A system and method for grouting gob area of working face in inclined coal seam and application thereof

Abstract

This invention discloses a grouting system, method, and application for the goaf in inclined coal seam mining faces, belonging to the field of coal mine safety technology. The system includes a control system, an above-ground grouting system, an underground grouting system, and a spontaneous combustion monitoring system. The control system receives parameters such as the strike angle, dip angle, and porosity and permeability of the floating coal in the goaf of the mining face, and determines the target water-to-solid ratio of the grout accordingly. The above-ground grouting system automatically prepares the grout according to the target ratio. The underground grouting system transports the grout to the goaf for grouting. The spontaneous combustion monitoring system monitors the gas concentration in the goaf and return airway in real time; when the monitored value exceeds a threshold, it triggers the control system to execute supplementary grouting. This invention achieves precise grouting control based on the structural parameters of the goaf, and through automatic grout replenishment via monitoring linkage, significantly improves the targeting, safety, and reliability of fire prevention and extinguishing in the goaf of inclined coal seam mining faces.

Description

Technical Field

[0001] This invention belongs to the field of coal mine safety technology, specifically relating to a grouting fire prevention and extinguishing system, method, and application for goaf areas in inclined coal seam mining faces. It is applicable to goaf fire prevention and extinguishing projects under various inclined coal seams, steeply inclined coal seams, and similar complex spatial structure mining conditions, and is particularly suitable for working faces with heterogeneous goaf structures, uneven coal accumulation, and significant differences in permeability. Background Technology

[0002] Spontaneous combustion of residual coal in goaf areas is one of the major hazards threatening safe production in coal mines. Statistics show that internal fires caused by spontaneous combustion of residual coal in goaf areas account for over 60% of coal mine fire accidents in my country. In inclined coal seam mining faces, due to the large dip angle of the coal seam, the complex spatial structure of the goaf, and the uneven distribution of loose coal accumulation, the air leakage channels are complex and variable, significantly increasing the risk of oxidation and temperature rise of residual coal, making fire prevention and extinguishing far more difficult than in gently inclined coal seams.

[0003] Currently, goaf fire prevention and extinguishing technologies mainly include grouting, nitrogen injection, gel injection, and air leakage sealing. Among these, grouting is widely used in Chinese coal mines due to its readily available materials, low cost, and good sealing effect. Traditional grouting methods often use grout with a fixed water-to-solid ratio, injected into the goaf through buried pipes or boreholes, relying on the grout flow to cover and seal the floating coal. However, due to significant differences in the dip angle, goaf structure, floating coal accumulation state, and permeability characteristics of different subsurface mining faces, fixed-ratio grout often encounters the following problems in practical applications: for steeply dipped, high-permeability goafs, the grout flows too quickly and is difficult to effectively accumulate in the target area; for shallowly dipped, low-permeability goafs, the grout's diffusion capacity is insufficient, tending to accumulate near the end and failing to cover deeper areas. These problems severely restrict the targetedness and reliability of grouting fire prevention and extinguishing effects.

[0004] To address the aforementioned issues, scholars and engineers both domestically and internationally have conducted extensive research. For example, existing patent CN113202541A discloses an intermittent grouting fire prevention and extinguishing system and method for hydraulic supports in fully mechanized mining faces. This system avoids thixotropic grout clogging pipelines by real-time monitoring of grout viscosity and feedback adjustment of stirring speed. It also employs an intermittent, alternating grouting method to allow the grout to accumulate along the dip from the floor to higher elevations within the goaf. However, this technology primarily focuses on improving the grouting process and viscosity control, neglecting the influence of structural parameters such as the working face dip angle, goaf porosity, and permeability on the grout flow characteristics, and failing to establish a linkage mechanism between grouting operations and gas monitoring.

[0005] Existing patent CN105401971A proposes a combined surface and underground regional grouting method for ultra-large goaf areas in shallow-buried, closely spaced coal seam mining. It calculates the grouting volume for areas such as the overlying goaf and the cut-in area of ​​the local coal seam to achieve on-demand grouting. While this patent involves parameters such as top coal thickness, fragmentation coefficient, and porosity, its grouting volume calculation formula primarily serves to control the total grouting volume, rather than dynamically determining the grout mix ratio, and it does not address the matching of grout flow time and solidification time.

[0006] Existing patent CN113283998A discloses a method for preventing spontaneous combustion of coal in the goaf of steeply inclined coal seams. It constructs a prevention and control system including early prediction, spontaneous combustion prevention, spontaneous combustion forecasting, and emergency fire response, and proposes technical measures such as accelerating the working face advance, equalizing ventilation, and sealing leaks. Although this patent involves the division of the "three zones" of the goaf and the analysis of air leakage patterns, grouting is only used as an auxiliary means, and the grout mix ratio is not precisely controlled.

[0007] In summary, existing technologies for grouting in the goaf of inclined coal seam mining faces still have the following shortcomings in fire prevention and extinguishing: (1) The water-to-solid ratio of the grout is mostly a fixed value and is not dynamically adjusted according to parameters such as the working face dip angle, goaf porosity, and permeability; (2) The grouting operation and the goaf gas monitoring system are independent of each other and cannot automatically trigger supplementary grouting based on changes in ignition indicators such as CO concentration; (3) No matching model for grout flow time and solidification time has been established, making it difficult to achieve the ideal effect of "timely solidification after grout flow." Therefore, it is urgent to develop a grouting system and method that can combine the structural parameters of the mining face for precise grouting control and work in conjunction with the spontaneous combustion monitoring system. Summary of the Invention

[0008] To address the problems of poor grout adaptability, uneven grouting effect, and disconnect between grouting operations and goaf spontaneous combustion monitoring in existing inclined coal seam mining faces, this invention patent proposes a grouting system, method, and application for inclined coal seam mining faces.

[0009] This invention aims to improve the targeting, safety, and reliability of fire prevention and extinguishing in the goaf of inclined coal seam mining faces by constructing a collaborative relationship between the control system, the surface grouting system, the underground grouting system, and the goaf spontaneous combustion monitoring system, thereby achieving grouting control based on the structural parameters of the goaf and automatically triggering supplementary grouting operations when necessary.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A grouting system for the goaf of an inclined coal seam mining face includes:

[0012] The control system is configured to acquire the geological structure parameters of the mining face and the physical property parameters of the goaf, and determine the target mix ratio of the grouting slurry based on the parameters.

[0013] The well-ground slurry preparation system, connected to the control system, is configured to automatically prepare slurry according to the target ratio;

[0014] The downhole grouting system, connected to the surface grouting system, is configured to transport and inject the prepared grout into the goaf.

[0015] The spontaneous combustion monitoring system is connected to the control system and is configured to monitor the combustion indicators of the goaf in real time and send an early warning signal to the control system when the monitored value exceeds the threshold.

[0016] The control system is also used to control the surface grouting system and the downhole grouting system to perform supplementary grouting operations after receiving the warning signal.

[0017] Furthermore, in the aforementioned system, the geological structural parameters acquired by the control system include at least the strike angle α and dip angle β of the submerged working face; the physical property parameters include at least the porosity n and permeability k of the floating coal in the goaf.

[0018] Furthermore, the above-mentioned system, the surface slurry preparation system includes: a silo, a screw feeder connected to the control system, a weighing sensor, and a mixer;

[0019] The downhole grouting system includes: a pressure pump and grout delivery pipeline;

[0020] The spontaneous combustion monitoring system includes at least one sensor deployed in the goaf and / or return air corner, the sensor including a CO sensor and a temperature sensor.

[0021] This invention also discloses a grouting method for the goaf of an inclined coal seam mining face based on the above system, comprising the following steps:

[0022] 1) Parameter input steps: Input the geological structure parameters of the mining face and the physical property parameters of the goaf into the control system;

[0023] 2) Proportioning determination step: The control system determines the target water-to-solid ratio of the grouting slurry based on the input parameters and a preset slurry flow and solidification matching model;

[0024] 3) Grouting process: The surface grouting system prepares the grout according to the target water-solid ratio and injects it into the goaf by the underground grouting system;

[0025] 4) Monitoring and grouting steps: The spontaneous ignition monitoring system monitors the ignition index in real time. When the index exceeds the threshold, the control system automatically triggers the grouting operation.

[0026] Furthermore, in the above method, in step 2) of determining the proportion, the control system determines the theoretical flow velocity of the slurry in the goaf based on the input strike angle α and dip angle β; and determines the theoretical flow time of the slurry in the oxidation and heating zone of the goaf based on the input porosity n and permeability k.

[0027] Furthermore, in the above method, step 2) of determining the proportion further includes:

[0028] 21) The control system calculates the actual flow velocity v of the slurry in the goaf based on the preset pressure gradient term ΔP / L, and in combination with the permeability k, porosity n, and the components of gravitational acceleration in the strike angle α and dip angle β directions;

[0029] 22) Calculate the actual flow time t of the slurry based on the width L of the oxidation heating zone and the actual flow velocity v;

[0030] 23) Match the actual flow time t with the pre-stored "water-solid ratio-curing time relationship database" and select the water-solid ratio whose curing time is close to and less than the actual flow time t as the target water-solid ratio.

[0031] Furthermore, in the above method, step 2) of determining the proportion specifically includes:

[0032] S1: Based on geological surveys and roadway inclination measurements, the strike dip angle α and dip angle β of the submerged working face are obtained. It is determined that α≠0 and β≠0. In three-dimensional coordinate space, the component of the gravitational acceleration g at the strike dip angle α is determined as g·secα, and the component at the dip angle β is determined as g·secβ. The ideal resultant velocity is:

[0033] V=g ;

[0034] S2: Determine the fragmentation coefficient of the coal and rock mass in the goaf. :

[0035] ;

[0036] in:

[0037] m1, m2 — fully mechanized mining height and coal release height, in meters;

[0038] ∑h——Direct top thickness, m;

[0039] h—the gap between the caving zone rock mass and the roof, in meters;

[0040] C – Top coal recovery rate, %

[0041] Kpc – Coefficient of breakage and expansion of residual coal in goaf.

[0042] L—Distance for roof control at the working face, in meters;

[0043] L0 — Periodic step distance, m;

[0044] S3: Determine the porosity of the coal and rock mass in the goaf. :

[0045] ;

[0046] Substitute the coal and rock mass fragmentation coefficient in the goaf The formula can be used to obtain the porosity. :

[0047] ;

[0048] S4: Determine the permeability k of the coal and rock mass in the goaf:

[0049] ;

[0050] porosity Substituting the permeability k into the formula for the coal and rock mass in the goaf, we get:

[0051] ;

[0052] S5: Determine the actual flow velocity v of the slurry within the goaf:

[0053] ;

[0054] Where ΔP / L is the pressure gradient term, ΔP is the pressure difference between the two ends of the fluid, and L is the width of the oxidation heating zone.

[0055] S6: Determine the actual flow time t of the slurry:

[0056] ;

[0057] S7: Determine the water-solid ratio R (W / S) of the slurry: Based on the relationship between the water-solid ratio of the slurry and the curing time, determine the water-solid ratio R that is close to but less than the actual flow time.

[0058] Furthermore, in the above method, during the supplementary grouting operation triggered by the spontaneous combustion monitoring system, the supplementary grouting volume is 30% to 50% of the initial grouting volume, and it is preferentially injected into the grouting holes corresponding to the warning area.

[0059] Furthermore, in the above method, the grouting step also includes a dynamic correction process: during the grouting process, the viscosity of the grout, the grouting pressure and the flow rate are monitored in real time, and the target water-to-solid ratio is dynamically fine-tuned based on the monitoring results;

[0060] After the grouting and injection steps, a pipeline flushing step is also included: after the grouting is completed, the pipeline flushing program is started to clean the grouting device and the grouting pipeline to prevent the grout residue from solidifying.

[0061] The present invention also discloses the application of the above-mentioned system or method in the preparation of slurry for fire prevention and extinguishing in coal mine goaf areas.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] (I) Precise proportioning control based on goaf structural parameters

[0064] This invention establishes a matching model between slurry flow time and solidification time by introducing parameters such as the strike angle α and dip angle β of the submerged working face, and the porosity n and permeability k of the floating coal in the goaf, thereby dynamically determining the water-to-solid ratio. Timely solidification after the slurry reaches its destination avoids pipe blockage and slurry loss, significantly improving the adaptability of grouting for fire prevention and extinguishing under complex conditions.

[0065] (ii) Linking grouting with monitoring to achieve a dynamic closed loop for fire prevention and extinguishing.

[0066] This invention deeply integrates a spontaneous combustion monitoring system with a control system, constructing an automatic closed-loop mechanism of "monitoring-early warning-grouting". When indicators such as CO concentration and temperature exceed thresholds, the system automatically triggers supplementary grouting, realizing real-time response and dynamic adjustment of fire prevention and extinguishing measures, and effectively improving the ability to control the risk of spontaneous combustion in goaf areas.

[0067] (III) Matching flow and curing time to solve the problem of uncontrollable grouting effect

[0068] This invention is the first to incorporate the components of gravitational acceleration in the direction of the directional and inclined angles into the calculation of grout flow velocity. Combined with parameters such as the fragmentation coefficient, porosity, and permeability, a formula for calculating the actual flow time of the grout is established. Furthermore, quantitative matching is achieved through a "water-solid ratio-solidification time relationship database," enabling the grouting effect to move from empirical judgment to scientific calculation.

[0069] (iv) High degree of automation, improving operational reliability

[0070] The system adopts a modular design, realizing fully automated control of the entire process from parameter input, slurry preparation, grouting implementation to monitoring and replenishment. The viscosity is monitored and dynamically corrected in real time during the slurry preparation process, and the pressure and flow rate are monitored in real time during the grouting process. After grouting, pipeline flushing is automatically performed, greatly reducing reliance on manual labor and improving the reliability of system operation.

[0071] (v) It has a wide range of applications and high promotion value.

[0072] This invention is not only applicable to inclined coal seam mining faces, but its technical concept can also be extended to fire prevention and extinguishing projects in steeply inclined coal seams, large-angle coal seams, and goaf areas with complex spatial structures, and has good versatility and application value.

[0073] In summary, this invention, through technological innovations such as parameterized proportioning, monitoring linkage, and flow-solidification time matching, effectively solves the problems of poor slurry adaptability, uneven grouting effect, and disconnection between monitoring and grouting in existing technologies, and significantly improves the targeting, safety, and reliability of fire prevention and extinguishing in the goaf of inclined coal seam mining faces. Attached Figure Description

[0074] Figure 1 This is a schematic diagram of the system of the present invention;

[0075] Figure 2 This is a flowchart of the grouting method of the present invention. Detailed Implementation

[0076] like Figure 1 As shown, this invention patent provides a grouting system for the goaf of an inclined coal seam mining face, including a control system, an above-ground grouting system, an underground grouting system, and a goaf spontaneous combustion monitoring system.

[0077] Specifically, this includes:

[0078] Control System: The control system is an intrinsically safe programmable logic controller (PLC) for mining, specifically a Siemens S7-1200 explosion-proof control cabinet. It includes: a CPU processing module; an analog input module; a digital output module; a human-machine interface (HMI); and the PLC has a built-in database: the "water-solid ratio-curing time relationship database" of the formula calculation algorithm program described in claim 4, established through indoor experiments to record the curing time of the slurry corresponding to different water-solid ratios.

[0079] In-ground pulping system: such as Figure 1 As shown, it includes: a silo, a variable frequency screw feeder, a weighing sensor, and a twin-shaft forced mixer. Example parameters: Mixer volume: 2m³; the mixer is a twin-shaft forced mixer equipped with a viscometer and level gauge, used to mix grouting materials with water to prepare a homogeneous slurry; mixing speed: 60rpm; viscosity monitoring range: 200~800mPa·s.

[0080] Downhole grouting system: This includes a hydraulically driven pressure pump and grout delivery pipeline. Example parameters: Rated pressure: 6MPa; Working pressure: 1.5~2.5MPa; Maximum flow rate: 15m³ / h; Output flow rate can be adjusted via a frequency converter. The grout delivery pipeline uses DN100 seamless steel pipe, laid along the return airway to the grouting hole in the goaf. Pressure sensors and electromagnetic flow meters are installed on the pipeline.

[0081] Spontaneous Ignition Monitoring System for Goaf: Includes CO sensor and temperature sensor. Deployment locations: 30m, 50m, and 80m in the goaf and at the return air corner. Upload cycle: The sensors are intrinsically safe for mining and are connected to the analog input module of the control system via a mining communication cable, uploading data every 10 seconds; Warning conditions: CO ≥ 24ppm, temperature ≥ 40℃, heating rate ≥ 0.5℃ / h.

[0082] like Figure 2 As shown, the working process of this invention is as follows:

[0083] (a) Parameter acquisition and input

[0084] The strike angle α and dip angle β of the submerged working face were obtained through geological surveys and roadway inclinometers; the porosity n and permeability k of the loose coal in the goaf were obtained through on-site sampling and laboratory testing. The above parameters were input into the human-machine interface of the control system (1) via an explosion-proof keyboard.

[0085] (II) Calculation of water-to-solid ratio

[0086] The PLC of the control system automatically executes the formula described in claim 4 to calculate, based on the input α, β, n, and k, sequentially obtaining the gravitational acceleration component velocity, fragmentation coefficient, porosity, permeability, slurry flow velocity, and flow time. Then, the PLC matches a water-to-solid ratio R that is close to but less than the calculated flow time from a pre-stored "water-to-solid ratio-curing time relationship database." This database was established through indoor experiments and records the curing times of slurries with different water-to-solid ratios.

[0087] (III) Slurry Preparation

[0088] The control system converts the water-to-solid ratio R into a frequency signal for the screw feeder and the opening time of the water inlet solenoid valve. The screw feeder starts, quantitatively extracting inorganic self-expanding grouting material and fly ash from the hopper, which is then fed into the mixer after verification by a weighing sensor. Simultaneously, the water inlet solenoid valve opens, adding water quantitatively according to the water-to-solid ratio R. The mixer stirs at 60 rpm for 5 minutes to prepare a homogeneous slurry. During stirring, a viscometer monitors the slurry viscosity in real time. If the viscosity exceeds the set range (200~800 mPa·s), the control system fine-tunes the water addition or feed rate.

[0089] (iv) Grouting implementation

[0090] After mixing, the control system opens the grout release valve, allowing the grout to flow by gravity into the storage tank of the pressure pump. The pressure pump starts, pressurizing the grout to the set pressure (usually 1.5~2.5MPa), and then transports it to the grouting holes in the goaf through the grout delivery pipeline. During grouting, pressure sensors and flow meters monitor the grouting pressure and flow rate in real time, and the data is fed back to the control system. If the pressure exceeds 3.0MPa, the control system reduces the pressure pump frequency or stops grouting; if the flow rate is below 5m³ / h, it indicates pipeline blockage. Grouting automatically stops once the grout volume reaches the design value (calculated based on the goaf volume).

[0091] (v) Pipeline flushing

[0092] After grouting is completed, the control system closes the grout discharge valve, opens the flushing water valve, and starts the pressure pump to flush the pipeline with clean water. The flushing time should be no less than 5 minutes, until the effluent is clear. After flushing is completed, the flushing water valve is closed and the pressure pump is stopped.

[0093] (vi) Monitoring and grouting

[0094] The goaf spontaneous combustion monitoring system (4) continuously monitors the CO concentration and temperature in the goaf and return air corner. When the CO concentration at any monitoring point exceeds 24 ppm, or the temperature exceeds 40℃, or the temperature rise rate exceeds 0.5℃ / h, the control system (1) determines it as a spontaneous combustion warning and automatically triggers the supplementary grouting procedure. The supplementary grouting adopts the same water-solid ratio as the initial grouting, and the grouting volume is 30%~50% of the initial grouting volume, and priority is given to injecting into the grouting holes corresponding to the warning area. After the supplementary grouting is completed, the pipeline flushing procedure is executed again.

[0095] Through the above process, the present invention achieves precise grouting and dynamic fire prevention and extinguishing control of the goaf area in the inclined coal seam mining face.

[0096] The present invention will be further described below through specific embodiments.

[0097] Example 1:

[0098] 1: Example of grouting for fire prevention and extinguishing in moderately inclined, conventionally permeable goaf areas

[0099] A submerged coal seam working face in a certain mine has a strike angle of 15° and a dip angle of 22°. Goaf parameter testing revealed that the porosity of the loose coal in the goaf is 0.32 and the permeability is 1.8 × 10⁻⁶. -12 m 2 .

[0100] After receiving the strike angle, dip angle, porosity and permeability parameters, the control system determines the water-solid ratio of the grout to be 2.0:1 according to the preset grouting diffusion matching model, and outputs control commands to the surface grouting system.

[0101] The surface grouting system quantitatively adds and mixes grouting materials according to the water-to-solid ratio parameters output by the control system to prepare a grout that meets the grouting requirements. The underground grouting system then transports the grout to the goaf for grouting, forming a covering layer and localized filling within the goaf, thereby reducing the contact between floating coal and air and lowering the oxidation rate.

[0102] The spontaneous combustion monitoring system for goaf areas is deployed in the goaf and return airway areas to monitor carbon monoxide concentration, oxygen concentration, and temperature in real time. When the carbon monoxide concentration in the return airway reaches the preset threshold of 24 ppm, the goaf spontaneous combustion monitoring system sends an early warning signal to the control system, which then controls the surface grouting system and the underground grouting system to perform supplementary grouting operations.

[0103] After supplemental grouting, the carbon monoxide concentration in the return airway decreased and stabilized below 10 ppm, the temperature change in the goaf tended to be stable, and the risk of spontaneous combustion was reduced.

[0104] For any aspects not covered in this embodiment, please refer to the foregoing embodiments. The parameters described above are merely illustrative and do not constitute a limitation on the scope of protection of this invention.

[0105] Appendix: Calculation process

[0106] The strike angle α = 15°, and the dip angle β = 22°. Geological surveys yielded the following results: immediate roof thickness ∑h = 12.5m, gap between the caving zone and roof Δh = 0.3m, fully mechanized mining height m1 = 3.2m, coal release height m2 = 2.8m, roof control distance L = 5.2m, periodic pressure step distance L0 = 18.6m, top coal recovery rate C = 85%, and goaf residual coal fragmentation coefficient Kpc = 1.25. The average coal and rock block size Dm = 0.005m, the oxidation heating zone width L = 45m, and the pressure gradient ΔP / L = 150Pa / m. (The oxidation heating zone width L was determined through field measurement or based on the empirical formula for dividing the goaf into "three zones"; the pressure gradient ΔP / L was calculated based on the pressure difference ΔP at both ends of the goaf (measured by buried pressure sensors) and the oxidation heating zone width L.)

[0107] (I) Calculation process of water-solid ratio

[0108] S1: The result of gravity acceleration

[0109] ;

[0110] S2: Coefficient of fragmentation Kp

[0111] ;

[0112] S3: Porosity n

[0113] ;

[0114] Substitute into the complete formula to verify:

[0115] ;

[0116] S4: Permeability k

[0117] ;

[0118] Compared with the measured permeability of 1.8×10 -12 m 2 The match is basically correct.

[0119] S5: Actual flow velocity v

[0120] ;

[0121] (The viscosity of the slurry μ is taken as 0.001 Pa·s, and the density of the slurry ρ is taken as 1200 kg / m³) 3 )

[0122] S6: Actual flow time t

[0123] ;

[0124] S7: Target water-to-solid ratio R

[0125] Query the pre-stored "water-solid ratio-curing time relationship database":

[0126] Water-to-solid ratio 1.5:1, curing time 45 min

[0127] Water-to-solid ratio 2.0:1, curing time 32 min

[0128] Water-to-solid ratio 2.5:1, curing time 25 min

[0129] The selected curing time of 32 min is close to and less than the actual flow time of 35.7 min, therefore the target water-to-solid ratio is determined to be 2.0:1.

[0130] Example 2:

[0131] Example of directional sealing of high-angle, high-permeability goaf

[0132] A coal seam is being mined from an inclined face in a mine, with a strike angle of 20° and a dip angle of 35°. The porosity of the loose coal in the goaf is 0.38, and the permeability is 3.6 × 10⁻⁶. -12 m 2 The goaf has significant air leakage, posing a risk of spontaneous combustion.

[0133] After receiving the parameters, the control system determines that the permeability of the goaf is high. In order to improve the sealing ability and molding strength of the grout, the water-solid ratio of the grout is set to 1.5:1, and the control command is output to the surface grouting system.

[0134] The surface grouting system quantitatively adds and mixes the grouting material according to the stated water-to-solid ratio to prepare a high-concentration grout. The underground grouting system transports the prepared grout to the goaf for grouting operations, prioritizing directional grouting in high-leakage areas on the return air side. This allows the grout to form a continuous filling in the fissures and voids of the goaf, thereby weakening the seepage channels in the goaf.

[0135] The goaf spontaneous combustion monitoring system monitors the gas and temperature in the goaf in real time. When the oxygen concentration rises from 10.5% to 13.0% and the carbon monoxide concentration continues to rise and reaches 30 ppm, an early warning signal is triggered. Based on the early warning signal, the control system controls the surface grouting system and the underground grouting system to perform supplementary grouting operations, using a grout with a water-to-solid ratio of 1.5:1 to intensify the grouting in the warning area.

[0136] After supplemental grouting, the oxygen concentration decreased and stabilized below 9%, the carbon monoxide concentration decreased and remained stable, the air leakage intensity in the goaf decreased, and the fire prevention and extinguishing effect was significant.

[0137] For any aspects not covered in this embodiment, including specific formula calculations, please refer to the foregoing implementation methods and Embodiment 1. The above parameters are for illustrative purposes only and do not constitute a limitation on the scope of protection of this invention.

[0138] Example 3:

[0139] Example of deep coverts in low-permeability goaf areas with small dip angles

[0140] A coal seam is being mined from an inclined face in a mine, with a strike angle of 8° and a dip angle of 14°. The porosity of the loose coal in the goaf is 0.26, and the permeability is 0.9 × 10⁻⁶. -12 m 2 The overall permeability of the goaf is low, and the slurry tends to accumulate at the near end, making it difficult to diffuse into the deeper parts of the goaf.

[0141] After receiving the parameters, the control system determines the water-to-solid ratio of the grout to be 2.5:1 in order to improve the diffusion capacity and coverage of the grout, and outputs control commands to the surface grouting system.

[0142] The surface grouting system quantitatively adds and mixes the grouting material according to the water-to-solid ratio parameters to prepare a grout with good fluidity. The underground grouting system transports the grout to the goaf for grouting, allowing it to diffuse along the fracture channels in the goaf and form a continuous overburden layer deep within the goaf to reduce the contact between the floating coal and air and inhibit oxidation.

[0143] The goaf spontaneous combustion monitoring system monitors gas concentration and temperature changes in the goaf in real time. When the goaf temperature rises from 32℃ to 40℃ and the carbon monoxide concentration reaches 18ppm, the goaf spontaneous combustion monitoring system sends an early warning signal to the control system. The control system then controls the surface grouting system and the underground grouting system to initiate a supplementary grouting procedure, continuing to use a grout with a water-to-solid ratio of 2.5:1 to supplement the grouting in the heated area.

[0144] After supplemental grouting, the temperature in the goaf decreased and stabilized below 35°C, and the carbon monoxide concentration decreased and remained stable, thus achieving continuous control over the risk of spontaneous combustion in the goaf.

[0145] For any aspects not covered in this embodiment, including specific formula calculations, please refer to the foregoing implementation methods and Embodiment 1.

[0146] Comparative Example 1:

[0147] Fixed water-to-solid ratio grouting (compared to Example 1)

[0148] The geological conditions were exactly the same as in Example 1 (strike angle 15°, dip angle 22°, porosity 0.32, permeability 1.8×10⁻⁶). -12 m 2 However, the traditional fixed water-to-solid ratio grouting method was used, and the ratio was not dynamically adjusted according to the parameters of the goaf.

[0149] (I) Grouting process

[0150] Based on conventional experience, a commonly used water-to-solid ratio of 2.0:1 was directly selected to prepare the grout, which was then injected into the goaf through buried pipes. The actual flow time of the grout was not calculated during the grouting process, nor was the matching relationship between the grout solidification time and the flow time considered.

[0151] (II) Grouting effect

[0152] After grouting was implemented, monitoring by sensors pre-embedded in the goaf revealed that the grout flowed too quickly within the goaf. Actual measurements showed that it took only 28 minutes for the grout to flow from the injection port to the depths of the goaf (45m), while the solidification time for a 2.0:1 grout was 32 minutes. Because the flow time was shorter than the solidification time, the grout flowed out of the target area before fully solidifying, resulting in poor coverage of the deep goaf.

[0153] On the third day after grouting, the CO concentration in the return air corner rose from an initial 15 ppm to 22 ppm; on the fifth day, it reached 28 ppm, exceeding the warning threshold. Although supplementary grouting was performed, the effect was limited because the same water-to-solid ratio was still used, and the CO concentration only briefly dropped to 18 ppm before rising again.

[0154] (III) Comparison with Example 1

[0155] Table 1: Comparison with Example 1

[0156] Comparison items Comparative Example 1 (fixed water-to-solid ratio) Example 1 (Invention) Method for determining water-solid ratio Fixed 2.0:1 The curing time was matched to a flow time of 35.7 min and a curing time of 32 min. Slurry flow time 28 minutes (actual measurement) 35.7 min (calculated value) Slurry curing time 32min 32min Flow-Cure Matching Flow time < curing time (slurry loss) Curing time < flow time (cures after reaching the desired position) CO concentration after grouting 28ppm (rebound) Below 10ppm (stable) goaf coverage effect Insufficient deep coverage Form an effective blockade

[0157] The results show that the present invention, by matching the flow-curing time, ensures that the grout cures in a timely manner after flowing into place, thus significantly improving the grouting effect.

[0158] Comparative Example 2

[0159] Grouting method without monitoring linkage (compared with Example 2)

[0160] The geological conditions were exactly the same as in Example 2 (strike angle 20°, dip angle 35°, porosity 0.38, permeability 3.6×10⁻⁶). -12 m 2 However, the grouting system and the gas monitoring system are independent of each other and no linkage control mechanism has been established.

[0161] (I) Grouting process

[0162] The target water-to-solid ratio was calculated to be 1.4:1 (after correction) according to the method of this invention, and the initial grouting was completed. However, after the grouting was completed, the monitoring system was only used for manual inspection and was not linked with the control system, so it could not automatically trigger supplementary grouting.

[0163] (II) Grouting effect

[0164] Seven days after the initial grouting, the oxygen concentration in the goaf gradually increased from 9.5% to 12.8%, and the CO concentration increased from 12 ppm to 28 ppm, exceeding the warning threshold. However, because the monitoring data was not automatically transmitted to the grouting system, on-site personnel failed to detect the anomaly in time. It wasn't until the tenth day, during a manual inspection, that the CO concentration was found to have reached 35 ppm, at which point the supplementary grouting procedure was manually initiated. By then, the oxidation and temperature rise in the goaf had become quite significant.

[0165] Although the CO concentration decreased after supplementary grouting, it took a long time, and the temperature in the goaf had risen to 42°C, requiring multiple grouting sessions to control it.

[0166] (III) Comparison with Example 2

[0167] Table 2: Comparison with Implementation: 2

[0168] Comparison items Comparative Example 2 (No monitoring linkage) Example 2 (Invention) Monitoring and Grouting Relationship Independent of each other, manual inspection System linkage, automatic triggering Anomaly detection time Day 10 (Manual Inspection) Day 7 (Real-time monitoring) CO concentration when supplementary grouting is triggered 35ppm 30ppm Supplement grouting response time Delayed for 3 days Instant automatic trigger Final control effect Multiple grouting operations are required, with the temperature rising to 42℃. Rapid control, stable temperature

[0169] The results show that the present invention, through the linkage of monitoring and grouting, achieves real-time response and dynamic control of the risk of spontaneous combustion in the goaf, thus avoiding the spread of the fire due to untimely detection.

[0170] In summary, this invention achieves precise grouting fire prevention and extinguishing control in the goaf of inclined coal seam mining faces by constructing a collaborative working architecture of a control system, an above-ground grouting system, an underground grouting system, and a spontaneous combustion monitoring system. Its core technology lies in the following: First, by acquiring key parameters such as the strike angle α and dip angle β of the submerged working face, as well as the porosity n and permeability k of the floating coal in the goaf, the actual flow time t of the slurry in the goaf is determined based on the calculation model described in S1 to S7. Second, the flow time t is matched with a pre-stored "water-solid ratio-solidification time relationship database" to select a target water-solid ratio R that is close to and less than t, ensuring that the slurry solidifies in time after flowing into place, thus avoiding the risk of pipe blockage and preventing slurry loss. Third, parameters such as slurry viscosity, pressure, and flow rate are monitored in real time during the grouting process, and the water-solid ratio is dynamically corrected to ensure grouting quality. Finally, the CO concentration and temperature in the goaf and return air corner are tracked in real time through a spontaneous combustion monitoring system. Once the threshold is exceeded, supplementary grouting is automatically triggered, forming a closed-loop control of "monitoring-early warning-grouting".

[0171] The various embodiments and comparative examples fully verify the technical effects of the present invention: Examples 1-3 demonstrate that under goaf conditions with different dip angles and different permeability characteristics, the optimized water-solid ratio determined by flow-solidification time matching achieves ideal grouting coverage effects; Comparative Example 1 proves that if a fixed water-solid ratio is used without time matching, grout loss or pipe blockage will occur, significantly reducing the grouting effect; Comparative Example 2 proves that without monitoring and linkage, delayed fire detection will increase the difficulty of control. The above comparisons further highlight the significant advantages of the present invention in terms of grouting accuracy, response timeliness, and system reliability.

[0172] This invention is not only applicable to inclined coal seam mining faces, but its technical concept can also be extended to fire prevention and extinguishing projects in steeply inclined coal seams, large-angle coal seams, and goaf areas with complex spatial structures, demonstrating good versatility and application value.

[0173] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A grouting system for the goaf of an inclined coal seam mining face, characterized in that, include: The control system is configured to acquire the geological structure parameters of the mining face and the physical property parameters of the goaf, and determine the target mix ratio of the grouting slurry based on the parameters. The well-ground slurry preparation system, connected to the control system, is configured to automatically prepare slurry according to the target ratio; The downhole grouting system, connected to the surface grouting system, is configured to transport and inject the prepared grout into the goaf. The spontaneous combustion monitoring system is connected to the control system and is configured to monitor the combustion indicators of the goaf in real time and send an early warning signal to the control system when the monitored value exceeds the threshold. The control system is also used to control the surface grouting system and the downhole grouting system to perform supplementary grouting operations after receiving the warning signal.

2. The grouting system according to claim 1, characterized in that, The geological structural parameters acquired by the control system include at least the strike angle α and dip angle β of the submerged working face; the physical property parameters include at least the porosity n and permeability k of the floating coal in the goaf.

3. The grouting system according to claim 2, characterized in that, The surface slurry preparation system includes: a silo, a screw feeder connected to the control system, a weighing sensor, and a mixer; The downhole grouting system includes: a pressure pump and grout delivery pipeline; The spontaneous combustion monitoring system includes at least one sensor deployed in the goaf and / or return air corner, the sensor including a CO sensor and a temperature sensor.

4. A grouting method for the goaf of an inclined coal seam mining face based on the system described in any one of claims 1 to 3, characterized in that, Includes the following steps: 1) Parameter input steps: Input the geological structure parameters of the mining face and the physical property parameters of the goaf into the control system; 2) Proportioning determination step: The control system determines the target water-to-solid ratio of the grouting slurry based on the input parameters and a preset slurry flow and solidification matching model; 3) Grouting process: The surface grouting system prepares the grout according to the target water-solid ratio and injects it into the goaf by the underground grouting system; 4) Monitoring and grouting steps: The spontaneous ignition monitoring system monitors the ignition index in real time. When the index exceeds the threshold, the control system automatically triggers the grouting operation.

5. The grouting method according to claim 4, characterized in that, In step 2) of determining the proportion, the control system determines the theoretical flow velocity of the slurry in the goaf based on the input strike angle α and dip angle β; and determines the theoretical flow time of the slurry in the oxidation and heating zone of the goaf based on the input porosity n and permeability k.

6. The grouting method according to claim 5, characterized in that, The step 2) of determining the proportions further includes: 21) The control system calculates the actual flow velocity v of the slurry in the goaf based on the preset pressure gradient term ΔP / L, and in combination with the permeability k, porosity n, and the components of gravitational acceleration in the strike angle α and dip angle β directions; 22) Calculate the actual flow time t of the slurry based on the width L of the oxidation heating zone and the actual flow velocity v; 23) Match the actual flow time t with the pre-stored "water-solid ratio-curing time relationship database" and select the water-solid ratio whose curing time is close to and less than the actual flow time t as the target water-solid ratio.

7. The grouting method according to claim 5, characterized in that, The step 2) of determining the proportions specifically includes: S1: Based on geological surveys and roadway inclination measurements, the strike dip angle α and dip angle β of the submerged working face are obtained. It is determined that α≠0 and β≠0. In three-dimensional coordinate space, the component of the gravitational acceleration g at the strike dip angle α is determined as g·secα, and the component at the dip angle β is determined as g·secβ. The ideal resultant velocity is: V=g ; S2: Determine the fragmentation coefficient of the coal and rock mass in the goaf. : ； in: m1, m2 — fully mechanized mining height and coal release height, in meters; ∑h——Direct top thickness, m; h—the gap between the caving zone rock mass and the roof, in meters; C – Top coal recovery rate, % Kpc—Coefficient of breakage and expansion of residual coal in goaf; L—Distance for roof control at the working face, in meters; L0 — Periodic step distance, m; S3: Determine the porosity of the coal and rock mass in the goaf. : ； Substitute the coal and rock mass fragmentation coefficient in the goaf The formula can be used to obtain the porosity. : ； S4: Determine the permeability k of the coal and rock mass in the goaf: ； porosity Substituting the permeability k into the formula for the coal and rock mass in the goaf, we get: ； S5: Determine the actual flow velocity v of the slurry within the goaf: ； Where ΔP / L is the pressure gradient term, ΔP is the pressure difference between the two ends of the fluid, and L is the width of the oxidation heating zone; S6: Determine the actual flow time t of the slurry: ； S7: Determine the water-solid ratio R of the slurry: Based on the relationship between the water-solid ratio of the slurry and the curing time, determine the water-solid ratio R that is close to but less than the actual flow time.

8. The grouting method according to claim 4, characterized in that, In the supplementary grouting operation triggered by the spontaneous combustion monitoring system, the supplementary grouting volume is 30% to 50% of the initial grouting volume, and priority is given to injecting into the grouting holes corresponding to the warning area.

9. The grouting method according to claim 4, characterized in that, The grouting process also includes a dynamic correction process: during the grouting process, the viscosity, grouting pressure and flow rate of the grout are monitored in real time, and the target water-solid ratio is dynamically fine-tuned based on the monitoring results; After the grouting and injection steps, a pipeline flushing step is also included: after the grouting is completed, the pipeline flushing program is started to clean the grouting device and the grouting pipeline to prevent the grout residue from solidifying.

10. The grouting system for the goaf of an inclined coal seam mining face according to any one of claims 1 to 3, or the grouting method according to any one of claims 4 to 9, in the preparation of grout for fire prevention and extinguishing in coal mine goafs.

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