A construction method of a steel hanging box variable steel cofferdam suitable for deep water soft soil layer conditions

Abstract

The application discloses a construction method of a steel hanging box variable steel cofferdam suitable for deep water soft soil layer conditions, and comprises the following steps: sinking a steel casing, and continuously assembling a formwork segment on the top along the outer periphery to form a bottom formwork which is surrounded by sides; sinking the bottom formwork to the bottom of the steel casing along the height direction; sinking a steel cofferdam wall body which is sleeved outside the bottom formwork at intervals and forms an annular pouring space together with the bottom formwork, then pouring underwater concrete at the bottom of the steel cofferdam wall body to form a bottom surrounding purlin; partially grading pumping in the steel cofferdam, and after each stage of pumping is completed, corresponding installation of the surrounding purlin and an inner support member is performed above the current water level, when pumping is performed to a set height below the top end of the steel pipe pile, a platform surrounding purlin and a steel platform are installed on the inner side of the steel cofferdam wall body; and the construction of each underwater foundation structure is completed respectively. The steel hanging box structure is optimized to a driven type steel cofferdam, and a water-remaining pressure reduction mode is adopted to reduce the design water head difference of the steel cofferdam, so that the applicability and construction efficiency of the cofferdam construction are improved, and the construction cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of cofferdam construction technology. More specifically, this invention relates to a construction method for a steel caisson-to-steel cofferdam suitable for deep water and soft soil conditions. Background Technology

[0002] Currently, due to the need for safety and stability in the construction environment, underwater foundations are often constructed using steel cofferdams. However, in the southeastern coastal areas, the geological conditions of the construction areas are mostly soft soil layers composed of silt and sand, with water depths reaching up to 20 meters. Furthermore, due to the influence of tides, the design and construction water level of the cofferdam is high. Under these construction conditions, several common steel cofferdam construction methods all have certain drawbacks: 1. Double-walled steel cofferdam: This type of cofferdam has high overall rigidity and is suitable for deep-water foundations. It can be assembled as a whole and then sunk, manufactured in the factory and floated in the water, or it can be assembled in sections on the construction platform without the need for additional templates. It has the smallest outward expansion size and lower requirements for bottom sealing thickness. However, the amount of steel used in the cofferdam is relatively large, the processing and manufacturing requirements are high, the amount of welding work is large, the sinking into the mud is difficult, and underwater cutting is required during dismantling, which affects the overall construction period. II. Cofferdam with Interlocking Steel Pipe Pile: This type of cofferdam has a stable structure, is simple and quick to manufacture, and can be installed simultaneously with pile foundation construction using lightweight hoisting equipment. It has advantages such as high material recycling rate, strong adaptability to soft soil layers, and short construction period. However, the water-stopping requirements at the interlocking joint of the steel pipe pile are high. After multiple uses, the interlocking joint is prone to deformation and leakage, resulting in low turnover efficiency. In addition, there is a large concentrated stress at the contact point between the steel pipe pile and the waler, which requires reinforcement treatment, increasing additional material costs. 3. Steel sheet pile cofferdam: This type of cofferdam structure is simple to manufacture and is well-suited for geological conditions with relatively hard soil layers. Small hoisting equipment can be used to complete the single-piece driving, making assembly highly flexible and construction relatively easy. However, the length of steel sheet piles is mostly fixed, with the maximum length of common specifications being 18m. When the design height of the cofferdam exceeds 18m, additional lengthening is required. In actual construction, there are problems such as high requirements for steel sheet pile driving, poor overall cofferdam structure, and easy leakage. In addition, commonly used structures such as U-shaped sheet piles have poor bending stiffness and are not suitable for the construction of foundations with water depths exceeding 15m.

[0003] To address the aforementioned issues, it is necessary to design a construction method for steel cofferdams that can be converted from steel caissons to steel cofferdams, suitable for deep water and soft soil conditions. This would improve the applicability of cofferdam construction under unfavorable conditions, while ensuring construction efficiency and quality, and controlling construction costs. Summary of the Invention

[0004] The purpose of this invention is to provide a construction method for steel cofferdams adapted to deep water and soft soil conditions. The method optimizes the steel cofferdam structure into an driven steel cofferdam and reduces the design head difference of the steel cofferdam by using water retention and pressure reduction, thereby reducing the bending strength requirements of the cofferdam wall. As a result, the number of walers is reduced while ensuring structural stability, which improves the applicability and efficiency of cofferdam construction and reduces construction costs.

[0005] To achieve these objectives and other advantages according to the present invention, a construction method for a steel caisson-to-steel cofferdam suitable for deep-water soft soil conditions is provided, comprising: S1. Sink multiple steel casings according to the designed pile positions, and continuously assemble template segments along the outer perimeter of the top to form a bottom template that surrounds the sides; S2. The bottom template is lowered along the height direction to the bottom of the steel casing and fixedly connected to it. The bottom end of the bottom template is buried in the underwater stratum. S3. Construct the steel cofferdam wall at the designed location, with it spaced outside the bottom formwork to form an annular pouring space. Then, pour a layer of underwater concrete at the bottom of the annular pouring space to form the bottom waler. S4. Dewater the interior of the steel cofferdam in stages. After each stage of dewatering is completed, install walers and internal support components above the current water level. When the water is pumped to a set height below the top of the steel pipe piles, install platform walers on the inner side of the steel cofferdam wall and build a steel platform based on them. S5. Install the formwork for the underwater foundation structures other than the pile foundations on the steel platform, and then pour concrete from bottom to top starting from the steel casing to complete the construction of each underwater foundation structure. S6. After removing the template and the steel platform, water is injected into the steel cofferdam in stages. After each stage of water injection is completed, the adjacent inner support above the current water level is removed. When the water levels inside and outside the steel cofferdam are equal, the steel cofferdam wall is pulled out.

[0006] Preferably, in the construction method for the steel cofferdam adapted to deep water and soft soil conditions, the template segments are correspondingly set one-to-one with the outer edge of the plurality of steel casings. Each template segment is connected to the corresponding steel casing by a clamp. The clamp is fitted onto the steel casing and slidably connected to it. The clamp is equipped with a locking device, which tightens the opening of the clamp in the locked state, so that the clamp is pressed inward and fixed on the steel casing.

[0007] Preferably, the construction method for the steel cofferdam adapted to deep water and soft soil conditions includes the following for any template segment: a vertical plate, which is vertically installed on the outside of the corresponding steel casing and fixedly connected to the clamp; a bottom plate, which is horizontally fixed to the side of the vertical plate away from the steel casing and together with it forms a T-shaped structure, the bottom plate dividing the vertical plate into an upper baffle and a lower insert plate; and a plurality of stiffening plates, which are spaced apart along the length of the bottom plate, any one of which is vertically installed between the bottom plate and the baffle and fixedly connected to it.

[0008] Preferably, in the construction method of the steel caisson-to-steel cofferdam suitable for deep water and soft soil conditions, the two stiffening plates at the ends of the bottom plate are respectively flush with the outer end face of the bottom plate, and two adjacent template segments are fixedly connected by a connecting segment. The connecting segment has the same structure as a single template segment and is not connected to the clamp. The stiffening plate at the end of the connecting segment is in contact with and fixedly connected to the stiffening plate at the end of the template segment.

[0009] Preferably, in the construction method for steel cofferdams adapted to deep water and soft soil conditions, a mounting plate is provided between the connecting segment and the template segment. The mounting plate is parallel to and attached to the baffles of the connecting segment and the template segment. A strip-shaped connecting hole is provided in the middle of the mounting plate along the length direction, and connecting bolts are provided at both ends of the mounting plate corresponding to the connecting segment and the template segment, respectively. Any connecting bolt is used to fix and lock the mounting plate and the baffle.

[0010] Preferably, the construction method for the steel cofferdam adapted to deep water and soft soil conditions includes a steel platform comprising multiple crossbeams spaced apart along the width of the cofferdam, each crossbeam being positioned along the length of the cofferdam and having both ends fixedly abutting against the inner wall of the platform waler; multiple longitudinal beams spaced apart on top of the crossbeams along the length of the cofferdam, each longitudinal beam being positioned along the width of the cofferdam and having both ends fixedly abutting against the inner wall of the platform waler; and multiple sets of corbels corresponding one-to-one with the multiple steel pipe piles, each set of corbels comprising two corbels fixedly mounted on both sides of the corresponding steel pipe pile, each corbel being fixedly supported at the bottom of one or more crossbeams on the same side.

[0011] Preferably, in the construction method of the steel cofferdam for deep water and soft soil conditions, the intersection of the longitudinal beam and each transverse beam is fixedly connected by a connecting node, and the two outermost transverse beams and two longitudinal beams respectively abut against the outer wall of a row of steel pipe piles on the same side.

[0012] Preferably, in the construction method of the steel cofferdam for deep water and soft soil conditions, in step S4, after the steel platform is erected, water is first injected into the steel cofferdam up to the bottom of the crossbeam before proceeding with the subsequent construction steps; in step S6, before the steel platform is dismantled, water is first pumped out of the steel cofferdam until the corbel is exposed above the water surface before proceeding with the subsequent construction steps.

[0013] Preferably, in the construction method of the steel cofferdam for deep water soft soil conditions, in step S5, before the template is installed, the interference between each internal support of the steel cofferdam and the underwater foundation structure to be constructed is assessed, and the internal support with interference is removed; after the underwater foundation structure is constructed to the design height, temporary support is reinstalled at the positions of the removed internal support, which is set horizontally and its two ends are fixedly abutted against the corresponding waler and underwater foundation structure respectively.

[0014] The present invention has at least the following beneficial effects: 1. This invention optimizes the steel caisson structure into an driven steel cofferdam, and at the same time adopts the water retention and pressure reduction method to reduce the design head difference of the steel cofferdam, thereby reducing the requirements for the bending strength and section bending modulus of the cofferdam wall. Thus, it can reduce the number of waler supports as much as possible while ensuring structural stability, thereby reducing the amount of steel used in the steel cofferdam. This is conducive to the efficient completion of underwater foundation construction, shortens the construction period, improves the applicability and construction efficiency of cofferdam construction in deep water and soft soil conditions, and reduces construction costs. 2. This invention employs a specific bottom template that can cooperate with the steel cofferdam wall to form an annular pouring space at the bottom of the steel cofferdam. After pouring underwater concrete, it forms an underwater concrete strip, isolating the seepage path between the steel cofferdam and the stratum. This helps maintain the water level within the cofferdam to preserve a low head difference and reduces the stress imbalance on both sides of the cofferdam wall. Simultaneously, it can also serve as the bottom waler of the steel cofferdam, reducing the span between the last waler and the anchoring point, further enhancing the cofferdam's stability. Furthermore, compared to the traditional single-layer pouring structure for bottom sealing concrete, this underwater concrete strip significantly reduces concrete usage while ensuring water isolation, resulting in better economic benefits and meeting green and environmentally friendly construction requirements. 3. This invention addresses construction environments where water remains within the cofferdam. A steel platform is erected at a suitable location in the middle of the steel cofferdam to form a dry construction platform. The platform is supported by main beams (horizontal beams and longitudinal beams) that engage with the platform walers. Simultaneously, it is supported by corbels on the steel casings within the cofferdam. This allows the cofferdam and its internal components to form a unified load-bearing structure during construction, effectively ensuring the stability of the steel platform. The main beams of the steel platform can also serve as a bracing element within the cofferdam, further enhancing the reliability, stability, and safety of the cofferdam construction structure.

[0015] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the construction structure of S1 in a construction method for a steel caisson-to-steel cofferdam suitable for deep water and soft soil conditions according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the construction structure of S2 in the above embodiment; Figure 3 This is a schematic diagram of the construction structure of S3 in the above embodiment; Figure 4 This is a schematic diagram of the construction structure of S4 in the above embodiment; Figure 5 This is a schematic diagram of the construction structure of S5 in the above embodiment; Figure 6 This is a schematic diagram of the construction structure of S6 in the above embodiment; Figure 7 This is a schematic diagram of the clamp structure described in the above embodiments; Figure 8 This is a schematic diagram of the side elevation structure of the template segment described in the above embodiments; Figure 9 This is a schematic diagram of the planar structure connecting the template segment and the clamp in the above embodiment; Figure 10 This is a schematic diagram of the planar structure connecting the template segment and the connecting segment in the above embodiments; Figure 11 This is a schematic diagram of the structure of the mounting plate described in the above embodiments; Figure 12 This is a schematic diagram of the planar structure of the bottom template described in the above embodiments; Figure 13 This is a schematic diagram of the planar structure of the bottom waler described in the above embodiments; Figure 14 This is a schematic diagram of the planar structure of the steel platform described in the above embodiments.

[0017] Explanation of reference numerals in the attached figures: 1. Steel casing; 2. Bottom formwork; 3. Underwater strata; 4. Steel cofferdam wall; 5. Bottom waler; 6. Guide pipe; 7. Internal support components; 8. Crossbeam; 9. Longitudinal beam; 10. Corbel; 11. Distribution beam; 12. Platform waler; 13. Pile foundation; 14. Pier cap; 15. Tower base; 16. Temporary support components; 17. Hoop; 18. Locking device; 19. Base plate; 20. Baffle plate; 21. Insert plate; 22. Stiffening plate; 23. Stiffening rib; 24. Formwork segment; 25. Connecting segment; 26. Anti-loosening bolt; 27. Adhesive plate; 28. Strip connecting hole; 29. ​​Connecting bolt; 30. Temporary operating platform. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0019] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified. In the description of this invention, the terms "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0020] like Figure 1-14 As shown, this invention provides a construction method for a steel cofferdam adapted to deep water and soft soil conditions, comprising: S1. Sink multiple steel casings according to the designed pile positions, and continuously assemble template segments along the outer perimeter of the top to form a bottom template that surrounds the sides; S2. The bottom template is lowered along the height direction to the bottom of the steel casing and fixedly connected to it. The bottom end of the bottom template is buried in the underwater stratum. S3. Construct the steel cofferdam wall at the designed location, with it spaced outside the bottom formwork to form an annular pouring space. Then, pour a layer of underwater concrete at the bottom of the annular pouring space to form the bottom waler. S4. Dewater the interior of the steel cofferdam in stages. After each stage of dewatering is completed, install walers and internal support components above the current water level. When the water is pumped to a set height below the top of the steel pipe piles, install platform walers on the inner side of the steel cofferdam wall and build a steel platform based on them. S5. Install the formwork for the underwater foundation structures other than the pile foundations on the steel platform, and then pour concrete from bottom to top starting from the steel casing to complete the construction of each underwater foundation structure. S6. After removing the template and the steel platform, water is injected into the steel cofferdam in stages. After each stage of water injection is completed, the adjacent inner support above the current water level is removed. When the water levels inside and outside the steel cofferdam are equal, the steel cofferdam wall is pulled out.

[0021] In the aforementioned technical solution, the steel cofferdam adopts a water-retention and pressure-reducing construction method. This means that a certain water level is maintained within the cofferdam throughout the entire construction process to reduce the head difference between the inside and outside of the cofferdam, thereby reducing the unbalanced stress on the steel cofferdam wall under deep-water construction conditions. Simultaneously, by pouring underwater concrete between the bottom formwork and the steel cofferdam wall to form a ring-shaped underwater concrete strip, the seepage path between the steel cofferdam and the strata is isolated, which helps maintain the water level within the cofferdam to preserve a low head difference. Furthermore, this underwater concrete strip also serves as the bottom waler of the steel cofferdam, reducing the span between the last waler and the anchoring point, and, combined with the steel pipe piles, enhances the overall stability of the cofferdam structure under soft soil conditions. In addition, the steel platform provides a dry working platform for the foundation structure construction and, in conjunction with the platform walers, forms a horizontal brace for the steel cofferdam, further strengthening the stability of the internal support structure of the cofferdam. The aforementioned construction structure and methods, combined, enable the steel cofferdam to maintain sufficient stability with fewer walers. Specifically, the number of walers and internal supports (pumping stages) in S4 can be controlled within a small range, with their exact quantity selected based on the cofferdam design and construction conditions. This reduces the amount of steel used in cofferdam construction by decreasing the number of walers and the amount of bottom sealing concrete by using underwater concrete strips, effectively reducing material costs. It also saves time and labor costs associated with corresponding procedures, facilitating efficient underwater foundation construction, shortening the construction period, and improving the applicability and efficiency of cofferdam construction in deep water and soft soil conditions.

[0022] Specifically, in S3, after the steel cofferdam is in place, the main seepage path is the cut surface between the steel pipe piles (steel cofferdam wall) and the underwater strata. Casting water-stopping concrete (underwater concrete) around the outermost steel casing and the inner wall of the steel cofferdam achieves both good water-stopping effect and cost-effectiveness. Therefore, a specific bottom formwork structure was designed, which is set around the outermost steel casing and can sink to the bottom along the height of the steel casing, forming a ring-shaped casting space with the steel cofferdam wall. Fine aggregate concrete can be used for the underwater concrete, which is poured using a tremie pipe inserted into the bottom of the ring-shaped casting space. During underwater concrete pouring, the spread must be controlled to minimize underwater flow and allow for rapid accumulation. The pouring thickness is controlled at approximately 50cm to isolate the seepage path, maintain the water level within the cofferdam as required by the design, maintain a low head difference, reduce the stress on the cofferdam wall, and prevent submersion of the construction platform (steel platform) within the cofferdam. In S4, the walers and internal supports adopt conventional structures. Each layer of walers forms a ring around the inner perimeter of the steel cofferdam wall. The walers can be fixed to the steel cofferdam wall by welding. The internal supports are strut-type members, horizontally positioned with both ends fixed to the inner sidewalls of the corresponding walers. During design and installation, the internal supports should avoid passing through the central area of ​​the cofferdam, i.e., be positioned close to the steel cofferdam wall to avoid interference with other underwater foundation structures (such as foundations). The steel platform is designed to provide a dry working platform within the steel cofferdam containing water. The height below the top of the steel pipe piles corresponds to the designed installation position of the steel platform; that is, the water level at this point is slightly lower than the bottom of the designed installation position of the steel platform. In S5, before the formwork is installed, a portion of the steel casing protruding above the water surface (within the cofferdam) is uniformly cut off. To further improve construction efficiency, a bolted assembly structure is adopted at the top of each steel casing. This involves dividing the steel casing along its height into fixed and reusable segments. The height of the fixed segment is equal to the design height of the pile foundation, and its bottom is submerged in the underwater strata. The reusable segment is detachably connected to the top of the fixed segment via a socket joint. This allows for quick and convenient removal of the top segment (reusable segment) of the steel casing before the formwork is installed in S5. This design also allows for the reuse of the reusable segment, resulting in a high turnover rate. The male and female ends of the socket joint are fixed to the bottom of the reusable segment and the top of the fixed segment, respectively. Multiple bolt holes are provided on both the male and female ends, spaced circumferentially along the steel casing. Quick assembly and disassembly of the fixed and reusable segments can be achieved by installing / removing the bolts at these bolt holes. In S6, the inner support members are removed layer by layer as the water level rises. That is, before the water level inside the cofferdam approaches the position of any inner support member, the inner support member is removed before water is injected.

[0023] In another technical solution, the construction method for the steel cofferdam with a caisson adapted to deep water and soft soil conditions is described, wherein the template segments are set one-to-one with the outer edge of the plurality of steel casings, and any template segment is connected to the corresponding steel casing by a clamp. The clamp is fitted on the steel casing and slidably connected to it. The clamp is provided with a locking device, which tightens the opening of the clamp in the locked state, so that the clamp is pressed inward and fixed on the steel casing.

[0024] Each template segment is fixedly welded to a clamp via stiffening ribs. The clamp is made by bending a rectangular steel plate, such as... Figure 7 As shown, after the steel plates are assembled, both ends are bent outwards to form parallel connecting surfaces. Corresponding openings are made on each connecting surface. The locking device can be a bolt, which passes through the openings on the connecting surfaces and has adjusting nuts at both ends, forming a pull-pull structure. When the adjusting nuts are tightened inwards, the opening of the clamp is closed, thus pressing and fixing the clamp onto the steel casing. The adjustable length of the locking device is set to 15cm, and it has a nut anti-loosening function, allowing for free adjustment of tightness. When the bottom template is lowered, the nuts are loosened so that the clamp can drive the bottom template to sink synchronously along the height direction of the steel casing. After the bottom template is in place, the nuts are tightened to achieve relative fixation between the clamp and the steel casing.

[0025] In another technical solution, the construction method for the steel cofferdam adapted to deep water and soft soil conditions includes a formwork segment comprising a vertical plate, which is vertically installed on the outside of the corresponding steel casing and fixedly connected to the clamp; a bottom plate, which is horizontally fixed to the side of the vertical plate away from the steel casing and together with it forms a T-shaped structure, the bottom plate dividing the vertical plate into an upper baffle and a lower insert plate; and a plurality of stiffening plates, which are spaced apart along the length of the bottom plate, any one of which is vertically installed between the bottom plate and the baffle and fixedly connected to it.

[0026] Specifically, such as Figure 8 As shown, the cross-section of the template segment is T-shaped. When the bottom template sinks to the bottom of the steel casing, the bottom plate is used to fit and support the underwater stratum surface to limit the bottom template from sinking further. The baffle is located above the underwater stratum surface and is used to form a pouring space together with the steel cofferdam wall to constrain the underwater concrete. The insert plate is inserted into the underwater stratum to fix the template segment. The dimensions of a single template segment are 150×60cm (length×width), the baffle height is 60cm, the insert plate height is 50cm, and the thickness of the insert plate, bottom plate, baffle, and clamp steel plate is 1cm. The stiffening plate is a right-angled trapezoidal structure, with its bottom edge welded to the bottom plate and its right-angled side welded to the baffle. In addition to ensuring the stability of the bottom template itself, it also helps to strengthen the structural strength of the underwater concrete layer (bottom waler).

[0027] In another technical solution, the construction method of the steel caisson-to-steel cofferdam suitable for deep water and soft soil conditions is described, wherein two stiffening plates located at the ends of the bottom plate are respectively flush with the outer end face of the bottom plate, and two adjacent template segments are fixedly connected by a connecting segment. The connecting segment has the same structure as a single template segment and is not connected to the clamp. The stiffening plate located at the end of the connecting segment abuts against the stiffening plate located at the end of the template segment and is fixedly connected by anti-loosening bolts.

[0028] Among them, such as Figure 12 As shown, the bottom template is a rectangular structure, with each template segment at the four corners adopting an L-shaped structure. Both sides (segments) of the L-shape can be connected to clamps on the same steel pipe pile via stiffening ribs. Other template segments can adopt a conventional straight-line structure. The connecting template is oriented in the same direction as the corresponding two template segments. After two adjacent stiffening plates at the ends of the connecting and template segments are fitted together, they can be fixedly connected by anti-loosening bolts passing through the two stiffening plates. The bolt length is 15cm. Similar to the locking device on the clamps, the tightening degree of these anti-loosening bolts is adjustable. They remain loose when the bottom template is lowered and tighten after the bottom template is in place, ensuring that the template segments are connected to form a stable bottom template structure.

[0029] In another technical solution, the construction method for steel cofferdams adapted to deep water and soft soil conditions includes a mounting plate between the connecting segment and the template segment. The mounting plate is parallel to and attached to the baffles of the connecting segment and the template segment. The mounting plate has a strip-shaped connecting hole in the middle along the length direction, and connecting bolts are respectively provided at both ends of the mounting plate and the template segment. Any connecting bolt is used to fix and lock the mounting plate and the baffle.

[0030] The connecting bolts are inserted into the baffles of the connecting segment or template segment through the strip-shaped connecting holes on the plate and tightened on the plate surface for fixation. This, in conjunction with the anti-loosening bolts at the stiffening plate, achieves a stable connection between the connecting segment and the template segment, improving the overall stability of the bottom template structure. The connecting bolts can be anti-loosening bolts with a length of 4cm.

[0031] In another technical solution, the construction method for the steel cofferdam adapted to deep water soft soil conditions includes a steel platform comprising multiple crossbeams spaced apart along the width of the steel cofferdam, each crossbeam being positioned along the length of the steel cofferdam and having both ends fixedly abutting against the inner wall of the platform waler; multiple longitudinal beams spaced apart on top of the multiple crossbeams along the length of the steel cofferdam, each longitudinal beam being positioned along the width of the steel cofferdam and having both ends fixedly abutting against the inner wall of the platform waler; and multiple sets of corbels corresponding one-to-one with the multiple steel pipe piles, each set of corbels comprising two corbels fixedly mounted on both sides of the corresponding steel pipe pile, each corbel being fixedly supported at the bottom of one or more crossbeams on the same side.

[0032] In the above technical solution, the steel platform provides a dry working platform within the cofferdam while simultaneously using its main beams (horizontal and vertical beams) to act as an internal support for the cofferdam, further reducing the number of walers and internal support components required above the steel platform and improving the space utilization above the platform. Specifically, two corbels in the same group are spaced apart along the width of the steel cofferdam and located at the radial ends of the steel casing (i.e., opposite each other on both sides of the steel casing). Any corbel is positioned along the width of the steel cofferdam and supports the bottom of the corresponding horizontal beam. Multiple distribution beams are also provided at the top of the longitudinal beams, spaced apart along the width of the steel cofferdam, with any horizontal beam positioned along the length of the steel cofferdam. These beams support the formwork for underwater foundation structures other than pile foundations, helping to optimize the stress structure, prevent steel platform deformation, and ensure construction stability and safety.

[0033] In another technical solution, the construction method of the steel caisson-cofferdam suitable for deep water and soft soil conditions is described in which the intersections of the longitudinal beams and each of the transverse beams and each of the distribution beams are fixedly connected by connecting nodes, and the two outermost transverse beams and two longitudinal beams respectively abut against the outer wall of a row of steel pipe piles on the same side.

[0034] Specifically, connection nodes are set at the intersection of any longitudinal beam with each transverse beam and each distribution beam. These nodes can be in the form of node plates. The node plates at the bottom of the longitudinal beam correspond to the node plates on each transverse beam, and the node plates at the top of the longitudinal beam correspond to the node plates on each distribution beam. By welding the corresponding sets of node plates firmly, a stable steel platform structure can be formed. This ensures the stability and safety of the main beam as a brace (internal support), further enhancing the overall (connection) stability and the stress (force transmission to steel pipe piles) stability.

[0035] In another technical solution, the construction method for the steel cofferdam adapted to deep water and soft soil conditions includes the following steps: In step S4, after the steel platform is erected, water is first injected into the steel cofferdam up to the bottom of the crossbeam before proceeding with subsequent construction steps, in order to minimize the water pressure difference on both sides of the steel cofferdam wall during construction and avoid affecting the stability of the cofferdam support; In step S6, before the steel platform is dismantled, water is first pumped out of the steel cofferdam until the corbel is exposed above the water surface before proceeding with subsequent construction steps, so as not to affect the smooth and efficient progress of the dismantling construction.

[0036] In another technical solution, the construction method for the steel cofferdam adapted to deep-water soft soil conditions, in step S5, involves assessing the interference between the internal supports of the steel cofferdam and the underwater foundation structure to be constructed before the template installation, and removing any interfering internal supports. After the underwater foundation structure is constructed to the designed height, temporary supports are reinstalled at the locations of the removed internal supports. These supports are horizontally positioned and their ends are fixedly abutted against the corresponding walers and underwater foundation structure, respectively. This ensures the stability of the internal supports of the steel cofferdam during subsequent construction.

[0037] In the above technical solution, each inner support component is detachably connected to the corresponding waler via a support, which is fixed to the waler to facilitate repeated and rapid assembly and disassembly of the inner support components of each layer. The end of the temporary support component is provided with a joint that is the same as that of the original inner support component and matches the support, so that the temporary support can be quickly installed through the support at the original position when installing the temporary support component.

[0038] The construction method of the steel caisson-cofferdam applicable to deep water soft soil conditions is described using a specific underwater foundation construction project as an example.

[0039] In this embodiment, the structure and dimensions of each component (waler, internal support, bottom formwork, steel platform, etc.) required for construction are first determined based on the cofferdam design structure. After being custom-made in the factory according to the design dimensions, they are transported to the construction site. The construction method for the steel caisson-to-steel cofferdam suitable for deep water and soft soil conditions is as follows: S1. Sink the steel casing according to the designed pile position, and then install a temporary operating platform with the top of the steel casing as the supporting foundation. Assemble the template segments on the temporary operating platform and connect them to form a complete bottom template. S2. Adjust (loosen) the anti-loosening bolts and locking devices on the clamps between each template section so that the bottom template can be smoothly lowered to the bottom of the riverbed along the height direction of the steel casing. Then, divers go into the water to tighten the anti-loosening bolts and locking devices to fix the bottom template to the bottom of the steel casing. S3. Construct the steel cofferdam wall at the designed location, with it spaced outside the bottom formwork to form an annular pouring space. Then, use the tremie pipe method to pour a layer of underwater concrete at the bottom of the annular pouring space to form the bottom waler. S4. Pump water inside the steel cofferdam to 100cm below the designed installation position of the first waler, and install the first waler and its corresponding internal support components; continue pumping water to 100cm below the designed installation position of the second waler, and install the second waler and its corresponding internal support components; continue pumping water to 50cm below the designed installation position of the steel platform corbel, and install the platform waler and steel platform (corbel, crossbeam, longitudinal beam, distribution beam), wherein the crossbeam and longitudinal beam are respectively set to abut against the platform waler; S5. After the steel platform passes inspection, fill the cofferdam with water until the water level is close to the bottom of the crossbeams of the steel platform. Then, remove the inner support components corresponding to the second layer of walers and the turnover sections at the top of each steel casing. Next, install the formwork for the underwater foundation structure other than the pile foundation on the steel platform. Pour concrete into each steel pipe pile to complete the pile foundation construction. Pour concrete into the formwork to complete the construction of the pier cap and tower base in sequence. After the tower base is constructed to protrude 4-5m above the water surface outside the cofferdam, install temporary support components at the second layer of walers. The two ends of the support rods are respectively pressed against the pier cap and the steel cofferdam wall. Continue to complete the construction of all underwater foundation structures. S6. Remove the template, then pump water from inside the cofferdam outwards until the corbel is exposed above the water surface, and then remove the steel platform; inject water into the cofferdam to 100cm below the temporary support, and then remove the temporary support; continue to inject water into the cofferdam to 100cm below the first waler, and then remove the internal support corresponding to the first waler; continue to inject water into the cofferdam until the water levels inside and outside the steel cofferdam are equal, and then pull out the steel cofferdam wall.

[0040] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A construction method for a steel caisson-to-steel cofferdam suitable for deep water and soft soil conditions, characterized in that, include: S1. Sink multiple steel casings according to the designed pile positions, and continuously assemble template segments along the outer perimeter of the top to form a bottom template that surrounds the sides; S2. The bottom template is lowered along the height direction to the bottom of the steel casing and fixedly connected to it. The bottom end of the bottom template is buried in the underwater stratum. S3. Construct the steel cofferdam wall at the designed location, with it spaced outside the bottom formwork to form an annular pouring space. Then, pour a layer of underwater concrete at the bottom of the annular pouring space to form the bottom waler. S4. Dewater the interior of the steel cofferdam in stages. After each stage of dewatering is completed, install walers and internal support components above the current water level. When the water is pumped to a set height below the top of the steel pipe piles, install platform walers on the inner side of the steel cofferdam wall and build a steel platform based on them. S5. Install the formwork for the underwater foundation structures other than the pile foundations on the steel platform, and then pour concrete from bottom to top starting from the steel casing to complete the construction of each underwater foundation structure. S6. After removing the template and the steel platform, water is injected into the steel cofferdam in stages. After each stage of water injection is completed, the adjacent inner support above the current water level is removed. When the water levels inside and outside the steel cofferdam are equal, the steel cofferdam wall is pulled out.

2. The construction method for steel cofferdams adapted to deep water and soft soil conditions as described in claim 1, characterized in that, The template segment is set one-to-one with the outer edge of the steel casing in the plurality of steel casings. Each template segment is connected to the corresponding steel casing by a clamp. The clamp is sleeved on the steel casing and slidably connected to it. The clamp is provided with a locking device, which tightens the opening of the clamp in the locked state, so that the clamp is pressed inward and fixed on the steel casing.

3. The construction method for steel cofferdams adapted to deep-water soft soil conditions as described in claim 2, characterized in that, Each template segment includes a vertical plate, which is vertically installed on the outside of the corresponding steel casing and fixedly connected to the clamp; a bottom plate, which is horizontally fixed to the side of the vertical plate away from the steel casing and together with it forms a T-shaped structure, the bottom plate dividing the vertical plate into an upper baffle and a lower insert plate; and multiple stiffening plates, which are spaced apart along the length of the bottom plate, any one of which is vertically installed between the bottom plate and the baffle and fixedly connected to it.

4. The construction method for steel cofferdams adapted to deep water and soft soil conditions as described in claim 3, characterized in that, Two stiffening plates located at the ends of the base plate are flush with the outer end face of the base plate. Two adjacent template segments are fixedly connected by a connecting segment. The connecting segment has the same structure as a single template segment and is not connected to the clamp. The stiffening plate at the end of the connecting segment abuts against and is fixedly connected to the stiffening plate at the end of the template segment.

5. The construction method for steel cofferdams adapted to deep-water soft soil conditions as described in claim 4, characterized in that, A mounting plate is also provided between the connecting segment and the template segment. The mounting plate is parallel to and attached to the baffle of the connecting segment and the template segment. A strip-shaped connecting hole is provided in the middle of the mounting plate along the length direction. Connecting bolts are provided at both ends of the mounting plate, corresponding to the connecting segment and the template segment, respectively. Any connecting bolt is used to fix and lock the mounting plate and the baffle.

6. The construction method for steel cofferdams adapted to deep-water soft soil conditions as described in claim 1, characterized in that, The steel platform includes multiple crossbeams spaced apart along the width of the steel cofferdam, each crossbeam being positioned along the length of the steel cofferdam and having both ends fixedly abutting against the inner wall of the platform waler; multiple longitudinal beams spaced apart on top of the multiple crossbeams along the length of the steel cofferdam, each longitudinal beam being positioned along the width of the steel cofferdam and having both ends fixedly abutting against the inner wall of the platform waler; and multiple sets of corbels corresponding one-to-one with the multiple steel pipe piles, each set of corbels including two corbels fixedly mounted on both sides of the corresponding steel pipe pile, each corbel being fixedly supported at the bottom of one or more crossbeams on the same side.

7. The construction method for steel cofferdams adapted to deep-water soft soil conditions as described in claim 6, characterized in that, The intersections of the longitudinal beams and the transverse beams are fixedly connected by connecting nodes. The two outermost transverse beams and the two outermost longitudinal beams abut against the outer wall of a row of steel pipe piles on the same side.

8. The construction method for steel cofferdams adapted to deep-water soft soil conditions as described in claim 6, characterized in that, In S4, after the steel platform is erected, water is first injected into the steel cofferdam until the bottom of the crossbeam before proceeding with the subsequent construction steps; in S6, before the steel platform is dismantled, water is first pumped out of the steel cofferdam until the corbel is exposed above the water surface before proceeding with the subsequent construction steps.

9. The construction method for steel cofferdams adapted to deep-water soft soil conditions as described in claim 1, characterized in that, In S5, before the template is installed, the interference between the inner support components of the steel cofferdam and the underwater foundation structure to be constructed is assessed, and the inner support components that cause interference are removed. After the underwater foundation structure is constructed to the design height, temporary support components are reinstalled at the locations of the removed inner support components. These temporary support components are set horizontally and their two ends are fixedly connected to the corresponding walers and underwater foundation structure, respectively.

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