Deepwater cofferdam and first supporting and lowering construction method

Abstract

The invention provides a deepwater cofferdam and a first supporting and lowering construction method. The method comprises the steps that a plurality of steel protection cylinders are inserted and hit in water, and the steel protection cylinders are linearly arranged; the top ends of the multiple steel casings are heightened to a preset height; mounting a hoisting system at the top end of the steel casing; the hanging system sequentially penetrates through the second ring beam, the third ring beam and the fourth ring beam through a hanging line to form a supporting frame; the brackets on the multiple steel casings are dismantled, and the whole supporting frame is lowered to the designed elevation through the hoisting system; mounting a bracket for assembling a first ring beam on the plurality of steel casings, and connecting the first ring beam with the bracket; pumping water in the foundation pit to a certain height below each ring beam, and constructing and padding mortar in a dry environment; according to the deepwater cofferdam and the first supporting and lowering construction method, the problems that a cofferdam in deepwater is low in construction efficiency and high in installation and maintenance cost are solved.

Description

A method for constructing a deep-water cofferdam and lowering pre-supports. Technical Field

[0001] This invention relates to the technical field of deep-water cofferdams, and in particular to a deep-water cofferdam and a method for lowering pre-supports during construction. Background Technology

[0002] Deep-water cofferdams are key facilities used in hydraulic engineering projects such as water conservancy and bridges to construct temporary or permanent structures (such as bridge piers and dam foundations) in deep water. Their main function is to isolate the water body from the work area during construction, creating a dry environment for excavation, pouring and other operations.

[0003] Currently, existing deep-water cofferdams suffer from the following technical problems: 1. Low construction efficiency: Traditional deep-water cofferdams are constructed using the post-support method. Since this method involves driving retaining piles first and then lowering the walers layer by layer, it's difficult to guarantee the positioning accuracy of the driven piles, and the construction time is long and inefficient. 2. High installation and maintenance costs: The traditional post-support method involves complex construction methods and numerous steps, requiring more auxiliary equipment and manpower, thus increasing the cost of installation and maintenance. 3. Unfavorable stress on retaining piles: Because the post-support method involves driving retaining piles first, and then pumping water into the cofferdam before installing the supporting walers, the resulting water level difference between the inside and outside of the cofferdam causes the retaining piles to bear a water pressure from the outside to the inside of the cofferdam. This is unfavorable for calculating the stress on the retaining piles. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the technical problem to be solved by the present invention is to provide a deep-water cofferdam and a method for lowering the pre-support, which solves the problems of low construction efficiency, high installation and maintenance costs, and unfavorable stress on the retaining piles in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for the pre-supporting and lowering construction of a deep-water cofferdam, comprising:

[0006] Multiple steel casings are driven into the water and arranged linearly; the tops of the multiple steel casings are raised to a preset height; at least one bracket is installed on each of the multiple steel casings, and the fourth ring beam is connected to the bracket on the multiple steel casings.

[0007] Install a connecting system on the fourth ring beam, and use the connecting system to vertically install the third ring beam on the fourth ring beam. Repeat the above steps to install a connecting system on the third ring beam, and use the connecting system to vertically install the second ring beam on the third ring beam.

[0008] A hoisting system is installed at the top of the steel casing;

[0009] The hoisting system is passed sequentially through the second, third, and fourth ring beams via a hoisting line to form a support frame; the brackets on the multiple steel casings are removed, and the support frame is lowered as a whole to the design elevation using the hoisting system; then, brackets for assembling the first ring beam are installed on the multiple steel casings, and the first ring beam is connected to the brackets;

[0010] Retaining piles are driven into the water, and steel plates are used to pad between each ring beam and each retaining pile to ensure that each ring beam and each retaining pile fits tightly together.

[0011] Water was pumped out of the foundation pit to a certain height below each of the ring beams. Corbels were installed below each of the ring beams and welded to the retaining piles. Mortar was then applied in a dry environment.

[0012] After completing the above steps, water is pumped into the pit to the bottom, and the base structure is poured to complete the cofferdam.

[0013] As a more preferred approach, the support frame consists of multiple vertically spaced ring beams and multiple connecting systems. The connecting systems include horizontal or diagonal connecting members positioned between adjacent ring beams. Through the connection of these connecting members, the multiple ring beams are combined into a single rigid three-dimensional truss structure. Traditional planar ring beam structures (horizontally arranged only) are susceptible to water pressure, wave forces, or impact loads during lowering in deep water environments, resulting in out-of-plane bending or local instability (such as deflection of a single ring beam due to its large span). By connecting multiple ring beams into a rigid three-dimensional truss through a connecting system (horizontal / diagonal connecting members), a three-dimensional spatial force system is formed: the horizontal connecting members can constrain the horizontal displacement of adjacent ring beams and suppress the lateral sway of the ring beams; the diagonal connecting members (similar to truss web members) use the principle of triangular stability to convert the bending load of a single ring beam into axial tensile and compressive loads, significantly reducing the bending moment of the ring beam and avoiding excessive local deformation. This makes the support frame more "stable" during underwater lowering or dewatering, less prone to torsion or instability due to external forces, and ensures the accuracy of subsequent retaining pile installation and structural safety. In addition, the loads of deep-water cofferdams (such as water pressure, retaining pile reaction force, and their own weight) need to be evenly transferred to the steel casing or lowering system through the support frame. If traditional layered ring beams rely solely on brackets or simple connections, the load is easily concentrated in a few ring beams (such as the lowest ring beam bearing most of the retaining pile reaction force), leading to local stress exceeding limits. Multiple ring beams form a parallel force transmission path through a connecting system, allowing the load to spread gradually along the ring beams to the connecting system and then to other ring beams, thus avoiding overloading of a single ring beam. The introduction of diagonal members can decompose the vertical load (such as the self-weight when lowered) into the axial force of the ring beam, reducing moment concentration and extending the service life of the ring beam.

[0014] As a preferred method, the hoisting system includes a hollow jack and an electrical control cabinet that works with the hollow jack. The hoisting line is a steel strand, one end of which is fixed above the hollow jack, and the other end passes through each ring beam of the support frame sequentially before being fixed to the bottom of the fourth ring beam. The steel strand is retracted or extended by the lifting or lowering stroke of the hollow jack to lower or raise the support frame as a whole. The support frame is composed of multiple vertically spaced ring beams connected by a connecting system. If the displacement of each ring beam is not synchronized during lowering (e.g., the upper ring beam is lowered faster than the lower one), it can easily lead to shearing of the connecting system or misalignment of the ring beams, compromising the structural integrity of the frame. By having the steel strand pass through the preset lifting points (such as the node plates of the ring beams) of each ring beam sequentially, it is equivalent to "connecting" all the ring beams with a continuous steel strand. When the hollow jacks raise and lower the steel strands, all ring beams are lifted or lowered synchronously (with consistent displacement), avoiding frame twisting or connection failure caused by asynchronous movement, thus making the lowering process of the support frame smoother. Furthermore, in deep-water cofferdam construction, the lowering speed of the support frame needs to be dynamically adjusted according to water depth and frame weight, while controlling the lowering posture. The hollow jacks, through hydraulic cylinder lifting and retraction, can accurately raise and lower the steel strands, and the coordinated action of multiple lifting points prevents the support frame from tilting, maintaining the stability of the lowering system. Moreover, given the unpredictable factors in the aquatic environment (such as frame swaying due to water flow impact or slight settlement of the steel casing), the design of fixing one end of the suspension line to the top of the hollow jack and the other end to the bottom of the fourth ring beam creates a closed-loop force, preventing the risk of single-end detachment. If a certain lifting point becomes loose due to an accident (such as cracking of the weld of the ring beam lifting lug), the steel strand can still transfer the load through other lifting points to prevent the frame from falling, reduce the risk of structural damage caused by equipment failure or environmental disturbance, and ensure the safety of construction personnel and equipment.

[0015] As a more preferred embodiment, the hoisting system further includes a load-bearing beam assembly for mounting on top of the steel casing. The load-bearing beam assembly includes one or more spreader beams transversely positioned on top of the steel casing, and at least one distribution beam connected above the spreader beams and providing an installation plane for the hoisting system. The hoisting system is fixedly mounted on the distribution beam. By adding a load-bearing beam assembly (spreader beam + distribution beam) to the hoisting system and fixing the hoisting system to the distribution beam, in the pre-support lowering construction of deep-water cofferdams, the overall weight of the support frame is significant. If the weight is directly borne by a few lifting points or a single steel casing, it is easy to cause local overload or even instability. The spreader beams spanning multiple steel casings can evenly distribute the concentrated load to each steel casing, fully utilizing the load-bearing capacity of the steel casing group, significantly reducing the stress level of a single steel casing, preventing deformation or damage, and improving the stability and safety of the lowering process. Secondly, the distribution beam provides a flat and continuous installation plane for the hoisting system, ensuring symmetrical force distribution at the hoisting points and preventing frame tilting, twisting, or jamming caused by uneven equipment layout or uneven force distribution during hoisting, thereby improving lowering accuracy and success rate. Furthermore, the introduction of the load-bearing beam assembly enhances the overall rigidity and vibration resistance of the hoisting system. During hoisting, water flow, waves, or equipment operation may cause vibrations; the rigid platform formed by the spreader beam and distribution beam effectively suppresses vibration transmission, maintaining stable operation of the hoisting system and reducing the risk of ring beam displacement or abnormal stress on the connection system due to swaying. Moreover, this load-bearing beam assembly facilitates construction and equipment layout: the spreader beam and distribution beam can be assembled on-site, making installation convenient and safe, reducing the risks of working at heights or near water.

[0016] As a preferred approach, the connections between the spreader beam and the steel casing, as well as between the spreader beam and the distribution beam, are all welded and fixed to jointly bear the weight of the hoisting system and the support frame, as well as the dynamic loads during the lowering process. Welding is used to fix the spreader beam to the steel casing and the spreader beam to the distribution beam. Welded connections create a continuous and seamless force transmission path, allowing the spreader beam, steel casing, and distribution beam to function as a single frame under working loads. This avoids loosening, slippage, or gaps that may occur with bolted or snap-fit ​​connections, thus maintaining shape stability when bearing the weight of the hoisting system and support frame, preventing local deformation or instability. Secondly, welding can efficiently transfer static and dynamic loads. During the lowering of a deep-water cofferdam, in addition to the structure's own weight, it is also subject to dynamic loads such as starting / braking inertial forces, water flow impact forces, and wave excitation. The high rigidity and integrity of the welded joints can quickly and evenly distribute these loads to each steel casing, reducing stress concentration and fatigue damage, and improving the safety of the lowering process. Furthermore, compared to bolted connections, welded joints do not require regular checks of tightness and eliminate the risk of loose nuts or worn pins, making them particularly suitable for temporary underwater or above-water load-bearing structures. This reduces the workload and failure rate of operation and maintenance. Welding also creates a stable upper platform between the spreader beam and the distribution beam, allowing for the secure installation of the hollow jacks, control boxes, and other equipment in the hoisting system. This prevents displacement due to vibration or load changes, ensuring accurate hoisting point positioning and symmetrical force distribution, thereby improving the stability and precision of lowering the support frame.

[0017] As a preferred method, the connecting system is welded and fixed to the second, third, and fourth ring beams respectively using circumferential fillet welds. By using circumferential fillet welds to fix the connecting system to the second, third, and fourth ring beams, the continuous circumferential welds firmly "wrap" the connecting system and the ring beams into a single unit, eliminating the gaps and looseness that may occur with traditional intermittent or single-sided welding. This makes the connecting system and the ring beams behave as a rigid node under stress, effectively suppressing relative rotation or displacement between them and ensuring the geometric accuracy and positional stability of the multiple ring beams during the launching process. Secondly, the circumferential fillet welds can evenly transmit multi-directional loads. During the lowering of the cofferdam and subsequent use, the connecting system will bear bending moments, shear forces, and axial forces from different directions (such as lowering impact, water flow loads, and earth pressure). The continuous circumferential distribution of the circumference of the welds can evenly distribute the load along the circumference of the ring beams, avoiding local stress concentration, reducing the risk of weld fatigue cracking, and improving the durability and safety of the connecting system. Furthermore, since the connecting system and the ring beam form a rigid closed loop, the support frame has a stronger overall coordinated deformation capacity when subjected to uneven loads or vibrations, which can significantly reduce the probability of local instability or connection failure and ensure the stability of the cofferdam during the construction and operation periods.

[0018] To address the aforementioned technical problems, the present invention also provides a deep-water cofferdam, comprising:

[0019] A support component, and a waler component disposed around the outer ring of the support component;

[0020] The support assembly includes: a ring beam, a bracket, and support beams; the ring beam is connected to the steel casing through the bracket, and the two ends of each support beam are fixedly overlapped on the adjacent sides of the ring beam; multiple support beams within each ring beam are arranged alternately.

[0021] The waler assembly includes: retaining piles and fasteners; a plurality of the retaining piles are connected by the fasteners to form a square waler around the support assembly.

[0022] As a preferred approach, the ring beam is a steel truss beam with internal stiffening ribs to enhance its rigidity. Using a steel truss beam structure with built-in stiffening ribs in the ring beam, with the material primarily distributed away from the neutral axis due to the steel truss beam's triangular stabilizing elements, allows for high bending and shear stiffness with relatively low self-weight. This is particularly suitable for large-span cofferdam ring beams subjected to large-area water and soil pressure in deep-water environments. The addition of stiffening ribs further suppresses local buckling of the ring beam's web and flanges under compression, significantly improving the out-of-plane and nodal stability of the truss beam, thereby enhancing its overall load-bearing capacity. Secondly, the steel truss beam has a clear and uniform force path, with loads redistributed at the truss nodes, avoiding stress concentration. The stiffening ribs further homogenize the stress distribution in the nodal areas, reducing fatigue risks at welds or bolted connections, thus improving durability. Because the spatial stress system formed by the steel truss beam and the internal stiffening ribs has high resistance to bending, shear and buckling, the ring beam deforms less under the action of cofferdam dewatering, wave impact and uneven earth pressure, and can maintain the geometric accuracy of the cofferdam and the fit of the water-stopping structure, thereby improving the safety and reliability of the entire cofferdam.

[0023] As a preferred method, the bracket is a steel support welded to the top of the steel casing, used to temporarily fix the ring beam during the lowering of the cofferdam. In the pre-support lowering construction of deep-water cofferdams, the ring beam needs to be assembled and connected in multiple layers on the steel casing. Without reliable temporary fixation, it is susceptible to displacement or overturning due to disturbances caused by hoisting, welding, and personnel operations. The rigid welded connection between the steel support and the steel casing ensures that the ring beam maintains a fixed elevation and planar position during prefabrication, guaranteeing the relative geometric accuracy between each ring beam and providing a stable foundation for subsequent cable laying and overall lowering of the hoisting system. Furthermore, the steel support has a simple structure and is easy to install. It can be prefabricated or quickly cut and welded on-site, requiring no additional embedded parts or complex assembly, significantly shortening the process connection time and improving construction efficiency. Furthermore, the welded joints directly transfer the ring beam load to the steel casing. The steel section can be selected based on the weight of the ring beam and the construction load, ensuring that no yielding or instability occurs during hoisting, connection system installation, and tensioning of the hoisting system. Compared to temporary bolts or clamps, welded fixing eliminates the risk of loosening and prevents ring beam displacement due to vibration or impact during construction. Moreover, as a temporary structure, the steel support frame does not remain in the final cofferdam structure after the support frame is lowered and dismantled, avoiding long-term space occupation or impact on subsequent processes, thus improving material utilization and reducing material costs.

[0024] As a preferred method, the fasteners are connecting hooks and locks, which are respectively installed on the outer wall of adjacent retaining piles. The connecting hooks are looped onto the locks to connect and fix two adjacent retaining piles. In deep-water cofferdam construction, retaining piles often need to be driven and positioned one by one on site. By using loop-type fasteners with connecting hooks and locks between the retaining piles, the assembled connection of the hooks and locks can be directly looped and fixed after the piles are in place, which greatly shortens the waler closure time and improves construction efficiency. This is especially suitable for cofferdam projects with tight schedules or requiring multiple disassemblies and reassemblies. Secondly, this connection method avoids structural damage to the retaining pile body. Welding or bolt penetration will create a heat-affected zone on the pile body or weaken the cross section of the borehole, reducing the bearing capacity and water-stopping performance of the pile. The hooks and locks are installed on the pre-set supports on the outer wall of the pile, without damaging the main structure of the pile body, maintaining the original strength and water-stopping sealing of the retaining pile, and ensuring that the overall water-blocking and stress-bearing performance of the cofferdam is not affected. In addition, the interlocking structure can ensure sufficient tensile, shear and impact resistance in the design, and the anti-loosening pins or locking bolts can prevent accidental disengagement caused by vibration or water flow impact, ensuring the connection stability of the waler under deep water environment load.

[0025] As described above, the deep-water cofferdam pre-support and lowering construction method of the present invention has the following beneficial effects: When using the deep-water cofferdam pre-support and lowering construction method of the present invention, multiple ring beams and connecting systems are pre-assembled on the steel casing to form a stable support frame. Then, the entire structure is lowered to the design elevation in one go using a hoisting system. This ensures that the position, elevation, and verticality of each ring beam are achieved in one go, avoiding the cumulative errors caused by layer-by-layer underwater installation, and improving the geometric accuracy and overall structural stability of the cofferdam. The ring beams, connecting systems, etc., are assembled in a safe environment above or near the water surface, which reduces construction safety risks and equipment investment, and improves construction efficiency.

[0026] By pumping water from the foundation pit to a certain height below the ring beam to create a dry environment, the corbels are installed and the mortar is applied. This ensures that the mortar is full and dense, tightly bonded to the ring beam and retaining piles, avoiding voids and insufficient strength caused by underwater casting, and significantly improving the water-stopping and load-bearing performance of the cofferdam. The tight fit between the ring beam and retaining piles, the dense mortar, and the integral casting of the base structure form a continuous and reliable water-retaining system, significantly improving the water-stopping effect and long-term durability of the cofferdam and reducing the risk of leakage.

[0027] The process of first supporting and then lowering, installing ring beams layer by layer, steel plate padding, and dry environment mortar construction helps to shorten the construction period. The space frame structure formed by the equally spaced steel casing and the multi-layer ring beams has high rigidity and good integrity, which can effectively resist the action of deep water waves, water flow and soil pressure, and improve the service life of the cofferdam.

[0028] When the deep-water cofferdam of the present invention is in use, the staggered arrangement of the support beams distributes the load along multiple paths in the circumference of the ring beam, avoiding overloading of a single support point; the brackets transfer the load of the ring beam to the steel casing, and the group of steel casings evenly bears the overall weight and external water and soil pressure, reducing local stress concentration and improving structural safety and durability.

[0029] The retaining piles are connected by fasteners to form a square waler, which surrounds the outer ring of the support components to form a continuous and closed water barrier, which can effectively prevent external water from seeping into the foundation pit; the fasteners ensure a tight connection between the retaining piles, reduce the risk of leakage at the joints, and improve the water-stopping effect of the cofferdam.

[0030] The internal support components are responsible for bearing and distributing the load and maintaining the geometric shape, while the external waler components are responsible for blocking water and protecting the structure. Together, they form a composite structural system of "internal support and external protection", which not only improves the overall stability of the cofferdam, but also enhances its waterproof and erosion resistance.

[0031] The supporting beams are lapped and fixed on the adjacent sides of the ring beam, and the retaining piles are connected by fasteners. Both can be quickly assembled into a closed waler in water or dry environments, which is convenient for installation and maintenance. Moreover, the materials can be reused, which helps to reduce project costs. Attached Figure Description

[0032] Figure 1 shows a front view of the construction method for deep-water cofferdam and pre-support lowering according to the present invention;

[0033] Figure 2 shows a top view of the deep-water cofferdam and pre-support lowering construction method of the present invention;

[0034] Figure 3 shows a magnified view of a portion of point A in Figure 2;

[0035] Figure 4 shows a schematic diagram of the hoisting system of a deep-water cofferdam and pre-support lowering construction method according to the present invention.

[0036] Component designation explanation

[0037] 1. Support Components 11. Ring Beam 111 First Ring Beam 112 Second Ring Beam 113 Third Ring Beam 114 Fourth Ring Beam 12. Bracket 13. Support Beam 2. Waler Components 21. Retaining Piles 22. Fasteners 3. Steel Casing 4. Lifting System 41. Load-bearing Beam Components 411. Spreader Beam 412. Distribution Beam 42. Hanging Line 5. Connection System surface Detailed Implementation

[0038] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0039] It should be understood that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation of the invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the disclosed technical content. The following detailed description should not be considered restrictive, and the scope of the embodiments of this application is limited only by the claims of the published patents. The terminology used herein is for describing specific embodiments only and is not intended to limit the application. Spatial terms such as "upper," "lower," "left," "right," "below," "below," "lower part," "above," "upper part," etc., may be used in the text to illustrate the relationship between one element or feature shown in the figures and another element or feature.

[0040] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," and "holding" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0041] Furthermore, as used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context indicates otherwise. It should be further understood that the terms “comprising,” “including,” indicate the presence of the stated feature, operation, element, component, item, kind, and / or group, but do not preclude the presence, occurrence, or addition of one or more other features, operations, elements, components, items, kinds, and / or groups. The terms “or” and “and / or” as used herein are interpreted as inclusive, or mean any one or any combination thereof. Thus, “A, B, or C” or “A, B, and / or C” means “any one of: A; B; C; A and B; A and C; B and C; A, B, and C.” Exceptions to this definition arise only when combinations of elements, functions, or operations are inherently mutually exclusive in some manner.

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the invention.

[0043] As shown in Figures 1 to 4, the present invention provides a method for the pre-supporting and lowering construction of a deep-water cofferdam, comprising:

[0044] Multiple steel casings 3 are driven into the water and are arranged linearly; the tops of the multiple steel casings 3 are raised to a preset height; at least one bracket 12 is installed on each of the multiple steel casings 3, and the fourth ring beam 114 is connected to the bracket 12 on the multiple steel casings 3.

[0045] Install the connecting system 5 on the fourth ring beam 114, and install the third ring beam 113 vertically on the fourth ring beam 114 through the connecting system 5. Repeat the above steps to install the connecting system 5 on the third ring beam 113, and install the second ring beam 112 vertically on the third ring beam 113 through the connecting system 5.

[0046] A hoisting system 4 is installed at the top of the steel casing 3;

[0047] The hoisting system 4 is passed sequentially through the second ring beam 112, the third ring beam 113, and the fourth ring beam 114 via the hoisting line 42 to form a support frame; the brackets 12 on the multiple steel casings 3 are removed, and the support frame is lowered to the design elevation as a whole via the hoisting system 4; then, brackets 12 for assembling the first ring beam 11111 are installed on the multiple steel casings 3, and the first ring beam 111 is connected to the brackets 12;

[0048] Retaining piles 21 are driven into the water, and steel plates are used to pad between each ring beam 11 and each retaining pile 21 so that each ring beam 11 and each retaining pile 21 are tightly fitted together.

[0049] Pump water into the foundation pit to a certain height below each ring beam 11, install corbels below each ring beam 11 and weld them to the retaining piles 21, and construct the padding mortar in a dry environment.

[0050] After completing the above steps, water is pumped into the pit to the bottom, and the base structure is poured to complete the cofferdam.

[0051] In some embodiments of the present invention, as shown in Figures 2 and 4, the support frame consists of multiple vertically spaced ring beams 11 and multiple connecting systems 5. The connecting system 5 includes horizontal or oblique connecting members disposed between adjacent ring beams 11. Through the connection of the connecting members, the multiple ring beams 11 are combined into a rigid three-dimensional truss structure. Traditional planar ring beam 11 structures (horizontally arranged only) are susceptible to water pressure, wave force, or impact loads during the lowering process in deep water environments, resulting in out-of-plane bending or local instability (such as deflection of a single ring beam 11 due to its large span). The multiple ring beams 11 are connected into a rigid three-dimensional truss by the connecting system 5 (horizontal / diagonal connecting members), forming a three-dimensional spatial force system: the horizontal connecting members can constrain the horizontal displacement of adjacent ring beams 11 and suppress the lateral sway of the ring beams 11; the diagonal connecting members (similar to truss web members) use the principle of triangular stability to convert the bending load of a single ring beam 11 into an axial tensile and compressive load, significantly reducing the bending moment of the ring beam 11 and avoiding excessive local deformation. This makes the support frame more "stable" during underwater lowering or pumping, less prone to torsion or instability due to external forces, and ensures the installation accuracy and structural safety of the subsequent retaining piles 21. In addition, the load of the deep-water cofferdam (such as water pressure, reaction force of retaining piles 21, and its own weight) needs to be evenly transferred to the steel casing 3 or lowering system through the support frame. If the traditional layered ring beams 11 are only connected by brackets 12 or simple connections, the load is easily concentrated on a few ring beams 11 (such as the lowest ring beam 11 bearing most of the reaction force of the retaining piles 21), resulting in local stress exceeding the limit. Multiple ring beams 11 form a "parallel" force transmission path through the connecting system 5. The load can be distributed step by step along the ring beams 11 to the connecting system 5 and then to other ring beams 11, avoiding overloading of a single ring beam 11. The introduction of diagonal members can decompose the vertical load (such as the self-weight when lowered) into the axial force of the ring beams 11, reducing moment concentration and extending the service life of the ring beams 11.

[0052] In some embodiments of the present invention, as shown in Figure 4, the hoisting system includes a hollow jack and an electrical control cabinet that cooperates with the hollow jack. The hoisting line is a steel strand, one end of which is fixed above the hollow jack, and the other end passes through each ring beam of the support frame in sequence and is then fixed to the bottom of the fourth ring beam. The steel strand is retracted or extended by the lifting or lowering stroke of the hollow jack to lower or lift the support frame as a whole. The support frame is composed of multiple vertically spaced ring beams connected by a connecting system. If the displacement of each ring beam is not synchronized during lowering (e.g., the upper ring beam is lowered faster than the lower one), it is easy to cause shearing of the connecting system or misalignment of the ring beams, which will damage the integrity of the frame structure. By passing the steel strand through the preset lifting points (such as the node plates of the ring beams) of each ring beam in sequence, it is equivalent to "connecting" all the ring beams with a continuous steel strand. When the hollow jacks raise and lower the steel strands, all ring beams are lifted or lowered synchronously (with consistent displacement), avoiding frame twisting or connection failure caused by asynchronous movement, thus making the lowering process of the support frame smoother. Furthermore, in deep-water cofferdam construction, the lowering speed of the support frame needs to be dynamically adjusted according to water depth and frame weight, while controlling the lowering posture. The hollow jacks, through hydraulic cylinder lifting and retraction, can accurately raise and lower the steel strands, and the coordinated action of multiple lifting points prevents the support frame from tilting, maintaining the stability of the lowering system. Moreover, given the unpredictable factors in the aquatic environment (such as frame swaying due to water flow impact or slight settlement of the steel casing), the design of fixing one end of the suspension line to the top of the hollow jack and the other end to the bottom of the fourth ring beam creates a closed-loop force, preventing the risk of single-end detachment. If a certain lifting point becomes loose due to an accident (such as cracking of the weld of the ring beam lifting lug), the steel strand can still transfer the load through other lifting points to prevent the frame from falling, reduce the risk of structural damage caused by equipment failure or environmental disturbance, and ensure the safety of construction personnel and equipment.

[0053] In some embodiments of the present invention, as shown in FIG4, the hoisting system 4 further includes a load-bearing beam assembly 41 for mounting on the top of the steel casing 3; the load-bearing beam assembly 41 includes one or more horizontally arranged spreader beams 411 on the top of the steel casing 3, and at least one distribution beam 412 connected above the spreader beams 411 and providing an installation plane for the hoisting system 4; the hoisting system 4 is fixedly installed on the distribution beam 412. By adding the load-bearing beam assembly 41 (spreader beam 411 + distribution beam 412) to the hoisting system 4 and fixing the hoisting system 4 to the distribution beam 412, in the construction of deep-water cofferdam pre-support lowering, the overall weight of the support frame is large. If it is directly supported by a few hoisting points or a single steel casing 3, it is easy to cause local overload or even instability. The spreader beam 411 spans multiple steel casings 3, evenly distributing the concentrated load to each casing 3. This fully utilizes the load-bearing capacity of the group of casings 3, significantly reducing the stress level of individual casings 3, preventing deformation or damage, and improving the stability and safety of the lowering process. Secondly, the distribution beam 412 provides a flat and continuous installation plane for the lowering system 4, ensuring symmetrical force distribution at the lifting points and preventing frame tilting, twisting, or jamming due to uneven equipment layout or uneven force distribution during lowering, thereby improving lowering accuracy and success rate. Furthermore, the introduction of the load-bearing beam assembly 41 enhances the overall rigidity and vibration resistance of the lowering system 4. During lowering, water flow, waves, or equipment operation may cause vibration. The rigid platform formed by the spreader beam 411 and the distribution beam 412 effectively suppresses vibration transmission, maintaining the stable operation of the lowering system 4 and reducing positional displacement of the ring beam 11 or abnormal stress on the connection system 5 caused by swaying. Furthermore, the load-bearing beam assembly 41 facilitates construction and equipment layout: the spreader beam 411 and the distribution beam 412 can be assembled on-site, making installation convenient and safe, and reducing the risks of working at heights or near water.

[0054] In some embodiments of the present invention, as shown in FIG4, the connections between the spreader beam 411 and the steel casing 3, and between the spreader beam 411 and the distribution beam 412, are all welded and fixed to jointly bear the weight of the hoisting system 4 and the support frame, as well as the dynamic load during the lowering process. Welding is used to fix the spreader beam 411 to the steel casing 3 and to the distribution beam 412. Welded connections form a continuous and seamless force transmission path, allowing the spreader beam 411, the steel casing 3, and the distribution beam 412 to function as a single frame under working loads. This avoids loosening, slippage, or gaps that may occur with bolt or snap-fit ​​connections, thereby maintaining shape stability when bearing the weight of the hoisting system 4 and the support frame, and preventing local deformation or instability. Secondly, welding can efficiently transfer static and dynamic loads. During the lowering of deep-water cofferdams, in addition to the structure's own weight, it is also subject to dynamic loads such as starting / braking inertia, water flow impact, and wave excitation. The high rigidity and integrity of welded joints can quickly and evenly distribute these loads to each steel casing 3, reducing stress concentration and fatigue damage, and improving the safety of the lowering process. In addition, compared with bolted connections, welded joints do not require regular checks on tightness and there is no risk of loose nuts or worn pins. They are particularly suitable for temporary load-bearing structures underwater or above water, reducing the workload and failure rate of operation and maintenance. Furthermore, welding forms a stable upper platform between the spreader beam 411 and the distribution beam 412, allowing the hollow jacks, control boxes, and other equipment of the hoisting system 4 to be securely installed without displacement due to vibration or load changes. This ensures accurate hoisting point positioning and symmetrical force distribution, thereby improving the stability and accuracy of the lowering of the support frame.

[0055] In some embodiments of the present invention, as shown in FIG4, the connecting system 5 is welded and fixed to the second ring beam 112, the third ring beam 113, and the fourth ring beam 114 by circumferential fillet welds. By welding and fixing the connecting system 5 to the second, third, and fourth ring beams 11 by circumferential fillet welds, the continuous circumferential welds firmly "wrap" the connecting system 5 and the ring beams 11 into one unit, eliminating the gaps and looseness that may be caused by traditional intermittent welding or single-sided welding. This makes the connecting system 5 and the ring beams 11 behave as a rigid node when under stress, effectively suppressing the relative rotation or displacement between the two, and ensuring the geometric accuracy and positional stability of the multiple ring beams 11 during the launching process. Secondly, the circumferential fillet welds can evenly transfer multi-directional loads. During the lowering of the cofferdam and its subsequent use, the connecting system 5 will bear bending moments, shear forces, and axial forces from different directions (such as lowering impact, water flow loads, and earth pressure). The circumferential welds are continuously distributed along the circumference, which can evenly spread the load along the ring beam 11, avoiding local stress concentration, reducing the risk of weld fatigue cracking, and improving the durability and safety of the connecting system 5. In addition, since the connecting system 5 and the ring beam 11 form a rigid closed loop, the supporting frame has a stronger overall coordinated deformation capacity when subjected to uneven loads or vibrations, which can significantly reduce the probability of local instability or connection failure, ensuring the stability of the cofferdam during construction and operation.

[0056] As shown in Figures 1 to 4, the present invention also provides a deep-water cofferdam, comprising:

[0057] Support component 1, and waler component 2 arranged around the outer ring of the support component 1;

[0058] The support assembly 1 includes: a ring beam 11, a bracket 12, and a support beam 13; the ring beam 11 is connected to the steel casing 3 through the bracket 12, and the two ends of each support beam 13 are respectively fixedly attached to the adjacent two sides of the ring beam 11; the multiple support beams 13 in each ring beam 11 are arranged alternately.

[0059] The waler assembly 2 includes: retaining piles 21 and fasteners 22; a plurality of retaining piles 21 are connected by the fasteners 22 to form a square waler around the support assembly 1.

[0060] In some embodiments of the present invention, as shown in Figure 2, the ring beam 11 is a steel truss beam, and stiffening ribs are provided inside the ring beam 11 to improve its stiffness. The use of a steel truss beam structure with built-in stiffening ribs in the ring beam 11, due to the steel truss beam being based on triangular stable elements and the material mainly distributed away from the neutral axis, allows for high bending and shear stiffness with relatively low self-weight, making it particularly suitable for large-span cofferdam ring beams 11 to withstand large-area water and soil pressure in deep-water environments. The addition of stiffening ribs further suppresses local buckling of the web and flanges of the ring beam under compression, significantly improving the out-of-plane and nodal stability of the truss beam, thereby enhancing the overall load-bearing capacity of the ring beam 11. Secondly, the force path of the steel truss beam is clear and uniformly distributed, with loads redistributed at the truss nodes, avoiding stress concentration; the stiffening ribs further homogenize the stress distribution in the nodal area, reducing the fatigue risk at welds or bolted connections, thereby improving durability. Because the spatial stress system formed by the steel truss beam and the internal stiffening ribs has high resistance to bending, shear and buckling, the ring beam 11 deforms less under the action of cofferdam dewatering, wave impact and uneven earth pressure, and can maintain the geometric accuracy of the cofferdam and the fit of the water-stopping structure, thereby improving the safety and reliability of the entire cofferdam.

[0061] In some embodiments of the present invention, as shown in Figures 2 and 4, the bracket 12 is a steel support welded to the top of the steel casing 3, used to temporarily fix the ring beam 11 during the lowering of the cofferdam. During the pre-support lowering construction of the deep-water cofferdam, the ring beam 11 needs to be assembled and connected in multiple layers on the steel casing 3. Without reliable temporary fixing, it is easily displaced or overturned due to disturbances caused by hoisting, welding, and personnel operations. The rigid welded connection between the steel support and the steel casing 3 ensures that the ring beam 11 maintains a fixed elevation and planar position during prefabrication, guaranteeing the relative geometric accuracy between each ring beam 11, and providing a stable foundation for the subsequent threading and overall lowering of the hoisting system 4. Furthermore, the steel support has a simple structure and is easy to install. It can be prefabricated in advance or quickly cut and welded on-site, without the need for additional embedded parts or complex assembly, significantly shortening the process connection time and improving construction efficiency. Furthermore, the welded joints directly transfer the load of the ring beam 11 to the steel casing 3. The steel section can be selected according to the weight of the ring beam 11 and the construction load, ensuring that no yielding or instability occurs during hoisting, installation of the connection system 5, and tensioning of the hoisting system 4. Compared with temporary bolts or clamps, welding fixation eliminates the risk of loosening and avoids displacement of the ring beam 11 due to vibration or impact during construction. Moreover, as a temporary structure, the steel support frame does not remain in the final cofferdam structure after the support frame is lowered and dismantled, avoiding long-term space occupation or impact on subsequent processes, thus improving material utilization and reducing material costs.

[0062] In some embodiments of the present invention, as shown in Figures 1 to 3, the fastener 22 is a connecting hook and a locking buckle. The connecting hook and the locking buckle are respectively installed on the outer wall surface of adjacent retaining piles 21, and the connecting hook is looped onto the locking buckle to connect and fix two adjacent retaining piles 21. In the construction of deep-water cofferdams, retaining piles 21 often need to be driven and positioned on site one by one. By using a loop-type fastener 22 with connecting hooks and locking buckles between the retaining piles 21, the assembled connection of the hooks and locking buckles can be directly looped and fixed after the piles are in place, which greatly shortens the waler closure time and improves construction efficiency. It is particularly suitable for cofferdam projects with tight schedules or requiring multiple disassemblies and reassemblies. Secondly, this connection method avoids structural damage to the retaining pile 21 itself. Welding or bolt penetration would create a heat-affected zone on the pile or weaken the cross-section of the borehole, reducing the pile's bearing capacity and water-stopping performance. The hooks and locks are installed on the pre-set supports on the outer wall of the pile, without damaging the main structure of the pile, maintaining the original strength and water-stopping sealing of the retaining pile 21, and ensuring that the overall water-blocking and stress-bearing performance of the cofferdam is not affected. In addition, the ring-lock structure can ensure sufficient tensile, shear and impact resistance in the design, and the anti-loosening pins or locking bolts can prevent accidental disengagement caused by vibration or water flow impact, ensuring the connection stability of the waler under deep-water environmental loads.

[0063] As described above, the deep-water cofferdam pre-support and lowering construction method of the present invention has the following beneficial effects: When using the deep-water cofferdam pre-support and lowering construction method of the present invention, multiple ring beams 11 and connecting systems 5 are pre-assembled on the steel casing 3 to form a stable support frame, and then lowered to the design elevation in one go by the hoisting system 4. This ensures that the position, elevation, and verticality of each ring beam 11 are in place in one go, avoiding the cumulative errors caused by layer-by-layer underwater installation, and improving the geometric accuracy and overall structural stability of the cofferdam. The ring beams 11, connecting systems 5, etc. are assembled in a safe environment above or near the water surface, which can reduce construction safety risks and equipment investment, and improve construction efficiency.

[0064] By pumping water out of the foundation pit to a certain height below the ring beam 11 to create a dry environment, the corbels are installed and the mortar is applied. This ensures that the mortar is full and dense, tightly bonded to the ring beam 11 and the retaining piles 21, avoiding voids and insufficient strength caused by underwater casting, and significantly improving the water-stopping and load-bearing performance of the cofferdam. The tight fit between the ring beam 11 and the retaining piles 21, the dense mortar, and the integral casting of the base structure form a continuous and reliable water-retaining system, significantly improving the water-stopping effect and long-term durability of the cofferdam and reducing the risk of leakage.

[0065] The process of first supporting and then lowering, installing the ring beam 11 layer by layer, using steel plate pads, and applying dry environmental mortar helps to shorten the construction period. The steel casing 3, which is inserted at equal intervals, forms a spatial frame structure with the multi-layer ring beam 11. It has high rigidity and good integrity, and can effectively resist the effects of deep water waves, water flow and soil pressure, thereby improving the service life of the cofferdam.

[0066] When the deep-water cofferdam of the present invention is in use, the staggered arrangement of the support beams 13 disperses the load along multiple paths around the ring beam 11, avoiding overload of a single support point; the bracket 12 transfers the load of the ring beam 11 to the steel casing 3, and the group of steel casings 3 evenly bears the overall weight and external water and soil pressure, reducing local stress concentration and improving structural safety and durability.

[0067] The retaining piles 21 are connected by fasteners 22 to form a square waler, which surrounds the outer ring of the support component 1 to form a continuous and closed water barrier, which can effectively prevent external water from seeping into the foundation pit; the fasteners 22 ensure a tight connection between the retaining piles 21, reduce the risk of leakage at the joints, and improve the water-stopping effect of the cofferdam.

[0068] The internal support component 1 is responsible for bearing and distributing the load and maintaining the geometric shape, while the external waler component 2 is responsible for blocking water and protecting the structure. Together, they form a composite structural system of "internal support and external protection", which not only improves the overall stability of the cofferdam, but also enhances its waterproof and erosion resistance.

[0069] The support beam 13 is lapped and fixed on the adjacent side of the ring beam 11, and the retaining piles 21 are connected by fasteners 22. Both can be quickly assembled into a closed waler in water or dry environments, which is convenient for installation and maintenance. The materials can be reused, which helps to reduce project costs.

[0070] In summary, the deep-water cofferdam and pre-support lowering construction method of the present invention has the following advantages:

[0071] 1. High overall structural stability:

[0072] Multiple ring beams 11 and connecting systems 5 are pre-assembled on the steel casing 3 to form a stable support frame. Then, the entire structure is lowered to the design elevation in one go through the hoisting system 4, avoiding the cumulative error caused by layer-by-layer underwater installation and improving the geometric accuracy and overall structural stability of the cofferdam.

[0073] 2. Improve construction efficiency:

[0074] The assembly of various structures, including ring beam 11, in a safe environment above or near the water surface reduces construction safety risks and equipment investment, and improves construction efficiency.

[0075] 3. High rigidity and long service life:

[0076] The process of first supporting and then lowering, installing the ring beam 11 layer by layer, using steel plate pads, and applying dry environmental mortar helps to shorten the construction period. The steel casing 3, which is inserted at equal intervals, forms a spatial frame structure with the multi-layer ring beam 11. It has high rigidity and good integrity, and can effectively resist the effects of deep water waves, water flow and soil pressure, thereby improving the service life of the cofferdam.

[0077] In summary, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0078] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for constructing a deep-water cofferdam by first setting up and lowering it, characterized in that, include: Multiple steel casings are driven into the water, and the multiple steel casings are arranged in a linear manner; and the top of the multiple steel casings is raised to a preset height. At least one bracket is installed on each of the multiple steel casings, and a fourth ring beam is connected to the brackets on the multiple steel casings; a connecting system is installed on the fourth ring beam, and a third ring beam is vertically installed on the fourth ring beam through the connecting system; the above steps are repeated, and a connecting system is installed on the third ring beam, and a second ring beam is vertically installed on the third ring beam through the connecting system; a hoisting system is installed at the top of the steel casings; the hoisting system is passed sequentially through the second ring beam, the third ring beam, and the fourth ring beam via a hanging line to form a support frame; the brackets on the multiple steel casings are removed, and the connecting system is connected to the fourth ring beam through the fourth ring beam. The hoisting system lowers the entire support frame to the design elevation; then, brackets for assembling the first ring beam are installed on multiple steel casings, and the first ring beam is connected to the brackets; retaining piles are driven into the water, and steel plates are used to pad between each ring beam and each retaining pile to ensure a tight fit between each ring beam and each retaining pile; water is pumped out of the pit to a certain height below each ring beam, corbels are installed below each ring beam and welded to the retaining piles, and padding mortar is applied in a dry environment; after completing the above steps, water is pumped out of the pit to the bottom, and the base structure is poured to complete the cofferdam.

2. The method for constructing a deep-water cofferdam by first setting up and lowering it according to claim 1, characterized in that: The supporting frame consists of multiple ring beams spaced vertically and multiple connecting systems. The connecting system includes horizontal or diagonal connecting members set between adjacent ring beams. Through the connection of the connecting members, the multiple ring beams are combined into a rigid three-dimensional truss structure.

3. The method for constructing a deep-water cofferdam by first setting up and lowering it according to claim 1, characterized in that: The hoisting system includes a hollow jack and an electrical control cabinet that works with the hollow jack; the hoisting line is a steel strand, one end of which is fixed above the hollow jack, and the other end passes through each ring beam of the support frame and is fixed to the bottom of the fourth ring beam; the steel strand is retracted or extended by the lifting or lowering stroke of the hollow jack to lower or lift the support frame as a whole.

4. The method for constructing a deep-water cofferdam by first setting up and lowering it according to claim 1, characterized in that: The hoisting system also includes a load-bearing beam assembly for mounting on the top of the steel casing; the load-bearing beam assembly includes one or more spreader beams arranged laterally on the top of the steel casing, and at least one distribution beam connected above the spreader beams and providing an installation plane for the hoisting system; the hoisting system is fixedly installed on the distribution beam.

5. The method for constructing a deep-water cofferdam by first setting up and lowering it according to claim 4, characterized in that: The connections between the spreader beam and the steel casing, as well as between the spreader beam and the distribution beam, are all welded and fixed to jointly bear the weight of the hoisting system and the support frame, as well as the dynamic load during the lowering process.

6. The method for constructing a deep-water cofferdam by first setting up and lowering it according to claim 1, characterized in that: The connecting system is welded and fixed to the second, third, and fourth ring beams respectively using circumferential fillet welds.

7. A deep-water cofferdam, obtained by the deep-water cofferdam pre-support and lowering construction method according to any one of claims 1 to 6, characterized in that, Includes: a support assembly, and a waler assembly disposed around the outer ring of the support assembly; The support assembly includes: a ring beam, a bracket, and support beams; the ring beam is connected to the steel casing through the bracket, and the two ends of each support beam are fixedly overlapped on the adjacent sides of the ring beam; multiple support beams within each ring beam are arranged alternately; the waler assembly includes: retaining piles and fasteners; multiple retaining piles are connected by the fasteners to form a square waler around the support assembly.

8. A deep-water cofferdam according to claim 7, characterized in that: The ring beam is a steel truss beam, and stiffening ribs are provided inside the ring beam to improve its rigidity.

9. A deep-water cofferdam according to claim 7, characterized in that: The bracket is a steel support welded to the top of the steel casing, used to temporarily fix the ring beam during the lowering of the cofferdam.

10. A deep-water cofferdam according to claim 7, characterized in that: The fasteners are connecting hooks and locks. The connecting hooks and locks are respectively installed on the outer wall surfaces of adjacent retaining piles. The connecting hooks are looped onto the locks to connect and fix two adjacent retaining piles.

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