A method for partitioned and differential grouting of mining fissures of a composite roof in a gob-side entry retaining

Abstract

The application discloses a kind of along empty roadway composite roof mining fracture zoning differential grouting construction methods, it includes the following construction steps: ① in the along empty roadway of lagging stope, roof separation observation is carried out, and the range of composite roof stable interval section is determined;② composite roof of along empty roadway is drilled and peeps, and the distribution range and development direction of its composite roof mining fracture are judged;③ from the vertical direction and horizontal direction of along empty roadway cross section, along empty roadway composite roof mining fracture is divided into several partitions.The method can avoid the problem of insufficient grouting, which causes insufficient overall bearing strength of along empty roadway composite roof, or the problem of excessive grouting, which causes high maintenance cost, ensures the grouting effect of composite roof, improves the stability and safety of composite roof, and realizes the scientific control of along empty roadway composite roof mining fracture grouting reinforcement.

Description

Technical Field

[0001] This invention relates to the field of mining engineering, and in particular to a method for differentiated grouting of mining-induced fracture zones in composite roof structures along goaf-retention tunnels. Background Technology

[0002] With the continuous improvement of coal mining methods and the advancement of machinery and equipment, gob-side roadway retention has become one of the scientific models and important directions for technological development in deep coal mining in my country. It is an important way to achieve the co-mining of coal and gas in deep coal seams and has developed rapidly in my country's coal industry, occupying a prominent position in many mining areas. However, the deep gob-side roadway retention mining mode inevitably leads to a significant increase in the range and peak value of lateral support pressure in the stope, a more severe impact of mining, and a more serious manifestation of mine pressure. In addition, the wide distribution of soft rock in deep coal-bearing strata and the increased cross-sectional size of roadways due to the construction and development of large-scale intensive mines make it difficult or even impossible for traditional gob-side roadway retention surrounding rock control theories and technologies to adapt to the new deep mine mining production technology conditions and the development of research on the main body of ensuring the safe and smooth operation of deep gob-side roadways—roof deformation, failure, and control. Especially in gob-side roadway retention under composite roof conditions, roof collapse accidents account for a considerable proportion, seriously threatening coal mine safety production.

[0003] In the field engineering practice of gob-side roadway retention under deep composite roof conditions, it was found that after severe mining, the composite roof with high-strength support still exhibited severe crack development and fracturing in both vertical and horizontal directions, leading to numerous support structure loosening failures and even roof collapses. At the construction site, grouting was attempted to reinforce the mining-induced cracks in the composite roof of the gob-side roadway retention area. However, due to the different stages of mining at different times, different areas of the mining-induced cracks in the gob-side roadway retention area were at different stages of fracturing and softening. The degree of crack development, crack distribution characteristics, and crack opening varied greatly. Grouting reinforcement using a single, non-zonal grouting method based solely on engineering experience was ineffective, resulting in poor density of the grouted consolidation body in the composite roof, making it difficult to form a complete load-bearing structure. This failed to effectively guarantee the integrity, stability, and safety of the composite roof of the gob-side roadway retention area. Consequently, some mines did not achieve the expected results when applying gob-side roadway retention technology, and some even experienced failure, thus limiting the wider application of this technology in my country. Summary of the Invention

[0004] This invention provides a differentiated grouting construction method specifically for mining-induced fractures in composite roofs of roadways with goaf retention. The aim is to improve the density of the grouting consolidation body in the mining-induced fractures of composite roofs in roadways with goaf retention, ensure that the composite roof forms a complete load-bearing structure, and guarantee the integrity, stability, and safety of the roadway roof.

[0005] This invention is achieved through the following technical solution:

[0006] A method for differentiated grouting of mining-induced fracture zones in a composite roof with a goaf-retention tunnel includes the following steps.

[0007] The first step is to conduct composite roof separation observation in the goaf-side roadway of the delayed mining area to determine the range of stable sections of the composite roof.

[0008] The second step is to drill holes to inspect the composite roof along the goaf and determine the distribution range and development direction of the mining-induced fractures in the composite roof.

[0009] The third step is to divide the composite roof mining fracture zone into multiple zones along the vertical and horizontal directions of the cross-section of the goaf-retaining roadway.

[0010] The fourth step is to determine the rock mass integrity of each zone in the mining-induced fracture zone of the composite roof of the gob-side retaining roadway, determine the grouting parameters for each zone, and calculate the grouting volume for each zone of the composite roof of the gob-side retaining roadway.

[0011] The fifth step is to implement the grouting reinforcement scheme for the composite roof slab along the goaf, carry out grouting construction of the composite roof slab, and complete the differentiated grouting work for each zone of the composite roof slab.

[0012] Furthermore, roof separation monitoring stations are arranged in the composite roof of the goaf retention roadway within a range of 100-200m in the delayed mining area. The boreholes of the roof separation monitoring stations are located in the middle of the composite roof and arranged vertically. 6-17 roof separation monitoring stations are arranged along the roadway axis, with the last roof separation monitoring station 5m away from the filling area and the distance between each roof separation monitoring station being 15m.

[0013] Furthermore, when the length of the composite roof in the stable section of the goaf-retention roadway reaches 15m, roof inspection boreholes are arranged in the composite roof that first enters the stable section. Three roof inspection boreholes are arranged on the same cross-section of the goaf-retention roadway. The roof inspection boreholes are located on the side of the roof separation monitoring station near the filling area and at a horizontal distance of 250mm~400mm. The roof inspection boreholes near the composite roof near the filling area are inclined at 15°~30° towards the goaf. The roof inspection boreholes in the middle of the composite roof are arranged vertically. The roof inspection boreholes near the solid coal side are inclined at 15°~30° to the left. The borehole depth is 1~2 times the thickness of the composite roof and the borehole diameter is 25~35mm.

[0014] Furthermore, based on the distribution range and development direction of the composite roof mining-induced fractures on the cross-section of the goaf-side roadway, the development degree of the composite roof mining-induced fractures is divided vertically from bottom to top into a strongly developed zone, a moderately developed zone, and a weakly developed zone; and horizontally, the development degree of the composite roof mining-induced fractures is divided from the unmined solid coal face to the goaf into a strongly developed zone, a moderately developed zone, and a weakly developed zone. The mining-induced fracture zone can be divided into nine zones: the upper part of the filling wall is designated as Zone I, Zone II, and Zone III from bottom to top; the upper part of the goaf-side roadway is designated as Zone IV, Zone V, and Zone VI from bottom to top; and the upper part of the solid coal face is designated as Zone VII, Zone VIII, and Zone IX from bottom to top.

[0015] Furthermore, three roof grouting boreholes are arranged on each cross-section of the goaf retention roadway: grouting borehole A is arranged in zones I, II, and III; only grouting borehole B is arranged in zones IV, V, and VI; and only grouting borehole C is arranged in zones VII, VIII, and IX.

[0016] The formula for calculating the grouting volume of each zone is Q. i= S i × η × β

[0017] The formula for calculating the theoretical grouting volume per unit length of composite roof slab is as follows:

[0018]

[0019] In the formula: Q i —Composite roof plate per unit length i Grouting volume of the rock mass in the area, m 3 S i —Composite roof panel i Cross-sectional area of ​​the rock mass in the area, m 3 Q 总 — Grouting volume per unit length of composite roof slab, in meters 3 ; η —Rock mass porosity, % β —The effective filling coefficient of the grout within the rock mass fissures, and the formula for calculating the grouting volume per unit length of the composite roof in each zone are as follows:

[0020] Q I、II、III =Q 钻孔A =Q I +Q II +Q III

[0021] Q IV、V、VI =Q 钻孔B =Q IV +Q V +Q VI

[0022] Q VII、VIII、IX =Q 钻孔C =Q VII +Q VIII +Q IX

[0023] The formula for calculating the grouting time for each borehole is:

[0024]

[0025] In the formula: t 钻孔i —Drilling and grouting time, m 3 v—grouting speed, m 3 / s.

[0026] Furthermore, one of each of the grouting boreholes A, B, and C is installed on the same cross-section of the goaf-retaining roadway. The cross-sections where the grouting boreholes are installed are evenly distributed between two adjacent roof separation monitoring stations in the stable zone. The bottom opening of grouting borehole A is 100-300mm away from the filling wall and is inclined at 20° towards the goaf side. Borehole B is located in the middle of the roof and is arranged vertically. The bottom opening of grouting borehole C is 100-300mm away from the solid coal face and is inclined at 20° towards the solid coal face. The diameter of each of the grouting boreholes A, B, and C is 22-32mm, and the borehole length L = composite roof thickness h + 500mm.

[0027] Furthermore, the grouting reinforcement scheme for the composite roof of the goaf-retaining tunnel is as follows: hollow grouting anchor cables are installed in the grouting boreholes A, B, and C, and the surrounding rock of the goaf-retaining tunnel is sealed by spraying grout.

[0028] Furthermore, each grouting cycle is defined as the completion of a 15m stable section of the composite roof slab along the goaf. When the stable section of the composite roof slab along the goaf reaches 15m again, the next stage of grouting can begin.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) By drilling into the composite roof along the goaf, the development status and direction of mining-induced fractures in the stable section of the composite roof along the goaf can be promptly determined. The mining-induced fractures of the composite roof are divided into 9 zones from both vertical and horizontal directions, and the grouting volume per unit length of the composite roof and the grouting requirement per unit length of the entire roof can be accurately calculated. This method of quantifying the grouting volume of the composite roof avoids the problem of insufficient overall bearing strength of the roof due to insufficient grouting volume, or the problem of excessive maintenance costs due to excessive grouting.

[0031] (2) Differentiated grouting of composite roof in gob-side roadway is achieved in two aspects: First, the mining-induced cracks in the composite roof are divided into 9 zones, and the grouting volume of each zone is accurately calculated, thus realizing differentiated grouting of zones; Second, after completing a grouting cycle, when the stable section of the composite roof in the gob-side roadway reaches a certain distance again, this construction method is repeated, and the grouting volume of the composite roof in each grouting cycle is adjusted in a timely manner, thus realizing the differentiated grouting requirements of the composite roof in different gob-side roadway sections.

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0033] Figure 1 Plan view of the layout of the roadway along the goaf and the arrangement of the composite roof separation monitoring stations;

[0034] Figure 2 yes Figure 1 Section II of the composite roof separation monitoring station in the middle of the goaf;

[0035] Figure 3 yes Figure 1 Profile of composite roof inspection borehole II-II in the stable section of the goaf-retention tunnel;

[0036] Figure 4 This is a schematic diagram of a core sample restored from a borehole image of a roof section in a composite roof section with a goaf retention tunnel.

[0037] Figure 5 It is a composite roof profile of mining-induced fracture zoning in the stable section of the goaf-retaining roadway;

[0038] Figure 6 yes Figure 1 Layout diagram of grouting boreholes in the III-III section of the roof of the stable section of the goaf-retaining roadway.

[0039] Explanation of reference numerals in the attached diagrams: 1. Solid coal seam; 2. Goaf roadway; 3. Filling wall; 4. Goaf; 5. Filling area; 6. Sectional level roadway; 7. Stope; 8. Roof separation monitoring station; 81. Claw of the separation instrument; 82. Scale of the separation instrument; 9. Composite roof; 10. Overlying strata; 11. Roof inspection borehole; 121. Grouting borehole A; 122. Grouting borehole B; 123. Grouting borehole C; 13. Mining-induced fracture zone; 14. Coal mining face; 151. Zone I; 152. Zone II; 153. Zone III; 154. Zone IV; 155. Zone V; 156. Zone VI; 157. Zone VII; 158. Zone VIII; 159. Zone IX. Detailed Implementation

[0040] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 As shown, a method for differentiated grouting of mining-induced fracture zones in a composite roof with a goaf-retention tunnel is characterized by the following steps:

[0041] The first step is to conduct separation observation of the composite roof 9 in the goaf retention roadway 2 of the delayed mining area 7 to determine the range of the stable section of the composite roof 9.

[0042] Specifically, during the mining of the 14th longwall face, roof delamination monitoring stations 8 were rapidly deployed in the goaf retainer 2 of the delayed mining area 7 to monitor the degree of delamination and subsidence of the composite roof in the goaf retainer 2 within a range of 100-200m. The layout of the goaf retainer and the arrangement of the composite roof delamination monitoring stations 8 are as follows: Figure 1 and Figure 2 As shown, each roof delamination monitoring station 8 is located in the middle of the composite roof 9 and arranged vertically. 6 to 17 monitoring stations are arranged along the roadway axis, with the last station 8 being 5m from the filling area. The spacing between all monitoring stations is 15m. Each monitoring station is equipped with one roof delamination instrument, and three pawl assemblies are located at the deep, middle, and shallow parts of the monitoring borehole, respectively. Data from all monitoring stations are collected and analyzed periodically. Once the delamination and subsidence of the composite roof in the goaf-stayed roadway has stabilized and the length of the stable interval has reached 15m, the next stage of construction work begins.

[0043] The second step involves drilling to inspect the composite roof 9 along the goaf, determining the distribution range and development direction of mining-induced fractures in the composite roof 9. When the length of the composite roof 9 in the stable section of the goaf 2 reaches 15m, a roof inspection borehole 11 is arranged in the composite roof 9 that first enters the stable section. Three roof inspection boreholes 11 are arranged on the same cross-section of the goaf 2, with a borehole spacing of 1200mm~2000mm, all located on the side of the roof separation monitoring station 8 near the filling area and at a distance from the water level. The horizontal distance is 250mm~400mm. The roof inspection boreholes 11 near the composite roof 9 of the filling area 5 are inclined at 15°~30° towards the goaf 4. The roof inspection boreholes 11 located in the middle of the composite roof 9 are arranged vertically. The roof inspection boreholes 11 near the solid coal side 1 are inclined at 15°~30° to the left. The drilling depth is 1~2 times the thickness of the composite roof 9 and the drilling diameter is 25~35mm. Each roof separation monitoring station 8 is equipped with a set of roof inspection boreholes 11.

[0044] Specifically, when the length of the stable section of the composite roof in the gob-side retaining roadway reaches 15m, a set of roof inspection boreholes 11 are arranged on the cross-section of the gob-side retaining roadway that first enters the stable section. Generally, three roof inspection boreholes are arranged. Figure 3As shown. The roof inspection borehole 11 near the roof of the filling area is inclined at 20° to the right of the goaf, the roof inspection borehole 11 in the middle of the roof is arranged vertically, and the roof inspection borehole 11 near the solid coal side is inclined at 20° to the left. The drilling depth is 1.5 times the thickness of the composite roof, and the drilling diameter is 25~35mm.

[0045] Using 4D ultra-high-definition fully intelligent in-hole television equipment, the width and spacing of fractures in the shallow and deep sections of each roof inspection borehole were measured. This equipment can reconstruct the images of each roof inspection borehole into actual core images, such as... Figure 4 As shown. Then, by comparing and analyzing the data on the development of deep and shallow fractures in the roof boreholes at each cross-section of the goaf, the distribution range and development direction of the mining-induced fractures in the composite roof are determined.

[0046] The third step involves moving the composite roof 9 along the vertical and horizontal directions of the cross-section of the goaf.

[0047] The fractured zone is divided into multiple sections;

[0048] Based on the distribution range and development direction of the composite roof mining-induced fractures on the cross-section of the goaf 2, the development degree of the composite roof mining-induced fractures is divided vertically from bottom to top into a strongly developed zone, a moderately developed zone, and a weakly developed zone; and horizontally, the development degree of the composite roof mining-induced fractures is divided from the unmined solid coal face 1 to the goaf 4 into a strongly developed zone, a moderately developed zone, and a weakly developed zone. The mining-induced fracture zone can be divided into nine zones: the upper part of the filling wall 3 is designated as Zone I 151, Zone II 152, and Zone III 153 from bottom to top; the upper part of the goaf 2 is designated as Zone IV 154, Zone V 155, and Zone VI 156 from bottom to top; and the upper part of the solid coal face 1 is designated as Zone VII 157, Zone VIII 158, and Zone IX 159 from bottom to top.

[0049] The fourth step is to determine the rock mass integrity of each zone in the mining-induced fracture zone of the composite roof 9 along the gob-side roadway, determine the grouting parameters for each zone, and calculate the grouting volume for each zone of the composite roof 9 along the gob-side roadway.

[0050] Three roof grouting boreholes are arranged on each cross section of the goaf-retention tunnel 2. Grouting borehole A121 is arranged in zones I, II, and III; only grouting borehole B122 is arranged in zones IV, V, and VI; and only grouting borehole C123 is arranged in zones VII, VIII, and IX.

[0051] The formula for calculating the grouting volume of each zone is Q. i= S i × η × β

[0052] The formula for calculating the theoretical grouting volume per unit length of composite roof slab is as follows:

[0053]

[0054] In the formula: Q i —Composite roof plate per unit length i Grouting volume of the rock mass in the area, m 3 S i —Cross-sectional area of ​​the i-th zone of the composite roof rock mass, m 3 Q 总 — Grouting volume per unit length of composite roof slab, in meters 3 ; η — Rock mass porosity, %; β—Effective filling coefficient of grout in rock mass fissures, the formula for calculating the grouting volume per unit length of composite roof (9) for each zone is:

[0055] Q I、II、III =Q 钻孔A =Q I +Q II +Q III

[0056] Q IV、V、VI =Q 钻孔B =Q IV +Q V +Q VI

[0057] Q VII、VIII、IX =Q 钻孔C =Q VII +Q VIII +Q IX

[0058] The formula for calculating the grouting time for each borehole is:

[0059]

[0060] In the formula: t 钻孔i —Drilling and grouting time, m 3 v—grouting speed, m 3 / s.

[0061] Specifically, based on data such as the crack width and crack spacing of the composite roof on each cross-section of the goaf-side roadway, the rock mass integrity index for each zone of each cross-section is determined. The quantitative index of rock mass integrity is the rock mass integrity coefficient K. v Expression. As shown in Table 1 below, K v Value and number of joints in rock mass J v The values ​​(determined based on the degree of fracture development) correspond one-to-one with the completion level, rock mass structure type, and rock mass porosity of each zone of the composite roof. ηand the effective filling coefficient of grout in the fracture β These parameters correspond to each other, providing important parameters for grouting in the 15m stable section of the composite roof of the goaf-keeping tunnel.

[0062] Table 1 Classification of Rock Strata Integrity

[0063]

[0064] Because the cross-sectional area S of each section of the roof plate above the goaf retainer cross-section i Different, rock mass porosity η and the effective filling coefficient of grout in the fracture β If they are different, then the formula for calculating the grouting volume per unit length of the composite roof slab is:

[0065] Q i= S i × η × β

[0066] The formula for calculating the theoretical grouting volume per unit length of composite roof slab is as follows:

[0067]

[0068] In the formula: Q i —Composite roof plate per unit length i Grouting volume of the rock mass in the area, m 3 S i —Composite roof panel i Cross-sectional area of ​​the rock mass in the area, m 3 Q 总 — Grouting volume per unit length of composite roof slab, in meters 3 ; η —Rock mass porosity, % β —The effective filling coefficient of the grout within the rock mass fissures. Referring to Table 1, the corresponding coefficients for different rock mass structures can be obtained. η Value and β value.

[0069] Generally, three roof grouting boreholes are arranged on each cross-section of the goaf-retaining roadway: borehole A is arranged in zones I, II, and III; borehole B is arranged in zones IV, V, and VI; and borehole C is arranged in zones VII, VIII, and IX. The formula for calculating the grouting volume per unit length of composite roof is as follows:

[0070] Q I、II、III =Q 钻孔A =Q I +Q II +Q III

[0071] Q IV、V、VI =Q钻孔B =Q IV +Q V +Q VI

[0072] Q VII、VIII、IX =Q 钻孔C =Q VII +Q VIII +Q IX

[0073] The formula for calculating the grouting time for each borehole is:

[0074]

[0075] In the formula: t 钻孔i —Drilling and grouting time, m 3 ; v — Grouting speed, m 3 / s.

[0076] The precise calculation of the grouting volume for each zone of the composite roof along the goaf is used as a reference standard for the grouting volume per unit length of the stable section of the composite roof.

[0077] The sixth step is to implement the reinforcement and strengthening scheme of the composite roof slab 9 along the goaf, carry out grouting construction of the composite roof slab 9, and complete the differentiated grouting work for each zone of the composite roof slab 9.

[0078] Three grouting boreholes are arranged on the same cross-section of the goaf retaining roadway. Grouting boreholes A121, B122, and C123 are each installed on the same cross-section of the goaf retaining roadway. The cross-sections where the grouting boreholes are installed are evenly distributed between two adjacent roof separation monitoring stations 8 in the stable zone. The borehole spacing is 1200mm~2000mm, and the row spacing is 1200mm~2000mm.

[0079] The bottom of grouting borehole A121 is 100-300mm from the filling wall and is inclined at 20° towards the goaf 4 side; grouting borehole B122 is located in the middle of the roof and is arranged vertically; the bottom of grouting borehole C123 is 100-300mm from the solid coal face and is inclined at 20° towards the solid coal face 1 side. The grouting boreholes are evenly distributed on a 15m stable section of the composite roof. The diameter of grouting boreholes A121, B122, and C123 is 22-32mm, and the borehole length L = composite roof thickness h + 500mm.

[0080] The reinforcement scheme for the composite roof of the goaf-retaining tunnel is as follows: hollow grouting anchor cables are installed in the grouting boreholes A121, B122, and C123, and the surrounding rock of the goaf-retaining tunnel 2 is sealed by spraying grout.

[0081] Specifically, the first construction step is to install hollow grouting anchors. Hollow grouting anchors are chosen because they allow for grouting and further enhance the strength of the composite roof support. Hollow grouting anchor parameters: diameter 15.24~22mm, hollow grouting pipe diameter 6~10mm, anchor length l = composite roof thickness h + 800mm.

[0082] Generally, the width of the goaf retainer is between 3200 and 4200 mm. This example uses a 3200 mm wide goaf retainer as an example, arranging anchor cable boreholes within a 15 m stable section of the composite roof. It is suitable to arrange 3 boreholes per row in the roof. Grouting borehole A is 200 mm from the filling wall and inclined at 20° towards the goaf side; grouting borehole B is located in the middle of the roof and is arranged vertically; grouting borehole C is 200 mm from the solid coal face and inclined at 20° to one side. The borehole spacing is 1400 mm, and the row spacing is 1000 mm. Figure 6 As shown. The drilling diameter is 22-32mm, the drilling length L = composite top plate thickness h + 500mm, and the drilling equipment adopts ZQJJ120 / 2.3 column-supported drilling rig.

[0083] Construction Step Two: Shotcrete Sealing of the Surrounding Rock in the Goaf Retention Tunnel. To improve the grouting effect of the composite roof in the goaf retention tunnel and prevent grout leakage during grouting, shotcrete is applied as a grout-stopping layer to the stable section of the surrounding rock in the goaf retention tunnel before grouting. The shotcrete parameters are as follows: high-grade 425# cement is used, the shotcrete layer thickness is 70-100mm, and the strength is C20. The material ratio is: cement: yellow sand: gravel = 1:2:2, the water-cement ratio is 0.8-1, and the accelerator dosage is 2.5-4% of the cement weight. After shotcreting, the hollow grouting anchor cables are also sealed, with their tails exposed to the outside for connection to the grouting pipe.

[0084] Construction Step 3: Composite Roof Grouting. Grouting sequence for the composite roof: Drill hole A, Drill hole B, Drill hole C. Grouting parameters: High-grade 425# cement is used; the water-cement ratio of the grout is 1:2; ACZ-I grouting additive is used at 8% of the cement dosage. Its main functions are water reduction, plasticization, reinforcement, and micro-expansion, overcoming the problems of high water-cement ratio, low strength, hardening shrinkage, and high pumping resistance in cement grout.

[0085] Grouting equipment operation process: Connect the grouting pipeline of the grouting equipment to the grouting joint at the tail of the hollow grouting anchor cable, and start the equipment to begin grouting. When the grouting volume reaches the set value for each borehole, the grouting of one hollow grouting anchor cable is completed. Then, grout the other hollow grouting anchor cables one by one according to the grouting sequence until all hollow grouting anchor cables have been grouted.

[0086] Furthermore, each grouting cycle is defined as the completion of a 15m stable section of the composite roof slab along the goaf. When the stable section of the composite roof slab along the goaf reaches 15m again, the next stage of grouting can begin.

[0087] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or its equivalents are included in this invention.

Claims

1. A method for differentiated grouting of mining-induced fracture zones in a composite roof with a goaf-retention tunnel, characterized in that, Includes the following steps, The first step is to conduct delamination observation of the composite roof (9) in the goaf-side roadway (2) of the delayed mining area (7) to determine the range of the stable section of the composite roof (9); The second step is to drill through the composite roof (9) along the goaf to determine the distribution range and development direction of the mining-induced cracks in the composite roof (9). The third step is to divide the mining fracture zone of the composite roof (9) into multiple zones along the vertical and horizontal directions of the cross-section of the goaf-retaining roadway. The fourth step is to determine the rock mass integrity of each zone in the mining fracture zone of the composite roof (9) along the goaf, determine the grouting parameters of each zone, and calculate the grouting volume of each zone in the composite roof (9) along the goaf. The fifth step is to implement the reinforcement scheme of the composite roof slab (9) along the goaf, carry out grouting construction of the composite roof slab (9), and complete the differentiated grouting work of each section of the composite roof slab (9); Among them, roof separation monitoring stations (8) are arranged in the composite roof (9) of the goaf retention roadway within the range of 100-200m in the delayed mining area (7). The boreholes of the roof separation monitoring stations (8) are located in the middle of the composite roof (9) and arranged vertically. 6 to 17 roof separation monitoring stations (8) are arranged along the roadway axis. The last roof separation monitoring station (8) is 5m away from the filling area (5). The distance between each roof separation monitoring station (8) is 15m. When the length of the composite roof (9) in the stable section of the goaf-retention roadway (2) reaches 15m, roof inspection boreholes (11) are arranged on the composite roof (9) that first enters the stable section. The roof inspection boreholes (11) are located on the side of the roof separation monitoring station (8) near the filling area and at a horizontal distance of 250mm~400mm. Three roof inspection boreholes (11) are arranged on the same cross section of the goaf-retention roadway. The roof inspection boreholes (11) near the composite roof (9) in the filling area (5) are inclined at 15°~30° towards the goaf (4). The roof inspection boreholes (11) in the middle of the composite roof (9) are arranged vertically. The roof inspection boreholes (11) near the solid coal side (1) are inclined at 15°~30° to the left. The drilling depth is 1~2 times the thickness of the composite roof (9) and the drilling diameter is 25~35mm. Based on the distribution range and development direction of the composite roof mining-induced fractures on the cross section of the goaf (2), the development degree of the composite roof mining-induced fractures is divided into strong development zone, medium development zone and weak development zone from bottom to top in the vertical direction; and then divided into strong development zone, medium development zone and weak development zone from the unmined solid coal side (1) to the goaf (4) in the horizontal direction. The mining-induced fracture zone can be divided into nine zones. The upper part of the filling wall (3) is set as zone I (151), zone II (152) and zone III (153) from bottom to top, the upper part of the goaf (2) is set as zone IV (154), zone V (155) and zone VI (156) from bottom to top, and the upper part of the solid coal side (1) is set as zone VII (157), zone VIII (158) and zone IX (159) from bottom to top. Three roof grouting boreholes are arranged on each cross section of the goaf (2). Grouting borehole A (121) is arranged in Zone I, Zone II and Zone III, grouting borehole B (122) is arranged in Zone IV, Zone V and Zone VI, and grouting borehole C (123) is arranged in Zone VII, Zone VIII and Zone IX. One grouting borehole A (121), one grouting borehole B (122), and one grouting borehole C (123) are each set in the same cross section of the goaf-retaining roadway. The cross section of the grouting boreholes is evenly distributed between two adjacent roof separation monitoring stations (8) in the stable zone. The bottom of the grouting borehole A (121) is 100~300mm away from the filling wall and is set at a 20° angle towards the goaf (4). The borehole B (122) is located in the middle of the roof and is arranged vertically. The bottom of the grouting borehole C (123) is 100~300mm away from the solid coal side and is set at a 20° angle towards the solid coal side (1). The diameter of the grouting boreholes A (121), B (122), and C (123) is 22-32mm, and the borehole length L = composite roof thickness h + 500mm. The grouting reinforcement scheme for the composite roof of the goaf-retaining tunnel is as follows: hollow grouting anchor cables are installed in the grouting boreholes A (121), B (122), and C (123), and the surrounding rock of the goaf-retaining tunnel (2) is sealed by grouting.

2. The method for differentiated grouting of mining-induced fracture zones in a composite roof with a goaf-retention tunnel as described in claim 1, characterized in that: The formula for calculating the grouting volume for each zone is Q. i= S i × η × β The formula for calculating the theoretical grouting volume per unit length of composite roof slab is: Q = ... i — Grouting volume per unit length of the composite roof in the i-th zone of the rock mass, in m 3 ; S i —Cross-sectional area of ​​the i-th zone of the composite roof rock mass, m 3 ; Q 总 — Grouting volume per unit length of composite roof slab, in meters 3 ; η — Rock mass porosity, %; β—Effective filling coefficient of grout in rock mass fissures, the formula for calculating the grouting volume per unit length of composite roof (9) for each zone is: Q I、II、III =Q 钻孔A =Q I +Q II +Q III Q IV、V、VI =Q 钻孔B =Q IV +Q V +Q VI Q VII、VIII、IX =Q 钻孔C =Q VII +Q VIII +Q IX The formula for calculating the grouting time for each borehole is: In the formula: t 钻孔i —Drilling and grouting time, m 3 v—grouting speed, m 3 / s.

3. The method for differentiated grouting of mining-induced fracture zones in a composite roof with a goaf-retention tunnel as described in claim 1, characterized in that, Each grouting cycle is considered complete when a 15m stable section of the composite roof slab along the goaf is grouted. When the stable section of the composite roof slab along the goaf reaches 15m again, the next stage of grouting can begin.

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