Seasonal frozen soil area has highway subgrade heat preservation water prevention frost heaving structure and construction method

Abstract

The present application belongs to the technical field of highway subgrade engineering, and discloses a heat preservation, water prevention and frost heaving prevention structure for existing highway subgrade in seasonally frozen soil area and a construction method thereof, which aims to solve the problem of subgrade frost heaving and thawing sinking. The structure comprises a side drainage ditch outside the slope feet of the subgrade, a grouting drainage pipe transversely penetrating the subgrade and a hydrophobic drainage layer formed by grouting. The grouting drainage pipe is a double-pipe structure integrally formed by co-extrusion, and the interlayer is provided with a fan-shaped energy storage cavity filled with phase change energy storage material, which has the functions of heat preservation and drainage. The reaction type silane hydrophobic slurry reacts with the moisture of the subgrade to generate carbon dioxide to extrude the accumulated water, and there is no solidification residue, which is convenient for later maintenance. The construction adopts the method of sectional excavation of the drainage ditch and installation of the grouting drainage pipe by horizontal directional drilling, and does not need large-scale excavation, so the traffic interference is small. The structure realizes the integration of heat preservation, hydrophobicity and drainage, and is efficient in construction and controllable in cost, can significantly reduce the frost heaving hazard and prolong the service life of the highway.

Description

Technical Field

[0001] This invention relates to the field of highway subgrade engineering technology, and in particular to the thermal insulation, water-proofing and frost-heave prevention structure and construction method of existing highway subgrades in seasonally frozen soil areas. Background Technology

[0002] In seasonally frozen soil areas, roadbeds are prone to frost heave in winter and thaw settlement in summer, leading to road surface cracking, subsidence and other defects, which seriously affect the service life of the road and driving safety. The main cause of frost heave is that the water in the roadbed freezes and expands in volume at sub-zero temperatures. In order to mitigate the damage caused by frost heave, existing technologies usually adopt methods such as setting up insulation layers, replacing antifreeze materials, and laying drainage facilities.

[0003] However, traditional insulation materials such as insulation boards or foamed concrete are prone to aging and deformation during long-term use, resulting in a decrease in insulation performance. Moreover, these materials usually require large-scale excavation of the roadbed for paving, which has a significant impact on traffic on existing highways, with long construction cycles and high costs. Furthermore, existing technologies are often single insulation or drainage solutions, failing to integrate insulation, drainage, and frost heave prevention into one integrated solution. After one-time construction, when the protective effect diminishes, it is difficult to carry out convenient and effective repair and maintenance, resulting in high maintenance costs in the later stages. In particular, large-scale reconstruction is often impractical for existing highways. How to achieve roadbed reconstruction and disease treatment without interrupting traffic or with minimal impact on traffic is a huge challenge currently facing the engineering field. Summary of the Invention

[0004] The technical problem to be solved by this invention is that existing roadbed frost heave prevention measures have limited insulation effect, incomplete drainage, difficulty in solving deep frost heave, high maintenance cost and complex construction. To this end, we propose a thermal insulation, water-proof and frost heave prevention structure and construction method for existing highway roadbeds in seasonally frozen soil areas.

[0005] To achieve the above objectives, this application adopts the following technical solution: a thermal insulation, water-proofing and frost-heave prevention structure and construction method for existing highway subgrade in seasonally frozen soil areas, including: a side drainage ditch excavated at a specific distance from the toe of the slope on both sides of the existing highway subgrade, a grouting drainage pipe that runs transversely through the subgrade and is sealed and connected to the drainage ditch at one end, and a hydrophobic drainage layer formed by directional injection of reactive silane hydrophobic slurry into the frost-heave sensitive layer of the subgrade through the grouting drainage pipe; The grouting drainage pipe is made of a high thermal conductivity polymer composite material through co-extrusion molding and includes an outer pipe and an inner pipe. The outer pipe and the inner pipe are fixedly connected by four sets of double-layer partitions. The inner pipe, outer pipe and double-layer partitions are integrally extruded and molded. The double-layer partitions separate the outer pipe and the inner pipe into four independent fan-shaped energy storage cavities. The fan-shaped energy storage cavities are filled with phase change energy storage material. Grouting channels are set between the double-layer partitions. The grouting channels are connected to the inside of the inner pipe. Grouting holes are opened on the outside of the grouting channels. The reactive silane hydrophobic grout undergoes a hydrolysis reaction with the roadbed moisture to generate carbon dioxide, which forces the water out of the roadbed. After the reaction, there are no solidified or hardened products, and it does not block the grouting channels or inner pipes.

[0006] Furthermore, the outer pipe, inner pipe, double-layer partition, fan-shaped energy storage cavity, and grouting channel of the grouting drainage pipe are manufactured using a co-extrusion integrated molding process. The fan-shaped energy storage cavity consists of four circumferentially distributed independent sealed chambers. A first sealing end cap is provided at the end of the grouting drainage pipe away from the side drainage ditch. The first sealing end cap is sealed to the outer pipe by hot-melt welding. The welding temperature is controlled at 220℃-250℃, the weld width is ≥8mm, and there are no false welds or leaks. A second sealing end cap is provided at the end of the grouting drainage pipe near the side drainage ditch. The second sealing end cap is threaded to the outer pipe and is sealed with a rubber ring. A grout connection port is provided on the second sealing end cap. The grout connection port is used for connection with the grouting equipment and drainage of roadbed water.

[0007] Furthermore, the polymer composite material used in the grouting drainage pipe is polyphenylene sulfide reinforced with 15%–20% carbon fiber by mass, and its thermal conductivity is ≥12 W / (m). K), tensile strength ≥85MPa, flexural strength ≥120MPa, weathering temperature range -45℃-90℃, acid and alkali corrosion resistance performance meets the requirement of strength retention rate ≥90% after immersion in 5% H2SO4 or 5% NaOH solution for 1000h; outer tube outer diameter 90-110mm, wall thickness 6-7mm, with a set of grouting holes every 300-400mm along the axial direction of the outer tube, corresponding to the grouting channel, 4 holes per set, hole diameter 10-11mm; inner tube inner diameter 45-55mm, wall thickness 3.5-4.5mm, inner tube inner wall is treated with polytetrafluoroethylene coating, coating thickness 5-10μm.

[0008] Furthermore, the phase change energy storage material is a composite system of 85%–90% paraffin wax and 10%–15% expanded graphite by mass. The phase change temperature of the paraffin wax is -1℃ to 3℃, its latent heat is ≥185J / g, and its thermal conductivity is ≥0.9W / (m²). K), phase change cycle stability ≥ 1200 cycles and performance decay rate ≤ 4%, volume expansion rate ≤ 7%, reserve 6%-7% volume expansion space during filling, and control the filling density at 0.88-0.92 g / cm³.

[0009] Further, the reactive silane hydrophobic slurry consists of the following components in mass percentage: 42%-48% isooctyltriethoxysilane, 12%-14% low molecular weight polyisocyanate, 26%-29% silane emulsion, 6%-7% polyethylene glycol, 0.6%-0.9% dibutyltin dilaurate and 0.2%-0.3% hydroquinone, and the sum of the mass percentages of all components is 100%; wherein the purity of isooctyltriethoxysilane is ≥99%; wherein the low molecular weight polyisocyanate has an NCO content of 12%-13% and a molecular weight of 500-800; the silane emulsion has a solid content of 35%-38% and a particle size of 50-100nm; the polyethylene glycol has a molecular weight of 200 and a purity of ≥99%; the purity of dibutyltin dilaurate is ≥98%; the purity of hydroquinone is ≥99.5%; all components are stirred and mixed at 20°C-25°C with a stirring speed of 300-500r / min for a stirring time of 20-30min, and the mixed slurry is left to stand for defoaming for 10-15min before use.

[0010] Further, the reactive silane hydrophobic slurry has a viscosity of 80-120mPa at 25°C s, and a reaction rate with water of 0.6-0.9mol / (L h), each 1kg of slurry consumes 0.9kg-1.1kg of water and generates 0.16-0.19m³ of carbon dioxide gas under standard conditions; the modified subgrade soil and rock has a static contact angle ≥125°, a dynamic contact angle ≥115°, a capillary water rise height ≤0.25m, the subgrade porosity remains ≥42%, and the permeability coefficient ≥1×10— 3 cm / s, and the water absorption rate of the subgrade soil and rock is ≤2%.

[0011] Further, the adjacent grouting channels have an axial spacing of 60-70mm, one group is arranged every 90° in the circumferential direction, and each group has 4 channels; the inner wall of the grouting channel is subjected to plasma silanization hydrophobic treatment with a treatment power of 1000-1500W and a treatment time of 3-5min, and the contact angle after treatment is >125°.

[0012] Further, the side drainage ditch is arranged 1.0-1.5m outside the slope toe on one side of the subgrade, and adopts a segmented excavation method of mechanical excavation by an excavator combined with manual trimming, with the excavation length of each section being 20-30m, and the excavation sequence advancing from the drainage outlet to the source; the excavation depth is the subgrade frost depth H+0.8-1.2m, where H is the locally measured maximum seasonal frost depth; The excavation width is dynamically adjusted according to the frost depth: when H≤2.0m, the ditch width is 1.2-1.5m; when 2.0m<H≤3.0m, the ditch width is 1.5-1.6m; when H>3.0m, the ditch width is 1.6-1.8m; the ditch bottom slope is 3‰-5‰; Furthermore, the side drainage ditch is unidirectionally inclined towards the drainage outlet, and the flatness error of the ditch bottom is ≤3cm. After excavation, the ditch wall is sloped with a slope of 1:0.75-1:1. If silty soil and clay layers are encountered, geogrid is laid on the ditch wall for reinforcement and protection. The side drainage ditch is constructed from bottom to top as follows: a 10cm thick medium-coarse sand cushion layer, a reverse filter geotextile, a drainage blind pipe, and a coarse sand and gravel backfill layer. The medium-coarse sand cushion layer has a particle size of 0.5-2.0mm, a mud content of <2%, and a compaction degree of ≥90% after laying. The reverse filter geotextile has a basis weight of ≥400g / m², a tensile strength of ≥25kN / m, and a CBR puncture strength of ≥3.5kN. It covers the bottom and sidewalls of the ditch, with the upper edge extending 50cm above the top of the ditch, and an overlap width of ≥100mm, using double-stitched connections. The needle spacing is 10-15mm; the drainage blind pipe uses HDPE double-wall corrugated pipe with an outer diameter of 160-200mm, a wall thickness of ≥6mm, an opening rate of ≥8%, and an opening diameter of 2-3mm. It is fixedly installed along the inner side of the ditch wall at a distance of 30cm from the bottom of the ditch, with a fixing spacing of 1.0-1.2m, and is connected to the ditch wall with pipe clamps and anchor nails; the coarse sand and gravel backfill layer has a particle size of 10-30mm, a mud content of <3%, a continuous particle size distribution, and is backfilled and compacted in layers, with each layer being 20-30cm thick and having a compaction degree of ≥93%. A geogrid with a tensile strength ≥80kN / m, an elongation at break ≤10%, and a mesh size of 20×20mm is laid on top of the ditch. The geogrid covers an area 0.5m beyond the ditch edge. A 20cm thick layer of planting soil is laid on top of the geogrid, with an organic matter content ≥5% and a pH value of 6.5-7.5. Tall fescue and alfalfa are planted on the planting soil. A C30 concrete water-cutting edge is set on the outer side of the drainage ditch 0.3-0.5m from the ditch edge, with a height of 15-20cm and a width of 20-30cm, flush with the planting soil on top of the ditch.

[0013] Furthermore, the layout parameters of the grouting drainage pipe are as follows: it runs horizontally through the roadbed and intersects perpendicularly with the axis of the drainage ditch. The pipe spacing is dynamically adjusted according to the roadbed porosity: when the roadbed porosity n≥40%, the spacing is 2.5-3.0m; when 30%≤n<40%, the spacing is 2.0-2.5m; when n<30%, the spacing is 1.5-2.0m; the pipe depth is H+0.5-1.0m, where H is the local measured maximum seasonal frost depth, and the pipe depth is more than 0.3m greater than the groundwater level; the angle between the pipe axis and the horizontal plane is ≤2° to ensure that the drainage slope is consistent with the drainage ditch; the other end of the pipe extends 0.3-0.5m into the slope protection on the other side of the roadbed.

[0014] This invention provides another technical solution: a construction method for thermal insulation, water-proofing, and frost heave prevention structures for existing highway subgrades in seasonally frozen soil areas includes the following steps: S1. Pre-construction preparation: Through drilling and ground-penetrating radar detection, determine the maximum frost depth H of the roadbed, the groundwater level depth W, the soil and rock particle size distribution and porosity n, and determine the drainage ditch excavation parameters, grouting diversion pipe layout parameters and grout usage. Clear weeds, loose soil and construction waste within 1.5-2.0m outside the toe of the slope on both sides of the roadbed, repair cracks on the roadbed surface, fill cracks with silane sealant with a width ≥5mm, and seal cracks with a width <5mm by applying silane emulsion. S2. Excavation and laying of side drainage ditches: Lay out lines 1.0-1.5m outside the toe of the slope on both sides of the roadbed, use an excavator for mechanical excavation, and manually trim the bottom and walls of the ditch. Excavate in sections of 20-30m each. During the excavation process, use a slope gauge to control the slope of the ditch walls between 1:0.75 and 1:1. When encountering soft soil and quicksand layers, use steel sheet piles for temporary support. After leveling the bottom of the ditch, lay a 10cm thick medium-coarse sand cushion layer and compact it with a plate vibrator to a compaction degree ≥90%. Lay a reverse filter geotextile to ensure complete coverage and no damage. Fix drainage blind pipes along the inner side of the ditch wall 30cm from the bottom of the ditch, with pipe clamps spaced 1.0-1.2m apart. The blind pipe joints are hot-melt welded. Backfill the ditch with coarse sand and gravel in layers, each layer 20-30cm, and compact it with a small vibratory roller to a compaction degree ≥93%. Stop backfilling 0.5m from the top of the ditch, leaving space for the installation of grouting drainage pipes. S3. Grouting and drainage pipe installation and inspection: A horizontal directional drilling rig is used to drill holes from the drainage ditch side to the roadbed. The angle between the drilling axis and the horizontal plane is ≤2°, the drilling deviation is ≤3%, and the drilling depth is H+0.5—1.0m. The co-extruded grouting pipe is slowly inserted into the borehole to avoid collision damage; the second sealing end cap at one end of the grouting pipe is connected to the drainage blind pipe flange, and the other end of the grouting pipe is connected to the first sealing end cap; the gap between the grouting pipe and the borehole is filled and sealed with polyurethane foam, and the outside is wrapped with geotextile to prevent mud and sand from seeping in. S4. Preparation and Injection of Reactive Silane Hydrophobic Slurry: Prepare reactive silane hydrophobic slurry according to the formula and process of claim 5, and use it within 3 hours after preparation; seal the grouting equipment with the inner tube of the grouting drainage pipe, and adopt a low-pressure slow injection process: grouting pressure 0.1-0.2MPa, grouting speed 3-5L / min, pause for 1-2 minutes every 5-10 minutes of grouting for intermittent venting; the grouting volume is adjusted according to the length of the grouting drainage pipe by 1.0-1.5L per meter combined with the porosity. When n≥40%, the grouting volume is 1.3-1.5L / m, and when n<40%, the grouting volume is 1.0-1.3L / m. The grouting sequence adopts skip-hole grouting, and the grouting interval between adjacent holes is ≥24 hours; stop grouting when continuous air bubbles overflow from the roadbed surface or the grouting volume reaches the design value. S5. Venting and Curing and Backfilling of Side Drainage Ditches: After grouting, keep the inner pipe open for 30-60 minutes to expel residual carbon dioxide and trace amounts of unreacted grout; cure for 24 hours, avoiding disturbance to the roadbed during curing; after curing, connect the grout inlet to the drainage blind pipe; continue backfilling the side drainage ditch with coarse sand and gravel to the top of the ditch, with a compaction degree ≥93%; lay geogrid, with the geogrid covering 0.5m beyond the edge of the ditch, and the geogrid overlap width ≥100mm, fixed with U-shaped nails at 1.0m intervals; lay 20cm thick planting soil and plant a mixed crop of tall fescue and alfalfa; pour C30 concrete water-cutting edge 0.3-0.5m outside the drainage ditch, using formwork support, and cure for 7 days after pouring; S6. Quality Inspection and Long-Term Monitoring: Hydrophobicity Test: Drill core samples at a depth of 0.5-2.0m, one core sample every 20m, and test the soil-rock contact angle, water absorption rate and porosity to ensure that the soil-rock contact angle is ≥125°, the water absorption rate is ≤2%, the porosity is ≥42%, and there are no solidified residues in the core sample pores.

[0015] The technical effects and advantages of this invention are as follows: 1. This invention achieves multiple functions of drainage, heat preservation, and drainage through a grouting drainage pipe. The phase change energy storage material inside the grouting drainage pipe provides heat preservation, effectively delaying the freezing depth and time of the roadbed; the grouting forms a drainage layer to remove water from the roadbed; and the grouting drainage pipe itself acts as a drainage channel, which can drain accumulated water from the roadbed for a long time. This integrated design fundamentally reduces the moisture content and freezing depth in the roadbed, significantly reducing the damage caused by frost heave.

[0016] 2. This invention uses side drainage ditch excavation and horizontal directional drilling to install grouting diversion pipes, avoiding large-scale roadbed excavation, minimizing disruption to existing highway traffic operations, and achieving high construction efficiency and relatively low cost.

[0017] 3. The reactive silane hydrophobic slurry of this invention reacts with the water in the roadbed to generate carbon dioxide, and uses the pressure of CO2 gas to force the water out of the roadbed, ensuring thorough drainage; and there are no solidified or hardened products after the reaction, so as not to block the grouting channel and inner pipe, which makes it possible to replenish the slurry through the grouting drainage pipe in the later stage, greatly reducing the long-term maintenance cost. Attached Figure Description

[0018] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts: Figure 1 This is a schematic diagram of the thermal insulation, water-proofing, and frost-heave prevention structure for existing highway subgrades in seasonally frozen soil regions, as per the present invention. Figure 2 This is a schematic diagram of the grouting drainage pipe structure of the present invention; Figure 3 This is a schematic diagram of the internal structure of the grouting drainage pipe of the present invention.

[0019] Legend: 1. Side drainage ditch; 2. Grouting drainage pipe; 201. Outer pipe; 202. Inner pipe; 203. Double-layer partition; 204. Fan-shaped energy storage cavity; 205. Grouting channel; 206. Grouting hole; 3. First sealing end cap; 4. Second sealing end cap; 5. Grouting connection port; 6. Drainage layer. Detailed Implementation

[0020] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The components of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of this application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. It should be noted that similar reference numerals and letters in the following drawings indicate similar items; therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0021] Example 1 like Figure 1 , Figure 2 and Figure 3 As shown, the present invention provides a thermal insulation, water-proofing and frost-heave prevention structure for existing highway subgrade in seasonally frozen soil areas. The structure includes: a side drainage ditch 1 excavated at a specific distance from the toe of the slope on both sides of the existing highway subgrade; a grouting drainage pipe 2 that runs transversely through the subgrade and is sealed and connected to the drainage ditch 1 at one end; and a hydrophobic drainage layer 6 formed by injecting reactive silane hydrophobic slurry into the frost-heave sensitive layer of the subgrade through the grouting drainage pipe 2.

[0022] The grouting drainage pipe 2 is integrally formed by co-extrusion of a high-thermal-conductivity polymer composite material. Specifically, the grouting drainage pipe 2 includes an outer pipe 201 and an inner pipe 202, which are fixedly connected by four sets of double-layer partitions 203. To ensure the integrity and stability of the structure, the inner pipe 202, the outer pipe 201, and the double-layer partitions 203 are integrally extruded. The double-layer partitions 203 cleverly separate the outer pipe 201 and the inner pipe 202 into four independent fan-shaped energy storage cavities 204. These fan-shaped energy storage cavities 204 are filled with phase change energy storage material to provide insulation. Grouting channels 205 are provided between the double-layer partitions 203. The grouting channels 205 are connected to the inside of the inner pipe 202 to facilitate the transportation of grout. Grouting holes 206 are opened on the outside of the grouting channels 205, which allow the grout to be injected evenly into the frost-susceptible layer of the roadbed.

[0023] The reactive silane hydrophobic grout is the key material of this invention. Its characteristic is that it can undergo a hydrolysis reaction with the roadbed moisture to generate carbon dioxide. The generated carbon dioxide gas is used to force the water in the roadbed to be squeezed out, thereby achieving the purpose of drainage. More importantly, this grout does not have solidified and hardened products after the reaction, and will not block the grouting channel 205 and the inner pipe 202, which provides convenience for subsequent maintenance and repeated grouting.

[0024] Furthermore, the outer pipe 201, inner pipe 202, double-layer baffle 203, fan-shaped energy storage cavity 204, and grouting channel 205 of the grouting drainage pipe 2 adopt a co-extrusion integrated molding process, which ensures the integrity and strength of each part of the pipeline. The fan-shaped energy storage cavity 204 consists of four independent sealed chambers evenly distributed in the circumference, which ensures the uniform distribution and stable operation of the phase change energy storage material. A first sealing end cap 3 is provided at the end of the grouting drainage pipe 2 away from the side drainage ditch 1. The first sealing end cap 3 is sealed to the outer pipe 201 by hot-melt welding. The welding temperature is controlled at 220℃-250℃, the weld width is ≥8mm, and there must be no false welding or leakage welding to ensure the reliability of the seal. A second sealing end cap 4 is provided at the end of the grouting drainage pipe 2 near the side drainage ditch 1. The second sealing end cap 4 is threaded to the outer pipe 201 and is sealed with a rubber ring for easy installation and disassembly. A grout connection port 5 is opened on the second sealing end cap 4. The grout connection port 5 is used to connect to the grouting equipment and also serves as a drainage channel for roadbed water accumulation, realizing the drainage function.

[0025] In a preferred embodiment, the grouting drainage pipe 2 uses a polymer composite material reinforced with 15%–20% carbon fiber by mass of polyphenylene sulfide. This material has excellent thermal conductivity, with a thermal conductivity coefficient ≥12 W / (m·K), ensuring the heat transfer efficiency of the phase change energy storage material. It also possesses high strength, with a tensile strength ≥85 MPa and a flexural strength ≥120 MPa. Its weathering temperature range is -45℃ to 90℃, and it exhibits excellent resistance to acid and alkali corrosion. After immersion in 5% H₂SO₄ or 5% NaOH solution for 1000 hours, the strength retention rate is ≥90%, thus ensuring long-term stability in complex permafrost environments. The outer pipe 201 has an outer diameter of 90–110 mm and a wall thickness of 6–7 mm. The outer tube 201 has a set of grouting holes 206 every 300-400mm along the axial direction, corresponding to the grouting channels 205. Each set has 4 grouting holes with a diameter of 10-11mm to ensure uniform injection of grout. The inner tube 202 has an inner diameter of 45-55mm and a wall thickness of 3.5-4.5mm. The inner wall of the inner tube 202 is coated with polytetrafluoroethylene with a coating thickness of 5-10μm. This coating has good lubricity and non-adhesion to ensure smooth flow of grout during the grouting process and prevent clogging.

[0026] In another preferred embodiment, the grouting drainage pipe 2 uses a polymer composite material of 25%-30% graphite-filled polyetheretherketone (PEEK). PEEK itself has excellent mechanical properties, heat resistance, and chemical corrosion resistance. By filling it with 25%-30% high thermal conductivity graphite, the overall thermal conductivity of the material is further improved, enabling it to efficiently transfer the heat of the phase change energy storage material. This composite material has high strength, wear resistance, and excellent thermal conductivity, making it particularly suitable for applications that require long-term operation in complex and harsh permafrost environments.

[0027] In another preferred embodiment, the grouting drainage pipe 2 uses a polymer composite material that is modified nylon with a ceramic powder mass fraction of 30%-35%. Nylon is widely used due to its good toughness and ease of processing. By modifying it with a high thermal conductivity ceramic powder mass fraction of 30%-35%, the thermal conductivity of the material can be significantly improved without significantly reducing its mechanical properties. This modified nylon composite material has relatively low cost, is easy to integrally mold, and has good impact resistance, providing an economical and efficient material choice for the grouting drainage pipe.

[0028] In a preferred embodiment, the phase change energy storage material is a composite system of 85%–90% paraffin wax and 10%–15% expanded graphite by mass. Paraffin wax has a phase change temperature of -1℃ to 3℃, which covers the main freezing temperature range of permafrost, and its latent heat is ≥185J / g, enabling it to absorb / release a large amount of heat. Expanded graphite improves the thermal conductivity of the composite system, making it ≥0.9W / (m·K), thus accelerating heat transfer. This composite system exhibits excellent phase change cycle stability, with a cycle life of ≥1200 cycles and a performance degradation rate ≤4%, and a volume expansion rate ≤7%. A 6%–7% volume expansion space is reserved during filling, and the filling density is controlled at 0.88–0.92 g / cm³, ensuring the stability and safety of the material during the phase change process.

[0029] In another preferred embodiment, the phase change energy storage material is a composite system of 75%–80% fatty acid and 20%–25% ceramsite by mass. The fatty acid is a binary composite of decanoic acid and lauric acid, and its phase change temperature can be controlled between 0℃ and 4℃, which highly matches the freeze-thaw temperature range of the roadbed, providing efficient latent heat storage and release capabilities. Ceramsite, as a lightweight porous material with a particle size of 2mm–5mm, can not only act as a carrier to adsorb fatty acids, reducing their leakage and volume change, but also possesses certain thermal insulation properties and can effectively improve the thermal conductivity uniformity of the composite system. This composite system has good thermal stability, chemical stability, and reusability, and the fatty acid source is widely available and environmentally friendly.

[0030] The reactive silane hydrophobic slurry is composed of the following components by mass percentage: 42%–48% isooctyltriethoxysilane, 12%–14% low molecular weight polyisocyanate, 26%–29% silane emulsion, 6%–7% polyethylene glycol, 0.6%–0.9% dibutyltin dilaurate, and 0.2%–0.3% hydroquinone, with the sum of the mass percentages of each component being 100%. The main hydrophobic active ingredient is isooctyltriethoxysilane with a purity ≥99%; low molecular weight polyisocyanate with an NCO content of 12%–13% and a molecular weight of 500–800 serves as a curing agent; the silane emulsion has a solid content of 35%–38% and a particle size of 50–100 nm to ensure dispersibility and penetration; polyethylene glycol with a molecular weight of 200 and a purity ≥99% serves as a solvent and dispersant; dibutyltin dilaurate with a purity ≥98% serves as a catalyst; and hydroquinone with a purity ≥99.5% serves as a stabilizer. All components are mixed at 20℃–25℃ at a stirring speed of 300–500 r / min for 20–30 min. After mixing, the slurry is allowed to stand for 10–15 min to degas before use, ensuring uniform mixing and the absence of air bubbles.

[0031] The reactive silane hydrophobic slurry has a viscosity of 80-120 mPa·s at 25°C, which ensures good pumpability and permeability. Its reaction rate with water is 0.6-0.9 mol / (L·h), which ensures a moderate reaction rate to fully utilize CO₂ gas to squeeze out accumulated water. Each 1 kg of slurry consumes 0.9 kg-1.1 kg of water and generates 0.16-0.19 m³ of carbon dioxide gas under standard conditions, providing an accurate dosage reference. The static contact angle of the modified subgrade soil and rock is ≥125°, the dynamic contact angle is ≥115°, the capillary water rising height is ≤0.25 m, the subgrade porosity remains ≥42°, and the permeability coefficient is ≥1×10 - ³ cm / s, and the water absorption rate of the subgrade soil and rock is ≤2%. These indicators all show that the slurry effectively improves the hydrophobic performance and drainage capacity of the subgrade soil and rock.

[0032] The axial spacing between adjacent grouting passages 205 is 60-70 mm, one set is arranged every 90° in the circumferential direction, and each set has 4 passages. Such a design ensures that the grouting path of the slurry in the subgrade is uniform with a wide coverage. The inner wall of the grouting passage 205 is subjected to plasma silanization hydrophobic treatment at a treatment power of 1000-1500 W for a treatment time of 3-5 min, and the contact angle after treatment is >125°. This treatment enhances the hydrophobicity of the grouting passage itself, prevents the slurry from adhering to the inner wall of the passage, and further ensures the smooth flow of the slurry.

[0033] The side drainage ditch 1 is arranged 1.0-1.5 m outside the slope toe on one side of the subgrade, adopting a sectional excavation method of excavator mechanical excavation combined with manual trimming, with an excavation length of 20-30 m per section. The excavation proceeds from the drainage outlet to the source, which ensures the correct drainage direction and high construction efficiency. The excavation depth is the subgrade frost depth H + 0.8-1.2 m, where H is the locally measured maximum seasonal frost depth. Such a depth ensures that the drainage ditch can effectively intercept groundwater and surface runoff to prevent frost heave.

[0034] The excavation width is dynamically adjusted according to the frost depth: when H ≤ 2.0 m, the ditch width is 1.2-1.5 m; when 2.0 m < H ≤ 3.0 m, the ditch width is 1.5-1.6 m; when H > 3.0 m, the ditch width is 1.6-1.8 m, which realizes the flexibility and economy of the design.

[0035] The ditch bottom slope is 3‰-5‰ to ensure smooth drainage, and the side drainage ditch 1 is unidirectionally inclined towards the drainage outlet, with a ditch bottom flatness error of ≤3 cm, which ensures the drainage effect. After excavation, the ditch wall is subjected to slope grading treatment with a slope of 1:0.75-1:1. In case of silty soil and clay layers, geogrid is laid on the ditch wall for reinforcement protection, which improves the stability of the ditch wall.

[0036] The side drainage ditch 1 is constructed from bottom to top as follows: a 10cm thick medium-coarse sand cushion layer, a reverse filter geotextile, a drainage blind pipe, and a coarse sand and gravel backfill layer. The medium-coarse sand cushion layer has a particle size of 0.5-2.0mm, a mud content of <2%, and a compaction degree of ≥90% after laying, serving as a good permeable foundation.

[0037] The geotextile has a basis weight ≥400g / m², a tensile strength ≥25kN / m, a CBR puncture strength ≥3.5kN, covers the bottom and sidewalls of the ditch, with the upper edge extending 50cm above the top of the ditch, and an overlap width ≥100mm. It is connected by double-line stitching with a stitch spacing of 10-15mm, effectively preventing mud and sand from entering the drainage layer while ensuring the strength and connection reliability of the geotextile.

[0038] The drainage blind pipe uses HDPE double-wall corrugated pipe with an outer diameter of 160-200mm, a wall thickness of ≥6mm, an opening rate of ≥8%, and an opening diameter of 2-3mm. It is fixedly installed along the inner side of the ditch wall at a distance of 30cm from the bottom of the ditch, with a fixing interval of 1.0-1.2m. It is connected to the ditch wall with pipe clamps and anchors to ensure the stability and effective collection function of the drainage blind pipe.

[0039] The coarse sand and gravel backfill layer has a particle size of 10-30mm, a mud content of <3%, and a continuous particle size distribution. It is backfilled and compacted in layers, each 20-30cm thick, with a compaction degree ≥93%, creating an effective drainage channel. A geogrid with a tensile strength ≥80kN / m, elongation at break ≤10%, and a mesh size of 20×20mm is laid on top of the trench. The geogrid extends 0.5m beyond the trench edge, providing top reinforcement. A 20cm layer of planting soil is laid on top of the geogrid. The planting soil has an organic matter content ≥5% and a pH value of 6.5-7.5 for vegetation restoration and to improve ecological benefits. A mixture of tall fescue and alfalfa is planted on the planting soil to further protect the slope and prevent soil erosion. A C30 concrete water-stopping edge is installed 0.3-0.5m away from the edge of the drainage ditch. The water-stopping edge is 15-20cm high and 20-30cm wide, and is flush with the top of the ditch with the planting soil. This effectively intercepts surface water and prevents it from flowing into the drainage ditch.

[0040] The layout parameters of grouting drainage pipe 2 are as follows: it runs laterally through the roadbed and intersects perpendicularly with the axis of the drainage ditch, ensuring its lateral impact on the roadbed. The pipe spacing is dynamically adjusted according to the roadbed porosity: when the roadbed porosity n≥40%, the spacing is 2.5-3.0m; when 30%≤n<40%, the spacing is 2.0-2.5m; when n<30%, the spacing is 1.5-2.0m. This dynamic adjustment strategy ensures the uniformity and economy of the grouting effect. The pipe depth is H+0.5-1.0m, where H is the local measured maximum seasonal frost depth, and the pipe depth is more than 0.3m greater than the groundwater level depth, ensuring that the pipe body is located below the frost heave sensitive layer and the groundwater level, effectively intercepting moisture. The angle between the pipe axis and the horizontal plane is ≤2°, ensuring that the drainage slope is consistent with the drainage ditch. The other end of the pipe extends 0.3-0.5m into the slope protection on the other side of the roadbed, avoiding structural damage on the other side.

[0041] Example 2 This invention also provides a construction method for an existing highway subgrade insulation, waterproofing, and frost heave prevention structure in seasonally frozen soil regions, applied to the aforementioned structure. The specific steps are as follows: S1. Pre-construction preparations: First, through professional methods such as drilling and ground-penetrating radar detection, key geological and hydrological information such as the maximum frost depth H of the roadbed, the groundwater level depth W, the soil particle size distribution, and the porosity n are comprehensively determined. These data form the basis for determining the subsequent drainage ditch excavation parameters, the grouting diversion pipe 2 layout parameters, and the amount of grout used. For example, if the measured maximum frost depth H is 2.5m, the groundwater level depth W is 1.5m, and the porosity n is 35%.

[0042] Secondly, clear weeds, loose soil, and construction waste within 1.5-2.0m outside the toe of the slope on both sides of the roadbed to create a clean working surface for subsequent construction.

[0043] Finally, the cracks on the roadbed surface are repaired. Cracks with a width of ≥5mm are filled with silane sealant to provide better waterproofing and adhesion; cracks with a width of <5mm are sealed with silane emulsion to prevent moisture seepage.

[0044] S2. Excavation and laying of side drainage ditch 1: Layout and Excavation: Based on the parameters prepared before construction, precise lines are laid out 1.0-1.5m outside the toe of the slope on both sides of the roadbed. Mechanical excavation is carried out using excavators, with manual labor assisting in the fine finishing of the ditch bottom and walls. Considering construction efficiency and stability, a segmented excavation method is adopted, with each segment controlled to a length of 20-30m. To ensure smooth drainage, the excavation sequence proceeds from the drainage outlet towards the source. During the excavation process, the slope of the ditch walls is strictly controlled between 1:0.75 and 1:1 using a slope gauge. If soft soil or quicksand layers are encountered, temporary support using steel sheet piles must be used in a timely manner to ensure construction safety.

[0045] According to the assumed H=2.5m in S1, the excavation depth of the drainage ditch is H+0.8-1.2m, which is taken as 1.0m, that is, 2.5+1.0=3.5m; the ditch width is taken as 1.5-1.6m according to the condition of 2.0m<H≤3.0m, and is taken as 1.5m here.

[0046] Laying of cushion layer and geotextile: After the ditch bottom is leveled, a 10cm-thick medium-coarse sand cushion layer with a particle size of 0.5-2.0mm and a mud content of <2% is laid, which is compacted with a plate vibrator to a compaction degree of ≥90%. Subsequently, a reverse-filter geotextile is laid to ensure complete coverage without damage, covering the ditch bottom and side walls, with the upper edge 50cm higher than the ditch top, the lap width ≥100mm, and connected by double-thread stitching with a stitch pitch of 10-15mm.

[0047] Installation and backfilling of blind drainage pipe: The blind drainage pipe is fixed along the inner side of the ditch wall at a position 30cm from the ditch bottom, with a pipe clamp spacing of 1.0-1.2m. The joints of the blind pipe are welded by hot melting to ensure tight connection. After that, coarse sand and gravel are backfilled into the ditch in layers, with each layer having a thickness of 20-30cm, and compacted by a small vibratory roller to a compaction degree of ≥93%. The backfilling of coarse sand and gravel is stopped when it is 0.5m away from the ditch top, reserving the installation space for the grouting drainage pipe 2.

[0048] S3. Installation and detection of grouting drainage pipe 2: Drilling: A horizontal directional drilling rig is used to drill holes from the drainage ditch side to the roadbed. The included angle between the drilling axis and the horizontal plane is ≤2°, and the drilling deviation is ≤3%, which ensures the layout accuracy of the pipeline and the drainage gradient. According to the assumed H=2.5m in S1, the drilling depth is taken as H+0.5-1.0m, and here it is taken as H+0.7m, that is, 2.5+0.7=3.2m.

[0049] Pipeline insertion and sealing: The co-extruded integrally formed grouting drainage pipe 2 is slowly inserted into the drilled hole, and special attention shall be paid to avoid collision damage to the pipe body during operation. The second sealing end cover 4 at one end of the grouting drainage pipe 2 is flanged to the blind drainage pipe in the drainage ditch to ensure reliable sealing and realize drainage communication, while the other end of the grouting drainage pipe 2 is connected with the first sealing end cover 3 for sealing. In order to prevent groundwater infiltration and fix the pipeline, the annular gap between the grouting drainage pipe 2 and the drilled hole is filled and sealed with polyurethane foam, and at the same time, the outer side of the pipeline is wrapped with geotextile to further prevent sediment infiltration.

[0050] S4. Preparation and injection of reactive silane hydrophobic slurry: Slurry preparation: Prepare reactive silane hydrophobic slurry strictly according to the formulation and process requirements of claim 5. For example, the formulation uses 45% isooctyltriethoxysilane, 13% low molecular weight polyisocyanate, 28% silane emulsion, 6.5% polyethylene glycol, 0.8% dibutyltin dilaurate, and 0.2% hydroquinone. Stir at 20℃-25℃, stirring speed of 300-500r / min, stirring time of 20-30min, and standing for 10-15min to remove bubbles. To ensure the activity of the slurry, it must be used within 3 hours after preparation.

[0051] Grout injection: The grouting equipment is sealed and connected to the inner tube 202 of the grouting diversion pipe 2. A low-pressure slow injection process is used for grouting, with the grouting pressure controlled at 0.1-0.2 MPa and the grouting speed at 3-5 L / min. To ensure sufficient grout penetration and carbon dioxide gas discharge, the grouting is paused for 1-2 minutes every 5-10 minutes for intermittent venting. The grouting volume is adjusted according to the length of the grouting diversion pipe 2 and the porosity assumed in S1. At this time, the grouting volume is 1.0-1.3 L / m. In order to achieve uniform distribution of grout in the subgrade, a skip-hole grouting method is adopted, with an interval of ≥24 hours between adjacent holes. Grouting can be stopped when continuous air bubbles are observed to overflow from the subgrade surface or when the grouting volume reaches the design value.

[0052] S5. Exhaust maintenance and backfilling of side drainage ditch 1: Venting and curing: After grouting, keep the inner pipe 202 open for 30-60 minutes to fully vent residual carbon dioxide gas and trace amounts of unreacted grout. Then, carry out 24 hours of curing. During this period, avoid disturbing the roadbed to ensure that the grout reacts fully and the structure is stable. After curing, connect the grout connection port 5 to the drainage blind pipe to achieve long-term drainage function.

[0053] Backfilling and Top Treatment of Drainage Ditches: Continue backfilling the side drainage ditch 1 to the top with coarse sand and gravel, ensuring a compaction degree of ≥93%. Lay geogrid on the top of the ditch, extending 0.5m beyond the ditch edge with an overlap width of ≥100mm, and secure it with U-shaped nails spaced 1.0m apart. Cover the geogrid with a 20cm thick layer of planting soil containing ≥5% organic matter and a pH of 6.5-7.5. Sow a mixture of tall fescue and alfalfa on the planting soil for ecological restoration and slope protection. Finally, construct a C30 concrete water-stopping edge 0.3-0.5m outside the drainage ditch, using formwork support for pouring. Curing should be carried out for 7 days after pouring to ensure its strength and stability, ensuring it is flush with the planting soil at the top of the ditch to effectively intercept surface water.

[0054] S6. Quality Inspection and Long-Term Monitoring: After construction, the drainage effect was tested. Core samples were drilled at depths of 0.5–2.0 m, with one core sample every 20 m. The contact angle, water absorption rate, and porosity of the extracted soil cores were tested to ensure that the soil-rock contact angle was ≥125°, the water absorption rate was ≤2%, the porosity was ≥42%, and there were no solidified residues in the core sample pores, thus verifying the drainage effect. Simultaneously, a long-term monitoring system was established to regularly monitor changes in roadbed temperature, humidity, frost depth, and the operation of the grouting drainage pipes to ensure the long-term effectiveness of the structure and provide data support for future maintenance.

[0055] The above are merely embodiments of this application and are not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A thermal insulation, water-proofing, and frost-heave-preventing structure for existing highway subgrades in seasonally frozen soil regions, characterized in that: include: The side drainage ditch is excavated at a specific distance from the toe of the slope on both sides of the existing roadbed, the grouting diversion pipe runs horizontally through the roadbed and is sealed and connected to the drainage ditch at one end, and the hydrophobic drainage layer is formed by injecting reactive silane hydrophobic slurry into the frost heave sensitive layer of the roadbed through the grouting diversion pipe. The grouting and drainage pipe is integrally formed by co-extrusion of a high thermal conductivity polymer composite material and includes an outer pipe and an inner pipe. The outer pipe and the inner pipe are fixedly connected by four sets of double-layer partitions. The inner pipe, the outer pipe and the double-layer partitions are integrally extruded. The double-layer partitions divide the outer pipe and the inner pipe into four independent fan-shaped energy storage cavities. The fan-shaped energy storage cavities are filled with phase change energy storage material. A grouting channel is provided between the double-layer partitions. The grouting channel is connected to the inside of the inner pipe. A grouting hole is opened on the outside of the grouting channel. The reactive silane hydrophobic slurry undergoes a hydrolysis reaction with the roadbed moisture to generate carbon dioxide, thereby forcibly squeezing out the accumulated water. After the reaction, there are no solidified or hardened products, and it does not block the grouting channels or inner pipes.

2. The thermal insulation, water-proofing, and frost-heave prevention structure for existing highway subgrades in seasonally frozen soil areas according to claim 1, characterized in that, The outer pipe, inner pipe, double-layer partition, fan-shaped energy storage cavity, and grouting channel of the grouting diversion pipe are manufactured using a co-extrusion integral molding process. The fan-shaped energy storage cavity consists of four circumferentially distributed independent sealed chambers. A first sealing end cap is provided at the end of the grouting diversion pipe away from the side drainage ditch. The first sealing end cap is sealed to the outer pipe by hot-melt welding. A second sealing end cap is provided at the end of the grouting diversion pipe near the side drainage ditch. The second sealing end cap is threaded to the outer pipe and is sealed with a rubber ring. A grout connection port is provided on the second sealing end cap. The grout connection port is used for connection with the grouting equipment and drainage of roadbed water.

3. The thermal insulation, water-proofing, and frost-heave prevention structure for existing highway subgrades in seasonally frozen soil areas according to claim 1, characterized in that, The grouting drainage pipe uses a polymer composite material that is reinforced with 15%-20% carbon fiber by mass of polyphenylene sulfide.

4. The thermal insulation, water-proofing, and frost-heave prevention structure for existing highway subgrades in seasonally frozen soil areas according to claim 1, characterized in that, The phase change energy storage material is a composite system of 85%–90% paraffin wax and 10%–15% expanded graphite by mass. The phase change temperature of the paraffin wax is -1℃ to 3℃, its latent heat is ≥185J / g, and its thermal conductivity is ≥0.9W / (m²). K), phase change cycle stability ≥ 1200 cycles and performance decay rate ≤ 4%, volume expansion rate ≤ 7%, reserve 6%-7% volume expansion space during filling, and control the filling density at 0.88-0.92 g / cm³.

5. The thermal insulation, water-proofing, and frost-heave prevention structure for existing highway subgrades in seasonally frozen soil areas according to claim 1, characterized in that, The reactive silane hydrophobic slurry is composed of the following components by mass percentage: 42%–48% isooctyltriethoxysilane, 12%–14% low molecular weight polyisocyanate, 26%–29% silane emulsion, 6%–7% polyethylene glycol, 0.6%–0.9% dibutyltin dilaurate, and 0.2%–0.3% hydroquinone, with the sum of the mass percentages of each component being 100%. The components are stirred and mixed at 20℃–25℃ at a stirring speed of 300–500 r / min for 20–30 min. After mixing, the slurry is allowed to stand for 10–15 min to degas before use.

6. The thermal insulation, water-proofing, and frost-heave prevention structure for existing highway subgrades in seasonally frozen soil areas according to claim 5, characterized in that, The reactive silane hydrophobic slurry has a viscosity of 80-120 mPa at 25°C. The reaction rate with water is 0.6–0.9 mol / (L). (h), each 1kg of slurry consumes 0.9kg-1.1kg of water and generates 0.16-0.19m³ of carbon dioxide gas under standard conditions; the modified subgrade soil and rock have a static contact angle ≥125°, a dynamic contact angle ≥115°, a capillary rise height ≤0.25m, a subgrade porosity ≥42%, and a permeability coefficient ≥1×10— 3 cm / s, water absorption rate of roadbed soil and rock ≤2%.

7. The thermal insulation, water-proofing, and frost-heave prevention structure for existing highway subgrades in seasonally frozen soil areas according to claim 1, characterized in that, The axial spacing between adjacent grouting channels is 60-70mm, and a group is arranged every 90° in the circumferential direction, with 4 channels in each group; the inner wall of the grouting channel is treated with plasma silanization hydrophobicity, and the contact angle after treatment is >125°.

8. The thermal insulation, water-proofing, and frost-heave prevention structure for existing highway subgrades in seasonally frozen soil areas according to claim 1, characterized in that, The side drainage ditch is laid 1.0-1.5m outside the toe of the slope on one side of the roadbed. It adopts a segmented excavation method with mechanical excavation by excavator and manual trimming. Each segment is 20-30m long. The excavation sequence is from the drainage outlet to the source. The excavation depth is the roadbed frost depth H+0.8-1.2m, where H is the local measured maximum seasonal frost depth. The excavation width is dynamically adjusted according to the frost depth: when H ≤ 2.0m, the trench width is 1.2-1.5m; when 2.0m < H ≤ 3.0m, the trench width is 1.5-1.6m; when H > 3.0m, the trench width is 1.6-1.8m; the trench bottom gradient is 3‰-5‰; And the side drainage ditch is unidirectionally inclined towards the drainage outlet, the flatness error of the trench bottom is ≤3cm, the trench wall after excavation is subjected to slope grading treatment with a gradient of 1:0.75-1:1, and if silty soil and clay layers are encountered, the trench wall is paved with geogrid for reinforcement protection; Inside the side drainage ditch, the following layers are arranged sequentially from bottom to top: a 10cm-thick medium-coarse sand cushion layer, a reverse-filter geotextile, a blind drainage pipe, and a coarse sand and stone backfill layer; A geogrid is paved on the top of the ditch, 20cm-thick planting soil is paved above the geogrid, mixed sown herbaceous plants of tall fescue and alfalfa are planted on the planting soil, and a C30 concrete water interception edge is set at a position 0.3-0.5m away from the ditch edge on the outer side of the drainage ditch.

9. The thermal insulation, water-proofing, and frost-heave prevention structure for existing highway subgrades in seasonally frozen soil areas according to claim 1, characterized in that, The layout parameters of the grouting drainage conduit are as follows: it transversely penetrates the roadbed and intersects perpendicularly with the axis of the drainage ditch, and the pipe spacing is dynamically adjusted according to the roadbed porosity: when the roadbed porosity n ≥ 40%, the spacing is 2.5-3.0m; when 30% ≤ n < 40%, the spacing is 2.0-2.5m; when n < 30%, the spacing is 1.5-2.0m; the pipe depth is H+0.5-1.0m, where H is the locally measured maximum seasonal frost depth, and the pipe depth is more than 0.3m greater than the buried depth of the groundwater level; the included angle between the pipe axis and the horizontal plane is ≤2°, ensuring that the drainage gradient is consistent with that of the drainage ditch; the other end of the pipe extends 0.3-0.5m into the slope protection on the other side of the roadbed.

10. A construction method for an existing highway subgrade insulation, waterproofing, and frost heave prevention structure in seasonally frozen soil regions, applicable to the existing highway subgrade insulation, waterproofing, and frost heave prevention structure described in any one of claims 1-9, characterized in that... The method includes the following steps: S1. Pre-construction preparation: through drilling and ground penetrating radar detection, the maximum frost depth H of the roadbed, the buried depth W of the groundwater level, the particle size distribution of soil and rock, and the porosity n are clarified, and the excavation parameters of the drainage ditch, the layout parameters of the grouting drainage conduit and the slurry consumption are determined; Clear weeds, loose soil and construction waste within the range of 1.5-2.0m outside the slope toes on both sides of the roadbed, repair cracks on the roadbed surface, fill cracks with a width ≥5mm with silane sealant, and brush and seal cracks with a width <5mm with silane emulsion; S2. Excavation and laying of the side drainage ditch: set out lines at 1.0-1.5m outside the slope toes on both sides of the roadbed, adopt an excavator for mechanical excavation, manually trim the trench bottom and trench walls, carry out segmented excavation with each section being 20-30m, use a gradient ruler to control the trench wall gradient between 1:0.75 and 1:1 during the excavation process, and adopt steel sheet piles for temporary support when soft soil and quicksand layers are encountered; after the trench bottom is leveled, pave a 10cm-thick medium-coarse sand cushion layer, and compact it with a plate vibrator to a compaction degree of ≥90%; pave the reverse-filter geotextile to ensure complete coverage without damage; fix the blind drainage pipe at a position 30cm away from the trench bottom on the inner side of the trench wall, the spacing of pipe clamps is 1.0-1.2m, and the joints of the blind pipe are welded by hot melting; backfill coarse sand and stone into the trench in layers, each layer is 20-30cm thick, compact it with a small vibratory roller to a compaction degree of ≥93%, stop backfilling when it is 0.5m away from the top of the ditch, and reserve space for installing the grouting drainage conduit; S3. Grouting and drainage pipe installation and inspection: A horizontal directional drilling rig is used to drill holes from the drainage ditch side to the roadbed. The angle between the drilling axis and the horizontal plane is ≤2°, the drilling deviation is ≤3%, and the drilling depth is H+0.5—1.0m. The co-extruded integral grouting drainage pipe is slowly inserted into the borehole to avoid collision damage; the second sealing end cap at one end of the grouting drainage pipe is connected to the drainage blind pipe flange, and the other end of the grouting drainage pipe is connected to the first sealing end cap; the gap between the grouting drainage pipe and the borehole is filled and sealed with polyurethane foam, and the outside is wrapped with geotextile to prevent mud and sand from seeping in. S4. Preparation and Injection of Reactive Silane Hydrophobic Slurry: Prepare reactive silane hydrophobic slurry according to the formula and process described in claim 5, and use it within 3 hours after preparation; seal the grouting equipment with the inner tube of the grouting drainage pipe, and adopt a low-pressure slow injection process: grouting pressure 0.1-0.2MPa, grouting speed 3-5L / min, pause for 1-2 minutes every 5-10 minutes of grouting for intermittent venting; the grouting volume is adjusted according to the length of the grouting drainage pipe by 1.0-1.5L per meter combined with the porosity. When n≥40%, the grouting volume is 1.3-1.5L / m, and when n<40%, the grouting volume is 1.0-1.3L / m. The grouting sequence adopts skip-hole grouting, and the grouting interval between adjacent holes is ≥24 hours; stop grouting when continuous air bubbles overflow from the roadbed surface or the grouting volume reaches the design value; S5. Venting and Curing and Backfilling of Side Drainage Ditches: After grouting, keep the inner pipe open for 30-60 minutes to expel residual carbon dioxide and trace amounts of unreacted grout; cure for 24 hours, avoiding disturbance to the roadbed during curing; after curing, connect the grout inlet to the drainage blind pipe; continue backfilling the side drainage ditch with coarse sand and gravel to the top of the ditch, with a compaction degree ≥93%; lay geogrid, with the geogrid covering 0.5m beyond the edge of the ditch, and the geogrid overlap width ≥100mm, fixed with U-shaped nails at 1.0m intervals; lay 20cm thick planting soil and plant a mixed crop of tall fescue and alfalfa; pour C30 concrete water-cutting edge 0.3-0.5m outside the drainage ditch, using formwork support, and cure for 7 days after pouring; S6. Quality Inspection and Long-Term Monitoring: Hydrophobicity Test: Drill core samples at a depth of 0.5-2.0m, one core sample every 20m, and test the soil-rock contact angle, water absorption rate and porosity to ensure that the soil-rock contact angle is ≥125°, the water absorption rate is ≤2%, the porosity is ≥42%, and there are no solidified residues in the core sample pores.

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