Method for determining thickness of isolating layer from open-pit mining to underground mining

Abstract

The invention discloses a method for determining the thickness of an isolating layer from open-pit mining to underground mining, which relates to the technical field of mining, and comprises the following steps of: firstly, investigating the technical status of a mine, and determining the mining technical conditions and occurrence conditions of underground ore bodies; planning an underground ore body mining stage and a mining method according to the actual condition of the underground ore body; calculating the value range of the safety thickness of the open-pit-to-underground isolation ore pillar, and simulating underground mining by adopting a numerical simulation means; according to the recommended safety thickness, establishing a test model similar to the open-pit-to-underground structure of the mine; then exploiting the test model according to the formulated plan; after the test model is established without errors, mining the ore body, and meanwhile, monitoring whether the structural strength of the isolation ore pillar reaches the standard or not; the technical problem that precise calculation needs to be carried out so as to guarantee the safety of workers in a goaf in order to guarantee that the isolation pillars can guarantee that underground mining does not affect an open stope is solved.

Description

Technical Field

[0001] The invention relates to the technical field of mining, and in particular to a method for determining the thickness of an isolation layer in transition from open-pit to underground mining. Background Art

[0002] The transition of a mine from open pit to underground mining usually goes through three stages: a single open pit mining period, a period of simultaneous open pit and underground mining, and a single underground mining period. In the process of converting open pit to underground mining, isolation pillars can be set up to allow open pit and underground mining to be carried out simultaneously, but this may also bring some safety hazards. If the reserved thickness is too thin, the isolation pillars may collapse suddenly. The collapsed pillars may compress the air in the goaf, and the resulting air waves are highly destructive, threatening underground facilities and personnel safety. If the reserved thickness is too thick, it may cause a waste of mineral resources, and the investment cost of the mine will also increase accordingly.

[0003] In the process of converting open-pit mining to underground mining, since open-pit mining and underground mining are carried out simultaneously, the isolation pillars are affected by the load brought by open-pit mining as well as the disturbance caused by underground mining. Therefore, there are many factors that affect the stability of the isolation pillars, which are usually divided into internal factors and external factors. Internal factors include engineering geological and hydrological conditions, physical and mechanical properties of ore and rock, etc. External factors include mining methods, stope structure parameters, mining sequence, blasting disturbance and water influence, etc. All of them will affect the stability of the isolation pillars. In order to ensure that underground mining will not affect the open-pit mine, precise calculations are required to ensure the safety of workers in the goaf. Summary of the invention

[0004] The purpose of the present invention is to provide a method for determining the thickness of the isolation layer for converting open-pit to underground mining, so as to solve the technical problem that precise calculations are needed to ensure that underground mining will not affect the open-pit mine, thereby ensuring that open-pit and underground mining will not affect each other and ensuring the safety of surface structures and underground workers.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for determining the thickness of an isolation layer in transitioning from open pit to underground mining comprises the following steps:

[0007] S1: First, conduct a technical survey of the mine, including determining the data of the mine's minimum mining level, the final slope angle of the upper wall, the final slope angle of the lower wall, the length and width of the open pit bottom, the horizontal thickness of the ore body and the inclination of the ore body, and determine the technical conditions for underground ore body mining and its occurrence;

[0008] S2: According to the actual situation of the ore body, plan the mining stage of the ore body, and determine the height of each mining stage, and at the same time determine the mining method of each stage, determine the mining height of each middle section and the method of setting the pillars;

[0009] S3: The load transfer intersection method and structural mechanics method are used to calculate the safe thickness of the isolation pillars. Finally, the minimum safe thickness of the isolation pillars is determined based on the structural parameters of the mine, the surrounding rock load and the rock hardness.

[0010] S4: FLAC 3D software is used to simplify the modeling of deep ore mining from open pit to underground, and numerical simulation is used to simulate underground mining. The reasonable safety thickness of the isolation pillars and slope stability is recommended based on the numerical simulation.

[0011] S5: Establish a test model similar to the mine and ore body structure, bury stress gauges and displacement gauges in the test model, and arrange the stress gauges in the isolation pillars, hanging wall surrounding rock, external surrounding rock and open-pit slope steps. After the model is maintained, the model is demoulded;

[0012] S6: According to the planned mining test model, during the excavation process, observe whether there is obvious collapse or crack deformation in the top and bottom plates of the empty area and the upper and lower plates, and whether the isolation pillars from open pit to underground and the isolation pillars in the lower plate area are stable. At the same time, the stress meter detects the stress change under the mining state, and the displacement meter measures the sinking of the surface open pit steps;

[0013] S7: After the test model simulates mining correctly, the ore body is mined. During the excavation, the data of several groups of deformation monitoring points set inside the isolation pillars and the open-pit mine slope rock mass are recorded. The deformation monitoring points are used to extract the settlement values ​​of each point during the deep mining process, and to draw the settlement deformation curve to monitor whether the structural strength of the isolation pillars meets the standards.

[0014] Preferably, the mining method in S2 is phased mining. According to different ore body heights, each phase of the project is divided into several mining stages, and the backfilling method is used after mining.

[0015] Preferably, the test model in S5 is a proportionally reduced version of the actual mine and ore body.

[0016] Preferably, the simulation material of the test model satisfies the geometric similarity ratio, density similarity ratio and strength similarity ratio, and satisfies the strength similarity ratio=geometric similarity ratio×density similarity ratio.

[0017] Preferably, in S7, when mining the ore body, it is necessary to monitor the deformation monitoring points in real time. When the data detected by the deformation monitoring points are abnormal, the construction is stopped in time, and the technical personnel make corresponding adjustments.

[0018] Preferably, the calculation process of the load transfer intersection method in S3 is as follows:

[0019] The pillar roof load is diffused at an angle of 30 to 35 degrees along the central vertical line of the roof and transmitted downward. When the transmission line is located outside the intersection of the side wall of the goaf and the roof, it is defined that the side wall of the goaf directly supports the external load of the roof and the deadweight of the rock. At this time, the roof is safe, and the height difference between the center of the roof and the intersection is the minimum safe thickness of the roof. The diffusion angle is represented by θ, and the calculation formula for the minimum safe thickness of the roof is: H = Ln / (2×tanθ);

[0020] Where: By adjusting different diffusion angles θ, the relationship between different goaf spans and roof thicknesses can be obtained; Ln is the goaf span, in m.

[0021] Preferably, the calculation process of the structural mechanics method in S3 is as follows:

[0022] The isolation pillar is regarded as a fixed flat beam with good support at both ends. The calculation is solved according to the plane problem of elastic mechanics. The unit width is taken for calculation. The formula is as follows:

[0023]

[0024] Where:

[0025] γ—bulk density of top pillar rock mass, t / m 3 , γ=3.71;

[0026] B—stope span, m;

[0027] b—unit width, b=1m;

[0028] q—pressure above the isolation pillar, MPa;

[0029] σxu=σji / nKc, σxu—allowable tensile stress, MPa;

[0030] σ extreme - ultimate tensile strength, MPa;

[0031] n—safety factor, ranging from 2 to 3;

[0032] Kc—Structural weakening coefficient.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The method for determining the thickness of the isolation layer for converting open-pit to underground mining of the present invention can first calculate the minimum safe thickness of the isolation pillars when the workers are mining the mine, and at the same time make a test model, and then carry out simulated mining on the test model. After confirmation, the mine can be mined, which can prevent collapse during mining. At the same time, when mining the mine, it is monitored in real time to ensure early warning, and when safety hazards in the isolation pillars occur, they are discovered in time, which solves the technical problem of requiring precise calculations to ensure that underground mining will not affect the open-pit mine, thereby ensuring that open-pit and underground mining will not affect each other and ensuring the safety of surface structures and underground workers. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a numerical overall model diagram of the open-pit to underground deep mining according to an embodiment of the present invention;

[0036] Figure 2 This is a numerical internal model diagram of open-pit to underground deep mining according to an embodiment of the present invention;

[0037] Figure 3 It is a layout design diagram of stress and displacement sensors for a similar simulation test according to an embodiment of the present invention;

[0038] Figure 4 This is a schematic diagram of the excavation and filling completion of the 6th middle section (+1160~+1205m ore body) of an embodiment of the present invention;

[0039] Figure 5 A curve diagram of settlement values ​​from point 1 to point 4 of a deep mining exploration line section according to an embodiment of the present invention;

[0040] Figure 6 This is a relationship diagram between the stope span and the thickness of the isolation pillar under the medium load transfer intersection line in an embodiment of the present invention;

[0041] Figure 7 This is a relationship diagram between the stope span and the thickness of the isolation pillars using the structural mechanics method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] In an embodiment of the present invention, a method for determining the thickness of an isolation layer in transition from open pit to underground mining is provided, comprising the following steps:

[0044] S1: First, conduct a technical survey of the mine, including determining the data of the mine's minimum mining level, the final slope angle of the upper wall, the final slope angle of the lower wall, the length and width of the open pit bottom, the horizontal thickness of the ore body and the inclination of the ore body, and determine the technical conditions for underground ore body mining and its occurrence;

[0045] S2: According to the actual situation of the ore body, the mining stage of the ore body is planned, and the height of each mining stage is determined. At the same time, the mining method of each stage is determined, and the height of each middle section mining and the method of setting the pillars are determined; among them, the mining method is phased mining. According to the different ore body heights, each phase of the project is divided into several mining stages for mining, and the backfilling method is adopted after the mining is completed;

[0046] S3: The load transfer intersection method and structural mechanics method are used to calculate the safe thickness of the isolation pillars. Finally, the minimum safe thickness of the isolation pillars is determined based on the structural parameters of the mine, the surrounding rock load and the rock hardness.

[0047] S4: FLAC 3D software is used to simplify the modeling of deep ore mining from open pit to underground, and numerical simulation is used to simulate underground mining. The reasonable safety thickness of the isolation pillars and slope stability is recommended based on the numerical simulation.

[0048] S5: Establish a test model similar to the mine and ore body structure. The test model is a proportional reduction of the actual mine and ore body. Stress gauges and displacement gauges are embedded in the test model. The stress gauges are arranged in the isolation pillars, the upper wall surrounding rock, the external surrounding rock and the open-pit slope steps. After the model is maintained, the model is demolded. The simulation material of the test model meets the geometric similarity ratio, density similarity ratio and strength similarity ratio, and meets the strength similarity ratio = geometric similarity ratio × density similarity ratio.

[0049] S6: According to the planned mining test model, during the excavation process, observe whether there is obvious collapse or crack deformation in the top and bottom plates of the empty area and the upper and lower plates, and whether the isolation pillars from open pit to underground and the isolation pillars in the lower plate area are stable. At the same time, the stress meter detects the stress change under the mining state, and the displacement meter measures the sinking of the surface open pit steps;

[0050] S7: After the test model simulates mining correctly, the ore body is mined. During the excavation, the data of several groups of deformation monitoring points set inside the isolation pillars and the open-pit mine slope rock mass are recorded. The deformation monitoring points are used to extract the settlement values ​​of each point in the deep mining process, and draw the settlement deformation curve to monitor whether the structural strength of the isolation pillars meets the standards. Specifically, when mining the ore body, it is necessary to monitor the deformation monitoring points in real time. When the data detected by the deformation monitoring points is abnormal, the construction is stopped in time, and the technical personnel make corresponding adjustments.

[0051] In order to further verify and illustrate this embodiment, the present invention provides the following specific application cases:

[0052] Take a large open-pit metal mine in western my country as an example. It has an annual production capacity of 5 million t / a and has been in service for more than half a century. It is currently entering the final stage of open-pit mining and is about to reach the lowest elevation of the open-pit boundary, with a mining depth of over 400m. After deep exploration, there are still more than 100 million tons of resources in the deep. After research, it is planned to mine deep resources by converting from open pit to underground. Underground mining is planned to adopt large-scale deep hole blasting mining plus filling. To this end, in order to smoothly transfer the mining area to underground production, the safe thickness of the isolation pillars must be determined to ensure that underground mining will not have a safety impact on the open-pit slopes and the surface. The specific implementation includes the following steps:

[0053] Step 1: Determine the minimum mining level of the mine, the final slope angle of the upper wall, the final slope angle of the lower wall, the length and width of the open pit bottom, the horizontal thickness of the ore body and the inclination of the ore body, etc. Figure 1 and Figure 2 shown.

[0054] Step 2: Comprehensively consider the structural parameters of the mine site, surrounding rock load and rock hardness, use the load transfer intersection method and structural mechanics method to calculate the safe thickness of the isolation pillars, and determine the safe thickness of the mine isolation pillars based on relevant experience. The results show that the thickness of the isolation pillars in the open-pit mine should be 20 to 30 meters. In this embodiment, the thickness of the isolation pillars is set to 25 meters.

[0055] The third step: adopt phased mining. The first phase mines the ore body between 900m and 1200m, and the second phase mines the ore body between 600m and 900m. The ore body below 600m is not considered for the time being.

[0056] Step 4: Use FLAC 3D software to simplify modeling of deep ore body mining from open pit to underground, and then establish a test model similar to the mine and ore body structure. The test model is a proportional reduction of the actual mine and ore body. At the same time, stress gauges and displacement gauges are embedded in the test model. The stress gauges are mainly arranged in the isolation pillars, the upper wall surrounding rock, the external surrounding rock and the open pit slope steps, such as Figure 3 As shown; the ratio of similar simulation materials has an important influence on the test results. Strictly speaking, the simulation materials of similar simulation tests should satisfy the geometric similarity ratio, density similarity ratio and strength similarity ratio, and should try to satisfy the strength similarity ratio = geometric similarity ratio × density similarity ratio.

[0057] Step 5: According to the planned mining test model, the deep ore body at the bottom of the open pit was excavated. Starting from the +910m level, the excavation and filling cycle was carried out from bottom to top every 50m until the 6th section was filled. Then, the model before deep excavation was compared with the similar model after deep excavation and filling. After the excavation of the deep 1st section to the 6th section, there was no obvious collapse or crack deformation on the top and bottom plates of the goaf and the upper and lower plates. The isolation pillars from open pit to underground and the isolation pillars in the lower plate area were still stable. Figure 4 As shown;

[0058] At the same time, the stress value reflected by the stress gauge did not show any obvious fluctuation, and the displacement meter did not measure any obvious displacement, indicating that the isolation top column was less affected by the mining of the lower ore body. From the entire excavation process, the isolation top column did not show any deformation, cracking or other damage, and remained stable. Therefore, the thickness of the isolation top column in this embodiment is set to 20m.

[0059] Step 6: After the test model simulates the mining correctly, the ore body is mined. The first phase adopts the upward method, that is, mining from bottom to top, and the first mining middle section is the 900m middle section; the first phase is divided into 5 mining stages, each stage is 60m high, and the goaf is mined by filling method without leaving top and bottom pillars; after the filling of this stage is completed, it will be transferred to the next stage of mining. The underground ore body mining starts from +900m, starting from the first stage mining, and mining from bottom to top to the fifth stage in sequence. After the first phase mining is completed, the second phase ore body will be mined in the same way;

[0060] During excavation, data from several groups of deformation monitoring points set up inside the isolation pillars and open-pit mine slope rock masses are recorded. The deformation monitoring points are used to extract the settlement values ​​of each point during deep mining, draw settlement deformation curves, and monitor whether the structural strength of the isolation pillars meets the standards.

[0061] Step 7: The tensile stress concentration area is mainly the roof of the empty area after the stope excavation and the interior of the inter-panel column. The maximum tensile stress value is about 0.68-0.69Mpa, which is less than the tensile strength of the rock mass. The maximum tensile stress area is only in a small local area, indicating that the stope remains stable as a whole during deep mining.

[0062] The range of the tensile stress concentration area in the inter-panel column is also relatively small, with the maximum value generally being 0.3-0.4Mpa, which occurs after the mining of the stope. The stress concentration phenomenon is reduced after the stope is filled, and the stress value is reduced, indicating that the filling body has a good effect on improving the stress of the inter-panel column;

[0063] The four deformation monitoring points respectively extracted the settlement values ​​of each point during the deep mining process and drew the settlement deformation curve, such as Figure 5As shown in the figure, the settlement curves of each point show that the deformation and settlement of each point inside the rock mass of the isolation top pillar and the open pit slope show a linear and slow growth trend with the deep mining in the mine. The settlement value is within 40mm. The settlement of the upper wall slope is larger than that of the isolation pillar, which is related to the development of the ore body to the south.

[0064] Judging from the relative value and development trend of deformation, the deformation of the isolation pillar and the rock mass at the slope of the mining area is a normal deformation under the influence of mining, and the rock mass at various locations is in a relatively stable state. It can be seen that the numerical simulation method shows that the thickness of the isolation pillar is 20m.

[0065] Test example:

[0066] Including test example 1: load transfer intersection method; test example 2: structural mechanics method.

[0067] Test Example 1: Load transfer intersection method:

[0068] That is, the roof load spreads at an angle of 30 to 35 degrees along the central vertical line of the roof and is transmitted downward. When the transfer line is located outside the intersection of the side wall of the goaf and the roof, it is considered that the side wall of the goaf directly supports the external load of the roof and the deadweight of the rock. At this time, the roof can be considered safe, and the height difference between the center of the roof and the intersection is the minimum safe thickness of the roof.

[0069] The diffusion angle is represented by θ, and the minimum roof safety thickness calculation formula is: H = Ln / (2×tanθ)

[0070] In the formula: By adjusting different diffusion angles θ, the relationship between different goaf spans and roof thickness can be obtained.

[0071] Ln—stope span, m, take 20m;

[0072] θ—The angle between the load transfer intersection line and the center line of the roof, usually 30-35°, here 33°; Substituting the value into the above formula, the thickness of the isolation pillar is:

[0073] H=20 / (2×tan33°)=15.4m

[0074] Calculated according to the calculation formula, the results are shown in Table 1.1.

[0075]

[0076]

[0077] Table 1.1 Calculation results of isolation pillar thickness under different safety factors

[0078] The calculated results are analyzed to obtain the relationship between the thickness of the isolation pillar and the span of the stope at different angles, such as Figure 6 shown.

[0079] From the above calculations, it can be seen that when the load transfer intersection method is used to calculate the thickness of the isolation pillar, under the same span, the larger the angle between the load transfer intersection line and the center line of the roof, the smaller the isolation pillar; under the same angle, the larger the span, the thicker the isolation pillar; when the angle is 30°, the calculated result of the thickness of the isolation pillar is 17.3m.

[0080] Test Example 2: Structural Mechanics Method:

[0081] This method regards the isolation pillar as a fixed flat beam with good support at both ends. The calculation is solved according to the plane problem of elastic mechanics, and the unit width is taken for calculation. The formula is as follows:

[0082]

[0083] Where:

[0084] γ—bulk density of top pillar rock mass, t / m 3 , γ=3.71;

[0085] B—stope span, m, take 20m;

[0086] b—unit width, b=1m;

[0087] q—pressure above the isolation pillar, MPa;

[0088] σxu=σji / nKc, σxu—allowable tensile stress, MPa;

[0089] σ pole - ultimate tensile strength, MPa. According to the rock mechanics test conducted in the early stage, the tensile strength of the top pillar magnetite is 8.593 MPa;

[0090] n—safety factor, ranging from 2 to 3, in this paper, n=1.4;

[0091] Kc—structural weakening coefficient; the Kc value depends on factors such as the rock's solidity, rock cracks, and interlayer weak surfaces. When blasting, additional stress will be generated in the top column, weakening the rock mass strength and increasing the cracks in the rock mass. Therefore, the structural weakening coefficient Kc is generally taken as 7 to 10, and this article takes Kc = 8;

[0092] Substitute into the calculation: σ Xu = 8.593 / (1.4×8) = 0.767

[0093] H=17.1m

[0094] The thickness of the isolation pillar is calculated according to the calculation formula, and the thickness of the isolation pillar is obtained by taking different mining spans. The results are shown in Table 2.1.

[0095] Serial number Stope span (m) Thickness of isolation pillar (m) 1 4 2.5 2 6 3.9 3 8 5.4 4 10 7.0 5 12 8.8 6 14 10.6 7 16 12.7 8 18 14.8 9 20 17.1

[0096] Table 2.1 Calculation results of isolation pillar thickness using structural mechanics method

[0097] The calculated results are analyzed to obtain the relationship between the thickness of the isolation pillar and the span of different stopes, such as Figure 7 shown.

[0098] From the above calculations, it can be seen that when the structural mechanics method is used to calculate the thickness of the isolation pillars, as the span of the mining area increases, the isolation pillars increase, and the calculated thickness of the isolation pillars is 17.1m.

[0099] Combining the calculation results of Test Case 1 and Test Case 2 and relevant experience, and taking into account the mine site structural parameters, surrounding rock load and rock hardness, the minimum safe thickness of the isolation pillar is determined to be 20m.

[0100] To ensure adequate safety, it is considered to increase the minimum safety thickness of the isolation pillars to 25m to ensure that underground mining will not affect the open-pit mine.

[0101] To sum up: the method for determining the thickness of the isolation layer for open-pit to underground mining provided by the present invention solves the technical problem of requiring precise calculations to ensure that the isolation pillars can protect underground mining from affecting the open-pit mine, thereby ensuring the safety of workers in the goaf.

[0102] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for determining the thickness of the isolation layer in the transition from open pit to underground mining, characterized in that: The following steps are involved: S1: First, conduct a technical survey of the mine, including determining the data of the mine's minimum mining level, the final slope angle of the upper wall, the final slope angle of the lower wall, the length and width of the open pit bottom, the horizontal thickness of the ore body and the inclination of the ore body, and determine the technical conditions for underground ore body mining and its occurrence; S2: According to the actual situation of the ore body, plan the mining stage of the ore body, and determine the height of each mining stage, and at the same time determine the mining method of each stage, determine the mining height of each middle section and the method of setting the pillars; S3: The load transfer intersection method and structural mechanics method are used to calculate the safe thickness of the isolation pillars. Finally, the minimum safe thickness of the isolation pillars is determined based on the structural parameters of the mine, the surrounding rock load and the rock hardness. S4: FLAC 3D software is used to simplify the modeling of deep ore mining from open pit to underground, and numerical simulation is used to simulate underground mining. The reasonable safety thickness of the isolation pillars and slope stability is recommended based on the numerical simulation. S5: Establish a test model similar to the mine and ore body structure, bury stress gauges and displacement gauges in the test model, and arrange the stress gauges in the isolation pillars, hanging wall surrounding rock, external surrounding rock and open-pit slope steps. After the model is maintained, the model is demoulded; S6: According to the planned mining test model, during the excavation process, observe whether there is obvious collapse or crack deformation in the top and bottom plates of the empty area and the upper and lower plates, and whether the isolation pillars from open pit to underground and the isolation pillars in the lower plate area are stable. At the same time, the stress meter detects the stress change under the mining state, and the displacement meter measures the sinking of the surface open pit steps; S7: After the test model simulates mining correctly, the ore body is mined. During the excavation, the data of several groups of deformation monitoring points set inside the isolation pillars and the open-pit mine slope rock mass are recorded. The deformation monitoring points are used to extract the settlement values ​​of each point during the deep mining process, and to draw the settlement deformation curve to monitor whether the structural strength of the isolation pillars meets the standards.

2. The method for determining the thickness of the isolation layer in the transition from open-pit to underground mining according to claim 1, characterized in that: The mining method in S2 is phased mining. According to the different ore body heights, each phase of the project is divided into several mining stages, and the backfilling method is used after mining.

3. The method for determining the thickness of the isolation layer in the transition from open-pit to underground mining according to claim 1, characterized in that: The test model in S5 is a scaled-down version of the actual mine and ore body.

4. The method for determining the thickness of the isolation layer in the transition from open-pit to underground mining according to claim 3, characterized in that: The simulation material of the test model satisfies the geometric similarity ratio, density similarity ratio and strength similarity ratio, and satisfies the strength similarity ratio=geometric similarity ratio×density similarity ratio.

5. The method for determining the thickness of the isolation layer in the transition from open-pit to underground mining according to claim 1, characterized in that: When mining the ore body in S7, it is necessary to monitor the deformation monitoring points in real time. When the data detected by the deformation monitoring points is abnormal, the construction is stopped in time and the technical staff makes corresponding adjustments.

6. The method for determining the thickness of the isolation layer in the transition from open-pit to underground mining according to claim 1, characterized in that: The calculation process of the load transfer intersection method in S3 is as follows: The pillar roof load is diffused at an angle of 30 to 35 degrees along the central vertical line of the roof and transmitted downward. When the transmission line is located outside the intersection of the side wall of the goaf and the roof, it is defined that the side wall of the goaf directly supports the external load of the roof and the deadweight of the rock. At this time, the roof is safe, and the height difference between the center of the roof and the intersection is the minimum safe thickness of the roof. The diffusion angle is represented by θ, and the calculation formula for the minimum safe thickness of the roof is: H = Ln / (2×tanθ); Where: By adjusting different diffusion angles θ, the relationship between different goaf spans and roof thicknesses can be obtained; Ln is the goaf span, in m.

7. The method for determining the thickness of the isolation layer in the transition from open-pit to underground mining according to claim 1, characterized in that: The calculation process of the structural mechanics method in S3 is as follows: The isolation pillar is regarded as a fixed flat beam with good support at both ends. The calculation is solved according to the plane problem of elastic mechanics. The unit width is taken for calculation. The formula is as follows: Where: γ—bulk density of top pillar rock mass, t / m 3 , γ=3.71; B—stope span, m; b—unit width, b=1m; q—pressure above the isolation pillar, MPa; σxu=σji / nKc, σxu—allowable tensile stress, MPa; σji—ultimate tensile strength, MPa; n—safety factor, ranging from 2 to 3; Kc—Structural weakening coefficient.

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