Combined Cofferdam Structure and Construction Method

Abstract

The present invention provides a combined cofferdam structure, which includes at least three casing pipes located on the same closed ring, and adjacent two casing pipes are connected by a connecting component. Each connecting component includes two groups of chutes extending vertically downward and two first closing plates arranged vertically downward. The two groups of chutes are respectively located on the corresponding two casing pipes. Two end portions of each first closing plate slide vertically in the corresponding two groups of chutes, and a precast pile extending to the riverbed is arranged between the two first closing plates. And concrete is poured between the two first closing plates of each connecting component; a construction method is also provided. In the present invention, the first closing plate sinks to a specified position along the chute, and its cooperation with the concrete can realize the insertion and positioning of the precast pile, avoiding the technical problems that the conventional cofferdam must be underwater blasted or drilled and grooved to take root, and avoiding problems such as underwater assembly and welding, and alleviating the construction difficulty of the cofferdam taking root and fixing under the condition of inclined cross-section bare rock.

Description

Technical Field

[0001] The present invention relates to a bridge, and in particular to a combined cofferdam structure and a construction method. Background Art

[0002] At present, there are many patents and literatures related to cofferdams, but most of them are cofferdam structures used under the conditions of soil and soft weathered rock riverbeds, and the problems of cofferdam bedding and fixation are solved by directly driving or grooving treatment with a pile driver. For the problems of bedding and fixation of cofferdam structures used under the conditions of high-strength rock riverbeds, the prior art mostly uses underwater blasting for treatment (a small part uses drilling and grooving), which has a great impact on the surrounding environment, high safety risks, and low construction efficiency. At present, there are no relevant patents and literatures on cofferdam structures that do not require blasting or drilling and grooving under the conditions of high-strength bare rock riverbeds. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a combined cofferdam structure and a construction method.

[0004] The present invention is implemented as follows:

[0005] The present invention provides a combined cofferdam structure, which includes at least three casing pipes located on the same closed ring. Along the circumferential direction of the closed ring, each casing pipe has two adjacent casing pipes, and adjacent two casing pipes are connected by a connecting component. Each connecting component includes two groups of chutes extending vertically downward and two first closing plates arranged vertically downward. The two groups of chutes are respectively located on the corresponding two casing pipes. Two ends of each first closing plate slide vertically in the corresponding two groups of chutes, and a precast pile extending to the riverbed is arranged between the two first closing plates. And concrete is poured between the two first closing plates of each connecting component.

[0006] Further, an installation structure is welded on the outer surface of each casing pipe, and the chute is installed and fixed on the installation structure.

[0007] Further, the installation structure includes a plurality of channel steels welded on the outer surface of the casing pipe and a bent plate installed and fixed on the channel steels. The channel steels and the bent plate both extend along the length direction of the casing pipe. The channel steels are sequentially and spaced apart along the circumferential direction of the casing pipe, and the openings of the channel steels face the casing pipe. The bent plate includes a plurality of flat plate segments connected in sequence, and each bent plate is installed and fixed on the plurality of channel steels. Each flat plate segment is connected and fixed to one of the channel steels, and the flat plate segment in the middle is connected and fixed to the chute.

[0008] Further, concrete is poured between the channel steel and the casing pipe and between the channel steel and the bent plate.

[0009] Further, the sliding groove includes sliding plates that are oppositely arranged and extend along the length direction of the casing, and both of the two sliding plates are welded to the corresponding flat plate sections.

[0010] Further, a second closing plate extending vertically downward is arranged in each of the sliding grooves, and the second closing plate is welded to two opposite inner walls of the corresponding sliding groove. A guiding frame for the sinking of the precast pile is further arranged between the two first closing plates, and the guiding frame is welded to the second closing plate.

[0011] Further, a sealing material is arranged at the bottom of the first closing plate.

[0012] Further, it further includes an inner purlin and an outer purlin. The inner purlin is arranged inside the precast pile, and the outer purlin is arranged on the tops of the casings.

[0013] The embodiment of the present invention further provides a construction method for the above combined cofferdam structure, including the following steps:

[0014] S1. Combining the requirements of the construction working face and the safety distance, comprehensively determine the central positions of the casings.

[0015] S2. At the positions corresponding to the casings, drill to the designed depth.

[0016] S3. After the drilling is completed, scan the riverbed within a certain range inside and outside the center line of the casing, and draw a three-dimensional riverbed elevation map.

[0017] S4. Use a hoisting device to accurately lower the installed casing into the drilled hole that has been constructed. After verifying the accurate position, pour anchoring concrete inside and outside the casing.

[0018] S5. Under the action of its own gravity, the two first closing plates of each connecting component sink along the corresponding sliding groove to the bedrock surface of the riverbed, and press down appropriately to ensure close biting with the bedrock surface.

[0019] S6. According to the three-dimensional riverbed elevation map, check and number the length of each precast pile. After confirming that the jacking direction and sequence are correct, sink each precast plate into place between the two first closing plates of the corresponding connecting component.

[0020] S7. After the precast piles are jacked, promptly pour concrete between the two first closing plates of the connecting component.

[0021] S8. Use a pumping device to pump out the water inside the cofferdam, and promptly install the inner purlins layer by layer.

[0022] Furthermore, when pouring concrete between the two first closed plates of each connecting component, when the rock surface has a large inclination, a batching treatment is carried out in the horizontal direction, and the minimum height of pouring concrete in each bin shall not be less than 100 cm.

[0023] The present invention has the following beneficial effects:

[0024] In the cofferdam structure of the present invention, the first closed plate can sink along the chute to a designated position, and the precast pile can sink along the corresponding two first closed plates, and then concrete is poured between the two. The whole process not only avoids the technical problems of underwater blasting or drilling and grooving for rooting that must be carried out in the conventional cofferdam landing, but also avoids problems such as underwater assembly and welding. The construction is more convenient, safe, environmentally friendly and economical. In addition, it greatly alleviates the construction difficulty of cofferdam landing and fixing under the condition of inclined-section bare rock. It can be flexibly used on uneven or inclined rock surfaces, and has stronger adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0026] Figure 1 is a schematic structural diagram of the combined cofferdam structure provided by the embodiment of the present invention;

[0027] Figure 2 is a schematic structural diagram of the bottom of the combined cofferdam structure provided by the embodiment of the present invention;

[0028] Figure 3 is a schematic structural diagram of the top of the combined cofferdam structure provided by the embodiment of the present invention;

[0029] Figure 4 is a schematic diagram of the cooperation structure among the casing, the installation structure and the connecting component of the combined cofferdam structure provided by the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0031] See Figures 1 - 4, an embodiment of the present invention provides a combined cofferdam structure, which can be applied to the condition of a high-strength bare rock riverbed. It includes at least three casing pipes 1, and each casing pipe 1 is a steel casing pipe 1, which is a cylindrical hollow structure. Each casing pipe 1 is sequentially connected to the same closed ring, which is the fulcrum of the cofferdam structure. The shape of the closed ring is related to the shape of the cofferdam structure. For example, if it is rectangular, six casing pipes 1 can be provided, with casing pipes 1 arranged at all four vertex positions, and in addition, casing pipes 1 are also arranged at the middle positions of each long side. Adjacent two casing pipes 1 are connected by a connecting component 2. Thus, each casing pipe 1 and each connecting component 2 enclose the above-mentioned closed ring; refining the structure of the connecting component 2, it includes two groups of chutes 21 and two first closing plates 22, and both the two groups of chutes 21 and the two first closing plates 22 are arranged vertically downward. The two groups of chutes 21 are respectively located on the corresponding two casing pipes 1 and the openings of the two groups of chutes 21 are arranged opposite to each other. The two ends of the two first closing plates 22 slide vertically in the corresponding two groups of chutes 21, that is, the first closing plate 22 and the chute 21 are in contact sliding connection. Specifically, the opening of the chute 21 is an outward flared opening, which can facilitate the insertion of the end of the first closing plate 22 into the corresponding chute 21. In the vertical direction, the bottom of the first closing plate 22 can extend to the riverbed, and in the horizontal direction, it can connect the corresponding two casing pipes 1. Of course, the two first closing plates 22 of each connecting component 2 are arranged opposite to each other, and there is a gap between them, so as to form a certain sealing structure between adjacent two casing pipes 1. The upper end of the sealing structure is an opening, and the lower end is sealed by the riverbed. A precast pile 3 is arranged between the two first closing plates 22 of each connecting component 2. Generally speaking, the precast pile 3 can be a steel sheet pile. The precast pile 3 extends from the upper end of the sealing structure, and its bottom also extends to the riverbed. And concrete 7 is poured between the two first closing plates 22 of the connecting component 2. The precast pile 3 is located in the poured concrete 7. The height of the first closing plate 22 is limited, and it is located at the root of the precast pile 3 at the corresponding position. It is mainly used to cooperate with the concrete to position the root of the precast pile 3, so as to achieve the purpose of inserting and positioning the precast pile 3 on the riverbed. In fact, when the first closing plate 22 is sunk, sealing materials such as cotton quilts, geotextiles or glass glue can be arranged at the bottom of the first closing plate 22. Of course, the sealing materials should be laid along the length direction of the first closing plate 22, which can ensure the sealing between the bottom of the first closing plate 22 and the riverbed, and is convenient for pouring concrete 7.In the present invention, the chute 21 of the connection component 2 can be pre-installed on the casing 1 and can be installed together with the casing 1 to the riverbed. There is no connection relationship such as welding between the first closing plate 22 of the connection component 2 and the chute 21. It only needs to be sunk along the chute 21 to the riverbed, thereby avoiding underwater assembly welding operations. Especially for the case where the riverbed has a large slope, the heights of the first closing plate 22 and the precast pile 3 can be controlled according to the actual situation of the riverbed, with high flexibility and strong adaptability. Furthermore, it can also avoid the problems of underwater blasting and underwater drilling and grooving for rooting, and the construction is convenient, fast, safe, environmentally friendly and economical.

[0032] See Figures 2 - 4, Optimize the above embodiments. An installation structure 4 is welded on the outer surface of each casing 1, and the chute 21 is fixedly installed on the installation structure 4. The installation structure 4 is a transfer structure between the casing 1 and the chute 21, mainly used to conveniently and stably install the chute 21 on the casing 1. Specifically, the installation structure 4 includes a plurality of channel steels 41 and bending plates 42 fixedly installed on the channel steels 41. Since the outer surface of the casing 1 is arc-shaped, the channel steels 41 are used to connect and fix with the casing 1. Specifically, the side of the channel steel 41 with a notch faces the outer surface of the casing 1. The channel steels 41 extend along the length direction of the casing 1, and the ends of its two legs (the corresponding parts of the side walls) are in contact with the surface of the casing 1 and are fully welded, that is, the channel steels 41 are welded and fixed on the outer surface of the casing 1. Since there are a plurality of channel steels 41, and each channel steel 41 is sequentially and spaced apart along the circumferential direction of the casing 1, generally mainly distributed at the positions corresponding to the chutes 21; for the bending plate 42, it includes a plurality of flat plate segments connected in sequence, and the included angle between adjacent two flat plate segments is greater than 90 degrees, preferably about 145 degrees. Each flat plate segment corresponds to a channel steel 41, and it is installed and fixed on the waist of the corresponding channel steel 41 (the part corresponding to the bottom of the groove, opposite to the surface of the casing 1), and the middle flat plate segment is connected and fixed with the chute 21. In this embodiment, there are two ways for the bending plate 42. One is that each casing 1 corresponds to one bending plate 42, and two groups of chutes 21 are installed on the bending plate 42. In this structural form, the bending plate 42 has five flat plate segments. Correspondingly, five groups of channel steels 41 are arranged on the casing 1. Each flat plate segment is attached to the outer surface of the waist of the corresponding channel steel 41, and then bolted and fixed. Along the circumferential direction of the casing 1, define one end of the channel steel 41 as the No. 1 channel steel 41 and the other end as the No. 5 channel steel 41, then chutes 21 can be installed and fixed on the No. 2 channel steel 41 and the No. 4 channel steel 41; in the other way, each casing 1 corresponds to two bending plates 42, and each bending plate 42 has three flat plate segments, but the number of channel steels 41 can be five. The middle channel steel 41 is the common connection point of the two bending plates 42. A chute 21 is formed on the middle flat plate segment of each bending plate 42, or the number of channel steels 41 is six, and three channel steels 41 are in a group corresponding to one bending plate 42. For example, for the casing 1 in the middle position of the long side of the closed ring, the two chutes 21 on it are arranged oppositely, and the two bending plates 42 cannot share the connection point.

[0033] See specifically Figure 4, through the installation structure 4 with the above structural form, the channel steel 41 is fixed on the outer surface of the casing 1 by welding, and the connection stability is very high. And through the transfer of the bending plate 42, on the one hand, there can be a large connection area between the bending plate 42 and the channel steel 41, and on the other hand, it is convenient to install and form the chute 21, so that the overall structural stability is very high. For the chute 21, it includes two opposite sliding plates 211. Both sliding plates 211 extend along the length direction of the casing 1 and are welded to the corresponding flat plate segments of the corresponding bending plates 42. Thus, the two sliding plates 211 and the corresponding flat plate segments enclose a groove structure, and the groove opening is on the side where the flat plate segments are opposite. The ends of the two sliding plates 211 far from the flat plate segments are bent outward, so that the groove opening is a flared structure, which is convenient for the first closing plate 22 to extend into the chute 21.

[0034] Further, when the channel steel 41 is welded to the outer surface of the casing 1, there is a gap between the channel steel 41 and the outer surface of the casing 1. And since each bending plate 42 is connected to multiple channel steels 41, there is also a gap between the bending plate 42 and the adjacent two channel steels 41. When the casing 1 is applied to the cofferdam structure, concrete 7 can be poured into these gaps, which can improve the sealing performance of the cofferdam structure and reduce the possibility of water penetration.

[0035] See Figure 1 and Figure 2 , in another embodiment provided by the present invention, a second closing plate 212 extending vertically downward is arranged in each chute 21, and the second closing plate 212 is welded to the two opposite inner walls of the corresponding chute 21, that is, the second closing plate 212 is welded to the inner surfaces of the corresponding two sliding plates 211. A guide frame 31 is also arranged between the two first closing plates 22, and the guide frame 31 is welded to the second closing plate 212. Through the guide frame 31, it is convenient to sink each precast pile 3 to the designated position. In the present invention, since the riverbed is uneven, the heights of the precast piles 3 need to correspond to the riverbed during the construction of the cofferdam structure. Thus, the positions of the precast piles 3 between the two first closing plates 22 are determined. If only the precast pile 3 is sunk alone, it is very difficult to position it. Therefore, a guide frame 31 is also arranged between the two first closing plates 22. The guide frame 31 is fully welded to the second closing plate 212, and a positioning structure cooperating with the precast pile 3 is also arranged on the guide frame 31. Each precast pile 3 can sink along the corresponding positioning structure, and thus the position accuracy of the precast pile 3 can be ensured. Of course, the guide frame 31 can be set in multiple groups, and each group of guide frames 31 is sequentially spaced along the height direction of the first closing plate 22. Generally, it can be three groups, corresponding to the upper, middle and lower layers respectively, and can be made of HN-shaped steel.

[0036] See Figure 1 and Figure 3, Further, the cofferdam structure further includes an inner purlin 5 and an outer purlin 6. The inner purlin 5 is installed inside the precast piles 3, and the outer purlin 6 is installed on the top of each casing 1. The outer purlin 6 is mainly installed at the top position of the casing 1 and is made of HN700 steel. A square can be formed by enclosing with four outer purlins 6, and the casing 1 and the connecting components 2 are all located within the square enclosed by the outer purlins 6. And there are multiple groups of inner purlins 5 corresponding to each connecting component 2. The inner purlins 5 are arranged at intervals along the vertical direction of the corresponding precast piles 3. For example, a group can be set at intervals of 3 - 5m, and on the same layer, adjacent two inner purlins 5 can also be connected by diagonal braces 51 to enhance the stability of the overall structure.

[0037] Refer to again Figures 1 - 4 , The embodiment of the present invention also provides a construction method for the above-mentioned cofferdam structure, including the following steps:

[0038] S1. Combining the requirements of the construction working face and the safety distance, comprehensively determine the central positions of each casing 1. Generally, a bearing platform 8 should be constructed at the bottom of the cofferdam. Determine the central positions of each casing 1 according to the position and size of the bearing platform 8, and it must meet the requirements of the construction working face and the safety distance. In fact, since precast piles 3, specifically steel sheet piles, need to be placed between two casings 1, it is required that the distance between the chute 21 components of two casings 1 should be an integer multiple of the steel sheet pile; cross braces are welded and erected at equal intervals inside the casing 1 to ensure that the casing 1 does not deform. An annular steel plate protection belt is added inside the bottom opening of the casing 1 to prevent the bottom opening from being squeezed flat, and gusset plates are welded at the joints of the casings 1.

[0039] S2. At the positions corresponding to each casing 1, drill to the designed depth, specifically using a large drill bit to drill with clear water to the set depth.

[0040] S3. After drilling is completed, scan the riverbed within a certain range inside and outside the center line of the casing 1 and draw a three-dimensional riverbed elevation map.

[0041] S4. Use a lifting device to accurately lower the installed casing 1 into the drilled hole that has been constructed. After verifying the accurate position, pour anchor concrete 7 inside and outside the casing 1; during the pouring process, the casing 1 can be gently lifted to utilize the good fluidity of the underwater concrete 7, so that the concrete 7 inside and outside the casing 1 is consistent (the same as the elevation of the original riverbed bedrock surface). A hammer can be used to press down the casing 1 in the middle to ensure that the casing 1 sinks in place, and then continue to pour the concrete 7 inside the casing 1 until it is flush with the top of the first closing plate 22;

[0042] Actually, before hoisting the casing 1, each component should be pre-installed on the casing 1 as follows:

[0043] Multiple channel steels 41 are welded on the casing 1. Among them, 5 channel steels 41 are arranged at equal intervals at a 45° angle within the semi-circular range near the bearing platform 8 on the casings 1 at the four corners, and 3 channel steels 41 arranged at equal intervals at a 45° angle are arranged on each side of the remaining casings 1. The channel steels 41 are fully welded to the casing 1. The top of the channel steel 41 is flush with the top of the casing 1, and the bottom is 20 cm above the bottom opening of the casing 1.

[0044] The bending plates 42 are connected to the installed channel steels 41. Each bending plate 42 is connected to three channel steels 41. The two ends are fully welded, and the middle is bolted with four bolts. The bolting is not arranged at equal intervals along the height direction of the steel plate, and the spacing is 100 cm.

[0045] Four sliding plates 211 are welded at the middle position of the bending plate 42 to form two sliding grooves 21 for the installation and positioning of the first closing plate 22. For the convenience of installing the first closing plate 22, the top of the sliding plate 211 can be appropriately bent into a Y shape towards the outside of the sliding groove 21. It should be noted that the part of the sliding plate 211 extending below the rock riverbed needs to be processed into a serrated shape in combination with the aperture of the fresh water drilling and the three-dimensional riverbed elevation map to ensure the full contact between the sliding plate 211 and the riverbed.

[0046] The above-mentioned channel steels 41, bending plates 42, and sliding plates 211 are flush and at the same height.

[0047] Two second closing plates 212 with different lengths are connected inside the sliding groove 21 and are fully welded. The top of the second closing plate 212 is flush with the top of the casing 1, and the bottom reaches the bedrock surface of the riverbed.

[0048] S5. Under the action of its own gravity, the two first closing plates 22 of each connecting component 2 sink along the corresponding sliding groove 21 to the bedrock surface of the riverbed and are appropriately pressed down to ensure tight biting with the bedrock surface. The bottom opening size of the first closing plate 22 must be precisely designed and processed according to the three-dimensional riverbed elevation map. The above measures can greatly ensure the high coincidence degree between the bottom opening of the first closing plate 22 and the riverbed. However, due to the limitations of measurement accuracy and on-site processing conditions, it is actually difficult to achieve zero error. To ensure the sealing and water impermeability of the bottom opening of the first closing plate 22, a sealing material with a certain width, such as cotton quilt, geotextile, glass glue, etc., can be first stuffed along the length direction at the bottom opening of the first closing plate 22. The sealing material is wedged into the inner seam of the bottom opening and is pressed tightly by the self-gravity of the first closing plate 22. In addition, the peripheral purlin 6 should be installed on the outer side of the top of the casing 1 in a timely manner.

[0049] S6. According to the three-dimensional riverbed elevation map, the length of each precast pile 3 is checked and numbered. After confirming that the jacking direction and sequence are correct, each precast slab is lowered into place between the two first closing plates 22 of the corresponding connecting component 2.

[0050] Actually, before sinking the precast slab, guide frames 31 are welded on the slide plate 211 and the second closing plate 212 of the chute 21. A total of three guide frames 31 are arranged at the upper, middle and lower parts along the height direction of the cofferdam. The precast piles 3 are sunk in place by using the guide frames 31. When the rock surface of the riverbed is inclined greatly, support members such as steel bars and section steels can be welded under the precast piles 3 on the side with a lower rock surface to ensure the self-stability of the precast piles 3.

[0051] S7. After the precast piles 3 are inserted and driven, concrete 7 is poured in time between the two first closing plates 22 of the connecting assembly 2. When the rock surface of the riverbed is inclined greatly, it can be divided into compartments in the horizontal direction, but the minimum height of pouring concrete 7 in each compartment shall not be less than 100 cm to ensure the anchoring quality of the precast piles 3. Moreover, the hollow parts between the channel steel 41 and the bent plate 42, and between the slide plate 211 and the second closing plate 212 are sealed by pouring concrete 7, so as to ensure that the cofferdam structure is sealed and watertight.

[0052] S8. A pumping device is used to pump out the water in the cofferdam, and the inner girders 5 are installed layer by layer in time. One inner girder 5 is arranged every 3 - 5 m in the height direction of the precast piles 3. At the same height, two adjacent inner girders 5 can also be connected by diagonal braces 51 to enhance the stability of the overall structure.

[0053] In the above process, the precast piles 3 do not need to be inserted into the rock, the installation speed is greatly increased, the cost and time are saved, and the construction difficulty of the cofferdam landing and fixing under the condition of inclined-section bare rock is greatly alleviated. On the uneven or inclined rock surface, the above method can be flexibly used to construct the cofferdam structure, with stronger adaptability, avoiding the technical problems of underwater blasting or drilling and grooving for rooting in the conventional cofferdam landing, and basically avoiding the problems of underwater assembly and welding. The construction is more convenient, environmentally friendly, safe and economical.

[0054] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A combined cofferdam structure, comprising at least three casing pipes located on the same closed ring. Each of the casing pipes has two adjacent casing pipes along the circumferential direction of the closed ring, and adjacent two of the casing pipes are connected by a connecting component. It is characterized in that: Each of the connecting components includes two groups of chutes extending vertically downward and two first closing plates arranged vertically downward. The two groups of chutes are respectively located on the corresponding two casing pipes. Two end portions of each first closing plate slide vertically in the corresponding two groups of chutes, and a precast pile extending to the riverbed is arranged between the two first closing plates. And concrete is poured between the two first closing plates of each connecting component; An installation structure is welded on the outer surface of each casing pipe, and the chute is fixedly installed on the installation structure; A sealing material is arranged at the bottom of the first closing plate.

2. The combined cofferdam structure according to claim 1, wherein: The installation structure includes a plurality of channel steels welded on the outer surface of the casing pipe and a bent plate fixedly installed on the channel steels. The channel steels and the bent plate both extend along the length direction of the casing pipe. The channel steels are sequentially and evenly distributed along the circumferential direction of the casing pipe, and the notch of each channel steel faces the casing pipe. The bent plate includes a plurality of flat plate segments connected in sequence, and each bent plate is fixedly installed on a plurality of channel steels. Each flat plate segment is fixedly connected to one of the channel steels, and the middle flat plate segment is fixedly connected to the chute.

3. The combined cofferdam structure according to claim 2, characterized in that: Concrete is poured between the channel steel and the casing pipe and between the channel steel and the bent plate.

4. The combined cofferdam structure according to claim 2, characterized in that: The chute includes two sliding plates arranged opposite to each other and extending along the length direction of the casing pipe. The two sliding plates are both welded to the corresponding flat plate segment.

5. The combined cofferdam structure according to claim 1, wherein: A second closing plate extending vertically downward is arranged in each chute, and the second closing plate is welded to the two opposite inner walls of the corresponding chute. A guiding frame for the sinking of the precast pile is also arranged between the two first closing plates, and the guiding frame is welded to the second closing plate.

6. The combined cofferdam structure according to claim 1, characterized in that: It further includes an inner collar and an outer collar. The inner collar is arranged inside the precast pile, and the outer collar is arranged on the tops of the casing pipes.

7. A construction method of the combined cofferdam structure as described in claim 1, characterized in that, It includes the following steps: S1. Combining the requirements of the construction working face and the safety distance, comprehensively determine the central positions of the casing pipes; S2. Drill holes to the designed depth at the positions corresponding to the casing pipes; S3. After the drilling is completed, scan the riverbed within a certain range inside and outside the center line of the casing pipe, and draw a three-dimensional riverbed elevation map; S4. Use a hoisting device to accurately lower the installed casing pipe into the drilled hole that has been constructed. After verifying the accurate position, pour anchoring concrete inside and outside the casing pipe; S5. Under the action of its own gravity, the two first closing plates of each connecting component sink along the corresponding chutes to the bedrock surface of the riverbed, and are appropriately pressed down to ensure tight biting with the bedrock surface; S6. According to the three-dimensional riverbed elevation map, check and number the length of each precast pile. After confirming that the jacking direction and sequence are correct, sink each precast plate into place between the two first closing plates of the corresponding connecting component; S7. After the precast piles are jacked, pour concrete between the two first closing plates of the connecting component in time; S8. Use a pumping device to pump out the water in the cofferdam, and install the inner collar layer by layer in time.

8. The construction method of the combined cofferdam structure according to claim 7, characterized in that: When pouring concrete between the two first closed plates of each connecting component, when the rock surface has a large inclination, compartmentalization treatment is carried out in the horizontal direction, and the minimum height of concrete pouring in each compartment shall not be less than 100 cm.

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