Method and system for determining roadway roof support density with double-threshold additional compressive stress field

Abstract

A double-threshold additional pressure stress field roadway roof support density determination method and system, the method: collect engineering geological parameters; determine high and low double thresholds; support scheme modeling; quantify stress field volume; determine the roof support density through iterative optimization; construction according to the roof support density; engineering safety verification; system: the geological parameter acquisition module is used for collecting engineering geological parameters; the double threshold calculation module is used for calculating the high load threshold and the low load threshold; the numerical modeling module is used for establishing a three-dimensional model of the roadway; the stress field volume quantification module is used for counting the total volume of high stress field and low stress field units; the roof support density determination module determines the optimal anchor rod / anchor cable spacing and the optimal anchor rod / anchor cable spacing; the safety monitoring feedback module is used for correcting the optimal anchor rod / anchor cable spacing and the optimal anchor rod / anchor cable spacing. The method and system can scientifically and reasonably determine the roadway roof support density and provide reliable safety guarantee for deep coal mining.

Description

Technical Field

[0001] This invention belongs to the field of coal mine roadway surrounding rock control technology, specifically relating to a method and system for determining the support density of roadway roof under a dual-threshold additional compressive stress field. Background Technology

[0002] As deep coal mining extends to depths exceeding 1,000 meters, the stability control of surrounding rock in roadways faces multiple challenges, including high ground stress, strong mining disturbances, and complex geological structures. As a core means of ensuring roadway safety, the density decision of bolt / cable anchors directly restricts mine economic benefits and tunneling efficiency. Traditional designs suffer from systemic cognitive biases and technical bottlenecks: the safety paradox of high-density support: blindly adopting small-spacing, dense support schemes leads to excessive overlap of the additional compressive stress fields generated by adjacent anchors. This overlap forms tensile stress concentration zones between bolts / cables, easily disrupting the continuity of the surrounding rock and inducing delamination weak zones. Engineering practice shows that high-density schemes not only fail to eliminate the risk of roof fracture and collapse but also exacerbate local imbalances due to the interference effect of group anchor stress. Optimization of decision-making technology gaps: Although existing methods can obtain the stress state of the surrounding rock, they have not established a quantitative mapping relationship between the spatial coordinated distribution of the stress field and the support density, resulting in the inability of the support layout to balance the needs of overall safety and density reduction; lack of economic control mechanism: the control law of anchor bolt / anchor cable parameters on the volume of the surrounding rock stress field has not been fully explored and utilized. For example, the increase of preload can expand the effective compressive stress range, but this characteristic has not been transformed into a scientific basis for optimizing the spacing.

[0003] Existing technologies are mired in a double dilemma: overall safety is out of control: the stress interference effect of high-density support creates a "safety depression" in the roof, and traditional methods cannot eliminate the risk of stress superposition, nor can they accurately cover the weak tensile areas of the roof and the potential collapse arch range; lack of density reduction technology: there is a lack of a closed-loop optimization mechanism based on the coordinated control of the stress field and constrained by the volume coverage rate, especially unable to solve the core problem of "scientifically expanding the spacing under the premise of eliminating the interference of the anchor group"; insufficient dynamic adaptability: the real-time control logic of geological characteristics is not integrated, and the protection focus cannot be dynamically switched according to the roof conditions.

[0004] Therefore, it is urgent to break through the traditional constraint of "density equals safety" and innovate and develop a safe density reduction system for spatially coordinated control of stress fields. This system needs to construct a closed-loop path of "eliminating stress interference → coordinated volume coverage → iterative density optimization" to achieve a synergistic breakthrough in scientific density reduction and intrinsic safety while preventing the harmful superposition of multiple anchors. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method and system for determining the roof support density of roadways under a dual-threshold additional compressive stress field. This method is simple to implement and has low implementation costs. It can scientifically and rationally determine the roof support density of roadways, providing reliable safety assurance for deep coal mining. The system has a simple structure, high level of intelligence, and can efficiently and accurately determine the roof support density scheme of roadways.

[0006] To achieve the above objectives, the present invention provides a method for determining the roof support density of a roadway under a dual-threshold additional compressive stress field, comprising the following steps:

[0007] Step 1: Collect engineering geological parameters;

[0008] Engineering geological parameters are obtained through a combination of geological exploration and laboratory testing. These parameters include: tunnel span B (in meters), tunnel depth H (in meters), coal seam dip angle α (in degrees), and thickness h of each roof stratum. i The unit is m, and the unit weight γ of each rock layer in the top plate is... i The unit is kN / m³, and the elastic modulus E of each rock layer in the top plate is... i The unit is GPa, and the anchoring rock layer firmness coefficient f b The internal friction angle φ of the coal seam, in degrees.

[0009] Step 2: Determine the high and low threshold values ​​for the critical stress;

[0010] S21: Based on the composite beam theory, the maximum unit area load acting on the direct top is calculated according to formula (1), and is used as the high load threshold σ. max ;

[0011] (1);

[0012] In the formula, (q n )1 represents the load exerted by the nth layer of the roof on the first layer of the roadway roof, in kPa;

[0013] S22: Based on the natural equilibrium arch theory, the self-weight load of the potential collapse block is calculated according to formula (2), which serves as the low load threshold σ. min ;

[0014] (2);

[0015] In the formula, The density of the top slab is expressed in kN / m³. 3 h r The thickness of the unstable rock layer at the top. k y f is the stability coefficient of the rock layer to be anchored. nh is the strength coefficient of the anchored rock layer. c This represents the depth of coal seam failure in the roadway under the critical stress corresponding to the unstable surrounding rock layer, expressed in meters (m). K c The stress concentration factor around the tunnel is determined based on the tunnel's cross-sectional shape and width-to-height ratio. The average unit weight of the subsurface layer between the top of the tunnel and the surface, expressed in kN / m³. 3 K B f is a dimensionless parameter characterizing the degree of impact of mining. y h is the coal seam firmness coefficient. s This refers to the thickness of the coal seam or the thickness of the coal interlayer within the roadway outline, in meters (m).

[0016] Step 3: Model the support scheme;

[0017] A three-dimensional model of the tunnel was established in FLAC3D. The anchor bolts / cables were simulated using cable elements, and the preload application error of the anchor bolts / cables was ≤5%. The Mohr-Coulomb criterion was selected for the rock mass constitutive model, and the mechanical parameters were determined based on the engineering geological parameters.

[0018] Step 4: Quantify the volume of the stress field;

[0019] Extract the load of a single anchor bolt / cable from the simulation results. The total volume V of the high-stress field element satisfies formula (3) H The unit is m 3 Simultaneously, the load on a single anchor bolt / cable is extracted from the simulation results. The total volume V of the low-stress field element that satisfies formula (4) L The unit is m 3 ;

[0020] (3);

[0021] (4);

[0022] Step 5: Determine the roof support density through iterative optimization;

[0023] S51: Set the initial support scheme for the roof; set the initial anchor bolt / anchor cable spacing S0 and the initial anchor bolt / anchor cable row spacing R0;

[0024] S52: Set the optimization iteration termination condition for the roof support density; calculate the roadway roof fracture development index I based on the RQD value of the borehole core. f If the development index of cracks in the tunnel roof is I f If the index of the roadway roof fissure development is greater than or equal to 0.6, then the iteration will terminate if the condition of not satisfying formula (5) is met. fIf < 0.6, then the iteration terminates when formula (6) is not satisfied;

[0025] V L / k L Bh r S 控 ≥ 1.0 (5);

[0026] In the formula, S 控 The controlled area of ​​a single anchor bolt / cable is calculated as the product of the spacing between adjacent anchor bolts / cables and the row spacing. This is the adjustment coefficient for the high load threshold during fracture development;

[0027] V H / k H B 2 h ≥ 1.0 (6)

[0028] In the formula, This is the adjustment factor for the low load threshold when the top plate is intact. The thickness of the direct top plate is expressed in meters (m).

[0029] S53: The roof support density is determined through iterative optimization; based on the initial anchor bolt / anchor cable spacing S0 and the initial anchor bolt / anchor cable row spacing R0, the anchor bolt / anchor cable spacing S0 is gradually increased in increments of 0.1m. i And anchor bolt / anchor cable spacing R i Increasing the anchor bolt / anchor cable spacing S i And anchor bolt / anchor cable spacing R i During the process, when the crack development index I of the roadway roof is... f If the value is ≥0.6 and there is a situation where formula (5) is not satisfied, the anchor bolt / anchor cable spacing S is traced back to the previous anchor bolt / anchor cable spacing that satisfies formula (5). i And anchor bolt / anchor cable spacing R i As the minimum density scheme When the crack development index I of the roadway roof is f If the value is less than 0.6 and there is a situation where formula (6) is not satisfied, the anchor bolt / anchor cable spacing S is traced back to the previous one that satisfies formula (5). i And anchor bolt / anchor cable spacing R i As the optimal density scheme Among them, S opt For the optimal anchor bolt / anchor cable spacing, R opt To achieve the optimal anchor bolt / anchor cable spacing;

[0030] Step Six: Carry out construction according to the determined roof support density;

[0031] Based on the optimal density scheme Install anchor bolts / anchor cables on the top slab;

[0032] Step 7: Engineering safety verification;

[0033] Maximum displacement of the top plate Monitoring will be conducted, if If <0.002B, then the engineering safety requirements are met. If the value is ≥0.002B, then the engineering safety requirements are not met. Furthermore, according to S... new =0.9S opt R new =0.9R opt Adjust the support density until... <0.002B, the corrected anchor bolt / anchor cable spacing S is obtained. new And the corrected anchor bolt / anchor cable spacing R new .

[0034] As a preferred option, in step five, S52, I is calculated according to formula (7). f ;

[0035] (7).

[0036] As a preferred embodiment, in step five, S52, k L =1.2, with an error of ±0.1, k H =0.9, with an error of ±0.05, which stems from the uncertainty in rock mass parameter testing.

[0037] As a preferred embodiment, in step three, the simulated value F of the anchor bolt / anchor cable preload... sim The formula (8) is satisfied, and the Cable unit parameters are set according to the actual anchor bolt / anchor cable specifications;

[0038] F sim = (0.95~1.05)×F design (8);

[0039] In the formula, F design This is the design value for the preload of the anchor bolt / anchor cable.

[0040] As a preferred embodiment, in step five, S52, when S i >1.5~1.8 S 0 or R >1.5~1.8 R 0 The iteration process is forcibly terminated at certain times to ensure effective overlap of anchor bolts / cables.

[0041] As a preferred embodiment, in step five, S53, the anchor bolt / anchor cable spacing... Sopt ∈ (1.5~1.8) S 0) m, the anchor bolt / anchor cable spacing R opt ∈ (1.5~1.8) R 0)m.

[0042] This invention overcomes the shortcomings of existing coal mine roadway roof support density design, such as the lack of spatial coordination and control, safety risks induced by high-density schemes, and lack of basis for density reduction decisions. It provides a method for determining roadway roof support density using a dual-threshold additional compressive stress field. First, by collecting roadway geological parameters, high-load and low-load thresholds are dynamically calculated, serving as critical stress thresholds for high pressure to prevent roof fracture and low pressure to prevent roof collapse, respectively. The high-load threshold effectively ensures the active support strength provided by the support when a high compression zone forms in the roadway roof, preventing direct roof fracture and instability. The low-load threshold ensures the balance of unstable rock layer loads on the roadway roof, preventing large-scale roof collapse and instability, while maintaining the active support strength provided by the support. Secondly, by extracting the spatial volume of the high-pressure stress field to prevent fracture and the spatial volume of the low-pressure stress field to prevent collapse through three-dimensional numerical simulation, a reliable data foundation can be provided for determining the subsequent roof support density. Next, under the premise of eliminating the interference of group anchor stress, the spacing between anchor bolts / cables and the row spacing are gradually increased using a step-size iterative algorithm. The minimum safe density is determined as the optimal density scheme by backtracking with the dual stress field volume coverage rate as the constraint target. Then, by dynamically prioritizing the high-pressure or low-pressure field volume requirements based on the roof crack characteristics and performing closed-loop correction based on displacement monitoring, the optimal support scheme can be upgraded and optimized a second time based on feedback information from specific implementation situations, further ensuring the reliability and economy of the support scheme. This invention employs stress field spatial collaborative reconstruction, dual-volume full-domain coverage, and density adaptive iteration technologies to overcome three core challenges of traditional methods: uncontrolled stress interference from group anchors (unable to avoid the risk of tensile stress weak zones caused by high-density support), lack of spatial collaboration between dual mechanisms (difficult to achieve collaborative protection by continuously covering the tensile weak zone of the roof with the high-pressure field and completely enveloping the potential collapse arch with the low-pressure field), and lack of scientific constraints on density reduction decisions (lacking a support density compression mechanism with volume coverage rate as a hard indicator). By constructing a closed-loop system of "geological parameters - stress field collaboration - volume coverage - density iteration", it achieves an inherently safe reduction in support density while eliminating stress interference, thus achieving a synergistic breakthrough in roof full-domain stability and tunneling efficiency.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] 1) Elimination of high-density safety risks: By quantifying the coordinated distribution of three-dimensional stress fields, weak areas of tensile stress formed by the superposition of multiple anchor stresses are avoided. The spacing between anchor bolts / cables is scientifically expanded to achieve continuous and uniform coverage of the stress field, eliminating the risk of delamination and collapse induced by traditional high-density schemes, and breaking through the cognitive limitation of "density equals safety".

[0045] 2) Scientific density reduction and precise control: Using the volume coverage rate of the dual stress field as a rigid constraint boundary, the support density is dynamically determined by a step-size iterative algorithm. This achieves the minimum safe density solution while eliminating stress interference, completely eliminating redundancy or inadequacy caused by trial and error.

[0046] 3) Geological dynamic adaptation enhancement: Based on the characteristics of roof fracture development, the protection focus is automatically switched (high pressure field volume is emphasized in intact rock strata / low pressure field volume is prioritized in fractured areas), and the real-time closed-loop correction scheme through displacement monitoring significantly improves the adaptability to complex geological conditions.

[0047] 4) Safety, density reduction, efficiency improvement and synergy: By scientifically expanding the distance to eliminate interference from multiple anchors, the single-cycle support time is significantly shortened; by integrating parametric modeling and automatic volume extraction technology, the inherent safety improvement and breakthrough leap in tunneling efficiency are achieved simultaneously.

[0048] This method is simple to implement and has low implementation costs. It can scientifically and rationally determine the support density of the roadway roof, and can provide reliable safety guarantees for the mining of deep coal.

[0049] The present invention also provides a system for determining the roof support density of a roadway under a dual-threshold additional compressive stress field, which is used to implement a method for determining the roof support density of a roadway under a dual-threshold additional compressive stress field. The system includes a geological parameter acquisition module, a dual-threshold calculation module, a numerical modeling module, a stress field volume quantification module, a roof support density determination module, and a safety monitoring feedback module.

[0050] The geological parameter acquisition module is used to collect engineering geological parameters and send them to the dual threshold calculation module and the numerical modeling module.

[0051] The dual threshold calculation module is connected to the geological parameter acquisition module and is used to calculate the high load threshold and low load threshold based on engineering geological parameters.

[0052] The numerical modeling module is connected to the geological parameter acquisition module and is used to establish a three-dimensional model of the tunnel based on engineering geological parameters.

[0053] The stress field volume quantification module is connected to the dual threshold calculation module and the numerical modeling module respectively, and is used to calculate the total volume of high stress field units with loads greater than or equal to the high load threshold and the total volume of low stress field units with loads less than or equal to the low load threshold based on the three-dimensional model of the tunnel.

[0054] The roof support density determination module is connected to the stress field volume quantification module, which is used to calculate the RQD value of the borehole core and the roadway roof fracture development index, and to determine the optimal anchor bolt / anchor cable spacing and the optimal anchor bolt / anchor cable row spacing based on the roadway roof fracture development index.

[0055] The safety monitoring feedback module is connected to the roof support density determination module. It is used to collect the maximum displacement data of the roof and correct the optimal anchor bolt / anchor cable spacing and the optimal anchor bolt / anchor cable row spacing based on the maximum displacement data of the roof. It obtains and outputs the corrected anchor bolt / anchor cable spacing and the corrected anchor bolt / anchor cable row spacing.

[0056] Furthermore, to facilitate real-time display, a display module is also included; the display module is connected to the top plate support density determination module and the safety monitoring feedback module respectively, and is used to display the optimal anchor bolt / anchor cable spacing, the optimal anchor bolt / anchor cable row spacing, the corrected anchor bolt / anchor cable spacing, and the corrected anchor bolt / anchor cable row spacing in real time.

[0057] In this invention, the geological parameter acquisition module serves as a data receiving channel for both the dual-threshold calculation module and the numerical modeling module, facilitating the acquisition of engineering geological parameters. The dual-threshold calculation module enables the calculation of high-load and low-load thresholds, which are then used as critical stress thresholds for preventing high-pressure failure and low-pressure collapse, respectively. The numerical modeling module facilitates the establishment of a three-dimensional tunnel model based on engineering geological parameters, enabling the simulation and reconstruction of the additional compressive stress field of the rock mass supported by anchor bolts / cables. The stress field volume quantification module allows for the automated extraction of the spatial volume of the high-pressure stress field preventing failure and the low-pressure stress field preventing collapse. The roof support density determination module efficiently and accurately determines the optimal anchor bolt spacing and the optimal anchor bolt / cable spacing, leading to the optimal density scheme. The safety monitoring feedback module facilitates further optimization of the optimal density scheme based on actual implementation results.

[0058] Based on the dual-threshold additional compressive stress field roadway roof support density determination system, this invention has the following advantages: 1) Spatial collaborative density reduction: Quantifying the stress field distribution avoids superposition risks, scientifically expanding the distance to achieve continuous and uniform coverage, and eliminating the hidden dangers of tensile stress weak areas in high-density schemes; 2) Dual-mechanism full-domain protection: Integrating the seamless coverage of tensile weak zones by the high-pressure field and the complete envelopment of the collapse arch by the low-pressure field, constructing a collaborative protection system under density reduction conditions; 3) Closed-loop dynamic optimization: Establishing an adaptive mechanism of geological characteristics-volume coverage-density iteration-safety verification. This invention breaks through the cognitive limitation of "density equals safety," achieving an inherently safe reduction in support density and a synergistic leap in tunneling efficiency under the premise of eliminating stress interference. The system has a simple structure, a high degree of intelligence, and can efficiently and accurately determine the roadway roof support density scheme. Attached Figure Description

[0059] Figure 1 This is a flowchart of the method part of the present invention.

[0060] Figure 2 This is a principle block diagram of the system part of the present invention. Detailed Implementation

[0061] The invention will now be further described with reference to the accompanying drawings.

[0062] like Figure 1 As shown, the present invention provides a method for determining the roof support density of a roadway under a dual-threshold additional compressive stress field, comprising the following steps:

[0063] Step 1: Collect engineering geological parameters;

[0064] Engineering geological parameters were obtained through a combination of geological exploration and laboratory testing. These parameters included: tunnel span B (in meters, accurate to 0.01m), tunnel depth H (in meters, accurate to 1m), coal seam dip angle α (in degrees, accurate to 0.1°), and thickness h of each roof stratum. i The unit is m, and the unit weight γ of each rock layer in the top plate is... i The unit is kN / m³, accurate to 0.1 kN / m³, and the elastic modulus E of each rock layer in the top plate. i The unit is GPa, accurate to 0.1 GPa, and the anchoring rock layer firmness coefficient f. b The internal friction angle φ of the coal seam, determined by Protodyakonov coefficient, is expressed in degrees, accurate to 0.5°.

[0065] Step 2: Determine the high and low threshold values ​​for the critical stress;

[0066] S21: Based on the composite beam theory, the maximum unit area load acting on the direct top is calculated according to formula (1), and is used as the high load threshold σ. max ;

[0067] (1);

[0068] In the formula, (q n )1 represents the load exerted by the nth layer of the roof on the first layer (basic roof) of the roadway roof, in kPa;

[0069] S22: Based on the natural equilibrium arch theory, the self-weight load of the potential collapse block is calculated according to formula (2), which serves as the low load threshold σ. min ;

[0070] (2);

[0071] In the formula, The density of the top slab is expressed in kN / m³. 3 h r The thickness of the unstable rock layer at the top (collapse limit). k yf is the stability coefficient of the rock layer to be anchored (valued according to the rock firmness coefficient classification table, generally 0.5~1.5). n h is the strength coefficient of the anchored rock layer. c This represents the depth of coal seam failure in the roadway under the critical stress corresponding to the unstable surrounding rock layer, expressed in meters (m). K c The stress concentration factor around the tunnel is determined based on the tunnel's cross-sectional shape and width-to-height ratio. The average unit weight of the subsurface layer between the top of the tunnel and the surface, expressed in kN / m³. 3 K B A dimensionless parameter characterizing the degree of mining-induced impact (its value ranges from 1.5 to 2.5, depending on the degree of mining-induced impact), f y h is the coal seam firmness coefficient. s This refers to the thickness of the coal seam or the thickness of the coal interlayer within the roadway outline, in meters (m).

[0072] Step 3: Model the support scheme;

[0073] A three-dimensional model of the tunnel was established in FLAC3D. The anchor bolts / cables were simulated using cable elements, and the preload application error of the anchor bolts / cables was ≤5%. The Mohr-Coulomb criterion was selected for the rock mass constitutive model, and the mechanical parameters were determined based on the engineering geological parameters.

[0074] Step 4: Quantify the volume of the stress field;

[0075] Extract the load of a single anchor bolt / cable from the simulation results. The total volume V of the high-stress field element satisfies formula (3) H The unit is m 3 Simultaneously, the load on a single anchor bolt / cable is extracted from the simulation results. The total volume V of the low-stress field element that satisfies formula (4) L The unit is m 3 ;

[0076] (3);

[0077] (4);

[0078] Step 5: Determine the roof support density through iterative optimization;

[0079] S51: Set the initial support scheme for the roof; set the initial anchor bolt / anchor cable spacing S0 and the initial anchor bolt / anchor cable row spacing R0;

[0080] S52: Set the optimization iteration termination condition for the roof support density; calculate the roadway roof fracture development index I based on the RQD value of the borehole core. fIf the development index of cracks in the tunnel roof is I f If the index of the roadway roof fissure development is greater than or equal to 0.6, then the iteration will terminate if the condition of not satisfying formula (5) is met. f If < 0.6, then the iteration terminates when formula (6) is not satisfied;

[0081] V L / k L Bh r S 控 ≥ 1.0 (5);

[0082] In the formula, S 控 The controlled area of ​​a single anchor bolt / cable is calculated as the product of the spacing between adjacent anchor bolts / cables and the row spacing. This is the adjustment coefficient for the high load threshold during fracture development;

[0083] V H / k H B 2 h ≥ 1.0 (6)

[0084] In the formula, This is the adjustment factor for the low load threshold when the top plate is intact. The thickness of the direct top plate is expressed in meters (m).

[0085] S53: The roof support density is determined through iterative optimization; based on the initial anchor bolt / anchor cable spacing S0 and the initial anchor bolt / anchor cable row spacing R0, the anchor bolt / anchor cable spacing S0 is gradually increased in increments of 0.1m. i And anchor bolt / anchor cable spacing R i Increasing the anchor bolt / anchor cable spacing S i And anchor bolt / anchor cable spacing R i During the process, when the crack development index I of the roadway roof is... f If the value is ≥0.6 and there is a situation where formula (5) is not satisfied, the anchor bolt / anchor cable spacing S is traced back to the previous anchor bolt / anchor cable spacing that satisfies formula (5). i And anchor bolt / anchor cable spacing R i As the minimum density scheme When the crack development index I of the roadway roof is f If the value is less than 0.6 and there is a situation where formula (6) is not satisfied, the anchor bolt / anchor cable spacing S is traced back to the previous one that satisfies formula (5). i And anchor bolt / anchor cable spacing R i As the optimal density scheme Among them, S opt For the optimal anchor bolt / anchor cable spacing, R opt To achieve the optimal anchor bolt / anchor cable spacing;

[0086] Step Six: Carry out construction according to the determined roof support density;

[0087] Based on the optimal density scheme Install anchor bolts / anchor cables on the top slab;

[0088] Step 7: Engineering safety verification;

[0089] After implementing the optimal density scheme, the maximum displacement of the top plate Monitoring will be conducted, if If <0.002B, then the engineering safety requirements are met. If the value is ≥0.002B, then the engineering safety requirements are not met. Furthermore, according to S... new =0.9S opt R new =0.9R opt Adjust the support density until... <0.002B, the corrected anchor bolt / anchor cable spacing S is obtained. new And the corrected anchor bolt / anchor cable spacing R new .

[0090] As a preferred option, in step five, S52, I is calculated according to formula (7). f ;

[0091] (7).

[0092] As a preferred embodiment, in step five, S52, k L =1.2, with an error of ±0.1, k H =0.9, with an error of ±0.05.

[0093] As a preferred embodiment, in step three, the simulated value F of the anchor bolt / anchor cable preload... sim The formula (8) is satisfied, and the Cable unit parameters are set according to the actual anchor bolt / anchor cable specifications;

[0094] F sim = (0.95~1.05)×F design (8);

[0095] In the formula, F design This is the design value for the preload of the anchor bolt / anchor cable.

[0096] As a preferred embodiment, in step five, S52, when S i >1.5~1.8 S 0 or R >1.5~1.8 R 0 The iteration process is forcibly terminated at that time.

[0097] As a preferred embodiment, in step five, S53, the anchor bolt / anchor cable spacing... S opt ∈ (1.5~1.8) S 0) m, the anchor bolt / anchor cable spacing R opt ∈ (1.5~1.8) R 0)m.

[0098] This invention overcomes the shortcomings of existing coal mine roadway roof support density design, such as the lack of spatial coordination and control, safety risks induced by high-density schemes, and lack of basis for density reduction decisions. It provides a method for determining roadway roof support density using a dual-threshold additional compressive stress field. First, by collecting roadway geological parameters, high-load and low-load thresholds are dynamically calculated, serving as critical stress thresholds for high pressure to prevent roof fracture and low pressure to prevent roof collapse, respectively. The high-load threshold effectively ensures the active support strength provided by the support when a high compression zone forms in the roadway roof, preventing direct roof fracture and instability. The low-load threshold ensures the balance of unstable rock layer loads on the roadway roof, preventing large-scale roof collapse and instability, while maintaining the active support strength provided by the support. Secondly, by extracting the spatial volume of the high-pressure stress field to prevent fracture and the spatial volume of the low-pressure stress field to prevent collapse through three-dimensional numerical simulation, a reliable data foundation can be provided for determining the subsequent roof support density. Next, under the premise of eliminating the interference of group anchor stress, the spacing between anchor bolts / cables and the row spacing are gradually increased using a step-size iterative algorithm. The minimum safe density is determined as the optimal density scheme by backtracking with the dual stress field volume coverage rate as the constraint target. Then, by dynamically prioritizing the high-pressure or low-pressure field volume requirements based on the roof crack characteristics and performing closed-loop correction based on displacement monitoring, the optimal support scheme can be upgraded and optimized a second time based on feedback information from specific implementation situations, further ensuring the reliability and economy of the support scheme. This invention employs stress field spatial collaborative reconstruction, dual-volume full-domain coverage, and density adaptive iteration technologies to overcome three core challenges of traditional methods: uncontrolled stress interference from group anchors (unable to avoid the risk of tensile stress weak zones caused by high-density support), lack of spatial collaboration between dual mechanisms (difficult to achieve collaborative protection by continuously covering the tensile weak zone of the roof with the high-pressure field and completely enveloping the potential collapse arch with the low-pressure field), and lack of scientific constraints on density reduction decisions (lacking a support density compression mechanism with volume coverage rate as a hard indicator). By constructing a closed-loop system of "geological parameters - stress field collaboration - volume coverage - density iteration", it achieves an inherently safe reduction in support density while eliminating stress interference, thus achieving a synergistic breakthrough in roof full-domain stability and tunneling efficiency.

[0099] Compared with the prior art, the present invention has the following advantages:

[0100] 1) Elimination of high-density safety risks: By quantifying the coordinated distribution of three-dimensional stress fields, weak areas of tensile stress formed by the superposition of multiple anchor stresses are avoided. The spacing between anchor bolts / cables is scientifically expanded to achieve continuous and uniform coverage of the stress field, eliminating the risk of delamination and collapse induced by traditional high-density schemes, and breaking through the cognitive limitation of "density equals safety".

[0101] 2) Scientific density reduction and precise control: Using the volume coverage rate of the dual stress field as a rigid constraint boundary, the support density is dynamically determined by a step-size iterative algorithm. This achieves the minimum safe density solution while eliminating stress interference, completely eliminating redundancy or inadequacy caused by trial and error.

[0102] 3) Geological dynamic adaptation enhancement: Based on the characteristics of roof fracture development, the protection focus is automatically switched (high pressure field volume is emphasized in intact rock strata / low pressure field volume is prioritized in fractured areas), and the real-time closed-loop correction scheme through displacement monitoring significantly improves the adaptability to complex geological conditions.

[0103] 4) Safety, density reduction, efficiency improvement and synergy: By scientifically expanding the distance to eliminate interference from multiple anchors, the single-cycle support time is significantly shortened; by integrating parametric modeling and automatic volume extraction technology, the inherent safety improvement and breakthrough leap in tunneling efficiency are achieved simultaneously.

[0104] This method is simple to implement and has low implementation costs. It can scientifically and rationally determine the support density of the roadway roof, and can provide reliable safety guarantees for the mining of deep coal.

[0105] like Figure 2 As shown, the present invention also provides a system for determining the roof support density of a roadway under a dual-threshold additional compressive stress field, which is used to implement a method for determining the roof support density of a roadway under a dual-threshold additional compressive stress field. The system includes a geological parameter acquisition module, a dual-threshold calculation module, a numerical modeling module, a stress field volume quantification module, a roof support density determination module, and a safety monitoring feedback module.

[0106] The geological parameter acquisition module is used to collect engineering geological parameters and send them to the dual threshold calculation module and the numerical modeling module.

[0107] The dual threshold calculation module is connected to the geological parameter acquisition module and is used to calculate the high load threshold and low load threshold based on engineering geological parameters.

[0108] The numerical modeling module is connected to the geological parameter acquisition module and is used to establish a three-dimensional model of the tunnel based on engineering geological parameters.

[0109] The stress field volume quantification module is connected to the dual threshold calculation module and the numerical modeling module respectively, and is used to calculate the total volume of high stress field units with loads greater than or equal to the high load threshold and the total volume of low stress field units with loads less than or equal to the low load threshold based on the three-dimensional model of the tunnel.

[0110] The roof support density determination module is connected to the stress field volume quantification module, which is used to calculate the RQD value of the borehole core and the roadway roof fracture development index, and to determine the optimal anchor bolt / anchor cable spacing and the optimal anchor bolt / anchor cable row spacing based on the roadway roof fracture development index.

[0111] The safety monitoring feedback module is connected to the roof support density determination module. It is used to collect the maximum displacement data of the roof and correct the optimal anchor bolt / anchor cable spacing and the optimal anchor bolt / anchor cable row spacing based on the maximum displacement data of the roof. It obtains and outputs the corrected anchor bolt / anchor cable spacing and the corrected anchor bolt / anchor cable row spacing.

[0112] To facilitate real-time display, a display module is also included; the display module is connected to the top plate support density determination module and the safety monitoring feedback module respectively, and is used to display the optimal anchor bolt / anchor cable spacing, the optimal anchor bolt / anchor cable row spacing, the corrected anchor bolt / anchor cable spacing, and the corrected anchor bolt / anchor cable row spacing in real time.

[0113] In this invention, the geological parameter acquisition module serves as a data receiving channel for both the dual-threshold calculation module and the numerical modeling module, facilitating the acquisition of engineering geological parameters. The dual-threshold calculation module enables the calculation of high-load and low-load thresholds, which are then used as critical stress thresholds for preventing high-pressure failure and low-pressure collapse, respectively. The numerical modeling module facilitates the establishment of a three-dimensional tunnel model based on engineering geological parameters, enabling the simulation and reconstruction of the additional compressive stress field of the rock mass supported by anchor bolts / cables. The stress field volume quantification module allows for the automated extraction of the spatial volume of the high-pressure stress field preventing failure and the low-pressure stress field preventing collapse. The roof support density determination module efficiently and accurately determines the optimal anchor bolt / cable spacing and the optimal anchor bolt / cable row spacing, leading to the optimal density scheme. The safety monitoring feedback module facilitates further optimization of the optimal density scheme based on actual implementation results.

[0114] Based on the dual-threshold additional compressive stress field roadway roof support density determination system, this invention has the following advantages: 1) Spatial collaborative density reduction: Quantifying the stress field distribution avoids superposition risks, scientifically expanding the distance to achieve continuous and uniform coverage, and eliminating the hidden dangers of tensile stress weak areas in high-density schemes; 2) Dual-mechanism full-domain protection: Integrating the seamless coverage of tensile weak zones by the high-pressure field and the complete envelopment of the collapse arch by the low-pressure field, constructing a collaborative protection system under density reduction conditions; 3) Closed-loop dynamic optimization: Establishing an adaptive mechanism of geological characteristics-volume coverage-density iteration-safety verification. This invention breaks through the cognitive limitation of "density equals safety," achieving an inherently safe reduction in support density and a synergistic leap in tunneling efficiency under the premise of eliminating stress interference. The system has a simple structure, a high degree of intelligence, and can efficiently and accurately determine the roadway roof support density scheme.

Claims

1. A method for determining the roof support density of a roadway under a dual-threshold additional compressive stress field, characterized in that, Includes the following steps; Step 1: Collect engineering geological parameters; Engineering geological parameters are obtained through a combination of geological exploration and laboratory testing. Engineering geological parameters include: tunnel span B (in meters), tunnel depth H (in meters), coal seam dip angle α (in degrees), and thickness h of each roof stratum. i The unit is m, and the unit weight γ of each rock layer in the top plate is... i The unit is kN / m³, and the elastic modulus E of each rock layer in the top plate is... i The unit is GPa, and the anchoring rock layer firmness coefficient f b The internal friction angle φ of the coal seam, in degrees. Step 2: Determine the high and low threshold values ​​for the critical stress; S21: Based on the composite beam theory, the maximum unit area load acting on the direct top is calculated according to formula (1), and is used as the high load threshold σ. max ; （1）； In the formula, (q n )1 represents the load exerted by the nth layer of the roof on the first layer of the roadway roof, in kPa; S22: Based on the natural equilibrium arch theory, the self-weight load of the potential collapse block is calculated according to formula (2), which serves as the low load threshold σ. min ; （2）； In the formula, The density of the top slab is expressed in kN / m³. 3 h r The thickness of the unstable rock layer at the top. k y f is the stability coefficient of the rock layer to be anchored. n h is the strength coefficient of the anchored rock layer. c This represents the depth of coal seam failure in the roadway under the critical stress corresponding to the unstable surrounding rock layer, expressed in meters (m). K c The stress concentration factor around the tunnel is determined based on the tunnel's cross-sectional shape and width-to-height ratio. The average unit weight of the subsurface layer between the top of the tunnel and the surface, expressed in kN / m³. 3 K B f is a dimensionless parameter characterizing the degree of impact of mining. y h is the coal seam firmness coefficient. s This refers to the thickness of the coal seam or the thickness of the coal interlayer within the roadway outline, in meters (m). Step 3: Model the support scheme; A three-dimensional model of the tunnel was established in FLAC3D. The anchor bolts / cables were simulated using cable elements, and the preload application error of the anchor bolts / cables was ≤5%. The Mohr-Coulomb criterion was selected for the rock mass constitutive model, and the mechanical parameters were determined based on the engineering geological parameters. Step 4: Quantify the volume of the stress field; Extract the load of a single anchor bolt / cable from the simulation results. The total volume V of the high-stress field element satisfies formula (3) H The unit is m 3 Simultaneously, the load on a single anchor bolt / cable is extracted from the simulation results. The total volume V of the low-stress field element that satisfies formula (4) L The unit is m 3 ; （3）； （4）； Step 5: Determine the roof support density through iterative optimization; S51: Set the initial support scheme for the roof; set the initial anchor bolt / anchor cable spacing S0 and the initial anchor bolt / anchor cable row spacing R0; S52: Set the optimization iteration termination condition for the roof support density; calculate the roadway roof fracture development index I based on the RQD value of the borehole core. f If the development index of cracks in the tunnel roof is I f If the index of the roadway roof fissure development is greater than or equal to 0.6, then the iteration will terminate if the condition of not satisfying formula (5) is met. f If < 0.6, then the iteration terminates when formula (6) is not satisfied; V L / k L Bh r S 控 ≥ 1.0 (5); In the formula, S 控 The controlled area of ​​a single anchor bolt / cable is calculated as the product of the spacing between adjacent anchor bolts / cables and the row spacing. This is the adjustment coefficient for the high load threshold during fracture development; V H / k H B 2 h ≥ 1.0 (6); In the formula, This is the adjustment factor for the low load threshold when the top plate is intact. The thickness of the direct top plate is in meters (m). S53: The roof support density is determined through iterative optimization; based on the initial anchor bolt spacing S0 and the initial anchor bolt / anchor cable spacing R0, the anchor bolt / anchor cable spacing S0 is gradually increased in increments of 0.1m. i And anchor bolt / anchor cable spacing R i Increasing the anchor bolt / anchor cable spacing S i And anchor bolt / anchor cable spacing R i During the process, when the crack development index I of the roadway roof is... f If the value is ≥ 0.6 and there is a situation where formula (5) is not satisfied, the anchor bolt / anchor cable spacing S is traced back to the previous anchor bolt / anchor cable spacing that satisfies formula (5). i And anchor bolt / anchor cable spacing R i As the minimum density scheme When the crack development index I of the roadway roof is f If the value is less than 0.6 and there is a situation where formula (6) is not satisfied, the anchor bolt / anchor cable spacing S is traced back to the previous one that satisfies formula (5). i And anchor bolt / anchor cable spacing R i As the optimal density scheme Among them, S opt For the optimal anchor bolt / anchor cable spacing, R opt To achieve the optimal anchor bolt / anchor cable spacing; Step Six: Carry out construction according to the determined roof support density; Based on the optimal density scheme Install anchor bolts / anchor cables on the top slab; Step 7: Engineering safety verification; Maximum displacement of the top plate Monitoring is conducted, if If <0.002B, then the engineering safety requirements are met. If the value is ≥0.002B, then the engineering safety requirements are not met. Furthermore, according to S... new =0.9S opt R new =0.9R opt Adjust the support density until... <0.002B, the corrected anchor bolt / anchor cable spacing S is obtained. new And the corrected anchor bolt / anchor cable spacing R new .

2. The method for determining the roof support density of a roadway under a dual-threshold additional compressive stress field according to claim 1, characterized in that, In step S52 of step five, I is calculated according to formula (7). f ; （7）。 3. The method for determining the roof support density of a roadway under a dual-threshold additional compressive stress field according to claim 1 or 2, characterized in that, In step five, S52, k L =1.2, with an error of ±0.1, k H =0.9, with an error of ±0.

05.

4. The method for determining the roof support density of a roadway under a dual-threshold additional compressive stress field according to claim 3, characterized in that, In step three, the simulated value F of the anchor bolt / anchor cable preload. sim The formula (8) is satisfied, and the Cable unit parameters are set according to the actual anchor bolt / anchor cable specifications; F sim = (0.95~1.05)×F design (8); In the formula, F design This is the design value for the preload of the anchor bolt / anchor cable.

5. The method for determining the roof support density of a roadway under a dual-threshold additional compressive stress field according to claim 4, characterized in that, In step five, S52, when S i The iteration process is forcibly terminated when R > 1.8S0 or R > 1.8R0.

6. The system for determining the roof support density of a roadway under a dual-threshold additional compressive stress field according to claim 5, characterized in that, In step five, S53, the anchor bolt / anchor cable spacing S opt The value range is 1.5S0~1.8S0 m, and the anchor bolt / anchor cable spacing R opt The value range is 1.5R0~1.8R0 m.

7. A system for determining the roof support density of a roadway under a dual-threshold additional compressive stress field, used to implement the method for determining the roof support density of a roadway under a dual-threshold additional compressive stress field as described in any one of claims 1 to 6, characterized in that, It includes a geological parameter acquisition module, a dual threshold calculation module, a numerical modeling module, a stress field volume quantification module, a roof support density determination module, and a safety monitoring feedback module; The geological parameter acquisition module is used to collect engineering geological parameters and send them to the dual threshold calculation module and the numerical modeling module. The dual threshold calculation module is connected to the geological parameter acquisition module and is used to calculate the high load threshold and low load threshold based on engineering geological parameters. The numerical modeling module is connected to the geological parameter acquisition module and is used to establish a three-dimensional model of the tunnel based on engineering geological parameters. The stress field volume quantification module is connected to the dual threshold calculation module and the numerical modeling module respectively, and is used to calculate the total volume of high stress field units with loads greater than or equal to the high load threshold and the total volume of low stress field units with loads less than or equal to the low load threshold based on the three-dimensional model of the tunnel. The roof support density determination module is connected to the stress field volume quantification module, which is used to calculate the RQD value of the borehole core and the roadway roof fracture development index, and to determine the optimal anchor bolt / anchor cable spacing and the optimal anchor bolt / anchor cable row spacing based on the roadway roof fracture development index. The safety monitoring feedback module is connected to the roof support density determination module. It is used to collect the maximum displacement data of the roof and correct the optimal anchor bolt / anchor cable spacing and the optimal anchor bolt / anchor cable row spacing based on the maximum displacement data of the roof. It obtains and outputs the corrected anchor bolt / anchor cable spacing and the corrected anchor bolt / anchor cable row spacing.

8. The system for determining the density of roadway roof support under a dual-threshold additional compressive stress field according to claim 7, characterized in that, It also includes a display module; The display module is connected to the top plate support density determination module and the safety monitoring feedback module respectively, and is used to display the optimal anchor bolt / anchor cable spacing, the optimal anchor bolt / anchor cable row spacing, the corrected anchor bolt / anchor cable spacing, and the corrected anchor bolt / anchor cable row spacing in real time.

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