Key stratum screening method for overburden-separation grouting in a coal mine

Abstract

Disclosed in the present invention is a key stratum screening method for overburden-separation grouting in a coal mine, comprising the following steps: selecting overall analysis objects on the basis of coal mine planning; performing primary screening on the analysis objects on the basis of the range of a subsidence area; performing secondary screening on the analysis objects on the basis of whether an old mined-out area exists or not; carrying out key stratum identification on the screened analysis objects, carrying out priority sorting on the key strata on the basis of the number of separation spaces and a separation height range, setting a safety height of about 50 m on the basis of a water-conducting fissure zone, and in combination with a potential separation space and the rock stratum water-resisting property, performing priority sorting on the number of groutable strata; performing priority sorting on the groutable strata on the basis of the extent to which the groutable strata are affected by a fault; and comprehensively analyzing the priorities of grouting of the key strata on the basis of the results of the three priority sorting operations, and performing grouting on the separation of the key strata in the order of priority. The present invention has the advantage that the problem of surface subsidence is solved with low cost and high efficiency.

Description

A method for screening key strata for grouting of overburden separation layer in coal mines Technical Field

[0001] The invention relates to the technical field of grouting and filling of overburden rock separation layers, and in particular to a method for screening key strata for grouting of overburden rock separation layers in coal mines. Background Art

[0002] my country is rich in coal resources, but significant amounts of coal are being compressed by land, water, and other factors. This is particularly true in East China's major coal-producing regions, where densely populated villages and buildings create a significant problem. Surface subsidence caused by coal mining can ultimately lead to catastrophic damage to buildings, water bodies, farmland, railways, and bridges, bringing with it a host of social and environmental problems that seriously impact the sustainable economic development of mining areas.

[0003] Due to the cumulative effect of post-mining overburden expansion caused by unloading, the space in the delamination layer is suppressed. This space is replaced by the expansion of the rock mass in the collapse zone and the expansion of the rock mass in the fracture zone. Only when a key stratum, typically capable of controlling the overburden, exists in the stratum can the delamination layer persist for a period of time as the underlying rock mass compacts. (The distribution of the delamination layer before and after the key stratum breaks is shown in Figure 1.) Without effective intervention in the delamination layer, achieving a high injection-to-production ratio and subsidence reduction rate is difficult. A low delamination layer grouting ratio, close to the delamination volume in its original state, fails to form an effective support structure for the overburden. This indicates that the goaf below the filling layer is not receiving sufficient forces, resulting in numerous residual voids and high compressibility. During multi-face mining, the goaf will further compress, exacerbating surface subsidence. This is a major reason for the low surface subsidence reduction rate of delamination layer grouting. Accurately identifying key strata for grouting and optimizing the timing of grouting to cost-effectively and efficiently address the "three-down" compression coal mining and control surface subsidence is an urgent task.

[0004] The literature "Chen Chao, Hu Zhenqi. Application Status and Progress of Key Layer Theory in Mining Subsidence [J]. Journal of Mining Science, 2017, 2(03): 209-218." Although the application status and progress of key layers in mining subsidence have been studied, there is no research on the grouting layer of the key layer, so it is impossible to perform reasonable grouting operations on the key layers of different analysis objects in the mining area, and it is impossible to solve the surface subsidence problem at low cost and high efficiency.

[0005] Summary of the Invention

[0006] The technical problem to be solved by the present invention is that the existing technology lacks a method for screening key strata for grouting of overburden separation layers in coal mines, and is unable to solve the problem of surface subsidence at low cost and high efficiency.

[0007] The present invention solves the above technical problems by the following technical means: a method for screening key strata for grouting of overburden separation layer in coal mines, comprising the following steps:

[0008] Step 1: Select the overall analysis object according to the coal mine planning;

[0009] Step 2: Based on the scope of the subsidence area, screen the analysis objects;

[0010] Step 3: Conduct secondary screening of the analysis objects based on whether there are old goaf areas;

[0011] Step 4: Identify the key layers of the analyzed objects that have passed the screening, and prioritize them based on the number of detached spaces and the range of detached layer heights. Based on the water-conducting fracture zone, set a safety height of about 50m. Combined with the potential detached space and the water-proofness of the rock formation, prioritize the number of grouting layers.

[0012] Step 5: Prioritize the grouting layers based on the impact of the fault;

[0013] Step 6: Based on the results of the three priority rankings, comprehensively analyze the priority of grouting in the key layer, and grout the separation layer of the key layer in order of priority.

[0014] Furthermore, the method for screening key strata for grouting of overburden separation layer in coal mines further includes step seven:

[0015] If the separation layer of the screened key layer involves the gas protection layer, the screened separation layer will be downgraded or eliminated.

[0016] Furthermore, the step 1 includes:

[0017] The working faces under the areas where ground subsidence has occurred and the working faces in the mining areas that have been mined are not selected as analysis objects. The working faces planned for mining are selected as analysis objects.

[0018] Furthermore, the step 2 includes:

[0019] If the analysis object is within the subsidence area or at the boundary, the analysis object is eliminated and the analysis objects outside the boundary of the subsidence area are retained.

[0020] Furthermore, the step three includes:

[0021] If the analysis object has an old goaf, the analysis object will be eliminated, and the analysis object without the old goaf will be retained.

[0022] Furthermore, in the step 4, the key layer identification software KSPB for mining rock strata is used to identify the key layers of the analysis objects that have passed the screening.

[0023] Furthermore, in step 4, the key layers are prioritized based on the number of separation spaces and the separation height range, including:

[0024] The level is excellent if the number of detached spaces is greater than 5 and the detached height range and the critical layer is greater than 200m;

[0025] The level of the key layer with the number of detached spaces between 3 and 5 and the total detached height range of 100 to 200 m is medium;

[0026] The level of the critical layer with the number of separation spaces less than 3 or the separation height range less than 100m is considered inferior;

[0027] All key layers are prioritized in the order of best to worst, and the order of key layers in the same level is random.

[0028] Furthermore, in step 4, a priority sorting is performed based on the number of groutable layers, including:

[0029] The level of key layers with the number of groutable layers greater than 5 is excellent;

[0030] The level of the key layer with the number of groutable layers ranging from 1 to 5 is medium;

[0031] The grade of key layers without grouting positions is poor;

[0032] All key layers are prioritized in the order of best to worst. The order of key layers in the same level is random. When the priority is based on the number of groutable layers and the level of "bad" appears, it means that there are no groutable layers and there is no need to analyze them. Therefore, the analysis object is directly excluded.

[0033] Furthermore, the step five includes:

[0034] Based on the location of the grouting layer,

[0035] The level of key layers that can be grouting and are not affected by faults is excellent;

[0036] The level of the critical layer where part of the groutable layer is cut by faults is medium;

[0037] The critical layer where all groutable layers are cut by faults is rated as inferior;

[0038] All key layers are prioritized in the order of best to worst, and the order of key layers in the same level is random.

[0039] Furthermore, the step six includes:

[0040] If at least two of the three priority judgment processes are at the same level, then this level is the priority level for grouting of the key layer. If the results of the three judgments are excellent, medium, and poor respectively (if the grouting layer is poor, the influence of the detachment and fault at this position will no longer be considered and it will be directly eliminated), then the priority level for grouting of the key layer is medium, and grouting of the detachment layer of the key layer will be carried out according to the priority order of grouting of the key layer.

[0041] The advantages of the present invention are:

[0042] (1) The present invention sets the scope of the subsidence area and whether there is an old goaf as the preconditions for screening working faces to quickly screen a large number of working faces in the mining area, improve the efficiency of key layer screening, and proposes grading indicators for key layers, groutable layers, and faults. Based on the grading indicators, the grouting advantage target areas are ranked comprehensively. Finally, reasonable grouting operations are performed on the key layers of different analysis objects in the mining area in order of priority, thereby solving the surface subsidence problem at a low cost and high efficiency.

[0043] (2) The present invention combines the mine's gas protection requirements and comprehensively considers safety factors to perform necessary downgrading and elimination on the selected advantageous target areas, that is, the separated layers of the selected key layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a schematic diagram of the distribution of separation layers before and after the key layer breaks;

[0045] FIG2 is a flow chart of a method for screening key strata for grouting of overburden separation layers in a coal mine disclosed in an embodiment of the present invention;

[0046] FIG3 is a schematic diagram of an interface for inputting data into a key layer calculation software in a method for screening key layers for grouting of overburden separation layers in a coal mine disclosed in an embodiment of the present invention;

[0047] FIG4 is a schematic diagram of the output of the calculation results of the key layer software after inputting data into a key layer screening method for grouting the overburden separation layer in a coal mine disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0049] As shown in FIG2 , the present invention provides a method for screening key strata for grouting of overburden separation layers in coal mines, comprising the following steps:

[0050] S1: Select the overall analysis object based on the coal mine planning framework; the selection principles are as follows:

[0051] (1) The working surface under the area where ground subsidence has occurred is not selected as the analysis object. The key overburden layer in the subsidence area has suffered varying degrees of damage, and delamination grouting cannot be implemented or the effect is weak.

[0052] (2) The working faces of the mining areas that have been mined are not selected as the objects of analysis and research. The working faces of the mining areas that have been mined have basically formed a stable static mining basin. Generally speaking, the detached space has tended to be closed, and the actual benefit of grouting is relatively low.

[0053] (3) In comparison, selecting the working face planned for mining as the analysis object and studying the injectability of the overburden strata of the working face to be mined has higher economic and social value.

[0054] (4) Based on the gas concentration points in the mining area, for working faces with protective layers, the mine may comprehensively consider the necessity of grouting based on the needs of safety management and subsidence reduction, on the basis of analyzing the grouting conditions of the overburden layer.

[0055] Based on the aforementioned selection principles, the overburden delamination grouting priority can be determined according to the workflow shown in Figure 2. First, all working faces within the planned coal mine period should be covered as much as possible. Next, working faces unsuitable for delamination grouting should be largely eliminated based on two criteria: surface subsidence above the mining face and the presence of old goafs. Key stratum locations of the remaining working faces are then calculated based on key stratum theory. Working faces with unreasonable key stratum distribution are analyzed and eliminated. Finally, grouting faces are prioritized based on the performance of specific indicators. The following details the grouting face selection process.

[0056] S2: Determine the extent of the mining subsidence zone based on collected data (materials, drilling, mining conditions, test observation data) and on-site investigations (industrial squares, mining surface). Based on the extent of the subsidence zone, screen the analysis objects. If the analysis object is within the subsidence zone or at the boundary, it will be eliminated, and the analysis objects outside the subsidence zone boundary will be retained;

[0057] S3: Based on the geological mining data, determine whether the analysis object retained in S2 has an old goaf. If the above analysis object has an old goaf, then eliminate the object and retain the analysis object without the old goaf;

[0058] S4: Identify the key layers of the analysis objects that have passed the screening, and prioritize the key layers based on the number of separation spaces and the range of separation heights. Based on the water-conducting fracture zone, set a safety height of about 50m. Combined with the potential separation space and the water-proofness of the rock formation, prioritize the number of grouting layers. The specific process is as follows:

[0059] The drilling data and rock physical and mechanical property test results provided by the mine are collated as basic data (if data is missing, the lithologic parameters of the surrounding area are considered or empirical values ​​are used). The basic data are input into KSPB (key layer identification software for mine rock formations) for calculation.

[0060] Step 401: Under the condition that the pre-screening is passed, the present invention uses the Zhangji Mine 1616 (3) working face as an example to perform key layer identification. The data in Table 1 is input into KSPB software (mine rock stratum key layer identification software) for calculation, as shown in Figure 3. The analysis results are exported, as shown in Figure 4.

[0061] Table 1. Information on rock formations above the working face of Zhangji 1616(3) and selection of mechanical parameters (holes 6-75)

[0062] Step 402: Based on the analysis objects screened out in S3, step 401 is repeated to obtain key layers of different screened objects.

[0063] Step 403: Prioritize the key layers based on the number of separation spaces and the separation height range, including:

[0064] The level is excellent if the number of detached spaces is greater than 5 and the detached height range and the critical layer is greater than 200m;

[0065] The level of the key layer with the number of detached spaces between 3 and 5 and the total detached height range of 100 to 200 m is medium;

[0066] The level of the critical layer with the number of separation spaces less than 3 or the separation height range less than 100m is considered inferior;

[0067] All key layers are prioritized in the order of best to worst, and the order of key layers in the same level is random.

[0068] Step 404: Prioritize the number of groutable layers based on the height of the water-conducting fracture zone, setting a 50m protection height. The number of groutable layers is then selected based on the potential separation space and the water-resistance of the rock formation. (The formula for the water-conducting fracture zone is calculated based on the "Specifications for Coal Pillar Retention and Compressed Coal Mining in Buildings, Water Bodies, Railways, and Major Shafts") If:

[0069] The level of key layers with the number of groutable layers greater than 5 is excellent;

[0070] The level of the key layer with the number of groutable layers ranging from 1 to 5 is medium;

[0071] The grade of key layers without grouting positions is poor;

[0072] All key layers are prioritized in the order of best to worst. The order of key layers in the same level is random. When the priority is based on the number of groutable layers and the level of "bad" appears, it means that there are no groutable layers and there is no need to analyze them. Therefore, the analysis object is directly excluded.

[0073] S5: Prioritize the grouting layers based on the impact of faults; specifically, analyze the fault conditions of the grouting layers:

[0074] The level of key layers that can be grouting and are not affected by faults is excellent;

[0075] The level of the critical layer where part of the groutable layer is cut by faults is medium;

[0076] The critical layer where all groutable layers are cut by faults is rated as inferior;

[0077] All key layers are prioritized in the order of best to worst, and the order of key layers in the same level is random.

[0078] S6: Based on the results of the three priority sortings, the priority of the key layer grouting is comprehensively analyzed, and the separation layer of the key layer is grouted in the order of priority. Specifically, if at least two of the three priority determination processes are at the same level, then the level is the priority level of the key layer grouting. If the results of the three determinations are respectively excellent, medium, and poor, then the priority level of the key layer grouting is medium, and the separation layer of the key layer is grouted according to the priority order of the key layer grouting. However, when the groutable layer is ranked as poor, the influence of the separation layer and the fault is no longer considered and it is directly eliminated. For example, if the determination results of step 403, step 404, and S5 for the same key layer are respectively excellent, excellent, and medium, then the priority level of the key layer grouting is excellent. If the determination results of step 403, step 404, and S5 for the same key layer are respectively medium, excellent, and medium, then the priority level of the key layer grouting is medium. If the determination results of step 403, step 404, and S5 for the same key layer are respectively medium, excellent, and poor, then the priority level of the key layer grouting is medium.

[0079] S7: If the grouting layer of the screened out separation layer involves the gas protection layer, whether to downgrade or eliminate the screened out separation layer shall be considered comprehensively based on safety factors.

[0080] Taking the Huainan mining area as an example, the benefits of the above method of the present invention are explained.

[0081] (1) Economic benefit analysis

[0082] Vast quantities of coal resources in the Huainan mining area are stored beneath buildings, water bodies, and railways. Mining this coal inevitably involves a series of challenges, including village relocation, ground subsidence, and land reclamation. Failure to mine this coal would waste resources and hinder the smooth transition of mining areas. The use of overburden separation grouting technology can effectively release the coal resources buried under these "three underburdens," increasing the amount of recoverable coal resources. Currently, the Huainan Mining Group spends an average of 600 to 800 million yuan annually on land acquisition and relocation. Traditional relocation methods would have faced challenges such as high investment costs, difficulty selecting resettlement sites, and complex communication and coordination between the mine and the mining company. The implementation of overburden separation grouting has significantly reduced ground subsidence around the mining area, effectively reducing the need to relocate towns and villages, and thus significantly reducing land acquisition and relocation expenses. Furthermore, the implementation of separation grouting technology facilitates capacity replacement for coal enterprises. Implementing separation grouting in the Huainan mining area can effectively minimize damage to arable land, thereby reducing the group's expenses on compensation for young crops in subsidence areas.

[0083] (2) Social benefit analysis

[0084] A large number of towns and villages are located above the mining faces of some coal mines in the Huainan mining area. As mining continues, it will inevitably cause ground subsidence, affecting the normal production and life of surrounding residents. The implementation of the present invention is conducive to solving the problem of building subsidence and protecting the buildings and farmland above the coal mining face, with significant social benefits. Table 2 shows the key layer classification table obtained according to step 403, Table 3 shows the groutable layer classification table obtained according to step 404, Table 4 shows the working face fault classification table obtained according to S5, and Table 5 shows the working face grouting priority according to S6 of the present invention.

[0085] Table 2 Key layer classification table

[0086] Table 3 Grading table of grouting layers

[0087] Table 4 Fault classification table of working face

[0088] Table 5 Grouting priority of working face

[0089] Table 5

[0090] The working principle of this invention is that the cumulative effect of overburden expansion after mining suppresses the formation of delamination. Specifically, the delamination is replaced by the expansion of the rock mass in the collapse zone and the expansion of the rock mass in the fracture zone. Delamination can only exist for a certain period of time when a typical key layer that can control the overburden exists in the local stratum as the underlying rock mass compacts. Without effective intervention in the delamination, it is difficult to achieve a high injection-production ratio and subsidence reduction rate.

[0091] The separation space required for overburden grouting is closed. The adjacent upper and lower layers of rock must maintain their overall continuous movement without any fracture damage. Only in this way can the separation space be used for grouting. This ensures that the water in the slurry does not leak into the stope and affect normal and safe mining.

[0092] Based on the above working principle, the present invention takes the scope of the subsidence area and the status of the old goaf as two important indicators. According to the scope of the subsidence area and whether there is an old goaf, all working faces in the mining area are first screened on a large scale, and working faces with certain value in the mining area are efficiently screened out. After the pre-screening is passed, the key layer is optimized by comprehensively considering the separation layer, grouting layer and fault combined with the gas protection layer delineated in the mining area, and a suitable grouting target area is selected. Before the key layer breaks, the separation layer is filled with high-pressure grouting to compact the lower broken rock mass, thereby expanding the injection space and increasing the injection-production ratio. A compacted bearing structure is formed in the goaf to effectively support the key layer, increase the subsidence reduction rate, reduce the grouting cost, and improve the grouting effect.

[0093] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for screening key strata for grouting of overburden separation layer in coal mines, characterized in that: The following steps are involved: Step 1: Select the overall analysis object according to the coal mine planning; Step 2: Screen the analysis objects based on the scope of the subsidence area; Step 3: Conduct secondary screening of the analysis objects based on whether there are old goaf areas; Step 4: Identify the key layers of the analyzed objects that have passed the screening, and prioritize the key layers based on the number of delamination spaces and the range of delamination heights. Based on the water-conducting fracture zone, set a safety height of 50m, and prioritize the number of grouting layers in combination with the potential delamination space and rock stratum water-resistance. Step 5: Prioritize the grouting layers based on the impact of the fault; Step 6: Based on the results of the three priority rankings, comprehensively analyze the priority of grouting in the key layer, and grout the separation layer of the key layer in order of priority.

2. A method for screening key strata for grouting of overburden separation layer in coal mines according to claim 1, characterized in that: Also includes step seven: If the separation layer of the screened key layer involves the gas protection layer, the screened separation layer will be downgraded or eliminated.

3. A method for screening key strata for grouting of overburden separation layer in coal mines according to claim 1, characterized in that: The step one comprises: The working faces under the areas where ground subsidence has occurred and the working faces in the mining areas that have been mined are not selected as the analysis objects. The working faces planned for mining are selected as the analysis objects.

4. A method for screening key strata for grouting of overburden separation layer in coal mines according to claim 1, characterized in that: The second step comprises: If the analysis object is within the subsidence area or at the boundary, the analysis object is eliminated and the analysis objects outside the boundary of the subsidence area are retained.

5. The method for selecting key strata for grouting of overburden separation layer in coal mine according to claim 1, characterized in that: The step three comprises: If the analysis object has an old goaf, the analysis object will be eliminated, and the analysis object without the old goaf will be retained.

6. A method for screening key strata for grouting of overburden separation layer in coal mines according to claim 1, characterized in that: In the step 4, the key layers of the analysis objects that have passed the screening are identified using the mining rock key layer identification software KSPB.

7. A method for screening key strata for grouting of overburden separation layer in coal mines according to claim 1, characterized in that: In the step 4, the key layers are prioritized based on the number of separation spaces and the separation height range, including: The level of the separation space number>5 and the separation height range and key layer>200m is excellent; The level of the key layer with the number of detached space between 3 and 5 and the range of detached height between 100 and 200 m is medium; The level of the critical layer with the number of separation spaces less than 3 or the separation height range or less than 100m is inferior; All key layers are prioritized in the order of best to worst, and the order of key layers in the same level is random.

8. The method for selecting key strata for grouting of overburden separation layer in coal mine according to claim 1, characterized in that: In step 4, a priority sorting is performed based on the number of layers that can be grouted, including: The level of key layers with more than 5 layers that can be grouted is excellent; The level of key layers with 1 to 5 groutable layers is medium; The level of key layers without grouting positions is poor; All key layers are prioritized in the order of best to worst. The order of key layers in the same level is random. When the priority is sorted based on the number of groutable layers, if the level of "bad" appears, it means that there is no groutable layer and the analysis object is directly eliminated.

9. A method for screening key strata for grouting of overburden separation layer in coal mines according to claim 1, characterized in that: The step five comprises: Based on the location of the grouting layer, The level of key layers that can be grouted and are not affected by faults is excellent; The level of the critical layer where part of the groutable layer is cut by faults is medium; The level of the key layer where all grouting layers are cut by faults is inferior; All key layers are prioritized in the order of best to worst, and the order of key layers in the same level is random.

10. The method for selecting key strata for grouting of overburden separation layer in coal mine according to claim 1, characterized in that: Step 6 include:. If at least two of the three priority judgments are at the same level, then this level is the priority level for grouting of the key layer. If the results of the three judgments are excellent, medium and poor respectively, then the priority level for grouting of the key layer is medium. Grouting is performed on the delamination layer of the key layer according to the priority order of grouting of the key layer. However, when the groutable layer is ranked as poor, the influence of the delamination layer and fault is no longer considered and it is directly eliminated.

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