A grouting control method for preventing invalid diffusion of slurry in a near goaf

Abstract

The application discloses a kind of near goaf prevention slurry invalid diffusion control method, comprising: step one: according to the position of goaf of mine mining plane figure, according to the relationship between regional management borehole and goaf, the invalid diffusion risk of grouting is classified;Step two: for the borehole with slurry running risk, when the spatial distance S1 of borehole trajectory distance goaf or distance fault plane L, carry out once grouting;Step three: when the spatial distance of borehole trajectory distance goaf is less than S1, carry out n times control grouting;When fault plane is drilled, carry out once control grouting;Step four: when the spatial distance S2 of borehole trajectory distance goaf or pass through fault plane L, carry out once check grouting.The application is based on the position of goaf, according to the spatial distance of borehole design trajectory and goaf and drilling fault case invalid diffusion risk of grouting is classified, realize the scientific control of slurry invalid diffusion.

Description

Technical Field

[0001] This invention relates to the technical field of coal mine water hazard prevention and control, and in particular to a control method for preventing the ineffective diffusion of slurry in near-goaf areas. Background Technology

[0002] Currently, regional management techniques are commonly used to control water hazards in the roof and floor of coal seams.

[0003] Surface area remediation technology is used when conditions are not available before mining or underground. It involves accurately probing water-conducting channels such as faults and collapse columns using multi-branch horizontal directional drilling technology on the surface, and then using high-pressure grouting to modify and reinforce the underlying water-rich aquifer and vertical channels. However, since the shallow upper coal seam and part of the lower coal seam have already been mined out, numerous goaf areas exist. During the process of using area remediation technology to control water hazards in the lower coal seam, the drilling trajectory is often very close to the goaf. The main difficulty in grouting at this time is that, to ensure the remediation effect, fracturing grouting is often used when grouting to modify the aquifer. High-pressure grouting time, exceeding 8 MPa, accounts for more than 40% of the total grouting time. At this point, the surrounding rock stress near the goaf is relatively low, and the grout, under high pressure, can easily fracture the karst fissures in the area near the goaf, spreading into the goaf. Currently, for grouting near goaf areas, the common approach after ineffective grout diffusion is to reduce the grouting flow rate or pressure. Effective grouting control technology for near goaf areas has not yet been established. Traditional grouting control methods only apply to grouting processes within intact rock strata and are primarily used in curtain grouting to prevent excessive ineffective curtain thickness. However, without control during grouting near goaf areas, either excessive ineffective grout diffusion leads to waste of grouting materials, poor economic efficiency, and significant delays, or grouting is stopped to prevent excessive ineffective diffusion, resulting in insufficient aquifer modification and water channel sealing, leading to unsatisfactory water hazard control in the near goaf area.

[0004] Therefore, it is urgent to propose grouting control methods to prevent ineffective diffusion of grout under near-goaf conditions, while ensuring the treatment effect. Grouting parameters should be adjusted for boreholes with ineffective diffusion risks to provide scientific guidance for the treatment of water hazards in the roof and floor of near-goaf areas. Summary of the Invention

[0005] This invention provides a control method for preventing the ineffective diffusion of slurry in near-goaf areas, filling the gap in existing technologies that cannot effectively prevent the ineffective diffusion of slurry.

[0006] To achieve the objective of this invention, the provided technical solution is as follows:

[0007] A control method for preventing ineffective diffusion of grout near a goaf includes: Step 1: Determining the location of the goaf based on the mine excavation plan, and classifying the risk of ineffective grout diffusion based on the relationship between the regional treatment borehole and the goaf; Step 2: For boreholes with the risk of grout leakage, performing grouting once when the borehole trajectory is at a spatial distance S1 from the goaf or at a distance L from the fault plane; Step 3: Performing n control grouting operations when the borehole trajectory is less than S1 from the goaf; performing control grouting once when the borehole encounters a fault plane; Step 4: Performing a check grouting operation when the borehole trajectory is at a spatial distance S2 from the goaf or when it passes through the fault plane L.

[0008] Optionally, in step one, the spatial location of the goaf is delineated based on the mining plan and the results of the old goaf exploration; the risk of ineffective diffusion during the grouting process of this borehole is classified according to the minimum spatial distance between the borehole and the goaf and the fault encountered.

[0009] Optionally, the risk classification specifically includes:

[0010] Spatial distance between borehole trajectory and the boundary of the goaf: The coordinates of the borehole drilling location in space are (a, b, c). The boundary of the goaf from one side of the borehole can be generalized as a line in space. Calculate the spatial distance S from each point on the borehole trajectory to the line, and determine the minimum distance S. min ;

[0011]

[0012] No risk requires only routine grouting; Level 3 risk and above require controlled grouting; Level 2 risk and above also require inspection grouting; and Level 1 risk requires the addition of aggregate during grouting.

[0013] Optionally, in step two, the slurry diffusion radius under intact rock strata conditions is: In the formula, r is the slurry diffusion radius, in meters; k is the permeability of the injected rock layer, in meters. 2 h is the grouting pressure head, m; t is the grouting time, h; n is the porosity of the rock stratum being grouted; β is the ratio of grout viscosity to water viscosity; r0 is the grouting borehole radius, m; S1 is determined to be 2r, and L is 30-40m.

[0014] Optionally, for boreholes with the risk of ineffective diffusion, a conventional grouting should be performed when the borehole trajectory is at a spatial distance S1 from the goaf or a distance L from the fault plane. During the conventional grouting process, cement should be selected as the grouting material, with a grouting specific gravity range of 1.2 to 1.5, and the final grouting pressure should be 2 to 2.5 times the water pressure of the aquifer in the grouting section.

[0015] Cement grout is injected into the borehole via a ground grouting pump. The initial grouting specific gravity is 1.2, and the flow rate is 500 L / min. The grouting specific gravity is gradually increased while the grouting flow rate is decreased until the grouting pressure reaches the final pressure, at which point grouting is stopped. The borehole is then swept to the bottom for a water pressure test. If the permeability is less than 0.01 L / (min·m·m), the grouting is considered complete. If the permeability is greater than 0.01 L / (min·m·m), the conventional grouting process is repeated until the permeability is less than 0.01 L / (min·m·m).

[0016] Optionally, in step three, for boreholes with a risk of ineffective diffusion, when the distance between the borehole trajectory and the goaf is less than S1, n controlled grouting operations are performed; and when the fault plane is encountered, one controlled grouting operation is performed, n = P / 200, where n is the number of grouting segments; P is the length of the borehole design trajectory that is less than S1 from the goaf, in meters; and n is rounded up.

[0017] Optionally, in the controlled grouting, cement is selected as the main grouting material, and aggregate is used as the auxiliary grouting material. The grouting specific gravity ranges from 1.3 to 1.6, and the final grouting pressure is 1 to 1.5 times the water pressure of the aquifer in the grouting section. (Gross with a higher specific gravity has a shorter diffusion distance. Lower grouting pressure results in less fracturing of the rock mass and a shorter grout diffusion distance.)

[0018] Cement grout is injected into the borehole via a ground grouting pump. The initial grouting specific gravity is 1.3 and the flow rate is 500 L / min. The grouting specific gravity is gradually increased while the grouting flow rate is decreased until the grouting pressure reaches the final pressure, at which point grouting is stopped. The borehole is then swept to the bottom for a water pressure test. If the permeability is less than 0.01 L / (min·m·m), the grouting is considered complete. If the permeability is greater than 0.01 L / (min·m·m), the grouting process is repeated until the permeability is less than 0.01 L / (min·m·m).

[0019] Optionally, in step four, for boreholes with a risk of ineffective diffusion, a test grouting is performed when the borehole trajectory is at a spatial distance S2 from the goaf or when it passes through the fault plane L, to test the effect of the previous grouting; where S2 = 1.5S1 and L is 30-40m.

[0020] Optionally, during the grouting inspection process, cement is selected as the grouting material, with a grouting specific gravity range of 1.2 to 1.5, and the final grouting pressure is 1.5 to 2 times the water pressure of the aquifer in the grouting section;

[0021] Cement grout is injected into the borehole via a ground grouting pump. The initial grouting specific gravity is 1.2, and the flow rate is 500 L / min. The grouting specific gravity is gradually increased while the grouting flow rate is decreased until the grouting pressure reaches the final pressure, at which point grouting is stopped. The borehole is then swept to the bottom for a water pressure test. If the permeability is less than 0.01 L / (min·m·m), the grouting is considered complete. If the permeability is greater than 0.01 L / (min·m·m), the conventional grouting process is repeated until the permeability is less than 0.01 L / (min·m·m).

[0022] Beneficial results:

[0023] 1. Based on the location of the goaf, the risk of ineffective grout diffusion is classified according to the spatial distance between the borehole design trajectory and the goaf, as well as the fault encountered during drilling. This provides a scientific solution and principle for the grouting location and grouting process of different boreholes during long-distance directional drilling near the goaf, thereby achieving scientific control of ineffective grout diffusion.

[0024] 2. Controlled grouting is performed at certain locations before the goaf and before the fault plane is encountered to pre-reinforce the grouting section. When closer to the goaf and when the fault plane is encountered, controlled grouting is implemented by adjusting factors such as grouting specific gravity, grouting material, and termination pressure to prevent ineffective grout diffusion. Inspection grouting is performed at certain locations after the goaf and after the fault plane is encountered to verify the effectiveness of the initial grouting. This approach achieves reasonable control over ineffective grout diffusion during grouting near the goaf while ensuring the treatment effect. Attached Figure Description

[0025] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0026] Figure 1 This is a roadmap for grouting control technology to prevent ineffective diffusion of grout in near-goaf areas;

[0027] Figure 2 This is a schematic diagram of the borehole plan near the goaf;

[0028] 1-D1 borehole, 2-goaf, 3-minimum spatial distance between borehole and goaf, 4-spatial distance between borehole and goaf is S1, 5-spatial distance between borehole and goaf is S2, A-point with minimum spatial distance between borehole and goaf, BC-length of borehole section with spatial distance between borehole and goaf not greater than S1, D-point with spatial distance between borehole and goaf S2, 6-boundary of goaf on one side of borehole. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0030] Combination Figure 1 The method for controlling the ineffective diffusion of slurry in the near-goaf area of ​​the present invention includes:

[0031] Step 1: Determine the location of the goaf based on the mine excavation plan, and classify the risk of ineffective grouting diffusion based on the relationship between the regional treatment boreholes and the goaf.

[0032] Step 2: For boreholes with a risk of grout leakage, perform grouting once when the borehole trajectory is at a spatial distance S1 from the goaf or a distance L from the fault plane.

[0033] Step 3: When the distance between the borehole trajectory and the goaf is less than S1, perform n controlled grouting operations; when the borehole encounters a fault plane, perform one controlled grouting operation.

[0034] Step 4: When the borehole trajectory is at a spatial distance S2 from the goaf or when it passes through the fault plane L, perform a check grouting.

[0035] Specifically, in step one, the spatial location of the goaf is delineated based on the mining plan and the results of the exploration of the old goaf; the risk of ineffective diffusion during the grouting process of this borehole is classified according to the minimum spatial distance between the borehole and the goaf and the fault encountered.

[0036] Specifically, risk classification includes:

[0037] Spatial distance between borehole trajectory and the boundary of the goaf: The coordinates of the borehole drilling location in space are (a, b, c). The boundary of the goaf from one side of the borehole can be generalized as a line in space. Calculate the spatial distance S from each point on the borehole trajectory to the line, and determine the minimum distance S. min ;

[0038]

[0039] No risk requires only routine grouting; Level 3 risk and above require controlled grouting; Level 2 risk and above also require inspection grouting; and Level 1 risk requires the addition of aggregate during grouting.

[0040] Specifically, in step two, the grout diffusion radius under intact rock strata conditions is: In the formula, r is the slurry diffusion radius, in meters; k is the permeability of the injected rock layer, in meters.2 h is the grouting pressure head, m; t is the grouting time, h; n is the porosity of the rock stratum being grouted; β is the ratio of grout viscosity to water viscosity; r0 is the grouting borehole radius, m; S1 is generally determined to be 2r, and L is generally determined to be 30-40m.

[0041] Specifically, for boreholes with the risk of ineffective diffusion, a conventional grouting should be performed when the borehole trajectory is at a spatial distance S1 from the goaf or a distance L from the fault plane. During the conventional grouting process, cement should be selected as the grouting material, with a grouting specific gravity range of 1.2 to 1.5, and the final grouting pressure should be 2 to 2.5 times the water pressure of the aquifer in the grouting section.

[0042] Cement grout is injected into the borehole via a ground grouting pump. The initial grouting specific gravity is 1.2, and the flow rate is 500 L / min. The grouting specific gravity is gradually increased while the grouting flow rate is decreased until the grouting pressure reaches the final pressure, at which point grouting is stopped. The borehole is then swept to the bottom for a water pressure test. If the permeability is less than 0.01 L / (min·m·m), the grouting is considered complete. If the permeability is greater than 0.01 L / (min·m·m), the conventional grouting process is repeated until the permeability is less than 0.01 L / (min·m·m).

[0043] Specifically, in step three, for boreholes with the risk of ineffective diffusion, when the distance between the borehole trajectory and the goaf is less than S1, n controlled grouting operations are performed; and when the fault plane is encountered, one controlled grouting operation is performed, n = P / 200, where n is the number of grouting segments; P is the length of the borehole design trajectory that is less than S1 from the goaf, in meters; and n is rounded up.

[0044] Specifically, the grouting process is controlled, with cement selected as the primary grouting material and aggregate as the secondary material. The specific gravity of the grouting material ranges from 1.3 to 1.6, and the final grouting pressure is 1 to 1.5 times the water pressure of the aquifer in the grouting section. (Gross grout with a higher specific gravity has a shorter diffusion distance. Lower grouting pressure results in less fracturing of the rock mass and a shorter grout diffusion distance.)

[0045] Cement grout is injected into the borehole via a ground grouting pump. The initial grouting specific gravity is 1.3 and the flow rate is 500 L / min. The grouting specific gravity is gradually increased while the grouting flow rate is decreased until the grouting pressure reaches the final pressure, at which point grouting is stopped. The borehole is then swept to the bottom for a water pressure test. If the permeability is less than 0.01 L / (min·m·m), the grouting is considered complete. If the permeability is greater than 0.01 L / (min·m·m), the grouting process is repeated until the permeability is less than 0.01 L / (min·m·m).

[0046] If the grouting pressure suddenly drops by more than 2 MPa or suddenly drops to 0 MPa during the controlled grouting process, it indicates that the goaf may have been connected, and ineffective diffusion of the grout has occurred. Add sawdust, fine sand, and other aggregates to the grout to quickly seal the fissures near the goaf and prevent the grout from flowing into the goaf through the fissures. The aggregate-to-cement ratio is 0.2:1. Stop grouting when the final pressure is reached. If the grouting pressure fails to reach the final pressure for an extended period, stop grouting, clean the borehole, and allow it to set. Then repeat step three.

[0047] Specifically, in step four, for boreholes with the risk of ineffective diffusion, a test grouting is performed when the borehole trajectory is at a spatial distance S2 from the goaf or when it passes through the fault plane L, to test the effect of the previous grouting; where S2 = 1.5S1, and L is generally 30 to 40m.

[0048] In the grouting inspection process of this invention, cement is selected as the grouting material, the grouting specific gravity ranges from 1.2 to 1.5, and the final grouting pressure is 1.5 to 2 times the water pressure of the aquifer in the grouting section;

[0049] Cement grout is injected into the borehole via a ground grouting pump. The initial grouting specific gravity is 1.2, and the flow rate is 500 L / min. The grouting specific gravity is gradually increased while the grouting flow rate is decreased until the grouting pressure reaches the final pressure, at which point grouting is stopped. The borehole is then swept to the bottom for a water pressure test. If the permeability is less than 0.01 L / (min·m·m), the grouting is considered complete. If the permeability is greater than 0.01 L / (min·m·m), the conventional grouting process is repeated until the permeability is less than 0.01 L / (min·m·m).

[0050] If the grouting pressure suddenly drops by more than 2 MPa or suddenly drops to 0 MPa during the grouting process, it indicates that the grouting effect in steps two and three is not ideal and has not achieved the purpose of sealing cracks and controlling grouting. In this case, the controlled grouting in step three should be repeated until the grouting end standard is met.

[0051] The present invention will be described in detail below with reference to specific embodiments.

[0052] Example 1:

[0053] A coal mine is mining Permian Shanxi Formation coal seams, primarily seams 3, 4, 5, and 6. After years of mining, seams 3, 4, 5, and most of seam 6 have been exhausted. The area surrounding the currently mining seam 6 has numerous goafs, with well-developed karst and numerous faults. Surface directional drilling technology is being used to treat the thin layer of Taiyuan Formation limestone at the bottom of seam 6 at a certain working face. The D1 borehole is used as an example for illustration.

[0054] Step 1: Determine the location of goaf 2 based on the mine excavation plan, and determine whether the borehole encountered a fault based on the 3D seismic analysis results. The boundary 6 of the goaf from one side of the borehole can be generalized as a line in space. Then, use Formula 2 to calculate the spatial distance S from each point on the borehole trajectory to this line, and determine the minimum distance S. min After calculation, such as Figure 2 As shown, at point A, the minimum spatial distance 3 between borehole 1 (D1) and the boundary 6 of the goaf on one side of the borehole is 27m, and there are no faults encountered on the trajectory of borehole 1 (D1). According to the table below, the risk of ineffective grouting diffusion is determined to be level two. In addition to conventional grouting, controlled grouting and inspection grouting are required, and cement can be selected as the grouting material.

[0055]

[0056] Step 2: Under the condition of intact strata in the thin-layered limestone of the Taiyuan Formation, the grout diffusion radius is determined by formula 2: In the formula, k is the permeability of the injected rock layer (m³). 2 Let h be the grouting pressure head (m); t be the grouting time (h); n be the porosity of the rock stratum being grouted; β be the ratio of grout viscosity to water viscosity; and r0 be the radius of the grouting borehole. The calculated grout diffusion radius r = 30m, therefore S1 = 2r = 60m. Thus, for borehole D1, when the trajectory reaches point B and the borehole is 60m from the goaf, a conventional grouting operation is performed.

[0057] In conventional grouting, cement was selected as the grouting material. Since the water pressure of the target layer was 5–6 MPa, the final grouting pressure was determined to be 14 MPa. A ground-based grouting pump was used to inject cement slurry into the borehole. The initial grouting specific gravity was 1.2, and the flow rate was 500 L / min. When the grouting pressure reached 4 MPa, 480 tons of grout were injected, increasing the specific gravity to 1.3 and decreasing the flow rate to 380 L / min. When the grouting pressure reached 8 MPa, 820 tons of grout were injected, increasing the specific gravity to 1.4 and decreasing the flow rate to 250 L / min. When the grouting pressure reached 12 MPa, 1000 tons of grout were injected, increasing the specific gravity to 1.5 and decreasing the flow rate to 60 L / min. When the grouting pressure reached 14 MPa, grouting was stopped, and 1160 tons of grout were injected. A water pressure test was conducted at the bottom of the borehole, and the calculated permeability was 0.0031 L / (min·m·m). This grouting operation was then completed.

[0058] Step 3: After calculation, the distance between the borehole trajectory at point C and the goaf is 60m. The distance between the borehole trajectory and the goaf between sections BC is less than 60m. The borehole depth of section BC is 563m. Based on formula 3: n=P / 200, n=2.815 is determined, and three controlled grouting operations are performed.

[0059] During the grouting process, cement was selected as the grouting material. Since the water pressure in the target layer was 5–6 MPa, the final grouting pressure was determined to be 8 MPa. A ground-based grouting pump was used to inject cement slurry into the borehole. The initial grouting specific gravity was 1.3, and the flow rate was 500 L / min. When the grouting pressure reached 3 MPa, 220 tons of grout were injected, increasing the specific gravity to 1.4 and reducing the flow rate to 380 L / min. When the grouting pressure reached 6 MPa, 420 tons of grout were injected, increasing the specific gravity to 1.5 and reducing the flow rate to 250 L / min. When the grouting pressure reached 8 MPa, grouting was stopped, with 540 tons injected. This effectively controlled the grouting volume in the near-mined area. A water pressure test was conducted at the bottom of the borehole, and the calculated permeability was 0.0064 L / (min·m·m). This marked the end of the grouting operation.

[0060] Step 4: When the borehole trajectory is 90m away from the goaf, perform a check grouting to verify the effect of the previous grouting.

[0061] During the grouting process, cement was selected as the grouting material. Since the water pressure of the target layer was 5–6 MPa, the final grouting pressure was determined to be 12 MPa. A ground-based grouting pump was used to inject cement slurry into the borehole. The initial grouting specific gravity was 1.2, and the flow rate was 500 L / min. When the grouting pressure reached 4 MPa, 180 tons of grout were injected, increasing the specific gravity to 1.3 and reducing the flow rate to 380 L / min. When the grouting pressure reached 8 MPa, 180 tons of grout were injected, increasing the specific gravity to 1.4 and reducing the flow rate to 250 L / min. When the grouting pressure reached 10 MPa, 275 tons of grout were injected, increasing the specific gravity to 1.5 and reducing the flow rate to 60 L / min. When the grouting pressure reached 12 MPa, grouting was stopped, and 350 tons of grout were injected. A water pressure test was conducted after drilling to the bottom of the hole, and the permeability was calculated to be 0.0009 L / (min·m·m). The test showed that the grouting volume was small and the permeability was also small, indicating that the karst fissures in the near-mining area were fully sealed by controlled grouting, and the treatment effect was good. Grouting was then completed.

[0062] When drilling and grouting in similar near-goaf areas of the same mine, the grouting control method proposed in this invention to prevent ineffective diffusion of grout was not adopted. The drilling section near the goaf was 355m long, 4600t of cement was consumed, and the grouting took nearly 20 days.

[0063] After the remediation project was completed, 24 verification boreholes were drilled downhole to test the remediated strata. Of these, 22 boreholes were dry, and 2 boreholes had a stable single-hole water inflow of less than 2 m³. 3 / h indicates that the grouting control method for preventing ineffective diffusion of grout proposed in this invention not only avoids ineffective diffusion and saves cement usage, but also achieves the effect of treating and transforming the target aquifer.

[0064] The preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0065] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0066] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for controlling the ineffective diffusion of slurry near a goaf, characterized in that, include: Step 1: Determine the spatial location of the goaf based on the mining plan and the results of the old goaf exploration; The risk of ineffective diffusion during the grouting process of this borehole is classified according to the minimum spatial distance between the borehole and the goaf and the fault encountered during drilling. Risk classification specifically includes: Spatial distance between borehole trajectory and the boundary of the goaf: S= The coordinates of the borehole drilling location in space are (a, b, c), and the boundary of the goaf from one side of the borehole is generalized as a line in space. Calculate the spatial distance S from each point on the borehole trajectory to this line, and determine the minimum distance S. min ; No risk requires only routine grouting; Level 3 risk and above require controlled grouting; Level 2 risk and above also require inspection grouting; and Level 1 risk requires the addition of aggregate during grouting. Step Two: For boreholes with a risk of grout leakage, perform a conventional grouting operation when the borehole trajectory is at a spatial distance S1 from the goaf or a distance L from the fault plane; grout diffusion radius under intact rock strata conditions: In the formula, r is the slurry diffusion radius (m); k is the permeability of the injected rock layer (m). 2 h is the grouting pressure head, m; t is the grouting time, h; n is the porosity of the rock stratum being grouted; β is the ratio of grout viscosity to water viscosity; r0 is the grouting borehole radius, m; S1 is determined to be 2r, and L is 30-40m; Step 3: For boreholes with the risk of ineffective diffusion, when the distance between the borehole trajectory and the goaf is less than S1, n controlled grouting operations are performed; and when the fault plane is encountered, one controlled grouting operation is performed, n=P / 200, where n is the number of grouting segments; P is the length of the borehole design trajectory that is less than S1 from the goaf, in meters; n is rounded up. Step 4: For boreholes with the risk of ineffective diffusion, a test grouting should be performed when the borehole trajectory is at a spatial distance S2 from the goaf or at a distance L from the fault plane to check the effect of the previous grouting; where S2 = 1.5S1 and L is 30-40m. For the conventional grouting, cement is selected as the grouting material, with a grouting specific gravity range of 1.2 to 1.

5. The final grouting pressure is 2 to 2.5 times the water pressure of the aquifer in the grouting section. Cement slurry is injected into the borehole through a ground grouting pump. The initial grouting specific gravity is 1.2, and the flow rate is 500 L / min. The grouting specific gravity is gradually increased, and the grouting flow rate is decreased until the grouting pressure reaches the final pressure. At this point, grouting is stopped, and the borehole is swept to the bottom for a water pressure test. If the permeability is less than 0.01 L / (min·m·m), the grouting is completed. If the permeability is greater than 0.01 L / (min·m·m), the conventional grouting process is repeated until the permeability is less than 0.01 L / (min·m·m). The controlled grouting process uses cement as the main grouting material and aggregate as the auxiliary grouting material. The grouting specific gravity ranges from 1.3 to 1.6, and the final grouting pressure is 1 to 1.5 times the water pressure of the aquifer in the grouting section. Cement slurry is injected into the borehole via a ground grouting pump. The initial grouting specific gravity is 1.3, and the flow rate is 500 L / min. The grouting specific gravity is gradually increased, and the grouting flow rate is decreased until the final grouting pressure is reached. At this point, grouting is stopped, and the borehole is swept to the bottom for a water pressure test. If the permeability is less than 0.01 L / (min·m·m), the grouting is considered complete. If the permeability is greater than 0.01 L / (min·m·m), the controlled grouting process is repeated until the permeability is less than 0.01 L / (min·m·m). For the aforementioned grouting inspection, cement is selected as the grouting material, with a grouting specific gravity range of 1.2 to 1.

5. The final grouting pressure is 1.5 to 2 times the water pressure of the aquifer in the grouting section. Cement grout is injected into the borehole via a ground grouting pump. The initial grouting specific gravity is 1.2, and the flow rate is 500 L / min. The grouting specific gravity is gradually increased, and the grouting flow rate is decreased until the grouting pressure reaches the final pressure. At this point, grouting is stopped, and the borehole is swept to the bottom for a water pressure test. If the permeability is less than 0.01 L / (min·m·m), the grouting is considered complete. If the permeability is greater than 0.01 L / (min·m·m), the grouting inspection process is repeated until the permeability is less than 0.01 L / (min·m·m).

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