Gradual change pipe diameter ventilation pipe embankment rigid transition structure of road and bridge transition section in permafrost region

Abstract

This invention discloses a rigid transition structure for roadbed subgrade with gradually changing diameter ventilation pipes in the transition section of a road-bridge system in permafrost regions, belonging to the field of permafrost engineering technology. It includes a permafrost foundation, a pavement structure layer, and a bridge abutment. A roadbed fill is connected to the back of the abutment. A three-dimensional geogrid layer is laid between the top surface of the permafrost foundation and the roadbed fill. The three-dimensional geogrid layer forms a gradient structure with gradually increasing stiffness from the far end to the near end of the abutment along the driving direction. The roadbed fill includes, from bottom to top, a gradually changing riprap cushion layer, an intelligent gradually changing honeycomb ventilation pipe layer, and a fill layer. The thickness and riprap particle size of the gradually changing riprap cushion layer gradually increase from the far end to the near end of the abutment along the driving direction. The diameter and wall thickness of the honeycomb ventilation pipes in the intelligent gradually changing honeycomb ventilation pipe layer simultaneously increase gradually from the far end to the near end of the abutment along the driving direction. This invention solves the problem of differential settlement in the road-bridge transition section in permafrost regions, ensuring safe and stable vehicle operation.

Description

Technical Field

[0001] This invention relates to a road-bridge transition section structure, specifically to a rigid transition structure for a roadbed with a gradually changing diameter ventilation pipe in a road-bridge transition section in permafrost regions, belonging to the field of permafrost engineering technology. Background Technology

[0002] In permafrost regions, the road-bridge transition section is a critical area connecting the roadbed and bridge abutments. After construction, the original hydrothermal balance is disrupted, leading to permafrost degradation and significant permanent settlement, which in turn causes engineering defects such as bridge approach slab settlement and structural cracking. Bridge abutments, as rigid structures, have minimal settlement, while the roadbed soil is prone to plastic deformation under freeze-thaw cycles and vehicle loads. The significant difference in stiffness between the two creates a sudden interface of rigidity and flexibility, exacerbating the differential settlement problem in the road-bridge transition section.

[0003] In permafrost regions, road-bridge transition sections are crucial. They prevent uneven settlement of the roadbed caused by permafrost thawing or freezing, avoid pavement cracking, misalignment, and bridge structural damage, ensure the smoothness of the road-bridge connection, and guarantee driving safety and comfort. This is of great significance for maintaining the long-term stable operation of transportation infrastructure. Existing methods for addressing differential settlement in road-bridge transition sections in permafrost regions mainly include: using lightweight materials, such as foamed concrete; reinforcing deformation-resistant technologies, such as composite geogrids; and using precast pipe pile systems. However, these measures still have significant limitations.

[0004] Insufficient material properties and durability; lightweight materials show significant strength loss under freeze-thaw cycles; reinforced materials are prone to embrittlement at low temperatures; and differences in interfacial thermal expansion cause interlayer voids, making it difficult to meet the long-term stability requirements of permafrost regions.

[0005] The high cost of economics and maintenance, the increased transportation costs of lightweight materials in cold regions, the extremely high cost per kilometer of precast pipe piles and the high maintenance costs, and the excessively high life-cycle cost of existing technologies restrict their large-scale application.

[0006] Insufficient coordination between ecological protection and engineering, construction thermal disturbance and material hardening processes disrupt the local hydrothermal balance, and the risk of co-degradation of permafrost and ecosystem is significant.

[0007] Therefore, there is an urgent need for a new roadbed structure for controlling differential settlement in the transition section of roads and bridges in permafrost regions. Summary of the Invention

[0008] To address the problem of differential settlement in the transition section between roads and bridges in permafrost regions of high altitudes, and to minimize the limitations of existing methods, this invention proposes a rigid transition structure for the roadbed with gradually changing diameter ventilation pipes in the transition section between roads and bridges in permafrost regions, ensuring safe and stable vehicle operation.

[0009] The technical solution adopted by the present invention to solve the above problems is as follows: A rigid transition structure for a roadbed with a gradually changing diameter ventilation duct in a bridge transition section in permafrost regions includes a permafrost foundation, a pavement structure layer, and a bridge abutment. The bridge abutment is located between the top surface of the permafrost foundation and the bottom surface of the pavement structure layer. A roadbed fill is connected to the back of the abutment. A three-dimensional geogrid layer is laid between the top surface of the permafrost foundation and the roadbed fill. Along the driving direction, the three-dimensional geogrid layer is sequentially divided into a flexible drainage zone, a semi-rigid transition zone, and a rigid anchoring zone from the far end to the near end of the abutment, forming a gradient structure with progressively increasing stiffness. The roadbed fill... The structure comprises, in sequence, a gradient ripple cushion layer, an intelligent gradient honeycomb ventilation pipe layer, and a backfill layer. The thickness and ripple size of the gradient ripple cushion layer increase progressively from the far end to the near end of the abutment along the driving direction, and are divided into a conventional section at the far end, a transition section in the middle, and a reinforced section at the near end. The intelligent gradient honeycomb ventilation pipe layer includes multiple rows of honeycomb ventilation pipes arranged along the driving direction. The diameter and wall thickness of the honeycomb ventilation pipes increase synchronously from the far end to the near end of the abutment along the driving direction, forming a continuous stiffness gradient field that matches the three-dimensional geogrid layer and the gradient ripple cushion layer.

[0010] Furthermore, the diameter D of the honeycomb ventilation duct satisfies the following piecewise linear function:

[0011] Where x is the distance from the bridge abutment, and L is the total length of the road-bridge transition section. The maximum pipe diameter near the abutment. is the minimum pipe diameter at the far end of the bridge abutment, and n is the gradient index, ranging from 1.2 to 1.5.

[0012] Furthermore, the wall thickness t of the honeycomb ventilation duct increases synchronously with the increase of the diameter D, satisfying the following relationship:

[0013] in, The minimum pipe wall thickness at the far end of the bridge abutment. This represents the maximum wall thickness of the pipe near the abutment.

[0014] Furthermore, the cross-section of the honeycomb ventilation duct is a hexagonal honeycomb nested structure, and the material of the honeycomb ventilation duct is nickel-chromium-molybdenum alloy steel.

[0015] Furthermore, the outer wall of the honeycomb ventilation duct is coated with an anti-corrosion coating, and the inner wall is coated with an organosilicon fluorine coating.

[0016] Furthermore, the outer wall of the honeycomb ventilation duct is integrated with a piezoelectric fiber layer.

[0017] Furthermore, the honeycomb ventilation duct is equipped with a temperature-controlled louver at its opening, and the drive rod of the temperature-controlled louver is made of shape memory alloy.

[0018] Furthermore, the temperature-controlled louvers integrate a wind speed sensor and a temperature sensor, which are communicatively connected to the control terminal.

[0019] Furthermore, adjacent sections of the honeycomb ventilation duct are connected by alloy bolts and polyurethane rubber seals.

[0020] Furthermore, the three-dimensional geogrid layer is a double-layer geogrid structure, with an insulation layer sandwiched between the two geogrid layers, and an air-guiding groove with a thickness that extends through the insulation layer.

[0021] Furthermore, the surface of the three-dimensional geogrid layer is coated with a phase change material coating.

[0022] Furthermore, the phase change material coating uses a paraffin-based phase change material.

[0023] Furthermore, the paving thickness of the distal conventional section is 0.5m, and the stone particle size is 200~300mm; the paving thickness of the middle transition section is 0.6~0.7m, and the stone particle size ranges from 300mm~400mm from the distal end to the proximal end; the paving thickness of the proximal reinforcing section bedding layer is 0.8~1.0m, and the stone particle size is 400~600mm.

[0024] Furthermore, a geotextile filter is laid on the top surface of the gradient boulders cushion layer.

[0025] Furthermore, an L-shaped heat pipe is buried within the permafrost foundation.

[0026] Furthermore, there are multiple L-shaped heat pipes, which are arranged in a longitudinally equidistant and laterally staggered array along the centerline of the roadbed.

[0027] The beneficial effects of this invention are: 1. This invention addresses the problem of differential settlement caused by abrupt changes in stiffness between bridge abutments and roadbeds. The intelligent gradient honeycomb ventilation pipe ventilation layer forms a continuous stiffness gradient by varying the pipe diameter and wall thickness from the far end to the near end of the bridge abutment. The ventilation pipe, which adopts a hexagonal honeycomb nested structure, achieves coordinated gradual changes in pipe diameter and wall thickness. With its excellent geometric characteristics, it significantly enhances the axial compressive stiffness and lateral stability of the pipe body, extends the service life of the structure under freeze-thaw cycles, and the composite stiffness field formed by it and the upper backfill soil has a smoother and more continuous transition, completely bridging the abrupt stiffness-flexibility interface between the roadbed and the bridge abutment.

[0028] 2. This invention addresses the thaw settlement and frost heave problems caused by the imbalance of water and heat in permafrost. Temperature-controlled louvers and wind speed sensors work together with gradually changing diameter corrugated steel pipes to dynamically adjust the ventilation volume. In winter, this reduces cold intrusion and activates the heat pipe cooling system. In summer, it enhances ventilation and cooling, maintains the thermal stability of permafrost, and inhibits thaw settlement of permafrost. In conjunction with the stiffness transition effect of the gradually changing diameter corrugated steel pipes, it solves the problem of uneven settlement in the transition section of roads and bridges.

[0029] 3. This invention addresses the stress concentration problem caused by the uniform stiffness of traditional grids by employing a gradient modification design to create a three-region gradual change that matches the stiffness field of the abutment and subgrade, thereby synergistically suppressing differential settlement. 4. In view of the defect that the insulation layer hinders water and heat exchange, the present invention opens air channels in the insulation layer to form a dual channel for insulation and ventilation that conducts cold in winter and blocks heat in summer, which significantly stabilizes the temperature of frozen soil. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the longitudinal section of the roadbed in the transition section between the road and bridge of this invention; Figure 2 This is a schematic diagram of the cross-section of the roadbed in the transition section of the bridge and road system of the present invention; Figure 3 This is a schematic diagram of the cross-section of a honeycomb ventilation duct; Figure 4 This is a schematic diagram of a temperature-controlled louver structure; Figure 5 This is a schematic diagram of the upper geogrid unit structure; Figure 6 This is a schematic diagram of the lower layer geogrid unit structure; Figure 7 This is a cross-sectional view of the geogrid insulation layer.

[0031] In the diagram, 1. Permafrost foundation, 2. L-shaped heat pipe, 3. Insulation layer, 4. Three-dimensional geogrid layer, 5. Gradient riprap cushion layer, 6. Intelligent gradient honeycomb ventilation duct layer, 7. Fill layer, 8. Road structure layer, 9. Bridge abutment, 10. Temperature-controlled louvers, 11. Solar panel, 12. Battery, 13. Control terminal, 14. Drainage ditch, 101. Honeycomb nested structure, 102. Piezoelectric fiber layer, 104. Organosilicon fluorine coating, 105. Anti-corrosion coating, 106. Honeycomb ventilation duct wall, 107. Louver blades, 108. Wind speed sensor and temperature sensor, 41. Upper geogrid layer, 42. Dovetail groove, 43. Lower geogrid layer, 51. Upper insulation board, 52. Lower insulation board. Detailed Implementation

[0032] Specific implementation method one: Combining Figure 1-7 This implementation method is described as follows: Figure 1 and Figure 2As shown in this embodiment, a rigid transition structure for a road-bridge transition section with gradually changing diameter ventilation pipes in permafrost regions specifically relates to a non-uniform settlement control structure for road-bridge transition sections in permafrost regions. The application scenario for this rigid transition structure is the road-bridge transition section, specifically the connection section between the rigid abutment 9 at the end of the bridge structure and the flexible roadbed of the main road. All gradually changing stiffness structures are arranged within this connection section along the driving direction. The rigid transition structure includes a permafrost foundation 1, a pavement structure layer 8, and an abutment 9. The abutment 9 is located between the top surface of the permafrost foundation 1 and the bottom surface of the pavement structure layer 8. The permafrost foundation 1 is the natural bearing layer of the entire transition section structure and is located at the bottom layer. The abutment 9 is the rigid reference end of the transition section and is anchored into the permafrost foundation 1. The roadbed fill is the core carrier of the stiffness transition, filling the space between the back of the abutment 9 and the conventional roadbed, and above the top surface of the permafrost foundation 1. The road structure layer 8 is the vehicle load-bearing surface layer, which is laid on the top surface of the roadbed fill and smoothly connects with the bridge deck pavement of the abutment 9 to achieve a continuous transition of the vehicle surface.

[0033] The bridge abutment 9 is connected to a roadbed fill body, which is located between the top surface of the permafrost foundation 1 and the pavement structure layer 8. A three-dimensional geogrid layer 4 is laid between the top surface of the permafrost foundation 1 and the roadbed fill body, mainly to isolate the permafrost and prevent it from intruding into the permafrost foundation 1 and changing its hydrothermal conditions, and also to provide insulation and drainage, and prevent permafrost disturbance.

[0034] The three-dimensional geogrid layer 4 is divided into a flexible drainage zone, a semi-rigid transition zone, and a rigid anchoring zone along the driving direction from the far end of the abutment to the near end, forming a gradient structure with progressively increasing stiffness. In the driving direction, the stiffness of the geogrid cross-section gradually increases from the far end to the near end of the abutment. The far end uses a polymer composite material with a low elastic modulus, while the near end incorporates a steel fiber reinforced geogrid. Preferably, the flexible drainage zone uses a polymer composite geogrid with a low elastic modulus, the semi-rigid transition zone uses a steel fiber reinforced composite geogrid, and the rigid anchoring zone uses a high-content steel fiber reinforced geogrid, achieving a continuous gradient increase in stiffness. This stiffness gradient between the flexible drainage zone, the semi-rigid transition zone, and the rigid anchoring zone matches the stiffness change trend of the gradually changing diameter ventilation duct, synergistically mitigating abrupt changes in stiffness between the abutment and the roadbed.

[0035] like Figure 5-7As shown, the three-dimensional geogrid layer 4 is a double-layer geogrid structure comprising an upper geogrid layer 41 and a lower geogrid layer 43, with an insulation layer 3 sandwiched between the two layers. Specifically, the three-dimensional geogrid layer 4 has a specially designed insulation layer 3 in the middle of the double-layer geogrid, and the interfaces of each layer are tightly bonded together with an adhesive to ensure overall stress coordination. The insulation layer 3 is made of closed-cell foam glass insulation board, and air-guiding grooves with a continuous thickness are formed on the insulation layer 3. Preferably, the insulation board has hexagonal air-guiding grooves perpendicular to the driving direction, forming a dual channel for insulation and ventilation. In winter, it guides cold air downwards to activate the frozen soil, and in summer, it blocks heat from invading upwards. Composite permeable geotextile is laid inside the hexagonal air-guiding grooves, and the longitudinal slope of the air-guiding grooves is 0.5%, ensuring that cold air is introduced into the deep subgrade layer along the slope in winter. The insulation layer 3 includes an upper insulation board 51 and a lower insulation board 52. The upper insulation board 51 has a rectangular groove, and the lower insulation board 52 has a rectangular protrusion that matches the rectangular groove. The upper and lower insulation boards 52 are spliced ​​together through a concave-convex structure and fixed with adhesive. The upper insulation board 51 forms a rectangular slot, and the lower insulation board 52 is a rectangular protrusion, completing a high-strength splicing. The edges of the grid units of the three-dimensional geogrid layer 4 are provided with bidirectional dovetail tenon grooves 42. Adjacent grid units are spliced ​​and fixed through the dovetail tenon grooves 42 to form a continuous integral structure. The surface of the grid of the three-dimensional geogrid layer 4 is coated with a phase change material coating. The phase change material coating is a paraffin-based phase change material. The phase change material coating is embedded in the grid. In winter, when the temperature is low, the coating cures to enhance the grid stiffness. In summer, when the temperature is high, the coating softens to absorb freeze-thaw deformation energy. At the same time, the latent heat of phase change regulates the local ground temperature and reduces the damage of freeze-thaw cycles to the interface between the grid and the soil.

[0036] The roadbed fill, from bottom to top, comprises a gradient riprap cushion layer 5, an intelligent gradient honeycomb ventilation pipe layer 6, and a soil fill layer 7. The gradient riprap cushion layer 5 is laid on top of the three-dimensional geogrid layer 4, the intelligent gradient honeycomb ventilation pipe layer 6 is embedded in the gradient riprap cushion layer 5, the soil fill layer 7 covers the intelligent gradient honeycomb ventilation pipe layer 6, and the pavement structure layer 8 is laid on top of the soil fill layer 7. Preferably, the pavement structure layer 8 is an asphalt pavement structure, comprising a lower layer of AC-20 asphalt mixture and an upper layer of SMA-13 ​​asphalt mixture, wherein the asphalt mixture contains phase change microcapsules; the soil fill layer 7 is constructed by layering and compacting gravelly soil with a gravel content ≥60% and a plasticity index Ip ≤6.

[0037] The gradient paving stone layer 5, along the driving direction, gradually increases in thickness and stone particle size from the far end to the near end of the abutment, and is divided into a conventional section at the far end, a transition section in the middle, and a reinforced section at the near end. The stone adopts a gradual change strategy in thickness and particle size. The conventional section at the far end has a paving thickness of 0.5m and a stone particle size of 200-300mm; the transition section in the middle has a paving thickness of 0.6-0.7m and a stone particle size of 300mm-400mm from the far end to the near end; the reinforced section at the near end has a paving thickness of 0.8-1.0m and a stone particle size of 400-600mm. The conventional section at the far end has a paving stone thickness of 0.5m, the transition section in the middle (5-10m from the abutment) increases to 0.6-0.7m, and the reinforced section at the near end (0-5m from the abutment) further increases to 0.8-1.0m. The increased thickness enhances local bearing capacity, matching the rigid support requirements of abutment 9 and reducing vehicle bounce impact caused by differential settlement. The near-end reinforced section uses extra-large stones with a particle size of 400-600mm, which can be mechanically compacted to form an interlocking structure, improving the overall stiffness and impact resistance of the subbase and reducing plastic deformation under vehicle loads. The far-end conventional section uses medium-sized stones with a particle size of 200-300mm, which can be compacted in layers using a small vibratory compactor, with each layer controlled at a thickness of 0.25m. The middle transition section uses a gradual particle size paving process, with the stone particle size gradually increasing from 300mm to 400mm from the far end to the near end of abutment 9. Heavy rollers are used for reciprocating compaction to ensure a tightly embedded structure of the stones. Preferably, a geotextile mesh is laid on the top surface of the gradual stone subbase 5. The geotextile mesh has a pore size of 5-10mm, and its edges are provided with reverse-wrapping anchoring sections. A high-strength geotextile with a pore size of 5-10mm is laid on top of the gradient rubble cushion layer 5 to isolate fine particles from the fill layer 7 and prevent clogging of the pores, while retaining water permeability.

[0038] like Figure 3 and Figure 4As shown, the intelligent gradient honeycomb ventilation pipe layer 6 includes multiple rows of honeycomb ventilation pipes arranged along the driving direction, preferably three rows. The diameter and wall thickness of the honeycomb ventilation pipes increase synchronously and gradually from the far end of the bridge abutment to the near end along the driving direction, forming a continuous stiffness gradient field that matches the three-dimensional geogrid layer 4 and the gradient riprap cushion layer 5, realizing the rigid transition and differential settlement control of the road-bridge transition section. Specifically, three rows of intelligent gradient honeycomb ventilation pipes are arranged along the driving direction, with their diameters increasing gradually from the far end to the near end of the bridge abutment 9. This causes the thickness of the fill layer 7 from the top of the pipe to the road surface to decrease accordingly, further forming a continuous stiffness field. The small diameter at the far end maintains a thicker fill layer 7, the pipe diameter in the middle section transitions with a step-by-step increase in stiffness, and the large diameter and thin soil layer at the near end of the bridge abutment 9 completely bridge the interface between rigid and flexible materials, suppressing differential settlement. The soil arching effect significantly improves the equivalent stiffness of the road surface in this area. The wall thickness of the ventilation pipes also increases synchronously with the pipe diameter, enhancing the structural stiffness and deformation resistance of the pipes themselves. The coordinated gradual change in pipe diameter and wall thickness constitutes a continuous stiffness transition system from the flexible subgrade to the rigid abutment 9. The rigid transition is achieved through intelligent, gradually changing honeycomb ventilation pipes, which also function as ventilation and cooling systems for the subgrade, effectively controlling differential settlement in the road-bridge transition section. By gradually increasing the size of the ventilation pipes from the far end to the near end of the abutment 9, a rigid transition in the road-bridge transition section is achieved, controlling differential settlement and solving problems existing in current technologies.

[0039] The diameter D of the honeycomb ventilation duct satisfies the following piecewise linear function:

[0040] Where x is the distance from bridge abutment 9, and L is the total length of the road-bridge transition section. The maximum pipe diameter near the abutment. (k=0.35~0.45, H is the height of the bridge abutment). The minimum pipe diameter at the far end of the bridge abutment is usually set to 0.6 m to 0.8 m, and n is the gradient index, which ranges from 1.2 to 1.5 to achieve nonlinear gradient and better match the stiffness variation requirements.

[0041] The diameter of the ventilation duct decreases as the distance x from the bridge abutment increases, and a piecewise linear function is used to achieve a smooth transition.

[0042] The wall thickness t of the honeycomb ventilation duct increases synchronously with the increase of the diameter D, satisfying the following relationship:

[0043] in, The minimum pipe wall thickness at the far end of the bridge abutment can be taken as 3mm. The maximum wall thickness near the abutment can be taken as 6mm.

[0044] The pipe wall thickness t increases synchronously with the increase of pipe diameter to ensure local stiffness and load-bearing capacity at the large pipe opening near the end.

[0045] Preferably, the cross-section of the honeycomb ventilation duct is a hexagonal honeycomb nested structure 101. This hexagonal honeycomb nested structure 101, with its excellent geometric properties, significantly enhances the axial compressive stiffness and lateral stability of the duct body, extending the service life of the structure under freeze-thaw cycles. The wall material 106 of the honeycomb ventilation duct is nickel-chromium-molybdenum alloy steel. Using high-strength, low-temperature resistant, and corrosion-resistant nickel-chromium-molybdenum alloy steel as the wall material of the corrugated steel pipe extends its service life and meets the long-term use requirements of harsh environments in permafrost regions.

[0046] The outer wall of the honeycomb ventilation duct is coated with a self-healing active anti-corrosion coating 105, and the inner wall is coated with an organosilicon fluorine drag-reducing and anti-scaling coating. The outer wall coating uses an active anti-corrosion coating 105. When the coating is slightly damaged, the repair agent inside can be automatically released and repair the damaged parts, continuously protecting the steel corrugated pipe from external corrosion and enhancing the reliability of the structure.

[0047] The adjacent sections of the honeycomb ventilation duct are connected by alloy bolts and polyurethane rubber seals. The connecting parts between the ventilation duct sections use alloy bolts and seals. The seals are made of low-temperature resistant, highly elastic polyurethane rubber, which can effectively fill the gaps between the sections, prevent moisture leakage and air leakage, and ensure the overall performance of the steel corrugated pipe.

[0048] The honeycomb ventilation duct is equipped with a temperature-controlled louver 10 at its opening. The drive rod of the temperature-controlled louver 10 is made of shape memory alloy. Specifically, the temperature-controlled louver 10 is a passive intelligent temperature-controlled louver 10, using shape memory alloy (SMA) to make the louver drive rod, which automatically contracts and closes when the ambient temperature is below -5℃ and expands and opens when the temperature is above 5℃, achieving adaptive temperature control without an external power source and improving the reliability of the system in extreme environments.

[0049] The temperature-controlled louvers 10 integrate wind speed and temperature sensors to automatically control their opening and closing based on ambient temperature. These sensors are communicatively connected to a control terminal 13. The control terminal 13 dynamically adjusts the opening angle of the louvers based on real-time monitored temperature and wind speed data, achieving precise ventilation control. Specifically, an intelligent ventilation control system can be integrated, incorporating wind speed and temperature sensors at the ventilation duct inlet. By combining real-time monitored temperature and wind speed data and using a pre-set intelligent algorithm, the optimal opening angle of the louvers is dynamically determined, achieving precise ventilation control.

[0050] The outer wall of the honeycomb ventilation duct is integrated with a piezoelectric fiber layer 102, which is electrically connected to the battery 12. Preferably, the battery 12 is connected to a solar panel 11 for solar energy storage. The integration of the piezoelectric fiber layer 102 PVDF on the outer wall of the intelligent ventilation duct can convert the vibration energy caused by vehicle passage into electrical energy, which is stored in the battery 12 to power the temperature control louver 10 and its sensors, forming a self-powered closed-loop system and reducing dependence on external energy.

[0051] Preferably, multiple L-shaped heat pipes 2 are embedded in the permafrost foundation 1, arranged in a longitudinally equidistant and laterally staggered array along the roadbed centerline. The bottom of each L-shaped heat pipe 2 is buried 1.5 to 2.0 meters below the upper limit of the permafrost. The L-shaped heat pipe 2 uses a copper-ammonia working fluid, with spiral fins welded to the surface of its evaporation section and a nano-hydrophobic coating on its condensation section. During winter operation, the heat pipes conduct heat from the foundation through a thermosiphon effect.

[0052] Example The present invention will now be described in detail with reference to specific embodiments. These embodiments are mainly divided into the following two parts: Part One: Pre-treatment of permafrost foundation 1. Surface treatment is divided into two stages. First, a low-impact excavator is used to remove the surface vegetation and loose cover layer with a thickness of ≤0.5m, preserving the original permafrost structure. Then, dry ice spraying is used to pre-cool the exposed permafrost surface to further suppress thermal disturbance during construction.

[0053] The L-shaped heat pipes are installed in a staggered array, following the principle of longitudinal equidistant spacing and lateral stagger. They are laid out with a longitudinal spacing of 5m along the center line of the roadbed and a lateral offset of 0.5m.

[0054] The drilling adopts a low-temperature mud circulation drilling process with a hole diameter of 200mm. The hole depth is dynamically adjusted according to the upper limit of the frozen soil to ensure that the bottom of the heat pipe is buried 1.5~2.0m below the upper limit of the frozen soil and the top is exposed 0.3m.

[0055] L-shaped heat pipe 2 uses copper-ammonia working fluid, with an evaporation section length of 3m and spiral fins welded to the surface to increase the heat exchange area; the condensation section is 1.2m long and covered with a nano-hydrophobic coating to improve heat dissipation efficiency. During winter operation, the heat pipe conducts heat from the foundation through the thermosiphon effect.

[0056] Three-dimensional geogrid layer 4 is laid. During the construction of the lower geogrid layer, injection-molded geogrid units with dimensions of 1.5m×1.5m×0.1m are laid on the surface of the permafrost foundation 1. The mesh size is 80mm×80mm and the polymer composite matrix is ​​high-density polyethylene.

[0057] The edge of the grid unit is provided with a two-way dovetail tenon groove 42, and the tenon cross section is a trapezoid with an upper base of 20mm, a lower base of 25mm, and a height of 15mm.

[0058] The stiffness gradient design is achieved through material modification: 10% polyurethane elastomer is added to the far end grid; 15% steel fiber is added to the transition section (5~10m); and steel fiber composite grid with a steel fiber content of 25% is used near the abutment end (0~5m).

[0059] The insulation layer 3 is installed using prefabricated rectangular protrusions made of closed-cell foam glass, measuring 1.0m × 1.0m × 0.1m, with a protrusion height of 20mm. The upper insulation board 51 has a pre-reserved rectangular groove measuring 0.8m × 0.8m, which is bonded to the lower protrusions with two-component epoxy resin. Polyurethane foam is injected at the joints to form a continuous sealing layer.

[0060] The hexagonal air-guiding channel has a side length of 0.2m and a depth of 0.1m. The channel is lined with composite permeable geotextile and has a longitudinal slope of 0.5% to ensure that cold air is introduced into the deep subgrade layer along the slope in winter.

[0061] The phase change material coating is made of paraffin wax and is applied using a high-pressure airless spraying process, with a coating thickness of 2.0 mm.

[0062] The construction of the rubble subbase involves laying basalt in layers, employing a gradual transition strategy.

[0063] Near the abutment end (0~5m), a three-layer progressive paving method is adopted: the bottom layer is paved with 400~500mm stones, the middle layer is filled with 500~600mm stones, and the top layer is tamped with a hydraulic hammer to form a gabion effect structure with high interlocking density.

[0064] The gradual change in stone size in the transition section (5~10m) is achieved through progressive screening: the proportion of 300mm stones in each linear meter of gradation decreases by 10% daily, while the proportion of 400mm stones increases by 10% daily.

[0065] The geomembrane is made of polyester and spliced ​​by hot-melt welding, with a weld width of ≥100mm. A 0.5m back wrapping section is reserved at the edge of the geomembrane and anchored to the roadbed slope with U-shaped nails to prevent fine particles from the fill layer from seeping down and clogging the pores.

[0066] The intelligent gradient honeycomb ventilation ducts are arranged in three rows along the driving direction, with their diameter gradually increasing from the far end to the near end of the abutment, forming a continuous stiffness gradient. The ventilation ducts use a piecewise linear function to achieve a smooth transition in diameter, as shown in the following formula:

[0067] Where D is the diameter (m) of the ventilation pipe located x meters from the bridge abutment. Maximum pipe diameter near the abutment (k = 0.35~0.45, H is the height of the bridge abutment) The minimum pipe diameter at the far end of the roadbed is usually set to 0.6 ~ 0.8 (m), L is the total length of the road-bridge transition section, and n is the gradient index, which is taken as n=1.2~1.5 to achieve non-linear gradient and better match the stiffness change requirements.

[0068] The pipe wall thickness t increases synchronously with the increase of the pipe diameter to ensure local stiffness and load-bearing capacity near the large pipe opening:

[0069] t is the pipe wall thickness (mm) at a distance x meters from the bridge abutment. The minimum wall thickness (far end) can be 3mm. The maximum wall thickness (near end) can be 6mm.

[0070] The ventilation duct uses high-strength, low-temperature resistant, and corrosion-resistant nickel-chromium-molybdenum alloy steel as the base material. The outer wall is coated with an active anti-corrosion coating 105, which has self-healing capabilities. The inner wall is coated with an organosilicon fluorine coating 104, with a thickness of 80 mm. The electrostatic spraying process is used to reduce flow resistance and prevent scaling.

[0071] The gradually stiffening intelligent ventilation duct uses high-strength nickel-chromium-molybdenum alloy steel strip, cold-rolled into continuous pipe sections with a hexagonal honeycomb nested structure (101). The dense stiffening ribs formed by its honeycomb units greatly improve the section moment of inertia of the pipe body, effectively resisting local deformation under the load of backfill and vehicle dynamics. To ensure the preload and sealing of the connection points in low-temperature environments, the pipe sections are connected by alloy bolts and polyurethane rubber seals.

[0072] A passive intelligent temperature-controlled louver 10 is integrated at the ventilation duct inlet. The louver blades 107 are made of aluminum alloy with an anodized surface. The drive rod is made of shape memory alloy (SMA), which automatically retracts and closes when the ambient temperature is below -5℃ and extends and opens when it is above 5℃, achieving adaptive temperature control without external power.

[0073] The louver system integrates wind speed and temperature sensors, and the data is transmitted to the control terminal 13 in real time. The opening and closing angle of the louvers is dynamically adjusted through a preset algorithm to achieve precise control of ventilation and maintain the water and heat balance of the permafrost.

[0074] During the construction of fill layer 7, the fill material is gravelly soil with a gravel content of ≥60% and a plasticity index Ip≤6. The layer thickness is 0.3m, and it is compacted 6 times with an 18t block roller.

[0075] During the construction of asphalt pavement layers, phase change microcapsules are incorporated into the asphalt mixture, and a two-layer paving process is adopted: the lower layer is AC-20 with a thickness of 8cm and an asphalt-aggregate ratio of 4.5%, and the upper layer is SMA-13 ​​with a thickness of 4cm and an asphalt-aggregate ratio of 6.0%.

[0076] Part Two: The gradual change in the diameter and wall thickness of the ventilation duct creates a continuous stiffness field from the flexible subgrade to the rigid abutment. The smaller diameter at the far end maintains a thicker fill layer 7, the transition in the middle section of the duct diameter achieves a step-by-step increase in stiffness, and the larger diameter at the near end thins the fill layer 7, completely bridging the interface between rigid and flexible structures and suppressing differential settlement.

[0077] A coordinated ventilation-cooling-drainage mechanism is implemented. In winter, the ventilation pipes can introduce cold air into the deep layers of the roadbed to accelerate the freezing of the foundation. In summer, the ventilation volume is adjusted by temperature-controlled louvers 10 to weaken heat convection, maintain the hydrothermal stability of the frozen soil, and prevent thaw settlement and frost heave diseases.

[0078] The outer wall of the ventilation duct is integrated with a piezoelectric fiber layer 102 (PVDF) to convert vehicle vibration energy into electrical energy, which is stored in the battery 12 to power the temperature control louvers 10 and sensors, forming a self-powered closed-loop system and improving the reliability and sustainability of the project in extreme environments.

[0079] Meanwhile, drainage ditches 14 are installed on the outer sides or toes of the slopes of the roadbed fill, extending longitudinally along the direction of traffic. These drainage ditches 14 are located on the outer side of the pavement structure layer above the permafrost foundation, and are situated on the lateral drainage path of the intelligent gradient honeycomb ventilation pipe layer and the riprap cushion layer. Together with the gradient riprap cushion layer and the intelligent gradient honeycomb ventilation pipe layer, they form an internal drainage system for the roadbed, longitudinally collecting and draining seepage and accumulated water from the roadbed body and cushion layer outside the roadbed area. The drainage ditches 14, the riprap cushion layer, and the corrugated steel pipes together constitute a complete drainage system, quickly draining accumulated water during periods of roadside water accumulation or heavy rainfall, ensuring the roadbed remains dry and stable.

[0080] Improved performance of ventilation duct materials: Nickel-chromium-molybdenum alloy steel has high strength and toughness at low temperatures and good corrosion resistance, thus extending the service life of corrugated steel pipes.

[0081] The inner wall features a silicone fluorine coating (104) to reduce airflow resistance and prevent scaling; the outer wall has a smart coating for active corrosion protection and self-healing. Shape memory alloy bolts automatically return to their preset shape at low temperatures, ensuring a tight connection; polyurethane rubber seals prevent leakage.

[0082] Temperature-controlled louvers 10 and a wind speed sensor enable precise adjustment of ventilation volume, maintaining the optimal hydrothermal state of the permafrost.

[0083] Modular assembly with tenon joints for geogrids facilitates construction and meets fatigue resistance requirements.

[0084] The double-layer gradation design of the riprap subbase (coarse on top, fine on the bottom) and the interlocking structure of extra-large riprap near the abutment improve the subbase's stiffness and impact resistance. Phase change materials are incorporated into the asphalt surface layer to reduce freeze-thaw cycle damage.

[0085] This invention focuses on differential settlement control, multi-mechanism synergy, ecological protection, engineering performance improvement, and structural design innovation, effectively solving the challenges of road-bridge transition sections in permafrost regions. Addressing the issue of differential settlement caused by abrupt changes in stiffness between the abutment and the subgrade, the intelligent gradient honeycomb ventilation duct creates a continuous stiffness gradient through variations in pipe diameter and wall thickness from the far end to the near end of the abutment. The ventilation duct, employing a hexagonal honeycomb nested structure, achieves a coordinated gradient in pipe diameter and wall thickness while significantly enhancing the axial compressive stiffness and lateral stability of the duct body due to its superior geometric characteristics, extending the structure's service life under freeze-thaw cycles. The composite stiffness field formed by the duct and the overlying fill is smoother and more continuous, completely bridging the abrupt stiffness-flexibility interface between the subgrade and the abutment. To address the thaw settlement and frost heave problems caused by permafrost hydrothermal imbalance, temperature-controlled louvers and wind speed sensors work in conjunction with gradually changing diameter corrugated steel pipes to dynamically adjust ventilation volume. In winter, this reduces cold intrusion and activates heat pipe cooling, while in summer, it enhances ventilation and cooling, maintaining the thermal stability of permafrost and inhibiting permafrost thaw settlement. This, combined with the stiffness transition effect of the gradually changing diameter corrugated steel pipes, solves the problem of uneven settlement in the transition section of the road and bridge. To address the stress concentration problem caused by the uniform stiffness of traditional grids, a gradient modification design is adopted to create a three-zone gradient that matches the stiffness field of the abutment-subgrade, synergistically suppressing differential settlement. To address the defect of insulation layers hindering water and heat exchange, hexagonal air channels are created within the closed-cell foam glass insulation layer, constructing a dual-channel system of insulation and ventilation that conducts cold in winter and blocks heat in summer, significantly stabilizing permafrost temperature. To address the challenges of construction in high-altitude and cold regions, a modular dovetail tenon and slot assembly structure uses trapezoidal tenons to achieve fatigue-resistant and maintenance-free connections, greatly improving construction efficiency and service life.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A rigid transition structure for a roadbed with a gradually changing diameter ventilation duct in a transition section between roads and bridges in permafrost regions, comprising a permafrost foundation (1), a pavement structure layer (8), and abutments (9), wherein the abutments (9) are disposed between the top surface of the permafrost foundation (1) and the bottom surface of the pavement structure layer (8), characterized in that... The abutment (9) is connected to the roadbed fill body. A three-dimensional geogrid layer (4) is laid between the top surface of the permafrost foundation (1) and the roadbed fill body. The three-dimensional geogrid layer (4) is divided into a flexible drainage zone, a semi-rigid transition zone and a rigid anchoring zone along the driving direction from the far end of the abutment to the near end of the abutment, forming a gradient structure with gradually increasing stiffness. The roadbed fill body includes a gradient block cushion layer (5), an intelligent gradient honeycomb ventilation pipe layer (6) and a fill layer (7) from bottom to top. The stone cushion layer (5) is laid with increasing thickness and stone particle size from the far end of the bridge abutment to the near end along the driving direction, and is divided into a conventional section at the far end, a transition section in the middle, and a reinforced section at the near end. The intelligent gradient honeycomb ventilation pipe layer (6) includes multiple rows of honeycomb ventilation pipes laid along the driving direction. The pipe diameter and pipe wall thickness of the honeycomb ventilation pipes increase synchronously from the far end of the bridge abutment to the near end along the driving direction, forming a continuous stiffness gradient field that matches the three-dimensional geogrid layer (4) and the gradient stone cushion layer (5).

2. The rigid transition structure for the roadbed of the gradually changing diameter ventilation duct in the transition section of a road and bridge in permafrost regions according to claim 1, characterized in that... The diameter D of the honeycomb ventilation duct satisfies the following piecewise linear function: Where x is the distance from the bridge abutment, and L is the total length of the road-bridge transition section. The maximum pipe diameter near the abutment. is the minimum pipe diameter at the far end of the bridge abutment, and n is the gradient index, ranging from 1.2 to 1.

5.

3. The rigid transition structure for the roadbed of the gradually changing diameter ventilation pipe in the transition section of the road and bridge in permafrost areas according to claim 2, characterized in that... The wall thickness t of the honeycomb ventilation duct increases synchronously with the increase of the diameter D, satisfying the following relationship: in, The minimum pipe wall thickness at the far end of the bridge abutment. This represents the maximum wall thickness of the pipe near the abutment.

4. The rigid transition structure for the roadbed of the gradually changing diameter ventilation pipe in the transition section of the road and bridge in permafrost areas according to claim 3, characterized in that... The cross-section of the honeycomb ventilation duct is a hexagonal honeycomb nested structure (101), and the material of the honeycomb ventilation duct is nickel-chromium-molybdenum alloy steel.

5. The rigid transition structure for the roadbed of the gradually changing diameter ventilation pipe in the transition section of the road and bridge in permafrost areas according to claim 4, characterized in that... The outer wall of the honeycomb ventilation duct is coated with an anti-corrosion coating (105), and the inner wall is coated with an organosilicon fluorine coating (104).

6. The rigid transition structure for the roadbed of the gradually changing diameter ventilation pipe in the transition section of the road and bridge in permafrost areas according to claim 5, characterized in that... The honeycomb ventilation pipe is provided with a temperature-controlled louver (10) at the pipe opening, and the drive rod of the temperature-controlled louver (10) is made of shape memory alloy.

7. The rigid transition structure for the roadbed of the gradually changing diameter ventilation pipe in the transition section of the road and bridge in permafrost areas according to claim 1, characterized in that... The three-dimensional geogrid layer (4) is a double-layer geogrid structure with an insulation layer (3) sandwiched between the two geogrid layers. The insulation layer (3) has a through-thickness air channel.

8. The rigid transition structure for the roadbed of the gradually changing diameter ventilation pipe in the transition section of the road and bridge in permafrost areas according to claim 7, characterized in that... The surface of the three-dimensional geogrid layer (4) is coated with a phase change material coating.

9. The rigid transition structure for the roadbed of the gradually changing diameter ventilation pipe in the transition section of the road and bridge in permafrost areas according to claim 1, characterized in that... The thickness of the conventional section at the far end is 0.5m, and the particle size of the stones is 200~300mm; the thickness of the transition section in the middle is 0.6~0.7m, and the particle size of the stones ranges from 300mm~400mm from the far end to the near end; the thickness of the subbase layer in the reinforcing section at the near end is 0.8~1.0m, and the particle size of the stones is 400~600mm.

10. The rigid transition structure for the roadbed of the gradually changing diameter ventilation pipe in the transition section of the road and bridge in permafrost areas according to claim 1, characterized in that... An L-shaped heat pipe (2) is buried in the permafrost foundation (1).

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