Mountain wind machine foundation frost heaving and thawing sinking comprehensive prevention and control treatment method

Abstract

The application discloses a mountain wind machine foundation frost heaving and thawing sinking comprehensive prevention and control processing method and relates to the field of mountain wind machine foundation frost heaving and thawing sinking processing. Before construction, the minimum design thickness of the continuous graded gravel replacement layer is calculated according to the site natural frost depth parameters combined with the site slope direction, slope and machine position. Before the main body of the construction foundation, a ring-shaped drainage ditch is excavated on the top of the slope, the gravel replacement layer, the water-permeable anti-slurry layer and the sealed high-density polystyrene temperature insulation layer are layered and laid around the foundation, and the temperature insulation and drag reduction coating is brushed on the side wall of the foundation. The improved planting soil, three-dimensional geotechnical net mat and cold-resistant deep-rooted vegetation are laid in the diffusion water area outside the foundation to form an ecological holding layer, and the water-permeable flexible pipe is arranged along the ring direction in the replacement layer. The application is adapted to the non-uniform heat flow distribution characteristics of the mountain terrain, reasonably compresses the construction cost under the premise of guaranteeing the frost heaving prevention and control effect, and cuts off the frost heaving occurrence inducement from the source through the multi-dimensional water-heat collaborative resistance and control structure.

Description

Technical Field

[0001] This invention relates to the field of frost heave and thaw settlement treatment for mountain wind turbine foundations, and in particular to a comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations. Background Technology

[0002] Currently, the mainstream frost heave control technology in the industry is the replacement method. Its core principle is to excavate the highly frost-sensitive silty clay, silt, and other soils within the foundation bearing layer and replace them with non-frost-heave materials such as crushed stone and gravel, thus blocking the material basis for frost heave. This method has mature technology and readily available materials, and is widely used in plain wind power projects with stable control effects. However, the frost depth calculation method adapted to plain areas does not consider the non-uniform heat flow distribution characteristics caused by slope aspect and gradient in mountainous areas. When applied to mountainous turbine sites, it is prone to problems such as insufficient replacement thickness leading to frost depth intrusion into the bearing layer and causing frost heave damage, or excessive replacement thickness leading to a significant increase in excavation and material costs. At the same time, the existing replacement layer does not have a dedicated drainage structure, and residual water and slope infiltration water during construction can easily remain in the replacement layer, which can exacerbate the frost heave potential.

[0003] Another mainstream technology is the thermal insulation layer method, which involves laying extruded polystyrene insulation boards under the foundation slab to block the transmission of external low temperatures to the lower soil, reducing the frost depth of the bearing layer. This method is fast to construct and can reduce the self-weight load of the foundation, and has been gradually promoted in wind power projects in cold regions in recent years. However, this type of technology is not suitable for the characteristics of mountain slopes with strong water catchment and freeze-thaw erosion. The joints of the insulation boards are prone to forming thermal bridges or seepage channels. The foundation sidewalls are not equipped with drag-reducing protective structures and are easily deformed by tangential frost heave forces. At the same time, the surface protective structures such as drainage layers can easily lead to water infiltration after frost heave cracking, further aggravating the risk of frost heave around the foundation.

[0004] Both existing technologies simply copy mature experiences from plains areas without systematically adapting to the topography, hydrological and thermal characteristics, and ecological needs of mountainous regions. They generally suffer from shortcomings such as insufficient targeted prevention and control, difficulty in cost management, and lack of dynamic monitoring methods for later operation and maintenance, and cannot meet the engineering needs of large-scale wind power development in mountainous areas. Summary of the Invention

[0005] This invention proposes a comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations, in order to solve the problems mentioned in the prior art, such as poor adaptability, high cost, insufficient long-term reliability, and lack of dynamic operation and maintenance mechanism in existing frost heave and thaw settlement prevention and control methods for mountain wind turbine foundations.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations, comprising the following steps: S1. In view of the characteristics of mountainous terrain with large undulations, significant spatial differences in frost depth, and complex slope runoff paths, a detailed geological survey was conducted on the proposed wind turbine site to determine the standard frost depth, frost heave rate of each soil layer, thaw settlement coefficient, groundwater level, slope gradient, and solar radiation duration on slope aspect. The surface of the site was cleared of loose rocks, humus, and frost-sensitive topsoil. The foundation was leveled with a transverse slope of no more than 5%. A closed ring-shaped intercepting drainage ditch was excavated along the outer edge of the site's influence range to block the mountain slope runoff from entering the foundation's influence area from the source, thus preventing the soil moisture content from increasing the frost heave potential. S2. Excavate the highly frost-sensitive soil layer within a predetermined depth range below the standard frost depth line from the base. From bottom to top, lay a coarse sand leveling layer, a permeable grout-blocking layer, and a continuous graded crushed stone replacement layer. The minimum thickness of the replacement layer is determined by calculating the synergistic resistance relationship between the non-uniform frost depth in mountainous terrain. The calculation relationship is as follows: The parameters are uniformly measured using general engineering units. The minimum design thickness of the continuous graded crushed stone replacement layer, the standard frost depth of the natural site, and the actual laying thickness of the insulation layer are all in meters. The thermal conductivity of the natural frost-susceptible soil and the equivalent thermal conductivity of the replacement layer and the insulation layer are all in watts per meter Kelvin. The slope angle of the natural slope where the machine is located is in degrees. The slope aspect heat flow correction coefficient is a dimensionless empirical value, with 0.15 for sunny slopes and 0.25 for shady slopes.

[0007] The calculations fully adapt to the non-uniform freezing depth characteristics caused by the heat flow shift in the mountains, and reduce the amount of replacement work while ensuring that the freezing front does not intrude into the bearing layer. A high-density polystyrene insulation layer is laid on the top surface of the replacement layer, and the joints of the insulation layer are sealed by hot-melt welding to avoid the formation of thermal bridges or water seepage channels; S3. Tie the wind turbine extended foundation steel reinforcement frame above the insulation layer, lay prestressed anchor bolts that penetrate the replacement layer and extend into the lower stable soil layer, and cover the outside of the anchor bolts with insulating and anti-corrosion sleeves. Cast the wind turbine foundation structure with frost-resistant and impermeable concrete in one go. Construct an outward-sloping drainage structure on the top surface of the foundation to quickly drain the surface water of the foundation; S4. Surface ecological retention: Backfill the surface of the replacement area around the foundation with planting soil mixed with anti-frost modifier, and plant cold-resistant deep-rooted herbaceous vegetation to achieve ecological retention of the slope around the foundation and reduce surface soil erosion and freeze-thaw erosion.

[0008] Furthermore, the annular intercepting drainage ditch is set at a distance of 3 to 5 meters from the outer edge of the wind turbine foundation. A composite geomembrane seepage prevention layer is laid at the bottom of the ditch. The geomembrane splices are hot-melt welded, with an overlap width of not less than 20 centimeters. The ditch is filled with washed graded pebbles with a particle size of 3 to 5 centimeters to form a drainage blind ditch. The bottom of the ditch is set with a longitudinal slope of not less than 0.3%. The drainage outlet is connected to the natural mountain gully or the existing drainage system. During the excavation of the intercepting drainage ditch, isolated rocks and loose deposits on the mountain are avoided. Dry-laid stone slope protection is used for the weak sections of the ditch wall to prevent the ditch wall from collapsing and blocking the drainage channel during the rainy season. This prevents water from accumulating in the ditch and seeping into the foundation's influence layer, completely cutting off the lateral seepage replenishment path of the slope water catchment. This solves the problem that the existing mountain wind turbine foundation drainage system does not consider the large kinetic energy of the slope water catchment and the random seepage path, and eliminates the external moisture conditions caused by frost heave.

[0009] Furthermore, the permeable grout barrier layer is composed of a double-layer polypropylene flat filament woven geotextile sandwiched with a 2 cm thick polyethylene closed-cell foam board. The geotextile has a unit area mass of not less than 400 grams per square meter, a tensile strength of not less than 10 kN per meter, and an equivalent pore size that meets the requirements that the lower layer of coarse sand particles cannot penetrate and the upper layer of concrete grout cannot seep down. At the same time, it allows the permeable water in the replacement layer to be freely drained laterally. When laying the geotextile, it should be kept flat and wrinkle-free, with an overlap width of not less than 15 cm between adjacent sections. It is connected by nylon rope stitching to prevent soil particles from entering the grout barrier layer and affecting the permeability. The compression permanent deformation rate of polyethylene closed-cell foam board is no more than 2%, which can buffer the normal stress generated by frost heave, avoid stress concentration causing cracking of the foundation slab, and at the same time ensure that the pores of the replacement layer are unobstructed for a long time and are not blocked by grout, thus solving the problem that the existing replacement structure is easily blocked by cement grout and loses its drainage capacity.

[0010] Furthermore, the continuously graded crushed stone replacement layer contains no silt or clay impurities. The crushed stone particles are continuously graded with a diameter of 2 to 5 cm. After layered vibration compaction, the compaction degree is not less than 96%, and the compaction thickness of a single layer does not exceed 30 cm. The replacement layer is internally equipped with permeable hoses with a diameter of 100 mm wrapped in geotextile filter cloth, arranged alternately in the transverse and longitudinal directions. The permeable hoses are spaced 2 meters apart, with a longitudinal slope of not less than 0.5%. The permeable hoses are laid straight without bends, and the overlaps of the filter cloth are tightly sewn to prevent crushed stone particles from entering the pipes and causing blockages. The ends of the permeable hoses are connected to a ring-shaped drainage ditch to promptly drain stagnant and infiltrated water and gravity water released during freeze-thaw cycles within the replacement layer. This reduces the soil moisture content within the replacement layer, weakening the material basis for frost heave from its root cause and solving the problem of poor drainage and water accumulation exacerbating frost heave within the existing replacement layer.

[0011] Furthermore, the density of the high-density polystyrene insulation layer is not less than 30 kg / m³, the compressive strength is not less than 200 kPa, the water absorption rate is not greater than 1%, the distance of the insulation layer extending beyond the outer edge of the wind turbine foundation is not less than 1.2 times the local standard frost depth, the insulation layer adopts a staggered laying method, and the joints of adjacent panels are staggered by not less than 50 cm. Before laying the insulation layer, it is confirmed that the surface of the coarse sand leveling layer is flat and free of sharp stones to avoid puncturing the insulation board during construction and causing a decrease in insulation performance. A 0.2 mm thick plastic film is laid on the top surface of the insulation layer to prevent mortar from entering the joints of the slab during concrete pouring and affecting the insulation effect. The low thermal conductivity of the film blocks the transmission of external low temperature to the bearing layer, reduces the freeze-thaw cycle intensity and freezing depth of the underlying soil, and solves the problems of heat leakage at the joints and excessive freezing depth in existing insulation structures.

[0012] Furthermore, the prestress value applied by the prestressed anchor bolt is determined according to 1.2 times the estimated maximum frost heave force of the foundation. The length of the anchor bolt's anchoring section extending into the lower stable soil layer is not less than one-third of the total anchor bolt length. Calcium-based grease is filled between the anchor bolt and the insulating and anti-corrosion sleeve to achieve a seal. The insulating and anti-corrosion sleeve is made of high-density polyethylene with a wall thickness of not less than 3 mm. A water-swellable rubber waterstop ring is installed at the contact position between the lower end of the sleeve and the top surface of the stable soil layer, with a water-swellable rate of not less than 300%. After the anchor bolts are installed, the sealing performance of each sleeve is tested. Concrete pouring is only carried out after confirming that there are no leaks or damage. This prevents cement slurry from entering the sleeve and affecting the prestress application effect, blocks the channel for water to seep down around the anchor bolt, and simultaneously counteracts the frost heave normal uplift force through rigid anchoring, preventing uneven uplift deformation of the foundation and solving the problems of insufficient frost pull-out resistance of existing foundations and easy corrosion of anchor bolts due to water seepage.

[0013] Furthermore, air-entraining agent and polypropylene coarse fiber are added to the frost-resistant and impermeable concrete. The amount of air-entraining agent is controlled according to the air content of the concrete from four to five percent. The length of the polypropylene coarse fiber is 19 mm, and the amount added per cubic meter of concrete is 0.9 kg. The frost resistance grade of the formed concrete is not lower than F300 and the impermeability grade is not lower than P10. The layered insertion vibration process is used to ensure the compactness during the pouring process. After the concrete is poured, it is kept moist and kept warm for curing for no less than 14 days. During the curing period, construction loads should not be directly applied to the foundation surface to avoid structural damage. The side surface of the foundation in contact with the surrounding soil is uniformly coated with a polyurethane thermal insulation and anti-corrosion coating with a thickness of no less than 2 mm. The coating adhesion is no less than 1.5 MPa and the thermal conductivity is no more than 0.03 W / m Kelvin. This reduces the freezing cohesion between the foundation sidewall and the frozen soil, reduces the drag effect of frost heave tangential force on the foundation, improves the long-term frost resistance and durability of the structure, and solves the problems of insufficient frost resistance and excessive tangential frost heave force on the sidewall of the existing concrete foundation.

[0014] Furthermore, the apron structure is cast using frost-resistant concrete with a strength grade of not less than C30, and its width extends 20 cm beyond the outer edge of the insulation layer. Cold-drawn steel wire mesh with a diameter of 4 mm is laid inside the apron, with a longitudinal and transverse spacing of 150 mm. The surface of the apron has an outward slope of not less than 5%. When the apron is poured, a geomembrane isolation layer with a thickness of 2 mm is laid at the contact point with the surrounding soil to prevent the apron structure from cracking due to frost heave deformation of the soil. A 2-cm wide expansion joint is reserved at the junction of the drainage apron and the side wall of the wind turbine foundation. The joint is filled with asphalt-impregnated hemp fibers to a depth of not less than 1.5 times the width of the joint. The joint opening is sealed with neutral silicone sealant to a thickness of not less than 5 mm, ensuring a firm bond with the structures on both sides without gaps. This prevents surface water from seeping down the foundation joint and reduces the thermal bridging effect at the foundation side wall, thus solving the problems of easy cracking of the existing drainage apron structure and increased frost heave around the foundation due to water seepage at the joint.

[0015] Furthermore, the antifreeze modifier added to the planting soil is composed of fly ash, rice husk charcoal and polyacrylamide mixed in a mass ratio of 60:35:5. The modifier dosage is 15% of the dry mass of the planting soil, and the frost heave rate of the modified planting soil is no more than 1%. The thickness of the planting soil backfill should be no less than 30 cm. After backfilling, lay a three-dimensional geonet with a unit area mass of no less than 260 grams per square meter on the slope. The overlap width of the geonet should be no less than 10 cm. Fix it with U-shaped iron nails. Select cold-resistant deep-rooted herbaceous plants such as old wheatgrass and crested wheatgrass. The sowing density is 30 grams per square meter. After the plants are sown, cover them with a thin layer of non-woven fabric to retain moisture. Remove the non-woven fabric after the seedling rate reaches more than 90% to ensure that the survival rate of the plants meets the requirements for soil stabilization. By reducing the sensitivity of surface soil to frost heave with soil conditioners, and by using vegetation roots and netting to hold the slope soil in place, the soil loss caused by freeze-thaw erosion and runoff can be reduced, thus solving the problem of weak erosion resistance of the surface soil around the existing foundation and uneven thawing settlement caused by soil erosion.

[0016] Furthermore, after the wind turbine foundation construction is completed, frost heave and thaw settlement monitoring sensors are evenly deployed in the soil layers at different depths around the foundation. The sensors include three types: moisture content sensors, temperature sensors, and displacement sensors. The deployment depths are 20 cm, 50 cm below the ground surface, and the local standard frost depth line, with 4 monitoring points evenly deployed in the circumference at each depth. The monitoring data is connected to the wind farm's remote monitoring platform via a solar-powered low-power wireless transmission module. During the freeze-thaw period, the data collection frequency is once per hour, and during the non-freeze-thaw period, it is once per day. When the monitored value reaches 80% of the foundation's allowable deformation value, an early warning signal is automatically issued. After the early warning signal is triggered, maintenance personnel can promptly carry out drainage and insulation reinforcement at abnormal points to prevent the deformation from continuing to expand and causing wind turbine operation failures. This achieves dynamic perception and early handling of freeze-thaw settlement risks, solving the existing problems of no real-time monitoring of freeze-thaw settlement risks and untimely detection of deformation exceeding limits, which affect the safe operation of wind turbines.

[0017] Compared with existing technologies, the beneficial effects of this invention are: This invention determines the thickness of the replacement layer by quantifying the relationship between non-uniform freezing depth and resistance control in mountainous areas. It adapts to the non-uniform heat flow distribution characteristics caused by slope aspect and gradient in mountainous areas. Under the premise of ensuring that the freezing front never intrudes into the underlying bearing layer, it reduces unnecessary replacement engineering work. It effectively solves the problem that existing freezing depth calculation methods in plain areas do not consider the heterogeneity of heat flow in mountainous terrain, resulting in insufficient replacement thickness leading to frost heave structure damage or excessive thickness leading to increased project investment. It balances the reliability of prevention and control with cost economy.

[0018] This invention forms a multi-dimensional hydrothermal synergistic control system by constructing a ring-shaped intercepting drainage ditch, a replacement layer drainage network, a permeable grout barrier layer, a sealed high-density thermal insulation layer, and a thermal insulation and drag-reducing coating on the foundation sidewall. This system cuts off the path of slope runoff infiltration into the foundation's influence zone from the source, promptly drains water trapped in the replacement layer, blocks the transmission of low temperatures to the bearing layer, and weakens the drag effect of frost heave tangential forces on the foundation. It effectively solves the problem that existing control structures are not adapted to the characteristics of strong water runoff and strong freeze-thaw cycles in mountainous areas, and have inherent defects such as seepage channels and thermal bridges, resulting in insufficient long-term reliability of frost heave control.

[0019] This invention utilizes a combined retaining structure formed by improved planting soil, three-dimensional geonet, and cold-resistant deep-rooted vegetation, along with a dynamic monitoring and early warning system for frost heave and thaw settlement throughout the entire life cycle. This not only enhances the frost heave and runoff erosion resistance of the surface soil surrounding the foundation, reducing the risk of soil erosion and uneven thaw settlement, but also captures abnormal frost heave and thaw settlement signals in real time and triggers early warnings, facilitating early risk management by maintenance personnel. It effectively solves the problems of existing technologies, such as the lack of long-term operation and maintenance monitoring methods, delayed detection of deformation risks, high handling costs, and poor compatibility of rigid protective structures with mountain ecosystems.

[0020] This invention is suitable for wind power development projects in various mountainous areas at high latitudes and altitudes in my country. It can cover all types of turbine locations with different slopes and aspects. The required materials are all commonly used building materials in engineering. There is no need to change the existing main structure design of the wind turbine foundation. It can be implemented by relying on conventional wind power construction teams. It can be directly embedded into the existing wind power engineering construction and operation and maintenance process, and has extremely strong industry promotion and adaptability. Attached Figure Description

[0021] Figure 1 This is an overall flowchart of the comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations proposed in this invention; Figure 2 This is a flowchart of the site survey and drainage foundation pretreatment process of the present invention; Figure 3 This is a flowchart illustrating the construction process of the layered heat exchange structure and thermal insulation of the present invention. Figure 4 This is a flowchart illustrating the construction process of wind turbine foundation pouring and freeze-thaw resistance enhancement according to the present invention. Figure 5 This is a flowchart of the surface ecological retention and real-time monitoring and early warning process of the present invention. Detailed Implementation

[0022] 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 only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Reference Figures 1 to 5 This invention discloses a comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations, which includes four core implementation stages: site survey and foundation pretreatment, layered barrier structure laying, wind turbine foundation pouring and frost-resistant strengthening, and surface ecological fixation. Each stage is closely connected to form a full-chain prevention and control system from water and heat blocking and structural strengthening to long-term fixation and dynamic monitoring.

[0024] First, site survey and foundation pretreatment were carried out. In view of the characteristics of the mountainous terrain with large undulations, significant spatial differences in frost depth, and complex slope water runoff paths, a detailed geological survey was carried out on the proposed wind turbine site. A combination of drilling, long-term ground temperature monitoring and in-situ frost heave rate testing was used to measure the standard frost depth, frost heave rate of each soil layer, thaw settlement coefficient, groundwater level, slope gradient and solar radiation duration on slope aspect at each point. Loose rocks, humus and frost-sensitive topsoil within a thickness of 30 to 50 centimeters were removed from the site. A grader and manual leveling were used to level the foundation to a transverse slope of no more than 5% to avoid local depressions and water accumulation.

[0025] A closed-loop intercepting and drainage ditch was excavated along the outer edge of the station's influence area to block the flow of water from the mountain slope into the foundation's influence area from the source. This prevents the soil moisture content from increasing the potential for frost heave and addresses the core defects commonly found in the construction of existing mountain wind turbine foundations, such as insufficient survey accuracy and unorganized infiltration of water from the slope that exacerbates frost heave.

[0026] Secondly, the layered resistance structure laying operation is carried out. A hydraulic excavator is used in conjunction with manual cleaning to remove the highly frost-sensitive soil layer from the base to the preset depth below the standard frost depth line. Over-excavation is strictly prohibited to disturb the lower stable rock and soil layer. If over-excavation occurs in some areas, the same type of crushed stone is used for backfilling and compaction.

[0027] The layers are laid sequentially from bottom to top: a coarse sand leveling layer, a permeable grout-blocking layer, and a continuous graded crushed stone replacement layer. The coarse sand leveling layer uses clean medium-coarse sand with a mud content of no more than 3%, and is 10 cm thick. After laying, it is compacted using a plate vibratory compactor to ensure that the surface flatness error does not exceed 5 mm, providing a uniform support surface for the upper structure and avoiding local stress concentration that could lead to damage to the insulation board. The minimum laying thickness of the continuous graded crushed stone replacement layer is determined by calculating the synergistic resistance control relationship of non-uniform freezing depth in mountainous areas. The calculation process relies on the evolution law of freezing depth in multi-layer media in unsteady heat conduction theory, and derives a quantitative relationship by combining the heat flow migration characteristics of mountain slopes. All parameters in the formula are measured using general engineering units. The minimum design thickness of the continuous graded crushed stone replacement layer is in meters. The standard frost depth of the natural site is in meters. The actual laying thickness of the high-density polystyrene insulation layer is in meters. The thermal conductivity of the natural frost-susceptible soil is in watts per meter Kelvin. The equivalent thermal conductivity of the replacement layer and insulation layer combination is in watts per meter Kelvin. The slope angle of the natural slope where the machine is located is in degrees. The slope aspect heat flow correction coefficient is a dimensionless empirical value, which is 0.15 for sunny slopes and 0.25 for shady slopes.

[0028] The entire calculation process is integrated into the on-site construction parameter calculation module. After the on-site technicians input the basic parameters obtained from the survey, the module can automatically output the design thickness value of the replacement layer. This fully adapts to the non-uniform freezing depth characteristics caused by the shift of mountain heat flow along the slope direction. Under the premise of ensuring that the freezing front always stays within the replacement layer and does not intrude into the underlying bearing layer, it maximizes the reduction of unnecessary replacement work. This solves the defects of existing freezing depth calculation methods in plain areas that do not consider the influence of mountain slope aspect and slope, resulting in thin replacement thickness leading to frost heave damage or excessive replacement thickness causing project waste.

[0029] After the replacement layer is laid, a high-density polystyrene insulation layer is laid on top of it. The joints of the insulation panels are continuously welded and sealed using a special hot melt welding gun. The weld width of the joint is not less than 3 cm. After welding, the sealing of the weld is checked one by one to avoid the formation of thermal bridges or water seepage channels at the joints. After the insulation layer is laid, heavy machinery is prohibited from walking directly on the panel surface to prevent the panel from cracking and breaking.

[0030] After the layered insulation structure is laid, the wind turbine foundation is poured and the antifreeze strengthening work is carried out. The wind turbine extended foundation steel reinforcement skeleton is tied above the insulation layer according to the design drawings. Prestressed anchor bolts are laid through the replacement layer and extend into the lower stable soil layer. The anchor bolts are fixed with steel positioning frames during installation to ensure that the verticality deviation of the anchor bolts does not exceed one-thousandth. The outer side of the anchor bolts is covered with an insulating and anti-corrosion sleeve. The two ends of the sleeve are temporarily sealed to prevent debris from entering the sleeve during construction.

[0031] The frost-resistant and impermeable concrete, which is centrally mixed at a commercial concrete batching plant, is transported to the site by tanker truck and then continuously poured into the wind turbine foundation structure in one go. During the pouring process, the vibrator rod is kept away from directly touching the anchor bolts, insulation layer and sleeve. After the foundation is poured and before the concrete has initially set, an outward-sloping drainage structure base is constructed on the top surface of the foundation to quickly drain the water on the foundation surface and prevent water from seeping down along the foundation joints.

[0032] Finally, surface ecological stabilization work was carried out. The surface of the replacement area around the foundation was backfilled with planting soil mixed with antifreeze modifier. Large stones and construction waste were avoided during the backfilling of the planting soil. After leveling, cold-resistant deep-rooted herbaceous plants were sown to achieve ecological stabilization of the slope around the foundation, reduce soil erosion and freeze-thaw erosion of the surface soil, and solve the defects of poor compatibility between the existing rigid protection structure and the mountain ecology and soil loss caused by long-term freeze-thaw erosion.

[0033] This invention also discloses the specific construction parameters and functional implementation method of the annular intercepting drainage ditch. The annular intercepting drainage ditch is set at a distance of 3 to 5 meters from the outer edge of the wind turbine foundation. The ditch body has an inverted trapezoidal cross-section with an upper width of 80 cm, a lower width of 40 cm, and a depth of 60 cm. A two-layer geomembrane composite geomembrane is laid at the bottom of the ditch as an anti-seepage layer. The geomembrane splices are hot-melt welded, with an overlap width of not less than 20 cm. After welding, an air-filling test is conducted to check the sealing performance and prevent water from seeping into the ditch. The ditch is filled with washed graded pebbles with a particle size of 3 to 5 cm to form a drainage blind ditch. The pebble filling height is level with the top of the ditch. The bottom of the ditch is set with a longitudinal slope of not less than 0.3%. The drainage outlet connects to the natural mountain gully or the existing road drainage system.

[0034] When encountering isolated boulders during the excavation of drainage ditches, static crushing methods should be used to handle them. Blasting construction is strictly prohibited to prevent loosening of the surrounding soil. For ditch wall sections with a slope greater than 25 degrees, 30 cm thick dry-laid stone slope protection should be used to prevent slope runoff from eroding the ditch wall and causing it to collapse and block the drainage channel. This will prevent water from accumulating in the ditch and seeping into the foundation layer, completely cutting off the lateral seepage supply path of slope water. This will solve the problems of the existing mountain wind turbine foundation drainage system not taking into account the large kinetic energy of slope water, random seepage paths, and easy blockage of drainage ditches, and eliminate the external moisture conditions caused by frost heave.

[0035] This invention also discloses the specific structure and performance parameters of the permeable grout-blocking layer. The permeable grout-blocking layer is composed of a double-layer polypropylene flat filament woven geotextile sandwiched with a 2 cm thick polyethylene closed-cell foam board. The upper geotextile layer primarily functions to prevent cement grout from seeping into the pores of the replacement layer during the pouring of the upper concrete layer. The lower geotextile layer primarily functions to prevent coarse sand particles from entering the replacement layer and causing pore blockage due to seepage. The intermediate polyethylene closed-cell foam board can buffer the normal stress generated by winter frost heave, preventing stress concentration from directly acting on the foundation slab and causing structural cracking. The geotextile has a unit area mass of not less than 400 grams per square meter, a tensile strength of not less than 10 kN / m, and an equivalent pore size in the range of 0.07 to 0.2 mm, meeting the requirements that coarse sand particles in the lower layer cannot penetrate and that grout from the upper concrete pouring layer cannot seep down, while allowing permeable water in the replacement layer to drain freely laterally.

[0036] When laying geotextile, it should be kept flat and wrinkle-free, without any gaps or tightness. The overlap width between adjacent sections should not be less than 15 cm, and high-strength nylon rope should be used for double-stitched connections with a stitch spacing of no more than 10 mm to prevent soil particles from entering the grout barrier layer through the joints and affecting the permeability. The compression permanent deformation rate of polyethylene closed-cell foam board should not exceed 2%, and the water absorption rate should not exceed 0.5%. During laying, each piece should be spliced ​​and aligned without gaps between the pieces to ensure that the permeability, grout barrier, and buffering functions of the grout barrier layer are achieved synergistically. This solves the problem that existing replacement structures are easily blocked by cement grout, resulting in loss of drainage capacity, and the lack of buffer space for frost heave stress, leading to foundation cracking.

[0037] This invention also discloses the construction process and drainage structure of the continuous graded crushed stone replacement layer. The crushed stone particles in the continuous graded crushed stone replacement layer are washed with water and do not contain powdery clay particles or weathered and weak particle impurities. The crushed stone particle size distribution is a continuous distribution of 2 to 5 cm, with a non-uniformity coefficient greater than 5 and a curvature coefficient in the range of 1 to 3. This ensures that the pore structure formed after compaction is stable and has smooth water conduction, avoiding the reduction of drainage capacity caused by fine particles filling the pores.

[0038] The crushed stone paving adopts a layered spreading and layered vibration compaction process. The thickness of a single layer should not exceed 30 cm. A 20-ton vibratory roller is used to compact the stone at least 6 times. Small plate vibratory rollers are used to compact the corners and edges. The upper layer of material can only be laid after the compaction degree is tested to be no less than 96%.

[0039] The replacement layer is constructed with 100mm diameter permeable hoses wrapped in geotextile filter cloth, arranged alternately in the horizontal and vertical directions. The hoses are spaced 2 meters apart, and a 10cm thick layer of crushed stone is placed at the bottom of each hose to ensure a longitudinal slope of no less than 0.5%. The hoses are laid straight without bends, and special straight connectors are used for pipe section connections. The outer filter cloth is folded and tightly wrapped at the joints to prevent crushed stone particles from entering the pipes and causing blockages. The ends of the permeable hoses are connected to the gravel layer of the ring-shaped intercepting drainage ditch at a 2% slope to promptly drain the stagnant and infiltrated water in the replacement layer, as well as the gravity water released during the spring freeze-thaw period. This keeps the volumetric moisture content of the soil in the replacement layer below 12% in the long term, thereby weakening the material basis for frost heave from the root and solving the problem of the lack of drainage structure in the existing replacement layer, which leads to water retention and exacerbates frost heave.

[0040] This invention also discloses the layout parameters and construction requirements of the high-density polystyrene insulation layer. The high-density polystyrene insulation layer uses extruded polystyrene boards with a density of not less than 30 kg / m³, a compressive strength of not less than 200 kPa, a water absorption rate of not more than 1%, and a thermal conductivity of not more than 0.03 W / m Kelvin, ensuring that it does not produce excessive compression deformation and that its thermal insulation performance remains stable over a long period of time under the long-term action of the upper foundation load.

[0041] The insulation layer should extend beyond the outer edge of the wind turbine foundation by at least 1.2 times the local standard frost depth to prevent lateral intrusion of low temperatures at the foundation edge, which could lead to excessive frost depth in some areas. The insulation layer should be laid using a staggered joint method, with the joints of adjacent panels staggered by at least 50 cm. There should be no continuous vertical joints. Before laying the insulation layer, inspect each panel of the coarse sand leveling layer, removing any sharp stones and protruding hard lumps to prevent puncturing the insulation board during construction and causing a decrease in insulation performance.

[0042] After the insulation layer is laid, a 0.2 mm thick polyethylene plastic film isolation layer is laid on top of it. The overlap width of the film is not less than 20 cm. It is sealed with tape to prevent cement mortar from entering the joints of the slab during concrete pouring and forming thermal bridges that affect the insulation effect. The low thermal conductivity of the film blocks the transmission of external low temperature to the bearing layer, controlling the annual temperature fluctuation range of the lower bearing layer to within 2 degrees Celsius. This reduces the freeze-thaw cycle intensity and freezing depth of the lower soil, solving the problems of heat leakage at the joints of existing insulation structures and local freezing depth exceeding the limit due to insufficient laying range.

[0043] This invention also discloses the installation process and sealing protection structure of prestressed anchors. The prestressed anchors are made of high-strength alloy steel. The prestress value applied to a single anchor is determined according to 1.2 times the estimated maximum frost heave force of the foundation. The pre-applied tensile stress is used to offset the normal heave force generated by frost heave, thus preventing the foundation from separating from the underlying soil.

[0044] The length of the anchoring section extending into the lower stable soil layer shall not be less than one-third of the total length of the anchoring bolt. The anchoring section shall be firmly bonded to the stable soil layer using anchoring adhesive or high-strength grouting material to provide sufficient pull-out bearing capacity.

[0045] The entire outer side of the anchor bolt is covered with an insulating and corrosion-resistant sleeve made of high-density polyethylene. The sleeve wall thickness is not less than 3 mm. The space between the anchor bolt and the insulating and corrosion-resistant sleeve is filled with calcium-based grease to achieve a seal. On the one hand, this isolates the anchor bolt from direct contact with the surrounding soil and concrete to avoid electrochemical corrosion of the anchor bolt. On the other hand, it allows the anchor bolt to undergo slight elastic deformation within the sleeve to coordinate the deformation difference between the foundation and the anchor bolt.

[0046] A water-swellable rubber sealing ring is installed at the contact point between the lower end of the casing and the top surface of the stable soil layer. The sealing ring is 2 cm thick, with an inner diameter matching the outer diameter of the casing. Its water expansion rate is no less than 300%. During installation, the sealing ring is tightly fitted onto the outside of the casing and pressed against the soil layer to block the channels for water seepage along the perimeter of the anchor bolts. After the anchor bolts are installed, the sealing performance of each casing is tested. Air pressure is used to confirm there are no leaks before subsequent concrete pouring. This prevents cement slurry from entering the casing and causing the anchor bolts to solidify with the concrete, affecting the prestressing effect. Simultaneously, the rigid anchoring action counteracts the frost heave normal uplift force, preventing uneven uplift deformation of the foundation and addressing the problems of insufficient frost pull-out resistance of the existing foundation and the anchor bolts' susceptibility to water corrosion, which reduces structural durability.

[0047] This invention also discloses the mix proportions and construction process of frost-resistant and impermeable concrete. The frost-resistant and impermeable concrete is mixed with ordinary Portland cement with a strength grade of not less than 42.5. Cement varieties with poor frost resistance, such as pozzolanic Portland cement, must not be used. An appropriate amount of air-entraining agent and polypropylene coarse fiber are added to the concrete. The air-entraining agent is a rosin-based thermal polymer air-entraining agent, and its dosage is controlled according to the air content of the concrete after mixing (4% to 5%). The introduced micro-closed air bubbles can buffer the internal stress generated by ice crystal growth during frost heave, improving the concrete's resistance to freeze-thaw cycles. The polypropylene coarse fiber has a length of 19 mm and a diameter of 0.1 mm, with a dosage of 0.9 kg per cubic meter of concrete. The fiber is evenly and randomly distributed within the concrete, inhibiting the generation of early shrinkage cracks and improving the concrete's crack resistance.

[0048] After mix proportion testing, the frost resistance grade of the formed concrete is no less than F300 and the impermeability grade is no less than P10, meeting the structural durability requirements under long-term freeze-thaw cycles in mountainous and cold regions. The concrete pouring process employs a layered immersion vibration method, with each layer not exceeding 50 cm in thickness. The vibrator is inserted 5 to 10 cm into the lower layer of concrete to ensure compaction and prevent segregation caused by under-vibration or over-vibration.

[0049] After the concrete is poured, it should be covered with geotextile and watered to keep it moist and warm. The curing period should not be less than 14 days. During the curing period, water should not be sprayed when the ambient temperature is below 5 degrees Celsius. Insulating cotton blankets should be used for curing to avoid construction loads acting directly on the foundation surface and causing structural damage.

[0050] A polyurethane thermal insulation and anti-corrosion coating with a thickness of not less than 2 mm is uniformly applied to the side surface of the foundation in contact with the surrounding soil. The coating adhesion is not less than 1.5 MPa and the thermal conductivity is not greater than 0.03 W / m Kelvin. Before coating, the concrete laitance and debris on the foundation sidewall surface are cleaned to ensure that the coating is continuous and without any gaps. This reduces the freezing cohesion between the foundation sidewall and the frozen soil, reduces the drag effect of frost heave tangential force on the foundation, improves the long-term frost resistance and durability of the structure, and solves the problems of insufficient frost resistance of existing concrete foundations and excessive frost heave force on the sidewalls leading to foundation deformation.

[0051] This invention also discloses the construction and building requirements of the drainage apron structure. The drainage apron structure is cast using frost-resistant concrete with a strength grade of not less than C30 and a frost resistance grade of not less than F200. The width of the drainage apron extends 20 cm beyond the outer edge of the insulation layer, and the thickness of the drainage apron is 15 cm. Cold-drawn steel wire mesh with a diameter of 4 mm is laid inside the drainage apron, with a longitudinal and transverse spacing of 150 mm. The mesh is positioned in the middle of the concrete thickness of the drainage apron to improve its crack resistance and prevent breakage due to frost heave or settlement. The surface of the drainage apron has an outward slope of not less than 5% to ensure that rainwater and snowmelt can quickly drain into the surrounding intercepting drainage ditches, preventing water accumulation.

[0052] During the pouring of the drainage apron, a 2 mm thick geomembrane isolation layer is laid at the contact point with the surrounding soil to reduce the force of soil frost heave deformation on the drainage apron structure and prevent the apron from cracking due to frost heave. A 2 cm wide expansion joint is reserved at the junction of the drainage apron and the side wall of the wind turbine foundation. The joint is filled with asphalt-impregnated hemp fiber to a depth of not less than 1.5 times the joint width. The joint opening is sealed with neutral silicone weather-resistant sealant to a thickness of not less than 5 mm, ensuring a firm and seamless bond with the structures on both sides. This prevents surface water from seeping down the foundation joint and weakens the thermal bridging effect at the foundation side wall, reducing the local frost depth around the foundation and solving the problems of easy cracking of the existing drainage apron structure and water seepage at the joint exacerbating frost heave around the foundation.

[0053] This invention also discloses the improvement and vegetation planting process of the surface ecological holding layer. The planting soil is preferably selected from the original surface mature soil excavated around the site, and large pieces of gravel, tree roots and construction waste in the soil are removed. The antifreeze modifier added to the planting soil is composed of fly ash, rice husk charcoal and polyacrylamide in a mass ratio of 60:35:5. The modifier dosage is 15% of the dry mass of the planting soil. Fly ash and rice husk charcoal can optimize the particle size distribution of the planting soil, reduce the capillary rise height of the soil, and reduce the migration of water to the freezing front in winter. Polyacrylamide can enhance the aggregate structure stability of the soil and improve the erosion resistance of the surface soil.

[0054] Indoor geotechnical tests verified that the frost heave rate of the improved planting soil is no more than 1%, classifying it as non-frost-susceptible soil. The planting soil backfill thickness should be no less than 30 cm, spread and leveled in layers, and then moderately compacted, with the compaction degree controlled at around 80% to meet the porosity requirements for vegetation growth. After backfilling, a three-dimensional geonet with a unit area mass of no less than 260 grams per square meter is laid on the slope, with an overlap width of no less than 10 cm. It is fixed with 15 cm long U-shaped iron nails, spaced 1 meter apart, to ensure a tight fit between the geonet and the planting soil surface.

[0055] Cold-resistant, deep-rooted herbaceous plants such as *Leymus chinensis* and *Leymus chinensis* were selected and sown in a 1:1 ratio by weight at a density of 30 grams per square meter. After sowing, the plants were covered with a 1-cm layer of fine soil, followed by a thin non-woven fabric to retain moisture. Regular watering was carried out. Once the germination rate of the plants reached over 90%, the non-woven fabric was removed to ensure that the survival rate of the plants met the requirements for soil stabilization.

[0056] By reducing the sensitivity of surface soil to frost heave through soil conditioner, and by using the combined action of vegetation roots and three-dimensional mesh to stabilize the slope soil, soil loss caused by freeze-thaw erosion and runoff can be reduced, thus solving the problem of weak erosion resistance of the surface soil around the existing foundation and uneven settlement caused by soil erosion around the foundation.

[0057] This invention also discloses the deployment and early warning logic of a dynamic monitoring system for frost heave and thaw settlement. After the wind turbine foundation construction is completed, frost heave and thaw settlement monitoring sensors are uniformly deployed circumferentially in soil layers at different depths around the foundation. The sensors include three types: frequency domain reflectance moisture content sensors, platinum resistance temperature sensors, and vibrating wire displacement sensors. The deployment depths are 20 cm, 50 cm below the ground surface, and the local standard frost depth line. Four monitoring points are uniformly deployed circumferentially at each depth. The fixed end of the displacement sensor is anchored into the lower stable rock and soil layer, and the measuring end deforms synchronously with the soil at the corresponding depth, which can accurately capture the displacement of frost heave and thaw settlement.

[0058] All sensors are connected to the on-site data acquisition terminal via waterproof cables. The data acquisition terminal is equipped with a solar power panel and lithium battery pack, enabling long-term stable operation without external mains power. The collected monitoring data is transmitted to the wind farm's remote monitoring platform via a LoRa low-power wireless transmission module. During the freeze-thaw period (November to May of the following year), data is collected hourly; outside the freeze-thaw period, it is collected daily, reducing equipment power consumption and extending its service life. The monitoring platform has a built-in frost heave and thaw settlement early warning algorithm. When the monitored soil frost heave displacement or thaw settlement value reaches 80% of the foundation's allowable deformation value, an early warning signal is automatically sent to the wind farm's operation and maintenance personnel via platform pop-ups and SMS push notifications. The early warning information includes the circumferential location of the abnormal point, its burial depth, real-time monitoring value, risk level, and preliminary handling guidelines, avoiding blind investigation by operation and maintenance personnel.

[0059] After the warning signal is triggered, maintenance personnel can promptly take targeted measures for abnormal locations: if the moisture content exceeds the limit, the drainage blind ditches and permeable hoses in the corresponding area will be cleared to drain the stagnant water; if the local frost heave is too large, insulation materials will be laid in the corresponding location to reduce the transfer of cold; if the topsoil is lost, the planting soil will be backfilled and improved, and vegetation will be replanted.

[0060] The entire monitoring system eliminates the need for frequent on-site data collection by personnel. It can continuously track the dynamics of frost heave and thaw settlement around the foundation throughout the entire life cycle of the wind turbine, preventing structural safety failures such as tower tilting and excessive operating vibration caused by the continuous expansion of deformation. It enables dynamic perception and early handling of frost heave and thaw settlement risks, solving the problems of lack of routine real-time monitoring of frost heave and thaw settlement risks in existing mountain wind turbine foundations, untimely detection of deformation exceeding limits, and delayed handling that affects the safe operation of the wind turbine.

[0061] Reference Figure 1 This flowchart illustrates the macroscopic construction and monitoring logic for preventing frost heave and thaw settlement disasters in mountain wind turbine foundations. At the start of the project, a geological survey of the turbine site is conducted to determine key parameters such as frost depth. Unsuitable topsoil is cleared, and a drainage system is excavated to pre-treat the foundation. Subsequently, frost-sensitive soil layers are removed, and from bottom to top, a leveling layer, a permeable grout-blocking layer, a replacement layer, and a thermal insulation layer are laid to completely block the underground conduction of moisture and low temperatures. The framework is then tied to the grout-blocking structure, anti-corrosion anchors are installed, and frost-resistant and impermeable concrete is poured to complete the main body of the wind turbine foundation. After the foundation is formed, frost-resistant improved soil is backfilled around the perimeter, and vegetation is planted to achieve ecological stabilization. Finally, a real-time sensor monitoring network covering the area around the foundation is constructed to provide 24 / 7 early warning of frost heave and thaw settlement hazards, forming a closed-loop prevention and control system throughout the entire lifecycle.

[0062] Reference Figure 2This flowchart details the geological environment survey and foundation drainage protection work in the early stages of the project. Construction personnel first thoroughly surveyed the standard frost depth, soil frost heave rate, and groundwater level of the site, and comprehensively cleared sensitive topsoil such as loose stones and humus that are highly susceptible to frost heave. After leveling the foundation according to a strict transverse slope, a closed ring-shaped intercepting drainage ditch was systematically excavated at the outer edge of the affected area. To ensure drainage efficiency, a composite geomembrane was laid inside the ditch for seepage prevention, and a blind drainage ditch was constructed using washed graded pebbles. Finally, by setting a reasonable longitudinal slope, the blind ditch was connected to a natural mountain gully or the existing drainage system, cutting off the seepage path of surface water to the bottom of the wind turbine foundation at its source.

[0063] Reference Figure 3 This flowchart illustrates the installation process of a layered barrier structure used to cut off capillary water rise and low-temperature water transfer. The construction team first excavates the base soil layer below the standard frost line, then meticulously lays a coarse sand leveling layer and a permeable grout barrier layer from bottom to top. This grout barrier layer prevents the upper cement grout from seeping down while allowing lateral water conduction. On top of this, a continuously graded crushed stone replacement layer is compacted in layers, with permeable hoses interlaced inside to connect to drainage ditches, quickly draining any stagnant water. Finally, a high-density polystyrene insulation layer, calculated based on site thermal conductivity parameters, is laid extensively on top of the replacement layer. The joints are tightly sealed using hot-melt welding, and a plastic film isolation layer is applied, creating a robust, cold-proof, and water-resistant barrier.

[0064] Reference Figure 4 This flowchart illustrates the main structure pouring and frost-resistant waterproofing measures for the wind turbine extended foundation. After the steel reinforcement cage is tied above the insulation layer, prestressed anchor bolts are precisely installed, reaching the underlying stable rock strata. The anchor bolts are fully encased in insulating and corrosion-resistant sleeves, supplemented with calcium-based grease and water-swellable rubber sealing rings to completely seal the tiny channels through which water seeps down the anchor bolts. Subsequently, frost-resistant and impermeable concrete, incorporating air-entraining agents and fibers, is poured in layers using continuous vibration compaction. Once the foundation is formed, a thick polyurethane insulating and corrosion-resistant coating is evenly applied to the foundation sidewalls. Furthermore, an frost-resistant drainage structure with specific expansion joints is constructed outwards from the top of the foundation. Utilizing the outward slope and sealant treatment, rapid and safe drainage of rainwater from the top surface of the foundation is achieved.

[0065] Reference Figure 5This flowchart illustrates the slope ecological protection and automated safety monitoring mechanism in the later stages of foundation construction. In the replacement area around the foundation, an antifreeze modifier made from a mixture of fly ash, rice husk charcoal, and polyacrylamide is used to modify the backfill soil, significantly reducing the frost heave rate of the shallow soil. After ensuring the backfill thickness meets the standards, a three-dimensional geonet is laid and deep-rooted, cold-resistant herbaceous vegetation is planted to achieve windbreak, soil stabilization, and ecological restoration. Simultaneously, frost heave and thaw settlement monitoring sensors are embedded at different depths around the foundation to collect core physical data such as moisture content, normal displacement, and settlement in real time and at high frequency. This data is synchronized to a remote monitoring platform in real time via a low-power wireless transmission module, automatically triggering an alarm when safety thresholds are exceeded, ensuring the long-term stable operation of the wind turbine.

[0066] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations, characterized in that, Includes the following steps: S1. Conduct geological surveys at the proposed site of the mountain wind turbine, determine the standard freezing depth, frost heave rate of each soil layer, thaw settlement coefficient and groundwater level, clear the surface of the site of loose rocks, humus and frost-sensitive topsoil, level the foundation with a transverse slope of no more than 5%, and excavate a closed ring-shaped intercepting drainage ditch along the outer edge of the site's influence range to block the runoff from the mountain slope into the foundation's influence area. S2. Excavate the high frost-susceptible soil layer within the preset depth range below the standard frost depth line from the base. Lay a coarse sand leveling layer, a permeable grout barrier layer, and a continuous graded crushed stone replacement layer from bottom to top. Lay a high-density polystyrene insulation layer on the top surface of the replacement layer. The joints of the insulation layer are sealed by hot-melt welding. S3. Tie the wind turbine extended foundation steel skeleton above the insulation layer, lay prestressed anchor bolts that penetrate the replacement layer and extend into the lower stable soil layer, cover the outside of the anchor bolts with insulating and anti-corrosion sleeves, pour anti-freeze and anti-seepage concrete to form the wind turbine foundation structure in one go, and construct an outwardly inclined drainage structure on the top surface of the foundation to drain the water accumulated on the foundation surface. S4. Backfill the surface of the replacement area around the foundation with planting soil mixed with antifreeze modifier, and plant cold-resistant deep-rooted herbaceous vegetation to achieve ecological stabilization of the slope around the foundation.

2. The comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations according to claim 1, characterized in that, The bottom of the annular intercepting drainage ditch is laid with a composite geomembrane impermeable layer, and the ditch is filled with washed graded pebbles to form a drainage blind ditch. The bottom of the ditch is set with a longitudinal slope of not less than three per thousand, and the drainage outlet is connected to the natural mountain gully or the existing drainage system.

3. The comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations according to claim 1, characterized in that, The permeable grout barrier layer is composed of a double-layer polypropylene flat filament woven geotextile sandwiched with a 2 cm thick polyethylene closed-cell foam board. The equivalent pore size of the geotextile meets the requirements that the coarse sand particles in the lower layer cannot penetrate and the concrete grout in the upper layer cannot seep down, while allowing the permeable water in the replacement layer to be freely drained laterally.

4. The comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations according to claim 1, characterized in that, The crushed stone particles in the continuous graded crushed stone replacement layer are free of silt and clay impurities. After being compacted in layers, the compaction degree is not less than 96%. The replacement layer is equipped with permeable hoses wrapped with geotextile filter cloth arranged horizontally and vertically. The ends of the permeable hoses are connected to a ring-shaped drainage ditch to promptly drain the stagnant seepage water in the replacement layer.

5. The comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations according to claim 1, characterized in that, The thickness of the high-density polystyrene insulation layer is determined by calculation based on the site frost depth and thermal conductivity parameters. The insulation layer extends beyond the outer edge of the wind turbine foundation by a distance of not less than 1.2 times the local standard frost depth. A plastic film isolation layer is laid on the top surface of the insulation layer.

6. The comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations according to claim 1, characterized in that, The length of the anchoring section of the prestressed anchor bolt extending into the lower stable soil layer is not less than one-third of the total length of the anchor bolt. The anchor bolt and the insulating and anti-corrosion sleeve are sealed with calcium-based grease. A water-swellable rubber water-stop ring is installed at the contact position between the lower end of the sleeve and the top surface of the stable soil layer to block the channel for water to seep down along the periphery of the anchor bolt.

7. The comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations according to claim 1, characterized in that, The antifreeze and impermeable concrete is mixed with an appropriate amount of air-entraining agent and polypropylene coarse fiber. The concrete antifreeze grade is not lower than F300 and the impermeability grade is not lower than P10. The pouring process adopts a layered insertion vibration process. The side surface of the foundation in contact with the surrounding soil is uniformly coated with a polyurethane thermal insulation and anti-corrosion coating with a thickness of not less than 2 mm.

8. The comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations according to claim 1, characterized in that, The apron structure is made of antifreeze concrete and its width extends 20 cm beyond the outer edge of the insulation layer. A 2 cm wide expansion joint is reserved at the junction of the apron and the side wall of the wind turbine foundation. The joint is filled with asphalt hemp fiber and then sealed with neutral silicone sealant. The surface of the apron has an outward slope of not less than 5%.

9. The comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations according to claim 1, characterized in that, The antifreeze modifier added to the planting soil is composed of fly ash, rice husk charcoal and polyacrylamide mixed in a preset mass ratio. The frost heave rate of the modified planting soil is no more than one percent, the backfill thickness of the planting soil is no less than 30 cm, and a three-dimensional geonet is laid on the slope after the backfill is completed.

10. The comprehensive prevention and control method for frost heave and thaw settlement of mountain wind turbine foundations according to claim 1, characterized in that, After the wind turbine foundation construction in S3 is completed, frost heave and thaw settlement monitoring sensors are evenly deployed circumferentially in soil layers at different depths around the foundation to collect data on soil moisture content, frost heave normal displacement, and thaw settlement in real time. The monitoring data is connected to the wind farm remote monitoring platform through a low-power wireless transmission module. When the monitored value exceeds the preset threshold, an early warning signal is automatically issued.

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