Method for controlling overburden activity in a rock mass fracture network weakened caving stope

Abstract

The application discloses a method for weakening and controlling overburden rock activity in a rock fracture network, and relates to the technical field of mine exploitation. Firstly, the mining conditions, geological characteristics and mechanical parameters are collected, and the rock three-zone range is demarcated; then, the thickness and quantity of the rock to be transformed are deduced through a filling balance formula; subsequently, directional drilling is arranged and the fracture network is weakened, and high-position thick hard rock layers can be supplemented by ground pulse fracturing; finally, multi-dimensional monitoring and evaluation are carried out, and the parameters are dynamically optimized. The application improves the rock fragmentation and swelling by constructing a continuous fracture network, converts the lower fracture zone into a caving zone, and fully fills the mined-out area after the caving rock is fully fragmented and swelled, thereby inhibiting the violent activity of the rock. The application is suitable for mine shock and rock burst prevention and control, coal and gas outburst prevention and control, coal measure associated and accompanying mineral coordinated exploitation and water conservation mining, and provides a new technical path for mine disaster prevention and control and multi-resource coordinated exploitation.

Description

Technical Field

[0001] This invention relates to the field of mining technology, specifically to a method for controlling the activity of overlying strata in a stope by weakening and fracturing rock fracture networks. Background Technology

[0002] In underground mining operations such as coal and metal mines, the stability control of overlying strata is crucial for safe and efficient production. Traditional roof management primarily relies on the natural caving method. This method utilizes the natural fracturing of the immediate roof after coal seam mining and the fracturing and filling of the goaf by the underlying roof, limiting excessive subsidence of the overlying strata. It is suitable for scenarios where the immediate roof is prone to collapse and the mechanical parameters of the underlying roof are moderate. However, it has significant limitations under complex roof conditions dominated by thick, hard strata. Natural caving of thick, hard strata is difficult, requiring prolonged exposure before fracturing. During this period, elastic energy easily accumulates, becoming a major energy source for mine earthquakes and rock bursts. Even after fracturing, its low coefficient of fragmentation prevents sufficient filling of the goaf, resulting in a lack of effective support for subsequent critical strata at higher levels, making them prone to instantaneous fracturing and further exacerbating roof risks and potential disaster hazards. To address this problem, existing technologies employ top-cutting and stress-relief techniques such as deep-hole blasting, conventional hydraulic fracturing, and CO2 phase transformation fracturing. These techniques reduce stress concentration in areas prone to rockbursts and mine-induced tremors by cutting off a layer of hard, thick rock above the coal seam, thus shifting high-stress areas from the shallow to the deeper layers of the rock mass and preventing rockbursts and mine-induced tremors. However, multiple layers of hard, thick rock are often distributed above the coal seam and to the surface. Cutting off a layer using top-cutting and stress-relief techniques provides localized stress relief and has a certain short-term effect on preventing rockbursts. However, higher layers may still contain hard, thick rock. As the cut rock layer fractures and subsides, delamination easily occurs between it and the higher-level hard, thick rock. With the increasing amount of delamination, the higher-level hard rock may fracture instantaneously, still posing a risk of inducing mine-induced tremors. Therefore, current top-cutting and stress-relief technologies cannot fundamentally solve the problem of mine-induced tremors. Summary of the Invention

[0003] The purpose of this invention is to propose a method for controlling the activity of overlying strata in the mining area by weakening the fracture network of rock strata. This method shifts from the traditional method of cutting the top to relieve pressure to supporting the overlying strata. By actively supporting the overlying strata, it avoids the delamination caused by uneven settlement of the strata, thereby preventing the hard and thick strata from breaking due to delamination, and ultimately avoiding the risk of mine tremors from the root.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is: a method for controlling the activity of overlying strata in a mining area by weakening and fracturing rock fracture networks, characterized by comprising the following steps:

[0005] Step S1: Collect core parameters based on mining conditions and roof geological characteristics of the mining face:

[0006] (1) Determine the working face height, advance speed, mining length and coal seam depth, and calculate the free space of the goaf. ;

[0007] (2) Obtain the horizontal and vertical stress distribution of the working face through ground stress monitoring;

[0008] (3) The mechanical parameters of the thick and hard rock layers in the direct top and lower fracture zones and the thick and hard rock layers in the upper position, including thickness, uniaxial compressive strength, tensile strength, elastic modulus and natural swelling coefficient, were determined by drilling and rock mechanics test.

[0009] (4) The range of the caving zone, fracture zone and bending subsidence zone was delineated by the "three-zone" measurement method, and the natural rupture coefficient of each rock layer was marked;

[0010] Step S2: Based on the analysis results of Step S1, with the goal of completely filling the goaf with rock fragments, the thickness of the rock strata to be modified is derived using the goaf filling balance formula. The balance formula includes equations (1) to (6), where S0 in equation (1) is the free space of the goaf before the fracture mesh weakening:

[0011] Mode ;

[0012] In the formula, The thickness of the coal seam being mined is in meters (m). The thickness of the direct top is in meters (m). The direct top natural expansion rate is dimensionless; For the first Thickness of the rock layer, in meters; For the first Natural fragmentation rate of the rock layer, dimensionless;

[0013] like When the value is ≤0, natural fracturing can fill the goaf; if When the value is greater than 0, there are still remaining gaps that need to be filled artificially. Therefore, the target rock layer needs to be weakened by fracture mesh treatment, and the fragmentation rate of the target rock layer becomes... Let the number of rock layers requiring fracture mesh weakening be... There are , and their index set is denoted as . Its thickness is ;

[0014] Free space after mesh weakening : Mode ;

[0015] In the formula, For the free space in the goaf after the mesh weakens, m; For the first The thickness of the rock strata is weakened by the fracture network, in meters; For the first Artificial fragmentation rate of rock strata, dimensionless; To include the weakened set of each layer in the mesh in the formula;

[0016] Relating equation (2) with equation (1) as follows: Mode ;

[0017] In the formula: For the first The natural rupture rate of the rock strata;

[0018] To achieve the equilibrium condition of exactly filling or leaving no gaps, take: Mode ,

[0019] Right now: Mode ;

[0020] Let the contribution of each fracture network weakened candidate stratum to filling the free space be... ,according to Arranged in descending order , It is a set The total number of intermediate rock layers is the minimum number of weakened layers. satisfy:

[0021] Mode ;

[0022] In the formula: The minimum number of rock layers required to weaken the fracture network is dimensionless.

[0023] Step S3: Arrange directional boreholes according to the target rock layer range to weaken the fracture network of the target rock layer, and at the same time arrange observation boreholes at the edge of the fracture network expansion area to monitor fracture development;

[0024] Step S4: After completing the S3 fracture mesh weakening construction, assess the ground settlement situation: If monitoring shows that the ground settlement control effect meets the standard, with no obvious settlement or the settlement amount is within the allowable range, proceed directly to the S5 effect acceptance stage; if monitoring reveals ground settlement (including a small amount of settlement caused by the recompaction of gangue in the goaf), supplementary control measures need to be taken for the high-level thick and hard rock layers, namely, using ground pulse fracturing technology. This can be achieved by drilling horizontal wells on the ground and performing segmented pulse fracturing to form a fracture cushion layer. The fracture cushion layer can be used to fill the delamination space and absorb deformation energy, thereby weakening the impact of violent rock layer movement on the ground from the source and effectively controlling ground settlement.

[0025] Step S5: Evaluate the weakening effect of the fracture network using multi-dimensional methods including borehole inspection and stress displacement monitoring: Focus on monitoring the fracture density, continuity, and filling effect of the collapsed rock layer. If fracture development or insufficient fragmentation is found, optimize the borehole layout and weakening parameters in a timely manner based on the monitoring results to ensure that the filling effect of the goaf reaches the preset requirements, thereby ensuring that the movement of the overlying rock layer in the mining area is always under control.

[0026] As a further improvement of the present invention, in step S3, pulse fracturing or blasting is used as a means of weakening the seam mesh.

[0027] As a further improvement of the present invention, when the method is used to prevent and control rockbursts and mine tremors, in step S1, it is also necessary to measure the coal seam gas content and the surrounding rock stress distribution; in step S3, long boreholes are arranged in the roadway on both sides of the mining area towards the thick and hard roof and fracture mesh weakening is implemented, so that the rock strata are broken and filled into the delamination space, and the high-level thick and hard rock strata slowly bend and sink, inhibiting the excessive accumulation of elastic energy, thereby alleviating rockbursts and mine tremors.

[0028] As a further improvement of the present invention, when the method is used for the coordinated mining of coal-bearing associated minerals, the lithology and mechanical parameters of the coal seam and associated mineral layers are comprehensively measured in step S1; in step S3, fracture weakening is implemented in the overlying strata of the coal seam and the roof of the associated mineral layers respectively, so that the coal seam and the mineral layers form corresponding fracture bearing zones and buffer zones, guiding the upper and lower strata to sink evenly and absorb deformation energy, reducing stress transmission between different mineral layers, and realizing the coordinated and safe mining of multiple mineral resources.

[0029] As a further improvement of the present invention, when the method is used for water-conserving mining of a composite resource system of "upper aquifer-middle coal seam-lower oil and gas layer", the hydrogeological parameters of the upper aquifer and the characteristics of the aquitard need to be measured in step S1; in step S3, fracture network weakening is implemented in the overlying strata of the coal seam, so that the upper strata form a uniformly distributed fracture network in advance and fully bulge. The bulging zone bears the vertical load of the overlying strata and guides it to settle slowly and uniformly, avoiding the fracture zone from penetrating to the upper aquifer. At the same time, the uniform settlement significantly reduces the disturbance to the aquitard and the lower oil and gas cap layer.

[0030] As a further improvement of the present invention, when this method is used for weakening the fracture network of rock strata in mining roadways, in step S1, the bedding, lithology, thickness, compressive and tensile strength and in-situ stress of the rock strata above the roadway need to be measured, and the spatial relationship between the coal pillars, roadway layout and goaf area needs to be determined; in step S3, boreholes are drilled in the two roadways according to the design and fracture network weakening is implemented, the lower fracture zone is transformed into a breccia filling body, and the overlying thick and hard rock strata are guided to slowly sink, reducing the load on the roadway caused by long-distance overhang and instantaneous fracture.

[0031] Compared with the prior art, the present invention has the following technical advantages:

[0032] (1) This invention transforms the lower fracture zone into a caving zone through pulse fracture network fracturing. The fragmented mass fully fills the goaf and supports the overlying strata, fundamentally preventing large-span overhangs and instantaneous fractures of thick, hard rock strata. This not only inhibits the excessive accumulation of elastic energy in high-level rock strata and effectively curbs the incubation and occurrence of mine tremors, but also eliminates the inducing factors of rockbursts, achieving the dual goals of "rockburst prevention and earthquake control". At the same time, the uniform settlement of the rock strata reduces the concentration of mining stress, provides conditions for gas dissipation and ensures the stability of the extraction borehole, and synergistically reduces the risk of coal and gas outbursts, completely changing the limitations of traditional single-hazard prevention and control technologies.

[0033] (2) Based on the measured data of the "three zones", this invention uses a directional fracture network to weaken the underlying key rock strata, avoiding the cumbersome process of constructing into high-level hard and thick rock strata. The drilling depth is short and the amount of work is small. This invention uses pulse fracturing, with water or special fracturing fluid as the medium. The cost of equipment and materials is much lower than that of CO2 phase change fracturing, and there is no need for the safety management costs of storing and transporting explosives. At the same time, the construction can be carried out simultaneously with the advancement of the working face, without interrupting the production rhythm and greatly reducing the losses from production stoppage.

[0034] (3) Optimizing the morphology of rock strata subsidence: The subsidence of the fracture zone is reduced, and the thickness of the fracture zone is decreased. This invention actively promotes the collapse and fragmentation of the lower fracture zone strata by weakening the rock strata fracture network. The fragmented and swollen bodies fully fill the goaf, forming an effective "active support" for the upper fracture zone strata. This support significantly reduces the free space and room for transformation of the upper fracture zone strata, thereby directly inhibiting its overall subsidence and degree of fracture development. As a result, the maximum subsidence displacement of the fracture zone strata is reduced, and at the same time, due to insufficient fracture and delamination, the height (thickness) of the fracture zone itself is also compressed, forming a more compact fracture development zone;

[0035] (4) Regulation of bending subsidence characteristics: The bending subsidence zone shifts downward and the amount of subsidence decreases. As the underlying fracture zone strata are transformed into caving zones and play a key supporting role, the bending deformation originally borne by the fracture zone is largely offset by the fracturing and swelling of the caving zone. The starting point of large-scale bending deformation of the strata is thus forced to shift upward to the upper strata, which is manifested as the relative downward shift of the bending subsidence zone. At the same time, as the lower support is more solid and uniform, the final amount of subsidence of the overlying bending subsidence strata is also significantly reduced, thereby mitigating the degree of surface subsidence;

[0036] (5) Improved uniformity of settlement: The curvature of the rock strata above the fracture zone decreases during bending and settlement, and the change in the curvature inflection point promotes uniform settlement. From the front of the coal face to the middle of the goaf, the settlement curve shape of the overlying rock strata is optimized. Due to the improved support conditions, the radius of curvature of the rock strata increases, which means that the bending deformation is more gradual and the curvature value is reduced. In particular, the curvature change is more significant at the curvature inflection point (maximum curvature point) in front of the coal face and at the inflection point where sufficient settlement is achieved in the goaf. This change makes the settlement profile of the entire rock strata smoother, effectively avoids local strain concentration, and achieves uniform and coordinated settlement from the front of the coal face to the middle of the goaf, greatly reducing the risk of cracking or stress concentration caused by abrupt curvature changes;

[0037] (6) Reduced mining pressure manifestation: The strata activity is reduced, the concentration of mining stress and the manifestation of mining pressure are weakened, and the roadway deformation is reduced. The reduction of the overall strata movement directly leads to a smoother redistribution of mining stress. The range and peak stress level of the high stress concentration zone are significantly reduced. Reflected in the stope, the manifestation of mining pressure at the working face is reduced: the fluctuation of the support working resistance is reduced, and the intensity and severity of the pressure are weakened. For mining roadways, the intensity of the dynamic pressure source on the surrounding rock is reduced, the stress concentration is reduced, and the deformation such as the approach of the roof and floor and the convergence of the sidewalls can be effectively controlled, the roadway stability is significantly improved, and the maintenance cost is reduced;

[0038] (7) Root Cause Prevention of Rockburst: The essence of rockburst is the sudden and violent release of highly concentrated elastic energy in coal and rock mass. This invention, by providing effective lower support, suppresses large-span overhangs and instantaneous fractures of the overlying hard rock strata, thereby avoiding severe dynamic loading on the underlying coal and rock mass. At the same time, uniform settlement reduces stress concentration, allowing energy in the coal body to be released slowly or prevent excessive accumulation. This eliminates the main cause of rockburst from the source, realizing a fundamental shift from localized artificial pressure relief to active support;

[0039] (8) Mechanistic control of mine tremors: Mine tremors often originate from sudden fractures after energy accumulation due to the bending and settling of high-lying, hard rock strata. This invention, through fragmentation and effective support, prevents the full development of the delamination space at the junction of the fracture zone and the bending and subsidence zone, forcing the overlying strata to transform into a slower bending and subsidence mode with better integrity. This process greatly inhibits the rapid accumulation of elastic energy in high-lying rock strata, preventing it from reaching the critical conditions for violent, instantaneous fractures, thereby mechanistically controlling the gestation and occurrence of mine tremors and solving the problem of "controlling impact but not tremor" in traditional methods.

[0040] (9) Coal and gas outbursts are the result of the combined effects of ground stress, gas pressure, and the physical and mechanical properties of the coal body. This invention reduces the mechanical load and stress gradient acting on the coal body by mitigating the concentration of mining stress and easing the manifestation of mine pressure, thereby reducing the deformation and fracturing speed of the coal body. This not only destroys the stress conditions for outbursts but also provides more time for gas to dissipate. At the same time, the easing of rock strata activity ensures the stability of drainage boreholes and improves gas drainage efficiency, thus reducing the risk of outbursts in a coordinated manner from the aspects of stress control and gas management.

[0041] (10) Promoting coordinated mining of associated minerals in coal-bearing strata and controlling the superimposed effects of mining-induced strata activity: Coal-bearing strata often contain multiple associated minerals (such as coalbed methane, shale gas, bauxite, etc.). The superimposed effects of strata activity caused by multiple mining operations of different minerals can easily lead to mutual interference and resource loss. This invention significantly reduces the range and intensity of strata disturbance caused by mining of a single working face by effectively controlling the mining activities of associated minerals. This enables more accurate prediction and control of the strata movement boundary and impact degree under multiple mining operations when planning the sequential coordinated mining of associated minerals, avoiding damage to adjacent strata, and providing key technical support for achieving safe, efficient, and coordinated resource development.

[0042] (11) In a complex resource system of "upper aquifer-middle coal seam-lower oil and gas layer", traditional mining activities are prone to causing water-conducting fractures to penetrate the overlying aquifer, resulting in water loss or pollution. This invention effectively protects the integrity of the key aquifer by inhibiting fracture zone development, reducing its height and conductivity, and preventing mining damage from affecting the aquifer upwards. At the same time, the uniform and slow settlement pattern also reduces the risk of shear damage to the caprock of the lower oil and gas reservoir. Thus, it achieves the maximum protection of upper water resources and lower oil and gas resources while safely extracting coal resources in the middle, promoting the coordinated mining of multiple resource layers in the "upper-middle-lower" range. Attached Figure Description

[0043] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] Figure 1 This is a flowchart of the method for controlling the activity of overlying strata in a mining area by weakening and fracturing rock fracture network according to the present invention;

[0045] Figure 2 This is a diagram illustrating the natural collapse state of rock strata under the scenarios of preventing rockbursts and mine earthquakes in Embodiment 1 of the present invention.

[0046] Figure 3 This is a schematic diagram of the fracture mesh weakening of the target rock strata in the scenario of preventing rockburst and mine earthquake in Embodiment 1 of the present invention;

[0047] Figure 4This is a schematic diagram of fracture mesh weakening of high-level thick and hard rock strata in the scenario of preventing rockburst and mine earthquake in Embodiment 1 of the present invention;

[0048] Figure 5 This is a state diagram of the weakened rock fracture network in the scenario of preventing rockburst and mine earthquake in Embodiment 1 of the present invention;

[0049] Figure 6 This is a diagram of the natural collapse state of rock strata under the scenario of coordinated mining of coal-bearing associated minerals in Embodiment 2 of the present invention;

[0050] Figure 7 This is a schematic diagram of the weakening of rock fracture network under the scenario of coordinated mining of coal-associated minerals in Embodiment 2 of the present invention;

[0051] Figure 8 This is a state diagram of the weakened seam mesh under the scenario of coordinated mining of coal-associated minerals in Embodiment 2 of the present invention;

[0052] Figure 9 This is a diagram of the rock strata collapse state under the water-conserving mining scenario in Embodiment 3 of the present invention;

[0053] Figure 10 This is a schematic diagram of the weakening of the mesh in the water-conserving mining scenario in Embodiment 3 of the present invention;

[0054] Figure 11 This is a state diagram of the weakened mesh under the water-conserving mining scenario in Embodiment 3 of the present invention;

[0055] Figure 12 This is a schematic diagram of rock strata collapse in the scenario of protecting the mining roadway in Embodiment 4 of the present invention;

[0056] Figure 13 This is a schematic diagram of the weakening of the seam mesh in the scenario of protecting the mining roadway in Embodiment 4 of the present invention;

[0057] Figure 14 This is a state diagram of the weakened mesh in the mining roadway protection scenario of Embodiment 4 of the present invention.

[0058] In the diagram, 1-topsoil layer, 2-high-level thick hard rock layer, 3-fracture zone, 4-cavitation zone, 5-goaf gangue pile, 6-directional borehole, 7-fracturing section, 8-target rock layer A weakened by fracture mesh, 9-pulse fracturing equipment, 10-hydraulic support, 11-surface fracturing well, 12-surface directional borehole, 13-surface fracturing section, 14-goaf gangue pile A weakened by fracture mesh, 15-floor fracture zone B, 16-bauxite roof, 17-bauxite pillar, 18-bauxite mine. 19-Target rock stratum B weakened by the fracture mesh, 20-Roof weakening borehole, 21-Gange pile B in the goaf after fracture mesh weakening, 22-Bauxite stripping waste rock, 23-Aquifer, 24-Floor fracture zone C, 25-Oil and gas layer caprock, 26-Oil and gas layer, 27-Target rock stratum C weakened by the fracture mesh, 28-Gange pile C in the goaf after fracture mesh weakening, 29-Track roadway, 30-High-level thick and hard rock stratum D, 31-Target rock stratum D weakened by the fracture mesh, 32-Gange pile D in the goaf after fracture mesh weakening. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0060] This invention is based on the fundamental nature of mine pressure and rock strata movement. By weakening and modifying the rock strata's fragmentation and swelling characteristics through a fracture network, a continuous fracture network is formed within the target thick and hard rock strata using downhole pulse fracturing or blasting. Pulse fracturing uses high-frequency pulse waves to connect microscopic fractures under cyclic loading and impact. Blasting creates uniform fractures through precise detonation, transforming the natural fragmentation and swelling coefficient of the rock strata into an artificial one, converting the lower fracture zone into a caving zone. The fragmented material can completely fill the goaf and provide uniform support to the overlying rock strata, preventing the accumulation of elastic energy. If there are high-level thick and hard rock strata, a fractured cushion layer can be formed by segmented pulse fracturing through horizontal well drilling on the surface. This cushion layer can be used to fill the delamination space and absorb deformation energy, ultimately achieving active and controllable overburden activity.

[0061] The method for controlling the activity of overlying strata in a mining area by weakening and fracturing rock fracture networks according to the present invention includes:

[0062] Step S1: Through core drilling and laboratory tests, determine the working face height, advance speed, and mining length, calculate the free space height of the goaf, and clarify the filling requirements; with the help of geostress monitoring equipment and rock sample mechanical testing, obtain the thickness, uniaxial compressive strength, tensile strength, and natural rupture coefficient of the immediate roof, lower fracture zone, and upper thick hard rock layer; use the "three-zone" measurement method (such as borehole inspection and displacement sensor monitoring) to delineate the range of the caving zone, fracture zone, and bending subsidence zone, mark the lower fracture zone thick hard rock layer section that needs to be weakened by fracture mesh and the distribution of the upper thick hard rock layer that needs to be coordinated and controlled, while ensuring that the integrity of the immediate roof is not affected by subsequent construction, and accurately locate the control target to avoid blind operation.

[0063] Step S2: Based on the previously obtained free space height and natural swelling coefficient of each rock layer, establish a filling balance relationship and calculate the difference between the natural swelling body and the filling requirement of the goaf; determine the artificial swelling coefficient of the rock layer through laboratory simulation fracture network weakening test, determine the target rock layer for fracture network weakening according to the calculation formula, and clarify the weakening range and expected swelling effect of each target rock layer; if there is a high-level thick and hard rock layer, calculate its separation space height to determine the target area of ​​ground fracturing and fracture network development requirements. Quantitative calculation avoids excessive modification that increases costs and also prevents insufficient modification that leads to inadequate filling.

[0064] Step S3: Arrange directional boreholes according to the target rock stratum range, and simultaneously arrange observation boreholes at the edge of the fracture network expansion area to monitor fracture development; if pulse fracturing technology is used, adjust the peak pulse pressure and action time according to the rock stratum mechanical properties, and use periodic pulse loads to stimulate microscopic fractures to form a continuous fracture network. During construction, monitor the weakened boundary in real time to ensure that the immediate roof is not damaged; if blasting is used, design a segmented charge structure and control the detonation sequence through millisecond delay detonators to form uniform through fractures. Before blasting, check the gas concentration and set up a buffer section to protect the immediate roof. Through precise construction, the lower fracture zone is transformed into a caving zone.

[0065] Step S4: To prevent and control ground subsidence, if early monitoring reveals risks of delamination and overhang in high-lying, thick, hard rock strata, which could easily lead to instantaneous rock strata fracture and subsequent ground subsidence, supplementary control measures are required: 1. Precisely construct horizontal fracturing wells on the ground according to the distribution of high-lying rock strata, ensuring the final borehole location strictly avoids sensitive layers such as aquifers and precisely lands within the high-lying rock strata to avoid secondary subsidence risks caused by construction disturbance; 2. Employ pulse fracturing technology to form a uniformly fractured cushion layer within the high-lying rock strata. This cushion layer fully fills the delamination spaces between layers and efficiently absorbs the deformation energy of the upper rock strata through its compressibility, thus weakening the impact of violent rock strata movement on the ground from the source; 3. Simultaneously, use a ground microseismic monitoring system and borehole inspection instruments to verify the fracturing effect of the high-lying rock strata in real time, ensuring a reduction in the overhang span, curvature, and subsidence, ultimately achieving effective control of ground subsidence.

[0066] Step S5: Use a borehole inspection instrument to check the fracture density and continuity of the target rock strata. If insufficient continuity of local fractures is found, immediately drill additional denser boreholes for secondary weakening. Select representative monitoring points in the goaf to measure the fragmentation performance of the collapsed rock strata. If the fragmentation degree does not meet the filling requirements, analyze the weakening parameters (such as pulse pressure and detonation sequence) and make targeted adjustments. Analyze the stress distribution and subsidence deformation of the rock strata using stress sensors and displacement gauges. Combine this with the microseismic monitoring system to record the frequency and energy scale of mine tremors. If abnormal stress concentration, excessive subsidence, or failure to reduce mine tremor risk occur, review the parameter design of the previous steps. Conduct a full-process review from basic condition analysis and control index setting to the implementation of weakening methods, and dynamically optimize the scheme to ensure that the overburden movement is always within a controllable range.

[0067]

Example 1

[0068] This embodiment is used for scenarios involving rock bursts and weakening of rock strata fracture networks during mining earthquakes.

[0069] like Figure 2 As shown, the No. 8 coal seam in a certain mine has an average burial depth of 820 m and a thickness of 6.2 m. Above it, at a depth of 55 m, there is a 32 m thick layer of hard siltstone with a tensile strength of 8 MPa. During the mining process, the filling height of the goaf gangue pile 5 was insufficient, resulting in a large separation space below the high-level thick hard rock layer 2. Elastic energy accumulated in the rock mass, and the stress concentration peak in the advanced support section of the roadway reached 35 MPa. The safety valve of the hydraulic support 10 at the working face frequently opened. Due to insufficient support height, rock bursts occurred frequently, threatening operational safety. Furthermore, the high-level thick hard rock layer 2 is close to the topsoil layer 1, and its fracture could easily trigger mine tremors, affecting the surface.

[0070] like Figure 3 As shown, to solve this problem, mining parameters such as working face height and burial depth were measured, and the free space of the goaf was calculated. Horizontal and vertical stress distributions were obtained through geostress monitoring. The thickness of the siltstone and immediate roof was measured by drilling. Uniaxial compressive strength, tensile strength, and natural swelling coefficient were obtained through rock mechanics tests. The ranges of caving zone 4 and fracture zone 3 were delineated using the "three-zone" measurement method. With the goal of completely filling the goaf with swell, the goaf filling balance formula was derived, and the 32 m thick siltstone was identified as the target rock layer A8 for fracture network weakening. Oriented boreholes 6 were drilled into the siltstone along the two roadways. Pulse fracturing equipment 9 was used for segmented fracturing. The fracturing section 7 covered the target rock layer A8, weakening it with a fracture network. The peak pulse pressure and duration were controlled to create a continuous fracture network. Monitoring boreholes were installed at the edges to ensure no damage to the immediate roof. After the working face advanced, the weakened fracture network was fully filled by the goaf pile A14, effectively supporting the overlying strata, preventing delamination, and significantly improving rockburst and mine tremor phenomena. Figure 5As shown. Given that the high-level, thick, hard rock layer 2 is close to the surface, a surface fracturing well 11 can be deployed, and a surface directional horizontal well 12 can be constructed to fracture the high-level, thick, hard rock layer 2, forming a fractured cushion layer to further fill the delamination space and prevent surface subsidence. Figure 4 As shown, boreholes are used to inspect for fracture penetration, stress-displacement monitoring is used to monitor rock strata subsidence and stress, microseismic monitoring is used to monitor mine seismic frequency, and construction parameters are dynamically adjusted.

[0071]

Example 2

[0072] This embodiment is used for the scenario of weakening rock fracture network in the coordinated mining of coal-bearing associated minerals.

[0073] like Figure 6 As shown, a coalfield contains bauxite resources beneath its coal seam. The bauxite layer, located 20 m below the coal seam floor and 3 m thick, is a high-quality mineral resource. During upward mining operations, the rock strata movement caused by coal seam mining is transmitted both upwards and downwards. The fracture zone B15 in the coal seam floor extends to the bauxite roof 16. The bauxite pillar 17 is severely damaged due to mining stress, increasing the risk of rock strata collapse below the coal seam goaf. Therefore, coordinated mining of coal and bauxite is urgently needed.

[0074] like Figure 7 As shown, to solve this problem, the thickness and lithology of the coal seam and bauxite layer were measured. The uniaxial compressive strength, tensile strength, and natural swelling coefficient of the coal seam overburden and bauxite roof 16 were measured through rock mechanics tests. The stress transmission law during mining was monitored to clarify the stress state of the isolation layer. According to the goaf filling balance formula, the thickness of the rock layers requiring weakening for the coal seam overburden and bauxite roof 16 were calculated to determine the two target rock layers. For the target rock layer B 19 of the coal seam overburden weakening, pulse fracturing was selected to form a swelling zone; for the target rock layer 16 of the bauxite roof, roof weakening boreholes 20 were arranged for pulse fracturing. After the fracture network weakening, the goaf gangue pile B 21 fully filled the goaf, and the bauxite stripping waste rock 22 played a supporting role in the coal seam floor, significantly improving the stress environment, reducing the depth of the floor fracture zone development, and reducing the risk of rock collapse below the coal seam goaf. Figure 8 As shown, monitoring the development of the fracture field between the coal seam and bauxite, verifying the support and buffering effect of the fracture zone, adjusting the weakening parameters, reducing stress transmission, and ensuring safe mining of the coal seam.

[0075]

Example 3

[0076] This embodiment is used for the scenario of weakening rock fracture network in water-conserving mining (coordinated mining of upper water, middle coal and lower oil and gas).

[0077] like Figure 9As shown, a certain mining area has a composite structure of "upper aquifer-middle coal seam-lower oil and gas layer": the upper aquifer 23 is 80m thick and serves as the regional water source; the coal seam is 5.0m thick and buried at a depth of 600m; the lower oil and gas layer 26 is buried at a depth of 2300m. Traditional mining methods can easily cause water-conducting fractures to penetrate the aquifer, and the bottom plate fracture zone C 24 can easily penetrate the caprock 25 and the oil and gas layer 26, causing leakage of oil and gas resources and increasing the risk of spontaneous combustion in the goaf.

[0078] like Figure 10 As shown, to solve this problem, the thickness, permeability coefficient, and characteristics of the aquifer, coal seam mining height and burial depth, and mechanical parameters of the oil and gas caprock were measured. The "three-zone" measurement method was used to delineate the three zones of the coal seam overburden, and the free space of the goaf was calculated. With the goal of preventing fractures from penetrating the aquifer and protecting the oil and gas caprock, a thick, hard overlying rock layer, C27, was identified as the target rock layer for fracture network weakening through the derivation of the filling balance formula. Directional boreholes were drilled in the target rock layer, and pulse fracturing (considering both gas and fracture control) was used. The pressure and action time were adjusted to form a uniform fracture network, promoting premature fracture expansion of the rock layer. The changes in aquifer water level, the integrity of the aquifer, and the deformation of the oil and gas caprock were monitored. Fracture development was checked through borehole inspection to ensure that the gangue pile C28 in the goaf, after fracture network weakening, bears the load and guides uniform settlement, preventing fractures from penetrating sensitive layers, such as... Figure 11 As shown.

[0079]

Example 4

[0080] This embodiment is used for the scenario of weakening the fracture network of rock strata in mining roadways.

[0081] like Figure 12 As shown, track roadway 29 in a coal mine is excavated along the floor of coal seam #5. The cross-section is rectangular, with a width × height of 5.4 m × 4.0 m, and uses a combination of anchor, mesh, cable, and shotcrete support. The roadway is 680 m deep, with a 12 m thick layer of fine sandstone on the roof, possessing a tensile strength of 5 MPa. Interlayer joints are poorly developed. Towards the end of the mining period, the roadway is affected by the dynamic pressure of mining combined with the static pressure of the high-lying, thick, hard rock layer D30. The roof and floor of track roadway 29 move closer together by 380 mm / month, and the sidewalls converge by 260 mm / month. The area of ​​concentrated mining stress is large and has a high peak value, leading to frequent repairs and severely restricting production efficiency.

[0082] like Figure 13As shown, to solve this problem, the cross-sectional dimensions and burial depth of the roadway, the thickness, tensile strength, and natural swelling coefficient of the fine sandstone were measured; the distribution of stress in the surrounding rock of the roadway, the spatial relationship between the coal pillar and the goaf, and the free space of the goaf were monitored. According to the filling balance formula, the 12 m thick fine sandstone was determined as the target rock layer D31 for fracture network weakening, ensuring that the overhead load and instantaneous fracture load of the high-level thick hard rock layer 30 were reduced after swelling. Determined boreholes were drilled in the two roadways towards the fine sandstone for segmented fracturing. The boreholes were used to inspect for fracture penetration, and the deformation of the roadway roof and floor and the sidewalls, as well as the stress of the rock strata, were monitored. Based on the monitoring results, additional boreholes were drilled or parameters were adjusted to ensure that after fracture network weakening, the goaf gangue pile D32 guides the overlying rock strata to slowly subside, controlling the deformation of track roadway 29, as shown. Figure 14 As shown.

[0083] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes that can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention are all within the protection scope of the claims of the present invention.

Claims

1. A method for controlling the movement of overlying strata in a mining area by weakening and fracturing rock fracture networks, characterized in that, Includes the following steps: Step S1: Collect core parameters based on mining conditions and roof geological characteristics of the mining face: (1) Determine the working face height, advance speed, mining length and coal seam depth, and calculate the free space of the goaf. ; (2) Obtain the horizontal and vertical stress distribution of the working face through ground stress monitoring; (3) The mechanical parameters of the thick and hard rock layers in the direct top and lower fracture zones and the thick and hard rock layers in the upper position, including thickness, uniaxial compressive strength, tensile strength, elastic modulus and natural swelling coefficient, were determined by drilling and rock mechanics test. (4) The range of the caving zone, fracture zone and bending subsidence zone was delineated by the "three-zone" measurement method, and the natural breccia coefficient of each rock layer was marked; Step S2: Based on the analysis results of step S1, with the goal of completely filling the goaf with rock fragments, the thickness of the rock strata to be modified is derived using the goaf filling balance formula. The balance formula includes formulas (1) to (6), where formula (1) is used. To weaken the free space in the pre-mined goaf by using mesh reinforcement: Mode ; In the formula, The thickness of the coal seam being mined is in meters (m). The thickness of the direct top is in meters (m). The direct top natural expansion rate is dimensionless; For the first Thickness of the rock layer, in meters; For the first Natural fragmentation rate of the rock layer, dimensionless; like When the value is ≤0, natural fracturing can fill the goaf; if When the value is greater than 0, there are still remaining gaps that need to be filled artificially. Therefore, the target rock layer needs to be weakened by fracture mesh treatment, and the fragmentation rate of the target rock layer becomes... Let the number of rock layers requiring fracture mesh weakening be... There are , and their index set is denoted as . Its thickness is ; Free space after mesh weakening : Mode ; In the formula, For the free space in the goaf after the mesh weakens, m; For the first The thickness of the rock strata is weakened by the fracture network, in meters; For the first Artificial fragmentation rate of rock strata, dimensionless; To include the weakened set of each layer in the mesh in the formula; Relating equation (2) with equation (1) as follows: Mode ; In the formula: For the first The natural rupture rate of the rock strata; To achieve the equilibrium condition of exactly filling or leaving no gaps, take: Mode , Right now: Mode ; Let the contribution of each fracture network weakened candidate stratum to filling the free space be... ,according to Arranged in descending order , It is a set The total number of intermediate rock layers is the minimum number of weakened layers. satisfy: Mode ; In the formula: The minimum number of rock layers required to weaken the fracture network is dimensionless. Step S3: Arrange directional boreholes according to the target rock layer range to weaken the fracture network of the target rock layer, and at the same time arrange observation boreholes at the edge of the fracture network expansion area to monitor fracture development; Step S4: After completing the S3 seam mesh weakening construction, assess the ground settlement: If the monitoring shows that the ground settlement control effect meets the standard, with no obvious settlement or the settlement amount is within the allowable range, then proceed directly to the S5 effect acceptance stage. If ground subsidence is detected by monitoring, supplementary prevention and control measures should be taken for the high-level thick and hard rock layers. This means using ground pulse fracturing technology, which can be used to form a fracture cushion layer by drilling horizontal wells on the ground and performing segmented pulse fracturing. The fracture cushion layer is used to fill the delamination space and absorb deformation energy, thereby weakening the impact of violent rock movement on the ground from the source and effectively controlling ground subsidence. Step S5: Evaluate the weakening effect of the fracture network using multi-dimensional methods including borehole inspection and stress displacement monitoring: Focus on monitoring the fracture density, continuity, and filling effect of the collapsed rock layer. If fracture development or insufficient fragmentation is found, optimize the borehole layout and weakening parameters in a timely manner based on the monitoring results to ensure that the filling effect of the goaf reaches the preset requirements, thereby ensuring that the movement of the overlying rock layer in the mining area is always under control.

2. The method for controlling the activity of overlying strata in a mining area by weakening and fracturing rock strata according to claim 1, characterized in that, In step S3, pulse fracturing or blasting is used as a means of weakening the seam mesh.

3. The method for controlling the activity of overlying strata in a mining area by weakening and fracturing rock strata according to claim 1, characterized in that, When this method is used to prevent rockbursts and mine tremors, in step S1, it is also necessary to determine the gas content of the coal seam and the stress distribution of the surrounding rock. In step S3, long boreholes are arranged along the roadway on both sides of the mining area towards the thick and hard roof and fracture mesh weakening is implemented to make the rock strata break and fill the delamination space, so that the high-level thick and hard rock strata slowly bend and sink, inhibiting the excessive accumulation of elastic energy, thereby alleviating rockbursts and mine tremors.

4. The method for controlling the activity of overlying strata in a mining area by weakening and fracturing rock strata according to claim 1, characterized in that, When this method is used for the coordinated mining of coal-bearing associated minerals, the lithology and mechanical parameters of the coal seam and associated mineral layers are comprehensively measured in step S1. In step S3, fracture weakening is implemented in the overlying strata of the coal seam and the roof of the associated mineral layers, so that the coal seam and mineral layers form corresponding fracture bearing zones and buffer zones, guiding the upper and lower strata to sink evenly and absorb deformation energy, reducing stress transmission between different mineral layers, and realizing the coordinated and safe mining of multiple mineral resources.

5. The method for controlling the activity of overlying strata in a mining area by weakening and fracturing rock strata according to claim 1, characterized in that, When this method is used for water-conserving mining in a composite resource system of upper aquifer-middle coal seam-lower oil and gas layer, the hydrogeological parameters of the upper aquifer and the characteristics of the aquitard need to be determined in step S1; in step S3, fracture network weakening is implemented in the overlying strata of the coal seam, so that the upper strata form a uniformly distributed fracture network in advance and fully bulge. The bulging zone bears the vertical load of the overlying strata and guides it to settle slowly and uniformly, avoiding the fracture zone from penetrating to the upper aquifer. At the same time, the uniform settlement significantly reduces the disturbance to the aquitard and the lower oil and gas cap layer.

6. The method for controlling the activity of overlying strata in a mining area by weakening and fracturing rock strata according to claim 1, characterized in that, When this method is used to weaken the fracture network of rock strata in mining roadways, in step S1, the bedding, lithology, thickness, compressive and tensile strength and in-situ stress of the rock strata above the roadway need to be measured, and the spatial relationship between the coal pillars, roadway layout and goaf needs to be determined; in step S3, boreholes are drilled in the two roadways according to the design and fracture network weakening is implemented to transform the lower fracture zone into a breccia-filled body, guide the overlying thick and hard rock strata to slowly sink, and reduce the load on the roadway caused by long-distance overhang and instantaneous fracture.

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