Composite pier structure for bridge in complex geological condition area and design and construction method

Abstract

The invention discloses a composite pier structure for a bridge in a region with complex geological conditions and a design and construction method, and belongs to the technical field of design and construction processes of bridge engineering structures. The composite pier structure and the design and construction method can well adapt to high seismic intensity and a deep and thick covering layer foundation. The composite pier structure comprises a pier body arranged in an earthquake high fortification intensity area reservoir area, and further comprises a pile foundation and a bearing platform, and the pile foundation, the bearing platform and the pier body are composited into a whole from bottom to top in sequence in the vertical direction. The pile foundation is inserted into a deep covering layer foundation in a reservoir area of an earthquake high fortification intensity area according to a specified position, and the bearing platform of the non-solid structure is cushioned between the pile foundation at the top of the deep covering layer foundation and the pier body; the pile foundation and the bridge pier body which are compounded into a whole are in smooth transition with the rigidity of the composite bridge pier structure through a bearing platform of a non-solid structure, and stiffening ribs and / or energy dissipaters are further arranged between the side wall of the bottom of the bridge pier body and the top face of the bearing platform.

Description

Technical Field

[0001] The present invention relates to a composite bridge pier structure, in particular to a composite bridge pier structure for bridges in areas with complex geological conditions, belonging to the technical field of bridge engineering structure design and construction technology. The present invention also relates to a design and construction method for constructing the composite bridge pier structure for bridges in areas with complex geological conditions. Background Art

[0002] For the design of bridge foundations with thick covering layers at the bridge site, the existing technology generally has three treatment methods: one is to reinforce the foundation, such as using full-section deep foundation reinforcement technology, ultra-high pressure rotary jet pile reinforcement, etc., to improve the bearing capacity and stability of the foundation; the second is to use caisson foundation, make and sink concrete caissons through the thick covering layer into the stable stratum, to provide sufficient resistance and stability; the third is to take soil and replace filling within the influence range of the foundation, and use a shallow foundation after replacement.

[0003] Pile foundation is currently a commonly used foundation form for bridges, with mature technology, controllable costs, and a large amount of engineering practice experience. When encountering a foundation with a thick overburden layer, the use of end-bearing piles requires the pile foundation to pass through the thick overburden layer to reach a stable bearing layer, which is greatly affected by the thickness of the overburden layer and may even be impossible to achieve; when using friction piles, the thick overburden layer has low friction resistance, requiring a thicker pile diameter and an extra-long pile length to meet the bearing capacity, and the settlement is difficult to predict and control.

[0004] Specifically, the prior art has the following disadvantages:

[0005] 1) The foundation reinforcement method is time-consuming and labor-intensive, and the reinforcement effect is greatly affected by factors such as construction quality and is difficult to control. It is also prohibited in some places with high environmental protection requirements.

[0006] 2) The cost of caisson foundation is very high, the construction is difficult, and the sinking depth is limited.

[0007] 3) The shallow foundation replacement method is affected by the replacement quality, construction period and effect, and is not suitable for large bridges. It is still necessary to verify the bearing capacity and stability of the weak underlying layer. The risk of water settlement and deterioration of the replacement body in the later stage is high.

[0008] 4) For pile foundations, if friction piles are used, the pile foundation will be very long, exceeding the range recommended by the specifications. There is no specification to refer to for bearing capacity and settlement calculations. Extra-long pile foundations have multiple damage risks such as insufficient bearing capacity of the pile body, insufficient stability, and penetration and sinking. If end-bearing piles are used, it is necessary to penetrate a deep covering layer to reach a good bearing layer. The pile foundation will also exceed the length limit or even be impossible to achieve.

[0009] 5) When using pile foundation, it is also necessary to consider the coupled vibration of pile + water + structure under the action of earthquake. The pile body close to the pedestal often cracks or even breaks due to excessive horizontal force and bending moment.

[0010] 6) A large number of pile groups are used, such as corner piles, outer piles, inner piles, core piles and other piles in different positions. The conventional design of uniform pile diameter and pile length will lead to huge differences in the actual forces on each pile. The corner piles and outer piles will be damaged first, while the inner and core piles will be subjected to less force.

[0011] 7) The existing structural form and design concept do not take into account the geometric factors of the high piers and super-long pile foundations of the reservoir area bridges and the coupling effects of environmental factors such as reservoir water, thick soft cover layer, and liquefied sand layer. Such a structure presents a complex vibration mode of a super-long "column" under different lateral constraints in the vertical direction. The conventional pedestal, as a sudden change in stiffness, can easily lead to damage to the piers and pile foundations.

[0012] 8) Existing foundation forms and design methods cannot reduce and eliminate the impact of siltation. Summary of the invention

[0013] The technical problem to be solved by the present invention is to provide a composite pier structure for bridges in areas with complex geological conditions that can better adapt to high seismic intensity and thick overburden foundation, as well as a design and construction method for constructing the composite pier structure for bridges in areas with complex geological conditions.

[0014] The technical solution adopted to solve the above technical problems is: a composite pier structure for bridges in areas with complex geological conditions, including a pier body arranged in a reservoir area with high seismic fortification intensity, the composite pier structure also includes a pile foundation and a cap, the pile foundation, the cap and the pier body are composited into a whole in sequence from bottom to top vertically, the pile foundation is inserted into the thick covering layer foundation in the reservoir area with high seismic fortification intensity according to the specified position, and the cap of the non-solid structure is padded between the pile foundation at the top of the thick covering layer foundation and the pier body;

[0015] The composite pile foundation and the pier body smoothly transition the rigidity of the composite pier structure through a non-solid structure cap. Stiffening ribs and / or energy absorbers are also arranged between the side wall at the bottom of the pier body and the top surface of the cap.

[0016] Furthermore, a reinforced concrete cushion layer is arranged between the pile foundation and the pedestal. The bottom where the reinforced concrete cushion layer is connected to the pile foundation is a flat surface, a naturally slightly undulating surface, a shallow slope rib structure or a deep groove rib structure. The composite pier structure during operation dissipates energy through friction between the reinforced concrete cushion layer and the corresponding parts of the thick covering layer foundation.

[0017] A preferred embodiment of the above scheme is that the pile foundation is a pile group foundation, and each single pile constituting the pile group foundation includes at least two types of bored concrete cast single piles of different lengths and at least two types of different diameters;

[0018] The same abutment or the same bridge shall contain no more than three types of single piles of different lengths and single piles of different branch diameters.

[0019] Furthermore, the pedestal includes a hollow box and bearing beams and columns, and the closable hollow structure is circumferentially arranged on the side walls of the hollow box, and bearing beams and columns are arranged in the hollow box at least below the pier body; the pile foundation and the pier body are composited into one, and the stiffness of the composite pier structure is smoothly transitioned through the bearing beams and columns with the cooperation of the hollow box.

[0020] A preferred embodiment of the above scheme is that the hollow box body includes a top plate, a bottom plate and hollow cofferdam side plates extending along the circumference, the load-bearing beams include longitudinal partition beams and / or transverse partition beams connected between the top plate and the bottom plate, and slots are arranged on the hollow sides of the hollow cofferdam side plates; the hollow box body during the construction process forms a construction cofferdam through the hollow cofferdam side plates and the external steel cofferdam, and the hollow box body during the working process forms a self-cofferdam through the external plug-in plates inserted in the slots with the cooperation of the cushion layer.

[0021] Furthermore, the top plate, bottom plate and side plates of the hollow cofferdam are all cast-in-place parts, and the longitudinal diaphragm and / or transverse diaphragm are cast-in-place parts or ECC prefabricated parts; when cast-in-place parts are used, cast-in-place parts cast together with the top and bottom node ECC and the middle RC are used; the lower end of the pier body is pressed onto at least two rows of load-bearing beams and columns along the width direction through the top plate, and is pressed onto at least three rows of load-bearing beams and columns along the length direction.

[0022] The design and construction method for building the composite pier structure for bridges in areas with complex geological conditions is as follows: first, a design concept is formulated based on the pile foundation, cushion layer, cap and upper pier body as an integrated structure; then, the length, diameter and arrangement of each single pile constituting the pile foundation in the foundation, the thickness and bottom shape of the reinforced concrete constituting the cushion layer, the structure, overall height, load-bearing surface size of the bearing beam and column and the requirements for reinforcement in concrete of the cap, and the connection method between the cap and the pier body are designed in sequence; finally, the design and construction of the composite pier structure is completed in the order of first constructing the pile foundation and cushion layer, then constructing the cap, and finally constructing the pier body and the stiffening ribs and / or energy absorbers between the pier body and the cap from bottom to top.

[0023] When the design concept is formulated according to the integrated structure, the design calculation should at least include the cracking and / or local plastic hinge state of the abutment.

[0024] During construction, the completed pile foundation, cushion layer, cap and upper pier body are combined into a whole.

[0025] Furthermore, when designing the pile foundation, friction piles are used. Based on the single pile bearing capacity test and the specified number of finite element analyses, the basic pile diameter and pile length parameters of the pile foundation are determined by calculation according to the average force of each pile. Finally, a high-order finite element analysis of the pile-soil-structure-reservoir water coupling linkage is used, and the pile foundation lengths at different positions are determined based on the principle of consistency between short-term and long-term settlements to complete the design of the pile foundation.

[0026] The total bearing capacity Q of the friction column is calculated according to the following formula:

[0027] Q=∑(f·S)+Q end , f is the unit friction of the pile body, in kN / m 2 (or N / m 2 ); S is the friction surface area of ​​the friction pile, in m 2 ;Q end is the end resistance of the pile end, in kN / m 2 (or N / m 2 ).

[0028] The preferred method of the above scheme is to jointly consider the pile foundation parameters when designing the cap, and use the finite element analysis of pile-soil-structure-reservoir water coupling to determine the most basic height of the cap, the size of the load-bearing beams and columns, and the reinforcement parameters. Finally, under the condition of cracking of the cap structure and the occurrence of local plastic hinges in the load-bearing beams and columns under the E2 analysis, the design of the cap is completed by iteratively determining the height of the cap, the size of the load-bearing beams and columns, and the reinforcement parameters.

[0029] Furthermore, the composite pier structure is still designed using an iterative design method as a whole, and its phase flow is as follows:

[0030] First calculate the pile length and pile diameter → design the foundation → calculate the stiffness ratio → not satisfied → change the pile diameter → calculate the pile length again → design the foundation → calculate the stiffness ratio again... until a satisfactory stiffness ratio is obtained.

[0031] The beneficial effects of the present invention are as follows: the technical solution provided by the present application is based on the existing pier body arranged in the reservoir area of ​​the high seismic fortification intensity zone, and the composite pier structure of the present application is formed by adding pile foundations and pedestals, and the pile foundations, pedestals and pier body are composited into a whole in sequence from bottom to top vertically, and then the pile foundations are inserted into the thick covering layer foundation in the reservoir area of ​​the high seismic fortification intensity zone at the prescribed position, and the pedestal of the non-solid structure is padded between the pile foundation and the pier body at the top of the thick covering layer foundation; finally, during the structural working process, the composite pile foundation and the pier body are smoothly transitioned through the pedestal of the non-solid structure to achieve the stiffness of the composite pier structure, and stiffening ribs and / or energy absorbers are also arranged between the side wall at the bottom of the pier body and the top surface of the pedestal. In this way, the technical problem in the prior art that the entire pier structure is easily failed due to excessive stiffness of the pedestal is solved. At the same time, since the composite pier structure of the present application is a whole that combines the pile foundation, the pedestal and the pier body in a vertical order from bottom to top, it can also better adapt to the use requirements of high seismic intensity and thick covering layer foundation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a front view of the composite pier structure of the present invention used for bridges in areas with complex geological conditions;

[0033] Figure 2 Schematic diagrams of three structures of cushion layers involved in the composite pier structure of bridges in areas with complex geological conditions according to the present invention;

[0034] Figure 3 Two structural schematic diagrams of the composite pier structure for bridges in areas with complex geological conditions of the present invention, in which the pier body is pressed onto the bearing beam column of the abutment;

[0035] Figure 4 A schematic structural diagram of the connection between the pier body and the cap involved in the composite pier structure for bridges in areas with complex geological conditions of the present invention;

[0036] Figure 5 A flow chart for determining the pile diameter and pile length involved in the design and construction method of the composite pier structure for bridges in areas with complex geological conditions according to the present invention.

[0037] Marked in the figure are: pier body 1, stiffening rib 2, energy absorber 3, reinforced concrete cushion 4, single pile 5, hollow box 6, bearing beam column 7, and cap 8. DETAILED DESCRIPTION

[0038] Explanation of terms

[0039] Reservoir bridges: Bridges located within the reservoir area and within the reservoir influence area. Affected by reservoir water storage, water level changes, flood discharge, etc., reservoir bridges are more complicated than ordinary bridges in terms of foundation design, pier design, management and maintenance. If the bridge is built before the reservoir, the impact of water storage on foundation settlement needs to be considered. If the reservoir is built before the bridge, the underwater construction of the foundation needs to be considered. When located in an earthquake-fortified area, it is also necessary to consider that the bridge piers will vibrate in the reservoir water environment under the action of an earthquake and have a large additional mass. Reservoir bridges also need to consider the impact of siltation.

[0040] High seismic intensity areas: High seismic intensity areas generally refer to areas with a seismic intensity of 8 or above. These areas have historically experienced frequent seismic activity and high potential seismic risks, so stricter seismic standards must be followed in building design and infrastructure construction.

[0041] Cap: refers to the horizontal structural member located at the top of the bridge pier (bridge pier or abutment) to support the bridge superstructure (such as beams, slabs, arches, etc.). It is usually made of concrete and transfers the load of the upper part of the bridge to the pile foundation or pier below.

[0042] like Figure 1 to Figure 5The composite pier structure provided by the present invention can better adapt to the complex geological conditions of high seismic intensity and thick overburden foundation, and a design and construction method for building the composite pier structure for bridges in complex geological conditions. The composite pier structure includes a pier body 1 arranged in the reservoir area of ​​the high seismic fortification intensity zone, and the composite pier structure also includes a pile foundation and a cap 8. The pile foundation, the cap 8 and the pier body 1 are combined into a whole in sequence from bottom to top vertically. The pile foundation is inserted into the thick overburden foundation in the reservoir area of ​​the high seismic fortification intensity zone at a specified position, and the cap 8 of the non-solid structure is padded between the pile foundation and the pier body at the top of the thick overburden foundation; the composite pile foundation and the pier body 1 smoothly transition the stiffness of the composite pier structure through the cap 8 of the non-solid structure, and stiffening ribs 2 and / or energy dissipators 3 are also arranged between the side wall of the bottom of the pier body and the top surface of the cap 8. The technical solution provided by the present application is based on the existing pier body arranged in the reservoir area of ​​the high seismic fortification intensity zone, and the composite pier structure of the present application is formed by adding pile foundations and pedestals, and the pile foundations, pedestals and pier body are composited into a whole in sequence from bottom to top vertically, and then the pile foundations are inserted into the thick covering layer foundation in the reservoir area of ​​the high seismic fortification intensity zone at the specified position, and the pedestal of the non-solid structure is padded between the pile foundation and the pier body at the top of the thick covering layer foundation; finally, during the structural working process, the composite pile foundation and the pier body are smoothly transitioned through the pedestal of the non-solid structure to achieve the stiffness of the composite pier structure, and stiffening ribs and / or energy absorbers are also arranged between the side wall at the bottom of the pier body and the top surface of the pedestal. In this way, the technical problem of the prior art that the entire pier structure is easily ineffective due to the excessive rigidity of the pedestal is solved. At the same time, since the composite pier structure of the present application is a composite of the pile foundation, the pedestal and the pier body in the vertical order from bottom to top, it can also better adapt to the use requirements of high earthquake intensity and thick overburden foundation. Combined with the characteristics of the reservoir area in the high earthquake fortification intensity area and the thick overburden foundation, in order to further reduce the damage of high-intensity earthquakes to the composite pier structure, the present application also arranges a reinforced concrete cushion layer 4 between the pile foundation and the pedestal. The bottom of the reinforced concrete cushion layer 4 connected to the pile foundation is a flat surface, a naturally slightly undulating surface, a shallow slope rib structure or a deep groove rib structure; the composite pier structure in the working process consumes energy through friction between the reinforced concrete cushion layer 4 and the corresponding parts of the thick overburden foundation.

[0043] Accordingly, in order to improve the bearing capacity of each component of the composite pier structure of the present application, and to adapt to the deformation requirements of the thick covering layer foundation in the reservoir area of ​​the high seismic fortification intensity zone, and also to facilitate the construction during construction, the pile foundation of the present application is a pile group foundation, and each single pile 5 constituting the pile group foundation includes at least two different lengths and at least two different diameters of cast-in-place concrete single piles; and the single piles 5 of different lengths and the single piles 5 of different branch diameters included in the same pedestal 8 or the same bridge are no more than three. The pedestal 8 of the present application includes a hollow box 6 and a bearing beam column 7, and the enclosed hollow structure is arranged on the side wall of the hollow box 6 along the circumferential direction, and the bearing beam column 7 is arranged in the hollow box 6 at least below the pier body; the composite pile foundation and the pier body 1 are smoothly transitioned through the bearing beam column 7 in the cooperation of the hollow box to achieve the stiffness of the composite pier structure. Furthermore, the hollow box body 6 of the present application includes a top plate, a bottom plate and hollow cofferdam side plates extending along the circumference, and the bearing beam column 7 includes a longitudinal partition beam and / or a transverse partition beam connected between the top plate and the bottom plate, and a slot is set on the hollow side of the hollow cofferdam side plate; the hollow box body 6 during the construction process forms a construction cofferdam with the external steel cofferdam through the hollow cofferdam side plate, and the hollow box body 6 during the working process forms a self-cofferdam with the cooperation of the cushion layer through the external plug-in plate plugged into the slot. A more specific structure is that the top plate, the bottom plate and the hollow cofferdam side plates are all cast-in-place parts, and the longitudinal partition beam and / or the transverse partition beam are cast-in-place parts or ECC prefabricated parts; when cast-in-place parts are used, cast-in-place parts cast together with the top and bottom nodes ECC and the middle RC are used; the lower end of the pier body 1 is pressed on at least two rows of bearing beam columns 7 along the width direction through the top plate, and on at least three rows of bearing beam columns 7 along the length direction.

[0044] In accordance with the above structure, the design and construction method of the composite pier structure for bridges in areas with complex geological conditions in the present application is to first formulate a design concept according to the pile foundation, cushion layer, cap 8 and the upper pier body as an integrated structure; then, the length, diameter and arrangement form of each single pile constituting the pile foundation, the thickness and bottom surface shape of the reinforced concrete constituting the cushion layer, the structure, overall height, load-bearing surface size of the bearing beam and column and the requirements for reinforcement in concrete of the hollow box constituting the cap 8, and the connection method between the cap 8 and the pier body are designed in sequence; finally, the design and construction work of the composite pier structure is completed in the order of first constructing the pile foundation and cushion layer, then constructing the cap, and finally constructing the pier body and the stiffening ribs and / or energy dissipators between the pier body and the cap from bottom to top. Among them, when formulating the design concept according to the integrated structure, the design calculation should at least include the occurrence of cracks and / or local plastic hinge state of the cap. During construction, the completed pile foundation, cushion layer, cap and the upper pier body are combined into a whole. Combined with the existing technology and the requirements of design and construction regulations, this application adopts friction piles in the design of pile foundations. Based on the single pile bearing capacity test and the specified number of finite element analyses, the basic pile diameter and pile length parameters of the pile foundation are determined by calculation according to the average force of each pile. Finally, a high-order finite element analysis of pile-soil-structure-reservoir water coupling is adopted, and the pile foundation lengths at different positions are determined based on the principle of consistency between short-term settlement and long-term settlement to complete the design of the pile foundation.

[0045] The total bearing capacity Q of the friction column is calculated according to the following formula:

[0046] Q=∑(f·S)+Q end , f is the unit friction of the pile body, in kN / m 2 (or N / m 2 ); S is the friction surface area of ​​the friction pile, in m 2 ;Q end is the end resistance of the pile end, in kN / m 2 (or N / m 2 ). When designing the cap, the pile foundation parameters are considered together and the pile-soil-structure-reservoir water coupling finite element analysis is used to determine the most basic height of the cap, the size of the bearing beams and columns, and the reinforcement parameters. Finally, the cap design is completed by iteratively determining the height of the cap, the size of the bearing beams and columns, and the reinforcement parameters when the cap structure cracks and the bearing beams and columns have local plastic hinges under the E2 analysis.

[0047] In general, the composite pier structure of the present application is still designed using an iterative design method as a whole, and its phase process is as follows: first calculate a pile length and pile diameter → design a foundation → calculate the stiffness ratio → not satisfied → change the pile diameter → calculate the pile length again → design the foundation again → calculate the stiffness ratio again... until a satisfactory stiffness ratio is obtained.

[0048] In summary, the technical solution provided by this application comprehensively considers the influence of high earthquake intensity, high piers of bridges in reservoir areas, thick covering layers and certain liquefied layers, and starts from the essence of pile foundation bearing capacity, and provides a new form and design method of pile foundation in such areas, including a cap form including a cushion structure that adapts to deformation coordination, a length-to-diameter ratio design that adapts to low friction resistance, a pile group arrangement form that adapts to earthquake effects and coordinated pile foundation parameterization, providing a new form and new design concept and method for the foundation of such complex areas, and ultimately forming a form that adapts to the seismic action under high earthquake intensity, as well as the deformation coordination of pile groups under thick covering layers, and the reduction of settlement caused by sand liquefaction. It also has the following advantages,

[0049] 1. Adopting the integrated design concept, the overall reliability of the foundation is improved.

[0050] 2. The pile foundation resistance requirements are consistent.

[0051] 3. The cap and pile foundation can be jointly adjusted to have the same stiffness to reduce earthquake damage, that is, the stiffness and damage energy consumption can be adjusted through the cap design, and the structure of the cap frame plus longitudinal and transverse beams is convenient for repair. The stiffening ribs and / or energy absorbers set on the top can improve the node strength and assist in dissipating earthquake energy.

[0052] 4. The cushion layer can realize friction energy dissipation.

[0053] 5. The damage to the foundation can be repaired quickly.

[0054] 6. Avoid damage to the pile foundation by damaging the pedestal and cushion layer.

[0055] The technical solution of the present application is further described below through specific embodiments:

[0056] The present invention is a pile foundation form and design method for a reservoir bridge in a high seismic fortification zone that is adapted to a foundation in a thick overburden layer. The pile foundation form can adapt to the ground motion under high seismic intensity, coordinate the deformation of the pile group under the thick overburden layer, and reduce the settlement caused by sand liquefaction.

[0057] 1. Composition and function of the integrated foundation of pier cap pile foundation

[0058] 1) The integrated system consists of four parts: pile foundation, cap, cushion layer and pier.

[0059] 2) Pile foundation: Based on the single pile bearing capacity test and a large number of finite element analyses, the basic parameters of the pile foundation, the pile diameter and length, are determined. At this time, the pile is calculated based on the average force. Then, a high-order finite element analysis is performed, that is, the coupling linkage of pile-soil-structure-reservoir water is considered, and the pile foundation length at different locations is determined based on the principle of consistency between short-term settlement and long-term settlement.

[0060] 3) Pad: The pad has two functions. One is to facilitate the construction of the pedestal formwork. The outer ring of the pedestal is a cofferdam-like structure. Its function is to dissipate energy through friction with the surrounding soil, especially the soil under the pedestal, during an earthquake, so as to reduce the concentration of seismic vibrations caused by the concentration of the pedestal mass. Therefore, the shape of the pad needs to be specially designed.

[0061] 4) Cap: The cap of this structure is a non-solid cap with a closed outer ring and internal longitudinal and transverse beams. It is similar to a raft foundation. A top plate is set at the corresponding position of the bridge pier. The outer ring beam of the cap forms a circle, which together with the upper temporary steel cofferdam and the bottom cushion layer form a complete cofferdam, which is convenient for underwater construction. There is a slot reserved for the steel cofferdam for future repair on the upper part of the outer ring beam of the cap. The cross-sectional size and reinforcement amount of the longitudinal and transverse beam structure can be determined based on the finite element analysis of the coupling linkage of pile-soil-structure-reservoir water. The principle is that the stiffness of the cap and the entire structure should transition smoothly so as not to form an excessively large rigid domain. Specifically, the stiffness of the cap is weakened, and the cap is not made into a full-section entity, but into a beam grid raft type or a hollow beam column type. For this reason, cracking of the cap structure and local plastic hinges of the longitudinal and transverse beams can be allowed under the E2 analysis. After the earthquake, the gaps in the middle of the longitudinal and transverse beam structures are suitable for repair. During the repair, the steel cofferdam is inserted into the slot reserved in the outer ring beam of the pedestal. After pumping out the water, the interior can be entered for inspection and repair. After completion, the steel cofferdam is removed.

[0062] 5) Connection between the abutment and the pier: A connecting top plate is set at the corresponding position of the pier. The connection between the top plate and the pier may have stiffening ribs or additional energy absorbers in high-intensity defense areas.

[0063] 2. Form and design of pile foundation

[0064] 1) Diameter and pile length

[0065] The pile diameter and pile length jointly determine the bearing capacity of a single pile. Due to the limited conditions, the perfect combination of diameter and pile length cannot be obtained through simple pile calculations. It is necessary to comprehensively consider the coupling of multiple factors such as pile-soil-structure-water-seismic vibration. In the integrated foundation of pier cap pile foundation, the pile foundation diameter and pile length need to be determined by iterative analysis. The flow chart is as follows: Figure 2 As shown. First, according to the vertical bearing capacity, the pile diameter and pile length are initially planned. Then, it is arranged in the overall structural model, and a high-order finite element analysis considering the coupling of multiple factors such as pile-soil-structure-water-seismic motion is carried out. During this period, the adjustment of the abutment structure and the adjustment of the piles will be involved. Generally speaking, the pile diameter should not be too much, and there should be no more than three types for the same abutment or the same bridge. The pile length can be adjusted based on the principle that the settlement after the single pile is basically consistent, and then the strength is verified in the seismic analysis. Finally, the pile length is determined based on the consistency of the resistance-effect ratio. There should be no more than three types of pile lengths for the same abutment. After the abutment structure is adjusted, the pile diameter and length will be fine-tuned, and the length of the arranged piles will most of the time be like this. Figure 1The "heart" shape shown below.

[0066] 2) Construction method

[0067] The drilling and pouring of pile foundation are the same as those of ordinary pile foundation. It should be noted that due to the influence of pile layout, pile diameter and pile length, in geological conditions prone to hole collapse, the completion sequence of plum blossom shape can be considered to reduce the soil flow between piles caused by the construction sequence.

[0068] 3. Form and design of cushion

[0069] The structure and thickness of the cushion layer must meet the requirements of its function. The thickness must be guaranteed to meet the requirements of the cofferdam bottom during construction. The structure should be set according to the geological conditions of the base to be flat, naturally slightly undulating, with shallow slope ribs, with deep groove ribs, etc. Figure 2 As shown, the cap on it can slide when an earthquake occurs, effectively absorbing friction energy and reducing earthquake damage. Therefore, the cushion layer of this structure needs to be equipped with steel bars. The reinforcement is calculated by referring to the bottom plate of the raft foundation. Considering that the cap has a bottom plate, the calculated reinforcement amount can be configured by multiplying it by 0.6.

[0070] 4. Form and design of the platform

[0071] 1) Style and design

[0072] The height of the pedestal, the size of the longitudinal and transverse beams, and the reinforcement all need to be determined by the coupled linkage finite element analysis considering piles-soil-structure-reservoir water, and can be determined iteratively by considering the pile foundation parameters together. Since the pedestal structure is allowed to crack and the longitudinal and transverse beams are allowed to have local plastic hinges under the E2 analysis, it is necessary to reserve space for repair in the later stage. When repairing, the formwork can be supported in the space, reinforcement can be arranged, and ECC can be poured. Alternatively, the space can be directly filled after reinforcement.

[0073] The top plate is set locally on the cap to connect the bridge piers. The thickness and reinforcement of the top plate are determined based on the connection strength and the shear force of the piers. Generally, stiffening ribs can be set at the connection between the top plate and the piers to increase the connection effect. For those with higher seismic requirements, energy absorbers can also be set here to avoid premature damage to the connection between the piers and the cap during an earthquake.

[0074] The overall shape of the base can be determined based on calculations, such as rectangle, octagon, hexagon, etc.

[0075] 2) Construction

[0076] The cap is similar to raft foundation + caisson. During construction, the outer ring is made first, usually prefabricated on the shore, and then sunk. After connecting to the upper steel cofferdam, it is sunk into place, pumped out, the bottom is cleaned, the cushion structure is set, the cushion reinforcement is tied, the cushion is poured, and the bottom is completely sealed. The formwork is set, the reinforcement is tied, and the vertical and horizontal internal partition beams are poured. The top plate is poured and the bridge pier dowels are set.

[0077] The longitudinal and transverse diaphragms can also be prefabricated, and the nodes are cast with ECC with better tensile properties and toughness, and its fluidity can ensure that vibration is not required. When the whole is cast in place, it can be considered to cast the node ECC and the middle RC together. The use of ECC at the node can greatly improve the node toughness and overall resistance.

[0078] 5. Integration of design concepts

[0079] The design concept of this structure is to integrate the pile foundation, pedestal and superstructure into one.

[0080] 1) Stiffness ratio of integrated design structure. To reduce the damage caused by the incoordination of structural deformation under the action, especially under the action of earthquake, it is necessary to coordinate the stiffness ratio of these components and adopt an iterative design calculation method until a satisfactory stiffness ratio is achieved.

[0081] 2) Integrated consideration of earthquake damage and repair. In principle, pile foundations are not allowed to have broken piles, cushion friction energy consumption, and energy dissipation blocks can be damaged. The cap can crack or even have plastic hinges in some parts, which can be quickly repaired and reinforced in earthquake damage.

[0082] 3) The early and long-term settlement of the pile foundation are integrated, and with the effect of the cushion layer, uneven settlement is not easy to occur. The resistance requirement ratio of each pile is basically the same, and it is also integrated into yielding.

[0083] In summary, the key technical requirements of the present invention are as follows:

[0084] 1) According to the complex stress, the pile diameter and pile length of the pile foundation are iteratively determined and arranged flexibly, with the principle of consistent coordinated settlement and consistent resistance demand ratio.

[0085] 2) The cushion layer has the dual functions of energy dissipation and bottom sealing. It is a structural component rather than an auxiliary setting.

[0086] 3) The pedestal is designed as a longitudinal and transverse beam grid with a partial top plate and a bottom plate, and is adjusted according to the principle of integration to achieve a coordinated stiffness ratio.

[0087] 4) ECC material is used at the intersection of the longitudinal and transverse beams of the pedestal.

[0088] 5) The foundation can be prefabricated + node cast-in-place ECC.

[0089] 6) The outer ring of the foundation also serves as a cofferdam, with a slot left between it and the upper steel cofferdam, and combined with the cushion layer as the bottom cover, it realizes self-cofferdam. It can also be used when repairing damage.

[0090] 7) Vibration reduction and isolation are achieved through friction energy dissipation of the cushion layer.

[0091] 8) By "sacrificing" the foundation, cracking the longitudinal and transverse beams, and even forming plastic hinges, energy can be consumed and earthquake damage can be reduced.

[0092] 9) The damage to the foundation can be repaired quickly.

[0093] 10) Pile foundation, pedestal and cushion layer, integrated design concept.

[0094] Embodiment 1

[0095] In pile foundation design, the pile length (or pile foundation length) of the friction pile is designed based on the friction force and the friction coefficient of the soil, and is often used to calculate the bearing capacity of the friction pile. The design of the friction pile must not only consider the friction of the pile body, but also the properties of the soil layer and the type of pile.

[0096] The calculation of friction pile length usually involves the analysis of friction bearing capacity. The following is a common calculation formula for friction pile length:

[0097] The bearing capacity (Q) of a friction pile can be calculated by the resultant force of friction and end resistance. Usually, the bearing capacity of a friction pile is mainly provided by the friction of the pile body, and the end resistance is relatively small, especially for friction piles on soft soil foundations.

[0098] The total bearing capacity (Q) of the friction pile can be calculated by the following formula:

[0099] Q=∑(f·S)+Q end ,

[0100] in:

[0101] f is the unit friction of the pile body (related to the friction coefficient of the soil, the diameter of the pile, etc.), the unit is kN / m 2 (or N / m 2 );

[0102] S is the friction surface area of ​​the friction pile (i.e. the area where the surface of the pile contacts the surrounding soil), in m 2 ;

[0103] Q end It is the end resistance of the pile end (usually smaller for friction piles). The condition is satisfied if the force transmitted from the upper part is not greater than the total bearing capacity!

[0104] The following concepts are also involved in the integrated design structure of this application:

[0105] 1. About energy consumption devices

[0106] In structural seismic design, an energy dissipator is a device specifically used to absorb and dissipate seismic forces or other dynamic loads. It aims to reduce the amplitude of structural vibration and alleviate damage to structures such as buildings or bridges, thereby improving the seismic performance of the structure.

[0107] 1) The role of energy dissipator

[0108] Energy absorbers convert part of the energy input by the earthquake into heat or other forms of energy (such as plastic deformation energy) and "consume" it from the structure to reduce the energy transmitted to the structure by seismic waves. This can not only effectively reduce the vibration amplitude of the structure, but also avoid or reduce the damage caused by excessive vibration of the structure.

[0109] 2) Working principle of energy absorber

[0110] Energy dissipation is usually achieved through the following methods:

[0111] Plastic deformation: Through the plastic deformation of the material, part of the energy in the seismic wave is absorbed, which is common in metal energy absorbers and viscous dampers.

[0112] Friction energy consumption: energy is consumed through the heat generated by friction, which is common in friction type energy absorbers (such as friction dampers).

[0113] Viscous energy dissipation: Energy is consumed through the resistance generated by a fluid or semi-fluid (such as a viscous liquid), commonly seen in viscous dampers.

[0114] 3) Common types of energy absorbers

[0115] Viscous damper: uses liquid or gas as the working medium, creates resistance through the flow of the medium, and thus consumes energy. Common examples include hydraulic dampers.

[0116] Friction energy dissipator: Friction dampers are commonly used in bridges and high-rise buildings. For example, metal friction dampers or high-friction materials (such as rubber, steel, etc.) are used to manufacture friction damping equipment.

[0117] Buckling absorber: This absorber uses the buckling deformation of metal materials to absorb energy. When a vibration occurs, the material will buckle or locally deform plastically, thereby absorbing the energy input from the earthquake.

[0118] Superelastic energy dissipator: uses materials with superelasticity (such as shape memory alloys) to dissipate energy through the deformation and recovery process of the material.

[0119] Articulated energy absorber: A special articulated device is used to make the structure undergo a small displacement under the action of an earthquake, and the deformation generated by the displacement dissipates energy.

[0120] 4) Application of energy dissipators

[0121] High-rise buildings: In high-rise buildings, especially super-high-rise buildings, installing energy absorbers can greatly reduce structural vibration during earthquakes, avoid excessive deformation of the structure, and reduce construction and maintenance costs.

[0122] Bridges: Bridge structures, especially those with longer spans, also usually use energy absorbers to reduce the impact of seismic loads and avoid serious post-earthquake damage to the bridge.

[0123] Cultural relics buildings: For some historic and non-demolished buildings, energy absorbers can effectively protect them from damage by dynamic loads such as earthquakes.

[0124] Infrastructure and public facilities: such as tunnels, chimneys, water towers and other facilities, also often use energy absorbers to improve earthquake resistance.

[0125] 5) Advantages of energy absorbers

[0126] Improved seismic performance: By reducing the amplitude of structural vibration, the seismic performance is significantly improved.

[0127] Reduce damage: effectively reduce damage to structural and non-structural components and reduce repair costs.

[0128] Space saving: Compared with traditional reinforcement methods, energy absorbers take up less space and can be installed without significantly changing the appearance of the structure.

[0129] Reduced construction costs: For some buildings with complex designs, installing energy absorbers may be more cost-effective than reinforcing the structure.

[0130] 6) Conclusion

[0131] Energy absorbers are an important part of modern earthquake-resistant design. They effectively absorb earthquake energy in a variety of ways and reduce earthquake damage to structures. With the advancement of technology, the types of energy absorbers are constantly enriched, and the designs are becoming more and more sophisticated. They have gradually become the standard for earthquake-resistant design of various buildings, bridges and other structures.

[0132] 2. About E2 analysis

[0133] E2 analysis (or E2 method) in seismic design refers to a seismic analysis method based on the energy method, which focuses on the energy dissipation characteristics of the structure under seismic loads. This analysis method evaluates the seismic capacity and damage risk of the structure by considering the energy transfer and dissipation process of the structure under seismic action.

[0134] 1) Background and significance of E2 analysis

[0135] "E2" is the abbreviation of Energy-based Evaluation, which is usually related to the energy dissipation characteristics of the structure. In seismic design, energy analysis not only considers the mechanical effects of seismic loads on the structure, but also considers how the seismic energy is converted and consumed in different ways (such as material yielding, friction energy dissipation, plastic deformation, etc.) when the seismic wave passes through the structure. Specifically, E2 analysis is to evaluate the seismic performance of the structure through the energy conversion of the structure in an earthquake.

[0136] 2) Basic ideas of E2 analysis

[0137] The core of the E2 analysis method is to consider how the structure dissipates seismic energy in different ways under earthquake action, mainly in the following aspects:

[0138] Elastic and plastic deformation capacity of structures: Analyze the elastic and plastic responses of structures during earthquakes, especially how the plastic deformation area can reduce the impact of earthquakes by dissipating energy.

[0139] Energy dissipation system: The energy dissipation characteristics of devices such as energy absorbers and dampers introduced in the design. These devices reduce the vibration amplitude of the structure by absorbing the energy generated by the earthquake.

[0140] The conversion process of earthquake energy: Through the dynamic analysis of the structure, the input and output of earthquake energy are calculated to ensure that the structure can effectively convert and dissipate energy, thereby avoiding excessive deformation or damage of the structure.

[0141] 3) Steps and methods of E2 analysis

[0142] E2 analysis usually includes the following steps:

[0143] Calculate seismic loads: First, perform seismic load analysis to obtain the time history, amplitude, and input energy of the seismic waves.

[0144] Structural dynamic response analysis: Analyze the response of the structure through the dynamic model, including the displacement, acceleration and velocity of the structure. Especially for structures with nonlinear behavior, it is necessary to consider the nonlinear deformation of the structure through time history analysis and other means.

[0145] Energy conversion and dissipation analysis: Analyze the energy conversion process of the structure under the action of seismic loads. Including the input of seismic energy, the storage (such as elastic energy) and dissipation (such as plastic deformation, friction, damper effect, etc.) of energy in the structure. This analysis can help determine which parts have greater energy consumption, and then evaluate the seismic resistance and durability of these parts.

[0146] Evaluate the effectiveness of energy absorbers: If energy absorbers (such as dampers, friction absorbers, etc.) are incorporated into the design, it is necessary to analyze how these devices help the structure dissipate seismic energy and evaluate their contribution to the seismic reduction effect.

[0147] 4) Application of E2 analysis

[0148] High-rise building and bridge design: E2 analysis is particularly important in high-rise building and bridge design. Through this method, designers can ensure that the structure will not be excessively deformed or damaged under strong earthquakes, and effectively use external energy dissipation systems (such as viscous dampers, friction dampers, etc.) to improve seismic performance.

[0149] Nonlinear seismic analysis: The E2 method is often used in conjunction with nonlinear dynamic analysis to analyze the nonlinear response of structures in strong earthquakes, especially the structural behavior under large earthquakes.

[0150] Evaluate and optimize seismic design: Through E2 analysis, engineers can evaluate the performance of existing structures in earthquakes and optimize seismic design based on the results, such as adjusting the configuration of energy absorbers, optimizing the toughness and energy absorption capacity of the structure, etc.

[0151] 5) Advantages of E2 analysis

[0152] Comprehensive consideration of energy conversion and dissipation: E2 analysis can more comprehensively consider the energy flow and structural response under earthquake action, rather than just traditional analysis methods such as structural displacement and internal force.

[0153] Improved seismic performance: A deeper understanding of a structure’s energy dissipation capabilities can lead to the design of structures or facilities that are more earthquake-resistant, especially in high-risk areas.

[0154] Adapt to complex earthquake environments: The E2 analysis method can handle factors such as complex seismic motion time history and soil-structure interaction, and is more in line with the actual earthquake environment.

[0155] 3. About iterative design

[0156] Iterative Design is a design method that repeatedly improves and perfects the design process. It emphasizes the gradual improvement of the design plan through loop feedback, evaluation and adjustment until the best effect is finally achieved. This method is used in many fields, especially in product design, software development, architecture, engineering design and so on.

[0157] 1) Basic concepts of iterative design

[0158] Iterative design is a "trial and error" design process. Designers first propose a preliminary design plan, and then find problems and make adjustments through testing, feedback and evaluation. Then, a new design is made and verified, and the cycle repeats until all requirements are met or the ideal effect is achieved.

[0159] This process is sometimes called the "design-test-feedback" cycle, which means that each design output is optimized and improved after feedback from users or stakeholders. This process is usually not necessarily linear, but a dynamic cycle.

[0160] 2) Key features of iterative design

[0161] Continuous Improvement: Designs are continually refined, with each iteration getting closer to the final goal than the last.

[0162] Feedback-driven: Each round of design depends on the feedback from the previous round. Feedback is the core driving force of iterative design.

[0163] Flexibility and adaptability: Iterative design allows designers to flexibly adjust solutions during the process to respond to changes or new requirements.

[0164] Early Prototyping: Prototyping early helps the design team understand potential problems and make adjustments, rather than waiting until the final product development stage to discover problems.

[0165] 3) Iterative design steps

[0166] Iterative design generally includes the following main steps:

[0167] Requirements gathering and analysis: Understand project goals and user needs, and identify design issues.

[0168] Preliminary design and prototyping: Based on existing requirements and constraints, propose preliminary design plans and make preliminary prototypes.

[0169] Testing and feedback: Give the initial design or prototype to users or stakeholders for testing, collect feedback, and identify problems and deficiencies.

[0170] Improve the design: Based on the feedback, adjust the design plan, improve the prototype or refine the design.

[0171] Re-test and feedback: Re-test, evaluate the improvement effect, collect feedback again, and move on to the next iteration.

[0172] Final optimization: After several rounds of iterations, the final design solution tends to be perfect or meets the requirements.

[0173] 4) Advantages of iterative design

[0174] Quickly identify problems: Through continuous testing and feedback, problems in the design can be identified and solved early, reducing the cost and time of later modifications.

[0175] Better in line with user needs: User feedback is reflected in each round of iteration to ensure that the design is more in line with actual needs and usage habits.

[0176] Reduce risk: Through gradual implementation and optimization, the risk of one-time large-scale failure can be avoided and uncertainty can be reduced.

[0177] Flexible and adaptable: The design can be adjusted according to emerging needs and technological advances, making the product or solution more adaptable.

[0178] 5) Application of iterative design

[0179] Product Design: In product design, iterative design helps designers verify product functions, appearance, and user experience at every stage. Through prototype testing and user feedback, products are continuously optimized.

[0180] Software development: In Agile Development and Scrum methods, iterative design is the core working method. After each iteration, the development team will deliver a usable version and carry out the next round of development based on user feedback and requirements.

[0181] Architectural Design: In architectural design, iterative designs can be initially evaluated through means such as building models and virtual reality, and adjusted based on functional requirements, budget constraints and environmental feedback.

[0182] Engineering Design: In complex engineering projects, iterative design helps adjust the design plan according to the requirements, technical limitations and budget at different stages, reducing the risks in project execution.

[0183] 6) Comparison between iterative design and traditional design

[0184] Compared with traditional design methods, iterative design has the following significant differences:

[0185] Traditional design is usually completed within a design cycle, and the designer completes all design work before starting production or implementation. Feedback is usually obtained after the design is completed, and changes often require greater costs and time.

[0186] Iterative design provides feedback and improvements in each cycle, with design and testing happening in parallel, which usually allows for faster adaptation to changes and problem solving.

[0187] 7) Challenges of iterative design

[0188] Although iterative design has many advantages, it also faces some challenges:

[0189] Time and cost control: Although each iteration may make the design better, if the feedback cycle and modification scope are not controlled well, it may cause the project to be delayed or over budget.

[0190] Over-reliance on feedback: Sometimes, over-reliance on user or stakeholder feedback can lead to designs that are too conservative or sacrifice innovation.

[0191] Difficult to quantify results: Each iteration may bring small improvements, and it is difficult to see large-scale results in the short term, which requires continuous investment over a long period of time.

[0192] 8) Conclusion

[0193] Iterative design is a very effective design method, especially when facing complex and rapidly changing requirements. It can continuously optimize the design to ensure that the final product can meet user needs and project goals to the greatest extent. Through this process of continuous trial, feedback and improvement, designers can discover and solve problems in a relatively short period of time, improve design quality and reduce the risk of failure.

[0194] 4. About plastic hinge

[0195] In structural design, a plastic hinge refers to the phenomenon that a part of a structural member (such as a beam, column, frame, etc.) undergoes plastic deformation due to exceeding its elastic limit under the action of force. At this location, the internal force distribution of the structure is no longer a linear elastic change, but a plastic flow occurs, causing the rotation of this location to become very significant.

[0196] 1) Basic concept of plastic hinge

[0197] Plastic hinges usually appear at a certain node or fulcrum of a structure, which means that the material yields due to excessive force at that part, and the deformation enters the plastic stage, resulting in significant rotation and plastic deformation. This "hinge" is not a real hinge, but a place that is more flexible than a hinge and can withstand greater bending moments and rotations.

[0198] At the plastic hinge, the material has gone beyond the elastic stage and entered the plastic stage, so the position can continue to rotate, but no restorative deformation occurs. Usually, the stiffness of the structural element decreases significantly where the plastic hinge occurs.

[0199] 2) Formation conditions of plastic hinge

[0200] The formation of plastic hinges is closely related to the magnitude of internal forces such as bending moment and shear force of structural components. Generally speaking, when a structural component is subjected to bending moment, if the bending moment exceeds the yield moment of the component, the material will yield and form a plastic hinge.

[0201] Specifically:

[0202] The yield moment refers to the moment when a material is subjected to external force and the bending moment reaches a certain value, causing plastic deformation of the material.

[0203] The formation of a plastic hinge occurs when the bending moment at a certain position in the structure exceeds the yield moment, and plastic deformation occurs at that position, resulting in increased rotation of that position.

[0204] 3) The role and significance of plastic hinge

[0205] Plastic hinges have several key functions and significances in structural design:

[0206] Energy absorption: Plastic hinges help absorb the energy of external loads and earthquakes on the structure. Especially in seismic design, plastic hinges can effectively disperse and consume seismic energy to avoid fracture or excessive damage to other parts of the structure.

[0207] Deformation capacity: By controlling the position and number of plastic hinges, the structure can have a certain deformation capacity when subjected to extreme loads, thus avoiding sudden failure of the structure.

[0208] Stability and toughness: The formation of plastic hinges does not mean structural failure, but indicates that the structure is in a controllable plastic deformation state, which is beneficial to enhancing the toughness and stability of the structure.

[0209] 4) The difference between plastic hinge and elastic hinge

[0210] Elastic hinge: When a structure bends, the material in the bending area has not reached the yield strength, the deformation is completely elastic, and it can be fully recovered after the load is removed. Elastic hinges have good stiffness.

[0211] Plastic hinge: Unlike elastic hinge, plastic hinge is when the external force exceeds the yield point of the structure, the material enters the plastic stage and the deformation becomes non-recoverable. Plastic hinge makes the structure not return to its original shape when it deforms, but this deformation is controllable and helps absorb energy and avoid damage.

[0212] 5) Application of plastic hinges in seismic design

[0213] The concept of plastic hinges is very important in earthquake-resistant design. Designers usually arrange the location of plastic hinges to ensure that the structure does not collapse as a whole under earthquake. For example, during an earthquake, a frame structure can gradually undergo plastic deformation at the ends of beams or columns through plastic hinges, thereby absorbing and dissipating earthquake energy and avoiding brittle failure of key load-bearing components.

[0214] 6) Design of plastic hinge

[0215] In practical design, the occurrence and control of plastic hinges are usually considered from the following aspects:

[0216] Material selection: Select materials with good plastic deformation ability.

[0217] Structural layout: By adjusting the size and strength of beams and columns, ensure that plastic hinges occur in specific locations and avoid them where they should not occur.

[0218] Earthquake-resistant design: When designing, ensure that the location and number of plastic hinges are consistent with the earthquake-resistant requirements to avoid excessive concentration and prevent sudden structural damage.

Claims

1. A composite pier structure for bridges in areas with complex geological conditions, comprising a pier body (1) arranged in a reservoir area in an area with high seismic fortification intensity, characterized in that: The composite pier structure further comprises a pile foundation and a cap (8), wherein the pile foundation, the cap (8) and the pier body (1) are composited into a whole in a vertical order from bottom to top, wherein the pile foundation is inserted into a thick covering layer foundation in a reservoir area of ​​a high seismic fortification intensity zone at a prescribed position, and the cap (8) of a non-physical structure is cushioned between the pile foundation at the top of the thick covering layer foundation and the pier body; The pile foundation and the pier body (1) are composited into one and the rigidity of the composite pier structure is smoothly transitioned through a cap (8) of a non-solid structure. Stiffening ribs (2) and / or energy dissipators (3) are also provided between the side wall at the bottom of the pier body and the top surface of the cap (8).

2. The composite pier structure for bridges in areas with complex geological conditions according to claim 1 is characterized by: A reinforced concrete cushion layer (4) is also arranged between the pile foundation and the cap (8); the bottom of the reinforced concrete cushion layer (4) connected to the pile foundation is a flat surface, a naturally slightly undulating surface, a shallow slope rib structure or a deep groove rib structure; during operation, the composite pier structure dissipates energy through friction between the reinforced concrete cushion layer (4) and the corresponding parts of the thick covering layer foundation.

3. The composite pier structure for bridges in areas with complex geological conditions according to claim 1 or 2, characterized in that: The pile foundation is a pile group foundation, and each single pile (5) constituting the pile group foundation includes at least two types of bored concrete cast single piles of different lengths and at least two types of different diameters; The number of single piles (5) of different lengths and single piles (5) of different branch diameters included in the same cap (8) or the same bridge does not exceed three.

4. The composite pier structure for bridges in areas with complex geological conditions according to claim 3 is characterized by: The pedestal (8) comprises a hollow box (6) and a bearing beam (7); a closable hollow structure is arranged on the side wall of the hollow box (6) along the circumferential direction, and a bearing beam (7) is arranged in the hollow box (6) at least below the pier body; the pile foundation and the pier body (1) are combined into one body, and the bearing beam (7) smoothly transitions the rigidity of the composite pier structure in cooperation with the hollow box.

5. The composite pier structure for bridges in areas with complex geological conditions according to claim 4 is characterized by: The hollow box body (6) comprises a top plate, a bottom plate and hollow cofferdam side plates extending along the circumference, the bearing beam column (7) comprises a longitudinal partition beam and / or a transverse partition beam connected between the top plate and the bottom plate, and a slot is arranged on the hollow side of the hollow cofferdam side plate; during the construction process, the hollow box body (6) forms a construction cofferdam through the hollow cofferdam side plates and the external steel cofferdam, and during the working process, the hollow box body (6) forms a self-cofferdam through the external plug-in plate plugged into the slot with the cooperation of the cushion layer.

6. The composite pier structure for bridges in areas with complex geological conditions according to claim 5 is characterized by: The top plate, bottom plate and hollow cofferdam side plates are all cast-in-place parts, and the longitudinal diaphragm and / or transverse diaphragm are cast-in-place parts or ECC prefabricated parts. When cast-in-place parts are used, the top and bottom nodes ECC and the middle RC are cast together. The lower end of the pier body (1) is pressed onto at least two rows of bearing beams (7) in the width direction through the top plate, and is pressed onto at least three rows of bearing beams (7) in the length direction.

7. A design and construction method for constructing a composite pier structure for bridges in areas with complex geological conditions as claimed in claim 6, characterized in that: The design and construction method first formulates a design concept based on the pile foundation, cushion layer, cap and the upper pier body as an integrated structure; then sequentially designs the length, diameter and arrangement form of each single pile constituting the pile foundation, the thickness and bottom surface shape of the reinforced concrete constituting the cushion layer, the structure, overall height, load-bearing surface size of the bearing beam and column and the requirements for reinforcement in concrete of the cap, and the connection method between the cap and the pier body; finally, the design and construction of the composite pier structure is completed in the order of first constructing the pile foundation and the cushion layer, then constructing the cap, and finally constructing the pier body and the stiffening ribs and / or energy absorbers between the pier body and the cap from bottom to top. When the design concept is formulated according to the integrated structure, the design calculation should at least include the cracking and / or local plastic hinge state of the abutment. During construction, the completed pile foundation, cushion layer, cap and upper pier body are combined into a whole.

8. The design and construction method according to claim 7, characterized in that: When designing the pile foundation, friction piles are used. Based on the single pile bearing capacity test and the specified number of finite element analyses, the basic pile diameter and pile length parameters of the pile foundation are determined by calculation according to the average force of each pile. Finally, the high-order finite element analysis of pile-soil-structure-reservoir water coupling is adopted, and the pile foundation lengths at different positions are determined based on the principle of consistency between short-term settlement and long-term settlement to complete the design of the pile foundation. The total bearing capacity Q of the friction column is calculated according to the following formula: Q=∑(f·S)+Q end , f is the unit friction of the pile body, in kN / m 2 (or N / m 2 ); S is the friction surface area of ​​the friction pile, in m 2 ;Q end is the end resistance of the pile end, in kN / m 2 (or N / m 2 ).

9. The design and construction method according to claim 8, characterized in that: When designing the cap, the pile foundation parameters are taken into consideration, and the pile-soil-structure-reservoir water coupled finite element analysis is used to determine the basic height of the cap, the size of the load-bearing beams and columns, and the reinforcement parameters. Finally, under the E2 analysis, the cap structure is allowed to crack and local plastic hinges appear in the load-bearing beams and columns. The cap design is completed by iteratively determining the height of the cap, the size of the load-bearing beams and columns, and the reinforcement parameters.

10. The design and construction method according to claim 7, characterized in that: The composite pier structure is still designed using the iterative design method as a whole, and its phase flow is as follows: First calculate the pile length and pile diameter → design the foundation → calculate the stiffness ratio → not satisfied → change the pile diameter → calculate the pile length again → design the foundation → calculate the stiffness ratio again... until a satisfactory stiffness ratio is obtained.

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