An optimization method for reserving thickness of water-resisting rock

Abstract

The present application relates to a kind of optimization methods of water-resisting stratum thickness reservation, belong to metal ore mining method technical field.The technical scheme of the present application is: by using numerical simulation analysis the sensitivity of stope stability and water pressure value;Then, under the condition of different water pressure, water-resisting stratum thickness, stoping is analyzed, and then the best water-resisting stratum thickness under each water pressure value is obtained, and the water-resisting stratum thickness of metal ore mining reservation under the water-rich karst aquifer is reasonably determined.The beneficial effects of the present application are: the plastic zone expansion law of pressure-bearing mining can be better evolved, the stress, displacement, plastic zone and water inrush safety factor are comprehensively considered with the change trend of water pressure and roof, which is more suitable for mining practice.

Description

TECHNICAL FIELD

[0001] The application relates to a method for optimizing thickness of reserved water-resisting stratum, and belongs to the technical field of metal ore mining methods. BACKGROUND

[0002] Skarn type iron ore deposit is usually located in the contact zone of rock mass and carbonate, and thus is mostly a large water deposit. The carbonate surrounding rock often contains a large number of dissolution voids and dissolution pores with different development degrees, and water inrush accidents are easily caused during mining, especially when the broken rock mass with poor stability is mined, the broken rock mass often contains a large number of water-conducting fissures, and a water prevention and control scheme must be prepared in advance. Common treatment schemes include advanced exploration and water-resisting layer reservation. In general, the water-resisting layer is a rock mass with good integrity, which can effectively maintain the safety of the underlying stope, but when the water-resisting layer is a ore body, with the progress of the mining, the water-resisting layer will be the direct roof of the mining room, and the integrity of the water-resisting layer is damaged under the influence of excavation and blasting. Therefore, the selection of the thickness of the water-resisting layer affects the safety production and economic benefits of the mine. If the thickness of the water-resisting layer is not reasonably selected, two situations will occur, one is that the thickness of the roof water-resisting layer is too large, which will cause waste of resources, and the other is that the thickness of the water-resisting layer is too small, which cannot effectively prevent the connection of the excavation loosened zone and the water-conducting zone, and thus roof fall and water inrush accidents are easily caused. Therefore, the optimization of the thickness of the water-resisting layer and the analysis of the stability of the water-resisting layer according to different water pressures have very important engineering practical value.

[0003] Regarding the water-resisting rock thickness optimization method, the existing technology mainly includes: Hu Shao-ping et al. constructed a numerical calculation model of coal pillar in mine pressure influence area and effective water-resisting area, and optimized the reasonable width of water-resisting coal pillar; Li Zhu et al. proved the water-resisting ability and stability evolution law of water-resisting coal pillar under different coal pillar width conditions through theoretical analysis and FLAC3D, and proposed a "seepage area + elastic compression water-resisting area + plastic area" three-area combined water-resisting coal pillar width determination method; Jin Aibing et al. studied the coal pillar support pressure distribution law and stress and plastic deformation of different width coal pillars during the mining period of upper and lower section working faces by numerical simulation, and obtained the reasonable width; Huang Hui et al. studied the stress distribution and spatial failure characteristics of gently inclined floor under mining based on the theory of elasticity and numerical simulation, and proposed a water inrush risk evaluation method considering the spatial characteristics of floor failure; Su Chengzhi et al. predicted the water-conducting fractured zone by numerical simulation, obtained the maximum damage depth of surrounding rock, and then optimized the mining method; Zou Guanghua et al. obtained the conclusion that the mining height should be reduced to prevent the water-conducting zone from being connected by inversing the stress change during mining by numerical simulation; Ma Haitao et al. analyzed the water inrush safety of a certain iron mine by numerical simulation taking stress and strain as evaluation indexes; Cha Chunlei et al. obtained the floor failure depth and stress change law during mining by numerical simulation, and prevented floor water disaster; Yao Xuancheng et al. analyzed the crack propagation law from multiple angles such as theory and numerical simulation to explore the formation mechanism of water inrush and sand inrush, and obtained a crack propagation prediction model; Meng Wenqing et al. studied the upper limit of aquifer mining by similarity test and numerical simulation, and obtained the safe mining height.

[0004] In summary, the existing technology mainly focuses on the determination method of water-resisting coal pillar width and the determination of water-resisting coal seam thickness according to empirical formula, and the research on the optimization method of water-resisting rock thickness under rich water karst aquifer and metal mine mining is very limited. SUMMARY

[0005] The purpose of the present application is to provide an optimization method for reserving water-resisting rock thickness, which analyzes the sensitivity of stope stability and water pressure value by numerical simulation; then analyzes the stability under different water pressure and water-resisting layer thickness conditions, and further obtains the best water-resisting rock thickness under each water pressure value, reasonably determines the water-resisting rock thickness reserved for mining under rich water karst aquifer and metal mine, can better evolve the plastic zone expansion law of pressure mining, comprehensively considers the stress, displacement, plastic zone and water inrush safety factor with water pressure and roof change trend, and is more suitable for mining practice, which effectively solves the above problems in the background technology.

[0006] The technical scheme of the present application is: an optimization method for reserving water-resisting rock thickness, comprising the following steps:

[0007] S1, monitoring the water pressure of the typical water outlet point in the underground mine, and analyzing the water pressure monitoring results of the measuring point;

[0008] S2. Use FLac 3D to establish mining models under different initial water pressure conditions and conduct stope stability-water pressure sensitivity analysis;

[0009] S3. Determine the numerical simulation optimization scheme for the thickness of the waterproof layer on the top plate of the mining area. By changing the water pressure value and the thickness of the waterproof layer, compare and analyze the stress, displacement and plastic zone of the top plate of the mining area to further determine the reasonable thickness of the waterproof layer on the top plate.

[0010] S4. Optimization of the thickness of the water-resistant rock layer under different types of water pressure. The maximum principal stress of the roof, the minimum principal stress of the roof, the roof displacement, and the plastic zone of the stope are selected as the basis for stability analysis. The stability analysis of the stope is carried out under different water pressure and different thicknesses of the water-resistant rock layer.

[0011] S5. Optimization of the thickness of the waterproof layer under different water pressure conditions: Study the influence of the thickness of the waterproof layer on various indicators of the roof under different water pressure values, compare and analyze the interaction between water pressure and waterproof layer thickness on the damage to the roof, and further optimize the thickness of the waterproof layer under different water pressure conditions.

[0012] In step S1, to determine the actual water pressure underground, YHY-type mine water pressure monitoring instruments with an error of ≤±1% are installed at 4-5 typical water outlets with different flow rates for long-term monitoring.

[0013] In step S2

[0014] A standard hexahedral mesh was used, with the mesh gradually becoming sparser from the center outwards. The minimum mesh length was 2m. The x, y, and z axes were taken as the strike, dip, and height of the ore body, respectively. The model was 600m long, 400m wide, and 500m high. Normal displacement constraints were applied to the bottom and side surfaces of the model, and a uniformly distributed load was applied to the top to simulate the mining depth. The unit cell adopted the Mohr-Coulomb constitutive model, and the mechanical parameters were obtained from existing mechanical tests. The water pressure value was assigned according to the pore water pressure. It was assumed that the water-conducting fracture zone was located in the upper part of the direct roof of the stope, and the upper part of the stope roof was assigned pore water pressure.

[0015] A numerical simulation scheme was determined. Based on the on-site water pressure monitoring results, water pressure values ​​of 0MPa, 0.1MPa, 0.2MPa, 0.5MPa, 1MPa, 1.5MPa and 2MPa were selected. Combined with the mining technology scheme, excavation calculations were carried out with a mining length of 50m, a mining width of 15m and a mining height of 60m, and an impermeable layer thickness of 0.1m.

[0016] Using the maximum displacement of the roof as the stability index of the mining area, the changes in the maximum displacement of the roof after excavation stabilization at various water pressure values ​​were obtained and analyzed. Based on the rock mass ultimate displacement criterion, typical water pressure values ​​of 0.1MPa, 0.5MPa, 1.0MPa, 1.5MPa and 2.0MPa were selected to optimize the thickness of the aquitard.

[0017] In the step S3, the typical water pressure values are selected as 0.1 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa and 2.0 MPa, and the roof water-resisting layer thicknesses are selected as 0 m, 2 m, 4 m and 8 m, respectively, to optimize the water-resisting layer thickness.

[0018] In the step S4, the Average discrimination method is selected to discriminate the plastic zone, that is, when more than 50% of the volume in the unit body is damaged, it is determined that the unit body is damaged; the maximum principal stress, the minimum principal stress, the displacement and the plastic zone cloud diagram of the roof are obtained when the water pressure is 0.1 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa and 2.0 MPa, respectively, and the water-resisting layer thicknesses are 0.1 m, 2 m, 4 m and 8 m, respectively, and the stability is analyzed.

[0019] In the step S5, the maximum value of the maximum principal stress, the minimum value of the maximum principal stress, the maximum subsidence amount of the roof and the plastic zone damage depth index value of each scheme at the 0.1 m slice of the upper part of the roof are extracted, the influence of the water-resisting layer thickness on each index under the condition of different water pressure values is studied, and the interaction of the water pressure and the water-resisting layer thickness on the roof damage is compared and analyzed, which are as follows:

[0020] (1) Stress concentration change analysis: the maximum value of the maximum principal stress of each scheme is obtained under the condition of different water pressure, and the curve graph of the maximum value of the maximum principal stress changing with the water-resisting layer thickness is obtained, and the change of the stress concentration of the roof of the mining field with the change of the water-resisting layer thickness and the water pressure is analyzed;

[0021] (2) Stress release change analysis: the minimum value of the maximum principal stress of each scheme is obtained under the condition of different water pressure, and the curve graph of the minimum value of the maximum principal stress changing with the water-resisting layer thickness is obtained, and the change of the stress release of the roof of the mining field with the change of the water-resisting layer thickness and the water pressure is analyzed;

[0022] (3) Roof displacement amount analysis: the roof displacement amount of each scheme is obtained under the condition of different water pressure, and the curve graph of the roof displacement amount changing with the water-resisting layer thickness is obtained, and the change of the roof displacement amount of the mining field with the change of the water-resisting layer thickness and the water pressure is analyzed;

[0023] (4) Plastic zone analysis: when the mining field is excavated, the plastic damage of the surrounding rock will be caused, when the damage zone and the water-bearing fractured zone are connected, the water will flow into the mining field through the plastic zone, causing the roof water inrush accident, in order to directly show the connection of the damage zone and the fractured zone, the water inrush safety factor S is defined, when S is greater than 2, it indicates that there is basically no water inrush risk,

[0024] S = H P - Z w Z

[0025] In the formula, S is the water inrush safety factor, Pw is the water pressure, MPa, H is the water-resisting layer thickness, m, and Z is the plastic zone damage depth, m;

[0026] Calculate the safety factor of water inrush in the stope under different water pressures and different thicknesses of the water-resistant rock layer, draw a line graph of the water inrush safety factor with the thickness of the water-resistant rock layer under different water pressures, and extract its critical thickness as the initial thickness of the water-resistant layer under different water pressure conditions.

[0027] (5) By considering the trends of stress, displacement, and plastic zone variation with water pressure and top plate, the final optimal thickness of the waterproof layer under different water pressure conditions is obtained.

[0028] The beneficial effects of this invention are: by using numerical simulation to analyze the sensitivity of the stope stability to water pressure values; then conducting stability analysis on mining under different water pressure and aquitard thickness conditions, the optimal aquitard thickness under each water pressure value is obtained, and the reserved aquitard thickness for metal mining under water-rich karst aquifers is reasonably determined. This can better evolve the expansion law of the plastic zone in pressure-bearing mining, and comprehensively consider the trends of stress, displacement, plastic zone and water inrush safety factor with water pressure and roof changes, which is more in line with actual mining conditions. Attached Figure Description

[0029] Figure 1 This is a flowchart of the present invention;

[0030] Figure 2 This is the numerical model for analyzing the stability of the mining area and its sensitivity to water pressure in this embodiment of the invention;

[0031] Figure 3 This is a schematic diagram of the pressure bearing of the mining roof in an embodiment of the present invention;

[0032] Figure 4 This is a graph showing the change in roof displacement under different water pressure values ​​in an embodiment of the present invention;

[0033] Figure 5 This is the maximum principal stress cloud diagram of the top plate in Scheme 1 of the present invention (H=0.1);

[0034] Figure 6 This is the minimum principal stress cloud diagram of the top plate in Scheme 1 of the present invention (H=0.1);

[0035] Figure 7 This is a cloud diagram of the vertical displacement of the top plate in Scheme 1 of the present invention (H = 0.1);

[0036] Figure 8 This is a cloud map of the plastic zone in Scheme 1 of the present invention (H = 0.1);

[0037] Figure 9 This is the maximum principal stress cloud diagram (H=2) of the top plate in Scheme 2 of the present invention;

[0038] Figure 10 This is the minimum principal stress cloud diagram (H=2) of the top plate in embodiment 2 of the present invention;

[0039] Figure 11 is a vertical displacement nephogram of the roof in the scheme 2 in the embodiment of the present application (H=2) ;

[0040] Figure 12 is a plastic zone nephogram of the stope in the scheme 2 in the embodiment of the present application (H=2) ;

[0041] Figure 13 is a maximum principal stress nephogram of the roof in the scheme 3 in the embodiment of the present application (H=4) ;

[0042] Figure 14 is a minimum principal stress nephogram of the roof in the scheme 3 in the embodiment of the present application (H=4) ;

[0043] Figure 15 is a vertical displacement nephogram of the roof in the scheme 3 in the embodiment of the present application (H=4) ;

[0044] Figure 16 is a plastic zone nephogram of the stope in the scheme 3 in the embodiment of the present application (H=4) ;

[0045] Figure 17 is a maximum principal stress nephogram of the roof in the scheme 4 in the embodiment of the present application (H=8) ;

[0046] Figure 18 is a minimum principal stress nephogram of the roof in the scheme 4 in the embodiment of the present application (H=8) ;

[0047] Figure 19 is a vertical displacement nephogram of the roof in the scheme 4 in the embodiment of the present application (H=8) ;

[0048] Figure 20 is a plastic zone nephogram of the stope in the scheme 4 in the embodiment of the present application (H=8) ;

[0049] Figure 21 is a curve graph of the maximum value Max of the maximum principal stress and the thickness of the aquiclude in the embodiment of the present application;

[0050] Figure 22 is a curve graph of the minimum value Min of the maximum principal stress and the thickness of the aquiclude in the embodiment of the present application;

[0051] Figure 23 is a curve graph of the roof displacement and the thickness of the aquiclude in the embodiment of the present application;

[0052] Figure 24 is a calculation result of the water inrush safety factor in the embodiment of the present application;

[0053] Figure 25 is a broken line graph of the water inrush safety factor and the thickness in the embodiment of the present application. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical scheme and advantages of the embodiment of the application clearer, the technical scheme in the embodiment of the application will be clearly and completely described below in conjunction with the drawings in the embodiment. Obviously, the described embodiment is only a part of the embodiments of the application, and not all the embodiments of the application. Based on the embodiment in the application, all the other embodiments obtained by a person of ordinary skill in the art without creative labor belong to the protection scope of the application.

[0055] An optimization method for reserving water-resisting rock thickness, comprising the following steps:

[0056] S1, water pressure monitoring is performed on a typical water outlet point in a well, and the water pressure monitoring result of the measuring point is analyzed;

[0057] S2, a mining model under different initial water pressure conditions is established by using FLac 3D, and a stope stability-water pressure sensitivity analysis is performed;

[0058] S3, a numerical simulation optimization scheme of the water-resisting layer thickness of the stope roof is determined, the stope roof stress, displacement and plastic zone are compared and analyzed by changing the water pressure value and the water-resisting layer thickness, and a reasonable water-resisting layer thickness of the roof is further determined;

[0059] S4, water-resisting rock layer thickness optimization under different water pressures, the maximum principal stress of the roof, the minimum principal stress of the roof, the displacement of the roof and the plastic zone of the stope are selected as the basis for stability analysis, and the stope stability analysis under different water pressures and different water-resisting rock layer thicknesses is performed;

[0060] S5, water-resisting layer thickness optimization under different water pressure conditions, the influence of the water-resisting layer thickness on the roof indicators under different water pressure values is studied, the interaction of water pressure and water-resisting layer thickness on the roof damage is compared and analyzed, and the water-resisting layer thickness under different water pressure conditions is further optimized.

[0061] In the step S1, in order to find out the actual water pressure in the well, YHY type mine water pressure monitor is installed at 4-5 typical water outlet points with different flow rates, the error is ≤±1%, and long-term monitoring is performed.

[0062] In the step S2,

[0063] Standard hexahedral grids are adopted, the grids gradually change from the center to the periphery, the minimum grid length is 2m, the x, y and z axes are respectively the ore body strike, inclination and height, the model is 600m long, 400m wide and 500m high; the model is subjected to normal displacement constraints on the bottom and side surfaces, and a uniform load is applied on the top to simulate the mining depth; the Mohr-Coulomb constitutive model is adopted for the unit body, the mechanical parameters are obtained according to the existing mechanical test; the water pressure value is assigned according to the pore water pressure, and it is assumed that the water flowing fractured zone is located on the upper part of the immediate roof of the ore room, and the pore water pressure is assigned to the upper part of the stope roof;

[0064] Determination of numerical simulation scheme, based on the field water pressure monitoring results, select water pressure value is 0 MPa, 0.1 MPa, 0.2 MPa, 0.5 MPa, 1 MPa, 1.5 MPa and 2 MPa, combined with the mining technology scheme, according to the length of 50 m, mining width 15 m and mining height 60 m, the thickness of the aquiclude is 0.1 m, the excavation calculation is carried out;

[0065] Taking the maximum displacement of the roof as the stability index of the stope, the maximum displacement change of the roof after excavation under each water pressure value is obtained and analyzed; combined with the limit displacement criterion of rock mass, the typical water pressure values of 0.1 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa and 2.0 MPa are selected to optimize the thickness of the aquiclude.

[0066] In the step S3, when the typical water pressure values are 0.1 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa and 2.0 MPa, and the thickness of the roof aquiclude is 0 m, 2 m, 4 m and 8 m, the optimization of the thickness of the aquiclude is carried out.

[0067] In the step S4, the Average discrimination method is selected for plastic zone discrimination, that is, when more than 50% of the volume in the unit body is damaged, it is determined that the unit body is damaged; the maximum principal stress, the minimum principal stress, the displacement and the plastic zone cloud of the roof are obtained when the water pressure is 0.1 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa and 2.0 MPa, and the thickness of the aquiclude is 0.1 m, 2 m, 4 m and 8 m, respectively, and the stability is analyzed.

[0068] In the step S5, the maximum value of the maximum principal stress, the minimum value of the maximum principal stress, the maximum settlement of the roof and the plastic zone damage depth index value of each scheme at the 0.1 m slice of the upper part of the roof are extracted, the influence of the thickness of the aquiclude on each index under different water pressure values is studied, and the interaction of water pressure and aquiclude thickness on the roof damage is compared and analyzed, as follows:

[0069] (1) Stress concentration change analysis, the maximum value of the maximum principal stress of each scheme under different water pressure conditions is obtained, and the change of the stress concentration of the roof of the stope with the change of the thickness of the aquiclude and the water pressure is analyzed;

[0070] (2) Stress release change analysis, the minimum value of the maximum principal stress of each scheme under different water pressure conditions is obtained, and the change of the stress release of the roof of the stope with the change of the thickness of the aquiclude and the water pressure is analyzed;

[0071] (3) Roof displacement analysis, obtain the roof displacement curve of each scheme under different water pressure conditions with the change of the thickness of the aquiclude, analyze the change of the roof displacement of the stope with the change of the thickness of the aquiclude and water pressure;

[0072] (4) Plastic zone analysis, when the stope is excavated, plastic failure of surrounding rock will be caused, when the failure zone and the water-bearing fractured zone are connected, water will flow into the stope through the plastic zone, causing roof water inrush accident, in order to intuitively show the connection of the failure zone and the fractured zone, define the water inrush safety factor S, when S is greater than 2, it indicates that there is basically no water inrush risk,

[0073] S = H-Z

[0074] P w

[0075] In the formula, S is the water inrush safety factor, Pw is the water pressure, MPa, H is the thickness of the aquiclude, m, and Z is the plastic zone failure depth, m.

[0076] The stope water inrush safety factor under different water pressures and different aquiclude thicknesses is calculated respectively, the water inrush safety factor under different water pressures is drawn with the change of the aquiclude thickness, and the critical thickness is extracted as the initial thickness of the aquiclude under different water pressure conditions;

[0077] (5) The final optimal thickness of the aquiclude under different water pressure conditions is obtained by comprehensively analyzing the stress, displacement and plastic zone with the change trend of water pressure and roof.

[0078] In practical application, the present application comprises the following steps:

[0079] Firstly, the water pressure of typical water outlet points in the underground is monitored. In order to find out the actual water pressure in the underground, YHY type mine water pressure monitor (error ≤ ± 1%) is installed at 4-5 typical water outlet points with different flow rates for long-term monitoring, and the water pressure monitoring results of the measuring points are analyzed.

[0080] Secondly, FLac 3D is used to establish a mining model under different initial water pressure conditions, and stope stability-water pressure sensitivity analysis is carried out, so as to provide a basis for determining the numerical simulation optimization scheme of the stope roof aquiclude thickness. Standard hexahedral mesh is adopted, and the mesh gradually changes from the center to the periphery, and the minimum mesh length is 2 m. The x, y and z axes are taken as the ore body strike, inclination and height respectively, the model is 600 m long, 400 m wide and 500 m high. The normal displacement constraint is applied to the bottom and side surfaces of the model, and the uniform load is applied to the top to simulate the mining depth. The Mohr-Coulomb constitutive model is adopted for the unit body, and the mechanical parameters are obtained according to the existing mechanical test. The water pressure value is assigned according to the pore water pressure, and it is assumed that the water conducting fractured zone is located in the upper part of the immediate roof of the ore room, and the pore water pressure is assigned to the upper part of the stope roof.

[0081] Determination of numerical simulation scheme. Based on the results of field water pressure monitoring, the water pressure values of 0 MPa, 0.1 MPa, 0.2 MPa, 0.5 MPa, 1 MPa, 1.5 MPa and 2 MPa were selected, combined with the mining technical scheme, the mining length of 50 m, the mining width of 15 m, the mining height of 60 m and the thickness of 0.1 m of the aquifuge were calculated.

[0082] The rock mass displacement can more directly reflect the roof rock mass stability, and the maximum displacement of the roof is taken as the stability index of the stope, the maximum displacement of the roof after excavation under different water pressure values is obtained and analyzed, and the thickness of the aquifuge is optimized by selecting the typical water pressure values of 0.1 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa and 2.0 MPa.

[0083] Third step, determination of numerical simulation optimization scheme of the thickness of the roof aquifuge of the stope. The stability of the roof of the stope is affected by the water pressure value Pw and the thickness H of the roof aquifuge (the distance between the direct roof and the water-bearing layer). By changing the water pressure value and the thickness of the aquifuge, the stress, displacement and plastic zone of the roof of the stope are compared and analyzed to further determine the reasonable thickness of the roof aquifuge. The thickness of the aquifuge is optimized by selecting the typical water pressure values of 0.1 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa and 2.0 MPa and the thickness of the roof aquifuge of 0 m, 2 m, 4 m and 8 m.

[0084] Fourth step, optimization of the thickness of the roof aquifuge under different water pressure. The protection of the roof aquifuge to the stope mainly reflects in the stress, displacement and prevention of the plastic zone and the fracture water-conducting zone from being connected, therefore, the maximum principal stress of the roof, the minimum principal stress of the roof, the displacement of the roof and the plastic zone of the stope are selected as the basis for stability analysis. In order to facilitate the description of the failure depth, the Average method is selected for the plastic zone discrimination, that is, when more than 50% of the volume in the unit body is damaged, the unit body is considered to be damaged. The numerical simulation based on the measured water pressure and the actual mining parameters can better evolve the plastic zone expansion law of the pressure-bearing mining, and further optimize the thickness of the aquifuge.

[0085] The stability of the stope under different water pressures and different thicknesses of the aquifuge is analyzed respectively. The maximum principal stress, minimum principal stress, displacement and plastic zone cloud of the roof under different thicknesses of the aquifuge (0.1 m, 2 m, 4 m and 8 m) under the water pressure of 0.1 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa and 2.0 MPa are obtained, and the stability is analyzed.

[0086] In the fifth step, the thickness of the water-resisting layer is optimized under different water pressure conditions. In order to more intuitively compare the stress, displacement, and plastic zone variation of each scheme, the maximum value of the maximum principal stress, the minimum value of the maximum principal stress, the maximum subsidence of the roof, and the plastic zone failure depth of each scheme at the 0.1 m slice of the upper part of the roof are extracted, the influence of the thickness of the water-resisting layer on each index under different water pressure values is studied, the interaction of water pressure and the thickness of the water-resisting layer on the roof failure is compared and analyzed, and the thickness of the water-resisting layer under different water pressure conditions is further optimized.

[0087] (1) Stress concentration variation analysis. The maximum value of the maximum principal stress under different water pressure conditions is obtained, and the variation of the stress concentration of the roof of the stope with the change of the thickness of the water-resisting layer and water pressure is analyzed.

[0088] (2) Stress release variation analysis. The minimum value of the maximum principal stress under different water pressure conditions is obtained, and the variation of the stress release of the roof of the stope with the change of the thickness of the water-resisting layer and water pressure is analyzed.

[0089] (3) Roof displacement analysis. The roof displacement under different water pressure conditions is obtained, and the variation of the roof displacement with the change of the thickness of the water-resisting layer and water pressure is analyzed.

[0090] (4) Plastic zone analysis. When the stope is excavated, plastic failure of the surrounding rock will occur. When the failure zone and the water-bearing fractured zone are connected, water will flow into the stope through the plastic zone, causing roof water inrush accident. In order to intuitively show the connection between the failure zone and the fractured zone, the water inrush safety factor S is defined. When S is greater than 2, it indicates that there is basically no water inrush risk.

[0091]

[0092] In the formula, S is the water inrush safety factor; Pw is the water pressure, MPa; H is the thickness of the water-resisting layer, m; and Z is the plastic zone failure depth, m.

[0093] The water inrush safety factor of the stope under different water pressures and different thicknesses of the water-resisting rock layer is calculated, the variation of the water inrush safety factor with the thickness of the water-resisting rock layer under different water pressures is plotted, and the critical thickness is extracted as the initial thickness of the water-resisting layer under different water pressure conditions.

[0094] (5) The variation trend of stress, displacement, and plastic zone with water pressure and roof is obtained, and the final optimized thickness of the water-resisting layer under different water pressure conditions is obtained.

[0095] Embodiment:

[0096] (1) A certain iron mine in Hebei is a large water karst mine, the hydrogeological conditions of the ore body are relatively complex, it belongs to a typical large water deposit, and the quality grade of surrounding rock belongs to Ⅳ to Ⅴ grade broken rock mass. At present, the mining middle section is-230m~ -170m level. In order to ensure the safety of mining, it is urgent to carry out the research on the thickness optimization of the roof water-resisting layer and the groundwater control under the pressure.

[0097] In order to find out the water pressure of-170m level of the mine, YHY type mine water pressure monitor (error ≤ ± 1%) was installed in four typical water outlets with different flow rates for long-term monitoring. The water pressure monitoring results of each measuring point are shown in Table 1, and the water pressure is basically between 0.1~2MPa.

[0098] Table 1 Water pressure monitoring results

[0099]

[0100] (2) The FLac 3D was used to establish the mining model under different initial water pressure conditions, and the stability of the stope and the water pressure sensitivity were analyzed.

[0101] The standard hexahedral mesh was adopted, and the mesh gradually changed from the center to the periphery, and the minimum mesh length was 2m. The x, y and z axes were taken as the ore body trend, inclination and height respectively, the model was 600m long, 400m wide and 500m high. The model was applied with the normal displacement constraint of the bottom and side surface, and the uniform load was applied on the top to simulate the mining depth. The model diagram is shown in Figure 2 . The Mohr-Coulomb constitutive model was used for the unit body, and the mechanical parameters were obtained according to the existing mechanical test, as shown in Table 2. The water pressure value was assigned according to the pore water pressure, and it was assumed that the water flowing fractured zone was located in the upper part of the ore room roof, and the upper part of the stope roof was assigned with the pore water pressure, as shown in Figure 3 .

[0102] Table 2 Mechanical parameters of mine rock

[0103]

[0104] The numerical simulation scheme was determined. Based on the field water pressure monitoring results, the water pressure values of 0MPa, 0.1MPa, 0.2MPa, 0.5MPa, 1MPa, 1.5MPa and 2MPa were selected, combined with the mining technical scheme, the excavation calculation was carried out according to the mining length of 50m, the mining width of 15m, the mining height of 60m and the water-resisting layer thickness of 0.1m. The rock mass displacement can more directly reflect the roof rock mass stability, and the maximum displacement of the roof was taken as the stability index of the stope, and the maximum displacement change of the roof after excavation under each water pressure value was obtained, as shown in Figure 4 . The maximum displacement of the roof under different water pressure values is shown in Figure 4It is known that the presence of water pressure significantly increases the maximum displacement of the roof. The roof displacement is positively correlated with the water pressure value; the increase in roof displacement increases with increasing water pressure. Furthermore, the increase in roof displacement when the water pressure is 0–1.0 MPa is much smaller than that when the water pressure is 1.0–2.0 MPa. Based on the rock mass ultimate displacement criterion, for this ore body, the presence of water pressure will pose a risk of instability in the stope. When the water pressure is 0.1–1.0 MPa, the stope may face instability risk. When the water pressure is 1.0–2.0 MPa, the roof deformation is large, leading to stope instability and collapse. Therefore, the thickness of the aquitard layer is optimized using typical water pressure values ​​of 0.1 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa, and 2.0 MPa.

[0105] (3) Determine the numerical simulation optimization scheme for the thickness of the aquitard layer in the stope roof. The stability of the stope roof is affected not only by the water pressure value Pw but also by the thickness H of the aquitard layer (the height of the direct roof from the aquifer). By changing the water pressure value and the aquitard layer thickness, a comparative analysis of the stress, displacement, and plastic zone of the stope roof is conducted to further determine a reasonable aquitard layer thickness. Typical water pressure values ​​of 0.1 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa, and 2.0 MPa, and aquitard layer thickness of 0 m, 2 m, 4 m, and 8 m, respectively, are selected for optimization of the aquitard layer thickness. The 20 simulated technical schemes are detailed in Table 3.

[0106] Table 3 Numerical Simulation Scheme

[0107]

[0108] Due to space limitations, this analysis only considers the maximum principal stress, minimum principal stress, displacement, and plastic zone contour maps of the roof for four technical schemes with different impermeable rock layer thicknesses of 0.1m, 2m, 4m, and 8m at a water pressure of 0.1MPa, and performs stability analysis accordingly. Roof maximum principal stress, minimum principal stress, displacement, and plastic zone contour maps for other technical schemes are omitted.

[0109] (4) Optimization of the thickness of the aquitard layer under different water pressures. The protective role of the aquitard layer in the stope is mainly reflected in the stress and displacement of the roof and the prevention of the plastic zone from communicating with the fractured water-conducting zone. Therefore, the maximum principal stress, minimum principal stress, displacement, and plastic zone of the stope are selected as the basis for stability analysis. To facilitate the description of the failure depth, the Average discrimination method is selected for the plastic zone discrimination, that is, when more than 50% of the volume in a unit cell fails, the unit cell is considered to have failed. Numerical simulation based on measured water pressure and actual mining parameters can better evolve the expansion law of the plastic zone in pressure mining, thereby optimizing the thickness of the aquitard layer. The stability analysis of the stope under different water pressures and different aquitard layer thicknesses is carried out separately.

[0110] 1) Water pressure is 0.1MPa when the different water-resisting layer thickness stability analysis. Water pressure value is 0.1MPa, the different water-resisting layer thickness of the roof maximum principal stress, minimum principal stress, displacement, plastic zone nephogram as shown in 5-20. After the excavation of stope, the roof and side meet the size of about 28.123-28.486MPa stress concentration zone, and the width direction of the concentration phenomenon is obviously greater than the length direction; direct roof forms 0.477-0.541MPa stress release zone, and in the stope width direction adjacent room roof forms semicircular stress release zone; roof displacement is elliptical distribution, size is about 48.220-51.748mm, between stable-unstable; the maximum damage depth is less than 3m, water-resisting layer thickness is 0.1m: the roof mainly for tensile failure, roof and two side meet only for tensile failure. With the increase of water-resisting layer thickness, the shear failure number greatly reduces.

[0111] 2) Water pressure is 0.5MPa when the different water-resisting layer thickness stability analysis. Water pressure value is 0.5MPa, the different water-resisting layer thickness of the roof maximum principal stress, minimum principal stress, displacement, plastic zone nephogram omitted. After the excavation of stope, the roof and side meet the size of about 28.173-28.517MPa stress concentration zone, and the width direction of the concentration phenomenon is obviously greater than the length direction; direct roof forms 0.316-0.547MPa stress release zone, and in the stope width direction adjacent room roof forms semicircular stress release zone; roof displacement is elliptical distribution, size is about 48.331-53.853mm, between stable-unstable; water-resisting layer thickness is 0.1m: the roof mainly for tensile failure, the maximum damage depth is less than 5m, and in the roof and two side meet shear-tensile failure; water-resisting layer thickness is greater than 2m, the maximum damage depth of the roof reduces to less than 3m, and the roof and two side meet only for tensile failure. With the increase of water-resisting layer thickness, the shear failure number greatly reduces.

[0112] 3) Water pressure is 1.0 MPa, different water-resisting layer thickness stability analysis. Water pressure value is 1.0 MPa, different water-resisting layer thickness roof maximum principal stress, minimum principal stress, displacement, plastic zone cloud atlas omitted. After the stope excavation, the roof and the side of the intersection formed 28.297-28.561 MPa stress concentration zone, and the width direction of the concentration phenomenon is obviously greater than the length direction; the immediate roof formed 0.205-0.549 MPa stress release zone, and in the stope width direction adjacent room roof formed semicircular stress release zone; the roof displacement is oval type distribution, the size is about 48.573-63.389 mm, between stable-unstable; water-resisting layer thickness is 0.1 m: the roof mainly shows tensile failure, the maximum damage depth is less than 5 m, and there is shear-tensile failure at the intersection of the roof and the two sides; water-resisting layer thickness is 2 m: the roof maximum damage depth is less than 5 m, the intersection of the roof and the two sides still shows more shear-tensile failure; water-resisting layer thickness is greater than 4 m: the roof maximum damage depth is reduced to less than 3 m, the intersection of the roof and the two sides only shows tensile failure. With the increase of water-resisting layer thickness, the shear failure number is greatly reduced.

[0113] 4) Water pressure is 1.5 MPa, different water-resisting layer thickness stability analysis. Water pressure value is 1.5 MPa, different water-resisting layer thickness roof maximum principal stress, minimum principal stress, displacement, plastic zone cloud atlas omitted. After the stope excavation, the roof and the side of the intersection formed 28.775-28.597 MPa stress concentration zone, and the width direction of the concentration phenomenon is obviously greater than the length direction; the immediate roof formed 0.167-0.554 MPa stress release zone, and in the stope width direction adjacent room roof formed semicircular stress release zone; the roof displacement is oval type distribution, the size is about 48.657-142.25 mm, between stable-unstable; water-resisting layer thickness is 0.1 m: the roof mainly shows tensile failure, the maximum damage depth is less than 5 m, and there is shear-tensile failure at the intersection of the roof and the two sides; water-resisting layer thickness is 2 m: the roof maximum damage depth is less than 5 m, the intersection of the roof and the two sides still shows more shear-tensile failure; water-resisting layer thickness is greater than 4 m: the roof maximum damage depth is reduced to less than 3 m, the intersection of the roof and the two sides only shows tensile failure. With the increase of water-resisting layer thickness, the shear failure number is greatly reduced.

[0114] 5) Stability analysis of different impermeable layer thicknesses at a water pressure of 2.0 MPa. The maximum principal stress, minimum principal stress, displacement, and plastic zone contour plots of the top plate with different impermeable layer thicknesses are omitted when the water pressure is 2.0 MPa. After the stope excavation, a stress concentration zone of 28.453–29.027 MPa was formed at the junction of the roof and sidewalls, with the concentration in the width direction being significantly greater than that in the length direction. A stress release zone of 0.846–0.605 MPa was formed in the immediate roof, and a semi-circular stress release zone was formed in the adjacent stope roof in the width direction of the stope. The roof displacement exhibited an elliptical distribution, with a size of approximately 48.925–∞ mm, falling between stable, unstable, and instable states, indicating the possibility of stope instability. With an aquitard thickness of 0.1 m, the roof mainly exhibited large-scale tensile failure, with a maximum failure depth of less than 5 m, and numerous shear-tensile failure zones existed at the junction of the roof and sidewalls. With an aquitard thickness of 2 m, the maximum failure depth of the roof increased to less than 7 m, but the failure area decreased significantly. With an aquitard thickness of 4–8 m, the failure depth decreased to less than 3 m, and only shear failure was observed at the junction of the roof and sidewalls. The number of shear failures decreased significantly with increasing aquitard thickness.

[0115] (5) Optimization of the thickness of the aquitard under different water pressure conditions. To more intuitively compare the stress, displacement, and plastic zone changes of each scheme, the maximum value of the maximum principal stress, the minimum value of the maximum principal stress, the maximum settlement of the roof, and the depth of plastic zone failure of each scheme were extracted from the 0.1m section at the top of the mining area roof. The influence of the thickness of the aquitard on each index under different water pressure conditions was studied. The interaction between water pressure and the thickness of the aquitard on the roof failure was compared and analyzed to further optimize the thickness of the aquitard under different water pressure conditions.

[0116] 1) Stress concentration variation analysis. Obtain the curves showing the maximum principal stress of each scheme under different water pressure conditions as a function of the impermeable layer thickness, as shown below. Figure 21 As shown in the figure, the stress concentration in the stope roof is analyzed in relation to the thickness of the aquitard and water pressure. The figure shows that the maximum principal stress is influenced by both rock and water pressure, and is positively correlated with both when the stope is in a stable state. When the water pressure is between 0.1 and 0.5 MPa, increasing the water pressure has little effect on roof stability; at this point, the stress change mainly originates from the surrounding rock. When the water pressure is between 0.5 and 2.0 MPa, stress concentration increases with increasing aquitard thickness. When the thickness increases from 0 to 4 m, the influence of water pressure on stress concentration gradually decreases, indicating that the stress change at this point mainly originates from water pressure, and increasing the roof thickness is beneficial for roof stability. When the thickness increases from 4 to 8 m, the rate of change of stress concentration with increasing water pressure does not change significantly, indicating that the stress change originates from the surrounding rock, and water pressure has little effect on roof stability.

[0117] The stress concentration changes with the thickness of the aquiclude and water pressure. When the water pressure is large, the stress concentration has a minimum thickness of the aquiclude, which is between 2-6m. When the thickness of the aquiclude is small, the stress concentration increases with the water pressure, and the slope of the curve has a critical value of water pressure, which is between 1.0-1.5MPa. From the perspective of stress concentration, technical solutions 2-4, 6-8, 10-12, 15, 16, 19, and 20 have good stability.

[0118] 2) Stress release change analysis. The minimum value of the maximum principal stress of each scheme under different water pressure conditions changes with the thickness of the aquiclude as shown in Figure 22 The stress release changes with the thickness of the aquiclude and water pressure. When the thickness of the aquiclude is 0-2m, the stress release degree is negatively correlated with the water pressure value, and the stress release rate increases with the water pressure. When the thickness of the aquiclude is 2-4m, the stress and water pressure value gradually changes from negative correlation to positive correlation with the increase of thickness. When the thickness of the aquiclude increases to 6-8m, the stress value increases, but the change is not obvious, and the stress and water pressure value remains positively correlated. Therefore, when the thickness of the aquiclude is small, the stress release degree is mainly affected by the water pressure value, which hinders the roof pressure relief and is not conducive to the stability of the mining field. When the thickness of the aquiclude is large, the direct effect of water pressure on the roof is weakened and the influence is small. From the perspective of stress release, technical solutions 1-12, 15, 16, 19, and 20 have good stability.

[0119] 3) Roof displacement analysis. The roof displacement of each scheme under different water pressure conditions changes with the thickness of the aquiclude as shown in Figure 23 The roof displacement changes with the thickness of the aquiclude and water pressure. Overall, the maximum settlement of the roof is negatively correlated with the thickness of the aquiclude, and the displacement decreases with the increase of thickness. The maximum settlement of the roof is positively correlated with the water pressure, and the stress increment increases with the increase of water pressure. According to the rock mass limit displacement criterion (50mm), technical solutions 2-4, 6-8, 10-12, 15, 16, 19, and 20 have good stability.

[0120] 4) Plastic zone analysis. When the mining field is excavated, it will cause plastic damage to the surrounding rock. When the damage zone and the water-bearing fracture zone are connected, water will flow into the mining field through the plastic zone, causing roof water inrush accident. To intuitively show the connection between the damage zone and the fracture zone, the water inrush safety factor S is defined. When S is greater than 2, it indicates that there is basically no water inrush risk.

[0121]

[0122] In the formula, S is a water inrush safety factor, Pw is water pressure, MPa, H is the thickness of the water-resisting layer, m, and Z is the plastic zone failure depth, m.

[0123] The water inrush safety factors of the stope under different water pressures and different water-resisting layer thicknesses are calculated respectively, and the results are shown in Figure 24 . To obtain more accurate water-resisting layer thickness, it is assumed that the adjacent thicknesses are in a linear relationship, a broken line graph of the water inrush safety factor with the water-resisting layer thickness under different water pressures is drawn as Figure 25 , and the critical thickness is extracted. When the water pressure is 0.1 MPa, the plastic zone depth is greater than the water-resisting layer thickness when the water-resisting layer thickness is less than 1.8 m, and the stope has a water inrush risk. When the water-resisting layer thickness is greater than 1.8 m, the plastic zone depth is less than the water-resisting layer thickness, and the stope stability is good, and the water-resisting layer thickness is not less than 1.8 m. Similarly, when the water pressure is 0.5 MPa, the water-resisting layer thickness needs to be not less than 3 m, when the water pressure is 1.0 MPa, the water-resisting layer thickness needs to be not less than 4 m, when the water pressure is 1.5 MPa, the water-resisting layer thickness needs to be not less than 5.6 m, and when the water pressure is 2.0 MPa, the water-resisting layer thickness needs to be not less than 7.1 m.

[0124] 5) Based on the stress, displacement, and plastic zone change trends with water pressure and roof, the final optimal thickness of the water-resisting layer under different water pressures is obtained: when the water pressure is 0.1 MPa, the water-resisting layer thickness needs to be not less than 1.8 m; when the water pressure is 0.5 MPa, the water-resisting layer thickness needs to be not less than 3 m; when the water pressure is 1.0 MPa, the water-resisting layer thickness needs to be not less than 4 m; when the water pressure is 1.5 MPa, the water-resisting layer thickness needs to be not less than 5.6 m; and when the water pressure is 2.0 MPa, the water-resisting layer thickness needs to be not less than 7.1 m.

[0125] The present application firstly establishes a mining model based on the measured water pressure, analyzes the stope stability-water pressure sensitivity, and proposes a numerical simulation optimization scheme for the water-resisting layer thickness of the stope roof based on the analysis results. The numerical simulation based on the measured water pressure and actual mining parameters can better evolve the plastic zone expansion law of pressure-bearing mining, and the metal mine water inrush safety factor calculation formula is optimized. Based on the stress, displacement, and plastic zone change trends with water pressure and roof, the water-resisting layer thickness is further optimized, and the optimization results are more suitable for the actual underground mining, and have good engineering guiding significance.

Claims

1. A method of optimizing the thickness of a water barrier reservation, characterized in that Includes the following steps: S1. Conduct water pressure monitoring at typical water outlets in the well and analyze the water pressure monitoring results at the monitoring points; S2. Use FLac 3D to establish mining models under different initial water pressure conditions and conduct stope stability-water pressure sensitivity analysis; S3. Determine the numerical simulation optimization scheme for the thickness of the waterproof layer on the top plate of the mining area. By changing the water pressure value and the thickness of the waterproof layer, compare and analyze the stress, displacement and plastic zone of the top plate of the mining area to further determine the reasonable thickness of the waterproof layer on the top plate. S4. Optimization of the thickness of the impermeable stratum under different water pressures: The maximum principal stress, minimum principal stress, displacement, and plastic zone of the stope were selected as the basis for stability analysis. Stability analyses were conducted at different water pressures and with different impermeable stratum thicknesses. The Average discrimination method was used to determine the plastic zone; a unit was considered to have failed when more than 50% of its volume failed. Maximum principal stress, minimum principal stress, displacement, and plastic zone contour maps of the roof were obtained for water pressures of 0.1 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa, and 2.0 MPa, with impermeable stratum thicknesses of 0.1 m, 2 m, 4 m, and 8 m, respectively, and stability analyses were performed. S5. Optimization of the waterproof layer thickness under different water pressure conditions: The influence of the waterproof layer thickness on various roof parameters under different water pressure values ​​is studied. The interaction between water pressure and waterproof layer thickness on roof damage is compared and analyzed. Further optimization of the waterproof layer thickness under different water pressure conditions is then achieved, specifically: The maximum and minimum values ​​of the maximum principal stress, the maximum roof settlement, and the failure depth of the plastic zone were extracted from the top 0.1m section of the stope roof for each scenario. The influence of the aquitard thickness on each index under different water pressure conditions was studied, and the interaction between water pressure and aquitard thickness on roof failure was compared and analyzed, as follows: (1) Stress concentration variation analysis: obtain the maximum value of the principal stress of each scheme under different water pressure conditions as a function of the thickness of the water-proof layer, and analyze the stress concentration of the mining roof as a function of the thickness of the water-proof layer and the water pressure. (2) Stress release variation analysis: Obtain the curve of the minimum value of the maximum principal stress of each scheme under different water pressure conditions as a function of the thickness of the water-proof layer, and analyze the stress release of the mining roof as a function of the thickness of the water-proof layer and the water pressure. (3) Analysis of roof displacement: Obtain the roof displacement curves of each scheme under different water pressure conditions as a function of the thickness of the aquitard layer, and analyze the changes in roof displacement of the mining area as a function of the thickness of the aquitard layer and water pressure. (4) Plastic zone analysis: When the stope is excavated, the surrounding rock will undergo plastic failure. When the failure zone is connected with the water-bearing fracture zone, water will flow into the stope through the plastic zone, causing a roof water inrush accident. In order to intuitively show the connection between the failure zone and the fracture zone, a water inrush safety factor S is defined. When S is greater than 2, it indicates that there is basically no risk of water inrush. ， In the formula, S is the safety factor for water inrush; Pw is the water pressure, MPa; H is the thickness of the waterproof layer, m; Z is the failure depth of the plastic zone, m; The water inrush safety factors under different water pressures and different thicknesses of the water-resisting stratum are calculated respectively, the broken line graph of the water inrush safety factor changing with the thickness of the water-resisting stratum under different water pressures is drawn, and the critical thickness is extracted as the preliminary selected thickness of the water-resisting stratum under different water pressures; (5) The final selected thickness of the water-resisting stratum under different water pressures is obtained by comprehensively considering the stress, displacement and plastic zone changing with the water pressure and the roof.

2. The method of claim 1, wherein: In the step S1, in order to find out the actual water pressure underground, YHY mine water pressure monitor is installed at 4-5 typical water outlets with different flow rates to monitor for a long time, and the error is ≤±1%.

3. The method of claim 1, wherein: In the step S2, standard hexahedral grid is adopted, the grid gradually changes from the center to the periphery, the minimum grid length is 2m, the x, y and z axes are the ore body strike, inclination and height respectively, the model length is 600m, the width is 400m, and the height is 500m; the model is applied with the bottom and side normal displacement constraints, and the top is applied with the uniform load to simulate the mining depth; the Mohr-Coulomb constitutive model is adopted for the unit body, the mechanical parameters are obtained according to the existing mechanical test; the water pressure value is assigned according to the pore water pressure, and it is assumed that the water flowing fractured zone is located in the upper part of the immediate roof of the ore room, and the pore water pressure is assigned to the upper part of the roof of the stope; The numerical simulation scheme is determined, based on the field water pressure monitoring results, the water pressure values of 0MPa, 0.1MPa, 0.2MPa, 0.5MPa, 1MPa, 1.5MPa and 2MPa are selected, combined with the mining technical scheme, the mining length is 50m, the mining width is 15m, the mining height is 60m, and the thickness of the water-resisting stratum is 0.1m, the excavation calculation is carried out; The maximum displacement of the roof is taken as the stability index of the stope, the maximum displacement change of the roof after excavation under each water pressure value is obtained and analyzed; combined with the limit displacement criterion of the rock mass, the typical water pressure values of 0.1MPa, 0.5MPa, 1.0MPa, 1.5MPa and 2.0MPa are selected for the optimization of the thickness of the water-resisting stratum.

4. The method of claim 1, wherein: In the step S3, the typical water pressure values of 0.1MPa, 0.5MPa, 1.0MPa, 1.5MPa and 2.0MPa are selected, and the thicknesses of the water-resisting stratum of the roof are 0m, 2m, 4m and 8m respectively, and the optimization of the thickness of the water-resisting stratum is carried out.

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