Paraffin-based grouting material for reconstruction of mining bed separation aquiclude and method

Abstract

The application discloses a paraffin-based grouting material for reconstruction of mining bed separation water-resisting layer and a method, relates to a water-resisting layer reconstruction grouting material and method for protecting water-bearing layer, belongs to a flowable slurry capable of controlling setting time, and can be fully filled in the bed separation and fissure generated below the water-bearing layer during coal seam mining. The paraffin-based grouting material comprises desert sand, talcum powder and paraffin, and the three are mixed with lubricating oil, heated and stirred to form the paraffin-based grouting material. The application can fill and block pores during the generation of bed separation of the water-resisting layer by implementing grouting engineering near the water-resisting rock layer, the injected slurry uniformly diffuses into the fissure and bed separation space in a fluid form, and then solidifies into a solid support rock layer, preventing the upper rock layer from continuously moving downward and deforming, leading to the water-bearing layer losing water again, at this time, the grouting material and the original damaged water-resisting layer are reconstructed to form a new rock layer with stronger water-resisting property, the water-bearing layer can be stably protected for a long time, and the loss of underground water is avoided.

Description

Technical Field

[0001] This invention relates to a grouting material and method for reconstructing aquifers to protect aquifers, and is particularly applicable to the grouting implementation method for reconstructing aquifers during coal seam mining operations where protection of the upper aquifer is required. Background Technology

[0002] During underground coal seam mining, the goaf gradually subsides as the roof loses its load-bearing capacity. The overlying strata gradually bend and break down until they reach the surface. When a natural aquifer exists within these strata, the underlying aquitard will deform and fail, leading to water loss and disaster. According to the theory of rock strata movement, the aquitard will first bend and delaminate during the advancement of the working face, followed by breakage. Therefore, preventing the overlying strata from continuing to deform and cause further water loss from the aquifer has become a pressing technical problem for those in this field.

[0003] Currently, existing technologies for aquifer grouting and sealing or reconstruction include patent CN202310279539.4, which discloses neutralized slag cement grout, its preparation method, and its application in mine aquifer reinforcement. This patent's application is limited to the vicinity of the mine roof, and the construction scope varies. It uses cement-based grouting materials, and because cement has a fixed setting time, it is almost unaffected by external factors, thus limiting the construction distance. Furthermore, cement materials are prone to solidifying and clogging pipes, making it unsuitable for long-distance transport. Patent CN202210791263.3 discloses a dynamic grouting interception and water-blocking method for aquifers with completely fractured overburden caused by mining. This method mainly describes the grouting repair and water-saving process. The methods for construction, drilling layout, and spacing are applicable to grouting in large, completely fractured faults and within the fracture range, but they do not mention the solidification and sealing capabilities of the grouting materials used or the water-tightening effect of the grout on the aquifer. Patent CN202210309982.7 discloses a coal-based solid waste overburden isolation grouting and filling water-retaining coal mining method. This method uses fly ash slurry to be implemented near the separation zone above the working face, with the same construction range as this method. However, the characteristic of fly ash slurry is that fly ash itself does not have binding properties. It needs to be injected into a closed space and allowed to settle to achieve partial water-tightening and rock-supporting effects. If there are fractures in the grouting space, the fly ash slurry will flow out with the fractures and lose its sealing effect.

[0004] Considering the existing technology of using cementing liquids for infiltration grouting, such as cement-based, epoxy resin-based, or molten wax, the target objects are usually loose soil with well-developed pores or rock structures with high permeability and open pores. If the target object is buried at a great depth and has poor permeability, it will be difficult to inject. When cementing liquid is directly injected into the soil and rock mass, the first part of the soil and rock that comes into contact and penetrates will be affected by dynamic viscosity, forming a permeability barrier with a large difference in flow velocity around the grouting point, making it difficult for subsequent grout to penetrate further. On the other hand, direct contact between the cementing material and the soil and rock mass will trigger the solidification threshold. For example, paraffin-like materials will solidify due to localized cooling upon contact, which greatly limits the injectable range. Therefore, how to use cementing liquids to solve the technical problem of gradual subsidence of such goaf areas due to the loss of roof support has become a technical barrier in this field. Summary of the Invention

[0005] To address the above problems, this invention proposes a paraffin-based grouting material and method for reconstructing the aquitard layer during mining. The fluid grout, which can control the setting time, can fully fill the fissures generated below the aquifer during coal seam mining, sealing the fissures near the aquitard layer to form a sealing layer, ensuring that the aquifer water no longer flows along the water-conducting fissure zone, and avoiding coal seam water inrush accidents.

[0006] The technical solution of the present invention is as follows: the paraffin-based grouting material includes desert sand, talc powder and paraffin wax, and the volume ratio of the three is 15:1:1 to 7:1:1. The three are mixed with lubricating oil and heated and stirred to form the paraffin-based grouting material.

[0007] The desert sand has a particle size of less than 0.8 mm, and the paraffin wax is semi-refined paraffin wax with a melting point between 42°C and 50°C.

[0008] The heating temperature should not exceed 180℃ when heating and stirring.

[0009] A method for reconstructing a water-tight layer after mining-induced delamination includes the following steps: Step 1: Confirm the location of the aquifer and the water-retaining layer in the overlying strata above the coal face where water-retaining mining is required. The water-retaining layer is a soft rock with strong water-retaining properties located below the aquifer. Step 2: After determining the location of the aquifer and the impermeable layer, arrange multiple main boreholes along the strike centerline above the working face. After the main boreholes extend to the height of the aquifer, they are dispersed in an L-shape to the surrounding area as branch boreholes and grouting pipes are installed. Step 3: Connect all the grouting branch pipes and the storage location of the paraffin-based grouting material through the material conveying pipeline, and install temperature sensors and electric heaters on the material conveying pipeline; When the working face begins to be mined, when a separation space is generated at the position of the water-resistant layer above the goaf, molten paraffin-based grouting material is pumped into the material transport pipeline via the grouting pump. The grout flows to the original water-resistant layer, and the heating power of the electric heater is adjusted according to the feedback of the temperature sensor to ensure that the grout is in a molten state. When injection ceases, the flowing paraffin-based grouting material covers the entire delamination space, forming a reconstructed grouting cover layer and sealing most of the cracks. After cooling, it becomes a solid support rock layer that no longer bends or sinks.

[0010] Each main borehole is constructed with three sections of pipeline. The first section, 8, is drilled vertically downwards from the ground surface until it penetrates the topsoil and extends for 10m. A cement grouting sleeve is then poured to fix and protect the grout delivery pipeline. The ground is hardened and an electric heater 18 is installed on the pipeline. The second section, 9, is drilled into the impermeable layer and a larger main pipeline is installed. The third section, 11, consists of multiple horizontally extending boreholes. Four to eight grouting branch pipes 12 are installed in a circular array around the main borehole and inserted into the impermeable layer. The ground surface, the first section, 8, and the second section, 9, are all covered with an insulation layer 10 to ensure that the grout delivery pipeline remains a fluid above the melting point of paraffin wax during the grout delivery process.

[0011] This invention involves grouting near aquitard strata. During the delamination process of the aquitard, the pores are filled and sealed. The injected grout diffuses evenly into the cracks and delamination spaces in a fluid form, and then solidifies into a solid supporting stratum. This prevents the upper stratum from continuing to move downward and deform, which would cause the aquifer to lose water again. At this time, the grouting material and the original damaged aquitard are reconstructed to form a new stratum with greater thickness and stronger water-impermeability, which can stably protect the aquifer for a long time and prevent groundwater loss.

[0012] Compared to traditional molten wax infiltration grouting technology, this project mixes paraffin wax and sand. The differences lie in two aspects: First, the target application is different. Based on the rock strata movement patterns, rock strata of different strengths bend and subside asynchronously. This strength difference leads to significant delamination spaces between strata. The volume of these delamination spaces is affected by the height of the underlying goaf, not by the permeability of the rock strata themselves. Therefore, this method can be used for any stratum where delamination spaces occur. Second, the injection components are different. This technology uses sand as aggregate, paraffin wax as binder, and oil as both a heat conductor and fluid with good thermal insulation properties. This allows the injected material to achieve good strength without penetrating the rock mass. During flow, it possesses the fluidity of molten wax and oil, with a low cooling rate. Even if the temperature drops in localized areas of contact with the rock mass, the high internal thermal conductivity of the fluid ensures the overall temperature remains above the melting point, guaranteeing the grout's flow and diffusion range. Compared to molten wax infiltration grouting technology, this method places greater emphasis on understanding the rock strata movement patterns at the construction site, has a wider applicability, higher grouting efficiency, and a larger effective range.

[0013] The apparatus and method of the present invention have achieved the following beneficial technical effects: I. The aggregate material of this invention is desert sand available in most parts of Xinjiang. The raw material is easy to obtain and has low cost. The material ratio verified by experiments has corresponding compressive strength and fluidity. When the prepared slurry is in a molten state, it can be transported to a designated location through pipelines. When the slurry solidifies, it becomes a non-hydrophilic rock-like solid.

[0014] Second, the material of the present invention is particularly suitable for the reconstruction of the aquifer. Due to its molten flow characteristics, it can fill most of the cracks and form a whole. Since the material itself is non-hydrophilic, it has water-proof characteristics within the material coverage area. After the material solidifies, it has similar properties to the original aquifer and has a certain load-bearing capacity and elasticity, thereby protecting the aquifer.

[0015] Third, the method and materials of the present invention do not pollute water bodies during the grouting process. The grout has stable physical and chemical properties, contains no soluble ions, and has no potential pollution risk. Even if mixed with water, it will only solidify and precipitate without reacting, making it an environmentally friendly material.

[0016] IV. The construction process of the present invention is based on delamination grouting engineering, which is a relatively mature and feasible surface grouting scheme with low construction difficulty, high equipment versatility, and complete supporting facilities.

[0017] Fifth, the method of the present invention is suitable for construction in most normal temperature weather. It only needs to maintain the internal temperature of the pipeline to ensure smooth material transportation. There is no pipe blockage phenomenon in common grouting projects. The maintenance cost is small and the application range is wide. Attached Figure Description

[0018] Figure 1 This is a top view of the implementation process.

[0019] Figure 2 This is a schematic diagram of the grouting process for the AA section.

[0020] Figure 3 Flowchart of grouting process for BB section.

[0021] 1: Grouting cover layer two; 2: Grouting cover layer one; 3: Ground grouting borehole two; 4: Ground grouting borehole one; 5: Mining line advancement position one; 6: Mining line advancement position two; 7: Grouting working face; 8: Section one pipeline; 9: Section two pipeline; 10: Pipeline insulation layer; 11: Section three pipeline; 12: Grouting branch pipe; 13: Grout; 14: Delamination space; 15: Water-conducting fissure; 16: Temperature sensor; 17: Material conveying pipeline; 18: Electric heater; 19: No. one storage tank; 20: No. two storage tank; 21: No. three storage tank; 22: No. four storage tank; 23: Heating and mixing tank; 24: Buffer tank; 25: Grouting pump. Detailed Implementation

[0022] To clearly illustrate the technical features of this patent, the following detailed description is provided through specific embodiments and in conjunction with the accompanying drawings.

[0023] During underground coal seam mining, the rock strata above the goaf will gradually collapse and subside. When this affects the aquitard below the aquifer, delamination will first occur, followed by cracks and water leakage. This method is implemented within the space created by the delamination to prevent subsequent cracks and water leakage. Specifically, it includes using a paraffin-based hot-melt cementing material, a heated, stirred, transported, and pumped device placed on the surface, vertical boreholes at specially selected locations and depths, and corresponding material transport pipelines.

[0024] A paraffin-based hot-melt adhesive material, namely paraffin-based grouting material, is formulated from desert sand with high roundness and particle size less than 0.8 mm, semi-refined paraffin wax with a melting point between 42°C and 50°C, lubricating oil and talc powder. After solidification, the material has a uniaxial compressive strength of not less than 0.8 MPa and a saturated water absorption rate of less than 2%.

[0025] The material preparation method is to heat the material to a temperature not exceeding 180°C to prevent high-temperature denaturation, and to stir it continuously until the material is completely melted into a fluid. It is then pumped and transported in a pipeline containing an insulation layer or a heating function. During surface transportation, it is recommended that the temperature in the pipeline be at least 40°C higher than the melting point of paraffin. After the material flows out of the three-section pipeline, the ambient temperature must not be lower than 0°C.

[0026] A set of heated, stirred, transported, and pumped equipment placed on the ground includes a No. 1 storage tank 19 for storing desert sand, a No. 2 storage tank 20 for storing talc powder, a No. 3 storage tank 21 for storing paraffin wax, and a No. 4 storage tank 22 for storing lubricating oil. Among them, the No. 1 storage tank 19, the No. 2 storage tank 20, and the No. 3 storage tank 21 are cylindrical vertical storage tanks for storing solid particles, and are sealed storage tanks with a volume ratio between 15:1:1 and 7:1:1. The No. 3 storage tank 21 must be made of heat-insulating material. The No. 4 storage tank 22 stores lubricating oil. The pipelines of the above storage tanks are connected to a heated and stirred tank 23 for sealed heating and stirring, and the heating temperature is maintained between 100℃ and 180℃. A buffer tank 24 is connected in parallel to the heated and stirred tank. The buffer tank is a heated and insulated type, mainly providing storage space for mixed but not pumped materials. A grouting pump 25 is connected after the heated and stirred tank. The grouting pump is directly connected to the transport pipeline 17. All connecting pipelines of the grouting pump and the ground are insulated.

[0027] The main borehole has three vertical construction pipelines: pipeline 8, pipeline 9, and pipeline 11. A heater 18 and a temperature sensor 16 are installed on the material transport pipeline 17. Pipeline 8 is constructed in the loose topsoil layer and extends 10m below the topsoil layer, requiring cement-cast casing and pipe positioning. Pipeline 9 is an inclined section that extends through the aquifer towards the planned grouting point. The end of pipeline 9 is located within the impermeable layer below the aquifer, and the pipeline is covered with insulation material. Pipeline 11 is a shotcrete pipe, located within the impermeable layer and cut perpendicular to the working face, primarily for grout pumping.

[0028] The technical implementation steps of this invention are as follows: Step 1: Identify the locations of the aquifer and aquitard in the overlying strata above the coal face where water retention is required. The aquitard is a soft rock with good plasticity. Considering that after the mining face advances, the aquitard above the corresponding goaf outline will sink and bend with the rock strata, creating large horizontal fissures between the aquifer and the aquitard, i.e. Figure 3 As shown in the figure, the delamination layer 14, at the same time, the water-resistant layer corresponding to the goaf outline generates vertical cracks, namely water-conducting cracks 15. The main targets of this technology are the aforementioned horizontal cracks and vertical cracks.

[0029] Step 2: After determining the location of the aquifer and impermeable layer, arrange multiple main boreholes along the strike centerline above the working face, i.e., as shown below. Figure 1 The ground grouting boreholes 2 (3) and 4 (4) shown in the diagram extend from the main borehole to the height of the aquifer and are then distributed in an L-shape around the perimeter as branch boreholes, with grouting pipes 12 installed at the ends of all branch boreholes. Each main borehole and its branch boreholes cover a construction unit for one grouting project. As the working face moves, the construction units are gradually covered along the working face to complete the reconstruction of the aquifer.

[0030] The grouting pipeline must be kept warm from the ground grouting site to the grout outlet at the grouting layer, and heated if necessary, to ensure that the grout is at its melting temperature and flows and diffuses into the delamination zone in the form of a fluid. When the temperature is higher than the melting point of paraffin, the grout can be pumped and flows normally, but it should not exceed 180°C to prevent the paraffin material from denaturing. Within a controllable range, the grout has excellent fluidity and diffusion, which can perfectly seal the entire delamination space and various gaps.

[0031] Each main borehole is constructed with three sections of pipeline. The first section, 8, is drilled vertically downwards from the ground surface until it penetrates the topsoil and extends for 10m. A cement grouting sleeve is then poured to fix and protect the grouting pipeline. The ground is hardened and an electric heater 18 is installed on the pipeline. The second section, 9, is drilled to extend into the waterproof layer and a larger main pipeline is installed. The third section, 11, consists of multiple horizontally extending boreholes. Four to eight grouting branch pipes 12 are installed in a circular array around the main borehole and inserted into the waterproof layer. The ground surface, the first section, 8, and the second section, 9, are all covered with an insulation layer 10. It is recommended that the grouting pipeline be in a fluid state 40°C above the melting point of paraffin wax during the grouting process. If the insulation capacity is limited, the temperature of the grouting pipeline should at least be ensured to be no lower than the melting point of paraffin wax throughout the transportation process. Step 3: When the working face begins to be mined and a separation space 14 is generated at the water-resistant layer above the goaf, the following method is implemented: Desert sand, talc powder, paraffin wax, and lubricating oil in storage bins 19, 20, 31, and 42 are transported to a heating and mixing tank in a certain proportion for heating and mixing. When the material temperature is stable, it is pumped to the pipeline by a transport pump. The slurry flows through three sections of pipeline to the original water-resistant layer. The heating power of the electric heater 16 is adjusted according to the feedback from several temperature sensors 18 installed in the pipeline to ensure that the slurry is in a molten state.

[0032] The principle for the number of temperature sensors and heaters is that temperature sensors and heaters should be added or removed in groups, and the spacing between them on the ground should be as equal as possible. The temperature gradient between adjacent temperature sensors should not be too large. If it is greater than 10°C, it is necessary to add more temperature sensors and heaters, rather than increasing the power of the heaters. Excessive local power of the heaters will cause the local temperature to exceed 180°C, which will affect the material properties. The feedback principle between the temperature sensor and the heater is that each group of temperature sensors controls the heater to operate at higher power when the temperature is below the melting point of paraffin wax, and to stop heating immediately when the temperature is above 180°C. The optimal temperature range is about 40°C above the melting point of paraffin wax.

[0033] The grouting speed should be matched with the working face advance speed. When the working face advances beyond the range of the grouting hole, the grouting volume should be no less than 10% of the mined-out volume, that is, the dynamic grouting-mining ratio should be no less than 10%, so as to ensure that the grout completely covers the reconstructed water-resistant layer.

[0034] When the grout flows out from the end of the three-section pipe 11 and covers the surrounding fissures, and a significant increase in pressure occurs, part of the grouting branch pipe 12 is pulled back, but not removed from the delamination space 14. Grouting continues until no more can be injected. At this point, the flowing grout covers the entire delamination space 14, forming a reconstructed grouting cover layer 21 and a grouting cover layer 12, and sealing most of the fissures 15. After solidification, it becomes a solid supporting rock layer that no longer bends and sinks, and the implementation in this area is complete.

[0035] There are many specific ways to implement this invention. The above description is only a preferred embodiment of this invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of this invention, and these improvements should also be considered within the scope of protection of this invention.

Claims

1. A method for reconstructing a water-resistant layer after mining, characterized in that, Based on paraffin-based grouting material, the paraffin-based grouting material includes desert sand, talc powder and paraffin wax, with a volume ratio of 15:1:1 to 7:1:

1. The three are mixed with lubricating oil and heated and stirred to form paraffin-based grouting material. The desert sand has a particle size of less than 0.8 mm, and the paraffin wax is semi-refined paraffin wax with a melting point between 42°C and 50°C; the heating temperature during heating and stirring does not exceed 180°C, and the conveying temperature is not lower than the melting point of the paraffin wax. The method for reconstructing the aquitard layer after mining includes the following steps: Step 1: Confirm the location of the aquifer and the water-retaining layer in the overlying strata above the coal face where water-retaining mining is required. The water-retaining layer is a soft rock with strong water-retaining properties located below the aquifer. Step 2: After determining the location of the aquifer and the impermeable layer, arrange multiple main boreholes along the strike centerline above the working face. After the main boreholes extend to the height of the aquifer, they are dispersed in an L-shape to the surrounding area as branch boreholes and grouting pipes are installed. Step 3: Connect all the grouting branch pipes and the storage location of the paraffin-based grouting material through the material conveying pipeline, and install temperature sensors and electric heaters on the material conveying pipeline; When the working face begins to be mined, when a separation space is generated at the position of the water-resistant layer above the goaf, molten paraffin-based grouting material is pumped into the material transport pipeline via the grouting pump. The grout flows to the original water-resistant layer, and the heating power of the electric heater is adjusted according to the feedback of the temperature sensor to ensure that the grout is in a molten state. The number of temperature sensors and electric heaters should be matched with the specific construction temperature. When the local temperature is low, if there is a gradient difference of more than 10°C between adjacent temperature sensors on the transport pipeline, the number of temperature sensors and electric heaters needs to be increased. When the gradient difference between adjacent temperature sensors is less than 5°C, the number of sensors and electric heaters is appropriate. The power of the electric heaters should not be too large, and the local heating temperature should not exceed 180°C. When grouting reaches a point where it can no longer be injected, the flowing paraffin-based grouting material covers the entire delamination space, forming a reconstructed grouting cover layer and sealing most of the cracks. After cooling, it becomes a solid support rock layer that no longer bends or sinks.

2. The method for reconstructing a mining-induced aquitard layer according to claim 1, characterized in that, Each main borehole is constructed with three sections of pipeline. The first section (8) is drilled vertically downward from the ground surface until it penetrates the topsoil layer and extends for 10m. A cement grouting sleeve is poured to fix and protect the grouting pipeline. The ground is hardened and an electric heater (18) is installed on the pipeline. The second section (9) is drilled to extend into the waterproof layer and a thicker main pipeline is installed. The third section (11) consists of multiple horizontally extending boreholes. Four to eight grouting branch pipes (12) are installed in a circular array around the main borehole. The grouting branch pipes (12) are inserted into the waterproof layer. The ground surface, the first section (8), and the second section (9) are all covered with an insulation layer (10) to ensure that the grouting pipeline is a fluid above the melting point of paraffin wax during the grouting process.

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