Grounding resistance reduction method based on repeated water pressure blasting fracturing

Abstract

The invention relates to the technical field of water conservancy and hydropower engineering, and discloses a grounding resistance reduction method based on repeated water pressure blasting fracturing, which comprises the following steps: drilling a deep hole in a rock area with high soil resistivity and cleaning the hole; carrying out micro-damage initial fracturing by utilizing small-dose radial non-coupling charging, and inducing a guided initial fracture on the premise of keeping the integrity of a hole wall; crack distribution data are obtained through in-hole visual feedback scanning, and crack areas are divided; a composite charging structure comprising emulsion explosives and water bags is assembled in a differentiated mode, and repeated water pressure blasting is carried out to drive deep expansion of cracks and pre-implantation of conducting media; and finally, a metal grounding electrode is installed in the deep hole, and high-pressure grouting of the physical resistance reducing agent is carried out by adopting a graded pressurization strategy. According to the invention, through staged fracturing and visual feedback adjustment, three-dimensional controlled expansion of a fracture network and deep penetration of a conductive medium are realized, and the grounding resistance reduction efficiency of a high-resistance rock area is improved.

Description

Technical Field

[0001] This invention relates to the field of water conservancy and hydropower engineering technology, specifically to a grounding resistance reduction method based on repeated water pressure bursting. Background Technology

[0002] Substations, power plants, and transmission towers are often built in areas with high soil resistivity. Constructing lightning protection grounding and equipment grounding systems in these areas presents challenges such as large engineering workloads and difficulties in reducing resistance. Common engineering practices include expanding the grounding grid area, increasing the length of grounding electrodes, and using deep well grounding to reduce grounding resistance. However, in special environments with extremely high resistivity and limited grounding device coverage, the rock geological conditions make conventional resistance reduction measures difficult to implement. Deep-hole blasting fracturing technology has become an economical and effective way to reduce resistance.

[0003] Existing deep-hole blasting grounding technology involves drilling a predetermined diameter and depth vertically or inclined using a deep-hole drilling rig. Construction workers place a fixed amount of explosives inside the deep hole for blasting operations. The explosive energy causes cracks in the rocks surrounding the deep hole. The construction workers then press low-resistivity materials into the rock cracks. By improving the conductivity of the rock medium around the deep hole, the soil resistivity is reduced, thereby reducing the grounding resistance.

[0004] Because traditional deep-hole blasting technology struggles to precisely control energy distribution within narrow, deep holes, the extremely high peak pressure of the shock wave generated during the explosion directly impacts the hole wall, causing severe compressive and pulverizing damage to the surrounding rock. The resulting rock dust and debris tightly fill the openings of primary and newly formed fractures, physically blocking the grouting channels. Since the rock pulverization zone around the hole consumes most of the energy generated by the explosion, the quasi-static pressure energy used to drive the fractures to extend far into the rock is insufficient, limiting the effective extension length of the fracture network. Furthermore, due to the blockage of the grouting channels and the limited fracture extension range, the resistance-reducing grout cannot effectively penetrate a wide area deep within the rock, limiting the effective conductive contact volume between the metal grounding electrode and the rock medium. Ultimately, this results in the power frequency grounding resistance value of the grounding system failing to meet engineering design requirements. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a grounding resistance reduction method based on repeated water pressure blasting to reduce cracks, aiming to solve the problems of traditional deep hole blasting easily leading to hole wall crushing and blockage, restricted crack propagation, and difficulty in effective penetration of resistance-reducing agents.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a grounding resistance reduction method based on repeated water pressure bursting, comprising the following steps: S1. Determine the drilling parameters based on the soil resistivity and grounding resistance target values, drill deep holes in rock areas of high soil resistivity strata, and clean the inside of the deep holes to ensure the integrity of the protective wall. S2. Based on deep holes, directional blasting technology or small-charge radial decoupled charge technology is used to implement micro-damage initial fracturing. By controlling the charge structure and the amount of charge per shot, directional initial fractures are induced in the rock around the deep hole, while maintaining the integrity of the deep hole wall. S3. Perform secondary cleaning of the deep hole, use in-hole visual feedback technology to probe into the deep hole, scan and observe the entire hole wall to obtain the initial fracture distribution data, and divide the fracture dense area and fracture sparse area accordingly. S4. Assemble a composite hydraulic fracturing charge structure based on distribution data and perform repeated hydraulic blasting in a deep hole; the composite hydraulic fracturing charge structure includes an emulsion explosive cartridge and a water bag, using the fluid in the water bag as a pressure transmission medium to drive the initial fracture to extend into the deep rock and form a three-dimensional fracture network, while pre-filling the micro fractures with a conductive medium. S5. Install metal grounding electrodes in the deep hole and construct a hole sealing structure. Use a graded pressurization strategy to implement high-pressure grouting, press the resistance-reducing agent into the deep hole and three-dimensional fracture network, and construct a conductive channel that is tightly integrated with the rock. S6. After the resistance-reducing agent has solidified, remove the auxiliary construction facilities, connect the metal grounding electrode to the horizontal grounding grid, and measure the final power frequency grounding resistance value.

[0007] Preferably, in step S1, the process of determining the borehole parameters includes: measuring the soil resistivity distribution data at different depths in the rock area at the site, and setting the target power frequency grounding resistance value; calculating the minimum required deep hole depth based on the power frequency grounding resistance estimation logic of the vertical grounding electrode, which is established based on the functional relationship between soil resistivity, the burial depth of the vertical grounding electrode, and the equivalent diameter of the grounding electrode; wherein, the equivalent diameter of the grounding electrode is taken as the equivalent calculated value of the borehole diameter and the expected fracture propagation range, and the deep hole depth is designed to penetrate the high resistivity layer and enter the low resistivity layer.

[0008] Preferably, in step S2, the specific method for implementing micro-damage initial fracturing is as follows: a small-volume radially decoupled charge technique is used, the emulsion explosive cartridge is placed in the center of the deep hole, and an air annular gap is maintained between the emulsion explosive cartridge and the deep hole wall; a radial decoupling coefficient is set, which is defined as the ratio of the deep hole diameter to the emulsion explosive cartridge diameter, and this ratio is set to a value greater than 2.0; the air annular gap is used as a buffer layer to reduce the peak pressure of the explosion shock wave, suppress the formation of the rock compression and crushing ring around the deep hole wall, and only tensile fracturing occurs in the hole wall.

[0009] Preferably, in step S2, the design and placement process of the charge structure includes: constructing an air-gap charge structure along the axial direction of the deep hole; fixing the emulsion explosive cartridges to the steel wire at a preset interval, without filling the spaces between the cartridges with solid material; setting sponge pads at the upper and lower ends of the emulsion explosive cartridges; positioning the emulsion explosive cartridges at the center of the deep hole cross-section using the sponge pads; suspending the assembled charge structure inside the deep hole; filling the hole opening section with plugging clay; and detonating the emulsion explosive cartridges using a detonating detonator.

[0010] Preferably, in step S3, the specific process of obtaining the initial fracture distribution data includes: using an air compressor to force ventilation and remove smoke and bottom debris from the deep hole; controlling the probe of the in-hole television imaging device to move up and down in the deep hole, recording video of the hole wall and simultaneously recording depth information, identifying and recording the opening, extension length and distribution density of the initial fractures; counting the number of initial fractures in different depth segments, marking areas where the fracture opening is less than a preset threshold or the number of fractures per unit hole depth is less than a preset value as fracture sparse areas, and marking the remaining areas as fracture dense areas.

[0011] Preferably, in step S4, the method of assembling the composite hydraulic fracturing charge structure is as follows: take a steel wire as the main skeleton, and alternately tie the emulsion explosive cartridge and water bag along the axial direction of the steel wire; the diameter of the water bag is smaller than the diameter of the deep hole; set a sponge pad at the connection between the emulsion explosive cartridge and the water bag, and lay the detonating cord along the entire length of the composite hydraulic fracturing charge structure; fill the deep hole opening with plugging clay to form a sealed cavity, and use the high temperature and high pressure shock wave generated by the explosion to squeeze the water bag and generate a hydraulic fracturing effect.

[0012] Preferably, in step S4, the specific logic for differentiated configuration of the composite hydraulic fracturing charge structure based on distribution data is as follows: in the sparse fracture zone determined in step S3, the proportion of emulsion explosive cartridges is increased, and an arrangement pattern of one emulsion explosive cartridge spaced between one water bag is adopted; in the dense fracture zone determined in step S3, the proportion of emulsion explosive cartridges is reduced, and an arrangement pattern of one emulsion explosive cartridge spaced between two water bags is adopted; the blasting energy distribution is adjusted through differentiated configuration, driving the initial fractures to extend further and interconnect.

[0013] Furthermore, in step S5, the process of installing the metal grounding electrode and constructing the orifice sealing structure includes: selecting hot-dip galvanized flat steel as the metal grounding electrode, binding and fixing the grouting pipe and the flat steel in parallel along the axial direction, and setting insulating support components on the flat steel at preset intervals; sending the flat steel and grouting pipe assembly into the center of the deep hole, and installing a grout stop plug at a preset depth from the ground orifice; the grout stop plug is tightly fitted to the deep hole wall and the flat steel and grouting pipe that pass through it, and backfilling quick-setting cement or compacting the hole-blocking mud above the grout stop plug for reinforcement.

[0014] Preferably, in step S5, the process of implementing high-pressure grouting using a staged pressurization strategy includes: Carbon-based or graphite-based physical drag-reducing slurry is selected as the drag-reducing agent, and the grouting truck and the grouting pipe in the hole are sealed together. The grouting truck is turned on and the drag-reducing agent is filled into the main channel of the deep hole in a low-pressure, high-flow mode to discharge the accumulated water and gas. The grouting pressure is increased to the design range, and the high pressure is used to make the drag-reducing agent overcome the flow resistance and penetrate and diffuse into the rock depth along the three-dimensional fracture network generated in steps S2 and S4 until the grouting pressure is stable and the grouting volume no longer increases.

[0015] Furthermore, step S6 specifically includes: maintaining a static state for curing; after the resistance-reducing agent has cured to form a conductive network structure, cutting off the exposed grouting pipes and auxiliary facilities, leaving only the metal grounding electrode; connecting the metal grounding electrode to the horizontal grounding grid using welding, and performing anti-corrosion treatment on the welded parts; testing the power frequency grounding resistance value using the three-electrode method, ensuring that the arrangement direction of the current electrode and voltage electrode avoids the main development direction of the initial crack observed in step S3; if the measured value is greater than the target power frequency grounding resistance value, then drilling new deep holes along the extension line of the initial crack development direction and repeating the above steps.

[0016] This invention provides a grounding resistance reduction method based on repeated water pressure bursting. It has the following beneficial effects: 1. This invention employs a staged fracturing process combining minimally invasive initial fracturing with repeated hydraulic blasting. First, minimally invasive blasting with a large decoupling coefficient establishes an initial fracture channel around the deep hole, which helps reduce the risk of hole wall pulverization and collapse caused by traditional powerful blasting and helps maintain the integrity of the grouting and operation channels. By utilizing composite hydraulic blasting technology, the impact energy of the explosion is converted into uniform quasi-static hydraulic pressure, which helps drive the fracture to extend a long distance into the deep rock and increases the conductive contact area inside the rock.

[0017] 2. This invention introduces a visual feedback mechanism to achieve feedback adjustment of construction parameters. It obtains the true distribution data of the initial fractures through in-hole television imaging technology and uses this data as the basis for subsequent charge structure configuration. This helps to achieve key reinforcement of sparse fracture areas and appropriate maintenance of dense fracture areas, which is beneficial to reduce uneven fracture effects or engineering hazards caused by empirical charging.

[0018] 3. This invention uses a water bag as a water pressure blasting medium. This medium is incompressible and can transmit the explosion pressure to generate a water wedge effect. At the same time, the fine water mist formed by the water bag after the explosion can effectively adsorb the blasting dust, play a role in dust reduction and cooling, optimize the working environment inside the hole, and provide a wetting channel interface for the subsequent penetration of drag-reducing agents. Attached Figure Description

[0019] Figure 1This is a flowchart of a method according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the repetitive hydraulic blasting charge structure according to an embodiment of the present invention; Figure 3 This embodiment of the invention uses in-hole television to observe the development of fractures; Figure 4 This invention provides a numerical simulation of the repeated hydraulic pressure burst fracture development in an embodiment of the invention. Among them, 1 is the first fracture, and 2 is the second fracture; Figure 5 This refers to the area filled with drag-reducing material formed after multiple blasting fractures in the rock mass, as described in this embodiment of the invention.

[0020] Among them, 1. emulsion explosive; 2. water bag; 3. sponge pad; 4. steel wire; 5. detonating cord; 6. plugging mud; 7. supporting steel bar; 8. rock; 9. flat steel; 10. grout stop plug; 11. grouting pipe; 12. grouting truck; 13. fissure; 14. drag reducing agent; 15. gravel. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] See attached document Figure 1 -Appendix Figure 5 This invention provides a grounding resistance reduction method based on repeated hydraulic pressure blasting fracturing. This method, targeting the characteristics of high soil resistivity strata, combines a step-by-step fracturing strategy with a composite conductive medium to construct deep and three-dimensional conductive channels within the rock mass. The method includes the following steps: S1. Deep hole drilling operation: In rock zones 8 of high soil resistivity strata, deep holes are drilled using down-the-hole drills based on the design requirements for grounding resistance and the site's geological environment. These deep holes serve as the main access points for subsequent blasting fracturing and grounding electrode installation; their depth is generally designed to be over 10 meters, and their diameter to be over 60 millimeters. Depending on site constraints, deep holes can be drilled vertically or at an angle. After drilling is completed, any accumulated water and drill cuttings inside the deep hole are removed to ensure the integrity of the borehole wall and provide working space for subsequent processes.

[0023] S2. Implement minimal-damage initial fracturing: Based on the deep hole drilled in step S1, the first blast is carried out inside the deep hole. Step S2 prioritizes directional blasting technology or low-charge radial decoupled charging technology. The purpose of implementing micro-damage initial fracturing is to induce the formation of directional initial fractures 13 in the rock mass surrounding the deep hole, constructing the basic framework of the fracture network 13. At the same time, by strictly controlling the charge per blast and the blasting energy density, the degree of crushing of the rock 8 around the bottom and walls of the hole is minimized to prevent the collapse or blockage of the deep hole due to excessive crushing zones, thus preserving a complete working channel for subsequent repeated hydraulic blasting and grouting operations.

[0024] S3. In-hole visual feedback and hole cleaning: Based on the initial fracturing completed in step S2, a secondary cleaning is performed on the deep borehole. After cleaning, an in-hole television imaging device is used to probe the interior of the deep borehole and perform a full-section scanning observation of the borehole wall. The visual feedback from inside the borehole includes the longitudinal distribution location of the initial fracture 13, the density of the initial fracture 13, the opening of the initial fracture 13, and the integrity of the borehole wall. Step S3 aims to confirm that there is no serious collapse of the deep borehole and to obtain digital feedback information on the effect of the initial fracturing, as a basis for subsequent adjustment of process parameters.

[0025] S4. Parameter optimization and composite charge assembly: Based on the visual feedback results obtained in step S3 or combined with numerical simulation calculations, the blasting parameters for subsequent hydraulic blasting are dynamically optimized. The optimization includes the explosive charge, decoupling coefficient, and the placement of the medium bag. Based on the optimized parameters, a repeatable hydraulic blasting charge structure is assembled. In this embodiment, the emulsion explosive 1 and the water bag 2 are assembled into a string-like spaced charge structure using steel wire 4 and sponge pads 3, and suspended inside the deep hole.

[0026] S5. Repeated water pressure bursting and crack widening with media pre-implantation: The explosive charge structure, assembled and inserted into the deep hole based on step S4, is then sealed at the hole opening before detonation. Utilizing the incompressibility and rheological properties of the medium in water bag 2, a water wedge effect and a medium implantation effect are generated. The explosive shock wave is converted into hydraulic energy, driving the initial fracture 13 to further extend deeper and generate a secondary fracture network 13. Simultaneously, the high pressure of the explosion atomizes the conductive gel and forces it into the micro-fractures 13 in the deep rock 8, achieving pre-implantation of the conductive medium before the rock 8 elastically rebounds and closes. After the blast, step S3 can be performed again for observation. If the fracture development does not meet design expectations, steps S4 to S5 can be repeated as needed until a dense fracture network 13 is formed that meets the requirements.

[0027] S6. Grounding electrode installation and high-pressure grouting mesh formation: Based on the fracture network 13 formed in step S5, a flat steel bar 9 is vertically placed as the main grounding conductor in the fractured deep hole. Subsequently, a grout stop plug 10 is installed at the opening of the deep hole, or grouting material is used to seal the opening, and the grouting pipe 11 is connected to the grouting truck 12. A low resistivity reducing agent 14 is injected into the deep hole and the fractures 13 that have been expanded by blasting using a high-pressure grouting machine. The reducing agent 14 fills the macroscopic fractures 13 and overlaps and fuses with the conductive gel layer pre-implanted deep into the micro-fractures 13 in step S5, ultimately forming a continuous, three-dimensional, dendritic conductive grounding network from the inside out and from the macroscopic to the microscopic.

[0028] See attached document Figure 1 In step S1, when conducting deep-hole drilling operations in strata with high soil resistivity, drilling parameters must be determined based on geological exploration results and the target value of grounding resistance, and a drilling process adapted to rock hardness 8 must be adopted. Step S1 specifically includes the following sub-steps: S101. Calculation and determination of drilling parameters: Before drilling operations, the resistivity parameters of the rock in area 8 need to be measured. The Wenner four-electrode method or other equivalent geophysical exploration methods are used to obtain soil resistivity distribution data at different depths. Based on the measured resistivity of the soil and rock layers, combined with the target power frequency grounding resistance value, the borehole depth is determined.

[0029] For vertical grounding electrodes, the estimated power frequency grounding resistance is calculated using the following formula to determine the minimum required borehole depth: ; In the formula, This is an estimated value for the power frequency grounding resistance of the vertical grounding electrode; The resistivity of the soil and rock layer is taken as the average value within the deep hole depth range; This refers to the burial depth of the vertical grounding electrode, i.e., the corresponding deep hole depth. This is the equivalent diameter of the grounding electrode.

[0030] In this embodiment, considering the diameter expansion effect caused by subsequent blasting and the increased conductive cross-section due to the filler layer of drag-reducing agent 14, the equivalent diameter of the grounding electrode is taken as the equivalent calculated value of the borehole diameter and the expected expansion range of the crack 13.

[0031] Based on the above calculations and the capabilities of the construction machinery, the depth of deep boreholes is generally determined to be no less than 10 meters. In areas with distinct geological stratification and where the resistivity of the deep soil is significantly lower than that of the surface layer, the depth of deep boreholes should be designed to penetrate the high-resistivity layer and reach at least 2 meters into the low-resistivity layer.

[0032] S102. Selection of Drilling Equipment and Drilling Operations: Based on the determined borehole coordinates, drilling equipment is installed on the surface of rock 8. For the high-hardness rock 8 formation, down-the-hole drills or pneumatic impact drills are used, equipped with carbide ball-tooth drill bits, and high-pressure gas is used to drive the impactor to break the rock 8.

[0033] The selection of the deep hole diameter must meet the requirements for the subsequent insertion of the composite charge structure and the thickness of the grouting layer. The deep hole diameter is set between 60 mm and 150 mm. If the deep hole diameter is too small, it will cause difficulty in inserting the charge structure containing the emulsion explosive 1, water bag 2 and auxiliary support components, or cause scraping of the hole wall; if the deep hole diameter is too large, it will increase drilling costs and the amount of subsequent drag-reducing agent 14 injected.

[0034] The drilling rig angle is adjusted according to the terrain limitations of the working face and the orientation of the underground rock strata. Drilling patterns are divided into vertical deep holes and inclined deep holes: in flat and open areas, vertical drilling is carried out, with the drill rod axis perpendicular to the horizontal plane; in mountainous slopes or narrow working areas, inclined drilling is carried out, with the angle between the drill rod axis and the vertical direction controlled between 0° and 45°. Inclined drilling is beneficial for penetrating bedding fissures 13, increasing the contact projection area between the grounding electrode and the rock 8.

[0035] During drilling, the straightness of the drilling trajectory is maintained by adjusting the axial thrust and rotation speed of the drilling rig. The operation of the down-the-hole drill and air compressor, the connection of the drill rod, and the calibration of verticality fall within the scope of machining well known to those skilled in the art and are performed in accordance with the relevant equipment operating specifications.

[0036] S103. Quality verification of hole cleaning and hole forming: After drilling to the designed depth, stop drilling and lift the drill bit. Use the high-pressure airflow generated by the air compressor to blow the rock powder, bottom gravel 15, and accumulated water out of the hole through the air supply pipe until there are no obvious large rock fragments in the discharged airflow.

[0037] After the borehole cleaning is completed, the quality of the deep borehole is verified. The verification standards include: the depth error of the deep borehole is controlled within ±0.2 meters of the design depth; the borehole wall is smooth and flat, without obvious narrowing or internal protruding rock blocks, ensuring that the standard diameter inspection gauge can pass through the entire borehole smoothly, and ensuring the smooth raising and lowering of the charging structure and the borehole television probe in subsequent steps.

[0038] In this embodiment, by combining the precise calculation of soil resistivity parameters and equivalent diameter, as well as the strict hole cleaning and verification process, the geometric accuracy and cleanliness of the deep hole channel are ensured, and the standardized construction of the physical operation channel is realized. This helps to ensure the smooth implementation of subsequent non-destructive insertion of composite media charge structures and directional fracturing operations.

[0039] See attached document Figure 1 Appendix Figure 4In step S2, when performing initial micro-damage fracturing operations on the deep hole drilled in step S1, it is necessary to construct a basic fracture framework 13 in the surrounding rock 8 using directional blasting or radial decoupled charging techniques, and strictly protect the integrity of the borehole wall structure to prevent borehole collapse. Step S2 specifically includes the following sub-steps: S201. Selection of fracturing technology and charge structure design: Based on the mechanical properties of rock 8 and the deep hole diameter determined in step S1, directional fracture blasting technology or small-charge radial decoupled blasting technology is selected as the initial fracturing method.

[0040] When the joint development direction of rock 8 is clear or the grounding grid needs to be extended along a specific direction, directional fracture blasting technology is selected. A shaped charge tube is used as the charge carrier, with symmetrical slits cut along the axial direction on the sidewall of the tube. When the emulsion explosive 1 detonates, the detonation products and shock wave energy are preferentially released from the slits, generating a concentrated stress concentration effect in rock 8, thereby guiding the fracture 13 to extend along the direction of the slits.

[0041] When the rock 8 is highly homogeneous or requires the formation of radial fractures 13, a small-charge radial decoupled blasting technique is used. The emulsion explosive 1 cartridge is placed directly in the center of the deep hole, with an air annular gap maintained between the emulsion explosive 1 and the hole wall. Air, as a compressible medium, provides a buffering effect at the moment of explosion, reducing the peak pressure of the shock wave and prolonging the action time of the explosive gases. This keeps the pressure acting on the hole wall within a range below the compressive strength of the rock 8 but above its tensile strength.

[0042] S202. Calculation of blasting parameters and setting of radial decoupling coefficient: To achieve the goal of micro-destructive fracturing, i.e., generating radial cracks 13 without pulverizing the borehole wall and producing a large amount of gravel 15, the radial decoupling coefficient needs to be accurately calculated. The radial decoupling coefficient is calculated using the following formula: ; In the formula, The radial decoupling coefficient; The diameter of the deep hole; The diameter of one cartridge of emulsion explosive.

[0043] In the initial crack initiation stage of micro-damage in this embodiment, the radial decoupling coefficient The value is set to be greater than 2.0, with a specific range of 2.0 to 4.0. The large radial decoupling coefficient ensures the thickness of the air gap layer, which greatly reduces the pressure of the explosion shock wave acting on the borehole wall after attenuation by the air layer. This effectively suppresses the formation of the compression crushing ring of the rock 8 around the borehole wall, and only causes tensile fractures in the borehole wall.

[0044] S203, Axial Spacer Charge Assembly and Insertion To further reduce the total charge per hole and the density of the linear charge, an air-gap charging structure or a low-energy detonating cord 5 initiation structure is adopted along the axial direction of the deep hole. The emulsion explosive 1 cartridges are fixed on the steel wire 4 at a preset interval, without filling the spaces between the cartridges with solid material, thus forming an axial air gap.

[0045] The axial spacing of the emulsion explosive cartridges is determined based on the rock integrity coefficient, and is generally controlled between 0.5 meters and 1.0 meters. Sponge pads 3 are installed at both ends of the cartridges as positioning supports to ensure that the cartridge string remains centered on the borehole cross-section after being placed in the deep hole, thus ensuring the uniformity of the radial air annulus. The assembled explosive structure is slowly fed into the deep hole until it reaches the predetermined position at the bottom of the hole.

[0046] S204. Orifice Protection and Detonation Procedures: After the explosive charge structure is inserted, the upper end of the steel wire 4 is fixed to the supporting steel bar 7 located at the borehole opening to maintain the suspension state of the explosive charge structure. Subsequently, the borehole opening section is filled with plugging mud 6 for plugging, with a plugging length of not less than 1.5 meters, to prevent the explosive gas from rushing out of the borehole opening too early and to ensure the quasi-static pressure action time in the borehole. The detonation network adopts the in-hole delayed detonation or instantaneous detonation method, and the emulsion explosive 1 in the deep hole is detonated by the detonating cord 5. The energy generated by the explosion is mainly used to drive the rock 8 to generate radial initial cracks 13, rather than to throw or break it to generate a large amount of gravel 15.

[0047] In this embodiment, by employing a large radial decoupling coefficient in conjunction with an axially spaced charge structure, and utilizing the buffering and peak-shaving effect of the air medium, an initial fracture skeleton 13 distributed radially or directionally was successfully induced on the rock 8 of the deep borehole wall. Simultaneously, the damage to the borehole wall from the blast was limited to elastic deformation or microcracks, avoiding the risks of borehole collapse and blockage. This preserved a clear and structurally intact physical channel for subsequent borehole observation and repeated hydraulic blasting operations. See attached document Figure 1 Appendix Figure 3 In step S3, based on the initial micro-damage fracturing completed in step S2, the deep hole needs to be cleaned a second time, and the development characteristics of the fractures 13 and the integrity of the hole wall should be investigated using visual detection equipment. This provides quantitative data support for the dynamic optimization of subsequent repeated hydraulic blasting parameters. Step S3 specifically includes the following sub-steps: S301, Deep-hole smoke exhaust and secondary cleaning: After the initial fracturing operation, blasting fumes and a small amount of detached rock fragments (15) remain inside the deep borehole. These fumes and fragments can interfere with the observation results of the optical imaging equipment. A high-pressure airflow is then supplied to the bottom of the borehole again using an air compressor to implement forced ventilation and smoke removal. This continues until the gas exiting the borehole opening has no obvious fumes color and is free of dust, ensuring that the air transparency inside the borehole meets imaging requirements. If large pieces of rock fragments (15) accumulate at the bottom of the borehole and cannot be blown out by the airflow, a specialized rock-grabbing tool must be used for cleaning to prevent the probe from being obstructed or stuck during descent.

[0048] S302, Full-bore panoramic scanning imaging: Assemble the borehole television imaging system and check the probe light source brightness and cable connection status. Slowly lower the probe into the deep borehole at a speed controlled between 1 and 2 meters per minute to ensure image clarity and continuity. During descent, the probe performs a 360-degree panoramic or rotating scan of the entire borehole wall, recording real-time video of the borehole wall and simultaneously recording depth information. Focus on observing the formation of fractures 13 on the surface of rock 8 in the blasting section, identifying and recording the opening, extension length, orientation, and distribution density of fractures 13.

[0049] S303, Fracture Inducing Effect Assessment and Zonal Feedback: The acquired borehole images were transmitted to a ground-based processing terminal, where image processing software was used to unfold the borehole wall into a planar image. The initial fracturing effect was then quantitatively evaluated based on the observation results. Check whether there is large-area collapse of the hole wall or over-diameter phenomenon that hinders the loading of explosives, and confirm whether the stability of the deep hole structure meets the requirements for subsequent composite placement of water bag 2 and emulsion explosive 1. The number of fractures (13) at different depths was counted, dividing the borehole depth range into fracture-dense and fracture-sparse areas. Areas with a fracture opening less than 0.5 mm or fewer than 3 fractures per unit borehole depth were designated as enhanced fracture-inducing zones; areas with well-developed fractures (13) were designated as sustained fracture-inducing zones. The zoning data and evaluation results will serve as the basis for adjusting the charge distribution and media placement in step S4.

[0050] In this embodiment, the digital monitoring of the internal state of the deep hole was realized through secondary hole cleaning and in-hole visualization feedback technology, which verified the safety of the micro-destructive fracturing in step S2. By obtaining the real distribution data of the internal fractures 13 of rock 8, a closed-loop control logic for fracturing, monitoring and optimization was established, avoiding the engineering risks caused by increasing the amount of reagent in subsequent operations.

[0051] See attached document Figure 1 Appendix Figure 2 and appendix Figure 4In step S4, based on the fracture development and distribution data obtained in step S3, a composite hydraulic fracturing charge structure is constructed using a water bag 2 and emulsion explosive 1. Repeated hydraulic blasting is then carried out in a deep hole to drive fractures 13 to extend further and interconnect in the deeper part of rock 8. Step S4 specifically includes the following sub-steps: S401. Assembly and Differentiated Configuration of Composite Hydraulic Charge Structure: Based on the dense and sparse fracture zones of fracture 13 defined in step S3, a composite hydraulic charge structure is pre-assembled on the ground. A steel wire 4 with a length greater than the depth of the deep hole is used as the main frame, and emulsion explosive cartridges 1 and water bags 2 are alternately tied along the axis of the steel wire 4.

[0052] The diameter of water bag 2 is slightly smaller than the diameter of the deep hole to ensure smooth entry into the hole and provide sufficient volume of water pressure medium. The axial configuration of the charge structure is dynamically adjusted based on feedback data from step S3: in the sparse area of ​​crack 13 determined in step S3, the proportion of emulsion explosive 1 is increased, and a dense arrangement of one roll of emulsion explosive 1 spaced between one water bag 2 is adopted; in the dense area of ​​crack 13 determined in step S3, the proportion of emulsion explosive 1 is decreased, and a sparse arrangement of one roll of emulsion explosive 1 spaced between two water bags 2 is adopted.

[0053] A sponge pad 3 is installed at the connection between the emulsion explosive 1 and the water bag 2. The diameter of the sponge pad 3 matches the diameter of the deep hole, which plays a centering and correcting role, ensuring that the explosive structure is located at the geometric center of the deep hole and preventing uneven energy transmission caused by the eccentricity of the explosive cartridge. At the same time, the detonating cord 5 is laid along the entire length of the explosive structure and reliably connected to each section of emulsion explosive 1.

[0054] S402. Insertion of the charge structure and sealing of the orifice: The assembled composite hydraulic charge structure is slowly lowered into the deep hole using steel wire 4 until it reaches the bottom. The upper end of steel wire 4 is securely tied to the supporting steel bar 7 at the hole opening, so that the entire charge structure is suspended and stretched inside the hole, preventing the charge cartridges from shifting due to their own weight.

[0055] After the explosive charge structure is positioned, fill the top of the deep hole with plugging clay 6. The filling length of the plugging clay 6 should be determined according to the minimum resistance line calculation and should not be less than 2.0 meters to form a high-pressure sealed cavity, preventing the high-pressure gas and energy generated by the explosion from leaking out of the hole too early, and ensuring that the energy is mainly used to compress the water bag 2.

[0056] S403, Hydraulic fracturing initiation and fracture 13 propagation: After the detonation network is connected, the detonating cord 5 detonates the emulsion explosive 1 in the deep hole. The high-temperature and high-pressure shock wave generated by the explosion of the emulsion explosive 1 directly acts on the adjacent water bag 2. The fluid in the water bag 2, as an incompressible medium, undergoes water pressure fracturing under the action of the shock wave, converting the instantaneous impact pressure generated by the explosion into uniform quasi-static hydraulic pressure.

[0057] High-pressure gel fluid is rapidly injected into the initial fractures 13 formed in step S2. Under the wedging and splitting action of the high-pressure gel fluid, stress concentration occurs at the tips of the fractures 13 inside the rock 8, leading to secondary fractures. This forces the fractures 13 to continue extending deeper into the rock 8, inducing secondary microcracks. Ultimately, a three-dimensional fracture network 13 with a radius several times larger than the initial fracture range is formed around the deep hole. Compared to the traditional blasting method where explosives directly contact the rock wall, the water pressure blasting using water bags 2 effectively buffers the direct crushing effect on the hole wall, reduces the generation of gravel 15, and preserves the connectivity of the fracture channels 13.

[0058] In this embodiment, by using the water bag 2 as an energy transmission and buffering medium and applying the monitoring data from step S3 to the differentiated configuration of the charge structure, controlled secondary fracturing of the rock 8 is achieved. While avoiding pulverizing damage to the borehole wall, the volume of the fractures 13 in the deep rock mass is increased, providing an effective filling space for the subsequent penetration and diffusion of the drag-reducing agent 14.

[0059] See attached document Figure 1 and attached Figure 5 In step S5, after repeated hydraulic blasting and the formation of a three-dimensional fracture network 13, a metal grounding electrode needs to be installed in the deep hole and pressure grouting is implemented. High pressure is used to force a resistance-reducing material into the deep fractures 13 to construct a large-volume conductive channel tightly bonded to the rock 8. Step S5 specifically includes the following sub-steps: S501. Grounding electrode fabrication and deployment: Hot-dip galvanized flat steel 9 is selected as the vertical grounding electrode. The flat steel 9 is cut to the depth of the hole determined in step S1. The length of the flat steel 9 should be greater than the depth of the hole to meet the requirements for connection with the horizontal grounding grid. The grouting pipe 11 is tied and fixed to the flat steel 9 in parallel along the axial direction. The grouting pipe 11 is made of high-pressure resistant PE pipe or steel pipe. The grout outlet at the bottom of the grouting pipe 11 is located 0.3 to 0.5 meters from the bottom of the hole.

[0060] The bundled flat steel 9 and grouting pipe 11 assembly are slowly lowered into the center of the deep hole until they reach the bottom. During the lowering process, insulating supports are installed on the flat steel 9 at regular intervals to ensure that the flat steel 9 is located in the center of the borehole cross section, so as to ensure that the thickness of the drag-reducing agent 14 coating layer around it is uniform.

[0061] S502. Installation of orifice sealing device: To achieve pressure grouting and allow the drag-reducing agent 14 to enter the micro-cracks 13, a pressure-bearing sealing structure needs to be constructed at the borehole opening. A grout stop plug 10 is installed at a depth of 0.5 to 1.0 meters from the ground opening. The grout stop plug 10 must fit tightly against the borehole wall and the passing flat steel 9 and grouting pipe 11 to prevent high-pressure grout from overflowing from the borehole opening.

[0062] After installation, quick-setting cement or compacted plugging mud 6 is backfilled above the grout stop plug 10 for secondary reinforcement to ensure that the pressure bearing capacity of the orifice sealing structure is higher than the maximum design pressure of subsequent grouting operations. At the same time, an vent hole is reserved on the grout stop plug 10 to release residual gas in the hole. After the grout overflows from the vent hole, the vent hole is sealed.

[0063] S503, High-Pressure Grouting Operation Implementation: Reliably connect the discharge pipe of the ground-mounted grouting truck 12 to the grouting pipe 11 inside the hole. Start the grouting truck 12 and pump liquid drag-reducing agent 14 into the deep hole. The drag-reducing agent 14 is a carbon-based or graphite-based physical drag-reducing slurry with good fluidity, low shrinkage after curing, and low resistivity.

[0064] The grouting process employs a staged pressurization strategy. First, the grouting truck 12 is activated in a low-pressure, high-flow mode to fill the main channel of the deep hole with the drag-reducing agent 14, expelling accumulated water and gas from the deep hole. Subsequently, the parameters of the grouting truck 12 are adjusted to increase the grouting pressure to 1.0 MPa to 3.0 MPa. High pressure is used to allow the drag-reducing agent 14 to overcome flow resistance and penetrate and diffuse deep into the rock 8 along the radial fractures 13 generated in steps S2 and S4, filling the cavities and microcracks created by the blasting.

[0065] S504. Determination of Pressure Holding and Grouting Completion: During the grouting process, the grouting pressure and grouting volume are monitored in real time by instruments on the grouting truck 12. When the grouting pressure stabilizes within the design range of 1.0 MPa to 3.0 MPa and the grouting volume no longer increases, or when a small amount of grout appears on the ground around the grout stop plug 10, it is determined that the grout has filled the crack network 13.

[0066] When the above conditions are met, stop pumping and close the high-pressure valve on the grouting pipe 11 for pressure stabilization and curing. The pressure holding time shall not be less than 20 minutes to compensate for the penetration loss and volume shrinkage of the drag-reducing agent 14 in the crack 13, ensuring that the drag-reducing agent 14 can fully fill the crack 13, forming a dendritic distribution of the drag-reducing agent 14 filling structure, and completing the construction of the deep hole grounding body.

[0067] See attached document Figure 1 and attached Figure 5 In step S6, after the grout in the borehole has solidified, the auxiliary construction facilities are removed, the vertical grounding electrode is connected to the horizontal grounding grid, and the final power frequency grounding resistance value is measured. Step S6 specifically includes the following sub-steps: S601. Slurry curing and auxiliary facility cleaning: After the grouting and pressure holding in step S5 are completed, the plant is kept in a static state for curing. The curing time is set according to the curing characteristics of the drag-reducing agent 14, generally 24 to 48 hours, to ensure that the drag-reducing agent 14 filling the cracks 13 and deep holes undergoes physical solidification or chemical hardening to form a dendritic conductive structure.

[0068] After the resistance-reducing agent 14 reaches the predetermined strength, remove the grout stop plug 10 at the borehole opening. If the grout stop plug 10 is a one-time pre-embedded part, leave the grout stop plug 10 inside the hole. Use a cutting tool to cut off the grouting pipe 11, steel wire 4, and supporting steel bar 7 that are exposed above ground, leaving only the flat steel 9 as an electrical connection point. Clean up the overflowing grout and gravel 15 around the borehole opening, and backfill with the original soil until it is level with the ground.

[0069] S602. Grounding grid connection and anti-corrosion treatment: Excavate a horizontal grounding trench, bend the upper end of flat steel 9 to overlap it with the horizontally laid grounding main grid. Use exothermic welding or double-sided arc welding to connect the flat steel 9 to the horizontal grounding main grid. The welding length must be no less than twice the width of the flat steel 9, and at least three edges must be welded.

[0070] After welding is completed, the welding slag is removed, and the surface of the welded parts and the exposed section of flat steel 9 is coated with asphalt paint or wrapped with anti-corrosion tape for anti-corrosion treatment to prevent metal corrosion from causing an increase in grounding resistance or a break in electrical connection.

[0071] S603, Resistance Testing and Project Acceptance: The power frequency grounding resistance value of a vertical grounding electrode, composed of a flat steel column 9, a deep-hole resistance-reducing agent 14 column, and a conductive network of deep fissures 13 in the rock 8, was determined using a three-electrode method or a clamp meter grounding resistance tester. When using the three-electrode method, the arrangement of the current electrode and the voltage electrode should, as far as possible, avoid the main development direction of the fissures 13 observed in step S3, in order to obtain the true current dissipation resistance.

[0072] Compare the measured resistance value with the target power frequency grounding resistance value set in step S1. If the measured value is less than or equal to the target value, the current deep hole grounding electrode construction is deemed qualified; if the measured value is greater than the target value, a new deep hole needs to be drilled along the extension line of the development direction of crack 13 determined in step S3, and steps S1 to S6 need to be repeated until the total grounding resistance after parallel connection meets the design requirements.

Claims

1. A method for grounding resistance reduction based on repeated hydraulic pressure blasting fracturing, characterized in that, The method comprises the following steps: S1, determining drilling parameters according to soil resistivity and target grounding resistance value, and drilling a deep hole in a rock area of a high soil resistivity stratum; S2, performing micro-damage initial cracking in the deep hole to form initial cracks in the rock area around the deep hole, and keeping the hole wall of the deep hole intact; S3, cleaning the deep hole and obtaining distribution data of the initial cracks; S4, assembling a composite water pressure cracking charge structure based on the distribution data, and performing repeated water pressure blasting in the deep hole; the composite water pressure cracking charge structure comprises an emulsion explosive cartridge and a water bag, the water bag is extruded by blasting pressure to drive the initial cracks to expand to the deep part of the rock and form a three-dimensional crack network; S5, installing a metal grounding electrode in the deep hole and constructing a hole mouth sealing structure, and performing high-pressure grouting to press a resistance reducing agent into the deep hole and the three-dimensional crack network; S6, connecting the metal grounding electrode with a horizontal grounding network after the resistance reducing agent solidifies, and measuring a power frequency grounding resistance value.

2. The method of ground resistance reduction by repeated water pressure blasting fracturing according to claim 1, characterized in that, In the step S1, the determination of the drilling parameters specifically comprises: measuring distribution data of the soil resistivity at different depths of the rock area on site, and setting a target power frequency grounding resistance value; calculating a required minimum deep hole depth according to a power frequency grounding resistance estimation logic of a vertical grounding electrode, the power frequency grounding resistance estimation logic being established based on a functional relationship among the soil resistivity, the burial depth of the vertical grounding electrode, and the equivalent diameter of the grounding electrode; wherein the equivalent diameter of the grounding electrode is an equivalent calculation value of the drilling diameter and the expected crack expansion range.

3. The method of ground resistance reduction by repeated water pressure blasting fracturing according to claim 1, characterized in that, In the step S2, the performance of the micro-damage initial cracking specifically comprises: selecting a small explosive charge radial uncoupling charge technology, placing an emulsion explosive cartridge at the center of the deep hole, and reserving an air annular gap between the emulsion explosive cartridge and the hole wall of the deep hole; setting a radial uncoupling coefficient, the radial uncoupling coefficient being a ratio of the diameter of the deep hole to the diameter of the emulsion explosive cartridge, and the ratio being set to a value greater than 2.0; using the air annular gap as a buffer layer to reduce the peak pressure of the explosion shock wave, and only generating tensile fracture on the hole wall.

4. The method of ground resistance reduction by repeated water pressure blasting fracturing according to claim 3, characterized in that, In the step S2, the design and placement of the charge structure specifically comprises: building an air spacing charge structure along the axial direction of the deep hole, fixing the emulsion explosive cartridges on a steel wire at a preset interval, and not filling solid materials between the cartridges; setting sponge gaskets at the upper and lower ends of the emulsion explosive cartridges, positioning the emulsion explosive cartridges by the sponge gaskets to make the emulsion explosive cartridges located at the center position of the cross section of the deep hole; suspending the assembled charge structure inside the deep hole, filling hole plugging stemming in the hole mouth section, and initiating the emulsion explosive cartridges by detonating cord.

5. The method of ground resistance reduction by repeated water pressure blasting fracturing according to claim 1, characterized in that, In the step S3, the obtaining of the distribution data of the initial cracks specifically comprises: exploring into the deep hole by using a borehole television imaging device to scan and observe the whole section of the hole wall; identifying and recording the opening degree, extension length, and distribution density of the initial cracks; Counting the number of initial fractures in different depth sections, and marking the area where the fracture aperture is less than a preset threshold or the number of fractures per unit hole depth is less than a preset value as a fracture sparse area, and marking the rest of the area as a fracture dense area; The data of the fracture sparse area and the fracture dense area are used as the basis for adjusting the composite hydraulic fracturing charge structure in step S4.

6. The method of ground resistance reduction by repeated water pressure blasting fracturing according to claim 1, characterized in that, In the S4 step, assembling the composite hydraulic fracturing charge structure specifically includes: Taking a steel wire as the main skeleton, and alternately binding the emulsion explosive cartridge and the water bag along the axial direction of the steel wire; The diameter of the water bag is smaller than the diameter of the deep hole; A sponge gasket is arranged at the connection between the emulsion explosive cartridge and the water bag, and a detonating cord is laid along the full length of the composite hydraulic fracturing charge structure.

7. The method of ground resistance reduction by repeated water pressure blasting fracturing according to claim 5 or 6, characterized in that, In the S4 step, differentiating the configuration of the composite hydraulic fracturing charge structure specifically includes: In the fracture sparse area determined in the S3 step, the proportion of the explosive charge of the emulsion explosive cartridge is increased, and the arrangement mode of one emulsion explosive cartridge interval one water bag is adopted; In the fracture dense area determined in the S3 step, the proportion of the explosive charge of the emulsion explosive cartridge is reduced, and the arrangement mode of one emulsion explosive cartridge interval two water bags is adopted.

8. The method of ground resistance reduction by repeated water pressure blasting fracturing according to claim 1, characterized in that, In the S5 step, installing the metal grounding electrode and constructing the hole sealing structure specifically includes: Hot-dip galvanized flat steel is selected as the metal grounding electrode, the grouting pipeline and the flat steel are fixed by being bound in parallel along the axial direction, and insulating supports are arranged on the flat steel at a preset interval; The flat steel and the grouting pipeline assembly are sent into the center of the deep hole, and a grout stopping plug is installed at a position with a preset depth from the ground hole; The grout stopping plug closely fits the hole wall and the flat steel and the grouting pipeline passing through, and fast-setting cement or rammed stemming is backfilled above the grout stopping plug for reinforcement.

9. The method of ground resistance reduction by repeated water pressure blasting fracturing according to claim 8, characterized in that, In the S5 step, implementing high-pressure grouting specifically includes: Carbon-based or graphite-based physical resistance-reducing grout is selected as the resistance-reducing agent, and the grouting vehicle and the grouting pipeline in the hole are sealed and connected; The grouting vehicle is started to inject the resistance-reducing agent into the main channel of the deep hole in a low-pressure and large-flow mode, and the accumulated water and gas are discharged; A staged pressurization strategy is adopted to increase the grouting pressure to a design range, and the resistance-reducing agent is made to overcome the flow resistance by high pressure, penetrate and diffuse along the three-dimensional fracture network to the deep part of the rock, until the grouting pressure is stable and the grouting amount no longer increases.

10. The method of ground resistance reduction by repeated water pressure blasting fracturing according to claim 8, characterized in that, The S6 step specifically includes: Maintenance is maintained in a static state, and after the resistance-reducing agent is solidified to form a conductive network structure, the grouting pipeline and auxiliary facilities exposed to the ground are cut off, and only the metal grounding electrode is retained; The metal grounding electrode is connected with the horizontal grounding net by welding, and the welded part is subjected to corrosion protection treatment; The power frequency grounding resistance value is tested by the three-pole method, and the arrangement direction of the current pole and the voltage pole avoids the main development direction of the initial fracture; If the measured value is greater than the target power frequency grounding resistance value, a new deep hole is drilled on the extension line of the initial fracture development direction, and the S1 step to the S6 step are repeated.

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