A method for water-saving coal mining under a surface reservoir

Abstract

A method for water-saving coal mining under a surface reservoir, the steps include: before coal mining, artificially intercepting the dynamic supply river of the reservoir; draining the static water of the reservoir; sampling and analyzing the bottom mud of the reservoir; arranging the coal mining face according to the shape of the reservoir so that the surface reservoir is included in the ground projection range of the coal mining face arranged underground; recovering the coal resources under the reservoir and in the area where the coal pillar should be reserved, and recording the spatial position of the coal mining crack area in the reservoir area; after coal mining, excavating the clay soil replaced or retained in the reservoir; grouting on the cement layer or bedrock surface; after the grouting is left to stand for a set time, brushing anti-seepage coating on the surface of the grouting body, and conducting water seepage experiments in the coal mining crack area; installing a waterproof gate underground in the goaf formed by coal mining, and the gate's pressure resistance is greater than the set value; closing the artificial interception, and re-storing the reservoir. The present invention realizes the mining of coal resources covered by the reservoir area while protecting the reservoir water resources.

Description

Technical Field

[0001] The invention relates to a method for water-preserving coal mining under a surface water reservoir, belonging to the technical field of safe coal mining. Background Art

[0002] Water resources are relatively scarce in western my country, so a certain number of surface reservoirs have been built. In coal distribution areas, the construction of surface reservoirs will inevitably cover a large number of coal areas, resulting in a decrease in the recovery rate of coal resources. Conventional mining under surface reservoirs mainly involves leaving protective coal pillars and backfilling coal mining, but there are the following problems: too many coal pillars are left, which reduces the recovery rate of coal resources; leaving coal pillars makes it difficult to arrange the working face of coal mining, reducing coal mining efficiency; and the cost of backfilling mining is high. Summary of the invention

[0003] The object of the present invention is to provide a method for water-preserving coal mining under a surface water reservoir, which can improve the recovery rate and coal mining efficiency of coal resources and reduce mining costs.

[0004] In order to achieve the above object, the present invention provides a method for water-preserving coal mining under a surface water reservoir, comprising the following steps:

[0005] S1. Before coal mining in the reservoir area, artificial diversion of the dynamic recharge river of the reservoir is carried out;

[0006] S2. Drain the static water in the reservoir;

[0007] S3. Take samples of the bottom mud of the reservoir for particle analysis. If the bottom mud is non-cohesive soil, dig it out and replace it with cohesive soil, and make the soil layer thickness reach the set value; if it is cohesive soil, ensure that the soil layer thickness reaches the set value;

[0008] S4. Arrange the coal mining working face according to the shape of the reservoir so that the surface reservoir is included in the ground projection range of the coal mining working face arranged underground;

[0009] S5. Mining the coal resources under the reservoir and in the area where the coal pillar should be left, and recording the spatial location of the coal mining fracture area in the reservoir area;

[0010] S6. After coal mining, excavation of replaced or retained clay soil in the reservoir is stopped at the reservoir cement layer or bedrock;

[0011] S7. Grouting on the cement layer or bedrock surface;

[0012] S8, after the grouting is left to stand for a set time, apply anti-seepage coating on the surface of the grouting body, and conduct water seepage test in the coal mining crack area of ​​S5;

[0013] S9. Install waterproof gates underground in the goaf formed by S5 coal mining. The gate's pressure resistance is greater than the set value. Close the artificial diversion and re-store water in the reservoir.

[0014] Furthermore, in S1, the specific method of artificially intercepting the dynamic supply river of the reservoir is: selecting the dry season, using a pipeline to temporarily divert the river that dynamically supplies the reservoir, the drainage flow of the pipeline is greater than the maximum flow of the river, and the deformation of the pipeline is greater than a, and the calculation formula is:

[0015] a=m×k, k=min(1, y×(1+P1 / P2));

[0016] Wherein, m is the mining thickness, which is obtained through the coalfield exploration drilling column chart; k is the correction coefficient; min(1, y×(1+P1 / P2)) means that k takes the minimum value of 1 and y×(1+P1 / P2); y is the maximum subsidence coefficient of coal mining, which is obtained through ground observation of the coal mining working face without a reservoir; P1 is the hydrostatic pressure of the maximum water storage of the reservoir, which is obtained through the surface reservoir design drawing; P2 is the pressure of the overlying rock stratum of the coal seam, which is obtained by sampling and testing the rock density and then calculating according to P2=ρgh, where ρ is the density of the overlying rock stratum of the coal seam, g is the gravitational acceleration, and h is the thickness of the overlying rock stratum of the coal seam, which is obtained through the drilling column chart.

[0017] Furthermore, in S2, the specific method of draining the static water in the reservoir is: draining the water in the reservoir and injecting it into the aquifer at a depth of less than W+10 meters below the coal seam, and the water inrush coefficient T of the injected aquifer is less than 0.06;

[0018] W is calculated according to the following formula: W = 0.0085 (UN) + 0.01665α + 0.1079L - 4.3579, where U is the average burial depth of the coal seam in the reservoir area, obtained through the drilling column chart; N is the water level height of the reservoir in the dry season, obtained through observation; α is the inclination of the coal seam, obtained through measurement; L is the inclined length of the coal mining face, obtained through the mining design drawing;

[0019] T is calculated according to the following formula: T = (P3 + P1) ÷ D, where P3 is the natural water pressure of the aquifer injected by the water in the reservoir, obtained through water level observation; D is the distance between the aquifer injected by the water in the reservoir and the bottom of the coal seam, obtained through the borehole column chart.

[0020] Furthermore, in S3, if the bottom mud is non-cohesive soil, the soil is hollowed out and replaced with cohesive soil, and the moisture content of the replaced cohesive soil is controlled to be 10% to 30%, and the soil is naturally piled up; the moisture content control method is to measure the soil content by a moisture content measuring instrument, and to control the moisture content by adding water or drying; the set value of the soil layer thickness is e, and the calculation method of e is as follows:

[0021] e=m×(1-y)+P1×E S ;

[0022] In the formula, E S is the elastic modulus of reservoir sediment, obtained through geotechnical experiments.

[0023] Furthermore, in the S4, the ground projection range of the underground coal mining working face includes a surface water reservoir, wherein the closest distance between the reservoir and the opening eye, the withdrawal line and the two lanes of the ground projection of the coal mining working face is greater than 10i meters, wherein i is the stress concentration factor, and the calculation formula is as follows:

[0024] i=r1÷r2;

[0025] In the formula, r1 is the larger value of the vertical height value and the horizontal width value of the slope around the reservoir;

[0026] r2 is the smaller value of the vertical height and the horizontal width of the slope around the reservoir.

[0027] Furthermore, in S6, coal mining lasts for more than one year, and the clay soil replaced or retained in the reservoir is excavated.

[0028] Furthermore, in S7, the grouting materials are cement, clay and water, and the grouting thickness is 1 to 10 meters; Bacillus pasteurianus, urea and calcium nitrate are fixed in the clay; the mass ratio of solid to liquid in the grouting material is 1:1 to 1:2, and the mass ratio of cement to clay is 1:2 to 1:4. In the mass of clay, clay, Bacillus pasteurianus, urea and calcium nitrate account for 200 parts, 1 to 2 parts, 1 to 4 parts and 1 to 4 parts respectively, and the Bacillus pasteurianus powder contains more than 1 billion effective live bacteria per gram.

[0029] Furthermore, in S8, the set time for the grouting to stand is more than 10 days; the anti-seepage coating applied on the surface of the grouting body is polyurethane; the water seepage test is that the water level of the reservoir drops by less than 0.01 meters under the highest water level condition within 24 hours without considering evaporation. If the water seepage test fails to meet the requirements, the unqualified area will be excavated and re-grouted and the anti-seepage coating will be thickened until the test requirements are met.

[0030] Furthermore, in S9, the gate's pressure resistance is greater than a set value P4, and the calculation formula of P4 is as follows:

[0031] P4 = ρ1 × g × U;

[0032] Where ρ1 is the density of water, and U is the average burial depth of the coal seam in the reservoir area.

[0033] The present invention artificially intercepts the dynamic supply river of the reservoir before coal mining in the reservoir area; drains the static water of the reservoir; samples the bottom mud at the bottom of the reservoir for particle analysis; if the bottom mud is non-cohesive soil, it is hollowed out and replaced with cohesive soil, and the thickness of the soil layer reaches a set value; if it is cohesive soil, the thickness of the soil layer is guaranteed to reach a set value; arranges the coal mining working face according to the shape of the reservoir, so that the ground projection range of the coal mining working face arranged underground includes the surface reservoir; and the area under the reservoir and where the coal pillar should be reserved is The coal resources are mined, and the spatial position of the mining crack area in the reservoir area is recorded; after mining, the clay soil replaced or retained in the reservoir is excavated and stopped at the cement layer or bedrock of the reservoir; grouting is carried out on the cement layer or bedrock surface; after the grouting is left to stand for a set time, an anti-seepage coating is applied on the surface of the grouting body, and a water seepage test is carried out in the mining crack area of ​​S5; a waterproof gate is implemented underground in the goaf formed by coal mining in step 5, and the pressure resistance of the gate is greater than the set value; the artificial interception is closed, and the reservoir is refilled with water. The present invention transfers water resources before mining coal resources, takes into account the water pressure effect of the reservoir, increases the reservoir pressure in the prediction of the bottom plate damage depth, takes into account the influence of the reservoir pressure on the mining deformation in the temporary diversion of the surface water body, and at the same time, based on the mine pressure and rock formation movement theory, takes into account the stress concentration effect of the reservoir to mine the coal within the disturbance range of the reservoir with the minimum impact on the reservoir, thereby realizing the mining of the coal resources covered by the reservoir area, improving the recovery rate of the coal resources and the coal mining efficiency, while protecting the reservoir water resources and reducing the mining cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the accompanying drawings.

[0036] like Figure 1 As shown, a method for water-preserving coal mining under a surface reservoir comprises the following steps:

[0037] S1. Before coal mining in the reservoir area, artificial diversion of the dynamic recharge river of the reservoir is carried out;

[0038] S2. Drain the static water in the reservoir;

[0039] S3. Take samples of the bottom mud of the reservoir for particle analysis. If the bottom mud is non-cohesive soil, dig it out and replace it with cohesive soil, and make the soil layer thickness reach the set value; if it is cohesive soil, ensure that the soil layer thickness reaches the set value;

[0040] S4. Arrange the coal mining working face according to the shape of the reservoir so that the surface reservoir is included in the ground projection range of the coal mining working face arranged underground;

[0041] S5. Mining the coal resources under the reservoir and in the area where the coal pillar should be left, and recording the spatial location of the coal mining fracture area in the reservoir area;

[0042] S6. After coal mining, excavation of replaced or retained clay soil in the reservoir is stopped at the reservoir cement layer or bedrock;

[0043] S7. Grouting on the cement layer or bedrock surface;

[0044] S8, after the grouting is left to stand for a set time, apply anti-seepage coating on the surface of the grouting body, and conduct water seepage test in the coal mining crack area of ​​S5;

[0045] S9. For the goaf formed by S5 coal mining, a waterproof gate is installed underground. The pressure resistance of the gate is greater than the set value; the artificial diversion is closed and the reservoir is refilled with water.

[0046] Embodiment: The coal resources under a reservoir in Shaanxi Province of my country are very rich, but the conventional coal pillar setting technology cannot be used. Therefore, the method of the present invention is used to achieve the purpose of water conservation coal mining. The specific steps are as follows:

[0047] Step 1: Before coal mining in the reservoir area, the dynamic recharge river of the reservoir is artificially intercepted. The time of artificial interception is the dry season, and the water flow is temporarily diverted by pipeline. Among them, the water flow capacity of the pipeline should be greater than the maximum flow of the recharge river. The artificial interception is implemented upstream of the dynamic recharge river, and the pipeline is used to connect the downstream of the reservoir. The deformable amount of the pipeline is 3 meters, which is greater than a=m×k=3×0.84=2.52 meters, k=min(1,y×(1+P1 / P2))=min(1,0.6×(1+0.5 / 1.25))=0.84, where m=3 meters is the coal mining thickness, obtained through the coalfield exploration drilling column chart, y=0.6 is the maximum sinking coefficient, obtained through ground observation of the coal mining face without a reservoir; P1 is the hydrostatic pressure of the maximum water storage of the reservoir, obtained through the design of the surface reservoir, which is 0.5MPa; P2 is the pressure of the overlying rock layer of the coal seam, obtained by sampling and testing the rock density, and calculated according to P2=ρgh=1.25MPa, where ρ=2.5g / cm 3 is the density of the overlying rock layer of the coal seam, g = 10m / s 2 is the acceleration due to gravity, h = 50 m is the thickness of the overlying rock layer of the coal seam, obtained from the borehole histogram;

[0048] Step 2: Before coal mining in the reservoir area, the static water in the reservoir is drained. The water in the reservoir is drained and injected into the aquifer 40 meters below the coal seam. The water inrush coefficient T of the aquifer is 0.0375, which is less than 0.06. W is calculated according to the following formula: W = 0.0085 (UN) + 0.01665α + 0.1079L - 4.3579

[0049] =0.0085(92-18)+0.01665×1+0.1079×310-4.3579=0.629+0.01665+33.449-4.3579=29.73675 meters;

[0050] Among them, U = 92 meters is the average burial depth of the coal seam in the reservoir area, obtained through the drilling column chart; N = 18 meters is the water level height of the reservoir in the dry season, obtained through observation; α = 1° is the inclination of the coal seam, obtained through measurement; L = 310 meters is the inclined length of the coal mining face, obtained through the mining design drawing;

[0051] T is calculated according to the following formula: T = (P3 + P1) ÷ D = 1.5 ÷ 40 = 0.0375, where P3 is the natural water pressure of the injected aquifer, obtained through water level observation; P1 is the reservoir water pressure; D is the distance from the injected aquifer to the coal seam floor, obtained through the borehole histogram;

[0052] Step 3: Take samples of the bottom mud of the reservoir for particle analysis. If the bottom mud is clay, the retained thickness is e = m × (1-y) + P1 × E S =3×0.4+0.5×0.3=1.35 meters; the moisture content control method is measured by a moisture content measuring instrument, and the moisture content is controlled by adding water and drying;

[0053] Step 4: Arrange the coal mining face according to the shape of the reservoir. The ground projection range of the underground coal mining face includes the surface reservoir. The closest distance between the reservoir and the opening eye, the withdrawal line and the two lanes of the ground projection of the coal mining face is greater than 20 meters, and is 25 to 35 meters. i is the stress concentration factor, which is calculated according to the following formula:

[0054] i=r1÷r2=60÷30=2, r1 is the larger value of the vertical height value and the horizontal width value of the slope around the reservoir;

[0055] r2 is the smaller value of the vertical height value and the horizontal width value of the slope around the reservoir;

[0056] Step 5: Mining the coal resources under the reservoir and in the area where the coal pillar should be left, and recording the spatial location of the coal mining cracks in the reservoir area. A total of 24 cracks were recorded;

[0057] Step 6: More than 1 year after coal mining, excavate the replaced or retained clay soil in the reservoir and stop at the reservoir cement or bedrock;

[0058] Step 7: Grouting is performed on the cement and bedrock surface. The grouting materials are cement, clay (Bacillus pasteurianus, urea and calcium nitrate are fixed in the soil) and water. The mass ratio of solid to liquid is 1:1, and the mass ratio of cement to clay is 1:2. In the mass of clay, clay, Bacillus pasteurianus, urea and calcium nitrate account for 200 parts, 2 parts, 4 parts and 4 parts respectively. Each gram of Bacillus pasteurianus powder contains more than 1 billion effective live bacteria. The grouting thickness is 3 meters.

[0059] Step 8: After 12 days of grouting in step 7, apply anti-seepage coating polyurethane to the grouting surface, and conduct water seepage test at the coal mining cracks in step 5. Among them, 2 water seepage tests failed to meet the requirements, and the unqualified areas were excavated and re-grouted and painted with anti-seepage coating until the conditions were met;

[0060] Step nine: Install a waterproof gate underground in the goaf formed by coal mining in step five. The gate's pressure resistance should be 5MPa, which is greater than P4=ρ1×g×U=0.92MPa. Then close the artificial diversion in step one and re-store water in the reservoir.

[0061] The present invention realizes the mining of coal resources covered by the reservoir area while protecting the water resources of the reservoir, thus achieving the purpose of water-saving coal mining.

Claims

1. A method for water-saving coal mining under a surface reservoir, characterized in that: The steps include: S1. Before coal mining in the reservoir area, artificial diversion of the dynamic recharge river of the reservoir is carried out; The specific method of artificially intercepting the dynamic supply river of the reservoir is: select the dry season, use a pipeline to temporarily divert the river that dynamically supplies the reservoir, the drainage flow of the pipeline is greater than the maximum flow of the river, and the deformation of the pipeline is greater than a, and the calculation formula is: a=m×k, k=min(1, y×(1+P1 / P2)); Wherein, m is the coal mining thickness, obtained through the coalfield exploration drilling column chart; k is the correction coefficient; min(1, y×(1+P1 / P2)) means that k takes the minimum value of 1 and y×(1+P1 / P2); y is the maximum coal mining subsidence coefficient, obtained through ground observation of the coal mining working face without a reservoir; P1 is the hydrostatic pressure of the maximum water storage of the reservoir, obtained through the surface reservoir design drawing; P2 is the pressure of the overlying rock layer of the coal seam, obtained by sampling and testing the rock mass density and calculating according to P2=ρgh, where ρ is the density of the overlying rock layer of the coal seam, g is the gravitational acceleration, and h is the thickness of the overlying rock layer of the coal seam, obtained through the drilling column chart; S2. Drain the static water in the reservoir; S3. Take samples of the bottom mud of the reservoir for particle analysis. If the bottom mud is non-cohesive soil, dig it out and replace it with cohesive soil, and make the soil layer thickness reach the set value; if it is cohesive soil, ensure that the soil layer thickness reaches the set value; S4. Arrange the coal mining working face according to the shape of the reservoir so that the surface reservoir is included in the ground projection range of the coal mining working face arranged underground; S5. Mining the coal resources under the reservoir and in the area where the coal pillar should be left, and recording the spatial location of the coal mining fracture area in the reservoir area; S6. After coal mining, excavation of replaced or retained clay soil in the reservoir is stopped at the reservoir cement layer or bedrock; S7. Grouting on the cement layer or bedrock surface; S8, after the grouting is left to stand for a set time, apply anti-seepage coating on the surface of the grouting body, and conduct water seepage test in the coal mining crack area of ​​S5; S9. Install waterproof gates underground in the goaf formed by S5 coal mining. The gate's pressure resistance is greater than the set value. Close the artificial diversion and re-store water in the reservoir.

2. The method for water-saving coal mining under a surface water reservoir according to claim 1, characterized in that: In S2, the specific method of draining the static water in the reservoir is: draining the water in the reservoir and injecting it into the aquifer at a depth of less than W+10 meters below the coal seam, and the water inrush coefficient T of the injected aquifer is less than 0.06; W is calculated according to the following formula: W = 0.0085 (UN) + 0.01665α + 0.1079L - 4.3579, where U is the average burial depth of the coal seam in the reservoir area, obtained through the drilling column chart; N is the water level height of the reservoir in the dry season, obtained through observation; α is the inclination of the coal seam, obtained through measurement; L is the inclined length of the coal mining face, obtained through the mining design drawing; T is calculated according to the following formula: T = (P3 + P1) ÷ D, where P3 is the natural water pressure of the aquifer injected by the water in the reservoir, obtained through water level observation; D is the distance between the aquifer injected by the water in the reservoir and the bottom of the coal seam, obtained through the borehole column chart.

3. The method for water-saving coal mining under a surface water reservoir according to claim 1, characterized in that: In S3, if the bottom mud is non-cohesive soil, it is hollowed out and replaced with cohesive soil, and the moisture content of the replaced cohesive soil is controlled to be 10% to 30%, and naturally piled; the moisture content control method is to measure it through a moisture content measuring instrument, and control the moisture content by adding water or drying; the set value of the soil layer thickness is e, and the calculation method of e is as follows: e=m×(1-y)+P1×E S ; In the formula, E S is the elastic modulus of reservoir sediment, obtained through geotechnical experiments.

4. The method for water-saving coal mining under a surface water reservoir according to claim 1, characterized in that: In S4, the surface projection of the underground coal mining face includes a surface water reservoir, wherein the closest distance between the reservoir and the opening eye, the withdrawal line and the two lanes of the ground projection of the coal mining face is greater than 10i meters, wherein i is the stress concentration factor, and the calculation formula is as follows: i＝r1÷r2； In the formula, r1 is the larger value of the vertical height value and the horizontal width value of the slope around the reservoir; r2 is the smaller value of the vertical height and the horizontal width of the slope around the reservoir.

5. The method for water-saving coal mining under a surface water reservoir according to claim 1, characterized in that: In said S6, coal mining has been carried out for more than one year, and the clay soil replaced or retained in the reservoir is excavated.

6. The method for water-saving coal mining under a surface water reservoir according to claim 1, characterized in that: In S7, the grouting materials are cement, clay and water, and the grouting thickness is 1 to 10 meters; Bacillus pasteurianus, urea and calcium nitrate are fixed in the clay; the mass ratio of solid to liquid in the grouting material is 1:1 to 1:2, and the mass ratio of cement to clay is 1:2 to 1:

4. In the mass of clay, clay, Bacillus pasteurianus, urea and calcium nitrate account for 200 parts, 1 to 2 parts, 1 to 4 parts and 1 to 4 parts respectively, and each gram of the Bacillus pasteurianus powder contains more than 1 billion effective live bacteria.

7. The method for water-saving coal mining under a surface water reservoir according to claim 1, characterized in that: In S8, the set time for the grouting to stand is more than 10 days; the anti-seepage coating applied on the surface of the grouting body is polyurethane; the water seepage test is that the water level of the reservoir drops by less than 0.01 meters under the highest water level condition within 24 hours without considering evaporation. If the water seepage test fails to meet the requirements, the unqualified area will be excavated and re-grouted and the anti-seepage coating will be thickened until the test requirements are met.

8. The method for water-saving coal mining under a surface water reservoir according to claim 1, characterized in that: In S9, the gate's pressure resistance is greater than the set value P4, and the calculation formula of P4 is as follows: P4 = ρ1 × g × U; Where ρ1 is the density of water, and U is the average burial depth of the coal seam in the reservoir area.

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