Straight and inclined pile combined railroad bridge pile group structure and construction method thereof

Abstract

According to the straight and inclined pile combined railroad bridge pile group structure and the construction method thereof, three rows of piles are transversely arranged on a line, two rows of inclined piles are arranged on the two sides of the line respectively, the vertical inclination angle of the inclined piles ranges from 10 degrees to 30 degrees, the inclined piles lean against the direction of a bearing platform to improve the overall stability of the pile group, two rows of vertical piles are arranged in the middle, and the pile group structure is provided with two rows of piles in the longitudinal direction of the line. Three piles are arranged in each row, two inclined piles and one straight pile are arranged, and six piles, two vertical piles and four inclined piles are arranged in total; the pile top and the bearing platform are connected in a semi-rigid connection mode that the bent anchoring steel bars and the rubber layer are arranged around the pile top, and the deformation capacity and the ductility capacity of the joint are improved. Compared with a vertical pile group pile foundation, the straight-inclined combined pile group foundation can reduce shearing force and bending moment caused by the horizontal load effect, the horizontal bearing capacity is fully played, the horizontal displacement is reduced to a certain extent, meanwhile, a load transmission path can be optimized through the angle of the inclined piles, and therefore the shock resistance, integrity and stability of the whole structure are improved.

Description

Technical Field

[0001] The present invention relates to a structure, in particular to a railway bridge pile group structure composed of straight and oblique piles and a construction method thereof, belonging to the technical field of bridge engineering pile foundations. Background Art

[0002] A bridge pile group foundation consists of multiple piles connected to the pedestal at the top, which jointly bear the dynamic and static loads of the superstructure and transfer the loads to the soil layer with good bearing capacity deeper underground to meet the requirements of bearing capacity and settlement. Bridge pile group foundations mostly use a full vertical pile arrangement, but their horizontal shear capacity is limited. Under earthquake or soft soil settlement conditions, the pile body is prone to cracking or even overall instability due to concentrated bending moments. A single inclined pile arrangement makes it difficult to coordinate the transfer efficiency of vertical and horizontal loads, and the insufficient ductility of the connection area between the pile top and the pedestal can easily lead to brittle failure. The overall lateral stiffness of a single pile group foundation of a railway bridge is greater than the longitudinal stiffness. Under the action of an earthquake, the longitudinal stiffness of the pile group foundation needs to be strengthened. Therefore, inclined piles are set in the longitudinal direction of the pile group foundation to improve the overall longitudinal stiffness. Longitudinal inclined piles are set at the four corner points of the commonly used bridge pile foundation.

[0003] The design of pile-group foundations for bridges in high-intensity seismic zones typically involves strengthening the abutment with spiral stirrups, seismic strengthening of the pile body, segmented variable-section design, optimized shear reinforcement, the addition of steel casing or carbon fiber reinforcement layers, foundation reinforcement, and seismic isolation. Overall, these measures have achieved generally good results. However, some projects have also experienced failures such as foundation failure and reduced bearing capacity (soil liquefaction and slip, fault movement, and ground rupture), pile structural damage (shear and flexural failure of the pile body, failure of the connection between the pile top and the abutment), and damage to ancillary structures (coordinated failure of the abutment and pile foundation, and linked failure of the bearing and pile foundation). These failures are particularly severe in unique locations, such as fault zones and liquefied soils. Therefore, it is imperative that comprehensive measures, such as coordinated lateral displacement of straight and inclined piles and ductility optimization of semi-rigid joints, be combined with relevant code requirements to form a systematic seismic-resistance system for bridge pile-group foundations in high-intensity zones, significantly improving the seismic resilience of bridges in complex sites.

[0004] A single pile foundation supported by inclined piles and its construction method (202111024991.3) consists of one large-diameter single pile and six inclined piles, evenly spaced at 60° intervals along the cap. The cap is a cast-in-place reinforced concrete structure used to connect and consolidate the large-diameter single pile and the inclined piles. This single pile foundation is primarily used to strengthen the strength and rigidity of offshore wind turbine single pile foundations but is not suitable for seismic-resistant bridge pile groups. An inclined pile (202310548144.X) used for foundation pit support comprises an upper end, a connecting portion, and a lower end. Both ends of the connecting portion are slidably connected to a connecting ring. The upper and lower ends are each provided with a connecting assembly for detachable connection to the corresponding connecting ring. The connecting portion is equipped with a drive assembly for driving the connecting ring. The inclined pile is tested by applying pressure with a jack, eliminating the need for manual cutting. The simple detachable connection effectively improves work efficiency. However, this feature is not suitable for railway bridge pile foundations constructed in one go. Summary of the Invention

[0005] In order to solve the defects in the prior art, the present invention discloses a railway bridge pile group structure composed of straight and oblique piles, and its technical solution is as follows: A railway bridge pile group structure with a combination of straight and oblique piles is characterized by comprising: three rows of pile foundations arranged transversely of the line, wherein one row on each side comprises two oblique piles (1), the vertical inclination angle of the oblique piles (1) being 10° to 30° and all inclined toward the bearing platform (3) to improve the overall stability of the pile group, and the middle row comprises two straight piles (2); and two rows of pile foundations arranged longitudinally of the line, each row comprising three piles, arranged in an oblique, straight and oblique manner, for a total of six pile foundations, including four oblique piles (1) and two straight piles (2).

[0006] The connection method between the pile top and the pedestal (3) is a semi-rigid connection (4), including a rubber layer (5) and bent anchor steel bars (6) arranged around the pile top, wherein the bent anchor steel bars have a bending angle of 30° to 45° and are connected to the main bars of the pedestal (3) through welding or mechanical connection to form an integral force system; the compression rate of the rubber layer (5) is 15% to 20%, and is used to absorb horizontal displacement and reduce stress concentration.

[0007] Preferably, the inclined piles (1) and vertical piles (2) are circular piles made of cast-in-situ reinforced concrete or prefabricated pipe piles, and the pile diameter ranges from 0.8m to 1.5m.

[0008] Preferably, the material of the rubber layer (5) is chloroprene rubber or natural rubber, the elastic modulus thereof is 3MPa-8MPa, and the thickness is 20mm-50mm.

[0009] Preferably, the bending angle of the bent anchor steel bar is optimized based on the bending moment distribution at the pile top and the pull-out resistance requirement, and the length of the bent section is not less than 10 times the diameter of the steel bar.

[0010] Preferably, the inclination angle of the inclined pile (1) is dynamically optimized through a parameterized model, and the model input parameters include the site ground motion peak acceleration, the soil layer shear wave velocity and the pile foundation material strength.

[0011] The present invention also discloses a construction method for a railway bridge pile group structure based on the above-mentioned straight and oblique pile combination, which is characterized by comprising the following steps: Step 1: Determine the inclination angle range and pile foundation arrangement parameters of the inclined pile (1) according to the site geological conditions; Step 2: Use a rotary drilling rig or static pressure method to construct the inclined pile (1) and the vertical pile (2), and ensure that the pile top elevation is consistent; Step 3: Pre-embed the bent anchor steel bars at the pile top, with the bending angle controlled at 30°~45°, and weld or mechanically connect them to the main reinforcement of the pile cap (3); Step 4: Set a rubber layer (5) around the pile top and adjust the compression rate to 15% to 20% to form a semi-rigid connection node; Step 5: Pour the concrete of the foundation (3) and carry out post-tensioning prestressing reinforcement.

[0012] Preferably, in step 1, the inclination angle of the inclined pile (1) is dynamically adjusted by finite element simulation combined with on-site static load test to ensure that the horizontal bearing capacity of the pile group meets the design requirements. Beneficial effects

[0013] The proposed straight-and-slanted railway bridge pile group structure exhibits complementary dynamic response. The characteristic frequency of straight piles remains stable (0-2 Hz) during vibration, while the characteristic frequency of the inclined piles decreases with increasing vibration intensity, creating a dynamic complementarity with the straight piles. This complementarity disperses the concentrated bending moment of seismic waves of varying frequencies on the pile shaft, resulting in a more uniform overall bending moment distribution. The inclined piles, through their lateral support provided by their inclination angle, suppress the horizontal displacement of the straight piles. When the inclination angle is 10°-20°, the maximum displacement of the straight piles is significantly reduced. The inclined piles effectively transfer horizontal loads to the deep, stable soil, reducing the peak lateral bending moment of the straight piles. Compared to rigid connections, semi-rigid connections reduce the overall stiffness between the pile top and the abutment through localized flexibility (such as elastic pads or partially constrained nodes), thereby minimizing the likelihood of resonance during seismic action. This stiffness adjustment suppresses the transfer of high-frequency vibration energy to the pile shaft, thereby reducing the peak dynamic response. Tests have shown that the use of semi-rigid components such as rubber pads can increase the equivalent damping ratio of pile foundation systems to 1.2 to 1.5 times that of rigid connections, significantly reducing seismic wave energy accumulation. These synergistic effects reduce the maximum bending moment of the piles and flatten their distribution, thereby reducing reinforcement requirements and concrete usage, resulting in cost savings while maintaining equivalent seismic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a side view of pile group foundation; Figure 2 This is a front view of pile group foundation; Figure 3 This is a top view of pile group foundation; Figure 4 Schematic diagram of the semi-rigid connection between the pile top and the cap.

[0015] Among them: 1 inclined pile, 2 vertical pile, 3 bearing platform, 4 semi-rigid connection method, 5 rubber layer, 6 bent anchor steel bar. DETAILED DESCRIPTION Example 1

[0016] A railway bridge pile group structure with a combination of straight and oblique piles. The pile group foundation consists of oblique piles, vertical piles, a cap, and a semi-rigid connection between the pile tops and the cap. The oblique and vertical piles are circular piles and can be cast-in-place reinforced concrete piles or prefabricated pipe piles. The pile group structure is arranged in three rows across the line, with two oblique piles on each side and two vertical piles in the middle. The pile group structure has two rows of three oblique, vertical, and oblique piles in the longitudinal direction of the line, for a total of six piles: four oblique piles and two vertical piles. The semi-rigid connection method uses bent anchor steel bars and a rubber layer around the pile tops to improve the deformation and ductility of the nodes.

[0017] The vertical inclination angle of the inclined piles ranges from 10° to 30°, and they are all tilted toward the abutment to improve the overall stability of the pile group. The bending angle of the anchor reinforcement in the connection method should be controlled at 30° to 45°. The bent reinforcement and the main reinforcement of the abutment are welded or mechanically connected to form an integrated force-bearing system, enhancing the shear and pullout resistance of the connection area. A rubber ring is placed around the pile top to reduce the top constraint. The rubber ring has a compression rate of 15%–20%. The rubber ring absorbs horizontal displacement of the pile top caused by earthquakes or loads through elastic deformation, reducing stress concentration between the pile body and the abutment and avoiding brittle failure caused by rigid connection.

[0018] The proposed straight-and-slanted railway bridge pile group foundation optimizes the distribution of bending moments at the pile heads through the synergistic effect of straight and inclined piles. The straight piles bear the primary vertical load, while the inclined piles share lateral shear and torque, reducing the risk of shear failure and the overall dynamic response amplitude of the pile foundation. The ability of the inclined piles to share lateral loads allows for a reduced reinforcement ratio in the straight piles, lowering concrete usage and achieving cost savings while maintaining equivalent seismic performance. Example 2

[0019] Based on the structure in Example 1, the present invention discloses a construction method for a railway bridge pile group structure based on the above-mentioned straight and oblique pile combination, comprising the following steps: Step 1: Determine the inclination angle range and pile foundation arrangement parameters of the inclined pile (1) according to the site geological conditions; Step 2: Use a rotary drilling rig or static pressure method to construct the inclined pile (1) and the vertical pile (2), and ensure that the pile top elevation is consistent; Step 3: Pre-embed the bent anchor steel bars at the pile top, with the bending angle controlled at 30°~45°, and weld or mechanically connect them to the main reinforcement of the pile cap (3); Step 4: Set a rubber layer (5) around the pile top and adjust the compression rate to 15% to 20% to form a semi-rigid connection node; Step 5: Pour the concrete of the foundation (3) and carry out post-tensioning prestressing reinforcement.

[0020] Determine the inclination angle range and pile foundation arrangement parameters of the inclined pile (1) according to the geological conditions of the site; 1. Basic formula for inclination angle based on seismic load decomposition (1) Decomposition formula of horizontal seismic force and vertical force The inclined piles need to resist the vertical gravity load at the same time ( G ) and horizontal earthquake force ( F eq ),inclination( α ) and the load component are: Horizontal component of force caused by earthquake force:

[0021] Vertical component of force caused by earthquake force:

[0022] Tilt angle constraints: To prevent the pile foundation from being subjected to excessive horizontal bending moment, the following conditions must be met: F h ≤ k h ⋅Δ max ·in k h is the horizontal stiffness of the pile foundation, Δ max To allow horizontal displacement (usually ≤10mm).

[0023] Typical values: When the earthquake intensity is 8 or higher, the inclination angle is usually 10° to 25° to balance the horizontal and vertical loads.

[0024] (2) Penzien earthquake response spectrum method modified formula Considering the influence of earthquake motion characteristics on the bearing capacity of inclined piles, the inclination angle and the horizontal earthquake influence coefficient ( α max ) is:

[0025] in Q seismicis the designed bearing capacity of the pile foundation under earthquake action, and g is the acceleration of gravity.

[0026] Tilt angle limit: When α When the angle is >25°, the increase in horizontal force caused by earthquake exceeds 15%, and the pile foundation reinforcement needs to be strengthened.

[0027] 2. Inclination angle optimization formula based on pile foundation dynamic stiffness (1) Inclination correction of the dynamic stiffness matrix of inclined piles Considering the ground motion frequency ( ω ) on the stiffness of inclined piles. The typical formula is: Horizontal dynamic stiffness: Vertical dynamic stiffness: in k h0 / k v0 is the static stiffness, ω n is the natural frequency of the pile foundation.

[0028] Inclination angle optimization: To make the pile foundation frequency avoid the dominant period of earthquake motion, the inclination angle should meet the following requirements:

[0029] in ω g It is the most prominent frequency of earthquake motion.

[0030] (2) Inclination angle-spacing formula under pile group effect Under earthquake action, the mutual influence of pile groups is intensified, and the inclination angle and pile spacing ( s ) is:

[0031] in γ is the seismic influence coefficient (1.0 for the 7-degree zone, 1.2 for the 8-degree zone, and 1.5 for the 9-degree zone), and D is the pile diameter.

[0032] Restriction conditions: When the inclination angle is > 20°, the pile group spacing needs to be increased by 20%~30% compared with the static load condition.

[0033] 3. Seismic standards and typical inclination angle ranges Application Scenario Regulatory basis Recommended inclination range Theoretical formula support Bridge pile foundation in high-intensity areas Code for Seismic Design of Highway Engineering (JTG / T 2231-01-2020) 15°∼25° Seismic force decomposition formula, Newmark displacement method Liquefied foundation bridge Technical Specifications for Building Pile Foundations JGJ 94-2008 10°∼20° Seed dynamic balance method, stiffness correction formula Slope bridge support piles Code for Seismic Design of Railway Engineering GB 50111-2006 20°∼30° Slider displacement method, pile group effect formula inclined pile foundation of sea-crossing bridge Code for Seismic Design of Water Transport Engineering (JTS 146-2012) 25°∼35° Wave-seismic coupled load decomposition and dynamic stiffness formula Use a rotary drilling rig or static pressure method to construct the inclined piles (1) and the vertical piles (2), and ensure that the pile top elevations are consistent; Embed the bent anchor steel bars at the top of the pile, with the bending angle controlled at 30°~45°, and weld or mechanically connect them to the main reinforcement of the pile cap (3); A rubber layer (5) is provided around the pile top, and the compression rate is adjusted to 15% to 20% to form a semi-rigid connection node; concrete is poured on the cap (3), and post-tensioning prestressing reinforcement is performed.

[0034] The inclination angle of the inclined pile (1) is dynamically adjusted through finite element simulation combined with on-site static load tests to ensure that the horizontal bearing capacity of the pile group meets the design requirements.

[0035] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions merely illustrate the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A railway bridge pile group structure with a combination of straight and oblique piles, characterized in that: include: Three rows of pile foundations are arranged in the transverse direction of the line, wherein each row on both sides comprises two inclined piles (1), wherein the vertical inclination angle of the inclined piles (1) is 10° to 30° and the inclined piles (1) are all inclined toward the pedestal (3) to improve the overall stability of the pile group; the middle row comprises two vertical piles (2); two rows of pile foundations are arranged in the longitudinal direction of the line, each row comprises three piles, and the arrangement is inclined, vertical and inclined, for a total of six pile foundations, including four inclined piles (1) and two vertical piles (2); the connection between the pile top and the pedestal (3) is a semi-rigid connection (4), comprising a rubber layer (5) and a bent anchor steel bar (6) arranged around the pile top, wherein the bent anchor steel bar has a bending angle of 30° to 45° and is connected to the main reinforcement of the pedestal (3) by welding or mechanical connection to form an integral force system; the compression rate of the rubber layer (5) is 15% to 20%, and is used to absorb horizontal displacement and reduce stress concentration.

2. The railway bridge pile group structure of straight and oblique pile combination according to claim 1 is characterized by: The inclined piles (1) and vertical piles (2) are circular piles made of cast-in-situ reinforced concrete or prefabricated pipe piles, and the pile diameter ranges from 0.8m to 1.5m.

3. The railway bridge pile group structure with straight and oblique piles according to claim 1 is characterized by: The material of the rubber layer (5) is chloroprene rubber or natural rubber, and its elastic modulus is 3MPa~8MPa, and its thickness is 20mm~50mm.

4. The railway bridge pile group structure of straight and oblique pile combination according to claim 1 is characterized by: The bending angle of the bent anchor steel bar (6) is optimized based on the bending moment distribution at the pile top and the pull-out resistance requirement, and the length of the bent section is not less than 10 times the diameter of the steel bar.

5. The railway bridge pile group structure with straight and oblique piles according to claim 1 is characterized by: The inclination angle of the inclined pile (1) is dynamically optimized through a parameterized model, and the model input parameters include the site earthquake peak acceleration, the soil shear wave velocity and the pile foundation material strength.

6. A construction method for a railway bridge pile group structure of straight and oblique pile combination according to any one of claims 1 to 5, characterized in that The following steps are involved: Step 1: Determine the inclination angle range and pile foundation arrangement parameters of the inclined pile (1) according to the site geological conditions; Step 2: Use a rotary drilling rig or static pressure method to construct the inclined pile (1) and the vertical pile (2), and ensure that the pile top elevation is consistent; Step 3: Pre-embed the bent anchor steel bars at the pile top, with the bending angle controlled at 30°~45°, and weld or mechanically connect them to the main reinforcement of the pile cap (3); Step 4: Set a rubber layer (5) around the pile top and adjust the compression rate to 15% to 20% to form a semi-rigid connection node; Step 5: Pour the concrete of the foundation (3) and carry out post-tensioning prestressing reinforcement.

7. The construction method of the straight-and-inclined pile combined railway bridge pile group structure according to claim 6 is characterized by: In step 1, the inclination angle of the inclined pile (1) is dynamically adjusted through finite element simulation combined with on-site static load testing to ensure that the horizontal bearing capacity of the pile group meets the design requirements.

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