Method for constructing and developing working face to liberate shallow security coal pillar resources

Abstract

The invention discloses a method for constructing and developing a working face to liberate shallow security coal pillar resources, which comprises the following steps of: 1, analyzing mining conditions, and determining a roof water prevention and control thought: determining a water prevention and control thought of grouting transformation; 2, grouting transformation objects and range are determined, wherein the grouting transformation objects are a water-containing sand layer at the bottom of the unconsolidated formation, a wind oxidation zone and the top of a key fault; 3, drilling and grouting construction parameters are determined; 4, engineering construction and dynamic scheme optimization are conducted, specifically, a grouting P-Q-T dynamic curve is drawn, and scheme design is adjusted; and step 5, engineering effect inspection and evaluation. According to the method, comprehensive grouting transformation is conducted on the unconsolidated formation bottom containing, wind oxidation zone and fault structure, the roof aquifer within the mining influence range is transformed into a relative water-resisting layer, meanwhile, a fault water and sand inrush channel is blocked, the stability of roof surrounding rock is improved, three forming conditions of a water and sand source, water pressure and an inrush channel are destroyed, and the mining effect is improved. And dual disaster prevention and control of a source and a channel are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of coal water control, and relates to a method for liberating shallow protective coal pillar resources in a working face with developed structures. Background Technique

[0002] The coal resources in the eastern mining area are gradually exhausted, and the mining and excavation connection in the mining area is tense. The shallow protective coal pillar resources left in the past are rich and the roadway development workload is small. They are valuable coal resources that can be key developed in the future and are also important measures to practice a resource-saving society. However, the amount of coal under water in the eastern mining area is huge. The coal resources of the loose layer waterproof protective coal and rock pillars left in the coal mines in Jiangsu, Shandong, Henan, and Anhui reach up to 5 billion tons, of which only 1.5 billion tons are in the Huainan and Huaibei coal fields in Anhui. Safely liberating the shallow protective coal pillar resources can effectively relieve the tense situation of production replacement in the eastern mining area and create huge social and economic values.

[0003] At present, the main water disaster threat to the shallow protective coal pillar resources is the roof water and sand inrush disaster. The occurrence of the water and sand inrush disaster requires three key conditions: water and sand source, inrush channel, and water pressure. The loose layer grouting transformation is to "drive water and solidify sand" through grouting diffusion, transform the aquifer into a relatively water-resistant layer, and destroy the two key conditions of water and sand source and water pressure to achieve disaster prevention and control from the source. For example, the industrial test of the local roof loose layer transformation in a working face carried out in Wugou Coal Mine in Anhui has successfully liberated 100,000 t of coal pillar resources. It is the first engineering example in China to pre-grout the loose layer on the ground and improve the mining upper limit.

[0004] In the past, the scope of the industrial test of the loose layer grouting transformation was small and the structure was relatively undeveloped, avoiding the structural problems. However, the working face fault structure is widespread and is also the main influencing factor that exacerbates the formation of the inrush channel. In the case of developed structures, the integrity of the roof bedrock is damaged, the height of the caving and fracturing zone increases significantly after mining disturbance, the inrush channel becomes wider, and the safety of the protective coal and rock pillars left according to the conventional method is greatly reduced. At the same time, due to the non-uniformity problem of the loose layer grouting transformation, the risk of water and sand inrush disaster is still relatively high. Practices have shown that water inrush and sand inrush (mud inrush) accidents are mostly related to the development and activation of faults. For example, water inrush and sand inrush (mud inrush) disasters have occurred successively in Zhaogu No. 1 Coal Mine in Henan, Taoyuan Coal Mine in Anhui, Qidong Coal Mine in Anhui, and Xinhu Coal Mine in Anhui, causing major life disasters and economic losses. Summary of the Invention

[0005] The invention provides a method for liberating shallow protective coal pillar resources in a working face with developed structures, aiming to solve the problem of the risk of water and sand inrush in liberating shallow protective coal pillar resources in a thin bedrock working face under the condition of developed structures, eliminate the hidden dangers of the "three elements" of water and sand inrush, and realize the safe mining of the working face.

[0006] The technical solution adopted by the invention is as follows:

[0007] A method for liberating shallow protective coal pillar resources in a tectonically developed working face, comprising the following steps:

[0008] Step 1: Analyze the mining conditions and determine the idea of water control for the roof: For the working face with the risk of water inrush and sand or mud bursting, determine the idea of water control for grouting and reforming the loose layer, the weathered oxidation zone and the fault structure, and leave a sand-proof safety coal and rock pillar;

[0009] Step 2: Determine the object and scope of grouting reform: The objects of grouting reform are the water-bearing sand layer at the bottom of the loose layer, the weathered oxidation zone and the top of the fault with the risk of water inrush and sand bursting; The scope of grouting reform includes the planar scope and the vertical space scope; The planar scope is to determine the upper mining limit according to the calculation formula of the sand-proof safety coal and rock pillar, calculate the mining influence range of the working face roof as the upper boundary of grouting reform, and calculate the position of the waterproof safety coal and rock pillar as the lower boundary of grouting reform; The vertical space scope is from the water-bearing sand layer at the bottom of the loose layer to the normal bedrock, and at the same time includes the top area of the fault with the risk of water inrush and sand bursting;

[0010] Step 3: Determine the drilling and grouting construction parameters: Determine the drilling type, hole spacing, construction sequence and drilling design of the grouting reform object, as well as the grouting construction parameters for different grouting reform objects;

[0011] Step 4: Engineering construction and dynamic optimization of the plan: Carry out engineering construction, count the key information of drilling and grouting, calculate the water permeability before and after grouting, draw the dynamic curve of grouting P-Q-T, and optimize the plan in the case of large changes in the bottom thickness of the loose layer, changes in the fault position, large grouting volume in the grouting section, abnormal suspension of grouting in the grouting section, slurry leakage between adjacent boreholes and underground slurry running, and adjust the drilling and grouting design;

[0012] Step 5: Inspection and evaluation of engineering effects: After the project is completed, use ground direct hole coring verification and underground exploration hole water release verification to evaluate the engineering treatment effect.

[0013] Optionally, the characteristics of the risk of water inrush and sand or mud bursting in the working face with the risk of water inrush and sand or mud bursting in step 1) are as follows: (1) The working face is tectonically developed, with many dip faults, the fault throw is greater than 5m, and there are potential risks of water inrush and sand bursting; (2) The bottom water-bearing layer of the loose layer is widely developed, the total proportion of gravel and fine sand thickness in the bottom water-bearing layer exceeds 50%, the water-richness is non-uniform, and the water pressure is greater than 2MPa; (3) There is no stable clay aquitard at the bottom; (4) The weathered oxidation zone develops at the top of the bedrock, and the height of the water-conducting fracture zone exceeds the thickness of the normal bedrock.

[0014] Optionally, in step 2), the planar scope of grouting reform is to determine the vertical height Hs of the upper mining limit under the sand-proof safety coal and rock pillar according to the Code for Pillar Setting and Coal Mining under Buildings, Water Bodies, Railways and Main Roadways, calculate the mining influence range of the working face roof as the upper boundary L1 of grouting reform, and calculate the vertical height H of the upper mining limit of the waterproof safety coal and rock pillarsh The contour line of the elevation where it is located serves as the lower boundary of the grouting reconstruction. The width from the upper limit of the sand control safety coal and rock pillar mining to the upper limit of the waterproof safety coal and rock pillar mining is denoted as L2. The width of the grouting reconstruction range is calculated as L according to formula (1):

[0015]

[0016] In the formula: H j —The thickness of the bedrock of the coal seam roof, m; H d —The thickness of the bottom aquifer, m; φ—The comprehensive mining-induced movement angle, degree; H sh —The vertical height of the upper limit of the waterproof safety coal and rock pillar mining, m; Hs—The vertical height of the upper limit of the sand control safety coal and rock pillar mining, m; α—The average dip angle of the coal seam, degree;

[0017] In the vertical space range, the grouting horizon of the loose layer is from the top of the bottom aquifer of the loose layer to the normal bedrock; the grouting horizon of the fault is the top area of the fault, located within the protection layer of the sand control coal and rock pillar, and arranged in the interval between the top of the normal bedrock and the weakly weathered zone.

[0018] Optionally, in step 3) to determine the drilling and grouting construction parameters: determine the hole layout method, hole spacing, drilling construction sequence and sectional design for different treatment objects, and determine the grouting construction parameters for different treatment objects, including slurry density, slurry flow rate, construction sequence and grouting pressure standard;

[0019] Hole layout method: Use directional wells for grouting reconstruction of the loose layer and the weathered oxidized zone, and use horizontal wells for grouting reconstruction of the fault;

[0020] Hole spacing: According to the experience of slurry diffusion in grouting, design the spacing of directional wells to be 40 - 80 m, and adjust it dynamically according to the thickness of the loose layer; The horizontal well focuses on strengthening the fault zone, and the designed final hole spacing is 20 - 40 m;

[0021] Drilling construction sequence: First construct directional wells and then construct horizontal wells. The grouting slurry of the horizontal well migrates upward to strengthen the grouting effect of the roof;

[0022] Sectional design: The directional well grouts downward in sections, with the sectional length of 5 - 10 m; The horizontal well adopts the "three-section grouting method" and divides it into three sections: "before the fault, in the fault zone, after the fault"; When the grouting volume is more than 2000 tons, add 1 - 2 more sections to further explore and verify the abnormal area; When the drilling fluid consumption exceeds 5 m 3 / h, lift the drill and grout; If there is no obvious consumption, grout according to the sectional requirements;

[0023] Grouting construction parameters: In terms of slurry density, design the slurry density of the loose layer grouting to be 1.55 - 1.65 g / cm 3 and design the slurry density of the fault and the weathered oxidized zone grouting to be 1.4 - 1.6 g / cm 3 ;

[0024] Slurry flow rate: The designed slurry flow rate for grouting in the loose layer is 10 - 40 m 3 / h, and the designed slurry flow rate for grouting in the fault and weathered oxidation zone is 10 m - 20 m 3 / h;

[0025] Grouting sequence: Priority should be given to constructing the upper row of directional holes first and then the lower row of directional holes, and the loose layer directional holes first and then the fault horizontal holes;

[0026] Grouting pressure standard: The orifice pressure at the end of grouting in the loose layer and weathered oxidation zone should not be higher than 2 times the hydrostatic pressure, and the orifice pressure at the end of grouting in the fault zone should not be lower than 2 times the hydrostatic pressure.

[0027] Optionally, the key drilling information described in step 4) includes: directional trajectory information, formation lithology information, drilling fluid consumption information, and drilling time information, which reflect the borehole trajectory, key formation boundaries, and the water-richness of the aquifer;

[0028] The key grouting information described in step 4) includes: the grouting volume of each grouting section, the dynamic change process of grouting pressure, the phenomenon of abnormal increase or decrease in pressure, the unit grouting volume t / m, the water level change of the nearby long-term observation hole, which reflect the injectability of the treatment area and the hydraulic connection between aquifers;

[0029] As described in step 4), the optimization and adjustment of the drilling and grouting design include:

[0030] If the thickness of the bottom aquifer in the loose layer changes by more than ±5 m compared with the design, optimize the borehole spacing, densify the boreholes in the area where the thickness increases, and enlarge the borehole spacing in the area where the thickness decreases;

[0031] If the position of the fault changes, adjust the sectional position to ensure that the second grouting section completely passes through the fault zone;

[0032] If the grouting volume of the grouting section is large, set the grouting volume threshold to 5000 tons for the central hole and the horizontal hole in the fault zone, and set the grouting volume threshold to 2000 tons for the boundary hole and the horizontal hole in the normal bedrock section. If the grouting volume exceeds the threshold, reduce the grouting flow rate and increase the density of the cement slurry, quickly end the grouting of this section, and continue to construct forward;

[0033] If the grouting is stopped abnormally due to external reasons, it is necessary to ream the hole for re-grouting until the grouting pressure is reached;

[0034] If the adjacent boreholes are grouted in series, adjust the borehole spacing of the grouting boreholes and grout in a staggered manner; if there is no room for adjustment, perform synchronous grouting;

[0035] If there is slurry leakage underground, it is necessary to first determine the grouting borehole, then gradually block the slurry leakage channel, and then perform reaming grouting verification.

[0036] Optionally, for the inspection and evaluation of the engineering effects in step 5): After the project is completed, ground direct coring is used for verification and underground water exploration holes are used for water discharge verification to evaluate the project treatment effects.

[0037] For direct coring, there is no drilling loss. The consolidation effect between the loose layer sand layer and cement is good. Cement filling can be seen at the loose layer and the bedrock fissures, which is regarded as good grouting effect.

[0038] For the pumping test, if the specific yield is less than 0.1 min / L·m, it is regarded as good grouting effect.

[0039] The stable water discharge q of a single-hole water exploration hole < 2 m 2 / h is regarded as qualified; the stable water discharge q of the treatment area < 10 m 2 / h is regarded as qualified.

[0040] The beneficial effects of the present invention are as follows:

[0041] 1. The method for liberating shallow protective coal pillar resources in a structure-developed working face disclosed by the present invention comprehensively grouts and reforms the "bottom aquifer of the loose layer, the weathered oxidation zone, and the fault structure", transforms the roof aquifer within the mining influence range into a relatively water-resistant layer, blocks the water and sand gushing channels of the fault, improves the stability of the roof surrounding rock, destroys the three formation conditions of "water and sand source, water pressure, and gushing channel", and realizes the dual disaster prevention and control of "source and channel".

[0042] 2. On the basis of the conventional grouting reform of the bottom water-bearing sand layer of the loose layer, the present invention further considers the adverse effects of structural factors on the mining of the working face, forms a systematic comprehensive grouting reform technology for the roof of the "loose layer, weathered oxidation zone, and fault", further improves the safety of the development of shallow protective coal pillar resources, has a wide adaptability, is a supplement and improvement to the loose layer grouting reform technology, and effectively guarantees the safe recovery of shallow protective coal pillar resources and the in-situ protection of water resources.

[0043] 3. The present invention determines the differential borehole structure and grouting parameters according to different treatment objects of the "loose layer, weathered oxidation zone, and fault", and dynamically optimizes the construction plan according to the changes of treatment conditions to achieve the optimal treatment effect, has strong practicability, and has important reference value. Description of the Drawings

[0044] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification, and are used to explain the present invention together with the following specific embodiments, but do not constitute a limitation to the present invention. In the drawings:

[0045] Figure 1 is the flow chart of the system for liberating shallow protective coal pillar resources in a structure-developed working face of the present invention;

[0046] Figure 2It is a schematic diagram of the grouting reform scope of the working face roof;

[0047] Figure 3 It is a schematic diagram of the comprehensive management of the working face roof;

[0048] Figure 4 It is a schematic cross-section diagram of the air roadway of the working face in Embodiment 1;

[0049] Figure 5 It is the maximum water inflow isoline map for verifying the effect of underground water exploration and drainage;

[0050] The labels in the figure are as follows:

[0051] 1. Grouting reform width; 2. Roof mining influence width outside the working face; 3. Grouting reform width inside the working face; 4. Water-bearing sand layer at the bottom of the loose layer; 5. Coal seam; 6. Comprehensive mining movement angle; 7. Waterproof safety coal (rock); 8. Height of the anti-sand safety coal (rock) pillar; 9. Vertical depth of the coal seam roof to bottom including the top; Pillar height; 10. Fault; 11. Directional well; 12. Horizontal well; Specific implementation manners

[0052] The present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0053] The overall idea of water control of the present invention is to reduce the threats of the "three elements" of water inrush and sand inrush in the working face. The "bottom aquifer of the loose layer, the weathered oxidation zone, and the fault structure" are selected as the objects of grouting reform. The necessary grouting reform scope of the working face is determined according to the specifications of the coal and rock pillars. Differentiated borehole structures and grouting parameters are determined according to different reform objects. The construction plan is dynamically optimized according to the changes in the treatment conditions. Finally, a method for testing and evaluating the engineering effect is proposed.

[0054] Therefore, the present invention is a comprehensive solution for liberating the shallow security coal pillar resources of the working face with developed structures and actively preventing and controlling the risks of water inrush and sand inrush, and has good applicability and popularization value.

[0055] Combined with Figure 1 、 2 and 3, the present invention provides a method for liberating the shallow security coal pillar resources of the working face with developed structures, including the following steps:

[0056] Step 1: Analyze the mining conditions and determine the idea of roof water control: For the working face with thin bedrock of the roof, developed structures, difficult water drainage and dewatering, and the water pressure of the water-bearing sand layer at the bottom of the loose layer is greater than 2 MPa, there is a risk of water inrush and sand inrush (mud), determine the idea of grouting reform of the loose layer, the weathered oxidation zone, and the fault structure for water control, and leave an anti-sand safety coal (rock) pillar.

[0057] Step 2: Determine the objects and scope of grouting improvement: The objects of grouting improvement are the water-bearing sand layer at the bottom of the loose layer, the wind-oxidized zone, and the top of the fault with the risk of water inrush and sand outburst. The scope of grouting improvement includes the planar scope and the vertical space scope. The planar scope is to determine the upper mining limit according to the calculation formula of the sand control safety coal (rock) pillar, calculate the mining influence range of the working face roof as the upper boundary of grouting improvement, and calculate the position of the waterproof safety coal (rock) pillar as the lower boundary of grouting improvement. The vertical space scope is from the water-bearing sand layer at the bottom of the loose layer to the normal bedrock, and also includes the area at the top of the fault with the risk of water inrush and sand outburst.

[0058] Step 3: Determine the drilling and grouting construction parameters: Determine the drilling type, hole spacing, construction sequence, and drilling design of the grouting improvement objects, as well as the grouting construction parameters for different grouting improvement objects, such as slurry density, slurry flow rate, grouting sequence, and grouting pressure standard, etc.

[0059] Step 4: Engineering construction and dynamic optimization of the plan: Carry out engineering construction, count the key information of drilling and grouting, calculate the water permeability before and after grouting, draw the grouting P-Q-T dynamic curve, and optimize the plan under the conditions of large changes in the thickness of the bottom aquifer of the loose layer, changes in the fault position, large grouting volume in the grouting section, abnormal suspension of grouting in the grouting section, cross-grouting of adjacent boreholes, and underground slurry leakage, etc., and adjust the drilling and grouting design.

[0060] Step 5: Inspection and evaluation of the engineering effect: After the project is completed, use surface direct core sampling verification and underground exploration hole water release verification to evaluate the engineering treatment effect.

[0061] Describe the complete steps of the method of the present invention:

[0062] Step 1) Analyze the mining geological conditions in the study area. If there is a risk of water inrush and sand (mud) outburst in the working face with a sand control safety coal (rock) pillar reserved, the roof loose layer, wind-oxidized zone, and structure should be grouted and improved.

[0063] Furthermore, the characteristics of the working face with the risk of water inrush and sand (mud) outburst are as follows: (1) The working face is structurally developed, with many inclined faults, the fault throw is greater than 5m, and there are certain potential risks of water inrush and sand outburst. (2) The bottom aquifer of the loose layer is widely developed, the total proportion of the thickness of gravel and fine sand in the bottom aquifer exceeds 50%, the water-richness is non-uniform, the water pressure is greater than 2MPa, the difficulty of water drainage and dewatering is large, and it is not drainable. (3) There is no stable clayey soil aquitard at the bottom, the bedrock is thin, and the height of the water-conducting fracture zone exceeds the thickness of the bedrock. (4) The wind-oxidized zone is developed at the top of the bedrock, and the height of the water-conducting fracture zone exceeds the thickness of the normal bedrock.

[0064] In Step 2), the plane scope of grouting transformation is determined as follows: According to the Code for Pillaring and Coal Mining under Buildings, Water Bodies, Railways and Main Shaft Roadways, the upper limit vertical height (Hs) of coal (rock) pillar for sand prevention is determined, and the mining influence range of the working face roof is calculated as the upper boundary (L1) of grouting transformation. The contour line where the upper limit vertical height (H sh ) is located is used as the lower boundary of grouting transformation. The width from the upper limit of coal (rock) pillar for sand prevention to the upper limit of coal (rock) pillar for water prevention is denoted as L2, and the width of grouting transformation range L is calculated according to formula (1).

[0065] Furthermore, the formula in Step 2) is as follows:

[0066]

[0067] In the formula: H j —The thickness of the bedrock of the coal seam roof, m; H d —The thickness of the bottom aquifer, m; φ—The comprehensive mining movement angle, degree; H sh —The upper limit vertical height of coal (rock) pillar for water prevention, m; Hs—The upper limit vertical height of coal (rock) pillar for sand prevention, m; α—The average dip angle of the coal seam, degree.

[0068] Furthermore, in the vertical space scope, the grouting horizon for the loose layer is from the top of the bottom aquifer of the loose layer to the normal bedrock. The grouting horizon for the fault is the top area of the fault, which is within the protection layer of the sand prevention coal and rock pillar. In principle, it is arranged in the interval between the top of the normal bedrock and the weakly weathered zone.

[0069] Step 3) Determine the drilling and grouting construction parameters: Determine the hole layout method, hole spacing, drilling construction sequence and sectional design for different treatment objects. Determine the grouting construction parameters for different treatment objects, such as slurry density, slurry flow rate, construction sequence and grouting pressure standard.

[0070] Furthermore, the hole layout method: Use directional wells to carry out grouting transformation on the loose layer and the wind-oxidized zone, and use horizontal wells to carry out grouting transformation on the fault. The grouting of the two diffuses and complements each other.

[0071] Furthermore, the hole spacing: According to the experience of slurry diffusion in grouting, design the spacing of directional wells to be 40 - 80 m, and adjust it dynamically according to the thickness of the loose layer; The horizontal well focuses on strengthening the fault zone, and the designed final hole spacing is 20 - 40 m.

[0072] Furthermore, the drilling construction sequence: In principle, construct the directional well first and then the horizontal well. The grouting slurry of the horizontal well migrates upward to strengthen the grouting effect of the roof.

[0073] Furthermore, sectional design: For the directional well, grouting is carried out in sections downward, with the sectional length being 5 - 10 m; for the horizontal well, the "three-section grouting method" is adopted, dividing it into three sections: "before the fault, in the fault zone, and after the fault". In areas with a large grouting volume, such as when the grouting volume is greater than 2000 tons, 1 - 2 additional sections are added to further explore and verify the abnormal area. When the consumption of drilling fluid exceeds 5 m 3 / h, stop drilling and carry out grouting. If there is no obvious consumption, grouting shall be carried out according to the sectional requirements.

[0074] Furthermore, grouting construction parameters: In terms of slurry density, the designed slurry density for grouting in the loose layer is 1.55 - 1.65 g / cm 3 , and the designed slurry density for grouting in the fault and weathered oxidation zone is 1.4 - 1.6 g / cm 3 . When the grouting volume is large, such as when the grouting volume is greater than 2000 tons, the slurry density is gradually increased to control the diffusion range.

[0075] Furthermore, slurry flow rate: The designed slurry flow rate for grouting in the loose layer is 10 - 40 m 3 / h, and the designed slurry flow rate for grouting in the fault and weathered oxidation zone is 10 m - 20 m 3 / h. When the grouting volume is large, such as when the grouting volume is greater than 2000 tons, the slurry flow rate is reduced to control the diffusion range.

[0076] Furthermore, grouting sequence: Priority is given to constructing the upper row of directional holes and then the lower row of directional holes, and first the directional holes in the loose layer and then the horizontal holes in the fault.

[0077] Furthermore, grouting pressure standard: The ending orifice pressure for grouting in the loose layer and weathered oxidation zone shall not be higher than 2 times the hydrostatic pressure, and the ending orifice pressure for grouting in the fault zone shall not be lower than 2 times the hydrostatic pressure.

[0078] Step 4) Project construction and dynamic optimization of the plan: Carry out project construction, statistically analyze the key information of drilling and grouting, calculate the water permeability before and after grouting, draw the dynamic grouting P - Q - T curve, and optimize the plan under the circumstances of large changes in the thickness of the bottom aquifer in the loose layer, changes in the fault position, large grouting volume in the grouting section, abnormal suspension of grouting in the grouting section, cross - grouting in adjacent boreholes, and underground slurry leakage, etc., and adjust the drilling and grouting design.

[0079] In step 4), the key drilling information includes: directional trajectory information, formation lithology information, drilling fluid consumption information, drilling time information, etc., which reflect the borehole trajectory, key formation boundaries, and the water - rich property of the aquifer.

[0080] In step 4), the key grouting information includes: the grouting volume of each grouting section, the dynamic change process of grouting pressure, the phenomenon of abnormal increase or decrease in pressure, the unit grouting volume t / m, and the water level change in the nearby long - term observation well, which reflect the injectability of the treatment area and the hydraulic connection between aquifers.

[0081] In step 4), the optimization scenarios of the plan and the corresponding treatment measures:

[0082] Furthermore, if there are significant changes in the thickness of the bottom layer of the loose layer, for example, if the thickness of the bottom layer of the loose layer varies from the design value by more than ±5 m, the drilling spacing should be optimized. The drilling should be densified in the areas where the thickness increases, and the drilling spacing should be enlarged in the areas where the thickness decreases.

[0083] Furthermore, if the position of the fault changes, the segmented position should be adjusted to ensure that the second grouting section completely penetrates the fault zone.

[0084] Furthermore, if the grouting volume in the grouting section is large, the grouting volume threshold values are set as 5000 tons for the central hole and the horizontal holes in the fault zone, and 2000 tons for the boundary holes and the horizontal holes in the normal bedrock section. If the grouting volume exceeds the threshold value, the grouting flow rate should be reduced and the density of the cement slurry should be increased to quickly end the grouting in this section and continue the construction forward.

[0085] Furthermore, if the grouting stops abnormally due to external reasons, such as slurry leakage in the mine, drilling hole cross - flow, power failure, or too long equipment maintenance time, etc., it is necessary to re - drill through the hole for re - grouting until the grouting pressure is reached.

[0086] Furthermore, if there is cross - flow between adjacent drilling holes, the drilling spacing of the grouting holes should be adjusted and the grouting should be carried out in a staggered manner; if there is no space for adjustment, synchronous grouting should be carried out.

[0087] Furthermore, if there is slurry leakage in the mine, it is necessary to first determine the grouting holes, and then gradually block the slurry leakage channels by means such as low - pressure, thick slurry, small - flow grouting, and intermittent grouting, and then carry out through - hole grouting verification. Subsequently, control the grouting pressure under similar geological conditions to reduce the impact on the mine.

[0088] Step 5) Inspection and evaluation of the engineering effect: After the project is completed, ground direct - hole coring verification and underground exploration hole water - discharging verification are used to evaluate the engineering treatment effect.

[0089] Furthermore, for direct - hole coring, if there is no loss during drilling, the consolidation effect between the sand layer of the loose layer and the cement is good, and cement filling can be seen at the fissures of the loose layer and the bedrock, it is considered that the grouting effect is good.

[0090] Furthermore, for the pumping test, if the unit water inflow is less than 0.1 min / L.m, it is considered that the grouting effect is good.

[0091] Furthermore, for a single - hole water - exploration hole, a stable water - discharging volume q < 2 m 2 / h is considered qualified. For the governance area, a stable water - discharging volume q < 10 m 2 / h is considered qualified.

[0092] The following specifically describes the present invention with specific embodiments.

[0093] Embodiment 1:

[0094] Taking a certain coal mine in Bozhou City, Anhui Province as an example.

[0095] 1. Project Background

[0096] In November 2023, a roof water inrush occurred in Coal Mine A in Bozhou City, Anhui Province. The maximum water inflow exceeded 300 m 3 / h, and a large amount of sediment was carried, causing the mine to be flooded. The main roadway system of the mine was filled with sediment, making it difficult to recover. The minimum vertical distance between Coal Seam 8 in Working Face 815 and the Quaternary aquifer in the loose layer of the Cenozoic (referred to as "Fourth Aquifer") is 120 m, far exceeding the height of the safety coal (rock) pillar for sand prevention, which is 56 m. The water source of the water inrush is the water in the "Fourth Aquifer". During the mining process of the working face, Fault 815F16 was exposed. This fault is a high-angle normal fault with a throw of 7.5 m. Under the combined action of factors such as mine pressure, overlying rock movement and deformation, and in-situ stress, it became activated, resulting in the outburst of water and sediment from the "Fourth Aquifer", leaving a profound lesson. Therefore, it is particularly important to prevent the hidden dangers of water and sand inrush from the bottom aquifer of the loose layer caused by fault activation.

[0097] Coal Mine B in Bozhou City belongs to the same mining area, and its roof hydrogeological conditions are similar. Its characteristics are that Coal Seam 8 is thick, inclined, and the bedrock is thin. The mining intensity of top coal caving is high, faults are developed, the "Fourth Aquifer" is under pressure, and there are similar risks in the working face mining, and it is necessary to prevent fault activation and hidden dangers of water and sand inrush.

[0098] Step 1) Analyze the mining geological conditions in the study area: Working Face 851 in Coal Mine B in Bozhou City is the first fully mechanized top coal caving working face in the 85th mining area. The strike length is about 735 m, the inclined width is about 120 m, the dip angle of the coal (rock) seam is 20 - 35°, the average thickness of Coal Seam 8 is 9.3 m, and the recoverable reserve is 1.15 million t. According to the measured "two-zone" observation holes, calculated by the coal thickness of 9.3 m, its caving ratio is about 3.2 - 3.8 times, and the fracture ratio is about 7.3 - 8.4 times. The bedrock of the working face roof is relatively thin. Among them, the rock pillar in the air return roadway is 56.8 - 116.6 m, and the rock pillar in the machine roadway is 118.5 - 150 m. The roof bedrock is mainly composed of mudstone, siltstone and fine sandstone, and the overlying rock type is soft - medium hard.

[0099] The loose layer of the Cenozoic on the working face roof can be divided into "Fourth Aquifer and Three Impermeable Layers". The average thickness of the "Three Impermeable Layers" is 108 m, mainly composed of sandy and calcareous clay, with good water isolation properties; the lithology of the "Fourth Aquifer" is marl, fine sand, limestone gravel, sandstone gravel and clay gravel, with a thickness of 2.7 - 14.55 m, an average of 7.8 m, uneven water abundance, large static reserves, and a cumulative water exploration and drainage of 50,000 m 3 , the water level dropped by 70 m, and the water pressure of the "Fourth Aquifer" is 3.3 MPa. The mining level of the "Fourth Aquifer" water body is Class II. The average thickness of the weathered zone at the bottom of the "Fourth Aquifer" is 30 m, and the thickness of the strong weathered zone is about 15 m.

[0100] Faults are well developed in the working face. A total of 20 faults are exposed in the air return roadway and the conveyor roadway, and 4 major faults affecting coal mining are respectively the dip fault 851FF3 (throw H = 7m), 851FF4 (throw H = 6m), GF256 (throw H = 3 - 6m) and the strike fault GF248 (throw H = 0 - 5m). See the schematic cross-section of the air return roadway of the working face in Figure 4 .

[0101] In summary, there are several major characteristics of the risk of water and sand inrush in the 851 working face. To reserve a safety coal (rock) pillar for sand control, it is necessary to grout and reform the fourth aquifer, the wind-oxidized zone and the fault zone to eliminate the hidden danger of water and sand inrush.

[0102] Step 2: Determine the grouting reform scope and horizon: First, determine the vertical height of the upper limit of mining under the safety coal (rock) pillar for sand control. Then, according to the measured and empirical data, the floor elevation of the loose layer is -365m, the coal thickness A = 9.3m, H k = 3.8A; H b1 = 2A; H j = Hs; H d = 7.8m; H li = 8.4A; H b2 = 3A; φ = 60°; α = 30°. Calculate the vertical height of the upper limit of mining under the safety coal (rock) pillar for sand control to be -419m through the standard formula. Calculate the width L of the grouting reform scope to be 125.7m through Formula 1. The grouting reform horizon ranges from the top of the fourth aquifer at the bottom of the loose layer to the normal bedrock and the top area of the fault.

[0103] Furthermore, the vertical height of the upper limit of mining under the safety coal (rock) pillar for sand control: H S = H k + H b1 = 3.8A + 2A = 5.8A = 54m. The floor elevation of the loose layer is -365m, and the corresponding upper limit elevation of mining is: -365 - H S = -419m; The difference between the vertical height of the upper limit of mining under the safety coal (rock) pillar for water control and the vertical height of the upper limit of mining under the safety coal (rock) pillar for sand control is: H Sh - H s = H li + H b2 - H k - H b1 = 52m, and the corresponding coal seam elevation is -471m.

[0104] Furthermore, the width of the grouting reform scope:

[0105]

[0106] Step 3: Determine the drilling and grouting construction parameters: In terms of drilling construction parameters, according to the calculation results of Step 2, the directional wells are arranged on both sides of the air roadway, and the directional horizontal wells penetrate the dip fault at a large angle. The final hole spacing of the directional holes is 50 - 90 m, where the hole spacing is large in the thin layer area of the fourth aquifer and small in the thick layer area; the final hole spacing of the horizontal wells is 25 - 35 m. In terms of the construction sequence, the directional wells are constructed first and then the horizontal wells. In terms of sectional design, the directional wells are grouted in sections, with the sectional length being 5 - 10 m, and the horizontal wells are constructed using the three - section grouting method, and the sectional length does not exceed 200 m.

[0107] During the actual construction process, the slurry density in the loose layer is 1.5 - 1.65 m 3 / h, and the slurry density in the fault and the weathered oxidation zone is 1.4 - 1.6 m 3 / h. The drilling footage of the directional horizontal holes is 2190 m, 8779 t of cement is injected, the final grouting pressure is 4.5 - 6.2 MPa, and the unit grouting volume is 5.4 t / m; the drilling footage of the directional inclined holes is 7682 m, 29501 t of cement is injected, the final grouting pressure is 4.0 - 5.6 MPa, and the unit grouting volume is 41.8 t / m; the injectability of the "fourth aquifer" formation is better than that of the fault fracture zone. During the drilling construction process, faults, the "fourth aquifer", and the weathered zone are exposed. The drilling fluid is consumed normally without obvious leakage, indicating that the development scale of fault fractures, dissolution fractures in the "fourth aquifer", pore fractures in the loose layer, and weathered zone fractures is limited, and no large holes, karst caves, pore spaces, and fracture channels are explored and exposed.

[0108] S4: Engineering construction, dynamically optimize the plan: The ground project started on November 21, 2023 and was completed on March 23, 2024, lasting for 124 days. A total of 5 horizontal wells and 18 directional wells were constructed, with a drilling footage of 9872 m and 38280 t of cement injected. 58 groups and 116 times of simple water pressure tests were carried out. The water permeability rate of the aquifer before grouting of the fault treatment holes is 0.15 - 1.11 Lu, and the water permeability rate of the aquifer before grouting of the "fourth aquifer" and weathered zone treatment holes is 1.27 - 12.61 Lu. The Lu Rong value of the final hole section of each hole is less than 1 Lu, and the water permeability rate after grouting has a significant decrease compared with that before grouting. Re - grouting was carried out for the grouting sections with a large grouting volume and the grouting holes that did not reach the grouting end pressure. During grouting, there were 4 cases of slurry cross - flow between adjacent boreholes. The construction sequence of the directional wells was adjusted, and hole - skipping construction or synchronous grouting was carried out. There were 4 cases of underground slurry leakage. The grouting pressure in the weathered zone was controlled, and additional boreholes were drilled to explore and verify the suspected abnormal areas or blank areas.

[0109] S5: Engineering effect inspection and evaluation: After the ground grouting was completed, 13 water - discharging holes were constructed in the study area for verification. Most of the boreholes had no water or only a small amount of dripping water. The maximum water inflow of the borehole is 0.8 m 3 / h, the water inflow is 3.1 m 3 / h, and the cumulative water discharge is 2973 m 3, the verification of the water exploration and drainage effect underground can be seen in Figure 5 . The water inflow detected during the through-hole inspection of the previously drilled holes with large water inflow was all less than 1 m 3 / h. In summary, it is reflected that the "Fourth Aquifer", weathered zone and fault fracture zone in the treatment area have been grouted and reinforced. Currently, the working face has been safely mined for 100 m without water inflow underground. At the same time, surface coring holes and hydrogeological holes were constructed in the study area. The core is in a consolidated state, with relatively pure texture, karst caves are seen, the dissolution phenomenon is obvious, cement is seen on the fracture surface of marl, large cement stones are seen in the bottom weathered zone, and cement is seen in the returned slag and cuttings. The hydrogeological hole test shows weak water-richness, further verifying that the fault grouting indirectly reinforces the "Fourth Aquifer" and the weathered zone.

[0110] Although the present invention has been described in detail with general descriptions and specific implementation schemes in the above text, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A method for liberating shallow protective coal pillar resources in a tectonically developed working face, characterized in that, It includes the following steps: Step 1: Analyze the mining conditions and determine the idea of water control for the roof: For the working face with the risk of water inrush and sand or mud burst, determine the idea of water control by grouting to reform the loose layer, the wind-oxidized zone and the fault structure, and leave a safety coal and rock pillar for sand prevention. Step 2: Determine the objects and scope of grouting reform: The objects of grouting reform are the water-bearing sand layer at the bottom of the loose layer, the wind-oxidized zone and the top of the fault with the risk of water inrush and sand burst; the scope of grouting reform includes the planar scope and the vertical space scope; the planar scope is to determine the upper limit of mining according to the calculation formula of the safety coal and rock pillar for sand prevention, calculate the mining influence range of the working face roof as the upper boundary of grouting reform, and calculate the position of the safety coal and rock pillar for water prevention as the lower boundary of grouting reform. The vertical space scope is from the water-bearing sand layer at the bottom of the loose layer to the normal bedrock, and at the same time includes the top area of the fault with the risk of water inrush and sand burst. Step 3: Determine the drilling and grouting construction parameters: Determine the drilling type, hole spacing, construction sequence and drilling design of the objects of grouting reform, as well as the grouting construction parameters for different objects of grouting reform. Step 4: Project construction and dynamic optimization of the plan: Carry out project construction, count the key information of drilling and grouting, calculate the water permeability before and after grouting, draw the dynamic curve of grouting P-Q-T, and optimize the plan in the cases of large changes in the thickness of the bottom aquifer of the loose layer, changes in the fault position, large grouting volume in the grouting section, abnormal suspension of grouting in the grouting section, cross-grouting of adjacent holes and underground slurry leakage, and adjust the drilling and grouting design. Step 5: Inspection and evaluation of the project effect: After the project is completed, use core sampling from surface vertical holes and water release from underground exploration holes to verify and evaluate the project treatment effect.

2. The method for liberating shallow protective coal pillar resources in a structural development working face according to claim 1, characterized in that The characteristics of the risk of water inrush and sand or mud burst in the working face with the risk of water inrush and sand or mud burst in step 1) are as follows: (1) The structure of the working face is developed, there are many inclined faults, the fault throw is greater than 5m, and there are potential risks of water inrush and sand burst; (2) The bottom aquifer of the loose layer is widely developed, the total proportion of gravel and fine sand thickness in the bottom aquifer exceeds 50%, the water richness is uneven, and the water pressure is greater than 2MPa; (3) There is no stable clayey soil water isolation layer at the bottom; (4) The wind-oxidized zone develops at the top of the bedrock, and the height of the water-conducting fracture zone exceeds the thickness of the normal bedrock.

3. The method for liberating the resources of the shallow protective coal pillar in the structural development working face according to claim 1 or 2, characterized in that In step (2), the horizontal range of grouting modification is determined according to the Code for Setting and Pressing Coal Mining under Coal Pillars of Buildings, Water Bodies, Railways and Main Roadways. The upper limit vertical height Hs of mining under the anti-sand safety coal and rock pillar is calculated, and the mining influence range of the working face roof is calculated as the upper boundary L1 of grouting modification. The upper limit vertical height H of mining the waterproof safety coal and rock pillar sh The contour line at the elevation where it is located is used as the lower boundary of grouting modification. The width from the upper limit of mining the anti-sand safety coal and rock pillar to the upper limit of mining the waterproof safety coal and rock pillar is denoted as L2, and the width of the grouting modification range is calculated as L according to formula (1): Where: H j — The thickness of the bedrock above the coal seam roof, m; H d — The thickness of the bottom aquifer, m; φ — The comprehensive mining movement angle, degree; H sh — The vertical height of the upper limit of the waterproof safety coal and rock pillar mining, m; Hs — The vertical height of the upper limit of the sand prevention safety coal and rock pillar mining, m; α — The average dip angle of the coal seam, degree; In the vertical space scope, the grouting horizon of the loose layer is from the top of the bottom aquifer of the loose layer to the normal bedrock; the grouting horizon of the fault is the top area of the fault, which is located within the protection layer of the safety coal and rock pillar for sand prevention and is arranged in the interval between the top of the normal bedrock and the weakly weathered zone.

4. The method for liberating shallow protective coal pillar resources in a tectonically developed working face according to claim 1 or 2, characterized in that Step 3) determines the drilling and grouting construction parameters: Determine the hole layout method, hole spacing, hole construction sequence and sectional design for different treatment objects, and determine the grouting construction parameters for different treatment objects, including slurry density, slurry flow rate, construction sequence and grouting pressure standard. Hole layout method: Use directional wells to carry out grouting reform on the loose layer and the wind-oxidized zone, and use horizontal wells to carry out grouting reform on the fault. Hole spacing: According to the experience of slurry diffusion in grouting, design the spacing of directional wells to be 40 - 80m, and adjust it dynamically according to the thickness of the loose layer; the horizontal well focuses on strengthening the fault zone, and the designed final hole spacing is 20 - 40m. Hole construction sequence: First construct directional wells and then horizontal wells. The grouting slurry of the horizontal well migrates upward to strengthen the grouting effect of the roof. Segmented design: For directional wells, grouting is carried out in segments downward, with the segment length being 5 - 10 m; for horizontal wells, the "three - segment grouting method" is adopted, dividing into three segments of "before the fault, fault zone, after the fault"; when the grouting volume is more than 2000 tons, 1 - 2 additional segments are added to further explore and verify the abnormal area; when the consumption of drilling fluid exceeds 5 m 3 / h, stop drilling and carry out grouting; if there is no obvious consumption, grouting is carried out according to the segmented requirements; Grouting construction parameters: In terms of slurry density, the designed slurry density for grouting in the loose layer is 1.55 - 1.65 g / cm 3 , and the designed slurry density for grouting in faults and weathered oxidation zones is 1.4 - 1.6 g / cm 3 ; Slurry flow rate: The designed slurry flow rate for grouting in the loose layer is 10 - 40 m 3 / h, and the designed slurry flow rate for grouting in faults and weathered oxidation zones is 10 m - 20 m 3 / h; Grouting sequence: First construct the upper row of directional holes and then the lower row of directional holes, and first construct the directional holes in the loose layer and then the horizontal holes in the fault zone; Grouting pressure standard: The orifice pressure at the end of grouting in the loose layer and the wind-oxidized zone shall not be higher than 2 times the hydrostatic pressure, and the orifice pressure at the end of grouting in the fault zone shall not be lower than 2 times the hydrostatic pressure.

5. The method for liberating the resources of the shallow protective coal pillar in the structural development working face according to claim 1 or 2, characterized in that The key drilling information described in step 4) includes: directional trajectory information, formation lithology information, drilling fluid consumption information, and drilling time information, which reflect the borehole trajectory, key formation boundaries, and the water-richness of the aquifer; The key grouting information described in step 4) includes: the grouting volume of each grouting section, the dynamic change process of the grouting pressure, the phenomenon of abnormal increase or decrease in pressure, the unit grouting volume t / m, the water level change of the nearby long-term observation hole, which reflect the injectability of the treatment area and the hydraulic connection between aquifers; As described in step 4), the optimization and adjustment of the drilling and grouting design include: If the thickness of the bottom aquifer in the loose layer changes by more than ±5m compared with the design, optimize the borehole spacing, densify the boreholes in the area where the thickness increases, and enlarge the borehole spacing in the area where the thickness decreases; If the position of the fault changes, adjust the segmented position to ensure that the second grouting section completely penetrates the fault zone; If the grouting volume of the grouting section is large, set the grouting volume threshold at 5000 tons for the central hole and the horizontal holes in the fault zone, and set the grouting volume threshold at 2000 tons for the boundary holes and the horizontal holes in the normal bedrock section. When the grouting volume exceeds the threshold, reduce the grouting flow rate and increase the density of the cement slurry, quickly end the grouting of this section, and continue to construct forward; If the grouting stops abnormally due to external reasons, it is necessary to ream the hole for re-grouting until the grouting pressure is reached; If there is cross-grouting in adjacent boreholes, adjust the borehole spacing of the grouting boreholes and grout in a staggered manner; if there is no room for adjustment, perform synchronous grouting; If there is slurry leakage in the underground, it is necessary to first determine the grouting borehole, then gradually block the slurry leakage channel, and then perform reaming grouting verification.

6. The method for liberating the resources of the shallow protective coal pillar in the structural development working face according to claim 1 or 2, characterized in that, The inspection and evaluation of the engineering effect in step 5) described above: After the project is completed, use the ground direct hole coring verification and the underground exploration hole water discharge verification to evaluate the engineering treatment effect; For direct hole coring, if there is no leakage during drilling, the consolidation effect of the sand layer in the loose layer and the cement is good, and cement filling can be seen at the fissures of the loose layer and the bedrock, it is regarded as good grouting effect; For the pumping test, if the specific yield is less than 0.1min / L.m, it is regarded as good grouting effect; The stable water discharge q of a single-hole water exploration and drainage hole is less than 2 m 2 / h is regarded as qualified; the stable water discharge q of the treatment area is less than 10 m 2 / h is regarded as qualified.

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