Railway bed disease treatment double-layer waterproof closed-loop treatment construction process

Abstract

This invention relates to the field of chemical material construction technology, and discloses a double-layer waterproof closed-loop treatment construction process for railway subgrade defects. The construction method includes: cleaning the subgrade surface and adjusting the drainage slope; repositioning the sleepers and checking the track geometry parameters; high-pressure spraying a sealed sealing mixture of continuous graded gravel and petroleum asphalt-based curing agent onto the subgrade surface to form an asphalt-gravel sealed bottom layer; fully laying polyester non-woven waterproof felt on the asphalt-gravel sealed bottom layer to form a double-layer waterproof composite structure; backfilling primary crushed stone ballast in layers and mechanically compacting each layer to the specified elevation.

Description

Technical Field

[0001] This invention relates to the field of chemical material construction technology, and more specifically, to a double-layer waterproof closed-loop treatment construction process for railway subgrade defects. Background Technology

[0002] The existing operating railway ballast track subgrade is subjected to the combined effects of train cyclic dynamic loads, rainwater infiltration, and capillary uplift of groundwater over a long period of time. The continuous migration of fine particles in the subgrade soil causes water damage such as frost heave, mud pumping, water accumulation in the subgrade, dirt and siltation of the track bed, and local uneven settlement.

[0003] Existing remediation techniques typically employ the following methods: First, localized treatment is carried out on visible defect points; second, a single grouting or single-layer spraying method is used to seal the seepage channels; third, the traditional double-layer waterproofing construction sequence of first laying a waterproof felt isolation layer and then sealing the surface is adopted; fourth, after the waterproof layer is laid, the ballast is backfilled directly without layered compaction and buffering.

[0004] The existing technology has the following shortcomings: Localized treatments fail to seal surrounding seepage channels, allowing rainwater and groundwater to continuously infiltrate the subgrade along newly formed pores, creating a vicious cycle of "seepage, mud accumulation, softening, and frost heave" that cannot be stopped; capillary upwelling channels in the subgrade are not sealed, allowing groundwater carrying mud to continuously rise to the track bed; in the traditional double-layer waterproofing construction sequence, sharp gravel in the subgrade easily punctures the waterproofing felt, and the lack of a sealed bottom layer causes rainwater to accumulate and bulge at the bottom of the waterproofing felt, leading to rapid failure of the waterproofing system; after the waterproofing layer is laid, ballast is directly backfilled without layered compaction and buffering, and repeated impacts from trains cause the ballast edges to squeeze and cut the waterproofing layer, resulting in hollowing, tearing, and delamination. These shortcomings lead to a short service life for the treatment system, and water damage cannot be effectively controlled in the long term. Summary of the Invention

[0005] This invention provides a double-layer waterproof closed-loop treatment construction process for railway subgrade disease treatment, which solves the technical problems in related technologies where the waterproof layer is single after the treatment of mud pumping and frost damage in existing railway subgrades, and the repeated intrusion of groundwater and seepage water leads to disease recurrence.

[0006] This invention discloses a double-layer waterproof closed-loop treatment construction process for railway subgrade defects, comprising the following steps: Step 1, removing the defective soil and silt from the subgrade, leveling the base surface, and adjusting the drainage slope to achieve a transverse drainage slope of 2% to 4%; Step 2, mixing continuously graded aggregate and petroleum asphalt-based curing agent at a mass ratio of 100:8 to 100:15 to prepare a sealing mixture, and then spraying the sealing mixture onto the treated subgrade surface using high-pressure jetting at a pressure of 0.3 kJ / kg. The pressure is 0.1 MPa to 0.8 MPa, the spray thickness is 30 mm to 60 mm, and it is left to cure until solid, forming a sealed base layer of asphalt macadam; Step 3, a waterproof felt isolation layer is fully laid on the surface of the sealed base layer of asphalt macadam, and the overlapping areas are bonded by hot melt welding or adhesive to form a double-layer waterproof composite structure; Step 4, ballast is backfilled in layers on top of the double-layer waterproof composite structure, with each backfill layer being 100 mm to 200 mm thick, and each backfill layer is mechanically compacted until the track bed is restored to the required elevation.

[0007] Furthermore, the particle size of the continuously graded aggregate is 2.36 mm to 9.5 mm, wherein the passing rate of the 9.5 mm sieve is 95% to 100%, the passing rate of the 4.75 mm sieve is 40% to 70%, and the passing rate of the 2.36 mm sieve is 0% to 15%; the penetration of the petroleum asphalt-based coagulant is 60 to 80 0.1 mm particles at 25°C, 100 g, and 5 s, the softening point is 46°C to 54°C, and the ductility is not less than 100 cm at 15°C.

[0008] Furthermore, in step two, when preparing the sealed plugging mixture, after heating the petroleum asphalt-based coagulant to 150°C to 170°C and making it flowable, add the continuously graded aggregate preheated to 80°C to 100°C to the petroleum asphalt-based coagulant and stir continuously for no less than 3 minutes.

[0009] Furthermore, in step two, polyester short fibers are incorporated into the sealed plugging mixture at a dosage of 0.1% to 0.3% of the mass of the continuously graded aggregate, with a fiber length of 6 mm to 12 mm and a diameter of 15 μm to 30 μm.

[0010] Furthermore, the waterproof felt isolation layer is made of polyester non-woven fabric-based waterproof felt with a basis weight of 300g / m². Up to 500g / The thickness is 1.5mm to 2.5mm, the longitudinal tensile strength is not less than 8kN / m, the transverse tensile strength is not less than 6kN / m, and the hydrostatic pressure resistance is not less than 0.3MPa.

[0011] Furthermore, in step three, the longitudinal overlap width of the polyester nonwoven waterproof felt shall not be less than 150mm, and the transverse overlap width shall not be less than 100mm; when hot-melt welding is used, the welding temperature shall be 220℃ to 260℃, and the welding speed shall be 1.5m / min to 3.0m / min.

[0012] Furthermore, in step four, a medium-coarse sand buffer layer with a thickness of 20mm to 30mm is first laid on the surface of the waterproof felt isolation layer. The medium-coarse sand has a particle size of 0.5mm to 2mm. After laying, leveling and compacting, the ballast is backfilled in layers.

[0013] Furthermore, in step four, the ballast is grade one crushed stone ballast with a compressive strength of not less than 100 MPa, a Los Angeles abrasion rate of not more than 20%, a particle size of 25 mm to 63 mm, a needle-like particle content of not more than 15%, and a mud content of not more than 1%.

[0014] Furthermore, in step four, the mechanical tamping frequency is 25Hz to 35Hz, the tamping clamping force is 10kN to 16kN, the tamping duration at each insertion point is 0.8s to 1.5s, and the number of tamping passes per layer is no less than 2.

[0015] Furthermore, in step one, the flatness deviation of the base surface shall not exceed 10mm; after step one is completed, the sleepers shall be reset and the center distance deviation between adjacent sleepers shall be corrected to not exceed [a certain value]. The elevation deviation of the track does not exceed The track gauge deviation does not exceed Horizontal deviation not exceeding .

[0016] This invention employs a reverse double-layer waterproofing construction sequence. First, an asphalt-aggregate sealed base layer is constructed, followed by a full-coverage waterproof felt isolation layer, forming a double-layer waterproof composite structure. This solves the technical problems of traditional double-layer waterproofing processes, such as the waterproof felt being easily punctured by sharp gravel on the substrate and water accumulation at the bottom causing bulging and waterproofing failure. The asphalt-aggregate sealed base layer provides a smooth support surface for the waterproof felt isolation layer, eliminates the risk of puncture, and seals the path of water accumulation at the bottom. Furthermore, this invention uses a sealed-sealing mixture prepared from continuously graded aggregate and petroleum asphalt-based curing agent, which is then injected under high pressure to penetrate and fill cracks and pores in the substrate. This solves the technical problem of traditional single waterproof membranes only serving an isolation function and failing to reinforce the substrate soil. It achieves the technical effects of sealing rainwater infiltration channels and capillary rise paths of groundwater, and improving the overall strength of the substrate surface layer. This invention adopts a method of backfilling primary crushed stone ballast in layers and mechanically compacting each layer, which solves the technical problem that the ballast edges cut the waterproof layer when backfilling ballast directly after the waterproof layer is laid. It achieves the technical effect of buffering the dynamic load transmission of trains through dense track bed and reducing the concentrated squeezing effect of ballast edges on the double-layer waterproof composite structure. Attached Figure Description

[0017] Figure 1 This is a flowchart of the preparation process of the reverse double-layer waterproofing treatment method for existing railway subgrade defects provided in this embodiment of the invention; Figure 2 This is a schematic diagram comparing the porosity and permeability coefficient of the closed bottom layer of asphalt macadam in various embodiments and comparative examples provided in the present invention. Figure 3 This is a schematic diagram comparing the disease recurrence indicators of each test unit after 12 months of operation, provided in an embodiment of the present invention. Figure 4 This is a schematic diagram comparing the longitudinal and transverse resistance of the track bed in each test unit provided in the embodiments of the present invention; Figure 5 This is a schematic diagram illustrating the improvement rate of disease recurrence index in Example 3 compared to the comparative example provided in this embodiment of the invention; Figure 6 This is a schematic diagram of the SEM morphology of the closed bottom layer of asphalt macadam provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the SEM morphology of the surface of the polyester nonwoven waterproof felt provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the FTIR spectrum of the closed bottom layer of asphalt macadam provided in an embodiment of the present invention. Detailed Implementation

[0018] This invention discloses a double-layer waterproof closed-loop treatment construction process for railway subgrade defects, which solves the following technical problems in the prior art: The existing ballast track subgrade of operating railways is subjected to the coupled effects of cyclical dynamic loads from trains, rainwater infiltration, and capillary uplift of groundwater over long periods. This leads to continuous migration of fine particles in the subgrade soil, causing water damage such as mud pumping, water accumulation in the subgrade, sludge buildup and blockage of the track bed, and uneven local settlement. Current remediation techniques have the following shortcomings: First, traditional remediation only treats visible defects locally, without sealing surrounding seepage channels. Rainwater and groundwater continue to infiltrate the subgrade along newly formed pores, and the vicious cycle of "seepage, sludge accumulation, softening, and mud pumping" cannot be stopped. Second, conventional waterproofing techniques often use single grouting or single-layer spraying, leaving the capillary uplift channels in the subgrade unsealed. Groundwater carrying mud continues to rise to the track bed, and water-soil exchange cannot be prevented. Third, traditional double-layer waterproofing involves first laying a waterproof felt isolation layer, followed by a surface sealing layer. First, sharp gravel at the base easily punctures the waterproof felt, and the lack of a sealed bottom layer causes rainwater to accumulate and bulge at the bottom of the waterproof felt isolation layer, leading to rapid failure of the waterproof system; second, after the waterproof layer is laid, ballast is backfilled directly without layered compaction and buffering. Repeated impacts from trains cause the ballast edges to squeeze and cut the waterproof layer, resulting in hollowing, tearing, and delamination; third, simply laying waterproof membrane only serves as an isolation function and cannot reinforce the loose subgrade soil. Rainwater erosion and train vibration continuously strip away surface fine particles, creating new seepage channels and resulting in a short service life for the treatment system.

[0019] This invention discloses a double-layer waterproof closed-loop treatment construction process for railway subgrade defects, including: Step 1, Base surface cleaning and treatment The railway line is closed during designated maintenance windows, and sleepers are removed and reinforced. A combination of manual and mechanical work removes aged ballast, accumulated mud, loose slag, and all soft and weak soil, cleaning accumulated mud from the pores of the subgrade. The subgrade surface is leveled and the drainage slope is adjusted to a transverse drainage slope of 2% to 4%, preferably 3%. Sharp protrusions on the subgrade surface are removed, ensuring a flatness deviation of no more than 10mm. The subgrade surface is guaranteed to be firm, free of debris and water accumulation, and all existing seepage and slurry return channels are thoroughly eliminated. Only after passing inspection can the next process begin.

[0020] It should be noted that the drainage slope range mentioned above is 2% to 4%, preferably 3%. This drainage slope range ensures that surface water on the base surface is smoothly drained into the drainage ditches on both sides of the roadbed, avoiding the impact of local water accumulation on the subsequent construction quality of the asphalt macadam sealed base layer.

[0021] It should be noted that the above-mentioned base surface flatness deviation of no more than 10mm refers to the unevenness of any position on the base surface measured with a 2m straightedge. The flatness of the base surface directly affects the uniformity of the subsequent asphalt macadam spraying layer and the compactness of the waterproof felt isolation layer. Excessive deviation will result in uneven thickness of the sealed asphalt macadam base layer and localized gaps in the waterproof felt isolation layer.

[0022] Furthermore, the cleared silt, softened soil, and aged ballast must be promptly transported to a designated storage area outside the roadbed and must not be stored within the subgrade area to prevent fine particles in the cleared materials from flowing back to the treated subgrade surface under rainfall or disturbance conditions and contaminating the subsequent construction interface.

[0023] Step 2: Sleeper repositioning and track leveling After the base surface is inspected and accepted, the sleepers will be precisely returned to their original positions, and the sleeper spacing will be adjusted to ensure that the center distance deviation between adjacent sleepers does not exceed [the specified value]. ,in The allowable deviation range is defined as follows: positive values ​​indicate a larger spacing, and negative values ​​indicate a smaller spacing. Track geometry parameters such as gauge, level, elevation, and direction are checked. A track jack is used to uniformly adjust the track elevation to ensure that the track elevation deviation does not exceed [the allowable range]. The track gauge deviation does not exceed Horizontal deviation not exceeding Once the track alignment is smooth and the stress is even, it provides a working surface for the construction of the double-layer waterproof composite structure.

[0024] It should be noted that the permissible deviation values ​​for the above track geometry parameters apply to conventional passenger and freight railways. For high-speed railway sections, the elevation deviation should be controlled within [specific range]. Within a certain range, the track gauge deviation should be controlled within a certain range. Within this range, the specific maintenance and repair standards shall be followed according to the corresponding line level.

[0025] Step 3: High-pressure asphalt macadam spraying seals the surface of the subgrade. Continuously graded aggregate and petroleum asphalt-based coagulant are mixed at a mass ratio of 100:8 to 100:15, preferably 100:12, to prepare a closed-cell sealing mixture. The continuously graded aggregate has a particle size of 2.36 mm to 9.5 mm, and the gradation should meet the following requirements: 95% to 100% passing through a 9.5 mm sieve, 40% to 70% passing through a 4.75 mm sieve, and 0% to 15% passing through a 2.36 mm sieve. Continuous gradation allows particles of different sizes to interlock and fill each other, reducing the internal porosity of the mixture and increasing the density of the closed-cell asphalt aggregate layer.

[0026] It should be noted that the penetration (25℃, 100g, 5s) of the above-mentioned petroleum asphalt-based coagulant is 60 to 80 (0.1mm), the softening point is 46℃ to 54℃, and the ductility (15℃) is not less than 100cm. The petroleum asphalt-based coagulant has suitable fluidity at room temperature, enabling it to fully encapsulate continuously graded aggregate particles and penetrate into the pores of the substrate under high-pressure spraying conditions, forming a continuous and closed asphalt cement after solidification. The preferred mass ratio of continuously graded aggregate to petroleum asphalt-based coagulant is 100:12, as this ratio results in the lowest porosity and the best sealing effect in the mixture.

[0027] The sealing mixture described above is sprayed onto the treated substrate surface obtained in step 1 using a high-pressure spraying device. The spraying pressure is 0.3 MPa to 0.8 MPa, preferably 0.5 MPa to 0.6 MPa, and the spraying thickness is 30 mm to 60 mm, preferably 40 mm to 50 mm. Under high pressure, the sealing mixture penetrates and fills the fine cracks and through pores in the substrate, forming a seamless, high-density asphalt-aggregate sealed base layer. After spraying, the substrate is left to cure for at least 2 hours until the asphalt-aggregate sealed base layer is completely dry and solidified, thus obtaining the asphalt-aggregate sealed base layer.

[0028] It should be noted that if the spraying pressure is too low, the sealing mixture will not be able to effectively penetrate the pores of the subgrade, resulting in insufficient sealing depth; if the pressure is too high, the loss of the sealing mixture due to splashing will increase, and it may also disturb the treated subgrade surface. The above-mentioned preferred spraying thickness range can ensure the overall continuity of the asphalt macadam sealed subbase and sufficient impermeability strength.

[0029] Furthermore, the heating temperature of the sealed mixture during spraying is 150°C to 170°C, preferably 160°C, to ensure that the petroleum asphalt-based coagulant has sufficient fluidity during spraying, fully coating the continuously graded aggregate particles and penetrating into the pores of the substrate bed. The heating temperature must not exceed 180°C to prevent the petroleum asphalt-based coagulant from undergoing thermal oxidative aging and reducing its bonding performance.

[0030] Furthermore, when petroleum asphalt-based curing agents are heated to 150°C to 170°C, asphalt fumes will be generated. Operators should work upwind, wear respirators and heat-resistant gloves to avoid inhaling asphalt fumes and being burned by hot asphalt splashes. Fire extinguishers should be available at the construction site, and high-temperature asphalt and heating equipment must be kept away from areas where flammable materials are stored.

[0031] Furthermore, when preparing the sealed plugging mixture, the petroleum asphalt-based coagulant is heated to 150°C to 170°C until it is in a fluid state. Then, the continuously graded aggregate, preheated to 80°C to 100°C, is slowly added to the petroleum asphalt-based coagulant and continuously stirred until uniform. The stirring time is not less than 3 minutes to ensure that the petroleum asphalt-based coagulant fully coats the surface of the continuously graded aggregate particles, and to avoid local clumping or uneven coating due to improper feeding sequence.

[0032] Furthermore, to improve the erosion resistance of the asphalt macadam sealed subbase, polyester short fibers can be incorporated into the sealed mixture at a dosage of 0.1% to 0.3% of the mass of the continuously graded aggregate, preferably 0.2%. The fiber length is 6 mm to 12 mm, and the diameter is 15 μm to 30 μm. The polyester short fibers form a three-dimensionally dispersed reinforcing network in the asphalt binder, improving the tensile strength and crack resistance of the asphalt macadam sealed subbase and delaying fatigue cracking under repeated train dynamic loads.

[0033] Furthermore, after the asphalt macadam sealed base layer is cured, a visual inspection should be conducted on its surface. The inspection should include checking the continuity of the sealed base layer, the presence of cracks, any missed areas, and the surface smoothness. Any missed areas or cracks discovered must be repaired with a sealing mixture of the same mix proportion before step 4. The overlap between the repaired area and the original asphalt macadam sealed base layer should be no less than 50mm. After repair, the area should be allowed to cure statically for at least 1 hour. Only after passing the inspection can step 4 proceed.

[0034] Furthermore, the waste sealing mixture generated from spraying operations (including splashed material and equipment cleaning waste) contains petroleum asphalt components and must not be discarded or buried at will. It must be collected centrally and handed over to a professional solid waste treatment agency for disposal. Asphalt-containing waste liquid generated from equipment cleaning must be collected and stored separately and must not be discharged into surface water bodies or rainwater drainage systems. It must be handed over to a professional waste liquid treatment agency for treatment.

[0035] Step 4, fully lay the waterproof felt insulation layer After the asphalt macadam sealed base layer obtained in step 3 has completely dried and solidified, a waterproof felt isolation layer is fully laid on the surface of the asphalt macadam sealed base layer.

[0036] It should be noted that the waterproof felt used in the above-mentioned waterproof felt isolation layer is a polyester non-woven waterproof felt with a basis weight of 300g / m². Up to 500g / The preferred weight is 400g / The thickness ranges from 1.5mm to 2.5mm, with 2.0mm being preferred. The longitudinal tensile strength is not less than 8kN / m, the transverse tensile strength is not less than 6kN / m, and the hydrostatic pressure resistance is not less than 0.3MPa. This specification of polyester nonwoven waterproof felt possesses sufficient tensile strength and puncture resistance to withstand the repeated effects of ballast backfilling and train dynamic loads.

[0037] During installation, the longitudinal overlap width of the polyester nonwoven waterproof felt should be no less than 150mm, and the transverse overlap width should be no less than 100mm. The overlap areas should be bonded using hot-melt welding or a special adhesive, ensuring that the peel strength of the overlap is no less than 80% of the strength of the polyester nonwoven waterproof felt itself. For hot-melt welding, the welding temperature should be between 220℃ and 260℃, preferably 240℃, and the welding speed should be between 1.5m / min and 3.0m / min, preferably 2.0m / min, to ensure uniform fusion and no missed welds or overheating in the overlap areas. During installation, each section should be inspected to eliminate hollow areas, wrinkles, damage, and missed areas, ensuring a tight bond between the waterproof felt isolation layer and the asphalt-aggregate sealed bottom layer, forming a continuous and complete physical waterproof barrier, resulting in a double-layer waterproof composite structure.

[0038] It should be noted that this invention adopts a reverse double-layer waterproofing construction sequence. Unlike the traditional sequence of "laying a waterproof felt isolation layer first, then sealing the surface," this method first constructs an asphalt-aggregate sealed base layer, and then lays the waterproof felt isolation layer on top of the asphalt-aggregate sealed base layer. The asphalt-aggregate sealed base layer forms a flat and dense support surface, eliminating the risk of sharp gravel and soil edges puncturing the waterproof felt isolation layer; at the same time, the asphalt-aggregate sealed base layer seals the pores and seepage channels of the subgrade, preventing rainwater from seeping and accumulating at the bottom of the waterproof felt isolation layer, avoiding the waterproofing failure caused by long-term water accumulation and bulging at the bottom of the waterproof felt isolation layer in traditional double-layer waterproofing processes. The asphalt-aggregate sealed base layer seals the seepage of the subgrade, and the waterproof felt isolation layer isolates the water and soil exchange between the track bed and the subgrade soil, blocking the capillary uplift of groundwater and the upward flow of mud, forming a double-layer synergistic protection of "sealing water at the bottom and isolating slurry at the top."

[0039] Further, during hot melt welding, the surface temperature of the welding equipment can reach as high as 220°C to 260°C. Operators must wear heat-resistant protective gloves, combustibles such as surplus polyester non-woven fabric-based waterproofing felt shall not be stacked in the welding operation area, and fire extinguishers shall be provided at the construction site. If a special adhesive bonding method is adopted, the adhesive may contain volatile organic solvents. Operators shall work under well-ventilated conditions and wear gas masks, and open flames are strictly prohibited at the construction site.

[0040] Further, after the laying of the waterproof felt isolation layer is completed, concealed engineering acceptance shall be carried out for the entire polyester non-woven fabric-based waterproofing felt. The acceptance contents include: lap width, weld continuity, hollowing and damage. For weld quality, an inflation detection method can be used to inspect the lap weld section by section. The inflation pressure is 0.05MPa to 0.10MPa, and the pressure holding time is no less than 30 seconds. If the pressure does not drop significantly, the weld is determined to be qualified. For the detected damaged points, a patch made of the same material of polyester non-woven fabric-based waterproofing felt shall be used for repair. The size of the patch shall extend beyond the edge of the damage by no less than 100mm, and the periphery of the patch shall be edge-sealed by hot melt welding, and it can only proceed to step 5 after passing the re-inspection.

[0041] Further, waste scraps generated from cutting the polyester non-woven fabric-based waterproofing felt and damaged waterproof felt replaced during construction shall be collected centrally, shall not be left within the subgrade range or discarded along the line, and shall be transported to the designated stacking area for disposal in accordance with solid waste classification.

[0042] Step 5, layered backfilling of ballast and layered mechanical tamping After the concealed engineering of the double-layer waterproof composite structure passes the acceptance, clean high-strength hard ballast is used for layered backfilling on the upper part of the double-layer waterproof composite structure obtained in step 4.

[0043] It should be noted that the aforementioned ballast is made of first-class crushed stone ballast, with a compressive strength of not less than 100MPa, a Los Angeles abrasion rate of not more than 20%, a particle size of 25mm to 63mm, and a content of needle-like and flake particles of not more than 15%. The surface of the first-class crushed stone ballast shall be clean without soil coating, and the silt content shall not be more than 1%.

[0044] Further, in order to protect the double-layer waterproof composite structure from extrusion damage caused by the edges and corners of the first-class crushed stone ballast, a medium-coarse sand buffer cushion with a thickness of 20mm to 30mm can be laid on the surface of the waterproof felt isolation layer first, and then layered backfilling of first-class crushed stone ballast is carried out. The medium-coarse sand has a particle size of 0.5mm to 2mm, and it is leveled and compacted after laying. The medium-coarse sand buffer cushion forms a flexible transition layer between the waterproof felt isolation layer and the first-class crushed stone ballast, disperses the concentrated stress from the edges and corners of the first-class crushed stone ballast, and reduces the risk of extrusion and cutting of the waterproof felt isolation layer by the first-class crushed stone ballast under the repeated action of train dynamic loads.

[0045] Each backfill layer should be 100mm to 200mm thick, preferably 150mm. After each layer of primary crushed stone ballast is backfilled, it should be leveled, and then mechanical tamping equipment should be used to tamp the ballast layer evenly, ensuring that the primary crushed stone ballast particles are tightly interlocked and evenly stressed. Each layer should be tamped at least twice until the ballast surface is flat, dense, and free of obvious loose areas. Layered backfilling and tamping should be alternated until the ballast is restored to the required elevation.

[0046] Furthermore, during mechanical tamping, the tamping frequency is 25Hz to 35Hz, preferably 30Hz; the tamping clamping force is 10kN to 16kN, preferably 13kN; and the tamping duration at each insertion point is 0.8s to 1.5s, preferably 1.0s. These parameters ensure that the tamping energy is fully transferred to the bottom of each layer of primary crushed stone ballast, resulting in a uniform and dense interlocking structure of the primary crushed stone ballast particles. Simultaneously, excessive tamping energy is avoided to prevent impact damage to the underlying double-layer waterproof composite structure.

[0047] It should be noted that if the thickness of a single backfill layer is too large, the compaction energy cannot be transferred to the bottom, leaving loose interlayers inside the primary crushed stone ballast layer; if the thickness of a single backfill layer is too small, the construction steps increase and the construction time at the skylight points is insufficient. A single layer thickness of 150mm is preferred, balancing compaction quality and construction efficiency.

[0048] Furthermore, after the track bed is backfilled to the required elevation, the top surface of the track bed should be tested for compaction. The testing method is the track bed resistance test. The longitudinal track bed resistance should not be less than 8 kN / sleeper, and the transverse track bed resistance should not be less than 10 kN / sleeper. Sections that fail the test must be further compacted until the above resistance requirements are met before the line can be opened to traffic.

[0049] Furthermore, asphalt-containing wastewater, equipment cleaning wastewater, and mud-containing wastewater generated during construction must not be directly discharged into railway drainage ditches or natural water bodies. They must be collected separately and handed over to professional wastewater treatment facilities. Solid waste generated during construction, such as abandoned ballast, waste waterproof felt scraps, and waste medium-coarse sand, must be collected separately and transported to designated locations for disposal according to solid waste classification. This invention uses a petroleum asphalt-based coagulant to replace traditional chemical grouting materials (such as cement grout and chemical grouting fluid). After the asphalt-aggregate sealed base layer solidifies, it exhibits good chemical stability and does not release harmful leachates into the subgrade soil and groundwater, thus reducing the impact of the remediation project on the surrounding soil and water environment.

[0050] Technical effects of the present invention This invention employs a reverse double-layer waterproofing construction process. First, a high-pressure asphalt gravel spray is applied to the surface of the base bed to seal the bottom layer. Then, a waterproof felt cloth isolation layer is fully laid, thus forming a double-layer waterproof composite structure of "bottom water sealing and top grout separation".

[0051] In sealing water seepage channels in the subgrade, a sealed mixture of continuously graded aggregate and petroleum asphalt-based curing agent, under high-pressure jetting, penetrates and fills the fine cracks and through pores on the subgrade surface, forming a seamless asphalt-aggregate sealed base layer after solidification. This sealed base layer blocks rainwater infiltration channels and the capillary rise path of groundwater at its source. Simultaneously, the petroleum asphalt-based curing agent binds the continuously graded aggregate into the pores of the subgrade surface, enhancing the overall strength and erosion resistance of the subgrade surface, thus overcoming the shortcomings of traditional waterproof membranes that only provide isolation and fail to reinforce the subgrade soil.

[0052] In terms of construction sequence, the reverse construction sequence provides a smooth and dense support surface for the upper waterproof felt isolation layer by sealing the asphalt macadam base layer, eliminating the risk of sharp gravel puncturing the waterproof felt isolation layer in traditional processes. Because the asphalt macadam base layer has blocked the water seepage channels in the subgrade, rainwater no longer accumulates at the bottom of the waterproof felt isolation layer, avoiding the waterproofing failure caused by long-term water accumulation and bulging at the bottom of the waterproof felt isolation layer in traditional double-layer waterproofing processes.

[0053] In terms of track bed protection, clean, high-strength primary crushed stone ballast is backfilled in layers and mechanically compacted layer by layer. This ensures that the primary crushed stone ballast particles are tightly interlocked to form a uniform load-bearing structure. The compacted track bed buffers the downward transmission of dynamic loads from trains, reduces the concentrated compression and cutting effect of the primary crushed stone ballast edges on the double-layer waterproof composite structure, and extends the service life of the double-layer waterproof composite structure.

[0054] In terms of construction applicability, all procedures are completed in stages within the railway maintenance window, without the need for large-scale deep excavation and full-section replacement. The procedures are closely connected, and the curing time of the asphalt macadam sealed base layer is short, meeting the requirements for rapid resumption of operation of existing lines.

[0055] In summary, this invention, through the synergistic combination of reverse double-layer waterproofing construction sequence, asphalt macadam spraying and sealing, waterproof felt isolation, and layered compaction of the roadbed, breaks the vicious cycle of "water seepage, mud accumulation, softening, and frost heave," and achieves long-term treatment of water damage to the roadbed.

[0056] Example 1 Step 1: Utilize railway maintenance windows to close the line, and use a combination of manual and mechanical methods to remove aging ballast, silt, and loose slag. Level the base surface and adjust the drainage slope. The transverse drainage slope of the base surface should be 2%, and the flatness deviation of the base surface should not exceed 10mm. After passing the inspection, proceed to the next step.

[0057] Step 2: Accurately reposition the sleepers, correcting the center-to-center distance deviation between adjacent sleepers to no more than [percentage missing]. A track jack is used to adjust the track elevation so that the track height deviation does not exceed [the specified value]. The track gauge deviation does not exceed Horizontal deviation not exceeding After passing the inspection, proceed to step 3.

[0058] Step 3: Select continuously graded aggregate with a particle size ranging from 2.36 mm to 9.5 mm, where the passing rate through a 9.5 mm sieve is 95%, through a 4.75 mm sieve is 40%, and through a 2.36 mm sieve is 0%. Use a petroleum asphalt-based coagulant with a penetration of 60 (0.1 mm) and a softening point of 46℃, and prepare a sealed-off mixture at a mass ratio of continuously graded aggregate to petroleum asphalt-based coagulant of 100:8. Heat the petroleum asphalt-based coagulant to 150℃ until it reaches a fluid state, then add the continuously graded aggregate preheated to 80℃, and continue stirring for at least 3 minutes. Simultaneously, incorporate polyester short fibers at a dosage of 0.1% of the mass of the continuously graded aggregate, with a fiber length of 6 mm and a fiber diameter of 15 μm. The sealing mixture is sprayed onto the treated substrate surface using a high-pressure spraying device at a pressure of 0.3 MPa and a thickness of 30 mm. After static curing for no less than 2 hours, the asphalt macadam sealed base layer is obtained after passing the visual inspection.

[0059] Step 4: Fully cover the surface of the sealed asphalt gravel base layer with polyester non-woven waterproof felt, with a weight of 300g / m². The thickness is 1.5mm. The longitudinal overlap width is not less than 150mm, and the transverse overlap width is not less than 100mm. Hot-melt welding is used at a welding temperature of 220℃ and a welding speed of 1.5m / min. The lap welds are inspected segment by segment using the air inflation test method. The air inflation pressure is 0.05MPa, and the pressure holding time is not less than 30 seconds. If there is no significant pressure drop, the weld is deemed qualified. After the concealed works pass the acceptance inspection, a double-layer waterproof composite structure is obtained.

[0060] Step 5: First, lay a 20mm thick medium-coarse sand buffer layer on the surface of the double-layer waterproof composite structure. The medium-coarse sand has a particle size of 0.5mm. After leveling and compacting, use clean first-grade crushed stone ballast with a particle size of 25mm for backfilling in layers. Each backfill layer is 100mm thick. After each backfilling is completed, use mechanical tamping equipment to tamp the layers evenly. The tamping frequency is 25Hz, the tamping clamping force is 10kN, the tamping duration at each insertion point is 0.8s, and the number of tamping passes is not less than 2. The layered backfilling and layered tamping are carried out alternately until the track bed is restored to the required elevation. After the track bed resistance test is passed, the line can be opened to traffic.

[0061] Example 2 Step 1: The horizontal drainage slope of the base surface is 4%, and the remaining operations are the same as Step 1 of Example 1.

[0062] Step 2: Same as Step 2 in Example 1.

[0063] Step 3: The continuous graded aggregate has a 100% pass rate through a 9.5mm sieve, a 70% pass rate through a 4.75mm sieve, and a 15% pass rate through a 2.36mm sieve. The petroleum asphalt-based coagulant has a penetration of 80 (0.1mm) and a softening point of 54℃. The mass ratio of continuous graded aggregate to petroleum asphalt-based coagulant is 100:15. The petroleum asphalt-based coagulant is heated to 170℃, and then the preheated continuous graded aggregate (to 100℃) is added, with continuous stirring for at least 3 minutes. The polyester short fiber content is 0.3% of the mass of the continuous graded aggregate, with a fiber length of 12mm and a fiber diameter of 30μm. The spraying pressure is 0.8MPa, the spraying thickness is 60mm, and static curing is allowed for at least 2 hours. After passing visual inspection, a sealed asphalt-aggregate base layer is obtained.

[0064] Step 4: The weight of the polyester nonwoven waterproof felt is 500g / m². The thickness is 2.5mm, the hot melt welding temperature is 260℃, the welding speed is 3.0m / min, the gas filling test pressure is 0.10MPa, and the remaining operations are the same as step 4 of Example 1.

[0065] Step 5: The thickness of the medium-coarse sand buffer layer is 30mm, the particle size of the medium-coarse sand is 2mm, the particle size of the ballast is 63mm, the thickness of each backfill layer is 200mm, the tamping frequency is 35Hz, the tamping clamping force is 16kN, the tamping duration at each insertion point is 1.5s, and the remaining operations are the same as Step 5 of Example 1.

[0066] Example 3 Step 1: The horizontal drainage slope of the base surface is 3%, and the remaining operations are the same as Step 1 of Example 1.

[0067] Step 2: Same as Step 2 in Example 1.

[0068] Step 3: The passing rate of the continuously graded aggregate through a 9.5mm sieve is 97.5%, through a 4.75mm sieve is 55%, and through a 2.36mm sieve is 7.5%. The petroleum asphalt-based coagulant has a penetration of 70 (0.1mm) and a softening point of 50℃. The mass ratio of continuously graded aggregate to petroleum asphalt-based coagulant is 100:12. The petroleum asphalt-based coagulant is heated to 160℃, and then the continuously graded aggregate preheated to 90℃ is added. Stirring is continued for at least 3 minutes. The polyester short fiber content is 0.2% of the mass of the continuously graded aggregate, with a fiber length of 9mm and a fiber diameter of 22μm. The spraying pressure is 0.5MPa, the spraying thickness is 40mm, and static curing is allowed for at least 2 hours. After passing visual inspection, a sealed asphalt-aggregate base layer is obtained.

[0069] Step 4: The weight of the polyester nonwoven waterproof felt is 400g / m². The thickness is 2.0 mm, the hot melt welding temperature is 240℃, the welding speed is 2.0 m / min, the gas filling test pressure is 0.075 MPa, and the remaining operations are the same as step 4 of Example 1.

[0070] Step 5: The thickness of the medium-coarse sand buffer layer is 25mm, the particle size of the medium-coarse sand is 1.25mm, the particle size of the ballast is 44mm, the thickness of each backfill layer is 150mm, the tamping frequency is 30Hz, the tamping clamping force is 13kN, the tamping duration at each insertion point is 1.0s, and the remaining operations are the same as Step 5 of Example 1.

[0071] Example 4 Steps 1 to 2: Same as in Example 3.

[0072] Step 3: The gradation parameters, mass ratio, heating temperature, preheating temperature, stirring time, and polyester short fiber content of the continuous graded aggregate and petroleum asphalt-based coagulant are the same as in Example 3. The spraying pressure is adjusted to 0.6 MPa, the spraying thickness is adjusted to 50 mm, and static curing is allowed for no less than 2 hours. After passing the appearance inspection, the asphalt crushed stone sealed bottom layer is obtained.

[0073] Steps 4 and 5: Same as in Example 3.

[0074] Comparative Example 1 Steps 1 to 2: Same as in Example 3.

[0075] Step 3: Skip the construction of the asphalt macadam sealed base layer, do not perform any sealing treatment on the treatment base surface, and proceed directly to Step 4.

[0076] Step 4: Directly lay polyester non-woven waterproof felt on the entire surface of the treatment base. All parameters of the waterproof felt and the overlapping and welding operations are the same as in Step 4 of Example 3. After the concealed works pass the acceptance inspection, a single-layer waterproof structure is obtained.

[0077] Step 5: Same as step 5 in Example 3.

[0078] Comparative Example 2 Steps 1 to 2: Same as in Example 3.

[0079] Step 3 (first layer in traditional sequence): Fully cover the treated substrate with polyester non-woven waterproof felt. All parameters of the waterproof felt and the overlapping and welding operations are the same as in step 4 of Example 3, as the first layer of construction.

[0080] Step 4 (Second layer in traditional sequence): Spray an asphalt macadam layer on top of the waterproof felt. The preparation parameters of the sealing mixture, spraying pressure, spraying thickness and curing time are the same as in Step 3 of Example 3, as the second layer of construction.

[0081] Step 5: Same as step 5 in Example 3.

[0082] Experimental Objective The reverse double-layer waterproofing treatment method of the present invention was verified in the treatment of ballast track subgrade defects on existing railway lines. The waterproofing and sealing performance, waterproof felt integrity and track bed stability were verified. The method was compared with a single-layer waterproofing scheme that omitted the asphalt macadam sealing layer (Comparative Example 1) and a traditional sequential double-layer waterproofing scheme (Comparative Example 2). The reverse construction sequence and the contribution of the asphalt macadam sealing layer to the overall waterproofing system were quantified.

[0083] Experimental sample preparation A section of an existing conventional passenger and freight railway line suffering from mud pumping and frost damage was selected. The surface layer of the subgrade in this section is silty clay, with a groundwater depth of approximately 0.8m. During the rainy season, the subgrade moisture content exceeds the standard, and the track bed shows significant dirt and siltation. Six test units of equal length were selected in this section, each 20m long, corresponding to Examples 1 to 4 and Comparative Examples 1 and 2, respectively. The initial degree of damage in each test unit was assessed as comparable.

[0084] According to the process parameters specified in each embodiment and comparative example, the rectification and construction of each test unit were completed within the railway maintenance window. After the construction was completed, the line was opened, and the cumulative operation observation period was 12 months.

[0085] Experimental conditions During construction, the temperature ranged from 18°C ​​to 26°C, the relative humidity from 55% to 70%, and there was no rainfall. During the operational observation period, the axle load and traffic density of trains passing through each test unit were the same, the annual rainfall was approximately 820 mm, and there were no significant differences in groundwater level conditions.

[0086] Experimental steps (1) After construction, core samples were taken from the sealed bottom layer of asphalt macadam in each test unit, the porosity of the core samples was determined, and the permeability coefficient of the sealed bottom layer of asphalt macadam was tested according to relevant industry standards using the vacuum saturation method. (Unit: cm / s).

[0087] (2) When the waterproof felt is accepted as a concealed project, the number of puncture points of the waterproof felt in each test unit (unit: point / 20m) shall be recorded to evaluate the integrity of the waterproof felt.

[0088] (3) After the track bed backfilling and compaction are completed, the longitudinal track bed resistance of each test unit is tested using the track bed resistance test method. (Unit: kN / sleeper) and transverse track bed resistance (Unit: kN / pillow)

[0089] (4) After 12 months of operation and observation, a disease re-examination was conducted on each test unit, and the following indicators were recorded: the percentage of the area where water accumulation and bulging occurred at the bottom of the waterproof felt. (Unit: %) Percentage of recurrence length of basal surface frost heave and mud shedding (Unit: %), Track bed dirt index (Scores range from 0 to 10, with lower scores indicating cleaner track beds).

[0090] (5) Summarize the data of each test unit and calculate the performance improvement rate of each embodiment relative to the comparative example.

[0091] Experimental or test results Table 1 Summary of main process parameters for each embodiment and comparative example

[0092] Table 2. Test results of physical properties of asphalt-aggregate sealed subbase and integrity of waterproof felt.

[0093] Permeability coefficient According to Darcy's law Calculation, where Infiltration flow rate (unit: ), For hydraulic gradient, Cross-sectional area of ​​water passage (unit: ).

[0094] Table 2 shows that the permeability coefficients of the asphalt macadam sealed substrates obtained in Examples 1 to 4 are... All in to The permeability is within the range of cm / s, meeting the impermeability requirements. Example 1, due to its lowest spraying pressure (0.3 MPa), thinnest spraying thickness (30 mm), and least amount of asphalt (mass ratio 100:8), has the highest relative porosity (6.8%) and the largest relative permeability coefficient, but it is still within an acceptable range. Examples 3 and 4 have better porosity and permeability coefficients than Example 1, consistent with the preferred parameter combination.

[0095] Regarding the integrity of the waterproof felt, the number of puncture points per 20m was 0 in Examples 1 to 4. This is because the asphalt-aggregate sealed substrate provided a smooth and dense support surface for the waterproof felt, eliminating the risk of punctures from sharp gravel on the substrate. Comparative Example 1 (no sealed substrate, waterproof felt laid directly on the treated substrate) had 7 puncture points per 20m, and Comparative Example 2 (conventional sequence, waterproof felt laid directly on the substrate) had 5 puncture points per 20m. Both were damaged due to residual sharp gravel or soil edges on the substrate. The number of puncture points in Examples 1 to 4 was reduced by 100% compared to Comparative Examples 1 and 2.

[0096] Table 3. Test results of track bed resistance after backfilling and compaction

[0097] Table 3 shows that the track bed resistance of Examples 1 to 4 and the two comparative examples all meet the acceptance requirements. Example 1, due to its smallest backfill thickness (100mm) and lowest tamping parameters, has a relatively low track bed resistance but is still acceptable. Example 2, with its highest tamping parameters, has the highest track bed resistance. The small differences in initial track bed resistance among the examples and comparative examples indicate that the track bed resistance is mainly controlled by the tamping parameters and has little relation to the construction sequence. This provides a benchmark for comparing the recurrence rate of track defects during the subsequent operation period, excluding differences in the initial track bed resistance.

[0098] Table 4 Comparison of disease recurrence after 12 months of operation

[0099] As shown in Table 4, after 12 months of operation, the percentage of water bulges at the bottom of the waterproof felt in Examples 1 to 4 was [not specified]. The percentage of recurrence length of basal surface frost heave and mud shedding does not exceed 1.2%. The dirt index of the track bed does not exceed 2.5%. All scores are no more than 2.1 points, indicating a significant overall waterproofing effect.

[0100] Compared with Comparative Example 1, Example 3 It decreased from 18.7% to 0.6%, a drop of 96.8%; It decreased from 22.4% to 1.1%, a drop of 95.1%. The score dropped from 6.8 to 1.5, a decrease of 77.9%. This indicates that the sealed bottom layer of asphalt macadam is the key layer for blocking the water seepage channels of the subgrade and preventing water accumulation and bulging at the bottom of the waterproof felt. After omitting this layer (Comparative Example 1), water accumulated at the bottom of the waterproof felt for a long time, and the bulging area and the recurrence rate of frost heave increased significantly, which is consistent with the analysis of the shortcomings of the traditional process in the specific implementation.

[0101] Compared with Comparative Example 2, Example 3 It decreased from 12.3% to 0.6%, a drop of 95.1%; It decreased from 16.8% to 1.1%, a drop of 93.5%; The score dropped from 5.4 to 1.5, a decrease of 72.2%. This indicates that the reverse construction sequence (sealing the base layer first, then applying the waterproofing felt) significantly reduces the risk of waterproofing failure compared to the traditional sequence (waterproofing felt first, then sealing layer). In Comparative Example 2, the waterproofing felt was laid directly on the substrate, and sharp gravel on the substrate caused 5 puncture points per 20m (see Table 2). In addition, the sealing layer was constructed above the waterproofing felt and could not seal the seepage channels in the substrate. Rainwater could still seep down along the gaps in the substrate and accumulate at the bottom of the waterproofing felt, resulting in a significantly higher rate of blistering and grouting recurrence compared to the reverse construction examples.

[0102] Example 1, due to its thinnest spray thickness (30mm) and lowest asphalt content (mass ratio 100:8), had the highest relative porosity in the sealed bottom layer, resulting in incomplete sealing of some seepage channels. and Slightly higher than Examples 2 to 4, but still a significant improvement over the two comparative examples, indicating that even with the minimum parameter combinations, the method of the present invention can effectively break the vicious cycle of "water seepage, mud accumulation, softening, and frost heave." Example 2, due to its largest spray thickness (60mm) and highest asphalt content (mass ratio 100:15), had the densest sealed bottom layer. and The lowest efficiency is achieved, but the amount of construction materials used increases accordingly. Examples 3 and 4 employ optimized parameters to achieve a better balance between waterproofing performance and material usage. and All are close to the level of Example 2.

[0103] Based on the above experimental results, the reverse double-layer waterproofing treatment method of this invention achieves long-term treatment of water damage to the subgrade through the synergistic effect of the following three aspects: First, the asphalt-crushed stone sealed bottom layer seals the micro-cracks and penetrating pores in the subgrade from the source, reducing the permeability coefficient. achieve to The speed is on the order of cm / s, effectively blocking rainwater infiltration channels and capillary rise paths of groundwater; secondly, the reverse construction sequence allows the sealed bottom layer of asphalt macadam to provide a flat and dense support surface for the waterproof felt, reducing the number of puncture points on the waterproof felt from 7 per 20m in Comparative Example 1 and 5 per 20m in Comparative Example 2 to 0 per 20m, a reduction of 100%, while eliminating the cause of water accumulation and bulging at the bottom of the waterproof felt; thirdly, the clean first-grade crushed stone ballast is backfilled in layers and mechanically compacted layer by layer, ensuring that the longitudinal resistance of the track bed is not less than 8kN / sleeper and the lateral resistance is not less than 10kN / sleeper. The dense track bed effectively buffers the downward transmission of dynamic loads from trains, extending the service life of the double-layer waterproof composite structure. After 12 months of operation, the proportion of recurrence length of frost heave and mud spillage on the track surface in each embodiment did not exceed 2.5%, and the track bed dirt index did not exceed 2.1 points. Compared with the two comparative examples, there was a significant improvement, which proved that the method of the present invention can effectively block the vicious cycle of "water seepage, mud accumulation, softening, and frost heave" and achieve long-term treatment of water damage to the track bed of existing railway lines.

[0104] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A double-layer waterproof closed-loop treatment construction process for railway subgrade defects, characterized in that, Includes the following steps: Step 1: Remove the damaged soil and silt from the subgrade, level the base surface and adjust the drainage slope to make the transverse drainage slope of the base surface 2% to 4%; Step 2: Mix the continuously graded aggregate and petroleum asphalt-based curing agent at a mass ratio of 100:8 to 100:15 to prepare a sealing and plugging mixture. Apply the sealing and plugging mixture to the treated subgrade surface through high-pressure spraying at a pressure of 0.3 MPa to 0.8 MPa and a thickness of 30 mm to 60 mm. Allow it to stand and cure until solidified to form a sealed asphalt aggregate base layer. Step 3: Fully cover the surface of the sealed asphalt macadam base layer with a waterproof felt isolation layer, and use hot melt welding or adhesive to bond the overlapping areas to form a double-layer waterproof composite structure. Step 4: Backfill the ballast in layers on top of the double-layer waterproof composite structure. Each layer should be 100mm to 200mm thick. After each layer is backfilled, compact it mechanically until the track bed is restored to the required elevation.

2. The double-layer waterproof closed-loop treatment construction technology for railway subgrade defects according to claim 1, characterized in that, The continuously graded aggregate has a particle size of 2.36 mm to 9.5 mm, wherein the passing rate of a 9.5 mm sieve is 95% to 100%, the passing rate of a 4.75 mm sieve is 40% to 70%, and the passing rate of a 2.36 mm sieve is 0% to 15%; the penetration of the petroleum asphalt-based coagulant is 60 to 80 0.1 mm particles at 25°C, 100 g, and 5 s, the softening point is 46°C to 54°C, and the ductility is not less than 100 cm at 15°C.

3. The double-layer waterproof closed-loop treatment construction technology for railway subgrade defects according to claim 1, characterized in that, In step two, when preparing the sealed plugging mixture, the petroleum asphalt-based coagulant is heated to 150°C to 170°C and then added to the petroleum asphalt-based coagulant at 80°C to 100°C and stirred continuously for no less than 3 minutes.

4. The double-layer waterproof closed-loop treatment construction technology for railway subgrade defects according to claim 1, characterized in that, In step two, polyester short fibers are incorporated into the sealed plugging mixture at a dosage of 0.1% to 0.3% of the mass of the continuously graded aggregate, with a fiber length of 6 mm to 12 mm and a diameter of 15 μm to 30 μm.

5. The double-layer waterproof closed-loop treatment construction technology for railway subgrade defects according to claim 1, characterized in that, The waterproof felt isolation layer is made of polyester non-woven waterproof felt with a basis weight of 300g / m². Up to 500g / The thickness is 1.5mm to 2.5mm, the longitudinal tensile strength is not less than 8kN / m, the transverse tensile strength is not less than 6kN / m, and the hydrostatic pressure resistance is not less than 0.3MPa.

6. The double-layer waterproof closed-loop treatment construction technology for railway subgrade defects according to claim 1, characterized in that, In step three, the longitudinal overlap width of the polyester nonwoven waterproof felt shall not be less than 150mm, and the transverse overlap width shall not be less than 100mm; when hot-melt welding is used, the welding temperature shall be 220℃ to 260℃, and the welding speed shall be 1.5m / min to 3.0m / min.

7. The double-layer waterproof closed-loop treatment construction technology for railway subgrade defects according to claim 1, characterized in that, In step four, a medium-coarse sand buffer layer with a thickness of 20mm to 30mm is first laid on the surface of the waterproof felt isolation layer. The medium-coarse sand has a particle size of 0.5mm to 2mm. After laying, leveling and compacting, the ballast is backfilled in layers.

8. The double-layer waterproof closed-loop treatment construction technology for railway subgrade defects according to claim 1, characterized in that, In step four, the ballast is grade one crushed stone ballast with a compressive strength of not less than 100 MPa, a Los Angeles abrasion rate of not more than 20%, a particle size of 25 mm to 63 mm, a needle-like and flaky particle content of not more than 15%, and a mud content of not more than 1%.

9. The double-layer waterproof closed-loop treatment construction technology for railway subgrade defects according to claim 1, characterized in that, In step four, the mechanical tamping frequency is 25Hz to 35Hz, the tamping clamping force is 10kN to 16kN, the tamping duration at each insertion point is 0.8s to 1.5s, and the number of tamping passes per layer is no less than 2.

10. The double-layer waterproof closed-loop treatment construction technology for railway subgrade defects according to claim 1, characterized in that, In step one, the flatness deviation of the base surface shall not exceed 10mm; after step one is completed, the sleepers shall be reset and the center distance deviation between adjacent sleepers shall be corrected to not exceed [a certain value]. The elevation deviation of the track does not exceed The track gauge deviation does not exceed Horizontal deviation not exceeding .

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