A method of delayed infiltration drainage of overburden in open pit to underground mining

Abstract

The application discloses a kind of open pit to underground mining covering layer's delayed infiltration drainage method, method steps are as follows: 1) in the lower disc side slope of open pit bottom, along vein water channel is set, along vein water channel is connected with drainage ditch in horizontal roadway, drainage ditch is connected with upper water sump;2) using caving method mining, form comprehensive covering layer in open pit;3) waterproof and anti-seepage layer is set on the surface of comprehensive covering layer;4) surface water can be guided to the lower disc side slope by waterproof and anti-seepage layer again along the crack of waterproof and anti-seepage layer edge and the crack on the rock of lower disc side slope to underground stope seepage, and the water of seepage is intercepted by along vein water channel and enters upper water sump.This method adopts three-dimensional delayed infiltration method of upper guide, middle lead and lower discharge, can effectively avoid the increase of drainage cost caused by guiding water into the lowest water sump, greatly increases the water-resisting capacity of covering layer, makes the original open pit become temporary water pool, delays the impact of heavy rainfall on underground drainage capacity.

Description

Technical Field

[0001] This invention relates to a mining method, and more particularly to a method for slow-seepage drainage of overburden in open-pit to underground mining. Background Technology

[0002] In mines transitioning from open-pit to underground mining, caving is a highly efficient method if conditions permit. Since open-pit slopes are typically located within the deformation and subsidence zones of underground mining, drainage ditches constructed on these slopes become ineffective due to slope deformation and cracking. Therefore, the standard design typically diverts atmospheric precipitation collected at the original open-pit boundary through the overburden, crushed ore, and underground shafts into underground water reservoirs, which are then pumped out of the mine. This drainage method has several drawbacks: first, the underground water reservoirs and drainage capacity must be designed according to the maximum rainfall intensity of the open-pit runoff; otherwise, flooding may occur; second, diverting surface water to the lowest-elevation water reservoir before releasing it to the surface results in significant power and drainage equipment losses; and third, large floods carry fine particles from the crushed ore in the overburden to the underground water reservoirs, placing immense pressure on the sedimentation tank cleaning process and posing a risk of mudflows. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for slow-seepage drainage of overburden in open-pit to underground mining with energy saving, safety and good drainage effect.

[0004] To solve the above technical problems, the method steps adopted by the present invention are as follows: 1) A water inlet channel is set on one side of the lower slope of the open pit bottom, the water inlet channel is connected to the drainage ditch in the guide horizontal tunnel, and the drainage ditch is connected to the upper water tank.

[0005] 2) The caving method is used for mining to form a comprehensive overburden layer in the open pit;

[0006] 3) A waterproof and seepage-proof layer is installed on the surface of the integrated covering layer;

[0007] 4) Surface water can be guided by the waterproof and seepage-proof layer to one side of the lower slope and then seep into the underground mining area along the cracks at the edge of the waterproof and seepage-proof layer and the gaps in the rocks of the lower slope. The seeping water is intercepted by the water inlet channel and enters the upper water tank.

[0008] Furthermore, in step 3), when additional crushed stone is needed as mining progresses, a waterproof and seepage-proof layer is then applied to the surface of the replenished comprehensive cover layer.

[0009] Furthermore, the comprehensive overburden formation process in step 2) is as follows: an ore overburden is formed by caving down the hanging ore and releasing ore, a coarse waste rock overburden is formed by caving down the upper side slope, and then fine waste rock is covered on the coarse waste rock overburden to form a fine waste rock overburden. All the above layers together form the comprehensive overburden.

[0010] Furthermore, a sedimentation tank is provided at the inlet end of the upper water tank.

[0011] Furthermore, the waterproof and seepage-proof layer is composed of two layers of organic polymer materials, with a foamed layer at the bottom and a dense layer at the top.

[0012] The beneficial effects of adopting the above technical solution are as follows:

[0013] 1. Preventing surface rainwater from flowing into the lowest point of the underground mining area and then being discharged effectively saves drainage energy;

[0014] 2. The waterproof and seepage-proof layer at the bottom of the pit can slow down the seepage of heavy rainfall, allowing the open pit to accumulate a large amount of rainwater, reducing the impact on the drainage capacity of the well and preventing flooding.

[0015] 3. Prevent rainwater from directly eroding the overburden layer, thus avoiding mudflows caused by fine particles in the overburden layer being washed into the well site;

[0016] 4. Due to the excellent sealing and thermal insulation properties of the waterproof and seepage-proof layer, the thickness of the covering layer can be appropriately reduced without affecting the thermal insulation and air leakage prevention functions of the covering layer;

[0017] 5. It can greatly reduce the size of the underground water tank and the underground drainage capacity reserve; since the waterproof layer can turn the open pit into a temporary water storage pool, the amount of water entering the underground mining area will not increase suddenly during heavy rainfall, so the size of the water tank can be reduced, and at the same time the drainage capacity prepared for heavy rainfall can also be reduced.

[0018] 6. It can prevent the original groundwater from being polluted by surface water; some mine groundwater resources can be processed into mineral water, but it is difficult to maintain and restore the original quality after mixing with surface water.

[0019] This invention employs a three-dimensional delayed infiltration method of top guidance, middle diversion, and bottom drainage, which can effectively avoid the increased drainage costs caused by diverting water to the lowest water tank, greatly increase the water-proofing and heat-insulating performance of the cover layer, and turn the original open pit into a temporary water accumulation pool, thus delaying the impact of heavy rainfall on the drainage capacity of the well. Attached Figure Description

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0021] Figure 1This is a schematic diagram of the structure of the open-pit to underground mining operation described in this invention;

[0022] Figure 2 This is a schematic diagram of the structure of the mine after the caving method is used to cavitate the ore along the side of the mine according to the present invention;

[0023] Figure 3 This is a schematic diagram of the structure of the ore covering layer and the waterproof and seepage-proof layer described in this invention;

[0024] Figure 4 This is a schematic diagram of the delayed infiltration drainage structure of the present invention;

[0025] Figure 5 This is a schematic diagram of the structure of the water inlet channel along the vein as described in this invention;

[0026] Figure 6 This is a schematic diagram of the structure of the water inlet channel along the vein described in this invention;

[0027] Figure 7 This is a schematic diagram of the cross-sectional parameters of the water inlet channel along the lower plate of the present invention;

[0028] Figure 8 This is a schematic diagram of the structure of the waterproof and seepage-proof layer described in this invention;

[0029] Figure 9 This is a flowchart of the drainage steps of the present invention.

[0030] In the diagram: 1. Shaft; 2. Open pit; 3. Lower slope; 4. Upper slope to be blasted; 5. Blasting hole; 6. Horizontal cross-vein roadway; 7. Horizontal along-vein roadway; 8. Collapsed waste rock cover layer; 81. Ore cover layer; 82. Coarse-grained waste rock cover layer; 9. Fine-grained waste rock cover layer; 10. Waterproof and seepage-proof layer; 10. Foamed layer; 101. Dense layer; 102. Water guide strip; 11. Along-vein water receiving channel; 12. Guide horizontal roadway; 13. External drainage shaft; 14. Upper water tank; 15. Main transport horizontal roadway perpendicular to the ore body; 16. Shaft; 17. Main transport horizontal roadway parallel to the ore body; 18. Detailed Implementation

[0031] The method steps for the delayed-seepage drainage method for overburden in open-pit to underground mining are as follows:

[0032] Figure 1 As shown, according to the mine's mining plan, when open-pit mining reaches a certain depth, preparations for underground mining development and recovery work begin. This method is based on the caving mining method used in underground mining. The necessary engineering systems for underground mining are completed before the end of open-pit mining activities. Figure 4As shown, the main shaft and tunnel works include: excavating a vertical shaft 17 from the surface to the lowest level of the ore body; then excavating horizontal tunnels from the shaft, namely the main haulage tunnel 16 perpendicular to the ore body and the main haulage tunnel 18 parallel to the ore body, to enter the ore body, thereby recovering ore and transporting it to the surface. The two side slopes of the open pit 2 are the slope 4 to be blasted and the footwall slope 3, respectively; blast holes 5 are set in the slope 4 to be blasted for subsequent blasting and collapse.

[0033] 1) Figures 1-4 As shown, the drainage system of the shaft and tunnel project includes a guide horizontal tunnel 13, an external drainage shaft 14, and a water reservoir. The guide horizontal tunnel 13 is used to guide the outflow of water from the horizontal tunnel. The water reservoir is connected to the drainage ditch of the guide horizontal tunnel 13 and is used to collect the outflow of water from the horizontal tunnel. Generally, there are two water reservoirs, an inner and an outer one. Among the water reservoirs, the water reservoir located in the same middle section as the water receiving channel 12 is the upper water reservoir 15. The upper water reservoir 15 is set near the shaft or inclined shaft, and its level is lower than the horizontal tunnel that draws water to it. A sedimentation tank is set at the inlet end of the water reservoir. The arrangement of the sedimentation tank is selected according to the amount of mud in the water flow. When the mud content is high, a separate sedimentation tank is arranged at the inlet of the water reservoir. When the mud content is low, a sunken sedimentation tank or a baffle sedimentation tank is generally used at the bottom of the water reservoir. The external drainage shaft 14 is used to collect the water from each tunnel and pump it to the surface, or transfer it to the main shaft 17 and then pump it to the surface.

[0034] 2) Install water inlet trough 12 along the vein: Figure 4 As shown, a water collection trough 12 is installed on one side of the lower slope 3 to be preserved at the bottom of the open pit 2. After the blast holes are detonated, a small portion of rock will be thrown into the ore, causing some ore dilution, but most of the rock will remain in place, supporting a trough-shaped outline composed of gravel, thereby diverting the intercepted water into the drainage ditch of the access roadway. The water collection trough 12 is located at the bottom of the lower slope 3, extending along the entire length of the lower slope 3 in a strip-shaped trough structure; the opening of the water collection trough 12 faces the ore body, its direction is perpendicular and it connects to the ore access roadway. Figure 4 , Figure 5 , Figure 6 As shown, the outlet of the vein-fed water collection trough 12 is arranged in the guide horizontal tunnel 13, at the interface between the ore body and the surrounding rock, located on one side of the surrounding rock. The bottom of the vein-fed water collection trough 12 has an inclined structure, with the outlet side lower and the side away from the outlet higher, sloping upwards at an angle of 10° to 15° with the horizontal direction from the outlet to both sides, in order to collect the water flowing down along the surrounding rock wall. The outlet of the vein-fed water collection trough 12 is connected to the drainage ditch in the guide horizontal tunnel 13. After the vein-fed water collection trough 12 is set up, the water flowing down along the interface between the footwall surrounding rock and the ore body will be intercepted by the vein-fed water collection trough and introduced into the drainage ditch of the ore access roadway, and then introduced into the upper water tank 15 through the drainage ditch of the guide horizontal tunnel 13, and then discharged to the surface by the water pump of the vertical shaft 17.

[0035] The formula for calculating the cross-sectional dimensions of the water inlet 12 along the vein is as follows:

[0036] S The effective drainage area is determined by the amount of a long-duration rainstorm that the open pit can withstand once every thirty years and the designed discharge time in m. The calculation formula is as follows: (I):

[0037] (I)

[0038] In formula (Ⅰ): A The catchment area of ​​the open pit is m. 3 ; h 1. Rainfall in 24 hours during a 30-year return period to heavy rainfall event, mm / d; 2. Duration of the 30-year return period to heavy rainfall event, d; 3. Duration of the open pit designed to drain accumulated water; 4. Flow velocity of water in the water receiving channel along the lower plate of the vein, m / d.

[0039] Figure 7 As shown, the parameters of the cross-section are then calculated from S as follows (II):

[0040] (II)

[0041] In formula (II): S is the effective water-conducting area; k is the water-conducting porosity coefficient in loose rock, which is related to the degree of rock fragmentation and should be measured on-site. Based on experience, k can be taken as approximately 0.15; α is taken as 90° to 120°; β is taken as 60° to 70°; a and b are... Figure 7 For the cross-section shown, a=b can generally be taken on both sides, but it can also be adjusted according to the lithology.

[0042] 3) Forming a comprehensive covering layer within the open pit: Figure 2 , 3As shown in Figure 4, the comprehensive overburden layer includes an ore overburden layer 81, and a coarse waste rock overburden layer 82 and a fine waste rock overburden layer 9 covering the ore overburden layer 81. The formation process of the ore overburden layer 81 is as follows: the blasted ore is left at the bottom of the open pit and not transported out to form the first ore overburden layer; the top of the hanging ore overburden layer is formed by the collapse of the ore at the bottom of the open pit; the first ore overburden layer and the hanging ore overburden layer together form the ore overburden layer 81. The collapse of the upper slope forms a coarse-grained waste rock cover layer 82. If the collapsed rock does not meet the particle size requirement of the coarse-grained waste rock cover layer 82, dump trucks are needed to bring waste rock of suitable particle size and dump it from the top of the upper slope downwards to achieve the designed thickness. According to the ore release ellipsoid theory, the coarse-grained waste rock cover layer 82 and the ore layer at the bottom of the open pit and below have a loose body and release body relationship. In order to prevent premature dilution during the ore release process and to prevent seepage damage from carrying away fine particles to form debris flows, the ideal particle size structure of the coarse-grained waste rock cover layer 82 should be close to the particle size structure of the ore layer in the mining area. The coarse-grained waste rock cover layer 82 described in this method has a particle size of not less than 20 mm (after screening out fine particles), a particle size of not less than 40% of particles larger than 100 mm, and a thickness of not less than 20 m. The ore cover layer 81 and the coarse-grained waste rock cover layer 82 constitute the collapsed waste rock cover layer 8. Then, fine-grained waste rock is dumped from the top of the upper slope onto the coarse-grained waste rock cover layer 82 using dump trucks to form a fine-grained waste rock cover layer 9. The main function of the fine-grained waste rock cover layer 9 is to prevent wind erosion and delay the infiltration of rainwater. Therefore, the particle size composition of this layer must meet the requirements of porosity and density. According to the particle size composition of the waste rock in the example, the main particle size composition of the fine-grained waste rock cover layer 9 is required to be: the volume ratio of fine particles with a particle size of less than 5 mm to coarse particles with a particle size of more than 5 mm in this layer is 3:7, and the thickness of the fine-grained waste rock cover layer 9 is not less than 25 m. The slope of the overall cover layer, i.e. the slope of the fine-grained waste rock cover layer 9, is a sloping surface that slopes downward from the slope 4 to be blasted down to the upper slope 3. Since 82 and 9 are slopes naturally formed by dump trucks, their slope angle is the natural angle of repose. The overall thickness of the coarse-grained waste rock cover layer 82 and the fine-grained waste rock cover layer 9 should not be less than 45m. Considering the formation mode of the waste rock cover layer, the optimal thickness is 48m.

[0043] 4) Formation of a waterproof and seepage-proof layer 10: Figure 3 , Figure 4 As shown, a waterproof and seepage-proof layer 10 is constructed on the fine-grained waste rock cover layer 9, and the waterproof and seepage-proof layer 10 extends as one layer on the slope. Figure 8 As shown, the waterproof and seepage-proof layer 10 is composed of a lower foamed layer 101 and an upper dense layer 102.

[0044] The foam layer 101 can be laid using pre-processed flexible foam rolls or by on-site foaming. The advantage of roll laying is that the quality of the roll is easier to control, but the disadvantage is that there is no adhesion between the foam roll and the gravel substrate. On-site foaming has the opposite advantages and disadvantages, and the choice should be made based on the technical conditions and adaptability of the site. For example, using a polyurethane foam spraying machine, the two components of the raw materials can be heated to the required temperature on-site, then fully mixed at the nozzle and pneumatically sprayed to form a foam surface layer. The foam layer material can be polyurethane, phenolic resin, polyurethane foam board, etc. The thickness of the foam layer 101 is 3–6 cm.

[0045] The dense layer can be made of modified bitumen waterproofing materials, polymer-modified waterproof membranes, synthetic polymer waterproof membranes, or polyurea sprayed on-site, depending on the availability of local materials and their compatibility with the foaming layer material. This example uses polyurea as an example. An agricultural pesticide spraying quadcopter drone is used to uniformly spray a mixture of two components of polyurea onto the foaming layer 101. The nozzle flow rate is controlled so that a solidified layer of 0.5–1 mm thickness is formed on the foaming layer with each flight. Multiple flights can be performed to form the dense layer 102. The thickness of the dense layer 102 is preferably 2.5–3.5 mm.

[0046] The foamed layer 101 has the advantages of small quantity and good coverage, which can prevent leakage in the gaps between stones when the dense layer is not cured, saving the amount of dense layer 102 used, and also has good thermal insulation performance. The dense layer 102 has good toughness, weather resistance and service life. The foamed layer 101 and the dense layer 102 are used together to make the comprehensive covering layer waterproof and drainage, and enhance its thermal insulation function, which can appropriately reduce the thickness of the comprehensive covering layer. The comprehensive covering layer treated in the above way can achieve an ultimate elongation at break of 400% at -30°C and does not leak when covered with 20 meters of water.

[0047] 5) Because the waterproof and seepage-proof coating 10 can prevent or delay water from seeping downward into the ore overburden, in the event of rain, surface water such as atmospheric precipitation flows down the direction of the waterproof and seepage-proof coating 10 towards the footwall slope 3, forming a water guide zone 11. The water flowing to the footwall slope 3 then seeps into the underground mining area along the gap between the waterproof and seepage-proof coating and the footwall slope 3, as well as the gaps on the rocks of the footwall slope 3. The seeping water is intercepted by the vein-connecting water channel 12 and enters the water ditch in the guide horizontal roadway 13 (mine access roadway). After sedimentation in the sedimentation tank, it is guided into the upper water tank 15 and pumped to the surface through the external drainage shaft 14.

[0048] 6) When the ore is discharged, some settlement pits will appear on the surface of the comprehensive cover layer. However, since the slope of the comprehensive cover layer surface is large enough (10% to 20%), the ore cover layer is thick enough, and the waterproof and seepage-proof layer 10 has great extensibility, the waterproof and seepage-proof layer 10 will not fail to perform its waterproof and water-conducting functions.

[0049] 7) Replenishment of the Overall Overburden: As mining progresses, the initial overall overburden is typically thinned due to over-mining. When its thickness decreases to 2 / 3 or less of its original thickness, it can be replenished by bringing in waste rock from outside. The block size and structure of this waste rock will be the same as the initial overburden. Because the waterproof and seepage-proof layer on the overall overburden will lose its waterproof and seepage-proof function due to vehicle pressure and impacts during waste rock unloading, the replenishment of the overall overburden should be completed before the rainy season. After replenishment, a waterproof and seepage-proof layer 10 should be sprayed (laid) on its surface again.

[0050] Figure 9 As shown, the drainage steps of this delayed-seepage drainage method for the overburden layer in open-pit to underground mining are as follows: In the event of rain, surface water such as atmospheric precipitation flows from the open-pit 2 and flows down the slope 3 of the waterproof and seepage-proof layer 10, forming a water guide zone 11; the water flowing to one side of the slope 3 then flows down the surrounding rock of the slope 3; the flowing water flows into the vein-connecting water channel 12 and from the outlet of the vein-connecting water channel 12 into the water ditch of the guide horizontal tunnel 13, and after sedimentation in the sedimentation tank, it enters the upper water tank 15; then it is pumped to the surface drainage ditch through the external drainage shaft 14 or transferred to the main shaft 17 to be pumped to the surface for discharge.

Claims

1. A method for delayed infiltration drainage of overburden in open-pit to underground mining operations, characterized in that, The method steps are as follows: 1) The drainage system of the shaft project includes a horizontal guide tunnel (13), an external drainage shaft (14), and a water reservoir; the horizontal guide tunnel (13) is used to guide the outflow of water in the horizontal tunnel; the water reservoir is connected to the drainage ditch of the horizontal guide tunnel (13) and is used to collect the outflow of water in the horizontal tunnel; a water inlet channel (12) is set on one side of the lower slope (3) of the bottom of the open pit (2), and the water inlet channel (12) is connected to the drainage ditch in the horizontal guide tunnel (13) to drain water. The ditch connects to the upper water tank (15); the trough (12) along the vein is set at the bottom of the lower slope (3) and extends along the entire length of the lower slope (3) as a strip-shaped trough structure; the bottom of the trough (12) along the vein is an inclined structure, with the outlet side being lower and the side away from the outlet being higher; for the trough (12) along the vein, S is the effective water guiding area, which is determined by the amount of long-term rainstorm that the open pit can withstand once every thirty years and the design discharge time m, and the calculation formula is as follows (Ⅰ): （Ⅰ） In formula (Ⅰ): A is the catchment area of ​​the open pit, m 3 h is the 24-hour rainfall of a once-in-30-year long-duration rainstorm, mm / d; n is the number of days of the once-in-30-year long-duration rainstorm, d; m is the number of days designed to drain the water from the open pit; r is the flow velocity of water in the trough along the vein, m / d. 2) The caving method is used to mine the ore and form a comprehensive cover layer in the open pit (2). The process of forming the comprehensive cover layer is as follows: the ore cover layer (81) is formed by caving the hanging ore and releasing the ore, and then the upper side slope is caved to form a coarse waste rock cover layer (82). Then the crushed fine waste rock is covered on the coarse waste rock cover layer (82) to form a fine waste rock cover layer (9). All the above layers together form a comprehensive cover layer. 3) A waterproof and seepage-proof layer (10) is set on the surface of the comprehensive cover layer. When additional crushed stone is needed as mining progresses, another waterproof and seepage-proof layer (10) is set on the surface of the supplemented comprehensive cover layer. 4) The surface water is guided by the waterproof and seepage-proof layer (10) to the side of the lower slope (3) and then seeps into the underground mining area along the cracks at the edge of the waterproof and seepage-proof layer and the cracks in the rock of the lower slope (3). The seeping water is intercepted along the vein water inlet (12) and enters the upper water tank (15).

2. The delayed-seepage drainage method for overburden in open-pit to underground mining as described in claim 1, characterized in that: In step 1), the bottom of the water-receiving trough (12) is inclined upward from the outlet to both sides at an angle of 10° to 15° with the horizontal direction, in order to receive the water flowing down along the surrounding rock wall; the outlet of the water-receiving trough (12) is connected to the drainage ditch in the horizontal guide tunnel (13).

3. The delayed-seepage drainage method for overburden in open-pit to underground mining as described in claim 1, characterized in that: In step 1), the cross-sectional dimensions of the water inlet channel (12) are calculated from S using the following formula (II): （Ⅱ） In formula (II): S is the effective water-conducting area; k is the water-conducting porosity coefficient in loose rock, which is related to the degree of rock fragmentation and should be measured on site; α is taken as 90° to 120°; a and b are the two sides of the cross section, and a=b is taken.

4. The delayed-seepage drainage method for overburden in open-pit to underground mining as described in claim 1, characterized in that: The upper water tank (15) is equipped with a sedimentation tank at its inlet end.

5. A method for delayed infiltration drainage of overburden in open-pit to underground mining operations according to any one of claims 1-4, characterized in that: The waterproof and seepage-proof layer (10) is composed of two layers of organic polymer materials, with the lower layer being a foamed layer (101) and the upper layer being a dense layer (102).

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