Permafrost region road and bridge transition section structure based on long and short pile composite foundation

Abstract

The invention provides a permafrost region road and bridge transition section structure based on a long and short pile composite foundation, and belongs to the technical field of road and bridge engineering in civil engineering. The permafrost region road and bridge transition section structure based on the long and short pile composite foundation comprises the long and short pile composite foundation, a foundation cushion layer, a bridge pier and abutment body and a transition section roadbed body, the long and short pile composite foundation comprises long piles and short piles, the long piles penetrate through a permafrost movable layer and extend into the position 6 m below the upper limit of permafrost, and the short piles penetrate through the long piles. The short piles stretch into the upper limit of frozen soil by 1 m. The composite foundation composed of the long piles and the short piles is arranged, the vertical and plane arrangement of the composite foundation is defined, the long piles effectively transmit loads to stable deep frozen soil and mainly bear vertical loads and horizontal frost heaving force, and the short piles reinforce and stabilize a shallow movable layer and work together with the long piles, so that the stability of the shallow movable layer is improved. The uneven load originally concentrated on the bridge pier and abutment body is dispersed to a wider foundation range, and the risk of differential settlement is reduced fundamentally.

Description

Technical Field

[0001] This invention relates to the field of road and bridge engineering technology in civil engineering, and more specifically, to a road and bridge transition section structure based on a composite foundation of long and short piles in permafrost regions. Background Technology

[0002] Permafrost regions are characterized by low temperatures, frequent freeze-thaw cycles, and the stability of permafrost is easily affected by external disturbances. As a key part connecting bridge piers and roadbeds, the structural stability of the road-bridge transition section directly determines the traffic safety of the entire road-bridge project.

[0003] Existing foundation treatment technologies for road and bridge transition sections in permafrost regions require a large amount of material to penetrate the thick permafrost layer when using only long piles, resulting in high costs and construction difficulties. When using only short piles, deep loads cannot be effectively transferred, and uneven roadbed settlement is easily caused by deformation of the active permafrost layer, which is inconsistent with the deformation of the bridge piers and abutments. The replacement method requires the excavation of a large amount of permafrost, which damages the original permafrost environment, and the replacement material is prone to cracking due to freeze-thaw cycles in the later stages. The grouting reinforcement method has high requirements for the sealing of the permafrost and poor load distribution, making it difficult to control long-term settlement. Summary of the Invention

[0004] To overcome the above deficiencies, the present invention provides a road and bridge transition section structure based on a composite foundation of long and short piles in permafrost regions that overcomes or at least partially solves the above technical problems.

[0005] This invention is implemented as follows:

[0006] This invention provides a road-bridge transition section structure based on a composite foundation of long and short piles in permafrost regions, comprising a composite foundation of long and short piles, a foundation cushion layer, bridge piers and abutments, and the main body of the transition section road. The composite foundation of long and short piles includes long piles and short piles. The long piles penetrate the active layer of permafrost and extend 6m below the upper limit of the permafrost, while the short piles extend 1m below the upper limit of the permafrost. The long and short piles are arranged in an equilateral triangle in plan, with a single long pile as the center and three short piles surrounding it. The foundation cushion layer is set on top of the long and short piles, with a thickness of 0.5m, and is made of a mixture of coarse aggregate, sand, and gravel.

[0007] In a preferred embodiment, the long pile is a precast reinforced concrete pile with a diameter of 500-800mm, the short pile is a cement-soil mixing pile with a diameter of 300-500mm and a cement content of 3%-5%, the center distance between adjacent long piles is 3-5m, the center distance between the short pile and the long pile is 1-1.5m, and the length of the long pile can be adjusted according to the upper limit depth of the frozen soil.

[0008] In a preferred embodiment, the top of the long pile and the short pile is provided with a pile cap, and the top of the pile cap is provided with an integrated air-inflatable adjustment unit, which includes an air-inflatable adjustment bag and a distance measuring component for monitoring its height.

[0009] In a preferred embodiment, the top of the integrated inflation adjustment unit is provided with a rigid stress diffusion plate, and a modified mattress layer is laid on top of the rigid stress diffusion plate.

[0010] In a preferred embodiment, a gradient stiffness foamed concrete transition body is provided between the bridge pier body and the transition section road body, and the integrated air-conditioning unit also includes a central controller for adjusting the internal pressure of the air-conditioning pack based on the data fed back by the ranging component.

[0011] In a preferred embodiment, the integrated inflation regulating unit further includes a pressure sensor, and the ranging component includes a laser rangefinder mounted on the pile cap and a reflective target fixed to the bottom of a rigid stress diffusion plate.

[0012] In a preferred embodiment, both the laser rangefinder and the pressure sensor are signal-connected to the central controller, which is connected to a pressure regulator.

[0013] In a preferred embodiment, the improved mattress layer is a sandwich structure comprising a lower layer of graded crushed stone, a middle layer of geogrid, and an upper layer of coarse aggregate.

[0014] In a preferred embodiment, the density and stiffness of the gradient stiffness foamed concrete transition body decrease in a gradient from the bridge pier body to the roadbed body of the transition section.

[0015] In a preferred embodiment, a connecting rod is pre-embedded in the gradient stiffness foamed concrete transition body, with one end of the connecting rod anchored into the bridge pier body and the other end extending into the roadbed body of the transition section.

[0016] The road and bridge transition section structure based on a composite foundation of long and short piles provided by this invention has the following beneficial effects:

[0017] 1. By setting up a composite foundation consisting of long piles and short piles, and clearly defining their vertical and horizontal layout, the long piles effectively transfer the load to the stable deep frozen soil, mainly bearing the vertical load and horizontal frost heave force, while the short piles reinforce and stabilize the shallow active layer. Working together with the long piles, they disperse the uneven load originally concentrated on the bridge piers and abutments to a wider foundation area, thereby reducing the risk of differential settlement from the source.

[0018] 2. By setting a foundation cushion layer of a specific thickness, a stress diffusion layer is formed at the top of the pile, which can effectively buffer and redistribute the upper load, avoid stress concentration from damaging the pile, and absorb some freeze-thaw deformation. By treating the roadbed of the transition section in a special way, post-construction settlement can be eliminated in advance, unstable soil can be replaced, or the soil strength can be enhanced, thus ensuring the initial stability and deformation resistance of the roadbed of the transition section.

[0019] 3. By setting an integrated air-inflating adjustment unit on the pile cap, it becomes highly adjustable, providing a basis for subsequent intelligent leveling. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the planar arrangement of long and short piles provided by an embodiment of the present invention;

[0022] Figure 2 A vertical cross-sectional view of the road-bridge transition section is provided for embodiments of the present invention;

[0023] Figure 3 A three-dimensional structural schematic diagram provided for an embodiment of the present invention.

[0024] In the diagram: 1. Long pile; 2. Short pile; 3. Bridge pier body; 4. Transition section road base; 5. Upper limit of frozen soil; 6. Permafrost layer; 7. Bridge pier base; 8. Pile cap; 9. Integrated air-filled regulating unit; 10. Rigid stress diffusion plate; 11. Graded crushed stone layer; 12. Geogrid; 13. Coarse aggregate layer. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Reference Figures 1-3This invention provides a technical solution: a road-bridge transition section structure based on a composite foundation of long and short piles in permafrost areas, comprising a composite foundation of long and short piles, a foundation cushion layer, a bridge pier body 3, and a transition section road base 4. The composite foundation of long and short piles includes long piles 1 and short piles 2. The long piles 1 penetrate the active layer of permafrost and extend 6m below the upper limit of the permafrost layer 5. The short piles 2 extend 1m below the upper limit of the permafrost layer 5. The long piles 1 and short piles 2 are arranged in an equilateral triangle in the plane, with a single long pile 1 as the center and three short piles 2 surrounding it. The foundation cushion layer is set on top of the long piles 1 and short piles 2, with a thickness of 0.5m, and the material is a mixture of coarse aggregate, sand, and gravel. The transition section road base 4 is treated by preloading, excavation and filling, or reinforcement methods.

[0027] By setting up a composite foundation consisting of long piles 1 and short piles 2, and clearly defining its vertical and horizontal layout, long piles 1 effectively transfer the load to the stable deep frozen soil, mainly bearing the vertical load and horizontal frost heave force. Short piles 2 reinforce and stabilize the shallow active layer, working together with long piles 1 to disperse the uneven load originally concentrated on the bridge pier body 3 to a wider foundation area, reducing the risk of differential settlement from the root. By setting up a foundation cushion layer of a specific thickness, a stress diffusion layer is formed at the top of the piles, which can effectively buffer and redistribute the upper load, avoid stress concentration from damaging the pile body, and absorb some freeze-thaw deformation. By performing special treatment on the transition section road base body 4, post-construction settlement is eliminated in advance, unstable soil is replaced, or the soil itself is strengthened, ensuring the initial stability and deformation resistance of the transition section road base body 4.

[0028] Reference Figures 1-3 Long pile 1 is a precast reinforced concrete pile or bored pile with a diameter of 500-800mm and a concrete strength grade ≥C30. Short pile 2 is a cement-soil mixing pile or crushed stone pile with a diameter of 300-500mm and a cement content of 3%-5%. The center distance between adjacent long piles 1 is 3-5m, and the center distance between short pile 2 and long pile 1 is 1-1.5m. In the foundation cushion layer, the coarse aggregate particle size is 5-30mm, the mud content of the sand is ≤5%, and the compaction degree of the mixture is ≥95%. In the excavation and filling method of the basic body 4 of the transition section road, the layer excavation thickness is ≤0.5m, the compaction degree of the backfill non-frost-susceptible fill material is ≥96%, the preloading load of the preloading method is 1.2 times the design load, and the preloading time is 30-60 days. The length of long pile 1 can be adjusted according to the upper limit of the frozen soil depth 5, and the adjustment range is from the upper limit of the frozen soil depth 5 + 6m to the upper limit of the frozen soil depth 5 + 8m.

[0029] By specifically defining the material, size, and key process parameters of long pile 1 and short pile 2, it is ensured that long pile 1 has sufficient strength and durability to penetrate the active layer and anchor to the permafrost layer 6, while short pile 2 can effectively improve the properties of shallow soil and form a reliable composite foundation. By optimizing the pile spacing and center distance, the most effective coverage and reinforcement of the foundation soil is achieved while ensuring the bearing capacity of the foundation, avoiding reinforcement blind spots. By strictly defining the particle size, mud content, and compaction degree of the cushion layer material, it is ensured that it has ideal permeability, strength, and stress diffusion capacity. By refining the treatment parameters of the basic road body 4 of the transition section, the controllability and reliability of the treatment effect are ensured by standardized processes, laying a solid foundation for the long-term stability of the entire transition section structure.

[0030] Reference Figures 1-3 The top of the long pile 1 and the short pile 2 is provided with a pile cap 8, and the top of the pile cap 8 is provided with an integrated air-inflatable adjustment unit 9. The integrated air-inflatable adjustment unit 9 includes an air-inflatable adjustment bag and a distance measuring component for monitoring its height.

[0031] By setting up the pile cap 8, a stable and flat installation reference surface is provided for the superstructure, and the bearing capacity of a single pile is converted into surface bearing capacity. By setting up an integrated air-inflatable adjustment unit 9 on the pile cap 8, it has height adjustability, providing a basis for subsequent intelligent leveling.

[0032] Reference Figures 1-3 The top of the integrated inflation adjustment unit 9 is provided with a rigid stress diffusion plate 10, and the top of the rigid stress diffusion plate 10 is covered with a modified mattress layer.

[0033] By setting up a rigid stress diffusion plate 10, the concentrated load from the upper roadbed is transformed into a uniformly distributed load and evenly transmitted to each air-filled regulating unit below. This avoids the failure of the regulating unit or measurement inaccuracy caused by excessive local pressure, and ensures the uniformity and accuracy of pressure and displacement regulation.

[0034] Reference Figures 1-3 A gradient stiffness foamed concrete transition body is provided between the bridge pier body 3 and the transition section road body 4. The integrated air-inflating adjustment unit 9 also includes a central controller, which is used to adjust the internal pressure of the air-inflating adjustment bag according to the data fed back by the ranging component.

[0035] By setting up a gradient stiffness foam concrete transition body, a smooth and continuous transition of roadbed stiffness from flexible roadbed to rigid bridge pier body 3 is achieved, effectively avoiding stress concentration and track irregularities caused by sudden stiffness changes. By introducing a central controller and forming a closed-loop control system with the ranging component and inflatable adjustment package, it can sense settlement deformation in real time and make active and precise adjustments, thus achieving proactive protection of the smoothness of the road-bridge transition section.

[0036] Reference Figures 1-3 The integrated inflation adjustment unit 9 also includes a pressure sensor, and the ranging components include a laser rangefinder installed on the pile cap 8 and a reflective target fixed at the bottom of the rigid stress diffusion plate 10.

[0037] By setting up a pressure sensor and a high-precision ranging system consisting of a laser rangefinder and a reflective target, comprehensive and reliable decision data is provided to the central controller, ensuring the accuracy and efficiency of the control process.

[0038] Reference Figures 1-3 Both the laser rangefinder and the pressure sensor are connected to the central controller. The central controller is connected to a pressure regulator. The central controller is configured to receive the altitude data from the laser rangefinder and compare it with a preset threshold. When the altitude data exceeds the limit, the pressure regulator controls the corresponding inflatable adjustment package to inflate or deflate.

[0039] By establishing the above complete execution logic chain, the system achieves fully automatic and intelligent operation. When uneven settlement occurs, the system can automatically identify the points exceeding the standard and generate precise lifting or settling forces by changing the air pressure in a specific adjustment pack, thereby achieving dynamic leveling of the foundation plane and keeping the differential settlement within the allowable range of millimeters.

[0040] Reference Figures 1-3 The improved mattress layer is a sandwich structure, including a lower layer of graded crushed stone 11, a middle layer of geogrid 12 and an upper layer of coarse aggregate 13;

[0041] By designing the mattress layer as a sandwich structure, it not only retains the stress diffusion and drainage functions of the traditional mattress layer, but also significantly enhances the overall tensile strength and shear deformation resistance of the mattress layer due to the reinforcement effect of the geogrid 12 in the middle layer, thus becoming a high-performance stress transfer and transition layer that works in conjunction with the underlying intelligent control system.

[0042] Reference Figures 1-3 The density and stiffness of the gradient stiffness foam concrete transition body decrease gradually from the bridge pier body 3 to the road body 4 of the transition section.

[0043] By making the stiffness of the transition body decrease gradually from the bridge pier body 3 to the roadbed, the huge stiffness difference between the bridge pier body 3 and the roadbed is perfectly matched, so that the support stiffness of the track foundation changes smoothly when the train passes, which greatly improves the stability and comfort of the train and reduces the impact of dynamic load on the structure.

[0044] Reference Figures 1-3A connecting rod is pre-embedded in the gradient stiffness foam concrete transition body. One end of the connecting rod is anchored into the bridge pier body 3, and the other end extends into the roadbed body 4 of the transition section.

[0045] By pre-embedding connecting rods and connecting the bridge pier body 3, the transition body and the roadbed body in series, the three originally relatively independent parts are tightly connected into a coordinated whole, which effectively constrains the relative displacement between the components, enhances the integrity and stability of the structure under dynamic loads and freeze-thaw cycles, and prevents defects such as separation or detachment between the transition body and the bridge pier body 3 or the roadbed.

[0046] Example

[0047] This invention was applied in a highway bridge transition section project in a permafrost region of the Qinghai-Tibet Plateau. The upper limit of the permafrost depth 5 in the project area is 2.5m, the thickness of the permafrost layer 6 is 15-20m, the ice content is 20%-30%, the characteristic value of the bearing capacity of the active layer soil is 120kPa, and the design load of the transition section is Highway-I.

[0048] First, drilling was conducted using an XY-150 drilling rig (drilling depth 10m), and combined with ground-penetrating radar geophysical exploration, the upper limit of the frozen soil layer 5 was accurately determined to be 2.5m, and the ice content of the permafrost layer 6 was 20%-30%. Through on-site plate load tests, the characteristic value of the bearing capacity of the active soil layer was measured to be 120kPa. Construction began with the construction of the composite foundation. Long pile 1 was a 600mm diameter C30 concrete bored pile, with a length calculated based on the frozen soil upper limit 5 depth + 6m, totaling 8.5m, ensuring its anchorage depth matched the burial depth of the bridge pier foundation 7 to maintain long-term stability. Short pile 2 was a 400mm diameter cement-soil mixing pile with a cement content of 4%, and its length was calculated based on the frozen soil upper limit 5 depth + 1m. 3.5m long piles 1 and short piles 2 are arranged in an equilateral triangle on the plane, with a spacing of 4m between the long piles 1. Three short piles 2 are arranged around each long pile 1, with a center-to-center distance of 1.2m between the short piles 2 and the long piles 1. This arrangement aims to achieve uniform load transfer to the foundation. After all long piles 1 and short piles 2 are constructed, pile caps 8 are poured on top of the piles to provide a flat installation reference surface for the superstructure. Subsequently, integrated inflatable adjustment units 9 are precisely installed on each pile cap 8. The core of this unit is an inflatable adjustment bag with a pressure sensor integrated at its bottom. Simultaneously, a laser rangefinder is installed on the pile cap 8, and in subsequent steps, a reflective target is installed at the corresponding position on the bottom of the rigid stress diffusion plate 10, together forming a high-precision ranging system to complete the adjustment. After the unit sections are laid out, a rigid stress diffusion plate 10 is laid on top of them. This plate evenly distributes the upper load to each adjustment unit. Next, a modified cushion layer is laid on the stress diffusion plate. This cushion layer has a three-layer structure: the lower layer is graded crushed stone, the middle layer is geogrid 12 with a tensile strength of not less than 80kN / m, and the upper layer is a mixture of coarse aggregate with a particle size of 5-20mm and sand in a 7:3 mass ratio. It is laid in two layers, each 0.25m thick, and compacted using vibration to a compaction degree of not less than 96%. Next, the construction of the transition section road base 4 is carried out, using a cut-and-fill preloading method: first, the top 2.5m thick unstable frozen soil is excavated in layers, each layer no more than 0.5m thick, and then graded crushed stone is backfilled simultaneously. The compaction layer thickness is 0.3m, and the compaction degree reaches 97%. After backfilling, the roadbed is preloaded with 1.2 times the design load for 45 days to eliminate post-construction settlement. A gradient stiffness foamed concrete transition body is constructed between the bridge pier body 3 and the treated transition section roadbed body 4. This transition body is constructed by pouring three different densities of foamed concrete in sections, so that its stiffness decreases smoothly from the bridge pier body 3 to the roadbed. In this transition body, a connecting rod is pre-embedded. One end of the connecting rod is anchored into the bridge pier body 3, and the other end extends into the transition section roadbed body 4 to enhance the integrity. Finally, the signal lines of all laser rangefinders and pressure sensors are connected to the central controller, and the controller is connected to the pressure regulator.The system was jointly debugged, and the allowable elevation fluctuation threshold was set to ±3mm. After the system was powered on, the central controller started to run automatically, monitor the elevation and pressure of each point in real time, and control the pressure regulator to inflate or deflate the inflatable regulating bag to dynamically maintain the flatness and stability of the foundation of the entire transition section, ensuring that its deformation is always coordinated with the bridge pier body 3.

Claims

1. A transition section structure for road and bridge sections in permafrost regions based on a composite foundation of long and short piles, characterized in that, The structure includes a composite foundation of long and short piles, a foundation cushion layer, a bridge pier body (3), and a transition section road body (4). The composite foundation of long and short piles includes long piles (1) and short piles (2). The long piles (1) penetrate the active layer of permafrost and extend 6m below the upper limit of the permafrost (5). The short piles (2) extend 1m below the upper limit of the permafrost (5). The long piles (1) and short piles (2) are arranged in an equilateral triangle in the plane, with a single long pile (1) as the center and three short piles (2) surrounding it. The foundation cushion layer is set on the top of the long piles (1) and short piles (2), with a thickness of 0.5m, and the material is a mixture of coarse aggregate, sand, and gravel.

2. The transition section structure for road and bridge sections in permafrost regions based on a composite foundation of long and short piles according to claim 1, characterized in that, The long pile (1) is a precast reinforced concrete pile with a diameter of 500-800mm. The short pile (2) is a cement-soil mixing pile with a diameter of 300-500mm and a cement content of 3%-5%. The center distance between adjacent long piles (1) is 3-5m. The center distance between the short pile (2) and the long pile (1) is 1-1.5m. The length of the long pile (1) can be adjusted according to the upper limit of the frozen soil depth (5).

3. The transition section structure for road and bridge sections in permafrost regions based on a composite foundation of long and short piles as described in claim 1, characterized in that, The top of the long pile (1) and the short pile (2) is provided with a pile cap (8), and the top of the pile cap (8) is provided with an integrated air-inflatable adjustment unit (9), which includes an air-inflatable adjustment bag and a distance measuring component for monitoring its height.

4. The transition section structure for road and bridge sections in permafrost regions based on a composite foundation of long and short piles as described in claim 3, characterized in that, The top of the integrated inflation adjustment unit (9) is provided with a rigid stress diffusion plate (10), and the top of the rigid stress diffusion plate (10) is covered with a modified mattress layer.

5. The transition section structure for road and bridge sections in permafrost regions based on a composite foundation of long and short piles according to claim 3, characterized in that, A gradient stiffness foamed concrete transition body is provided between the bridge pier body (3) and the transition section road body (4). The integrated air-inflating adjustment unit (9) also includes a central controller, which is used to adjust the internal pressure of the air-inflating adjustment bag according to the data fed back by the ranging component.

6. The transition section structure for road and bridge sections in permafrost regions based on a composite foundation of long and short piles as described in claim 5, characterized in that, The integrated inflation adjustment unit (9) also includes a pressure sensor, and the ranging component includes a laser rangefinder installed on the pile cap (8) and a reflective target fixed at the bottom of the rigid stress diffusion plate (10).

7. The transition section structure for road and bridge sections in permafrost regions based on a composite foundation of long and short piles as described in claim 6, characterized in that, Both the laser rangefinder and the pressure sensor are connected to the central controller via signal transmission, and the central controller is connected to a pressure regulator.

8. The transition section structure for road and bridge sections in permafrost regions based on a composite foundation of long and short piles according to claim 4, characterized in that, The improved mattress layer is a sandwich structure, comprising a lower layer of graded crushed stone (11), a middle layer of geogrid (12), and an upper layer of coarse aggregate (13).

9. The transition section structure for road and bridge sections in permafrost regions based on a composite foundation of long and short piles according to claim 5, characterized in that, The density and stiffness of the gradient stiffness foamed concrete transition body decrease in a gradient from the bridge pier body (3) to the roadbed body (4) of the transition section.

10. The transition section structure for road and bridge sections in permafrost regions based on a composite foundation of long and short piles according to claim 5, characterized in that, The gradient stiffness foamed concrete transition body has a pre-embedded connecting rod. One end of the connecting rod is anchored into the bridge pier body (3), and the other end extends into the roadbed body (4) of the transition section.

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