A water-saving coal mining method based on coal seam stratified mining

Abstract

A water-saving coal mining method based on coal seam stratified mining, the steps include determining the upper stratified mining thickness, drilling and observing the thickness of each rock layer overlying the coal seam before coal seam mining, observing the thickness of the rock layer overlying the coal seam after a crushing expansion and the crushing expansion coefficient of each rock layer, and observing the range of the upper stratified mining caving zone of the coal seam through drilling, injecting cement slurry into the caving zone of the upper stratified coal seam underground in the coal mine to reinforce and form a lining layer, and freezing after determining the main freezing layer position, freezing temperature and freezing thickness, and finally mining the lower stratified coal seam, and thawing the frozen in the pressure range of each coal mining range when the remaining time workload of coal seam mining is completed, until the mining of the lower stratified resources of the coal seam is completed. The present invention protects static water, improves the water-saving coal mining effect, does not reduce the thickness of stratified mining, improves the recovery rate of coal resource mining, and has a small grouting workload, which is simple and easy to implement.

Description

Technical Field

[0001] The invention relates to a water-preserving coal mining method based on coal seam stratified mining, belonging to the technical field of safe coal mine mining. Background Art

[0002] The ecological environment in the areas where my country's coal resources are currently mined is fragile and water resources are scarce, so water-saving coal mining is necessary. There are many types of water-saving coal mining methods, among which layered mining for thick coal seams is a commonly used method.

[0003] The traditional stratified water-conserving coal mining method has the following problems: since the main focus is on the effect of roof bonding, large-scale grouting reinforcement is carried out, which makes the roof harder and increases the height of the water-conducting fracture zone, which is not conducive to water-conserving coal mining; different methods are used for water-conserving coal mining and stratified mining roof reinforcement. For example, delamination grouting is used to reduce settlement to achieve water-conserving coal mining. Since the delamination space formed by coal mining is large, more engineering work is generated; in order to achieve the goal of water-conserving coal mining, part of the stratified mining thickness is sacrificed and the water-conducting fracture zone is shortened, but the coal recovery rate is low.

[0004] At present, there is a method of using freezing curtain technology for water-saving coal mining, which mainly reduces the dynamic recharge of the aquifer, but cannot fully protect the static water volume. In addition, since the curtain freezing method cannot freeze for a long time, the water-saving coal mining effect will inevitably decrease after the ice melts, and the effect is not good. Summary of the invention

[0005] The object of the invention is to provide a water-preserving coal mining method based on coal seam stratified mining, which can protect static water, improve the water-preserving coal mining effect without reducing the thickness of stratified mining, improve the coal resource mining recovery rate, and has a small grouting workload and is simple and easy to implement.

[0006] In order to achieve the above object, the present invention provides a water-preserving coal mining method based on coal seam stratified mining, comprising the following steps:

[0007] S1, determine the upper layer mining thickness m1, and m1≤m2, m2 is the lower layer mining thickness of the coal seam;

[0008] S2. Drill vertically into the coal seam and obtain the thickness Mn of each rock layer overlying the coal seam through the borehole column chart, where n is the rock layer number, and when the thickness of a rock layer is less than 1 meter, it is merged and recorded with the adjacent rock layers;

[0009] S3, after mining the upper layer of the coal seam, the thickness M1n of each rock layer overlying the coal seam after the first crushing and expansion is observed through the borehole in S2, and the first crushing and expansion coefficient of each rock layer is Observe the range of the caving zone of the upper layer mining of the coal seam through the borehole in S2, and record the height of the caving zone as Hc;

[0010] S4. In the coal mine, cement slurry is injected into the upper layer of the coal seam within a thickness of 0.5 to 2 meters to reinforce the lining layer. The grouting completion standard is that the uniaxial compressive strength of the lining layer sample test reaches 10 to 20 MPa, and the thickness of the lining layer is recorded as hq;

[0011] S5. In the interval above the grouting range and within the caving zone, select the layer with the largest primary expansion coefficient value in S3 and determine the layer as the main freezing layer;

[0012] S6. Take a rock sample from the main frozen layer after the first expansion, add water to the sample and freeze it until the uniaxial compressive strength reaches 20-40 MPa. The temperature is recorded as T; the average value of the secondary expansion coefficient of the frozen-thawed rock sample at temperature T is recorded as X; the secondary expansion coefficient V1 is the volume of the rock sample after freezing and thawing, and V2 is the volume of the rock sample before freezing and thawing; the average time taken to reach the secondary expansion coefficient is recorded as t1;

[0013] S7. Determine the frozen thickness Y by the formula m2-m1=X×Y; if Y>Hc-hq, continue the freeze-thaw process by lowering the temperature T or increasing the freeze-thaw time t until Y≤Hc-hq;

[0014] S8, freezing is performed according to the main freezing layer, freezing temperature and freezing thickness determined in S5 to S7;

[0015] S9, mining the layers below the coal seam, and when the remaining t2 time workload of each coal seam mining pressure range is reached, start to thaw the frozen area within the pressure range until the mining of the layers below the coal seam is completed; t2=t1.

[0016] Furthermore, in S1, the height of the water-conducting fracture zone generated by the thickness of the upper layer m1 is not greater than the sum of the distance between the coal seam and the protected aquifer and the thickness of the protective layer, and m1 takes the maximum value under this constraint; wherein, the calculation method of the water-conducting fracture zone height is: H f is the height of the water-conducting fracture zone, m is the mining thickness, when mining the upper layer, m=m1, and the thickness of the protective layer is 10 to 20 meters.

[0017] Furthermore, in S2, the drilling is carried out vertically downward from the ground, the drilling depth is 3 to 5 meters below the coal seam floor, and is located within the coal mining face, more than 20 meters away from the two tunnels, and more than 100 meters away from the cutting eye and the harvesting line.

[0018] Furthermore, in said S3, the thickness of each rock layer overlying the coal seam after one crushing and expansion is observed by using the natural gamma logging method in the borehole to obtain the precise thickness of the rock layer; and the range of the caving zone is determined by the flushing fluid consumption method.

[0019] Furthermore, in S6, the average time t1 used for the secondary expansion coefficient is obtained by testing at least 3 parallel rock samples and taking the average value.

[0020] The present invention determines the upper layer mining thickness, drills holes before coal seam mining and observes the thickness of each rock layer overlying the coal seam, observes the thickness of the rock layer overlying the coal seam after the first crushing expansion and the first crushing expansion coefficient of each rock layer, and observes the range of the upper layer mining caving zone of the coal seam through drilling holes at the same time, injects cement slurry into the upper layer caving zone of the coal seam in the coal mine to reinforce the lining layer, and freezes after determining the main freezing layer, freezing temperature and freezing thickness, and finally mines the lower layer of the coal seam, and starts to thaw the freezing within the pressure range when the remaining time workload of each coal mining pressure range coal seam mining is completed until the lower layer resource mining of the coal seam is completed. The present invention adopts freeze-thaw technology, and uses the roof to have a certain strength when frozen to provide surrounding rock conditions for the lower layer mining, selects the stratum with a higher secondary crushing expansion coefficient for the freeze-thaw layer, and effectively suppresses the height of the water-conducting fracture zone by selecting the freezing temperature. The selection of the freezing thickness realizes that the newly added crushing expansion space makes up for the crushing expansion space brought by the newly added coal mining thickness increment, and the selected melting time allows the crushing expansion to give full play to the crushing expansion while providing good surrounding rock conditions for the lower layer mining. The invention protects static water, improves the water-retaining coal mining effect, and does not reduce the thickness of layered mining, thereby improving the recovery rate of coal resource mining. The grouting workload is small and the implementation is simple and easy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the accompanying drawings.

[0023] like Figure 1 As shown, a water-saving coal mining method based on coal seam stratified mining includes the following steps:

[0024] S1, determine the upper layer mining thickness m1, and m1≤m2, m2 is the lower layer mining thickness of the coal seam;

[0025] S2. Drill vertically into the coal seam and obtain the thickness Mn of each rock layer overlying the coal seam through the borehole column chart, where n is the rock layer number, and when the thickness of a rock layer is less than 1 meter, it is merged and recorded with the adjacent rock layers;

[0026] S3, after mining the upper layer of the coal seam, the thickness M1n of each rock layer overlying the coal seam after the first crushing and expansion is observed through the borehole in S2, and the first crushing and expansion coefficient of each rock layer is Observe the range of the caving zone of the upper layer mining of the coal seam through the borehole in S2, and record the height of the caving zone as Hc;

[0027] S4. In the coal mine, cement slurry is injected into the upper layer of the coal seam within a thickness of 0.5 to 2 meters to reinforce the lining layer. The grouting completion standard is that the uniaxial compressive strength of the lining layer sample test reaches 10 to 20 MPa, and the thickness of the lining layer is recorded as hq;

[0028] S5. In the interval above the grouting range and within the caving zone, select the layer with the largest primary expansion coefficient value in S3 and determine the layer as the main freezing layer;

[0029] S6. Take a rock sample from the main frozen layer after the first expansion, add water to the sample and freeze it until the uniaxial compressive strength reaches 20-40 MPa. The temperature is recorded as T; the average value of the secondary expansion coefficient of the frozen-thawed rock sample at temperature T is recorded as X; the secondary expansion coefficient V1 is the volume of the rock sample after freezing and thawing, and V2 is the volume of the rock sample before freezing and thawing; the average time taken to reach the secondary expansion coefficient is recorded as t1;

[0030] S7. Determine the frozen thickness Y by the formula m2-m1=X×Y; if Y>Hc-hq, continue the freeze-thaw process by lowering the temperature T or increasing the freeze-thaw time t until Y≤Hc-hq;

[0031] S8, freezing is performed according to the main freezing layer, freezing temperature and freezing thickness determined in S5 to S7;

[0032] S9, mining the layers below the coal seam, and when the remaining t2 time workload of each coal seam mining pressure range is reached, start to thaw the frozen area within the pressure range until the mining of the layers below the coal seam is completed; t2=t1.

[0033] As a preferred implementation, in S1, the height of the water-conducting fracture zone generated by the thickness of the upper layer m1 is not greater than the sum of the distance between the coal seam and the protected aquifer and the thickness of the protective layer, and m1 takes the maximum value under this constraint; wherein, the height of the water-conducting fracture zone is calculated as follows: H f is the height of the water-conducting fracture zone, m is the mining thickness, when mining the upper layer, m=m1, and the thickness of the protective layer is 10 to 20 meters.

[0034] As a preferred embodiment, in S2, the drilling is carried out vertically downward from the ground, the drilling depth is 3 to 5 meters below the coal seam floor, and is located within the coal mining face, more than 20 meters away from the two tunnels, and more than 100 meters away from the cutting eye and the harvesting line.

[0035] As a preferred embodiment, in S3, the thickness of each rock layer overlying the coal seam after one crushing and expansion is observed by using the natural gamma logging method in the borehole to obtain the precise thickness of the rock layer; and the range of the caving zone is determined by the flushing fluid consumption method.

[0036] As a preferred implementation, in S6, the average time t1 used for the secondary expansion coefficient is obtained by testing at least 3 parallel rock samples and taking the average value.

[0037] Embodiment: The coal thickness of a coal mine in northern Shaanxi is relatively large, about 9 meters on average. The coal seam is covered with a certain aquiclude, and there is precious water resources (Salawusu Formation aquifer) on the aquiclude. The Salawusu Formation aquifer cannot be fully protected when using high-intensity mining processes such as fully mechanized caving mining. Therefore, stratified water-saving coal mining is considered, and the method of the present invention is used. The specific steps are as follows:

[0038] Step 1: Determine the upper layer mining thickness m1: According to the distance between the coal seam and the aquifer + the protective layer, it is calculated that 4.0 meters is the most suitable for the first layer mining, that is, m1 = 4.0 meters, m2 = 5.0 meters;

[0039] Step 2: Before coal seam mining, a borehole is drilled to reveal the thickness of each rock layer overlying the coal seam, Mn, where n is the number of the rock layer. If the thickness of the rock layer is less than 1 meter, the adjacent rock layers are combined and recorded. Mn ranges from 2.5 to 42 meters.

[0040] Step 3: Mining the upper layer of the coal seam, and observing the thickness M1n of the rock layer overlying the coal seam after the first expansion through the drilling hole in step 2, and recording the first expansion coefficient of each rock layer is 1.02~1.06; In addition, the range of the caving zone of the upper layer mining of the coal seam was observed through the drilling in step 2, and the height of the caving zone was recorded as Hc, which was 16.7 meters;

[0041] Step 4: Before mining the lower layer of the coal seam, cement slurry is injected into the upper layer of the coal seam within a thickness of 1 meter to reinforce the lining layer in the coal mine. The grouting completion standard is that the uniaxial compressive strength of the lining layer sample test reaches 10~0MPa, and its thickness hq is 1 meter;

[0042] Step 5: Determine the main frozen layer: In the interval above the grouting range and within the caving zone, select the layer with the largest primary expansion coefficient value in step 3 as a group of mudstone, and determine this layer as the main frozen layer;

[0043] Step 6: Determine the freezing temperature: Take a rock sample from the frozen layer after it has been crushed and expanded, and test the rock sample after it has been crushed and expanded. Add water and freeze it to a temperature of -10°C. Its uniaxial compressive strength reaches the range of 20 to 40 MPa, and the T value is as close to 0 degrees Celsius as possible.

[0044] Step 7: Determine the frozen thickness. m2-m1=X×Y=1, where X is the average value of the secondary expansion coefficient after freeze-thaw of the rock layer within the caving zone determined in step 3 at the temperature T determined in step 6, which is 1.10 obtained through indoor sampling test. At the same time, the average time t1=20 hours used to reach the secondary expansion coefficient is recorded, and Y is the frozen thickness of 0.91 meters; in this embodiment, Y<Hc-hq, and multiple freeze-thaw operations are not required;

[0045] Step 8: Before mining the coal seam layer by layer, freeze the coal seam according to the freezing parameters determined in steps 5 to 7;

[0046] Step 9: Start mining the layers under the coal seam. When the remaining time workload of mining in each coal seam pressure range is t2 = 20 hours, start thawing the frozen area within the pressure range until all the resources under the coal seam are mined.

[0047] Compared with the fully mechanized caving mining, the present invention achieves better the effect of stratified water-saving mining, which is manifested in that the water level of the Salawusu Formation aquifer has not dropped significantly, and there is no obvious degradation of the surface ecology. In addition, the entire 9-meter-thick coal seam is mined without wasting coal resources, thus realizing green and efficient mining of coal resources.

Claims

1. A water-saving coal mining method based on coal seam stratified mining, characterized in that: The steps include: S1, determine the upper layer mining thickness m1, and m1≤m2, m2 is the lower layer mining thickness of the coal seam; S2. Drill vertically into the coal seam and obtain the thickness Mn of each rock layer overlying the coal seam through the borehole column chart, where n is the rock layer number, and when the thickness of a rock layer is less than 1 meter, it is merged and recorded with the adjacent rock layers; S3, after mining the upper layer of the coal seam, the thickness M1n of each rock layer overlying the coal seam after the first crushing and expansion is observed through the borehole in S2, and the first crushing and expansion coefficient of each rock layer is Observe the range of the caving zone of the upper layer mining of the coal seam through the borehole in S2, and record the height of the caving zone as Hc; S4. In the coal mine, cement slurry is injected into the upper layer of the coal seam within a thickness of 0.5 to 2 meters to reinforce the lining layer. The grouting completion standard is that the uniaxial compressive strength of the lining layer sample test reaches 10 to 20 MPa, and the thickness of the lining layer is recorded as hq; S5. In the interval above the grouting range and within the caving zone, select the layer with the largest primary expansion coefficient value in S3 and determine the layer as the main freezing layer; S6. Take a rock sample from the main frozen layer after the first expansion, add water to the sample and freeze it until the uniaxial compressive strength reaches 20-40 MPa. The temperature is recorded as T; the average value of the secondary expansion coefficient of the frozen-thawed rock sample at temperature T is recorded as X; the secondary expansion coefficient V1 is the volume of the rock sample after freezing and thawing, and V2 is the volume of the rock sample before freezing and thawing; the average time taken to reach the secondary expansion coefficient is recorded as t1; S7. Determine the frozen thickness Y by the formula m2-m1=X×Y; if Y>Hc-hq, continue the freeze-thaw process by lowering the temperature T or increasing the freeze-thaw time t until Y≤Hc-hq; S8, freezing is performed according to the main freezing layer, freezing temperature and freezing thickness determined in S5 to S7; S9, mining the layers below the coal seam, and when the remaining t2 time workload of each coal seam mining pressure range is reached, start to thaw the frozen area within the pressure range until the mining of the layers below the coal seam is completed; t2=t1.

2. The water-saving coal mining method based on coal seam stratified mining according to claim 1 is characterized in that: In S1, the height of the water-conducting fracture zone generated by the thickness of the upper layer m1 is not greater than the sum of the distance between the coal seam and the protected aquifer and the thickness of the protective layer, and m1 takes the maximum value under this constraint; wherein, the height of the water-conducting fracture zone is calculated as follows: H f is the height of the water-conducting fracture zone, m is the mining thickness, when mining the upper layer, m=m1, and the thickness of the protective layer is 10 to 20 meters.

3. The water-saving coal mining method based on coal seam stratified mining according to claim 1 is characterized in that: In S2, the drilling is carried out vertically downward from the ground, the drilling depth is 3 to 5 meters below the coal seam floor, and is located in the coal mining working face, the distance between the two tunnels is greater than 20 meters, and the distance between the cutting eye and the harvesting line is greater than 100 meters.

4. The water-saving coal mining method based on coal seam stratified mining according to claim 1 is characterized in that: In S3, the thickness of each rock layer overlying the coal seam after one crushing and expansion is observed by using the natural gamma logging method in the borehole to obtain the precise thickness of the rock layer; and the range of the caving zone is determined by the flushing fluid consumption method.

5. The water-saving coal mining method based on coal seam stratified mining according to claim 1, characterized in that: In S6, the average time t1 used for the secondary expansion coefficient is obtained by testing at least 3 parallel rock samples and taking the average value.

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