A separation grouting filling method under the condition of gob-side entry retaining with flexible mold wall

Abstract

The present invention discloses a method for separated seam grouting filling under the condition of gob-side entry retaining with flexible mold wall, belonging to the technical field of coal mine filling mining. The method includes the following steps: determining the performance parameters of fly ash-cement slurry, calculating the width and drilling depth of artificial support columns, constructing grouting filling artificial support columns, detecting the strength of support columns and taking reinforcement measures. Through the above steps, the present invention can realize the construction of artificial support columns for separated seam grouting filling under the condition of pillarless mining. The support columns can play a supporting role on the overlying strata, ensuring the smooth progress of the overlying strata isolation grouting work under the condition of pillarless mining.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mine backfill mining, and particularly relates to a separated seam grouting backfill method under the condition of gob-side entry retaining with flexible formwork walls. Background Art

[0002] Overlying strata isolated grouting backfill is a method of high-pressure grouting backfill into the closed separated seam space generated below the key stratum, compacting the swollen rock mass below the key stratum to form a compacted area, supporting the key stratum, and controlling the movement of rock strata and surface subsidence. This method requires leaving a certain width of coal pillars on both sides of the coal mining face to ensure the effect of overlying strata isolated grouting backfill.

[0003] When non-pillar mining is adopted between adjacent left and right working faces, a roadway on the left working face needs to be left for use as the roadway of the right working face. The specific implementation process is as follows: drilling and blasting are carried out at a certain angle with the plumb line along the roof of the reserved roadway towards the left working face to form a pre-splitting cut, and then supplemented with bolt, cable bolt and gangue retaining support to realize the roadway retention under the condition of non-pillar mining. After the left working face is mined, the overlying strata of the left working face collapse along the pre-splitting cut, and the strata above the reserved roadway do not collapse under the support of bolts and cable bolts. At the same time, gangue retaining support is carried out on the side of the reserved roadway close to the goaf of the left working face, such as constructing a flexible formwork wall, to prevent the collapsed gangue from entering the reserved roadway. However, when the right working face is mined, the overlying strata will lose the support of the original coal body and collapse under the action of the upper stratum pressure. The sub-key stratum i bends and sinks, and once it exceeds its maximum deflection, it will break and subside, losing the basic condition for grouting into the separated seam space (below the sub-key stratum i), and overlying strata isolated grouting backfill cannot be carried out.

[0004] In the existing patents, for the coal pillar-free continuous mining overburden separation grouting filling coal mining method in CN202211677467.0, during the mining process of the last coal mining face in two adjacent working faces, the grouting boreholes in the goaf of the last coal mining face are extended to below the water-conducting fissure zone, and the reinforcement slurry is injected into the water-conducting fissure zone and the caving zone through the grouting drill pipe to form a reinforcement area in the water-conducting fissure zone and the caving zone to support the overlying strata. For the overburden separation grouting subsidence reduction method with controllable lag subsidence in CN202210052201.0, grouting is carried out into the floor grouting layer and the secondary grouting layer through the inner cavity of the technical casing of the second grouting borehole to achieve the purpose of putting shoes and hats on the second grouting borehole. At this time, the second grouting borehole is a support pile including a casing, which not only supports the main key stratum but also avoids the possible phenomenon of formation lag subsidence after the implementation of the separation grouting subsidence reduction technology. For the overburden separation grouting subsidence reduction method with a shoe-and-hat type in CN202210052199.7, three layers of separation grouting horizons are designed, namely the main grouting layer near 120 m above the coal seam, the floor grouting layer (putting on shoes) in the floor rock stratum of the coal seam, and the secondary grouting layer (putting on a hat) set under the main key stratum, to improve the support strength for the key stratum and effectively control the surface subsidence. For the method for determining the grouting hole positions for adjacent goaf separation grouting in a strip filling mining working face in CN202211357284.0, first, the position and related parameters of the planned mining face are determined, then the position of the boundary of the coal pillar adjacent to the mining face and the filling rate of the filling face adjacent to the mining face are determined, and the position of the boundary of the equivalent coal pillar of the filling face is obtained according to the filling rate. This method improves the separation grouting filling effect. For the gangue-cemented downward filling coal mining method for extremely close coal seams in CN202310598268.9, by grouting at the roof overburden rock, the filling body and the floor in the upper goaf, the overlying strata, the goaf filling body and the floor form a stable rock mass, realizing the gangue-cemented filling mining of the extremely close coal seam in the lower part and effectively controlling the surface subsidence. The above patents mainly carry out grouting inside the goaf, cementing the caving gangue to support the overlying strata, realizing strata control and reducing surface subsidence, but no patent specifically involves the construction, monitoring and reinforcement methods of artificial support columns for overburden isolation grouting under the condition of coal pillar-free mining. Summary of the Invention

[0005] In order to solve the technical problems existing in the above-mentioned prior art, the present invention provides a separation grouting filling method under the condition of retaining roadway along the goaf with flexible mold walls. Along the advancing direction of the working face, a group of artificial support column grouting boreholes are arranged at intervals of L meters on one side of the cut seam of the reserved roadway. Four grouting boreholes are arranged in each group and grouted in sequence to complete the construction of the support columns. The formed support columns have good consolidation, and compared with fully grouting and filling the inside of the goaf to support the overlying strata, the cost can be effectively reduced.

[0006] To achieve the above object, the present invention provides the following technical solution: A separated layer grouting filling method under the condition of gob-side entry retaining with flexible mold wall, comprising the following steps:

[0007] S1. Determine the performance parameters of fly ash-cement slurry;

[0008] S2. Calculate the width of the artificial support column and the length of the grouting borehole;

[0009] S3. Construct the artificial support column for grouting filling;

[0010] S4. Monitor the strength of the constructed artificial support column, and take reinforcement measures according to whether the core sampling of the inspection borehole is successful.

[0011] As a preferred embodiment, in S1, a thickening agent is added to the fly ash-cement slurry to enable the slurry to concentrate in the target grouting area; the working performance of the fly ash-cement slurry is tested to determine the performance parameters of the fly ash-cement slurry after adding the thickening agent.

[0012] As a preferred embodiment, in S2, the width of the artificial support column is calculated according to the ultimate strength theory; the length of the grouting borehole is calculated according to the width of the upper surface of the grouting support column, the free flow angle of the slurry, the cutting seam angle and the height parameter.

[0013] As a preferred embodiment, the specific steps of constructing the artificial support column for grouting filling in S3 are as follows:

[0014] S31. Construct a grouting borehole ZK1 at an elevation angle of α1° at a distance of t1 meters from the roadway floor on one side of the cut seam on the reserved roadway roof. After the borehole construction is completed, flush the borehole with clean water, then install a perforated pipe, install a flange at the orifice of the perforated pipe for fixation, connect the outer orifice of the flange to a grouting pump to pump in the slurry, and the slurry enters the gob through the perforated pipe; stop grouting when the injected slurry covers the casing of the grouting borehole ZK1. The cross-sectional area of the consolidated body accumulated between the grouting borehole ZK1 and the floor is S1;

[0015] S32. Construct a grouting borehole ZK2 at an elevation angle of α2° at a distance of t2 meters from the roadway floor on one side of the cut seam on the reserved roadway roof, construct a grouting borehole ZK3 at an elevation angle of α3° on the reserved roadway roof, and construct a grouting borehole ZK4 at an elevation angle of α4° on the reserved roadway roof. The construction and grouting steps of the grouting boreholes ZK2 to ZK4 are the same as those of the grouting borehole ZK1. Stop grouting when the grouting slurry fills the area between the two boreholes. The cross-sectional areas of the formed consolidated bodies are S2, S3, and S4 respectively;

[0016] S33. Set a group of artificial support column grouting boreholes at intervals of L meters on one side of the cut seam of the reserved roadway along the working face advancing direction. After a group of artificial support column grouting boreholes are grouted, advance L meters to the next group of grouting boreholes to continue grouting until the construction of the artificial support column is completed.

[0017] As a preferred embodiment, in S4, borehole transient electromagnetic exploration is carried out in the middle of the roadway rib between two groups of grouting boreholes, and the exploration directions are horizontal, elevation angle α 5° and elevation angle α 6° to analyze the filling state and consolidation range of the support columns during the grouting process;

[0018] Inspection boreholes are constructed at an elevation angle α 7° at the junction of the reserved roadway flexible formwork wall and the roof. The inspection boreholes are located between two groups of grouting boreholes. When serious water leakage occurs or unconsolidated rock masses exist during the drilling of the inspection boreholes, additional grouting is carried out through the inspection boreholes; after the core sampling of the inspection boreholes is successful, standard specimens are made and uniaxial compressive tests are carried out to calculate whether the support force of the support columns formed by fly ash-cement slurry and crushed gangue meets the standards. If not, supplementary grouting is carried out through the inspection boreholes until the support force of the support columns meets the design requirements.

[0019] As a preferred embodiment, the calculation formula for the artificial support column obtained according to the ultimate strength theory is:

[0020]

[0021] In the formula, σ1 is the strength of the artificial support column, MPa; l1 is the width of the upper surface of the artificial support column, m; γ s is the unit weight of the loose layer, N / m 3 ; γ j is the unit weight of the bedrock, N / m 3 ; l3 is the width of the reserved roadway and the flexible formwork wall, m; H s is the thickness of the loose layer, m; H j1 is the thickness of the bedrock above the support column on the left working face, m; H j2 is the thickness of the bedrock above the coal seam on the right working face, m; l2 is the width of the lower surface of the artificial support column, m; b1 is the width of the non-compacted area on the left working face; b2 is the width of the non-compacted area on the right working face, m.

[0022] As a preferred embodiment, the calculation formula for the uniaxial compressive strength of the standard specimen made by core sampling of the artificial support column is:

[0023]

[0024] In the formula, σ c is the uniaxial compressive strength of the standard specimen made by core sampling of the artificial support column, MPa; D is the size of the standard specimen of the artificial support column, m; M1 is the height of the artificial support column, m; l1 is the width of the upper surface of the artificial support column, m; n is a coefficient, taking 1.4 when the width-height ratio of the artificial support column is greater than 5, and taking 1.0 otherwise.

[0025] As a preferred embodiment, the widths of the artificial support columns are the upper surface width l1 and the lower surface width l2 respectively; among them,

[0026]

[0027]

[0028] As a preferred embodiment, the calculation formula for checking the length of the borehole is:

[0029]

[0030] In the formula, L5 is the length of the inspection borehole, m; α7 is the elevation angle of the inspection borehole, °; l2 is the width of the lower surface of the artificial support column, m; h is the height of the reserved roadway, m; θ is the free flow angle of the fly ash-cement slurry.

[0031] Compared with the prior art, the present invention provides a separation layer grouting filling method under the condition of leaving a roadway along the goaf with a flexible mold wall, and has the following beneficial effects:

[0032] (1) In the present invention, the caving gangue is consolidated by grouting to artificially construct a support column with a certain strength to support the overlying strata, so that the key stratum does not break during the separation layer grouting mining, thereby controlling the strata movement and reducing the surface subsidence. After the support column is constructed, the sub-key stratum above the separation layer can be grouted without fracture, ensuring the smooth progress of the separation layer grouting filling work under the condition of no coal pillar.

[0033] (2) In the present invention, four grouting boreholes are set to complete the construction of the support column by grouting in sequence. The formed support column has good consolidation, and compared with the full grouting filling of the goaf interior to support the overlying strata, it can effectively reduce the cost.

[0034] (3) In the present invention, a thickening agent is added to the fly ash-cement slurry to increase the viscosity of the fly ash-cement slurry, reduce the flow degree of the fly ash-cement slurry injected into the goaf, make the slurry concentrate in the target grouting area, and reduce the slurry diffusion.

[0035] (4) In the present invention, the filling state, consolidation range, etc. of the support column during the grouting process are analyzed by downhole transient electromagnetic method, and inspection boreholes are constructed in the reserved roadway to detect the state and strength of the support column. If it is found that the consolidation effect of the support column is poor or the supporting force of the support column does not meet the requirements, the inspection boreholes are densified or supplementary grouting is carried out, and at the same time, the secondary utilization of the inspection boreholes is realized. Description of the Drawings

[0036] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, and do not constitute a limitation to the present invention. In the drawings:

[0037] Figure 1It is a flow chart of the construction, monitoring and reinforcement method of the separated layer grouting filling artificial support column under the condition of gob-side entry retaining with flexible mold wall;

[0038] Figure 2 It is a schematic diagram of large-scale similar engineering simulation experiment in the embodiment of the present invention;

[0039] Figure 3 It is a schematic diagram of the artificial support column under the condition of non-pillar mining in the embodiment;

[0040] Figure 4 It is a calculation model diagram of the width of the artificial support column under the condition of non-pillar mining in the embodiment;

[0041] Figure 5 It is a sectional view of the grouting borehole layout in the embodiment of the present invention;

[0042] Figure 6 It is a sectional view of the grouting filling of the artificial support column in the embodiment of the present invention;

[0043] Figure 7 It is a plan view of the grouting borehole layout in the embodiment of the present invention;

[0044] Figure 8 It is a sectional view of the layout of the detection points of the downhole transient electromagnetic exploration in the embodiment of the present invention;

[0045] Figure 9 It is a plan view of the inspection borehole layout in the embodiment of the present invention;

[0046] Figure 10 It is a sectional view of the inspection borehole layout in the embodiment of the present invention. Detailed implementation manners

[0047] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Usually, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the present invention to be protected, but only represents the selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0048] This embodiment proposes a separated layer grouting filling method under the condition of gob-side entry retaining with flexible mold wall, and the detailed steps are as Figures 1 - 10 shown:

[0049] (1) Determine the performance parameters of fly ash-cement slurry.

[0050] Add a thickener to the fly ash - cement slurry to increase its viscosity and reduce the fluidity of the fly ash - cement slurry injected into the goaf, so that the slurry can be concentrated in the target grouting area (the expected fluidity A and expected viscosity B of the fly ash - cement slurry after adding the thickener); conduct tests on the working performance such as the density, fluidity, and viscosity rate of the fly ash - cement slurry to determine the parameters such as the density, fluidity, and viscosity of the fly ash - cement slurry after adding the thickener. First, add different proportions of thickener to the fly ash - cement slurry, fill the slurry in a truncated cone mold, pour it on a fluidity test plate, and test whether the fluidity of the slurry meets the expected fluidity; use a beaker to hold a certain amount of fly ash - cement slurry and obtain the mass of the slurry with an electronic scale to further determine the density of the fly ash - cement slurry; take a certain amount of fly ash - cement slurry with a beaker, immerse the rotor of the viscometer into the slurry in the beaker, and test whether the viscosity of the slurry meets the expected viscosity. Combine the actual situation on the working face and carry out large - scale similar engineering simulation experiments according to a certain similarity ratio (1:50 or 1:100), such as Figure 2 shown. The model has a length of S1 and a height of S2. After the model is laid, set a cut - off seam and a flexible mold wall in the lower - right area to form a cut - top reserved roadway. After the model excavation is completed, apply a load F in the upper - left area on the model. Lay rubber sheets at the joints of each rock layer. The load F is transmitted downward through the rock layer and the rubber sheet and acts on the caving rock layer in the goaf to simulate the compaction effect of the gangue in the middle compaction area of the goaf, and no load is applied in other areas to simulate the non - compaction area in the goaf. Then, arrange grouting perforated pipes at a distance of h1 (along the elevation angle μ°) and h2 (along the horizontal direction) from the bottom on the right side of the model, carry out a grouting simulation test for the artificial support column in the goaf, test the flow of the slurry in the gangue, determine the free - flow angle θ of the slurry in the gangue. After the slurry solidifies, drill cores in the consolidated body to make standard specimens and then carry out uniaxial compression experiments to determine the strength of the consolidated body.

[0051] (2) Calculate the width of the support column and the length of the grouting borehole.

[0052] Calculate the width of the artificial support column according to the ultimate strength theory, that is, the width of the upper surface of the grouting support column in contact with the overlying rock. Calculate the length of the grouting borehole based on parameters such as the width of the upper surface of the grouting support column, the free - flow angle of the slurry, the cut - off seam angle, and the height.

[0053] As Figure 3 shown is a schematic diagram of the artificial support column under the condition of pillarless mining. Pillarless mining is adopted between the left and right working faces. A flexible mold wall is set on the side of the reserved roadway close to the goaf for gangue support. The included angle between the roof cut - off seam and the plumb line is α°. After the separated - layer grouting filling, a compaction area will be formed in the middle area of the goaf, and the two sides are non - compaction areas. After constructing the support column, the support column bears the weight of the overlying rock layer and half of the weight of the rock layer above the non - compaction areas on both sides of the goaf.

[0054] Simplify the force-bearing situation of the support pillars and establish a model. The calculation model diagram of the width of the artificial support pillars after simplification is as shown in Figure 4 the figure below.

[0055] When the working face length is determined, the width c1 of the compacted area is determined by the injection-production ratio K. Then, the width c1 of the compacted area on the left working face is:

[0056] c1 = K1a1 (1)

[0057] In the formula, c1 is the length of the compacted area on the left working face, m; K1 is the injection-production ratio of the left working face; a1 is the length of the left working face, m.

[0058] Therefore, the width b1 of the non-compacted area on the left working face is:

[0059]

[0060] In the formula, b1 is the width of the non-compacted area on the left working face, m.

[0061] Similarly, the widths of the compacted area and the non-compacted area on the right working face are respectively:

[0062] c2 = K2a2 (3)

[0063]

[0064] In the formula, c2 is the length of the compacted area on the right working face, m; K2 is the injection-production ratio of the right working face; a2 is the length of the right working face, m; b2 is the width of the non-compacted area on the right working face, m.

[0065] H 左 = H s + H j1 (5)

[0066] In the formula, H 左 is the thickness of the formation above the support pillars on the left working face, m; H s is the thickness of the loose layer, m; H j1 is the thickness of the bedrock above the support pillars on the left working face, m.

[0067] H 右 = H s + H j2 (6)

[0068] In the formula, H 右 is the thickness of the formation above the coal seam on the right working face, m; H j2 is the thickness of the bedrock above the coal seam on the right working face, m.

[0069] Since roof cutting is carried out between the left and right working faces, the height of the support pillars is:

[0070] H d = lcosα + h (7)

[0071] In the formula, H d is the height of the support column, m; l is the cutting depth, m; α is the angle between the cutting seam and the plumb line, °; h is the height of the reserved roadway, m.

[0072] H j1 = H j2 + M - H d (8)

[0073] In the formula, M is the coal seam thickness, m.

[0074] Since the width of the flexible mold wall is small, the supporting effect of the flexible mold wall is ignored. According to the ultimate strength theory, the calculation formula for the artificial support column is as follows:

[0075]

[0076] In the formula, σ1 is the strength of the artificial support column, MPa; l1 is the width of the upper surface of the artificial support column, m; γ s is the unit weight of the loose layer, N / m 3 ; γ j is the unit weight of the bedrock, N / m 3 ; l3 is the width of the reserved roadway and the flexible mold wall, m.

[0077]

[0078] In the formula, σ c is the uniaxial compressive strength of the standard specimen made by core drilling of the artificial support column, MPa; D is the size of the standard specimen of the artificial support column (the diameter of the cylindrical specimen or the side length of the cubic specimen), m; M1 is the height of the artificial support column, m; n is a coefficient, taking 1.4 when the width-to-height ratio of the artificial support column is greater than 5, and taking 1.0 otherwise.

[0079] From Equation (9) and Equation (10), we get:

[0080]

[0081]

[0082] In the formula, l2 is the width of the lower surface of the artificial support column, m.

[0083] As Figure 5 shown in the sectional view of the grouting borehole layout, the length of the grouting borehole ZK1 is calculated according to parameters such as the width of the upper surface of the grouting support column, the free flow angle of the grout, the cutting seam angle, and the height:[[]]

[0084]

[0085] In the formula, L1 is the length of the grouting borehole ZK1, in m; θ is the free flow angle of the fly ash-cement slurry, in °; α1 is the upward angle of the grouting borehole ZK1, in °; t1 is the distance from the front end of the grouting borehole ZK1 to the bottom of the roadway, in m.

[0086] The length of the grouting borehole ZK2 is:

[0087]

[0088] In the formula, L2 is the length of the grouting borehole ZK2, in m; α2 is the upward angle of the grouting borehole ZK2, in °; t2 is the distance from the front end of the grouting borehole ZK2 to the bottom of the roadway, in m.

[0089] The length of the grouting borehole ZK3 is:

[0090]

[0091] In the formula, L3 is the length of the grouting borehole ZK3, in m; α3 is the upward angle of the grouting borehole ZK3, in °.

[0092] The length of the grouting borehole ZK4 is:

[0093]

[0094] In the formula, L4 is the length of the grouting borehole ZK4, in m; α4 is the upward angle of the grouting borehole ZK4, in °.

[0095] (3) Construct a grouting and filling artificial support column.

[0096] ① First, construct the grouting borehole ZK1 at an upward angle of α1° at a distance of t1 meters from the bottom of the roadway on one side of the reserved roadway roof cut. After the drilling construction is completed, flush the borehole with clean water, then install a perforated pipe, install a flange at the orifice of the perforated pipe for fixation, connect the outer orifice of the flange to a grouting pump to pump in the slurry. The slurry enters the goaf through the perforated pipe. The perforated pipe is evenly distributed with small holes, which can make the slurry flow out evenly and improve the grouting quality. Stop grouting when the injected slurry covers the casing of the grouting borehole ZK1. At this time, the cross-sectional area of the consolidation body accumulated between the grouting borehole ZK1 and the bottom plate is S1.

[0097] ② Then, construct the grouting borehole ZK2 at an upward angle of α2° at a distance of t2 meters from the bottom of the roadway on one side of the reserved roadway roof cut. The drilling construction and grouting steps are the same as those of the grouting borehole ZK1. Stop grouting when the grouting slurry fills the area between the grouting boreholes ZK2 and ZK1. At this time, the cross-sectional area of the consolidation body accumulated between the grouting boreholes ZK2 and ZK1 is S2.

[0098] ③ Then, construct a grouting borehole ZK3 at an upward angle of α3° on the roof of the reserved roadway towards the side of the cut seam. The final hole position of the grouting borehole ZK3 is in the upper fractured rock mass. The construction and grouting steps of the borehole are the same as those of the grouting borehole ZK1. Stop grouting when the grouting slurry fills the area between the grouting boreholes ZK2 and ZK1. At this time, the cross-sectional area of the consolidated body accumulated between the grouting boreholes ZK2 and ZK1 is S3 (excluding the cross-sectional area of the grouting area in the fractured rock mass above the support column).

[0099] ④ Then, construct a grouting borehole ZK4 on the roof of the reserved roadway along the direction of the roof cut seam on the side towards the cut seam. The final hole position of the grouting borehole ZK4 is in the upper fractured rock mass, and the upward angle of the borehole is α4°, where α4° = α°. The construction and grouting steps of the borehole are the same as those of the grouting borehole ZK1. Stop grouting when the grouting slurry fills the area between the grouting boreholes ZK2 and ZK1. At this time, the cross-sectional area of the cemented body accumulated between the grouting boreholes ZK2 and ZK1 is S4 (excluding the cross-sectional area of the grouting area in the fractured rock mass above the support column). The cross-sectional area of the artificial support column consists of four parts: S1, S2, S3, and S4, as Figure 6 shown.

[0100] ⑤ Set a group of artificial support column grouting boreholes at intervals of L meters on the side of the cut seam of the reserved roadway along the working face advancing direction. The spacing L of the grouting boreholes is comprehensively determined by parameters such as the slurry flow radius and the slurry free flow angle. Figure 7 is the layout plan of the grouting boreholes. After a group of artificial support column grouting boreholes are grouted, advance L meters to the next group of grouting boreholes to continue grouting until the construction of the artificial support column is completed.

[0101] (4) Support column strength monitoring and reinforcement measures

[0102] Conduct underground transient electromagnetic exploration at the middle of the roadway rib between two groups of grouting boreholes, with three directions for each group: horizontal, upward angle α5°, and upward angle α6°, and the spacing between each group is L meters. Analyze the filling state, consolidation range, etc. of the support column during the grouting process. The cross-sectional view of the transient electromagnetic exploration point layout is as Figure 8 shown, and the cross-sectional view of the point layout is the same as Figure 9 the inspection borehole layout in. After the consolidated body solidifies, construct an inspection borehole at an upward angle of α7° at the junction of the flexible formwork wall and the roof of the reserved roadway. The length of the inspection borehole is L5 meters. The inspection borehole is located between two groups of grouting boreholes. To avoid blockage of the inspection borehole, install a slotted pipe immediately after the borehole construction is completed.

[0103] The calculation formula for the length of the inspection borehole is:

[0104]

[0105] In the formula, L5 is the length of the inspection borehole, m; α7 is the upward angle of the inspection borehole, °.

[0106] When serious water leakage occurs during the inspection of borehole drilling or there are unconsolidated rock masses, additional grouting is carried out through the inspection boreholes. After successful core sampling from the inspection boreholes, standard specimens are made and uniaxial compressive tests are carried out to calculate whether the bearing capacity of the support columns formed by fly ash-cement slurry and broken gangue meets the standard. If not, supplementary grouting is carried out through the inspection boreholes until the bearing capacity of the support columns meets the design requirements.

[0107] In the description of the present invention, the terms "first", "second", "another", and "yet another" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more features. In the description of the embodiments of the present invention, the meaning of "a plurality" is two or more unless otherwise specifically defined.

[0108] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations. In addition, in the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more.

[0109] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for separated seam grouting filling under the condition of gob-side entry retaining with flexible mold wall, characterized in that, Including the following steps: S1. Determine the performance parameters of fly ash - cement slurry: Add a thickening agent to the fly ash - cement slurry to enable the slurry to concentrate in the target grouting area; Test the working performance of the fly ash - cement slurry to determine the performance parameters of the fly ash - cement slurry after adding the thickening agent; S2. Calculate the width of the artificial support column and the length of the grouting borehole: Calculate the width of the artificial support column according to the ultimate strength theory; Calculate the length of the grouting borehole based on the width of the upper surface of the grouting support column, the free - flow angle of the slurry, the cutting - slot angle, and the height parameter S3. Construct the grouting - filled artificial support column, and the specific steps are as follows: S31. At a distance of t 1 meters from the floor of the roadway on one side of the cut seam in the roof of the reserved roadway, drill a grouting borehole ZK1 at an elevation angle of α 1 °. After the drilling of the borehole is completed, flush the borehole with clean water, then install a perforated pipe, install a flange at the orifice of the perforated pipe for fixation, connect the outer orifice of the flange to a grouting pump to pump in the grout, and the grout enters the gob through the perforated pipe; stop grouting when the injected grout covers the casing of the grouting borehole ZK1. The cross-sectional area of the consolidation body accumulated between the grouting borehole ZK1 and the floor is S1; S32. At a distance of t 2 meters from the side of the cut seam on the roof of the reserved roadway and at an elevation angle of α 2 °, construct the grouting borehole ZK2. At an elevation angle of α 3 °, construct the grouting borehole ZK3 on the roof of the reserved roadway. At an elevation angle of α 4 °, construct the grouting borehole ZK4. The construction and grouting steps of the grouting boreholes ZK2 - ZK4 are the same as those of the grouting borehole ZK1. Stop grouting when the grouting slurry fills the area between two boreholes. The cross-sectional areas of the formed consolidated bodies are S2, S3, and S4 respectively; S33. Along the advancing direction of the working face, a set of grouting boreholes for artificial support columns is arranged at intervals of L meters on one side of the cut seam in the reserved roadway. After the grouting of a set of grouting boreholes for artificial support columns is completed, move forward L meters to the next set of grouting boreholes for continuous grouting until the construction of artificial support columns is completed; S4. Monitor the strength of the constructed artificial support pillars and take reinforcement measures according to whether the coring of the inspection boreholes is successful: Select the middle part of the roadway side between two groups of grouting boreholes for underground transient electromagnetic exploration. The exploration directions are horizontal, elevation angle α 5 °, and elevation angle α 6 °, and analyze the filling state and consolidation range of the support pillars during the grouting process; Construct an inspection borehole at an upward angle at the intersection of the flexible mold wall of the reserved roadway and the roof. α 7 ° The inspection borehole is located between two groups of grouting boreholes. When serious water leakage occurs during the drilling of the inspection borehole or there are unconsolidated rock masses, additional grouting is carried out through the inspection borehole. After successful core sampling of the inspection borehole, standard specimens are made and uniaxial compressive tests are carried out to calculate whether the bearing capacity of the support columns formed by fly ash-cement slurry and crushed gangue meets the standard. If not, supplementary grouting is carried out through the inspection borehole until the bearing capacity of the support columns meets the design requirements.

2. The method for separated seam grouting filling under the condition of gob-side entry retaining with flexible mold wall according to claim 1, wherein, The calculation formula for the artificial support column obtained according to the ultimate strength theory is: ； Wherein, σ 1 is the strength of the artificial support column, MPa; l 1 is the width of the upper surface of the artificial support column, m; γ s is the unit weight of the loose layer, N / m 3 ; γ j is the unit weight of the bedrock, N / m 3 ; l 3 is the width of the reserved roadway and the flexible mold wall, m; H s is the thickness of the loose layer, m; H j1 is the thickness of the bedrock above the support column on the left working face, m; H j2 is the thickness of the bedrock above the coal seam on the right working face, m; l 2 is the width of the lower surface of the artificial support column, m; b 1 is the width of the non-compacted area of the left working face; b 2 is the width of the non-compacted area of the right working face, m.

3. A separation grouting filling method under the condition of gob-side entry retaining with flexible mold wall according to claim 1, characterized in that, The calculation formula for the uniaxial compressive strength of the standard specimen made by core - drilling in the artificial support column is: ； In the formula, σ c is the uniaxial compressive strength of the standard specimen made by core drilling of the artificial support column, MPa; D is the size of the standard specimen of the artificial support column, m; M 1 is the height of the artificial support column, m; l 1 is the width of the upper surface of the artificial support column, m; n is a coefficient, taking 1.4 when the width-height ratio of the artificial support column is greater than 5, and taking 1.0 otherwise.

4. A separation grouting filling method under the condition of gob-side entry retaining with flexible formwork wall according to claim 3, characterized in that, The widths of the artificial support columns are the width of the upper surface l 1 and the width of the lower surface l 2 ; Among them, 。 5. A separation grouting filling method under the condition of gob-side entry retaining with a flexible mold wall according to claim 1, characterized in that The calculation formula for checking the length of the borehole is: ； In the formula, L 5 is the length of the inspection borehole, m; α 7 is the elevation angle of the inspection borehole, °; l 2 is the width of the lower surface of the artificial support column, m; h The height of the reserved roadway, m; θ is the free flow angle of the fly ash-cement slurry.

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