Cofferdam construction method for offshore separated floating structure

Abstract

The invention discloses a cofferdam construction method for offshore separated floating structures. Two groups of cofferdams are enclosed on two sides of a spacing area of two floating structures; an elastic sealing piece is arranged on the contact surface of the cofferdam and the floating structure; and a clamping groove structure is arranged on the floating structure. The method comprises the following steps: step 1, horizontally hoisting a group of cofferdams by a floating crane ship; 2, the cofferdam is roughly positioned in the transverse direction and the longitudinal direction so that the cofferdam can be aligned with the clamping groove structure in the vertical direction; 3, the heights of lifting points on the two sides of the cofferdam are adjusted in a differentiated mode so that the cofferdam can be overturned to the vertical 4, the perpendicularity of the cofferdam is adjusted; the cofferdam is lowered along the clamping groove structure until the connecting part is connected with the floating structure in a hanging mode; 5, the cofferdam is tightly jacked on the well wall of the floating structure through a jacking device; then the cofferdam is welded to the floating structure; sixthly, the other cofferdam is installed according to the first step to the sixth step; 7, pumping water in a space enclosed by the cofferdam and the floating structure; and then bottom sealing concrete is poured.

Description

Technical Field

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

[0002] With the development of cross-sea bridge projects towards deeper water and larger scale, deep-sea foundation structures need to have both high bearing capacity and the ability to adapt to complex environments. The caisson foundation has become one of the mainstream forms of deep-water foundations for offshore bridges due to its good overall stiffness and formation adaptability. In recent years, problems such as difficult transportation, difficult positioning, and low site adaptability caused by the ultra-wide and overweight of traditional integral caissons have gradually emerged. In specific projects, the separated caisson has significantly improved the construction efficiency through modular construction.

[0003] Regarding the connection construction of offshore separated steel caissons, the industry has proposed the dry operation technology of the steel caisson tie beam cofferdam. By constructing a closed operation space around the separated steel caisson, efficient construction in a water-free environment is achieved. This technology reduces the impact of the complex marine environment on the construction progress, improves the construction efficiency, and also improves the bearing capacity and stability of the caisson foundation.

[0004] The currently existing construction method uses a precast U-shaped cross-section tie beam steel shell, and its construction process includes: setting a tie beam steel shell with a connection section at the preset position of the caisson, and lowering the tie beam steel shell along the caisson guiding interface to the bottom corbel through a floating crane; then pouring underwater concrete to reinforce the bottom plate and the two side webs of the tie beam steel shell. After that, after completing the pumping operation of the U-shaped tie beam steel shell, the concrete pouring of the top plate and the tie beam is carried out. Although this process realizes the construction of a dry operation environment, significant defects are exposed during actual construction: First, the hoisting of the tie beam needs to maintain a high positioning accuracy under dynamic sea conditions, and the coupled action of wind, wave, and current easily causes the steel shell to collide with the caisson wall, resulting in structural damage; Second, a complex anti-floating and anti-sinking system needs to be configured during the concrete pouring stage to offset the buoyancy change caused by the tide rise and fall, and the difficulty of controlling the construction stability increases sharply; Third, the water stop of the cofferdam depends on high-precision underwater bolt connection and floating welding technology, and it is prone to seal failure due to the influence of water flow disturbance, and the welding quality is difficult to meet the onshore operation standard.

[0005] The above technical defects seriously restrict the construction efficiency and engineering safety. Especially in the sea areas with frequent typhoons and significant tidal differences, the applicability of traditional processes is more limited. How to break through the key technical problems such as accurate positioning, efficient sealing, and structural stability control of the cofferdam under complex marine environments has become the core proposition to promote the upgrading of the construction technology of offshore separated steel caissons. Summary of the Invention

[0006] The main technical problem to be solved by the present invention is to provide a cofferdam construction method for a marine separated floating structure, so as to more efficiently and safely enclose a stable dry operation space between the separated floating structures.

[0007] To solve the above technical problems, the present invention provides a cofferdam construction method for a marine separated floating structure, in which two groups of the cofferdams are relatively enclosed on both sides of the interval area between two adjacent floating structures; the floating structure is provided with a slot structure at the position connected to the cofferdam for guiding the cofferdam vertically; the cofferdam includes a bearing plate; a connecting portion extends from one side of the bearing plate facing the floating structure for hanging and fixedly connecting the cofferdam to the floating structure; an elastic seal is arranged along the height direction on the contact surface of the bearing plate with the floating structure; the cofferdam is prefabricated and then shipped to the construction sea area of the separated floating structure by ship; the construction method includes the following steps:

[0008] Step 1: Use a floating crane ship to horizontally lift any one group of cofferdams.

[0009] Step 2: Transversely and longitudinally roughly position the cofferdam by moving the floating crane ship or adjusting the boom of the floating crane, so as to align it with the slot structure in the vertical direction.

[0010] Step 3: Differentially adjust the heights of the lifting points on both sides of the cofferdam to turn the cofferdam 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, use a jacking device to push the cofferdam tightly against the shaft wall of the floating structure; then weld the connecting portion on the cofferdam to the floating structure.

[0013] Step 6: Install the other group of cofferdams according to Steps 1 to 6.

[0014] Step 7: Pump water from the space enclosed by the cofferdam and the floating structure; after the seepage volume drops to the allowable value, pour the bottom-sealing concrete.

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

[0016] In a preferred embodiment, in Step 2, the moving mode of the floating crane ship is: use cables to connect the first winch on the floating crane ship to two floating structures respectively; the first winch winds or pays out the cables to tow the floating crane ship to move.

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

[0018] In a preferred embodiment, step 5 further includes: Before using the jacking device to jack the bearing plate, use a towing rope to connect the cofferdam to the second winch on the floating structure; the second winch preliminarily fixes the cofferdam by tightening the towing rope.

[0019] In a preferred embodiment, step 7 further includes: Insert a water-stop steel plate into the slot structure, and jointly enclose a pouring cavity with the cofferdam, the well wall of the floating structure, and the slot structure; pump out the water in the pouring cavity and pour water-stop concrete.

[0020] In a preferred embodiment, the slot structure includes a longitudinal beam perpendicularly welded to the well wall of the floating structure and a cross beam perpendicularly welded to the cantilever end of the longitudinal beam; the two cross beams on the two floating structures extend towards each other to form a converging structure.

[0021] In a preferred embodiment, the contour of a part of the connection between the floating structure and the bearing plate is arc-shaped; a base is hermetically fixed at the connection of the floating structure; the base is a rigid space structure; the base fits the bearing plate through contour compensation of the floating structure.

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

[0023] In a preferred embodiment, the thickness of the bearing plate on the flow-facing side is greater than that of the bearing plate on the backflow-facing 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 realizes efficient sealing and structural stability. The construction method constructs a closed cofferdam system with outstanding compressive performance through the innovative design of the double-wall bearing plate and truss composite structure. The differential design of the double-wall steel plates on the flow-facing side and the backflow-facing side 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 cooperates with the slot structure that can be filled with water-stop concrete to form a "mechanical + material" double water-stop defense line. Compared with the traditional welding water-stop process, the risk of water leakage is significantly reduced, and complex underwater welding operations are not required.

[0026] (2) The three - level collaborative positioning system of floating crane - guy wire - card slot solves the problem of offshore construction positioning. The construction method adopts a three - level collaborative positioning system of floating crane - guy wire - card slot: the floating crane ship is roughly positioned by cable traction, multiple groups of guy wires are used to finely adjust the verticality of the cofferdam, and the guiding slideway of the card slot and the hydraulic jack complete the high - precision positioning. This system enables the cofferdam to be accurately installed under harsh hydrological conditions, greatly improving the positioning efficiency and success rate compared with traditional processes.

[0027] (3) Modular construction promotes a leap - forward improvement in project efficiency. In the construction method, the proportion of prefabricated steel components transported by ship is relatively high; on - site assembly realizes "Lego - style" rapid assembly through standard card slots; combined with the double - sling flipping technology, the installation cycle of a single - side cofferdam is significantly shortened. The overall construction efficiency has achieved a leap - forward improvement compared with wet construction, and the construction period has been greatly reduced.

[0028] (4) The multi - dimensional safety prevention and control system reduces the risks of offshore operations. The construction method innovatively uses ship transportation instead of floating transportation, reducing the risk of component drift at sea; lifting and lowering are carried out step by step, and multiple inspections and reviews of equipment and connections are set during hoisting construction; a force - limiting auxiliary sling is set to prevent imbalance; the amount of high - altitude work and the need for underwater welding are greatly reduced, and the construction accident rate is significantly reduced.

[0029] (5) The full - life - cycle cost advantage is significant. The double - wall structure design significantly optimizes the material usage, and the detachable sling and standardized card slot enable the efficient reuse of components, resulting in a significant reduction in the full - cycle maintenance cost. The modular design supports local replacement and repair, avoiding resource waste caused by overall demolition and reconstruction. Description of the Drawings

[0030] Figure 1 It is a position relationship diagram of the cofferdam and the separated steel caisson in the embodiment of the present invention;

[0031] Figure 2 It is a plan view of the cofferdam in the embodiment of the present invention (the corner of the steel caisson is a right angle);

[0032] Figure 3 It is a plan view of the cofferdam in the embodiment of the present invention (the corner of the steel caisson is an arc);

[0033] Figure 4 It is an elevation view of the cofferdam in the embodiment of the present invention (along the normal direction of the bearing plate);

[0034] Figure 5 It is an elevation view of the cofferdam in the embodiment of the present invention (along the in - plane direction of the bearing plate);

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

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

[0037] Figure 9 This is a construction schematic diagram of horizontally lifting one side cofferdam in the embodiment of the present invention;

[0038] Figure 10 This is a construction schematic diagram of horizontally roughly positioning one side cofferdam in the embodiment of the present invention;

[0039] Figure 11 This is a construction schematic diagram of adjusting the aerial attitude of one side cofferdam in the embodiment of the present invention;

[0040] Figure 12 This is a layout schematic diagram of the guy ropes on one side cofferdam in the embodiment of the present invention;

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

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

[0043] Figure 15 This is a layout schematic diagram of the guy ropes on the other side cofferdam in the embodiment of the present invention;

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

[0045] The markings in the figure are: 1 - Cofferdam, 11 - Bearing plate, 12 - Truss, 13 - Beam, 2 - Groove structure, 21 - Longitudinal beam, 22 - Cross beam, 23 - Stiffening plate, 24 - Groove wall steel plate, 25 - Threaded fastener, 3 - Elastic seal, 4 - Waterproof concrete, 41 - Insert slot, 42 - Waterproof steel plate, 5 - Foundation, 6 - Steel caisson, 61 - Second winch, 7 - Floating crane ship, 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 implementation manners

[0046] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention; obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0047] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "top / bottom end", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0048] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "provided with", "sheathed / connected", "connected", etc. should be understood in a broad sense. For example, "connected" 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 directly connected or indirectly connected through an intermediate medium. It can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] As Figures 1 to 16 shown, the embodiment of the present invention provides a cofferdam construction method for an offshore separable 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 will be described. Generally speaking, two groups of cofferdams 1 are relatively arranged on both sides of the spaced area of the split steel caisson 6 to jointly enclose a dry operation space with the split steel caisson 6. Each group of cofferdams 1 adopts a composite system of a steel structure bearing plate 11 and a truss 12, including a bearing plate 11 and several trusses 12. The bearing plate 11 adopts a double-wall structure and is composed of two relatively arranged steel plates welded by several angle steels. Both sides of the bearing plate 11 are hermetically connected to two separated steel caissons 6, playing the role of bearing the external water pressure and preventing water leakage. The truss 12 is a rigid space structure welded by several sections of steel, which belongs to a mature existing load-bearing structure. The truss 12 is welded horizontally on the side of the bearing plate 11 away from the dry operation space to improve the in-plane stiffness of the bearing plate 11 by balancing the differential loads in the middle and on both sides of the bearing plate 11. To improve the bearing limit and structural integrity, several groups of the trusses 12 are arranged at intervals in the height direction of the bearing plate 11. In this embodiment, considering the differences in the water flow conditions faced by the cofferdams 1 on both sides, the bearing plates 11 on both sides adopt different thicknesses. Specifically, on the backflow side, the double-wall spacing of the bearing plate 11 is 1.3 meters, while on the upstream side, the double-wall spacing of the bearing plate 11 is increased to 2.0 meters to improve the bearing capacity. A section of crossbeam 13 is also fixed on the top of the bearing plate 11, which is equivalent to the connecting part of the cofferdam 1 for hanging and fixing on the two steel caissons 6 on both sides. Therefore, it is not difficult to understand that the crossbeam 13 is arranged in the connection section between the bearing plate 11 and the steel caisson 6 and vertically extends out towards the side of the steel caisson 6, that is, the side facing away from the truss 12.

[0051] As Figure 2As shown in the figure, a clamping groove structure 2 is provided at the connection between the steel caisson 6 and the cofferdam 1. The clamping groove structure 2 has two functions: First, during installation construction, the clamping groove structure 2 is in limit cooperation with the bearing plate 11 in the horizontal direction to guide the cofferdam 1 vertically; Second, after the cofferdam 1 is in place, the clamping groove structure 2 can serve as a reaction support, and the cofferdam 1 is pushed against the wall of the steel caisson 6 by a jack. The main body of the clamping groove structure 2 is welded by several large-sized steel members, including longitudinal beams 21 and cross beams 22. The longitudinal beam 21 is perpendicularly welded to the wall of the steel caisson 6 and then extends out. The cross beam 22 is perpendicularly welded to the cantilever end of the longitudinal beam 21 to form an L-shaped limit structure. It can be understood that the two cross beams 22 on the two steel caissons 6 extend towards each other to form an inwardly convergent structure to bear the functions of the jacking support and horizontal limit. In this embodiment, the longitudinal beam 21 and the cross beam 22 are made of I-beams of HN700 and HN1000 models. A stiffening plate 23 with a thickness of 20 mm is also provided at the right-angle connection of the longitudinal beam 21 and the cross beam 22 to improve the stiffness of the clamping groove structure 2. On the side of the clamping groove structure 2 facing the cofferdam 1 (hereinafter defined as the "inner side"), a groove wall steel plate 24 with a thickness of 20 mm is welded along the height direction as a guiding slideway. In some embodiments, a number of threaded fasteners 25 are also provided on the cross beam 22. The several threaded fasteners 25 are arranged along the direction parallel to the longitudinal beam 21 and are spaced at intervals in the extending direction of the cross beam 22. The function of the threaded fasteners 25 is for auxiliary fixation. After the cofferdam 1 is in place, through the threaded cooperation with the cross beam 22, the cofferdam 1 is locked to the wall of the steel caisson 6 from the outside.

[0052] As Figure 2 shown, the water stop measures at the connection between the cofferdam 1 and the steel caisson 6 include an elastic seal 3 and water stop concrete 4. A full-height elastic seal 3 is provided on the contact surface of the bearing plate 11 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 bearing plate 11 to closely adhere to the wall of the steel caisson 6, causing the elastic seal 3 to be compressed to achieve self-sealing and form a reliable first water stop barrier. As an auxiliary water stop measure, the construction method of the water stop concrete 4 is as follows: As shown in the figure, a slot 41 is welded along the height direction on the inner wall of the clamping groove structure 2 and the side wall of the cofferdam 1 respectively. A full-height water stop steel plate 42 is inserted into the slot 41, and together with the groove wall steel plate 24, the wall of the steel caisson 6, and the cofferdam 1, a relatively sealed pouring cavity is enclosed. The pouring cavity is pumped, and after the seepage water volume drops to the allowable value, concrete is filled to form the second water stop barrier.

[0053] As Figure 3As shown, since some of the corners of the well wall of the steel caisson 6 are arc-shaped, it cannot be tightly installed with the bearing plate 11 at the position connected to the cofferdam 1. For this reason, at the arc-shaped corner, a base 5 is provided in the height direction to compensate for the contour of the well wall of the steel caisson 6. The base 5 is a rigid space structure welded by several steel plates and filled with concrete. The side of the base 5 facing the steel caisson 6 is arc-shaped and is fillet welded to the well 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 bearing plate 11. It is not difficult to understand that in this case, the elastic seal 3 of the bearing plate 11 abuts against the base 5.

[0054] Based on the above structural description, the construction method of the cofferdam 1 will be introduced below. The cofferdam 1 is prefabricated and then shipped by ship to the construction sea area of the separated steel caisson 6, and then the installation construction begins. The construction method includes the following steps:

[0055] Step 1: Horizontally lift the cofferdam

[0056] As Figure 1 shown, the floating crane 71's main hook is connected to the cofferdam 1 through a sling. The sling consists of a main sling and an auxiliary sling 74. The main sling includes a first sling 72 and a second sling 73. The first sling 72 and the auxiliary sling 74 are connected to the bearing plate 11 at the "top" of the cofferdam 1, and the second sling 73 is connected to the truss 12 on the other side. The "top" refers to the state of the cofferdam 1 after installation. Before lifting, focus on checking the integrity of the lifting tools, the balance of the components, and the reliability of the connections, and pay attention to the possible mechanical connection between the cofferdam 1 and the floating crane ship 7. After checking and confirming, start the lifting operation. The floating crane 71 slowly raises the hook to tighten the sling, and ensure that the lifting center of gravity coincides with the center line of the cofferdam 1. If not, adjust the length relationship of each sling through the hinge cable system of the floating crane 71 to make the cofferdam 1 horizontal. When the cofferdam 1 is lifted 20 - 30 cm away from the pier, pause and observe its horizontal state. After confirming that the cofferdam 1 is stable and without inclination, continue to lift the cofferdam 1 to a height of 10 m above the water surface. During the lifting process at this stage, the auxiliary sling 74 is continuously tightened, but the force is always controlled within 5 t.

[0057] Step 2: Horizontally roughly position the cofferdam

[0058] The horizontal positioning of the cofferdam 1 includes transverse rough positioning and longitudinal rough positioning. In this embodiment, the orientation of the floating crane ship 7 is perpendicular to the pre-installed position of the cofferdam 1. Therefore, the transverse and longitudinal directions are relative to the orientation of the floating crane ship 7. Specifically, the transverse direction is the direction parallel to the horizontal connection line of the two groups of card slot structures 2, and the longitudinal direction is the direction perpendicular to the horizontal connection line of the two groups of card slot structures 2. As Figure 8 、 Figure 9As shown in the figure, the floating crane ship 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. Then, the horizontal movement is achieved through the cooperation of taking in and paying out the cable by the first winch 75. At the same time, the floating crane ship 7 is assisted in moving by the anchor cable system 76 on both sides of the ship. When the axis of the cofferdam 1 in the horizontal direction is aligned with the horizontal connection line of the card slot structure 2, the horizontal rough positioning is completed. Then, the cofferdam 1 is lifted to a height of 20 m above the water surface for the next longitudinal movement. The first winch 75 takes in the cable at the same time, pulling the floating crane ship 7 longitudinally towards 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 card slot structure 2 in the height direction, and the longitudinal rough positioning is completed, as Figure 10 shown. When performing the 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 ship 7 is close enough to the installation position of the cofferdam 1, the traction of the floating crane ship 7 is not a necessary step, and the rough positioning of the cofferdam 1 can be achieved only by adjusting the boom of the floating crane 71.

[0059] Step 3: Adjust the aerial attitude of the cofferdam

[0060] As Figure 11 shown, the double sling cooperative operation technology is adopted for the flipping of the cofferdam 1. By continuously increasing the length difference between the first sling 72 and the second sling 73, the lifting point heights on both sides of the cofferdam 1 are differentially adjusted to achieve the flipping of the cofferdam 1. The second sling 73 is gradually lengthened to lower the cofferdam 1 on this side. At the same time, the first sling 72 and the auxiliary sling 74 are gradually tightened to lift the cofferdam 1 on this side until all the vertical loads are borne, and the cofferdam 1 is flipped. When flipping, it should be noted that the force on the auxiliary sling 74 does not exceed 5 t; ensure that the hanging center of gravity always coincides with the center line of the cofferdam 1.

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

[0062] Step 41: Before the cofferdam 1 is lowered into the card slot structure 2, the guy ropes 9 of the cofferdam 1 are installed for two purposes: to form a lateral restraint at the lower part of the cofferdam 1; to adjust the verticality of the cofferdam 1. At least four guy ropes 9 are provided for each cofferdam 1. As Figure 12 shown, for the cofferdam 1 on the side far from the floating crane ship 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 far 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 far from the cofferdam 1. As Figure 15As shown, for the cofferdam 1 near one side of the floating crane ship 7, two guy ropes 9 on the same side are connected to the first winch 75 on the floating crane ship 7 at the ends far from the cofferdam 1, and two guy ropes 9 on the other side are connected to the second winch 61 on the steel caisson 6 at the ends far from the cofferdam 1. The 1# and 2# guy ropes 9 are connected by an anchor boat for traction, and the 3# and 4# guy ropes 9 are connected by manual traction. Each of the above winches dynamically adjusts the verticality of the cofferdam 1 by means of the multi-directional traction guy ropes 9. It should be understood that using the guy ropes 9 is just one way to adjust the verticality of the cofferdam 1. In other embodiments, engineering equipment with telescopic arms and jibs can be used to adjust the attitude on both sides of the cofferdam 1.

[0063] Step 42: Adjust and control the verticality of the cofferdam 1 within 0.1% through the guy ropes 9. Adjust the proportion of the tensile load borne by the first sling 72 and the auxiliary sling 74.

[0064] Step 43: As Figure 13 shown, synchronize the first sling 72 and the auxiliary sling 74 to lower the cofferdam 1 along the slot structure 2. After lowering the cofferdam 1 by 10 m, pause and use an anchor boat to release the second sling 73 from the cofferdam 1 and the hook of the floating crane 71.

[0065] Step 44: Continue to lower the cofferdam 1 until the crosspiece 13 at the top of the cofferdam 1 hooks onto the steel caisson 6, as Figure 14 shown. During the lowering process, it should be noted that: the lowering speed does not exceed 10 m / h; constantly monitor the tensile force values of the first sling 72 and the auxiliary sling 74; dynamically adjust the verticality of the cofferdam 1; take necessary protective measures to ensure that the elastic seal 3 is not damaged.

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

[0067] Step 51: Conduct preliminary limiting and fixing of the cofferdam 1. Weld limiting structures on both sides in the extending direction of the crosspiece 13 to conduct preliminary limiting of the cofferdam 1. Use at least 2 towing ropes to connect the preset lifting lugs on the bearing plate 11 and the second winch 61 on the steel caisson 6 to conduct preliminary fixing of the cofferdam 1.

[0068] Step 52: The operator gets into the water and starts the jacking device pre-installed on the slot structure 2. In this embodiment, the jacking 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. As Figure 6As shown, the hydraulic jack 10 uses the cross beam 22 as the reaction seat to tightly press the cofferdam 1 against the wall of the steel caisson 6. Then the operator enters the water again and locks the self-locking mechanism of the hydraulic jack 10. Subsequently, for the embodiment provided with the threaded fastener 25, it is also necessary to lock the threaded fastener 25 towards the wall of the steel caisson 6 to press the cofferdam 1 against the wall.

[0069] Step 53: After the cofferdam 1 is completely in place, at the contact part between the bearing beam 13 and the steel caisson 6, full welding is carried out along the circumferential direction to achieve the rigid connection between the cofferdam 1 and the main structure of the steel caisson 6.

[0070] Step 6: Install the other side cofferdam

[0071] After the installation of the cofferdam 1 on one side is completed, using the top of the cofferdam 1 as the operation platform, the first sling 72 and the auxiliary sling 74 are untied from the top of the cofferdam 1. Then the slings are transferred to the cofferdam 1 on the other side according to the numbers, and the cofferdam 1 on the other side is installed according to Steps 1 to 4. As Figure 16 shown, the installation of the cofferdams 1 on both sides is completed.

[0072] Step 7: Construct the closed system

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

[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 realizes efficient sealing and structural stability. Through the innovative design of the composite structure of the double-wall bearing plate 11 and the truss 12, a closed cofferdam system with outstanding compressive performance is constructed. The differential design of the double-wall steel plates on the upstream and downstream sides achieves the balance between bearing capacity and economy. The elastic seal 3 forms a self-tightening water-stop barrier under the action of the water pressure difference, and cooperates with the slot 41 structure that can be filled with water-stop concrete 4 to form a "mechanical + material" double-sealing defense line. Compared with the traditional welded water-stop process, the risk of water leakage is significantly reduced, and complex underwater welding operations are not required.

[0076] (2) The three - level collaborative positioning system of the floating crane 71 - guy wire 9 - slot structure 2 cracks the problem of offshore construction positioning. The system uses the cable 77 to tow the floating crane ship 7 for rough positioning, multiple groups of guy wires 9 to achieve fine adjustment of the verticality of the cofferdam 1, and the guiding slideway of the slot structure 2 and the hydraulic jack 10 to complete high - precision positioning. This system enables the cofferdam 1 to be accurately installed under harsh hydrological conditions, greatly improving the positioning efficiency and success rate compared with traditional technologies.

[0077] (3) Modular construction promotes a leap - forward improvement in project efficiency. In the construction method, the proportion of prefabricated steel components transported by ship is relatively high; on - site assembly realizes "Lego - style" rapid assembly through the standard slot structure 2; combined with the double - sling flipping technology, the installation cycle of the single - side cofferdam 1 is significantly shortened. The overall construction efficiency has achieved a leap - forward improvement compared with wet construction, and the construction period has been greatly reduced.

[0078] (4) The multi - dimensional safety prevention and control system reduces the risks of offshore operations. Innovatively using ship transportation instead of floating transportation reduces the risk of component drift at sea; lifting and lowering are carried out step by step, and multiple inspections and verifications of equipment and connections are set during hoisting construction; a force - limiting auxiliary sling 74 is set to prevent imbalance; the amount of high - altitude work and the need for underwater welding are greatly reduced, and the construction accident rate is significantly reduced.

[0079] (5) The full - life - cycle cost advantage is significant. The double - wall structure design significantly optimizes the material usage, and the detachable sling and the standardized slot structure 2 enable the efficient reuse of components, making the full - cycle maintenance cost significantly reduced. The modular design supports local replacement and repair, avoiding resource waste caused by overall demolition and reconstruction.

[0080] The above is only a preferred specific implementation manner of the present invention, and does not limit the patent scope of the present invention. Any technical equivalent transformation made using the content of the specification of the present invention belongs to the protection scope of the present invention.

Claims

1. A cofferdam construction method for an offshore separated floating structure, characterized in that: Two groups of the cofferdams are relatively enclosed on both sides of the interval area between two adjacent floating structures; the floating structure is provided with a slot structure at the position connected with 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 then 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 lateral 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 part is connected 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 part on the cofferdam is welded to the floating structure; Step 6: Install another set of cofferdams according to Step 1 to Step 6; Step 7: Pumping water out of the space enclosed by the cofferdam and the floating structure; pouring the bottom concrete after the water seepage drops to the allowable value.

2. A cofferdam construction method for an offshore detachable floating structure according to claim 1, characterized in that: The cofferdam also includes a plurality of trusses; 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, characterized in that: In step 2, the floating crane is moved in the following manner: a first winch on the floating crane is connected to two floating structures respectively by using cables; and the first winch reels in or releases the cables to pull the floating crane to move.

4. The method for constructing a cofferdam of an offshore detachable floating structure according to claim 1, characterized in that: In step 4, the method for adjusting the verticality of the cofferdam is as follows: the cofferdam is connected with 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.

5. The method for constructing a cofferdam of an offshore detachable floating structure according to claim 1, characterized in that: The step 5 also 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, characterized in that: The step 7 also 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 of an offshore detachable floating structure according to claim 1, characterized in that: The slot structure comprises 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 of an offshore detachable floating structure according to claim 1, characterized in that: The contour of the connection between the floating structure and the pressure plate is arc-shaped; the floating structure is sealed and fixedly connected 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 of an offshore detachable floating structure according to claim 1, characterized in that: The pushing device adopts a self-locking hydraulic jack.

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

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