Goaf paste-powder solid waste mixed filling method and system

Abstract

The invention relates to a goaf paste-powder solid waste mixed filling method. The goaf paste-powder solid waste mixed filling method comprises the three steps of system construction, filling area construction and filling operation. Existing filling equipment and technologies are slightly changed, good adaptability and universality are achieved, on the premise that the cost of the fully-mechanized mining paste filling material is not increased, the concentration of the paste filling material is increased at the pipe conveying tail end, the setting time of the paste filling material is greatly shortened, filling bleeding is greatly reduced, and the early strength and the roof contact rate are improved; therefore, the blocking difficulty and the construction cost of the filling area are effectively reduced, the working efficiency of filling mining is improved, and the purposes of improving the quality of goaf treatment operation and reducing the difficulty and the cost of goaf comprehensive treatment operation are achieved.

Description

Technical Field

[0001] The invention relates to a method and system for mixed filling of paste-powder solid waste in goaf areas, belonging to the technical field of environmental management of goaf areas in coal mines. Background Art

[0002] In the treatment of coal mine goaf, the filling operation is mainly carried out by filling cementitious materials such as concrete in the goaf. In order to improve the efficiency of the filling operation and reduce the cost of filling, on the one hand, the paste filling material needs to have good fluidity during the pipeline transportation stage; on the other hand, the paste filling material is required to quickly solidify after entering the goaf and leveling, have high early strength, and low water seepage. At present, conventional methods cannot prepare paste filling materials that meet the above performance requirements. At present, the method of adding accelerators at the end of the filling pipe is generally used to solve the above problems, but this method is difficult to mix chemical additives with paste filling materials evenly, the process is complicated, and the effect is poor. At the same time, it also leads to a relatively high cost of filling materials; at the same time, the large-scale use of accelerators and early strength agents often deteriorates the later strength of the filling materials, which means that in order to ensure the later strength of the designed filling body, the amount of cementitious materials must be increased, which further increases the filling cost; in addition, accelerators and early strength agents cannot solve the problem of high water seepage of paste filling materials. The water seepage rate of the prepared paste filling material can even be as high as 20%. A large amount of filling water seepage not only seriously affects the sealing effect of the filling area, but also aggravates the drainage problem of the coal mining working face. In the case of mudstone bottom plate, the bottom plate mudification problem will also occur, which greatly affects the working environment of the working face.

[0003] To address this problem, there is an urgent need to develop a new filling method and filling operation system to meet the needs of actual work. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present invention makes little change to the existing filling equipment and technology, has good adaptability and versatility, and, without increasing the cost of the comprehensive mining paste filling material, increases the concentration of the paste filling material, greatly shortens the setting time of the paste filling material, greatly reduces filling seepage, improves the early strength and top connection rate, and reduces the difficulty of sealing the filling area.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A method for mixing and filling paste-powder solid waste in goaf, comprising the following steps:

[0007] S1, System construction. First, according to the geological structure characteristics of the filling area for filling operations, set the paste filling material and powder filling material for filling operations. Then, set up the corresponding dual-pipeline mixing filling system, complete the construction layout of the dual-pipeline mixing filling system, and at the same time establish a connection between the dual-pipeline mixing filling system and the external material supply system;

[0008] S2, Filling area construction. After completing step S1, add elastic sealing strips to the side surface positions of the hydraulic supports in the roadway to be filled. At the same time, install hydraulic push rods parallel to the horizontal plane for each hydraulic support. Driven by the hydraulic push rods, adjacent two hydraulic supports move relative to each other and abut against each other to achieve the sealing of the top and side walls of the roadway, forming a closed filling area structure;

[0009] S3, Filling operation. After completing step S2, drive the dual-pipeline mixing filling system to operate. The mixing mechanism, material supply pipeline, and end mixer operate simultaneously. First, the dual-pipeline mixing filling system, on the one hand, transports the prepared paste filling material, and then simultaneously pressurizes and transports the prepared paste filling material and powder filling material to the filling area. In the filling area, the dual-pipeline mixing filling system performs a proportioning and mixing operation on the paste filling material and powder filling material, and obtains a paste material with increased viscosity and reduced water content of the slurry. Finally, use the prepared paste material to carry out the filling operation on the filling area.

[0010] Further, in step S1, the paste filling material is composed of the following components in parts by weight: 5% - 25% of cementitious material; 0% - 50% of fly ash; 20% - 80% of coal gangue, and the balance is water; and during the transportation process of the paste filling material, the mass concentration of the paste filling material is 65% - 72%; the powder filling material includes, but is not limited to, any one or a mixture of powders of fly ash, desulfurized gypsum powder, carbide slag powder, cement, and cementitious material, with a water content of less than 1%.

[0011] Further, in step S3, during the paste filling operation, the mass concentration of the mixed filling slurry is 78% - 85%, the operation pressure is 2 - 20 MPa, and the flow rate is 50 - 450 m 3 / h; at the same time, the mixed filling slurry is used to complete the filling operation in 3 - 5 layers in the filling operation area. The width of each layer of the mixed filling slurry is 1.5 - 5 m, the thickness is 0.3 - 3.0 m, and the filling speed is 50 - 450 m 3 / h.

[0012] Further, in the step S1, the dual-pipeline mixing and filling system includes a mixing mechanism, a material supply pipeline, and an end mixer. The mixing mechanism is communicated with at least one end mixer through the material supply pipeline. When there are two or more end mixers, the end mixers are connected in parallel with each other. The mixing mechanism includes a material mixing station, at least three solid material storage bins, a gas storage tank, a booster pump, an air compressor, and a pressure regulating air pump. At least two of the solid material storage bins are communicated with the material mixing station. The material mixing station is communicated with the material supply pipeline through the booster pump. One end of the solid material storage bin not communicated with the material mixing station is communicated with the gas storage tank through the air compressor, and at the same time, the other end of the solid material storage bin is communicated with the material supply pipeline through the pressure regulating air pump. The material supply pipeline includes a paste material conveying pipeline, a high-pressure powder material conveying pipeline, and several positioning seats for connecting the paste material conveying pipeline and the high-pressure powder material conveying pipeline. The positioning seats are evenly distributed along the axis direction of the paste material conveying pipeline.

[0013] Further, the end mixer includes a mixing cavity, a grouting injection port, a paste drainage pipe, a powder drainage pipe, a feeding stirring motor, a mixing stirring motor, a driving auger, a stirring auger, a control valve, and a control circuit. The mixing cavity is a cylindrical hollow tubular structure. Its front end face is communicated with the grouting injection port and coaxially distributed. The rear end face is communicated with the paste drainage pipe through a flange and coaxially distributed. A drainage port perpendicular to its axis is arranged on the side wall of the mixing cavity and is communicated with the powder drainage pipe through the drainage port. The paste drainage pipe and the powder drainage pipe are connected in parallel and are parallel to each other. At the same time, control valves are arranged at the rear end faces of the paste drainage pipe and the powder drainage pipe and are communicated with the material supply pipeline through the control valves. The driving auger is embedded in the drainage port. Its axis is perpendicular to the axes of the mixing cavity and the drainage port respectively and intersects with the axis of the drainage port. The driving auger is connected with the mixing stirring motor through a transmission shaft. There are at least three stirring augers, which are located in the mixing cavity and are evenly distributed along the axis direction of the mixing cavity. At the same time, each stirring auger is perpendicular to and intersects with the axis of the mixing cavity, and the included angle between the axes of two adjacent stirring augers is 90°. At the same time, each stirring auger is connected with the mixing stirring motor through a transmission shaft. The feeding stirring motor and the mixing stirring motor are both located outside the mixing cavity and are connected with the outer side surface of the mixing cavity. The control circuit is connected with the outer side surface of the mixing cavity and is electrically connected with the feeding stirring motor, the mixing stirring motor, and the control valve respectively.

[0014] Further, a flow sensor and a pressure sensor are respectively arranged at the grouting injection port, the drainage port, inside the paste drainage pipe and the powder drainage pipe, and both the flow sensor and the pressure sensor are electrically connected to the control circuit. The diameter of the stirring auger increases step by step from the front to the back along the axis of the mixing chamber. The diameter of the frontmost stirring auger is 80% of the inner diameter of the mixing chamber. The drainage port and the powder drainage pipe are interconnected through a throttle valve, and the throttle valve is electrically connected to the control circuit.

[0015] Further, an auxiliary filling mechanism is additionally arranged outside the end mixer. The auxiliary filling mechanism includes a traveling chassis, a lifting driving mechanism, a turntable mechanism, a swinging mechanism and a bracket. The upper end surface of the traveling chassis is vertically connected to the lifting driving mechanism. At the same time, the upper end surface of the lifting driving mechanism is connected to the turntable mechanism and distributed coaxially. The upper end surface of the turntable mechanism is connected to the swinging mechanism and is hinged to the bracket through the swinging mechanism. The bracket is a frame structure with a "U"-shaped cross-section groove. The axis of the bracket intersects with the axis of the lifting driving mechanism and can be adjusted and swung within the range of 0° - 135° in the vertical direction through the swinging mechanism. The bracket covers the outside of the mixing chamber of the end mixer, and the axis of the mixing chamber is parallel to the axis of the bracket. The lifting driving mechanism, the turntable mechanism and the swinging mechanism are all electrically connected to the control circuit.

[0016] Further, at least two vibrators are respectively arranged on the paste material conveying pipeline and the high-pressure powder material conveying pipeline of the material supply pipeline along their axial directions. The vibrators are connected to the positioning seats through elastic bases, and the vibrators are respectively electrically connected to the control circuit of the end mixer.

[0017] Further, an external booster pump set is additionally configured every 10 - 30 meters in the material supply pipeline.

[0018] Compared with the prior art, the present invention makes minor modifications to the existing filling equipment and technology, has good adaptability and versatility. Without increasing the cost of the fully-mechanized mining paste filling material, by increasing the concentration of the paste filling material, the setting time of the paste filling material is significantly shortened, the filling bleeding is significantly reduced, the early strength and the roof contact rate are improved, and the plugging difficulty in the filling area is reduced. At the same time, during operation, on the one hand, the usage amounts of materials such as concrete and accelerant in the filling material can be effectively reduced, thus effectively reducing the filling cost. On the other hand, during operation, the defect that the accelerant and early strength agent cannot solve the high bleeding of the paste filling material is solved. Thus, while effectively improving the construction efficiency and construction quality of the filling operation area, it effectively overcomes the defects in the traditional filling operation that the drainage volume of the coal mining face increases and the floor is sludged due to a large amount of bleeding of the filling material, thereby achieving the purpose of improving the quality of the goaf treatment operation and reducing the difficulty and cost of the comprehensive goaf treatment operation. Description of the Drawings

[0019] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments;

[0020] Figure 1 It is a schematic structural diagram of the system of the present invention;

[0021] Figure 2 It is a schematic partial sectional structure diagram of the end mixer;

[0022] Figure 3 It is a schematic connection structure diagram of the end mixer and the auxiliary filling mechanism;

[0023] Figure 4 It is a schematic process flow diagram of the method of the present invention;

[0024] Figure 5 It is a flow performance curve diagram of the two-stage paste filling slurry under the influence of different mass concentrations and different number of stratification layers;

[0025] Figure 6 It is a bleeding characteristic curve diagram of the two-stage paste filling slurry under the influence of different mass concentrations and different number of stratification layers;

[0026] Figure 7 It is a setting time curve diagram of the two-stage paste filling slurry under the influence of different mass concentrations and different number of stratification layers;

[0027] Figure 8 It is a mechanical characteristic curve diagram of the two-stage paste filling material under the influence of different mass concentrations and different number of stratification layers. Specific embodiments

[0028] To make the technical means, creative features, achieved purposes and effects of the present invention easy to implement, the present invention will be further described below in conjunction with specific embodiments.

[0029] As Figures 1 - 8 shown, a method for mixed filling of goaf paste-powder solid waste includes the following steps:

[0030] S1. System construction. First, according to the geological structure characteristics of the filling area of the filling operation, set the paste filling material and powder filling material for the filling operation, then set the corresponding double-pipeline mixed filling system, and complete the construction layout of the double-pipeline mixed filling system. At the same time, establish a connection between the double-pipeline mixed filling system and the external material supply system;

[0031] S2. Construction of the filling area. After completing step S1, an elastic sealing strip is added to the side surface position of the hydraulic support in the roadway to be filled. At the same time, hydraulic push rods parallel to the horizontal plane are provided for each hydraulic support. Driven by the hydraulic push rods, adjacent two hydraulic supports move relative to each other and abut against each other to achieve the sealing of the top and side walls of the roadway, forming a closed filling area structure;

[0032] S3. Filling operation. After completing step S2, the dual-pipeline mixing filling system is driven to operate, and the mixing mechanism, the material supply pipeline, and the end mixer operate simultaneously. First, the dual-pipeline mixing filling system, on the one hand, transports the prepared paste filling material, and then simultaneously pressurizes and transports the prepared paste filling material and the powder filling material to the filling area. In the filling area, the dual-pipeline mixing filling system performs a proportioning and mixing operation on the paste filling material and the powder filling material to obtain a paste material with increased viscosity and reduced water content of the slurry. Finally, the prepared paste material is used to perform the filling operation on the filling area.

[0033] In this embodiment, the paste filling material in step S1 is composed of the following components in parts by weight: 5% - 25% of the gelling material; 0% - 50% of fly ash; 20% - 80% of coal gangue, and the balance is water; and during the transportation of the paste filling material, the mass concentration of the paste filling material is 65% - 72%; the powder filling material includes, but is not limited to, any one or a mixture of powders of fly ash, desulfurized gypsum powder, carbide slag powder, cement, and gelling material, and the water content is less than 1%.

[0034] In this embodiment, in step S3, during the paste filling operation, the mass concentration of the mixed filling slurry is 78% - 85%, the operating pressure is 2 - 20 MPa, and the flow rate is 50 - 450 m 3 / h; at the same time, the mixed filling slurry in the filling operation area is filled in 3 - 5 layers. The width of the mixed filling slurry for each layer is 1.5 - 5 m, the thickness is 0.3 - 3.0 m, and the filling speed is 50 - 450 m 3 / h.

[0035] It should be emphasized that in the step S1, the dual-pipeline mixing and filling system includes a mixing mechanism 101, a material supply pipeline 102, and an end mixer 103. The mixing mechanism 101 is connected to at least one end mixer 103 through the material supply pipeline 102. When there are two or more end mixers 103, the end mixers 103 are connected in parallel with each other. The mixing mechanism 101 includes a material mixing station 1, at least three solid material storage bins 2, a gas storage tank 3, a booster pump 4, an air compressor 5, and a pressure regulating air pump 6. At least two of the solid material storage bins 2 are connected to the material mixing station 1. The material mixing station 1 is connected to the material supply pipeline 102 through the booster pump 4. One end of the solid material storage bin 2 not connected to the material mixing station 1 is connected to the gas storage tank 3 through the air compressor 5, and at the same time, the other end of the solid material storage bin 2 is connected to the material supply pipeline 102 through the pressure regulating air pump 6. The material supply pipeline 102 includes a paste material conveying pipeline 21, a high-pressure powder material conveying pipeline 22, and a number of positioning seats 23 for connecting the paste material conveying pipeline 21 and the high-pressure powder material conveying pipeline 22. The positioning seats 23 are evenly distributed along the axis of the paste material conveying pipeline 21.

[0036] It should be emphasized that the end mixer 103 includes a mixing chamber 31, a grouting injection port 32, a paste drainage pipe 33, a powder drainage pipe 34, a feeding and mixing motor 35, a mixing and stirring motor 36, a driving auger 37, a stirring auger 38, a control valve 39, and a control circuit 30. The mixing chamber 31 is a cylindrical hollow tubular structure. Its front end face is connected to the grouting injection port 32 and is coaxially distributed. The rear end face is connected to the paste drainage pipe 33 through a flange 301 and is coaxially distributed. A drainage port 302 perpendicular to its axis is provided on the side wall of the mixing chamber 31 and is connected to the powder drainage pipe 34 through the drainage port 302. The paste drainage pipe 33 and the powder drainage pipe 34 are connected in parallel and are parallel to each other. At the same time, control valves 39 are provided at the rear end faces of the paste drainage pipe 33 and the powder drainage pipe 34, and are connected to the material supply pipeline 102 through the control valves 39. The driving auger 37 is embedded in the drainage port 302. Its axis is perpendicular to the axes of the mixing chamber 31 and the drainage port 302 respectively, and intersects with the axis of the drainage port 302. The driving auger 37 is connected to the mixing and stirring motor 36 through a transmission shaft. There are at least three stirring augers 38, which are located in the mixing chamber 31 and are evenly distributed along the axis of the mixing chamber 31. At the same time, each stirring auger 38 is perpendicular to and intersects with the axis of the mixing chamber 31, and the axes of adjacent two stirring augers 38 form a 90° angle. At the same time, each stirring auger 38 is connected to the mixing and stirring motor 36 through a transmission shaft. The feeding and mixing motor 35 and the mixing and stirring motor 36 are both located outside the mixing chamber 31 and are connected to the outer side surface of the mixing chamber 31. The control circuit 30 is connected to the outer side surface of the mixing chamber 31, and is electrically connected to the feeding and mixing motor 35, the mixing and stirring motor 36, and the control valve 39 respectively.

[0037] Among them, a flow sensor 7 and a pressure sensor 8 are respectively arranged at the grouting injection port 32, the drainage port 302, inside the paste drainage pipe 33 and the powder drainage pipe 34, and both the flow sensor 7 and the pressure sensor 8 are electrically connected to the control circuit 30. The diameter of the stirring auger 38 gradually increases from the front to the back along the axis of the mixing chamber 31, and the diameter of the frontmost stirring auger 38 is 80% of the inner diameter of the mixing chamber 31. The drainage port 302 and the powder drainage pipe 34 are interconnected through a throttle valve 10, and the throttle valve 10 is electrically connected to the control circuit 30.

[0038] It should be noted that an auxiliary filling mechanism 9 is additionally arranged outside the end mixer 103. The auxiliary filling mechanism 9 includes a walking chassis 91, a lifting drive mechanism 92, a turntable mechanism 94, a swinging mechanism 95, and a bracket 93. The upper end surface of the walking chassis 91 is vertically connected to the lifting drive mechanism 92. At the same time, the upper end surface of the lifting drive mechanism 92 is connected to the turntable mechanism 94 and is coaxially distributed. The upper end surface of the turntable mechanism 94 is connected to the swinging mechanism 95 and is hinged to the bracket 93 through the swinging mechanism 95. The bracket 93 is a frame structure with a "U"-shaped cross-section groove. The axis of the bracket 93 intersects with the axis of the lifting drive mechanism 92 and can be adjusted and swung within a range of 0° - 135° in the vertical direction through the swinging mechanism 95. The bracket 93 covers the outside of the mixing chamber 31 of the end mixer 103, and the axis of the mixing chamber 31 is parallel to the axis of the bracket 93. The lifting drive mechanism 92, the turntable mechanism 94, and the swinging mechanism 95 are all electrically connected to the control circuit 30.

[0039] Further optimized, the lifting drive mechanism 92 is at least two-stage telescopic column structure based on any one of a hydraulic telescopic column, a pneumatic telescopic column, and an electric telescopic rod.

[0040] In this embodiment, at least two vibrators 24 are additionally arranged on the paste material conveying pipeline 21 and the high-pressure powder material conveying pipeline 22 of the material supply pipeline 102 along their axial directions. The vibrators 24 are connected to the positioning seat 23 through elastic bases 25, and the vibrators 24 are respectively electrically connected to the control circuit 30 of the end mixer 103.

[0041] Further optimized, the control circuit 30 is a circuit system based on a programmable controller, and the control circuit is additionally provided with a control interface including but not limited to any one or more of a display, a potentiometer, a button, and a multi-stage switch.

[0042] In this embodiment, an external booster pump set is additionally configured every 10 - 30 meters on the material supply pipeline 102.

[0043] When the present invention performs a filling operation, it simultaneously drives the mixing mechanism, the material supply pipeline, and the end mixer to operate. First, the mixing mechanism is driven. On the one hand, the prepared paste filling material is pressurized and transported to the material supply pipeline; on the other hand, the powder filling material is transported to the material supply pipeline by high-pressure gas drive. Then, the paste filling material and the powder filling material are synchronously transported to the end mixer through the material supply pipeline. Then, the end mixer simultaneously introduces the paste filling material and the powder filling material transported by the material supply pipeline into its mixing cavity. And when the powder filling material enters the mixing cavity, the addition amount of the powder filling material is adjusted by the combined action of the throttle valve and the driving auger, so as to adjust the mixing ratio between the powder filling material and the paste filling material in the mixing cavity. Then, the materials in the mixing cavity are fully stirred and mixed by multiple stirring augers in the mixing cavity to increase the viscosity of the slurry and reduce the water content of the slurry. After that, it is ejected from the grouting injection port for filling operation. In this embodiment, in the S1 step, when constructing and laying the material supply pipeline, an additional external booster pump group is configured every 10 - 30 meters of the material supply pipeline.

[0044] In order to better illustrate and explain the technical content recorded in the present invention and facilitate those skilled in the art to fully understand the technical content involved in this application document, the technical solution of this application document will be further explained and illustrated by combining specific construction test research cases:

[0045] The filling material composition includes coal gangue, modified magnesium slag-based cementitious material, fly ash, and water. In order to study the influence of mass concentration on the strength of the filling body and reduce the influence of the modified magnesium slag-based cementitious material itself, fly ash is selected to replace the modified magnesium slag-based cementitious material, so as to control the overall mass concentration of the filling slurry.

[0046] In this study, the mass concentration of the slurry is controlled by adjusting the content of fly ash. First, a filling slurry with a mass concentration of 74% is prepared, and then dry fly ash is gradually added to increase the mass concentration of the filling slurry. The material ratio of the filling slurry with a mass concentration of 74% is as follows (taking the total mass of the slurry as 10000 g as an example): modified magnesium slag cementitious material: 1332 g, coal gangue: 4958 g, fly ash: 191 g, stirring water 2600 g. In addition, the mixing degree of fly ash and the filling slurry is controlled by the number of stratified joint surface layers. The specific preparation scheme is:

[0047]

[0048] The mass concentration of the raw slurry is 74%, and the solid mass proportion is as follows: modified magnesium slag cementitious material 18 wt%, coal gangue 67 wt%, fly ash 15 wt%. The sample preparation scheme is in the size of Taking the filled specimens as an example: For Group A1 (control group), the total mass of materials required for a single specimen is 2778 g. The total mass ratio of materials for a single specimen in the remaining experimental groups is still allocated according to 2778 g, so as to determine the mass of slurry and fly ash during the layered preparation of each group. However, considering the difference in the bulk density of materials between the experimental groups and the control group, the added mass of slurry and fly ash in the top two layers during sample preparation is adjusted proportionally. According to the addition amounts of low-concentration filling slurry and dry fly ash, the proportion of experimental materials in each group was recalculated in this study. Among them, the solid mass ratio of the modified magnesium slag cementitious material decreased from 18.0 wt% (Group A1) to 11.2 wt% (Group A5). In addition, the sample preparation methods for bleeding rate and setting time are the same as the above process. The test records show that the mass of a single sample for testing the bleeding rate in Group A1 is 3545 g, and the mass of a single sample for testing the setting time in Group A1 is 930 g.

[0049] Group A: The mass concentrations are 74%, 76%, 78%, 80% and 82%, and the number of layered joint surfaces is set to 31 layers. Group B: The mass concentration is 78%, and the number of layered joint surfaces is set to 7 layers, 19 layers, 31 layers, 43 layers and 55 layers. The filling slurry and fly ash at the end of the pipeline are superimposed and mixed in a spraying manner, and the mixing degree of the two will affect the mechanical properties of the filling body. Therefore, in this study, the number of layered joint surfaces is used to characterize the mixing degree of fly ash and filling slurry. When testing the mechanical properties of paste filling, if standard specimens are used, it is difficult to distinguish the influence of layered joint surfaces, so the standard specimen preparation is used instead. The curing ages for uniaxial compressive strength testing are set to 1, 3, 7 and 28 d. In addition, the prepared filling slurry and fly ash are added layer by layer into a 2000 ml measuring cylinder according to the design method in Table 1 for bleeding rate testing. At the same time, the sample for testing the setting time of the filling slurry is prepared by the same method as above.

[0050] ① Flow performance of paste-powder dual-pipeline mixed filling slurry

[0051] The flow performance of the filling slurry is an important index to evaluate its filling ability and transportation efficiency, and the mass concentration of the slurry is the key factor affecting its flow performance. The first stage of high-concentration quick-setting filling at the end is to transport the low-mass-concentration filling slurry to the filling area through the pipeline with excellent flow performance, that is, corresponding to preparing the filling slurry with a mass concentration of 74% in the experiment. The test results of the slump of the two-stage paste filling slurry under the influence of different mass concentrations and different numbers of layered layers in this study are shown in Figure 3 as follows.

[0052] Low-concentration filling materials in the pipeline transportation stage: When the mass concentration of the filling slurry is 74%, the slump of the gangue-cemented filling slurry is 142 mm (A1-74%), and the spread is 307 mm (A1-74%). The test results meet the requirements of the fluidity for the mine filling pipeline transportation. In addition, combined with the on-site application situation, this mass concentration exhibits excellent fluidity performance.

[0053] High-concentration filling materials in the filling stage: With the gradual addition of fly ash, the fluidity performance gradually decreases. The requirements for the fluidity performance of the paste filling at the end of the fully mechanized mining face are relatively low, and it can still meet the fluidity performance requirements at the end. As the mass concentration of the slurry increases (from 74% to 82%), the slump of the gangue-cemented filling slurry varies from 142 mm (A1-74%) to 104 mm (A5-72%), and the spread varies from 307 mm (A1-74%) to 69 mm (A5-72%). The change in fluidity performance is significant.

[0054] The number of different layers also has a certain impact on the fluidity performance of the filling slurry. As the number of layers increases, the mixing degree of the filling slurry will become better and better, and the fluidity performance will also be improved accordingly. The particle size distribution of the gangue used in the research ranges from 0 to 13.2 mm, and the gangue is in the shape of an irregular polyhedron with an uneven particle surface, which is likely to generate frictional resistance with the gel system of the filling slurry and is not conducive to the free flow of the slurry. In fact, fly ash can fill the pores in the backfill slurry, reduce the frictional resistance generated during the flow of the slurry, and play a role in promoting the lubrication of the slurry, thereby improving the flow characteristics of the backfill slurry. The improvement of the fluidity of the slurry by fly ash is mainly due to the microsphere effect of the fine particles of fly ash, which increases the viscosity and slipperiness of the slurry. Since the fly ash particles carry negative charges in the solution, and the other ions in the solution are metal cations, they will attract each other when they come into contact on the surface, promoting the more uniform distribution of the slurry.

[0055] When the concentration of the filling slurry is relatively low, the solid particles in the slurry are relatively few, and the interaction between the particles is weak. Therefore, the fluidity of the slurry is better. In this case, the viscosity of the slurry is low, and the yield stress is also small, making the slurry easy to flow in the pipeline. As the concentration of the filling slurry increases, the number of solid particles increases, and the interaction between the particles strengthens, resulting in a gradual increase in the viscosity of the slurry. At this time, the yield stress and viscosity of the slurry increase significantly, increasing the flow resistance in the pipeline. When the concentration of the filling slurry exceeds the critical value, the fluidity of the slurry becomes extremely poor. At this time, the slurry may present the form of a toothpaste-like cemented body and move as a plug flow in the pipeline as a whole. In this state, the yield stress and plastic viscosity of the slurry are extremely large, and an external force needs to be applied to overcome its yield stress to make it flow.

[0056] Combined with the on-site application situation, generally, after the mass concentration of the gangue filling slurry is higher than 80%, the pipeline transportation pressure of the slurry is extremely high and cannot meet the pipeline transportation requirements. Therefore, it is difficult to directly improve the mass concentration of the filling slurry and thus enhance the overall performance of the filling body with the existing technical ideas. The end high-concentration rapid-setting filling method proposed in this study can just well solve the above problems.

[0057] ② Bleeding characteristics of paste-powder double-pipeline mixed filling slurry

[0058] The bleeding of the filling slurry directly affects the normal production of the fully mechanized coal mining face. Higher bleeding conditions will exacerbate the slime phenomenon of the floor, thus severely restricting the mining operation. How to reduce the bleeding rate is the primary problem to be solved in two-stage filling. In fact, the bleeding characteristics of the filling slurry are a complex process, which is affected by various factors, including particle size distribution, ash-sand ratio, mass fraction, and dosage of water reducer, etc. For the bleeding characteristics of the two-stage filling slurry, we only consider the regulation depending on the addition amount of dry fly ash in the end high-concentration rapid-setting filling method. The bleeding process of the filling slurry can usually be divided into multiple stages, such as induction period, acceleration period, constant period, densification period, and consolidation period. During these stages, the formation, development, and closure evolution of bleeding channels accompany the entire bleeding cycle. The test results of the bleeding rates of the two-stage paste filling slurry under the influence of different mass concentrations and different numbers of stratified layers in this study are shown in Figure 4 as follows.

[0059] Low-concentration filling materials in the pipeline transportation stage: When the mass concentration of the filling slurry is 74%, the bleeding rate of the gangue-cemented filling slurry is 6.32% (A1-74%), and the test results are similar to the on-site application situation of strip filling mining. A relatively high bleeding rate has a relatively small impact on strip mining, but the large-scale three-machine matching equipment used in the fully mechanized longwall face mining is greatly affected by the bleeding rate, and this mass concentration is difficult to meet the on-site needs.

[0060] High-concentration filling materials in the filling stage: With the gradual addition of fly ash, the bleeding rate gradually decreases. The requirement for the bleeding rate of the slurry at the end of the paste filling behind the fully mechanized support is less than 3%. However, after the mass concentration is increased to 82%, due to the super strong water absorption capacity of fly ash, the bleeding rate can be reduced to 2.27%. With the increase of the slurry mass concentration (74%-82%), the bleeding rate of the gangue-cemented filling slurry varies from 6.32% (A1-74%) to 2.27% (A5-72%), and the bleeding characteristics are improved significantly.

[0061] The influence of different numbers of stratified layers on the bleeding characteristics of the filling slurry is not significant. The test results show that with the increase of the number of stratified layers, the bleeding rate of the paste filling slurry is always around 5.27%. This is because the ability of dry fly ash to absorb the excess water in the upper and lower layers of the slurry is limited.

[0062] One of the reasons for the reduction of bleeding rate is that fly ash has certain water absorption and significant water absorption expansion, which can consume the water in the slurry, reduce its moisture content, and thus reduce the bleeding rate of the slurry. Secondly, the saturated fly ash can support and suspend the large particle aggregates that precipitate and segregate downward in the slurry, making the particle distribution of the slurry more uniform, and the strength and permeability of the filling body after curing will also be improved accordingly. In addition, the fine particles of fly ash have a microsphere effect, which can improve the bonding force between the slurry particles. When bentonite swells after wetting and contacts the surface of gangue / tailings particles, they will attract each other to form a bound water film. The fly ash particles are connected in a chain structure through cations, reducing the free water in the paste, and thus significantly reducing the bleeding rate of the filling slurry.

[0063] ③ Coagulation characteristics of paste-powder double-pipeline mixed filling slurry

[0064] The setting time is an important index for evaluating the performance of mine filling materials and also a major resistance affecting the mine working procedures and operation progress. Usually, after the filling operation is completed, it is necessary to wait for a long time for the filling body to reach the standard of initial setting and final setting before other mining operations can be carried out nearby. This also shows that the core reason for the difficulty in popularizing the fully-mechanized caving filling technology is affected by the setting time. The standard setting time of coal mine gangue filling materials generally requires an initial setting time of about 4 hours and a final setting time of about 8 hours. However, it should be noted that considering the on-site application situation, the setting time of coal mine gangue filling materials is not absolutely constant and is affected by various factors such as the content of cementitious materials, the type and dosage of accelerators, environmental temperature and humidity, etc. Traditional strip filling is affected by time and space working procedures and does not have strict requirements for the setting time, and usually uses low-concentration filling slurry suitable for long-distance pipeline transportation. Therefore, in actual applications, the setting time of the existing 74% coal gangue filling slurry often exceeds the general requirements. The measurement results of the setting time in this study are shown in Figure 5 as follows.

[0065] Low-concentration filling materials in the pipeline transportation stage: When the mass concentration of the filling slurry is 74%, the setting time of the gangue-cemented filling slurry is 6.8 h for initial setting and 11 h for final setting (A1-74%), and the test results are similar to the on-site application situation of strip filling mining. In the gangue paste filling materials, the cementitious materials react with water to form hydration products, thus endowing the materials with strength. However, the hydration reaction requires a certain amount of time, which results in a long setting time of the filling materials and is difficult to meet the performance requirements of the paste filling materials behind the fully-mechanized caving support.

[0066] High-concentration filling materials in the filling stage: In this study, the method of increasing the mass concentration of the filling slurry by adding dry fly ash was selected to shorten its setting time, that is, the setting characteristics of the layered filling materials after two-stage filling. As the fly ash was gradually added, the setting time of the original filling slurry gradually shortened, showing a negative correlation with the fly ash addition amount. The initial setting time shortened from 6.8 h (A1-74%) to 1.4 h (A5-72%), and the final setting time shortened from 11 h (A1-74%) to 3.5 h (A1-74%). The addition of fly ash can accelerate the hydration reaction process and promote the formation of hydration products, thus shortening the setting time of the filling materials. This is because the active components in fly ash can react with calcium hydroxide in the cementitious material to form more stable calcium silicate hydrate. This reaction process not only consumes calcium hydroxide but also promotes the formation of hydration products, thus accelerating the setting process. Secondly, the particle morphology and particle size distribution of fly ash also affect the early setting time of the gangue paste filling materials. Fly ash particles are fine and uniform, which can fill between the cementitious material particles to form a more compact packing structure. This compact packing structure is conducive to the progress of the hydration reaction because more hydration products can be formed between the particles, thus accelerating the setting process. In addition, fly ash particles can also act as micro-aggregates for the hydration reaction, providing additional reaction areas and further promoting the progress of the hydration reaction. This method can greatly shorten the setting time of the gangue paste filling slurry. Fly ash has a significant impact on the early setting time of the gangue paste filling materials. By reasonably controlling the addition amount of fly ash and taking technical measures, the early strength and setting time of the filling materials can be significantly improved, which is suitable for the time requirements of paste filling behind fully mechanized mining supports.

[0067] In addition, this study also analyzed the influence of the mixing degree of the filling slurry on the setting time of the two-stage paste filling slurry. The more the number of stratified layers, the more uniform the slurry mixing, which has a certain improvement effect on the setting time of the gangue paste filling slurry. The setting time of the stratified filling body formed by the high-concentration and quick-setting filling method at the end is extremely significantly affected by the mass concentration, which is conducive to regulating the requirements of the paste filling process behind fully mechanized mining supports for the performance and cost of the filling materials and avoiding the use of other expensive admixtures.

[0068] ④ Mechanical properties of the paste-powder dual-pipeline mixed filling slurry

[0069] The advancing speed of the paste filling behind fully mechanized mining supports is restricted by the demolding time of the filling body behind, which has higher requirements for the setting time and early strength performance of the filling body. The rapid development of the early strength of the filling body is the core element to promote and improve the overall production efficiency of this process. Therefore, the mechanical properties are crucial for the long-term stability of the filling body and the filling treatment effect. Figure 6 The test results of the mechanical properties of the two-stage paste filling slurry under the influence of different mass concentrations and different numbers of stratified layers are shown.

[0070] Low-concentration filling materials in the pipeline transportation stage: When the mass concentration of the filling slurry is 74%, the early strength of the gangue-cemented filling slurry after 1 day is only 0.02 MPa (A1-74%). The test results are similar to the on-site application of strip filling mining, but it cannot meet the requirements of the paste filling process behind fully mechanized mining supports. In addition, after standard curing, the early strength of the gangue-cemented filling slurry after 3 days only reaches 0.41 MPa (A1-74%). The strength required for the detachable mold to move the support of the filling body generally needs to reach more than 0.2 MPa. The existing paste filling behind fully mechanized mining supports is restricted by the development of the early strength of the filling body, and the phenomenon that one mining and filling cycle exceeds 24 hours often occurs even after adding some admixtures. Therefore, if we want to achieve the advancement speed of one mining and filling cycle in 24 hours for the paste filling behind fully mechanized mining supports, the early strength of the filling body after 1 day must reach more than 0.2 MPa.

[0071] High-concentration filling materials in the filling stage: Higher mass concentration is generally accompanied by a shorter setting time and an increase in early strength. In this study, the method of increasing the mass concentration of the filling slurry by adding dry fly ash is selected to improve its early strength, that is, the strength characteristics of the layered filling materials after two-stage filling. With the gradual addition of fly ash, the setting time of the original filling slurry gradually shortens, and the uniaxial compressive strength is improved. The strength shows a positive correlation with the fly ash addition amount. The uniaxial compressive strength after 1 day increases from 0.02 MPa (A1-74%) to 0.31 MPa (A5-72%), and the uniaxial compressive strength after 3 days increases from 0.41 MPa (A1-74%) to 0.95 MPa (A5-72%). The above-mentioned addition of fly ash has a significant effect on improving the filling slurry.

[0072] The strengthening mechanism of fly ash mainly absorbs the excess water inside the original low-concentration filling slurry, which helps to promote the hydration reaction of the cementitious material, thereby improving the bonding characteristics of the cementitious material to the aggregate. At the same time, along with the microsphere effect of fly ash, filling more primary micro-porous structures in the filling body will also promote the strength development. However, when the curing age reaches 7 days and 28 days, the uniaxial compressive strength of the added fly ash will decrease.

[0073] In the first aspect, when the original low-concentration filling slurry was prepared, it was stirred evenly without layered joint surfaces. The newly added dry material fly ash was added layer by layer step by step, so more joint surfaces would be formed and the integrity was relatively poor, resulting in a decrease in its uniaxial compressive strength at 7 days and 28 days. The study found that as the number of layers of dry fly ash and the original low-concentration filling slurry increased, the uniaxial compressive strength of the filling body also increased. The uniaxial compressive strength at 1 day increased from 0.03 MPa (B1-7) to 0.36 MPa (B5-55), the uniaxial compressive strength at 3 days increased from 0.54 MPa (B1-7) to 1.04 MPa (B5-55), the uniaxial compressive strength at 7 days increased from 1.15 MPa (B1-7) to 2.04 MPa (B5-55), and the uniaxial compressive strength at 28 days increased from 3.13 MPa (B1-7) to 5.15 MPa (B5-55). The more the number of layers, the more evenly the dry fly ash and the original filling slurry are mixed, and the more significant the long-term strengthening effect of the uniaxial compressive strength of the filling body. Especially when comparing the filling body specimens with a curing age of 28 days, the influence of the layered joint surface is more significant. Therefore, when applying the high-concentration and quick-setting filling method at the end, the mixing degree of the high-concentration filling slurry at the end should be controlled. The end mixer in the paste-powder dual-pipeline mixing filling system solves this problem well.

[0074] In the second aspect, the addition of dry fly ash is in the form of an additive. As the proportion of fly ash increases, the mass concentration of the filling slurry will increase. Through inversion calculation, it is found that the proportion of the cementitious material in the same volume of the mixed filling slurry decreases. As the mass concentration of the gangue paste filling slurry continues to increase, the proportion of the cementitious material also decreases accordingly, which has a certain impact on the long-term strength development of the filling body. As we all know, the proportion of the cementitious material is the fundamental determinant of the strength development of the filling body and also the main cost of the filling material. Through inversion calculation of the proportion of the filling material in this study, when the mass concentration increases from 74% to 82%, the proportion of the cementitious material decreases from 18% to 11.2%, and the proportion of fly ash increases from 15.0% to 46.9%. Therefore, when there are different strength requirements for the strong-weak combined filling behind the fully mechanized mining support, the proportion of the cementitious material can be rechecked. The proportion of the original low-concentration filling slurry can be increased, and the actual proportion of the added cementitious material is the result of the inversion calculation with a mass concentration of 82%. The actual usage will be greatly reduced, and a certain amount of production cost can also be saved.

[0075] Compared with the prior art, the present invention makes minor modifications to the existing filling equipment and technology, has good adaptability and versatility. Without increasing the cost of fully-mechanized paste filling materials, by increasing the concentration of the paste filling materials, the setting time of the paste filling materials is significantly shortened, the bleeding of the filling is greatly reduced, the early strength and the roof contact rate are improved, and the difficulty of sealing the filling area is reduced. At the same time, during operation, on the one hand, the usage amounts of materials such as concrete and accelerator in the filling materials can be effectively reduced, thus effectively reducing the construction cost. On the other hand, during operation, the defect that the accelerator and early-strength agent cannot solve the high bleeding of the paste filling materials is solved. Thus, while effectively improving the construction efficiency and construction quality of the filling operation area, the defect that the water discharge amount of the coal mining face increases and the floor is sludged due to a large amount of bleeding of the filling materials in the traditional filling operation, which affects the working environment of the working face, is effectively overcome.

[0076] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A goaf paste-powder solid waste mixed filling method, characterized in that The said hybrid filling method comprises the following steps: S1. System construction: First, according to the geological structure characteristics of the filling area for filling operations, set the paste filling material and powder filling material for filling operations. Then, set up the corresponding dual-pipeline hybrid filling system and complete the construction layout of the dual-pipeline hybrid filling system. At the same time, establish a connection between the dual-pipeline hybrid filling system and the external material supply system; S2. Filling area construction: After completing step S1, add elastic sealing strips to the side surface positions of the hydraulic supports in the roadway to be filled. At the same time, install hydraulic push rods parallel to the horizontal plane for each hydraulic support. Driven by the hydraulic push rods, make adjacent two hydraulic supports move relatively and abut against each other to achieve the sealing and plugging of the top and side walls of the roadway, forming a closed filling area structure; S3. Filling operation: After completing step S2, drive the dual-pipeline hybrid filling system to operate. The mixing mechanism, material supply pipeline, and end mixer operate simultaneously. First, the dual-pipeline hybrid filling system, on the one hand, transports the prepared paste filling material, and then simultaneously pressurizes and transports the prepared paste filling material and powder filling material to the filling area. In the filling area, the dual-pipeline hybrid filling system performs a proportioning and mixing operation on the paste filling material and powder filling material, and obtains a paste material with increased viscosity and reduced water content in the slurry. Finally, use the prepared paste material to perform the filling operation on the filling area.

2. A goaf paste-powder solid waste mixed filling method according to claim 1, characterized in that In the said step S1, the paste filling material is composed of the following components in parts by weight: 5% - 25% of cementitious material; 0% - 50% of fly ash; 20% - 80% of coal gangue, and the balance is water; and during the transportation process of the paste filling material, the paste filling material with a mass concentration of 65% - 72%; the powder filling material includes, but is not limited to, any one or a mixture of powders of fly ash, desulfurized gypsum powder, carbide slag powder, cement, and cementitious material, with a moisture content of less than 1%.

3. A goaf paste-powder solid waste hybrid filling method according to claim 1, characterized in that, In the S3 step, during the paste filling operation, the mass concentration of the mixed filling slurry is 78% - 85%, the operation pressure is 2 - 20 MPa, and the flow rate is 50 - 450 m3 / h; at the same time, the mixed filling slurry completes the filling operation in 3 - 5 layers in the filling operation area. The width of the mixed filling slurry for each layer of filling is 1.5 - 5 m, the thickness is 0.3 - 3.0 m, and the filling speed is 50 - 450 m 3 / h.

4. A gob paste-powder solid waste mixed filling method according to claim 1, characterized in that In the said step S1, the dual-pipeline hybrid filling system includes a mixing mechanism, a material supply pipeline, and an end mixer. Among them, the mixing mechanism is connected to at least one end mixer through the material supply pipeline. When there are two or more end mixers, the end mixers are connected in parallel with each other. The mixing mechanism includes a material mixing station, at least three solid material storage bins, a gas storage tank, a booster pump, an air compressor, and a pressure regulating air pump. Among them, at least two of the solid material storage bins are connected to the material mixing station. The material mixing station is connected to the material supply pipeline through the booster pump. One end of the solid material storage bin not connected to the material mixing station is connected to the gas storage tank through the air compressor, and at the same time, the other end of the solid material storage bin is connected to the material supply pipeline through the pressure regulating air pump. The material supply pipeline includes a paste material transportation pipeline, a high-pressure powder material transportation pipeline, and several positioning seats for connecting the paste material transportation pipeline and the high-pressure powder material transportation pipeline. The positioning seats are evenly distributed along the axis direction of the paste material transportation pipeline.

5. A goaf paste-powder solid waste mixed filling method according to claim 4, characterized in that, The terminal mixer includes a mixing chamber, a grouting injection port, a paste drainage tube, a powder drainage tube, a feeding stirring motor, a mixing stirring motor, a driving auger, a stirring auger, a control valve and a control circuit. The mixing chamber is a cylindrical hollow tubular structure, the front end face of which is connected to the grouting injection port and coaxially distributed, and the rear end face is connected to the paste drainage tube through a flange and coaxially distributed. A drainage port perpendicular to the axis of the mixing chamber is provided on the side wall of the mixing chamber, and is connected to the powder drainage tube through the drainage port, and the paste drainage tube and the powder drainage tube are connected in parallel and distributed parallel to each other. At the same time, a control valve is provided on the rear end faces of the paste drainage tube and the powder drainage tube, and is connected to the material supply pipeline through the control valve. The auger is embedded in the drainage port, and its axis is perpendicular to the mixing chamber and the drainage port axis respectively, and intersects with the drainage port axis. The driving auger is connected to the mixing and stirring motor through a transmission shaft. There are at least three stirring augers, which are located in the mixing chamber and evenly distributed along the axis of the mixing chamber. At the same time, each stirring augers is perpendicular to and intersects with the axis of the mixing chamber, and there is an angle of 90° between the axes of two adjacent stirring augers. At the same time, each stirring augers is connected to the mixing and stirring motor through a transmission shaft. The feeding stirring motor and the mixing stirring motor are both located outside the mixing chamber and connected to the outer side of the mixing chamber. The control circuit is connected to the outer side of the mixing chamber, and is electrically connected to the feeding stirring motor, the mixing stirring motor and the control valve respectively.

6. The paste-powder solid waste mixed filling method for goaf according to claim 5, characterized in that, A flow sensor and a pressure sensor are provided at the grouting injection port, the drainage port, the paste drainage tube and the powder drainage tube, and the flow sensor and the pressure sensor are electrically connected to the control circuit. The diameter of the stirring auger increases step by step from front to back along the axis of the mixing chamber, and the diameter of the stirring auger at the front end is 80% of the inner diameter of the mixing chamber. The drainage port and the powder drainage tube are interconnected through a throttle valve, and the throttle valve is electrically connected to the control circuit.

7. A gob paste-powder solid waste mixed filling method according to claim 4 or 5, characterized in that, An auxiliary filling mechanism is arranged outside the terminal mixer, and the auxiliary filling mechanism comprises a walking chassis, a lifting drive mechanism, a turntable mechanism, a swing mechanism, and a bracket, wherein the upper end surface of the walking chassis is vertically connected to the lifting drive mechanism, and the upper end surface of the lifting drive mechanism is connected to the turntable mechanism and coaxially distributed, the upper end surface of the turntable mechanism is connected to the swing mechanism, and is hinged to the bracket through the swing mechanism, the bracket is a "凵"-shaped groove frame structure in cross section, the axis of the bracket intersects with the axis of the lifting drive mechanism, and is adjusted and swung in the range of 0°-135° in the vertical direction through the swing mechanism, the bracket is covered outside the mixing chamber of the terminal mixer, and the axis of the mixing chamber is distributed parallel to the axis of the bracket, and the lifting drive mechanism, the turntable mechanism, and the swing mechanism are all electrically connected to the control circuit.

8. A goaf paste-powder solid waste mixed filling method according to claim 4, characterized in that, The paste material conveying pipeline and the high-pressure powder material conveying pipeline of the material supply pipeline are each provided with at least two vibrators distributed along the axial direction thereof, and the vibrators are connected to the positioning seat via an elastic base, and the vibrators are electrically connected to the control circuit of the terminal mixer respectively.

9. A goaf paste-powder solid waste mixed filling method according to claim 4, characterized in that, The material supply pipeline is additionally equipped with an external booster pump set every 10-30 meters.

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