Super-thick coal seam hard roof small coal pillar gob-side roadway strong mine pressure comprehensive treatment method

Abstract

The invention relates to the technical field of coal mine stope mine pressure and roadway support, and discloses a strong mine pressure comprehensive treatment method for a hard roof small coal pillar gob-side roadway of an extra-thick coal seam. The super-thick coal seam hard roof small coal pillar gob-side roadway strong mine pressure comprehensive treatment method comprises the steps that roof layering hydraulic fracturing is carried out before stoping of a previous working face, and a damage characteristic database is constructed; actually measuring the damage depth of the coal pillar in a stoping period, and correcting and determining the reserved width of the small coal pillar by utilizing the database; drilling parameters are collected during tunneling of the working face, and connectivity discrimination indexes are calculated in combination with fracturing efficiency so as to judge the fracture state; differentiated grouting reinforcement is implemented in a grading manner; and deformation is monitored in the recovery period, and secondary grouting dynamic control is implemented based on historical classification results. According to the method, digital closed-loop linkage of pressure relief, design and reinforcement is achieved, the problems of strong mine pressure display and surrounding rock deformation control under the hard roof are effectively solved, and full-period stability of a roadway is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of coal mine mining pressure and roadway support technology, specifically a comprehensive management method for strong mining pressure in roadways with small coal pillars along the hard roof of extra-thick coal seams. Background Technology

[0002] In the mining of extra-thick coal seams, the presence of a hard roof often prevents the roof of the goaf from collapsing in time as the working face advances, easily forming large-area overhanging structures. This overhanging structure generates high-intensity lateral support pressure and pre-mining stress in the goaf-side roadway area along the small coal pillar, triggering severe mine pressure manifestations and causing large deformations of the surrounding rock, even rockburst disasters. As a key load-bearing structure isolating the goaf from the roadway, the stability of the small coal pillar directly affects the safety and efficiency of the mining operation.

[0003] Current technologies for addressing such problems typically employ deep-hole blasting or conventional hydraulic fracturing for roof cutting and pressure relief, combined with high-strength anchor cable support and grouting reinforcement to control surrounding rock deformation. Regarding coal pillar placement, the width of the pillar is often determined based on geological conditions through empirical formulas or theoretical calculations. During roadway maintenance, passive reinforcement support relies primarily on manual observation of deformation, and grouting processes generally use standardized materials and pressure parameters.

[0004] However, the aforementioned existing technologies have significant limitations in practical applications. On the one hand, traditional depressurization and coal pillar design processes lack data linkage. The coal pillar dimensions designed solely based on empirical formulas fail to fully consider the differences in the actual pre-fracture effects of the roof, making it difficult to guarantee the elastic bearing capacity of the coal pillar and prone to plastic instability due to insufficient design margin. On the other hand, existing grouting reinforcement methods lack refined identification of the connectivity of surrounding rock fractures. The use of uniform grouting parameters is difficult to adapt to surrounding rock environments with varying degrees of fracture development, often resulting in grout loss through through fractures or difficulty in penetration through micro-fractures. This governance model, with its relatively isolated processes and lack of full life-cycle data feedback, makes it difficult to achieve accurate and long-term control of strong mine pressure in roadways along the goaf under conditions of hard roofs in extra-thick coal seams.

[0005] Therefore, this invention proposes a comprehensive method for managing strong mine pressure in roadways with small coal pillars along hard roofs in extra-thick coal seams, in order to address the shortcomings of existing technologies. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a comprehensive management method for strong mine pressure in roadways with small coal pillars on hard roofs in extra-thick coal seams. This method solves the problems in existing technologies, such as the lack of data linkage between decompression and support processes, the failure of coal pillar design to consider actual roof damage differences, and the difficulty of adapting uniform grouting to complex fracture networks, which lead to poor surrounding rock control throughout the entire life cycle of roadways.

[0007] To achieve the above objectives, the present invention provides a comprehensive method for managing strong mine pressure in roadways with small coal pillars along hard roofs in extra-thick coal seams, comprising the following steps: S10, before the previous working face is mined, layered hydraulic fracturing is carried out on the roof of the coal seam. During the fracturing operation, pump injection pressure time series data is collected, fracturing efficiency index at the location of fracturing holes is calculated, and based on the discrete fracturing efficiency index, the roof prefabricated damage distribution curve distributed along the roadway direction is generated by interpolation calculation, and a roof damage characteristic database is constructed. S20, During the mining of the previous working face, mine pressure monitoring is carried out on the coal pillar side, the plastic failure depth of the coal pillar foundation is measured, the roof damage feature database is called, the fracturing efficiency index at the corresponding location is obtained, and the fracturing efficiency index is used to correct the coal pillar width calculated based on the plastic failure depth of the coal pillar foundation to determine the width of the small coal pillar. S30, during the excavation of the roadway along the working face, full-section shotcreting is implemented to seal the surface of the surrounding rock. During the drilling process of the grouting anchor cable, drilling parameters are collected in real time and the measured mechanical specific energy is calculated. The theoretical benchmark specific energy of the geological exploration rock is introduced to calculate the lithological deterioration degree, which characterizes the relative degree of rock fragmentation. The connectivity discrimination index is calculated by combining the fracturing efficiency index and the lithological deterioration degree, and the connectivity status of the surrounding rock fractures is determined accordingly. S40, the surrounding rock is divided into different levels according to the interconnection state of the surrounding rock fissures, and the grouting material type and grouting process parameters of the grouting anchor cable are adaptively adjusted for different level areas to carry out differentiated grouting reinforcement of the surrounding rock; S50 During the mining of this working face, the deformation of the roadway is monitored in real time. When the deformation of the roadway exceeds the set threshold, the historical classification results of the regional fracture connectivity status determined in step S30 are retrieved. Based on the historical classification results, grouting materials and process parameters are selected to implement dynamic control of secondary grouting.

[0008] Preferably, in step S10, the layered hydraulic fracturing of the coal seam roof before the previous working face is mined includes: For the low-lying hard roof within 0 to 30 meters above the coal seam, a geological crawler drilling rig is used to drill fracturing holes along the roadway toward the roof on the side of the coal pillar. The fracturing pressure is controlled within the range of 25 to 45 MPa, and the rock mass is fracturing by high-pressure water flow. For the hard roof in the middle and high position within the range of 30 to 100 meters above the coal seam, a directional drilling rig is used to construct directional long holes to the designated target layer. The drilling trajectory is laid out along the key layer of the roof to create a macroscopic fracture zone and cut off the stress transmission path of the high-level rock layer.

[0009] Preferably, in step S10, the calculation of the fracturing efficiency index at the location of the fracturing hole follows the following logic: The fracturing efficiency index is composed of a weighted sum of two parts; The first part is the ratio of the difference between the peak fracture pressure and the minimum instantaneous drop pressure after the rock strata fracture to the peak fracture pressure. The first part characterizes the degree of brittle failure of the rock mass. The second part is a numerical value containing the pressure fluctuation variance during the crack stabilization and propagation stage, processed by the natural logarithm function. This second part characterizes the crack network complexity.

[0010] Preferably, in step S20, during the mining of the previous working face, monitoring the mine pressure on the coal pillar side includes: Monitoring points, including stress gauges, strain gauges, and distributed fiber optic sensors, are arranged along the roadway side of the coal pillar. The monitoring grid density is set to 1.5 meters by 1.5 meters to capture the distribution of principal stress and strain changes inside the coal pillar in real time. A strain threshold is set. When the measured strain value at the monitoring point exceeds the strain threshold, the coal body at the corresponding location is determined to have entered a plastic failure state. The depth of plastic failure of the coal pillar foundation was determined by combining the borehole inspection results with the electromagnetic wave CT inversion imaging results.

[0011] Preferably, in step S20, the determination of the width of the small coal pillar follows the following logic: The design width of the coal pillar is equal to the sum of the basic design value and the feedforward correction increment; The basic design value is obtained by adding twice the plastic failure depth of the coal pillar foundation to the reserved safety margin; The feedforward correction increment is obtained by multiplying twice the plastic failure depth of the coal pillar foundation, the influence coefficient of roof integrity on stress transmission, and an exponential function term with the natural constant as the base. The exponential part of the exponential function term is the product of a negative sensitivity factor and the fracturing efficiency index; When the fracturing efficiency index is low, the exponential function term increases, and the calculated design width of the coal pillar increases.

[0012] Preferably, in step S30, the calculation of lithological deterioration degree and connectivity discrimination index includes: The measured mechanical specific energy is calculated based on the axial thrust, torque, rotational speed, and drilling speed of the drilling rig. The degree of lithological deterioration is obtained by subtracting the ratio of the measured mechanical specific energy to the theoretical benchmark specific energy of the geological exploration rock. The connectivity discrimination index is obtained by multiplying the fracturing efficiency index with the lithological deterioration degree obtained in the current process.

[0013] Preferably, in step S40, the differentiated grouting reinforcement of the surrounding rock includes: Set a high threshold and a low threshold for connectivity determination; When the connectivity discrimination index is greater than or equal to the connectivity determination high threshold, the surrounding rock is determined to be in a connected state. When the connectivity discrimination index is less than the connectivity determination high threshold and greater than or equal to the connectivity determination low threshold, the surrounding rock is determined to be in an intact state. When the connectivity discrimination index is less than the connectivity determination low threshold, the surrounding rock is determined to be in a dense state.

[0014] Preferably, in step S40, the adaptive adjustment of the grouting material type and grouting process parameters of the grouting anchor cable for different grade areas includes: For the connected surrounding rock area, cement-water glass dual-liquid grout is selected. The grouting process parameters are set as follows: the initial pressure is controlled at 3 to 5 MPa. After the grouting pressure stabilizes and rises, the process is switched to single-liquid grout for high-pressure fracturing grouting. The final pressure is controlled at 8 to 10 MPa. For the surrounding rock areas in the intact and dense states, a nano-modified single-liquid coal-loving grouting material is selected, and the grouting process parameters are set to control the grouting pressure at 8 to 15 MPa to ensure that the effective diffusion radius of the grout in the coal and rock mass is greater than or equal to 2.5 meters.

[0015] Preferably, in step S50, real-time monitoring of roadway deformation during the mining of this working face includes: Displacement sensors and crack observation instruments are installed in the roadway to monitor the roof subsidence, sidewall bulging, and surface crack width in real time. The set thresholds include a cumulative deformation threshold and a crack width threshold; When the real-time roadway deformation obtained by monitoring is greater than or equal to the cumulative deformation threshold, or when the real-time monitored crack width is greater than or equal to the crack width threshold, the secondary grouting dynamic control is triggered.

[0016] Preferably, in step S50, the step of selecting grouting materials and process parameters based on the historical classification results to implement dynamic control of secondary grouting includes: If the historical classification results show that the area was originally in the through state, cement-water glass dual-liquid grout should be selected, the gelation time should be controlled within the range of 30 to 45 seconds, and the grouting pressure should be controlled within the range of 8 to 10 MPa. If the historical classification results show that the region was originally in the dense state or the intact state, a cement-water glass two-component grout is selected, the gelation time is extended to the range of 45 to 60 seconds, and the grouting pressure is increased to 10 to 12 MPa.

[0017] This invention provides a comprehensive method for managing strong mine pressure in roadways with small coal pillars along the hard roof of extra-thick coal seams. It has the following beneficial effects: 1. This invention utilizes layered hydraulic fracturing and damage characteristic databases established before the previous working face is mined. It employs physical methods to three-dimensionally weaken the hard roof at different strata, reducing the overhanging roof area and blocking stress transmission from higher strata. Simultaneously, it constructs a roof damage characteristic database, enabling digital characterization and storage of the concealed pressure relief effect. This "physical pressure relief + digital database" model reduces the mine pressure intensity borne by the goaf roadway at its source, effectively solving the problem of strong mine pressure manifestation caused by large-area overhanging of hard roof in extra-thick coal seams.

[0018] 2. This invention establishes a modified model to dynamically optimize the width of small coal pillars by coupling measured mine pressure data with a roof damage characteristic database. It uses the fracturing efficiency index as a feedforward variable to correct the basic design value, eliminating the bias caused by traditional empirical formulas neglecting uneven roof fracturing, ensuring that the small coal pillar always retains an intact elastic bearing core under high stress conditions. This method achieves dynamic matching between geological conditions and support design, effectively solving the problems of insufficient bearing capacity and unreasonable size design of small coal pillars.

[0019] 3. This invention achieves precise identification and differentiated treatment of the surrounding rock fracture network through drill-pressure collaborative discrimination during the tunneling process and adaptive grouting based on connectivity status. The surrounding rock is quantified and graded according to the connectivity discrimination index, and rapid-setting sealing or permeability modification strategies are matched for either connected or intact regions, constructing a high-strength prestressed bearing shell within the surrounding rock. This overcomes the poor adaptability of traditional uniform grouting and solves the problems of severe surrounding rock fracturing and deformation control difficulties in roadways along the goaf.

[0020] 4. This invention utilizes dynamic control of secondary grouting during the working face mining process, retrieving historical classification results to guide current governance decisions, forming a closed-loop system covering the entire lifecycle of physical pressure relief, coal pillar optimization, initial reinforcement, and secondary defense. This method replaces traditional blasting with hydraulic fracturing, improving operational safety in high-gas mines. Furthermore, by effectively sealing fracture channels through grouting, it achieves synergy between mine pressure control and gas disaster prevention, ensuring the long-term stability of roadways under strong dynamic pressure. Attached Figure Description

[0021] Figure 1 This is a flowchart of the comprehensive management method for strong mine pressure in roadways with small coal pillars along the hard roof of extra-thick coal seams according to the present invention. Figure 2 This is a flowchart of the drilling-pressure collaborative discrimination and adaptive grouting decision logic of the present invention. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] See attached document Figure 1 This invention provides a comprehensive method for managing strong mine pressure in roadways with small coal pillars along the hard roof of extra-thick coal seams, comprising the following steps: S10: Layered hydraulic fracturing and damage characteristic database construction before the previous working face was mined. Before the previous working face was mined, layered hydraulic fracturing was performed on the coal seam roof to weaken the hard rock structure. During the fracturing operation, pump injection pressure time-series data was collected, and the fracturing efficiency index at each fracturing hole location was calculated. Based on the discrete fracturing efficiency index, a pre-existing roof damage distribution curve distributed along the roadway direction was generated through interpolation, constructing a roof damage characteristic database.

[0024] S20, Mine pressure monitoring and coal pillar optimization design during the previous working face mining process. During the previous working face mining, monitoring points were set up on the side of the coal pillar for mine pressure monitoring, and the plastic failure depth of the coal pillar foundation was measured. The roof damage feature database constructed in step S10 was called to obtain the fracturing efficiency index at the corresponding location. The fracturing efficiency index was used to correct the coal pillar width calculated based on the plastic failure depth of the foundation, and the final small coal pillar width was determined.

[0025] S30, Drill-Fracturing Coordination Judgment during the Excavation Process of this Working Face. During the excavation of the goaf-side roadway in this working face, full-section shotcreting is implemented to seal the surrounding rock surface. During the drilling process for constructing grouting anchor cables, drilling parameters are collected in real time and the measured mechanical specific energy is calculated. The theoretical benchmark specific energy of geological exploration rocks is introduced to calculate the lithological deterioration degree, which characterizes the relative degree of rock fragmentation. Combining the fracturing efficiency index in step S10 with the lithological deterioration degree obtained in the current process, a connectivity discrimination index is calculated to determine the connectivity status of the surrounding rock fractures.

[0026] S40, Adaptive grouting reinforcement based on connectivity status. Based on the fracture connectivity status determined in step S30, the surrounding rock is classified into different levels. For different level areas, the grouting material type and grouting process parameters of the grouting anchors are adaptively adjusted to implement differentiated grouting reinforcement of the surrounding rock.

[0027] S50, Dynamic control of secondary grouting during the working face mining process. During the working face mining process, the deformation of the roadway is monitored in real time. When the deformation exceeds a set threshold, the historical classification results of the fracture connectivity status in that area from step S30 are retrieved. Based on the historical classification results, the corresponding grouting materials and process parameters are selected to implement dynamic control of secondary grouting.

[0028] This method, through the aforementioned steps, links the physical decompression process with the chemical grouting process in a spatiotemporal dimension. The fracturing data generated in step S10 serves as feedforward information to guide the coal pillar design in step S20, and also as basic comparison data in the connectivity determination in step S30. Step S30 uses borehole data to perform feedforward verification of the fracturing effect of step S10, and directly determines the grouting strategy in step S40. Step S50 then utilizes historical state data for final defense throughout the entire lifecycle, forming a closed-loop governance system.

[0029] See attached document Figure 2 In step S10, in this embodiment, for the multi-layered hard rock structure existing within 200m above the extra-thick coal seam, three-dimensional layered hydraulic fracturing is pre-implemented before the start of the previous working face mining operation. This step aims to weaken the integrity of the hard roof through physical means, and simultaneously use digital means to extract the rock mass response characteristics during the fracturing process, providing a quantitative basis for subsequent coal pillar design and roadway excavation.

[0030] For the low-lying, hard roof within a range of 0 to 30 meters above the coal seam, low-level pressure relief is implemented. A geological tracked drilling rig is used to drill fracturing boreholes along the roadway direction towards the roof on the coal pillar side. The specific layout parameters for the boreholes are: borehole length 30 to 80 meters, borehole elevation angle 30 to 50 degrees, borehole diameter 60 to 75 mm, and spacing between adjacent boreholes 8 to 10 meters. During fracturing, the fracturing pressure is controlled within the range of 25 to 45 MPa, using high-pressure water flow to fracture the rock mass, achieving a single-hole fracture expansion radius of 10 to 15 meters. This operation weakens the "cantilever beam" structure of the near-field roof, ensuring that the low-lying, hard roof can collapse promptly after mining. The specific mechanical operation of the geological tracked drilling rig, the connection and sealing methods of the hydraulic fracturing pipelines are existing technologies well-known to those skilled in the art and will not be elaborated upon here.

[0031] Regional deep-hole pressure relief was implemented for the mid-to-high-level hard roof within a range of 30 to 100 meters above the coal seam. Directional drilling rigs were used to drill long directional holes to the designated target strata, with a length of 300 to 500 meters and a diameter of 90 to 120 mm. The drilling trajectory was laid out along the key strata of the roof. The fracturing pressure was also controlled at 25 to 45 MPa, aiming to create a macroscopic fracture zone with a vertical extension height of 15 to 20 meters and a horizontal extension width of 40 to 50 meters. This stratum fracturing aimed to pre-fracture the composite hard roof over a large area, weakening its overall strength and continuity, and effectively cutting off the stress transmission path of the high-level rock strata.

[0032] While performing the aforementioned stratified hydraulic fracturing, data acquisition was also conducted. Using a high-frequency pressure sensor and data acquisition unit installed at the fracturing pump station outlet, the pumping pressure time-series data for each fracturing hole was recorded in real time with a sampling period of 100ms. This data is represented as a curve of pumping pressure changing over time. It records the pressure response throughout the entire process of water injection and pressurization, rock strata fracturing, crack propagation, and pump shutdown and pressure relief.

[0033] To quantify the fracturing effect of rock strata in different regions, feature extraction was performed on the collected pumping pressure time-series data, and the fracturing efficiency index at each fracturing hole location was calculated. The fracturing efficiency index is a physical quantity characterizing the degree of brittle failure of the rock mass and the complexity of the fracture network. For coordinates along the tunnel strike... The first Each fracturing hole has a fracturing efficiency index. Calculate using the following formula: ; In the formula: This represents the peak pressure during the fracturing process, expressed in MPa, which is the highest pressure point in the pumping pressure time-series curve when the rock strata undergoes initial fracturing. It represents the minimum instantaneous pressure drop after the rock strata fracture, and the unit is MPa. That is, after the peak pressure is reached, the pressure is released due to the macroscopic cracks in the rock mass. This represents the variance of pressure fluctuations during the crack propagation and stabilization phase, in MPa. 2， The calculation interval is selected from the stable water injection stage in the pump injection pressure time series curve from the time of fracture drop to the time of pump stoppage. This value reflects the degree of pressure fluctuation when the fracture extends in heterogeneous rock strata. and The normalized weighting coefficients take values ​​that satisfy... In this embodiment, Take 0.6, Take 0.4; This represents the natural logarithm function.

[0034] Based on the above formula, a series of discretely distributed fracturing efficiency indices for fracturing hole locations are obtained. Considering the continuity of underground geological conditions, in order to obtain the roof damage distribution along the entire length of the roadway, Kriging interpolation is used to spatially interpolate the above discrete fracturing efficiency index data to generate indices along the roadway direction. Continuously distributed roof precast damage distribution curve The curve data and its corresponding spatial coordinates are stored in the computer system's storage medium to construct a roof damage feature database. This roof damage feature database characterizes the degree of damage at different locations of the roof after physical fracturing. Areas with higher values ​​indicate that the roof is sufficiently fractured. Areas with lower values ​​indicate that the roof is relatively dense or the fracturing effect is insufficient. This data will serve as the basis for subsequent coal pillar design corrections and grouting parameter adjustments.

[0035] See attached document Figure 2 In step S20, during the previous working face mining operation, real-time monitoring of mine pressure and coal body damage range is implemented on the coal pillar side. Combined with the roof damage characteristic database constructed in step S10, the dimensions of the small coal pillar are dynamically optimized. This step aims to eliminate the stress concentration hazard caused by uneven roof fracturing effects through the coupling of measured data and feedforward data, ensuring that the coal pillar has sufficient bearing capacity while maximizing resource recovery.

[0036] A mine pressure monitoring system is deployed along the roadway side of the coal pillar, with monitoring points spaced 10 to 15 meters apart. Each set of monitoring points includes stress gauges, strain gauges, and distributed fiber optic sensors (BOTDA). The monitoring grid density is set to 1.5m × 1.5m to capture the stress field (principal stress) inside the coal pillar in real time. , Distribution and strain changes. Simultaneously, to comprehensively analyze the damage to the coal pillar side, auxiliary detection is conducted using borehole inspection, microseismic monitoring, and electromagnetic CT technology. The specific installation methods, signal transmission, and demodulation principles of the stress gauges, strain gauges, distributed fiber optic sensors, borehole inspection equipment, microseismic monitoring instruments, and electromagnetic CT equipment are well-known existing technologies to those skilled in the art and will not be elaborated upon here.

[0037] Using data collected by the aforementioned mine pressure monitoring system, the boundary of the plastic zone in the coal seam is determined. A strain threshold is set as follows: When the measured strain value at the monitoring point exceeds the threshold, the coal body at that location is determined to have entered a state of plastic failure. The depth of basic plastic failure on the coal pillar side is determined by combining the macroscopic fracture observation results from borehole inspection with the inversion imaging results from electromagnetic CT. This value reflects the extent of natural coal seam failure under current geological and mining conditions, without considering differences in pre-existing roof damage.

[0038] After obtaining the measured depth of basic plastic failure, in order to compensate for the shortcomings of traditional design methods, which rely solely on formulas... (in the formula) The width of the coal pillar. To monitor the depth of the damage, The calculation (for safety factors) did not consider the differences in roof pre-cracking effects, and instead accessed the roof damage characteristic database stored in the computer system. This was based on the coordinates of the current monitoring point along the roadway direction. Extract the corresponding fracturing efficiency index from the precast damage distribution curves of the roof in the database. This index, as a feedforward correction variable, participates in the final calculation of the coal pillar width.

[0039] Based on measured basic plastic failure depth and the extracted fracturing efficiency index The modified model is used to calculate the position along the direction. The coal pillar design width at the location The calculation formula is as follows: ; In the formula: This indicates the depth of plastic failure of the coal pillar foundation as measured by the mine pressure monitoring system, in meters. This represents the safety margin reserved to ensure that there is a complete elastic bearing core at the center of the coal pillar, which is taken as 2 to 3m in this embodiment; The coefficient representing the influence of roof integrity on stress transmission is set to a range of 0.2 to 0.5. This coefficient reflects the degree of increase in lateral support pressure caused by an insufficiently fractured roof. This represents the sensitivity factor, used to adjust the correction weight of the fracturing efficiency index on the coal pillar width, with a value range of 1.0 to 2.0. Represented by natural constant An exponential function with base 0.

[0040] Based on the above formula, when the fracturing efficiency index at a certain location... When higher, the exponential term The width of the coal pillar approaches 0. Approaching the basic design value (For example: if) , ,but This indicates that the roof has collapsed sufficiently, and no additional coal pillar width is needed; when the fracturing efficiency index at a certain location... When the value is low, the exponent term increases, and the calculated coal pillar width increases. Automatically increases to compensate for the increased lateral support pressure caused by insufficient roof cut-off, preventing coal pillar instability.

[0041] During the mining advance, at positions of 50m and 100m, newly acquired mine pressure data and stress peak migration patterns were used to... A second review will be conducted. If the review is successful... Significant changes occur, and the design width of the coal pillar in the subsequent mining area is dynamically adjusted by substituting the values ​​into the above formula, ensuring that the coal pillar size always adapts to the current stress environment and roof damage state. Through this step, the minimum coal pillar width suitable for the geological characteristics of this working face is determined, providing a spatial geometric basis for subsequent roadway excavation and support.

[0042] See attached document Figure 1 and Figure 2 In step S30, during the excavation of the roadway along the working face, full-section shotcreting is implemented to seal the surrounding rock surface in the roadway area within 30 to 50 meters of the lagging excavation face. During the drilling process for constructing the grouting anchor cables, drilling parameters are collected in real time and the measured mechanical specific energy is calculated. The theoretical benchmark specific energy of geological exploration rocks is introduced to calculate the lithological deterioration degree, characterizing the relative degree of rock fragmentation. Combining the fracturing efficiency index from step S10 with the lithological deterioration degree obtained in the current process, a connectivity discrimination index is calculated to determine the connectivity status of the surrounding rock fractures. This step, through the combination of physical sealing and digital detection, provides a decision-making basis for subsequent differentiated grouting.

[0043] During tunnel excavation, surface treatment of the surrounding rock is carried out in the area 30 to 50 meters behind the face. C20 concrete is used for full-section shotcreting of the tunnel surface, with the shotcrete layer thickness controlled between 80 and 100 mm. This measure forms a continuous rigid protective layer on the tunnel roof and sides, effectively sealing micro-cracks on the surrounding rock surface and reducing weathering and initial loosening of the surrounding rock. Actual measurements show that shotcreting significantly reduces the surface roughness of the surrounding rock, increasing the rock integrity coefficient from 0.3 to 0.6, thus improving the stress boundary conditions of subsequent support structures. For the specific operating procedures of the shotcrete unit and the concrete mix design, those skilled in the art can refer to relevant coal mining industry standards, as these are well-known technologies in the field and will not be elaborated upon here.

[0044] After completing the full-section shotcreting, integrated support-grouting construction was implemented. Hollow high-pressure grouting anchors were used to replace some conventional support anchors. Specifically, two high-pressure grouting anchors were installed in each row of support on the tunnel roof and sidewalls, while conventional anchors were used in other locations. During the drilling process for the grouting anchors, the data acquisition unit integrated on the anchor drilling rig was used to collect the rig's operational dynamic parameters in real time. The collected parameters included the axial thrust, torque, rotational speed, and drilling rate of the drilling rig.

[0045] Based on the collected drilling parameters, the measured mechanical specific energy was calculated using the Teale specific energy equation. The measured mechanical specific energy reflects the energy consumed by the drill bit to break a unit volume of rock, and its value is positively correlated with the rock's strength and integrity. For locations along the tunnel direction... The borehole at that location actually measures the mechanical specific energy. Calculate using the following formula: ; In the formula: This indicates the axial thrust of the drilling rig, expressed in kN. This indicates the torque of the drilling rig, expressed in kN·m. This indicates the rotational speed of the drilling rig, expressed in r / min. This indicates the drilling speed, measured in m / min. This represents the cross-sectional area of ​​the borehole, in meters (m²). 2 ; Pi is the mathematical constant of a circle.

[0046] Because a single mechanical specific energy value is easily affected by variations in the hardness of the geological lithology itself (such as the natural strength difference between sandstone and mudstone layers), it may lead to misjudgments of the degree of fracture development. To eliminate this interference from geological background, the theoretical benchmark specific energy of rocks obtained during the geological exploration stage is introduced. This benchmark value corresponds to the theoretical specific energy of the rock strata at this location under intact and undamaged conditions. Based on the difference between the measured value and the benchmark value, the degree of lithological deterioration is calculated. This index characterizes the degree of fragmentation of a rock relative to its theoretically intact state. The calculation formula is as follows: ; In the formula, This is a dimensionless parameter. Based on this formula, the degree of lithological deterioration... The value varies with the measured mechanical specific energy. Relative specific energy of rock theory benchmark The ratio decreases and increases. When When the energy approaches 0, it indicates that the measured specific energy is close to the theoretical benchmark value, and the rock mass is intact; when When the value approaches 1, it indicates that the measured specific energy is significantly reduced, and there are a large number of cracks or cavities inside the rock mass.

[0047] To accurately determine whether the current borehole location has achieved effective connection with the pre-fabricated high-level fracturing fracture in step S10, the fracturing efficiency index in step S10 is used as a reference. Compared with the lithological deterioration degree obtained in the current process Construct a connectivity discriminant index This index is a core quantitative indicator for determining the connectivity of fractures in surrounding rock, and its calculation formula is as follows: ; Based on connectivity discriminant index The numerical value is used to determine the fracture connectivity of the surrounding rock. This judgment logic reflects the mutual verification between "pre-fracturing" and "sub-drilling": only when the fracturing efficiency index is high (indicating that the pre-fabricated fractures are fully developed) and the lithological deterioration degree is also high (indicating that the borehole measured a fracture zone), Only then will a high value be displayed, thus indicating the presence of a continuous fracture network. Specific judgment thresholds and corresponding state classifications will be explained in detail in the subsequent grouting steps. Through this step, the fracturing effect was verified using borehole data, achieving digital identification of hidden fracture networks.

[0048] See attached document Figure 1 and Figure 2 In this embodiment, step S40 is based on the connectivity discriminant index calculated in step S30. The connectivity status of fractures in the surrounding rock is quantitatively classified and graded into different levels. A high threshold for connectivity determination is set. and low threshold The surrounding rock is divided into three levels: through state (Type I, i.e., ), complete state (Type II, i.e.) ) and compact state (Type III, i.e. For different grade areas, the grouting material type and grouting process parameters of the grouting anchors are adaptively adjusted to implement differentiated grouting reinforcement of the surrounding rock. This step aims to solve the problem of grout loss or diffusion difficulties that occur in traditional uniform grouting under complex roof conditions, and to ensure the coordinated load-bearing capacity of the support system and the surrounding rock.

[0049] The specific grouting strategies for different grade areas are as follows: When the surrounding rock in the area is determined to be in a continuous state (Type I), it indicates that the macroscopic fractures generated by the hydraulic fracturing in step S10 have formed a continuous seepage channel with the natural fracture network exposed by the current borehole. At this point, to prevent the grout from flowing infinitely deeper along the large fractures, a "rapid-setting and sealing" strategy is adopted. Cement-water glass dual-liquid grout (CS grout) is selected as the grouting material, utilizing its controllable rapid-setting characteristics to quickly seal the continuous large fractures. The grouting process parameters are set as follows: initial pressure is controlled at 3 to 5 MPa; after the grouting pressure stabilizes and rises, it is switched to single-liquid grout for high-pressure fracturing grouting; final pressure is controlled at 8 to 10 MPa to ensure effective filling and sealing of the fracture network.

[0050] When the surrounding rock is classified as either intact (Type II) or dense (Type III), the rock mass is primarily characterized by micro-fractures or a relatively intact state. The main objective at this stage is to enhance the overall strength and deformation resistance of the surrounding rock, controlling initial deformation of the roadway. For these two different rock mass levels, a "high-pressure fracturing-penetration modification" strategy is adopted. A nano-modified single-liquid coal-affinity grouting material is selected. This material possesses low viscosity, high permeability, and good coal-rock affinity, enabling it to penetrate micron-level fractures. The grouting process parameters are set as follows: the high-pressure grouting pump is activated, and the grouting pressure is controlled between 8 and 15 MPa. Under high pressure, the grout overcomes fracture resistance, fracturing, expanding, and filling the micro-fractures. Through continuous high-pressure grouting, the effective diffusion radius of the grout within the coal and rock mass is ensured to be ≥2.5 m, filling the fractures around the roadway and forming a high-strength prestressed bearing shell within the surrounding rock.

[0051] After grouting is completed, a grouting effect inspection procedure is implemented. The filling of fissures in the grouting area is tested using borehole sampling. Core drilling is conducted between the grouting anchor cables in the roof and both sides. After extracting the core samples, the grout filling status within the fissures is observed, and the fissure filling rate is calculated. The judgment standard is set as follows: when the fissure filling rate is ≥85%, the grouting is considered qualified, the surrounding rock has achieved the expected reinforcement effect, and the next procedure can proceed; if the filling rate is less than 85%, additional grouting holes must be drilled in the corresponding area for repeated grouting until the stability of the surrounding rock meets the requirements of the high-stress environment during mining. Through the above differentiated grouting and strict quality inspection, deep repair and reinforcement of the integrity of the surrounding rock in the small coal pillar roadway is achieved.

[0052] See attached document Figure 1 In step S50, during the working face mining process, the surrounding rock may experience secondary instability due to the severe impact of mining support pressure. At this time, by real-time monitoring of roadway deformation and fracture development, and using the monitoring data as a trigger, the historical classification results of fracture connectivity in the area stored in step S30 are retrieved. Based on the intrinsic properties of the surrounding rock indicated by the historical classification results, corresponding grouting process parameters are selected to implement dynamic control of secondary grouting. This step achieves precise treatment based on the "full life cycle data" of the surrounding rock, combining the dual basis of measured deformation data and historical structural data.

[0053] During the longwall mining phase, the deformation and fracture development characteristics of the surrounding rock in the roadway are monitored in real time using established mine pressure and surface displacement monitoring stations. The main monitoring indicators include roof subsidence, sidewall bulging, and surface fracture width. Early warning thresholds for roadway deformation are set. and crack width threshold Based on the geological conditions of this embodiment, the cumulative deformation threshold is set. Set the crack width threshold to 200mm. The setting is 5mm. When the real-time roadway deformation is monitored... or crack width This indicates that the original support system has entered the yielding stage under high stress, and the stability of the surrounding rock is at risk of imbalance, triggering the dynamic control process of secondary grouting.

[0054] After triggering the secondary grouting process, based on the spatial coordinates of the current monitoring point along the tunnel direction... The historical classification results of the fracture connectivity state at that location (i.e., Type I through state, Type II intact state, or Type III compact state) determined in step S30 are retrieved from the database of the computer system.

[0055] For areas of different severity levels, the following differentiated secondary grouting control strategies are adopted: If historical classification results indicate that the area was originally in a continuous state (Type I), it means that the surrounding rock in this area had an extremely well-developed fracture network during excavation, and the current deformation is mainly due to the slippage and displacement of the original fractured rock skeleton under mining stress. For this type of "loosely structured" instability, the grouting objective focuses on rapid filling and skeleton consolidation. Cement-water glass dual-liquid grout (CS grout) is selected as the grouting material. The process parameters are adjusted as follows: the gel time is controlled within a relatively fast range of 30 to 45 seconds, utilizing the rapid setting characteristics of the grout to prevent its unlimited loss in the continuous large fractures; the grouting pressure is controlled at 8 to 10 MPa to ensure that the grout can fill the fractured zone without excessive diffusion.

[0056] If historical classification results indicate that the area was originally in a dense (Type III) or intact (Type II) state, it suggests that the surrounding rock mass has high strength. The current deformation is mainly due to the high support pressure causing new fracture surfaces within the rock mass, which is a type of "stress-induced" instability. In this case, cement-water glass dual-liquid grout (CS grout) is also used, but the process parameters need to be adjusted to meet the penetration requirements of the micro-fractures. The process parameters are adjusted as follows: the gelation time is extended to 45 to 60 seconds to increase the liquid flow time of the grout, allowing it to penetrate deep into the newly formed micro-fractures; the grouting pressure is increased to 10 to 12 MPa to overcome fracture resistance and achieve deep fracturing grouting.

[0057] The grouting holes are arranged alternately along the roof and sides of the roadway, with a depth of 3 to 5 meters and a spacing of 2 to 3 meters, forming a three-dimensional, intersecting reinforcement grid. Through secondary grouting, the grout solidifies inside the surrounding rock to form a high-strength rock mass network, cementing the fractured surrounding rock into a whole.

[0058] After secondary grouting, the deformation of the roadway in the area was continuously monitored, and the grouting effect was measured. The grouting volume and pressure were dynamically adjusted based on the mining progress and subsequent roadway deformation characteristics. Actual measurements showed that after implementing the above-mentioned secondary grouting, the fracture filling rate increased to over 95%, the roadway deformation rate decreased by 50%, and the roadway cross-sectional shrinkage rate was controlled within 10%, ensuring that the roadway cross-sectional area met the ventilation and transportation requirements during the working face mining period.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A comprehensive method for managing strong mine pressure in roadways with hard roofs and small coal pillars in extra-thick coal seams, characterized in that: Includes the following steps: S10, before the previous working face is mined, layered hydraulic fracturing is carried out on the roof of the coal seam. During the fracturing operation, pump injection pressure time series data is collected, fracturing efficiency index at the location of fracturing holes is calculated, and based on the discrete fracturing efficiency index, the roof prefabricated damage distribution curve distributed along the roadway direction is generated by interpolation calculation, and a roof damage characteristic database is constructed. S20, During the mining of the previous working face, mine pressure monitoring is carried out on the coal pillar side, the plastic failure depth of the coal pillar foundation is measured, the roof damage feature database is called, the fracturing efficiency index at the corresponding location is obtained, and the fracturing efficiency index is used to correct the coal pillar width calculated based on the plastic failure depth of the coal pillar foundation to determine the width of the small coal pillar. S30, during the excavation of the roadway along the working face, full-section shotcreting is implemented to seal the surface of the surrounding rock. During the drilling process of the grouting anchor cable, drilling parameters are collected in real time and the measured mechanical specific energy is calculated. The theoretical benchmark specific energy of the geological exploration rock is introduced to calculate the lithological deterioration degree, which characterizes the relative degree of rock fragmentation. The connectivity discrimination index is calculated by combining the fracturing efficiency index and the lithological deterioration degree, and the connectivity status of the surrounding rock fractures is determined accordingly. S40, the surrounding rock is divided into different levels according to the interconnection state of the surrounding rock fissures, and the grouting material type and grouting process parameters of the grouting anchor cable are adaptively adjusted for different level areas to carry out differentiated grouting reinforcement of the surrounding rock; S50 During the mining of this working face, the deformation of the roadway is monitored in real time. When the deformation of the roadway exceeds the set threshold, the historical classification results of the regional fracture connectivity status determined in step S30 are retrieved. Based on the historical classification results, grouting materials and process parameters are selected to implement dynamic control of secondary grouting.

2. The comprehensive management method for strong mine pressure in roadways with hard roof and small coal pillars in extra-thick coal seams according to claim 1, characterized in that, In step S10, the layered hydraulic fracturing of the coal seam roof before the previous working face is mined includes: For the low-lying hard roof within 0 to 30 meters above the coal seam, a geological crawler drilling rig is used to drill fracturing holes along the roadway toward the roof on the side of the coal pillar. The fracturing pressure is controlled within the range of 25 to 45 MPa, and the rock mass is fracturing by high-pressure water flow. For the hard roof in the middle and high position within the range of 30 to 100 meters above the coal seam, a directional drilling rig is used to construct directional long holes to the designated target layer. The drilling trajectory is laid out along the key layer of the roof to create a macroscopic fracture zone and cut off the stress transmission path of the high-level rock layer.

3. The comprehensive management method for strong mine pressure in roadways with small coal pillars along hard roofs in extra-thick coal seams according to claim 1, characterized in that, In step S10, the calculation of the fracturing efficiency index at the location of the fracturing hole follows the following logic: The fracturing efficiency index is composed of a weighted sum of two parts; The first part is the ratio of the difference between the peak fracture pressure and the minimum instantaneous drop pressure after the rock strata fracture to the peak fracture pressure. The first part characterizes the degree of brittle failure of the rock mass. The second part is a numerical value containing the pressure fluctuation variance during the crack stabilization and propagation stage, processed by the natural logarithm function. This second part characterizes the crack network complexity.

4. The comprehensive treatment method for strong mine pressure in roadways with small coal pillars along the hard roof of extra-thick coal seams according to claim 1, characterized in that, In step S20, during the mining of the previous working face, monitoring the mine pressure on the coal pillar side includes: Monitoring points, including stress gauges, strain gauges, and distributed fiber optic sensors, are arranged along the roadway side of the coal pillar. The monitoring grid density is set to 1.5 meters by 1.5 meters to capture the distribution of principal stress and strain changes inside the coal pillar in real time. A strain threshold is set. When the measured strain value at the monitoring point exceeds the strain threshold, it is determined that the coal body at the corresponding location has entered a plastic failure state. The depth of plastic failure of the coal pillar foundation was determined by combining the borehole inspection results with the electromagnetic wave CT inversion imaging results.

5. The comprehensive management method for strong mine pressure in roadways with small coal pillars along hard roofs in extra-thick coal seams according to claim 1, characterized in that, In step S20, the determination of the width of the small coal pillar follows the following logic: The design width of the coal pillar is equal to the sum of the basic design value and the feedforward correction increment; The basic design value is obtained by adding twice the plastic failure depth of the coal pillar foundation to the reserved safety margin; The feedforward correction increment is obtained by multiplying twice the plastic failure depth of the coal pillar foundation, the influence coefficient of roof integrity on stress transmission, and an exponential function term with the natural constant as the base. The exponential part of the exponential function term is the product of a negative sensitivity factor and the fracturing efficiency index; When the fracturing efficiency index is low, the exponential function term increases, and the calculated design width of the coal pillar increases.

6. The comprehensive treatment method for strong mine pressure in roadways with small coal pillars along hard roofs in extra-thick coal seams according to claim 1, characterized in that, In step S30, the calculation of lithological deterioration degree and connectivity discrimination index includes: The measured mechanical specific energy is calculated based on the axial thrust, torque, rotational speed, and drilling speed of the drilling rig. The degree of lithological deterioration is obtained by subtracting the ratio of the measured mechanical specific energy to the theoretical benchmark specific energy of the geological exploration rock. The connectivity discrimination index is obtained by multiplying the fracturing efficiency index with the lithological deterioration degree obtained in the current process.

7. The comprehensive treatment method for strong mine pressure in roadways with hard roof and small coal pillars in extra-thick coal seams according to claim 6, characterized in that, In step S40, the differentiated grouting reinforcement of the surrounding rock includes: Set a high threshold and a low threshold for connectivity determination; When the connectivity discrimination index is greater than or equal to the connectivity determination high threshold, the surrounding rock is determined to be in a connected state. When the connectivity discrimination index is less than the connectivity determination high threshold and greater than or equal to the connectivity determination low threshold, the surrounding rock is determined to be in an intact state. When the connectivity discrimination index is less than the connectivity determination low threshold, the surrounding rock is determined to be in a dense state.

8. The comprehensive treatment method for strong mine pressure in roadways with small coal pillars along the hard roof of extra-thick coal seams according to claim 7, characterized in that, In step S40, the adaptive adjustment of the grouting material type and grouting process parameters of the grouting anchor cable for different grade areas includes: For the connected surrounding rock area, cement-water glass dual-liquid grout is selected. The grouting process parameters are set as follows: the initial pressure is controlled at 3 to 5 MPa. After the grouting pressure stabilizes and rises, the process is switched to single-liquid grout for high-pressure fracturing grouting. The final pressure is controlled at 8 to 10 MPa. For the surrounding rock areas in the intact and dense states, a nano-modified single-liquid coal-loving grouting material is selected, and the grouting process parameters are set to control the grouting pressure at 8 to 15 MPa to ensure that the effective diffusion radius of the grout in the coal and rock mass is greater than or equal to 2.5 meters.

9. The comprehensive treatment method for strong mine pressure in roadways with small coal pillars along hard roofs in extra-thick coal seams according to claim 1, characterized in that, In step S50, during the mining of this working face, real-time monitoring of roadway deformation includes: Displacement sensors and crack observation instruments are installed in the roadway to monitor the roof subsidence, sidewall bulging, and surface crack width in real time. The set thresholds include a cumulative deformation threshold and a crack width threshold; When the real-time roadway deformation obtained by monitoring is greater than or equal to the cumulative deformation threshold, or when the real-time monitored crack width is greater than or equal to the crack width threshold, the secondary grouting dynamic control is triggered.

10. The comprehensive treatment method for strong mine pressure in roadways with small coal pillars along hard roofs in extra-thick coal seams according to claim 7, characterized in that, In step S50, the step of selecting grouting materials and process parameters based on the historical classification results to implement dynamic control of secondary grouting includes: If the historical classification results show that the area was originally in the through state, cement-water glass dual-liquid grout is selected, the gelation time is controlled within the range of 30 to 45 seconds, and the grouting pressure is controlled within the range of 8 to 10 MPa. If the historical classification results show that the region was originally in the dense state or the intact state, a cement-water glass two-component grout is selected, the gelation time is extended to the range of 45 to 60 seconds, and the grouting pressure is increased to 10 to 12 MPa.

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