Bearing platform structure suitable for large-span bridge under soft soil foundation condition, construction method and bridge

Abstract

The invention relates to a bearing platform structure suitable for a large-span bridge under the soft soil foundation condition, a construction method and the bridge. The bearing platform structure comprises multiple pile foundations which are arranged into multiple rows and multiple columns at intervals; the reinforced concrete bottom plate and the pile foundation are poured into a whole through reserved steel bars at the top of the pile foundation, and the reinforced concrete bottom plate is provided with a plurality of transverse prestressed steel bars and longitudinal prestressed steel bars which are vertically arranged; the bearing platform is located in the center of the reinforced concrete bottom plate. The height of the supporting beams is equal to that of the bearing platform, the supporting beams comprise the first supporting beams and the second supporting beams, and the multiple first supporting beams and the multiple second supporting beams form a grid structure; the reinforced concrete top plate is located above the bearing platform and the supporting beam and connected into a whole through reserved steel bars at the top of the bearing platform and the top of the supporting beam. The size and performance of the pile foundation are optimized by improving the stress state of the pile foundation, the diameter of the pile foundation of a large-span bridge under the same load condition is effectively reduced, and therefore input and construction time of special drilling equipment are reduced.

Description

Technical Field

[0001] The present application relates to the field of bridge construction, and in particular to a pedestal structure, a construction method and a bridge suitable for a long-span bridge under soft soil foundation conditions. Background Art

[0002] With the rapid development of transportation network and urban municipal construction, the bridge structure and span are also expanding. The wide application of large-span suspension bridges, cable-stayed bridges, arch bridges and other bridge forms has made the bridge span larger and larger, and the requirements for foundation bearing capacity have also increased. Especially in areas with soft soil foundation or deep rock formations, bridge construction faces greater challenges.

[0003] According to the "Highway Bridge and Culvert Foundation and Substructure Design Code" (JTG 3363-2019), the settlement of pile foundations in soft soil foundations must be controlled at L / 1500 (L is the span of the bridge). Although traditional large-diameter pile foundations (d≥2.5m) have high bearing capacity, they have a long construction period (a single φ4m pile takes ≥15 days) and cause serious vibration and noise pollution.

[0004] Under soft soil conditions, traditional pile foundation construction methods often require large-diameter and long-length piles to meet the bridge's foundation bearing capacity requirements. However, this construction method not only requires specialized drilling equipment, but may also lead to a significant increase in pile foundation costs and a significant extension of construction time. In addition, problems such as uneven settlement and insufficient bearing capacity of soft soil foundations also pose potential risks to the long-term stability and safety of bridges. Summary of the invention

[0005] The embodiments of the present application provide a pedestal structure, a construction method and a bridge suitable for a long-span bridge under soft soil foundation conditions, so as to solve the problem that the pile foundation with a large diameter and a long pile length is used in the related technology, which leads to a substantial increase in the cost of the pile foundation and a significant extension of the construction period.

[0006] In a first aspect, a cap structure suitable for a long-span bridge under soft soil foundation conditions is provided, comprising:

[0007] Pile foundations, a plurality of said pile foundations are arranged in a plurality of rows and columns at intervals;

[0008] A reinforced concrete base plate is cast integrally with the pile foundation through reserved steel bars at the top of the pile foundation, and a plurality of transverse prestressed steel bars and longitudinal prestressed steel bars arranged perpendicular to each other are provided in the reinforced concrete base plate;

[0009] The cap is located at the center of the reinforced concrete bottom plate.

[0010] A support beam, whose height is equal to that of the support platform, includes a first support beam and a second support beam, and a plurality of the first support beams and the second support beams form a grid structure;

[0011] The reinforced concrete top plate is located above the cap and the support beam, and is connected as a whole through the reserved steel bars on the top of the cap and the support beam.

[0012] In some embodiments, the distance between adjacent pile foundations is not less than 4 times the diameter of the pile foundation.

[0013] In some embodiments, the pile foundation has a diameter of 0.8 to 2.0 m.

[0014] In some embodiments, the intersection of the first support beam and the second support beam is collinear with the axis of the pile foundation.

[0015] In some embodiments, the wall thickness of the support beam is not less than the diameter of the pile foundation.

[0016] In some embodiments, the support beam is a lattice beam.

[0017] In a second aspect, a construction method for a cap structure of a long-span bridge under soft soil foundation conditions is provided, comprising the following steps:

[0018] According to the bridge structure design, calculate and determine the number and diameter of pile foundations that meet the bearing capacity of pile foundations, the size of the abutment and the design of the supporting beam frame, and the design of the prestressed steel bars of the reinforced concrete bottom slab;

[0019] During the construction of pile foundation, steel bars are reserved on the top of the pile foundation;

[0020] Construct a reinforced concrete base plate on top of the pile foundation, install and tension the transverse prestressed steel bars and longitudinal prestressed steel bars;

[0021] The middle solid cap is cast in situ in the middle of the reinforced concrete base plate;

[0022] Construct support beams around the solid cap in the middle;

[0023] Cast-in-place reinforced concrete top slab on top of cap and support beams;

[0024] Piers or towers are constructed on top of the reinforced concrete top slab.

[0025] In some embodiments, the prestressed steel bars of the reinforced concrete base plate are constructed using a post-tensioning method, and grouting is performed after the tensioning is completed.

[0026] In some embodiments, the support beams are constructed of factory-prefabricated reinforced concrete and assembled on site.

[0027] In a third aspect, a bridge is provided, comprising the abutment structure suitable for a long-span bridge under soft soil foundation conditions.

[0028] The embodiment of the present application provides a cap structure, construction method and bridge suitable for long-span bridges under soft soil foundation conditions. A grid-structured support beam is arranged around the cap. Compared with the conventional cap, the contact area between the cap and the pile foundation can be increased by about 3-4 times. Under the same pile diameter and pile spacing, the number of pile foundations can be increased by 3-4 times. Therefore, the bearing capacity requirement of a single pile foundation is reduced by 1 / 4 to 1 / 3 compared with the conventional design. Under the condition of a certain pile length, the bearing capacity of a single pile is in direct proportion to the pile diameter, which can effectively reduce the pile diameter of the pile foundation. Using a small pile diameter pile foundation instead of a large pile diameter pile foundation, the pile foundation construction technology is mature, the construction quality and accuracy are higher, and the construction time can be reduced exponentially (a pile foundation of the same length, with a diameter of 1.5m, can be completed in one day, but a pile foundation with a diameter of 4m can be completed in more than half a month); it can also reduce the investment in equipment such as large drilling rigs (the daily rental of a large drilling rig is several times or even dozens of times that of an ordinary drilling rig), while avoiding the problems of vibration and mud pollution that may be caused by the construction of large-diameter piles.

[0029] By tensioning the transverse and longitudinal prestressed steel bars on the reinforced concrete bottom plate, the loads transferred from the upper structure to the cap and the pile foundation itself are borne. Under the action of prestress, the stress state of the pile foundation will change as follows:

[0030] (1) Improve the force distribution of pile foundation

[0031] The prestressed tendons at the bottom of the pedestal generate compressive stress in the pile foundation, offsetting part of the tensile stress caused by external loads; and this compressive stress can be evenly distributed to the pile body and surrounding soil, reducing local stress concentration in the pile foundation.

[0032] (2) Resisting the shear force of pile foundation

[0033] Prestressed tendons can guide the load to be transferred to the pile foundation more evenly, optimize the load transfer path, and reduce local stress concentration; at the same time, the prestressed stress field formed in the base plate of the prestressed tendons can effectively offset the shear stress caused by the shear load of the pile foundation and improve the shear strength of the concrete of the base plate.

[0034] (3) Enhance the friction between pile and soil

[0035] Prestressing will make the contact between the pile body and the surrounding soil closer, increase the effective stress between the pile and the soil; and the increase in effective stress will increase the friction coefficient of the pile-soil interface, thereby enhancing the friction. Therefore, the bearing capacity per unit surface area of ​​the pile body is improved, and under the same load conditions, the required pile-soil contact area can be reduced, so a small diameter pile foundation can be used, which greatly reduces the cost and time of pile foundation construction.

[0036] (4) Reduce the settlement of pile foundation

[0037] Prestressing can reduce the settlement of the pile foundation under load and improve the stiffness of the pile foundation; and the reduction in settlement means smaller deformation of the pile foundation and more uniform stress distribution in the soil.

[0038] Therefore, the present application expands the contact area between the pedestal and the pile foundation by setting a grid-structured support beam around the pedestal, so that multiple small-diameter pile foundations can bear the load together. At the same time, a reinforced concrete base plate is set at the bottom of the pedestal and the support beam. The reinforced concrete base plate disperses the upper load to the pile foundation evenly through transverse and longitudinal prestressed steel bars, thereby reducing local stress concentration. The grid-shaped support beams, the prestressed steel bars set in the reinforced concrete base plate and the small-diameter pile foundation work together to form a complete force optimization system to improve the stress state of the pile foundation, thereby optimizing the size and performance of the pile foundation, and effectively reducing the pile foundation diameter of large-span bridges under the same load conditions, thereby reducing the investment in special drilling equipment and the construction time, which has a great promoting effect on reducing the cost and increasing the efficiency of the construction of large-span bridges, especially large-span bridges in areas with soft soil foundations or deep rock formations. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0040] Figure 1 A schematic diagram of the elevation structure of a cap structure suitable for a long-span bridge under soft soil foundation conditions provided in an embodiment of the present application;

[0041] Figure 2 A schematic plan view of a cap structure suitable for a long-span bridge under soft soil foundation conditions provided in an embodiment of the present application.

[0042] In the figure: 1. Pile foundation; 2. Reinforced concrete bottom plate; 21. Transverse prestressed steel bars; 22. Longitudinal prestressed steel bars; 3. Cap; 4. Support beam; 41. First support beam; 42. Second support beam; 5. Reinforced concrete top plate; 6. Bridge pier. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0044] The embodiment of the present application provides a pedestal structure suitable for long-span bridges under soft soil foundation conditions, which can solve the problem of using large-diameter and long-length pile foundations in related technologies, resulting in a significant increase in pile foundation costs and a significant extension of construction period.

[0045] like Figure 1 , Figure 2 As shown, a cap structure suitable for a long-span bridge under soft soil foundation conditions comprises:

[0046] A pile foundation 1, wherein a plurality of pile foundations 1 are arranged in a plurality of rows and columns at intervals;

[0047] The reinforced concrete bottom plate 2 is cast as a whole with the pile foundation 1 through the reserved steel bars on the top of the pile foundation 1. A plurality of transverse prestressed steel bars 21 and longitudinal prestressed steel bars 22 arranged perpendicular to each other are arranged in the reinforced concrete bottom plate 2, and the prestress control parameter is 0.75fptk;

[0048] The cap 3 is located at the center of the reinforced concrete base plate 2.

[0049] A support beam 4, the bottom of which is integrated with the upper surface of the reinforced concrete bottom plate 2, the height of the support beam 4 is equal to that of the cap 3, and includes a first support beam 41 and a second support beam 42, and a plurality of first support beams 41 and second support beams 42 form a grid structure;

[0050] The reinforced concrete top plate 5 is located above the cap 3 and the support beam 4, and is connected as a whole through the reserved steel bars on the top of the cap 3 and the support beam 4.

[0051] Furthermore, the diameter of the pile foundation 1 is 0.8 to 2.0 m.

[0052] Furthermore, the pile foundation 1 is a friction type pile foundation.

[0053] Specifically, the small-diameter friction pile foundation acts directly on the foundation. In this embodiment, the diameter is 1.2m. In some optional embodiments, the diameter is consistent with the pile diameters of other small-span bridges on the same line to facilitate the reuse of drilling construction equipment and reduce special equipment costs.

[0054] A cap structure suitable for long-span bridges under soft soil foundation conditions can bear the load transmitted from the upper structure through the transverse prestressed steel bars 21 and the longitudinal prestressed steel bars 22 in the reinforced concrete bottom plate 2, thereby improving the force distribution of the pile foundation 1. The prestressed steel bars at the bottom of the cap 3 generate compressive stress in the pile foundation 1, offsetting part of the tensile stress and reducing local stress concentration. The grid support beam 4 can increase the contact area between the cap 3 and the pile foundation 1. Under the same pile diameter and pile spacing, the number of pile foundations 1 can be increased, and the bearing capacity requirements of a single pile foundation can be reduced. When the circumference and cross-sectional area of ​​the small-diameter pile are reduced, the transverse and longitudinal prestressed steel bars of the reinforced concrete bottom plate 2 and the grid support beam 4 are used to closely contact the soil and enhance the pile-soil friction. The three work together to form a complete force optimization system, making the force of the entire structure more uniform and reasonable. Compared with conventional caps, the contact area between caps 3 and pile foundation 1 can be increased by about 3-4 times. Under the same pile diameter and pile spacing, the number of pile foundations 1 can be increased by 3-4 times. Therefore, the bearing capacity requirement of a single pile foundation 1 is reduced by 1 / 4 to 1 / 3 compared with conventional designs. The calculation formula for the bearing capacity of a single pile foundation 1 of friction type pile foundation 1 is as follows:

[0055]

[0056] K: safety factor (generally 2);

[0057] u: circumference of the pile body (u = πd, d is the pile diameter);

[0058] q sik : Characteristic value of lateral friction resistance of the i-th soil layer (provided by geological report);

[0059] l i : The length of the pile in the i-th soil layer;

[0060] q pk : characteristic value of pile end resistance;

[0061] A p :Pile end cross-sectional area (A p =πd 2 / 4).

[0062] For friction pile foundation, when the pile length is constant, the single pile bearing capacity is proportional to the pile diameter, which can effectively reduce the pile diameter of the pile foundation. The present invention improves the single pile bearing capacity by 30% to 40% through the synergistic effect of the transverse and longitudinal prestressed steel bars of the reinforced concrete base plate 2 and the grid support beam 4, and can reduce the pile diameter to φ1.2m, and shorten the construction period to 3 days / root. Using small pile diameter pile foundations instead of large pile diameter pile foundations, the pile foundation construction technology is mature, the construction quality and accuracy are higher, and the construction time can be reduced exponentially (a pile foundation of the same length, with a diameter of 1.2m, can be completed in three days, but a pile foundation with a diameter of 4m can be completed in more than half a month); it can also reduce the investment in equipment such as large drilling rigs (the daily rental of a large drilling rig is several times or even dozens of times that of an ordinary drilling rig), while avoiding the problems of vibration and mud pollution that may be caused by the construction of large diameter piles.

[0063] In this embodiment, the distance between adjacent pile foundations 1 is not less than 4 times the diameter of the pile foundation 1 .

[0064] As the arrangement area of ​​the pile foundation 1 increases, the pile diameter decreases, and the pile spacing increases, the number of pile foundations 1 can be adjusted, and the pile diameter and pile spacing can be optimized so that the pile spacing is ≥4d, thereby reducing the pile group effect and improving the utilization efficiency of the single pile bearing capacity of the friction pile foundation 1.

[0065] Furthermore, the cross-sectional area of ​​the reinforced concrete base plate 2 is 1 to 1.5 times the cross-sectional area of ​​the cap 3 .

[0066] Specifically, the volume of the support beams 4 around the pedestal 3, i.e., the expanded part of the pedestal, is only 1-1.5 times larger than that of the conventional pedestal, and prefabricated parts can be used for the concrete construction of the support beams 4. Compared with the conventional pedestal, the increased investment in materials, construction period, etc. of the lattice pedestal 3 is much less than that of the pile foundation, so the overall cost and construction period are significantly reduced.

[0067] A cap structure suitable for a long-span bridge under soft soil foundation conditions, the cap structure tensions transverse prestressed steel bars 21 and longitudinal prestressed steel bars 22 on a reinforced concrete bottom plate 2 to bear the load transferred from the upper structure to the cap and the pile foundation itself. Under the action of prestress, the stress state of the pile foundation 1 will undergo the following changes:

[0068] (1) Improve the force distribution of pile foundation 1

[0069] The prestressed tendons at the bottom of the pedestal 3 generate compressive stress in the pile foundation 1 to offset part of the tensile stress caused by the external load; and this compressive stress can be evenly distributed to the pile body and the surrounding soil, reducing the local stress concentration of the pile foundation 1.

[0070] (2) Resisting the shear force of pile foundation 1

[0071] The transverse prestressed steel bars 21 and the longitudinal prestressed steel bars 22 can guide the load to be transferred to the pile foundation 1 more evenly, optimize the load transfer path, and reduce local stress concentration; at the same time, the prestressed prestress field formed in the reinforced concrete base plate 2 at the bottom of the pedestal 21 can effectively offset the shear stress caused by the shear load of the pile foundation 1, and improve the shear strength of the reinforced concrete base plate 2 of the pedestal.

[0072] (3) Enhance the friction between pile and soil

[0073] Prestressing will make the contact between the pile body and the surrounding soil closer, increase the effective stress between the pile and the soil; and the increase in effective stress will increase the friction coefficient of the pile-soil interface, thereby enhancing the friction. Therefore, the bearing capacity per unit surface area of ​​the pile body is improved, and under the same load conditions, the required pile-soil contact area can be reduced, so a small diameter pile foundation 1 can be used, which greatly reduces the construction cost and time of the pile foundation 1.

[0074] (4) Reduce the settlement of pile foundation 1

[0075] Prestressing can reduce the settlement of the pile foundation 1 under load and improve the rigidity of the pile foundation 1; and the reduction of settlement means that the deformation of the pile foundation 1 is smaller and the stress distribution of the soil is more uniform.

[0076] The prestressing value of the transverse and longitudinal prestressed steel bars in the reinforced concrete base plate 2 is optimized to match the stiffness of the grid support beam 4, thereby strengthening the coordination between the reinforced concrete base plate 2, the support beam 4 and the pile foundation 1. The grid support beam has an appropriate stiffness (section moment of inertia ≥ 0.8m 4 ), can better cooperate with the prestressed steel bars, and the prestressed steel bars guide the load to be evenly transferred to the pile foundation 1, optimizing the load transfer path. The three work together to optimize the mechanical properties of the entire structural system, and the overall bearing capacity is improved by more than the sum of the effects of each part acting alone, showing a nonlinear improvement characteristic.

[0077] At the same time, the prestressed reinforced concrete base plate 2 of the embodiment of the present application bears most of the tensile stress, and the concrete around the pedestal 3 does not need to be solid. Therefore, the criss-cross lattice support beam 4 design can greatly reduce the amount of concrete used in the pedestal 3, and also reduce the difficulty and workload of temperature control of large-volume concrete.

[0078] In this embodiment, the base 3 is square. In some optional embodiments, the base may be rectangular, circular or track-shaped. In order to facilitate construction calculations, a square is preferred.

[0079] Furthermore, bridge piers 6 or bridge towers are arranged on the cap 3 .

[0080] In this embodiment, the support beam 4 is a lattice beam. The support beam 4 adopts a lattice type, which not only enhances the overall rigidity and bearing capacity of the support beam, but also optimizes the use efficiency of the material and reduces the deadweight of the structure.

[0081] In some embodiments, the support beam 4 can be produced by factory prefabrication. This prefabrication method can significantly improve construction quality and efficiency, reduce on-site construction time and labor costs, while ensuring the accuracy and consistency of component dimensions, thereby improving the safety and reliability of the overall project.

[0082] In this embodiment, the intersection of the first support beam 41 and the second support beam 42 is colinear with the axis of the pile foundation 1, ensuring that the force transmission path is more direct and efficient, thereby improving the stability and durability of the overall structure.

[0083] In this embodiment, the wall thickness of the support beam 4 is not less than the diameter of the pile foundation 1, which enhances the supporting force of the support beam 4 and ensures that the integrity and safety of the structure can be maintained when bearing a large load, thereby extending the service life of the structure.

[0084] A construction method for a cap structure of a long-span bridge suitable for use on a soft soil foundation comprises the following steps:

[0085] According to the bridge structure design, calculate and determine the number of piles and pile diameters that meet the bearing capacity of the pile foundation 1, the size of the cap 3 and the frame design of the support beam 4, and the prestressed steel bar design of the reinforced concrete bottom plate 2;

[0086] Construct pile foundation 1, and reserve steel bars on the top of pile foundation 1;

[0087] A reinforced concrete bottom plate 2 is constructed on the top of the pile foundation 1, and transverse prestressed steel bars 21 and longitudinal prestressed steel bars 22 are installed and tensioned;

[0088] A middle solid cap 3 is cast in situ in the middle of the reinforced concrete base plate 2;

[0089] Construct support beams 4 around the middle solid cap 3;

[0090] Cast-in-place reinforced concrete top slab 5 on top of cap 3 and support beam 4;

[0091] A bridge pier 6 or a bridge tower is constructed on top of the reinforced concrete top plate 5 .

[0092] It should be noted that the reinforced concrete base plate 2 is cast as a whole with the pile foundation 1 through the reserved steel bars at the top of the pile foundation 1, and longitudinal prestressed steel bars 22 and transverse prestressed steel bars 21 are arranged. It is constructed by post-tensioning method, and grouting is performed after tensioning is completed.

[0093] In some optional embodiments, the support beam 4 is constructed of factory-prefabricated reinforced concrete and assembled on site.

[0094] A bridge comprises a bearing platform structure suitable for a long-span bridge under soft soil foundation conditions.

[0095] In summary, the cap structure provided by the present invention optimizes the size and performance of the pile foundation 1 by improving the stress state of the pile foundation 1, effectively reducing the diameter of the pile foundation 1 of the long-span bridge under the same load conditions, thereby reducing the investment in special drilling equipment and the construction time; at the same time, the amount of structural concrete of the cap 3 is reduced and the difficulty of temperature control of large-volume concrete is reduced, thereby improving the construction quality of the cap 3; the assembly construction of the support beam 4 using prefabricated parts can also shorten the construction period and improve the construction quality. Therefore, the present invention has a great role in reducing costs and increasing efficiency in the construction of long-span bridges, especially long-span bridges in areas with soft soil foundations or deep rock formations.

[0096] In the description of the present application, it should be noted that the terms "upper", "lower", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0097] It should be noted that, in this application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0098] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A cap structure suitable for a long-span bridge under soft soil foundation conditions, characterized in that: include: Pile foundations (1), a plurality of the pile foundations (1) are arranged in a plurality of rows and columns at intervals; A reinforced concrete base plate (2) is cast integrally with the pile foundation (1) through reserved steel bars at the top of the pile foundation (1), wherein a plurality of transverse prestressed steel bars (21) and longitudinal prestressed steel bars (22) arranged perpendicular to each other are provided in the reinforced concrete base plate (2); A cap (3) located at the center of the reinforced concrete base plate (2); A support beam (4) having a height equal to that of the support platform (3), comprising a first support beam (41) and a second support beam (42), wherein a plurality of the first support beams (41) and the second support beams (42) form a grid structure; The reinforced concrete top plate (5) is located above the cap (3) and the support beam (4), and is connected as a whole through reserved steel bars at the top of the cap (3) and the support beam (4).

2. The cap structure suitable for long-span bridges under soft soil foundation conditions according to claim 1, characterized in that: The distance between adjacent pile foundations (1) is not less than 4 times the diameter of the pile foundation.

3. The cap structure suitable for long-span bridges under soft soil foundation conditions according to claim 1, characterized in that: The pile foundation (1) has a diameter of 0.8 to 2.0 m.

4. The cap structure suitable for long-span bridges under soft soil foundation conditions according to claim 1, characterized in that: The intersection of the first support beam (41) and the second support beam (42) is collinear with the axis of the pile foundation (1).

5. The cap structure suitable for long-span bridges under soft soil foundation conditions according to claim 1, characterized in that: The wall thickness of the support beam (4) is not less than the diameter of the pile foundation (1).

6. The cap structure suitable for long-span bridges under soft soil foundation conditions according to claim 1, characterized in that: The support beam (4) is a lattice beam.

7. A construction method for a cap structure of a long-span bridge suitable for soft soil foundation conditions according to any one of claims 1 to 6, characterized in that: The steps include: According to the bridge structure design, the number and diameter of pile foundations that meet the bearing capacity of the pile foundation (1), the size of the cap (3) and the frame design of the support beam (4), and the design of the prestressed steel bars of the reinforced concrete bottom plate (2) are calculated and determined; constructing a pile foundation (1), and reserving steel bars on the top of the pile foundation (1); A reinforced concrete base plate (2) is constructed on the top of the pile foundation (1), and transverse prestressed steel bars (21) and longitudinal prestressed steel bars (22) are installed and tensioned; Casting a middle solid cap (3) in the middle of the reinforced concrete base plate (2); Constructing support beams (4) around the middle solid cap (3); Casting a reinforced concrete top plate (5) on top of the cap (3) and the support beam (4); A bridge pier (6) or a bridge tower is constructed on the top of the reinforced concrete top plate (5).

8. The construction method of the pedestal structure of a long-span bridge suitable for soft soil foundation conditions as claimed in claim 7, characterized in that: The prestressed steel bars of the reinforced concrete base plate (2) are constructed using a post-tensioning method, and grouting is performed after the tensioning is completed.

9. The construction method of the pedestal structure of a long-span bridge suitable for soft soil foundation conditions as claimed in claim 7, characterized in that: The support beam (4) is constructed of factory-prefabricated reinforced concrete and is assembled on site.

10. A bridge, characterized in that: It comprises a cap structure suitable for a long-span bridge under soft soil foundation conditions as described in any one of claims 1 to 6.

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