Shallow sea tidal area hard rock pile foundation platform cofferdam integrated construction method and structure

Abstract

The application discloses a kind of hard rock pile foundation platform cofferdam integrated construction method and structure in shallow tidal zone, it is applicable to the bridge pile foundation and lower structure construction under the condition of hard rock in shallow tidal zone. The method adopts low-tide rock leveling, pre-buried steel ring beam pouring bottom sealing concrete to form underwater rigid foundation, upper beam-column skeleton first bears vertical load of piling platform and then converts into horizontal resistance of steel cofferdam inner support integrated construction idea, vertical piling load and horizontal cofferdam load are borne by the same set of beam-column force structure at different time sequences, and the structural function conversion of platform and cofferdam is realized. The application integrates piling platform force structure and steel cofferdam force structure, reduces construction investment, shortens construction period, and solves the problem of embedding difficulty and insufficient stability caused by separate erection of platform and cofferdam under hard rock condition.

Description

Technical Field

[0001] This invention relates to the field of bridge pile foundation construction and underwater cofferdam engineering technology, and in particular to an integrated construction method and structure for a pile foundation platform cofferdam in shallow sea tidal zones with hard rock, applicable to the construction of bridge pile foundations and piers in shallow sea tidal zones with seabed geology of hard rock (reef). Background Technology

[0002] To address the shortcomings of existing technologies, this invention provides an integrated construction method and structure for a pile foundation platform and cofferdam in hard rock in shallow sea tidal zones. This aims to solve the problems of high construction costs, long construction periods, difficulty in embedding and insufficient stability caused by the separate construction of the pile driving platform and the steel cofferdam under hard rock conditions.

[0003] To achieve the above objectives, the present invention adopts the following technical solution: A method for integrated construction of a pile-foundation platform and cofferdam in a shallow sea tidal zone with hard rock, employing an integrated construction approach: leveling the reef at low tide, pre-embedding steel ring beams and pouring bottom-sealing concrete to form an underwater rigid foundation, and then converting the upper beam-column framework to initially bear the vertical load of the pile-driving platform and subsequently to support the horizontal resistance of the steel cofferdam. This method achieves the structural function conversion between the platform and the cofferdam by having the same set of beam-column load-bearing structures bear both the vertical pile-driving load and the horizontal cofferdam load at different times. The method includes the following steps: S1: Leveling of reefs at low tide During low tide, mechanical methods are used to level the uneven, hard rocky reefs on the seabed, creating a foundation surface for construction.

[0004] S2: Foundation sealing construction According to the design dimensions of the steel platform and cofferdam, a steel ring beam was pre-embedded on the leveled reef foundation, and bottom sealing concrete was poured to form an underwater rigid pier foundation. The bottom sealing concrete covers the steel ring beam and extends outward to form an anchoring constraint on the superstructure.

[0005] The low-tide reef leveling and bottom sealing foundation construction are completed during the tidal window: mechanical leveling, steel ring beam positioning and pre-embedding, and bottom sealing concrete pouring are quickly completed during the low-tide period when the reef is exposed. This allows the bottom sealing concrete to initially harden before high tide, forming a stable underwater rigid foundation. The extended portion of the bottom sealing concrete interlocks firmly with the reef leveling surface, resisting seawater impact and the overturning moment of the superstructure.

[0006] S3: Beam-column frame installation The upper beam-column structural framework is installed on the bottom concrete foundation. The beam-column structural framework includes vertical columns, horizontal walers, and horizontal braces, and the components are connected by welding to form an integral load-bearing frame.

[0007] The selection of components and connection nodes in the beam-column structural framework simultaneously meet the load-bearing requirements of two stress conditions: the cross-section and slenderness ratio of the vertical columns must meet the vertical compressive stability requirements of the piling platform stage, and the vertical support requirements of the steel cofferdam stage; the cross-sections of the horizontal walers and braces must meet the horizontal stability requirements of the piling platform stage, and the internal support requirements for resisting circumferential water pressure in the steel cofferdam stage. Therefore, the cross-sectional design of the beam-column framework is not the optimal solution under a single stress condition, but rather an adaptive design under the coupling of two stress modes.

[0008] S4: Piling Platform Operation A detachable panel is laid on top of the beam-column structural frame to form a piling platform, where a piling machine is arranged to carry out pile foundation work. At this time, the beam-column structural frame serves as the vertical load-bearing system of the piling platform, with the columns bearing the vertical load and the walers and braces maintaining the platform's horizontal stability.

[0009] S5: Platform to Cofferdam After the pile foundation work is completed, the top removable panel is removed, leaving the beam-column structural framework. A steel cofferdam is constructed on the outside of the beam-column structural framework, with the side plates of the steel cofferdam tightly attached to the walers and firmly welded together to form a composite load-bearing section. At this point, the beam-column structural framework transforms into the internal support system of the steel cofferdam, with the walers and braces bearing the horizontal water pressure, and the columns maintaining the vertical stability of the cofferdam.

[0010] It is important to note that steps S4 and S5 above are not simply sequential procedures, but rather structural transformations of the same beam-column framework under different time sequences: the columns transform from "piling platform legs" to "cofferdam vertical supports," with their stress direction changing from primarily vertical compressive resistance to a coupling of vertical support and horizontal constraint; the walers and braces transform from "platform horizontal stabilizing components" to "cofferdam internal support ring beams," with their stress mode changing from maintaining platform horizontal stability to resisting external water pressure in the circumferential compression. These transformations require the beam-column framework's cross-sectional properties, connection nodes, and overall stiffness to simultaneously adapt to two drastically different stress states. Without adaptation to the vertical piling load, pile foundation work cannot be completed; without adaptation to the horizontal cofferdam load, it cannot resist water pressure. Both are indispensable, forming a systematic synergy distinct from a separately arranged platform and cofferdam system.

[0011] S6: Construction and dismantling within the cofferdam After the steel cofferdam is constructed, the foundation structure is constructed inside the cofferdam. The horizontal bracing is then transferred to the foundation, and the upper piers are constructed. After the piers are completed, the entire cofferdam system is dismantled.

[0012] As a further explanation of the above technical solution of the present invention: The welded connection between the steel cofferdam side plates and the walers forms a combined load-bearing section, allowing the walers and steel cofferdam side plates to jointly resist external water pressure, increasing the moment of inertia of the section and improving the overall bending stiffness. This connection method differs from the conventional approach of independently arranging the internal supports of the cofferdam: in the conventional approach, the cofferdam side plates and internal supports are separated in terms of force transmission, with the internal supports bolted to the cofferdam side plates via node plates, resulting in installation gaps and stress concentration; the present invention, through welding, forms a continuous combined section between the cofferdam side plates and the walers, resulting in uniform stress distribution and a direct force transmission path.

[0013] The horizontal bracing forms a circumferential closed support system during the cofferdam stage, and the support is transferred to the pier during the pier construction stage, realizing the phased utilization of the same component throughout the entire construction cycle and avoiding the waste of materials after the traditional bracing is removed.

[0014] The present invention produces the following beneficial effects: This invention solves the technical bottleneck of steel platforms and cofferdams being unable to be firmly embedded in the seabed under hard rock conditions by leveling reefs at low tide and pre-embedding steel ring beams and pouring bottom-sealing concrete to form an underwater rigid foundation. Through an integrated construction approach where the upper beam-column framework first bears the vertical load of the piling platform and then transforms it into the horizontal resistance of the steel cofferdam's internal support, the load-bearing structures of the piling platform and the steel cofferdam are combined into one, avoiding the repetitive investment of erecting and dismantling two independent structures in conventional step-by-step construction. By welding the steel cofferdam side plates and walers together, a continuous load-bearing section is formed, improving the overall bending stiffness and stability of the cofferdam. These technical features are systematically adapted to the hard rock tidal zone environment, and their overall construction efficiency and economy are significantly better than the simple sum of the individual effects of each technical feature. Summary of the Invention

[0015] To address the shortcomings of existing technologies, this invention provides an integrated construction method and structure for a pile foundation platform and cofferdam in hard rock in shallow sea tidal zones. This aims to solve the problems of high construction costs, long construction periods, difficulty in embedding and insufficient stability caused by the separate construction of the pile driving platform and the steel cofferdam under hard rock conditions.

[0016] To achieve the above objectives, the present invention adopts the following technical solution: A method for integrated construction of a pile-foundation platform and cofferdam in a shallow sea tidal zone with hard rock, employing an integrated construction approach: leveling the reef at low tide, pre-embedding steel ring beams and pouring bottom-sealing concrete to form an underwater rigid foundation, and then converting the upper beam-column framework to initially bear the vertical load of the pile-driving platform and subsequently to support the horizontal resistance of the steel cofferdam. This method achieves the structural function conversion between the platform and the cofferdam by having the same set of beam-column load-bearing structures bear both the vertical pile-driving load and the horizontal cofferdam load at different times. The method includes the following steps: S1: Leveling of reefs at low tide During low tide, mechanical methods are used to level the uneven, hard rocky reefs on the seabed, creating a foundation surface for construction.

[0017] S2: Foundation sealing construction According to the design dimensions of the steel platform and cofferdam, a steel ring beam was pre-embedded on the leveled reef foundation, and bottom sealing concrete was poured to form an underwater rigid pier foundation. The bottom sealing concrete covers the steel ring beam and extends outward to form an anchoring constraint on the superstructure.

[0018] The low-tide reef leveling and bottom sealing foundation construction are completed during the tidal window: mechanical leveling, steel ring beam positioning and pre-embedding, and bottom sealing concrete pouring are quickly completed during the low-tide period when the reef is exposed. This allows the bottom sealing concrete to initially harden before high tide, forming a stable underwater rigid foundation. The extended portion of the bottom sealing concrete interlocks firmly with the reef leveling surface, resisting seawater impact and the overturning moment of the superstructure.

[0019] S3: Beam-column frame installation The upper beam-column structural framework is installed on the bottom concrete foundation. The beam-column structural framework includes vertical columns, horizontal walers, and horizontal braces, and the components are connected by welding to form an integral load-bearing frame.

[0020] The selection of components and connection nodes in the beam-column structural framework simultaneously meet the load-bearing requirements of two stress conditions: the cross-section and slenderness ratio of the vertical columns must meet the vertical compressive stability requirements of the piling platform stage, and the vertical support requirements of the steel cofferdam stage; the cross-sections of the horizontal walers and braces must meet the horizontal stability requirements of the piling platform stage, and the internal support requirements for resisting circumferential water pressure in the steel cofferdam stage. Therefore, the cross-sectional design of the beam-column framework is not the optimal solution under a single stress condition, but rather an adaptive design under the coupling of two stress modes.

[0021] S4: Piling Platform Operation A detachable panel is laid on top of the beam-column structural frame to form a piling platform, where a piling machine is arranged to carry out pile foundation work. At this time, the beam-column structural frame serves as the vertical load-bearing system of the piling platform, with the columns bearing the vertical load and the walers and braces maintaining the platform's horizontal stability.

[0022] S5: Platform to Cofferdam After the pile foundation work is completed, the top removable panel is removed, leaving the beam-column structural framework. A steel cofferdam is constructed on the outside of the beam-column structural framework, with the side plates of the steel cofferdam tightly attached to the walers and firmly welded together to form a composite load-bearing section. At this point, the beam-column structural framework transforms into the internal support system of the steel cofferdam, with the walers and braces bearing the horizontal water pressure, and the columns maintaining the vertical stability of the cofferdam.

[0023] It is important to note that steps S4 and S5 above are not simply sequential procedures, but rather structural transformations of the same beam-column framework under different time sequences: the columns transform from "piling platform legs" to "cofferdam vertical supports," with their stress direction changing from primarily vertical compressive resistance to a coupling of vertical support and horizontal constraint; the walers and braces transform from "platform horizontal stabilizing components" to "cofferdam internal support ring beams," with their stress mode changing from maintaining platform horizontal stability to resisting external water pressure in the circumferential compression. These transformations require the beam-column framework's cross-sectional properties, connection nodes, and overall stiffness to simultaneously adapt to two drastically different stress states. Without adaptation to the vertical piling load, pile foundation work cannot be completed; without adaptation to the horizontal cofferdam load, it cannot resist water pressure. Both are indispensable, forming a systematic synergy distinct from a separately arranged platform and cofferdam system.

[0024] S6: Construction and dismantling within the cofferdam After the steel cofferdam is constructed, the foundation structure is constructed inside the cofferdam. The horizontal bracing is then transferred to the foundation, and the upper piers are constructed. After the piers are completed, the entire cofferdam system is dismantled.

[0025] As a further explanation of the above technical solution of the present invention: The welded connection between the steel cofferdam side plates and the walers forms a combined load-bearing section, allowing the walers and steel cofferdam side plates to jointly resist external water pressure, increasing the moment of inertia of the section and improving the overall bending stiffness. This connection method differs from the conventional approach of independently arranging the internal supports of the cofferdam: in the conventional approach, the cofferdam side plates and internal supports are separated in terms of force transmission, with the internal supports bolted to the cofferdam side plates via node plates, resulting in installation gaps and stress concentration; the present invention, through welding, forms a continuous combined section between the cofferdam side plates and the walers, resulting in uniform stress distribution and a direct force transmission path.

[0026] The horizontal bracing forms a circumferential closed support system during the cofferdam stage, and the support is transferred to the pier during the pier construction stage, realizing the phased utilization of the same component throughout the entire construction cycle and avoiding the waste of materials after the traditional bracing is removed.

[0027] The present invention produces the following beneficial effects: This invention solves the technical bottleneck of steel platforms and cofferdams being unable to be firmly embedded in the seabed under hard rock conditions by leveling reefs at low tide and pre-embedding steel ring beams and pouring bottom-sealing concrete to form an underwater rigid foundation. Through an integrated construction approach where the upper beam-column framework first bears the vertical load of the piling platform and then transforms it into the horizontal resistance of the steel cofferdam's internal support, the load-bearing structures of the piling platform and the steel cofferdam are combined into one, avoiding the repetitive investment of erecting and dismantling two independent structures in conventional step-by-step construction. By welding the steel cofferdam side plates and walers together, a continuous load-bearing section is formed, improving the overall bending stiffness and stability of the cofferdam. These technical features are systematically adapted to the hard rock tidal zone environment, and their overall construction efficiency and economy are significantly better than the simple sum of the individual effects of each technical feature. Attached Figure Description

[0028] Figure 1 This is an elevation view of the overall design scheme of the piling platform and steel cofferdam of the present invention.

[0029] Figure 2 This is a plan view of the bottom sealing of the structure and the positioning of the steel ring beam and steel casing of the present invention.

[0030] Figure 3 This is an elevation view of the beam-column structural framework of the structure of the present invention.

[0031] Figure 4 This is a plan view of the beams, columns, and internal supports of the structure of the present invention.

[0032] Figure 5 This is a schematic elevation view of the piling platform of the present invention being converted into a steel cofferdam for the construction of the internal structure of the cofferdam. Detailed Implementation

[0033] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0034] Example 1: Construction of Hard Rock Pile Foundations in Shallow Tidal Zones under Standard Working Conditions like Figures 1 to 4 , Figure 5 As shown, this embodiment is applied to the construction of bridge substructures in shallow tidal zones where the seabed geology is hard rock and reefs. The seabed in this area is uneven and lacks a soft overburden layer, making it impossible to embed conventional steel pipe piles. The traditional step-by-step construction method of "first build the platform, then dismantle it, and then build the cofferdam" is difficult to implement.

[0035] Step 1: Leveling the reefs at low tide Utilizing the tidal patterns of the sea, underwater leveling machinery is used during low tide when the reefs are exposed to mechanically level the uneven, hard rock reefs on the seabed. During the leveling process, the flatness and elevation are strictly controlled to ensure the uniform thickness of the subsequent bottom sealing concrete. After leveling, the bottom debris is removed to form a stable construction base surface.

[0036] Step Two: Foundation Sealing Construction According to the design dimensions of the steel platform and cofferdam, the steel ring beams were laid out and positioned on the leveled reef foundation, and then pre-embedded. In this embodiment, the steel ring beams are made of double-section 2H45a steel, arranged along the contour of the pier to form a closed ring beam. After the steel ring beams are positioned, the bottom sealing concrete is quickly poured during low tide, with the thickness controlled between 40cm and 50cm, and the elevation strictly controlled according to the design. The bottom sealing area extends 50cm outward from the outer edge of the steel ring beam, so that the bottom sealing concrete covers the ring beam and extends outward, forming an anchoring constraint on the superstructure, ensuring that the ring beam and the superstructure are not displaced by seawater impact.

[0037] Before pouring the bottom sealing concrete, steel casings for pile driving are pre-installed. The steel casings are precisely positioned according to the design location of the pile foundation so that subsequent pile foundation construction can directly use the steel casings for guidance and positioning, avoiding secondary measurement and setting out.

[0038] Step 3: Construction of the superstructure beam-column framework After the bottom sealing concrete reaches its design strength, the upper beam-column structural framework is installed on the bottom sealing concrete foundation. In this embodiment, the framework is designed as a two-layer structure: the vertical columns are made of Φ426×8 steel pipes, arranged at the designed spacing along the perimeter and interior of the foundation; the horizontal walers and horizontal beams are made of double-jointed 2H45a steel, forming a closed ring beam and longitudinal connecting beam between the columns; the horizontal bracing (i.e., the internal support of the cofferdam) is made of Φ630×10 steel pipes, set between the two layers of walers, forming a horizontal closed support system. All components are connected by welding, and full welding is required to ensure the strength of the welds, so that the columns, walers, and bracing form an integral load-bearing frame.

[0039] It should be noted that the cross-sectional selection of the aforementioned beam-column framework is not a conventional design for a single working condition, but rather a coupled design that simultaneously adapts to two stress modes: the slenderness ratio and moment of inertia of the columns must simultaneously meet the requirements for vertical compressive stability during the piling platform stage and vertical support during the cofferdam stage; the section modulus of the walers and braces must simultaneously meet the requirements for maintaining horizontal stability during the platform stage and resisting circumferential water pressure during the cofferdam stage. If designed only for platform loads, the waler section would be insufficient to resist the water pressure during the cofferdam stage; if designed only for cofferdam loads, the column stiffness might not meet the deformation control requirements under the concentrated load of the piling machine. Therefore, the cross-sectional and node design of this framework is the result of coordinated adaptation of two stress states, rather than a simple superposition.

[0040] Step 4: Piling Platform Operation A detachable panel is laid on the top layer of the beam-column structural framework to form a piling platform. In this embodiment, the panel system is laid with I32 I-beam crossbeams and I14 longitudinal beams, on which bridge deck panels are laid to form a platform surface that meets the operation requirements of the piling machine. The piling machine is positioned and guided by pre-embedded steel casings to carry out pile foundation construction. During this stage, the beam-column structural framework serves as the vertical load-bearing system of the piling platform. The columns directly bear the vertical loads of the piling machine and pile foundation construction, while the walers and braces maintain the platform's horizontal stability and ensure piling accuracy.

[0041] Step 5: Platform to Cofferdam After the pile foundation is completed, the top removable panels (horizontal beams, longitudinal beams, and bridge deck) are removed, leaving the beam-column structural framework. The steel cofferdam is then constructed using this framework. This embodiment uses a single-layer Larssen sheet pile cofferdam as an example: because the bottom is a hardened bottom-sealing concrete layer, the sheet piles cannot be driven in, and there are no traditional anchoring points at the bottom. During the sheet pile driving process, the sheet piles are tightly attached to the waler steel and firmly welded to the waler, forming a combined load-bearing section between the sheet pile side plates and the waler. The cofferdam system is stabilized only after the four sheet piles form a closed system. At this point, the beam-column structural framework transforms from the vertical load-bearing system of the pile driving platform into the internal support system of the steel cofferdam: the waler and bracing bear the horizontal loads of external seawater and soil pressure, forming a circumferential closed support; the columns maintain the vertical stability of the cofferdam and provide vertical constraints on the waler.

[0042] In the above transformation process, the welded connection between the waler and the sheet pile is a key node. This connection forms a continuous composite section between the waler and the sheet pile side plate, which together resist external water pressure. The moment of inertia of the section is significantly greater than that of the waler or the sheet pile working alone, resulting in uniform stress distribution. This avoids the installation gap and stress concentration problems that exist when conventional separate internal supports are connected through gusset plates.

[0043] Step Six: Construction and Demolition of the Internal Structure of the Cofferdam After the steel cofferdam is constructed, water is pumped out from within the cofferdam, and the foundation structure is constructed first. Once the foundation structure is completed, the second horizontal bracing is transferred to the foundation, utilizing the foundation to partially replace the original bracing's support function, and construction of the upper piers continues. After the piers are completed, the entire cofferdam system is dismantled, completing the substructure construction.

[0044] Technical explanation of the synergistic effect of the integrated structure In this embodiment, the technical features such as low-tide leveling, bottom-sealing concrete expansion anchoring, beam-column skeleton coupling design, detachable panels, waler welding composite sections, and phased bracing transformation form an inseparable systematic synergy in the hard rock tidal zone environment: The extended portion of the bottom-sealing concrete forms a solid interlocking structure with the flat surface of the reef, providing anti-overturning anchorage for the upper beam-column framework. Without this extended anchorage, the bottom of the framework is prone to slippage and instability under tidal currents and upper loads. The coupled design of the beam-column framework is suitable for both vertical and horizontal loads, ensuring the framework has load-bearing capacity in both the platform and cofferdam stages. Without this coupled design, it is impossible to safely achieve "one structure for two uses." The detachable panel design allows for the temporal separation of platform and cofferdam functions, ensuring that piling and cofferdam operations do not interfere with each other. If the panel is not detachable, the cofferdam side plates cannot be constructed tightly against the walers. The welded composite section of the walers and sheet piles improves the overall bending stiffness of the cofferdam, upgrading the walers from "internal support members" to "composite section flanges," significantly reducing the deformation of the cofferdam side plates. If conventional separate internal supports are used, the cofferdam side plates must independently resist water pressure, greatly increasing the difficulty of deformation control. The design of converting the bracing to the pier cap allows the same steel pipe to serve two functions throughout the entire cycle: supporting the cofferdam and supporting the pier cap formwork, thus avoiding material waste.

[0045] The aforementioned technical features are interdependent and progressive, working together to solve the specific technical problem of "integrated construction of piling platforms and steel cofferdams in hard rock tidal zones". The omission or substitution of any single feature will cause the overall technical solution to fail or significantly reduce its economic efficiency under hard rock tidal zone conditions, and therefore is not a conventional combination that would be easily conceived by those skilled in the art.

[0046] Example 2: Steel Cofferdam Construction The difference between this embodiment and Embodiment 1 lies in the type of steel cofferdam in step five. When the pier cap is large or the water depth is deep, a steel caisson cofferdam is used instead of Larssen sheet piles. The side plates of the steel caisson are also tightly attached to the waler steel and firmly welded to form a composite load-bearing section. The bottom of the steel caisson is attached to the top surface of the sealing concrete, using the sealing concrete as the bottom support of the steel caisson, eliminating the need for an additional sealing layer. The remaining steps are the same as in Embodiment 1 and will not be repeated here.

[0047] When using steel caisson cofferdams, the bottom of the caisson can be directly supported by the hardened bottom sealing concrete, eliminating the need for separate underwater bottom sealing concrete pouring required for traditional steel caisson cofferdams, thus further shortening the cofferdam construction cycle. At the same time, the overall stiffness of the steel caisson is greater than that of Larssen sheet piles, resulting in less lateral deformation under deep water and large span conditions, and a more significant combined section effect with the beam-column frame walers.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for integrated construction of a cofferdam for a platform with pile foundation in hard rock in shallow sea tidal zones, characterized in that, The method employs an integrated construction approach: leveling the reefs at low tide, pre-embedding steel ring beams and pouring bottom-sealing concrete to form an underwater rigid foundation, and then converting the upper beam-column framework to initially bear the vertical load of the piling platform before transforming it into a horizontal support within the steel cofferdam. This approach achieves the structural function conversion between the platform and the cofferdam by having the same set of beam-column load-bearing structures bear both the vertical piling load and the horizontal cofferdam load at different times. The method includes the following steps: S1: During low tide, mechanically level the uneven, hard rocky reefs on the seabed to form a construction base surface; S2: According to the design dimensions of the steel platform and cofferdam, a steel ring beam is pre-embedded on the leveled reef foundation, and bottom sealing concrete is poured to form an underwater rigid pier foundation; the bottom sealing concrete covers the steel ring beam and extends outward to form an anchoring constraint on the superstructure. S3: Install the upper beam-column structural frame on the bottom concrete foundation. The beam-column structural frame includes vertical columns, horizontal walers and horizontal braces. The components are connected by welding to form an overall load-bearing frame. S4: Lay a detachable panel on top of the beam-column structural frame to form a piling platform, and arrange a piling machine to carry out pile foundation work; at this time, the beam-column structural frame serves as the vertical load-bearing system of the piling platform, the columns bear the vertical load, and the walers and braces maintain the horizontal stability of the platform. S5: After the pile foundation work is completed, the top detachable panel is removed, and the beam-column structural skeleton is retained; a steel cofferdam is constructed on the outside of the beam-column structural skeleton, so that the side plates of the steel cofferdam are tightly attached to the walers and firmly welded to form a combined stress section; at this time, the beam-column structural skeleton is transformed into the internal support system of the steel cofferdam, the walers and the braces bear the horizontal water pressure, and the columns maintain the vertical stability of the cofferdam. S6: After the steel cofferdam is completed, the foundation structure is constructed inside the cofferdam. The horizontal bracing is then transferred to the foundation, and the upper piers are constructed. Finally, the entire cofferdam system is dismantled.

2. An integrated structure for a pile-foundation platform cofferdam in a shallow sea tidal zone with hard rock, characterized in that, include: The bottom sealing concrete foundation is poured on the hard rock reef after being leveled at low tide. A steel ring beam is pre-embedded inside. The bottom sealing concrete covers the steel ring beam and extends outward to form an anchoring constraint. The beam-column structural framework is set on the sealed concrete foundation and includes vertical columns, horizontal walers and horizontal braces. The components are welded together to form an overall load-bearing frame. A detachable panel is laid on top of the beam-column structural frame to form a piling platform; A steel cofferdam is installed on the outside of the beam-column structural frame. The side plates of the steel cofferdam are tightly attached to the walers and firmly welded to form a combined load-bearing section. The beam-column structural frame is transformed into the internal support system of the steel cofferdam after the detachable panels are removed.

3. The method or structure according to claim 1 or 2, characterized in that, In step S2, the thickness and elevation of the bottom sealing concrete are strictly controlled, and the bottom stone debris is cleaned up; the bottom sealing area is extended outward by a set distance along the outer edge of the steel ring beam to ensure that the steel ring beam is not displaced by seawater impact; and a pile driving steel casing is pre-embedded before pouring concrete to facilitate the positioning of subsequent pile foundation construction.

4. The method or structure according to claim 1 or 2, characterized in that, In step S3, the upper beam-column structure is a two-layer structure. The vertical columns are made of steel pipes, the horizontal walers are made of double H-beams, and the horizontal braces are made of steel pipes. All component connections are made by welding and must be fully welded to ensure the strength of the welds.

5. The method or structure according to claim 1 or 2, characterized in that, Steps S1-S2 utilize the low tide period to carry out underwater operations, completing mechanical leveling, pre-embedding of steel ring beams, and bottom sealing concrete pouring during the exposed reef period, forming an underwater rigid foundation during the tidal window.

6. The method or structure according to claim 1 or 2, characterized in that, In step S4, the detachable panel is laid on top of the beam-column structural frame to form a piling platform, which meets the stress requirements of the piling machine operation; in step S5, after the pile foundation operation is completed, the detachable panel is removed, and the same beam-column structural frame is transformed from a vertical load-bearing system to a horizontal resistance support system, realizing the structural function conversion between the platform and the cofferdam.

7. The method or structure according to claim 1 or 2, characterized in that, In step S5, the steel cofferdam adopts a steel caisson cofferdam or a Larssen sheet pile cofferdam; the side plates of the steel cofferdam are tightly attached to the walers and firmly welded, so that the walers and the side plates of the steel cofferdam form a combined section to jointly resist external water pressure, which is different from the conventional practice of independently arranging the internal support of the cofferdam.

8. The method or structure according to claim 1 or 2, characterized in that, In step S5, there are no anchoring points at the bottom of the steel cofferdam, and the welded connection between the side plates of the steel cofferdam and the walers forms a lateral stability constraint; the cofferdam system is only stable after the four sides of the steel cofferdam are formed as a whole.

9. The method or structure according to claim 1 or 2, characterized in that, In step S6, the foundation is constructed first inside the cofferdam. After the foundation structure is completed, the horizontal bracing is transferred to the foundation, and the upper piers are constructed. After the piers are completed, the entire cofferdam system is dismantled.

10. The method or structure according to claim 1 or 2, characterized in that, The integrated construction method combines the load-bearing structure of the piling platform with the load-bearing structure of the steel cofferdam into one, reducing construction investment and shortening the construction period by converting the same beam-column structural frame at different times.

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