Method for grouting reinforcement and accurate grouting amount control of reuse roof of gob-side entry retaining of coal mine

Abstract

The invention relates to a gob-side entry retaining grouting reinforcement technology in the field of mining engineering, provides a method for grouting reinforcement of a reuse roof of a gob-side entry retaining of a coal mine and accurate control of the grouting amount, and aims to realize real-time monitoring and control of the grouting amount in the grouting process. According to the method, pressure monitoring, flow velocity monitoring, low-frequency electromagnetic wave detection, ultrasonic detection and on-site drilling slurry discharge monitoring are combined, the grouting process is detected in real time through multiple monitoring means, and it is ensured that cement slurry fills cracks and does not flow into a goaf. And meanwhile, cement paste with different particle sizes is adopted for grouting step by step according to the size of the crack, and paste leakage is avoided while the filling effect is guaranteed. The method is suitable for grouting operation under complex geological conditions, has the characteristics of high efficiency and accuracy, and remarkably improves the stability and safety in the use process of a roadway.

Description

Technical Field

[0001] The invention relates to the technical field of grouting reinforcement for gob-side lane retaining in mining engineering, and in particular to a method for grouting reinforcement of a reused roof slab for gob-side lane retaining in coal mines and accurately controlling the grouting amount. Background Art

[0002] In mining engineering, the stability of gob-side tunnels is crucial to the safety of the entire mining area. In the early stage of gob-side tunneling, there may be a large roof subsidence. Therefore, in order to ensure the stability of the tunnel, grouting reinforcement modification is usually used to enhance the strength of the roof coal rock mass, high-strength and high-prestressed anchor cables to strengthen the roof structure, and increase the support length of the coal side. However, for grouting reinforcement technology, due to the complexity of underground rock formations, roof subsidence, and the influence of factors such as cement slurry flowing into the goaf due to the development of cracks, not only the effect of grouting is reduced, but also the stability of the tunnel is affected, and it may even cause ground settlement or collapse.

[0003] Existing grouting monitoring technologies include geological radar, distributed optical fiber strain measurement technology and other methods, but these technologies are often limited by geological conditions, equipment accuracy and operational complexity. For example, the monitoring depth and accuracy of geological radar may be limited by geological conditions, and distributed optical fiber strain measurement technology may have problems such as cumbersome installation, interference from human factors and reliance on continuous power supply.

[0004] To solve this problem, the present invention proposes a method for grouting reinforcement of the reused roof of the goaf-retained lane in coal mines and accurately controlling the grouting amount. The core of the method is to propose a comprehensive system combining pressure monitoring, flow velocity monitoring, low-frequency electromagnetic wave detection, ultrasonic detection and on-site drilling and grouting monitoring. Through multiple monitoring means, the flow conditions during the grouting process can be judged in real time, the grouting process can be fully monitored, and a method of staged grouting with cement slurry of different particle sizes can be coordinated to accurately control the grouting amount, ensure the complete filling of the cracks, and avoid the ineffective loss of cement slurry. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for grouting reinforcement and precise control of grouting amount which is easy to use, simple to maintain, zero pollution, high efficiency and strong stability.

[0006] The present invention proposes a method for grouting reinforcement of the reused roof of the gob-retained lane in a coal mine and accurately controlling the grouting amount. This technology can make full use of the underground space without changing the overall structure of the lane, and realize real-time monitoring of the grouting process by combining pressure monitoring, flow rate monitoring, low-frequency electromagnetic wave detection, ultrasonic detection and on-site drilling and grouting monitoring, and achieve accurate control of the grouting amount by combining the grouting method of stages and particle sizes. This method monitors through physical changes during the grouting process, achieving zero pollution to the environment, while minimizing the use loss of monitoring equipment and reducing costs to the greatest extent.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] (1) Before the grouting work begins, install the pressure monitoring equipment at the outlet of the grouting pump to monitor the pressure changes during the grouting process in real time. During the grouting process, when the cement slurry enters the closed cracks, the pressure will gradually rise and stabilize. If the pressure suddenly drops or cannot maintain balance, it proves that slurry leakage has occurred during the grouting process and the grouting material has flowed into the goaf. Install the Doppler ultrasonic flowmeter on the outside of the grouting pipe. The device works based on the Doppler effect. When the ultrasonic wave encounters particles or bubbles in the fluid, the frequency changes, and the change is proportional to the flow rate. Combining pressure data and flow rate data can help determine the fluid distribution during the grouting process and avoid ineffective loss of cement slurry.

[0009] (2) Grouting holes are set at a certain distance in the vertical direction in the middle of the roof and in the inclined direction near the goaf. The diffusion of cement slurry is judged by monitoring the adjacent grouting holes in real time to see whether there is grouting. If there is grouting in the adjacent holes and the grouting volume is higher than the set value, it indicates that the cement slurry is close to the goaf. At this time, grouting should be suspended and restarted after a period of time. This monitoring method is used as an auxiliary detection method for grouting effect and is used in combination with other monitoring equipment to provide more accurate judgment.

[0010] (3) Install the ultrasonic transmitter and receiver in the middle of the roof of the gob-side tunnel so that the ultrasonic wave is transmitted perpendicular to the rock layer to facilitate the reception of the reflected signal. Through the transmission and reception of the ultrasonic wave, it is judged whether the delamination zone in the middle of the tunnel roof is completely filled with cement slurry. Specifically, when the ultrasonic transmission signal enters the crack area, the intensity of the reflected wave can reflect the filling condition of the crack. If the received reflected signal is strong, it means that there are still large pores in the crack that have not been filled with cement slurry and air still exists. If the received reflected signal weakens and tends to be stable, it means that the cement slurry has gradually filled the crack and the pores have decreased.

[0011] (4) Carbon black is mixed into the cement slurry in a certain proportion to make the slurry have good conductivity. Cement slurry is used to spray the right angle of the upper part of the roof near the goaf to form an arc area. The arc-type low-frequency electromagnetic wave detector is coupled with the roof rock layer and the arc-shaped spraying area using a coupling agent. The arc-type low-frequency electromagnetic wave detector is used to transmit and receive electromagnetic wave signals. Grouting is performed on the side of the roof near the goaf, and the penetrating nature of low-frequency electromagnetic waves is used to penetrate the roof structure to achieve real-time detection of the spatial expansion of the slurry. Through the coordinated work of various devices, the system can provide comprehensive monitoring during the grouting process to ensure the effective filling of cement slurry, while preventing cement slurry from flowing into invalid areas such as goafs.

[0012] (5) In the initial grouting stage, in order to initially fill larger cracks and voids, establish the foundation support and gradually increase the pressure, micron-grade cement slurry with a cement content of 400 kg / m 3 -450kg / m 3 , the water-cement ratio is 0.7-0.8, and 1%-2% of alkaline water agent is added to enhance the fluidity of the slurry. The flow rate is controlled at 0.18m / s-0.36m / s so that the slurry can slowly fill the large crack area to ensure initial stability. The pressure should be properly monitored so that it can be adjusted in time to prevent the initial overpressure from causing slurry leakage.

[0013] (6) After the larger cracks are filled, in order to further fill the medium cracks, maintain a stable pressure and improve the filling effect, continue to use micron-grade cement slurry with a cement content of 450kg / m 3 -500kg / m 3 , the water-cement ratio is maintained at 0.6-0.7, and 2%-3% of expansion agent is added to ensure the density of the slurry during the solidification process. The pressure is gradually increased to maintain at about 5MPa and the flow rate is maintained at about 0.36m / s to achieve the filling effect of medium cracks.

[0014] By gradually adjusting the pressure and flow rate, the slurry can penetrate into the cracks.

[0015] (7) After restarting the grouting, due to the signs of slurry leakage during the filling process, the slurry was adjusted in time to adapt to the tiny cracks. The cement slurry was a mixture of nano-grade and micro-grade cement slurry with a cement content of 520 kg / m 3 -570kg / m 3 , water-cement ratio 0.3-0.5, flow rate gradually increased to 0.36m / s, and 5% expansion agent was added to ensure the slurry sealing effect.

[0016] Compared with other grouting monitoring technologies, the present invention has the following characteristics:

[0017] First, the present invention combines multiple monitoring methods to provide comprehensive monitoring through pressure monitoring, flow rate monitoring, low-frequency electromagnetic wave detection, ultrasonic detection and on-site drilling and grouting monitoring to ensure that the grouting process is efficient and accurate.

[0018] Second, the present invention has high sensitivity for real-time monitoring. The pressure detection equipment and the Doppler ultrasonic flowmeter can monitor the pressure changes of cement slurry in the grouting pipe in real time, providing a more direct and real-time monitoring method. At the same time, the invention makes full use of ultrasonic detection technology and low-frequency electromagnetic wave detection technology to accurately capture the filling effect and spatial distribution of cement slurry, thereby improving the efficiency of grouting.

[0019] Third, the present invention has the characteristics of precise control and strong adaptability. Through the selection of cement slurry and grouting control according to different stages and particle sizes, the proportion can be adjusted according to different crack sizes, and the adaptability is stronger. Micron-grade cement slurry is used for large cracks, and a mixture of nano-grade and micron-grade cement slurry is used for small cracks, so as to achieve precise filling.

[0020] Fourth, the present invention has the characteristics of high density and improved support effect. Using cement slurries of different particle sizes can effectively fill cracks, improve the density and structural stability after filling, improve the overall support effect of gob-side tunnels, and extend the service life of tunnels.

[0021] Fifth, the present invention can adapt to grouting operations under different temperatures and geological conditions and minimize environmental pollution. Pressure monitoring, flow rate monitoring, ultrasonic detection and low-frequency electromagnetic wave detection all belong to the physical category. They all use physical principles to achieve the purpose of monitoring and detection, do not involve chemical reactions, and have almost no pollution to the environment in the mine.

[0022] Sixth, the present invention has the characteristics of intelligent control, which can automatically process monitoring data and make decisions in time, such as automatically stopping grouting, which reduces human intervention and improves the intelligent level of operation.

[0023] Seventh, the present invention makes full use of underground space. The method uses underground space for grouting monitoring, which reduces the occupation of the ground and saves more ground resources compared with traditional grouting monitoring technology.

[0024] Eighth, the present invention greatly increases the service life of the equipment. The pressure monitoring equipment, Doppler ultrasonic flow meter, arc-type low-frequency electromagnetic wave detector and ultrasonic transceiver can be disassembled after the grouting operation is completed to achieve the purpose of recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Engineering section diagram

[0026] The parts in the attached figure are marked as: 1 roof rock layer, 2 separation zone, 3 grouting borehole, 4 fissure, 5 goaf, 6 flexible formwork concrete wall, 7 arc-type low-frequency electromagnetic wave detector, 8 ultrasonic transceiver, 9 goaf-side tunneling, 10 coal seam, 11 roof, 12 shotcrete arc zone.

[0027] Figure 2 Linear diagram of pressure and flow rate during grouting stage

[0028] Figure 3 Reflection wave signal change trend diagram

[0029] Figure 4 Grouting operation monitoring flow chart Specific implementation methods

[0031] In order to avoid ineffective loss of cement slurry and further damage to goaf areas, the present invention provides a method for grouting reinforcement of reused roof slabs along goaf-retained lanes in coal mines and precise control of grouting volume, which is further described below in conjunction with the accompanying drawings.

[0032] like Figure 2 As shown in the figure, during the grouting reinforcement process of goaf-retaining tunnels, different pressure and velocity change stages reflect the filling and loss of cement slurry. At the beginning of grouting, the velocity increases with the increase of pressure, indicating that the cement slurry enters the cracks smoothly and the grouting effect is normal. When slurry leakage occurs, the velocity increases with the decrease of pressure, indicating that the cement slurry may have entered the goaf, resulting in an increase in the velocity and affecting the grouting effect. Figure 3 As shown in the figure, the relationship between the filling rate of the crack and the intensity of the reflected wave during the grouting process reflects the change in the intensity of the ultrasonic reflection signal when the cement slurry gradually fills the crack. The vertical axis of the reflected wave intensity is presented in the form of 0.x, representing the relative intensity. This data is not an absolute energy value, but a standardized reflection intensity, which is used to represent the relative change of ultrasonic waves under different filling rate conditions. This numerical range is easy to monitor and analyze, which helps to timely judge the filling status of the cracks and adjust the grouting strategy.

[0033] Before the grouting operation begins, the equipment must first be installed and debugged to ensure the accuracy and stability of the monitoring process. The pressure monitoring device is installed at the outlet of the grouting pump to monitor the pressure changes of the cement slurry during the grouting process in real time. The device is connected to the grouting control system, which can transmit pressure data in a timely manner and automatically alarm when an abnormality is found. The Doppler ultrasonic flowmeter is installed on the outside of the grouting pipeline in an external clamping manner. The flow velocity of the cement slurry in the pipeline is detected by the Doppler effect, ensuring that the flow state of the cement slurry can be accurately measured without affecting the flow of the fluid inside the pipeline. The data of the two are combined to analyze the distribution of the cement slurry in the crack 4 in real time to find possible slurry leakage. The front-end empty lane reuses the working face for a certain distance, and the grouting borehole 3 is drilled in the vertical direction in the middle of the roof 11 and in the inclined direction on the side of the roof 11 close to the goaf 5. These boreholes are used to monitor the diffusion of cement slurry. The borehole slurry discharge monitoring is an important parameter. Combined with the pressure and flow rate monitoring results, it can effectively prevent the cement slurry from flowing into the goaf 5, avoiding material waste and grouting failure. In the start-up grouting stage, micron-grade cement slurry is used with a cement content of 400 kg / m 3 -450kg / m 3 , water-cement ratio 0.7-0.8, flow rate increased from 0.18m / s to 0.36m / s, which is mainly used to fill larger cracks and establish initial support. When the pressure rises and gradually stabilizes, continue to use micron-grade cement slurry with a cement content of 450kg / m 3 -500kg / m 3 , water-cement ratio of 0.6-0.7, flow rate maintained at 0.36m / s, pressure stabilized at 5MPa, further filling medium cracks to ensure that the cement slurry is dense and uniform. Regularly check the grouting borehole 3. If cement slurry is found to be discharged from the adjacent borehole and the discharge volume is greater than 3L, it indicates that the cement slurry has flowed to the vicinity of the goaf 5. At this time, the system will immediately suspend the grouting operation, and confirm the specific location of the cement slurry flow by analyzing the monitoring data, adjust the grouting strategy, and wait for 2-4 hours before restarting the grouting. When restarting the grouting to complete the filling stage, use a mixture of nano- and micro-grade cement slurry with a cement content of 520kg / m 3 -570kg / m 3, water-cement ratio of 0.3-0.5, flow rate controlled at 0.36m / s, pressure gradually increased to 6MPa, fill small cracks, and ensure that all areas are densely sealed. First, cement slurry is injected into the middle delamination area 2 of the tunnel roof 11, and the ultrasonic transmitter and receiver 8 is installed in the middle of the gob-retained roadway roof, so that the ultrasonic wave is emitted perpendicular to the rock formation to facilitate the reception of the reflected signal, and the change in the intensity of the ultrasonic reflected signal is monitored in real time. The filling condition of the cracks is judged by detecting the intensity of the reflected wave. When the reflected signal gradually decreases and reaches stability, the grouting is stopped. Then grouting is performed on the side of the roof 11 close to the goaf 5, and a certain proportion of carbon black is mixed into the cement slurry to increase the conductivity of the slurry. Cement slurry is used to spray the right angle of the upper part of the roof 11 near the goaf 5 into an arc shape to form a shotcrete arc area 12. The arc-type low-frequency electromagnetic wave detector 7 is coupled with the rock layer of the roof 11 and the shotcrete arc area 12 by using a coupling agent. The arc-type low-frequency electromagnetic wave detector 7 is used to detect the spatial expansion of the slurry in real time on the side of the tunnel roof 11 near the goaf 5. When the slurry expands to the vicinity of the edge of the goaf 5, it is coordinated with the borehole monitoring to determine whether there is a risk of cement slurry flowing into the goaf 5, and avoid slurry running into the goaf 5. This process realizes real-time detection of the grouting effect. When the system detects that the cement slurry is well filled and no slurry running occurs through the pressure monitoring equipment, flow meter, low-frequency electromagnetic wave detector, ultrasonic transceiver and borehole monitoring, the grouting operation is completed. All monitoring equipment automatically stops working, and the operator can disassemble the equipment, perform maintenance and prepare for the next operation.

Claims

1. A method for grouting reinforcement of the reused roof of a coal mine gob-side lane and accurately controlling the grouting amount, characterized in that: The method comprises the following steps: (a) The front-end empty lane is reused for a certain distance from the working face, and grouting holes are drilled in the vertical direction in the middle of the roof and in the inclined direction on the side of the roof close to the goaf; (b) Install the pressure monitoring equipment and Doppler ultrasonic flowmeter on the grouting pump and grouting pipeline respectively to monitor the pressure and flow rate of the slurry in real time to ensure that the slurry enters the cracks stably; (c) First, cement grout is injected into the delamination zone in the middle of the tunnel roof, and an ultrasonic transmitter and receiver is installed in the middle of the roof of the gob-side tunnel so that the ultrasonic wave is transmitted perpendicular to the rock layer to facilitate receiving the reflected signal. The intensity change of the ultrasonic reflected signal is monitored in real time. When the reflected signal gradually decreases and reaches stability, the grouting is stopped; (d) Grouting is then performed on the side of the roof near the goaf, and a certain proportion of carbon black is mixed into the cement slurry to increase the conductivity of the slurry; cement slurry is sprayed at a right angle on the upper part of the side of the roof near the goaf to form a grouting arc zone; a coupling agent is used to couple the arc-shaped low-frequency electromagnetic wave detector with the roof rock layer and the grouting arc zone; the characteristics of the arc-shaped low-frequency electromagnetic wave detector are used to detect the spatial expansion of the slurry in the upper part of the roof and the upper part of the goaf in real time on the side of the tunnel roof near the goaf, and the grouting is stopped when the slurry expands to the edge of the goaf to avoid slurry running into the goaf; (e) During the top plate grouting process, observe in real time whether there is grouting discharge from adjacent grouting holes. If grouting discharge occurs, grouting should be stopped to avoid grouting leakage, and grouting should be restarted after a certain period of time.

2. The method for grouting reinforcement of the reused roof slab of the gob-side lane retaining in a coal mine and accurately controlling the grouting amount according to claim 1 is characterized by: The pressure monitoring equipment is used to monitor the pressure changes of the slurry during the grouting process. When the pressure drop exceeds a value greater than 1MPa, the system determines that slurry leakage has occurred, automatically triggers the alarm module and suspends the grouting operation. The grouting operation will be restarted when the pressure recovers to between 1MPa-2MPa. The Doppler ultrasonic flowmeter is used to monitor the flow rate of the slurry. When the flow rate exceeds 0.5m / s, the system determines that slurry leakage may have occurred or the slurry may have flowed into the goaf, triggers the system, suspends grouting and issues an alarm, and resumes the grouting operation after the flow rate recovers to between 0.18m / s-0.36m / s.

3. The method for grouting reinforcement of the reused roof slab of the gob-side lane retaining in a coal mine and accurately controlling the grouting amount according to claim 1 is characterized in that: Grouting holes are set up at intervals of 8m-12m along the direction of the tunnel. The inclination angle of the boreholes on the roof close to the goaf is in the range of 60°-80°. The diffusion of slurry to the goaf is monitored through drilling slurry discharge. When the slurry discharge volume in the adjacent borehole is monitored to exceed 3 liters, the grouting operation is suspended for 2-4 hours and then grouting is resumed to prevent excessive diffusion of slurry and waste of materials.

4. The method for grouting reinforcement of the reused roof slab of the gob-side lane retaining in a coal mine and accurately controlling the grouting amount according to claim 1 is characterized in that: The ultrasonic transceiver is installed in the middle of the roof of the gob-side tunnel to monitor the changes in the intensity of the ultrasonic reflected signal in real time; the ultrasonic transceiver emits 40kHz-60kHz ultrasonic signals and determines the filling condition of the cracks by monitoring the intensity of the reflected wave; when the intensity of the reflected wave is less than 0.2, it indicates that the cracks have been fully filled with slurry; when the intensity of the reflected wave is higher than 0.6, it indicates that there is air in the cracks or the filling is insufficient, and the system needs further grouting.

5. The method for grouting reinforcement of the reused roof of the gob-side lane retaining in a coal mine and accurately controlling the grouting amount according to claim 1 is characterized in that: Carbon black is added to the cement slurry at a ratio of 1%-5%. The arc-shaped low-frequency electromagnetic wave detector is coupled to the roof rock layer and the arc-shaped cement slurry at the right angle of the roof near the goaf after spraying through a coupling agent. After grouting begins, the low-frequency electromagnetic wave detector emits a low-frequency electromagnetic wave in the frequency range of 100kHz-500kHz, and the resolution of the detector is set to 5cm-10cm. A spatial distribution image is generated by point-by-point scanning, so that the diffusion range and filling effect of the cement slurry can be observed in real time during the grouting process.

6. The method for grouting reinforcement of the reused roof of the gob-side lane retaining in a coal mine and accurately controlling the grouting amount according to claim 1 is characterized in that: Micron-grade cement slurry is used in the start-up grouting phase, with a cement content of 400-450 kg / m 3 The water-cement ratio is 0.7-0.8, and 1-2% of water reducer is added to enhance the fluidity of the slurry; after the larger cracks are filled, continue to use micron-grade cement slurry with a cement content of 450-500kg / m 3 , the water-cement ratio is 0.6-0.7, and 2-3% of expansion agent is added to ensure the density of the slurry during the solidification process; after restarting the grouting, a mixture of nano-scale and micro-scale cement slurry is used, and its cement content is 520-570kg / m 3 , the water-cement ratio is 0.3-0.5, and 5% of the expansion agent is added to ensure the slurry sealing effect.

7. The method for grouting reinforcement of the reused roof of the gob-side lane retaining in a coal mine and accurately controlling the grouting amount according to claim 1 is characterized in that: The system is equipped with an automatic control module that can automatically adjust the grouting pressure and flow rate based on the data from the pressure monitoring equipment, ultrasonic flow meter, grouting drilling hole, low-frequency electromagnetic wave detector and ultrasonic transceiver, and automatically stop the grouting operation after the slurry completely fills the cracks, thereby ensuring the slurry filling quality and avoiding material waste.

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