A cofferdam construction method for an offshore separated floating structure

Abstract

The present invention discloses a cofferdam construction method for an offshore separated floating structure, which uses two sets of cofferdams to enclose two sides of the separation area between the two floating structures; the cofferdams are provided with elastic seals on the contact surfaces with the floating structures; and the floating structures are provided with a slot structure. The method comprises: step 1: horizontally lifting one set of cofferdams by a floating crane; step 2: coarsely positioning the cofferdams in the horizontal and vertical directions to align them with the slot structure in the vertical direction; step 3: differentially adjusting the height of the lifting points on both sides of the cofferdams to flip them to a vertical position; step 4: adjusting the verticality of the cofferdams; lowering the cofferdams along the slot structure until the connecting portion is hooked to the floating structure; step 5: using a pushing device to press the cofferdams tightly against the well wall of the floating structure; then welding the cofferdams to the floating structure; step 6: installing another set of cofferdams according to steps 1 to 6; step 7: pumping water from the space enclosed by the cofferdams and the floating structure; then pouring the bottom seal concrete.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore engineering construction, and in particular to a cofferdam construction method for an offshore separated floating structure. Background Art

[0002] As cross-sea bridge projects progress toward deeper waters and larger structures, deepwater foundations must possess both high load-bearing capacity and adaptability to complex environments. Caisson foundations, with their superior overall rigidity and adaptability to the ground, have become a mainstream form of deepwater foundation for offshore bridges. In recent years, traditional integral caissons have become increasingly problematic due to their excessive width and weight, resulting in difficulties in transport, positioning, and site adaptability. In certain projects, the modular construction of detachable caissons has significantly improved construction efficiency.

[0003] For the connection construction of offshore split steel caissons, the industry has proposed a dry-construction technology for steel caisson tie beams and cofferdams. By creating an enclosed working space around the split steel caisson, this technology enables efficient construction in a waterless environment. This technology mitigates the impact of complex marine environments on construction progress, improves construction efficiency, and enhances the bearing capacity and stability of the caisson foundation.

[0004] The current construction method uses a prefabricated U-shaped tie beam steel shell. The construction process includes: setting a tie beam steel shell with a connecting section at a preset position in the caisson, lowering it along the caisson guide interface to the bottom bracket using a floating crane; then pouring underwater concrete to reinforce the bottom plate and side webs of the tie beam steel shell. After the U-shaped tie beam steel shell is pumped out, the top plate and tie beam concrete are poured. While this process achieves a dry working environment, it has significant drawbacks during actual construction. First, the tie beam installation requires high positioning accuracy in dynamic sea conditions, and the coupling of wind, waves and currents can easily cause the steel shell to collide with the caisson wall, causing structural damage. Second, the concrete pouring stage requires a complex anti-floating and anti-sinking system to offset the buoyancy changes caused by tidal fluctuations, which greatly increases the difficulty of controlling construction stability. Third, the cofferdam waterstop relies on high-precision underwater bolting and floating welding processes, which are prone to seal failure due to water disturbances, and the welding quality is difficult to meet onshore operation standards.

[0005] These technical deficiencies severely hampered construction efficiency and project safety, particularly in areas prone to frequent typhoons and significant tidal ranges, where the applicability of traditional techniques was further limited. Overcoming key technical challenges such as precise cofferdam positioning, efficient sealing, and structural stability control in complex marine environments has become a core challenge in advancing offshore detachable steel caisson construction technology. Summary of the Invention

[0006] The main technical problem to be solved by the present invention is to provide a cofferdam construction method for offshore detachable floating structures, which can more efficiently and safely enclose a stable dry working space between the detachable floating structures.

[0007] In order to solve the above-mentioned technical problems, the present invention provides a cofferdam construction method for an offshore detachable floating structure, comprising: two sets of cofferdams relatively enclosing two sides of a separation area between two adjacent floating structures; a slot structure is provided on the floating structure at a position connected to the cofferdam, for guiding the cofferdam vertically; the cofferdam includes a pressure plate; the pressure plate extends a connecting portion toward one side of the floating structure, for hanging and fixing the cofferdam on the floating structure; the pressure plate is provided with an elastic sealing member along the height direction on the contact surface with the floating structure; the cofferdam is prefabricated and then shipped to the construction sea area of the detachable floating structure; the construction method comprises the following steps:

[0008] Step 1: Use a floating crane to lift any set of cofferdams horizontally;

[0009] Step 2: performing rough transverse and longitudinal positioning of the cofferdam by moving the floating crane or adjusting the boom of the floating crane so as to align the cofferdam with the slot structure in the vertical direction;

[0010] Step 3: By differentially adjusting the heights of the hanging points on both sides of the cofferdam, the cofferdam is flipped from a horizontal state to a vertical installation posture;

[0011] Step 4: Adjust the verticality of the cofferdam to meet the requirements; lower the cofferdam along the slot structure until the connecting portion is hooked to the floating structure;

[0012] Step 5: Using the slot structure as a reaction seat, a pushing device is used to push the cofferdam tightly against the well wall of the floating structure; then, the connecting portion on the cofferdam is welded to the floating structure;

[0013] Step 6: Install another set of cofferdams according to steps 1 to 5;

[0014] Step 7: Pumping out water from the space enclosed by the cofferdam and the floating structure; pouring the bottom seal concrete after the water seepage drops to the allowable value.

[0015] In a preferred embodiment, the cofferdam further includes a plurality of trusses; the trusses are welded to the pressure plate in a horizontal direction.

[0016] In a preferred embodiment, in step 2, the floating crane is moved by connecting a first winch on the floating crane to two floating structures respectively using cables; and the first winch reels in or releases the cables to pull the floating crane to move.

[0017] In a preferred embodiment, in step 4, the method for adjusting the verticality of the cofferdam is as follows: the cofferdam is connected to a plurality of guy ropes along multiple directions; the ends of the guy ropes away from the cofferdam are respectively connected to a plurality of winches, and the verticality of the cofferdam is dynamically adjusted through multi-directional traction.

[0018] In a preferred embodiment, the step 5 further includes: before using the pushing device to push the pressure plate, using a traction rope to connect the cofferdam and a second winch on the floating structure; the second winch preliminarily fixes the cofferdam by tightening the traction rope.

[0019] In a preferred embodiment, the step 7 further includes: inserting a water-stopping steel plate into the slot structure to enclose a casting cavity together with the cofferdam, the well wall of the floating structure and the slot structure; pumping water from the casting cavity and casting water-stopping concrete.

[0020] In a preferred embodiment, the slot structure includes a longitudinal beam vertically welded to the well wall of the floating structure and a transverse beam vertically welded to the cantilevered end of the longitudinal beam; the two transverse beams located on the two floating structures extend toward each other to form an inward-retracted structure.

[0021] In a preferred embodiment, the contour of the connection between the floating structure and the pressure plate is arc-shaped; the floating structure is sealed and fixed with a base at the connection; the base is a rigid spatial structure; the base fits the pressure plate by compensating for the contour of the floating structure.

[0022] In a preferred embodiment, the pushing device adopts a self-locking hydraulic jack.

[0023] In a preferred embodiment, the pressure plate on the upstream side is thicker than the pressure plate on the downstream side.

[0024] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0025] (1) The double-wall cofferdam system achieves efficient sealing and structural stability. The construction method uses an innovatively designed double-wall pressure-bearing plate and truss composite structure to construct a closed cofferdam system with outstanding compressive resistance. The differentiated design of the double-wall steel plate on the upstream and downstream sides achieves a balance between bearing capacity and economy. The elastic seal forms a self-tightening water-stop barrier under the action of the water pressure difference, and the slot structure that can be poured with water-stop concrete forms a "mechanical + material" double sealing defense line. Compared with the traditional welding water-stop process, the risk of water leakage is significantly reduced, and no complicated underwater welding operation is required.

[0026] (2) Three-dimensional dynamic adjustment solves the problem of offshore construction positioning. The construction method adopts a three-level collaborative positioning system of floating crane, cable wind rope and slot: rough positioning is achieved by cable pulling the floating crane, multiple sets of cable wind ropes are used to achieve fine adjustment of the verticality of the cofferdam, and the guide slide of the slot and the hydraulic jack achieve high-precision positioning. This system enables the cofferdam to be accurately installed even under harsh hydrological conditions, significantly improving the positioning efficiency and success rate compared to traditional processes.

[0027] (3) Modular construction drives a significant improvement in project efficiency. The construction method involves a high proportion of prefabricated steel components shipped by ship; on-site assembly uses standard slots to achieve rapid "Lego-style" assembly; and the use of double-sling flipping technology significantly shortens the installation period of a single-sided cofferdam. Overall construction efficiency has been significantly improved compared to wet construction, significantly reducing the construction period.

[0028] (4) A multi-dimensional safety control system reduces the risk of offshore operations. The innovative construction method uses shipping instead of floating to reduce the risk of components drifting at sea; lifting and lowering are carried out step by step, and multiple inspections and reviews of equipment and connections are set up during the lifting construction; force-limiting auxiliary slings are set to prevent imbalance; the amount of high-altitude operations and underwater welding requirements are greatly reduced, and the construction accident rate is significantly reduced.

[0029] (5) Significant cost advantages throughout the entire life cycle. The double-wall structural design significantly optimizes material usage, and the detachable slings and standardized slots enable efficient reuse of components, significantly reducing maintenance costs throughout the entire life cycle. The modular design supports partial replacement and maintenance, avoiding the waste of resources caused by overall demolition and reconstruction. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A diagram showing the positional relationship between the cofferdam and the separate steel caisson in an embodiment of the present invention;

[0031] Figure 2 Schematic diagram of the cofferdam according to an embodiment of the present invention (the corners of the steel caisson are right angles);

[0032] Figure 3 Schematic diagram of the cofferdam according to an embodiment of the present invention (the corners of the steel caisson are arc-shaped);

[0033] Figure 4 Schematic elevation view of the cofferdam according to an embodiment of the present invention (along the normal direction of the bearing plate);

[0034] Figure 5 Schematic elevation view of the cofferdam according to an embodiment of the present invention (along the inner direction of the pressure plate);

[0035] Figure 6 It is a plan view schematic diagram of the hydraulic jack pushing the cofferdam in an embodiment of the present invention;

[0036] Figure 7 、 Figure 8 This is a top view schematic diagram of the cofferdams on both sides of the floating crane installed in an embodiment of the present invention;

[0037] Figure 9 Schematic diagram of the construction of horizontally lifting a cofferdam on one side according to an embodiment of the present invention;

[0038] Figure 10 Schematic diagram of construction for performing rough horizontal positioning of a cofferdam on one side in an embodiment of the present invention;

[0039] Figure 11 A schematic diagram of the construction of mid-air posture adjustment of a cofferdam on one side according to an embodiment of the present invention;

[0040] Figure 12 Schematic diagram of the arrangement of the guy ropes on one side of the cofferdam in an embodiment of the present invention;

[0041] Figure 13 A schematic diagram of the construction of lowering a cofferdam on one side in an embodiment of the present invention;

[0042] Figure 14 This is a schematic diagram of a cofferdam on one side after it is in place in an embodiment of the present invention;

[0043] Figure 15 Schematic diagram of the arrangement of the guy ropes on the other side of the cofferdam in an embodiment of the present invention;

[0044] Figure 16 This is a schematic diagram of the cofferdams on both sides after they are in place in an embodiment of the present invention.

[0045] Markings in the figure are: 1-cofferdam, 11-pressure plate, 12-truss, 13-support beam, 2-slot structure, 21-longitudinal beam, 22-cross beam, 23-stiffener plate, 24-slot wall steel plate, 25-threaded fastener, 3-elastic seal, 4-waterstop concrete, 41-slot, 42-waterstop steel plate, 5-base, 6-steel caisson, 61-second winch, 7-floating crane, 71-floating crane, 72-first sling, 73-second sling, 74-auxiliary sling, 75-first winch, 76-anchor cable system, 77-cable, 8-auxiliary construction ship, 9-guy rope, 10-hydraulic jack. DETAILED DESCRIPTION

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0047] In the description of the present invention, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0048] In the description of the present invention, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installed", "provided with", "set / connected", "connected", etc. should be understood in a broad sense. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be a direct connection or an indirect connection through an intermediate medium. It can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0049] like Figures 1 to 16 As shown, an embodiment of the present invention provides a cofferdam construction method for an offshore detachable floating structure. In this embodiment, the floating structure is specifically a steel caisson 6.

[0050] First refer to Figures 1 to 5, the cofferdam structure is described. Generally speaking, the two groups of cofferdams 1 are relatively arranged on both sides of the separation area of the separate steel caisson 6 to enclose a dry working space together with the separate steel caisson 6. Each group of cofferdams 1 adopts a composite system of a steel structure pressure plate 11 and a truss 12, including a pressure plate 11 and a number of trusses 12. The pressure plate 11 adopts a double-wall structure, which is composed of two oppositely arranged steel plates welded by a number of angle steels. The two sides of the pressure plate 11 are respectively sealed with two separate steel caissons 6 to withstand external water pressure and stop water leakage. The truss 12 is a rigid spatial structure welded by a number of steel sections, which is a mature existing load-bearing structure. The truss 12 is welded in the horizontal direction on the side of the pressure plate 11 away from the dry working space, and improves the in-plane stiffness of the pressure plate 11 by balancing the differentiated loads in the middle and on both sides of the pressure plate 11. In order to improve the pressure bearing limit and structural integrity, several groups of trusses 12 are spaced apart in the height direction of the pressure plate 11. In this embodiment, taking into account the differences in the water flow conditions faced by the cofferdam 1 on both sides, the pressure plates 11 on both sides adopt different thicknesses. Specifically, on the dorsoventral side, the double-wall spacing of the pressure plate 11 is 1.3 meters, while on the upstream side, the double-wall spacing of the pressure plate 11 is increased to 2.0 meters to improve the pressure bearing capacity. A beam 13 is also fixed on the top of the pressure plate 11, which is equivalent to the connecting portion of the cofferdam 1 for hanging and fixing on the steel caissons 6 on both sides. Therefore, it is not difficult to understand that the beam 13 is arranged in the connecting section between the pressure plate 11 and the steel caisson 6, and extends vertically toward one side of the steel caisson 6, that is, the side facing away from the truss 12.

[0051] like Figure 2As shown, a slot structure 2 is provided at the connection between the steel caisson 6 and the cofferdam 1. The slot structure 2 has two functions: first, during installation and construction, the slot structure 2 is limited in the horizontal direction with the pressure plate 11 to guide the cofferdam 1 in the vertical direction; second, when the cofferdam 1 is in place, the slot structure 2 can be used as a reaction support to push the cofferdam 1 to fit the wall of the steel caisson 6 through a jack. The main body of the slot structure 2 is welded by several large-sized steel components, including a longitudinal beam 21 and a transverse beam 22. The longitudinal beam 21 is vertically welded to the wall of the steel caisson 6 and then extends out, and the transverse beam 22 is vertically welded to the cantilevered end of the longitudinal beam 21 to form an L-shaped limiting structure. It can be understood that the two transverse beams 22 located on the two steel caissons 6 extend toward each other to form an inward-retracting structure to assume the role of a pushing support and a horizontal limit. In this embodiment, the longitudinal beam 21 and the cross beam 22 are made of HN700 and HN1000 I-beams. A 20 mm thick stiffening plate 23 is also provided at the right-angle connection between the longitudinal beam 21 and the cross beam 22 to increase the rigidity of the slot structure 2. On the side of the slot structure 2 facing the cofferdam 1 (hereinafter defined as the "inner side"), a 20 mm thick slot wall steel plate 24 is welded in the height direction as a guide slide. In some embodiments, a plurality of threaded fasteners 25 are also provided on the cross beam 22. The plurality of threaded fasteners 25 are arranged in a direction parallel to the longitudinal beam 21 and are spaced apart in the extension direction of the cross beam 22. The threaded fasteners 25 serve as auxiliary fixation. After the cofferdam 1 is in place, the cofferdam 1 is locked to the wall of the steel caisson 6 from the outside by cooperating with the thread of the cross beam 22.

[0052] like Figure 2 As shown, the water-stopping measures at the connection between the cofferdam 1 and the steel caisson 6 include an elastic seal 3 and water-stopping concrete 4. The pressure plate 11 is provided with a full-height elastic seal 3 on the contact surface with the wall of the steel caisson 6. When the cofferdam 1 is installed and the space enclosed by the cofferdam 1 and the steel caisson 6 is pumped, the internal and external water pressure difference forces the pressure plate 11 to cling to the wall of the steel caisson 6, causing the elastic seal 3 to be pressurized and self-sealed, forming a reliable first water-stopping barrier. As an auxiliary water-stopping measure, the water-stopping concrete 4 is applied as follows: as shown in the figure, a slot 41 is welded along the height direction on the inner wall of the slot structure 2 and the side wall of the cofferdam 1. A full-height water-stopping steel plate 42 is inserted into the slot 41, which together with the slot wall steel plate 24, the wall of the steel caisson 6 and the cofferdam 1 encloses a relatively sealed casting cavity. The pouring cavity is pumped out of water, and after the water seepage drops to an allowable value, concrete is filled in to form a second water-stop barrier.

[0053] like Figure 3As shown, since some corners of the wall of the steel caisson 6 are arc-shaped, it is impossible to install tightly with the pressure plate 11 at the position connected to the cofferdam 1. For this reason, a base 5 is provided in the height direction at the arc-shaped corner to compensate the contour of the wall of the steel caisson 6. The base 5 is a rigid spatial structure formed by welding a number of steel plates and filled with concrete. The side of the base 5 facing the steel caisson 6 is arc-shaped and is welded to the wall of the steel caisson 6. The side of the base 5 facing the cofferdam 1 is provided with a straight edge to fit with the pressure plate 11. It is not difficult to understand that in this case, the elastic seal 3 of the pressure plate 11 abuts against the base 5.

[0054] Based on the above structural description, the following describes the construction method of the cofferdam 1. The cofferdam 1 is prefabricated and shipped to the construction area of the separate steel caisson 6, and then the installation construction begins. The construction method includes the following steps:

[0055] Step 1: Lift the cofferdam horizontally

[0056] like Figure 1 As shown, the main hook of the floating crane 71 is connected to the cofferdam 1 via slings. The slings consist of a main sling and an auxiliary sling 74, with the main sling further comprising a first sling 72 and a second sling 73. The first sling 72 and auxiliary sling 74 are connected to the pressure plate 11 at the "top" of the cofferdam 1, while the second sling 73 is connected to the truss 12 on the other side. The "top" refers to the cofferdam 1 after installation. Before lifting, focus on inspecting the integrity of the sling, component balance, and connection reliability, paying attention to any mechanical connections between the cofferdam 1 and the floating crane 7. After verification, the lifting operation begins. The floating crane 71 slowly raises the hook to tighten the slings and ensure that the lifting center of gravity coincides with the center of gravity of the cofferdam 1. If this is not the case, the length relationship between the slings is adjusted by adjusting the floating crane 71's cable system to level the cofferdam 1. When the cofferdam 1 is lifted 20-30 cm from the pier, pause and observe its horizontal position. After confirming that the cofferdam 1 is stable and without tilt, the cofferdam 1 is continuously lifted to a height of 10m from the water surface. During the hoisting process at this stage, the auxiliary sling 74 is continuously tightened, but the force is always controlled within 5t.

[0057] Step 2: Roughly position the cofferdam horizontally

[0058] The horizontal positioning of the cofferdam 1 includes horizontal rough positioning and longitudinal rough positioning. In this embodiment, the direction of the floating crane 7 is perpendicular to the pre-installed position of the cofferdam 1. Therefore, the horizontal and longitudinal directions are relative to the direction of the floating crane 7. Specifically, the horizontal direction is parallel to the horizontal connection line of the two groups of slot structures 2, and the longitudinal direction is perpendicular to the horizontal connection line of the two groups of slot structures 2. Figure 8 、 Figure 9As shown, the floating crane 7 is connected to the steel caissons 6 on both sides in a "V" shape through the cable 77 led out by the first winch 75 on the deck, and then the lateral movement is achieved through the coordination of the cable reeling and releasing of the first winch 75. At the same time, the floating crane 7 is assisted in movement by the anchor cable system 76 on both sides of the ship. When the cofferdam 1 is aligned with the horizontal line connecting the slot structure 2 along the transverse axis, the transverse rough positioning is completed. Then, the cofferdam 1 is lifted to a height of 20m from the water surface for the next longitudinal movement. The first winch 75 reels in the cable at the same time, pulling the floating crane 7 longitudinally close to the pre-installed position of the cofferdam 1. Then the boom of the floating crane 71 is lowered to extend forward, so that the cofferdam 1 is aligned with the slot structure 2 in the height direction, and the longitudinal rough positioning is completed, as shown in FIG. Figure 10 As shown. During longitudinal rough positioning, attention should be paid to controlling the height difference between the bottom of the cofferdam 1 and the steel caisson 6. If necessary, the cofferdam 1 should be lifted. It should be understood that if the floating crane 7 is sufficiently close to the installation location of the cofferdam 1, towing the floating crane 7 is not necessary. Rough positioning of the cofferdam 1 can be achieved simply by adjusting the boom of the floating crane 71.

[0059] Step 3: Adjust the cofferdam's aerial posture

[0060] like Figure 11 As shown, the cofferdam 1 flipping is achieved using a dual-sling collaborative technique. By continuously increasing the length difference between the first and second slings 72 and 73, the heights of the lifting points on either side of the cofferdam 1 are differentially adjusted to achieve flipping. The second sling 73 is gradually lengthened to lower the cofferdam 1. Simultaneously, the first sling 72 and auxiliary sling 74 are gradually tightened to lift the cofferdam 1 until they bear the full vertical load, completing the flipping of the cofferdam 1. During flipping, care should be taken to ensure that the auxiliary sling 74 is subjected to no more than 5 tons of force, ensuring that the center of gravity of the sling always coincides with the center of gravity of the cofferdam 1.

[0061] Step 4: Lower the cofferdam to the slot structure

[0062] Step 41: Before the cofferdam 1 is lowered into the slot structure 2, the guy ropes 9 of the cofferdam 1 are installed. The purpose is twofold: to form a lateral constraint at the bottom of the cofferdam 1; and to adjust the verticality of the cofferdam 1. Each cofferdam 1 is equipped with at least four guy ropes 9. Figure 12 As shown, for the cofferdam 1 on the side away from the floating crane 7, the two guy ropes 9 on the same side are connected to the third winch on the auxiliary construction ship 8 at the end away from the cofferdam 1, while the two guy ropes 9 on the other side are connected to the second winch 61 on the steel caisson 6 at the end away from the cofferdam 1. Figure 15As shown, for the cofferdam 1 close to the floating crane 7, the two guy ropes 9 on the same side are connected to the first winch 75 on the floating crane 7 at the end away from the cofferdam 1, and the two guy ropes 9 on the other side are connected to the second winch 61 on the steel caisson 6 at the end away from the cofferdam 1. The 1# and 2# guy ropes 9 are connected by traction of the anchor boat, and the 3# and 4# guy ropes 9 are connected by manual traction. The above-mentioned winches dynamically adjust the verticality of the cofferdam 1 by multi-directional traction of the guy ropes 9. It should be understood that the use of guy ropes 9 is only one way to adjust the verticality of the cofferdam 1. In other embodiments, engineering equipment with telescopic arms and booms can be used to adjust the posture on both sides of the cofferdam 1.

[0063] Step 42: The verticality of the cofferdam 1 is adjusted and controlled within 0.1% by the guy rope 9. The ratio of the tensile loads borne by the first sling 72 and the auxiliary sling 74 is adjusted.

[0064] Step 43: Figure 13 As shown, the first sling 72 and the auxiliary sling 74 are synchronized to lower the cofferdam 1 along the slot structure 2. After the cofferdam 1 is lowered 10m, it is paused and the second sling 73 is released from the cofferdam 1 and the hook of the floating crane 71 by an anchor boat.

[0065] Step 44: Continue to lower the cofferdam 1 until the beam 13 at the top of the cofferdam 1 hooks the steel caisson 6. Figure 14 During the lowering process, the following should be noted: the lowering speed should not exceed 10 m / h; the tension of the first sling 72 and the auxiliary sling 74 should be constantly monitored; the verticality of the cofferdam 1 should be dynamically adjusted; and necessary protective measures should be taken to ensure that the elastic seal 3 is not damaged.

[0066] Step 5: Fasten the cofferdam to the steel caisson

[0067] Step 51: Initially position and secure the cofferdam 1. Positioning structures are welded on both sides of the supporting beam 13 in the direction of extension to initially position the cofferdam 1. At least two traction ropes are used to connect the pre-set lifting lugs on the bearing plate 11 to the second hoist 61 on the steel caisson 6 to initially secure the cofferdam 1.

[0068] Step 52: The operator goes into the water and starts the pushing device pre-installed on the slot structure 2. In this embodiment, the pushing device is a hydraulic jack 10 with a self-locking mechanism. Specifically, the operator connects the oil pipe of the hydraulic jack 10 and then starts the hydraulic jack 10. Figure 6As shown, the hydraulic jack 10, using the crossbeam 22 as a reaction seat, presses the cofferdam 1 against the wall of the steel caisson 6. The operator then re-enters the water and engages the self-locking mechanism of the hydraulic jack 10. Subsequently, for embodiments employing the threaded fasteners 25, the threaded fasteners 25 are further engaged toward the wall of the steel caisson 6, pressing the cofferdam 1 against the wall.

[0069] Step 53: After the cofferdam 1 is completely in place, the contact portion between the supporting beam 13 and the steel caisson 6 is fully welded and fixed along the circumference direction to achieve a rigid connection between the cofferdam 1 and the main structure of the steel caisson 6.

[0070] Step 6: Install the other side of the cofferdam

[0071] After the installation of the cofferdam 1 on one side is completed, the top of the cofferdam 1 is used as an operating platform to untie the first sling 72 and the auxiliary sling 74 from the top of the cofferdam 1. Then the slings are transferred to the cofferdam 1 on the other side according to the number, and the cofferdam 1 on the other side is installed according to steps 1 to 5. Figure 16 As shown, the cofferdams on both sides have been completed.

[0072] Step 7: Apply closed system

[0073] After the cofferdams 1 on both sides are in place, pumping operations are carried out in the space enclosed by the cofferdam 1 and the two steel caissons 6. During the pumping process, the water pressure on the outside forces the cofferdam 1 to fit tightly against the wall of the steel caisson 6, compressing the elastic seal 3 to achieve water stopping. Depending on the water stopping effect of the elastic seal 3, it is decided whether to implement the above-mentioned auxiliary water stopping measures, that is, whether to pour the water-stopping concrete 4 in the slot structure 2. After the amount of water seepage in the enclosed space drops to the allowable value, the bottom concrete is poured to provide a dry working environment for subsequent construction. The preliminary water-stopping measures at the bottom of the cofferdam 1 and the pouring of the bottom concrete are mature existing construction technologies, and are not the core technical features of the present invention, so they will not be elaborated in this article.

[0074] In summary, the construction method provided by the embodiment of the present invention has the following technical advantages:

[0075] (1) The double-wall cofferdam system achieves efficient sealing and structural stability. Through the innovative design of the double-wall pressure plate 11 and the truss 12 composite structure, a closed cofferdam system with outstanding compressive performance is constructed. The differentiated design of the double-wall steel plate on the upstream and downstream sides achieves a balance between bearing capacity and economy. The elastic seal 3 forms a self-tightening water-stopping barrier under the action of the water pressure difference, and cooperates with the slot 41 structure that can be poured with water-stopping concrete 4 to form a "mechanical + material" double sealing defense line. Compared with the traditional welding water-stopping process, the risk of water leakage is significantly reduced, and no complicated underwater welding operation is required.

[0076] (2) Three-dimensional dynamic adjustment solves the problem of positioning during offshore construction. A three-level collaborative positioning system consisting of a floating crane 71, a cable wind rope 9, and a slot structure 2 is used: coarse positioning is achieved by pulling the floating crane 7 with cables 77, multiple sets of cables wind ropes 9 achieve fine adjustment of the verticality of the cofferdam 1, and the guide slides of the slot structure 2 and the hydraulic jacks 10 achieve high-precision positioning. This system enables the cofferdam 1 to be accurately installed even under harsh hydrological conditions, significantly improving positioning efficiency and success rate compared to traditional processes.

[0077] (3) Modular construction drives a significant improvement in project efficiency. The construction method involves a high proportion of prefabricated steel components shipped by ship. On-site assembly utilizes a standard slot structure 2, enabling rapid "Lego-style" assembly. The use of double-sling flipping technology significantly shortens the installation period of the single-sided cofferdam 1. Overall construction efficiency is significantly improved compared to wet construction, significantly reducing construction time.

[0078] (4) A multi-dimensional safety control system reduces the risks of offshore operations. Innovative shipping is used instead of floating to reduce the risk of components drifting at sea; lifting and lowering are carried out step by step, and multiple inspections and reviews of equipment and connections are set up during the lifting construction; force-limiting auxiliary slings 74 are set up to prevent imbalance; the amount of high-altitude operations and underwater welding needs are greatly reduced, and the construction accident rate is significantly reduced.

[0079] (5) Significant cost advantages throughout the entire life cycle. The double-wall structure design significantly optimizes material usage, and the detachable slings and standardized slot structure2 enable efficient reuse of components, significantly reducing full-cycle maintenance costs. The modular design supports partial replacement and maintenance, avoiding resource waste caused by overall demolition and reconstruction.

[0080] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any technical equivalent transformation made using the contents of the present invention specification shall fall within the protection scope of the present invention.

Claims

1. A cofferdam construction method for an offshore detachable floating structure, characterized by: Two sets of cofferdams are used to relatively enclose the two sides of the separation area between two adjacent floating structures; the floating structure is provided with a slot structure at the position connected to the cofferdam, which is used to guide the cofferdam in the vertical direction; the cofferdam includes a pressure plate; the pressure plate extends a connecting portion toward one side of the floating structure, which is used to hang and fix the cofferdam on the floating structure; the pressure plate is provided with an elastic sealing member along the height direction on the contact surface with the floating structure; the cofferdam is prefabricated and shipped to the construction sea area of the separated floating structure; The construction method comprises the following steps: Step 1: Use a floating crane to lift any set of cofferdams horizontally; Step 2: performing rough transverse and longitudinal positioning of the cofferdam by moving the floating crane or adjusting the boom of the floating crane so as to align the cofferdam with the slot structure in the vertical direction; Step 3: By differentially adjusting the heights of the hanging points on both sides of the cofferdam, the cofferdam is flipped from a horizontal state to a vertical installation posture; Step 4: Adjust the verticality of the cofferdam to meet the requirements; lower the cofferdam along the slot structure until the connecting portion is hooked to the floating structure; Step 5: Using the slot structure as a reaction seat, a pushing device is used to push the cofferdam tightly against the well wall of the floating structure; then, the connecting portion on the cofferdam is welded to the floating structure; Step 6: Install another set of cofferdams according to steps 1 to 5; Step 7: Pumping out water from the space enclosed by the cofferdam and the floating structure; pouring the bottom seal concrete after the water seepage drops to the allowable value.

2. The method for constructing a cofferdam of an offshore detachable floating structure according to claim 1, wherein: The cofferdam further comprises a plurality of trusses, and the trusses are welded to the pressure plate in a horizontal direction.

3. The method for constructing a cofferdam of an offshore detachable floating structure according to claim 1, wherein: In step 2, the floating crane is moved by connecting the first hoist on the floating crane to the two floating structures respectively using cables; and the first hoist reels in or releases the cables to pull the floating crane to move.

4. The method for constructing a cofferdam for an offshore detachable floating structure according to claim 1, wherein: In step 4, the method for adjusting the verticality of the cofferdam is as follows: the cofferdam is connected to a plurality of guy ropes in multiple directions; the ends of the guy ropes away from the cofferdam are respectively connected to a plurality of winches, and the verticality of the cofferdam is dynamically adjusted through multi-directional traction.

5. The method for constructing a cofferdam of an offshore detachable floating structure according to claim 1, wherein: The step 5 further includes: before using the pushing device to push the pressure plate, using a traction rope to connect the cofferdam and a second winch on the floating structure; the second winch preliminarily fixes the cofferdam by tightening the traction rope.

6. The method for constructing a cofferdam of an offshore detachable floating structure according to claim 1, wherein: The step 7 further includes: inserting a water-stopping steel plate into the slot structure to enclose a casting cavity together with the cofferdam, the well wall of the floating structure and the slot structure; pumping water from the casting cavity and casting water-stopping concrete.

7. The method for constructing a cofferdam for an offshore detachable floating structure according to claim 1, wherein: The slot structure includes a longitudinal beam vertically welded to the well wall of the floating structure and a transverse beam vertically welded to the cantilevered end of the longitudinal beam; the two transverse beams located on the two floating structures extend toward each other to form an inward-retracted structure.

8. The method for constructing a cofferdam for an offshore detachable floating structure according to claim 1, wherein: The contour of the connection between the floating structure and the pressure plate is arc-shaped; the floating structure is sealed and fixed with a base at the connection; the base is a rigid spatial structure; the base fits the pressure plate by compensating for the contour of the floating structure.

9. The method for constructing a cofferdam for an offshore detachable floating structure according to claim 1, wherein: The pushing device adopts a self-locking hydraulic jack.

10. The method for constructing a cofferdam for an offshore detachable floating structure according to claim 1, wherein: For the two groups of cofferdams, the thickness of the pressure plate on the upstream side is greater than that on the downstream side.

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