeability coefficient of the aquitard layer described in this invention is generally 10. -9 Up to 10 -12 With a permeability of m / s, rainwater and groundwater cannot penetrate to the lower layers, thus forming an upper perched zone. The permeability coefficient of the rock mass / bedrock with good permeability described in the method of this invention is generally 10. -4 Up to 10 -7 It has a permeability coefficient of m / s and good water permeability.

[0008] The present invention provides a combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes, which is implemented through the following steps:

[0009] S1: Investigate the geological conditions of the open-pit mine slope area. Based on the location of seepage on the slope, after clearing the loose rocks from the surface of the open-pit mine bench slope, construct a shotcrete facing on the surface of the open-pit mine bench slope. The shotcrete is laid on the surface of the bench slope where the inclined drainage hole is located to protect the slope fissure zone and aquitard from external water erosion. Vertical boreholes are drilled on the top surface of the open-pit mine bench slope and the open-pit mine bench slope platform to obtain exploration boreholes. The exploration boreholes pass through the upper perched zone and aquitard from top to bottom, and penetrate into the rock mass with better permeability below the aquitard. The hydrogeological parameters of the rock layers at different depths in the borehole are obtained through permeability tests to determine the location of the upper perched zone, aquitard, and the rock mass with better permeability below the aquitard. The exploration borehole is then left as a vertical drainage hole.

[0010] S2: Determine the location and depth of the inclined and vertical drainage holes based on the transverse span of the open-pit mine slope and the corresponding hydrogeological parameters; the vertical drainage holes shall be laid vertically downwards; the inclined and vertical drainage holes shall extend at least 80mm beyond the surface of the open-pit mine bench slope.

[0011] S3 Vertical drainage hole layout:

[0012] ① Install casing inside the vertical borehole to prevent borehole collapse. The casing passes through the fracture zone in the slope of the open-pit mine bench and rests on stable bedrock. The inner diameter of the casing is the same as the diameter of the vertical drainage hole. A rigid permeable pipe is customized according to the depth of the fracture zone and the type of drainage hole. The water stop plug is placed 0.5~1m below the depth of the fracture zone. The water stop plug is pre-installed on the rigid permeable pipe and fits tightly. The outer diameter of the water stop plug is the same as the diameter of the vertical drainage hole to ensure the sealing effect of the water stop plug. The rigid permeable pipe has permeable holes below the water stop plug, but no permeable holes above the water stop plug.

[0013] ② Insert the rigid permeable pipe into the vertical drainage hole, and fill the annular gap above the waterstop with cement mortar to fix the rigid permeable pipe.

[0014] S4 Sloping drainage hole layout:

[0015] After the shotcrete in step S1 reaches the specified strength, a row of inclined drainage holes is laid from the outside to the inside and inclined upward above the waterproof layer inside the open-pit mine bench slope. Another row of inclined drainage holes is laid from the outside to the inside and inclined upward above the toe of the open-pit mine bench slope. The process of laying the sleeve, water stop plug and rigid permeable pipe is the same as steps ① and ② of S3.

[0016] S5: Drainage ditches are laid on the top surface of the open-pit mine bench slope, which is perpendicular to the outer perimeter of the top row of drainage holes, and at the foot of the slope of the open-pit mine bench where the inclined drainage holes are located, in order to collect the surface runoff of the open-pit mine bench slope. The drainage ditches are masonry drainage ditches, and the bottom of the ditches is plastered with mortar.

[0017] After the above-mentioned dewatering process, the perched water in the upper layer of the open-pit mine slope is guided to the deeper, more permeable rock mass or discharged outside the slope, ensuring the continuous stability of the surface fissure zone of the slope and improving the overall stability of the open-pit mine slope.

[0018] Based on experimental research and economic analysis, the length (depth) of the inclined drainage hole is 15~30m, the upward inclination is 5~10°, the horizontal spacing is 3~6m, the hole diameter is 90~110mm, and the diameter of the internal rigid permeable pipe is preferably 10~40mm smaller than the diameter of the inclined drainage hole.

[0019] Studies have shown that the horizontal spacing of the vertical drainage holes is preferably 3-6m, the hole diameter is 200-250mm, and the diameter of the internal rigid permeable pipe is preferably 20-30mm smaller than the hole diameter of the vertical drainage holes.

[0020] The preferred size of the drainage ditch is (0.5~1.2m)×(0.5~1.2m).

[0021] As a preferred embodiment of the present invention, the diameter of the rigid permeable pipe installed in the inclined drainage hole is 50~100mm.

[0022] As a preferred embodiment of the present invention, the diameter of the rigid permeable pipe installed in the vertical drainage hole is 150~200mm.

[0023] As a preferred embodiment of the present invention, the rigid permeable pipe is made of high-density polyethylene (HDPE) as the main raw material.

[0024] As a preferred embodiment of the present invention, the cement mortar is M20 cement mortar.

[0025] Furthermore, one row of inclined drainage holes is arranged from the outside inwards and inclined upwards in a row of inclined boreholes 0.5m above the water-resistant layer inside the slope of the open-pit mine bench, and the other row is arranged from the outside inwards and inclined upwards in a row of inclined boreholes 0.5m above the toe of the slope of the open-pit mine bench.

[0026] Compared with existing technologies, the combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes, as described in this invention, has the following beneficial effects after adopting the above technical solution:

[0027] (1) By rationally arranging inclined drainage holes, vertical drainage holes and drainage ditches, an efficient combined precipitation system is formed, which effectively guides the stagnant water in the upper layer of the open-pit mine slope to the deep, more permeable rock mass or discharges it outside the slope, thereby avoiding the erosion effect of water flow on the slope cracks.

[0028] (2) Through the unique design of the sleeve, water stop plug and water hole position, and the filling of the annular gap above the water stop plug with M20 cement mortar, groundwater seepage into the fracture zone is completely prevented. The use of shotcrete to protect the surface reduces the erosion of the fracture zone and the water-proof layer by external water flow, effectively reducing the risk of collapse in the fracture zone area of ​​the slope surface.

[0029] (3) By continuously reducing the water pressure near the aquitard layer through gravity drainage, the expected precipitation effect was achieved, the drainage cost was significantly reduced, the pore water pressure inside the slope was reduced, and the overall stability of the open-pit mine slope was improved. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of a combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes according to the present invention.

[0031] Figure 2 This is a schematic diagram of the drainage hole structure designed for a combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes, according to the present invention.

[0032] The attached diagram is labeled as follows: 1- Inclined drainage hole; 2- Vertical drainage hole; 3- Drainage ditch; 4- Shotcrete; 5- Rigid permeable pipe; 6- Drainage hole wall; 7- Permeable hole; 8- Water stop plug; 9- Sleeve. Detailed Implementation

[0033] To better describe the present invention, the following detailed description, in conjunction with the accompanying drawings, provides a combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes.

[0034] Depend on Figure 1 The diagram shown is a schematic representation of the overall structure of a combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes, as described in this invention. Figure 2As can be seen, this invention provides a combined dewatering and drainage method for the upper layer of perched water on open-pit mine slopes. The upper layer of the open-pit mine bench slope contains a fracture zone, and the slope contains an impermeable layer. An upper perched water zone is formed above the impermeable layer. A combined dewatering and drainage system is constructed using inclined drainage holes 1, vertical drainage holes 2, and drainage ditches 3. The inclined drainage holes 1 are arranged in two rows. One row is arranged from the outside inwards, inclined upwards, in a row of inclined boreholes above the impermeable layer within the open-pit mine bench slope. The other row is arranged from the outside inwards, inclined upwards, in a row of inclined boreholes above the toe of the open-pit mine bench slope. The inclined drainage holes 1 penetrate from the slope surface of the open-pit mine bench slope through the fracture zone and extend into the rear bedrock. The length of the inclined drainage holes 1 is 15-30m, the upward inclination is 5-10°, the horizontal spacing is 3-6m, and the diameter is 90-110mm. The diameter of the rigid permeable pipe 5 installed inside the inclined drainage holes 1 is 50-100mm. The vertical drainage holes 2 are arranged in three rows. Two rows are located in two rows of vertical boreholes on the top surface of the open-pit mine bench, and the other row is located in one row of vertical boreholes on the slope platform of the open-pit mine bench. The vertical drainage holes 2 pass through the upper water-retaining zone and the aquitard layer from top to bottom, and extend into the more permeable rock mass below the aquitard layer. The horizontal spacing of the vertical drainage holes 2 is 3-6m, the hole diameter is 200-250mm, and the diameter of the internal rigid permeable pipe 5 is 150-200mm. The rigid permeable pipe 5 is made of high-density polyethylene (HDPE) as the main raw material. There are two drainage ditches 3. One is located on the top of the open-pit mine bench surrounding the uppermost row of vertical drainage holes 2, and the other is located 0.5m above the toe of the slope of the open-pit mine bench where the inclined drainage hole 1 is located. The dimensions of the drainage ditch 3 are (0.5~1.2m) × (0.5~1.2m). The drainage ditch 3 is a masonry drainage ditch with a mortar finish on the bottom. Sleeves 9 are installed in the depth of the fracture zone for the inclined drainage hole 1 and the vertical drainage hole 2. Rigid permeable pipes 5 extend through the sleeves 9 into the inclined drainage hole 1 and the vertical drainage hole 2. Water stoppers 8 are installed in the annular gap between the rigid permeable pipe 5 and the drainage hole wall 6 of the inclined drainage hole 1 and the vertical drainage hole 2. Multiple permeable holes 7 are opened on the rigid permeable pipe 5 below the water stopper 8 in the vertical drainage hole 2 and on the rigid permeable pipe 5 below the water stopper 8 in the inclined drainage hole 1.

[0035] The present invention provides a combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes, which is implemented through the following steps:

[0036] S1: Investigate the geological conditions of the open-pit mine slope area. Based on the location of seepage on the slope, after clearing the loose rocks from the surface of the open-pit mine bench slope, construct a shotcrete 4 facing on the surface of the open-pit mine bench slope. The shotcrete 4 is laid on the surface of the bench slope where the inclined drainage hole 1 is located to protect the slope fissure zone and the aquitard from external water erosion. Vertical boreholes are drilled on the top surface of the open-pit mine bench slope and the open-pit mine bench slope platform to obtain exploration boreholes. The exploration boreholes pass through the upper water-retaining zone and the aquitard from top to bottom, and penetrate into the rock mass with better permeability below the aquitard. The hydrogeological parameters of the rock layers at different depths in the borehole are obtained through permeability tests to determine the location of the upper water-retaining zone, the aquitard, and the rock mass with better permeability below the aquitard. The exploration borehole is then left as a vertical drainage hole 2.

[0037] S2: Determine the location and depth of the inclined drainage hole (1) and vertical drainage hole 2 based on the transverse span of the open-pit mine slope and the corresponding hydrogeological parameters; the vertical drainage hole 2 is laid vertically downward; the inclined drainage hole 1 and the vertical drainage hole 2 extend at least 80mm beyond the surface of the open-pit mine bench slope.

[0038] S3 Vertical drainage hole layout:

[0039] ① Install casing 9 in the vertical borehole to prevent borehole collapse. Casing 9 passes through the fracture zone in the slope of the open-pit mine bench and sits on stable bedrock. The inner diameter of casing 9 is the same as the diameter of the drainage hole of vertical drainage hole 2. A rigid permeable pipe 5 is customized according to the depth of the fracture zone and the type of drainage hole. Water stop plug 8 is placed 0.5~1m below the depth of the fracture zone. Water stop plug 8 is pre-installed on the rigid permeable pipe 5 and fits tightly. The outer diameter of water stop plug 8 is the same as the diameter of the drainage hole of vertical drainage hole 2 to ensure the sealing effect of water stop plug. The rigid permeable pipe 5 has permeable holes 7 below the water stop plug 8, while there are no permeable holes above the water stop plug 8.

[0040] ② Insert the rigid permeable pipe 5 into the vertical drainage hole 2, and fill the annular gap above the waterstop 8 with M20 cement mortar to fix the rigid permeable pipe 5.

[0041] S4 Sloping drainage hole layout:

[0042] After the shotcrete 4 in step S1 reaches the specified strength, a row of inclined drainage holes 1 is installed above the impermeable layer inside the open-pit mine bench slope, from the outside in and inclined upwards. Another row of inclined drainage holes 1 is installed above the toe of the open-pit mine bench slope, from the outside in and inclined upwards. The installation process of the sleeve 9, water stop plug 8, and rigid permeable pipe 5 is the same as steps ① and ② in S3. One row of inclined drainage holes 1 is installed in a row of inclined boreholes 0.5m above the impermeable layer inside the open-pit mine bench slope, from the outside in and inclined upwards. The other row is installed in a row of inclined boreholes 0.5m above the toe of the open-pit mine bench slope, from the outside in and inclined upwards.

[0043] S5: Drainage ditches 3 are respectively laid on the top surface of the open-pit mine bench slope surrounding the uppermost row of vertical drainage holes 2 and at the foot of the slope of the open-pit mine bench where the inclined drainage hole 1 is located, in order to collect the surface runoff of the open-pit mine bench slope.

[0044] This invention discloses a combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes, which has been tested and applied in a large open-pit iron mine in China. Practical application shows that the combined dewatering system of this invention can effectively guide perched water in the upper layer of open-pit mine slopes to deeper, more permeable rock masses or drain it from the slope. Through the unique design of casings, water-stop plugs, and permeable holes, as well as cement mortar sealing, groundwater infiltration into the fracture zone is comprehensively prevented. Simultaneously, shotcrete facing reduces the erosion of the fracture zone and aquitard by external water flow. Through the continuous gravity dewatering effect of the combined dewatering system, the pore water pressure inside the slope is effectively reduced, improving the overall stability of the open-pit mine slope and reducing drainage costs.

Claims

1. A combined dewatering and drainage method for perched water in the upper layer of an open-pit mine slope, wherein the upper layer of the open-pit mine bench slope contains a fracture zone, the open-pit mine bench slope contains an impermeable layer, and an upper perched water zone is formed on top of the impermeable layer, characterized in that: It employs a combination of inclined drainage holes (1), vertical drainage holes (2), and drainage ditches (3) to form a combined precipitation and drainage system. The inclined drainage holes (1) consist of two rows, one row of which is arranged from the outside inwards and inclined upwards in a row of inclined boreholes above the aquitard layer on the slope of the open-pit mine bench, and the other row of which is arranged from the outside inwards and inclined upwards in a row of inclined boreholes above the toe of the slope of the open-pit mine bench. The inclined drainage holes (1) penetrate from the slope surface of the open-pit mine bench through the fissure zone and into the bedrock at the rear. The vertical drainage holes (2) consist of three rows, two rows of which are arranged in two rows of vertical boreholes on the top surface of the open-pit mine bench slope, and the other row of which is arranged in a row of vertical boreholes on the platform of the open-pit mine bench slope. The vertical drainage holes (2) penetrate from top to bottom through the upper water-retaining zone and the aquitard layer, and penetrate into the well-permeable rock mass below the aquitard layer. There are two drainage ditches (3). One of them is located on the top of the open-pit mine bench outside the uppermost row of vertical drainage holes (2). The other is located at the foot of the slope of the open-pit mine bench where the inclined drainage hole (1) is located. The inclined drainage hole (1) and the vertical drainage hole (2) are equipped with sleeves (9) within the depth of the fracture zone. The rigid permeable pipe (5) passes through the sleeve (9) and extends into the inclined drainage hole (1) and the vertical drainage hole (2). A water stop plug (8) is installed in the annular gap between the rigid permeable pipe (5) and the drainage hole wall (6) of the inclined drainage hole (1) and the vertical drainage hole (2). Multiple permeable holes (7) are opened on the rigid permeable pipe (5) below the water stop plug (8) in the vertical drainage hole (2) and on the rigid permeable pipe (5) below the water stop plug (8) in the inclined drainage hole (1). The following steps are adopted: S1: Investigate the geological conditions of the open-pit mine slope area. Based on the location of the seepage on the slope, after cleaning the loose rocks on the surface of the open-pit mine step slope, spray concrete (4) is applied to the surface of the open-pit mine step slope. Vertical drilling is carried out on the top surface of the open-pit mine step slope and the platform of the open-pit mine step slope to obtain exploration boreholes. The exploration boreholes pass through the upper water-retaining zone and the water-retaining layer from top to bottom, and penetrate into the rock mass with good permeability below the water-retaining layer. The hydrogeological parameters of the rock layers at different depths in the borehole are obtained through permeability tests. The location of the upper water-retaining zone, the water-retaining layer and the rock mass with good permeability below the water-retaining layer are determined, and the exploration borehole is left as a vertical drainage hole (2). S2: Determine the location and depth of the inclined drainage hole (1) and vertical drainage hole (2) based on the transverse span of the open-pit mine slope and the corresponding hydrogeological parameters; the vertical drainage hole (2) is laid vertically downward; the inclined drainage hole (1) and vertical drainage hole (2) extend beyond the surface of the open-pit mine bench slope by no less than 80mm; S3 Vertical drainage hole layout: ① Install a casing (9) in the vertical borehole to prevent the borehole from collapsing. The casing (9) passes through the fracture zone in the slope of the open-pit mine bench and sits on the stable bedrock. The inner diameter of the casing (9) is the same as the diameter of the drainage hole of the vertical drainage hole (2). A rigid permeable pipe (5) is customized according to the depth of the fracture zone and the type of drainage hole. The water stop plug (8) is placed 0.5~1m below the depth of the fracture zone. The water stop plug (8) is pre-installed on the rigid permeable pipe (5) and tightly fitted. The outer diameter of the water stop plug (8) is the same as the diameter of the drainage hole of the vertical drainage hole (2) to ensure the sealing effect of the water stop plug. The rigid permeable pipe (5) has a permeable hole (7) below the water stop plug (8), while there is no permeable hole above the water stop plug (8). ② Insert the rigid permeable pipe (5) into the vertical drainage hole (2), and fill the annular gap above the water stop plug (8) with cement mortar to fix the rigid permeable pipe (5). S4 Sloping drainage hole layout: After the shotcrete (4) in step S1 reaches the specified strength, a row of inclined drainage holes (1) is laid out from the outside to the inside and inclined upward above the water-proof layer inside the open-pit mine bench slope. Another row of inclined drainage holes (1) is laid out from the outside to the inside and inclined upward above the slope toe of the open-pit mine bench slope. The process of laying out the sleeve (9), water stop plug (8), and rigid permeable pipe (5) is the same as that of steps ① and ② in step S3. S5: Drainage ditches (3) are respectively placed on the top surface of the open-pit mine step slope outside the uppermost row of vertical drainage holes (2) and at the foot of the slope of the open-pit mine step where the inclined drainage hole (1) is located, so as to collect the surface runoff of the open-pit mine step slope. The drainage ditch (3) is a masonry drainage ditch, and the bottom of the ditch is plastered with mortar.

2. The combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes as described in claim 1, characterized in that: The inclined drainage hole (1) is 15~30m long, tilted upwards at 5~10°, with a horizontal spacing of 3~6m and a hole diameter of 90~110mm. The diameter of the internal rigid permeable pipe (5) is 10~40mm smaller than that of the inclined drainage hole (1).

3. The combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes as described in claim 1, characterized in that: The vertical drainage holes (2) are spaced 3-6m apart horizontally, with a diameter of 200-250mm. The diameter of the internal rigid permeable pipe (5) is 20-30mm smaller than that of the vertical drainage holes (2).

4. The combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes as described in claim 1, characterized in that: The drainage ditch (3) has dimensions of (0.5~1.2m) × (0.5~1.2m).

5. A combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes as described in claim 2, characterized in that: The diameter of the rigid permeable pipe (5) installed in the inclined drainage hole (1) is 50~100mm.

6. The combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes as described in claim 3, characterized in that: The diameter of the rigid permeable pipe (5) installed in the vertical drainage hole (2) is 150~200mm.

7. A combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes as described in claims 1, 2, 3, 4, 5, or 6, characterized in that: The rigid permeable pipe (5) is made of high-density polyethylene (HDPE) as the main raw material.

8. A combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes as described in claims 1, 2, 3, 4, 5, or 6, characterized in that: The cement mortar mentioned is M20 cement mortar.

9. A combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes as described in claims 1, 2, 3, 4, 5, or 6, characterized in that: One row of inclined drainage holes (1) is arranged from the outside to the inside and inclined upward in a row of inclined boreholes 0.5m above the water-resistant layer inside the slope of the open-pit mine bench, and the other row is arranged from the outside to the inside and inclined upward in a row of inclined boreholes 0.5m above the toe of the slope of the open-pit mine bench.

10. A combined dewatering and drainage method for perched water in the upper layer of open-pit mine slopes as described in claims 1, 2, 3, 4, 5, or 6, characterized in that: The sprayed concrete (4) is laid on the surface of the step slope where the inclined drainage hole (1) is located, so as to protect the slope crack zone and the water-proof layer from the erosion of external water flow.

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