A method for determining the width of a protective coal pillar for normal faults considering residual tectonic stress

Abstract

The present invention provides a method for leaving a normal fault protection coal pillar considering residual tectonic stress, which relates to the technical field of coal mine mining. The method includes: S1. Determining the position of the open-off cut of the working face and the mining direction according to the geological conditions; S2. Determining the geometric similarity ratio, density similarity ratio and strength similarity ratio of the similar material model, and simulating the distribution laws of the displacement field and stress field after the formation of the normal fault; S3. Determining the width L1 of the normal fault protection coal pillar in the similar material simulation test according to the maximum coal pillar width at the time of stopping mining; S4. Conducting a similar material simulation comparison test for prefabricating the normal fault and forming the normal fault protection coal pillar to determine the influence of the tectonic stress on the normal fault protection coal pillar; S5. Using PFC numerical simulation to carry out the simulation of the formation of the normal fault and determining the width L2 of the protection coal pillar; S6. Determining the width of the on-site protection coal pillar according to the results of the similar material simulation and numerical simulation, and monitoring the support resistance of the working face and the deformation amount of the surrounding rock of the roadway to ensure the safety of mining.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mining, and in particular to a method for setting a normal fault protection coal pillar considering residual tectonic stress. Background Art

[0002] A normal fault is a common geological structure in underground coal resource mining. During the formation of a normal fault, the integrity and continuity of the rock strata are damaged, resulting in obvious differences in the stress and failure mode of the surrounding rock mass. After the formation of a normal fault, a fault fracture zone appears, and a certain degree of tectonic stress remains in the surrounding rock strata. When constructing near a normal fault, the superimposed action of the fault tectonic stress and the mining-induced stress will make the mining response characteristics of the rock mass near the fault different from those of intact rock strata. If the normal fault becomes activated, a large amount of energy may be released, causing damage to the coal pillar and posing risks of inducing disasters such as fault rock bursts, coal and gas outbursts, and fault water inrusions, bringing great threats to life and property. Setting a reasonable fault protection coal pillar in the normal fault area can keep the rock strata in the fault area as stable as possible and reduce the risk of the normal fault becoming activated. In order to better simulate the stress occurrence environment in the normal fault area during the coal seam mining process and set a reasonable normal fault protection coal pillar under the influence of tectonic stress, a similar material simulation test is carried out.

[0003] The similar material simulation test is an effective method for studying geological structures. The test equipment used in similar material simulation mainly controls the deformation test of the experimental model through motion or force according to the similarity principle, and is a device for simulating or inversely inferring geological origins such as faults. In the simulation test, stress sensors are horizontally arranged inside the similar material, mainly used to monitor the vertical stress change during the formation of the normal fault, obtain the stress distribution law and characteristics after the formation of the normal fault, and lay a foundation for the next step of mining the coal seam on the basis of the formation of the normal fault and studying the setting of the normal fault protection coal pillar under the influence of tectonic stress. The PFC numerical simulation is simple to operate and has low cost, and can obtain the stress distribution law and characteristics of the whole field after the formation of the normal fault.

[0004] By carrying out the normal fault formation test through similar simulation and numerical simulation, tectonic stress remains in the surrounding rock mass after the formation of the normal fault. On this basis, mining the coal seam can create a stress occurrence environment in the area of the coal seam near the normal fault, and the set normal fault protection coal pillar is more in line with the actual situation on site, which can recover the coal resources in the fault area to the greatest extent while ensuring the safe mining of the mine. Summary of the Invention

[0005] In order to reasonably set the setting of the normal fault area protection coal pillar in coal mining, maximize the coal mining, and ensure the mining safety, the present invention provides a method for setting a normal fault protection coal pillar considering residual tectonic stress, and the specific technical solutions are as follows.

[0006] A method for determining the width of a protective coal pillar for a normal fault considering residual tectonic stress, the steps including:

[0007] S1. Determine the position and mining direction of the starting cut of the working face according to the geological conditions;

[0008] S2. Determine the geometric similarity ratio, density similarity ratio and strength similarity ratio of the similar material model according to the mining conditions and geological conditions, and simulate the distribution laws of the displacement field and stress field after the formation of the normal fault;

[0009] S3. Determine the designed width L1 of the protective coal pillar for the normal fault in the similar material simulation test according to the maximum width of the coal pillar when mining stops;

[0010] S4. Conduct a similar material simulation comparison test for prefabricating the normal fault and forming the protective coal pillar for the normal fault to determine the influence of the tectonic stress on the protective coal pillar for the normal fault;

[0011] S5. Use PFC numerical simulation to carry out the simulation of the formation of the normal fault and determine the designed width L2 of the protective coal pillar;

[0012] S6. Determine the width of the on-site protective coal pillar according to the results of the similar material simulation and numerical simulation, and monitor the support resistance of the working face and the deformation amount of the surrounding rock of the roadway.

[0013] Preferably, the similar material includes sand, gypsum, calcium carbonate and water, and the mixing ratio of the similar material is adjusted to simulate different rock layers.

[0014] Preferably, stress sensors are buried in the similar material, and the stress sensors are connected to a stress acquisition box to monitor the stress distribution law in the similar material; displacement monitoring points are arranged on the surface of the similar material, and total stations are used to monitor the displacement monitoring points.

[0015] Preferably, in the similar material simulation comparison test, monitor the stress change during the coal seam mining process. When the stress in the fault protective coal pillar reaches the maximum strength of the coal pillar, stop the mining simulation; when the fault is activated due to the fault displacement, stop the mining simulation; when the caving rock layer overlying the goaf is connected with the fault, stop the mining simulation; when the coal pillar in front of the working face is damaged, stop the mining simulation.

[0016] Preferably, the maximum width of the coal pillar is taken as the maximum value of W1, W2, W3, and W4, where: the width of the coal pillar determined when the stress borne by the coal pillar exceeds its ultimate strength is W1, the width of the coal pillar determined when the displacement of the normal fault changes is W2, the width of the coal pillar determined when the caving rock layer overlying the goaf is connected with the fault is W3, or the width of the coal pillar determined when the coal pillar in front of the working face is damaged is W4.

[0017] Preferably, in the PFC numerical simulation, a normal fault model is established to determine the stress field distribution law after the formation of the normal fault.

[0018] Preferably, in the normal fault model, coal seam excavation is simulated, and the retention of the protective coal pillar in the normal fault in the similar material simulation is used to determine the width of the protective coal pillar retained in the numerical simulation.

[0019] Further preferably, among the designed widths L1 and L2 of the protective coal pillar, the larger designed width is selected as the width of the protective coal pillar retained during the working face mining.

[0020] Further preferably, during the working face mining process, mine pressure gauges are installed at the upper, middle, and lower parts of the hydraulic support to monitor the working resistance of the hydraulic support.

[0021] Further preferably, roadway surface displacement observation stations are arranged every 20 m in the return airway.

[0022] The beneficial effect of a method for retaining a normal fault protective coal pillar considering residual tectonic stress provided by the present invention is that the formation process of the normal fault is reproduced through numerical simulation and similar material simulation, the stress distribution law after the formation of the normal fault is determined, and the occurrence environment of the coal seam is improved; after determining the normal fault protective coal pillar, the rationality of the coal pillar width setting is verified through on-site monitoring. By comparing and analyzing the characteristics of the normal fault protective coal pillar width during the coal seam mining process in two cases of forming a normal fault and prefabricating a normal fault, the influence characteristics of fault tectonic stress on the normal fault protective coal pillar are revealed. Setting the protective coal pillar considering residual tectonic stress is more in line with engineering practice and ensures the mining safety of passing through the fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow schematic diagram of a method for retaining a normal fault protective coal pillar considering residual tectonic stress;

[0024] Figure 2 is an arrangement diagram of a similar material simulation test;

[0025] Figure 3 is a vertical stress change curve of the formation of the normal fault;

[0026] Figure 4 is a vertical simulation model diagram;

[0027] Figure 5 is a schematic diagram of the working face layout;

[0028] Figure 6 is a schematic diagram of the arrangement of roadway end face displacement measurement stations;

[0029] Figure 7 is a schematic diagram of the displacement monitoring principle;

[0030] In the figure: 1 - high - speed camera; 2 - stress acquisition system; 3 - stress acquisition box; 4 - stress sensor; 51 - left - hand loading device; 52 - bottom hydraulic lifting device; 53 - angle adjustment device; 54 - test bench base; 55 - push rod device; 56 - right - hand loading device; 57 - upper - hand loading device; 58 - front - and - rear baffle; 6 - total station; 7 - hydraulic support, 8 - normal fault, 9 - displacement monitoring station, 10 - roadway section. Specific implementation method

[0031] Combined with Figures 1 to 7 As shown, the specific implementation method of a method for leaving a protective coal pillar for a normal fault considering residual tectonic stress provided by the present invention is described.

[0032] A method for leaving a protective coal pillar for a normal fault considering residual tectonic stress, the steps include:

[0033] S1. Determine the position and mining direction of the initial cutting roadway according to geological conditions.

[0034] The initial cutting roadway of the working face of this mine is opened at a place far from the normal fault and mined towards the normal fault. The actual geological conditions of the mine are clarified, including coal seam depth, dip angle of coal and rock strata, etc. The coal seam is mined on the basis of the existence of normal - fault tectonic stress, so as to determine a reasonable width of the protective coal pillar for the normal fault. The coal - seam mining direction should be consistent with the actual mining direction of the working face. The initial cutting roadway is opened at a place far from the fault and mined towards the fault. The data monitored by stress sensors in the coal seam, the characteristics of rock - layer deformation and failure, and the characteristics of displacement change during the coal - seam mining process are studied.

[0035] S2. Determine the geometric similarity ratio, density similarity ratio and strength similarity ratio of the similar - material model according to mining conditions and geological conditions, and simulate the distribution laws of the displacement field and stress field after the formation of the normal fault.

[0036] The similar materials include sand, gypsum, calcium carbonate and water. Adjust the mixing ratio of the similar materials. This material can ensure the similarity of the main characteristic factors between the prototype and the model material, and is convenient to manufacture and low - cost. The rock layers are stratified by mica powder, and different lithologic rock layers such as mudstone, coarse sandstone, fine sandstone and coal seam are simulated by mixing different proportions of river sand, calcium carbonate and gypsum. Stress sensors are buried in the similar materials, and the stress sensors are connected to the stress acquisition box to monitor the stress distribution law in the similar materials. Displacement monitoring points are arranged on the surface of the similar materials, and a total station is used to monitor the displacement monitoring points.

[0037] S3. Determine the designed width L1 of the protective coal pillar for the normal fault in the similar - material simulation test according to the maximum coal - pillar width at the time of stopping mining;

[0038] The maximum width of the coal pillar is taken as the maximum value of W1, W2, W3, and W4, where: the width of the coal pillar determined when the stress borne by the coal pillar exceeds its ultimate strength is W1, the width of the coal pillar determined when the displacement of the normal fault changes is W2, the width of the coal pillar determined when the caving strata overlying the goaf penetrates the fault is W3, or the width of the coal pillar determined when the coal pillar in front of the working face is damaged is W4.

[0039] S4. Conduct a similar material simulation and comparison test for the prefabrication of the normal fault and the formation of the protective coal pillar for the normal fault to determine the influence of tectonic stress on the protective coal pillar for the normal fault.

[0040] In the similar material simulation and comparison test, monitor the stress changes during the coal seam mining process. When the stress in the fault protective coal pillar reaches the maximum strength of the coal pillar, stop the mining simulation; when the fault is activated during the fault displacement, stop the mining simulation; when the caving strata overlying the simulated goaf penetrates the fault, stop the mining simulation; when the coal pillar in front of the working face is damaged during the working face mining, stop the mining simulation.

[0041] S5. Use PFC numerical simulation to carry out the simulation of the formation of the normal fault to determine the designed width L2 of the protective coal pillar.

[0042] In the PFC numerical simulation, establish a normal fault model to determine the distribution law of the stress field after the formation of the normal fault. Simulate the excavation of the coal seam in the normal fault model, and use the setting of the protective coal pillar for the normal fault in the similar material simulation to determine the width of the protective coal pillar set in the numerical simulation. In the numerical simulation, simulate the formation process of the normal fault through the PFC simulation software, apply a load on the upper part of the rock stratum to simulate the gravity of the rock stratum not simulated above, and combine with the distribution of the in-situ stress of the mine to apply a horizontal stress in the horizontal direction. The right boundary at the bottom of the model is fixed, and the left boundary moves to the lower left side at the same rate as the similar simulation test.

[0043] S6. Determine the width of the on-site protective coal pillar according to the results of the similar material simulation and numerical simulation, and monitor the resistance of the working face support and the deformation of the surrounding rock of the roadway.

[0044] Among the designed widths L1 and L2 of the protective coal pillar, select the larger designed width as the width of the protective coal pillar set during the working face mining. During the working face mining process, install mine pressure gauges on the upper, middle, and lower parts of the hydraulic support to monitor the working resistance of the hydraulic support. Arrange roadway surface displacement observation stations every 20m in the return airway.

[0045] During the coal seam mining process, there is a hydraulic support in front of the working face, which plays a role in ensuring the safe mining of the working face. Select the hydraulic supports on the upper, middle, and lower parts of the working face to install digital or pointer mine pressure gauges to analyze the working resistance during the working face mining process.

[0046] Observe the data change trend of the support working resistance when the mining face is mined to the selected design width. When the resistance increasing speed of the support is relatively slow, the overall change of the support resistance is not significant, the strata pressure manifestation of the working face is relatively gentle, and the working requirements of the support are met, it indicates that the reserved width of the fault protection coal pillar is reasonable. During the coal seam mining process, a measuring station is arranged every 20 m in the roadway near the fault position. The layout of the measuring stations is as shown in Figure 6 shown. The "cross observation method" is used to monitor the surface displacement of the roadway. Four measuring points are arranged on both sides of the roadway and the roof and floor of the same cross-section of each measuring station, and each measuring point is arranged at the center position of the roadway, as shown in Figure 7 shown. The width of the normal fault protection coal pillar is determined through similar simulation and numerical simulation. Observe the displacement change amount of both sides of the roadway and the roof and floor when the mining face is mined to this width. When the displacement change amount of both sides of the roadway and the roof and floor is not significant and within the maximum allowable deformation amount of the roadway specified in the mine design regulations, it indicates that the reserved width of the normal fault protection coal pillar is reasonable.

[0047] In this embodiment, combined with the actual test situation, the similar material simulation test is described in detail.

[0048] In the similar simulation, a fault simulation test device is used to reproduce the formation process of the normal fault, and the distribution law and characteristics of the tectonic stress field after the formation of the normal fault are obtained. The fault simulation test device mainly includes a loading device, a bottom hydraulic lifting device, an angle adjustment device, a test bench base, a push rod device, front and rear baffles, etc. The starting position and angle of the normal fault are determined through the bottom hydraulic lifting device, the angle adjustment device and the push rod device, and pressure is applied through the upper loading device and the side loading device, so as to simulate the vertical stress and horizontal stress in the actual rock formation. During the test process, the front and rear baffles are used for sealing. The maximum dimensions of the length, width and height that can be simulated by this test system are 2000 mm, 300 mm and 1000 mm respectively.

[0049] During the simulation of the normal fault formation process, the front and rear baffles are installed on the equipment to ensure that the whole test is in a sealed state. The front and rear baffles are both transparent acrylic plates to ensure that the camera can accurately monitor the rock formation deformation and failure characteristics during the normal fault formation process. Displacement monitoring points with a spacing of 5 cm×5 cm are arranged on the surface of the similar material. The displacement change characteristics after the formation of the normal fault are monitored through a total station, and the displacement field distribution law after the formation of the normal fault is obtained; the stress sensors are buried inside the similar material and connected to the stress acquisition box, and the stress acquisition box is connected to the computer. The stress change law during the normal fault formation process is monitored through the stress acquisition software, and the tectonic stress distribution law after the formation of the normal fault is obtained, providing a premise for the research on a method for reserving the normal fault protection coal pillar considering the residual tectonic stress. Specifically, the Donghua DH3816 test system can be used to collect the stress data during the normal fault formation process.

[0050] The upper loading device is pressurized, and the bottom hydraulic lifting device descends to form a normal fault. The stress change data and the characteristics of rock layer deformation and failure during the formation of the normal fault are monitored and recorded, and the distribution laws of the displacement field and stress field after the formation of the normal fault are obtained. After the formation of the normal fault, a certain degree of tectonic stress is retained in the surrounding rock layers, which provides a basis for the research on a method for leaving protective coal pillars for normal faults considering residual tectonic stress.

[0051] The methods for determining the width of the protective coal pillar include: (1) Determine the width of the normal fault protective coal pillar according to the stress sensor data in the coal seam during the mining process of the working face. The stress data monitored in the coal seam are converted into data in the actual engineering scale through the strength similarity ratio of the model. Combining with the maximum strength of the coal seam in the mine data, when the data monitored during the test are converted into engineering-scale data and are greater than the maximum strength of the coal seam, stop mining, and the coal pillar width at this time is the width of the normal fault protective coal pillar. (2) Determine the width of the normal fault protective coal pillar according to the displacement change data of the displacement monitoring points monitored by the total station during the mining process of the working face. When the displacement of the displacement monitoring points on both sides of the fault begins to change, it is regarded as the activation of the fault. To ensure the safe mining of the mine, the coal pillar width at this time is the width of the normal fault protective coal pillar. (3) Determine the width of the protective coal pillar left for the fault according to the caving shape of the goaf during the mining process of the working face. The characteristics of rock layer deformation and failure during the coal seam mining process are observed throughout by camera video recording. When the overlying caving rock layer in the goaf penetrates the fault, stop mining, and the coal pillar width at this time is the width of the normal fault protective coal pillar. (4) Determine the width of the normal fault protective coal pillar according to the shape of the coal pillar in front of the working face during the mining process of the working face. The characteristics of coal pillar deformation and failure during the coal seam mining process are observed throughout by camera video recording. When the coal pillar in front of the working face is damaged, stop mining, and the coal pillar width at this time is the width of the normal fault protective coal pillar.

[0052] Lay a prefabricated normal fault according to the ratio of each rock layer forming the normal fault. Stress sensors are buried inside the similar material, and the arrangement positions and quantities of the stress sensors are the same as those for forming the normal fault; displacement monitoring points are arranged on the surface of the similar material, and the arrangement positions and quantities of the displacement monitoring points are the same as those for forming the normal fault. Mine the coal seam on the basis of the prefabricated normal fault. The coal seam mining direction should be the same as that for forming the normal fault. Cut a drift at a distance from the fault and retreat towards the fault. Study the data monitored by the stress sensors in the coal seam, the characteristics of rock layer deformation and failure, and the displacement change characteristics during the coal seam mining process. Determine the width of the normal fault protective coal pillar according to the method for leaving the protective coal pillar for the formed normal fault.

[0053] Compare and analyze the characteristics of the width of the normal fault protective coal pillar during the coal seam mining process in the two cases of forming a normal fault and prefabricating a normal fault, and reveal the influence characteristics of tectonic stress on the normal fault protective coal pillar.

[0054] In this embodiment, combined with the numerical simulation test situation, the settings of the numerical simulation are described in detail.

[0055] A load is applied to the upper part of the rock formation to simulate the gravity of the rock formation not simulated in the upper part. Combining with the in-situ stress distribution of the mine, horizontal stress is applied in the horizontal direction. The right boundary at the bottom of the model is fixed, and the left boundary moves towards the lower left side at the same rate as in the similar simulation test to form a fault. On the basis of the formed fault, the coal seam is mined. The coal seam mining direction should be consistent with the actual retreat direction of the working face. The cutting hole is opened away from the fault and mined towards the fault. The stress change data in the coal seam, the deformation and failure characteristics of the rock formation, and the displacement change characteristics during the coal seam mining process are studied. According to the method for leaving protective coal pillars for normal faults formed in the similar simulation, the width of the protective coal pillar for the normal fault in the numerical simulation is determined.

[0056] This method of setting protective coal pillars considering the residual tectonic stress is more in line with engineering practice and ensures the mining safety when mining across faults. Specifically, this method uses simulation tests to reproduce the formation process of normal faults, obtains the stress distribution law after the formation of normal faults, and creates a stress occurrence environment in the normal fault area during the coal seam mining process. Then, on the basis of the formed normal fault, the coal seam is mined, and a method for leaving protective coal pillars for normal faults is proposed, and the width of the protective coal pillar for the normal fault is determined. Subsequently, a prefabricated normal fault is laid and the coal seam is mined. According to the method for leaving protective coal pillars for the formed normal fault, the width of the protective coal pillar for the normal fault is determined. By comparing the characteristics of the width of the protective coal pillar for the normal fault in the two mining cases of forming a normal fault and prefabricating a normal fault, the influence characteristics of tectonic stress on the protective coal pillar for the normal fault are revealed. Then, the numerical simulation of the formation process of the normal fault is carried out by using the PFC numerical simulation software. On the basis of the formed normal fault, the coal seam is mined, and the protective coal pillar for the normal fault is determined. Then, considering the width of the protective coal pillar for the normal fault left by the similar simulation and the numerical simulation comprehensively, the one with a larger coal pillar width is selected as the width of the protective coal pillar for the normal fault. Finally, the rationality of the method for leaving the protective coal pillar for the normal fault considering the residual tectonic stress is verified by on-site data. This method provides a scientific basis for leaving the protective coal pillar for the normal fault. This method of leaving can be closer to the actual situation on site and plays an important role in ensuring the safe production of the mine and improving the coal resources in the fault area.

[0057] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions, or substitutions made by those skilled in the art within the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for determining the width of a protective coal pillar for a normal fault considering residual tectonic stress, characterized in that the steps include: S1. Determine the position and mining direction of the initial cutting roadway of the working face according to geological conditions; S2. Determine the geometric similarity ratio, density similarity ratio and strength similarity ratio of the similar material model according to mining conditions and geological conditions, and simulate the distribution laws of the displacement field and stress field after the formation of the normal fault; S3. Determine the designed width L1 of the protective coal pillar for the normal fault in the similar material simulation comparison test according to the maximum coal pillar width at the time of stopping mining; S4. Conduct a similar material simulation comparison test for prefabricating the normal fault and forming the protective coal pillar for the normal fault to determine the influence of tectonic stress on the protective coal pillar for the normal fault; S5. Use PFC numerical simulation to carry out the simulation of the formation of the normal fault and determine the designed width L2 of the protective coal pillar; S6. Determine the width of the on-site protective coal pillar according to the results of the similar material simulation and numerical simulation, and monitor the support resistance of the working face and the deformation of the surrounding rock of the roadway; In the said similar material simulation comparison test, monitor the stress change during the coal seam mining process. When the stress in the fault protective coal pillar reaches the maximum strength of the coal pillar, stop the mining simulation; when the fault is activated during the fault displacement, stop the mining simulation; when the caving strata overlying the goaf are connected with the fault, stop the mining simulation; when the coal pillar in front of the working face is damaged, stop the mining simulation; The maximum coal pillar width is taken as the maximum value of W1, W2, W3, and W4, where: the coal pillar width determined by stopping mining when the stress borne by the coal pillar exceeds its ultimate strength is W1, the coal pillar width determined by stopping mining when the displacement of the normal fault changes is W2, the coal pillar width determined by stopping mining when the caving strata overlying the goaf are connected with the fault is W3, or the coal pillar width determined by stopping mining when the coal pillar in front of the working face is damaged is W4; In the said PFC numerical simulation, establish a normal fault model and determine the distribution law of the stress field after the formation of the normal fault; In the said normal fault model, simulate the excavation of the coal seam, and use the setting of the protective coal pillar for the normal fault in the similar material simulation to determine the width of the protective coal pillar in the numerical simulation; among the designed widths L1 and L2 of the protective coal pillar, select the larger designed width as the width of the protective coal pillar left during the mining of the working face.

2. A method for determining the width of a protective coal pillar for a normal fault considering residual tectonic stress according to claim 1, characterized in that the said similar material includes sand, gypsum, calcium carbonate and water, and adjust the mixing ratio of the similar material to simulate different rock strata.

3. A method for determining the width of a protective coal pillar for a normal fault considering residual tectonic stress according to claim 1, characterized in that stress sensors are buried in the said similar material, and the stress sensors are connected to a stress acquisition box to monitor the stress distribution law in the similar material; displacement monitoring points are arranged on the surface of the similar material, and a total station is used to monitor the displacement monitoring points.

4. A method for determining the width of a protective coal pillar for a normal fault considering residual tectonic stress according to claim 1, characterized in that during the mining process of the working face, mine pressure gauges are installed at the upper, middle and lower parts of the hydraulic support to monitor the working resistance of the hydraulic support.

5. A method for leaving a normal fault protection coal pillar considering residual structural stress according to claim 1, characterized in that, roadway surface displacement observation stations are arranged every 20m in the mining roadway.

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