A method and device for hydraulic fracturing roof cutting and roadway protection in coal mine preparation roadway

Abstract

The application discloses a method and device for hydraulic pressure cracking roof cutting and roadway protection in a coal mine preparation roadway, and relates to the technical field of coal mine preparation roadway hydraulic pressure cracking roof cutting and roadway protection. The method comprises the following steps: determining a preparation roadway needing roadway protection, a support layer and a collapse zone height; a first key layer is a rock layer above a coal seam, the thickness of the rock layer is greater than a preset thickness threshold, and the maximum uniaxial compressive strength of the rock layer is greater than a preset strength threshold; according to an acting load and a limit span, a jth key layer is continuously searched until the height of the jth key layer exceeds the collapse zone height, and the search for a j+1th key layer is stopped; a minimum roof hanging length is determined according to a rock layer breaking angle; and the rock layer and the key layer at an anchoring end are cracked to make the key layer and soft rock controlled by the key layer collapse synchronously into a goaf. The method can destroy the overburden rock structure above the roof, transfer the stress above the coal pillar to the goaf, reduce the stress of the coal pillar and the intensity of the roadway surrounding rock pressure appearance, and achieve the purposes of improving the roadway protection effect, reducing the roadway repair amount and realizing the stable control of the roadway.

Description

Technical Field

[0001] This invention relates to the field of coal mining technology, specifically to a method and apparatus for hydraulic fracturing and roof cutting and roadway protection in coal mine preparation roadways. Background Technology

[0002] Mine development roadways and mining area preparation roadways generally have a long service life, serving numerous functions such as material transportation and personnel access throughout the mining area. The stable control of these roadways is crucial for safe mine production. During coal mining, protective coal pillars are often installed to protect the roadways serving the entire mining period. After mining ends, the overlying strata shift downwards, and the protective coal pillars bear the pressure of the overlying strata. When the coal pillars are narrow, the pressure from the overlying strata can significantly impact the roadway ahead of the working face, causing substantial deformation and leading to problems such as roadway instability and large deformations.

[0003] In existing technologies, two common methods are used to prevent deformation of the coal pillar: support reinforcement and surrounding rock reinforcement. Support reinforcement includes using anchor bolts and cables. Anchor bolts can reinforce the surrounding rock strata, forming a load-bearing structure. Through the anchoring effect of anchor bolts, loose rocks in the surrounding rock are connected to stable rock masses, improving the overall strength of the surrounding rock. Surrounding rock reinforcement includes injecting cement grout or chemical grout into the surrounding rock, which can fill cracks and pores in the surrounding rock, improving its strength and integrity. However, while support reinforcement and surrounding rock reinforcement improve the deformation resistance of the protective coal pillar, they do not reduce the stress above the protective coal pillar and cannot fundamentally solve the problem of coal pillar deformation.

[0004] Therefore, those skilled in the art urgently need to find a new technical solution to address the aforementioned problems. Summary of the Invention

[0005] To overcome the problems existing in related technologies, this invention discloses a method and apparatus for hydraulic fracturing and roof cutting and roadway protection in coal mine preparation roadways.

[0006] According to a first aspect of the present invention, a method for hydraulic fracturing and roof cutting / roadway protection in a coal mine preparation roadway is provided, the method comprising:

[0007] The preparation roadway that needs protection, the support layer above the coal seam, and the height of the fracture zone are determined. The reason for the overhang and the lengthening of the overhang in the preparation roadway is the support layer.

[0008] The first rock stratum above the coal seam with a thickness greater than a preset thickness threshold and a maximum uniaxial compressive strength greater than a preset strength threshold is identified as the first critical stratum.

[0009] After determining the first key layer, based on the load and ultimate span of the key layer on other rock layers, the search continues for the second, third, ..., j, j+1 key layers until the height of the j-th key layer exceeds the height of the fracture zone, at which point the search for the j+1-th key layer stops. Specifically, the load exerted by the (m+1)-th rock layer above the j-th key layer on the j-th key layer is less than the load exerted by the (m)-th rock layer above the j-th key layer on the j-th key layer, and the ultimate span of the j+1-th key layer during the working face mining process is greater than the ultimate span of the j-th key layer during the working face mining process.

[0010] The minimum overhang length of the soft rock layer controlled by the key layer is determined based on the rock stratum fracture angle, the distance between the top of the key layer controlling the soft rock and the coal seam, and the width of the retreat roadway.

[0011] Fracturing is performed on the rock strata and key strata at the anchoring end so that the key strata and the soft rock controlled by the key strata collapse synchronously into the goaf.

[0012] Optionally, determining the roadways requiring protection includes:

[0013] Based on the first judgment condition, the second judgment condition, the third judgment condition, and the fourth judgment condition, it is determined whether the prepared roadway needs to be protected. If any one of the first judgment condition, the second judgment condition, the third judgment condition, and the fourth judgment condition is met, it is determined that the prepared roadway needs to be protected.

[0014] The first determination condition is to determine whether the surface displacement of the prepared roadway is significant. The first determination condition includes a first determination sub-condition, a second determination sub-condition, and a third determination sub-condition. The first determination sub-condition is to determine whether the cumulative subsidence of the roof exceeds 100mm. The second determination sub-condition is to determine whether the height of the floor heave exceeds 5% of the roadway height. The third determination sub-condition is to determine whether the convergence of the two sides exceeds 2 consecutive days, and whether the convergence amount exceeds 3mm / day or the total convergence amount exceeds 200mm. If any one of the first determination sub-condition, the second determination condition, and the third determination condition is met, then the first determination condition is established.

[0015] The second judgment condition is to determine whether the surrounding rock damage has worsened. The second judgment condition includes: a first judgment sub-condition and a second judgment sub-condition. The first judgment sub-condition is to determine whether the delamination within the anchorage range exceeds 10mm, and whether the delamination outside the anchorage range exceeds 30mm. The second judgment sub-condition is to determine whether the spalling depth exceeds 10cm, and whether the spalling area is greater than 1m². 2 If either the first decision sub-condition or the second decision sub-condition is satisfied, then the second decision condition is valid.

[0016] The third determination condition is to determine whether the support structure has failed. The third determination condition includes: a first determination sub-condition and a second determination sub-condition. The first determination sub-condition is to determine whether the anchor bolt / anchor cable has loosened or fallen off. The second determination sub-condition is to determine whether the shotcrete layer has peeled off and cracked, and the crack width exceeds 3mm and the depth exceeds 1 / 3 of the concrete layer thickness. If either the first determination sub-condition or the second determination sub-condition is met, the third determination condition is established.

[0017] The fourth determination criterion is to determine whether the prepared roadway affects production activities.

[0018] Optionally, determine the height of the rift zone, including:

[0019] Determine whether the mining company has provided a report on the "three belts" (mineral, gas, and coal seams) of the goaf;

[0020] If the mining company provides a report on the "three zones" of the goaf, the height of the fracture zone shall be determined based on the report.

[0021] If the mining company does not provide a report on the "three zones" of the goaf, the height of the fracture zone shall be determined based on the roof lithology and empirical formula for fracture zones.

[0022] Optionally, the preset thickness threshold is 2.0m, and the preset strength threshold is 60MPa.

[0023] Optionally, after determining the first key layer, based on the load and ultimate span of the key layer on other rock strata, the search continues for the second, third, ..., j, j+1 key layers until the height of the j-th key layer exceeds the height of the fracture zone, at which point the search for the j+1 key layer stops, including:

[0024] After determining the first key layer, calculate the first action load (q) of the m-th rock layer above the first key layer on the first key layer. m ) n , and the first limit span L1 when the first key layer fractures during the mining process of the working face, and so on, when searching for the second, third, ..., j, j+1 key layers, calculate the corresponding load and limit span;

[0025] Continue searching for the second, third, ..., j, j+1 key layers, where the second, third, ..., j, j+1 key layers satisfy the condition (q) m+1 ) n <(q) m ) n L j <Lj +1 Lj +1The limit span of the (j+1)th key layer when it fractures during the mining process at the working face;

[0026] The search for the (j+1)th key layer is stopped when the height of the found j-th key layer exceeds the height of the fracture zone.

[0027] Optionally, the first action load (q) of the m-th rock layer above the first key layer on the first key layer. m ) n for:

[0028]

[0029] Where, q n =r n h n q n For the load of the nth rock layer itself, r n Let h be the volume force of the nth rock layer. n Let E be the thickness of the nth rock layer, and E be the elastic modulus of the rock layer.

[0030] The ultimate span Lj when the j-th key layer fractures during the mining process of the working face is:

[0031]

[0032] Where Lj is the ultimate span when the j-th rock layer fractures, and R T Let be the tensile strength of the nth rock layer.

[0033] Optionally, determining the minimum overhang length of the key layer controlling the soft rock stratum based on the rock stratum fracture angle, the distance between the top of the key layer controlling the soft rock and the coal seam, and the width of the retreat roadway includes:

[0034] Based on the rock strata fracture angle, the distance between the top of the key layer controlling the soft rock and the coal seam, and the width of the retreat roadway, the minimum overhang length of the key layer controlling the soft rock is determined as follows:

[0035] Where b is the minimum overhang length of the soft rock layer controlled by the key layer, α is the rock layer fracture angle, h is the distance between the top of the soft rock layer controlled by the key layer and the coal seam, and w is the width of the retreat roadway.

[0036] According to a second aspect of the present invention, an apparatus for hydraulic fracturing and roof cutting in a coal mine preparation roadway is provided, the apparatus comprising:

[0037] The roadway information determination module determines the roadway that needs to be protected, the support layer above the coal seam, and the height of the fracture zone. The reason for the overhang and the lengthening of the overhang in the prepared roadway is the support layer.

[0038] The first key layer determination module is connected to the roadway information determination module. It determines the first key layer as the first rock layer that appears above the coal seam with a thickness greater than a preset thickness threshold and a maximum uniaxial compressive strength greater than a preset strength threshold.

[0039] The key layer determination module continues, connected to the first key layer determination module. After determining the first key layer, based on the load and ultimate span of the key layer on other rock layers, the search for the second, third, ..., j, j+1 key layers continues until the height of the j-th key layer exceeds the height of the fracture zone, at which point the search for the j+1-th key layer stops. Specifically, the load of the (m+1)-th rock layer above the j-th key layer on the j-th key layer is less than the load of the (m)-th rock layer above the j-th key layer on the j-th key layer, and the ultimate span of the j+1-th key layer during the working face mining process is greater than the ultimate span of the j-th key layer during the working face mining process.

[0040] The overhang length determination module is connected to the key layer determination module. Based on the rock stratum fracture angle, the distance between the top of the key layer controlled soft rock and the coal seam, and the width of the retreat roadway, the minimum overhang length of the key layer controlled soft rock layer is determined.

[0041] The hydraulic fracturing module, connected to the suspended length determination module, fractures the rock strata and key strata at the anchoring end so that the key strata and the soft rock controlled by the key strata collapse synchronously into the goaf.

[0042] Optionally, the tunnel information determination module includes:

[0043] The report information determination unit determines whether the mining party has provided a report on the "three zones" of the goaf.

[0044] The first height determination unit is connected to the report information determination unit. If the mine provides a report on the "three zones" of the goaf, the height of the fracture zone is determined based on the report on the "three zones" of the goaf.

[0045] The second height determination unit is connected to the report information determination unit. If the mine does not provide a report on the "three zones" of the goaf, the height of the fracture zone is determined based on the roof lithology and empirical formula for the fracture zone.

[0046] Optionally, the further determination of key layer modules includes:

[0047] The load calculation unit, after determining the first key layer, continues to search for the second, third, ..., j, j+1 key layers based on the load and ultimate span of the key layer on other rock layers, until the height of the j-th key layer exceeds the height of the fracture zone, at which point the search for the j+1-th key layer stops; wherein, the load of the (m+1)-th rock layer above the j-th key layer on the j-th key layer is less than the load of the (m)-th rock layer above the j-th key layer on the j-th key layer, and the ultimate span of the j+1-th key layer when it fractures during the working face mining process is greater than the ultimate span of the j-th key layer when it fractures during the working face mining process;

[0048] Continue identifying key layer units and connecting them to the load calculation unit, then continue searching for the second, third, ..., j, j+1 key layers. The second, third, ..., j, j+1 key layers must satisfy condition (q). m+1 ) n <(q) m ) n L j <Lj +1 Lj +1 The limit span of the (j+1)th key layer when it fractures during the mining process at the working face;

[0049] The search for the (j+1)th key layer is stopped when the height of the found j-th key layer exceeds the height of the fracture zone.

[0050] In summary, this invention discloses a method and apparatus for hydraulic fracturing and roof cutting in a coal mine preparation roadway. The method includes: determining the height of the preparation roadway, supporting layer, and fracture zone to be protected; identifying the first critical layer as the first rock stratum whose thickness exceeds a preset thickness threshold and whose maximum uniaxial compressive strength exceeds a preset strength threshold, based on the applied load and ultimate span; continuing to search for the j-th critical layer until its height exceeds the fracture zone height, at which point the search for the j+1-th critical layer stops; determining the minimum overhang length based on the rock stratum fracture angle; and fracturing the rock stratum and critical layer at the anchoring end to allow the critical layer and the soft rock controlled by it to simultaneously collapse into the goaf. This method can transfer stress above the coal pillar to the goaf by disrupting the overlying rock structure above the roof, reducing the stress on the coal pillar and the intensity of the surrounding rock pressure in the roadway, thereby improving the roadway protection effect, reducing roadway repair work, and achieving stable roadway control.

[0051] Other features and advantages disclosed in this invention will be described in detail in the following detailed description section. Attached Figure Description

[0052] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0053] Figure 1 This is a schematic flowchart illustrating a method for hydraulic fracturing and roof cutting in a coal mine preparation roadway, according to an exemplary embodiment.

[0054] Figure 2 Schematic diagram for preparing for the protection of coal pillars and roofs in roadways;

[0055] Figure 3 This is a schematic diagram of the suspension theory anchor support;

[0056] Figure 4 This is a schematic diagram of the theoretical anchor bolt support for composite beams.

[0057] Figure 5 This is a schematic diagram of the withdrawal tunnel and roof.

[0058] Figure 6 This is a structural block diagram of an apparatus for hydraulic fracturing, roof cutting, and roadway protection in a coal mine preparation roadway, according to an exemplary embodiment.

[0059] Figure 7 It is based on Figure 6 The diagram shown is a structural block diagram of a roadway information determination module.

[0060] Figure 8 It is based on Figure 6 The diagram illustrates a structural block diagram for further defining key layer modules. Detailed Implementation

[0061] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present disclosure.

[0062] Figure 1 This is a schematic flowchart illustrating a method for hydraulic fracturing and roof cutting / roadway protection in a coal mine preparation roadway, according to an exemplary embodiment. Figure 1 As shown, the method includes:

[0063] In step 101, the preparation roadway requiring roadway protection, the support layer above the coal seam, and the height of the fracture zone are determined.

[0064] The reason for the suspended roof and its lengthening in the preparation roadway is the support layer.

[0065] For example, the technical solution in the disclosed embodiments of the present invention, by destroying the overburden structure above the roof, transfers the stress above the coal pillar to the goaf, reduces the stress on the coal pillar and the intensity of the mine pressure manifestation in the surrounding rock of the roadway, thereby achieving the purpose of improving the roadway protection effect, reducing the amount of roadway repair, and realizing the stability control of the roadway.

[0066] Determining whether the roadway is severely deformed and requires roadway protection involves assessing whether the roadway surface displacement is significant, whether the surrounding rock damage has worsened, whether the support structure has failed, and whether it affects mine ventilation, vehicle movement, equipment handling, and other production activities.

[0067] Specifically, determining which roadways require protection involves: Based on a first, second, third, and fourth judgment condition, determining whether the roadway requires protection. If any one of these conditions is met, the roadway requires protection. The first judgment condition is whether the surface displacement of the roadway is significant. This condition includes a first sub-condition, a second sub-condition, and a third sub-condition. The first sub-condition is whether the cumulative roof subsidence exceeds 100mm, and the second sub-condition is whether the floor heave height exceeds the required level. The third judgment condition is to determine whether the convergence of the two sides exceeds 2 consecutive days, whether the convergence amount exceeds 3mm / day, or whether the total convergence amount exceeds 200mm. If any one of the first, second, and third judgment conditions is met, then the first judgment condition is valid. The second judgment condition is to determine whether the surrounding rock damage has intensified. The second judgment condition includes the first and second judgment conditions. The first judgment condition is to determine whether the delamination within the anchorage range exceeds 10mm, and whether the delamination outside the anchorage range exceeds 30mm. The second judgment condition is to determine whether the depth of the spalling exceeds 10cm, and whether the area of ​​the spalling is greater than 1m². 2 If either the first or the second sub-condition is met, the second condition is established. The third condition is to determine whether the support structure has failed. The third condition includes the first and the second sub-conditions. The first condition is to determine whether the anchor bolt / anchor cable has loosened or fallen off. The second condition is to determine whether the shotcrete layer has peeled off and cracked, and the crack width exceeds 3mm and the depth exceeds 1 / 3 of the concrete layer thickness. If either the first or the second condition is met, the third condition is established. The fourth condition is to determine whether the preparation roadway affects production activities.

[0068] For example, determining whether a roadway is severely deformed includes:

[0069] (1) Obvious surface displacement of the roadway: ① The cumulative subsidence of the roof exceeds 100mm; ② The height of the floor heave exceeds 5% of the roadway height; ③ The sides converge for more than 2 consecutive days, and the convergence exceeds the normal range (more than 3mm / day) or the total convergence exceeds the specified limit (more than 200mm); If any of the above conditions are met, it can be regarded as serious deformation of the roadway.

[0070] (2) The surrounding rock damage has worsened: ① Delamination within the anchorage area exceeds 10 mm, and delamination outside the anchorage area exceeds 30 mm; ② Spalling occurs frequently, with spalling depths exceeding 10 cm and areas greater than 1 m². 2 If any one of the above conditions is met, the tunnel can be considered to be severely deformed.

[0071] (3) Support structure failure: ① Anchor bolt (cable) failure: Check the working condition of the anchor bolts (cables). When the anchor bolts (cables) show signs of loosening, falling off, or breakage, it indicates that the support structure can no longer effectively control the deformation of the surrounding rock. ② Shotcrete spalling and cracking: When the shotcrete layer shows large-area spalling and cracking, and the crack width is large (e.g., exceeding 3mm) and the depth is deep (e.g., exceeding 1 / 3 of the concrete layer thickness), it indicates that the shotcrete can no longer effectively seal the surface of the surrounding rock and cannot provide sufficient support for the surrounding rock. In this case, the surrounding rock is easily affected by weathering, water erosion, and other factors, further aggravating the deformation of the preparation roadway. If any of the above conditions are met, it can be considered that the deformation of the preparation roadway is serious.

[0072] (4) It affects mine ventilation, vehicle movement, equipment handling and other production activities.

[0073] It is understandable that if any one of the four judgment conditions (1), (2), (3), and (4) is met, it can be considered that the roadway is severely deformed.

[0074] After confirming severe deformation of the preparation roadway, it is necessary to investigate the cause of the deformation and identify the roof-cutting and pressure-relieving rock strata in order to carry out subsequent roadway protection operations. When investigating the cause of the deformation, it is considered that the side of the preparation roadway's protective coal pillar is a retreat roadway. The retreat roadway serves as the exit channel for the "three-machine set" (working face, mining equipment, and machinery) of the working face. The retreat roadway is large, basically the same size as the opening cut. Based on the current mining equipment dimensions, the width of the retreat roadway is generally around 5m, and the height is generally 2-5m, with a maximum of 9m. This means that the overhang of the roof in the retreat roadway on the side of the preparation roadway's protective coal pillar is caused by the support structure. Combined with the inherent strength of the rock strata, this extends the overhang distance under the support. Furthermore, due to the support structure, the rock strata in the supported area failed to collapse, resulting in the rock strata above the supported area also failing to collapse in time, causing an even larger overhang. Consequently, the weight of the overhanging rock strata is entirely borne by the coal pillar of the protective roadway, leading to large deformation of the protective coal pillar, which indirectly causes large deformation of the roadway. The overhang of the protective coal pillar side of the preparation roadway... Figure 2As shown.

[0075] The process of determining the rock strata for roof cutting and pressure relief includes determining the support layer, and determining the key layer above the anchor support based on suspension theory, reinforced arch theory, etc. According to the key layer theory, only by destroying the key layer in the fracture zone can the key layer and the soft rock controlled by the key layer collapse synchronously into the goaf, thereby further reducing the load on the protective coal pillar of the preparation roadway and reducing the deformation rate of the protective coal pillar.

[0076] The suspension theory states that in coal roadways where one or more layers of false roofs are highly susceptible to collapse, a combined bolt and cable support method should be used, with the suspension theory applied in the design. The role of the bolts is to suspend the weaker, more easily collapsing rock layers on top of stable rock layers, thereby enhancing the stability of the weaker rock layers. According to the suspension theory, as long as the rock layer at the bolt's anchoring end is damaged, releasing the bolt's suspension effect, the supported rock layer will collapse. The collapsed rock layer into the goaf will reduce the load on the protective coal pillar in the prepared roadway, thus mitigating its deformation to some extent. A schematic diagram of bolt support based on the suspension theory is shown below. Figure 3 As shown.

[0077] The reinforced arch theory states that when anchor bolts are anchored in the surrounding rock, the anchoring force generates radial and tangential constraints within the rock. This creates multiple areas of compressive stress concentration in the surrounding rock, which overlap and connect to form a continuous arched reinforcement zone (compression arch) around the tunnel. This arched structure can withstand pressure from the surrounding rock mass and the superimposed rock mass, transmitting the pressure to deeper rock layers, thus maintaining the stability of the tunnel. According to the suspended reinforced arch theory, since the arched structure can withstand pressure from the surrounding rock mass and the superimposed rock mass, if the support layer is damaged, the weaker rock layers above the support layer can also collapse. A schematic diagram of anchor bolt support based on the composite beam theory is shown below. Figure 4 As shown.

[0078] A key stratum refers to a rock stratum within the overlying rock mass that controls its movement. In a multi-layered overlying rock system, a particular stratum possesses relatively high stiffness and strength. Bearing its own weight and the weight of the overlying strata, it exerts a significant control over the deformation and movement of the underlying strata; this stratum is the key stratum. According to the key stratum theory, only by destroying the key stratum within the fracture zone can the key stratum and the soft rock it controls simultaneously collapse into the goaf, further reducing the load on the protective coal pillars in the preparation roadway and slowing down the deformation rate of the protective coal pillars.

[0079] Further, determining the height of the fracture zone includes: determining whether the mining company has provided a report on the "three zones" of the goaf;

[0080] If the mine provides a report on the "three zones" of the goaf, the height of the fracture zone is determined based on the report; if the mine does not provide a report on the "three zones" of the goaf, the height of the fracture zone is determined based on the roof lithology and empirical formulas for fracture zones.

[0081] Specifically, the height of the fracture zone is determined using the fracture zone calculation formula or based on the "Three Zones" report of the goaf provided by the mine. The empirical formula for the fracture zone is shown in Table 1.

[0082] Table 1: Empirical Formulas for Fracture Zones

[0083]

[0084] Among them, H li ∑M represents the height of the fracture zone, in meters; ∑M represents the mining height, in meters.

[0085] In step 102, the first rock stratum above the coal seam whose thickness is greater than a preset thickness threshold and whose maximum uniaxial compressive strength is greater than a preset strength threshold is identified as the first key stratum.

[0086] Specifically, the preset thickness threshold is 2.0m and the preset strength threshold is 60MPa. That is, the first rock layer above the coal seam with a thickness greater than 2.0m and a maximum uniaxial compressive strength greater than 60MPa is the first key layer.

[0087] In step 103, after determining the first key layer, the search continues to find the second, third, ..., j, j+1 key layers based on the load and ultimate span of the key layer on other rock layers, until the height of the j-th key layer exceeds the height of the fracture zone, at which point the search for the j+1 key layer stops.

[0088] Among them, the load exerted by the (m+1)th rock layer above the j-th key layer on the j-th key layer is less than the load exerted by the (m)th rock layer above the j-th key layer on the j-th key layer, and the ultimate span of the (j+1)th key layer when it fractures during the working face mining process is greater than the ultimate span of the j-th key layer when it fractures during the working face mining process.

[0089] Specifically, after determining the first critical layer, based on the load exerted by the critical layer on other rock layers and the ultimate span, the search continues for the second critical layer, which is then used as the first critical layer for further searching. The search for the second critical layer continues until its height exceeds the height of the fracture zone, at which point the search for the second critical layer stops. This includes: after determining the first critical layer, calculating the first load (q) exerted by the m-th rock layer above the first critical layer on the first critical layer. m ) nAnd the first ultimate span L1 when the first key layer fractures during the mining process of the working face, and so on, when searching for the second, third, ..., j, j+1 key layers, calculate the corresponding applied load and ultimate span; continue to search for the second, third, ..., j, j+1 key layers, the second, third, ..., j, j+1 key layers satisfy the condition (q m+1 ) n <(q) m ) n L j <Lj +1 Lj +1 The limit span of the (j+1)th key layer when it fractures during the mining process at the working face; the search for the (j+1)th key layer is stopped when the height of the found key layer exceeds the height of the fracture zone.

[0090] The first action load (q) of the m-th rock layer above the first key layer on the first key layer. m ) n for:

[0091]

[0092] Where, q n =r n h n q n The load on the nth rock layer itself is expressed in kPa, r. n The volumetric force of the nth rock layer is expressed in kN / m. 3 h n The thickness of the nth rock layer is in meters (m), and E is the elastic modulus of the rock layer in gigabytes of pressure (GPa).

[0093] The ultimate span Lj of the j-th key layer when it fractures during the mining process is:

[0094]

[0095] Where Lj is the ultimate span at which the j-th critical layer fractures, in meters, and R... T This represents the tensile strength of the nth rock layer, expressed in MPa.

[0096] For example, using the critical layer theory, the critical layers (including the first, second, third, ..., j, j+1 critical layers, which can also be represented as the main critical layer, sub-critical layer, etc.) are calculated. When the height of the hard rock exceeds the height of the fracture zone, the determination of the critical layer is stopped, i.e., the search for the j+1th critical layer is stopped. Once the first critical layer is determined, it is used as the first rock layer whose load needs to be calculated. The load of the m-th rock layer above the first critical layer on the first critical layer is calculated. Let m = 1, n = 1, and calculate (q... m )n At this point, (q1)1 represents the load exerted by the key layer on itself; let n = 1, m = 2, calculate the load exerted by the first rock layer above the first key layer on the first key layer; let n = 1, m = 3, calculate the load exerted by the key layer on the first rock layer above it, and so on. Until (q m+1 ) n <(q) m ) n L j <Lj +1 When a second critical layer is found, for example, when the fifth rock layer above the first critical layer is the second critical layer, let n=6 and m=6. At this time, the load on the second critical layer itself is calculated. Based on the above calculation method, the load on the second critical layer from other rock layers above the second critical layer is calculated step by step. The loads when m=7 and n=6, m=8 and n=6, m=9 and n=6, and so on, are calculated step by step until the third critical layer is found. Then, the load on the third critical layer itself and the load on the third critical layer from the rock layers above the third critical layer are calculated.

[0097] It should be noted that m+1 here represents the second key layer. This is for the sake of explanation. When m is a certain value, the process of determining the next rock layer as the second key layer, i.e., layer m+1, is used.

[0098] In step 104, the minimum overhang length of the key layer controlling the soft rock is determined based on the rock stratum fracture angle, the distance between the top of the key layer controlling the soft rock and the coal seam, and the width of the retreat roadway.

[0099] Specifically, when considering rock strata fracture, the influence of the rock strata fracture angle must be taken into account. Based on the rock strata fracture angle, the distance between the top of the key stratum controlling the soft rock and the coal seam, and the width of the retreat roadway, the minimum overhang length of the key stratum controlling the soft rock is determined. This includes: determining the minimum overhang length of the key stratum controlling the soft rock based on the rock strata fracture angle, the distance between the top of the key stratum controlling the soft rock and the coal seam, and the width of the retreat roadway. Where b is the minimum overhang length of the soft rock layer controlled by the key layer, α is the rock layer fracture angle, h is the distance between the top of the soft rock layer controlled by the key layer and the coal seam, and w is the width of the retreat roadway.

[0100] In step 105, the rock strata and key strata at the anchoring end are fracturing so that the key strata and the soft rock controlled by the key strata collapse synchronously into the goaf.

[0101] Example 1:

[0102] According to the technical solution disclosed in this invention, the following exemplary embodiments are provided:

[0103] The process of hydraulic fracturing for roof cutting and roadway protection in a certain coal mine includes: determining whether the prepared roadway is severely deformed, identifying the cause of the deformation of the prepared roadway, determining the rock strata for roof cutting and pressure relief, fracturing and anchoring the rock strata at the anchoring end, and the key layer.

[0104] Specifically, to determine whether the preparation roadway is severely deformed: the roof of the coal mine preparation roadway has subsided by more than 100mm and the sidewalls have moved closer by more than 300mm, affecting mine ventilation, vehicle movement, equipment handling and other production activities, and is therefore classified as a severely deformed roadway.

[0105] The cause of the deformation in the prepared roadway was determined: the support of the retreat roadway in this coal mine was as follows: Figure 5 As shown in the diagram, the mining side is supported by fiberglass reinforced plastic (FRP), while the roof and coal pillar sides are supported by rebar. During mining, the mining side and FRP are removed, and the "three-machine set" (referring to the three mining machines) enters the retreat roadway. At this time, the roof and protective coal pillar side supports maintain the stability of the mining roadway, ensuring the safe retreat of the "three-machine set." The roof and protective coal pillar side supports also cause the protective coal pillar side to be suspended, at which point the coal pillar bears the weight of the suspended rock strata, increasing the deformation of the coal pillar.

[0106] Identifying the rock stratum for top-cutting and pressure relief: The rock stratum supported by the anchor bolts is the support layer, from... Figure 5 As can be seen, the support layer is 6.86m siltstone. According to the suspension theory and the reinforced arch theory, the hydraulic fracturing support layer can cause the 6.86m siltstone support layer to collapse, or it can cause the weak rock layers controlled by the support layer, namely the 1.28m limestone and the 8.01m silty mudstone, to collapse.

[0107] The key strata above the anchor bolt support were determined. The physical and mechanical parameters of each rock stratum in the coal mine are shown in Table 2.

[0108] Table 2 Physical and mechanical parameters of various rock strata in coal mines

[0109]

[0110]

[0111] According to the report on the "Three Zones" of the roof goaf provided by the mine, the coal seam of the mine is No. 4 coal seam with a thickness of 1.64m. The fracture zone (goaf of working face 11081) is 24.82m long. From the bottom plate of the goaf of working face 11081 above the boundary of the floor plate of 24.82m to the ground surface is the overlying rock bending and subsidence zone.

[0112] As shown in Table 2, the first rock layer above the coal seam is 20.59m of chert limestone with a uniaxial compressive strength of 104.20 MPa. Therefore, the 20.59m chert limestone is the first key layer. Since the fracture zone is 24.82m, the cumulative thickness of the 6.86m siltstone, 1.28m limestone, 8.01m silty mudstone, and 20.59m chert limestone above the coal seam is 6.86 + 1.28 + 8.01 + 20.59m = 36.74m, which is greater than the 24.82m fracture zone. The rock layers above the 20.59m chert limestone are not within the fracture zone and will not fracture; therefore, the determination of a key layer is no longer necessary (i.e., no second key layer is sought). Thus, the 20.59m chert limestone above the coal seam is the first key layer.

[0113] The critical layer failure angle ranges from 57° to 71°, while the physical similarity simulation failure angle ranges from 50° to 70°. Taking a failure angle of 50°, the minimum overhang length b is calculated based on this failure angle.

[0114]

[0115] The theoretical minimum suspended length of the coal pillar for roadway protection is 36.2m.

[0116] Based on the minimum overhang length, key layer, and support layer, the rock strata at the anchoring end and the key layer are fractured. The rock strata at the anchoring end are the support layer, namely siltstone with a rock stratum thickness of 6.86m, and the key layer is tuff limestone with a rock stratum thickness of 20.59mm.

[0117] Figure 6 This is a structural block diagram of an apparatus for hydraulic fracturing and roof cutting in a coal mine preparation roadway, according to an exemplary embodiment. Figure 6 As shown, the device 600 includes:

[0118] The roadway information determination module 610 determines the roadway that needs to be protected, the support layer above the coal seam, and the height of the fracture zone. The reason for the overhang of the roadway and the lengthening of the overhang is the support layer.

[0119] The first key layer determination module 620 is connected to the roadway information determination module and determines the first key layer as the first rock layer that appears above the coal seam with a thickness greater than a preset thickness threshold and a maximum uniaxial compressive strength greater than a preset strength threshold.

[0120] Continue to determine the key layer module 630, which is connected to the first key layer determination module. After determining the first key layer, based on the load and ultimate span of the key layer on other rock layers, similarly continue to search for the second, third, ..., j, j+1 key layers until the height of the j-th key layer exceeds the height of the fracture zone, at which point the search for the j+1-th key layer stops. Among these, the load of the (m+1)-th rock layer above the j-th key layer on the j-th key layer is less than the load of the (m)-th rock layer above the j-th key layer on the j-th key layer, and the ultimate span of the j+1-th key layer when it fractures during the working face mining process is greater than the ultimate span of the j-th key layer when it fractures during the working face mining process.

[0121] The overhang length determination module 640 is connected to the key layer determination module 630. Based on the rock stratum fracture angle, the distance between the top of the key layer controlled soft rock and the coal seam, and the width of the retreat roadway, the minimum overhang length of the key layer controlled soft rock layer is determined.

[0122] The hydraulic fracturing module 650, connected to the suspended length determination module 640, fractures the rock strata and key strata at the anchoring end so that the key strata and the soft rock controlled by the key strata collapse synchronously into the goaf.

[0123] Figure 7 It is based on Figure 6 The diagram shown is a structural block diagram of a roadway information determination module, such as... Figure 7 As shown, the tunnel information determination module 610 includes:

[0124] Report information determination unit 611 determines whether the mining party has provided a report on the "three zones" of the goaf;

[0125] The first height determination unit 612 is connected to the report information determination unit 611. If the mine provides a report on the "three zones" of the goaf, the height of the fracture zone is determined based on the report on the "three zones" of the goaf.

[0126] The second height determination unit 613 is connected to the report information determination unit 612. If the mine does not provide a report on the "three zones" of the goaf, the height of the fracture zone is determined based on the roof lithology and empirical formula of the fracture zone.

[0127] Figure 8 It is based on Figure 6 The diagram shown represents a further step in defining the key layer modules, such as... Figure 8 As shown, the critical layer module 630 is further defined, including:

[0128] The load calculation unit 631, after determining the first key layer, continues to search for the second, third, ..., j, j+1 key layers based on the load and ultimate span of the key layer on other rock layers, until the height of the j-th key layer exceeds the height of the fracture zone, at which point the search for the j+1-th key layer stops; wherein, the load of the (m+1)-th rock layer above the j-th key layer on the j-th key layer is less than the load of the (m)-th rock layer above the j-th key layer on the j-th key layer, and the ultimate span of the j+1-th key layer when it fractures during the working face mining process is greater than the ultimate span of the j-th key layer when it fractures during the working face mining process;

[0129] Continue to identify key layer unit 632, connect it to the applied load calculation unit 631, and continue to search for the second, third, ..., j, j+1 key layers. The second, third, ..., j, j+1 key layers satisfy the condition (q) m+1 ) n <(q) m ) n L j <Lj +1 Lj +1 The limit span of the (j+1)th key layer when it fractures during the mining process at the working face;

[0130] The search for the (j+1)th key layer is stopped when the height of the found j-th key layer exceeds the height of the fracture zone.

[0131] In summary, this invention discloses a method and apparatus for hydraulic fracturing and roof cutting in a coal mine preparation roadway. The method includes: determining the height of the preparation roadway, supporting layer, and fracture zone to be protected; identifying the first critical layer as the first rock stratum whose thickness exceeds a preset thickness threshold and whose maximum uniaxial compressive strength exceeds a preset strength threshold, based on the applied load and ultimate span; continuing to search for the j-th critical layer until its height exceeds the fracture zone height, at which point the search for the j+1-th critical layer stops; determining the minimum overhang length based on the rock stratum fracture angle; and fracturing the rock stratum and critical layer at the anchoring end to allow the critical layer and the soft rock controlled by it to simultaneously collapse into the goaf. This method can transfer stress above the coal pillar to the goaf by disrupting the overlying rock structure above the roof, reducing the stress on the coal pillar and the intensity of the surrounding rock pressure in the roadway, thereby improving the roadway protection effect, reducing roadway repair work, and achieving stable roadway control.

[0132] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0133] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0134] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for hydraulic fracturing roof cutting and roadway protection in a coal mine preparation roadway, characterized in that, The method comprises: determining a preparation roadway needing to be protected, a support layer above a coal seam, and a caving and cracking zone height; determining a first key layer as a first rock layer appearing above the coal seam, the first rock layer having a thickness greater than a preset thickness threshold value and a maximum uniaxial compressive strength greater than a preset strength threshold value; after determining the first key layer, according to the acting load and the limit span of the key layer on other rock layers, the second, third, …, j, j+1 key layers are continuously searched for, until the height of the jth key layer exceeds the caving and cracking zone height, and the search for the j+1 key layer is stopped; wherein the acting load of the m+1 layer rock layer above the jth key layer on the jth key layer is less than the acting load of the m layer rock layer above the jth key layer on the jth key layer, and the limit span of the j+1 key layer when breaking in the mining process of the working face is greater than the limit span of the jth key layer when breaking in the mining process of the working face; According to the rock fracture angle, the distance between the top of the key stratum controlled soft rock and the coal seam, and the width of the withdrawn roadway, the minimum overhang length of the key stratum controlled soft rock is determined, and the minimum overhang length of the key stratum controlled soft rock is determined according to the formula Determination, wherein, is the minimum overhang length of the key stratum controlled soft rock, a is the rock fracture angle, h is the distance between the top of the key stratum controlled soft rock and the coal seam, and w is the width of the withdrawn roadway. fracturing the rock layer at the anchoring end and the key layer to make the key layer and soft rock controlled by the key layer collapse synchronously into the goaf.

2. The method of preparing a coal mine gateway for hydraulic fracturing top- cutting and gateway protection according to claim 1, characterized in that, The method comprises: determining whether the preparation roadway needs to be protected according to a first determination condition, a second determination condition, a third determination condition, and a fourth determination condition, if any of the first determination condition, the second determination condition, the third determination condition, and the fourth determination condition is met, it is determined that the preparation roadway needs to be protected; wherein the first determination condition is to determine whether the surface displacement of the preparation roadway is obvious, the first determination condition comprises a first determination sub-condition, a second determination sub-condition, and a third determination sub-condition, the first determination sub-condition is to determine whether the roof cumulative subsidence exceeds 100 mm, the second determination sub-condition is to determine whether the floor heave height exceeds 5% of the roadway height, and the third determination sub-condition is to determine whether the convergence of the two sides exceeds 2 consecutive days, and the convergence amount exceeds 3 mm / day or the total convergence amount exceeds 200 mm, if any of the first determination sub-condition, the second determination sub-condition, and the third determination sub-condition is met, the first determination condition is established; The second determination condition is used to determine whether the damage of the surrounding rock is aggravated, and the second determination condition comprises a first determination sub-condition and a second determination sub-condition. 2 The first determination sub-condition is used to determine whether the separation distance in the anchoring range is greater than 10 mm and the separation distance outside the anchoring range is greater than 30 mm, and the second determination sub-condition is used to determine whether the slice depth is greater than 10 cm and the slice area is greater than 1 m 2 If any one of the first determination sub-condition and the second determination sub-condition is met, the second determination condition is established. the third determination condition is to determine whether the support structure fails, the third determination condition comprises a first determination sub-condition and a second determination sub-condition, the first determination sub-condition is to determine whether the anchor rod / anchor cable appears tray loosening or falling off, and the second determination sub-condition is to determine whether the shotcrete layer appears spalling and cracking, and the crack width exceeds 3 mm and the depth exceeds 1 / 3 of the thickness of the shotcrete layer, if any of the first determination sub-condition and the second determination sub-condition is met, the third determination condition is established; the fourth determination condition is to determine whether the preparation roadway affects production activities.

3. The method of preparing a coal mine gateway for hydraulic fracturing top- cutting and gateway protection according to claim 1, characterized in that, The method comprises: determining whether the mine provides a "three-zone" report of the goaf; if the mine provides the "three-zone" report of the goaf, determining the caving and cracking zone height according to the "three-zone" report of the goaf; if the mine does not provide the "three-zone" report of the goaf, determining the caving and cracking zone height according to the roof lithology and the caving and cracking zone empirical formula.

4. The method of preparing a coal mine gateway for hydraulic fracturing top- cutting and gateway protection according to claim 1, characterized in that, The preset thickness threshold value is 2.0 m, and the preset strength threshold value is 60 MPa.

5. The method of preparing a coal mine gateway for hydraulic fracturing top- cutting and gateway protection according to claim 1, characterized in that, After the first key layer is determined, the second, third, …, j, j+1 key layers are searched according to the acting load and the limit span of the key layer on other rock layers, and the search for the j+1 key layer is stopped until the height of the j key layer exceeds the caving and cracking zone height. After the first key layer is determined, the first action load of the mth stratum above the first key layer on the first key layer is calculated and the first limit span of the first key layer when it is broken during the mining of the working face In this way, the corresponding action load and limit span are calculated when the second, third, …, j, j+1 key layers are searched Continue to find second, third,..., j, j+1 key layers, which satisfy the condition , , is the limit span of the j+1 key layer when the j+1 key layer is fractured during the working face mining process; The search for the j+1 key layer is stopped until the height of the j key layer exceeds the caving and cracking zone height.

6. The method of preparing a coal mine gateway for hydraulic fracturing top-coal caving and gateway protection according to claim 5, characterized in that, The first action load of the mth stratum above the first key stratum on the first key stratum is: ； wherein, , is the load of the nth layer of rock itself, is the volume force of the nth layer of rock, is the thickness of the nth layer of rock, is the elastic modulus of the nth layer of rock; the limit span of the jth key stratum when it breaks during working face mining is: ； wherein, Lj is the ultimate span of the jth layer of rock strata when fractured, σn is the tensile strength of the nth layer of rock strata.

7. A device for hydraulic fracturing roof cutting and roadway protection in preparation of a coal mine roadway, characterized in that, The device comprises: A roadway information determination module for determining the preparation roadway needing to be protected, the support layer above the coal seam and the caving and cracking zone height; A first key layer determination module connected with the roadway information determination module, for determining the first key layer as the first rock layer appearing above the coal seam and having a thickness greater than a preset thickness threshold and a maximum uniaxial compressive strength greater than a preset strength threshold; A continue determination key layer module connected with the first key layer determination module, for determining the first key layer, and then searching for the second, third, …, j, j+1 key layers according to the acting load and the limit span of the key layer on other rock layers, and stopping the search for the j+1 key layer until the height of the j key layer exceeds the caving and cracking zone height; wherein the acting load of the m+1 layer rock layer above the j key layer on the j key layer is less than the acting load of the m layer rock layer above the j key layer on the j key layer, and the limit span of the j+1 key layer when fractured in the working face mining process is greater than the limit span of the j key layer when fractured in the working face mining process; The overhang length determining module is connected with the key layer determining module, and determines the minimum overhang length of the key layer controlling soft rock according to the rock breakage angle, the distance between the top of the key layer controlling soft rock and the coal seam, and the width of the withdrawn roadway, wherein the overhang length determining module determines the minimum overhang length according to the formula determines the minimum overhang length, wherein, the minimum overhang length of the key layer controlling soft rock, the rock breakage angle, the distance between the top of the key layer controlling soft rock and the coal seam, and the width of the withdrawn roadway. A hydraulic fracturing module connected with the hanging roof length determination module, for fracturing the rock layer and the key layer at the anchoring end, so that the key layer and the soft rock controlled by the key layer are synchronously caved into the goaf.

8. The device for hydraulic fracturing roof cutting and roadway protecting in preparation roadway of coal mine according to claim 7, characterized in that, The roadway information determination module comprises: A report information determination unit for determining whether the mine side provides a goaf "three zone" report; A first height determination unit connected with the report information determination unit, for determining the caving and cracking zone height according to the goaf "three zone" report if the mine side provides the goaf "three zone" report; A second height determination unit connected with the report information determination unit, for determining the caving and cracking zone height according to a top coal roof lithology and caving and cracking zone empirical formula if the mine side does not provide the goaf "three zone" report.

9. The device for hydraulic fracturing roof cutting and roadway protecting in preparation roadway of coal mine according to claim 7, characterized in that, The continue determination key layer module comprises: An acting load calculation unit for determining the first key layer, and then searching for the second, third, …, j, j+1 key layers according to the acting load and the limit span of the key layer on other rock layers, and stopping the search for the j+1 key layer until the height of the j key layer exceeds the caving and cracking zone height; wherein the acting load of the m+1 layer rock layer above the j key layer on the j key layer is less than the acting load of the m layer rock layer above the j key layer on the j key layer, and the limit span of the j+1 key layer when fractured in the working face mining process is greater than the limit span of the j key layer when fractured in the working face mining process; The key layer unit is connected with the action load calculation unit, and the second, third, …, j, j+1 key layers are continuously searched, wherein the second, third, …, j, j+1 key layers satisfy the conditions , , is the limit span of the j+1 key layer when the j+1 key layer is fractured during the working face mining process. The search for the j+1 key layer is stopped until the height of the j key layer exceeds the caving and cracking zone height.

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