Dynamic fracturing-grouting combined reinforcement construction method suitable for broken surrounding rock

Abstract

The invention discloses a dynamic fracturing-grouting combined reinforcement construction method suitable for broken surrounding rock, which comprises the following steps: acquiring a brittleness index, rock mass integrity, a crack development index and a crustal stress ratio of the surrounding rock, and calculating a comprehensive fracturing index according to the brittleness index, the crack development index, the rock mass integrity and the crustal stress ratio; according to the comprehensive fracturing indexes, the strata are divided into four grades including the extremely-easy fracturing grade, the fracturing grade, the difficult fracturing grade and the extremely-difficult fracturing grade; drilling holes are arranged according to stratigraphic division grades; monitoring sensors are arranged in the drill holes, and a real-time fracturing-grouting dynamic regulation and control system is established; a mixed solution of fracturing fluid and a propping agent is pumped into the well, fracturing operation is conducted, high-pressure fluid forms a crack in rock and enables the crack to extend, the propping agent is embedded into the crack face to resist the ground stress closing effect, the wellhead pressure, the injection volume and the pumping rate are monitored in real time in the whole process, and it is ensured that the fracturing process is stable and controllable; and grouting parameters are adjusted and controlled in a self-adaptive mode.

Description

Technical Field

[0001] This invention relates to the field of tunnel and coal mine construction technology, specifically to a construction method for combined fracturing and grouting reinforcement technology under adverse geological conditions. Background Technology

[0002] As underground engineering becomes deeper and more complex, traditional passive support technology can no longer meet the needs of tunnel engineering under high-risk geological conditions. Among them, the combined reinforcement technology of hydraulic fracturing and grouting has become the mainstream technology for tunnel surrounding rock reinforcement because it can actively improve the mechanical properties of the surrounding rock and enhance the overall structure. By pre-fracturing to form a crack network, and then grouting to fill it, the rock mass is cemented and strengthened, thereby significantly improving the bearing capacity of the surrounding rock.

[0003] However, existing fracturing-grouting combined reinforcement technologies still suffer from severe grout loss and poor reinforcement effects in practical applications. In fractured strata, due to the lack of precise fracture network control methods, the fractures formed by fracturing often connect with natural fractures, creating grout flow channels. This results in excessively high grout loss rates during grouting, increasing engineering costs and creating weak zones in the reinforced area due to insufficient filling. Furthermore, the fracturing and grouting processes are often disconnected. Failure to grout promptly after fracturing causes fractures to close under stress relaxation, making subsequent grouting insufficient and severely affecting the stability and reliability of the reinforcement effect.

[0004] To address the aforementioned problems, existing technologies have attempted improvements by optimizing the performance of grouting materials and modifying fracturing parameters, but these efforts have failed to fundamentally resolve the technical bottlenecks. Specifically: (1) The assessment method for formation fracturing capability is too simplistic: Existing technologies mostly rely on a single parameter (such as compressive strength) to judge the fracturing feasibility, and have not established a quantitative assessment system that coordinates multiple parameters. The coupling effect of rock brittleness characteristics, fracture development status and geostress distribution is ignored, resulting in a mismatch between the fracturing scheme and the actual formation characteristics, and the phenomenon of over-fracturing or under-fracturing.

[0005] (2) Poor synergy between fracturing and grouting: Existing technologies lack dynamic control mechanisms and have low precision in controlling the fracturing range. Problems often arise such as excessive crack expansion leading to grout loss or insufficient crack expansion limiting the reinforcement range. There is a lack of scientific threshold judgment for the conversion between fracturing and grouting. Premature conversion can easily lead to insufficient fracturing, while late conversion can reduce the grouting effect due to crack closure.

[0006] (3) Delayed evaluation of reinforcement effect: The lack of real-time monitoring and dynamic adjustment mechanism makes it impossible to identify weak areas during construction, resulting in delayed grouting decisions and seriously affecting the grouting reinforcement effect.

[0007] Therefore, to address the technical requirements for tunnel surrounding rock reinforcement under adverse geological conditions, there is an urgent need to develop a combined fracturing-grouting reinforcement technology that integrates precise geological assessment, dynamic fracturing control, real-time process switching, and effect evaluation. By establishing a comprehensive fracturability assessment model based on multi-parameter coupling and constructing a dynamic control system for fracturing-grouting, the synergistic optimization of proppant and grouting processes can be achieved. This will solve problems such as severe grout loss, poor reinforcement effect, and disjointed process connections in existing technologies, providing efficient and reliable technical support for tunnel surrounding rock reinforcement under adverse geological conditions. Summary of the Invention

[0008] In response to problems such as grout loss and poor reinforcement effect during tunnel excavation through fractured surrounding rock, this invention provides a dynamic fracturing-grouting combined reinforcement construction method suitable for fractured surrounding rock.

[0009] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a dynamic fracturing-grouting combined reinforcement construction method suitable for fractured surrounding rock, as follows: Step 1: Based on the tunnel geological exploration, obtain the brittleness index, rock mass integrity, crack development index, and geostress ratio of the surrounding rock. Calculate the comprehensive compressibility index based on the brittleness index, crack development index, rock mass integrity, and geostress ratio. Step 2: Based on the comprehensive fracturability index, the formation is divided into four levels: extremely easy to fracture, fracturable, difficult to fracture, and extremely difficult to fracture. Step 3: Arrange boreholes according to the stratigraphic classification. Step 4: Install monitoring sensors inside the borehole to establish a real-time fracturing-grouting dynamic control system; Step 5: Pump a mixture of fracturing fluid and proppant into the well to carry out fracturing operations. The high-pressure fluid forms and extends fractures in the rock, and the proppant is embedded in the fracture surface to resist the closure effect of geostress. The wellhead pressure, injection volume and pumping rate are monitored in real time throughout the process to ensure that the fracturing process is stable and controllable. Step 6: Dynamically evaluate the grouting reinforcement effect and adaptively adjust the grouting parameters.

[0010] As a further technical solution, the specific process of step 1 is as follows: Based on the geological conditions of the tunnel area, the compressive strength, tensile strength, shear strength, Young's modulus and Poisson's ratio of the rock mass were determined by rock mechanics tests, and the brittleness index BI was calculated. Ground-penetrating radar scans are used to obtain fracture density and average opening of individual fractures, and the fracture development index (FDI) is determined. Formations with high fracture density are more likely to form effective fracturing networks. The maximum horizontal principal stress, minimum horizontal principal stress, and vertical stress were tested using the hydraulic fracturing method to obtain the geostress ratio Sr. Formations with a lower geostress ratio are not conducive to the initiation and propagation of fractures. Based on the above indicators, the formation fracturability is assessed, a weighted model of the analytic hierarchy process is established, and the standardized parameters are weighted to obtain the comprehensive fracturability index (CFI).

[0011] As a further technical solution, the rock brittleness parameter BI is obtained by characterizing the susceptibility of rocks to fracture under stress using Young's modulus and Poisson's ratio. Formations with a high brittleness index are more easily fractured. The calculation formula is as follows: BI = (EE*) / (E* - EM); where E is Young's modulus, E* is Young's modulus at the plastic limit, and EM is Young's modulus at the rheological limit.

[0012] As a further technical solution, the aforementioned geostress ratio Sr = minimum horizontal principal stress / maximum principal stress.

[0013] As a further technical solution, the comprehensive compressibility index CFI is defined as: CFI = a·BI + b·RQD + c·FDI + d·Sr; where BI is the brittleness index; RQD is the rock quality index; FDI is the fracture development index; Sr is the geostress ratio; and a, b, c, and d are weighting coefficients.

[0014] As a further technical solution, in step 2, when the fracturing level is extremely easy, high-pressure pulse fracturing is used; when the fracturing level is manageable, segmented controlled pressure fracturing is used; when the fracturing level is difficult, hydraulic sandblasting pretreatment + fracturing is used; when the fracturing level is extremely difficult, chemical pretreatment + fracturing is used; during construction, parameters are re-measured every 50m and the fracturing method is adjusted to ensure dynamic matching between the process and formation characteristics.

[0015] As a further technical solution, in step 3... The hole spacing here refers to the staggered arrangement of the fracturing-grouting holes, that is, the straight-line distance between the centers of two adjacent fracturing-grouting holes, and is taken as 1.2 times the design fracture length. The simple grouting holes are arranged around the fracture extension edge of the fracturing-grouting holes, and their spacing from the fracturing-grouting holes is 0.5-0.8 times the design fracture length; no separate standard is set for the hole spacing between simple grouting holes.

[0016] When the fracturing level is extremely easy, fracturing-grouting holes account for 85%, and simple grouting holes account for 15%. The fracturing-grouting holes are arranged in a quincunx pattern, and the hole spacing is 1.2 times the design fracture length. When the fracturing grade is met, fracturing-grouting holes account for 70%, simple grouting holes account for 30%, and the hole spacing is 1.5 times the fracture length; When the fracturing grade is difficult, fracturing-grouting holes account for 40%, simple grouting holes account for 60%, and the hole positions are denser along the direction of minimum principal stress by 20%. When the fracturing level is extremely difficult, fracturing-grouting holes account for only 20%, while simple grouting holes account for 80%.

[0017] As a further technical solution, in step 4, by integrating fiber optic sensing and acoustic monitoring data, the fracturing-grouting conversion threshold is determined, and a real-time fracturing-grouting dynamic control system is established to achieve precise constraint of the fracturing range and timely conversion between fracturing and grouting hole fracturing and grouting processes.

[0018] As a further technical solution, in step 4, the method for determining the fracturing-grouting conversion threshold is as follows: the main threshold is set when the real-time pressure reaches 95% of the preset peak value, and the auxiliary thresholds include the measured fracture width of the optical fiber decreasing to 60% of the initial value and the acoustic emission energy attenuation rate being >20% / min, at which point the permeation grouting mode is switched; the fracturing-grouting conversion action is executed by the PLC system, and the valve switching time is ≤0.8s; when encountering high-pressure water inrush, the system prioritizes spraying fast-setting dual-liquid grout to seal the water flow and ensure the main grouting process.

[0019] As a further technical solution, in step 6, distributed optical fiber strain monitoring and acoustic wave velocity monitoring are adopted, with the uniformity index UI as the core indicator. When UI < 0.7, weak areas are automatically marked and grouting is started to ensure that the surrounding rock reinforcement effect meets the standard.

[0020] Compared with existing technologies and equipment, the significant advantages of this invention are: (1) A multi-parameter coupled comprehensive fracturability index (CFI) assessment system was constructed, which integrates key indicators such as rock brittleness index (BI), rock mass integrity (RQD), fracture development index (FDI) and geostress ratio (Sr), and realizes quantitative assessment of formation fracturability. At the same time, based on CFI, the formation is divided into four levels of fracturability and fracturing construction technology is matched accordingly to effectively avoid the problems of over-fracturing or under-fracturing.

[0021] (2) A multi-parameter coordinated fracturing-grouting conversion threshold was established, with the real-time pressure reaching 95% of the preset peak value as the main control index, and the fiber optic monitoring crack width decreasing to 60% of the initial value and the acoustic emission energy attenuation rate exceeding 20% / min as auxiliary criteria, so as to achieve rapid valve switching within 0.8s and effectively reduce the process connection time.

[0022] (3) A dynamic evaluation system for grouting reinforcement based on real-time monitoring data was established. Distributed optical fiber strain monitoring and acoustic wave velocity monitoring were adopted. The uniformity index UI was used as the core indicator. When UI < 0.7, the weak area was automatically marked and grouting was started to ensure that the surrounding rock reinforcement effect met the standard, which significantly improved the tunnel construction safety and long-term structural stability. Attached Figure Description

[0023] Figure 1 A flowchart of a dynamic fracturing-grouting combined reinforcement construction method suitable for fractured surrounding rock; Figure 2 A schematic diagram of the arrangement of grouting holes for fracturing at the tunnel face; Detailed Implementation It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless otherwise expressly indicated by the invention, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. The construction method of this embodiment will be described in detail below with reference to the accompanying drawings; The flowchart of the dynamic fracturing-grouting combined reinforcement construction method for fractured surrounding rock proposed in this invention is attached. Figure 1 The process mainly includes six steps: Step 1, based on the tunnel geological exploration, obtain the brittleness index, rock mass integrity, fracture development index, and geostress ratio of the surrounding rock, and calculate the comprehensive fracturing index based on these indices; Step 2, based on the comprehensive fracturing index, classify the formation into four levels: extremely easy to fracture, fracturable, difficult to fracture, and extremely difficult to fracture; Step 3, arrange boreholes according to the formation classification; Step 4, install monitoring sensors in the boreholes to establish a real-time fracturing-grouting dynamic control system; Step 5, pump a mixture of fracturing fluid and proppant into the well for fracturing operations. The high-pressure fluid forms and extends fractures in the rock, and the proppant is embedded in the fracture surface to resist the closure effect of geostress. The wellhead pressure, injection volume, and pumping rate are monitored in real time throughout the process to ensure that the fracturing process is stable and controllable. Step 6: Dynamically evaluate the grouting reinforcement effect and adaptively adjust the grouting parameters.

[0025] The specific construction layout plan is as follows: Step 1: Tunnel geological exploration and stratigraphic fracturing assessment. Based on the geological conditions of the tunnel area, rock mechanics tests are used to determine the compressive strength, tensile strength, shear strength, Young's modulus, and Poisson's ratio of the rock mass, and the brittleness index BI is calculated. Ground-penetrating radar scanning is used to obtain the fracture density (fractures / m²) and the average opening of a single fracture, and the fracture development index FDI is determined. Strata with high fracture density are more likely to form an effective fracturing network. The maximum horizontal principal stress, minimum horizontal principal stress, and vertical stress are tested using the hydraulic fracturing method to obtain the geostress ratio Sr. Strata with a low geostress ratio are not conducive to fracture opening and extension. The rock mass integrity index RQD is calculated. The rock mass integrity index RQD is the ratio (expressed as a percentage) of the total length of intact rock core segments ≥10cm in length in the borehole to the actual total drilling length, reflecting the degree of rock mass fragmentation by fractures. The higher the proportion of intact rock core length, the better the rock mass integrity, and the easier it is for fractures to extend along the designed path during fracturing; conversely, the rock mass is fragmented, and fracturing is easily interfered with by natural fractures.

[0026] Based on the above indicators, the formation fracturability is assessed, and a weighted model of the analytic hierarchy process (AHP) is established. The standardized parameters are weighted and calculated to obtain the comprehensive fracturability index (CFI).

[0027] Specifically, the rock brittleness parameter BI is obtained by characterizing the susceptibility of rocks to fracture under stress using Young's modulus and Poisson's ratio. Formations with a high brittleness index are more easily fractured. The calculation formula is as follows: BI = (EE*) / (E* - EM) Where E is Young's modulus, E* is Young's modulus at the plastic limit, and EM is Young's modulus at the rheological limit. The stress ratio Sr = minimum horizontal principal stress / maximum horizontal principal stress; Specifically, CFI = a·BI + b·RQD + c·FDI + d·Sr; where a, b, c, and d are the weighting coefficients of each parameter, determined through the Analytic Hierarchy Process (AHP) combined with expert scoring and engineering case verification, satisfying a+b+c+d=1 to ensure that the contribution of each parameter to the fracturability assessment matches the actual engineering situation. For example: CFI = 0.3BI + 0.15RQD + 0.25FDI +0.3Sr; BI stands for Brittleness Index, which primarily characterizes the ease with which rocks undergo brittle fracture under stress. It is a core indicator for determining whether a formation is susceptible to fracturing. The higher the brittleness index, the more easily the rock forms a network of interconnected fractures. The BI value ranges from 0 to 1, with ≥0.6 indicating high brittleness, 0.3-0.6 indicating moderate brittleness, and <0.3 indicating low brittleness.

[0028] RQD (Rock Quality Demand) is a rock quality index that reflects the degree of rock mass integrity and directly affects the propagation path and connectivity of hydraulic fracturing fractures. A higher RQD value indicates better rock mass integrity, making it easier for hydraulic fracturing fractures to propagate according to the designed morphology. Measurement method: Length statistics are performed on core samples taken from boreholes. The ratio of the total length of core segments ≥10cm to the total borehole footage is calculated and expressed as a percentage (RQD = ΣL≥10cm / Ltotal × 100%).

[0029] Fracturing Development Index (FDI) is a key parameter for assessing the density of the fracture network after fracturing, comprehensively characterizing the development intensity and connectivity potential of formation fractures. Calculation formula: ,in The crack density (unit: cracks / m²) is calculated by combining ground-penetrating radar scanning with borehole television observation to determine the number of cracks per unit area. The average opening of a single fracture (unit: mm) is calculated as the arithmetic mean of the openings of all fractures within the effective monitoring range, obtained through joint monitoring using sonic logging and fiber optic sensing.

[0030] Sr is the geostress ratio, reflecting the degree to which geostress distribution constrains crack propagation. Calculation formula: ,in The minimum horizontal principal stress (unit: MPa). The maximum principal stress on the same horizontal plane (unit: MPa, taking the larger value between the maximum horizontal principal stress and the vertical stress) is measured by hydraulic fracturing method or stress relief method.

[0031] Step 2, dynamic matching of fracturing methods. Based on the CFI value, the formation is divided into four levels: extremely easy to fracture (≥0.8), fracturable (0.6-0.8), difficult to fracture (0.4-0.6), and extremely difficult to fracture (<0.4).

[0032] Specifically, the corresponding fracturing process is selected based on the fracturability index (CFI): high-pressure pulse fracturing is used when CFI ≥ 0.8; staged controlled pressure fracturing is used when CFI < 0.8 when CFI ≤ 0.6; hydraulic sandblasting pretreatment + fracturing is used when CFI < 0.4; and chemical pretreatment + fracturing is used when CFI < 0.4. Parameters are re-measured every 50m during construction, and the fracturing method is adjusted to ensure dynamic matching between the process and formation characteristics.

[0033] Step 3: Drilling layout design based on the Comprehensive Fragility Index (CFI). Drilling locations are determined at the excavation face, with grouting holes and fracturing grouting holes placed on the tunnel roof and side walls. Based on the CFI, the borehole type and spatial layout are dynamically allocated using quantified geomechanical parameters.

[0034] Specifically, when CFI ≥ 0.8, the proportion of fracturing-grouting holes is 85% (15% for simple grouting holes), and the fracturing-grouting holes are arranged in a quincunx pattern with a spacing of 1.2 times the design fracture length; in the CFI = 0.6-0.8 range, fracturing-grouting holes account for 70% (30% for simple grouting holes), with a spacing of 1.5 times the fracture length; when CFI = 0.4-0.6, the proportion of fracturing-grouting holes drops to 40% (60% for simple grouting holes), and the hole positions are denser along the direction of minimum principal stress by 20%; in the extremely difficult fracturing layers with CFI < 0.4, fracturing-grouting holes account for only 20% (80% for simple grouting holes). Before drilling, it is essential to remove loose rock blocks in the tunnel, manually chisel away loose rocks and severely damaged areas, and then reinforce the surrounding rock of the roadway to enhance rock mass stability.

[0035] Specifically, the tunnel's CFI calculation result is 0.83, therefore the borehole layout is as follows: 2 grouting holes and 9 fracturing grouting holes. Specifically: ① Two grouting holes and three fracturing grouting holes are arranged in the roof; ② Three fracturing grouting holes are arranged in each of the left and right side walls, with a horizontal angle of 15° for the side wall boreholes; ③ The bottom slab needs to achieve the same support strength as the roof slab to ensure uniform stress on the tunnel face. However, due to spatial limitations, general measures cannot achieve the same support density and strength as the roof slab; therefore, self-drilling grouting anchor bolts are arranged in the bottom slab. A detailed schematic diagram of the tunnel face fracturing grouting hole layout can be found here. Figure 2 .

[0036] Step 4: Dynamic control of fracturing-grouting through multi-source monitoring. By integrating fiber optic sensing and acoustic monitoring data, the fracturing-grouting transition threshold is determined, and a real-time dynamic control system for fracturing-grouting is established to achieve precise constraint of the fracturing range and timely switching between fracturing and grouting procedures.

[0037] Specifically, based on distributed optical fiber (DAS) deployed along the borehole axis (0.5m spacing, strain accuracy ±5με), combined with a microseismic array on the rock surface (positioning accuracy ±1.5m), the strain field of crack propagation and acoustic emission events are captured in real time. By fusing strain gradient (threshold 500με / m) and microseismic cluster positioning, the three-dimensional model of the crack is dynamically reconstructed. When the crack tip is <2m from the tunnel outline or the acoustic emission event rate is >50 times / min, the injection of temporary plugging agent or the pressure reduction operation of 15% is automatically triggered to control the crack deviation within ±0.8m.

[0038] Specifically, the fracturing-grouting conversion thresholds are as follows: the main threshold is set when the real-time pressure reaches 95% of the preset peak value (achieved through a dual-channel pressure-resistant drill rod), and the auxiliary thresholds include the fiber optic measured fracture width decreasing to 60% of the initial value (triggering 80L / min high-speed grouting) and the acoustic emission energy attenuation rate being >20% / min (switching to the permeation grouting mode); the fracturing-grouting conversion action is executed by the PLC system, and the valve switching time is ≤0.8s; when encountering high-pressure water inrush, the system prioritizes spraying rapid-setting dual-liquid grout (initial setting 30s) to block the water flow and ensure the main grouting process.

[0039] Step 5: Proppant Selection and Performance Control. In integrated fracturing and grouting construction of fractured surrounding rock, the core role of proppant is to physically extend the effective opening time window of fractures, and to form a rigid propping-grout filling composite reinforcement system through second-level synergy with the grouting process. Fracturing fluid is pumped into the well to begin fracturing operations. The high-pressure fluid forms and extends fractures in the rock. Sand or other proppant is added to the fracturing fluid to ensure the opening of fractures in the surrounding rock. Parameters such as wellhead pressure, injection volume, and pumping rate are monitored continuously to maintain the effective progress of fracturing operations. During construction, fracturing fluid is first pumped into the borehole to initiate fracturing operations. The high-pressure fluid causes fractures in the rock mass to form and continue to extend. Proppant is injected simultaneously in proportion. The proppant embeds into the fracture surface to resist the closure effect of in-situ stress. Wellhead pressure (accuracy ±0.1MPa), injection volume (metering error ≤2%), and pumping rate (fluctuation control ≤5%) are monitored in real time throughout the process to ensure the fracturing process is stable and controllable.

[0040] Specifically, the appropriate proppant type and particle size must be selected based on parameters such as formation permeability, porosity, and closure pressure. The main objective of this fracturing invention is to improve the formation's conductivity, thereby enhancing the grouting reinforcement effect. Therefore, when selecting a proppant, its ability to meet the required conductivity must be considered, with high-performance proppants such as glass beads or resin-coated sand being preferred.

[0041] Specifically, the preparation method of the proppant is as follows: ① Determine the proppant type and particle size: Based on reservoir characteristics and fracturing operation requirements, select the appropriate proppant type and particle size. For example, determine the particle size by fracture width × 0.6 (error ±0.1mm). In high-stress areas (HSDC>0.6), select a particle size distribution (e.g., 40 / 70 mesh + 70 / 100 mesh = 3:1). ② Mix the proppant: Mix the selected proppant evenly in a certain proportion using a biaxial mixer at a stirring speed of 300-500 r / min and a mixing time ≥5 min to ensure uniform distribution of the proppant during fracturing operations, with a uniformity ≥90%. ③ Add to fracturing fluid: Add the mixed proppant to the fracturing fluid to form a proppant suspension. Add the proppant to the fracturing fluid according to a concentration gradient (5%-20%), using an online mixer to achieve continuous dispersion. Match the stirring speed to the pumping rate (10-30 L / min corresponding to 800-1200 r / min) to ensure uniform dispersion of the proppant in the fracturing fluid. ④ Adjust fracturing fluid properties: Adjust the fracturing fluid viscosity according to the proppant concentration (5%-10% corresponds to 30-50 mPa). s, 10%-20% corresponds to 50-80mPa s), add 0.2%-0.5% suspending agent to prevent settling. ⑤ Inject fracturing fluid: Inject the prepared fracturing fluid and proppant suspension into the reservoir to carry out fracturing operations.

[0042] Step 6: Dynamic evaluation and adjustment of grouting reinforcement effect. Based on real-time monitoring data from distributed optical fiber and acoustic wave sensors, an adaptive control mechanism for grouting parameters is established.

[0043] Specifically, an adaptive control mechanism for grouting parameters is established based on real-time monitoring data from distributed optical fibers (axial spacing 0.5m, strain accuracy ±5με, temperature ±0.1℃) and acoustic sensors (surface grid 10m, wave velocity error ≤1%).

[0044] Specifically, when the fiber strain gradient is greater than 100 με / m, the grouting pressure is increased by 0.5 MPa and the flow rate is reduced by 10%; when the temperature field diffusion stagnates, 0.2% water-reducing agent is added and the flow rate is increased by 10%; when the acoustic wave velocity increase rate is less than 8%, the flow rate is reduced to 70% and the pressure is increased by 0.3 MPa.

[0045] Determine whether the temperature field diffusion has stalled based on the threshold of the slurry temperature diffusion rate and the characteristics of temperature gradient changes.

[0046] (1) The grout temperature diffusion rate is less than the threshold. During the flow and solidification process, the grout releases heat of hydration. Under normal circumstances, the temperature field will extend outward synchronously with the grout diffusion, forming a temperature distribution with "grouting hole as the center and decreasing gradient". Temperature cloud maps at different times (t1, t2, 1 minute interval) are obtained through distributed optical fiber (sampling spacing ≤ 0.5m). The distance L1 from the highest temperature point (near the grouting hole) at time t1 to the 5℃ temperature difference boundary is measured, and the corresponding distance L2 at time t2 is measured. The diffusion rate v = (L2-L1) / (t2-t1). If v ≤ 0.1m / min for 3 consecutive calculations, the rate condition for stagnation judgment is met.

[0047] (2) Sudden change in temperature gradient.

[0048] During normal grouting, the axial and radial temperature gradients (temperature change per unit distance) of the borehole should maintain a stable decreasing trend. When the radial temperature gradient increases suddenly, such as a monitoring section where the radial temperature gradient rises from 2-5℃ / m to over 8℃ / m and remains unchanged for 2 minutes, it indicates that the grout is blocked at that section, preventing heat from being transferred outward and resulting in localized high-temperature accumulation. When a discontinuity appears in the axial temperature distribution, such as a sudden increase in the temperature difference between two adjacent fiber optic sampling points (0.5m apart) from 1-3℃ to over 10℃, or a discontinuity phenomenon of "sudden temperature drop after high temperature point" occurs, it indicates that the grout does not extend along the axial direction and only accumulates in a localized area.

[0049] Specifically, the core evaluation index is the uniformity index UI = 1 - (strain standard deviation / mean). By calculating the strain distribution within the borehole in real time (sampling rate 1kHz), when UI < 0.7 (critical point of rock mass strength dispersion), the coordinates of weak areas are automatically marked, and the grouting procedure is initiated. The grouting decision relies on a CNN model, which inputs a fiber optic strain field to generate a weak area distribution map and outputs contour coordinate positioning accuracy of ±0.1m.

[0050] The core evaluation indicator is the "Rock Mass Grouting Reinforcement Uniformity Index," a key parameter that quantifies the integrity of grout filling in the fracture network and the consistency of rock mass mechanical property improvement by real-time monitoring of rock strain distribution within the borehole. The uniformity of the reinforcement effect is inferred from the dispersion of strain data: a more concentrated strain distribution (lower dispersion) indicates more thorough grout filling and more uniform rock mass cementation, resulting in a higher UI value; conversely, weak areas exist, requiring the initiation of a grouting repair procedure.

[0051] Mean strain: The real-time average strain of the rock mass monitored by distributed fiber optic sensors within the borehole. Calculated using a high sampling rate of 1kHz fiber optics (1000 data points per second), the arithmetic mean strain of all sampling points at a given moment reflects the average level of overall stress and deformation of the rock mass. Standard deviation of strain: Measures the degree of deviation between the strain values ​​at all sampling points and the mean strain. A larger standard deviation indicates a more significant difference in rock mass strain at different locations, suggesting either excessively high strain (insufficient grout filling, large rock mass deformation) or excessively low strain (excessive grout accumulation, excessively rigid rock mass).

[0052] This invention constructs a multi-parameter coupled comprehensive fracturability index (CFI) assessment system, which integrates key indicators such as rock brittleness index (BI), rock mass integrity (RQD), fracture development index (FDI), and geostress ratio (Sr), to achieve quantitative assessment of formation fracturability. At the same time, based on CFI, the formation is divided into four fracturability levels, and fracturing construction technology is matched accordingly to effectively avoid the problems of over-fracturing or under-fracturing.

[0053] This invention establishes a multi-parameter coordinated fracturing-grouting conversion threshold, with the real-time pressure reaching 95% of the preset peak value as the main control index, and fiber optic monitoring of the fracture width decreasing to 60% of the initial value and acoustic emission energy attenuation rate exceeding 20% / min as auxiliary criteria, to achieve rapid valve switching within 0.8s and effectively reduce the process connection time.

[0054] This invention establishes a dynamic evaluation system for grouting reinforcement based on real-time monitoring data. It adopts distributed optical fiber strain monitoring and acoustic wave velocity monitoring, with the uniformity index UI as the core indicator. When UI < 0.7, weak areas are automatically marked and grouting is initiated to ensure that the surrounding rock reinforcement effect meets the standards, significantly improving the tunnel construction safety and long-term structural stability.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A dynamic fracturing-grouting combined reinforcement construction method suitable for fractured surrounding rock, characterized in that, as follows: Step 1: Based on the tunnel geological exploration, obtain the brittleness index, rock mass integrity, crack development index, and geostress ratio of the surrounding rock. Calculate the comprehensive compressibility index based on the brittleness index, crack development index, rock mass integrity, and geostress ratio. Step 2: Based on the comprehensive fracturability index, the formation is divided into four levels: extremely easy to fracture, fracturable, difficult to fracture, and extremely difficult to fracture. Step 3: Arrange boreholes according to the stratigraphic classification. Step 4: Install monitoring sensors inside the borehole to establish a real-time fracturing-grouting dynamic control system; Step 5: Pump a mixture of fracturing fluid and proppant into the well to carry out fracturing operations. The high-pressure fluid forms and extends fractures in the rock, and the proppant is embedded in the fracture surface to resist the closure effect of geostress. The wellhead pressure, injection volume and pumping rate are monitored in real time throughout the process to ensure that the fracturing process is stable and controllable. Step 6: Dynamically evaluate the grouting reinforcement effect and adaptively adjust the grouting parameters.

2. The dynamic fracturing-grouting combined reinforcement construction method for fractured surrounding rock as described in claim 1, characterized in that, The specific process of step 1 is as follows: Based on the geological conditions of the tunnel area, the compressive strength, tensile strength, shear strength, Young's modulus and Poisson's ratio of the rock mass were determined by rock mechanics tests, and the brittleness index BI was calculated. Ground-penetrating radar was used to obtain fracture density and average opening of individual fractures, and the fracture development index (FDI) was determined. The maximum horizontal principal stress, minimum horizontal principal stress, and vertical stress were tested using the hydraulic fracturing method to obtain the geostress ratio Sr. Based on the above indicators, the formation fracturability is assessed, a weighted model of the analytic hierarchy process is established, and the standardized parameters are weighted to obtain the comprehensive fracturability index (CFI).

3. The dynamic fracturing-grouting combined reinforcement construction method for fractured surrounding rock as described in claim 2, characterized in that, The brittleness parameter BI of rocks is obtained by characterizing the susceptibility of rocks to fracture under stress using Young's modulus and Poisson's ratio; where BI = (EE*) / (E*-EM); where E is Young's modulus, E* is Young's modulus at the plastic limit, and EM is Young's modulus at the rheological limit.

4. The dynamic fracturing-grouting combined reinforcement construction method for fractured surrounding rock as described in claim 2, characterized in that, The aforementioned stress ratio Sr = minimum horizontal principal stress / maximum horizontal principal stress.

5. The dynamic fracturing-grouting combined reinforcement construction method for fractured surrounding rock as described in claim 2, characterized in that, The comprehensive fracturability index CFI is defined as: CFI = a·BI + b·RQD + c·FDI + d·Sr, where BI is the brittleness index; RQD is the rock quality index; FDI is the fracture development index; Sr is the geostress ratio; and a, b, c, and d are weighting coefficients.

6. The dynamic fracturing-grouting combined reinforcement construction method for fractured surrounding rock as described in claim 1, characterized in that, In step 2, high-pressure pulse fracturing is used when the fracturing level is extremely easy; segmented controlled pressure fracturing is used when the fracturing level is manageable; hydraulic sandblasting pretreatment + fracturing is used when the fracturing level is difficult; and chemical pretreatment + fracturing is used when the fracturing level is extremely difficult. During construction, parameters are re-measured every 50m and the fracturing method is adjusted to ensure dynamic matching between the process and formation characteristics.

7. The dynamic fracturing-grouting combined reinforcement construction method for fractured surrounding rock as described in claim 6, characterized in that, In step 3, when the fracturing level is extremely easy, the fracturing-grouting holes account for 85%, and the simple grouting holes account for 15%. The fracturing-grouting holes are arranged in a quincunx pattern, and the hole spacing is 1.2 times the design fracture length. When the fracturing grade is met, fracturing-grouting holes account for 70%, and simple grouting holes account for 30%. The hole spacing of both fracturing-grouting holes and simple grouting holes is 1.5 times the fracture length. When the fracturing grade is difficult, fracturing-grouting holes account for 40%, and simple grouting holes account for 60%. The number of fracturing-grouting holes and simple grouting holes is increased by 20% along the direction of minimum principal stress. When the fracturing level is extremely difficult, fracturing-grouting holes account for only 20%, while simple grouting holes account for 80%.

8. The dynamic fracturing-grouting combined reinforcement construction method for fractured surrounding rock as described in claim 1, characterized in that, In step 4, by integrating fiber optic sensing and acoustic monitoring data, the fracturing-grouting conversion threshold is determined, and a real-time fracturing-grouting dynamic control system is established to achieve precise constraint of the fracturing range and timely conversion between fracturing and grouting hole fracturing and grouting processes.

9. The dynamic fracturing-grouting combined reinforcement construction method for fractured surrounding rock as described in claim 1, characterized in that, In step 4, the method for determining the fracturing-grouting conversion threshold is as follows: the main threshold is set when the real-time pressure reaches 95% of the preset peak value, and the auxiliary thresholds include the measured fracture width of the optical fiber decreasing to 60% of the initial value and the acoustic emission energy attenuation rate being >20% / min, at which point the permeation grouting mode is switched; the fracturing-grouting conversion action is executed by the PLC system, and the valve switching time is ≤0.8s; when encountering high-pressure water inrush, the system prioritizes spraying fast-setting dual-liquid grout to seal the water flow and ensure the main grouting process.

10. The dynamic fracturing-grouting combined reinforcement construction method for fractured surrounding rock as described in claim 1, characterized in that, In step 6, distributed optical fiber strain monitoring and acoustic wave velocity monitoring are adopted, with the uniformity index UI as the core indicator. When UI < 0.7, weak areas are automatically marked and grouting is started to ensure that the surrounding rock reinforcement effect meets the standard.

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