Method for optimizing grouting parameters of medium and shallow coal mine goaf based on slurry diffusion stage

Abstract

A method for optimizing grouting parameters in shallow to medium-depth coal mine goafs based on the slurry diffusion stage is proposed. The grouting process in shallow to medium-depth coal mine goafs is divided into four stages: initial low-pressure permeation, low-to-medium pressure filling, medium-to-high pressure compaction and permeation, and pressure stabilization and sealing. By dynamically and independently controlling the injection pressure, slurry water-cement ratio, and grouting rate at different stages, the method achieves the goals of clearing main fractures, filling medium and large voids, permeating and compacting micro-fractures, and stabilizing and solidifying to seal the holes. This method effectively improves grouting efficiency and the stability of the filled body, avoiding formation disturbance and insufficient filling. The final simulation results show that the filling distance and density are better than traditional methods, resulting in higher efficiency. The entire process is highly targeted, effectively improving grouting efficiency and the stability of the filled body, avoiding problems such as insufficient filling and formation disturbance caused by single parameters or constant processes. It is particularly suitable for grouting projects in shallow to medium-depth coal mine goafs without key support layers and with low coal reservoir pressure.

Description

Technical Field

[0001] This invention belongs to the field of grouting reinforcement technology in geotechnical engineering, and relates to a method for optimizing grouting parameters in shallow and medium-sized coal mine goaf based on the grout diffusion stage. Background Technology

[0002] The stability control of goaf areas in shallow and medium-depth coal mines is of great significance for mine safety and the prevention of surface subsidence. Grouting and filling is the core technical means for managing goaf areas. Goaf areas in shallow and medium-depth coal mines are usually shallow in burial depth and have small coal seam dip angles. The spatial distribution of caving zones and fracture zones in goaf areas is complex. During the grouting process, the diffusion of grout is affected by multiple factors such as stratum permeability, grout viscosity, and injection pressure, exhibiting significant stage characteristics. Moreover, there are spatial differences between core areas, transition zones, low-concentration zones, and blank areas.

[0003] However, in actual grouting operations, traditional techniques often employ single parameters or constant processes, making it difficult to adapt to the dynamic changes in grout diffusion. Taking the shallow-to-medium-depth goaf of the Upper Permian Longtan Formation as an example, this area lacks a key support layer and has low coal reservoir pressure. Traditional parameter settings easily lead to excessively high pressure in the initial stage, disturbing the strata or blocking channels; insufficient filling in the intermediate stage; and insufficient strength of the rock mass in the later stage. This not only reduces grouting efficiency but may also exacerbate surface subsidence. Existing technologies lack precise analysis of the characteristics of grout diffusion stages, making it impossible to dynamically optimize parameters for different stages and achieve efficient and coordinated filling of goaf areas. Summary of the Invention

[0004] In view of the defects and shortcomings of the existing technology, the purpose of this invention is to provide a method for optimizing grouting parameters in shallow and medium-sized coal mine goaf based on the slurry diffusion stage, which solves the problem that the existing technology lacks accurate analysis of the characteristics of the slurry diffusion stage, resulting in low grouting efficiency and even the possibility of aggravating surface subsidence.

[0005] To achieve the above-mentioned technical effects, the technical solution adopted by the present invention is as follows: A method for optimizing grouting parameters in shallow and medium-depth coal mine goafs based on slurry diffusion stages is disclosed. The grouting process includes a sequentially performed initial low-pressure permeation stage, a low-to-medium pressure filling stage, a medium-to-high pressure compaction and permeation stage, and a pressure-stabilizing and grouting stage. In the initial low-pressure permeation stage, grout with a first injection pressure and a first water-cement ratio is used to fill the main channel space around the grouting hole. In the low-to-medium pressure filling stage, grout with a second injection pressure and a second water-cement ratio is used to fill the medium and large voids in the goaf, with the second injection pressure being greater than the first injection pressure. In the medium-to-high pressure compaction and permeation stage, grout with a third injection pressure and a third water-cement ratio is used to permeate and compact fine cracks, with the third injection pressure being greater than the second injection pressure. In the pressure-stabilizing and grouting stage, a fourth injection pressure is maintained for a set time to ensure slurry solidification and complete hole sealing, with the fourth injection pressure being the maximum allowable injection pressure.

[0006] Preferably, the end condition for the initial low-pressure permeation stage is: the grouting pressure begins to increase; the end condition for the low-pressure to medium-pressure filling stage is: the grouting pressure reaches 50% of the maximum allowable injection pressure; the end condition for the medium-high pressure compaction and permeation stage is: the grouting pressure reaches 80%-90% of the maximum allowable injection pressure; and the end condition for the pressure stabilization and grouting stage is: the maximum allowable injection pressure and the lower limit of the grouting rate are reached, and the grouting is stabilized for 30 minutes before sealing.

[0007] Preferably, in the initial low-pressure infiltration stage, the first injection pressure is 0-20% of the maximum allowable injection pressure, the first water-cement ratio is 0.8-1.0, and the grouting rate is 0.1-0.5 m³ / min.

[0008] Preferably, the duration of the initial low-pressure infiltration stage is determined based on the goaf accumulation density and spatial development, and is usually 3 days or more; the main channel dredging status is judged by monitoring the pump injection pressure feedback, wherein when the pump injection pressure begins to rise steadily and the pressure increase is ≥0.1MPa / h, it is judged that the main channel has been filled.

[0009] Preferably, in the low-pressure to medium-pressure filling stage, the second injection pressure is 30%-50% of the maximum allowable injection pressure, and the second water-cement ratio is 0.6-0.8; the grouting method is intermittent grouting, including: single pressure increase ≤0.05MPa, and pressure stabilization for 30min after pressure increase.

[0010] Preferably, the duration of the low-pressure to medium-pressure filling stage is 24-72 hours; the saturation of the large voids is determined by the decay of the grouting volume per unit time. When the grouting volume injected by a single pressurization of ≤0.05MPa per unit time decays rapidly, it indicates that the large voids are approaching saturation, that is, when the wellhead pressure stabilizes for more than 30 minutes.

[0011] Preferably, in the medium-high pressure compaction and infiltration stage, the third injection pressure is 80%-90% of the design final pressure, and the third water-cement ratio is 0.5-0.6; the grouting method includes multiple step-by-step pressure increases, with each pressure increase followed by a 30-minute pressure stabilization period, and the pressure drop is ≤0.05MPa.

[0012] Preferably, the duration of the medium- and high-pressure compaction and permeation stage is less than 2 days; whether the micro-fractures are saturated is determined by whether the grouting volume decreases rapidly, i.e., whether the wellhead pressure stabilizes for more than 30 minutes.

[0013] Preferably, during the pressure stabilization and grouting stage, the fourth injection pressure is 1200-2000KPa, the grouting time is ≥30min, and the pressure drop is maintained at <5%; an integrated grouting-sealing operation is adopted, and the pore is sealed after the pressure is stabilized by a bypass valve.

[0014] Preferably, the duration of the pressure stabilization and grouting stage is determined according to the solidification characteristics of the grout. When a fast-setting grout is used, the duration of the pressure stabilization and grouting stage is 30-60 minutes, and when a slow-setting grout is used, the duration of the pressure stabilization and grouting stage is 2-4 hours.

[0015] The above technical solution has the following beneficial effects: (1) The present invention provides a method for optimizing grouting parameters in shallow and medium-sized coal mine goafs based on the slurry diffusion stage. This method overcomes the problems of low grouting efficiency and poor stability of the filling body caused by the lack of stage-specific parameter settings and difficulty in adapting to the dynamic changes of slurry diffusion during the grouting process in shallow and medium-sized coal mine goafs under the traditional grouting method. First, by utilizing the stage characteristics of slurry diffusion, the main channel is cleared in the initial low-pressure infiltration stage to lay the foundation for subsequent large-scale diffusion and avoid the risk of high-pressure disturbance or channel blockage in advance. Second, in the low-pressure to medium-pressure filling stage and the medium-high pressure compaction and infiltration stage, the injection pressure, water-cement ratio and other parameters are dynamically adjusted according to the slurry diffusion law to achieve full filling of medium and large voids and fine cracks in the goaf and improve the overall filling effect. Third, in the pressure stabilization and grouting stage, the slurry solidification is ensured by precise pressure maintenance to avoid filling defects caused by insufficient pressure and ensure that the filling body forms an integral stress-bearing structure.

[0016] (2) The present invention provides a method for optimizing grouting parameters in shallow and medium-sized coal mine goaf based on the slurry diffusion stage. The method achieves dynamic parameter optimization based on the division of slurry diffusion stages, which solves the problem that single parameters or constant processes are difficult to adapt to complex goaf environments. By controlling the upper limit of injection pressure and the pressure rise in stages, the method effectively avoids excessive disturbance of loose strata by high pressure and improves operational safety. The method matches the water-cement ratio and grouting rate according to the slurry diffusion characteristics of different stages, balances fluidity and stone strength, and improves the integrity and stability of the filling body. The process operation is closely integrated with the field geological conditions, making it convenient to implement and cost-controllable. It is suitable for shallow and medium-sized coal mine goafs with no key support layer and low coal reservoir pressure, and has significant economic and safety benefits. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a method for optimizing grouting parameters in shallow and medium-sized coal mine goaf based on the slurry diffusion stage, according to the present invention. Figure 2 This is a diagram showing the difference in diffusion distance between conventional grouting and staged stepped pressure grouting in a shallow coal mine goaf based on the grout diffusion stage, according to the present invention. Figure 3 This diagram illustrates the difference in filling density between conventional grouting and staged stepped pressure grouting in a shallow coal mine goaf based on the slurry diffusion stage, according to the present invention.

[0018] In the diagram: 1-Initial low-pressure infiltration stage; 2-Low-medium pressure filling stage; 3-Medium-high pressure compaction and infiltration stage; 4-Pressure stabilization and grouting stage; 5-Grouting time axis; 6-Grouting parameter variation axis; 7-Lower limit of grouting rate; 8-Grouting water-cement ratio; 9-Grouting rate; 10-Grouting pressure; 11-Maximum allowable injection pressure; 12-Grouting diameter diffusion distance at stable injection rate; 13-Grouting diameter diffusion distance at staged stepped pressure grouting; 14-Grouting density at stable injection rate; 15-Grouting density at staged stepped pressure grouting; 16-Grouting location; The specific content of the present invention will be further explained in detail below with reference to comparative examples. Detailed Implementation

[0019] The reagents and instruments used in this invention are all commercially available.

[0020] Example The present invention will be further described below with reference to the embodiments shown in the accompanying drawings: This invention provides a method for optimizing grouting parameters in shallow to medium-depth coal mine goafs based on the slurry diffusion stage, such as... Figure 1 As shown, through Figure 1This invention provides a clear visual representation of the relationship between each grouting stage and related parameters, facilitating understanding and implementation of the grouting process. The grouting process comprises four stages: initial low-pressure permeation stage 1, low-to-medium pressure filling stage 2, medium-to-high pressure compaction and permeation stage 3, and pressure stabilization and grouting stage 4. The specific steps are as follows: (a) Initial Low-Pressure Permeability Stage 1: The initial low-pressure permeability stage begins with the start of grouting in the shallow and medium-depth coal mine goaf, the initial appearance and stabilization of grouting pressure, and ends when the grouting pressure begins to rise. In the initial stage, on-site grouting personnel inject grout at low pressure using a grouting pump, controlling the flow rate. Simultaneously, the initial injection pressure at the wellhead should be controlled at 0-20% of the designed final pressure, typically 0-400 kPa. The initial water-cement ratio of the grout should be adjusted to 0.8-1.0, and the grouting rate should be maintained at a low, uniform injection rate of 0.1-0.5 m³ / min. During this process, the pressure feedback at the wellhead is crucial. Pressure changes are used to determine the filling status of the main channel; when the wellhead pressure begins to rise, it indicates that the main channel is about to be filled. Simultaneously, the diffusion range and filling degree can be determined by monitoring resistivity changes. These are common monitoring methods known to those skilled in the art. The diffusion range and density are identified through density changes. When the pressure shows a stable upward trend, i.e., an increase of ≥0.1MPa / h, it indicates that the main fractures and large voids around the grouting hole have been initially filled by the grout, the channels have been cleared, and the process can proceed to the next stage. This stage requires ensuring sufficient grout penetration to create continuous channels for subsequent large-scale diffusion, while avoiding excessive disturbance of the loose strata by high pressure.

[0021] (b) Low-to-medium pressure filling stage 2: From the start of grouting pressure increase, i.e., when the grout is injected, the wellhead pressure is always >0 MPa, until it reaches 50% of the maximum allowable injection pressure. On-site grouting personnel use a stepped pressurization method, gradually increasing the second injection pressure to 30%-50% of the designed final pressure, typically 600-1000 kPa, with a single pressure increase ≤0.05 MPa. Simultaneously, the second water-cement ratio of the grout is adjusted to 0.6-0.8 to balance grout fluidity and stone strength. This water-cement ratio allows the grout injected in the initial low-pressure permeation stage 1 to be further squeezed into large pores during injection. An intermittent grouting mode is adopted, i.e., after each pressure increase of 50 kPa, the pressure is stabilized for 30 minutes, and the uniform diffusion of the grout under pressure is observed during the stabilization time. During this stage, the grouting volume per unit time needs to be continuously recorded. When the grouting volume injected per unit time with a single pressure increase of ≤50KPa rapidly decreases, it indicates that the medium and large voids in the collapse zone have approached saturation, and the filling effect has reached the expected level. Simultaneously, monitoring data is used to verify whether the grout diffusion radius has reached the design value. This design value is related to the goaf area and the density of the collapse zone and is set according to actual working conditions, providing a basis for transitioning to the next stage. The duration of this stage is affected by the goaf volume; the larger the volume, the longer the duration, typically 24-72 hours.

[0022] (c) Medium- and high-pressure compaction and penetration stage 3: This stage begins when the maximum allowable injection pressure reaches 50% and ends when the injection pressure reaches 80%-90% of the design final pressure. On-site grouting personnel use a high-pressure grouting pump to increase the pressure in multiple steps, stabilizing the pressure every 100 kPa increase at the wellhead. The final pressure is generally set at an upper limit of approximately 2000 kPa. The third injection pressure in this stage is 80%-90% of the design final pressure, typically between 1000-1800 kPa. The third water-cement ratio of the grout is fine-tuned to 0.5-0.6 to increase the solid content and enhance the compaction effect. After each pressure increase, the pressure needs to be stabilized for 30 minutes to ensure a pressure drop ≤ 0.05 MPa, avoiding sudden pressure drops that could affect the grout penetration effect. This stage focuses on driving the grout to penetrate horizontally into the goaf, simultaneously squeezing the grout from the first two stages into fine fractures. The horizontal diffusion distance can be verified by monitoring points (fiber optic cables) or resistivity monitoring set in the roof area. When the grouting volume injected per unit time with a single pressure increase of ≤100KPa rapidly decreases, it indicates that the fine fractures are about to be fully filled by the grout, and the permeability is approaching saturation, at which point this stage can be ended. Strict control of the pressure increase is necessary to prevent high pressure from causing formation instability and safety issues such as bottom edge collapse. This stage typically lasts less than 2 days, depending on the degree of spatial development in the goaf.

[0023] (d) Pressure Stabilization and Grouting Stage 4: The pressure stabilization and grouting stage begins when the injection pressure is 80%-90% of the maximum allowable injection pressure 11 (there is no specific standard or experiment for the maximum allowable injection pressure 11; in actual grouting, excessively high wellhead pressure should be avoided; generally, the grouting pressure is controlled between 0-3 MPa). It ends when the maximum allowable injection pressure 11 and the lower limit of the grouting rate 7 are reached and stabilized for a period of time. The specific lower limit of the rate 7 is determined on-site; that is, a smaller grouting rate ensures that the rising pressure balances with the maximum allowable injection pressure 11 and does not exceed it. The existence of the lower limit of the grouting rate 7 is affected by the actual goaf area. For goaf areas with significant collapse and small pore fractures, the lower limit of the grouting rate 7 may not exist; conversely, the lower limit of the grouting rate 7 may be larger. Generally, the lower limit of the grouting rate does not exceed 0.1 m. 3 / h; Generally, excessively high pressure will cause the grout to diffuse along the cracks in the tunnel roof towards areas with lower pressure, resulting in "grout leakage" or "grout cross-contamination" accidents. Therefore, the final pressure is generally controlled at 2000 kPa, which can be adjusted according to the actual situation. At the same time, the water-cement ratio of the grout should be controlled at 0.4-0.5. On-site grouting personnel close the main grouting valve and maintain the injection pressure at the maximum allowable injection pressure through the bypass valve. The grouting time is ≥30 minutes, which can be extended to 2-4 hours depending on the grout's solidification characteristics. During this process, pressure changes are monitored in real time to ensure that the pressure drop is <5% to ensure that the grout fully solidifies under pressure and forms a stable stone body. When the pressure stabilizes for more than 30 minutes, a quick-setting agent can be injected into the grout for sealing. An integrated grouting-sealing operation is adopted. The pressure is maintained through the bypass valve until it stabilizes, i.e., the pressure drop is <5%, and then the hole is sealed to prevent the backflow of unsolidified grout, which could lead to filling defects. When using a fast-setting grout, the duration of stage 4 (pressure stabilization and grouting) is 30-60 minutes; when using a slow-setting grout, the duration of stage 4 is 2-4 hours. During this stage, it is necessary to ensure that the filling material in the goaf forms an integral load-bearing structure to prevent deformation caused by pressure release later, thus providing long-term support for the stability of the goaf.

[0024] To verify the differences between the stepped grouting method and the conventional grouting method, numerical simulation was used. The stable injection simulation employed a water-cement ratio of 0.6 and an injection pressure controlled at 1000 kPa. The staged stepped pressure grouting was simulated according to the method described in the patented scheme. Both simulations lasted 10 days. The simulation results are as follows: Figure 2As shown in the figure, the diffusion distance 12 of the grouting diameter under a stable injection rate is significantly smaller than that of the diffusion distance 13 of the staged stepped pressure grouting diameter. On the last day of the simulation, the diffusion distance using the method described in the patent was 28.46m, while the diffusion distance using the conventional method was 27.2m, a reduction of 1.26m compared to the method described in the patent. In terms of filling density, i.e., the filling effect of micro-cracks, the filling density of the patented scheme at the same distance is significantly higher than that of the conventional filling method. Taking the simulation results at a distance of 12.5m from the grouting position as an example, the filling density 14 of the stable injection rate grouting is 35%, while the filling density 15 of the staged stepped pressure grouting is 47%. The actual simulation results show that the scheme described in the patent has significant advantages over the conventional scheme.

[0025] Any modifications, equivalent substitutions, improvements, or other solutions made within the principles of this invention that do not depart from the technical scope of this invention, and are applied to any field, constitute an infringement of the protection scope of this invention and are included within the protection scope of this invention.

Claims

1. A method for optimizing grouting parameters in shallow to medium-depth coal mine goafs based on the slurry diffusion stage, characterized in that, The grouting process includes the initial low-pressure permeation stage (1), the low-pressure-medium-pressure filling stage (2), the medium-high pressure compaction and permeation stage (3), and the pressure stabilization and grouting stage (4), which are carried out in sequence. In the initial low-pressure infiltration stage (1), grout with a first injection pressure and a first water-cement ratio is used for grouting to fill the main channel space around the grouting hole; In the low-pressure-medium-pressure filling stage (2), grouting is carried out using grout with a second injection pressure and a second water-cement ratio to fill the medium and large voids in the goaf. The second injection pressure is greater than the first injection pressure. In the medium-high pressure compaction and penetration stage (3), grout with a third injection pressure and a third water-cement ratio is used for grouting to penetrate and compact the fine cracks. The third injection pressure is greater than the second injection pressure. During the pressure stabilization and grouting stage (4), the fourth injection pressure is maintained for a set time to ensure that the grout solidifies and the hole is sealed. The fourth injection pressure is the maximum allowable injection pressure (11).

2. The method for optimizing grouting parameters in shallow and medium-depth coal mine goafs based on the slurry diffusion stage according to claim 1, characterized in that, The termination condition of the initial low-pressure permeation stage (1) is: the grouting pressure (10) begins to increase; The termination condition for the low-pressure-medium-pressure filling stage (2) is: the grouting pressure (10) reaches 50% of the maximum allowable injection pressure (11); The termination condition of the medium-high pressure compaction and penetration stage (3) is: the grouting pressure (10) reaches 80%-90% of the maximum allowable injection pressure (11); The termination condition of the pressure stabilization and grouting stage (4) is: reaching the maximum allowable injection pressure (11) and the lower limit of the grouting rate (7), stabilizing for 30 minutes, and then performing the sealing operation.

3. The method for optimizing grouting parameters in shallow and medium-depth coal mine goafs based on the slurry diffusion stage according to claim 2, characterized in that, In the initial low-pressure infiltration stage (1), the first injection pressure is 0-20% of the maximum allowable injection pressure (11), the first water-cement ratio is 0.8-1.0, and the grouting rate (9) is 0.1-0.5 m³ / min.

4. The method for optimizing grouting parameters in shallow and medium-depth coal mine goafs based on the slurry diffusion stage according to claim 3, characterized in that, The duration of the initial low-pressure permeation stage (1) is determined according to the density of the goaf and the degree of spatial development, and is usually 3 days or more. The main channel is cleared by monitoring the pump injection pressure feedback. When the pump injection pressure starts to rise steadily and the pressure increase is ≥0.1MPa / h, it is determined that the main channel has been filled.

5. The method for optimizing grouting parameters in shallow and medium-depth coal mine goafs based on the slurry diffusion stage according to claim 2, characterized in that, In the low-pressure-medium-pressure filling stage (2), the second injection pressure is 30%-50% of the maximum allowable injection pressure (11), and the second water-cement ratio is 0.6-0.8; the grouting method is intermittent grouting, including: single pressure increase ≤0.05MPa, and pressure stabilization for 30min after pressure increase.

6. The method for optimizing grouting parameters in shallow and medium-depth coal mine goafs based on the slurry diffusion stage according to claim 5, characterized in that, The duration of the low-pressure-medium-pressure filling stage (2) is 24-72h; the large voids are filled to saturation by the decay of the grouting volume per unit time. When the grouting volume injected by a single pressurization of ≤0.05MPa per unit time decays rapidly, it indicates that the large voids are saturated, that is, when the wellhead pressure stabilizes for more than 30 minutes.

7. The method for optimizing grouting parameters in shallow and medium-depth coal mine goafs based on the slurry diffusion stage according to claim 2, characterized in that, In the medium-high pressure compaction and infiltration stage (3), the third injection pressure is 80%-90% of the design final pressure, and the third water-cement ratio is 0.5-0.6; the grouting method includes multiple step-by-step pressure increases, with each pressure increase followed by a 30-minute pressure stabilization period, and the pressure drop is ≤0.05MPa.

8. The method for optimizing grouting parameters in shallow and medium-depth coal mine goafs based on the slurry diffusion stage according to claim 7, characterized in that, The duration of the medium-high pressure compaction and permeation stage (3) is less than 2 days; the saturation of the micro-fractures is determined by whether the grouting volume drops rapidly, i.e., whether the wellhead pressure stabilizes for more than 30 minutes.

9. The method for optimizing grouting parameters in shallow and medium-depth coal mine goafs based on the slurry diffusion stage according to claim 2, characterized in that, In the pressure stabilization and grouting stage (4), the fourth injection pressure is 1200-2000KPa, the grouting time is ≥30min, and the pressure drop is maintained at <5%; the grouting-sealing integrated operation is adopted, and the pressure is maintained through the bypass valve until the pressure is stable before sealing.

10. The method for optimizing grouting parameters in shallow and medium-depth coal mine goafs based on the slurry diffusion stage according to claim 9, characterized in that, The duration of the pressure stabilization and grouting stage (4) is determined according to the solidification characteristics of the grout. When a fast-setting grout is used, the duration of the pressure stabilization and grouting stage (4) is 30-60 min. When a slow-setting grout is used, the duration of the pressure stabilization and grouting stage (4) is 2-4 h.

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