Method for steeping side slope angle of secondary stripping end slope of strip mine in subarea mining

Abstract

The invention discloses a subarea mining strip mine secondary stripping end slope angle steepening method which comprises the following steps: firstly, dividing a reinforced area, then, carrying out comprehensive reinforcement in a layered and staging manner, then, carrying out drainage, and finally, carrying out monitoring. According to the invention, through experiment and numerical simulation, the engineering construction accuracy is effectively improved; layered and staged comprehensive reinforcement is carried out according to different forms and displacement rules of a reinforcement area, so that the stability of the reinforcement area is effectively improved, the slope angle is increased, the secondary stripping amount is reduced, the stripping ratio of a post-mining area is reduced, and economic benefits are improved; the intercepting ditches and the drainage blind ditches are designed in a matched mode to form a three-dimensional drainage system, and erosion of atmospheric precipitation and underground water seepage to a reinforced area is avoided; the identification area is arranged, so that damage to the reinforcing area during subsequent secondary stripping is avoided; the construction process has similar engineering experience for reference, and the construction difficulty is low; normal dumping and dumping capacity of the strip mine are not affected, the whole process is controllable, accurate implementation is facilitated, tracking monitoring is implemented in the later period of reinforcement, and scheme feasibility is guaranteed.

Description

Technical Field

[0001] The present invention relates to a method for steepening the end slope angle, and more particularly to a method for steepening the end slope angle of the secondary stripping in a block-mined open-pit mine. Background Art

[0002] ‌A block-mined open-pit mine refers to dividing the entire mining area of the open-pit mine into several adjacent areas according to certain principles for separate mining. The mined area in the front will form a working slope, a non-working slope, and an end slope. As the stope space continuously expands and when the conditions for internal dumping are met, an internal dumping site will gradually form along the non-working slope and form a tracking dynamic advancement mode with the working slope.

[0003] In order to extract as much underground coal resources stored in the mining area as possible, the later mined area often invades a certain range of the previous mined area, and the end slope of the later mined area is constructed by means of secondary stripping of the internal dumping site of the adjacent previous mined area. However, since the internal dumping site of the previous mined area is artificially piled up and the materials are relatively loose, the slope angle of the end slope of the later mined area is not suitable to be too large, resulting in an increase in the stripping ratio of the later mined area and a decline in economic benefits.

[0004] If the strength of the internal dumped materials can be improved and the angle of the repeated stripping end slope can be increased, the stripping ratio of the later mined area can be reduced and the economic benefits of the later mined area can be improved. Therefore, the present invention combines theoretical experiments, numerical simulations, and mine construction to propose a method for steepening the end slope angle of the secondary stripping in a block-mined open-pit mine. Summary of the Invention

[0005] Aiming at the problems existing in the above-mentioned prior art, the present invention provides a method for steepening the end slope angle of the secondary stripping in a block-mined open-pit mine. By strengthening the secondary stripping end slope in layers and stages, the slope angle is increased, the stripping ratio is reduced, and the economic benefits are improved.

[0006] To achieve the above object, the present invention provides the following technical solutions: A method for steepening the end slope angle of the secondary stripping in a block-mined open-pit mine, comprising the following steps: First, obtain the shear strength parameters of the dumped materials in the secondary stripping area C and φ , and then obtain the maximum safety angle value of the secondary stripping end slope before reinforcement through numerical simulation β ; Then, according to the mine plan, set the slope angle △ β of the secondary stripping end slope to be increased, and establish a β+ △ β numerical model of the secondary stripping end slope. Simulate the slip range and slip surface of the secondary stripping end slope after the steep slope is formed. In the inner waste dump on the side of the front mining area close to the back mining area, with the position of the secondary stripping end slope of the future back mining area as the boundary and the sliding range of the secondary stripping end slope after the steep slope as the reference, extend each point on the edge of the sliding surface 10 - 20 m outward in the normal direction towards the front mining area to form the edge of the reinforcement area. The enlarged boundary and the surface of the secondary stripping end slope steps jointly enclose the reinforcement area. Along the direction perpendicular to the pit bottom, the reinforcement area is divided into the lower section, the middle section, and the upper section; Construction of shear-resistant piers in the lower section: During the mining process of the front mining area, when the waste dumping height in the reinforcement area reaches 10 - 15 m, drill grouting holes in the reinforcement area in a 5 m × 5 m grid along the direction perpendicular to the pit bottom, and then inject composite gelling slurry into the grouting holes under pressure to form shear-resistant piers; Tensile reinforcement in the middle section: After the construction of the shear-resistant piers in the lower section is completed, the inner waste dump continues to dump waste. When each layer of the bench is filled to 2 m away from the designed height, implement layered compaction of the dumped waste until the bench of this layer reaches the designed height. At this time, arrange tensile holes on the surface of this bench at an inclination angle of 15° - 20° and an angle with the normal direction of the sliding surface ≤ 10°; The tensile holes are oriented towards the sliding surface, and the arrangement of the tensile holes on the bench surface is in a 2.5 m × 2.5 m grid pattern. Install anchor cables to the bottom of the tensile holes, and grout and anchor the bottom section of the tensile holes; Reinforced plastic shaping reinforcement in the upper section: When the waste dump approaches the final designed elevation, within the range of the reinforcement area, implement layered reinforcement treatment for the upper 6 m of the secondary stripping end slope, with a layer height of 1.5 m, lay two-way geogrids in layers, and composite lay impermeable geotextiles and three-dimensional vegetation nets in the 0.5 m thick topsoil on the slope surface; Drainage: Set a catchment ditch outside the edge of the top surface of the reinforcement area, fill the ditch with gravel with a particle size of 20 - 40 mm. Along the advancing direction of the open-pit mine, in the reinforcement area, set drainage blind ditches with a depth of 0.5 m at a vertical interval of 20 m and a horizontal interval of 30 m. Fill the blind ditches with gravel with a particle size of 5 - 20 mm and install drain pipes inside. The outlets of the drainage blind ditches extend to the bottom of the open-pit mine.

[0007] Furthermore, the numerical simulation method is as follows: Use numerical simulation analysis to determine the stability coefficients corresponding to different end slope angles formed in the secondary stripping area β i when F si ; β i Starting from 5°, increase the slope angle step by step with a step size of 5° and calculate the stability coefficient. When the stability coefficient F si decreases to 1.2 and below, stop; From the degree at which it stops, decrease step by step by 1° for β i four times in succession and complete the corresponding stability coefficients F siCalculate the angle value where the stability coefficient is greater than 1.2 for the first time, which is the maximum safe angle value of the secondary peeling end. β .

[0008] Furthermore, the bottom of the ultra-deep reinforcement area of ​​the grouting hole is at least 2m, and the composite cementitious slurry is pressure-injected into the grouting hole with a water:cementitious material ratio of 0.6:1. The cementitious material is a mixture of cement and fly ash in a ratio of 7:3 and 3% accelerator is added. The grouting pressure is controlled at 0.5-1.2Mpa; the single-hole grouting volume Q=V×n×η, where V is the volume of the shear pier, n is the porosity, and η is the grouting filling coefficient.

[0009] Furthermore, in the step of constructing the lower shear pier, a drainage pipe is pre-buried 2m below the lowest point of the reinforcement area and extends into the mine. The opening rate of the drainage pipe is 15%, and a 0.8m thick gravel filter layer is laid on the upper part and covered with a double layer of geotextile.

[0010] Furthermore, when the soil is compacted layer by layer in the middle section tensile reinforcement step, the filling thickness of each layer shall not exceed 0.6m, the compaction degree shall be above 93%, the diameter of the tensile hole shall be 130mm and penetrate the sliding surface by at least 5m, the anchor cable arranged in the tensile hole shall be a pressure dispersion anchor cable, the anchor cable shall be placed from the hole mouth to the bottom of the hole and exceed the hole mouth by more than 1.5m, the bottom anchoring shall adopt cement mortar with a grade not less than M30, the anchor section length shall be ≥10m, and exceed the sliding surface by not less than 2m, the tension locking prestress shall be 1.2 times the design value; the frame beam shall adopt prefabricated C30 concrete components with a cross-sectional size of 400mm×600mm, the anchor base shall be embedded at the node and rigidly connected to the anchor cable head, a layer of steel mesh shall be pressed on the lower part of the frame beam grid, and the hole mesh size shall be smaller than the average block size of the waste; a group of flexible inclinometers shall be arranged at a spacing of 50m between the tensile holes to monitor the displacement deformation inside the slope in real time, and the daily displacement threshold shall be set to 3mm.

[0011] Furthermore, the bidirectional geogrid is anchored with U-shaped steel nails at a spacing of 1m. The steel nails are inserted into the soil to a depth of at least 1.2m. The grid overlap width must reach 0.3m. The geogrid anchor points are checked after rainfall. If the local settlement exceeds 30mm or the grid tensile deformation is greater than 5%, micropiles with a diameter of 200mm and a depth of 6m are immediately added.

[0012] Furthermore, after the construction of the reinforcement area is completed, a corrosion-resistant plastic sheet is laid on the surface of the second stripping end step, and 3-5m thick colored rock is disposed above it as an identification area.

[0013] Furthermore, after the upper section is reinforced and shaped, soil is continuously discharged from the upper part, and monitoring equipment is used to monitor the displacement and deformation of the slope and the drainage condition in real time; before the second stripping, slope monitoring equipment is used to monitor the reinforced area, the accuracy of the slope radar reaches the sub-millimeter level, the acquisition frequency of the GNSS ground receiver is 1 Hz, and the accuracy is at the millimeter level.

[0014] Compared with the prior art, through experiments and numerical simulations, the present invention effectively improves the accuracy of engineering construction; aiming at different forms and displacement laws of the reinforcement area, it conducts comprehensive reinforcement in layers and stages, effectively enhancing the stability of the reinforcement area, increasing the slope angle of the rib, reducing the secondary stripping volume, lowering the stripping ratio of the post-mining area, and improving economic benefits; the combined design of the intercepting ditch and the drainage blind ditch forms a three-dimensional drainage system, avoiding the erosion of the reinforcement area by atmospheric precipitation and underground seepage; by setting up an identification area, the damage to the reinforcement area during subsequent secondary stripping is avoided; there is similar engineering experience for reference during the construction process, and the construction difficulty is low; the present invention does not affect the normal soil dumping and soil dumping capacity of the open-pit mine, the whole process is controllable, it is convenient to implement accurately, and follow-up monitoring is carried out during the later stage of reinforcement to ensure the feasibility of the plan. Description of the Drawings

[0015] Figure 1 It is a schematic diagram of the mining area division; Figure 2 It is a schematic cross-sectional view of the secondary stripping of the present invention; Figure 3 It is a schematic cross-sectional view of the comprehensive reinforcement stage in layers and stages of the present invention; Figure 4 It is a schematic diagram of the installation positions of the drainage perforated pipe, the intercepting ditch and the drainage blind ditch of the present invention; In the figure: 1 - pre-mining area; 2 - post-mining area; 3 - secondary stripping area; 4 - secondary stripping end slope; 5 - slip range of the secondary stripping end slope behind the steep slope; 6 - slip surface; 7 - edge of the reinforcement area; 8 - secondary stripping end slope bench; 9 - reinforcement area; 10 - lower section; 11 - middle section; 12 - upper section; 13 - grouting hole; 14 - drainage perforated pipe; 15 - tensile hole; 16 - grille; 17 - intercepting ditch; 18 - advancing direction of the open-pit mine; 19 - drainage blind ditch; 20 - identification area. Detailed Embodiments

[0016] The present invention will be further described below with reference to the accompanying drawings.

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0018] The present invention provides a method for steepening the slope angle of the secondary stripping end slope of a partitioned open-pit mine, including the following steps: As Figures 1 to 4As shown in the figure, the first mining area 1 refers to the mining area that is mined first among two adjacent mining areas in a strip-mined open-pit mine. The subsequent mining area 2 is the mining area that lags behind the first mining area 1 in mining. The secondary stripping area 3 refers to the area of the internal dumping site in the first mining area 1 that needs to be re-excavated when the subsequent mining area 2 is mined after the internal dumping in the first mining area 1. The end slope of the subsequent mining area 2 formed after secondary stripping is called the secondary stripping end slope 4.

[0019] Reinforcement area division: This step mainly provides theoretical support for subsequent layered and phased comprehensive reinforcement and helps to determine relevant parameters in the process of comprehensive reinforcement.

[0020] I. First, determine the maximum safety angle of the slope of the secondary stripping area before reinforcement: Use a large-scale in-situ shear test (this test is a traditional mechanical test with a fixed operation method, which will not be introduced in detail here) to obtain the shear strength parameters of the waste materials in the secondary stripping area 3 C and φ . To ensure the accuracy of the experimental data, the sample size of the in-situ test is not less than 50 cm × 50 cm × 50 cm.

[0021] Use the C and φ, determined by the above test to establish an engineering geological numerical model of the secondary stripping area 3 using engineering software (the modeling process has been basically streamlined and belongs to common knowledge, which will not be introduced in detail here). Through numerical simulation, obtain the maximum safety angle value β of the secondary stripping end slope 4 before reinforcement.

[0022] The numerical simulation method is as follows: Use numerical simulation analysis to determine the stability coefficient β i corresponding to different end slope angles F si formed in the secondary stripping area 3. β i Starting from 5°, increase the slope angle step by step by 5° and calculate the stability coefficient. When the stability coefficient F si decreases to 1.2 and below, stop; from the degree at which it stops, decrease β i step by step by 1° four times and complete the calculation of the corresponding stability coefficient F si . Obtain the angle value at which the stability coefficient is greater than 1.2 for the first time, which is the maximum safety angle value β of the secondary stripping end slope 4.

[0023] II. Determine the shape and range of the most dangerous slip surface of the secondary stripping end slope 4 after the steep slope: According to the mine plan, set the angle △ β of the secondary stripping end slope to be increased. According to the general laws of mechanics and combining the mine production experience, △β is not infinitely large, generally not exceeding 10°, and establish β+ △ β a numerical model of the secondary stripping final slope in the pit (the modeling process has been basically streamlined and belongs to common knowledge, so it will not be introduced in detail here), calculate its stability coefficient, and simulate to obtain the secondary stripping final slope slip range 5 and the slip surface 6 after the steep slope.

[0024] III. Reinforcement area division: In the internal waste dump on the side of the pre-mining area 1 close to the post-mining area 2, with the position of the secondary stripping final slope 4 of the future post-mining area 2 as the boundary, and based on the secondary stripping final slope slip range 5 after the steep slope obtained from the above simulation, extend each point on the edge of the slip surface 6 10 - 20 m outward along the normal direction to the pre-mining area 1 side as the edge 7 of the reinforcement area, aiming to expand the treatment range, strengthen the connection between the treatment area and the non-treatment area, improve the treatment effect, and the enlarged boundary and the surface of the secondary stripping final slope bench 8 jointly enclose the reinforcement area 9. Along the vertical direction of the pit bottom, divide the reinforcement area 9 into the lower section 10, the middle section 11, and the upper section 12.

[0025] Stratified and staged comprehensive reinforcement: This step is based on the development law of the internal waste dump and conducts stratified and staged reinforcement on the reinforcement area 9 delimited in the previous step at different waste dumping stages.

[0026] Construction of shear-resistant piers in the lower section 10, mainly to fix the bottom of the reinforcement area 9, prevent its horizontal sliding, and improve the shear resistance of the bottom: During the mining process of the pre-mining area 1, pre-bury a PVC drainage perforated pipe 14 with a diameter of 200 mm at a position 2 m below the lowest point of the reinforcement area 9 and extend it into the mine pit, that is, arrange it along the open-pit mining direction 18 all the time, and the outlet is exposed at the pit bottom. The opening rate of the drainage perforated pipe 14 is 15% and a 0.8 m thick crushed stone filter layer is laid on the upper part and covered with double-layer geotextiles, which can not only prevent the injected composite cementitious slurry from blocking the drainage perforated pipe 14, but also drain the seepage water in the reinforcement area 9 to the mine pit in time to avoid the erosion of the reinforcement area 9 by the seepage water. When the waste dumping height of the reinforcement area 9 reaches 10 - 15 m, use a geological drill to drill grouting holes 13 with a diameter of 110 mm in the reinforcement area 9 along the vertical direction of the pit bottom according to a 5 m × 5 m grid. The grouting holes 13 are at least 2 m deeper than the bottom of the reinforcement area 9, and then inject composite cementitious slurry into the grouting holes 13 under pressure to form shear-resistant piers with a diameter of not less than 1.5 m; inject composite cementitious slurry into the grouting holes 13 under pressure, and the water:cementitious material ratio is 0.6:1. The cementitious material is a mixture of cement and fly ash in a ratio of 7:3 and 3% accelerating agent is incorporated. The grouting pressure is controlled at 0.5 - 1.2 Mpa; the single-hole grouting volume Q is calculated and determined according to the actual porosity of the materials in the reinforcement area 9, Q = V × n × η, where V is the volume of the shear-resistant pier, n is the porosity, and η is the grouting filling coefficient. To ensure the shear strength, the value is 0.7 - 0.9. Considering the loss and uneven diffusion of the slurry, the actual grouting volume is increased by 10% - 20% to ensure that the permeability rate does not exceed 5 Lu after 48 hours and ensure the formation of effective shear-resistant piers.

[0027] The middle section 11 is reinforced with tensile strength. By applying artificial tension, the middle part of the reinforced area 9 is fixed to prevent it from sliding vertically downward. After the construction of the shear pier in the lower section 10 is completed, the inner dumping yard continues to dump soil. When each layer of steps is filled to about 2m from the design height, an impact roller is used to carry out layered compaction of the soil. The thickness of each layer does not exceed 0.6m, and the compaction degree must reach more than 93%. Until the current step reaches the design height, at this time, tensile holes 15 with a diameter of 130mm are arranged on the surface of the step at an inclination of 15°-20° and an angle of ≤10° with the normal direction of the sliding surface 6; the tensile holes 15 face and penetrate the sliding surface 6 for at least 5m. The arrangement of the tensile holes 15 on the surface of the step is in a 2.5m×2.5m grid. Set pressure-dispersed anchor cables to the bottom of the hole, and anchor the bottom section of tension hole 15 with cement mortar under pressure. The anchor cables are placed from the hole mouth to the bottom of the hole and extend more than 1.5m beyond the hole mouth. The bottom of the hole is anchored with cement mortar of grade not less than M30. The length of the anchor section is ≥10m and exceeds the sliding surface 6 by not less than 2m. The tension locking prestress is 1.2 times the design value. The frame beam adopts prefabricated C30 concrete components with a cross-sectional size of 400mm×600mm. The anchor base is embedded at the node and rigidly connected to the anchor cable head. A layer of steel mesh is pressed under the grid of the frame beam, and the hole mesh size is smaller than the average block size of the waste. A group of flexible inclinometers are arranged at a spacing of 50m between tension holes 15 to monitor the displacement and deformation inside the slope in real time, and the daily displacement threshold is set at 3mm.

[0028] The reinforcement and shaping of the upper section 12 is mainly to integrate the upper part of the reinforcement area 9 into a relatively complete whole to prevent it from sliding down due to the sliding below: when the spoil dump is close to the final design elevation, within the scope of the reinforcement area 9, the upper 6m range of the secondary stripping end 4 is reinforced in layers, with a layer height of 1.5m, and bidirectional geogrids 16 with a tensile strength of not less than 80kN / m are laid in layers. The bidirectional geogrids 16 are anchored with U-shaped steel nails at a spacing of 1m, and the steel nails are at least 1.2m deep in the soil. The overlap width of the grid 16 must reach 0.3m and be locked with a special connector; 400g / m² anti-seepage geotextile and three-dimensional vegetation net are compositely laid in the 0.5m thick planting soil on the surface of the slope, and hydraulic spraying and planting grass technology is used for protection. Furthermore, after rainfall, focus on checking the anchor points of the geogrid 16. If the local settlement exceeds 30mm or the tensile deformation of the grid 16 is greater than 5%, immediately add micro piles with a diameter of 200mm and a depth of 6m.

[0029] Drainage: A drainage ditch 17 with a bottom width of 0.6m and a longitudinal slope of 2% is set outside the top edge of the reinforcement area 9 of the spoil dump in the front mining area 1. The ditch is filled with 20-40mm crushed stone to prevent surface runoff from flowing into the reinforcement area 9. Along the open-pit mine advancement direction 18, in the reinforcement area 9, a 0.5m deep drainage blind ditch 19 is set with a vertical spacing of 20m and a horizontal spacing of 30m. The drainage blind ditch 19 is filled with 5-20mm crushed stone and built-in permeable pipes. The slope of the permeable pipe is ≥1%. The outlet of the drainage blind ditch 19 extends to the bottom of the open-pit mine, that is, it is arranged along the open-pit mine advancement direction 18, and the outlet is exposed at the bottom of the pit, forming a three-dimensional drainage system to ensure the rapid discharge of surface seepage water.

[0030] Before each stage of construction, the slope shape is verified by using drone 3D modeling. After the construction of the reinforcement area 9 at each location is completed, a corrosion-resistant plastic sheet is laid on the surface of the step 8 at the secondary stripping end, and a 3-5m thick colored rock is discarded above it (except for the surface position) as the identification area 20. When the secondary stripping of the post-mining area 2 is performed, when the identification area 20 is touched, the construction refinement is improved to avoid damage to the reinforcement area 9 by the secondary stripping.

[0031] After the upper section 12 is reinforced and shaped, soil is continued to be discharged from the top. Monitoring equipment such as slope radar and GNSS ground receivers are used to monitor the displacement and deformation of the slope in real time, and monitor the drainage conditions. Before the second stripping, slope monitoring equipment is used to monitor the reinforced area 9 to ensure that there is no obvious deformation speed and cracks before operation. The accuracy of the slope radar reaches the sub-millimeter level, the acquisition frequency of the GNSS ground receiver is 1Hz, and the accuracy is at the millimeter level.

[0032] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0033] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any slight modification, equivalent substitution and improvement made to the above embodiment based on the technical essence of the present invention should be included in the protection scope of the technical solution of the present invention.

Claims

1. A method for steepening the slope angle of the secondary stripping end slope in a partitioned mining open-pit mine, characterized in that, The following steps are involved: First, obtain the shear strength parameters of the discharged materials in the secondary stripping area (3). C And φ , and then obtain the maximum safety angle value of the secondary stripping end slope (4) before reinforcement through numerical simulation β ; According to the mine plan, set the angle △ of the secondary stripping end slope to be increased β , establish β+ △ β numerical model of the secondary stripping end slope, and simulate the slip range (5) and slip surface (6) of the secondary stripping end slope after the steep slope In the inner dump near the rear mining area (2) of the front mining area (1), with the position of the secondary stripping end wall (4) of the future rear mining area (2) as the boundary and the sliding range (5) of the secondary stripping end wall after the steep wall as the reference, the edge of the sliding surface (6) is extended 10-20m to the front mining area (1) as the edge of the reinforcement area (7). The expanded boundary and the surface of the secondary stripping end wall step (8) jointly define the reinforcement area (9). Along the direction perpendicular to the pit bottom, the reinforcement area (9) is divided into a lower section (10), a middle section (11) and an upper section (12); Construction of shear piers in the lower section (10): During the mining process of the front mining area (1), when the dumping height of the reinforcement area (9) reaches 10-15m, grouting holes (13) are drilled in the reinforcement area (9) vertically in the direction of the pit bottom in a 5m×5m grid, and then composite gelling slurry is pressure-injected into the grouting holes (13) to form shear piers; Middle section (11) tensile reinforcement: After the construction of the shear pier of the lower section (10) is completed, the inner dumping site continues to dump soil. When each step is filled to a height of 2m from the design height, the soil is dumped in layers and compacted until the step reaches the design height. At this time, tensile holes (15) are arranged on the surface of the step at an angle of 15°-20° and an angle of ≤10° with the normal direction of the sliding surface (6). The tensile holes (15) face the sliding surface (6) and are arranged in a 2.5m×2.5m grid on the surface of the step. Anchor cables are arranged in the tensile holes (15) to the bottom of the holes, and the bottom section of the tensile holes (15) is grouted and anchored. Upper section (12) reinforcement and shaping: When the spoil dump is close to the final design elevation, within the reinforcement area (9), layered reinforcement treatment is carried out within the upper 6m range of the secondary stripping end wall (4), with a layer height of 1.5m, and bidirectional geogrids (16) are laid in layers. Anti-seepage geotextile and three-dimensional vegetation net are laid in the 0.5m thick planting soil on the surface of the slope; Drainage: A drainage ditch (17) is set outside the top edge of the reinforcement area (9), and the ditch is filled with 20-40 mm crushed stone. Along the advancement direction of the open-pit mine (18), a 0.5 m deep drainage blind ditch (19) is set in the reinforcement area (9) with a vertical spacing of 20 m and a horizontal spacing of 30 m. The drainage blind ditch (19) is filled with 5-20 mm crushed stone and has a built-in permeable pipe. The outlet of the drainage blind ditch (19) extends to the bottom of the open-pit mine.

2. The method for steepening the secondary stripping end slope angle of an open-pit mine with sectional mining according to claim 1, characterized in that The numerical simulation method is: Determine the stability coefficients corresponding to different end slope angles formed in the secondary stripping area (3) by numerical simulation analysis β i when F si , β i Starting from 5°, increase the slope angle step by step in 5° increments and calculate the stability coefficient. When the stability coefficient F si drops to 1.2 or less, stop; starting from the degree at which it stops, decrease it step by step by 1° β i four times in sequence and complete the calculation of the corresponding stability coefficient F si . Obtain the angle value at which the stability coefficient is greater than 1.2 for the first time, which is the maximum safety angle value of the secondary stripping end slope (4) β .

3. A method for steepening the slope angle of the secondary stripping end slope in a partitioned open-pit mine according to claim 1, characterized in that The grouting hole (13) is at least 2 m from the bottom of the super-deep reinforcement zone (9), and a composite cementitious slurry is pressure-injected into the grouting hole (13) with a water:cementitious material ratio of 0.6:

1. The cementitious material is a mixture of cement and fly ash in a ratio of 7:3 and 3% of a quick-setting agent is added. The grouting pressure is controlled at 0.5-1.2 MPa. The grouting volume per hole is Q=V×n×η, where V is the volume of the shear pier, n is the porosity, and η is the grouting filling coefficient.

4. A method for steepening the secondary stripping end slope angle of a partitioned open-pit mine according to claim 3, characterized in that In the step of constructing the shear pier of the lower section (10), a drainage pipe (14) is pre-buried at a position 2 m below the lowest point of the reinforcement area (9) and extends into the mine pit. The drainage pipe (14) has an opening rate of 15% and a 0.8 m thick crushed stone filter layer is laid on the upper part and covered with a double layer of geotextile.

5. A method for steepening the secondary stripping end slope angle of an open-pit mine with zoned mining, as claimed in claim 1, wherein During the tensile reinforcement step of the middle section (11), when the soil is compacted and discharged in layers, the thickness of each layer of filling shall not exceed 0.6 m, and the compaction degree shall reach more than 93%. The diameter of the tensile hole (15) is 130 mm and it penetrates the slip surface (6) by at least 5 m. The cable anchor in the tensile hole (15) is a pressure-dispersed cable anchor. The cable anchor is placed from the hole mouth to the hole bottom and extends more than 1.5 m beyond the hole mouth. The hole bottom is anchored with cement mortar with a grade not lower than M30, the length of the anchorage section is ≥10 m, and it exceeds the slip surface (6) by not less than 2 m. The tension locking prestress is 1.2 times the design value; the lattice beam is made of precast C30 concrete components with a cross-sectional size of 400 mm×600 mm. The anchor base is embedded at the node and rigidly connected to the cable anchor head. A layer of steel mesh is pressed under the grid of the lattice beam, and the hole size of the mesh is smaller than the average lump size of the waste. A set of flexible inclinometers is arranged at an interval of 50 m in the tensile holes (15) to monitor the internal displacement and deformation of the slope in real time, and the daily displacement threshold is set at 3 mm.

6. A method for steepening the secondary stripping end slope angle of a partitioned open-pit mine according to claim 1, characterized in that, The two-way geogrid (16) is anchored with U-shaped steel nails at an interval of 1 m, and the penetration depth of the steel nails into the soil is at least 1.2 m. The overlap width of the geogrid (16) shall reach 0.3 m. After rainfall, check the anchor points of the geogrid (16). If the local settlement exceeds 30 mm or the tensile deformation of the geogrid (16) is greater than 5%, immediately drive micro-piles with a diameter of 200 mm and a depth of 6 m.

7. A method for steepening the slope angle of the secondary stripping end slope in a partitioned open-pit mine according to claim 1, characterized in that After the construction of the reinforcement area (9) is completed, a corrosion-resistant plastic cloth is laid on the surface of the secondary stripping end bench (8), and 3-5 m thick colored rocks are discharged above it as the identification area (20).

8. A method for steepening the slope angle of the secondary stripping end slope in a partitioned open-pit mine according to claim 1, characterized in that After the upper section (12) is reinforced and shaped, soil is continuously discharged above it. Monitoring equipment is used to monitor the displacement and deformation of the slope in real time, and the drainage condition is monitored; before the secondary stripping, the reinforcement area (9) is monitored by slope monitoring equipment. The accuracy of the slope radar reaches the sub-millimeter level, and the acquisition frequency of the GNSS ground receiver is 1 Hz with an accuracy of the millimeter level.

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