A construction method of a steel hanging box cofferdam of a high-pile pile cap under a tidal environment and a steel hanging box

Abstract

This invention relates to the field of steel caisson cofferdam construction technology. It provides a construction method and steel caisson for high-pile foundation steel caisson cofferdams in tidal environments. The method involves prefabricating the bottom and side plates in sections and completing trial assembly; hoisting the bottom plate with pile foundation brackets and assembling the side plates and supports to complete cofferdam assembly; building a lowering system with double-nut lifting rods and jacks; lifting the cofferdam under the coordinated force of the double nuts; removing the brackets and lowering it to the design elevation; welding and fixing the tension rods to complete the force system conversion; sealing the gaps in the bottom plate of the casing and installing shear keys; and pouring the bottom sealing concrete followed by layered pouring of the foundation. This method achieves full control over the construction process of high-pile foundation steel caissons in tidal areas, reduces underwater operations, simplifies construction procedures, lowers the risk of cofferdam overturning and floating in strong tides, ensures structural water-stopping effect and installation accuracy, effectively shortens the construction period, and balances construction safety, quality, efficiency, and cost control.

Description

Technical Field

[0001] This invention relates to the field of steel cofferdam construction technology, and more specifically, to a construction method and steel cofferdam for high-pile foundation steel cofferdams under tidal conditions. Background Technology

[0002] As my country's transportation infrastructure construction continues to extend into deep-sea areas, the scale and technical difficulty of major marine engineering projects such as cross-sea super bridges are constantly increasing. As the core load-bearing component of cross-sea bridge structures, the construction quality of high-pile piers directly determines the overall structural safety and long-term service durability of the bridge. In the complex hydrological environment of tidal sea areas, steel cofferdams, as the core temporary water-retaining structure and formwork support system for deep-water high-pile pier construction, have become the mainstream technical solution for dry-operation construction of piers due to their advantages such as high structural rigidity, reliable waterproofing performance, and strong construction controllability. The optimization and innovation of their construction technology plays a crucial role in ensuring the construction safety of marine bridge projects and controlling the construction period and cost.

[0003] However, existing construction technology for high-pile steel cofferdams in tidal waters still faces many insurmountable bottlenecks. The strong tidal currents, deep water, high water pressure, and complex weather conditions in the marine environment significantly affect the construction process of the steel cofferdam due to seawater pressure, buoyancy, and tidal level fluctuations, making it prone to major safety hazards such as cofferdam overturning and overall floating. Traditional construction techniques rely on divers to complete key operations such as underwater shear key welding, sealing the gap between the casing and the bottom plate, and pouring bottom sealing concrete. This not only poses high safety risks for underwater operations but also makes it difficult to accurately control construction quality, easily leading to quality problems such as cofferdam leakage and bottom sealing structure failure. Meanwhile, the existing process requires the installation of a large number of tension and compression rod components to complete multiple stress system conversions, which is cumbersome, consumes a lot of steel, and has insufficient assembly and positioning accuracy of the cofferdam bottom plate and side plate. The joint sealing effect is difficult to guarantee in the long term. Problems such as structural tilting and asynchronous deformation are prone to occur during the cofferdam lowering process. In addition, the insufficient utilization of the tidal window period makes it impossible to effectively convert underwater operations to above-water dry operations, making it difficult to effectively compress the construction period. Furthermore, the construction of large-volume concrete foundations in the high-salt corrosion environment of the sea is prone to temperature cracks, which makes it difficult to meet the high durability design requirements of marine engineering structures. This seriously restricts the improvement of safety, quality and efficiency in the construction of high-pile foundations in tidal sea areas. Summary of the Invention

[0004] The purpose of this invention is to provide a construction method and steel caisson cofferdam for high pile foundations in tidal environments, which solves the problems of numerous underwater operations, complicated procedures, high risks, and difficulty in controlling the construction period and quality of high pile foundation steel caissons in tidal sea areas.

[0005] This invention is achieved through the following technical solution: a construction method for a high-pile cap steel cofferdam under tidal conditions, comprising the following steps: Step S1: Prefabricate the segmented base plate and side plates and perform trial assembly; Step S2: Horizontally insert the corbel into the installation hole opened in the pile foundation, and hoist the bottom plate into the corresponding corbel in sections. Then assemble the side plate onto the bottom plate, and then install the supporting structure outside the side plate to complete the steel caisson assembly. Step S3: Install anchor blocks on the base plate, install a spreader beam, support foot and jack at the top of the pile foundation, and connect the lifting rod to the anchor block after passing through the jack, support foot, spreader beam and tension rod in sequence. The lifting rod is threaded with a first nut that abuts against the jack and a second nut that is arranged between the support foot and the spreader beam. Step S4: Use jacks to lift the steel caisson so that the first nut bears the weight of the steel caisson. Then, tighten the second nut upwards along the lifting rod to the high position. Lower the jacks back down so that the first and second nuts support the steel caisson together. Remove the brackets and lower the steel caisson to the design elevation in a cyclical manner. Step S5: Weld the upper end of the tension rod to the pile foundation and fix the lower end of the tension rod to the anchor block. Then remove the hanger, jack and spreader beam in sequence. Step S6: Seal the gap between the pile foundation and the reserved hole in the bottom plate, pump out the water in the steel caisson, and connect shear keys between the pile foundation and the bottom plate in the circumferential direction; Step S7: After the bottom sealing concrete is poured, the foundation is poured in layers.

[0006] Furthermore, in step S2, a wet joint is poured between adjacent base plates, the gap between the bottom of the side plate and the base plate is sealed with grout, water-stop rubber pads are used to fasten the adjacent side plates with bolts, and rubber asphalt sealant is applied to the inside of the side plate joint to form a secondary waterproof layer.

[0007] Furthermore, in step S2, the base plate is hoisted symmetrically from the middle to both sides.

[0008] Furthermore, in step S2, before assembling the side panels, the vertical ribs are aligned with the pre-embedded parts on the outer periphery of the base plate for installation.

[0009] Furthermore, in step S4, the process of cyclically lowering the steel caisson includes the following steps: Step S41: Lift the jack so that the second nut is suspended and not under force, and then tighten the second nut to continue to the high position; Step S42: The jack is lowered back, allowing the steel caisson to be lowered smoothly for a distance until the second nut is stressed again; Step S43: Tighten the first nut upwards to the preset height, and lift the jack to make the first nut bear force; Step S44: Repeat steps S41 to S43 until the steel caisson is lowered to the design elevation.

[0010] Furthermore, in step S5, after the steel caisson is lowered into place, half of the shear keys are uniformly installed circumferentially between the base plate and the pile foundation during the low water level window of the tide.

[0011] Furthermore, in step S7, when sealing the gap, first use sandbags mixed with cement to seal the bottom of the gap at the lower step, and then pour micro-expansion sealing concrete at the upper step of the gap at low tide.

[0012] Furthermore, in step S6, when the foundation is poured in layers, cooling water pipes are laid out before each layer of concrete is poured.

[0013] A steel cofferdam for high pile cap steel cofferdam construction method under tidal conditions, as described above, includes a bottom plate and side plates. The bottom plate has a number of pre-embedded bolts evenly distributed around the reserved holes for connecting tension rods and shear keys.

[0014] Furthermore, the corbels are made of double I-beams arranged side by side, with steel wire ropes connected to the ends of the corbels, and the corbels on each pile foundation are on the same horizontal plane.

[0015] The present invention has at least the following advantages and beneficial effects: (1) The entire process of construction of high pile foundation steel caisson in tidal sea areas is controlled by the following methods: prefabricating the bottom plate and side plate in sections and completing trial assembly; hoisting the bottom plate and assembling the side plate and support with the pile foundation bracket to complete the cofferdam assembly; building the lowering system with double nut lifting rods and jacks; lifting the cofferdam with double nuts and pulling out the brackets to lower it to the design elevation; welding and fixing the tension rods to complete the force system conversion; sealing the gap of the bottom plate of the casing and installing shear keys; pouring the bottom sealing concrete and then pouring the foundation in layers. This method reduces underwater operations, simplifies construction procedures, reduces the risk of cofferdam overturning and floating in strong tides, ensures the water-stopping effect and installation accuracy of the structure, effectively compresses the construction period, and takes into account construction safety, quality, efficiency and cost control.

[0016] (2) The cyclical lowering process involves lifting the second nut with a jack so that it is suspended and no longer under force, then tightening it to a high position, lowering the cofferdam smoothly for a distance until the second nut is under force again, and tightening the first nut to a preset height before lifting the jack again to force the first nut. This process adopts a graded synchronous lowering mode with alternating forces on the double nuts, which enables the steel caisson to be lowered continuously and smoothly over a long distance without the need to frequently change the anchor points of the lifting equipment, greatly improving the lowering efficiency. At the same time, it ensures that the force on each lifting point is uniform and the lowering is synchronous, avoiding the cofferdam tilting and uneven loading and structural deformation, eliminating the risk of falling and overturning, and ensuring the construction safety and installation accuracy of the cofferdam lowering. Attached Figure Description

[0017] Figure 1 This invention provides a process flow diagram for the construction method of a high-pile foundation steel caisson cofferdam under tidal conditions.

[0018] Figure 2 This is a plan view of the bottom plate of a steel caisson provided by the present invention.

[0019] Figure 3 This is a plan view of a side plate in a steel caisson provided by the present invention.

[0020] Figure 4 This is a schematic diagram of the installation of the bracket in a steel caisson provided by the present invention.

[0021] Figure 5 This is a side view of a bracket in a steel caisson provided by the present invention.

[0022] Figure 6 This is a schematic diagram of the installation of the spreader beam in a steel caisson provided by the present invention.

[0023] Figure 7 This is a plan view of a spreader beam in a steel caisson provided by the present invention.

[0024] Figure 8 This is a schematic diagram of the installation of a jack in a steel jacking box, provided by the present invention.

[0025] Figure 9 This invention provides a plan view of the anchor points in a steel caisson.

[0026] Figure 10 This is a schematic diagram of the installation of a tension / compression rod in a steel caisson provided by the present invention.

[0027] Figure 11 This is a schematic diagram of the installation of a shear key in a steel caisson provided by the present invention.

[0028] Attached reference numerals: 1-Pile foundation, 11-Corner, 2-Base plate, 20-Reserved hole, 21-Embedded bolt, 3-Side plate, 4-Spreader beam, 41-Support foot, 42-Jack, 43-Hanging rod, 44-First nut, 45-Second nut, 5-Tension / compression rod, 6-Shear key. Detailed Implementation

[0029] The specific implementation method is described below with reference to the accompanying drawings.

[0030] Example like Figures 1 to 11 As shown in this embodiment, a construction method for a high-pile cap steel cofferdam under tidal conditions is mainly disclosed, including the following steps: Step S1: Prefabricate the segmented base plate 2 and side plates 3 and perform trial assembly; Step S2: Horizontally insert the corbel 11 into the installation hole opened in the pile foundation 1, and hoist the bottom plate 2 into the corresponding corbel 11 in sections. Then assemble the side plate 3 onto the bottom plate 2, and then install the supporting structure outside the side plate 3 to complete the steel caisson assembly. Step S3: Install anchor blocks on the base plate 2, install a spreader beam 4, a support leg 41 and a jack 42 at the top of the pile foundation 1, and connect the lifting rod 43 to the anchor blocks after passing through the jack 42, the support leg 41, the spreader beam 4 and the tension rod 5 in sequence. The lifting rod 43 is threaded with a first nut 44 that abuts against the jack 42 and a second nut 45 that is arranged between the support leg 41 and the spreader beam 4. Step S4: Jack 42 lifts the steel caisson, so that the first nut 44 bears the weight of the steel caisson. Then, the second nut 45 is screwed up along the lifting rod 43 to the high position. Jack 42 falls back down, so that the first nut 44 and the second nut 45 support the steel caisson together. The bracket 11 is pulled out, and the steel caisson is lowered to the design elevation in a cycle. Step S5: Weld the upper end of the tension rod 5 to the pile foundation 1, and fix the lower end of the tension rod 5 to the anchor block. Then remove the hanger 43, jack 42 and spreader beam 4 in sequence. Step S6: Seal the gap between the reserved hole 20 between the pile foundation 1 and the base plate 2, pump out the water in the steel caisson, and connect the shear key 6 between the pile foundation 1 and the base plate 2 in the circumferential direction; Step S7: After the bottom sealing concrete is poured, the foundation is poured in layers.

[0031] Specifically, before construction, a complete model of the steel cofferdam was created using Midas, dividing it into eight construction scenarios: assembly, lowering, force system conversion, bottom sealing, foundation pouring, and cofferdam dismantling. The most unfavorable scenario for each component was selected to complete strength and stiffness calculations, determine support parameters and component selection, and anticipate structural risks in advance, ensuring safety throughout the entire construction process. To shorten the overall construction period, prefabrication and pile foundation 1 construction were carried out simultaneously. The bottom slab 2 adopted a centralized prefabrication model, manufactured in blocks according to the number of pile foundation 1 units. Each prefabricated slab was 50cm thick, with precise pre-reserved holes for steel casing, 43 holes for precision-rolled threaded steel rods, connecting pipes, and various embedded parts, controlling installation accuracy from the source. The side slabs 3 were factory-modularly processed, with each panel 8mm thick, equipped with welded steel horizontal and vertical ribs. After processing, an overall trial assembly was conducted to eliminate on-site splicing errors and ensure structural integrity. On-site assembly utilizes the steel casing of pile foundation 1 as a temporary support carrier, eliminating the need for additional temporary platforms and reducing the workload of temporary measures. The lowering process employs a synchronous control system, with a computer main control base station centrally controlling multiple hydraulic pump stations and through-hole jacks 42. The system monitors the lowering speed, structural elevation, horizontal displacement, and deflection in real time throughout the process, ensuring a synchronous and stable lowering process and preventing structural tilting and deformation. The entire construction process leverages tidal water level changes, utilizing low tide windows to complete shear key 6 welding, gap sealing, and bottom sealing operations. This transforms traditional underwater operations into dry operations above water, significantly reducing the safety risks of drowning and underwater work. It also simplifies the installation of tension and compression rods 5 and the conversion of the force system, achieving comprehensive control over the construction period, safety, quality, and cost.

[0032] Furthermore, in specific implementation, in step S2 provided in the embodiment of the present invention, a wet joint is poured between adjacent base plates 2, the gap between the bottom of the side plate 3 and the base plate 2 is sealed tightly with grout, and adjacent side plates 3 are fastened with water-stop rubber pads and bolts. A secondary waterproof layer is formed by applying rubber asphalt sealant to the inner side of the joint of the side plates 3. Specifically, after the precast blocks of adjacent base plates 2 are hoisted into place, the embedded steel bars at the wet joint are adjusted, the laitance and debris on the concrete contact surface are cleaned, and micro-expansion concrete is poured after the formwork is installed, so that the segmented base plates 2 form a whole under load, ensuring the structural rigidity and seepage prevention performance of the base plates 2. The gap between the bottom of side plate 3 and the contact surface of the base plate 2 is sealed with high-strength grout in one go to prevent seepage channels at the bottom. When adjacent side plates 3 are spliced, a water-stop rubber pad is inserted at the joint. The first water-stop defense line is formed by tightening and pressing with high-strength bolts. Then, a layer of rubber asphalt sealant is evenly applied along the inner side of the joint to form a second redundant water-stop defense line. This double protection of the structure's water-stopping effect completely solves the problem of cofferdam joint leakage in marine environments and provides a stable and reliable dry working environment for the construction of the pier cap.

[0033] Furthermore, in specific implementation, in step S2 provided in this embodiment of the invention, the base plate 2 is hoisted symmetrically from the center outwards. Specifically, the hoisting of the base plate 2 follows the principle of symmetrical installation from the center to the periphery, prioritizing the hoisting of the precast blocks in the central area of ​​the platform, and then symmetrically hoisting the edge precast blocks to both sides, so that the hoisting load is evenly transferred to the lower bracket 11, avoiding support deformation and warping of the base plate 2 caused by unilateral loading. During the hoisting process, the suspended panel is not disengaged from the lifting equipment before the temporary effective connection between the suspended panel and the fixed panel is completed, which greatly improves the safety of high-altitude hoisting operations; for precast blocks with a long hoisting range, a dual-crane lifting operation is adopted, strictly controlling the load of a single crane to not exceed 80% of the rated lifting capacity, and the total load to not exceed 75% of the sum of the rated lifting capacities of the two cranes, with unified command by a dedicated person to ensure that the hoisting process is stable and controllable.

[0034] Furthermore, in specific implementation, in step S2 provided in this embodiment of the invention, before assembling the side plate 3, the vertical ribs are aligned with the pre-embedded parts on the periphery of the base plate 2 for installation. Specifically, before assembling the side plate 3, the steel vertical ribs welded to the outside of the side plate 3 are precisely aligned with the pre-embedded connecting bolts on the periphery of the base plate 2 to complete the initial positioning and fixing. Then, the side plates 3 are assembled piece by piece and connected into a whole by bolts. This installation method uses the pre-embedded parts of the base plate 2 as the positioning reference, eliminating the need for additional positioning brackets, simplifying the on-site installation process, and ensuring the verticality and planar position accuracy of the side plate 3 installation. This allows the side plate 3 and the base plate 2 to form a rigid connection, improving the cofferdam structure's resistance to water pressure and water flow impact, and preventing structural deformation and displacement under the action of strong tidal currents in the sea.

[0035] Furthermore, in specific implementation, in step S4 provided in the embodiments of the present invention, the process of cyclically lowering the steel caisson includes the following steps: Step S41: Jack 42 lifts the second nut 45 so that it is suspended and not under force, and then screws the second nut 45 to continue to the high position; Step S42: Jack 42 falls back down, allowing the steel caisson to be lowered smoothly for a distance until the second nut 45 is stressed again; Step S43: Tighten the first nut 44 upward to a preset height, and the jack 42 will lift it up, so that the first nut 44 is under force. Step S44: Repeat steps S41 to S43 until the steel caisson is lowered to the design elevation.

[0036] Specifically, the cyclic lowering operation adopts a graded, synchronous, and stable control principle. The single lowering stroke is matched with the rated stroke of jack 42. After each stroke is completed, the structural elevation and flatness are checked. If any posture deviation is found, the machine is stopped immediately for adjustment to ensure that the cofferdam is always lowered vertically. During the lifting operation of jack 42, all lifting equipment is controlled synchronously to ensure consistent output. After the second nut 45 is completely suspended and unloaded, the second nut 45 is then screwed upward along the lifting rod 43 to the highest position of the stroke to avoid deformation of the lifting rod 43 and structural unbalanced load caused by the force on one side of the nut. During the lowering operation of jack 42, a slow and uniform speed control mode is adopted to lower the steel box smoothly for one stroke until the second nut 45 is back in contact with the support surface and under force, completing a single lowering cycle. This cyclic operation mode enables the steel caisson to be lowered continuously and stably over long distances without the need to frequently change lifting tools and anchor points, greatly improving the efficiency of the lowering operation. At the same time, the alternating force of the first nut 44 and the second nut 45 ensures the structural safety throughout the lowering process and eliminates the risk of falling or overturning.

[0037] Furthermore, in specific implementation, in step S5 provided in this embodiment of the invention, after the steel caisson is lowered into place, half of the shear keys 6 are evenly installed circumferentially between the base plate 2 and the pile foundation 1 during the low tide window. Specifically, after the steel caisson is lowered to the design elevation, the tidal variation pattern of the construction area is statistically analyzed in advance to lock in the low tide window. At this time, the water level drops below the base plate 2, and the water level inside and outside the cofferdam is kept consistent through the communicating vessel. The structure is not affected by water pressure and buoyancy. In a dry working environment, half of the shear keys 6 are evenly installed circumferentially along the steel casing. One end of the shear key 6 is fixed by the pre-embedded bolts 21 in the base plate 2, and the other end is welded to the steel casing. This operation method eliminates the need for underwater operations by divers, completely eliminating the safety and quality hazards of underwater welding. At the same time, the partial force system conversion is completed in advance through the shear keys 6, which can greatly simplify or even eliminate the installation process of the tension and compression rods 5, reduce the amount of steel used and the amount of on-site welding work, and significantly shorten the construction period.

[0038] Furthermore, in specific implementation, in step S7 provided in the embodiment of the present invention, during gap sealing, sandbags mixed with cement are first used to seal the lower step of the gap, and then micro-expansion sealing concrete is poured at the upper step of the gap at low tide. Specifically, a 15cm wide gap is set between the steel casing and the reserved hole 20 in the bottom plate 2 to accommodate the verticality error of the steel casing construction. The gap sealing adopts a two-stage redundant sealing process. First, sandbags mixed with cement and fine sand are used to seal the lower step of the gap. The sandbags are fixed at the bottom by steel hooks to prevent them from falling. After the cement and fine sand solidify, the water-stopping performance and structural strength of the sandbags can be greatly improved. Then, in a dry working environment at low tide, micro-expansion sealing concrete is poured at the upper step of the gap to completely fill and compact the gap between the steel casing and the bottom plate 2. This sealing process does not require underwater operation, is convenient to operate, and the sealing density can be controlled. It can completely block the gap seepage channel and ensure a dry working environment for subsequent pumping and bottom sealing operations.

[0039] Furthermore, in specific implementation, in step S6 provided in the embodiments of the present invention, cooling water pipes are laid out before each layer of concrete is poured during the layered pouring of the foundation. Specifically, the foundation is a large-volume marine concrete structure with a total pouring height of 5m, constructed in two layers. The first layer has a pouring height of 2m, and the second layer has a pouring height of 3m. Before each layer of concrete is poured, cooling water pipes are laid out in a grid pattern to form an independent circulation loop. During the pouring process, the concrete temperature upon entering the formwork, the pouring speed, and the layer thickness are strictly controlled. After pouring, cooling water is continuously circulated, and the internal and surface temperatures of the concrete are monitored in real time. The internal and surface temperature differences, cooling rates, and interlayer temperature differences are controlled. At the same time, surface insulation and curing measures are implemented to reduce the peak concrete temperature from the source, avoid the generation of temperature cracks in the large-volume concrete, and ensure the structural strength, impermeability, and long-term durability of the foundation, making it suitable for the harsh service environment of high salinity, high humidity, and strong corrosion in marine areas.

[0040] In this embodiment, a steel caisson is also disclosed, including a base plate 2 and side plates 3. The base plate 2 has a plurality of pre-embedded bolts 21 evenly distributed around the pre-drilled holes 20 for connecting the tension rods 5 and the shear keys 6. Specifically, the steel caisson is a steel-concrete composite structure. The base plate 2 is made of precast concrete slab, and the side plates 3 are made of steel formwork. Multiple sets of pre-embedded bolts 21 are evenly distributed around the pre-drilled holes 20 in the steel casing on the base plate 2. The positions of the pre-embedded bolts 21 correspond one-to-one with the installation points of the tension rods 5 and the shear keys 6 (12 bolts are provided, of which 4 are for connecting the tension rods 5 and 8 are for connecting the shear keys 6). The pre-embedded bolts 21 are precisely positioned and installed simultaneously during the prefabrication of the base plate 2, and are welded and fixed to the steel reinforcement skeleton of the base plate 2 to ensure anchorage strength. During on-site installation, the tension rods 5 and shear keys 6 can be quickly assembled directly through the pre-embedded bolts 21 without the need for on-site drilling and rebar installation, which greatly improves installation efficiency. At the same time, it ensures a clear and reliable force transmission path, so that the cofferdam load is evenly transmitted to the steel casing of the pile foundation 1, thereby improving the overall stability of the structure.

[0041] Furthermore, in specific implementation, the brackets 11 provided in this embodiment of the invention are double-sectioned I-beams arranged side by side, with steel wire ropes connected to the ends of the brackets 11, and the brackets 11 on each pile foundation 1 are on the same horizontal plane. Specifically, before installing the brackets 11, matching installation holes are opened on both sides of the steel casing above sea level, and the double-sectioned I-beams are horizontally inserted into the installation holes. The top surfaces of all brackets 11 on a single pile foundation are controlled to be on the same horizontal plane, and the elevation error is strictly controlled within the allowable range of the specifications, ensuring that the top surface of the base plate 2 is flat and the stress is uniform after installation. Each bracket 11 is connected with a steel wire rope before installation, and the other end of the steel wire rope is fixed to the steel platforms on both sides. During subsequent dismantling, the brackets 11 can be directly pulled out from the installation holes through the steel wire rope, eliminating the need for underwater or high-altitude dismantling operations. The operation is convenient, safe, and efficient. At the same time, the I-beam brackets 11 can be reused for the construction of multiple pile foundations, significantly reducing the cost of temporary measures.

Claims

1. A method for constructing a steel hanging box cofferdam with high-pile pile caps in a tidal environment, characterized in that, The method comprises the following steps: Step S1, pre-assemble the bottom plate (2) and the side plate (3); Step S2, horizontally insert the bracket (11) into the installation hole of the pile foundation (1), hoist the bottom plate (2) to the bracket (11), assemble the side plate (3) to the bottom plate (2), and then install the support structure outside the side plate (3) to complete the assembly of the steel hanging box; Step S3, install the anchor block on the bottom plate (2), install the beam (4), the support leg (41) and the jack (42) on the top of the pile foundation (1), connect the suspender (43) to the anchor block through the jack (42), the support leg (41), the beam (4) and the tensioning rod (5) in sequence, and thread the first nut (44) and the second nut (45) on the suspender (43), wherein the first nut (44) abuts against the jack (42), and the second nut (45) is arranged between the support leg (41) and the beam (4); Step S4, the jack (42) lifts the steel hanging box, the first nut (44) bears the weight of the steel hanging box, the second nut (45) is screwed to the high position along the suspender (43), the jack (42) falls back, the first nut (44) and the second nut (45) jointly support the steel hanging box, the bracket (11) is pulled out, and the steel hanging box is lowered to the design elevation in a cycle; Step S5, the upper end of the tensioning rod (5) is welded to the pile foundation (1), the lower end of the tensioning rod (5) is fixed to the anchor block, and the suspender (43), the jack (42) and the beam (4) are removed in sequence; Step S6, seal the gap between the pile foundation (1) and the reserved hole (20) of the bottom plate (2), drain the accumulated water in the steel hanging box, and connect the shear key (6) between the pile foundation (1) and the bottom plate (2); Step S7, after the bottom sealing concrete is poured, the pile cap is poured in layers.

2. The method according to claim 1, wherein the method is characterized in that, In step S2, wet joints are poured between adjacent bottom plates (2), gaps between the bottom of the side plate (3) and the bottom plate (2) are sealed and compacted with grouting material, adjacent side plates (3) are fastened with water stop rubber pads and bolts, and a secondary waterproof layer is formed by applying rubber asphalt sealant to the inside of the side plate (3) joint.

3. The method according to claim 1, wherein the method is characterized by, In step S2, the bottom plate (2) is symmetrically hoisted from the middle to both sides.

4. The method according to claim 1, wherein the method is characterized by, In step S2, before assembling the side plate (3), the vertical ribs are aligned with the pre-embedded parts pre-installed on the periphery of the bottom plate (2).

5. The method according to claim 1, wherein the method is characterized by, In step S4, the process of lowering the steel hanging box in a cycle comprises the following steps: Step S41, the jack (42) lifts to make the second nut (45) suspended and not stressed, and then the second nut (45) is screwed to the high position; Step S42, the jack (42) falls back to stably lower the steel hanging box by a stroke until the second nut (45) is stressed again. Step S43: Twist the first nut (44) upward to a preset height, and the jack (42) will lift up, so that the first nut (44) is subjected to force; Step S44: Repeat steps S41 to S43 until the steel caisson is lowered to the design elevation.

6. The method according to claim 1, wherein the method is characterized by, In step S5, after the steel caisson is lowered into place, half of the shear keys (6) are evenly installed circumferentially between the base plate (2) and the pile foundation (1) during the low water level window of the tide.

7. The method according to claim 1, wherein the method is characterized by, In step S7, when sealing the gap, first use sandbags mixed with cement to seal the bottom of the gap at the lower step, and then pour micro-expansion sealing concrete at the upper step of the gap at low tide.

8. The method according to claim 1, wherein the method is characterized by, In step S6, when the foundation is poured in layers, cooling water pipes are laid out before each layer of concrete is poured.

9. A steel hanging box based on the construction method of a steel hanging box cofferdam of high-pile pile cap in a tidal environment according to any one of claims 1-8, characterized in that, The base plate (2) and the side plate (3) are included. The base plate (2) has a plurality of pre-embedded bolts (21) evenly distributed around the pre-reserved hole (20) for connecting the tension rod (5) and the shear key (6).

10. The steel hanging box according to claim 9, characterized in that, The brackets (11) are made of double I-beams arranged side by side. The ends of the brackets (11) are connected to steel wire ropes, and the brackets (11) on each pile foundation (1) are on the same horizontal plane.

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