Gradually-changed pile net structure for road and bridge transition section in deep soft soil area and design method of gradually-changed pile net structure

Abstract

The invention provides a gradual change type pile net structure for a road and bridge transition section in a deep and thick soft soil area and a design method thereof. The gradual change type pile net structure comprises a roadbed, and a plurality of reinforcing piles distributed in the longitudinal direction and the transverse direction are arranged below the roadbed; the reinforcing piles form an oblique line type pile section adjacent to the bridge abutment and a horizontal pile section far away from the bridge abutment; the pile lengths of the reinforcing piles of the oblique line type pile sections are linearly reduced in the direction from the bridge abutment to the roadbed, and the pile lengths of the reinforcing piles of the horizontal pile sections are equal. By means of the method, smooth transition of road-bridge connection rigidity is achieved, the problem that the road-bridge transition section in the deep soft soil area is prone to bumping at the bridge head is solved, the material consumption of the reinforcing piles can be remarkably reduced, pile length distribution is flexibly adjusted according to geological conditions and stress requirements, the construction period is shortened, and the construction cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of bridge engineering and road engineering, and in particular relates to a gradual pile network structure for a road-bridge transition section in a deep soft soil area and a design method thereof. Background Art

[0002] Bridge head bumping is a common quality defect in bridge and road projects. Bridge head bumping refers to the deformation, fracture, or even potholes of the road surface or planking in the connection area between the road and the bridge abutment, which causes the wheels of the car to vibrate up and down when passing through this section. The essence of bridge head bumping is due to the differential settlement of the abutment and the backfill behind the abutment. This settlement difference is particularly obvious in soft soil foundation sections, which will cause severe bumps when the vehicle passes. It will not only seriously affect driving comfort, but also accelerate the damage of the road surface structure, increase vehicle maintenance costs, and may induce traffic safety hazards. In severe cases, it may even cause damage to the abutment structure.

[0003] The differential settlement between the abutment and the backfill behind it is due to the fact that in the existing technology, the foundation of the road-bridge transition section is mainly reinforced with piles of equal length. This method will lead to a significant difference in foundation stiffness between the abutment area and the embankment area. The abutment area forms a high-stiffness area due to the support of the pile foundation, while the foundation modulus of the embankment area that has not been reinforced is usually low, and the stiffness mutation amplitude is large. Therefore, the foundation stiffness cannot be continuously transitioned, which ultimately leads to frequent vehicle jumping at the bridge head. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a gradual pile network structure for the transition section of the road bridge in deep soft soil areas, which realizes the smooth transition of the road-bridge connection stiffness and solves the problem of bridge head jumping easily occurring in the transition section of the road bridge in deep soft soil areas.

[0005] The technical solution adopted by the present invention is: a gradual pile network structure for the transition section of a road bridge in a deep soft soil area, including a roadbed, and a plurality of reinforcement piles arranged longitudinally and transversely are provided below the roadbed; the reinforcement piles form an oblique pile section adjacent to the abutment and a horizontal pile section away from the abutment; the length of the reinforcement piles in the oblique pile section decreases linearly from the abutment to the roadbed, and the length of the reinforcement piles in the horizontal pile section is set to be equal.

[0006] Furthermore, the top ends of the reinforcement piles are located at the same horizontal height.

[0007] Furthermore, the spacing between the reinforcement piles is 0.6 times the thickness of the roadbed fill near one end of the abutment.

[0008] Furthermore, the arrangement length of the reinforcement piles from the abutment to the roadbed is defined as L; the arrangement length of the oblique pile segment is 0.75L, and the arrangement length of the horizontal pile segment is 0.25L.

[0009] Furthermore, in,

[0010] H is the final differential settlement between the abutment and the roadbed in the long term;

[0011] ρ min The minimum radius of the vertical curve of the road.

[0012] Furthermore, the pile length of the reinforcement pile is defined as D, and the pile length of the reinforcement pile of the oblique pile section is determined by the following formula:

[0013] in,

[0014] D1 is the length of the reinforcement pile close to the abutment;

[0015] D2 is the length of the horizontal pile section;

[0016] L1 is the arrangement length of the oblique pile segments;

[0017] x is the distance between the reinforcement pile and the abutment.

[0018] A design method for a gradient pile-net structure for a road-bridge transition section in a deep soft soil area comprises the following steps:

[0019] Determine the spacing between fixed piles in the road-bridge transition section;

[0020] Based on the long-term differential settlement final value H between the abutment and the roadbed and the minimum radius of the road vertical curve, determine the arrangement length L of the reinforcement piles from the abutment to the roadbed;

[0021] Based on the arrangement length of the reinforcement piles, determine the arrangement length L1 of the oblique pile segments and the arrangement length L2 of the horizontal pile segments;

[0022] Based on the Terzaghi theory, the pile length D1 of the reinforcement pile of the oblique pile section close to the abutment is determined;

[0023] Determining the length D2 of the reinforced pile of the horizontal pile segment;

[0024] The lengths of the other reinforced piles in the oblique pile section are determined.

[0025] Furthermore, the final differential settlement value H is determined based on the allowable post-construction settlement values ​​of roads of different grades.

[0026] Furthermore, the minimum radius of the vertical curve of the road is determined based on the designed driving speed of the road.

[0027] Furthermore, the lengths of the other reinforcement piles in the oblique pile segment are determined by the following formula:

[0028] in,

[0029] D1 is the length of the reinforcement pile close to the abutment;

[0030] D2 is the length of the horizontal pile section;

[0031] L1 is the arrangement length of the oblique pile segments;

[0032] x is the distance between the reinforcement pile and the abutment along the length direction of the roadbed.

[0033] The advantages and positive effects of the present invention are:

[0034] (1) Through the above technical solution, compared with setting reinforcement piles of the same length in the road-bridge transition section, a smooth transition of the road-bridge connection stiffness is achieved, so that the settlement of the abutment end in the deep soft soil area slowly decreases, and a relatively smooth transition curve is formed between the roadbed end and the maximum settlement area. Finally, the settlement curve of the road-bridge transition section is evenly and smoothly distributed in the longitudinal space, thereby avoiding the differential settlement of the abutment and the backfill behind the abutment, effectively solving the problem of easy bridge head jumping in the road-bridge transition section in the deep soft soil area, which is conducive to the long-term stable operation of the road and ensures the safety of driving and bridge structure.

[0035] (2) By adopting the gradient pile network structure proposed in this application for the transition section of the road bridge in the deep soft soil area, the material consumption of the reinforcement pile can be significantly reduced, and the pile length distribution can be flexibly adjusted according to the geological conditions and force requirements, so that the pile foundation is more evenly stressed and the stress concentration phenomenon is reduced; the gradient pile network structure can adapt to various complex terrains, which is conducive to shortening the construction period and reducing the project cost, and has significant economic benefits and environmental advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of a specific embodiment of the present invention;

[0037] Figure 2 is a coordinate system diagram of a settlement curve of a specific embodiment of the present invention;

[0038] Figure 3 1 is a schematic diagram of a sedimentation curve of a specific embodiment of the present invention;

[0039] Figure 4 This is a model diagram of a road bridge transition section before use according to a specific embodiment of the present invention;

[0040] Figure 5 yes Figure 4 The road-bridge transition section in the paper uses the consolidation settlement deformation model after 30 years.

[0041] In the picture:

[0042] 1. Abutment; 2. Bridge; 3. Reinforcement piles; 4. Roadbed fill. DETAILED DESCRIPTION

[0043] The embodiments of the present invention are described below with reference to the accompanying drawings.

[0044] The present invention proposes a gradient pile-net structure and design method for bridge-road transition sections in deep soft soil areas, which are used in the fields of bridge engineering and road engineering. Due to the large vertical stiffness difference in bridge-road transition sections, the differential settlement between the abutment and roadbed ends often exceeds the required limit under long-term action, resulting in a serious "bridge head bump" hazard. In the prior art, the main treatment for bridge head bump, a typical road hazard in deep soft soil areas, is pile-net composite foundation reinforcement. In the bridge-roadbed transition section, reinforced piles of equal length are used. This equal-length pile design results in a significant difference in foundation stiffness between the abutment and embankment areas. The abutment area forms a high-stiffness region due to the pile foundation support, while the unreinforced embankment area typically has a lower foundation modulus and a large stiffness mutation, leading to a high incidence of bridge head bump. Furthermore, the completely uniform pile lengths result in a large engineering effort and high cost. By proposing a gradient pile network structure, this application can make the settlement curve of the road-bridge transition section in deep soft soil areas evenly and smoothly distributed in the longitudinal space, presenting a slow decline at the abutment end and forming a relatively smooth transition curve from the roadbed end to the maximum settlement area, thereby avoiding differential settlement of the abutment and the backfill behind the abutment, and effectively solving the problem of bridge head jumping easily occurring in the road-bridge transition section in deep soft soil areas, which is conducive to the long-term stable operation of the road and ensures driving safety and the safety of the bridge structure.

[0045] like Figure 1 As shown, the first aspect of the present application proposes a gradual pile network structure for a road-bridge transition section in a deep soft soil area, including a roadbed, a bridge abutment 1 on one side of the roadbed, a bridge 2 built above the abutment 1, and an abutment 1 pile foundation at the bottom of the abutment 1; a plurality of reinforcement piles 3 arranged longitudinally and transversely are provided below the roadbed fill 4; the reinforcement piles 3 form an oblique pile section adjacent to the abutment 1 and a horizontal pile section away from the abutment 1; the length of the reinforcement piles 3 of the oblique pile section decreases linearly from the abutment 1 to the roadbed, and the length of the reinforcement piles 3 of the horizontal pile section is set to be the same.

[0046] In an embodiment of the present application, the abutment 1 and the roadbed both have set widths, and the reinforcement piles 3 are arranged transversely within a set range in the width direction, and longitudinally within a set range in the length direction of the abutment 1 and the roadbed; the reinforcement piles 3 have set lengths and spacings, and the lengths of the reinforcement piles 3 located at the same cross section of the roadbed are the same; along the length direction of the abutment 1 and the roadbed, the lengths of the reinforcement piles 3 on the same longitudinal section are different, wherein the pile lengths of the reinforcement piles 3 within a set length range near the abutment 1 end are linearly arranged and gradually decrease from the abutment 1 toward the roadbed, forming a diagonal pile segment; and the reinforcement piles 3 away from the abutment end have the same pile length within a set length range, forming a horizontal pile segment; the diagonal pile segment and the horizontal pile segment form a continuous reinforcement pile 3 arrangement area.

[0047] Through the above technical solution, compared with setting reinforcement piles 3 of the same length in the road-bridge transition section, a smooth transition of the road-bridge connection stiffness is achieved, so that the settlement of the abutment end in the deep soft soil area slowly decreases, and a relatively smooth transition curve is formed between the roadbed end and the maximum settlement area, and finally the settlement curve of the road-bridge transition section is evenly and smoothly distributed in the longitudinal space, thereby avoiding the differential settlement of the abutment 1 and the backfill behind the abutment, and effectively solving the problem of bridge head jumping easily occurring in the road-bridge transition section in the deep soft soil area.

[0048] In this application, the geological conditions in the area where the road-bridge transition section is located are deep soft soil, which has the characteristics of high water content, low strength, slow consolidation and easy deformation. Therefore, reinforcement piles 3 are required to treat the foundation; the reinforcement piles 3 can be in the form of CFG piles, PHC piles or mixing piles, rotary jet piles, etc., and there is no restriction here.

[0049] Furthermore, in the embodiments of the present application, Figure 1 As shown, the top ends of the reinforcement piles 3 are at the same horizontal height; the top ends of the reinforcement piles 3 of the oblique pile section and the reinforcement piles 3 of the horizontal pile section are both at the same horizontal height. Since the pile length of the reinforcement piles 3 of the oblique pile section changes linearly, the line connecting the bottom ends of the reinforcement piles 3 of the oblique pile section on the longitudinal section of the roadbed is an oblique line inclined to the horizontal plane, while the line connecting the bottom ends of the reinforcement piles 3 of the horizontal pile section on the longitudinal section of the roadbed is a horizontal line; the end of the oblique pile section close to the abutment 1 is defined as its starting end, and the end of the oblique pile section close to the horizontal pile section is defined as its end end. Preferably, the difference between the pile length of the last row of reinforcement piles 3 at the end of the oblique pile section and the pile length of the reinforcement piles 3 of the horizontal pile section is consistent with the trend of linear change of the pile length of the reinforcement piles 3 of the oblique pile section, so that the line connecting the bottom ends of the reinforcement piles 3 on the longitudinal section of the roadbed is a connected oblique line and horizontal line, and there will be no misalignment in the height direction.

[0050] Furthermore, in the embodiment of the present application, the spacing between the reinforcement piles 3 is 0.6 times the thickness of the roadbed fill 4 near the abutment 1. In the application, the reinforcement piles 3 are arranged longitudinally at a set spacing to form a set length and transversely to form a set width. The number of reinforcement piles 3 and the length of the reinforcement piles 3 at different positions need to be calculated based on the spacing of the reinforcement piles 3. Based on the control analysis of the destructive arch effect, when the pile spacing is 0.6 times the thickness of the roadbed fill 4 near the abutment 1, it can not only avoid the destructive arch from invading the roadbed layer, but also balance the foundation bearing capacity and settlement control requirements.

[0051] Furthermore, in a specific embodiment of the present application, the thickness of the deep soft soil foundation is greater than 20m, and the length of the reinforcement piles 3 arranged from the abutment 1 toward the roadbed is defined as L; the length of the inclined pile segments is 0.75L, and the length of the horizontal pile segments is 0.25L. The inventors of the present application have discovered that when the above technical solution is adopted, the roadbed settlement curve generated by numerical simulation is the smoothest and most uniform, meeting the requirement for a gentle transition in stiffness in the road-bridge transition section.

[0052] In some other embodiments of the present application, according to different geological conditions and force requirements, the arrangement lengths of the diagonal pile segments and the arrangement lengths of the horizontal pile segments can also be other proportions, which can be determined through finite element numerical simulation, as long as a smooth transition of the stiffness gradient of the settlement curve can be achieved.

[0053] Furthermore, in the embodiment of the present application, the present application proposes a preferred value of the arrangement length:

[0054] in,

[0055] H is the final differential settlement between abutment 1 and the roadbed in the long term;

[0056] ρ min The minimum radius of the vertical curve of the road.

[0057] In the above embodiment, H is the allowable post-construction settlement determined according to the design parameters of the bridge 2 and the road. Under normal circumstances, the allowable post-construction settlement H is ≤ 0.30m for general sections of expressways and first-class highways; the allowable post-construction settlement H is ≤ 0.50m for general sections of second-class highways.

[0058] In the above embodiment, p min It is determined according to the design driving speed of the road. Generally, ρ min Determine according to the parameters in Table 1.

[0059] Table 1:

[0060]

[0061] The above-mentioned optimal arrangement length values ​​are achieved by simulating the settlement data using finite element methods, taking 0.75L and 0.25L for horizontal and diagonal pile segments, respectively, and a service life of 30 years as input values ​​to form settlement curves, and performing approximate fitting analysis on the curves.

[0062] Specifically, the derivation process is described below.

[0063] Assuming that the arrangement length of the reinforcement piles 3 from the abutment 1 to the roadbed is L, the inventors of this application have found that the range of nearly 0.25L after the length L is still within the range of the settlement curve; Figure 2 As shown in the figure, a right-handed rectangular coordinate system is established with the starting point O of the settlement curve as the origin. The origin is the starting point of the roadbed adjacent to one end of abutment 1, and the direction from abutment 1 to the roadbed is the X-axis, representing the distance between the roadbed and abutment 1 along the length of the roadbed; the Y-axis is the settlement value in the numerical simulation results; when the horizontal pile segment and the oblique pile segment are used as input values ​​of 0.75L and 0.25L respectively to form the settlement curve, the settlement curve can be regarded as an S curve, and a centrally symmetric quadratic curve is used for approximate fitting.

[0064] Refer to Figure 2 , set the end point A of the settlement curve as the maximum settlement value, and the corresponding settlement value is the final differential settlement value H between abutment 1 and the roadbed in the future. The coordinates of point A can be obtained as (1.25L, H); the coordinates of the midpoint S' on the settlement curve are By using the coordinates of the three points O, S' and A, and applying the mathematical function expression of the quadratic curve, the equation of the curve S can be obtained as follows:

[0065]

[0066] Differentiating the arc gives the curvature of the curve:

[0067]

[0068] Radius of curvature:

[0069]

[0070] Solve for extreme values:

[0071]

[0072] because Therefore, ρ ’ =0 is x = 0, and the vertex of the parabola is the position of maximum curvature. Therefore, when x = 0:

[0073]

[0074] The length of the reinforcement pile 3 from the abutment 1 to the roadbed can be obtained roll out.

[0075] In an embodiment of the present application, the arrangement length of the reinforcement piles 3 from the abutment 1 to the roadbed determined by the above method is the optimal value considering economy and satisfying uniform and smooth settlement, and is also the minimum value; in some other embodiments of the present application, the arrangement length of the reinforcement piles 3 from the abutment 1 to the roadbed may also be greater than the above optimal value, which can make the settlement of the road-bridge transition section smoother and the settlement value smaller.

[0076] Based on the above embodiment, the pile length of the reinforcement pile 3 is defined as D. The pile length of the reinforcement pile 3 of the oblique pile section is determined by the following formula:

[0077] in,

[0078] D1 is the length of the reinforcement pile 3 close to the abutment 1;

[0079] D2 is the pile length of the horizontal pile section;

[0080] L1 is the arrangement length of the oblique pile segment;

[0081] x is the distance between the reinforcement pile 3 and the abutment 1 along the length of the roadbed.

[0082] In the above embodiment, D1 is the length of a row of reinforcement piles 3 at the starting end of the oblique pile segment. This length is obtained by conventional calculation based on the Terzaghi theory. Its value is equal to the pile length when reinforcement piles 3 of equal length are used for reinforcement in the prior art. The determination process is prior art and will not be described in detail here.

[0083] In the above embodiment, D2 is the pile length of the horizontal pile section, which is obtained through force calculation and meets the rock-embedded depth requirement. Preferably, in deep soft soil areas, D2 is not less than 6m.

[0084] In a specific embodiment, Figure 3 As shown, through finite element numerical simulation of the settlement and deformation of the gradual pile network structure proposed in this application for the road-bridge transition section in deep soft soil areas after different service times, it can be seen that the settlement curve of the road-bridge transition section always maintains a uniform and smooth distribution in the longitudinal space.

[0085] The second aspect of the present application proposes a design method for a gradual pile-net structure for a road-bridge transition section in a deep soft soil area, comprising the following steps:

[0086] S1. Determine the spacing between fixed piles in the road-bridge transition section;

[0087] Specifically, in the embodiment of the present application, according to the soil quality of the deep soft soil area, PHC piles are used as the reinforcement piles 3, and the spacing between the reinforcement piles 3 is 0.6 times the thickness of the roadbed fill 4 close to the abutment 1.

[0088] S2. Determine the arrangement length L of the reinforcement piles 3 from the abutment 1 to the roadbed based on the long-term differential settlement final value H between the abutment 1 and the roadbed and the minimum radius of the road vertical curve;

[0089] Specifically, in this implementation, the final differential settlement value H between the abutment 1 and the roadbed in the long term is determined based on the allowable post-construction settlement values ​​of roads of different grades; the minimum radius of the road vertical curve is determined based on the road's designed driving speed; and the arrangement length L of the reinforcement piles 3 from the abutment 1 toward the roadbed is determined by the following formula:

[0090]

[0091] S3, based on the arrangement length of the reinforcement pile 3, determine the arrangement length L1 of the oblique pile segment and the arrangement length L2 of the horizontal pile segment;

[0092] In the embodiment of the present application, the arrangement length L1 of the oblique pile segments is 0.75, and the arrangement length L2 of the horizontal pile segments is 0.25L.

[0093] S4. Based on the Terzaghi theory, determine the pile length D1 of the reinforcement pile 3 of the oblique pile section close to the abutment 1;

[0094] S5. Determine the pile length D2 of the horizontal pile segment;

[0095] S6. Determine the pile length D of the other reinforcement piles 3 in the oblique pile segment.

[0096] Specifically, the length of the other reinforcement piles 3 in the oblique pile section is Where x is the distance between the reinforcement pile 3 and the abutment 1 along the length of the roadbed.

[0097] Through the above design method, the spacing of the reinforcement piles 3, the arrangement length L1 of the oblique pile section, the pile length of the reinforcement piles 3 of the oblique pile section, the arrangement length L2 of the horizontal pile section, the pile length of the reinforcement piles 3 of the horizontal pile section and the spacing of the reinforcement piles 3 can be obtained, so as to realize the design of the gradual pile network structure of the road-bridge transition section in the deep soft soil area; the reinforcement piles 3 are designed by the above method, which realizes the smooth transition of the road-bridge connection stiffness, so that the settlement of the abutment 1 end in the deep soft soil area shows a slow decrease, and a relatively smooth transition curve is formed between the roadbed end and the maximum settlement area, and finally the settlement curve of the road-bridge transition section is evenly and smoothly distributed in the longitudinal space, thereby avoiding the differential settlement of the abutment 1 and the backfill behind the abutment, and effectively solving the problem of bridge head jumping easily occurring in the road-bridge transition section in the deep soft soil area.

[0098] In some other embodiments of the present application, a trestle is provided in the road-bridge transition section for further controlling settlement, so as to form a smooth slope without causing a significant impact on the curvature; at the end of the horizontal pile section, a cement-soil mixing pile transition can be used, or a replacement transition method can be used to continue reinforcing the remaining areas prone to settlement, so as to achieve a smoother vertical line shape of the road on the roadbed side; the reinforcement piles 3 on both sides of the embankment adopt a thickened design or a denser design, and the geogrid appropriately increases the strength or number of layers to increase the stability of the embankment.

[0099] In a specific embodiment of the present application, the above method is used to set the reinforcement piles 3 of the road bridge transition section in the deep soft soil area, and the consolidation settlement deformation diagram of the road bridge transition section is established through finite element numerical simulation analysis. Figure 4 The figure shows the model diagram of the road-bridge transition section before use. Figure 5 The consolidation settlement deformation model of the road-bridge transition section after 30 years of use is shown. It can be seen that by adopting the gradient pile-net structure and design method proposed in this application for the road-bridge transition section in deep soft soil areas, the resulting settlement curve has a uniform and smooth distribution in the longitudinal space, with a slowly descending characteristic at the abutment 1 end. This effectively ensures a smooth transition in the stiffness gradient at the road-bridge junction, solves the problem of bridgehead jumps occurring easily in the road-bridge transition section in deep soft soil areas, and is conducive to achieving long-term stable operation of the road, ensuring driving safety and the structural safety of Bridge 2.

[0100] By adopting the gradient pile-net structure proposed in this application for the transition section of a road bridge in a deep soft soil area, the material consumption of the reinforcement pile 3 can be significantly reduced, and the pile length distribution can be flexibly adjusted according to the geological conditions and force requirements, so that the pile foundation is more evenly stressed and the stress concentration phenomenon is reduced; the gradient pile-net structure can adapt to various complex terrains, which is conducive to shortening the construction period and reducing the project cost, and has significant economic benefits and environmental advantages.

[0101] The embodiments of the present invention are described in detail above, but the contents described are only preferred embodiments of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A gradient pile-net structure for a road-bridge transition section in a deep soft soil area, characterized by: It includes a roadbed, under which a plurality of reinforcement piles arranged longitudinally and transversely are provided; the reinforcement piles form an oblique pile section adjacent to the abutment and a horizontal pile section away from the abutment; the length of the reinforcement piles in the oblique pile section decreases linearly from the abutment to the roadbed, and the length of the reinforcement piles in the horizontal pile section is set to be equal.

2. The gradient pile-net structure for a road-bridge transition section in a deep soft soil area according to claim 1 is characterized in that: The top ends of the reinforcement piles are located at the same horizontal height.

3. The gradient pile-net structure for a road-bridge transition section in a deep soft soil area according to claim 2 is characterized in that: The spacing between the reinforcement piles is 0.6 times the thickness of the roadbed fill near one end of the abutment.

4. The gradient pile-net structure for a road-bridge transition section in a deep soft soil area according to claim 3 is characterized by: The arrangement length of the reinforcement piles from the abutment to the roadbed is defined as L; the arrangement length of the oblique pile segment is 0.75L, and the arrangement length of the horizontal pile segment is 0.25L.

5. The gradient pile-net structure for a road-bridge transition section in a deep soft soil area according to claim 4 is characterized in that: in, H is the final differential settlement between the abutment and the roadbed in the long term; ρ min The minimum radius of the vertical curve of the road.

6. The gradient pile-net structure for a road-bridge transition section in a deep soft soil area according to claim 5 is characterized in that: The length of the reinforcement pile is defined as D. The length of the reinforcement pile of the oblique pile section is determined by the following formula: in, D1 is the length of the reinforcement pile close to the abutment; D2 is the length of the horizontal pile section; L1 is the arrangement length of the oblique pile segments; x is the distance between the reinforcement pile and the abutment along the length direction of the roadbed.

7. A design method for a gradient pile-net structure for a road-bridge transition section in a deep soft soil area, characterized in that: The following steps are involved: Determine the spacing between fixed piles in the road-bridge transition section; Based on the long-term differential settlement final value H between the abutment and the roadbed and the minimum radius of the road vertical curve, determine the arrangement length L of the reinforcement piles from the abutment to the roadbed; Based on the arrangement length of the reinforcement piles, determine the arrangement length L1 of the oblique pile segments and the arrangement length L2 of the horizontal pile segments; Based on the Terzaghi theory, the pile length D1 of the reinforcement pile of the oblique pile section close to the abutment is determined; Determining the length D2 of the reinforced pile of the horizontal pile segment; The lengths of the other reinforced piles in the oblique pile section are determined.

8. The gradient pile-net structure for a road-bridge transition section in a deep soft soil area according to claim 7 is characterized in that: The final differential settlement value H is determined based on the allowable post-construction settlement values ​​of roads of different grades.

9. The gradient pile-net structure for a road-bridge transition section in a deep soft soil area according to claim 8 is characterized in that: The minimum radius of the vertical curve of the road is determined based on the designed driving speed of the road.

10. The gradient pile-net structure for a road-bridge transition section in a deep soft soil area according to claim 7, characterized in that: The lengths of the other reinforcement piles in the oblique pile section are determined by the following formula: in, D1 is the length of the reinforcement pile close to the abutment; D2 is the length of the horizontal pile section; L1 is the arrangement length of the oblique pile segments; x is the distance between the reinforcement pile and the abutment along the length direction of the roadbed.

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