Anti-freezing resistance reducing agent composition for grounding resistance reduction construction in plateau alpine region, resistance reducing agent preparation method and construction method

Abstract

The application discloses an anti-freezing resistance reducing agent composition for grounding resistance reduction construction in a plateau alpine region, a resistance reducing agent preparation method and a construction method. The resistance reducing agent composition adopts sodium-based bentonite to provide a matrix and swelling; flaky graphite is used to construct a conductive network; modified starch is used to ensure long-term water retention; calcium sulfate is used to endow the resistance reducing agent with anti-freezing and curing functions; sodium chloride is used to improve initial conductivity; and the five components are used to realize mutual cooperation, so that the resistance reducing agent can simultaneously have low resistivity, high water retention, anti-freezing property and long-term stability under a plateau freeze-thaw environment. In combination with specific water-powder ratios, curing times, flexible substrates and layered ramming construction processes, the resistance reducing agent layer can maintain the integrity of the structure under freeze-thaw cycle conditions at-30 DEG C, and the problems that the structure of the resistance reducing agent layer is prone to damage and the grounding resistance is prone to rebound under freeze-thaw cycle working conditions are well solved.

Description

Technical Field

[0001] This invention belongs to the field of grounding resistance reduction construction technology, specifically relating to an antifreeze resistance reduction agent composition, a resistance reduction agent preparation method, and a construction method for grounding resistance reduction construction in high-altitude and cold regions. It is particularly suitable for grounding resistance reduction construction in strata with high altitude (above 3000 meters), severe freeze-thaw cycles, drought and low rainfall, and high soil resistivity. Background Technology

[0002] Highland gold mines are generally located in high-altitude, cold, arid and rain-scarce areas. The soil resistivity in these areas is extremely high, the freeze-thaw cycle is intense, the underground space is narrow, and the surrounding rock is hard. Conventional grounding measures are difficult to reduce the grounding resistance to below 2 ohms.

[0003] Currently, grounding resistance reducing agents are mainly classified into four categories: bentonite type, graphite type, chemical electrolyte type, and water-absorbing resin type. Existing technologies mostly employ multi-component compounding, with some products incorporating materials such as carbon fiber, polyaniline, and vapor phase corrosion inhibitors; however, existing technologies generally suffer from the following problems: 1. The soil resistivity in high-altitude areas is extremely high, and conventional grounding measures and ordinary resistance-reducing agents cannot make the grounding resistance meet the standards; 2. In arid environments, water evaporates quickly, causing the resistance-reducing agent to dry and crack, detach from the grounding electrode, and the grounding resistance to rebound rapidly. 3. Freeze-thaw cycles damage the structure of drag-reducing agents, resulting in unstable drag-reducing effects; 4. Existing drag-reducing agents have complex compositions and high costs, making them unsuitable for large-scale use in mines; 5. Some resistance-reducing agents contain strong electrolytes, which are highly corrosive to grounding electrodes and affect their service life. 6. Lack of standardized construction methods suitable for confined underground spaces.

[0004] CN102492202A discloses an intumescent grounding enhancer containing modified starch superabsorbent resin, polyethylene superabsorbent expanding resin, cryptocrystalline graphite powder, flake graphite powder, calcium-magnesium bentonite, and aluminosilicate cement. It is suitable for geological environments with high soil resistivity and extremely arid geological environments, but it cannot solve the problem of the impact of freeze-thaw cycles on the resistance reduction effect of the grounding enhancer.

[0005] CN104218334A discloses a method for reducing the corrosion of grounding electrodes by grounding resistance reducing agents. The formula uses calcium carbonate as a soil affinity agent to improve contact with the soil, but it is not applicable to the use conditions of freeze-thaw cycles. Summary of the Invention

[0006] The purpose of this invention is to provide an antifreeze resistance reducing agent composition, a resistance reducing agent preparation method, and a construction method for grounding resistance reduction construction in high-altitude and cold regions, so as to solve the problems that the resistance reducing agent layer structure is easily damaged and the grounding resistance will rebound under the conditions of confined space, drought and water shortage, and severe freeze-thaw cycles (-30℃) in high-altitude and cold mines.

[0007] This invention is achieved through the following technical solution: An antifreeze-type resistance-reducing agent composition for grounding resistance reduction construction in high-altitude and cold regions comprises the following components in parts by weight: Sodium-based bentonite, 100 parts; Flake graphite, 30-50 parts; Modified starch, 15-25 parts; Calcium sulfate, 5-15 parts; Sodium chloride, 3 to 8 parts.

[0008] In some embodiments, the calcium sulfate is anhydrous calcium sulfate or calcium sulfate hemihydrate.

[0009] In some embodiments, the sodium-based bentonite is activated sodium-based bentonite; And / or, the modified starch is corn starch or cassava starch that has been cross-linked with epichlorohydrin.

[0010] Sodium-based bentonite: As a base material for resistance-reducing agents, it has the functions of absorbing water and swelling, retaining water, and bonding. After adding water, it expands to form a dense colloid that tightly wraps the grounding electrode, constituting a continuous conductive matrix. This invention uses sodium-based bentonite because its expansion ratio can reach 15 to 20 times its original volume, which is much higher than that of calcium-based bentonite (3 to 8 times). In cold and water-scarce environments, its high expansion capacity ensures close contact between the resistance-reducing agent and the grounding electrode and surrounding soil.

[0011] Flake graphite: As a conductive filler, it constructs a conductive network within a bentonite matrix, significantly reducing the resistivity of the resistance-reducing agent. The flake-like structure of flake graphite facilitates the formation of continuous conductive paths.

[0012] Modified starch, as a water-retaining agent, possesses high water absorption and retention capabilities. In arid environments, it slows down moisture loss and maintains the wettability and electrical conductivity of drag-reducing agents. This invention utilizes modified starch to significantly reduce material costs while meeting water retention requirements, making it more suitable for large-scale applications in mines.

[0013] Calcium sulfate: used as a curing agent and antifreeze component. Calcium sulfate reacts with water to form calcium sulfate dihydrate, which gradually hardens the drag-reducing agent slurry, giving the drag-reducing agent layer resistance to cracking and leaching. More importantly, the introduction of calcium sulfate gives the drag-reducing agent antifreeze capabilities—under freeze-thaw cycles, the crystalline network formed by calcium sulfate hydration effectively inhibits the damage to the structure caused by water migration and ice crystal growth, maintaining the integrity of the drag-reducing agent layer.

[0014] Calcium sulfate exists in anhydrous calcium sulfate (CaSO4) and hemihydrate calcium sulfate (CaSO4). 4· 0.5H2O, its antifreeze mechanism is that calcium sulfate reacts with water to form calcium sulfate dihydrate CaSO4. 4· The 2H2O crystal network can fill pores, encapsulate conductive fillers, and inhibit moisture migration and ice crystal growth.

[0015] Sodium chloride: As an electrolyte, it reduces contact resistance at the interface between the resistance-reducing agent and the grounding electrode, improving initial conductivity. Its content is controlled at 3-8 parts to meet conductivity requirements while avoiding excessive amounts that could corrode the grounding electrode.

[0016] The drag-reducing agent composition of this invention uses five components that can achieve synergistic effects under specific ratios: sodium-based bentonite provides the matrix and expansibility; flake graphite constructs a conductive network; modified starch ensures long-term water retention; calcium sulfate imparts antifreeze and curing functions; sodium chloride improves initial conductivity; the five components work synergistically to enable the drag-reducing agent to simultaneously possess low resistivity, high water retention, antifreeze, and long-term stability in high-altitude freeze-thaw environments.

[0017] On the other hand, the present invention also provides a method for preparing an antifreeze resistance reducing agent for grounding resistance reduction construction in high-altitude and cold regions, comprising the following steps: Sodium-based bentonite activation treatment: Sodium-based bentonite is placed in a calcining furnace and calcined at 200-300℃ for 1-2 hours. After calcination, it is cooled to room temperature, ground and sieved to obtain activated sodium-based bentonite. Preparation of modified starch: Corn starch or cassava starch is mixed with water to form a slurry, heated in a water bath to 60-80℃, gelatinized for 30-60 minutes, and epichlorohydrin is added to carry out a cross-linking modification reaction. The reaction product is dried and pulverized to obtain modified starch. The activated sodium bentonite, modified starch, flake graphite, calcium sulfate, and sodium chloride were mixed and stirred evenly according to the weight ratio to obtain drag-reducing agent dry powder.

[0018] On the other hand, the present invention also provides a grounding resistance reduction construction method for high-altitude and cold regions, comprising the following steps: Excavate a grounding pit or grounding trench; The drag-reducing agent dry powder is mixed with water at a weight ratio of 1:0.8 to 1:1.2 to form a paste-like slurry; the drag-reducing agent dry powder is prepared by the aforementioned antifreeze drag-reducing agent composition or the aforementioned antifreeze drag-reducing agent preparation method. Place the grounding electrode in the center of the grounding pit or grounding trench, pour in paste-like slurry to wrap the grounding electrode, with a wrapping thickness of not less than 50 mm, and let it stand to cure for 30 to 90 minutes after pouring to form a resistance-reducing agent coating layer. A fine soil protective layer is formed by covering the surface of the drag-reducing agent coating layer, and then backfilling and compacting the fine soil protective layer in layers.

[0019] In some embodiments, before placing the grounding electrode, a layer of fine soil with a thickness of 50-100 mm is laid at the bottom of the pit or trench, and the grounding electrode is placed on the fine soil layer.

[0020] In some embodiments, for vertical grounding electrodes, an auxiliary guide frame is used to vertically center them in the center of the grounding pit, so that the eccentricity within the height range does not exceed 10mm. And / or, for horizontal grounding electrodes, use supports to suspend them in the air, so that the distance between the lower surface of the grounding electrode and the surface of the fine soil cushion layer at the bottom of the trench is not less than 50mm.

[0021] In some embodiments, the step of injecting drag-reducing agent slurry is as follows: For vertical grounding electrodes, a layered grouting and layer-by-layer curing method is adopted. Each grouting thickness is 100~150mm, and the electrode is left to stand for 10~15 minutes at intervals. After initial curing, the grouting is continued until the grounding electrode is completely covered. For horizontal grounding electrodes, first pour the resistance-reducing slurry into the bottom of the grounding electrode to fill all the gaps, and then pour it into the top and around the electrodes.

[0022] In some embodiments, a fine soil protective layer with a thickness of 50-100mm is first covered on the surface of the drag-reducing agent coating layer. The fine soil protective layer is not compacted. The original soil is used for backfilling in layers and compacted. The loose thickness of each layer is 150-200mm.

[0023] In some embodiments, the depth of the grounding pit is not less than 1.5 meters, so that the grounding electrode can penetrate the freeze-thaw active layer; the depth of the grounding trench is not less than 0.8 meters.

[0024] This invention introduces calcium sulfate as an antifreeze curing component into the resistance-reducing agent composition. Combined with a specific water-to-powder ratio, curing time, flexible substrate, and layered compaction process, the resistance-reducing agent layer can maintain its structural integrity under freeze-thaw cycles at -30°C. The resistance-reducing agent layer does not crack, leak, or detach from the grounding electrode, effectively solving the problems of easy damage to the resistance-reducing agent layer structure and rebound of grounding resistance under freeze-thaw cycle conditions.

[0025] This invention employs layered compaction to densify the backfill soil, reducing the penetration and accumulation of external moisture during freeze-thaw cycles, thus reducing the penetration and accumulation of external moisture into the drag-reducing agent layer and lowering external frost heave pressure. The crystalline network formed by the hydration of calcium sulfate in the drag-reducing agent layer can fill the internal pores of the drag-reducing agent layer, inhibiting the migration of internal moisture and ice crystal growth, and maintaining structural integrity. The two work synergistically to achieve the effect of resisting freeze-thaw cycle damage from both external blocking and internal strengthening dimensions.

[0026] This invention utilizes a fine soil cushion layer laid at the bottom of the pit / ditch as a flexible base, providing buffer space for the hydration and expansion of the drag-reducing agent and preventing cracking of the coating layer caused by rigid constraints at the bottom. Supported by the flexible base, the drag-reducing agent layer can expand freely, forming a dense coating layer without internal stress. The use of a fine soil protective layer, without compaction, allows the loose structure of the layer to slow down the evaporation of moisture from the drag-reducing agent, ensuring humidity for the continuous hydration of calcium sulfate in the arid environment of high-altitude areas. Under the moisturizing effect of the fine soil protective layer, calcium sulfate can continue to hydrate for a longer period, resulting in a more complete and dense crystal network.

[0027] The construction method of this invention adopts a construction process of flexible base, precise positioning of grounding body, dense wrapping of grounding body with resistance reducing agent, moisturizing and hydrating fine soil protective layer, and external layered compaction and sealing. Each process is interconnected and closely cooperates with the antifreeze mechanism of resistance reducing agent to form a protection system against freeze-thaw cycle, which can play a role in resisting freeze-thaw cycle damage.

[0028] This invention is not only applicable to underground environments in metal and non-metal mines, but can also be widely applied to the construction of grounding projects such as substations, wind farms, photovoltaic power stations, railway tunnels, and underground power stations in plateau areas, with good economic and social benefits. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a flowchart of the method for preparing drag-reducing agents according to an embodiment of the present invention.

[0031] Figure 2 This is a schematic diagram of the vertical grounding electrode resistance reduction construction structure according to an embodiment of the present invention.

[0032] Figure 3 This is a schematic diagram of the horizontal grounding electrode resistance reduction construction structure according to an embodiment of the present invention.

[0033] Figure 4 This is a graph comparing the long-term stability of the drag-reducing agent in this invention with that of existing common drag-reducing agents. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0035] The terminology and related explanations involved in the embodiments of this invention are as follows: Soil resistivity: an indicator of soil conductivity, measured in ohm-meters. A higher value indicates poorer soil conductivity and greater difficulty in grounding and reducing resistance.

[0036] Freeze-thaw cycle: The process by which moisture in soil or materials repeatedly freezes and thaws due to temperature changes. Freeze-thaw cycles can cause materials to become porous and cracked, and are one of the main technical challenges faced by grounding engineering projects in high-altitude and cold regions.

[0037] Water retention rate: The ability of a drag-reducing agent to retain moisture under specific environmental conditions, expressed as the percentage of remaining water content after a certain period of time compared to the initial water content.

[0038] Vertical grounding electrode: A metal grounding electrode that is vertically buried underground. According to GB 50070-2020 "Design Standard for Mine Power", tubular local grounding electrodes should be made of galvanized steel pipes.

[0039] Horizontal grounding electrode: For horizontally buried metal grounding electrodes in underground mines, in accordance with GB 50070-2020 "Design Standard for Mine Power Systems", plate-type local grounding electrodes should be made of galvanized steel plates, and their area should not be less than 0.60m². 2 The thickness should not be less than 3.5mm.

[0040] Curing: After the drag-reducing agent is added to water, components such as calcium sulfate undergo a hydration reaction, causing the slurry to gradually harden and solidify.

[0041] Long-term resistance reduction: The grounding resistance remains stable during long-term operation and does not rebound significantly due to environmental changes and the passage of time.

[0042] Sodium-based bentonite: a clay rock with montmorillonite as its main mineral component, containing sodium ions in the interlayer, and characterized by high swelling and water absorption.

[0043] In high-altitude mines, winter temperatures can reach below -30°C. During the spring thawing period, the moisture inside the resistance-reducing agent layer repeatedly freezes and thaws, causing the layer to become loose and cracked, resulting in a rebound in grounding resistance.

[0044] In response to the special working conditions of freeze-thaw cycles and drought in high-altitude and cold regions, this invention improves the composition, preparation method, and construction process of the resistance-reducing agent, and solves the above-mentioned problems in conventional grounding resistance-reducing construction under freeze-thaw cycle conditions in high-altitude and cold regions.

[0045] In some embodiments of the present invention, the antifreeze drag-reducing agent composition comprises the following components in parts by weight: Sodium-based bentonite: 100 parts; Flake graphite: 30-50 parts; Modified starch: 15-25 parts; Calcium sulfate: 5-15 parts; Sodium chloride: 3 to 8 parts.

[0046] As a preferred embodiment, the weight parts of each component in the drag-reducing agent composition are: 100 parts sodium bentonite, 40 parts flake graphite, 20 parts modified starch, 10 parts calcium sulfate, and 5 parts sodium chloride.

[0047] In some embodiments of the present invention, the preparation method of the antifreeze drag-reducing agent is as follows: Figure 1 As shown, it includes the following steps: 1) Activation treatment of sodium-based bentonite: Sodium-based bentonite is placed in a calcination furnace and calcined at 200-300℃ for 1-2 hours; after calcination, it is cooled to room temperature and ground through a 200-mesh sieve to obtain activated sodium-based bentonite.

[0048] Calcination activation removes adsorbed water from between bentonite layers, enhancing its water absorption and swelling capacity as well as its electrical conductivity. Under freeze-thaw cycles, its high expansibility maintains close contact between the resistance-reducing agent and the grounding electrode and soil.

[0049] 2) Preparation of modified starch: Add water to corn starch or cassava starch to make a slurry, heat it in a water bath to 60-80℃, and gelatinize it for 30-60 minutes; add epichlorohydrin to carry out cross-linking modification reaction, and dry and pulverize the reaction product to obtain modified starch.

[0050] Modified starch releases water slowly under arid conditions, which can ensure the continuous hydration of calcium sulfate.

[0051] 3) Mixing and Packaging: Activated sodium bentonite, modified starch, flake graphite, calcium sulfate, and sodium chloride are added to a mixer in the above weight ratio and thoroughly mixed to obtain a drag-reducing agent dry powder. The drag-reducing agent dry powder is then packaged in a moisture-proof, sealed container to obtain the finished product.

[0052] This invention employs a construction process that combines a resistance-reducing agent coating with a fine soil cushion layer, a fine soil protective layer, and layered compaction backfilling. This creates a more stable and longer-lasting "low resistivity microenvironment" around the grounding electrode than a natural water pit, solving problems such as the soaring grounding resistance caused by freezing in winter in high-altitude environments and the fluctuation in resistance-reducing effect due to unstable water volume.

[0053] In some embodiments of the present invention, the method for underground grounding resistance reduction includes the following steps: Step S1: Excavate a grounding pit or grounding trench.

[0054] Excavate a grounding pit or grounding trench at a designated location in the underground roadway.

[0055] For vertical grounding electrodes: Excavate a grounding pit with a depth of not less than 1.5 meters and a diameter of not less than 200 millimeters. The vertical grounding electrode needs to penetrate the active freeze-thaw layer to conduct current into deep, low-resistivity soil. Therefore, the excavation depth should ensure that the entire grounding electrode is below the frost layer. If the depth is less than 1.5 meters, the grounding electrode is in the active freeze-thaw layer, resulting in poor current dissipation and susceptibility to frost heave; if the depth is too great, it will increase the difficulty of underground construction.

[0056] For horizontal grounding electrodes: Excavate grounding trenches with a depth of no less than 0.8 meters and a width of no less than 200 millimeters. It should be noted that in high-altitude permafrost regions, the permafrost layer can be several meters thick. If horizontal grounding trenches were required to be excavated below the permafrost layer, the construction cost would be extremely high, and underground space would be difficult to achieve. Therefore, horizontal grounding electrodes are laid at the conventional depth, and their frost resistance and resistance reduction effects are jointly ensured by subsequent coating with resistance-reducing agents, a fine soil protective layer, and layered compaction processes.

[0057] This invention adopts a division of labor design where "vertical grounding electrodes are deeply buried through the permafrost layer to undertake the main current dissipation task, while horizontal grounding electrodes are laid at conventional depths to undertake the connection and auxiliary current dissipation tasks." This design can better adapt to the special construction conditions of high-altitude freeze-thaw environments and underground construction constraints. The two work together to construct a three-dimensional grounding network.

[0058] The excavation dimensions mentioned above were determined based on a combination of the depth of the permafrost layer in the plateau region and the underground space conditions. The depth of the vertical grounding pit ensures that the grounding electrode penetrates the freeze-thaw layer, while the depth of the horizontal grounding trench takes into account both construction feasibility and resistance reduction effect. The two work together to form a three-dimensional grounding network.

[0059] It should be noted that, according to GB 50070-2020 "Design Standard for Mine Power Systems", the main grounding electrode in an underground mine should be installed in a water tank, water basin, or sump, but the local grounding electrode can be installed in a drainage ditch, sump pit, or other suitable location. The vertical and horizontal grounding electrodes involved in this invention are local grounding electrodes in underground mines, therefore, the construction method of excavating pits and burying them fully complies with the standard requirements.

[0060] Step S2: Prepare drag-reducing agent paste slurry

[0061] Mix the prepared drag-reducing agent powder with on-site water at a weight ratio of 1:0.8 to 1:1.2. If the water-to-powder ratio is 1:1, mix thoroughly until a uniform paste is formed.

[0062] A water-to-powder ratio of 0.8 to 1.2:1 is used to ensure the full hydration of calcium sulfate and sodium bentonite under the arid and low-temperature conditions of the plateau.

[0063] Unlike existing technologies that involve directly pouring in dry powder or simply sprinkling water, this embodiment uses a specific water-to-powder ratio to prepare a paste-like slurry, which has the following effects and benefits: (1) Ensure that all components of the drag-reducing agent are fully hydrated. Sodium-based bentonite needs to fully absorb water to exert its expansive and adhesive properties; calcium sulfate needs to be fully hydrated to undergo a hardening reaction and form a solid body with antifreeze properties.

[0064] (2) The paste-like slurry has good fluidity and plasticity, and can evenly wrap the grounding body in the narrow space of the well, avoiding problems such as uneven wrapping and insufficient thickness that occur in dry powder construction.

[0065] (3) In the arid environment of the plateau, pre-hydration can avoid the drag-reducing agent competing with the soil for water, and prevent insufficient solidification and insufficient strength due to water shortage.

[0066] Step S3: Grounding electrode placement and positioning

[0067] Depending on the type of grounding electrode, the construction shall be carried out in the following manner: For vertical grounding electrodes, refer to Figure 2 : After the grounding pit is excavated, a layer of fine soil with a thickness of 50-100mm is first laid at the bottom of the pit and gently compacted as a flexible base.

[0068] Then, using auxiliary positioning blocks, auxiliary guide frames, or temporary supports, the vertical grounding electrode (galvanized steel pipe) is vertically centered in the center of the grounding pit. The auxiliary guide frame is equipped with upper and lower guide holes, through which the grounding electrode is vertically suspended, ensuring that its upper, middle, and lower ends maintain a uniform distance from the pit wall, with an eccentricity not exceeding 10mm across the entire height.

[0069] After positioning, ensure that the lower end of the grounding electrode makes natural contact with the fine soil cushion layer at the bottom of the pit, forming a stable support.

[0070] For horizontal grounding electrodes, refer to Figure 3 : After the grounding trench is excavated, a layer of fine soil with a thickness of 50-100mm is first laid at the bottom of the trench and gently compacted as a flexible base.

[0071] Then, place the horizontal grounding electrode (galvanized steel plate) horizontally and centered on the fine soil cushion layer. Use support plates, metal brackets, or small stones to support the grounding electrode at multiple points below it, ensuring its stable suspension. The distance between the lower surface of the grounding electrode and the surface of the fine soil cushion layer should not be less than 50mm.

[0072] In the above two grounding electrode positioning construction methods, the purpose of laying a fine soil cushion layer at the bottom of the pit or trench is to: 1) form a flexible base at the bottom of the pit or trench, evenly disperse the self-weight stress of the grounding electrode and the resistance-reducing agent coating layer, and avoid local stress concentration caused by unevenness at the bottom of the trench or pit; 2) absorb some of the frost heave deformation in the high-altitude freeze-thaw cycle environment, and reduce damage to the resistance-reducing agent coating layer; 3) provide a buffer space for the hydration expansion of the resistance-reducing agent, and avoid cracking of the resistance-reducing agent coating layer caused by rigid constraints at the bottom.

[0073] The purpose of using auxiliary positioning blocks to position the vertical grounding electrode is to ensure that the wrapping thickness around the grounding electrode is uniform (not less than 50mm) during subsequent injection of resistance-reducing agent, thus avoiding insufficient local resistance-reducing effect due to eccentricity. Simultaneously, only by forming a uniform wrapping layer can a complete antifreeze system be formed with the calcium sulfate crystal network; insufficient local thickness can become the starting point for freeze-thaw damage.

[0074] Step S4: Injection of drag-reducing agent slurry

[0075] Depending on the type of grounding electrode, the grouting construction shall be carried out according to the following methods: For vertical grounding electrodes: a layered injection and layer-by-layer curing process is adopted.

[0076] First, inject resistance-reducing slurry into the bottom of the pit, with a thickness of about 100-150mm, and let it stand for 10-15 minutes to allow it to initially solidify, forming a bottom anchoring layer, and fix the lower end of the grounding electrode. Then, continue grouting in 2 to 3 stages, with each grouting thickness not exceeding 500 mm, and allow it to stand for 10 to 15 minutes at intervals until the resistance-reducing agent slurry completely covers the grounding body.

[0077] Ensure that the thickness of the resistance-reducing agent wrapping around the grounding electrode is not less than 50mm.

[0078] The layered grouting construction method can avoid the problem of grounding electrode displacement caused by the impact force of grouting a large amount at once; at the same time, layer-by-layer curing can ensure that the resistance reducing agent is tightly bonded to each layer without leaving gaps.

[0079] For horizontal grounding electrodes: First, pour the resistance-reducing slurry under the supported grounding electrode until it fills all the gaps under the grounding electrode and reaches a thickness of more than 50mm.

[0080] Then, continue to pour resistance-reducing agent above and around the grounding electrode until the entire grounding electrode is evenly wrapped, with a total wrapping thickness of not less than 50mm.

[0081] Based on field tests, a coating thickness of 50mm for the drag-reducing agent was determined to be the optimal design parameter. Too thin a thickness would result in insufficient drag reduction and an inability to create an effective low-resistance zone; too thick a thickness would waste material and increase construction difficulty in the confined space of the well.

[0082] Step S5: Allow to cure statically

[0083] After the drag-reducing agent slurry is encapsulated and injected, it is left to stand and cure for 30 to 90 minutes to allow the drag-reducing agent slurry to initially harden and take shape. This can compensate for the slow hydration rate at low temperatures in high-altitude areas and ensure the overall formation of the crystallization network.

[0084] This curing time window is designed based on the calcium sulfate hydration reaction rate under the low-temperature environment of high altitude. The temperature downhole in high-altitude areas is typically low, and the calcium sulfate hydration reaction rate is slower than at room temperature, requiring sufficient curing time to form a stable structure. A curing time shorter than 30 minutes results in insufficient strength, making subsequent backfilling prone to deformation or damage to the drag-reducing agent layer; while a curing time exceeding 90 minutes is beneficial for achieving better structural strength, it can affect the construction progress.

[0085] Step S6: Backfilling the fine soil protective layer and compacting the original soil in layers.

[0086] After the resistance-reducing agent coating layer reaches the initial setting state, backfilling is carried out in the following two stages. This construction method is applicable to the construction of vertical and horizontal grounding electrodes.

[0087] Phase 1: Backfilling with fine soil protective layer Cover the surface of the drag-reducing agent coating layer with a 50-100mm thick layer of fine soil as a protective layer. The fine soil should be sieved and free of stones, hard objects, or construction waste. At this stage, the fine soil protective layer is not compacted; it should remain naturally compacted.

[0088] Its functions are: 1) to form a physical buffer and protect the drag-reducing agent layer from subsequent compaction impact; 2) to moisturize and promote hydration, slowing down the evaporation of internal moisture of the drag-reducing agent in the arid environment of the plateau, and providing the necessary humidity for the continuous hydration of calcium sulfate.

[0089] Phase Two: Layered compaction and backfilling of the original soil On top of the fine soil protective layer, the original soil generated from the excavation is used for layered backfilling and compaction.

[0090] Each layer is loosely laid with a thickness of 150-200mm, and is compacted layer by layer using a wooden rammer or vibratory rammer until it reaches a dense state. This process is repeated until the backfill soil is level with or slightly higher than the ground surface, forming an anti-settlement layer. Considering the impact of the low-temperature environment of the plateau on the compaction effect, this method of thinning and layering compaction ensures that each layer is effectively compacted.

[0091] The purpose of layered compaction is to: 1) ensure close contact between the backfill soil and the resistance-reducing agent layer and the surrounding soil, eliminate gaps, and reduce contact resistance; 2) prevent the backfill soil from naturally settling in the future, which could lead to exposure of the grounding body or loosening of the resistance-reducing agent layer; 3) under freeze-thaw cycle conditions, dense backfill soil can reduce the infiltration and accumulation of external moisture, and reduce the destructive effect of frost heave on the resistance-reducing agent layer.

[0092] Step S7, Maintenance and Inspection

[0093] After construction, allow it to cure naturally for 72 hours. During the curing period, avoid heavy machinery running over it or strong vibrations.

[0094] After 72 hours of curing, the grounding resistance value was measured using a grounding resistance tester. On-site testing showed that using the construction method of this invention, the grounding resistance could be stably reduced to below 2 ohms.

[0095] Reference Figure 4 The initial wet resistivity of the drag-reducing agent of this invention is no greater than 0.5 ohm-meters. Under the natural operating conditions of a plateau mine, the resistivity remains stable at less than 1.0 ohm-meters after 12 months, while the resistivity of ordinary drag-reducing agents has risen to more than 7.5 ohm-meters during the same period.

[0096] The drag-reducing agent of this invention has a water retention rate of not less than 35% and an antifreeze temperature of -30℃.

[0097] All components of the drag-reducing agent of this invention are commercially available conventional materials, and the cost is far lower than that of traditional products containing expensive resins or carbon fibers.

[0098] The construction process of this invention is simple, suitable for confined underground spaces, and requires no special equipment. The resistance-reducing agent is non-toxic and pollution-free, with an annual corrosion rate of less than 0.01 mm / year on galvanized steel grounding electrodes, making it environmentally friendly.

[0099] The effects of the present invention in engineering applications will be described below with reference to specific embodiments and comparative examples.

[0100] Example 1 The antifreeze drag-reducing agent composition consists of the following components in parts by weight: 100 parts sodium bentonite, 40 parts flake graphite, 20 parts modified starch, 10 parts calcium sulfate, and 5 parts sodium chloride.

[0101] The drag-reducing agent dry powder product was prepared using the above preparation method.

[0102] The above-mentioned grounding resistance reduction construction method is used for construction, and the water-to-powder ratio of the resistance reduction agent slurry is 1:1.

[0103] Example 2 The difference from Example 1 is that the antifreeze drag-reducing agent composition consists of the following components in parts by weight: 100 parts sodium bentonite, 30 parts flake graphite, 15 parts modified starch, 5 parts calcium sulfate, and 3 parts sodium chloride.

[0104] The preparation method of the resistance-reducing agent dry powder product and the grounding resistance-reducing construction method are the same as those in Example 1.

[0105] Example 3 The difference from Example 1 is that the antifreeze drag-reducing agent composition consists of the following components in parts by weight: 100 parts sodium bentonite, 50 parts flake graphite, 25 parts modified starch, 15 parts calcium sulfate, and 8 parts sodium chloride.

[0106] The preparation method of the resistance-reducing agent dry powder product and the grounding resistance-reducing construction method are the same as those in Example 1.

[0107] Comparative Example 1 The difference from Example 1 is that the drag-reducing composition consists of the following components in parts by weight: 100 parts sodium bentonite, 40 parts flake graphite, 20 parts modified starch, and 5 parts sodium chloride (calcium sulfate is not added to the components).

[0108] The preparation method of the resistance-reducing agent dry powder product and the grounding resistance-reducing construction method are the same as those in Example 1.

[0109] Comparative Example 2 The difference from Example 1 is that the drag-reducing agent composition consists of the following components in parts by weight: 100 parts sodium bentonite, 40 parts flake graphite, 20 parts modified starch, 10 parts conductive cement, and 5 parts sodium chloride (conductive cement is used instead of calcium sulfate in the components).

[0110] The preparation method of the resistance-reducing agent dry powder product and the grounding resistance-reducing construction method are the same as those in Example 1.

[0111] Comparative Example 3 The difference from Example 1 is that the water-to-powder ratio of the grounding resistance reduction agent slurry is 0.5:1 during the grounding resistance reduction construction.

[0112] The components of the drag-reducing agent composition and the preparation method of the drag-reducing agent dry powder product are the same as in Example 1.

[0113] Comparative Example 4 The difference from Example 1 is that the drag-reducing composition consists of the following components in parts by weight: 45 parts graphite, 35 parts calcium sulfate, 15 parts polyacrylamide, and 5 parts sodium methylene dinaphthalene sulfonate.

[0114] The preparation method of the resistance-reducing agent dry powder product and the grounding resistance-reducing construction method are the same as those in Example 1.

[0115] The initial wet resistivity, freeze-thaw cycle performance, and long-term operating grounding resistance rebound rate of the grounding resistance reduction construction system of the above embodiments and comparative examples were tested; the test data are shown in Table 1.

[0116] Freeze-thaw cycle performance test: 50 freeze-thaw cycles (freezing at -30℃ for 24 hours and thawing at +20℃ for 24 hours), measure the change rate of grounding resistance, and observe the appearance of the resistance-reducing agent layer after freeze-thaw cycles to see if it cracks, pulverizes, or detaches from the grounding body. Long-term operating grounding resistance rebound rate: Measure the rebound rate of grounding resistance after 12 months of long-term operation.

[0117] Table 1

[0118] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0119] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0120] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0121] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A frost-resistant resistance-reducing agent composition for grounding resistance reduction construction in high-altitude and cold regions, characterized in that, The components include the following parts by weight: Sodium-based bentonite, 100 parts; Flake graphite, 30-50 parts; Modified starch, 15-25 parts; Calcium sulfate, 5-15 parts; Sodium chloride, 3 to 8 parts.

2. The antifreeze drag-reducing composition according to claim 1, characterized in that, The calcium sulfate is anhydrous calcium sulfate or hemihydrate calcium sulfate.

3. The antifreeze drag-reducing composition according to claim 1, characterized in that, The sodium-based bentonite is sodium-based bentonite that has undergone activation treatment; And / or, the modified starch is corn starch or cassava starch that has been cross-linked with epichlorohydrin.

4. A method for preparing an antifreeze resistance-reducing agent for grounding resistance reduction construction in high-altitude and cold regions, characterized in that, Includes the following steps: Sodium-based bentonite activation treatment: Sodium-based bentonite is placed in a calcining furnace and calcined at 200-300℃ for 1-2 hours. After calcination, it is cooled to room temperature, ground and sieved to obtain activated sodium-based bentonite. Preparation of modified starch; Corn starch or tapioca starch is mixed with water to form a slurry, heated in a water bath to 60-80°C, gelatinized for 30-60 minutes, and then epichlorohydrin is added to carry out a cross-linking modification reaction. The reaction product is dried and pulverized to obtain modified starch. The activated sodium-based bentonite, modified starch, flake graphite, calcium sulfate, and sodium chloride were mixed and stirred evenly according to the weight ratio to obtain drag-reducing agent dry powder.

5. A grounding resistance reduction construction method for high-altitude and cold regions, characterized in that, Includes the following steps: Excavate a grounding pit or grounding trench; The drag-reducing agent dry powder is mixed with water at a weight ratio of 1:0.8 to 1:1.2 to form a paste. The drag-reducing agent dry powder is prepared by the antifreeze drag-reducing agent composition according to any one of claims 1-3 or the antifreeze drag-reducing agent preparation method according to claim 4. Place the grounding electrode in the center of the grounding pit or grounding trench, pour in paste-like slurry to wrap the grounding electrode, with a wrapping thickness of not less than 50 mm, and let it stand to cure for 30 to 90 minutes after pouring to form a resistance-reducing agent coating layer. A fine soil protective layer is formed by covering the surface of the drag-reducing agent coating layer, and then backfilling and compacting the fine soil protective layer in layers.

6. The grounding resistance reduction construction method for high-altitude and cold regions according to claim 5, characterized in that, Before placing the grounding electrode, lay a 50-100mm thick layer of fine soil at the bottom of the pit or trench, and then place the grounding electrode on the fine soil layer.

7. The grounding resistance reduction construction method for high-altitude and cold regions according to claim 6, characterized in that, For vertical grounding electrodes, an auxiliary guide frame is used to vertically center them in the center of the grounding pit, ensuring that the eccentricity within their height range does not exceed 10mm. And / or, for horizontal grounding electrodes, use supports to suspend them in the air, so that the distance between the lower surface of the grounding electrode and the surface of the fine soil cushion layer at the bottom of the trench is not less than 50mm.

8. The grounding resistance reduction construction method for high-altitude and cold regions according to claim 7, characterized in that, The steps for injecting drag-reducing agent slurry are as follows: For vertical grounding electrodes, a layered grouting and layer-by-layer curing method is adopted. Each grouting thickness is 100~150mm, and the electrode is left to stand for 10~15 minutes at intervals. After initial curing, the grouting is continued until the grounding electrode is completely covered. For horizontal grounding electrodes, first pour the resistance-reducing slurry into the bottom of the grounding electrode to fill all the gaps, and then pour it into the top and around the electrodes.

9. The grounding resistance reduction construction method for high-altitude and cold regions according to claim 5, characterized in that, First, cover the surface of the drag-reducing agent coating layer with a fine soil protective layer of 50~100mm thickness. Do not compact the fine soil protective layer. Use the original soil to backfill in layers and compact them. The loose thickness of each layer is 150~200mm.

10. The grounding resistance reduction construction method for high-altitude and cold regions according to claim 5, characterized in that, The depth of the grounding pit is not less than 1.5 meters, so that the grounding electrode can penetrate the freeze-thaw active layer; the depth of the grounding trench is not less than 0.8 meters.

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