Salinized soil roadbed pavement structure in seasonal frozen area

Abstract

The invention provides a seasonal frozen area salinized soil roadbed pavement structure and a construction method thereof, and the seasonal frozen area salinized soil roadbed pavement structure comprises drainage blind ditches, a waterproof mechanism layer, a rigidity reinforcing layer, a thermal insulation partition layer, a block gravel layer, a roadbed filler layer, a pavement base layer and a pavement layer, a waterproof mechanism layer, a rigidity reinforcing layer, a heat preservation partition layer, a block gravel layer, a roadbed filler layer, a pavement base layer and a pavement layer are sequentially arranged on the natural ground surface from bottom to top, a drainage pipe is embedded in the waterproof mechanism layer, geomembranes are laid on the waterproof mechanism layer and the block gravel layer, and salinized soil partition layers are arranged in the heat preservation partition layer and the roadbed filler layer. And a ventilation pipe is embedded in the block gravel layer. The roadbed structure is scientific and reasonable in structural design, ventilation can be effectively enhanced, water guiding, water seepage and drainage effects are good, rigidity and heat preservation and heat insulation can be effectively enhanced, capillary water partition and saline soil improvement and solidification can be achieved, and the roadbed structure is high in water permeability, high in strength and excellent in freezing resistance.

Description

Technical Field

[0001] This invention belongs to the field of roadbed engineering technology, specifically relating to a roadbed and pavement structure for saline soil in seasonally frozen areas. Background Technology

[0002] Saline soil is a general term for saline soil, alkaline soil, and various salinized and alkali-affected soils. In highway engineering, it generally refers to soil with an average soluble salt content greater than 0.3% within 1.0m below the surface, mainly distributed in inland areas such as Inner Mongolia, Qinghai, and Xinjiang. More and more foundation engineering projects are located in seasonally frozen saline soil areas. The series of adverse engineering properties of saline soil can severely damage roadbeds and directly affect the service life of roads. Permafrost refers to soil and rock with negative temperatures and containing ice. Based on the length of the freezing period, it can be divided into transient permafrost, seasonal permafrost, and perennial permafrost. my country is the third largest permafrost country in the world, with seasonal permafrost accounting for approximately 48% of its land area. Permafrost contains a large amount of ice crystals and unfrozen water, and its characteristics are extremely complex. It is also extremely sensitive to temperature. When the temperature rises, the ice crystals in the permafrost will melt into water, leading to a decrease in the bearing capacity of the permafrost, resulting in diseases such as frost heave and thaw settlement. In seasonally frozen soil regions, road frost damage is quite severe, with frost heave, road surface cracks, and frost heave damage to roads and ancillary structures being the most common problems.

[0003] Under the influence of seasonally frozen soil environments, water and salt in saline soil migrate, and groundwater and salt also infiltrate the roadbed structure, easily causing various degrees of damage, specifically manifested as salt swelling, frost heave, and frost heave. These phenomena can lead to roadbed cracking, heave, and expansion, thereby reducing the stability and strength of the roadbed. If the migration of salt in the lower part of the roadbed with groundwater or capillary water can be effectively prevented, the damage and impact caused by water and salt migration in saline soil can be effectively solved.

[0004] Existing saline soil subgrade structures in seasonally frozen areas have poor waterproofing and breathability, hindering the dissipation of water vapor from the subgrade. This leads to gas accumulation within and beneath the subgrade, creating weak interlayers. Traditional construction methods for saline soft soil subgrades often involve excavation and replacement, requiring large quantities of externally purchased soil, increasing construction time and costs. Furthermore, these methods are highly susceptible to external temperature and seasonal variations, often failing to adequately inhibit salt ion erosion from groundwater, severely impacting the durability of the subgrade structure and posing significant safety hazards to vehicles. Traditional soil improvement typically involves adding a series of highly polluting chemicals to the soil. However, due to the high content of various salts in saline soil, traditional solidification agents often cause problems. Saline soil subgrades inherently have low stiffness, which decreases further due to long-term freeze-thaw cycles. This leads to uneven settlement and deformation in seasonally frozen areas, ultimately resulting in reduced pavement smoothness or even damage, severely impacting driving safety.

[0005] Cement-stabilized aggregate base courses are characterized by high strength, high load-bearing capacity, high stability, and flexible construction, making them the mainstream base course form for high-grade highways in my country. However, they are prone to developing dense shrinkage cracks, which can lead to severe reflective cracks and a series of pavement defects, seriously affecting the service life of roads. In particular, the dry climate, large temperature difference, and severe freeze-thaw phenomenon in seasonally frozen areas, such as Xinjiang Uygur Autonomous Region, are important factors restricting their widespread application.

[0006] The strength of permeable concrete is much lower than that of ordinary concrete. Moreover, permeable concrete only meets the requirements of permeability, while its strength and frost resistance are poor, which limits the promotion of permeable concrete pavement. In particular, permeable concrete pavement in seasonally frozen areas has developed large cracks and granulation.

[0007] In view of this, the pavement of saline soil subgrade in seasonally frozen areas is becoming increasingly damaged, and existing technologies are difficult to meet the needs. It is necessary to overcome the defects of the existing technologies and propose a new type of pavement structure for saline soil subgrade in seasonally frozen areas. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a roadbed and pavement structure for saline soil in seasonally frozen areas, which addresses the shortcomings of the prior art. The structure is scientifically and rationally designed, which can enhance ventilation and permeability, and has good water conduction, seepage and drainage effects. It can effectively enhance rigidity and heat insulation, and can also achieve capillary water isolation and saline soil improvement and solidification. The roadbed structure has strong permeability, high strength and excellent frost resistance.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a roadbed and pavement structure for saline soil in seasonally frozen areas, characterized in that it includes drainage blind ditches, a waterproof mechanism layer, a rigidity reinforcement layer, a thermal insulation layer, a crushed stone layer, a roadbed filling layer, a pavement base layer, and a pavement layer. Drainage blind ditches are arranged along the roadbed laying direction on both sides of the compacted natural ground surface. The waterproof mechanism layer, rigidity reinforcement layer, thermal insulation layer, crushed stone layer, roadbed filling layer, pavement base layer, and pavement layer are arranged sequentially from bottom to top on the compacted natural ground surface. Drainage pipes are buried in the waterproof mechanism layer. Geomembranes are laid on both the waterproof mechanism layer and the crushed stone layer. The thermal insulation layer and the roadbed filling layer contain a saline soil isolation layer. Ventilation pipes are buried in the crushed stone layer. Multiple drainage pipes and ventilation pipes are arranged equidistantly along the roadbed cross-section direction.

[0010] Preferably, the drainage ditch is U-shaped overall. The inner surface of the drainage ditch is covered with non-woven geotextile. The bottom of the drainage ditch is constructed of concrete. A top drainage mesh is installed at the top opening of the drainage ditch. A groove is formed in the middle of the bottom layer of the drainage ditch, and a drainage mesh pipe is installed within the groove. The space between the drainage mesh pipe and the groove is filled with a lower medium-coarse aeolian sand permeable layer. Two vertical drainage meshes are symmetrically arranged between the bottom layer and the top drainage mesh, and a gravel permeable layer is filled between the two vertical drainage meshes. A vertical medium-coarse aeolian sand permeable layer is installed between the vertical drainage meshes and the sidewalls of the drainage ditch. The drainage mesh pipe is wrapped with permeable geotextile. The drainage mesh is made of high-strength filament structure with a thickness of 50-55mm and a porosity of not less than 90%. The drainage mesh pipe is also made of high-strength filament structure with a diameter of 100mm and a wall porosity greater than 75%.

[0011] Preferably, the waterproofing layer is composed of crushed stone or gravel. If a crushed stone layer is used, it should be made of permeable and hard crushed stone, with a fine mud content of ≤3% and free of plant residues, garbage, and other impurities. The width of the crushed stone layer should extend 0.5-1m beyond the roadbed on both sides to ensure an effective bearing surface for the upper roadbed during mechanical construction. If a gravel layer is used, it is composed of sand, gravel, clay, colloids, and pebble particles, with a particle size range of 0.075-60mm. The content of coarse-sized crushed stone is relatively high, ensuring that the amount of stone with a particle size greater than 5mm in the gravel soil exceeds 30%, the maximum particle size must be less than 37.5mm, and less than 2 / 3 of the loose layer thickness.

[0012] The drain pipe is an inverted V-shape with a high center and low sides. The slope of the drain pipe from the high center to the two outlets is 2%-5%. The two outlets of the drain pipe are close to the drainage blind ditch. Multiple sets of drainage holes are equidistantly arranged on the upper side wall of the drain pipe. The drain pipe with a high center and low sides can drain water by itself using the height difference.

[0013] Preferably, the geomembrane consists of three layers: the upper layer is a mixed fiber mesh or a loosely treated mixed fiber mesh; the middle layer is a polyethylene waterproof and breathable membrane with a pore size of 0.1-15μm; and the lower layer is a loosely treated mixed fiber mesh. The polyethylene waterproof and breathable membrane possesses good alkali resistance, flexibility, and high tensile strength in both warp and weft directions. The geomembrane can solve the problem of gas accumulation in the soil under the barrier layer, improving the safety of saline soil subgrades in seasonally frozen areas.

[0014] Preferably, the stiffness reinforcement layer comprises, from bottom to top, a geocell cushion layer, geocells, and a geocell protective layer. The geocells are filled with subgrade filler, which enhances the stiffness of the subgrade and can also diffuse additional loads transmitted by pedestrians or vehicles, reducing dynamic stress within the subgrade. The geocell protective layer is connected to the thermal insulation layer. The thickness of the geocell cushion layer is 80mm, the thickness of the geocell is 100mm, the side length of each geocell cell is 500mm, and the thickness of the geocell protective layer is 80mm. After backfilling the geocells with subgrade filler exceeding the space of the geocells and compacting it, the geocell protective layer is formed. After filling the surface of the waterproofing layer away from the saline soil subgrade substrate in the seasonally frozen zone with subgrade filler and compacting it, the geocell cushion layer is formed.

[0015] Preferably, the thermal insulation layer is made of one or more of polystyrene, polyurethane, injection-molded polystyrene, slag, mineral slag, foamed lightweight soil, foamed plastic, epoxy resin shell, styrene sponge plastic and concrete. The saline soil insulation layer consists of an upper medium-coarse aeolian sand layer, a middle insulation geomembrane layer and a lower medium-coarse aeolian sand layer from top to bottom. The middle insulation geomembrane layer is a waterproof and breathable geomembrane or an acid and alkali resistant composite geomembrane layer. The waterproof and breathable geomembrane in the saline soil isolation layer can facilitate the escape of gas from the lower part of the isolation layer while allowing water and salt to migrate and rise in the isolation soil, effectively controlling the occurrence of roadbed diseases in saline soft soil environments. The acid-alkali resistant composite geomembrane in the saline soil isolation layer should have long-term corrosion resistance and anti-aging properties against sulfates, chlorides, and carbonates. The acid-alkali resistant composite geomembrane adopts a two-layer fabric, two-layer membrane structure, consisting of a reinforcing base fabric, a PET film, a protective non-woven fabric, and another PET film from bottom to top, but is not limited to this composition. The inter-width overlap of the acid-alkali resistant composite geomembrane is achieved by welding, with a weld width of not less than 100mm, and the weld peel... The strength should not be less than 70kN. To ensure the quality of the overlap and closure, polypropylene (PP) split film yarns should not be used when welding the geomembrane material, and polyethylene (PE) film should not be used when bonding. The thickness of the thermal insulation layer should be 300-500mm. The thermal insulation layer can prevent heat from spreading to the lower subgrade and also prevent the loss of heat and moisture from the lower subgrade due to evaporation. A saline soil isolation layer is laid inside the thermal insulation layer, which completely blocks the erosion of the subgrade structure by capillary water carrying salt ions, thereby reducing the temperature change range of the subgrade. At the same time, it prevents the water in the saline soil subgrade in the seasonally frozen area from freezing and causing the subgrade to thaw and settle, maintaining the stability of the subgrade temperature, reducing salt migration, and improving its stability.

[0016] Preferably, the ventilation duct has an outer diameter of 200-500mm, a wall thickness of 30-50mm, a spacing of 1-5 times the outer diameter of adjacent ventilation ducts, and a center point of the ventilation duct 500-2500mm from the natural ground surface. Dustproof nets are installed at both ends of the ventilation duct, and dampers are installed at the pipe openings at both ends. A hollow stone layer is filled between adjacent ventilation ducts. The hollow stone layer consists of precast hollow concrete blocks with a side length of 50-300mm and a wall thickness of 20-50mm. The crushed stone layer is filled with crushed stone with a particle size of 100-350mm and a thickness of 500-2500mm. The dampers are temperature-sensing, automatically controlled dampers.

[0017] Preferably, the subgrade fill layer is constructed from subgrade filler containing saline soil, soluble calcium salts, urea, and microbial agents. The microbial agents contain urease and urease-producing bacteria. Different improvement schemes and proportions can be selected for the subgrade filler based on the salinity of the saline soil subgrade itself. The subgrade filler combines saline soil with microbial agents containing urease and urease-producing bacteria, soluble calcium salts, and urea, utilizing the Ca produced by the soluble calcium salts. 2+CO3 produced by the decomposition of urea by urease 2- It forms water-insoluble calcium carbonate crystals; the calcium carbonate crystals act as a cementing substance to bind the soil particles of saline soil, forming a saline soil particle skeleton. The saline soil particle skeleton is very stable, thereby improving the compressive strength of the saline soil. At the same time, it uses microorganisms that are widely present in the soil, which will not cause harm to the environment and human body, and has the advantage of being environmentally friendly. It can also shorten the curing cycle and improve construction efficiency.

[0018] The road base course is a cement-stabilized base course, with an anti-cracking agent added. This anti-cracking agent consists of 40%-60% fly ash, 8%-15% gypsum, 30%-45% mineral ash, 0.1%-0.5% organic fiber, and 1%-5% activator. The fly ash's main chemical components include SiO2 and Al2O3, with a moisture content ≤35%, loss on ignition ≤10%, and a specific surface area ≥2500 cm². 2 / g, 7d activity greater than 0.5 is acceptable; the gypsum includes one or more of anhydrite, dihydrate gypsum, fluorogypsum, and phosphogypsum, wherein the sulfur trioxide content is 40-50% by mass; the mineral ash includes one or more of coal ash, peat ash, and thermal power plant slag, whose main chemical components include CaO, SiO2, Al2O3, MgO, and Fe2O3, and whose original density is 2960 kg / m³. 3 The original specific surface area is 309 m². 2 / kg, the main chemical components in the mineral ash, by weight percentage, include: 10-15% CaO, 20-30% Al2O3, 10-20% MgO, and 35-60% oxides, wherein the oxides include one or both of SiO2 and Fe2O3; the organic fiber is polypropylene; the activator includes one or more of glycerol, sucrose, and citric acid; and the crack-resistant agent is a granular mixture.

[0019] Fly ash is a product of the combustion of pulverized coal in a cyclone furnace at a power plant. It is a composite mixture of porous debris, including glassy particles, crystals, and a small amount of unburned carbon. Its main component is spherical glassy particles, with crystals including quartz, mullite, and magnetite. The mass content of fly ash is 40%-60%. SiO2 and Al2O3 are the main sources of fly ash activity. Al2O3 not only improves the activity and crack resistance of fly ash but also provides the strength required for the base layer. The mass content of Al2O3 in fly ash is 35-45%. The larger the specific surface area of ​​fly ash, the greater its activity, preferably 3000 cm². 2 / g-4000cm 2 / g.

[0020] In crack-resistant agents, the gypsum content is 8%-15% by mass. When gypsum is incorporated into the base stabilizing aggregate, it undergoes a hydration reaction to form ettringite. The formation of ettringite involves water absorption and swelling, as well as crystal expansion. This micro-expansion achieves the purpose of compensating for micro-cracks caused by the hydration of ordinary silicates, compensating for shrinkage strain, and inhibiting crack formation. The specific surface area of ​​the gypsum is ≥2500 cm². 2 / g, preferably phosphogypsum. The main chemical components of phosphogypsum by weight include at least 30-35% CaO and 42-48% SO3. When the SO3 content is increased between 42% and 48%, it has a certain effect on improving the mechanical properties and crack resistance of the road base. However, if SO3 is added in excess, a large number of AFt crystals will be generated, which will produce reverse compressive stress inside the material, leading to structural damage and performance deterioration of the material.

[0021] The mineral ash is preferably slag from a thermal power plant, with a mass content of 30%-45%. The mineral ash used in this crack-resistant agent is a solid waste material; using this solid waste as a raw material to prepare the road base crack-resistant agent results in lower costs and is also environmentally friendly. The specific surface area of ​​the mineral ash is ≥2500 cm². 2 / g, the oxides in mineral ash include SiO2 and Fe2O3.

[0022] The organic fiber used is polypropylene fiber, which is made from propylene. Polypropylene fiber has the characteristics of high strength, good elasticity, wear resistance, corrosion resistance, and good toughness. It appears as fine filaments. Therefore, adding an appropriate amount of polypropylene fiber can more effectively connect the particles in the base course stabilizing aggregate, strengthening the base course's stability. Simultaneously, it allows the load-bearing capacity to be evenly distributed within the base course material, resulting in uniform subgrade settlement, effectively reducing pavement cracking, and improving the base course's crack resistance. Its diameter is 0.15-0.30 mm, and its density is 0.90-0.92 g / cm³. 3 The organic fiber has a mass content of 0.1%-0.5%.

[0023] The activator further stimulates the hydration of fly ash, activates the activity of clay particles in the cement-stabilized base layer, and improves the morphology of hydrates. Furthermore, some organic matter in the activator is insoluble in water and covers the surface of moisture, reducing the components in the cement-stabilized base layer that have a significant hydration mechanism with water. This allows the components of the crack-resistant agent to effectively hydrate and harden. Additionally, because some moisture is covered by organic matter, evaporation is reduced, lowering the drying shrinkage strain of the base material and reducing wet expansion and shrinkage, thereby reducing shrinkage and improving crack resistance. The activator has a mass content of 1%-5%.

[0024] In this crack-resistant agent, the weight ratio of fly ash, gypsum, and mineral ash is 3-4:0.7-0.9:2-3. Using this weight ratio, and adding organic fibers and activators, the crack-resistant agent effectively compensates for cracking caused by the shrinkage of the road base layer through the interaction of its components. This results in a better crack-resistant effect for road base materials used in seasonally frozen areas. The crack-resistant agent is used as an additive in the road base stabilizing aggregate. The weight percentages of each component in the road base material prepared using this crack-resistant agent are: fly ash 4%-10%, P.O325 cement 3.5%-4.5%, crack-resistant agent 6%-12%, and aggregate 70%-80%.

[0025] The pavement layer is made of basalt fiber permeable concrete, which comprises the following components: 1545-1610 parts aggregate, 395-425 parts cement, 1-5 parts basalt fiber, 20-23 parts silica fume, 1.3-2.3 parts water-reducing agent, and 125-140 parts water. The aggregate particle size is 2.5-10 mm, the basalt fiber length is 18-24 mm, and the basalt fiber diameter is 14-20 μm. The mass ratio of water to the total mass of cement and silica fume is 0.30-0.32, the silica fume addition is 4.5-5.5% of the total mass of cement and silica fume, and the water-reducing agent addition is 0.3-0.5% of the total mass of cement and silica fume. The porosity of the basalt fiber permeable concrete material is 15-20%, and it possesses good permeability, high strength, and excellent frost resistance.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. This invention combines ventilation pipes, a layer of crushed stone, a layer of hollow boulders, and an insulation layer to form a multi-layered cooling structure. The first cooling measure: In the warm season, the solar radiation and slope temperature differ between the shady and sunny slopes of the roadbed. This causes temperature differences between the left and right sides of the roadbed slope and ground within the embankment cross-section. A pressure difference is created at both ends of the ventilation pipe, allowing cold air to flow within it, thus cooling the roadbed. The second cooling measure: The large gaps between the stones in the crushed stone layer allow for convective heat transfer between different locations on the left and right sides of the roadbed. The ventilation pipe is located in the middle of the crushed stone layer, with a layer of hollow boulders laid between the pipes. These hollow boulders are staggered and also located in the middle of the crushed stone layer, enhancing the convective heat transfer effect and improving the cooling effect at different locations during the cold season. The same goal is to achieve uniform cooling to balance the ground temperature differences in the roadbed. The third cooling measure is that when the temperature rises in the warm season, the dampers automatically close, stopping the vertical convection heat transfer process inside the ventilation pipes, hollow blocks, and rubble layers. This significantly reduces the thermal conductivity and effectively stores the cold energy accumulated inside the roadbed during winter. The dampers are cyclically opened and closed in the warm season to continuously reduce the roadbed temperature. The fourth cooling measure is that the thermal insulation layer reduces the downward diffusion of heat, increases the cold reserve of the roadbed under the insulation layer, raises the upper limit of the frozen soil layer, and prevents the loss of heat and moisture from the lower roadbed due to evaporation. This reduces the amplitude of roadbed temperature changes, maintains roadbed temperature stability, and reduces salt migration.

[0028] 2. The thermal insulation layer of the present invention can prevent the water in the underlying subgrade from freezing. Since the subgrade is not frozen, there will be no thaw settlement. It can prevent the subgrade from freezing and swelling, and also prevent the subgrade stiffness from decreasing due to the freeze-thaw cycle in the seasonally frozen zone. This achieves the purpose of reducing the deformation of the saline soil subgrade in the seasonally frozen zone and ensures the stable operation of the subgrade structure.

[0029] 3. This invention utilizes a triple mechanism of ventilation, air circulation, convection, uniform heat exchange, heat absorption and insulation, and cold retention to effectively ensure uniform cooling of the roadbed while significantly improving the cooling effect. Although multiple cooling measures can effectively reduce the ground temperature of the roadbed and mitigate frost heave and thaw settlement in seasonally frozen areas to some extent, seasonal changes inevitably have a slight impact on the stability of the roadbed in these areas. The crushed stone layer and hollow boulders layer possess flexibility and self-stress balancing capabilities, which can alleviate the adverse effects of freeze-thaw cycles to a certain extent, significantly improving the stability of the roadbed.

[0030] 4. The partition layer in this invention is not only a reinforcement measure for the overall stability of the roadbed, but also an effective method to block the rise of capillary water in the lower structure of the roadbed, completely preventing capillary water carrying salt ions from eroding the roadbed structure. It is precisely because of the setting of multiple partition layers that the soluble salts in the untreated saline soil of the base layer are prevented from migrating and accumulating under evaporation and capillary action, thus preventing secondary salinization of the roadbed structure layer. The saline soil partition layer contains a waterproof and breathable geomembrane, which can block the migration and rise of water and salt in the soil, while also facilitating the dissipation of gas under the partition layer, effectively controlling the occurrence of roadbed diseases in the saline soft soil environment of the seasonally frozen zone.

[0031] 5. The waterproof structure layer of this invention has good permeability and hard texture. The drainage pipe is more conducive to guiding water inside the roadbed into the drainage blind ditch outside the roadbed. The two work together to guide surface precipitation, underground drainage and excess water in the structure to outside the roadbed area, ensuring that the roadbed is in a dry or moderately moist state. This can prevent softening or salt swelling and other diseases of the saline soil base in the seasonally frozen area, and avoid water damage.

[0032] 6. This invention utilizes the vertical confinement reinforcement effect of geocells to better solve the problem of uneven settlement of roadbeds in saline soils in seasonally frozen areas. By filling the roadbed with filler within a limited height, it ensures the roadbed has high rigidity and strength to withstand the load stress of large vehicles. Furthermore, sufficient friction can be generated between the geocells and the filler, effectively mitigating the early impact damage to the road surface caused by "bridge approach slab" defects. Simultaneously, the vertical reinforcement effect of geocells is among the best of all reinforcement materials, and it possesses excellent corrosion resistance, fully meeting the requirements for constructing high-grade highways in saline soils and expansive soils.

[0033] 7. In this invention, the roadbed fill layer includes a saline soil barrier layer. The formed calcium carbonate crystals are used as a cementing material to bond the soil particles of the saline soil, forming a highly stable saline soil particle skeleton, thereby improving the compressive strength of the saline soil. The roadbed fill layer and the saline soil barrier layer work together to have high compressive strength while blocking capillary water carrying salt ions from eroding the roadbed structure, thus greatly improving the stability of the roadbed.

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the front cross-section structure of the present invention.

[0036] Figure 2 This is a side view structural diagram of the present invention.

[0037] Figure 3 This is a schematic diagram of the drainage pipe in this invention.

[0038] Figure 4 This is a schematic diagram of the drainage blind ditch in this invention.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1—Natural ground surface; 2—Drainage ditch; 3—Waterproofing layer; 4—Drainage pipe; 5—Geomembrane; 6—Geocell cushion layer; 7—Geocell; 8—Stiffness reinforcement layer; 9—Geocell protective layer; 10—Thermal insulation layer; 11—Saline soil isolation layer; 12—Gravel layer; 13—Air door; 14—Dustproof net; 15—Ventilation pipe;

[0041] 16—Hollow rubble layer; 17—Subgrade fill; 18—Subgrade fill layer; 19—Roadway base course; 20—Roadway layer; 2-1—Non-woven geotextile; 2-2—Vertical medium-coarse aeolian sand permeable layer; 2-3—Crushed stone permeable layer; 2-4—Top drainage mesh mat;

[0042] 2-5—Vertical drainage mesh mat; 2-6—Lower medium-coarse aeolian sand permeable layer; 2-7—Drainage mesh pipe;

[0044] 2-8—Bottom of drainage ditch; 4-1—Drainage hole. Detailed Implementation

[0045] like Figures 1 to 4 As shown, the present invention includes a drainage ditch 2, a waterproofing layer 3, a rigidity reinforcement layer 8, a thermal insulation layer 10, a crushed stone layer 12, a roadbed filling layer 18, a road base layer 19, and a road surface layer 20. Drainage ditch 2 is laid on both sides of the compacted natural ground surface 1 along the roadbed laying direction. The waterproofing layer 3, rigidity reinforcement layer 8, thermal insulation layer 10, crushed stone layer 12, roadbed filling layer 18, road base layer 19, and road surface layer 20 are arranged sequentially from bottom to top on the compacted natural ground surface 1. Drainage pipes 4 are buried in the waterproofing layer 3. Geomembrane 5 is laid on both the waterproofing layer 3 and the crushed stone layer 12. The thermal insulation layer 10 and the roadbed filling layer 18 contain saline soil insulation layers 11. Ventilation pipes 15 are buried in the crushed stone layer 12. Multiple drainage pipes 4 and ventilation pipes 15 are equidistantly arranged along the roadbed cross-section direction.

[0046] In this embodiment, the drainage blind ditch 2 is U-shaped. The inner surface of the drainage blind ditch 2 is covered with non-woven geotextile 2-1. The bottom of the drainage blind ditch 2 is made of concrete to form a drainage ditch bottom layer 2-8. A top drainage mesh 2-4 is set at the top opening of the drainage blind ditch 2. A groove is opened in the middle of the drainage ditch bottom layer 2-8. A drainage mesh pipe 2-7 is set in the groove. The space between the drainage mesh pipe 2-7 and the groove is filled with a lower medium-coarse aeolian sand permeable layer 2-6. Two vertical drainage meshes 2-5 are symmetrically set between the drainage ditch bottom layer 2-8 and the top drainage mesh 2-4. The space between the two vertical drainage meshes 2-5 is filled with a gravel permeable layer 2-3. A vertical medium-coarse aeolian sand permeable layer 2-2 is set between the vertical drainage meshes 2-5 and the side wall of the drainage blind ditch 2. The drainage mesh pipe 2-7 is wrapped with permeable geotextile. The drainage mesh is made of high-strength filament structure with a thickness of 50-55mm and a porosity of not less than 90%. The drainage mesh pipe is also made of high-strength filament structure with a diameter of 100mm and a wall porosity of more than 75%.

[0047] In this embodiment, the waterproofing layer 3 is composed of crushed stone or gravel. If a crushed stone layer is used, it should be made of permeable and hard crushed stone, with a fine mud content of ≤3% and free of plant residues, garbage, and other impurities. The width of the crushed stone layer should extend 0.5-1m beyond the roadbed on both sides to ensure an effective bearing surface for mechanical construction of the upper roadbed. If a gravel layer is used, it is composed of sand, gravel, clay, colloids, and pebble particles, with a particle size range of 0.075-60mm. The content of coarse-sized crushed stone is relatively high, ensuring that the amount of stone with a particle size greater than 5mm in the gravel soil exceeds 30%, the maximum particle size must be less than 37.5mm, and less than 2 / 3 of the loose layer thickness.

[0048] The drain pipe 4 is an inverted V-shape with a high middle and low sides. The slope of the drain pipe 4 from the high point in the middle to the outlets at both ends is 2%-5%. The outlets at both ends of the drain pipe 4 are close to the drainage blind ditch 2. Multiple sets of drainage holes 4-1 are equidistantly arranged on the upper side wall of the drain pipe 4. The drain pipe 4 with a high middle and low sides can drain water by itself using the height difference.

[0049] In this embodiment, the geomembrane 5 consists of three layers: the upper layer is a mixed fiber mesh or a loosely treated mixed fiber mesh; the middle layer is a polyethylene waterproof and breathable membrane with a pore size of 0.1-15μm; and the lower layer is a loosely treated mixed fiber mesh. The polyethylene waterproof and breathable membrane possesses excellent alkali resistance, flexibility, and high tensile strength in both warp and weft directions. The geomembrane 5 can solve the problem of gas accumulation in the soil under the partition layer, improving the safety of saline soil subgrades in seasonally frozen areas.

[0050] In this embodiment, the stiffness reinforcement layer 8 includes, from bottom to top, a geocell cushion layer 6, a geocell 7, and a geocell protective layer 9. The geocell 7 is filled with roadbed filler 17, which enhances the roadbed stiffness and can also diffuse the additional load transmitted by pedestrians or vehicles, reducing the dynamic stress in the roadbed. The geocell protective layer 9 is connected to the thermal insulation layer 10. The thickness of the geocell cushion layer 6 is 80mm, the thickness of the geocell 7 is 100mm, the side length of each cell of the geocell 7 is 500mm, and the thickness of the geocell protective layer 9 is 80mm. After backfilling the roadbed filler 17 into the geocell 7 beyond the capacity of the geocell 7 and compacting it, the geocell protective layer 9 is formed. After filling the roadbed filler 17 on the surface of the waterproof mechanism layer 3 away from the saline soil roadbed substrate in the seasonally frozen zone and compacting it, the geocell cushion layer 6 is formed.

[0051] In this embodiment, the thermal insulation partition layer 10 is made of one or more of the following: polystyrene, polyurethane, injection-molded polystyrene, slag, mineral slag, foamed lightweight soil, foamed plastic, epoxy resin shell, styrene sponge plastic and concrete. The saline soil partition layer 11 is composed of an upper medium-coarse aeolian sand layer, a middle partition geomembrane layer and a lower medium-coarse aeolian sand layer from top to bottom. The middle partition geomembrane layer is a waterproof and breathable geomembrane or an acid and alkali resistant composite geomembrane layer. The waterproof and breathable geomembrane in the saline soil isolation layer 11 can facilitate the escape of gas from the lower part of the isolation layer while simultaneously allowing water and salt to migrate and rise in the isolation soil, effectively controlling the occurrence of roadbed diseases in saline soft soil environments. The acid-alkali resistant composite geomembrane in the saline soil isolation layer 11 should possess long-term corrosion resistance and anti-aging properties against sulfates, chlorides, and carbonates. The acid-alkali resistant composite geomembrane adopts a two-layer fabric, two-layer membrane structure, consisting of a reinforcing base fabric, a PET film, a protective non-woven fabric, and another PET film from bottom to top, but is not limited to this composition. The inter-layer overlap of the acid-alkali resistant composite geomembrane is achieved by welding, with a weld width of not less than 100mm and a weld peel strength of not less than [missing information]. For a load less than 70kN, to ensure the quality of the overlap and closure, polypropylene (PP) split film yarns must not be used during geomembrane welding, and polyethylene (PE) film must not be used during bonding. The thickness of the thermal insulation layer 10 is 300-500mm. The thermal insulation layer 10 can prevent heat from spreading to the lower subgrade and also prevent the loss of heat and moisture from the lower subgrade due to evaporation. A saline soil isolation layer 11 is laid inside the thermal insulation layer 10, which completely blocks the erosion of the subgrade structure by capillary water carrying salt ions, thereby reducing the temperature change range of the subgrade. At the same time, it prevents the water in the saline soil subgrade in the seasonally frozen area from freezing and causing the subgrade to thaw and settle, maintaining the stability of the subgrade temperature, reducing salt migration, and improving its stability.

[0052] In this embodiment, the outer diameter of the ventilation pipe 15 is 200-500mm, the wall thickness of the ventilation pipe 15 is 30-50mm, the spacing between adjacent ventilation pipes 15 is 1-5 times the outer diameter of the ventilation pipe 15, the center point of the ventilation pipe 15 is 1500-2500mm from the natural ground surface, dustproof nets 14 are installed at both ends of the ventilation pipe 15, and dampers 13 are installed at the pipe openings at both ends of the ventilation pipe 15. The space between adjacent ventilation pipes 15 is filled with a hollow stone layer 16, which is a precast hollow concrete block with a side length of 50-300mm and a wall thickness of 20-50mm. The crushed stone layer 12 is filled with crushed stone with a particle size of 100-350mm and a thickness of 500-2500mm. The damper 13 is a temperature-sensing automatic control damper.

[0053] In this embodiment, the subgrade fill layer 18 is constructed from subgrade fill 17. Subgrade fill 17 contains saline soil, soluble calcium salts, urea, and microbial agents. The microbial agents contain urease and urease-producing bacteria. The subgrade fill 17 can be modified according to the salinity of the saline soil subgrade, using different improvement schemes and proportions. The subgrade fill 17 combines saline soil with microbial agents containing urease and urease-producing bacteria, soluble calcium salts, and urea, utilizing the Ca produced by the soluble calcium salts. 2+ CO3 produced by the decomposition of urea by urease 2- It forms water-insoluble calcium carbonate crystals; the calcium carbonate crystals act as a cementing substance to bind the soil particles of saline soil, forming a saline soil particle skeleton. The saline soil particle skeleton is very stable, thereby improving the compressive strength of saline soil. At the same time, it uses microorganisms that are widely present in the soil, which will not cause harm to the environment and human body, and has the advantage of being environmentally friendly. It can also shorten the curing cycle and improve construction efficiency.

[0054] The road base course 19 is a cement-stabilized base course. An anti-cracking agent is added to the road base course 19. The anti-cracking agent consists of 40%-60% fly ash, 8%-15% gypsum, 30%-45% mineral ash, 0.1%-0.5% organic fiber, and 1%-5% activator. The main chemical components of fly ash include SiO2 and Al2O3, with a moisture content ≤35%, loss on ignition ≤10%, and a specific surface area ≥2500 cm². 2 / g, 7d activity greater than 0.5 is acceptable; gypsum includes one or more of anhydrite, dihydrate gypsum, fluorogypsum, and phosphogypsum, with a sulfur trioxide content of 40-50% by mass; mineral ash includes one or more of coal ash, peat ash, and thermal power plant slag, with main chemical components including CaO, SiO2, Al2O3, MgO, and Fe2O3, and an initial density of 2960 kg / m³. 3 The original specific surface area is 309 m². 2 / kg, the main chemical components in the mineral ash are expressed as a percentage by weight, including: 10-15% CaO, 20-30% Al2O3, 10-20% MgO, 35-60% oxides, including one or both of SiO2 and Fe2O3; the organic fiber is polypropylene; the activator includes one or more of glycerol, sucrose and citric acid; the crack-resistant agent is a granular mixture.

[0055] In crack-resistant agents, the gypsum content is 8%-15% by mass. When gypsum is incorporated into the base stabilizing aggregate, it undergoes a hydration reaction to form ettringite. The formation of ettringite involves water absorption and swelling, as well as crystal expansion. This micro-expansion achieves the purpose of compensating for micro-cracks caused by the hydration of ordinary silicates, compensating for their shrinkage strain, and inhibiting crack formation. The specific surface area of ​​the gypsum is ≥2500 cm². 2 / g, preferably phosphogypsum. The main chemical components of phosphogypsum by weight include at least 30-35% CaO and 42-48% SO3. When the SO3 content is increased between 42% and 48%, it has a certain effect on improving the mechanical properties and crack resistance of the road base. However, if SO3 is added in excess, a large number of AFt crystals will be generated, which will produce reverse compressive stress inside the material, leading to structural damage and performance deterioration of the material.

[0056] The preferred mineral ash is slag from a thermal power plant, with a mass content of 30%-45%. The mineral ash used in this crack-resistant agent is solid waste; using this solid waste as a raw material to prepare the road base crack-resistant agent results in lower costs and is also environmentally friendly. The specific surface area of ​​the mineral ash is ≥2500 cm². 2 / g, the oxides in mineral ash include SiO2 and Fe2O3.

[0057] The organic fiber used is polypropylene fiber, which is made from propylene. Polypropylene fiber has the characteristics of high strength, good elasticity, wear resistance, corrosion resistance, and good toughness. It appears as fine filaments, so incorporating an appropriate amount of polypropylene fiber can stabilize the base layer, improve the bonding between granular particles, enhance the stability of the base layer, and ensure uniform distribution of load within the base material, resulting in uniform subgrade settlement, effectively reducing pavement cracking, and improving the crack resistance of the base layer. Its diameter is 0.15-0.30 mm, and its density is 0.90-0.92 g / cm³. 3 The organic fiber content is 0.1%-0.5% by mass.

[0058] The role of the activator is to further stimulate the hydration of fly ash, activate the activity of clay particles in the cement-stabilized base layer, and improve the morphology of hydrates. In addition, some organic matter in the activator is insoluble in water and covers the surface of moisture, reducing the components in the cement-stabilized base layer that have a significant hydration mechanism with water. This allows the components of the crack-resistant agent to effectively hydrate and harden. Furthermore, because some moisture is covered by organic matter, the evaporation is reduced, which reduces the drying shrinkage strain of the base material and reduces wet expansion and drying shrinkage, thereby reducing the shrinkage rate and improving crack resistance. The mass content of the activator is 1%-5%.

[0059] In this crack-resistant agent, the weight ratio of fly ash, gypsum, and mineral ash is 3-4:0.7-0.9:2-3. Using this weight ratio, and adding organic fibers and activators, the crack-resistant agent effectively compensates for cracking caused by the shrinkage of the road base layer through the interaction of its components. This results in a better crack-resistant effect for road base materials used in seasonally frozen areas. The crack-resistant agent is used as an additive in the stabilizing aggregates of the road base layer. The weight percentages of each component in the road base material prepared using this crack-resistant agent are: fly ash 4%-10%, P.O325 cement 3.5%-4.5%, crack-resistant agent 6%-12%, and aggregate 70%-80%.

[0060] Pavement layer 20 is made of basalt fiber permeable concrete, which contains the following components: 1548.4 parts of gravel with a particle size of 5-10mm, 398.3 parts of cement, 2 parts of basalt fibers with a length of 18mm and a diameter of 14μm, 20.96 parts of silica fume, 2.1 parts of Q8081PCA liquid-balanced polycarboxylate-based high-performance water-reducing agent, and 125.78 parts of water; the mass ratio of water to the total mass of cement and silica fume is 0.30, the amount of silica fume added is 5% of the total mass of cement and silica fume, the amount of water-reducing agent added is 0.5% of the total mass of cement and silica fume, and the porosity of the basalt fiber permeable concrete material in the seasonally frozen zone is 15%.

[0061] When constructing the third layer of the waterproofing structure, a crushed stone layer is used. The crushed stone should be permeable and hard, with a fine mud content ≤3% and free of plant debris, garbage, and other impurities. The crushed stone layer is generally placed above the soft soil treatment layer and below the subgrade. Its width should generally extend 0.5-1m beyond the subgrade on both sides to ensure an effective bearing surface for mechanical construction of the upper subgrade. First, the qualified subgrade should be surveyed and laid out, the centerline stakes restored, and indicator stakes set on both sides to mark the loose thickness and design elevation of the crushed stone layer. Based on the volume calculated from the loose thickness of the test section, the material should be evenly unloaded using a grid method, and spread evenly using a grader in conjunction with a bulldozer. Second, a heavy roller should be used for compaction, following the principle of "slow first, then fast; static first, then vibratory; weak vibration first, then strong vibration" to ensure that there are no missed areas or dead corners in the compaction surface, that the compaction is uniform, and that the wheel track overlap is ≥500mm. Edges and corners that cannot be compacted by the roller should be compacted with a rammer, with each rammer overlapping the previous one, until the required compaction degree is achieved. The compaction degree should be ≥90%, and the surface of the compacted crushed stone layer should have no obvious wheel tracks.

[0062] When constructing the stiffness reinforcement layer 8, firstly, backfill the geocell 7 with subgrade filler 17 exceeding the capacity of the geocell 7 and compact it. After the structure is formed, the geocell protective layer 9 is formed. Then, fill the surface of the waterproof structure layer 3 away from the saline soil subgrade substrate in the seasonally frozen zone with subgrade filler 17 and compact it to form the geocell cushion layer 6. During the laying of the geocell 7, it should be tensioned and fixed, and the tensioned geocell 7 should be backfilled with subgrade filler 17. The backfill height of the subgrade filler 17 should exceed the top surface of the geocell 7. The specific excess value is calculated based on the loose laying coefficient of the subgrade filler 17 used on site. Then, the subgrade filler 17 is compacted with a road roller to form the geocell protective layer 9. Geocell 7 is a three-dimensional mesh structure formed by high-strength welding of reinforced materials. When roadbed filler 17 is filled into geocell 7, it forms a structure with strong lateral confinement and high rigidity, which can effectively enhance the bearing capacity of the roadbed and has the effect of dispersing load, thus greatly enhancing the roadbed rigidity.

[0063] When constructing the 12-layer block crushed stone layer, it is first divided into two parts: a block stone layer and a crushed stone layer. Stones with a design particle size range of 100mm-350mm are selected, grouped, and the required particle size for maximum porosity is calculated. This is used as the optimal particle size group ratio. Block stones are assembled according to the optimal particle size group ratio, and the block stone units are weighed. The thickness of the block stone layer is 900mm-1200mm, and the particle size is 150mm-350mm. A crushed stone layer is then laid on top of the block stone layer, with a thickness of 150mm-250mm and a particle size of 100mm-150mm. Next, the block stone layer is laid in layers, with stones piled on both sides of the roadbed and laid from both sides towards the middle. When the height of the block stone layer is 200mm-300mm below half the design height, it is compacted and vibrated using a heavy vibratory roller, and then manually leveled with crushed stone blocks. Next, ventilation pipes 15 are laid in the middle of the crushed stone layer 12, with hollow stone layers 16 laid between adjacent ventilation pipes 15. After laying, they are compacted and vibrated with a road roller, and then manually leveled with crushed stone. Finally, a stone layer is laid on top of the crushed stone, and at a distance of 200mm-300mm from the designed height of the stone layer, it is manually leveled and compacted and vibrated with a heavy vibratory roller. In the cold season, ventilation pipes 15 are opened, and the fluid inside the ventilation pipes 15 undergoes strong convective heat exchange with the low-temperature airflow outside, which can release a large amount of heat in the subgrade, thereby achieving the purpose of rapidly reducing the temperature of the surrounding embankment soil. During the ventilation process, the pipe wall temperature drops the fastest, and there are large gaps between the hollow stones around the pipe wall, so strong convective heat exchange can still occur within the hollow stone layer 16, thus meeting the requirements for inter-pipe cooling and improving the overall cooling process of the subgrade. In the warm season, ventilation pipes 15 are closed to prevent heat from entering and reduce the heat absorbed by the subgrade. Because the outside temperature is high at the top and low at the bottom, convective heat transfer is not likely to occur in the crushed stone layer 12 and the hollow crushed stone layer 16. Furthermore, because the damper 13 is in a closed state, its own thermal conductivity is weak. Therefore, it plays the role of preventing the transfer of external heat to the roadbed in the warm season. The geomembrane 5 on top of the crushed stone layer 12 can ensure that the porosity of the layer does not decrease significantly over a long period of time.

[0064] When preparing roadbed fill material, this saline soil roadbed fill material 17 contains saline soil, soluble calcium salts, urea, and microbial agents. The microbial agents contain urease and / or urease-producing bacteria. Saline soil refers to a general term for saline soil, alkaline soil, and various salinized and alkalized soils. Relative to 100 parts by weight of saline soil, the content of soluble calcium salts is 1-40 parts by weight, the content of urea is 2-30 parts by weight, and the content of microbial agents is 1-20 parts by weight. The salt content is determined by drying method or conductivity method, and the salt content of saline soil is ≥0.3% by weight. The particle size of saline soil is ≥0.05mm, and the moisture content can be 10-40% by weight. Saline soil can be chloride-saline soil, sulfate-saline soil, carbonate-saline soil, chlorite-saline soil, and sulfite-saline soil. At least one or more of the following: saline soils; soluble calcium salts may be in solution and / or solid form; when the soluble calcium salt is in solution form, it can be used directly; when the soluble calcium salt is in solid form, it can be first prepared into a solution for use, or water can be added to it to mix the solid soluble calcium salt with the remaining raw materials, and there are no special requirements for the type of soluble calcium salt, as long as it can provide free calcium ions; there are no special requirements for the form of the microbial preparation, as long as it can ensure that urease and / or urease-producing bacteria have biological activity; the urease-producing bacteria may be bacilli and / or cocci, preferably at least one of Bacillus, Bacillus cocci, Proteus and Micrococci, and the content of urease-producing bacteria is at least 1×10⁻⁶. 7 CFU / g; The pH value of saline soil roadbed filler 17 should be 6-9. If it is not within this range, a pH adjuster can be added. When mixing the above materials, simply mix the raw materials evenly. The mixing method can be manual stirring or mechanical stirring, and the mixing temperature should be 20-45℃. Specifically, the microbial preparation can be prepared by the following method: inoculate *Bacillus pasteurellus* into a culture medium with the following formula: 5 g / L beef extract, 15 g / L peptone, and 5 g / L sodium chloride. Incubate at 30℃ for 48 h to obtain a density of 1×10⁻⁶. 9 CFU / mL bacterial suspension.

[0065] Saline soil and roadbed filler were prepared using the following formula:

[0066] Sodium sulfate was added to soil particles, and after grinding and sieving, artificially prepared saline soils with salt contents of 1%, 3%, and 5% were obtained. Among them, soil particles with a diameter of 0.25-0.5 mm accounted for 20% of the total soil particle weight, soil particles with a diameter of 0.5-1 mm accounted for 20% of the total soil particle weight, and particles with a diameter of 1-2 mm accounted for 60% of the total soil particle weight.

[0067] Weigh 100g of saline soil with a salt content of 1% by weight, 5g of anhydrous calcium chloride powder, 8g of urea, 10mL of bacterial solution and 1g of sodium bicarbonate, and place them in a mixer and stir for half an hour at room temperature of 25℃ to obtain saline soil roadbed filler A1 (pH value of 8, water content of 25% by weight).

[0068] The unconfined compressive strength of the saline soil subgrade filler before and after A1 treatment was measured to be 21.5 kPa and 1414.5 kPa, respectively.

[0069] The method for constructing the road base layer 19 is as follows:

[0070] Step 1: Weigh the raw materials according to a certain ratio and mix them evenly;

[0071] Step 2: Calculate the amount of water to be added and the mass of the inorganic binder for each portion of material based on the compaction test and mix proportion;

[0072] Step 3: Place the weighed aggregate in a rectangular pan, add water to the aggregate and mix and let it sit. Inorganic binders can be mixed together with the aggregate. Spray the pre-calculated amount of water evenly onto the aggregate, and then put it into a sealed plastic bag to soak and set aside.

[0073] Step 4: Mold the specimen, demold it after 2-6 hours and seal it. Then cure it under standard curing conditions of 20℃±2℃ and humidity ≥95% until the specified age.

[0074] The preparation method of basalt fiber permeable concrete material is as follows:

[0075] Step 1: Put basalt fiber and aggregate into a mixer and mix for 30 seconds, then add 20% water and mix for another 30 seconds to obtain a premix.

[0076] Step 2: Mix the premix obtained in Step 1 with cement, silica fume, water-reducing agent and the remaining water in a mixer for 150 seconds to obtain the mixture.

[0077] Step 3: The mixture obtained in Step 2 is molded using a combination of tamping and vibration molding. A plastic film is then placed over the mold and cured for 48 hours under standard curing conditions (temperature 20±2℃, relative humidity ≥95%) combined with water spraying and film covering. After demolding, the basalt fiber permeable concrete specimens are cured for 28 days at 20±2℃ and ≥95% relative humidity to obtain basalt fiber permeable concrete material for the seasonally frozen region. Experiments were conducted to compare the compressive strength, splitting tensile strength, permeability coefficient, and frost resistance of the permeable concrete material.

[0078] The preferred mixing time for the mix material and water is 30 seconds; the preferred mixing time for the premix material with cement, silica fume, water-reducing agent and the remaining water is 140-150 seconds; the preferred curing time is 48 hours; after curing, it is also possible to choose whether to demold the specimens after curing and perform secondary curing, depending on the situation. Secondary curing is carried out under standard curing conditions, and the preferred curing time is 28 days. Secondary curing can further improve the compressive strength, splitting tensile strength, permeability and frost resistance of permeable concrete.

[0079] The compressive strength of basalt fiber permeable concrete reached 25.2 MPa, an increase of 26% over the standard value. This is because the basalt fiber can be tightly bonded to the cement matrix, and the cement paste around the basalt fiber is fully hydrated without a large amount of Ca(OH)2 crystals accumulating. The fiber surface can be covered by cementitious substances, and the active substances after cement hydration reaction play a certain role in wetting and adsorbing the basalt fiber, thereby strengthening the bonding ability between the fiber and the cement matrix interface, reducing defects in the interface transition zone, and macroscopically improving the road performance of permeable concrete. The splitting tensile strength reached 3.53 MPa, an increase of 41.2% over the standard value. This is because the basalt fiber with appropriate admixture index is uniformly dispersed in the permeable concrete matrix, and the three-dimensional skeleton formed can inhibit aggregate settlement and reduce matrix shrinkage deformation, thus significantly improving the road performance of permeable concrete. It is evident that under load, the internal structure of permeable concrete will be damaged, and microcracks will appear in the interface transition zone, causing the cementitious material to detach from the aggregate or the cementitious material and fibers. As the load continues to increase, the microcracks will continue to develop into microcracks. At this point, the basalt fibers incorporated into the permeable concrete can replace the permeable concrete in bearing the load, resisting the rapid development of internal cracks by changing the direction of microcrack development. The permeability coefficient is 6.31 mm / s, which is 1162% higher than the standard value. This is because the appropriately incorporated basalt fibers form a certain spatial network structure in the permeable concrete, which is conducive to the penetration of water molecules. If the added fiber diameter is too small and the length too short, the number of basalt fibers required per unit volume will increase. This will undoubtedly lead to clumping in the permeable concrete, clogging the pores. This not only fails to improve its mechanical properties but also reduces its permeability. If the fiber content is too low, it will not play a significant role in the permeable concrete; if the content is too high, clumping will occur. Therefore, only an appropriate basalt fiber content can improve the permeable concrete. Regarding freeze-thaw resistance, after 25 freeze-thaw cycles, the mass loss rate is 0. The mass loss rate was 0.14%, a decrease of 97.2% compared to the standard value; the compressive strength loss rate was 2.81%, a decrease of 85.95% compared to the standard value; after 50 freeze-thaw cycles, the mass loss rate was 0.24%, a decrease of 95.2% compared to the standard value; and the compressive strength loss rate was 4.78%, a decrease of 76.1% compared to the standard value. This is because after freeze-thaw cycles, the internal structure of the basalt fiber permeable concrete material in the frozen area was damaged, and cracks appeared at the interface, causing the binder and aggregate to fall off, thus reducing the integrity of the permeable concrete.When basalt fibers are added, the bond between the basalt fibers and the permeable concrete cement paste becomes less tight and the structure less dense with the increase of freeze-thaw cycles. This causes some fibers to be pulled out under macroscopic external loads. However, compared with permeable concrete without basalt fibers, the basalt fibers bear part of the load instead of the permeable concrete. Only when the number of freeze-thaw cycles and the external load exceed the range that the fibers can withstand will this part of the force be applied to the permeable concrete again, until the specimen fails.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A roadbed and pavement structure for saline soil in seasonally frozen areas, characterized in that, The system includes a drainage ditch (2), a waterproofing layer (3), a rigidity reinforcement layer (8), a thermal insulation layer (10), a crushed stone layer (12), a roadbed filling layer (18), a road base layer (19), and a road surface layer (20). Drainage ditches (2) are laid on both sides of the compacted natural ground surface (1) along the roadbed laying direction. The compacted natural ground surface (1) is provided with the waterproofing layer (3), rigidity reinforcement layer (8), thermal insulation layer (10), and crushed stone layer (12) sequentially from bottom to top. The roadbed filling layer (18), the road base layer (19) and the road surface layer (20) are provided. A drainage pipe (4) is buried in the waterproof mechanism layer (3). A geomembrane (5) is laid on the waterproof mechanism layer (3) and the crushed stone layer (12). A saline soil isolation layer (11) is provided in the thermal insulation layer (10) and the roadbed filling layer (18). A ventilation pipe (15) is buried in the crushed stone layer (12). Multiple drainage pipes (4) and ventilation pipes (15) are equidistantly arranged along the roadbed cross section.

2. The roadbed and pavement structure for saline soil in seasonally frozen areas according to claim 1, characterized in that, The drainage ditch (2) is U-shaped. The inner surface of the drainage ditch (2) is covered with non-woven geotextile (2-1). The bottom of the drainage ditch (2) is a concrete-cast drainage ditch bottom layer (2-8). A top drainage mesh pad (2-4) is installed at the top opening of the drainage ditch (2). A groove is opened in the middle of the drainage ditch bottom layer (2-8), and a drainage mesh pipe (2-7) is installed in the groove. The space between the drainage mesh pipe (2-7) and the groove is filled with... The drainage ditch consists of a medium-coarse aeolian sand permeable layer (2-6). Two vertical drainage net mats (2-5) are symmetrically arranged between the bottom layer (2-8) and the top drainage net mat (2-4). The space between the two vertical drainage net mats (2-5) is filled with a gravel permeable layer (2-3). A vertical medium-coarse aeolian sand permeable layer (2-2) is arranged between the vertical drainage net mat (2-5) and the side wall of the drainage blind ditch (2). The drainage net pipe (2-7) is wrapped with permeable geotextile.

3. The roadbed and pavement structure for saline soil in seasonally frozen areas according to claim 1, characterized in that, The waterproof structure layer (3) is filled with gravel or pebbles. The drainage pipe (4) is an inverted V-shape with a high middle and low sides. The slope of the drainage pipe (4) from the high point in the middle to the outlets at both ends is 2%-5%. The outlets at both ends of the drainage pipe (4) are close to the drainage blind ditch (2). Multiple sets of drainage holes (4-1) are equidistantly arranged on the upper side wall of the drainage pipe (4).

4. The roadbed and pavement structure for saline soil in seasonally frozen areas according to claim 1, characterized in that, The geomembrane (5) consists of three layers: the upper layer is a mixed fiber mesh or a loosely treated mixed fiber mesh, the middle layer is a polyethylene waterproof and breathable membrane with a pore size of 0.1-15μm, and the lower layer is a loosely treated mixed fiber mesh.

5. The roadbed and pavement structure for saline soil in seasonally frozen areas according to claim 1, characterized in that, The stiffness reinforcement layer (8) consists of a geocell cushion layer (6), a geocell (7), and a geocell protective layer (9) from bottom to top. The geocell (7) is filled with roadbed filler (17). The geocell protective layer (9) is connected to the thermal insulation partition layer (10). The thickness of the geocell cushion layer (6) is 80 mm. The thickness of the geocell (7) is 100 mm. The side length of each geocell in the geocell (7) is 500 mm. The thickness of the geocell protective layer (9) is 80 mm.

6. The roadbed and pavement structure for saline soil in seasonally frozen areas according to claim 1, characterized in that, The thermal insulation partition layer (10) is made of one or more of polystyrene, polyurethane, injection-molded polystyrene, slag, mineral slag, foamed lightweight soil, foamed plastic, epoxy resin shell, styrene sponge plastic and concrete. The saline soil partition layer (11) is composed of an upper medium-coarse aeolian sand layer, a middle partition geomembrane layer and a lower medium-coarse aeolian sand layer from top to bottom. The middle partition geomembrane layer is a waterproof and breathable geomembrane or an acid and alkali resistant composite geomembrane layer.

7. The roadbed and pavement structure for saline soil in seasonally frozen areas according to claim 1, characterized in that, The ventilation pipe (15) has an outer diameter of 200-500mm and a wall thickness of 30-50mm. The distance between adjacent ventilation pipes (15) is 1-5 times the outer diameter of the ventilation pipe (15). The center point of the ventilation pipe (15) is 500-2500mm from the natural ground surface (1). Dustproof nets (14) are installed at both ends of the ventilation pipe (15). Air dampers (13) are installed at the pipe openings at both ends of the ventilation pipe (15). Hollow stone layer (16) is filled between adjacent ventilation pipes (15). The hollow stone layer (16) is a precast concrete hollow block. The side length of the concrete hollow block is 50-300mm and the wall thickness is 20-50mm. The crushed stone layer (12) is filled with crushed stone with a particle size of 100-350mm and a thickness of 500-2500mm.

8. The roadbed and pavement structure for saline soil in seasonally frozen areas according to claim 1, characterized in that, The subgrade filler layer (18) is constructed from subgrade filler (17), which contains saline soil, soluble calcium salts, urea, and microbial agents. The microbial agents contain urease and urease-producing bacteria. The pavement base course (19) is a cement-stabilized base course. An anti-cracking agent is added to the pavement base course (19). The anti-cracking agent consists of 40%-60% fly ash, 8%-15% gypsum, 30%-45% mineral ash, 0.1%-0.5% organic fiber, and 1 The pavement layer (20) is composed of %-5% activator and is made of basalt fiber permeable concrete. The basalt fiber permeable concrete contains the following components: 1545-1610 parts of aggregate, 395-425 parts of cement, 1-5 parts of basalt fiber, 20-23 parts of silica fume, 1.3-2.3 parts of water-reducing agent and 125-140 parts of water. The aggregate has a particle size of 2.5-10 mm, the basalt fiber has a length of 18-24 mm and a diameter of 14-20 μm.

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