High fill airport roadbed structure in high-cold and saline soil area and construction method thereof

Abstract

The application relates to the technical field of airport roadbed treatment in high-cold and saline soil areas, and discloses a high-fill airport roadbed structure in high-cold and saline soil areas and a construction method thereof, which comprises, from top to bottom, a pavement structure layer, a coarse-grained replacement cushion layer, a medium-sand protection layer, a composite geomembrane isolation layer and drainage blind trenches arranged on the two sides of the coarse-grained replacement cushion layer. The two drainage blind trenches are arranged on the left and right sides of the coarse-grained replacement cushion layer and are communicated with the coarse-grained replacement cushion layer, so that water in the coarse-grained replacement cushion layer can flow into the drainage blind trenches along the horizontal slope or the vertical slope and then be drained; the composite geomembrane isolation layer is continuously laid in the entire pavement influence area and extends to the boundary of the coarse-grained replacement cushion layer or the vicinity of the roadbed treatment boundary on the two sides, so as to ensure the salt isolation continuity; and the medium-sand protection layer is covered above the composite geomembrane isolation layer and is completed with paving and leveling before the coarse-grained replacement cushion layer is laid.

Description

Technical Field

[0001] This invention relates to the field of airport runway treatment technology in high-altitude saline-alkali land areas, and particularly to a high-fill airport runway structure and its construction method in high-altitude saline-alkali land areas. Background Technology

[0002] As my country's civil aviation infrastructure construction continues to extend into complex geological regions such as the Northwest, Northeast, plateaus, and cold regions, airport projects are increasingly facing the challenge of subgrade treatment in high-altitude, cold, and saline soil areas. These areas typically exhibit significant seasonal variations in groundwater levels, intense evaporation, large diurnal temperature differences, frequent freeze-thaw cycles, and high soil salinity. In airport runway, taxiway, and apron pavement engineering, if the subgrade structure is affected by salt migration, frost heave, or moisture retention, it is prone to pavement bulging, cracking, frost heave, strength reduction, base layer corrosion, and uneven settlement, which can severely impact aircraft operational safety.

[0003] Currently, common measures for treating road or airport subgrades in saline-alkali land areas include: replacing saline soil with non-saline soil, setting up barrier layers, increasing the height of the subgrade or roadbed, pre-dissolving by immersion, chemical improvement, setting up drainage ditches, and laying geosynthetic materials. These methods can improve saline-alkali soil problems to some extent, but they still have insufficient adaptability in high-fill airport subgrade projects in high-altitude and cold regions. For example, simply setting up an impermeable membrane can block the rise of salt, but if the water accumulated on top of the impermeable membrane cannot be drained in time, it may form a frozen water layer in a low-temperature environment, causing frost heave; simply setting up a crushed stone cushion layer can improve drainage capacity, but it cannot completely block the rise of lower salt with capillary water; simply increasing the subgrade filling height can extend the salt migration path, but the workload is large and it cannot fundamentally solve the problem of water and salt migration; simply setting up lateral drainage ditches is difficult to prevent the upward migration of groundwater and its accumulation at the bottom of the pavement structure layer.

[0004] Existing airport runway subgrade treatment technologies in high-altitude saline-alkali soil areas have the following main defects and shortcomings: Single salt-barrier measures can easily lead to water accumulation problems in the upper layer: Existing technologies often use geomembranes or composite geomembranes as salt-barrier and seepage-proof layers, but if there is a lack of effective drainage channels above the barrier layer, rainwater, snowmelt, or construction residue water can easily accumulate above the barrier layer. In high-altitude and cold regions, this stagnant water will freeze and cause frost heave, which will then damage the pavement structure.

[0005] Single drainage measures are insufficient to effectively prevent salt rise: relying solely on gravel layers, blind drains, or drainage ditches can remove some seepage, but cannot reliably prevent the upward migration of salt-containing capillary water from the underlying saline soil. Over the long term, salt may still accumulate at the bottom of the pavement structure or base course, causing salt swelling and corrosion damage.

[0006] Coarse-grained cushion layers laid directly on the isolation layer are prone to damaging the geomembrane: In high embankment roadbeds, coarse-grained materials such as crushed stone and gravel are often used as drainage or replacement cushion layers. If the coarse-grained materials are in direct contact with the composite geomembrane, under the action of paving, rolling and long-term load, the large particle edges may puncture or wear the composite geomembrane, resulting in the failure of salt isolation and seepage prevention functions.

[0007] Insufficient measures to mitigate capillary water rise: A major cause of saline soil disease is the upward migration of saline water under capillary action; if the existing structure lacks a coarse-grained cushion layer with large pores and low capillary action, capillary water may continue to rise, increasing the risk of salt accumulation at the bottom of the pavement structure layer.

[0008] Insufficient control of frost heave in high-altitude and cold regions: Freeze-thaw cycles exist in high-altitude and cold regions. When drainage inside the structure is not smooth, the freezing and expansion of water will cause pavement bulges, cracks, misalignments and other defects. If the existing structure cannot simultaneously achieve rapid drainage and isolation from saline water supply, it will be difficult to maintain the stability of the pavement foundation in the long term.

[0009] High-fill airport pavement requires high overall stability and construction reliability: airport pavements bear aircraft loads, and the requirements for controlling structural deformation are stricter than those for ordinary roads. Traditional saline soil treatment methods, if the structural layers are unclear, the construction quality is difficult to control, or local functions are lacking, can easily affect the long-term smoothness and operational safety of the airport pavement.

[0010] In summary, existing technologies cannot simultaneously meet the comprehensive requirements of high-fill airport roadbeds in high-altitude and saline soil areas for salt isolation, waterproofing, drainage, frost heave prevention, corrosion prevention, and protective isolation layers. There is an urgent need for a composite roadbed structure and construction method that is simple in structure, has clear functions, is controllable in construction, has good durability, and is suitable for high-fill airport roadbeds. Summary of the Invention

[0011] The main objective of this invention is to provide a high-fill airport runway subgrade structure and its construction method in high-altitude saline-alkali soil areas, so as to solve the problem that the existing technology is unable to simultaneously meet the comprehensive requirements of salt isolation, waterproofing, drainage, frost heave prevention, corrosion prevention and protective isolation layer for high-fill airport runway subgrades in high-altitude saline-alkali soil areas.

[0012] To achieve the above objectives, the present invention provides the following technical solution: A high-fill airport roadbed structure in a cold and saline soil region includes: a pavement structure layer, a coarse-grained replacement cushion layer, a medium sand protective layer, a composite geomembrane isolation layer arranged from top to bottom, and drainage blind ditches set on both sides of the coarse-grained replacement cushion layer. The drainage blind ditches on both sides are located on the left and right sides of the coarse-grained replacement cushion layer and are connected to the coarse-grained replacement cushion layer, so that water in the coarse-grained replacement cushion layer can enter the drainage blind ditches along the cross slope or longitudinal slope and then be discharged; the composite geomembrane isolation layer should be continuously laid within the entire pavement influence area and extend to both sides to the boundary of the coarse-grained replacement cushion layer or the vicinity of the roadbed treatment boundary to ensure the continuity of salt isolation; the medium sand protective layer covers the composite geomembrane isolation layer and is laid and leveled before the coarse-grained replacement cushion layer is laid.

[0013] As a further improvement of the present invention, the coarse-particle replacement cushion layer adopts crushed stone, pebbles, gravel, natural graded round gravel, graded crushed stone or other coarse-particle materials.

[0014] As a further improvement of the present invention, the medium sand protective layer is laid with clean medium sand or medium-coarse sand.

[0015] As a further improvement of the present invention, the composite geomembrane isolation layer adopts a two-layer geotextile and one-layer membrane, one-layer geotextile and one-layer membrane, or three-layer geotextile and two-layer membrane structure. The geomembrane material is made of high-density polyethylene geomembrane, polyethylene geomembrane, or other geomembranes; The geotextile is made of polypropylene filament geotextile, polyester filament geotextile, or other geotextiles. The composite geomembrane isolation layer, together with the upper coarse-particle replacement layer and the drainage blind ditches on both sides, form a composite protection system that isolates salt, drains water, and prevents frost heave.

[0016] As a further improvement of the present invention, drainage blind ditches are set on both sides of the coarse particle replacement cushion layer, arranged longitudinally along the airport runway, and located at the edge of the coarse particle replacement cushion layer or on its outer side.

[0017] As a further improvement of the present invention, the interior of the drainage blind ditch is filled with crushed stone, pebbles or other permeable coarse materials; The exterior is wrapped with geotextile; The drainage blind ditch and the coarse-particle replacement bedding layer together form a transverse drainage channel.

[0018] As a further improvement of the present invention, the thickness of the coarse particle replacement cushion layer is 30cm to 150cm; The soluble salt content of the material used for coarse-particle replacement cushion layer should be less than 0.3%; the maximum particle size should preferably not exceed 2 / 3 of the compacted thickness of a single layer.

[0019] As a further improvement of the present invention, the thickness of the medium sand protective layer is 3cm to 15cm; The thickness of the geomembrane in the composite geomembrane isolation layer shall not be less than 0.3 mm.

[0020] As a further improvement of the present invention, the width of the drainage blind ditch is 0.5m to 3.0m; the depth of the blind ditch is 0.5m to 2.0m; and the particle size of the filler in the blind ditch is 2cm to 10cm. The unit area mass of the geotextile covering the drainage blind ditch shall not be less than 200g / ㎡.

[0021] To achieve the above objectives, the present invention also provides the following technical solution: A method for constructing a high-fill airport runway subgrade structure in a high-altitude saline-alkali land area, applicable to the aforementioned high-fill airport runway subgrade structure, comprising the following steps: Based on the airport pavement design documents, engineering geological survey data, distribution range of saline soil, groundwater level, seasonal freezing depth, embankment height, and drainage conditions of the airport area, the scope of subgrade treatment, thickness of replacement layer, scope of composite geomembrane laying, thickness of medium sand protective layer, and layout scheme of drainage blind drains are determined. The following contents are reviewed: soil salinity and type of saline soil; groundwater level and capillary rise height; freezing depth and freeze-thaw cycle characteristics of the airport area; design elevation and thickness of high embankment subgrade; pavement structural layer type and airport load rating; and connection conditions of the airport's overall drainage system. The construction area was cleared, removing surface plant roots, silt, organic soil, garbage, soft soil, and unsuitable filling materials. Lay a composite geomembrane isolation layer on the qualified underlying layer; overlap or weld between adjacent composite geomembranes; after laying, promptly check the composite geomembrane for defects such as damage, perforation, tearing or loose joints. A medium sand protective layer is laid on top of the composite geomembrane isolation layer; a continuous protective layer is formed first, and then the subsequent coarse-grained material is laid. A well-graded coarse-grained replacement layer is constructed in layers above the medium sand protective layer; the construction method is layered paving and layered compaction; after the replacement layer is completed, a drainage channel connected to the drainage blind ditches on both sides should be formed, and a transverse or longitudinal drainage slope should be set according to the design. Drainage blind ditches are excavated or simultaneously installed on both sides of the replacement sub-base. The drainage blind ditches are filled with permeable crushed stone, pebbles or other coarse materials and wrapped with geotextile on the outside. The drainage blind ditches are connected to the replacement sub-base and connected to the airport area drainage system, side ditches, collection wells, seepage wells or other drainage facilities. After the replacement subbase is completed and passes inspection, the airport pavement structure layer is constructed on top of it. The pavement structure layer may include a cement-stabilized base course, a lean concrete base course, a cement concrete surface course, an asphalt concrete surface course, or other airport pavement design structures. After construction is completed, a quality inspection will be conducted.

[0022] This invention utilizes a composite structure consisting of a composite geomembrane isolation layer, a medium sand protective layer, a coarse-grained replacement layer, and drainage ditches on both sides. This structure effectively blocks the upward flow of salt. The composite geomembrane isolation layer prevents the upward migration of saline water from the underlying saline soil, avoiding salt accumulation at the bottom of the pavement structure and reducing the risk of salt swelling and corrosion at the source. It also weakens capillary action; the coarse-grained replacement layer, with its large pore structure, exhibits weak capillary action, effectively reducing the ability of groundwater to carry salt upwards and decreasing salt migration to the upper structure. Furthermore, it rapidly removes rainwater and snowmelt infiltration; the coarse-grained replacement layer connects to the drainage ditches on both sides, quickly draining water that has entered the upper structure of the pavement, preventing water from stagnating below the pavement structure for extended periods. Finally, it reduces the risk of frost heave damage in cold regions; because water accumulated inside the structure can be drained promptly, the amount of frozen water is significantly reduced in low-temperature environments, mitigating the damage caused by frost heave forces to the pavement structure. Protecting the composite geomembrane and extending the lifespan of the salt barrier system, the medium sand protective layer prevents coarse-particle replacement material from directly puncturing and abrading the composite geomembrane, improving the integrity and durability of the isolation layer and ensuring long-term salt barrier effect. Improving the stability of high-fill airport subgrades, the coarse-particle replacement layer has good load-bearing and drainage performance, improving the stress state of the lower part of the pavement structure layer, reducing the risk of uneven deformation, and improving the overall stability of the airport subgrade. Reducing corrosion and damage to the pavement structure layer, this structure reduces the accumulation of salt and moisture at the bottom of the pavement structure layer, reducing the risk of salt corrosion to cement-stabilized materials, concrete structures, and other engineering materials, and extending the service life of the airport pavement. Simple structure, convenient construction, and strong engineering applicability. The composite geomembrane, medium sand, gravel, crushed stone, and blind drain materials and processes used are mature, facilitating on-site construction organization and suitable for large-area high-fill airport subgrade construction. Good economic efficiency. Compared with large-scale deep excavation and replacement, long-term dewatering, or complex chemical treatment, this structure, through the reasonable combination of salt barrier, drainage, and protective layers, can reduce the amount of treatment work and lower the overall cost. Meeting the safety and durability requirements of airport engineering, airport pavements require high levels of smoothness, stability, and durability. This invention can reduce the risks of various problems such as salt heave, frost heave, corrosion, and water accumulation, thus contributing to ensuring the long-term safe operation of airports. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the high-fill airport runway subgrade structure in high-altitude saline soil areas according to the present invention; Figure 2 This is a schematic flowchart illustrating the steps of an embodiment of the construction method for a high-fill airport runway subgrade structure in a cold and saline soil region according to the present invention. Figure 3 This is a flowchart illustrating the construction method of a high-fill airport runway subgrade structure in a high-altitude saline-alkali land area according to an embodiment of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] The terms "first," "second," and "third" used in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this invention are only used to explain the relative positional relationships and movements between components in a specific orientation (as shown in the accompanying drawings). If the specific orientation changes, the directional indications also change accordingly. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0026] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0027] This invention addresses the multiple problems caused by the coupling effect of water, salt, and temperature in the runway foundation of high-fill airports in cold and saline soil areas, including salt swelling, dissolution, frost heave, and corrosion. It proposes a multi-layered composite runway foundation protection structure. The core concept is to construct a three-dimensional protection system that combines prevention and drainage, with drainage as the main function and salt isolation as a supplement, and the structure works in synergy. This system is not a simple superposition of single functional layers, but rather an organic integration of multiple functions such as load diffusion, capillary water cutoff, groundwater isolation, and rapid surface water drainage through the upper load-bearing transition, the middle interface protection and water diversion, the lower salt barrier, and the edge directional collection and drainage. This system cuts off the chain of action of water and salt transmission to the runway structure layer from the root.

[0028] This invention establishes a clear collaborative working mechanism through the systematic correlation of various technical features in terms of spatial location, material properties, and mechanical matching. The coarse-particle replacement cushion layer is placed beneath the pavement structure layer. Its highly permeable, large-pore structure not only serves as a horizontal drainage channel but also physically cuts off the upward path of capillary water. Furthermore, it acts as a load-bearing transition layer to diffuse the loads from aircraft and vehicles above, improving the stress state of the high-fill pavement. Blind drainage ditches on both sides are arranged longitudinally along the edges of the cushion layer, directly connecting with it. This allows rainwater infiltration and snowmelt collected within the cushion layer to flow smoothly along the cross or longitudinal slope into the blind drains and outwards into the site drainage system. Together, they form a three-dimensional drainage network combining surface and line features, preventing the formation of a stagnant water layer within the cushion layer and effectively eliminating the risk of freezing and frost heave caused by water accumulation in high-altitude and cold regions. A medium sand protective layer is laid between the coarse-grained replacement cushion layer and the composite geomembrane isolation layer. It is constructed using clean medium or medium-coarse sand, providing a smooth, flexible, and uniform support surface for the underlying composite geomembrane. Simultaneously, under the paving and compaction of the upper coarse-grained cushion layer and operational loads, it effectively buffers and disperses the puncture stress and abrasion caused by the sharp edges of the coarse particles on the geomembrane, ensuring the physical integrity of the underlying salt barrier. The composite geomembrane isolation layer is continuously laid above the treated high-fill roadbed or saline-alkali soil foundation, extending laterally to the boundary of the coarse-grained replacement cushion layer or the roadbed treatment boundary to ensure salt barrier continuity. Utilizing the low permeability of the geomembrane, it effectively blocks the upward migration of saline water from the underlying saline soil. Simultaneously, it forms a water and salt regulation pattern with the upper medium sand protective layer and coarse-grained replacement cushion layer, significantly reducing the risk of salt accumulation at the bottom of the pavement structure and the adverse effects of groundwater level fluctuations on the superstructure.

[0029] The various layers of this invention are functionally tightly coupled, resulting in a significantly superior overall technical effect compared to the superposition of single measures. In terms of comprehensive disease prevention and control, the composite geomembrane isolation layer blocks the lower salt source, the coarse-grained cushion layer physically cuts off capillary upwelling channels, and the drainage blind drains quickly remove infiltrated water from the upper layer. This triple action synergistically achieves a systematic inhibition of salt swelling, dissolution, frost heave, and salt corrosion, effectively curbing the harmful chain of water-salt-temperature coupling. Regarding structural durability, the medium sand protective layer ensures that the composite geomembrane is protected from mechanical damage throughout construction and the entire operation cycle, allowing its salt-barrier and seepage-proof function to operate stably for a long time, thus significantly extending the service life of the pavement structure. In terms of improved hydraulic conditions, the transverse drainage system composed of the coarse-grained cushion layer and the blind drains on both sides ensures a water-free environment above the pavement, fundamentally eliminating the prerequisite for freezing and frost heave, while maintaining the long-term drainage capacity of the cushion layer. In terms of optimized stress performance, the coarse-grained replacement cushion layer, as a load-bearing transition layer, effectively diffuses the upper load, improves the stress distribution of high-fill pavement, and enhances the overall structural stability. Furthermore, this invention provides clear preferred ranges and adjustable intervals for key parameters such as subbase thickness, material gradation, geomembrane specifications, blind drain dimensions, and drainage slope. It can be adapted to different working conditions such as airport engineering level, fill height, saline soil type, groundwater level, and frost depth, and has good engineering adaptability and economic rationality.

[0030] like Figure 1 As shown, this embodiment provides an example of a high-fill airport runway subgrade structure in a high-altitude saline-alkali land area. Specifically, the high-fill airport runway subgrade structure in this embodiment includes, from top to bottom, a pavement structure layer 1, a coarse-grained replacement cushion layer 2, a medium sand protective layer 3, a composite geomembrane isolation layer 4, and drainage blind ditches 5 located on both sides of the coarse-grained replacement cushion layer 2. The drainage blind ditches 5 are located on the left and right sides of the coarse-grained replacement cushion layer 2 and are connected to it, allowing water in the coarse-grained replacement cushion layer 2 to enter the drainage blind ditches 5 along the cross slope or longitudinal slope and then drain out. The composite geomembrane isolation layer 4 should be continuously laid within the entire pavement influence area and extend to both sides to the boundary of the coarse-grained replacement cushion layer 2 or near the runway subgrade treatment boundary to ensure salt isolation continuity. The medium sand protective layer 3 covers the composite geomembrane isolation layer 4 and is laid and leveled before the coarse-grained replacement cushion layer 2 is laid.

[0031] Among them, the pavement structure layer 1 is set at the top of the high-fill airport pavement structure in high-altitude and saline soil areas, and can be airport cement concrete pavement structure, asphalt concrete pavement structure or airport rigid / semi-rigid composite pavement structure; the pavement structure layer 1 is used to directly bear aircraft load, vehicle load and environmental effects. The coarse-grained replacement layer 2, located below the pavement structure layer 1, is a layer of well-graded coarse-grained material. It can be composed of crushed stone, pebbles, gravel, natural graded round gravel, graded crushed stone, or other highly permeable coarse-grained materials. Its main functions include: forming a highly permeable drainage layer to allow for rapid lateral drainage of infiltrated water from pavement structure layer 1; utilizing the coarse-grained, large-pore structure to weaken capillary upwelling; extending the salt migration path and reducing the risk of salt accumulation at the bottom of the pavement structure layer; improving the stress conditions of the upper part of the high-fill pavement subgrade and enhancing structural stability; and serving as a load-bearing transition layer between the traditional pavement structure layer and the underlying isolation system.

[0032] The medium sand protective layer 3 is located below the coarse particle replacement cushion layer 2 and above the composite geomembrane isolation layer 4. The medium sand protective layer 3 is constructed using clean medium sand or medium-coarse sand. Its main functions are: to protect the lower composite geomembrane isolation layer 4; to prevent coarse and angular particles in the coarse particle replacement cushion layer 2 from puncturing or abrading the composite geomembrane under paving, compaction, and operational loads; to provide a relatively flat, flexible, and uniform support surface for the composite geomembrane; and to a certain extent, to play a role in local leveling and stress diffusion.

[0033] The composite geomembrane isolation layer 4 is installed below the medium sand protective layer 3 and laid above the treated high embankment or saline soil foundation. The composite geomembrane isolation layer 4 can adopt a two-layer geotextile and one-layer geomembrane, one-layer geotextile and one-layer geomembrane, or three-layer geotextile and two-layer geomembrane structure. The geomembrane material can be high-density polyethylene geomembrane, polyethylene geomembrane, or other geomembranes with good salt corrosion resistance and impermeability. The geotextile can be polypropylene filament geotextile, polyester filament geotextile, or other geotextiles that meet strength requirements. The composite geomembrane is pressed into the pavement structure layer by a certain width, mainly to prevent water from outside the pavement from entering the replacement layer and to reduce salt accumulation. Its main functions include: blocking the upward migration of salt-containing water from the lower saline soil; preventing salt accumulation at the bottom of the pavement structure layer 1; reducing the impact of groundwater level changes on the upper pavement structure layer; reducing the probability of salt swelling, dissolution, and corrosion; and forming a composite protection system for salt isolation, drainage, and frost heave prevention together with the upper coarse-particle replacement layer 2 and the drainage blind ditches on both sides 5.

[0034] Drainage blind drains 5 are installed on both sides of the coarse-grained replacement subbase 2, arranged longitudinally along the airport runway subgrade, located at or outside the edge of the coarse-grained replacement subbase 2. The drainage blind drains 5 can be filled with crushed stone, pebbles, or other permeable coarse-grained materials, and wrapped with geotextile to prevent fine particles from entering and causing blockage. Their main functions include: collecting and draining rainwater infiltration, snowmelt, and construction residue from the coarse-grained replacement subbase 2; preventing the formation of a stagnant water layer within the coarse-grained replacement subbase 2; preventing freezing and frost heave in cold regions due to water accumulation; lowering the water level within the coarse-grained replacement subbase 2 to maintain its long-term drainage function; and forming a transverse drainage channel together with the coarse-grained replacement subbase 2.

[0035] Based on the airport engineering grade, embankment height, saline soil type, groundwater level, frost depth, rainfall conditions, material sources, and pavement structure design requirements, the following parameters can be adjusted: The thickness of the coarse-grained replacement layer 2 should be 30cm to 150cm, preferably 50cm to 100cm. For high-fill airport runway foundations, areas with high groundwater levels, or areas with abundant rainwater and snowmelt, the thickness can be appropriately increased.

[0036] Material requirements for coarse-grained replacement subbase 2: It is advisable to use well-graded crushed stone, gravel, cobbles or coarse-grained soil; the soluble salt content should be less than 0.3%; the maximum particle size should not be greater than 2 / 3 of the compacted thickness of a single layer; the permeability should meet the requirements for rapid drainage; materials with excessive mud content, easy weathering, easy disintegration or high salt content should not be used.

[0037] The thickness of the medium sand protective layer 3 should be 3cm to 15cm, preferably 5cm to 10cm. If the particle size of the upper replacement layer is large or the edges are sharp, the thickness can be appropriately increased.

[0038] Parameters of composite geomembrane isolation layer 4: Two layers of geotextile and one layer of geomembrane or three layers of geotextile and two layers of geomembrane can be used; the thickness of the geomembrane can be selected according to the project requirements, preferably not less than 0.3mm, and preferably 0.5mm to 1.5mm; the overlap width should preferably not be less than 20cm; the joints can be made by hot-melt welding, adhesive bonding, sewing and welding or other reliable connection methods; the composite geomembrane should have tensile strength, tear strength, puncture resistance and salt corrosion resistance that meet the requirements of construction and operation.

[0039] The dimensions of the drainage blind ditch 5 are as follows: the width of the blind ditch should be 0.5m to 3.0m; the depth of the blind ditch should be 0.5m to 2.0m; the dimensions can be determined according to the airport drainage system layout, the thickness of the coarse particle replacement layer 2, and the site water catchment conditions; the particle size of the filler in the blind ditch should be 2cm to 10cm; the unit area mass of the geotextile wrapped around the drainage blind ditch 5 should be not less than 200g / ㎡, preferably not less than 300g / ㎡.

[0040] Slope setting: The bottom or top surface of the coarse particle replacement cushion layer 2 should be set with a certain transverse drainage slope in combination with the cross slope of the airport runway, so that the water in the cushion layer can flow to the drainage blind ditches on both sides; the drainage blind ditches 5 should have a drainage slope along the longitudinal direction and be connected to the site drainage system.

[0041] Preferably, in this embodiment, the saline water in the lower saline soil tends to migrate upwards under capillary action. The composite geomembrane isolation layer 4 forms a continuous seepage-proof and salt-barrier, preventing the lower saline water and salt from entering the upper structure. Even if some water migrates to below the isolation layer, it is difficult for it to continue upwards to the bottom of the pavement structure layer 1. After rainwater, snowmelt, or seepage water from pavement cracks enters below the pavement structure layer 1, it will enter the well-graded coarse-particle replacement cushion layer 2. Due to its large pores and high permeability, the water can flow laterally quickly and be discharged into the drainage blind ditches 5 on both sides, avoiding long-term stagnant water. The large pore structure of the coarse-particle replacement cushion layer 2 can also significantly weaken the capillary water upward action and reduce the water's ability to carry salt upwards. The medium sand protective layer 3 serves as a flexible protective transition layer, preventing large particles in the coarse-particle replacement cushion layer 2 from directly damaging the composite geomembrane and ensuring the long-term reliability of the salt-barrier system. The drainage blind ditches 5 on both sides continuously discharge the water accumulated inside the coarse particle replacement layer 2 to prevent the water level from rising; when the temperature drops in high-altitude and cold regions, the risk of frost heave is significantly reduced due to the low free water content inside the structure; thus, the structure can simultaneously achieve the comprehensive functions of salt isolation, seepage prevention, drainage, reducing capillary water, preventing frost heave and protecting the pavement structural layer.

[0042] This embodiment uses a composite geomembrane isolation layer 4 to block the upward migration of lower salt and saline capillary water; a medium sand protective layer 3 to protect the composite geomembrane from damage by the upper coarse-grained material; a coarse-grained replacement layer 2 to form a large-pore drainage channel to quickly drain rainwater, snowmelt, and pavement infiltration water, while weakening the upward effect of capillary water; and drainage blind ditches 5 on both sides to promptly drain water accumulated inside the coarse-grained replacement layer 2, preventing water level rise and freezing heave; ultimately, it prevents salt from accumulating at the bottom of the pavement structure layer, reducing the damage to the airport pavement structure caused by salt heave, freezing heave, and corrosion.

[0043] like Figure 2 As shown, this embodiment also provides an embodiment of a construction method for a high-fill airport runway subgrade structure in a high-altitude saline-alkali land area. In this embodiment, the construction method for a high-fill airport runway subgrade structure in a high-altitude saline-alkali land area is applied to the high-fill airport runway subgrade structure in the high-altitude saline-alkali land area described in the above embodiment. The implementation principle of this construction method for a high-fill airport runway subgrade structure in a high-altitude saline-alkali land area is as follows: Figure 3 As shown, the specific steps include: Step S1: Construction preparation and geological verification: Based on the airport pavement design documents, engineering geological survey data, distribution range of saline soil, groundwater level, seasonal freezing depth, embankment height and drainage conditions of the airport area, the scope of subgrade treatment, thickness of replacement layer, scope of composite geomembrane laying, thickness of medium sand protective layer and layout scheme of drainage blind ditch are determined. Before construction, the following should be verified: soil salinity and type of saline soil; groundwater level and capillary rise height; freezing depth and freeze-thaw cycle characteristics of the site; design elevation and thickness of high embankment roadbed; pavement structure layer type and airport load rating; and connection conditions of the site's overall drainage system.

[0044] Step S2: Surface cleaning and underlying layer treatment: The construction area was cleared, removing surface plant roots, silt, organic soil, garbage, soft soil, and unsuitable filling materials. If the underlying soil is saline, it should be leveled, compacted, or partially replaced according to design requirements. The underlying layer should meet the specified compaction and flatness requirements, and the surface should be free of sharp stones, protrusions, or obvious pits to avoid damaging the subsequently laid composite geomembrane.

[0045] Step S3: Laying the composite geomembrane isolation layer: Lay the composite geomembrane isolation layer on the properly treated underlying layer. Before laying, check whether the surface of the underlying layer is flat, dense, and free of sharp objects. During laying, the composite geomembrane should be laid flat and tightly against the underlying layer to avoid wrinkles, gaps, and excessive stretching. Adjacent composite geomembranes should be overlapped or welded, with an overlap width of no less than 20cm. For slopes or areas with drainage, the membrane at the uphill or higher position should overlap the membrane at the downhill or lower position to reduce the possibility of water entering the joint. After the composite geomembrane is laid, it should be inspected promptly for defects such as damage, perforation, tearing, or loose joints. If damage is found, it should be repaired with patches made of the same material. The edges of the patches should extend a certain width beyond the damaged area, and the seepage prevention in the repaired area should be continuous.

[0046] Step S4: Lay a medium sand protective layer: A medium sand protective layer is laid on top of the composite geomembrane isolation layer. The medium sand should be clean, have low mud content, and be free of sharp, large particles, frozen lumps, and debris.

[0047] During paving, avoid direct rolling of construction machinery over the exposed composite geomembrane. A combination of manual labor and small machinery can be used to form a continuous protective layer before proceeding with the subsequent laying of coarse-grained materials. The medium sand protective layer should be of uniform thickness, have a smooth surface, and completely cover the composite geomembrane isolation layer.

[0048] Step S5: Filling with coarse-grained replacement subbase: A well-graded coarse-grained replacement layer should be constructed in layers above the medium sand protective layer. During the filling process, the particle size, mud content, salt content, and gradation of the material should be controlled.

[0049] During paving, coarse particles should be avoided from concentrating and impacting the medium sand protective layer and composite geomembrane. Layered paving and compaction methods can be used, with the loose thickness of each layer determined based on the compaction equipment capacity and material particle size.

[0050] After the replacement layer is completed, a drainage channel should be formed that connects with the drainage blind ditches on both sides, and a horizontal or longitudinal drainage slope should be set according to the design so that the water in the layer can flow smoothly into the drainage blind ditches.

[0051] Step S6: Install drainage blind ditches on both sides: Drainage blind ditches are excavated or installed simultaneously on both sides of the replacement subgrade. The drainage blind ditches are filled with permeable crushed stone, pebbles or other coarse-grained materials, and wrapped with geotextile to prevent fine particles from entering the blind ditches with the water flow and causing siltation.

[0052] The drainage ditch should be connected to the replacement subgrade and connected to the airport area drainage system, side ditches, sump pits, seepage pits, or other drainage facilities. The bottom of the drainage ditch should preferably have a longitudinal drainage slope to ensure smooth water flow.

[0053] In high-altitude and cold regions, special attention should be paid to ensuring that the drainage path of blind drains is unobstructed to prevent water from freezing and causing blockages. If necessary, inspection wells, collection wells, or anti-freezing drainage structures can be installed according to the actual conditions of the project.

[0054] Step S7: Constructing the conventional airport pavement structure layer: After the replacement subbase is completed and passes inspection, the airport pavement structure layer is constructed on top of it. The pavement structure layer may include a cement-stabilized base course, a lean concrete base course, a cement concrete surface course, an asphalt concrete surface course, or other airport pavement design structures.

[0055] During the construction of the pavement structural layer, it is essential to ensure that the top surface of the replacement subbase is flat and compacted to avoid disturbing the underlying drainage and salt barrier structures. The pavement structural layer may be extended outward or pressed inward to a certain width on both sides according to design requirements to ensure the stability of the edge supports.

[0056] Step S8: Quality Inspection and Operation Maintenance After construction, the following quality inspections should be conducted: inspection of the integrity of the composite geomembrane laying; inspection of the thickness and flatness of the medium sand protective layer; inspection of the gradation, compaction, and drainage performance of the replacement subbase material; inspection of the connectivity and drainage capacity of the drainage blind drains; and inspection of the flatness, strength, and compaction quality of the pavement structure layer. During operation, the drainage blind drain outlets, sump pits, or related drainage facilities should be checked regularly for blockages to ensure long-term smooth drainage of the structure.

[0057] Preferably, the composite geomembrane isolation layer laying technology in this embodiment effectively blocks capillary water rise and salt migration in high-altitude saline soil areas, while preventing the impact of lower saline soil volume changes caused by freeze-thaw cycles on the upper structure. The medium sand protective layer forms a buffer interface above the composite geomembrane, dispersing the concentrated stress of the upper coarse-particle replacement layer and preventing mechanical construction damage to the impermeable layer. The gradation design of the coarse-particle replacement layer ensures high permeability, forming a synergistic drainage system with the drainage blind ditches on both sides, accelerating the removal of water infiltrating the layer and inhibiting frost heave damage caused by water accumulation during freezing. The drainage blind ditches are filled with permeable gravel and wrapped with geotextile, ensuring drainage efficiency while preventing clogging caused by fine particle intrusion. Their connection design with the site's overall drainage system ensures long-term drainage stability. The traditional pavement structure layers are constructed on a stable foundation treated with salt-isolated drainage, avoiding direct damage to the pavement structure from saline soil corrosion and frost heave. Layered compaction and quality control during construction ensure that each structural layer reaches the designed compaction degree, guaranteeing the long-term stability of the overall structure under aircraft dynamic loads. Continuous monitoring of the integrity of the impermeable layer and the smoothness of the drainage system during the operation and maintenance phase can promptly detect and repair local damage caused by freeze-thaw cycles or salt corrosion, maintaining the long-lasting effectiveness of the structure's salt-proof and drainage capabilities.

[0058] The specific embodiments of the invention have been described in detail above, but these are merely examples, and the invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications or substitutions to the invention are also within the scope of this invention. Therefore, all equivalent transformations, modifications, and improvements made without departing from the spirit and principles of this invention should be included within the scope of this invention.

Claims

1. A high fill airport pavement structure in an alpine saline soil region, characterized in that, The high-fill airport runway subgrade structure in the high-altitude saline-alkali land area includes: Below the pavement structure layer, from top to bottom, a coarse-grained replacement layer, a medium-sand protective layer, and a composite geomembrane isolation layer are laid sequentially. Drainage blind ditches are provided on both sides of the coarse particle replacement layer. The drainage blind ditches are connected to the coarse particle replacement layer so that water in the coarse particle replacement layer can be discharged laterally into the drainage blind ditches. The coarse-particle replacement cushion layer is a drainage layer composed of coarse-particle materials and has a transverse drainage slope toward the drainage blind ditch. The composite geomembrane isolation layer is laid horizontally and continuously below the pavement structure layer, and extends laterally to the boundary of the coarse-grained replacement layer or near the boundary of the subgrade treatment. The medium sand protective layer covers the composite geomembrane isolation layer and is located below the coarse-grained replacement cushion layer.

2. The high-fill airport pavement structure in an alpine saline soil region according to claim 1, characterized in that, The coarse-grained replacement subbase uses crushed stone, pebbles, gravel, natural graded round gravel, graded crushed stone or other coarse-grained materials. 3.The high fill airport pavement structure in high-cold and saline soil area according to claim 1, characterized in that, The medium sand protective layer is constructed using clean medium sand or medium-coarse sand.

4. The high fill airport pavement structure in cold and saline soil region according to claim 1, characterized in that, The composite geomembrane isolation layer adopts a two-layer geotextile and one-layer membrane, one-layer geotextile and one-layer membrane, or three-layer geotextile and two-layer membrane structure; The geomembrane material can be high-density polyethylene geomembrane, polyethylene geomembrane, or other geomembranes; The geotextile is made of polypropylene filament geotextile, polyester filament geotextile, or other geotextiles. The composite geomembrane isolation layer, together with the upper coarse-particle replacement layer and the drainage blind ditches on both sides, form a composite protection system that isolates salt, drains water, and prevents frost heave.

5. The high fill airport pavement structure in cold and saline soil region according to claim 1, characterized in that, Drainage blind ditches are set on both sides of the coarse particle replacement cushion layer, arranged longitudinally along the airport runway, and located at the edge of the coarse particle replacement cushion layer or on its outer side. 6.The high-fill airport pavement structure in an alpine saline soil region according to claim 5, wherein, The interior of the drainage blind ditch is filled with crushed stone, pebbles or other permeable coarse material; The exterior is wrapped with geotextile; The drainage blind ditch and the coarse-particle replacement bedding layer together form a transverse drainage channel.

7. The high-fill airfield pavement structure of claim 1, wherein, The thickness of the coarse-particle replacement layer is 30cm to 150cm; The soluble salt content of the material used for coarse-particle replacement cushion layer should be less than 0.3%; the maximum particle size should preferably not exceed 2 / 3 of the compacted thickness of a single layer. 8.The high-fill airport pavement structure in an alpine saline soil region according to claim 1, wherein, The thickness of the medium sand protective layer is 3cm to 15cm; The thickness of the geomembrane in the composite geomembrane isolation layer shall not be less than 0.3 mm.

9. The high-fill airport runway subgrade structure in high-altitude saline-alkali land areas according to claim 1, characterized in that, The width of the drainage blind ditch is 0.5m to 3.0m; the depth of the blind ditch is 0.5m to 2.0m; and the particle size of the filler inside the blind ditch is 2cm to 10cm. The unit area mass of the geotextile covering the drainage blind ditch shall not be less than 200g / ㎡.

10. A method for constructing a high-fill airport runway subgrade structure in a high-altitude saline-alkali land area, applicable to the high-fill airport runway subgrade structure in a high-altitude saline-alkali land area as described in any one of claims 1 to 9, characterized in that, The construction method for the high-fill airport runway subgrade structure in the high-altitude saline-alkali soil area includes the following steps: Based on the airport pavement design documents, engineering geological survey data, distribution range of saline soil, groundwater level, seasonal freezing depth, embankment height, and drainage conditions of the airport area, the scope of subgrade treatment, thickness of replacement layer, scope of composite geomembrane laying, thickness of medium sand protective layer, and layout scheme of drainage blind drains are determined. The following contents are reviewed: soil salinity and type of saline soil; groundwater level and capillary rise height; freezing depth and freeze-thaw cycle characteristics of the airport area; design elevation and thickness of high embankment subgrade; pavement structural layer type and airport load rating; and connection conditions of the airport's overall drainage system. The construction area was cleared, removing surface plant roots, silt, organic soil, garbage, soft soil, and unsuitable filling materials. Lay a composite geomembrane isolation layer on the qualified underlying layer; overlap or weld between adjacent composite geomembranes; after laying, promptly check the composite geomembrane for defects such as damage, perforation, tearing or loose joints. A medium sand protective layer is laid on top of the composite geomembrane isolation layer; a continuous protective layer is formed first, and then the subsequent coarse-grained material is laid. A well-graded coarse-grained replacement layer is constructed in layers above the medium sand protective layer; the construction method is layered paving and layered compaction; after the replacement layer is completed, a drainage channel connected to the drainage blind ditches on both sides should be formed, and a transverse or longitudinal drainage slope should be set according to the design. Drainage blind ditches are excavated or simultaneously installed on both sides of the replacement sub-base. The drainage blind ditches are filled with permeable crushed stone, pebbles or other coarse materials and wrapped with geotextile on the outside. The drainage blind ditches are connected to the replacement sub-base and connected to the airport area drainage system, side ditches, collection wells, seepage wells or other drainage facilities. After the replacement subbase is completed and passes inspection, the airport pavement structure layer is constructed on top of it. The pavement structure layer may include a cement-stabilized base course, a lean concrete base course, a cement concrete surface course, an asphalt concrete surface course, or other airport pavement design structures. After construction is completed, a quality inspection will be conducted.

Images