Cofferdam rapid construction method capable of effectively avoiding back silting by firstly supporting and then piling

Abstract

The invention relates to a cofferdam rapid construction method capable of effectively avoiding back silting through firstly supporting and then piling, and belongs to the technical field of cofferdam construction.The cofferdam rapid construction method includes the steps that on the basis of an existing firstly-supporting method, a part of construction platforms are firstly dismantled, a part of steel casings are heightened, a part of cofferdam steel pipe piles are inserted and driven, desilting is conducted in a cofferdam to be 0.5 m below the designed elevation of an inner support, and the remaining construction platforms are dismantled; cofferdam inner supports are assembled; a hanging system is installed, a cofferdam inner support is lowered, the cofferdam is closed, and desilting is conducted to the bottom elevation of bottom sealing concrete; water is pumped in the cofferdam, bottom sealing concrete is poured, a pile casing is cut, and a pile head is chiseled; and the bearing platform is constructed, after the upper-layer bearing platform reaches the design strength, the upper-layer inner support is dismantled, and the tower base is constructed. During construction, part of steel pipe piles are firstly inserted and driven to block most of back silting, favorable conditions are created for lowering an inner support in advance for cofferdam first-supporting method construction, and the problem that the construction period and the construction quality are affected due to the fact that sludge with large thickness and high flowability enters the cofferdam in the prior art is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of cofferdam construction, and in particular relates to a rapid cofferdam construction method which can effectively avoid silting by first supporting and then piling. Background Art

[0002] Cofferdam construction refers to underwater engineering in rivers, lakes or other waters. Under the geological conditions of soft covering layers, traditional cofferdam construction methods are easily affected by problems such as insufficient foundation bearing capacity and poor stability, which increases the difficulty and risk of construction. In order to overcome these difficulties, steel pipe pile cofferdam construction technology came into being.

[0003] At present, before designing the cofferdam, it is necessary to pre-design the construction platform. Then, when constructing the steel pipe pile cofferdam, the "pre-support method" is adopted. This method lowers the internal support into place first to provide a stable guide for the subsequent steel pipe pile insertion. Specifically, the construction personnel first install the internal support to the predetermined position, and then use these lowered internal supports as a guide to insert the cofferdam steel pipe piles in turn. Under the guidance of the internal support, the steel sheet piles can be smoothly inserted and closed to form a complete cofferdam structure. After the cofferdam is formed, the silt at the bottom of the cofferdam needs to be cleaned to ensure the stability of the inside of the cofferdam, and then underwater concrete bottom sealing is carried out. After the strength of the bottom sealing concrete reaches the requirement, the water in the cofferdam is drained to prepare for subsequent engineering construction.

[0004] However, the current pre-support method used in the construction of steel pipe pile cofferdams still has some problems in the specific construction: since the cofferdam construction itself is carried out underwater, the continuous water flow will carry sediments and easily form a thick silt layer. In addition, due to the action of the water flow, the silt will have a high fluidity, which ultimately leads to a large silt thickness and high fluidity during the cofferdam construction. The pre-support method is to lower the inner support into place first. Even if the inner support is installed in place, the sealing of the cofferdam structure may not be perfect, and there will still be tiny gaps or leaks. At this time, the thick and fluid silt will enter the cofferdam, affecting the construction period and construction quality. At the same time, the current pre-support method cannot be used when the drilling platform within the cofferdam is completely removed, and cannot meet the needs of rapid cofferdam construction. In this regard, a rapid cofferdam construction method that can effectively avoid siltation by first supporting and then piling is proposed. Summary of the invention

[0005] In order to solve the above-mentioned problems existing in the prior art, the present invention provides a method for rapid construction of a cofferdam by first supporting and then piling to effectively avoid siltation. The method solves the problem that when the prior art method of supporting first is used for construction, the sealing of the cofferdam structure cannot be absolutely perfect and there will still be tiny gaps or leaks. At this time, thick and highly fluid silt will enter the cofferdam, affecting the construction period and construction quality.

[0006] The purpose of the present invention can be achieved by the following technical solution: A rapid construction method for a cofferdam that effectively avoids silting by first supporting and then piling, comprising the following steps:

[0007] S1: First, dismantle part of the construction platform, raise part of the steel casing, and insert part of the cofferdam steel pipe piles;

[0008] S2: dredge the cofferdam to 0.5m below the design elevation of the inner support, remove the remaining construction platforms, and assemble the inner support of the cofferdam;

[0009] S3: Install the hanging system, lower the inner support of the cofferdam, close the cofferdam, and dredge to the bottom elevation of the bottom concrete;

[0010] S4: Pumping water out of the cofferdam, pouring bottom concrete, cutting casing, and chiseling pile heads;

[0011] S5: Construct the pedestal. After the upper pedestal reaches the designed strength, remove the upper internal support and construct the tower base.

[0012] As a further solution of the present invention, the part of the construction platform removed in S1 is the four corners of the construction platform, and the steel pipe piles at the removed construction platform are arranged in a concave shape.

[0013] As a further solution of the present invention, the steel casing at the elevated portion is a steel casing close to the steel pipe piles arranged in a concave shape.

[0014] As a further solution of the present invention, after the remaining construction platforms are removed in S2, brackets are welded on the steel casing, and then the inner supports of the cofferdam are assembled on the brackets.

[0015] As a further solution of the present invention, the steel pipe piles arranged in an inward concave shape are combined with transverse steel pipe piles and longitudinal steel pipe piles to form a closed area, the overall length of the transverse steel pipe piles is smaller than the overall length of the longitudinal steel pipe piles, and the inner supports of the cofferdam are assembled in the closed area formed by the steel pipe piles arranged in an inward concave shape, the transverse steel pipe piles and the longitudinal steel pipe piles.

[0016] As a further solution of the present invention, the inner supports at the transverse steel pipe piles are arranged in a V-shape, and the steel casings at the V-shape are arranged in a triangular shape.

[0017] As a further solution of the present invention, after the hanging system in S3 is installed, the hanging system is used to lower the inner support as a whole to the designed elevation, and then the steel pipe piles are driven in with the inner support as a guide to close the cofferdam. After the cofferdam is closed, the inner support is padded, and then the inside of the cofferdam is dredged to the bottom elevation of the bottom concrete.

[0018] As a further solution of the present invention, after the water in the cofferdam in S4 is pumped to the bottom elevation of the bottom concrete, the bottom concrete is poured.

[0019] As a further solution of the present invention, when constructing the cap in S5, first wait for the bottom concrete to reach the designed strength, remove the lower internal support and connection system, and then cast the lower and upper caps in sequence.

[0020] The beneficial effects of the present invention are:

[0021] On the basis of the existing advance support method, part of the construction platform is first dismantled, part of the steel casing is connected, and part of the cofferdam steel pipe piles are inserted and driven. The cofferdam is silted to 0.5m below the design elevation of the inner support, the remaining construction platforms are dismantled, and the inner supports of the cofferdam are assembled; the hanging system is installed, the inner supports of the cofferdam are lowered, the cofferdam is closed, and the silt is removed to the bottom elevation of the bottom concrete; water is pumped out of the cofferdam, the bottom concrete is poured, the casing is cut, and the pile heads are chiseled; the pedestal is constructed, and after the upper pedestal reaches the design strength, the upper inner support is removed, the tower base is constructed, and part of the steel pipe piles are first driven and driven to block most of the back siltation, creating favorable conditions for lowering the inner supports in advance during the construction of the cofferdam advance support method, solving the problem that the sealing of the cofferdam structure cannot be absolutely perfect during the construction of the advance support method in the prior art, and there will still be tiny gaps or leaks. At this time, the thick and highly fluid silt will enter the cofferdam, affecting the construction period and construction quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0023] Figure 1 It is a schematic diagram of the construction structure of the steel casing of the heightened part of the present invention;

[0024] Figure 2 It is a schematic diagram of the construction structure of the demolished part of the construction platform of the present invention;

[0025] Figure 3 This is a schematic diagram of the installation position of the inner support of the present invention;

[0026] Figure 4 It is a schematic diagram of the installation position of the hanging system of the present invention;

[0027] Figure 5 It is a schematic diagram of the overall construction structure of the steel pipe pile of the present invention;

[0028] Figure 6 It is a schematic diagram of the construction position of the bottom sealing concrete of the present invention;

[0029] Figure 7 It is a schematic diagram of the installation position of the support platform and the tower base of the present invention.

[0030] Description of main component symbols:

[0031] In the figure: 1. Part of the construction platform; 2. Steel casing; 3. Part of the cofferdam steel pipe piles; 4. The steel casing of the elevated part; 5. Corbel; 6. The remaining construction platform; 7. Internal support; 8. Hanging system; 9. Steel pipe piles; 10. Bottom sealing concrete; 11. Capping platform; 12. Tower base. DETAILED DESCRIPTION

[0032] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0033] See also Figure 1-7 This embodiment provides a method for quickly constructing a cofferdam by first supporting and then piling to effectively avoid silting, comprising the following steps:

[0034] S1: First, partially dismantle the construction platform 1, connect the high part of the steel casing 4, and insert and drive part of the cofferdam steel pipe piles 3; the purpose of dismantling part of the platform is to remove part of the existing construction platform or temporary structure so as to carry out the next step of construction. When connecting the high part of the steel casing 4, the existing steel casing 2 is raised to meet the needs of deeper construction, and then a certain number of steel pipe piles 9 are driven into the designated position of the cofferdam, and these piles will serve as the support of the cofferdam structure;

[0035] S2: dredge the cofferdam to 0.5m below the design elevation of the inner support, remove the remaining construction platforms, and assemble the inner support 7 of the cofferdam; dredge the cofferdam to 0.5m below the design elevation of the inner support, dredge the cofferdam inside, and remove the silt to a position 0.5m below the design elevation of the inner support 7 to ensure the stability and effectiveness of the inner support 7. The 0.5m selected here is set according to the construction standard, but for different situations, the specific value may be adjusted according to the soil conditions, the design of the support system and the specific requirements of the project. Next, remove the remaining construction platform 6 in the cofferdam to create space for the installation of the inner support 7, and then assemble the pre-designed inner support 7 structure and place it at the specified position inside the cofferdam to enhance the overall stability of the cofferdam;

[0036] S3: Install the hanging system 8, lower the inner support 7 of the cofferdam, close the cofferdam, and dredge to the bottom elevation of the bottom concrete. First, install the hanging system 8 for fixing and adjusting the position of the inner support 7, and then lower the inner support 7 to the designed position through the hanging system 8, close the opening part of the cofferdam, form a complete cofferdam structure, and dredge to the bottom elevation of the bottom concrete. Continue to dredge until the bottom elevation of the bottom concrete is reached, in preparation for the subsequent concrete pouring.

[0037] S4: Pumping water out of the cofferdam, pouring bottom sealing concrete 10, cutting the casing, and chiseling the pile heads; using a water pump to pump out the accumulated water in the cofferdam for the next step of construction, pouring a layer of concrete at the bottom of the cofferdam to seal the bottom and prevent water from entering, and then cutting the steel casing as needed to facilitate subsequent structural construction, and finally chiseling the pile heads exposed on the ground to keep the structure neat and beautiful;

[0038] S5: construct the pedestal 11, wait for the upper pedestal 11 to reach the design strength, remove the upper internal support 7, and construct the tower base 12; construct the pedestal inside the cofferdam, which is the basic part supporting the upper structure, wait for the upper pedestal 11 to reach the design strength, that is, wait for the pedestal concrete to reach the design strength, and remove the upper internal support 7. Because when the pedestal is stable enough, removing the upper internal support 7 can create space for subsequent construction, and construct the tower base 12 on the basis of the pedestal 11, and the tower base 12 is used to support the upper structure.

[0039] At present, before designing the cofferdam, it is necessary to pre-design the construction platform. Next, when constructing the steel pipe pile cofferdam, the "pre-support method" is adopted. This method first lowers the inner support 7 into place to provide a stable guide for the subsequent insertion of the steel pipe piles 9. Specifically, the construction personnel first install the inner support 7 to the predetermined position, and then use these lowered inner supports 7 as guides to insert the cofferdam steel pipe piles in turn. Under the guidance of the inner support 7, the steel pipe piles 9 can be smoothly inserted and closed to form a complete cofferdam structure. After the cofferdam is formed, the silt at the bottom of the cofferdam needs to be cleaned to ensure the stability of the inside of the cofferdam, and then the underwater concrete bottom is sealed. After the strength of the bottom concrete reaches the requirement, Drain the water in the cofferdam to prepare for the subsequent construction work. However, the pre-support method currently used in the steel pipe pile cofferdam construction still has some problems in the specific construction. For example, since the cofferdam construction itself is carried out underwater, the continuous water flow will carry sediments and easily form a thicker silt layer. In addition, due to the effect of the water flow, the silt will have a higher fluidity, which ultimately leads to a thicker silt thickness and high fluidity during the cofferdam construction. The pre-support method is to lower the inner support 7 into place first. Even if the inner support is installed in place, the sealing of the cofferdam structure may not be perfect, and there will still be tiny gaps or leaks. At this time, the thicker and more fluid silt will enter the cofferdam, affecting the construction period and construction quality.

[0040] In order to solve the above problems, in this embodiment, based on the existing pre-support method, firstly, part of the construction platform is dismantled, the steel casing 4 of the high part is connected, and part of the cofferdam steel pipe piles 3 are inserted and driven, the cofferdam is silted to 0.5m below the design elevation of the inner support, the remaining construction platform 6 is dismantled, and the cofferdam inner support 7 is assembled; the hanging system 8 is installed, the cofferdam inner support 7 is lowered, the cofferdam is closed, and the silt is removed to the bottom elevation of the bottom concrete; water is pumped out from the cofferdam, the bottom concrete is poured 10, the casing is cut, and the pile head is chiseled; the cap 11 is constructed, and after the upper cap reaches the design strength, the upper inner support 7 is dismantled, and the tower base 12 is constructed, and part of the steel pipe piles 9 are first driven and driven to prevent the upper cap from reaching the design strength. It blocks most of the back siltation and creates favorable conditions for lowering the internal support in advance during the cofferdam pre-support construction. It solves the problem that the sealing of the cofferdam structure cannot be absolutely perfect during the prior art pre-support construction, and there will still be tiny gaps or leaks. At this time, the thick and highly fluid silt will enter the cofferdam, affecting the construction period and construction quality. At the same time, it also saves construction period, improves the cofferdam construction efficiency and engineering quality, and can be constructed without completely dismantling the drilling platform within the cofferdam range, which can meet the needs of rapid cofferdam construction. In addition, this construction method can be adopted in different construction environments (ocean or inland river).

[0041] During the cofferdam construction, the unremoved construction platform may cause poor water flow, increase the possibility of sediment siltation, and affect the construction quality and progress. The construction platform may also interfere with the construction of steel pipe piles, affecting the accuracy and stability of the pile foundation. In order to solve this problem, in one embodiment, the removed part of the construction platform 1 in S1 is the four corners of the construction platform, and the steel pipe piles at the removed construction platform are arranged in a concave shape, such as Figure 2 As shown, during the cofferdam construction process, removing parts of the four corners of the construction platform helps to reduce the impact of water flow on the platform, thereby reducing the possibility of silt siltation. The concave steel pipe pile arrangement can form a natural diversion effect when water flows through, further reducing the siltation phenomenon. In addition, by removing part of the construction platform 1, that is, the four corners, more operating space can be provided for construction equipment, making pile foundation construction more convenient and efficient, thereby achieving the purpose of rapid construction of the cofferdam.

[0042] In order to ensure the stability of the cofferdam construction after removing part of the construction platform, in one embodiment, the steel casing 4 of the high part is a steel casing near the steel pipe piles 9 arranged in a concave shape, such as Figure 2As shown in FIG. 1 , the steel casing near the steel pipe piles arranged in an inward concave shape will be raised, that is, the steel casing 4 of the raised part will be connected. This raising treatment can increase the height of the cofferdam, thereby improving its ability to resist external water flow and soil pressure. The steel casing 4 of the raised part can also provide better protection for the subsequent cofferdam construction to prevent the cofferdam from being affected by silt during the construction process. After the remaining construction platform is removed in S2, the bracket 5 is welded on the steel casing 2, and then the cofferdam inner support 7 is assembled on the bracket 5, as shown in FIG. Figure 3 As shown, since the cofferdam construction is carried out underwater, when encountering an environment with rapid water flow or strong wind, dismantling part of the construction platform 1 at this time may increase the risk of the cofferdam structure being eroded or damaged. In order to compensate for this defect, the bracket 5 is welded on the steel casing 2, and then the cofferdam internal support 7 is assembled on the bracket 5 to compensate for the stability of the cofferdam structure. By welding the bracket 5, the stability of the steel casing 2 can be increased, so that it can better withstand the load in the subsequent construction process. By assembling the cofferdam internal support 7 on the bracket 5, the necessary support can be provided for the cofferdam, ensuring the overall stability of the cofferdam structure and preventing deformation or damage during the construction process. In addition, the setting of the cofferdam internal support helps to reduce the siltation caused by factors such as water flow and waves, and maintain the stability of the internal construction environment of the cofferdam. By assembling the internal support 7 on the bracket 5, the cofferdam can be quickly built, thereby improving construction efficiency and shortening the construction period.

[0043] In order to further increase the overall stability during the cofferdam construction, in one embodiment, the steel pipe piles 9 arranged in an inward concave shape are formed into a closed area by the transverse steel pipe piles 9 and the longitudinal steel pipe piles 9. The overall length of the transverse steel pipe piles is less than the overall length of the longitudinal steel pipe piles 9, and the overall length of the transverse steel pipe piles is less than the longitudinal steel pipe piles 9. The purpose is to optimize the use of materials and reduce unnecessary material waste. The inner support of the cofferdam is assembled in the closed area formed by the steel pipe piles 9 arranged in an inward concave shape, the transverse steel pipe piles 9 and the longitudinal steel pipe piles 9. The steel pipe piles 9 here are all vertically arranged, such as Figure 5In the figure, the transverse steel pipe piles 9 refer to the upper and lower sides, and the longitudinal steel pipe piles 9 refer to the left and right sides. In fact, the transverse steel pipe piles 9 and the longitudinal steel pipe piles 9 are a distribution area of ​​steel pipe piles 9, which are composed of a number of steel pipe piles 9 perpendicular to the ground. The inner support 7 at the transverse steel pipe piles is arranged in a V shape, and the steel casing at the V shape is arranged in a triangular shape. Through the joint action of the transverse steel pipe piles, the steel pipe piles arranged in an inward concave shape, and the longitudinal steel pipe piles, a closed support system is formed, which can effectively improve the stability of the overall structure and resist the impact of water flow. In addition, the V-shaped inner support setting of the transverse steel pipe piles and the longitudinal steel pipe piles helps to limit the lateral displacement of the steel pipe piles and maintain the geometric stability of the structure. The V-shaped inner support and the triangularly arranged steel casing 2 can effectively enhance the anti-overturning ability of the structure, especially during the cofferdam construction, under the condition of large lateral load, the effect is more significant.

[0044] In order to shorten the cofferdam construction period and enable the cofferdam to be constructed quickly, in one embodiment, after the hanging system 8 in S3 is installed, the hanging system 8 is used to lower the internal support as a whole to the designed elevation, and then the internal support is used as a guide to drive the steel pipe piles to the cofferdam to close it. The installed internal support is used as a guide to accurately drive the steel pipe piles 9, which can improve the positioning accuracy and construction quality of the piles. After the cofferdam is closed, the internal support is padded, and the method of lowering the internal support 7 as a whole is adopted, so that the cofferdam can be quickly closed, and then the silt inside the cofferdam is dredged to the bottom elevation of the bottom concrete. By dredging to the bottom elevation of the bottom concrete, good conditions can be created for the subsequent construction of the bottom concrete 10, ensuring the quality and progress of the project. In addition, the traditional cofferdam construction method requires piling first and then installing the support system. This is not only time-consuming, but also easily affected by external factors such as weather. This method can greatly shorten the construction period by using the hanging system to lower the internal support as a whole.

[0045] Since water and silt are inevitably present during the cofferdam construction, in order to further avoid silting, in one embodiment, after the water in the cofferdam is pumped to the bottom elevation of the bottom concrete 10 in S4, the bottom concrete 10 is poured. Here, by pouring the bottom concrete 10, water and silt can be effectively isolated to prevent silt from entering the construction area, thereby avoiding the occurrence of silting. At the same time, after the water in the cofferdam is pumped to the bottom elevation of the bottom concrete, the construction environment becomes dry, which is conducive to the work of construction machinery and personnel and improves construction efficiency. In addition, the pouring of the bottom concrete can form a solid foundation, provide stable support for subsequent construction links, help reduce the difficulty of subsequent underwater construction, and reduce construction risks.

[0046] In order to further improve construction efficiency, ensure construction safety, reduce the impact of siltation, and improve the quality and economic benefits of the entire project, in one embodiment, when constructing the pedestal 11 in S5, first wait for the bottom concrete 10 to reach the design strength, then remove the lower internal support 7 and the connection system, and then cast the lower and upper pedestals 11 in sequence. Wait for the bottom concrete to reach the design strength before removing the internal support 7 and the connection system, which can ensure the stability and safety of the entire structure. By first removing the lower internal support 7 and the connection system, and then casting the lower and upper pedestals 11 in sequence, the construction process can be simplified and the construction period can be shortened. The bottom concrete 10 is constructed first and reaches the design strength, which can effectively isolate and reduce the siltation of the soil below, creating a good construction environment for the subsequent casting of the pedestal 11, and casting the pedestal 11 in stages can better control the quality of concrete and construction quality, and ensure the bearing capacity and stability of the pedestal.

[0047] The working principle and use process of the present invention:

[0048] When carrying out the cofferdam construction, part of the construction platform 1 is dismantled, the steel casing that needs to be installed with the hanging system 8 is connected, and part of the cofferdam steel pipe piles 3 are inserted and driven. By inserting and driving some of the steel pipe piles, most of the silt is blocked from silting back, creating favorable conditions for lowering the inner support 7 in advance for the cofferdam pre-support construction, thereby improving the success rate. The silt in the cofferdam is cleared to 0.5m below the design elevation of the inner support 7, and the remaining construction platform 6 is dismantled. The bracket 5 is welded on the steel casing 2, and then the inner support 7 is assembled on the bracket 5. After the assembly of the inner support 7 is completed, the hanging system 8 is installed. The inner support 7 is lowered as a whole to the designed elevation using the hanging system 8; secondly, the steel pipe piles 9 are driven in with the inner support as a guide until the cofferdam is closed, and the inner support 7 is padded after the cofferdam is closed; finally, the cofferdam is dredged to the bottom elevation of the bottom concrete, water is pumped out of the cofferdam to the bottom elevation of the bottom concrete, and the bottom concrete 10 is poured. After the bottom concrete 10 reaches the designed strength, the lower inner support 7 and the connection system are removed, and the lower and upper caps 11 are poured in turn. After the upper cap 11 reaches the designed strength, the upper inner support 7 is removed, and the tower base 12 is constructed.

[0049] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A rapid cofferdam construction method that effectively avoids silting by first supporting and then piling, characterized in that: The following steps are involved: S1: First, dismantle part of the construction platform, raise part of the steel casing, and insert part of the cofferdam steel pipe piles; S2: dredge the cofferdam to 0.5m below the design elevation of the inner support, remove the remaining construction platforms, and assemble the inner support of the cofferdam; S3: Install the hanging system, lower the inner support of the cofferdam, close the cofferdam, and dredge to the bottom elevation of the bottom concrete; S4: Pumping water out of the cofferdam, pouring bottom concrete, cutting casing, and chiseling pile heads; S5: Construct the pedestal. After the upper pedestal reaches the designed strength, remove the upper internal support and construct the tower base.

2. A rapid cofferdam construction method for effectively avoiding silting by first supporting and then piling according to claim 1, characterized in that: The part of the construction platform removed in S1 is the four corners of the construction platform, and the steel pipe piles at the removed construction platform are arranged in a concave shape.

3. A rapid cofferdam construction method for effectively avoiding silting by first supporting and then piling according to claim 2, characterized in that: The steel casing at the elevated portion is a steel casing located close to the steel pipe piles arranged in a concave shape.

4. A rapid cofferdam construction method for effectively avoiding silting by first supporting and then piling according to claim 1, characterized in that: After the remaining construction platforms are removed in S2, brackets are welded on the steel casing, and then the inner supports of the cofferdam are assembled on the brackets.

5. A rapid cofferdam construction method for effectively avoiding silting by first supporting and then piling according to claim 2, characterized in that: The steel pipe piles arranged in an inward concave shape together with the transverse steel pipe piles and the longitudinal steel pipe piles form a closed area. The overall length of the transverse steel pipe piles is less than the overall length of the longitudinal steel pipe piles. The inner support of the cofferdam is assembled in the closed area formed by the steel pipe piles arranged in an inward concave shape, the transverse steel pipe piles and the longitudinal steel pipe piles.

6. A rapid cofferdam construction method for effectively avoiding silting by first supporting and then piling according to claim 5, characterized in that: The inner supports at the transverse steel pipe piles are arranged in a V shape, and the steel casings at the V shape are arranged in a triangular shape.

7. A rapid cofferdam construction method for effectively avoiding silting by first supporting and then piling according to claim 1, characterized in that: After the hanging system in S3 is installed, the hanging system is used to lower the inner support as a whole to the designed elevation, and then the steel pipe piles are driven in with the inner support as a guide until the cofferdam is closed. After the cofferdam is closed, the inner support is padded, and then the inside of the cofferdam is dredged to the bottom elevation of the bottom concrete.

8. The method for rapid cofferdam construction according to claim 1, wherein: After the water in the cofferdam in S4 is pumped to the bottom elevation of the bottom concrete, the bottom concrete is poured.

9. A rapid cofferdam construction method for effectively avoiding silting by first supporting and then piling according to claim 1, characterized in that: When constructing the cap in S5, first wait for the bottom seal concrete to reach the designed strength, remove the lower layer internal support and connection system, and then cast the lower and upper caps in sequence.

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