Method for evaluating disturbance degree of roof hydraulic fracturing on roadway surrounding rock stability

Abstract

The invention discloses a method for evaluating the disturbance degree of roof hydrofracture on roadway surrounding rock stability. The method comprises the steps that firstly, geological structure and rock mass mechanical parameters of a target stope, roadway engineering arrangement and support design parameters and key technological parameters of hydrofracture construction are collected and determined; a numerical model capable of accurately reflecting the actual stratum environment, the roadway spatial form and the hydraulic fracturing dynamic process is constructed, and simulation calculation is carried out; secondly, key mechanics and deformation indexes representing the stability of the surrounding rock are extracted from the simulation result, assignment is conducted on different threshold value intervals of the key indexes, an evaluation index formula of the stability of the fracture disturbance roadway is constructed, and meanwhile an evaluation index grading evaluation standard is formulated; finally, the disturbance level of the stability of the area where fracturing is planned to be carried out is obtained, support optimization and risk management and control countermeasures are put forward in a targeted mode according to the grading situation, and therefore the stability and safety of the roadway in the fracturing operation period and the subsequent mining process are effectively guaranteed.

Description

Technical Field

[0001] This application belongs to the field of hydraulic fracturing for preventing rockbursts in coal mines, and in particular relates to a method for assessing the degree of disturbance to the stability of the surrounding rock of the roadway caused by hydraulic fracturing of the roof. Background Technology

[0002] Currently, to mitigate the risk of rockburst in mines, the main methods employed are surface horizontal well fracturing and underground directional long-hole fracturing to weaken the strength and integrity of the hard roof. However, in actual engineering practice, it has been found that during fracturing operations, localized areas affected by hydraulic fracturing can trigger a series of surrounding rock stability problems around the roadway. These problems manifest as: the formation of new fissures in the surrounding rock, water seepage from the roof, and roadway deformation; increased stress on the support structure (anchor cables) and even partial failure; and in severe cases, roof subsidence exceeding 1.0m, leading to severe deformation or damage to the support system and threatening the safety of the working face roadway.

[0003] Therefore, there is an urgent need to propose a new assessment method that integrates geological, roadway, and fracturing process parameters and uses numerical simulation to predict the degree of disturbance to the roadway before fracturing. This method allows for the implementation of coordinated prevention and control measures such as reinforcement, monitoring, and pressure relief in roadway sections that may be significantly affected, thereby ensuring the stability and safety of the roadway during fracturing operations. This is the research direction required by this invention. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for assessing the degree of disturbance to the stability of the surrounding rock of a roadway caused by hydraulic fracturing of the roof. This method can predict the degree of disturbance to the roadway before hydraulic fracturing and take coordinated prevention and control measures such as reinforcement, monitoring, and pressure relief in advance for roadway sections that may be strongly affected, thereby ensuring the stability and safety of the roadway during fracturing operations.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a method for evaluating the degree of disturbance to the stability of the surrounding rock of a roadway caused by hydraulic fracturing of the roof, comprising the following steps: Step 1: Collect and determine the basic geological and tunneling parameters of the fracturing stope.

[0006] Step 2: Collect and determine the key parameters for hydraulic fracturing of the roof.

[0007] Step 3: Construct a numerical model to reflect the geological environment, tunnel spatial morphology and hydraulic fracturing process, and perform simulation calculations.

[0008] Step 4: Based on the simulation results in Step 3, extract the key indicators of the stability of the surrounding rock of the tunnel on the hydraulic fracturing response.

[0009] Step 5: Based on the key indicators extracted in Step 4, assign values ​​to different threshold ranges of the key indicators, construct an evaluation index formula for the stability of fracturing and disturbed roadways, and formulate a graded evaluation standard for the evaluation index.

[0010] Step Six: Using the evaluation index formula and grading evaluation standard from Step Five, and combining the assigned values ​​of the key indicators obtained in Step Four, the degree of disturbance to the stability of the underground roadway during pre-fracturing operations is evaluated, and corresponding measures are taken based on the evaluation results.

[0011] Furthermore, step one specifically includes: S1. Collect and determine basic geological parameters, including: the stratum where the tunnel is located, and the physical and mechanical parameters of the rock strata 10m below and 100m above it, including lithology, density, elastic modulus, Poisson's ratio, cohesion, and internal friction angle; the burial depth of the tunnel area, the magnitude of the ground stress and the lateral pressure coefficient, and the dip angle of the coal seam.

[0012] S2. Collect and determine the basic parameters of the roadway project, including: the cross-sectional dimensions of the roadway (width × height), the number, spacing and mechanical parameters of the anchor bolts and anchor cables used for roadway support, and the thickness of the bottom coal or top coal left in the roadway.

[0013] Furthermore, step two specifically involves: collecting and determining the process parameters of roof hydraulic fracturing, including: fracturing hole layout, fracturing hole diameter and number, water injection flow rate, and water injection duration; and determining the relative positional relationship between the roof hydraulic fracturing holes and the affected roadways, and statistically analyzing the shortest vertical and horizontal distances between the fracturing holes and the roadways that may be affected by fracturing, such as the working face cut-out, return airway, and transport roadway.

[0014] Furthermore, step three specifically includes: I. Determine the model size based on the positional relationship between the roadway and the fracturing hole. Based on the geological conditions and borehole columnar section, establish a two-dimensional UDEC discrete element numerical model of the hydraulic fracturing stope roadway. The rock strata within 15m above and below the fracturing hole, the area 10m above the roadway roof, and the area 5m on both sides of the roadway sidewall are divided into Trigon blocks, and the rest are divided into rectangular grids.

[0015] II. Define the material properties of the model, fix the horizontal displacement of the left and right boundaries and the vertical position of the bottom boundary; apply the equivalent vertical stress of the unsimulated top rock layer to the top of the model, and apply the horizontal stress according to the lateral stress coefficient λ.

[0016] III. Calculate the initial state of the model under given boundary mechanical and displacement conditions. Then, based on the basic tunnel engineering parameters collected in step one, perform tunnel simulation excavation calculations at the preset positions of the model. After installing anchor bolts and anchor cables to support the tunnel, recalculate and balance the model and save it.

[0017] IV. Based on the positional relationship between the roadway and the fracturing holes, determine the location of the fracturing holes in the fracturing layer. Based on the key parameters of the roof hydraulic fracturing operation determined in step II, simulate fracturing by injecting water at a constant flow rate in the fracturing hole area, and then recalculate and balance the model and save it.

[0018] Furthermore, step four specifically involves: extracting key indicators based on the simulation results from step three, including the vertical stress increase rate S on both sides of the roadway. y The rate of increase of horizontal stress in the roadway roof S x The growth rate of the length of the plastic zone on both sides of the tunnel L b The growth rate of the plastic zone above the tunnel roof (L) d The rate of increase in the number of fissures in the surrounding rock of the tunnel (N) c The growth rate of the total length of fractures in the surrounding rock of the tunnel, L w Roadway roof displacement growth rate U d Displacement growth rate U of the two sides of the tunnel b .

[0019] Furthermore, in step five, values ​​are assigned to different threshold ranges for the key indicators, specifically as follows: Determine the vertical stress increase rate S on both sides of the roadway y The sequence number is X1, and its threshold interval division and assignment are: S y >15% is assigned the value 3; 10% y ≤15% is assigned the value 2; 5% y ≤10% is assigned the value 1; S y ≤5% is assigned a value of 0.

[0020] Determine the rate of increase of horizontal stress S in the roadway roof x The sequence number is X2, and its threshold interval division and assignment are: S x >15% is assigned the value 3; 10% x ≤15% is assigned the value 2; 5% x ≤10% is assigned the value 1; S x ≤5% is assigned a value of 0.

[0021] Determine the growth rate L of the plastic zone development length on both sides of the roadway b The sequence number is X3, and its threshold interval division and assignment are: L b >40% is assigned the value 3; 25% <L b ≤40% is assigned a value of 2; 10% <L b ≤25% is assigned the value 1; L b ≤10% is assigned the value 0.

[0022] Determine the growth rate L of the plastic zone development height above the roadway roof. d The sequence number is X4, and its threshold interval division and assignment are: L d ​​​​>40% is assigned the value 3; 25% <L d ≤40% is assigned a value of 2; 10% <L d ≤25% is assigned the value 1; L d ≤10% is assigned the value 0.

[0023] Determine the rate of increase N in the number of fractures in the surrounding rock of the roadway. c The sequence number is X5, and its threshold interval division and assignment are: N c >35% is assigned the value 3; 25% <N c ≤35% is assigned a value of 2; 15% is assigned a value of 2. <N c ≤25% is assigned the value 1; N c ≤15% is assigned a value of 0.

[0024] Determine the growth rate L of the total length of fractures in the surrounding rock of the tunnel. w The sequence number is X6, and its threshold interval division and assignment are: L w >35% is assigned the value 3; 25% <L w ≤35% is assigned a value of 2; 15% is assigned a value of 2. <L w ≤25% is assigned the value 1; L w ≤15% is assigned a value of 0.

[0025] Determine the growth rate U of the roadway roof displacement d The sequence number is X7, and its threshold interval division and assignment are: U d >30% is assigned the value 3; 20% d ≤30% is assigned a value of 2; 10% d ≤20% is assigned the value 1; U d ≤10% is assigned the value 0.

[0026] Determine the displacement growth rate U of the two sides of the roadway b The sequence number is X8, and its threshold interval division and assignment are: U b >30% is assigned the value 3; 20% b ≤30% is assigned a value of 2; 10% b ≤20% is assigned the value 1; U b ≤10% is assigned the value 0.

[0027] Furthermore, the formula for constructing the evaluation index of the stability of the fracturing disturbance roadway in step five is as follows: (10) In the formula, X represents the stability index of the hydraulically fractured roadway; n represents the response index of the surrounding rock stability to hydraulic fracturing (label n = 1, 2, 3...8); X i This is represented by the value assigned to the i-th disturbance level index; X imax This represents the maximum value assigned to the i-th disturbance level index. ​​​​

[0028] Furthermore, in step five, the evaluation index grading standard is formulated as follows: When X≤0.25, the stability of the fracturing disturbance roadway is undisturbed.

[0029] When 0.25 < X ≤ 0.50, the stability of the fracturing disturbance roadway is considered to be a slight disturbance.

[0030] When 0.50 < X ​​≤ 0.75, the stability of the fracturing disturbance roadway is classified as general disturbance.

[0031] When X > 0.75, the stability of the fracturing disturbance roadway is characterized as a strong disturbance.

[0032] Furthermore, in step six, corresponding measures are taken based on the evaluation results, specifically as follows: If the assessment result is no disturbance, then maintain the regular inspection status.

[0033] If the assessment result indicates a minor disturbance, then under normal inspection conditions, increase the monitoring density of roadway deformation and microseismic monitoring.

[0034] If the assessment result is a general disturbance, active reinforcement is carried out by grouting anchor / cable integration to improve the integrity and bearing capacity of the surrounding rock; then, deformation and micro-vibration early warning thresholds are set to monitor the stability of the roadway surrounding rock in real time, and an alarm is triggered in real time when the monitored value exceeds the threshold.

[0035] If the assessment result indicates a strong disturbance, active reinforcement will be carried out using an integrated grouting anchor / cable method to improve the integrity and bearing capacity of the surrounding rock; a collapsible steel support and additional truss anchor cables will be installed to form a composite support; at the same time, pressure relief holes will be constructed on the sidewalls or floor of the disturbed area to relieve pressure; after completion, deformation and micro-vibration early warning thresholds will be set to monitor the stability of the roadway surrounding rock in real time, and an alarm will be triggered in real time when the monitored value exceeds the threshold.

[0036] Compared with existing technologies, this invention first collects and determines the geological structure and rock mechanics parameters of the target mining area, the roadway engineering layout and support design parameters, and the key process parameters for hydraulic fracturing construction. Based on this, a numerical model is constructed that accurately reflects the actual geological environment, roadway spatial morphology, and the dynamic process of hydraulic fracturing, and simulation calculations are performed. Next, key mechanical and deformation indices characterizing the stability of the surrounding rock are extracted from the simulation results, and values ​​are assigned to different threshold ranges for these key indices. An evaluation index formula for the stability of roadways disturbed by fracturing is constructed, and a grading evaluation standard for the evaluation index is established. Finally, by conducting a simulated pre-evaluation of the area where fracturing is to be implemented, the disturbance level of the designed fracturing scheme to the stability of the roadway surrounding rock is predicted, potential general disturbance zones and strong disturbance zones are identified, and targeted support optimization and risk management countermeasures are proposed based on the grading. In summary, this invention achieves a quantitative evaluation of the impact of fracturing disturbance, providing a scientific basis for fracturing design and roadway maintenance, thereby effectively ensuring the stability and safety of the roadway during fracturing operations and subsequent mining processes. Attached Figure Description

[0037] Figure 1 This is a flowchart illustrating an embodiment of the present invention.

[0038] Figure 2 This is a diagram showing the arrangement of fracturing holes on the ground surface of working face 4107 in an embodiment of the present invention.

[0039] Figure 3 This is a two-dimensional UDEC discrete element numerical model of a hydraulic fracturing stope roadway, taking the 4107 transport roadway and the horizontal section of the W4107-03L fracturing well as examples in this embodiment of the invention. Detailed Implementation

[0040] The present invention will be further described below.

[0041] This embodiment takes the 4107 working face of a certain mine as an example. The working face is 240m wide and 2623m long. It has been determined that the No. 4 coal seam and its roof and floor strata have a weak tendency to impact, and the No. 4 coal seam is assessed to have a moderate impact hazard. The 4107 working face also has a moderate impact hazard. After the haulage roadway, return air roadway, and opening cut of the 4107 working face are completed, the horizontal well fracturing at the surface may have a certain impact on the underground roadways. The method of this invention is used to construct a numerical model that reflects the roadway support, hydraulic fracturing, and formation environment of the 4107 working face. Based on the development characteristics of the roadway stress field, displacement field, and plastic zone before and after fracturing, the stability response of the already excavated 4107 roadway during surface fracturing is assessed in advance. Based on the assessment results, integrated hierarchical control measures of "monitoring-reinforcement-decompression" are adopted for the roadway. Figure 1 As shown, it includes the following steps: Step 1: Collect and determine the basic geological and roadway engineering parameters of the fracturing mine. Specifically, the roadways of the 4107 working face are all located in the No. 4 coal seam, with a burial depth of 529~714m, an average dip angle of 2°, and the stress field is dominated by horizontal stress. The maximum horizontal principal stress is 24.86~26.37MPa, and the lateral stress coefficient λ is 1.4.

[0042] Based on borehole 5-4, the physical and mechanical parameters of the coal seam at a depth of 539 m, and the rock strata 10 m below and 100 m above it are shown in Table 1: Table 1 Physical and mechanical parameters of the coal seam and the rock strata 10m below and 100m above it (5-4 borehole).

[0043] The basic parameters of the roadway engineering were collected and determined. Specifically, taking the transport roadway of the 4107 working face as an example, the transport roadway has a rectangular cross section, a net width of 5m and a net height of 4m. The roadway does not have bottom coal, and the top coal thickness is about 7.3m. Six anchor bolts and four anchor cables are installed on the roof of the roadway, with spacings of 1000mm and 1500mm respectively. Five anchor bolts are installed on the sidewalls with a spacing of 900mm. The mechanical parameters of the anchor bolts and anchor cables are shown in Table 2.

[0044] Table 2 Mechanical parameters of anchor bolts and anchor cables.

[0045] Step 2: Collect and determine the key parameters for hydraulic fracturing operations on the roof, specifically: S1. Collect and determine the process parameters for hydraulic fracturing of the roof, such as... Figure 2 The diagram shown is the surface fracturing design for the 4107 working face. It can be seen that three L-shaped horizontal surface wells (W4107-01L, W4107-02L, and W4107-03L) are arranged within the 4107 working face. The fracturing holes are located approximately 60m above the coal seam, with a diameter of 140mm and an injection flow rate of 14m³ / h. 3 / min, single-hole water injection time is 100min.

[0046] S2. Determine the relative positions of the hydraulic fracturing boreholes in the roof and the affected roadways. Taking the 4107 working face transport roadway and W4107-03L shaft as an example, considering that the roadway has a 7m layer of top coal, the shortest horizontal distance between W4107-03L shaft and 4107 transport roadway is 105m, and the shortest vertical distance is 67m (7m top coal thickness + 60m borehole distance from coal seam).

[0047] Step 3: Construct a numerical model to reflect the formation environment, tunnel spatial morphology, and hydraulic fracturing process, and perform simulation calculations, specifically: I. Taking the 4107 transport roadway and well W4107-03L as examples, their horizontal and vertical distances are 105m and 60m respectively. Considering boundary effects and other factors, the model dimensions are determined to be: length 250m and height 120m (of which, the floor thickness is 10m, the No. 4 coal seam thickness is 11m, and the roof thickness is only simulated as 99m). Based on geological conditions and borehole columnar section 5-4, a two-dimensional UDEC discrete element numerical model of the hydraulic fracturing stope roadway is established. Figure 3 As shown, the roadway is located at the bottom of coal seam 4, 40m from the left boundary. The area 10m above it and 5m on each side of the sidewall, along with the rock strata 45-75m above the coal seam (15m above and below the fracturing holes), are divided into Trigon blocks, and the rest are divided into rectangular grids.

[0048] II. Define the model's material properties, fix the horizontal displacement of the left and right boundaries and the vertical position of the bottom boundary; apply the equivalent vertical stress of the unsimulated top rock layer to the top of the model, and apply horizontal stress according to the lateral stress coefficient λ; the equivalent vertical stress of the unsimulated top rock layer is calculated as follows: (1) In the formula, S zs The equivalent vertical stress of the unsimulated top strata is expressed in MPa; M. s The thickness of the unsimulated top strata is shown in m; S zd Vertical stress applied to the bottom of the model, MPa; S zxd The horizontal stress applied to the bottom of the model is MPa.

[0049] In this embodiment, the material properties of the model are defined according to Table 1, and the horizontal displacement of the left and right boundaries and the vertical position of the bottom boundary of the model are fixed. Considering that borehole 5-4 shows that the burial depth of coal seam 4 is 539m, but only the 99m thick roof rock layer above coal seam 4 is actually simulated, the equivalent vertical stress to be applied to the top of the model is calculated to be 11MPa by formula (1). At the same time, the initial vertical stress and horizontal stress at the bottom of the model are 14MPa and 19.6MPa, respectively.

[0050] III. Calculate the initial equilibrium state of the model under the given boundary mechanical and displacement conditions. Subsequently, at the bottom of coal seam 4 and 40m away from the left boundary of the model, excavate a roadway 5m wide and 4m high. Assign parameters to the roadway support conditions according to the anchor bolt and anchor cable parameters determined in step one, calculate the equilibrium of the model again, save the model file and name it YLHD1.sav.

[0051] IV. Based on the location relationship between the roadway and the fracturing hole, the designed fracturing hole location is 105m to the right and 67m above the roadway. The designed water injection flow rate (constant flow rate) in this area is 14m³. 3 / min, water injection time 100min, recalculate the equilibrium of the model, keep the model file and name it YLHD2.sav.

[0052] Step 4: Based on the simulation results in Step 3, extract the key indicators of the roadway surrounding rock stability on the hydraulic fracturing response. Specifically, based on the simulation results in Step 3, extract the key indicators, including the vertical stress increase rate S on both sides of the roadway. y The rate of increase of horizontal stress in the roadway roof S x The growth rate of the length of the plastic zone on both sides of the tunnel L b The growth rate of the plastic zone above the tunnel roof (L) d The rate of increase in the number of fissures in the surrounding rock of the tunnel (N) c The growth rate of the total length of fractures in the surrounding rock of the tunnel, L w Roadway roof displacement growth rate U d Displacement growth rate U of the two sides of the tunnel b .

[0053] The specific calculation formulas for the above parameters are as follows: Read the roadway surrounding rock stability model files YLHD1.sav and YLHD2.sav before and after fracturing, respectively, and count the peak vertical stress on the left and right sides of the roadway. The peak stress on the left and right sides before fracturing is denoted as S. yq1 S yq2 The peak stresses after fracturing were S yh1 S yh2 The vertical stress increase rate S on both sides of the roadway is calculated using formula (2). y : (2).

[0054] The peak horizontal stress in the roadway roof region was statistically analyzed, and the peak horizontal stress in the roadway roof before and after fracturing was denoted as S. xq S xh The vertical stress increase rate S of the roadway roof is calculated using formula (3). x : (3).

[0055] The maximum development length of the plastic zone on both sides of the roadway sidewalls was statistically analyzed. The development lengths of the plastic zone on the left and right sides of the two sidewalls before fracturing were denoted as L. bq1 L bq2 The length of the plastic zone after fracturing is denoted as L. bh1 L bh2 The growth rate L of the plastic zone development length on both sides of the roadway is calculated using formula (4). b : (4).

[0056] The maximum height of the plastic zone in the roadway roof was statistically analyzed. The heights of the plastic zone before and after fracturing were denoted as L. dq L dh The growth rate L of the plastic zone development height of the roadway roof is calculated using formula (5). d : (5).

[0057] The number of fractures developed in the quadrilateral area formed by the area 10m above the tunnel and 5m to the left and right sides of the tunnel is counted. The number of fractures developed in the surrounding rock before and after hydraulic fracturing is denoted as N. cq N ch The increase rate N of the number of fractures in the surrounding rock of the roadway is calculated using formula (6). c : (6).

[0058] The total length of fracture development within the quadrilateral area formed by the tunnel 10m above and 5m to the left and right sides of the tunnel is recorded. The total length of fracture development in the surrounding rock before and after hydraulic fracturing is denoted as L. wq L wh The growth rate L of the total length of fractures in the surrounding rock of the roadway is calculated using formula (7). w : (7).

[0059] The peak displacement of the roadway roof is statistically analyzed, and the peak displacements of the roof before and after fracturing are denoted as U. dq U dh The displacement growth rate U of the roadway roof is calculated using formula (8). d : (8).

[0060] The peak displacement of the roadway sidewalls was statistically analyzed. The peak displacements of the two sidewalls before fracturing were denoted as U. bq1 U bq2 The peak displacement after fracturing is denoted as U. bh1 U bh2 The displacement growth rate U of the two sides of the road is calculated using formula (9). b : (9).

[0061] Table 3 shows the monitoring values ​​of each response index of the model before and after fracturing in this embodiment.

[0062] Table 3: Monitoring values ​​of various response indicators of the model before and after fracturing.

[0063] The vertical stress increase rate S on both sides of the roadway is calculated using formulas (2) to (9). y The rate of increase of horizontal stress in the roadway roof S x The growth rate of the length of the plastic zone on both sides of the tunnel L b The growth rate of the plastic zone above the tunnel roof (L) d The rate of increase in the number of fissures in the surrounding rock of the tunnel (N) c The growth rate of the total length of fractures in the surrounding rock of the tunnel, L w Roadway roof displacement growth rate U d Displacement growth rate U of the two sides of the tunnel b As shown in Table 4.

[0064] Table 4: Key index values ​​of roadway surrounding rock stability on hydraulic fracturing response.

[0065] Step 5: Based on the key indicators extracted in Step 4, assign values ​​to different threshold ranges of the key indicators, as shown in Table 5: Table 5: Evaluation index of stability response indicators for each roadway under fracturing disturbance.

[0066] The formula for assessing the stability of fracturing-disturbed roadways is as follows: (10) In the formula, X represents the stability index of the hydraulically fractured roadway; n represents the response index of the surrounding rock stability to hydraulic fracturing (label n = 1, 2, 3...8); X i This is represented by the value assigned to the i-th disturbance level index; X imax This represents the maximum value assigned to the i-th disturbance level index.

[0067] In this embodiment, the following calculation is obtained by substituting the above values ​​into formula (10): The assessment index for determining the stability of the fracturing-induced roadway was 0.375.

[0068] At the same time, a tiered evaluation standard for the assessment index was formulated, specifically as follows: When X≤0.25, the stability of the fracturing disturbance roadway is undisturbed; When 0.25 < X ≤ 0.50, the stability of the fracturing disturbance roadway is considered to be a slight disturbance. When 0.50 < X ​​≤ 0.75, the stability level of the fracturing disturbance roadway is general disturbance; When X > 0.75, the stability of the fracturing disturbance roadway is characterized as a strong disturbance.

[0069] In this embodiment, based on the above-mentioned grading evaluation criteria, it is determined that the stability of the 4107 transport roadway during the fracturing of the W4107-03L fracturing well is only slightly disturbed by the fracturing.

[0070] Step Six: Take corresponding measures based on the assessment results, as shown in Table 1: Table 6: Prevention and Control Strategies for Different Levels of Fracturing Disturbance to Roadway Stability In this embodiment, the disturbance is slight. According to Table 6, it is determined that during the fracturing of the W4107-03L fracturing well, the 4107 transport roadway only needs to increase the monitoring density of roadway deformation and microseismic monitoring while maintaining routine monitoring.

[0071] After completing the evaluation of this embodiment, the fracturing well was actually fracturing, and continuous monitoring was carried out throughout the fracturing process. No significant disturbance occurred in the surrounding roadways, which demonstrates the accuracy of the evaluation before fracturing in this invention.

[0072] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for assessing the degree of disturbance to the stability of the surrounding rock in a roadway caused by hydraulic fracturing of the roof, characterized in that, Includes the following steps: Step 1: Collect and determine the basic geological and tunneling parameters of the fracturing stope; Step 2: Collect and determine the key parameters for hydraulic fracturing of the roof; Step 3: Construct a numerical model to reflect the geological environment, tunnel spatial morphology, and hydraulic fracturing process, and perform simulation calculations; Step 4: Based on the simulation results in Step 3, extract the key indicators of the stability of the surrounding rock of the tunnel on the hydraulic fracturing response; Step 5: Based on the key indicators extracted in Step 4, assign values ​​to different threshold ranges of the key indicators, construct an evaluation index formula for the stability of fracturing and disturbed roadways, and formulate a graded evaluation standard for the evaluation index. Step Six: Using the evaluation index formula and grading evaluation standard from Step Five, and combining the assigned values ​​of the key indicators obtained in Step Four, the degree of disturbance to the stability of the underground roadway during pre-fracturing operations is evaluated, and corresponding measures are taken based on the evaluation results.

2. The method for assessing the degree of disturbance to the stability of the surrounding rock of a roadway caused by hydraulic fracturing of the roof according to claim 1, characterized in that, Step one specifically involves: S1. Collect and determine basic geological parameters, including: the stratum where the tunnel is located, and the physical and mechanical parameters of the rock strata 10m below and 100m above it, including lithology, density, elastic modulus, Poisson's ratio, cohesion, and internal friction angle; the burial depth of the tunnel area, the magnitude of the in-situ stress and the lateral pressure coefficient, and the dip angle of the coal seam; S2. Collect and determine the basic parameters of the roadway project, including: the cross-sectional dimensions of the roadway, the number and spacing of anchor bolts and cables used for roadway support and their mechanical parameters, and the thickness of the bottom coal or top coal left in the roadway.

3. The method for assessing the degree of disturbance to the stability of the surrounding rock of a roadway caused by hydraulic fracturing of the roof according to claim 1, characterized in that, Step two specifically involves: collecting and determining the process parameters of hydraulic fracturing of the roof, including: fracturing hole layout, fracturing hole diameter and number, water injection flow rate, and water injection duration; and determining the relative positional relationship between the hydraulic fracturing holes of the roof and the affected roadway.

4. The method for assessing the degree of disturbance to the stability of the surrounding rock of a roadway caused by hydraulic fracturing of the roof according to claim 1, characterized in that, Step three specifically involves: I. Determine the model size based on the positional relationship between the roadway and the fracturing borehole. Based on geological conditions and borehole columnar section, establish a two-dimensional UDEC discrete element numerical model of the hydraulic fracturing stope roadway. II. Define the material properties of the model, fix the horizontal displacement of the left and right boundaries and the vertical position of the bottom boundary; apply the equivalent vertical stress of the unsimulated top rock layer to the top of the model, and apply the horizontal stress according to the lateral stress coefficient λ. Ⅲ. Calculate the initial state of the model under given boundary mechanical and displacement conditions. Then, based on the basic tunnel engineering parameters collected in step one, perform tunnel simulation excavation calculations at the preset position of the model. After installing anchor bolts and anchor cables to support the tunnel, calculate and balance the model again and save it. IV. Based on the positional relationship between the roadway and the fracturing holes, determine the location of the fracturing holes in the fracturing layer. Based on the key parameters of the roof hydraulic fracturing operation determined in step II, simulate fracturing by injecting water at a constant flow rate in the fracturing hole area, and then recalculate and balance the model and save it.

5. The method for assessing the degree of disturbance to the stability of the surrounding rock of a roadway caused by hydraulic fracturing of the roof according to claim 1, characterized in that, Step four specifically involves: based on the simulation results from step three, extracting key indicators, including the vertical stress increase rate S on both sides of the roadway. y The rate of increase of horizontal stress in the roadway roof S x The growth rate of the length of the plastic zone on both sides of the tunnel L b The growth rate of the plastic zone above the tunnel roof (L) d The rate of increase in the number of fissures in the surrounding rock of the tunnel (N) c The growth rate of the total length of fractures in the surrounding rock of the tunnel, L w Roadway roof displacement growth rate U d Displacement growth rate U of the two sides of the tunnel b .

6. The method for assessing the degree of disturbance to the stability of the surrounding rock of a roadway caused by hydraulic fracturing of the roof according to claim 5, characterized in that, In step five, different threshold ranges for the key indicators are assigned values, specifically as follows: Determine the vertical stress increase rate S on both sides of the roadway y The sequence number is X1, and its threshold interval division and assignment are: S y >15% is assigned the value 3; 10% y ≤15% is assigned the value 2; 5% y ≤10% is assigned the value 1; S y ≤5% is assigned the value 0;​​ Determine the rate of increase of horizontal stress S in the roadway roof x The sequence number is X2, and its threshold interval division and assignment are: S x >15% is assigned the value 3; 10% x ≤15% is assigned the value 2; 5% x ≤10% is assigned the value 1; S x ≤5% is assigned the value 0;​​ Determine the growth rate L of the plastic zone development length on both sides of the roadway b The sequence number is X3, and its threshold interval division and assignment are: L b >40% is assigned the value 3; 25% <L b ≤40% is assigned a value of 2; 10% <L b ≤25% is assigned the value 1; L b ≤10% is assigned the value 0; Determine the growth rate L of the plastic zone development height above the roadway roof. d The sequence number is X4, and its threshold interval division and assignment are: L d >40% is assigned the value 3; 25% <L d ≤40% is assigned a value of 2; 10% <L d ≤25% is assigned the value 1; L d ≤10% is assigned the value 0; Determine the rate of increase N in the number of fractures in the surrounding rock of the roadway. c The sequence number is X5, and its threshold interval division and assignment are: N c >35% is assigned the value 3; 25% <N c ≤35% is assigned a value of 2; 15% is assigned a value of 2. <N c ≤25% is assigned the value 1; N c ≤15% is assigned the value 0; Determine the growth rate L of the total length of fractures in the surrounding rock of the tunnel. w The sequence number is X6, and its threshold interval division and assignment are: L w >35% is assigned the value 3; 25% <L w ≤35% is assigned a value of 2; 15% is assigned a value of 2. <L w ≤25% is assigned the value 1; L w ≤15% is assigned the value 0; Determine the growth rate U of the roadway roof displacement d The sequence number is X7, and its threshold interval division and assignment are: U d >30% is assigned the value 3; 20% d ≤30% is assigned a value of 2; 10% d ≤20% is assigned the value 1; U d ≤10% is assigned the value 0;​​ Determine the displacement growth rate U of the two sides of the roadway b The sequence number is X8, and its threshold interval division and assignment are: U b >30% is assigned the value 3; 20% b ≤30% is assigned a value of 2; 10% b ≤20% is assigned the value 1; U b ≤10% is assigned the value 0.​​ 7. The method for assessing the degree of disturbance to the stability of the surrounding rock of a roadway caused by hydraulic fracturing of the roof according to claim 6, characterized in that, The formula for constructing the evaluation index of the stability of the fracturing disturbance roadway in step five is as follows: In the formula, X represents the stability index of the hydraulically fractured roadway; n represents the response index of the surrounding rock stability to hydraulic fracturing (label n = 1, 2, 3...8); X i This is represented by the value assigned to the i-th disturbance level index; X i max This represents the maximum value assigned to the i-th disturbance level index.

8. The method for assessing the degree of disturbance to the stability of the surrounding rock of a roadway caused by hydraulic fracturing of the roof according to claim 7, characterized in that, Step five involves establishing a tiered evaluation standard for the assessment index, specifically as follows: When X≤0.25, the stability of the fracturing disturbance roadway is undisturbed; When 0.25 < X ≤ 0.50, the stability of the fracturing disturbance roadway is considered to be a slight disturbance. When 0.50 < X ​​≤ 0.75, the stability level of the fracturing disturbance roadway is general disturbance; When X > 0.75, the stability of the fracturing disturbance roadway is characterized as a strong disturbance.

9. The method for assessing the degree of disturbance to the stability of the surrounding rock of a roadway caused by hydraulic fracturing of the roof according to claim 8, characterized in that, Step six involves taking corresponding measures based on the evaluation results, specifically: If the assessment result is no disturbance, then maintain the regular inspection status; If the assessment result is a minor disturbance, then under normal inspection conditions, increase the monitoring density of roadway deformation and microseismic monitoring; If the assessment result is a general disturbance, active reinforcement is carried out by grouting anchor / cable integration to improve the integrity and bearing capacity of the surrounding rock; then, deformation and micro-vibration early warning thresholds are set to monitor the stability of the roadway surrounding rock in real time, and an alarm is triggered in real time when the monitored value exceeds the threshold. If the assessment result indicates a strong disturbance, active reinforcement will be carried out using an integrated grouting anchor / cable method to improve the integrity and bearing capacity of the surrounding rock; a collapsible steel support and additional truss anchor cables will be installed to form a composite support; at the same time, pressure relief holes will be constructed on the sidewalls or floor of the disturbed area to relieve pressure; after completion, deformation and micro-vibration early warning thresholds will be set to monitor the stability of the roadway surrounding rock in real time, and an alarm will be triggered in real time when the monitored value exceeds the threshold.

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