Active ice melting method and system for frozen soil of high-ice-content frozen soil foundation

Abstract

The invention discloses an active ice melting method and system for frozen soil of a high-ice-content frozen soil foundation. The method comprises the steps that S1, the position and the thickness of a high-ice-content frozen soil layer in a stratum are determined; s2, according to the position and the thickness of the high-ice-content frozen soil layer in the stratum, at least one center water injection vertical shaft and a plurality of water extraction vertical shafts formed around the center water injection vertical shaft are formed in the high-ice-content frozen soil foundation, and layered and fixed-point high-pressure hydraulic fracture forming is carried out in the center water injection vertical shaft, so that the high-ice-content frozen soil layer is obtained; enabling the crack to horizontally expand in the frozen soil layer until the crack is communicated with the water extraction vertical shaft to form a circulating convection field so as to melt frozen soil; s3, water injection is stopped, and foundation reinforcing slurry is injected into the settled and compacted soil body; and S4, backfilling the upper part of the settled earth surface area with filler layer by layer to a designed elevation. According to the method, the high-ice-content thermally unstable foundation can be safely and controllably reconstructed into the thermally stable composite foundation which meets engineering requirements and is high in bearing capacity.

Description

Technical Field

[0001] This invention relates to the field of frozen soil engineering technology, specifically to a method and system for active melting of frozen soil in high-ice-content frozen soil foundations. Background Technology

[0002] Global warming and human engineering activities have led to a warming and humidification trend on the Qinghai-Tibet Plateau, accelerating the degradation of permafrost and severely affecting the water accumulation on the surface and in the active layer. Coupled with the long-term effects of heavy traffic, some road sections have experienced significant uneven subsidence and deformation, with the maximum deformation exceeding 50 centimeters. This not only drastically reduces road traffic efficiency but also poses a serious threat to driving safety.

[0003] Permafrost, containing ice crystals or ice masses, is extremely sensitive to changes in external temperature and thermal disturbances. Linear engineering projects such as railways and highways built on permafrost inevitably alter the original surface conditions, affecting the balance of surface radiation energy and heat balance. This leads to an increase in the thickness of the active layer of permafrost beneath the roadbed and near the toe of the slope, an increase in permafrost temperature, and even permafrost thawing, forming thawing interlayers or causing a decrease in the permafrost upper limit. These changes ultimately weaken the stability of engineering structures, resulting in frequent roadbed subsidence, pavement cracking, and other defects. Taking the Qinghai-Tibet Highway as an example, this highway traverses a large area of ​​continuous permafrost. Since the paving of the asphalt concrete pavement, the temperature of the permafrost layer beneath the roadbed has continued to rise, and the permafrost upper limit has been continuously decreasing, indicating severe permafrost degradation and thawing, and increased thermal sensitivity. The result is overall roadbed subsidence, excessive deformation at the roadbed center, the disappearance or even transformation of the original road arch shape into a reverse arch, and the appearance of waves, potholes, and uneven settlement on the pavement, leading to longitudinal and transverse distortion of the roadbed.

[0004] To address these issues, the engineering community has implemented various measures, such as increasing the embankment height in permafrost regions, installing insulated roadways, and adding insulation materials, aiming to resolve subgrade defects caused by insufficient strength in the subgrade, base course, and pavement. However, as the thermal impact of asphalt concrete pavement on the permafrost beneath the subgrade becomes increasingly significant, and permafrost temperatures rise year by year, the continuous thawing of permafrost under the subgrade continues to cause and exacerbate subgrade and pavement defects. Survey data from 1991 to 2001 shows that the anthropogenic upper limit of permafrost beneath the asphalt concrete pavement on most sections of the Qinghai-Tibet Highway is decreasing, confirming that subgrade and pavement defects caused by the thawing of permafrost under the subgrade are a persistent and urgent problem.

[0005] In areas with high-temperature permafrost (permafrost with a ground temperature close to 0°C), despite the adoption of various protective measures aimed at protecting the permafrost, subgrade deformation problems remain prevalent on existing sections of permafrost highways such as the Qinghai-Tibet Highway and the Gongyu Expressway. The fundamental reason is that in high-ice-content sections, global warming has led to irreversible degradation of the high-temperature permafrost, rendering traditional subgrade treatment measures focused on "protecting the permafrost" ineffective. With the rise in average annual ground temperature, the decreasing upper limit of permafrost and the thickening of the active layer have become an irreversible trend, and subgrade thaw settlement deformation is expected to worsen further. In particular, high-ice-content permafrost (such as soil-ice layers and ice-rich permafrost) is most sensitive to rising ground temperature and is the area most severely affected by subgrade thaw settlement. Therefore, for such high-ice-content permafrost sections, there is an urgent need to research and apply new, proactive subgrade treatment methods to ensure the long-term stability and service quality of road engineering projects.

[0006] Faced with the limitations of the aforementioned "preservation-first" strategy, the engineering community has explored approaches such as "melting first, then solidifying" or "active ice melting." For example, in early mining and infrastructure construction, methods such as steam jetting or hot water injection were used to treat underground permafrost. However, these traditional methods of permafrost melting, as well as later developed methods such as electric heating and chemical additives, all have significant drawbacks.

[0007] Thermal melting methods (such as steam, hot water, and electric heating): These methods generally consume a huge amount of energy, and are subject to strict limitations in energy supply and cost when treating large areas of frozen soil. In addition, the heat transfer process is difficult to control precisely, often resulting in uneven melting or excessive melting, which may damage the stability of the surrounding frozen soil and increase the difficulty and economic burden of subsequent engineering maintenance.

[0008] Chemical additive method: Although using chemicals such as salts can effectively lower the freezing point and accelerate melting, this method will cause chemical pollution to the soil and groundwater environment, destroy the original soil structure and regional ecological balance, which does not meet the environmental protection requirements of modern engineering, and the treatment cost is high.

[0009] In conclusion, while existing active de-icing technologies have verified the feasibility of the "de-icing first, then solidification" approach, their inherent drawbacks in terms of energy consumption, environmental protection, and precise control highlight the urgent need to develop an efficient, economical, environmentally friendly, and controllable permafrost de-icing technology.

[0010] However, developing such an active solution for permafrost with high ice content faces extremely severe engineering challenges that current technologies have not yet fully addressed:

[0011] 1. Low melting efficiency: The high-ice-content frozen soil (especially the soil-ice layer) is geologically closer to ice, with almost zero permeability. Heat can only be transferred through inefficient heat conduction. This results in extremely low efficiency of traditional heat exchange methods through conventional drilling, making it impossible to achieve large-scale melting within an acceptable engineering timeframe. Furthermore, efficient heat convection (i.e., through circulating water) cannot establish a flow field due to the impermeability of the strata.

[0012] 2. Catastrophic Settlement and Safety Risks: The ice in these high-ice-content frozen soils forms the soil skeleton itself. Once it melts, it will inevitably lead to large deformation settlement (1-2 meters or even more). This severe and uneven settlement poses a fatal threat to the safety of construction equipment (such as pipelines and pumping stations) and may cause the melting process to get out of control. The existing "melt first, then consolidate" approach does not provide a reliable solution for safely managing and controlling this large deformation settlement.

[0013] 3. Drilling difficulties and grouting / water injection leakage: Drilling and installing water injection / extraction shafts in this type of formation is extremely difficult. The heat and vibration during drilling can cause the ice on the borehole wall to melt, forming an unstable mud sleeve, which can lead to rapid collapse of the borehole wall. Even if the pipe is successfully lowered, the mud sleeve or vertical weak surfaces in the formation can cause high-pressure fluid to leak back to the surface via a shortcut along the well wall, making fracturing operations impossible. Summary of the Invention

[0014] To address the aforementioned technical problems, this invention proposes a system and method for the comprehensive treatment of impermeable permafrost foundations with high ice content. This solution transforms the aforementioned challenges into controllable engineering steps through an innovative four-stage process, ultimately reconstructing the substandard foundation into a stable and solid engineering foundation.

[0015] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0016] A method for active de-icing of frozen soil in high-ice-content frozen soil foundations includes the following steps:

[0017] S1. Determine the location and thickness of the high-ice-content permafrost layer within the strata;

[0018] S2. Based on the location and thickness of the high-ice-content permafrost layer determined in step S1, at least a central water injection shaft and multiple extraction shafts surrounding the central water injection shaft are constructed on the high-ice-content permafrost foundation. Layered, targeted high-pressure hydraulic fracturing is implemented within the central water injection shaft to create cracks that extend horizontally within the permafrost layer until they connect with the extraction shafts, forming a circulating convection field to melt the permafrost. During this process, surface subsidence, ground temperature, and pore water pressure are monitored in real time. When the following three conditions are simultaneously met, proceed to step S3.

[0019] Condition 1: Ground temperature is greater than 0℃;

[0020] Condition 2: The surface subsidence rate is less than the subsidence rate control threshold;

[0021] Condition 3: The pore water pressure dissipation reaches the dissipation threshold.

[0022] S3. Stop water injection and inject foundation reinforcement grout into the settled and compacted soil through the central water injection shaft;

[0023] S4. After the foundation reinforcement grout has solidified, backfill the upper part of the settled surface area with filler material in layers to the design elevation.

[0024] Compared with the prior art, the present invention has the following significant advantages:

[0025] First, it achieves complete foundation reconstruction: This invention provides a complete four-stage engineering method: splitting and jointing, ice melting and settlement control, coordinated grouting reinforcement, and surface backfilling restoration. Through the intelligent closed-loop controller (triggering grouting based on ground temperature, settlement, and pore pressure data), large deformation and melting settlement are transformed into a controllable drainage and consolidation process. Under the condition of ensuring absolute construction safety, the high-ice-content, high-melting-settlement foundation is completely reconstructed into a dense, homogeneous, high-bearing-capacity, thermally stable composite foundation, effectively solving the problem.

[0026] As a further preferred embodiment of the method described above, step S2 specifically includes the following sub-steps:

[0027] S21. The down-the-hole drilling and casing drilling process is used to form the hole and the casing is simultaneously run in to support the hole wall.

[0028] S22. After drilling to the predetermined depth, remove the down-the-hole drill and casing, leaving the casing. Then, lower the sleeve valve pipe as the central water injection shaft into the hole through the casing. Next, inject the freezing-refreezing sealing medium into the annular gap between the sleeve valve pipe and the hole wall or casing. Stop the operation and wait for the surrounding natural permafrost to completely refreeze the drilled disturbed area and the freezing-refreezing sealing medium under the effect of the cold air, forming a high-strength, water-impermeable artificial permafrost seal.

[0029] S23. Insert a two-position packer into the sleeve valve tube, sit the two-position packer across the sleeve valve at the target split layer, and activate the setting seal to form a high-pressure sealed chamber inside the sleeve valve tube.

[0030] S24. The high-pressure injection system starts pumping water, and the high-pressure water flows into the sealed chamber through the central pipe of the double-position packer; the high-pressure water flows open the sleeve valve, crack the external artificial frozen soil seal, and finally tear a horizontal crack in the natural high-ice-content frozen soil layer.

[0031] S25. By moving the position of the dual packer, precise splitting at different depths and fixed points can be achieved.

[0032] Technical Effects: This invention provides a complete well-drilling process for permafrost. It solves the problem of unstable borehole wall collapse through down-the-hole drilling and casing technology; and utilizes the freeze-thaw sealing method to address sealing failure in the borehole disturbance zone using natural cooling, ensuring the pressure integrity of hydraulic fracturing. Steps S23-S25 achieve precise "layered and targeted" modification of deep permafrost layers, avoiding uneven thawing caused by indiscriminate water injection.

[0033] As a further preferred embodiment of the above method of the present invention, in step S2, for island-shaped or planar frozen soil areas, a plum blossom-shaped unit layout is adopted in which the central water injection shaft is arranged in the center and the extraction water shaft is arranged in the periphery.

[0034] For the foundation of linear engineering projects of highways and railways, a linear layout is adopted in which the central water injection shaft and the water extraction shaft are arranged alternately or intermittently along one or more parallel lines.

[0035] The straight-line distance L between the axis of the central water injection shaft and the axis of the extraction water shaft is obtained by the following formula:

[0036] ,in,

[0037] The volume of fluid injected in a single fracturing operation;

[0038] The volumetric efficiency coefficient considers fluid loss through microcracks for dense, high-ice-content permafrost. Pick ;

[0039] : Average crack width, obtained according to Sneddon's formula.

[0040] Technical Effects: For island-shaped or sheet-like frozen soil (such as large-area foundation treatment), a quincunx-shaped layout with central water injection and peripheral dewatering creates a pressure gradient radiating from the center. This layout utilizes central symmetry, allowing the high-temperature fluid to uniformly sweep across the entire treatment unit under pressure, minimizing dead zones and ensuring uniform thawing of the frozen soil within the square or circular area, preventing differential settlement of the foundation due to uneven thawing. Simultaneously, this formula allows engineers to adjust the frozen soil modulus (which affects...) based on on-site measurements. ) and density (affecting This allows for the reverse derivation of the required water injection volume or well spacing. This makes the concealed underground fissure-making process calculable and controllable, preventing de-icing failures caused by blind construction.

[0041] As a further preferred embodiment of the method described above, in step S2, the water injection pressure for high-pressure hydraulic fracturing and fracture creation is... satisfy:

[0042]

[0043] in, The critical initiation pressure for hydraulic fracturing is calculated using the following formula:

[0044]

[0045] in, For the minimum principal stress, This refers to the tensile strength of frozen soil.

[0046] To determine the ultimate pressure that causes shear uplift of the ground surface, a field water injection test was conducted. Before formal construction, test points were selected for gradual pressure injection, and minute surface uplift deformation was monitored. The injection pressure corresponding to the point where the monitored surface uplift rate showed a sudden change was determined. .

[0047] Beneficial effects: This technical solution achieves "controllable propagation of horizontal cracks" in the special medium of high-ice-content frozen soil by constructing a precise pressure working window, where the lower limit... An overpressure coefficient of 1.05 was set to overcome the tensile strength of frozen soil and the heterogeneity of the formation, ensuring the smooth formation of the crack network and avoiding "false splitting". Upper limit Forced horizontal orientation of the fractures prevents shear failure of the strata, as the overburden (or permafrost topspan) has a limited capacity to withstand pressure. Once the injection pressure exceeds the limit pressure that causes shear uplift of the surface, the strata will no longer tear horizontally, but will instead undergo vertical shear slip, resulting in a conical uplift of the surface. This would instantly destroy the artificial permafrost seal established in step S22, causing high-pressure fluid to erupt to the surface and the operation to fail. By setting a safety limit of 0.8 times, the fluid is forced to seek the path of least resistance (i.e., the horizontal bedding plane) for propagation. This utilizes the geological characteristic that the minimum principal stress is usually vertical stress, forcing the fractures to "grow laterally" only on the horizontal plane, thereby constructing an ideal layered thermal convection network.

[0048] As a further preferred embodiment of the above-mentioned method of the present invention, the value range of the settlement rate control threshold is 2mm / 24h to 10mm / 24h, and the value range of the pore water pressure dissipation threshold (i.e., soil consolidation degree) is 80% to 95%.

[0049] Beneficial Effects: This invention establishes a scientific standard for the "thaw settlement-consolidation-grouting" process conversion in high-ice-content frozen soil by setting clear settlement rate control thresholds (2~10mm / 24h) and dissipation thresholds (80%~95%). The pore water pressure dissipation threshold of 80%~95% ensures the recovery of effective stress in the soil skeleton, guaranteeing the quality of grouting reinforcement. The settlement rate control threshold of 2~10mm / 24h balances the contradiction between "sufficient deformation" and "construction efficiency."

[0050] As a further preferred embodiment of the above method of the present invention, in step S4, the foundation reinforcement grout is a cement-based grout.

[0051] Beneficial effects: This invention uses cement-based grout (such as pure cement grout or cement-fly ash grout) as the core material for foundation reconstruction after thawing and settling, achieving the best balance between technical reliability, economic feasibility, and environmental friendliness. It thoroughly binds the loose and weak soil skeleton after thawing into a "man-made stone body" with high load-bearing capacity, permanently eliminating thermal sensitivity.

[0052] As a further preferred embodiment of the above method of the present invention, the freezing-thawing sealing medium is a water-sand mixture.

[0053] This invention further discloses an active de-icing system for high-ice-content permafrost foundations, used to implement the method for active de-icing of high-ice-content permafrost foundations, comprising:

[0054] The high-pressure injection system is deployed in a safe zone outside the area affected by settlement.

[0055] At least one central water injection shaft is located within the work area, i.e., the non-settlement zone, and the central water injection shaft is connected to the high-pressure injection system via a flexible high-pressure pipeline;

[0056] At least one extraction water shaft is located within the work area and on the periphery of the central injection shaft;

[0057] The ground temperature monitoring unit is used to monitor the temperature of the soil on the ground surface.

[0058] Surface subsidence monitoring unit, used to monitor surface displacement;

[0059] A pore water pressure monitoring unit is used to monitor the pore water pressure in soil.

[0060] The controller is connected to the high-pressure injection system, the ground temperature monitoring unit, the surface subsidence monitoring unit, and the pore water pressure monitoring unit.

[0061] As a further preferred embodiment of the system described above, the surface subsidence monitoring unit includes a robotic total station deployed outside the subsidence influence area and a monitoring prism deployed within the treatment area.

[0062] As a further preferred embodiment of the system described above, it also includes a de-icing water filtration system and a slag discharge port, which are located at the edge of the work area and are used to treat the circulating water collected from the extraction water shaft. Attached Figure Description

[0063] Figure 1 This is a schematic diagram of a high-ice-content frozen soil foundation treatment system according to an embodiment of the present invention;

[0064] Figure 2 This is a schematic diagram of an intelligent integrated management and control process according to an embodiment of the present invention;

[0065] Figure 3 This is a schematic diagram of the down-the-hole drilling and casing drilling process of the present invention;

[0066] Figure 4 This is a schematic diagram of the pipe laying and grouting process;

[0067] Figure 5 This is a schematic diagram of the freeze-thaw sealing process;

[0068] Figure 6 This is a schematic diagram of the layered hydraulic fracturing process of the present invention;

[0069] Figure 7 A three-dimensional schematic diagram of the layered hydraulic fracturing process;

[0070] Figure 8 This is a flowchart of the control logic for the active de-icing method of the present invention for frozen soil in high-ice-content frozen soil foundations;

[0071] Figure 9 This is a schematic diagram of the staggered straight-line well network layout of the present invention.

[0072] The components include: 1. Surface water pumping and filtration system; 2. Pumping well; 3. Melting water filtration system; 4. High-pressure injection system; 5. Melting water tank; 6. Melting water filter residue discharge outlet; 7. Central injection well; 7a. Sleeve valve; 8. Controller; 9. Integrated monitoring device; 9a. Robotic total station; 9b. Monitoring prism; 9c. In-hole sensors (temperature, pore water pressure); 10. Grouting unit; 11. Flexible high-pressure pipe; 12. Down-the-hole drill and casing tool; 12a. Reamer; 13. Casing; 14. Drilling disturbance zone; 15. Freeze-refreeze sealing medium; 16. Artificial frozen soil seal; 17. Two-position packer; 18. Horizontal crack. Detailed Implementation

[0073] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0074] 1. System composition and security layout, refer to Figure 1 , Figure 2A system for comprehensive treatment of impermeable permafrost foundations with high ice content is classified as follows:

[0075] The safe zone, also known as the non-settlement zone, is a stable foundation located outside the predicted settlement impact area.

[0076] The work area, also known as the settlement area, is the foundation treatment area, where large deformation and settlement are expected.

[0077] The core fixed equipment of this invention is installed within the safety zone, including: a surface water pumping and filtration system 1 for drawing water from a surface water source and performing preliminary filtration; a de-icing water tank 5 for storing the filtered water; and a high-pressure injection system 4 configured to provide a pressure sufficient to induce hydraulic fracturing in the frozen soil foundation, for example, 0.5-2.0 MPa, which is higher than the fracturing pressure of frozen soil. The high-pressure injection system 4 is also configured to switch between pumping water and pumping grout provided by the grouting unit 10 according to instructions from the controller 8.

[0078] Grouting unit 10: Used for preparing and conveying grout, such as cement-fly ash grout.

[0079] Controller 8;

[0080] Robotic total station 9a: Deployed in a safe area for non-contact monitoring of settlement.

[0081] The work area, i.e., the settlement zone, is where only equipment that must move with the settlement is installed:

[0082] Central water injection shaft 7 and extraction water shaft 2.

[0083] Monitoring prism 9b is used to scan 9a to calculate settlement.

[0084] The in-hole sensor 9c includes a geothermometer and a pore water pressure gauge. Its cable has an S-shaped bend (not shown) reserved at the wellhead to absorb settlement.

[0085] Safety connection unit 11: used to connect the high-pressure injection system 4 in the safety zone and the central water injection shaft 7 in the settlement zone. The safety connection unit 11 is preferably a flexible high-pressure pipeline with reserved S-shaped or Ω-shaped expansion bends, so that its total length is much greater than the straight-line distance between the two points, thereby completely absorbing the vertical and horizontal displacement caused by the melting of the foundation and ensuring that the pipeline is not broken during the settlement process.

[0086] Ice melting water filtration system 3 and slag discharge port 6: can be installed at the edge of the working area (settling zone) to treat the circulating water collected from the extraction water shaft.

[0087] 2. Well network layout, refer to Figure 1 It can be implemented through various well network layouts, and the specific choice depends on the site conditions.

[0088] In a preferred embodiment, a quincunx-shaped unit layout is adopted, with a central water injection shaft 7 for water injection and extraction shafts 2 arranged around it for extraction. This layout is suitable for processing square or planar areas. The central water injection shaft 7 is located at the center of the processing area, and the extraction shafts 2 are located around the central water injection shaft 7 (such as at the corners of the processing unit).

[0089] In another preferred embodiment, namely the staggered straight-line layout, it is suitable for handling long and narrow areas such as highways and railways, for example... Figure 7 As shown in the diagram, this layout typically includes a row of central injection shafts 7 arranged along the centerline of the treatment area, and a row of extraction shafts 2 arranged on each side (such as at the toe of the roadbed slope); or the central injection shafts 7 and extraction shafts 2 are arranged intermittently along a straight line. This layout can efficiently establish a circulating flow field along the route.

[0090] 3. Construction preparation and high-pressure sealing process, refer to... Figures 3-5 As shown:

[0091] The construction preparation steps are as follows:

[0092] (a) Casing drilling, such as Figure 3 The process employs down-the-hole (DH) drilling with casing. A DH drill string 12, including its reaming blade 12a, is used for high-frequency impact drilling, while the casing 13 is advanced synchronously. The casing 13 provides real-time support to the borehole disturbance zone 14 formed by melting due to drilling disturbance, preventing borehole wall collapse.

[0093] (b) Piping and injection, such as Figure 4 After drilling to the predetermined depth, remove the down-the-hole drill string 12, leaving the casing 13. Then, lower the sleeve valve tube into the hole through the casing 13. Next, inject the freeze-refreeze sealing medium 15 into the annular gap between the sleeve valve tube and the hole wall or casing. The freeze-refreeze sealing medium is preferably a water-sand mixture. The preparation of the freeze-refreeze sealing medium 15 has specific engineering requirements: the sand is preferably clean fine or medium sand to ensure that it can form a high-strength particle skeleton after freezing; the water-sand mixture should be configured as a highly fluid, fully saturated mortar state, that is, to ensure that the pores between all sand particles are completely filled with water. Its beneficial effects are: (1) high fluidity ensures that the medium can be pumped to completely fill the annulus around the well; (2) complete saturation ensures that in step (c) freeze-refreeze, the pore water will freeze into ice, firmly cementing the sand particles into a high-strength, impermeable artificial frozen soil seal 16, thereby providing a reliable pressure seal for the high-pressure hydraulic cracking step.

[0094] (c) Freeze-thaw, such as Figure 5As shown: Stop work and wait, for example, 24-48 hours. Under the influence of the cold energy of the surrounding permafrost, the disturbed borehole zone 14 and the sealing medium 15 will completely refreeze, forming a high-strength, impermeable artificial permafrost seal 16. Acceptance criteria: To ensure that the strength and impermeability of the artificial permafrost seal 16 are sufficient to withstand the high pressure of the subsequent S1 step, acceptance testing must be conducted. One or more of the following criteria are preferred for acceptance testing:

[0095] Temperature indicators: Monitoring by in-hole sensor 9c confirmed that the temperature of the artificial permafrost seal 16 has dropped below freezing point and reached thermal stability with the surrounding natural permafrost temperature, such as -5℃.

[0096] Pressure Indicator (Key Indicator): Before the high-pressure hydraulic fracture-making step, a pressure integrity test is performed. This involves applying a predetermined pressure to the central injection shaft. This pressure should be higher than the injection pressure required to form a circulating convection field, but lower than the ultimate pressure that would cause shear uplift of the surface. The pressure should not decrease significantly within a predetermined time, such as 15 minutes.

[0097] Only after acceptance testing confirms the formation of a high-strength, watertight artificial frozen soil seal 16 can the next step be carried out. This artificial frozen soil seal 16 firmly freezes the sleeve valve pipe within it, achieving a high-pressure seal and solving the problem of leakage along the well wall.

[0098] 4. Layered hydraulic fracturing process, refer to Figure 8 and Figure 7 As shown, the steps are as follows:

[0099] ①In Figure 5 After the freeze-refreeze sealing is completed, a double-position packer 17 is lowered into the interior of the central water injection shaft 7. In this embodiment, the central water injection shaft 7 adopts a sleeve valve pipe.

[0100] ② The double-position packer 17 is precisely positioned so that it straddles the sleeve valve 7a at the target split layer, and the setting seal is activated to form a high-pressure sealed chamber inside the pipe. This precise positioning and straddling are achieved through precise depth control: before step S1, the operator obtains the burial depth of the sleeve valve pipe from the construction records, thereby calculating the precise completion depth of each sleeve valve 7a. The two sealing units of the double-position packer 17 are precisely positioned above and below the target sleeve valve 7a by strictly measuring the total length of the inserted tubing, and then the setting seal is activated to form a high-pressure sealed chamber inside the pipe.

[0101] ③ The high-pressure injection system 4 starts pumping water. The high-pressure water flows through the central pipe of the double-position packer 17 and enters the sealed chamber.

[0102] ④ The high-pressure water flow opens the sleeve valve 7a, cracks the external artificial frozen soil seal 16, and finally tears a horizontal crack 18 in the natural high-ice-content frozen soil layer.

[0103] ⑤ This process can be repeated, that is, by moving the position of the double packer 17, precise splitting at different depths and fixed points can be achieved.

[0104] Methods for determining preliminary survey and construction parameters:

[0105] 1. Determination of Melting Layers: A comprehensive exploration strategy combining exploratory drilling and high-density electrical resistivity tomography (ERT) is employed. Borehole core samples are used to obtain soil physical and mechanical parameters as a baseline. The two-dimensional / three-dimensional spatial distribution range of underground ice is delineated using ERT (to identify high-resistivity anomalies). The key treatment layer is defined as the area below the upper limit of frost to the maximum melting depth line, typically from -2m to -10m underground.

[0106] 2. Formula for determining hydraulic fracturing pressure parameters: To ensure horizontal fracture propagation without damaging the surface cover, the injection pressure... It must be strictly controlled between the initiation pressure and the overlying layer failure pressure.

[0107] Calculation of minimum principal stress (vertical stress):

[0108] ,

[0109] in Let be the unit weight (kN / m³) of the i-th soil layer. Let be the thickness (m) of the i-th soil layer.

[0110] Critical initiation pressure :

[0111] ,

[0112] in The tensile strength of frozen soil (which needs to be measured through in-situ field tests or low-temperature laboratory tests, generally within...) between).

[0113] Construction water injection pressure setting: The working pressure set on the controller. It should meet the following requirements:

[0114] ,

[0115] in This refers to the ultimate pressure that may cause shear uplift of the earth's surface.

[0116] Regarding the method for determining the hole spacing and splitting range: In order to ensure that the horizontal cracks can be effectively connected and cover the entire treatment area, and to avoid melting blind spots, the specific well spacing D needs to be determined before construction.

[0117] Estimation of the effective radius R of a single-hole splitting fracture: Based on linear elastic fracture mechanics and the toughness of frozen soil, the theoretical fracture radius R of a single splitting fracture can be estimated by the injection volume.

[0118] ,

[0119] in: Crack propagation radius (m); : Volumetric efficiency coefficient, taking into account fluid loss through microcracks, for dense permafrost with high ice content. Desirable . Average crack width, crack width It is not a constant value, but rather related to the formation's elastic modulus and pressure. According to the Sneddon formula:

[0120] ,

[0121] in:

[0122] Net pressure within the crack ( ).

[0123] : Elastic modulus of frozen soil.

[0124] Poisson's ratio.

[0125] 3.2 Arrangement principles and calculation formulas for the spacing of de-icing holes:

[0126] Simply connecting cracks does not signify the completion of ice melting. Ice melting is a process involving the coupling of heat conduction and convection. (Pore spacing) The design must ensure that the heat-affected zone of adjacent holes can effectively cover the entire processing area without leaving any dead corners.

[0127] 3.2.1 Calculation of the advance distance of the melting front

[0128] According to the approximate solution to the Stefan problem, a single crack acts as a heat source, transferring heat to the permafrost on both the upper and lower sides. During the cyclic thawing time... Within $t$, melting depth (Perpendicular to the crack surface) can be estimated as:

[0129] ,

[0130] in:

[0131] Circulating hot water temperature ( ).

[0132] Frozen soil phase transition temperature ).

[0133] Latent heat of frozen soil (J / kg).

[0134] The correction factor for enhancing convective heat transfer is typically taken as... .

[0135] 3.2.2 Calculation formula for hole spacing L to ensure complete ice melting

[0136] To ensure an effective circulating flow field is formed between the central injection shaft and the extraction shaft, and that the cracks in adjacent units can overlap, the hole spacing L must be less than the sum of the crack diameters.

[0137] When using a quincunx (triangular) well layout pattern, it is recommended that the fracture overlap rate be no less than 30% to ensure strong connectivity.

[0138]

[0139] Recommended engineering design formula:

[0140] ,

[0141] in To ensure a safety margin for overlap, if the crack ends are required to just touch, However, connectivity is extremely poor at this point. To ensure the formation of a wide fluid channel, it is recommended to take... .

[0142] By combining the crack radius formula, we obtain the final formula for calculating the hole spacing:

[0143] ,

[0144] Strategy for arranging the spacing of de-icing holes:

[0145] To ensure complete ice melting, in addition to calculating spacing, a strategic design is also needed in the plan layout:

[0146] Staggered row and column arrangement: suitable for highway and railway subgrades.

[0147] The water injection holes are located on the centerline of the roadbed.

[0148] The pumping holes are located outside the toe of the slope on both sides of the roadbed.

[0149] The longitudinal spacing is set according to the calculated value L, and the injection and extraction holes are staggered along the longitudinal direction. This creates a zigzag flow path, forcing the hot fluid to sweep across the largest area.

[0150] Unitized closed layout: suitable for large areas.

[0151] The hexagonal or quadrilateral unit with a center injection and peripheral extraction is used.

[0152] Key strategy: In the middle and late stages of ice melting, switch the functions of the water injection holes and the water pumping holes (reverse circulation) to use the reverse flushing of fluid to eliminate unmelted areas caused by dead zones in flow rate.

[0153] 5. The four-stage method and intelligent control logic, refer to... Figure 2 , Figure 8 :

[0154] S1: The high-pressure hydraulic joint-forming controller 8 commands the high-pressure injection system 4 to start and execute. Figure 8 The fracturing process shown establishes a horizontal fracture channel 18 between the central injection shaft 7 and the extraction shaft 2. To ensure successful fracturing, the controller 8 controls the operating pressure of the high-pressure injection system 4. The rupture pressure must be higher than that of the target stratum. The rupture pressure It can be determined by the minimum principal stress That is, vertical stress and tensile strength of frozen soil Estimate In Implementation Case 1, the rupture pressure was 1.6 MPa, and controller 8 controlled the working pressure. Slightly higher than this value, such as 1.65 MPa, to ensure proper suture formation.

[0155] S2: The circulating ice melting and settling control controller 8 instructs the high-pressure injection system 4 to switch to medium-pressure, high-flow-rate circulating water injection, and simultaneously instructs the pump set of the extraction water shaft 2 to start, establishing a circulating flow field. During this stage, the controller 8 performs dual monitoring tasks to manage the settling process:

[0156] This system adopts a phased, variable-frequency monitoring strategy, with the following specific indicators:

[0157] 1. High-frequency monitoring phase:

[0158] Monitoring frequency: The robotic total station automatically scans all monitoring prisms once every hour.

[0159] Safety warning threshold: When the hourly settlement at any monitoring point exceeds 20 mm / h or the daily cumulative settlement exceeds 200 mm / d, the controller will automatically trigger an alarm and stop water injection to prevent sudden collapse.

[0160] 2. Stability determination phase:

[0161] Monitoring frequency: Data is collected every 4 hours.

[0162] The specific definition of the "stability threshold" triggered by grouting is as follows:

[0163] The following two conditions must be met simultaneously for a site to be deemed ready for grouting:

[0164] (a) Settlement rate control threshold: The average settlement rate of the surface monitoring points is less than 2 mm / d for 3 consecutive days (i.e., the threshold is set at 2 mm / d).

[0165] (b) Pore pressure dissipation threshold: The excess pore water pressure dissipation in the soil reaches 85% or more.

[0166] S3: Collaborative grouting reinforcement, controller 8 continuously executes. Figure 7 The judgment logic shown is as follows:

[0167] ① Judgment 1, ice melting is complete: The ground temperature has met the preset ice melting completion threshold, for example, as described above, the ground temperature at the target depth has been above 0.5℃ for 48 hours;

[0168] ② Judgment 2, Settlement Stability: The surface settlement rate is less than a settlement rate control threshold preset by an engineer, for example, less than 5mm / 24 hours;

[0169] ③ Judgment 3, consolidation is complete: and the dissipation of pore water pressure 9c has reached a preset dissipation threshold, for example, the dissipation of excess pore water pressure exceeds 90%.

[0170] Trigger: When the above three conditions are met simultaneously, controller 8 determines that the foundation has completed its main consolidation and reached stability, and automatically triggers step S3, as follows. Figure 2 As shown, the grouting unit 10 and the high-pressure injection system 4 are instructed to start the grouting operation.

[0171] Loop: If the condition is not met, return to S2 and continue the ice melting loop.

[0172] S4: After the surface backfill is completed and the grout has solidified, fill the settled surface with qualified filler material in layers until the design elevation is restored.

[0173] Implementation Case 1: Comprehensive Treatment Project for Subgrade Fusion and Consolidation of New Highways in High-Altitude Areas

[0174] Background: In a newly constructed highway project at a high altitude, there is an island-shaped layer of soil-ice located at a depth of -6 to -8 meters below the roadbed design line. The melting of this ice layer is expected to cause a massive surface settlement of 1.2 meters. To ensure the long-term stability of the highway after completion, it was decided to adopt the comprehensive treatment scheme described in this invention before roadbed filling construction, dividing the road section into 10m x 10m square units.

[0175] Implementation steps:

[0176] S0: System Deployment

[0177] (a) Safety Zone and Well Network Layout: A safety zone is established on a stable foundation 50 meters outside the boundary of the treatment unit, where the controller 8, high-pressure injection system 4, ice-melting water tank 5, grouting unit 10, and robotic total station 9a are centrally deployed. A central water injection shaft 7 is drilled in the center of the treatment unit (operation area), and a water extraction shaft 2 is drilled in each of the four corners.

[0178] (b) Drilling and sealing, Figure 3 As shown:

[0179] Using a down-the-hole drill and casing drilling rig 12, boreholes are drilled and simultaneously a 152mm casing 13 is lowered to prevent the collapse of the drilling disturbance zone 14, i.e., the mud casing caused by borehole melting. The center hole is drilled to -9 meters, and the four corner holes are drilled to -8.5 meters.

[0180] Remove drill string 12, insert a 73mm sleeve valve tube into the center hole, and insert a 90mm extraction water vertical well pipe 2 into the four corner holes.

[0181] A freeze-refreeze sealing medium 15, preferably a water-sand mixture, is injected between the inner casing 13 and the sleeve valve tube of all wells in the annular gap.

[0182] Operations were halted and a 36-hour wait was initiated. The sealing medium 15 and the borehole disturbance zone 14 were then completely refrozen using the natural ground temperature of -5°C, forming an artificial frozen soil seal 16. A pressure test was subsequently conducted to verify the integrity of the wellhead seal.

[0183] (d) Safety connection: Using safety connection unit 11, namely a DN50 high-pressure flexible pipeline with a 4-meter-long S-shaped expansion bend, connect the high-pressure injection system 4 in the safety zone to the wellhead of the central water injection shaft 7 in the work area.

[0184] S1: High-pressure hydraulic joint creation, refer to... Figure 8 and Figure 7 As shown:

[0185] Controller 8 starts the high-pressure injection system 4.

[0186] By using the double-position packer 17 inserted into the sleeve valve tube, the valve is precisely positioned at a depth of -8 meters at the sleeve valve 7a, and the setting seal is initiated.

[0187] Water injection began, and the water pressure steadily rose to 1.65 MPa within 30 seconds. When it was slightly higher than the rupture pressure of 1.6 MPa, the pressure was monitored to drop instantly to 0.7 MPa, indicating that horizontal crack 18 had formed.

[0188] Raise the double packer 17 to -6 meters and repeat the splitting process.

[0189] During the fracturing process, almost synchronous water level (pressure) responses were monitored in all four peripheral extraction wells 2, verifying that the horizontal fracture 18 had successfully connected all the wells.

[0190] S2: Circulating De-icing and Settlement Control:

[0191] Controller 8 instructs high-pressure injection system 4 to switch to medium-pressure (0.5 MPa), high-flow (100 m³ / h) circulating water injection mode. At the same time, all pump sets in the extraction wells 2 are started to establish a circulating flow field with central injection and peripheral extraction.

[0192] The core task of controller 8 has been switched to settlement control. The robot total station 9a begins to monitor the settlement of the monitoring prism 9b in the work area 24 hours a day, and the sensor 9c in the borehole uploads ground temperature and pore water pressure data in real time.

[0193] During the 15 days of cyclical de-icing, the average ground subsidence in the work area was 1.15 meters as expected. The flexible expansion bend of safety connection unit 11 was stretched, and the system operated safely throughout the entire process without any pipeline leaks or equipment damage.

[0194] S3: Synergistic grouting reinforcement:

[0195] On the 15th day, the intelligent judgment logic of controller 8 was triggered:

[0196] Judgment 1: Controller 8 confirms that the ground temperature at a depth of -6 to -8 meters in the borehole sensor 9c has been above 0.5℃ for 48 consecutive hours, meeting the conditions for completing the de-icing process.

[0197] Judgment 2: Data from the 9a total station of the robot shows that the average surface settlement rate is less than 5 mm / 24 hours, which meets the settlement rate control threshold.

[0198] Judgment 3: Data from the pore water pressure gauge 9c shows that 92% of the excess pore water pressure has dissipated, meeting the threshold for pore water pressure dissipation.

[0199] Controller 8 determines that the foundation has reached stability and automatically triggers step S3, instructing grouting unit 10 to start.

[0200] The high-pressure injection system 4 is switched to pumping PO 42.5 cement grout (water-cement ratio 0.8:1), which is injected into the voids of the compacted soil through the central water injection shaft 7. A total of 22m³ of grout is injected until the injection pressure of 0.8MPa is reached.

[0201] S4: Surface backfilling and restoration:

[0202] After the grout has solidified for 72 hours, a 1.2-meter-thick layer of graded gravel is backfilled on the foundation that has settled by 1.15 meters, in layers of 30cm each, and then compacted to 95% heavy compaction standard using a heavy roller, so that the roadbed reaches the design elevation.

[0203] Implementation Results: Through the four-stage comprehensive treatment of this invention, the high-melt-settlement foundation containing soil and ice layers in this section was safely and controllably reconstructed into a dense, high-strength composite foundation. This solution not only proactively eliminates future melt-settlement problems, but also solves the construction safety problem under large deformation settlement through the safety design of the safety connection unit 11 and the intelligent settlement control of the controller 8.

[0204] Implementation Case 2: Roadbed Defect (Settlement) Treatment Project (Linear Engineering) for an Operating Highway on the Qinghai-Tibet Plateau

[0205] Background: A section of existing highway (a secondary highway) located on the Qinghai-Tibet Plateau has experienced severe uneven settlement (maximum settlement of 0.8 meters) and longitudinal and transverse cracks in its pavement due to the melting of the high-ice-content permafrost beneath the roadbed during long-term operation. To completely eradicate the damage, it was decided to close the 200-meter-long affected section and reconstruct the foundation using the solution of this invention.

[0206] Implementation steps:

[0207] Preparation: Close traffic, remove the old road structure, and level the site.

[0208] System deployment, refer to Figure 7 :

[0209] (a) Since the damaged road section is long and narrow, this case study preferably adopts an alternating straight-line layout, as shown in the attached diagram. Figure 7 As shown.

[0210] (b) A central water injection shaft 7 shall be installed every 10 meters along the center line of the highway.

[0211] (c) At 6 meters on each side of the center line (to the toe of the roadbed slope), two rows of water extraction shafts 2 are set up, with each row of shafts spaced 10 meters apart, and their positions are staggered with the central water injection shaft 7, for a total of 40 water extraction shafts 2.

[0212] (d) Safety zone equipment is deployed in a stable area 50 meters away from the roadbed.

[0213] Construction preparation, such as Figure 3 :

[0214] Using the same down-the-hole drilling and casing 12 and freeze-refreeze process as in Implementation Case 1, drilling, casing installation, and high-pressure sealing operations were completed for all 60 wells, 20 central water injection shafts, and 40 extraction shafts.

[0215] S1: High-pressure hydraulic joint formation:

[0216] The controller 8 starts the high-pressure injection system 4, and through the double-position packer 17, injects water into the 20 central water injection shafts 7 of the center line one by one and layer by layer (-6 meters and -8 meters).

[0217] The formed horizontal crack 18 extended to both sides, successfully connecting the staggered pumping shafts 2 located on both sides.

[0218] S2: Circulating De-icing and Settlement Control:

[0219] All 20 central water injection shafts 7 were activated for circulating water injection, while 60 extraction shafts 2 were activated for pumping water.

[0220] The controller 8 actively monitors the settlement of the entire 200-meter road section (average settlement of 0.75 meters) through the robot total station 9a.

[0221] S3: Collaborative grouting reinforcement: When controller 8 determines that the ice melting of the entire road section has been completed and the settlement rate and pore pressure have reached the stable threshold (refer to...). Figure 8 When the logic is true, the grouting unit 10 is automatically triggered. The high-pressure injection system 4 switches to pumping foundation reinforcement grout.

[0222] In this case (linear engineering), cement-fly ash slurry is preferred to balance cost and filling effect. PO 42.5 cement and Grade II fly ash are mixed at a mass ratio of 1:1, and the water-cement ratio (the ratio of water to the total mass of cementitious materials) is controlled at 0.9:1.

[0223] The controller 8 instructs the five central water injection shafts 7 along the center line to perform segmented grouting reinforcement on the compacted foundation until the preset rejection pressure of 0.8 MPa is reached.

[0224] S4: Surface backfilling and restoration:

[0225] After the foundation is reinforced, the subgrade material is backfilled and compacted to the design elevation, and the road surface is restored.

[0226] Implementation Results: The solution of this invention, through a complete four-stage intelligent process and an efficient staggered straight well network layout, reconstructs the unstable, high-ice-content permafrost beneath the long, strip-shaped road section into a solid, uniform, and stable new composite foundation in one go, completely eradicating the thaw settlement problem and ensuring the long-term operational safety of the highway.

[0227] The specific embodiments described herein are intended to aid in understanding the invention, but are not intended to limit the scope of the invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions of this invention after reading the above description, as long as they do not depart from the spirit and scope of the invention, should fall within the protection scope defined by the claims of this invention.

Claims

1. A method for active de-icing of frozen soil in high-ice-content permafrost foundations, characterized in that, Includes the following steps: S1. Determine the location and thickness of the high-ice-content permafrost layer within the strata; S2. Based on the location and thickness of the high-ice-content permafrost layer determined in step S1, at least one central water injection shaft and multiple extraction shafts are constructed around the central water injection shaft on the high-ice-content permafrost foundation. Layered, targeted high-pressure hydraulic fracturing is implemented in the central water injection shaft to create cracks, which then extend horizontally within the permafrost layer until they connect with the extraction shafts, forming a circulating convection field to melt the permafrost. During this process, surface subsidence, ground temperature, and pore water pressure are monitored in real time. When the following three conditions are simultaneously met, proceed to step S3. Condition 1: Ground temperature is greater than 0℃; Condition 2: The surface subsidence rate is less than the subsidence rate control threshold; Condition 3: The pore water pressure dissipation reaches the dissipation threshold. S3. Stop water injection and inject foundation reinforcement grout into the settled and compacted soil through the central water injection shaft; S4. After the foundation reinforcement grout has solidified, backfill the upper part of the settled surface area with filler material in layers to the design elevation.

2. The method for active melting of frozen soil in high-ice-content frozen soil foundations according to claim 1, characterized in that, Step S2 specifically includes the following sub-steps: S21. The hole is formed by down-the-hole drilling and casing drilling, and the casing (13) is simultaneously lowered to support the hole wall. S22. After drilling to the predetermined depth, remove the down-the-hole drill and casing tool (12), leaving the casing (13). Then, lower the sleeve valve pipe as the central water injection shaft into the hole through the casing (13). Next, inject the freezing-refreezing sealing medium (15) into the annular gap between the sleeve valve pipe and the hole wall or the casing. Stop the operation and wait. Under the effect of the coldness of the surrounding natural frozen soil, the drilling disturbance area (14) and the freezing-refreezing sealing medium (15) will completely refreeze, forming a high-strength, impermeable artificial frozen soil seal (16). S23. Insert a double-position packer (17) into the inside of the sleeve valve tube, sit the double-position packer (17) across the sleeve valve (7a) at the target split layer, and start the setting seal to form a high-pressure sealed chamber inside the sleeve valve tube. S24, the high-pressure injection system (4) starts pumping water, and the high-pressure water flows into the sealed chamber through the central pipe of the double-position packer (17); the high-pressure water flows open the sleeve valve (7a), crack the external artificial frozen soil seal (16), and finally tear a horizontal crack (18) in the natural high-ice-content frozen soil layer. S25. By moving the position of the double packer (17), precise splitting at different depths and fixed points can be achieved.

3. The method for active de-icing of frozen soil in high-ice-content frozen soil foundations according to claim 1, characterized in that, In step S2, for island-shaped or planar frozen soil areas, a plum blossom-shaped unit layout is adopted, with the central water injection shaft (7) arranged in the center and the extraction water shaft (2) arranged in the periphery. For the foundation of linear engineering projects of highways and railways, a linear layout is adopted in which the central water injection shaft (7) and the water extraction shaft (2) are arranged alternately or intersecting along one or more parallel lines; The straight-line distance L between the axis of the central water injection shaft and the axis of the extraction water shaft is obtained by the following formula: ,in, The volume of fluid injected in a single fracturing operation; The volumetric efficiency coefficient, considering fluid loss through microcracks, is used for dense, high-ice-content permafrost. Pick ; : Average crack width, obtained according to Sneddon's formula.

4. The method for active melting of frozen soil in high-ice-content frozen soil foundations according to claim 1, characterized in that, In step S2, the water injection pressure for high-pressure hydraulic fracturing and fracture creation... satisfy: ， in, The critical initiation pressure for hydraulic fracturing is calculated using the following formula: ， in, For the minimum principal stress, This refers to the tensile strength of frozen soil. To determine the ultimate pressure that causes shear uplift of the ground surface, a field water injection test was conducted. Before formal construction, test points were selected for gradual pressure injection, and minute surface uplift deformation was monitored. The injection pressure corresponding to the point where the monitored surface uplift rate showed a sudden change was determined. .

5. The method for active de-icing of frozen soil in high-ice-content frozen soil foundations according to claim 1, characterized in that, In step S2: the settling rate control threshold ranges from 2 mm to 10 mm / 24h; the pore water pressure dissipation threshold ranges from 80% to 95%.

6. The method for active de-icing of frozen soil in high-ice-content frozen soil foundations according to claim 1, characterized in that, In step S4, the foundation reinforcement grout is a cement-based grout.

7. The method for active de-icing of frozen soil in high-ice-content frozen soil foundations according to claim 2, characterized in that, The freezing-thawing sealing medium (15) is a water-sand mixture.

8. An active de-icing system for permafrost foundations with high ice content, used to implement the method for active de-icing of permafrost foundations with high ice content as described in any one of claims 1 to 7, characterized in that, include: The high-pressure injection system (4) is installed in a safe zone outside the settlement influence area; At least one central water injection shaft (7) is set in the working area, i.e., the non-settlement area, and the central water injection shaft (7) is connected to the high-pressure injection system (4) through a flexible high-pressure pipeline; At least one extraction well (2) is located in the working area and outside the central injection well (7); The ground temperature monitoring unit is used to monitor the temperature of the soil on the ground surface. Surface subsidence monitoring unit, used to monitor surface displacement; A pore water pressure monitoring unit is used to monitor the pore water pressure in soil. The controller (8) is connected to the high-pressure injection system (4), the ground temperature monitoring unit, the surface subsidence monitoring unit and the pore water pressure monitoring unit.

9. The active de-icing system for high-ice-content permafrost foundations according to claim 8, characterized in that, The surface subsidence monitoring unit includes a robotic total station (9a) deployed outside the subsidence influence area and a monitoring prism (9b) deployed within the treatment area.

10. The active de-icing system for high-ice-content permafrost foundations according to claim 8, characterized in that, It also includes a melting ice water filtration system (3) and a slag discharge port (6), which are located at the edge of the work area to treat the circulating water collected by the extraction water shaft (2).

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