Water-rich weakly-cemented sandstone roof fully-mechanized caving face water inrush and sand inrush prevention and control method

Abstract

The invention discloses a water-inrush and sand-inrush prevention and control method for a fully mechanized caving face of a water-rich weakly-cemented sandstone roof, and relates to the field of coal mining. The method comprises the steps that advanced grouting reinforcement is conducted on a roof coal seam and roof water-rich sandstone of a fully mechanized caving mining area; the reinforced working face is excavated, and a fully mechanized caving mining working support is installed; the top of a fully mechanized caving mining working support serves as a base point, a roof coal seam and roof water-rich sandstone are grouted and supported, and a curtain is formed; and the collapsed rock stratum after fully mechanized caving mining of the working support is subjected to grouting reinforcement. According to the method, grouting reinforcement is conducted on the top plate and the goaf in the mode of advance pre-grouting, frame top curtain grouting and frame rear isolation grouting, and water inrush and sand inrush accidents in the coal fully-mechanized caving mining process are avoided.

Description

Technical Field

[0001] This invention relates to the field of coal mining, and in particular to a method for preventing water inrush and sand collapse in a fully mechanized longwall mining face with a water-rich and weakly cemented sandstone roof. Background Technology

[0002] Roof inrushes and sand bursts are prone to occur in some mining areas due to complex geological conditions, including water-rich and loosely structured rock strata. Furthermore, some coal seams are shallowly buried with relatively unstable overlying strata, making them susceptible to water and sand flow during mining operations. Roof inrushes and sand bursts pose a significant hazard to mining production. These accidents severely compromise coal mine safety, are difficult to resolve, and are lengthy to recover from. Once they occur, they can have severe consequences, sometimes even leading to the abandonment of the entire mine. Therefore, before coal mining begins, detailed geological exploration should be conducted, and timely countermeasures should be implemented to prevent roof inrushes and sand bursts from impacting the safe mining of coal resources and causing property damage.

[0003] To prevent water inrush and sand collapse accidents, geological surveys are often conducted in advance, and measures such as grouting, reserving waterproof coal and rock pillars, and drainage and pressure reduction are used to modify the rock strata and ensure the smooth and safe operation of coal mining. For example, CN103643994A discloses a method for preventing water inrush and sand collapse in coal mines. It designs a grouting device to prevent water inrush and sand collapse, solving the problems of using drill bits to install grouting pipes and using grouting pipes to perform high-pressure grouting on specific strata. However, in fully mechanized longwall mining operations on water-rich, weakly cemented sandstone roofs, the need to release coal from the roof and the forward advancement of the working supports cause significant disturbance to the surrounding rock. Therefore, a single grouting operation cannot guarantee the prevention of water inrush and sand collapse accidents. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for preventing water inrush and sand collapse in fully mechanized longwall mining faces with water-rich and weakly cemented sandstone roofs. This method involves pre-grouting, curtain grouting on the roof, and isolation grouting after the roof is erected to reinforce the roof and prevent water inrush and sand collapse accidents during fully mechanized longwall mining.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: Embodiments of the present invention provide a method for preventing water inrush and sand collapse in a fully mechanized longwall mining face with a water-rich, weakly cemented sandstone roof, comprising: Advanced grouting reinforcement was carried out on the roof coal seam and roof sandstone of the fully mechanized mining area; Excavate the reinforced working face and install the fully mechanized longwall mining support; Using the top of the fully mechanized longwall mining support as the base point, grouting is injected into the roof coal seam and roof sandstone to form a curtain; Grouting was used to reinforce the collapsed rock strata behind the fully mechanized longwall mining support.

[0006] As a further implementation method, before advanced grouting reinforcement, the location and thickness of the top sandstone are obtained in advance to understand the rock strata.

[0007] As a further implementation method, the borehole wall is observed using a borehole inspection instrument to record the location and thickness of the top sandstone; the collected images and data are analyzed to assess the rock strata.

[0008] As a further implementation method, the advanced grouting reinforcement uses ordinary silicate cement + water glass as grouting material to reinforce the roof strata and coal seams in the fully mechanized mining area.

[0009] As a further implementation method, the grouting anchor rod is driven into the ground at an acute angle of 15° to the horizontal plane during pre-grouting reinforcement.

[0010] As a further implementation method, two types of grouting holes with different grouting ranges and intervals are selected to carry out pre-grouting reinforcement of the mining area.

[0011] As a further implementation, the two types of grouting holes and grouting anchors are arranged alternately along the mining direction.

[0012] As a further implementation method, the surrounding rock within the set range of the working support's advancement direction is reinforced by grouting. After the reinforcement is completed, the working face is excavated and the working support is installed.

[0013] As a further implementation method, grouting is carried out on the roof coal seam and roof sandstone using ultrafine cement + water-absorbing resin + nano silica + water glass + water-reducing agent as grouting materials.

[0014] As a further implementation method, ordinary silicate cement is used as the grouting material to reinforce the fractured rock behind the frame.

[0015] The beneficial effects of this invention are as follows: (1) The pre-grouting of the present invention uses ordinary silicate cement + water glass. Ordinary silicate cement has low cost and high setting strength. Adding water glass accelerates setting and promotes early strength. The curtain grouting of the top of the frame uses ultrafine cement + water-absorbing resin + nano silica + water glass + water-reducing agent. Ultrafine cement has high strength, small particle size and good injectability. Adding water-absorbing resin improves the impermeability of the grouting material to prevent water inrush and sand collapse accidents. Adding nano silica enhances the setting strength of the grouting material. Water glass adjusts the setting time. Water-reducing agent can improve the stability of the grout and reduce the water separation rate. The isolation grouting of the back of the frame uses ordinary silicate cement as the grouting material, which can provide strength and ensure the stability of the goaf. Therefore, by combining pre-grouting, curtain grouting of the top of the frame and isolation grouting of the back of the frame, the grouting reinforcement of the roof is achieved, and water inrush and sand collapse accidents are avoided during the coal mining process.

[0016] (2) The present invention takes the advancement of the fully mechanized caving working support of the coal seam roof and the mining process as the sequence. Through steps such as advance grouting, curtain grouting on the top of the support, and isolation grouting after the support, a water inrush and sand collapse prevention scheme for fully mechanized caving working face with water-rich and weakly cemented sandstone roof is formed. It can ensure the stability of the surrounding rock during the excavation of the working face and the installation of the working support, avoid accidents such as water inrush and sand collapse during coal mining, and ensure the stability of the rock strata after mining. Attached Figure Description

[0017] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] Figure 1 This is a flowchart of a method for preventing and controlling sudden water inrush and sand erosion according to one or more embodiments of the present invention; Figure 2 This is a side view of the pre-grouting in a fully mechanized longwall mining area according to one or more embodiments of the present invention; Figure 3 This is a cross-sectional view of the pre-grouting in a fully mechanized longwall mining area according to one or more embodiments of the present invention; Figure 4 This is a top view of the pre-grouting in a fully mechanized longwall mining area according to one or more embodiments of the present invention; Figure 5 This is a schematic diagram of the curtain grouting on the top of the fully mechanized longwall mining support according to one or more embodiments of the present invention; Figure 6 This is a schematic diagram of the isolation grouting of the goaf area after the support frame is erected in fully mechanized longwall mining according to one or more embodiments of the present invention. Detailed Implementation

[0019] Example 1: This embodiment provides a method for preventing water inrush and sand collapse in a fully mechanized longwall mining face with a water-rich, weakly cemented sandstone roof, such as... Figure 1 As shown, it includes the following steps: Step 1: Drill holes to explore and determine the location and thickness of the water-rich sandstone on the roof.

[0020] Drilling is performed on the top strata of the working support, ensuring the borehole reaches the water-rich sandstone layer. The borehole walls are observed using a borehole sight, and the location and thickness of the water-rich sandstone on the top strata are recorded. The acquired images and data are then analyzed to assess the condition of the rock strata.

[0021] Step Two: As Figures 2-4 As shown, the roof coal seam and roof sandstone of the fully mechanized mining area are reinforced by advance grouting.

[0022] The water-rich sandstone layer contains abundant water, numerous fissures, and has poor bearing capacity. During excavation, groundwater can enter the working face along the surrounding rock fissures, leading to water inrush and sand collapse accidents. Furthermore, due to the poor bearing capacity of both the water-rich sandstone layer and the coal seam, collapse accidents can occur during excavation. Therefore, pre-grouting reinforcement is necessary to strengthen the coal seam and surrounding rock in the mining area, ensuring the safe progress of subsequent mining operations.

[0023] Ordinary silicate cement combined with water glass was selected as the grouting material for reinforcing the roof sandstone and coal seams in the fully mechanized longwall mining area. This prevented roof collapse during face excavation and support installation. Ordinary silicate cement is relatively inexpensive and has high compressive and shear strength, but its initial setting time is relatively long. Adding water glass accelerates the setting time, improves early strength, and enhances the sealing effect. It can better seal some minor cracks, enhance water-stopping and leak-stopping capabilities, and can also adjust the fluidity and stability of the grout to a certain extent.

[0024] like Figure 2 As shown, pre-grouting reinforcement was carried out in the mining area. First, grouting holes with a spacing of 2.5m and a length of 50m were installed, and 5m long grouting anchors were used to reinforce the shallow coal and rock strata of the roof at a grouting pressure of 2MPa. Then, grouting holes with a spacing of 5m and a length of 100m were installed, and 5m long grouting anchors were used to reinforce the deep coal and rock strata of the roof at a grouting pressure of 5MPa. The grouting holes and grouting anchors were driven in at an angle of 15° to the horizontal plane.

[0025] When reinforcement is carried out using only 50m long grouting holes, the amount of grout injected into the coal and rock strata is relatively small, and the grout diffusion radius is small, making it difficult to inject into deep coal and rock strata. As a result, the reinforcement effect of the grout on the coal and rock strata is poor. When reinforcement is carried out using only 100m long grouting holes, the diffusion range of the grouting reinforcement is significantly increased, but this can easily lead to over-support, increasing support costs. Moreover, when the grouting hole length is longer, the grouting pressure should also be increased, resulting in high pressure around the grouting port, which can damage the coal and rock strata and cause grout leakage through the grouting port.

[0026] When grouting reinforcement is first carried out using 50m long grouting holes, and then grouting reinforcement is carried out using 100m long grouting holes, the shallow roof coal and rock strata can be reinforced into a whole to form a grout stop pad, which fixes the rock mass around the grouting port, effectively reducing the occurrence of grout leakage. At the same time, the grout diffusion range is large, and the reinforcement effect is guaranteed.

[0027] like Figure 4 As shown, the two types of grouting holes are arranged alternately along the mining direction.

[0028] Grouting reinforcement was carried out on the pre-designated working support area. After reinforcement, the working face was excavated and the working support was installed. Before advancing the working support, the surrounding rock within 5 meters of the advancing direction of the working support was grouted for reinforcement. After reinforcement, the working support was advanced.

[0029] Step 3: Excavate the working face and install the fully mechanized longwall mining support.

[0030] Based on the tunnel dimensions, prefabricate the supports and transport them to the vicinity of the installation location on the working face. Determine the precise installation position of the supports according to design requirements, and install the supports in sequence.

[0031] Step Four: As Figure 5 As shown, a grouting material consisting of ultrafine cement, water-absorbing resin, nano-silica, water glass, and water-reducing agent is selected. Using the top of the fully mechanized mining support as the base point, grouting is applied to the roof coal seam and the water-rich sandstone roof to form a curtain.

[0032] Water-rich sandstone in the roof can adversely affect the working face and supports, weakening the roof, increasing the risk of roof collapse, and making roof management more difficult. Groundwater softens the surrounding rock, reducing its stability and affecting normal mining operations. It can also cause significant water inrushes, impacting the mining environment, triggering water inrush and sand collapse accidents, and endangering personnel and equipment safety. Water in the rock strata also increases the moisture content of the coal, lowering its quality. Furthermore, it accelerates equipment corrosion and damage, reduces mining efficiency, and causes economic losses.

[0033] To prevent the water-rich sandstone roof from adversely affecting the mining face and to avoid water inrush and sand collapse accidents, curtain grouting reinforcement was carried out on the roof of the working support. This forms an underground water-resistant curtain on the roof, blocking the flow of groundwater, preventing water leakage, and protecting the project area from groundwater impact. This effectively reduces or avoids water inrush and sand collapse during underground construction, ensuring construction safety and smooth progress.

[0034] A grouting material consisting of ultrafine cement, water-absorbing resin, nano-silica, water glass, and a water-reducing agent was selected, and curtain grouting was performed using the top of the working support frame as the base point. Ultrafine cement has high strength, small particle size, and good injectability. The addition of water-absorbing resin improves the impermeability of the grouting material to prevent sudden water inrush and sandstorm accidents. Water-absorbing resin has high water absorption and retention properties, and its addition to the cement grouting material causes it to expand after setting, resulting in a tighter bond with the fissures in the water-rich sandstone layer of the roof, ensuring the impermeability of the rock layer. However, the addition of water-absorbing resin affects the strength of the grout-formed aggregate. Therefore, nano-silica is added to improve the setting strength of the grouting material.

[0035] Adding nano-silica enhances the setting strength of grouting materials. Nano-silica possesses high strength, good stability, and good durability. When added to grouting materials, it can solidify with cement hydration products, promoting the setting time and strength of the grouting material and enhancing the durability of the grout aggregate. However, nano-silica requires a large amount of water; therefore, water-reducing agents are added to improve the grout properties.

[0036] Water glass promotes early setting, shortens setting time, and improves early strength, while water-reducing agents enhance grout stability and reduce water separation. Ultrafine cement-water-absorbing resin-nano silica composite grouting material, when used to reinforce water-rich sandstone and coal seams, effectively improves the bearing capacity of the rock strata, preventing collapses and roof falls. It also prevents groundwater from seeping into the working face and affecting machinery and personnel, ensuring the normal operation of mining activities.

[0037] Step 5: As Figure 6 As shown, grouting was used to reinforce the collapsed rock strata behind the fully mechanized longwall mining support.

[0038] In coal seam mining, disturbance of the surrounding rock causes a redistribution of stress, disrupting the original stress balance. Furthermore, water-rich sandstone layers have weak bearing capacity. Therefore, roof rock collapses can occur. If the broken rock in the goaf is not dealt with promptly, it may lead to localized collapses, increasing the risk of roof falls and other accidents, threatening personnel safety. Furthermore, accumulated broken rock occupies working space, compresses supports, damages construction equipment, and reduces work efficiency. Therefore, grouting reinforcement can be performed on the broken rock behind the supports to ensure the stability of the surrounding rock.

[0039] Ordinary silicate cement, which is low in cost and has good load-bearing capacity, was selected as the grouting material to reinforce the broken rock behind the frame.

[0040] This embodiment employs a three-stage grouting process: pre-grouting before the support structure is erected, curtain grouting at the top of the support structure is erected, and isolation grouting at the rear of the support structure is performed. The pre-grouting uses ordinary silicate cement and water glass, the curtain grouting at the top of the support structure uses ultrafine cement, water-absorbing resin, nano-silica, water glass, and a water-reducing agent, and the isolation grouting at the rear of the support structure uses ordinary silicate cement as the grouting material. By selecting different grouting materials at different stages, the roof is reinforced through grouting, thus preventing water inrush and sand collapse accidents during fully mechanized coal mining.

[0041] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preventing water inrush and sand collapse in a fully mechanized longwall mining face with a water-rich, weakly cemented sandstone roof, characterized in that, include: Advanced grouting reinforcement was carried out on the roof coal seam and water-rich sandstone in the fully mechanized mining area. Excavate the reinforced working face and install the fully mechanized longwall mining support; Using the top of the fully mechanized longwall mining support as the base point, grouting is injected into the roof coal seam and the water-rich sandstone roof to form a curtain; Grouting was used to reinforce the collapsed rock strata behind the fully mechanized longwall mining support.

2. The method for preventing water inrush and sand collapse in a fully mechanized longwall mining face with a water-rich, weakly cemented sandstone roof as described in claim 1, characterized in that, Before advanced grouting reinforcement, the location and thickness of the water-rich sandstone on the top plate are obtained in advance to understand the rock strata.

3. The method for preventing water inrush and sand collapse in a fully mechanized longwall mining face with a water-rich, weakly cemented sandstone roof, as described in claim 2, is characterized in that... The borehole wall was observed using a borehole inspection instrument to record the location and thickness of the water-rich sandstone on the top plate; the collected images and data were analyzed to assess the condition of the rock strata.

4. A method for preventing water inrush and sand collapse in a fully mechanized longwall mining face with a water-rich, weakly cemented sandstone roof, as described in any one of claims 1-3, characterized in that, The advanced grouting reinforcement uses ordinary silicate cement + water glass as the grouting material to reinforce the water-rich sandstone and coal seam in the roof of the fully mechanized mining area.

5. A method for preventing water inrush and sand collapse in a fully mechanized longwall mining face with a water-rich, weakly cemented sandstone roof, as described in claim 4, is characterized in that... When performing pre-grouting reinforcement, the angle of the grouting hole should be 15° acute to the horizontal plane.

6. A method for preventing water inrush and sand collapse in a fully mechanized longwall mining face with a water-rich, weakly cemented sandstone roof, as described in claim 5, is characterized in that... Two types of grouting holes with different grouting ranges and intervals were selected to carry out pre-grouting reinforcement of the mining area.

7. A method for preventing water inrush and sand collapse in a fully mechanized longwall mining face with a water-rich, weakly cemented sandstone roof, as described in claim 6, is characterized in that... The two types of grouting holes are arranged alternately along the mining direction.

8. A method for preventing water inrush and sand collapse in a fully mechanized longwall mining face with a water-rich, weakly cemented sandstone roof, as described in claim 4, is characterized in that... Grouting is performed to reinforce the surrounding rock within the set range of the working support's advance direction. After reinforcement is completed, the working face is excavated and the working support is installed.

9. A method for preventing water inrush and sand collapse in a fully mechanized longwall mining face with a water-rich, weakly cemented sandstone roof, as described in claim 1, characterized in that... Grouting was carried out on the roof coal seam and water-rich sandstone layer using ultrafine cement, water-absorbing resin, nano silica, water glass and water-reducing agent as grouting materials.

10. A method for preventing water inrush and sand collapse in a fully mechanized longwall mining face with a water-rich, weakly cemented sandstone roof, as described in claim 1, characterized in that... Ordinary silicate cement was used as the grouting material to reinforce the broken rock behind the frame.

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