Long-short pile foundation structure and calculation method suitable for arch bridge with thrust abutment

Abstract

The application discloses a long-short pile foundation structure suitable for an arch bridge with a thrust abutment, which comprises a pile cap, a first pile foundation, a second pile foundation, and a pile cap. The pile bottom of the first pile foundation extends into a bearing stratum at a deep part of a bedrock or a foundation, and the pile top is rigidly connected with the pile cap supported thereby. The length of the second pile foundation is basically consistent with the length of the first pile foundation with a bending moment at the top. The top of the second pile foundation is also rigidly connected with the pile cap supported by the first pile foundation. The first pile foundation and the second pile foundation are arranged in multiple rows and multiple columns alternately, and the outer edges of the pile cap are all provided with the first pile foundation. The application further discloses a calculation method of the long-short pile foundation structure suitable for the arch bridge with the thrust abutment. The abutment structure has the advantages of clear stress, simple construction, low cost and the like.

Description

Technical Field

[0001] This invention belongs to the field of bridge construction engineering technology and is applicable to large and medium-span arch bridges with spans of 30 to 80m. Specifically, it relates to a long and short pile foundation structure and calculation method applicable to arch bridges with thrust abutments. Background Technology

[0002] In existing bridge construction projects, arch bridges are often used for aesthetic purposes. For medium and long span arch bridges, the abutments often need to bear a large horizontal thrust transmitted from the bridge superstructure. In particular, for some urban bridges, the vertical elevation of the bridge deck is constrained by the surrounding road network and urban land elevation. The load-bearing arch of the superstructure can only adopt a smaller rise-to-span ratio, so the horizontal thrust on the abutments will be more prominent.

[0003] For geological conditions where the foundation overburden is deep at the abutment location, the aforementioned arch bridge abutments with thrust need to resist a large horizontal thrust. The conventional design of such abutments basically adopts a reinforced concrete pile cap structure with piles of similar length and equal height and level. All piles are arranged vertically and are basically of equal length, and all piles need to penetrate into the bedrock or a relatively deep bearing soil layer with good mechanical properties.

[0004] For vertically arranged bridge abutment pile foundations, the sections providing the most vertical bearing capacity are mainly the pile bottom and the lower section of the pile perimeter. However, under horizontal thrust, the sections of the pile body experiencing bending moment and shear force are mainly distributed in a localized area above the pile top, with a length generally 4 to 8 times the pile diameter below the pile top. Due to this misaligned force characteristic between the sections resisting horizontal forces and bearing vertical forces in vertical piles, for abutments of thrust arch bridges, when the bedrock or bearing soil with good mechanical properties is buried at a deep depth, the conventional equal-length pile foundation design results in a complete misalignment between the main vertical bearing capacity contribution section and the horizontal force resistance section within the pile foundation's length. This means the bearing capacity of the pile foundation material is not fully utilized, inevitably leading to increased pile foundation costs and extended construction time.

[0005] Furthermore, when using a conventionally designed, level and equal-height reinforced concrete abutment structure, if it is necessary to reduce the horizontal thrust of the arch bridge by increasing the rise-to-span ratio while keeping the bridge span, superstructure, and deck elevation constant, then the abutments need to be lowered as a whole. This would lead to an increase in the depth of the abutment foundation pit, and the construction difficulty and project cost would also increase accordingly. Summary of the Invention

[0006] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0007] Another objective of this invention is to provide a long and short pile foundation structure and calculation method suitable for arch bridges with thrust abutments.

[0008] Therefore, the technical solution provided by this invention is as follows:

[0009] A long and short pile foundation structure suitable for thrust abutments of arch bridges includes:

[0010] Pile foundation cap;

[0011] The first pile foundation has its bottom extending into the bedrock or the bearing stratum deep in the foundation, while its top is rigidly connected to the pile cap it supports. The first pile foundation is also called a long pile.

[0012] The second pile foundation has a length that is basically the same as that of the first pile foundation with a bending moment at the top. The top of the second pile foundation is also rigidly connected to the pile foundation cap. The second pile foundation is also called a short pile.

[0013] The first pile foundation and the second pile foundation are arranged in multiple rows and columns, and the outer edge of the pile foundation cap is made of the first pile foundation.

[0014] Preferably, in the long and short pile foundation structure applicable to arch bridges with thrust abutments, the front side of the pile foundation cap adopts a locally descending stepped structure, the step being the arch foot point of the superstructure of the arch bridge, and the width of the step being greater than the thickness of the arch rib of the arch bridge.

[0015] Preferably, in the long and short pile foundation structure applicable to arch bridges with thrust abutments, the pile cap is a reinforced concrete pile group cap, and the first and second pile foundations are reinforced concrete pile foundations. The first pile foundation is a long reinforced concrete pile, and the second pile foundation is also referred to as a short reinforced concrete pile.

[0016] Preferably, in the long and short pile foundation structure applicable to arch bridges with thrust abutments, both the first pile foundation and the second pile foundation are cast-in-place pile structures, and the first pile foundation and the second pile foundation use the same pile diameter.

[0017] Preferably, in the long and short pile foundation structure applicable to arch bridges with thrust abutments, a row of the first pile foundations is arranged below the abutment position corresponding to the step on the front side of the abutment.

[0018] Preferably, in the long and short pile foundation structure applicable to arch bridges with thrust abutments, a pre-reserved grouting pipe is reserved inside the pile body of the second pile foundation.

[0019] Preferably, in the long and short pile foundation structure applicable to arch bridges with thrust abutments, the pile diameter of the first pile foundation and the second pile foundation, as well as the spacing and number of pile rows and columns, are determined comprehensively based on the stress and the structural requirements for pile arrangement and center-to-center distance in Article 6.2.6 of the current standard "Code for Design of Highway Bridge and Culvert Foundations" JTG 3363-2019.

[0020] Secondly, the calculation method for long and short pile foundation structures applicable to arch bridges with thrust abutments includes:

[0021] 1) Perform conventional pile group abutment pile foundation layout and structural stress calculation for bridges to determine the initial pile diameter, number of piles and arrangement of pile foundations that can meet safety requirements;

[0022] 2) Based on the calculation results of step 1), check the length of the upper section of the pile foundation with bending moment, and initially determine the length of the second pile foundation;

[0023] 3) Calculate the characteristic value of the vertical bearing capacity of the second pile foundation based on geological data;

[0024] 4) Based on the bearing stratum conditions at the bottom of the abutment pile foundation, initially adjust 1 / 3 to 1 / 2 of the number of piles determined in step 1) to be second pile foundations, and use the first pile foundations for the remaining number of piles.

[0025] 5) Based on the number of first and second pile foundations initially determined in step 4), rearrange the first and second pile foundations, using first pile foundations on the outer side, and take the length of the first pile foundation as determined in step 1). The first and second pile foundations are arranged alternately.

[0026] 6) Based on the parameters determined in steps 2) to 5), the structural stress of the abutment with the first pile foundation and the second pile foundation is verified using an overall model of the abutment and the superstructure of the bridge. The boundary conditions for the first pile foundation and the second pile foundation are as follows: the horizontal constraints of the pile foundation are both bidirectional horizontal constraints using the soil spring coefficient. The vertical displacement of the bottom of the first pile foundation is zero as a constraint. The vertical displacement of the bottom of the short pile is not constrained, but an upward concentrated force is applied. The magnitude of the concentrated force is equal to the magnitude of the characteristic value of the vertical bearing capacity calculated in step 3).

[0027] 7) Based on the calculation results of step 6), query the vertical reaction force of the first pile foundation, verify the vertical bearing capacity of the first pile foundation, and determine the pile length of the first pile foundation again.

[0028] 8) Based on the calculation results of step 6), query the internal forces of the first pile foundation and the second pile foundation respectively, and perform strength reinforcement calculations for the first pile foundation and the second pile foundation.

[0029] Preferably, the calculation method for long and short pile foundation structures applicable to thrust abutments of arch bridges further includes:

[0030] 9) Based on the calculation results of steps 7) and 8), steps 4) to 8) can be repeated to perform structural optimization analysis in order to obtain the optimal design scheme for the first and second pile foundations.

[0031] Preferably, the calculation method for long and short pile foundation structures applicable to thrust abutments of arch bridges further includes:

[0032] 10) After the construction of the second pile foundation is completed, the vertical bearing capacity of the pile foundation shall be tested to verify whether its vertical bearing capacity meets the bearing capacity characteristic value calculated in step 3). If it does not meet the requirements, the pile bottom grouting treatment can be carried out through the reserved grouting pipe in the pile body of the second pile foundation to ensure that the vertical bearing capacity of the second pile foundation meets the bearing capacity characteristic value calculated in step 3).

[0033] The present invention has achieved at least the following beneficial effects:

[0034] (1) This invention innovates the traditional arch bridge thrust-resistant abutment structure and proposes a new type of reinforced concrete abutment structure with long and short piles. This not only maximizes the bending and horizontal thrust resistance of the upper section of the long pile and the short pile under the abutment, but also fully utilizes the vertical bearing capacity of the long pile in the deep geological section of the foundation. This avoids the requirement that all piles of the traditional structure must be of equal length and enter the deep geological section of the foundation. It makes full use of the pile foundation material, reduces the cost of the pile foundation project and shortens the construction period.

[0035] (2) This invention proposes a stepped structure with a partial drop on the front side of the abutment, which breaks through the traditional practice of equal height and flat bridge abutment ... Attached Figure Description

[0036] Figure 1 This is a plan view of a long and short pile foundation structure applicable to a thrust abutment of an arch bridge in an embodiment of the present invention.

[0037] Figure 2 This is a cross-sectional schematic diagram of a long and short pile foundation structure applicable to a thrust abutment of an arch bridge in an embodiment of the present invention.

[0038] Figure 3 This is a side cross-sectional schematic diagram of a long and short pile foundation structure applicable to a thrust abutment of an arch bridge in an embodiment of the present invention.

[0039] Figure 4 This is a schematic diagram illustrating the calculation boundary conditions for long and short pile foundation structures applicable to arch bridges with thrust abutments, as described in this embodiment of the invention.

[0040] Among them, 1 is a reinforced concrete pile cap, 2 is a long reinforced concrete pile, 3 is a short reinforced concrete pile, 4 is a bedrock or foundation bearing layer, 5 is a stepped structure descending in front of the pile cap, 6 is the arch foot of the upper-bearing arch bridge, 7 is the soil spring constraint on the pile side, 8 is the characteristic value Rs of the vertical bearing capacity of the short pile bottom, 9 is the zero displacement constraint of the long pile bottom in three mutually perpendicular directions, and 10 is the axial pressure N and bending moment M transmitted from the arch foot of the upper-bearing arch bridge to the abutment pile cap. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0042] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0043] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below.

[0044] The purpose of this invention is to provide a long and short pile foundation structure and calculation method suitable for large and medium-span thrust arch bridge abutments with spans of 30-80m. For geological conditions with deep overburden at the abutment location, a novel thrust-resistant pile group abutment structure is proposed. Its fundamental principle is based on the staggered stress characteristics of the long piles bearing horizontal thrust and vertical forces. An innovative arrangement of long and short piles connected to the abutment cap is adopted, achieving full utilization of the abutment pile foundation material's bearing capacity and providing a reliable and easy-to-operate method for calculating the stress of long and short piles. Simultaneously, by locally varying the height of the abutment, the rise-to-span ratio of the arch bridge is increased, thereby reducing the horizontal thrust transmitted from the arch ribs to the abutment and increasing the resistance to bulldozing pressure on the abutment backfill. Through these technical measures, the abutment structure involved has advantages such as clear stress distribution, simple construction, and low cost.

[0045] Reference Figures 1-4 The present invention provides a long and short pile foundation structure suitable for arch bridges with thrust abutments, comprising: a first pile foundation, also known as a long pile, and a second pile foundation, also known as a short pile.

[0046] A long and short pile foundation structure suitable for thrust abutments of large and medium span arch bridges with spans of 30 to 80m is proposed. The abutment structure includes a reinforced concrete pile cap 1, a reinforced concrete long pile 2, a reinforced concrete short pile 3, and a stepped structure 5 with a local descent on the front side of the cap. This step is the arch foot point of the superstructure of the arch bridge, and its width is greater than the thickness of the arch rib.

[0047] The reinforced concrete pile cap 1 is provided with reinforced concrete long piles 2 and reinforced concrete short piles 3 rigidly connected to it. The long piles and short piles are arranged in multiple rows and columns. The pile diameter, the spacing between rows and columns and the number of piles are determined comprehensively according to the stress requirements and the requirements of Article 6.2.6 of the current standard "Code for Design of Highway Bridge and Culvert Foundations" JTG 3363-2019 regarding the arrangement and spacing of piles. The outer edge of the pile cap is made of long piles, and short piles are evenly inserted in the middle of the long piles.

[0048] Furthermore, the reinforced concrete long pile 2 is the main component that provides vertical bearing capacity to the pile cap. The pile bottom extends into the bedrock or a good bearing stratum with high bearing capacity deep in the foundation, so as to give full play to the vertical bearing capacity of the pile bottom and the lower part of the pile. At the same time, the top section of the reinforced concrete long pile also provides the pile cap with resistance to horizontal thrust.

[0049] Furthermore, the length of the reinforced concrete short piles is basically the same as that of the long piles with bending moment at the top, generally 4 to 8 times the pile diameter below the pile cap. When the geological conditions are good, a smaller value is taken, mainly to provide the pile cap with resistance to horizontal thrust.

[0050] Furthermore, both the long and short reinforced concrete piles are cast-in-place pile structures, and the long and short piles preferably use the same pile diameter.

[0051] Furthermore, the front side of the pier adopts a partially descending stepped structure, and the descending steps on the front side of the pier serve as the arch foot points of the superstructure of the arch bridge.

[0052] Furthermore, the front side of the pier cap features a partially descending step, with a row of long piles arranged below the corresponding pier cap location.

[0053] Furthermore, in order to ensure the safety and reliability of the bridge structure, a grouting pipe is reserved in the pile body of the short pile of the abutment. This can be reserved as a measure to determine whether to grout the pile bottom and the pile perimeter to improve its vertical bearing capacity and horizontal lateral bearing capacity, based on the pile foundation test results of the short pile.

[0054] A calculation method and process for long and short pile foundation structures applicable to thrust abutments of arch bridges is as follows:

[0055] (1) Based on the bridge layout diagram of medium and long span thrust arch bridges and the relevant design diagram of similar structures, the pile foundation layout and structural stress calculation are carried out according to the relevant provisions of the current standard "Code for Design of Highway Bridge and Culvert Foundations" JTG 3363-2019, in accordance with the conventional pile cap, to determine the initial pile diameter, number of piles and arrangement method that can meet the safety requirements.

[0056] (2) Based on the calculation results of (1), check the length of the section with bending moment at the top of the pile foundation, and use it as a reference to determine the length of the short pile;

[0057] (3) Based on the geological mechanics parameters of the site where the bridge is located, calculate the characteristic value of the vertical bearing capacity of the short piles in accordance with Article 6.3.3 of the current standard "Code for Design of Highway Bridge and Culvert Foundations" JTG 3363-2019;

[0058] (4) Based on the bearing stratum conditions of the long piles at the abutment location, it is initially considered to adjust 1 / 2 to 1 / 3 of the number of piles determined in (1) to short piles (trial calculation and adjustment are required);

[0059] (5) Based on the number of long and short piles initially determined in (4), according to the relevant provisions of Article 6.2.6 of the current standard "Design Specification for Highway Bridge and Culvert Foundations" JTG 3363-2019 regarding pile spacing, the long and short piles should be rearranged reasonably. The principle is that long piles are used on the outer side, the length of the long piles is temporarily taken as the length determined in (1), and the long and short piles are arranged alternately.

[0060] (6) Based on the parameters determined in (2) to (5), the bridge abutment and the bridge superstructure are used as an integral model. The structural verification calculation of the long and short pile abutment is performed using the general calculation software for bridge calculation. The boundary conditions for the long and short piles are as follows: the horizontal constraint of the pile foundation is based on the soil spring coefficient calculated by the m method specified in Appendix L of the current specification "Code for Design of Highway Bridge Foundation" JTG 3363-2019 for bidirectional horizontal constraint. The vertical displacement of the bottom of the long pile is zero as a constraint. The vertical displacement of the bottom of the short pile is not constrained, but an upward concentrated force is applied, the magnitude of which is the characteristic value of the vertical bearing capacity calculated in (3). In order to simplify the calculation, the soil pressure caused by the local drop of the abutment and the increased height is taken as a safety margin and is not considered to participate in the stress calculation.

[0061] (7) Based on the calculation results of (6), find out the vertical reaction force of the long pile, and perform the vertical bearing capacity verification of the long pile in accordance with the provisions of Article 6.3.3 or 6.3.7 of the current specification "Specification for Design of Highway Bridge Foundation" JTG 3363-2019, and determine the pile length of the long pile.

[0062] (8) Based on the calculation results of (6), look up the internal forces of the long pile and the short pile, and perform the cross-sectional strength reinforcement calculation of the long pile and the short pile in accordance with the provisions of Appendix F of the current specification "Design Specification for Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts" JTG 3362-2018.

[0063] (9) Based on the calculation results of (7) and (8), steps (4) to (8) can be repeated to perform structural optimization analysis in order to obtain the safest and most economical long and short pile design schemes.

[0064] Furthermore, in order to ensure the safety and reliability of the bridge structure, the vertical bearing capacity of the second pile foundation is tested after the pile foundation construction is completed to verify whether its vertical bearing capacity meets the bearing capacity characteristic value calculated in step 3). If it does not meet the requirement, the pile bottom can be grouted through the reserved grouting pipe in the pile body of the second pile foundation to ensure that the vertical bearing capacity of the second pile foundation meets the bearing capacity characteristic value calculated in step 3).

[0065] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A long and short pile foundation structure suitable for arch bridges with thrust abutments, characterized in that, include: Pile foundation cap; The first pile foundation has its bottom extending into the bedrock or the bearing stratum deep in the foundation, while its top is rigidly connected to the pile cap it supports. The length of the second pile foundation is basically the same as the length of the first pile foundation with bending moment at the top, and the top of the second pile foundation is also rigidly connected to the pile foundation cap. The first pile foundation and the second pile foundation are arranged in multiple rows and columns, and the outer edge of the pile foundation cap is made of the first pile foundation. The front side of the pile cap adopts a locally descending stepped structure. The step is the arch foot point of the superstructure of the arch bridge. The width of the step is greater than the thickness of the arch rib of the arch bridge. A row of the first piles is arranged below the pile cap position corresponding to the step on the front side of the pile cap. The pile cap is a reinforced concrete pile group cap, and the first pile foundation and the second pile foundation are reinforced concrete pile foundations; Both the first pile foundation and the second pile foundation are cast-in-place pile structures. The first pile foundation and the second pile foundation use the same pile diameter. The second pile foundation has a reserved grouting pipe at the pile bottom inside the pile body.

2. The long and short pile foundation structure for arch bridges with thrust abutments as described in claim 1, characterized in that, The pile diameter, spacing, and number of piles for the first and second pile foundations are determined comprehensively based on the stress and the structural requirements for pile arrangement and center-to-center distance in Article 6.2.6 of the current standard "Code for Design of Highway Bridge and Culvert Foundations" JTG 3363-2019.

3. The calculation method for long and short pile foundation structures of arch bridges with thrust abutments as described in claim 1, characterized in that, include: 1) Perform conventional pile group abutment pile foundation layout and structural stress calculation for bridges to determine the initial pile diameter, number of piles and arrangement of pile foundations that can meet safety requirements; 2) Based on the calculation results of step 1), check the length of the upper section of the pile foundation with bending moment, and initially determine the length of the second pile foundation; 3) Calculate the characteristic value of the vertical bearing capacity of the second pile foundation based on geological data; 4) Based on the bearing stratum conditions at the bottom of the abutment pile foundation, initially adjust 1 / 3 to 1 / 2 of the number of piles determined in step 1) to be second pile foundations, and use the first pile foundations for the remaining number of piles; 5) Based on the number of first and second pile foundations initially determined in step 4), rearrange the first and second pile foundations in the plan. Use first pile foundations on the outer side. The length of the first pile foundation is the length determined in step 1). The first and second pile foundations are arranged alternately. 6) Based on the parameters determined in steps 2) to 5), the abutment and the bridge superstructure are used as an integral model to perform stress verification on the abutment structure with the first pile foundation and the second pile foundation. The boundary conditions for the first pile foundation and the second pile foundation are as follows: the horizontal constraints of the pile foundation are both bidirectional horizontal constraints using the soil spring coefficient. The vertical displacement of the bottom of the first pile foundation is zero as a constraint. The vertical displacement of the bottom of the short pile is not constrained, but an upward concentrated force is applied. The magnitude of the concentrated force is equal to the magnitude of the characteristic value of the vertical bearing capacity calculated in step 3). 7) Based on the calculation results of step 6), query the vertical reaction force of the first pile foundation, verify the vertical bearing capacity of the first pile foundation, and determine the pile length of the first pile foundation again. 8) Based on the calculation results of step 6), query the internal forces of the first pile foundation and the second pile foundation respectively, and perform strength reinforcement calculations for the first pile foundation and the second pile foundation; 9) Based on the calculation results of steps 7) and 8), steps 4) to 8) can be repeated to perform structural optimization analysis in order to obtain the optimal layout design scheme of the first pile foundation and the second pile foundation; 10) After the construction of the second pile foundation is completed, the vertical bearing capacity of the pile foundation shall be tested to verify whether its vertical bearing capacity meets the bearing capacity characteristic value calculated in step 3). If it does not meet the requirements, the pile bottom grouting treatment can be carried out through the reserved grouting pipe in the pile body of the second pile foundation to ensure that the vertical bearing capacity of the second pile foundation meets the bearing capacity characteristic value calculated in step 3).

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