A method for evaluating the effect of fault zone grouting reconstruction based on horizontal exploration holes

Abstract

This invention discloses a method for evaluating the effect of grouting modification in fault zones based on horizontal exploration boreholes, specifically including the following steps: Step 1: Design and construct directional horizontal exploration boreholes; Step 2: Record and judge the drilling water output; if the borehole water output is large, proceed to Step 3; if the borehole water output is small, proceed to Step 4; Step 3: Water release test; Step 4: Water pressure test; Step 5: Evaluation of the anti-seepage effect of the fault modification zone; Step 6: Evaluation of the water pressure resistance of the modified rock mass; Step 7: Overall evaluation: If the anti-seepage and water pressure resistance of the modified fault zone both meet the requirements, then the fault grouting modification effect meets the requirements. This invention's method can comprehensively and accurately evaluate the grouting modification effect, promptly identify grouting defects and potential risks, provide a practical exploration technology evaluation method for coal mines, and provide a scientific basis for roadway construction, effectively reducing the risk of water inrush from the roadway floor.

Description

Technical Field

[0001] This invention belongs to the field of coal mine water control engineering technology, specifically relating to a method for exploring and evaluating the effect of grouting modification in fault zones based on horizontal exploration holes. Background Technology

[0002] As coal mining extends to deeper areas, the hydrogeological conditions faced by deep roadways become increasingly complex. The limestone aquifers at the floor are highly water-rich, and the presence of composite fault zones significantly increases rock mass fracturing and water conductivity, leading to a high risk of water inrush during roadway excavation and seriously threatening safe coal mine production. Grouting, as a key means of preventing floor water hazards, involves injecting grout into composite fault zones to fill rock fissures, reinforce fractured rock masses, reduce aquifer permeability, and enhance the floor's water-tightening performance.

[0003] After the grouting project is completed, a safety evaluation of the grouting modification effect of the fault zone needs to be conducted. The Lurong formula is a core formula for evaluating rock permeability in the fields of hydrogeology and geotechnical engineering. It mainly calculates the "Lurong value" (Lu) of the rock through a "water pressure test," quantifying the rock's permeability. It is an internationally accepted standard for evaluating rock permeability. my country's 1992 promulgated SL25-92 "Specifications for Borehole Water Pressure Tests in Water Conservancy and Hydropower Projects" stipulates that the Lurong test method must be used, and specifies the calculation method for the Lurong value. This specification stipulates that the permeability of the test section is expressed in units of Lurong value (Lu), and the calculation formula is as follows:

[0004]

[0005] Where q is the Lurong value (permeability) of the test section, in Lu; Q is the flow rate injected into the test section, in L / min; P is the pressure value acting in the test section, in MPa; and L is the length of the test section, in m.

[0006] The evaluation method for grouting repair in fault zones, which uses the "water pressure test-Lü Rong formula" to evaluate the grouting effect, has the following shortcomings: 1. The fault zone is large in scale, requiring the construction of multiple vertical inspection boreholes and multiple water pressure tests. The testing cycle is long, and local sampling is difficult to reflect the overall effect.

[0007] 2. A single vertical borehole water pressure test cannot cover the fault zone, cannot test vertical permeability, can only assess local permeability, and cannot reflect the mechanical properties such as tensile strength of the grout in the fault zone and the overall water-blocking capacity, resulting in low reliability of the evaluation results.

[0008] Grouting retrofitting projects along composite fault lines are concealed projects. Safety assessments require testing and evaluating the vertical permeability of the fault and assessing whether the water pressure resistance of the tunnel floor's waterproofing layer meets requirements. Currently, there is a lack of comprehensive, accurate, and efficient quality inspection and evaluation technologies, making it difficult to accurately determine the grouting effect. This lack of reliable data hinders subsequent safe construction and production in the tunnel. Therefore, a quantitative evaluation method that comprehensively reflects the vertical permeability and water pressure resistance of the grouting body along composite fault lines is urgently needed. Summary of the Invention

[0009] In view of the above-mentioned shortcomings and defects of the prior art, the purpose of this invention is to provide a method for exploring and evaluating the effect of grouting modification in fault zones based on horizontal exploration holes, which solves the problems of existing methods that local sampling is difficult to reflect the overall effect and can only evaluate local permeability, resulting in low reliability of evaluation results.

[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for exploring and evaluating the effect of grouting modification in fault zones based on horizontal exploration holes, specifically including the following steps: Step 1: Design and construct directional horizontal exploration boreholes.

[0011] Step 2: Record and determine the water output during drilling.

[0012] During drilling exploration and horizontal drilling, record the drilling speed, perform cuttings logging, and record the water production during drilling. If the water production from the borehole exceeds 10m³, [further details are needed]. 3 / h, proceed to step three; if the borehole water output is less than 10m³ / h. 3 / h, proceed to step four.

[0013] Step 3: Water release test, which includes the following steps: Initial water level H within the test horizontal section: Close the drain valve and allow the water flow in the horizontal section to stop, with the stopping time being ≥ 2 times the water level stabilization time.

[0014] The water level gauge probe is inserted into the horizontal section through a horizontal guide device to a depth of the middle of the horizontal section or the designed inlet section, and the initial water level is read and recorded.

[0015] Water release process: Control the flow rate and monitor water level changes. Slowly open the water release valve and adjust it to the preset stable flow rate Q of the horizontal well. Test in stages "from small to large" and monitor in real time with a flow meter. When the fluctuation range of the stable flow rate Q of the horizontal well is ≤5%, start timed monitoring of the water level. For the first 30 minutes, take a reading every 5 to 10 minutes. After that, if the water level change is ≤0.5cm / h, the reading can be extended to once every 15 to 30 minutes.

[0016] When the difference in water level between three consecutive readings is ≤0.2cm, the water level is considered stable, and the stable water level h at that flow rate is recorded. w .

[0017] The permeability coefficient k of the fault modification zone is calculated using the following formula:

[0018] Where: Q is the steady-state flow rate of the horizontal well, in m³ / d or m³ / s; k is the aquifer permeability coefficient, in m / d or m / s; M is the thickness of the borehole impermeable layer, in m; L is the length of the directional horizontal exploration borehole, in m; s is the drawdown, in m, s=H Where H is the initial water level within the horizontal segment, The water head in the well.

[0019] Step 4: Water pressure test, which includes the following steps: The test pressure adopts a three-level gradient pressure, with the maximum pressure not exceeding 80% of the rock mass fracture pressure, which is converted into a water head height s.

[0020] When the flow rate change rate is less than 5% / 10 minutes, it is considered stable. The final stable flow rate is recorded. The flow rate is maintained for 30-60 minutes at each pressure level to ensure that the seepage field is fully expanded.

[0021] when L <10 At time M, The permeability coefficient k is calculated using the following formula:

[0022] Q represents the steady-state flow rate of the horizontal well, in cubic meters per second (m³). 3 / d or m 3 / s; k is the aquifer permeability coefficient, in m / d or m / s; M is the borehole aquitard thickness, in m; L is the length of the directional horizontal exploration borehole, in m; s is the drawdown, in m.

[0023] When L>10M, the permeability coefficient k is calculated using the following formula:

[0024] Where: Q is the steady flow rate of the horizontal well, in m³ / d or m³ / s; k is the aquifer permeability coefficient, in m / d or m / s; M is the thickness of the borehole impermeable layer, in m; L is the length of the directional horizontal exploration borehole, in m; and s is the drawdown, in m.

[0025] Step 5: Evaluation of the anti-seepage effect of the fault modification zone.

[0026] When the permeability coefficient k satisfies, 10 -8 ≤k<10-6 m / s or 10 -6 ≤k<10 -4 When the flow rate is cm / s, the seepage resistance of the fault-modified zone meets the requirements for tunneling safety.

[0027] Step Six: Evaluation of the water pressure resistance of the modified rock mass: After the rock mass is grouted and modified in the fault zone, its resistance to water pressure still needs to be evaluated. Water pressure is detected during the construction of directional horizontal boreholes. The stress intensity factor of the horizontal open-hole borehole is calculated using fracture mechanics and then compared with the critical stress intensity factor of the rock mass. If the following formula is satisfied, cracks cannot be initiated and the resistance to water pressure meets the requirements.

[0028]

[0029] This represents the stress intensity factor for horizontal open-hole drilling.

[0030] in:

[0031] Type I stress intensity factor, unit: MPa m 1 / 2 P: Fracturing fluid pressure inside the borehole, unit: MPa; a: Crack half-length, unit: m; r: Horizontal directional drilling borehole radius, unit: m; Poisson's ratio of the geological strata, without units; Minimum horizontal principal stress in the formation, unit: MPa.

[0032] Step Seven: Overall Evaluation If the impermeability and water pressure resistance of the fault zone after modification meet the requirements, then the effect of fault grouting modification is satisfactory.

[0033] Compared with the prior art, the beneficial technical effects of this invention are: (I) The method of the present invention can comprehensively and accurately evaluate the effect of grouting modification, promptly detect grouting defects and potential risks, provide practical exploration technology evaluation methods for coal mines, provide scientific basis for roadway construction, and effectively reduce the risk of water inrush at the roadway floor.

[0034] (II) This invention proposes a method for testing the vertical permeability coefficient of fault-modified rock mass based on water release and pressure testing in horizontal exploration boreholes, as well as a method for calculating the stress intensity factor. It also establishes a standard for evaluating the effectiveness of fault grouting modification based on the vertical permeability coefficient of the rock mass and the fracture mechanics failure criterion of water-induced fracturing. This test can be combined with underground tunneling advance water release projects, reducing the amount of drilling work. Attached Figure Description

[0035] Figure 1This is a diagram showing the water pressure resistance of a horizontal borehole.

[0036] The meanings of the labels in the attached diagram are as follows: A - Directional horizontal exploration borehole, B - Fracture.

[0037] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0038] It should be noted that, unless otherwise specified, all raw materials used in this invention are those known in the prior art.

[0039] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0040] Example 1: A method for evaluating the effect of grouting modification in fault zones based on horizontal exploration holes, specifically including the following steps: Step 1: Design and construct directional horizontal exploration boreholes.

[0041] Step 1.1: Determining the borehole orientation: The directional horizontal exploration borehole follows the direction of the tunnel, crosses the fault zone, and enters the stable rock strata.

[0042] Step 1.2: Determining the length of the directional horizontal exploration borehole: directional horizontal exploration borehole length .

[0043] in: A: Safety factor, generally taken as 2 to 5; W: Tunnel span, unit: m, take the larger value of width / height; P: Hydrostatic pressure, unit: MPa; Kp: Tensile strength of coal / rock strata, unit: MPa.

[0044] The borehole design requirements stipulate that the boreholes should be arranged along the direction of roadway excavation, passing through fault zones, and that the borehole control range should meet the requirements for roadway side spacing control. Based on the water pressure of the limestone aquifer during roadway excavation according to the "Detailed Rules for Water Prevention and Control in Coal Mines," and using a critical water inrush coefficient of 0.06 MPa / m, the roadway side spacing is calculated using the formula.

[0045] Step 1.3: Determining the thickness of the borehole waterproofing layer: Drilled water-tight layer thickness M .

[0046] Where: P is water pressure, in MPa The critical inrush coefficient is taken as 0.06 MPa / m.

[0047] When tunneling through a complex fault zone, it is necessary to evaluate the water pressure resistance of the floor aquitard. Similarly, when constructing directional horizontal sections along the tunnel floor, it is essential to ensure that the upper aquitard meets water pressure resistance requirements. Therefore, the minimum thickness of the floor aquitard must be determined. According to the "Detailed Rules for Water Prevention and Control in Coal Mines," the minimum aquitard thickness is determined using a formula.

[0048] The impermeable layer is considered as a fixed beam with a thickness of m and a span of L, bearing a uniformly distributed water pressure P. (See attached diagram) Figure 1 .

[0049] Step 1.4: Determining the borehole structure: Based on the results obtained in steps 1.1, 1.2 and 1.3, directional horizontal exploration boreholes were constructed, adopting a four-section design of "vertical section - build-up section - stabilized section (horizontal section) - target section", with water pressure sensors installed at the borehole opening.

[0050] Step 2: Record and determine the water output during drilling.

[0051] During drilling exploration and horizontal drilling, record the drilling speed, perform cuttings logging, and record the water production during drilling. If the water production from the borehole exceeds 10m³, [further details are needed]. 3 / h, proceed to step three; if the borehole water output is less than 10m³ / h. 3 / h, proceed to step four.

[0052] Step 3: Water release test, which includes the following steps: Initial water level h in the test horizontal section: Close the drain valve and allow the water flow in the horizontal section to stop, with the stopping time being ≥ 2 times the water level stabilization time.

[0053] Insert the water level gauge probe into the horizontal section through a horizontal guide device, such as a PVC pipe elbow, to the middle of the horizontal section or the designed inlet section, avoiding stagnation in the dead water zone at the orifice; read and record the initial water level.

[0054] Water release process: Control the flow rate and monitor water level changes, slowly open the water release valve, adjust to the preset horizontal well stable flow rate Q, and test in stages "from small to large", such as Q1, Q2, Q3, with each flow rate corresponding to one set of stable water levels.

[0055] Using a flow meter for real-time monitoring, when the fluctuation range of the stable flow rate Q in the horizontal well is ≤5%, timed monitoring of the water level begins. For the first 30 minutes, take a reading every 5 to 10 minutes. After that, if the water level change is ≤0.5cm / h, the reading can be extended to once every 15 to 30 minutes.

[0056] When the difference in water level between three consecutive readings is ≤0.2cm or meets the design accuracy requirements, the water level is considered "stable," and the stable water level at that flow rate is recorded. .

[0057] The permeability coefficient k of the fault modification zone is calculated using the following formula.

[0058] The water flow in the horizontal section is a "composite flow"—the water flow at a distance still converges radially towards the overall influence area of ​​the horizontal well; closer to the surface, when the water reaches the vicinity of the horizontal section, due to the horizontal well axis, the flow direction changes to a linear flow along the length of the horizontal section (parallel to the horizontal well axis), eventually entering the borehole. In the formula, the radial range of the vertical well is replaced by the length L of the directional horizontal exploration borehole, and the logarithmic term becomes... Essentially, it uses the length L of a directional horizontal exploration borehole to characterize the path scale of a linear flow.

[0059] Steady-flow formula for horizontal wells in homogeneous isotropic confined aquifers

[0060]

[0061] roll out

[0062] in: Q represents the steady-state flow rate of the horizontal well, in cubic meters per second (m³). 3 / d or m 3 / s.

[0063] k is the aquifer permeability coefficient, in units of m / d or m / s.

[0064] M represents the thickness of the borehole waterproofing layer, in meters (m).

[0065] L represents the length of the directional horizontal exploration borehole, in meters (m).

[0066] s represents the drawdown, in meters (m), s = H Where H is the initial water level within the horizontal segment, The water head in the well.

[0067] Step 4: Water pressure test, which includes the following steps: The test pressure adopts a three-level gradient pressure, such as 0.3MPa, 0.6MPa, and 1.0MPa, with the maximum pressure not exceeding 80% of the rock mass fracture pressure, which is converted into a water head height s.

[0068] When the flow rate change rate is less than 5% / 10 minutes, it is considered stable. The final stable flow rate is recorded. The flow rate is maintained for 30-60 minutes at each pressure level to ensure that the seepage field is fully expanded.

[0069] when L <10 At time M, The permeability coefficient k is calculated using the following formula:

[0070] Q represents the steady-state flow rate of the horizontal well, in cubic meters per second (m³). 3 / d or m 3 / s; k is the aquifer permeability coefficient, in m / d or m / s; M is the borehole aquitard thickness, in m; L is the length of the directional horizontal exploration borehole, in m; s is the drawdown, in m.

[0071] When L>10M, the permeability coefficient k is calculated using the following formula:

[0072] Q is the steady-state flow rate of the horizontal well, in m³ / d or m³ / s; k is the aquifer permeability coefficient, in m / d or m / s; M is the thickness of the borehole impermeable layer, in m; L is the length of the directional horizontal exploration borehole, in m; s is the drawdown, in m.

[0073] Step 5: Evaluation of the anti-seepage effect of the fault modification zone.

[0074] When the permeability coefficient k satisfies, 10 -8 ≤k<10 -6 m / s or 10 -6 ≤k<10 -4 When the flow rate is cm / s, the seepage resistance of the fault-modified zone meets the requirements for tunneling safety.

[0075] Step Six: Evaluation of the water pressure resistance of the modified rock mass: After the rock mass is grouted and modified in the fault zone, its resistance to water pressure still needs to be evaluated. Water pressure is detected during the construction of directional horizontal boreholes. The stress intensity factor of the horizontal open-hole borehole is calculated using fracture mechanics and then compared with the critical stress intensity factor of the rock mass. If the following formula is satisfied, cracks cannot be initiated and the resistance to water pressure meets the requirements.

[0076]

[0077] This is the stress intensity factor for horizontal open-hole drilling; it is applicable to scenarios where cracks in horizontal open-hole drilling initiate naturally from the borehole wall, and the superposition effect of fracturing fluid pressure and formation stress needs to be considered.

[0078] in:

[0079] Type I stress intensity factor, unit: MPa m 1 / 2 This is the core indicator for determining whether a crack is propagating.

[0080] P: Borehole fracturing fluid pressure, unit: MPa, monitored in real time by the fracturing equipment. a: Crack half-length, unit: m, which is the length of the crack extending outward from the borehole wall. r: Horizontal directional drilling borehole radius, unit: m, determined according to the drill bit size, such as the common 150mm drill bit, r=0.075m. Poisson's ratio of the formation rock mass, without unit, obtained through laboratory core testing or field sonic logging, usually taken as 0.2-0.35. Minimum horizontal principal stress of the formation, unit: MPa, needs to be determined through in-situ stress testing, such as hydraulic fracturing, and is the key stress to resist crack propagation.

[0081] Step Seven: Overall Evaluation If the impermeability and water pressure resistance of the fault zone after modification meet the requirements, then the effect of fault grouting modification is satisfactory.

[0082] As a preferred embodiment: The water level stabilization time is: 30 min to 1 h for sand layers and 1 to 2 h for rock layers.

[0083] As a preferred embodiment: The permeability coefficient k corresponds to the rock mass permeability grade as follows: When the permeability coefficient k satisfies: k < 10 - ¹ 0 m / s or k < 10 -8 At a flow rate of cm / s, it is extremely permeable; there is almost no groundwater flow, and it can be regarded as an impermeable layer in engineering.

[0084] When the permeability coefficient k satisfies: 10 -10 ≤k<10 -8 m / s or 10 -8 ≤k<10 -6 At a flow rate of cm / s, it is considered slightly permeable; groundwater flows extremely slowly and only needs to be considered in long-term projects (such as high dam seepage prevention).

[0085] When the permeability coefficient k satisfies: 10 -8 ≤k<10 -6 m / s or 10 -6 ≤k<10 -4 At a flow rate of cm / s, the groundwater is considered weakly permeable; the groundwater flows slowly, and a small amount of seepage may occur in the foundation pit and tunnel.

[0086] When the permeability coefficient k satisfies: 10 -6 ≤k<10 -4 m / s or 10 -4 ≤k<10 - At a flow rate of 2 cm / s, the water permeability is moderate; groundwater flow is significant, and the project requires targeted seepage prevention (such as grouting).

[0087] When the permeability coefficient k satisfies: 10 -4 ≤k<10 - ²m / s or 10 - When ²≤k<1.0cm / s, it is considered highly permeable; groundwater flows rapidly, making piping and sudden water inrush (such as mine water inrush) likely to occur.

[0088] When the permeability coefficient k satisfies: k≥10 - When the flow rate is 2m / s or k≥1.0cm / s, it is extremely permeable; the fluid exhibits "pipe flow" characteristics, posing extremely high engineering risks (such as in karst caves and underground rivers).

[0089] Application example: 1. Project Background: The hydrogeological conditions of the north wing track and belt conveyor conversion roadway in Zhaogu Coal Mine are extremely complex. The limestone aquifer at the bottom of the coal seam is characterized by high water pressure and strong water-bearing capacity. The local water inrush coefficient of L2 limestone and L8 limestone is greater than 0.06 MPa / m. Furthermore, the north wing track and belt conveyor conversion roadway needs to pass through F 16 DF 46 DF 99 There are three faults with a drop of more than 20 meters, posing a risk of water inrush during tunnel excavation.

[0090] By employing surface-level water hazard control technology, advanced grouting reinforcement was carried out on the L8, L2, and O2 limestone aquifers at the bottom of the north wing track and conveyor belt transport modification tunnel within the project's treatment area. 16 DF 46 DF 99 The fault was reinforced with three-dimensional grouting, and pre-grouting reinforcement was carried out on the surrounding rock (partial sections) of the north wing track and conveyor belt transport conversion roadway. Through high-pressure grouting on the ground, the following measures were taken: First, the injected aquifer was transformed into an impermeable or weakly aquifer, reinforcing the fault, sealing fault fissures, improving the overall integrity of the rock strata within a certain thickness of the north wing track and conveyor belt transport conversion roadway floor, increasing the compressive strength of the rock strata separating the roadway floor from the L8, L2, and O2 limestone aquifers, improving water pressure resistance, and reducing the threat of water hazards during the excavation of the north wing track and conveyor belt transport conversion roadway; second, grouting reinforcement was carried out on the pre-excavated roadway (partial sections), sealing fissures in the surrounding rock, increasing the strength of the surrounding rock, and ensuring safe roadway excavation. After the conversion project was completed, the quality of the fault zone grouting conversion needed to be investigated and evaluated before roadway excavation.

[0091] 2. Exploration Drilling Design 1) Calculation of minimum aquitard thickness: The water pressure of the L8 aquifer in Zhaogu Mine is 4.5 MPa. Based on the critical water inrush coefficient T... M Calculated at 0.06 MPa / m, minimum waterproof layer thickness =75m, so the vertical distance between the horizontal borehole and the roadway should be greater than 75m.

[0092] 2) Determining the borehole length

[0093] Where P is the water pressure, and T M为 Critical water inrush coefficient.

[0094] Calculated with a critical water inrush coefficient of 0.06 MPa / m, the side-to-side distance of the tunneling face is... =4.5÷0.06=75 (m) =92+75=167 (m).

[0095] 3) Investigate the design parameters of the borehole The borehole design requires that the borehole be arranged along the direction of the roadway excavation, pass through the fault zone, be 92m above the roadway, and have a borehole control range that meets the roadway side distance requirement of 75m.

[0096] The drilling plan is divided into three core sections based on the wellbore trajectory and function: the vertical well section, the build-up section + upper horizontal section, and the target section of the horizontal section. The vertical well section has an opening diameter of Φ215.9mm, requiring the installation of Φ177.8mm casing to solidify the borehole and ensure a foundation for subsequent construction. Upon entering the build-up section and upper horizontal section, the opening diameter decreases to Φ152.4mm, using Φ139.7mm casing. The final target section of the horizontal section has an opening diameter of Φ118.0mm and operates as a bare borehole without casing.

[0097] 3. Horizontal hole discharge test 1) Drilling exploration: During horizontal drilling, record the drilling speed, perform cuttings logging and record the water output during drilling. If the borehole water volume is large, conduct a water release test.

[0098] 2) Water release test Test the initial water level h in the horizontal borehole: Close the drain valve and allow the water flow in the horizontal borehole to stagnate (the settling time should be ≥ 2 times the water level stabilization time, typically 30 min ~ 1 h for sand layers and 1 ~ 2 h for rock layers); read and record the initial water pressure p1 using a pressure gauge. Open the valve and test the flow rate using a flow meter, testing every 30 minutes until the flow rate stabilizes for 8 hours. After that, read the stable flow rate, quickly close the valve, and read the stable water pressure p2; the water pressure will decrease. , converted to a drop head s.

[0099] 4. Evaluation of exploration results 1) Evaluation of impermeability: The length of the directional horizontal exploration borehole is L=167m, and the borehole diameter is r w =0.118m, stable discharge volume Q=5.14m 3Given an initial water pressure P = 3 MPa and a stable water pressure of 0.7 MPa, the head drop s = 234.6 m, and the thickness of the modified rock strata M = 92.4 m, the appropriate formula is...

[0100] Calculate the vertical permeability coefficient m / s, so k < 10 -6 The speed is m / s, and the modified rock strata are weakly permeable. The permeability of the fault modification zone meets the requirements for tunneling safety.

[0101] 2) Evaluation of the water pressure resistance of the modified rock mass: After directional horizontal exploration drilling, the basic parameters are as follows: P: 3.5MPa, a: 0.1m (tiny cracks will still exist in the rock mass; after grouting modification, larger cracks will be sealed by grouting. Taking a crack length of 0.1m is much larger than the actual existing crack length), r: 0.118m. 0.25, 16.2 MPa (minimum horizontal principal stress of the rock mass, obtained from actual measurement). The critical stress intensity factor for sandstone and shale with the lowest resistance to water pressure is taken as approximately 1.0.

[0102] Substitute into the formula:

[0103] The stress intensity factor can be calculated.

[0104] so If the crack cannot be initiated, it meets the water pressure resistance requirement. A negative sign indicates that the crack tip is dominated by compressive stress and does not meet the tensile crack initiation condition.

[0105] 3) Overall evaluation of fault modification effect: The rock mass after fault modification has the required impermeability and water pressure resistance, and the fault grouting modification effect meets the requirements.

[0106] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions conceived by those skilled in the art within the scope of the technology disclosed in the present invention without creative effort are covered within the scope of protection of the present invention.

Claims

1. A method for evaluating the effect of grouting modification in fault zones based on horizontal exploration holes, characterized in that, Specifically, the steps include the following: Step 1: Design and construct directional horizontal exploration boreholes; Step 2: Record and determine the water output during drilling; During drilling exploration and horizontal drilling, record the drilling speed, perform cuttings logging, and record the water production during drilling. If the water production from the borehole exceeds 10m³, [further details are needed]. 3 / h, proceed to step three; if the borehole water output is less than 10m³ / h. 3 / h, proceed to step four; Step 3: Water release test, which includes the following steps: Initial water level H within the test horizontal section: Close the drain valve to allow the water flow in the horizontal section to stop, with the stopping time being ≥ 2 times the water level stabilization time; Insert the water level gauge probe into the horizontal section through the horizontal guide device, to the middle of the horizontal section or the designed water inlet section, and read and record the initial water level. Water release process: Control the flow rate and monitor water level changes. Slowly open the water release valve and adjust it to the preset stable flow rate Q of the horizontal well. Test in stages "from small to large" and monitor in real time with a flow meter. When the fluctuation range of the stable flow rate Q of the horizontal well is ≤5%, start timed monitoring of the water level. For the first 30 minutes, take a reading every 5 to 10 minutes. After that, if the water level change is ≤0.5cm / h, the interval can be extended to 15 to 30 minutes. When the difference in water level between three consecutive readings is ≤0.2cm, the water level is considered stable, and the stable water level h at that flow rate is recorded. w .

2. The permeability coefficient k of the fault modification zone is calculated using the following formula; in: Q represents the steady-state flow rate of the horizontal well, in cubic meters per second (m³). 3 / d or m 3 / s; k is the aquifer permeability coefficient, in m / d or m / s; M is the borehole impermeable layer thickness, in m; L represents the length of the directional horizontal exploration borehole, in meters; s represents the drawdown, in meters (m), s = H Where H is the initial water level within the horizontal segment, The water head in the well; Step 4: Water pressure test, which includes the following steps: The test pressure adopts a three-level gradient pressure, with the maximum pressure not exceeding 80% of the rock mass fracture pressure, which is converted into a water head height s. When the flow rate change rate is less than 5% / 10 minutes, it is considered stable. The final stable flow rate is recorded. The flow rate is maintained for 30-60 minutes at each pressure level to ensure that the seepage field is fully expanded. when L <10 At time M, The permeability coefficient k is calculated using the following formula. Q represents the steady-state flow rate of the horizontal well, in cubic meters per second (m³). 3 / d or m 3 / s; k is the aquifer permeability coefficient, in m / d or m / s; M is the borehole aquitard thickness, in m; L is the length of the directional horizontal exploration borehole, in m; s is the drawdown, in m; When L>10M, the permeability coefficient k is calculated using the following formula. Where: Q is the steady flow rate of the horizontal well, in m³ / d or m³ / s; k is the aquifer permeability coefficient, in m / d or m / s; M is the thickness of the borehole impermeable layer, in m; L is the length of the directional horizontal exploration borehole, in m; s is the drawdown, in m. Step 5: Evaluation of the anti-seepage effect of the fault modification zone; When the permeability coefficient k satisfies, 10 -8 ≤k<10 -6 m / s or 10 -6 ≤k<10 -4 At a speed of cm / s, the seepage resistance of the fault-modified zone meets the tunneling safety requirements; Step Six: Evaluation of the water pressure resistance of the modified rock mass: After the rock mass is grouted and modified in the fault zone, its water pressure resistance needs to be evaluated. Water pressure is detected during the construction of directional horizontal boreholes. The stress intensity factor of the horizontal open-hole borehole is calculated using fracture mechanics and then compared with the critical stress intensity factor of the rock mass. If the following formula is satisfied, cracks cannot be initiated and the water pressure resistance meets the requirements. The stress intensity factor for horizontal open-hole drilling; in: Type I stress intensity factor, unit: MPa m 1 / 2 P: Fracturing fluid pressure inside the borehole, unit: MPa; a: Crack half-length, unit: m; r: Horizontal directional drilling borehole radius, unit: m; Poisson's ratio of the geological strata, without units; Minimum horizontal principal stress in a formation, unit: MPa; Step Seven: Overall Evaluation If the impermeability and water pressure resistance of the fault zone after modification meet the requirements, then the effect of fault grouting modification is satisfactory.

3. The method for evaluating the effect of grouting modification in fault zones based on horizontal exploration holes as described in claim 1, characterized in that, Step one specifically includes: Step 1.1: Determining the borehole orientation: The directional horizontal exploration borehole follows the direction of the roadway, crosses the fault zone, and enters the stable rock strata; Step 1.2: Determining the length of the directional horizontal exploration borehole: directional horizontal exploration borehole length ; in: A: Safety factor; W: Tunnel span (m); P: Hydrostatic pressure (MPa); Kp: Tensile strength of coal / rock strata (MPa); Step 1.3: Determining the thickness of the borehole waterproofing layer: Drilled water-tight layer thickness M ; Where: P is water pressure, in MPa The critical inrush coefficient is taken as 0.06 MPa / m; Step 1.4: Determining the borehole structure: Based on the results obtained in steps 1.1, 1.2 and 1.3, directional horizontal exploration boreholes were constructed, using a four-section design of "vertical section - build-up section - horizontal section - target section", with water pressure sensors installed at the borehole opening.

4. The method for evaluating the effect of grouting modification in fault zones based on horizontal exploration holes as described in claim 1, characterized in that, The water level stabilization time is: 30 min to 1 h for sand layers and 1 to 2 h for rock layers.

5. The method for evaluating the effect of grouting modification in fault zones based on horizontal exploration holes as described in claim 1, characterized in that, The permeability coefficient k corresponds to the rock mass permeability grade as follows: When the permeability coefficient k satisfies: k < 10 - ¹ 0 m / s or k < 10 -8 At a speed of cm / s, it is extremely permeable; When the permeability coefficient k satisfies: 10 -10 ≤k<10 -8 m / s or 10 -8 ≤k<10 -6 At a speed of cm / s, it is slightly permeable; When the permeability coefficient k satisfies: 10 -8 ≤k<10 -6 m / s or 10 -6 ≤k<10 -4 At a speed of cm / s, it is considered weakly permeable; When the permeability coefficient k satisfies: 10 -6 ≤k<10 -4 m / s or 10 -4 ≤k<10 - At 2 cm / s, it is considered moderately permeable; When the permeability coefficient k satisfies: 10 -4 ≤k<10 - ²m / s or 10 - When ²≤k<1.0cm / s, it is considered highly permeable; When the permeability coefficient k satisfies: k≥10 - When the permeability is 2m / s or k≥1.0cm / s, it is considered extremely permeable.

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