Composite cofferdam structure and construction method on soft soil foundation in river channel

Abstract

This invention discloses a composite cofferdam structure on soft soil foundation in a river channel, comprising a first cofferdam body on the upstream side and a second cofferdam body on the downstream side, a trench formed between the first and second cofferdam bodies, a sheet pile wall driven into the trench, plain soil backfilling both sides of the sheet pile wall, and impermeable clay backfilling the top of the sheet pile wall. The sheet pile wall includes: channel-shaped steel sheet piles driven along the width of the river channel, with slots vertically provided in the middle of the inner wall of the channel bottom of the channel-shaped steel sheet piles; a flat steel plate disposed close to the outer wall of the channel bottom of the channel-shaped steel sheet piles, with connecting plates extending to the slots at both ends of the flat steel plate, and locking slots adapted to the slots at the ends of the connecting plates; and a top plate disposed on top of the channel-shaped steel sheet piles and the flat steel plate. The composite cofferdam structure of this invention has the advantages of good stability and good impermeability.

Description

Technical Field

[0001] This invention relates to the field of water conservancy engineering construction. More specifically, this invention relates to a composite cofferdam structure on soft soil foundation within a river channel and its construction method. Background Technology

[0002] In river management and water conservancy project construction, cofferdams are often required on soft soil foundations. However, soft soil foundations, such as those in rivers, lakes, or reclaimed tidal flats with deep silt layers, are mainly composed of clay and fine sand, exhibiting poor bearing capacity and large deformation, posing significant challenges to cofferdam construction. Traditional cofferdam structures, such as earth-rock cofferdams and concrete cofferdams, often suffer from insufficient stability, easy leakage, and long construction periods on soft soil foundations. Therefore, constructing cofferdams across rivers using traditional methods is extremely difficult. Summary of the Invention

[0003] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0004] To achieve these objectives and other advantages according to the present invention, a composite cofferdam structure on a soft soil foundation in a river channel is provided, comprising a first cofferdam body on an upstream side and a second cofferdam body on a downstream side, a trench formed between the first and second cofferdam bodies, a sheet pile wall driven into the trench, plain soil backfilling both sides of the sheet pile wall, and impermeable clay backfilling the top of the sheet pile wall, the sheet pile wall comprising:

[0005] Several channel-shaped steel sheet piles are driven along the width of the river channel, and adjacent channel-shaped steel sheet piles are spliced ​​together. The inner wall of the channel bottom of the channel-shaped steel sheet pile is provided with a slot in the vertical direction.

[0006] Several flat steel plates are provided, which are closely attached to the outer wall of the trench bottom of the channel sheet pile. The two ends of the flat steel plates extend to the middle of the trench opening of two adjacent channel sheet piles. Each end of the flat steel plate is provided with a connecting plate extending into a slot at the bottom of the adjacent channel sheet pile. The end of the connecting plate is provided with a locking slot that matches the slot. The locking slot is inserted into the slot at the bottom of the adjacent channel sheet pile. Several flat steel plates are respectively provided on the upstream and downstream sides of several channel sheet piles in the river channel. The top of the flat steel plates is flush with the top of the channel sheet pile.

[0007] A number of top plates are disposed on top of the channel steel sheet pile and the flat steel plate. The length of the top plate is the same as the length of the flat steel plate. The width of the top plate covers the area between the opposite flat steel plates on the water-facing and water-repellent sides. The top plate is fixedly connected to the opposite flat steel plates on the water-facing and water-repellent sides.

[0008] Preferably, the inner wall of the groove bottom of the channel sheet pile is provided with a bracket on each side of the slot, and a support assembly is provided on the bracket, the support assembly including:

[0009] Cylinder body, wherein a piston is disposed within the cylinder body;

[0010] A support rod, the lower end of which is connected to the top of the piston, and the upper end of which is connected to the top plate;

[0011] The cylinder body has a through hole at the bottom of its side wall, and a one-way valve that opens from outside the cylinder body into the cylinder body is installed in the through hole.

[0012] Preferably, the top plate and the outer wall of the flat steel plate are covered with a first geomembrane.

[0013] Preferably, the top plate and the outer wall of the flat steel plate are provided with a plurality of hook and loop fastener male surfaces at even intervals, and the inner surface of the first geomembrane is provided with a plurality of hook and loop fastener female surfaces corresponding to the plurality of hook and loop fastener male surfaces respectively. The hook and loop fastener female surfaces are pasted onto the corresponding hook and loop fastener male surfaces so that the first geomembrane covers the top plate and the outer wall of the flat steel plate.

[0014] Preferably, the cavity formed by the flat steel plate and the channel steel sheet pile is provided with a crushed stone layer, a gravel layer, a coarse sand layer, a medium sand layer and a fine sand layer from bottom to top.

[0015] Preferably, both the first and second weirs are formed by stacking sand-filled pipe bags.

[0016] Preferably, both the first and second weirs are provided with weir toe protection and weir slope protection, wherein the weir toe protection is made of gabion stone cages and the weir slope protection is made of a second geomembrane.

[0017] The present invention also provides a construction method for the above-mentioned composite cofferdam structure, comprising:

[0018] Step 1: Construct the first and second weirs along the width of the river channel;

[0019] Step 2: Drain the water from the trench formed by the first and second weirs, and drive trough-shaped steel sheet piles into the trench. Drive several trough-shaped steel sheet piles along the width of the river channel and splice adjacent trough-shaped steel sheet piles together.

[0020] Step 3: Insert flat steel plates into the upstream and downstream sides of several channel-shaped steel sheet piles located in the river channel, and lay a top plate on top of the channel-shaped steel sheet piles and the flat steel plates to form a sheet pile wall;

[0021] Step 4: Backfill plain soil on both sides of the sheet pile wall, and backfill impermeable clay on top of the sheet pile wall.

[0022] The present invention has at least the following beneficial effects: The present invention sets up two weirs in the river channel and drives sheet pile walls in the trench formed by the two weirs, forming a multi-layer waterproof structure. The weirs are on both sides of the sheet pile walls, which provides a relatively stable construction site for the sheet pile walls and also weakens the impact of water flow. The sheet pile walls are driven deep into the riverbed to play a good role in positioning and preventing seepage. Furthermore, the sheet pile wall is constructed using channel steel sheet piles, flat steel plates, and a top plate. Flat steel plates are placed on the upstream and downstream sides of the channel steel sheet piles, and a top plate is placed on top of the channel steel sheet piles. This results in a more stable sheet pile wall structure. Even if uneven settlement of the riverbed causes some channel steel sheet piles to have different top heights, because the top plate is located on top of multiple channel steel sheet piles and connected to different flat steel plates, the top plate of the channel steel sheet pile with more severe settlement will be supported by the surrounding channel steel sheet piles. The channel steel sheet piles move down along the interlocking joints, while the top plate and flat steel plate have strong overall structural integrity and minimal height change. This also avoids localized depressions on the surface of the impermeable clay at the top of the sheet pile wall. Moreover, some channel steel sheet piles move down along the interlocking joints, while the top plate and flat steel plate remain largely stationary, which effectively ensures the stability of the internal structure of the cofferdam and minimizes the possibility of the backfill soil becoming loose and seeping due to the movement of the channel steel sheet piles.

[0023] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0024] Figure 1 This is a schematic cross-sectional view of the composite cofferdam structure described in an embodiment of the present invention;

[0025] Figure 2 This is a top view of the internal structure of the sheet pile wall described in an embodiment of the present invention;

[0026] Figure 3 This is a top view of the top plate disposed on the top of the channel-shaped steel sheet pile according to an embodiment of the present invention;

[0027] Figure 4 This is a side view of the support component according to an embodiment of the present invention. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0029] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified. In the description of this invention, the terms "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0030] like Figure 1 As shown, this invention provides a composite cofferdam structure on soft soil foundation in a river channel, including a first cofferdam body 1 on the upstream side and a second cofferdam body 2 on the downstream side, a trench formed between the first cofferdam body 1 and the second cofferdam body 2, a sheet pile wall 3 driven into the trench, plain soil 4 backfilling both sides of the sheet pile wall 3, and impermeable clay 5 backfilling the top of the sheet pile wall 3, the sheet pile wall 3 comprising:

[0031] Several channel-shaped steel sheet piles 301 are driven along the width of the river channel, and adjacent channels-shaped steel sheet piles 301 are spliced ​​together. A slot 302 is provided in the middle of the inner wall of the channel bottom of the channel-shaped steel sheet pile 301 in the vertical direction.

[0032] A plurality of flat steel plates 303 are provided, which are closely attached to the outer wall of the bottom of the channel sheet pile 301. The two ends of the flat steel plates 303 extend to the middle of the slots of two adjacent channel sheet piles 301. Each end of the flat steel plate 303 is provided with a connecting plate 304 extending to the slot 302 at the bottom of the adjacent channel sheet pile 301. The end of the connecting plate 304 is provided with a locking slot 305 adapted to the slot 302. The locking slot 305 is inserted into the slot 302 at the bottom of the adjacent channel sheet pile 301. The plurality of flat steel plates 303 are respectively provided on the water-facing and back-facing sides of the plurality of channel sheet piles 301 in the river channel. The top of the flat steel plates 303 is flush with the top of the channel sheet pile 301.

[0033] A plurality of top plates 306 are disposed on top of the channel steel sheet pile 301 and the flat steel plate 303. The length of the top plate 306 is the same as the length of the flat steel plate 303. The width of the top plate 306 covers and is disposed between the opposite flat steel plates 303 on the water-facing side and the water-repellent side. The top plate 306 is fixedly connected to the opposite flat steel plates 303 disposed on the water-facing side and the water-repellent side.

[0034] In the above embodiment, two weirs are set in the river channel, and sheet pile walls 3 are driven into the trench formed by the two weirs, forming a multi-layer waterproof structure. The weirs are on both sides of the sheet pile wall 3, which provides a relatively stable construction site for the sheet pile wall 3 and also weakens the impact of water flow. The sheet pile wall 3 is driven deep into the riverbed to play a good role in positioning and preventing seepage. Furthermore, the sheet pile wall 3 is composed of channel steel sheet piles 301, flat steel plates 303, and a top plate 306. Flat steel plates 303 are installed on the water-facing and back-facing sides of the channel steel sheet piles 301, and a top plate 306 is installed on the top of the channel steel sheet piles 301. The resulting sheet pile wall 3 structure is more stable. Even if uneven settlement of the riverbed causes the top height of several channel steel sheet piles 301 to be different, since the top plate 306 is located on the top of multiple channel steel sheet piles 301 and is connected to different flat steel plates 303, the top plate 306 on the top of the channel steel sheet piles 301 with more severe settlement will be supported by the surrounding channel steel sheet piles 301. The channel steel sheet piles 301 move down along the slot 302, while the overall structure of the top plate 306 and flat steel plates 303 is strong and the height change is not obvious. At the same time, it can also avoid local depression defects on the surface of the impermeable clay 5 at the top of the sheet pile wall 3. Furthermore, some of the channel-shaped steel sheet piles 301 move down along the interlock 305, while the top plate 306 and the flat steel plate 303 remain basically unchanged. This can better ensure the stability of the internal structure of the cofferdam and minimize the possibility of the backfill soil becoming loose and leaking as the channel-shaped steel sheet piles 301 move.

[0035] In another embodiment, the inner wall of the groove bottom of the channel sheet pile 301 is provided with a bracket 307 on each side of the slot 302, and a support assembly is provided on the bracket 307. The support assembly includes:

[0036] Cylinder body 308, wherein piston 309 is disposed inside cylinder body 308;

[0037] The lower end of the support rod 310 is connected to the top of the piston 309, and the upper end of the support rod 310 is connected to the top plate 306.

[0038] The cylinder body 308 has a through hole at the bottom of its side wall, and a one-way valve 311 that opens from the outside of the cylinder body 308 to the inside of the cylinder body 308 is installed in the through hole.

[0039] In the above embodiment, the cylinder body 308 is mounted on the bracket 307, and the bracket 307 is mounted on the channel sheet pile 301. Therefore, when the channel sheet pile 301 moves downward along the locking joint 305, the cylinder body 308 moves downward together with the channel sheet pile 301. The piston 309 in the cylinder body 308 is connected to the top plate 306 through the support rod 310. Since the top plate 306 is located on top of multiple channel sheet piles 301 and is connected to different flat steel plates 303, the overall structure of the top plate 306 and flat steel plates 303 is strong. The downward movement of individual channel sheet piles 301 has little impact on the position of the top plate 306. Therefore, the piston 309 and the support rod 310 are basically different from the cylinder 308. The downward movement of the cylinder 308 will expand the space between the piston 309 and the cylinder 308, forming a negative pressure. Through the negative pressure, water that has seeped into the sheet pile wall 3 due to the settlement of the channel steel sheet pile 301 is drawn in through the one-way valve 311. Because of the backflow prevention function of the one-way valve 311, the water cannot be discharged after entering the cylinder 308, thus supporting the piston 309. In this way, the top plate 306 and the flat steel plate 303 can also transmit the pressure received to the settled channel steel sheet pile 301 through the support assembly, and then the channel steel sheet pile 301 transmits it to the riverbed base.

[0040] It is easy to see from the working process of the above embodiments that by setting the support components, the support effect of the channel steel sheet pile 301 that has settled on its top plate 306 and the flat steel plates 303 on both sides can be strengthened, which is conducive to maintaining the stability of the internal structure of the cofferdam and minimizing the occurrence of structural instability of the sheet pile wall 3.

[0041] In another embodiment, the outer walls of the top plate 306 and the flat steel plate 303 are covered with a first geomembrane. The first geomembrane can be used to prevent external water from seeping into the sheet pile wall 3 from the water-facing and water-repellent sides. The geomembrane has the advantages of low specific gravity, high elongation, high adaptability to changes, corrosion resistance, low temperature resistance and good frost resistance. It has a good seepage prevention effect when used in the cofferdam structure.

[0042] In another embodiment, the outer walls of the top plate 306 and the flat steel plate 303 are provided with a plurality of hook and loop fastener male surfaces at even intervals, and the inner surface of the first geomembrane is provided with a plurality of hook and loop fastener female surfaces corresponding to the plurality of hook and loop fastener male surfaces respectively. The hook and loop fastener female surfaces are pasted onto the corresponding hook and loop fastener male surfaces so that the first geomembrane covers the outer walls of the top plate 306 and the flat steel plate 303.

[0043] After the sheet pile wall 3 is constructed, plain soil 4 needs to be backfilled on both sides of the sheet pile wall 3. If the first geomembrane only covers the outer surface of the top slab 306 and the flat steel plate 303 without connecting with them, it is easily disturbed and moved by the backfilled plain soil 4, and cannot properly cover the outer surface of the top slab 306 and the flat steel plate 303. In the above embodiment, by providing a hook and loop fastener male surface on the outer surface of the top slab 306 and the flat steel plate 303, and providing a hook and loop fastener female surface corresponding to the hook and loop fastener female surface on the inner surface of the first geomembrane, the first geomembrane can cover the top slab 306 and the outer surface of the flat steel plate 303 more smoothly and completely, avoiding leakage and water seepage.

[0044] In another embodiment, the cavity formed by the flat steel plate 303 and the channel steel sheet pile 301 is provided with a crushed stone layer, a gravel layer, a coarse sand layer, a medium sand layer and a fine sand layer from bottom to top.

[0045] Specifically, the thickness of the crushed stone layer, gravel layer, coarse sand layer, medium sand layer, and fine sand layer is set according to actual construction needs, and no specific restrictions are imposed here.

[0046] In the above embodiments, by setting a layer of crushed stone, a layer of gravel, a layer of coarse sand, a layer of medium sand, and a layer of fine sand in the cavity formed by the flat steel plate 303 and the channel steel sheet pile 301, water that seeps into the sheet pile wall 3 due to the settlement of the channel steel sheet pile 301 can be filtered out, preventing the backfill soil 4 in the cofferdam from flowing away with the seepage water. At the same time, the crushed stone, gravel, coarse sand, medium sand, and fine sand layers filling the inside of the sheet pile wall 3 can also balance the pressure on both sides of the flat steel plate 303, preventing the flat steel plate 303 from deforming due to the pressure of the backfill soil 4 on one side.

[0047] In another embodiment, both the first weir 1 and the second weir 2 are formed by stacking sand-filled pipe bags.

[0048] Since sand-filled baghouses do not require investment in large equipment and factory buildings, and only require a small number of non-professional operators, they are economical. Furthermore, sand-filled baghouses have a simple structure, are quick and efficient to construct, and allow sand to be sourced from nearby rivers, avoiding the problems of transporting excavated soil and environmental pollution during transportation.

[0049] In another embodiment, both the first weir 1 and the second weir 2 are provided with weir toe protection and weir slope protection, the weir toe protection is made of gabion stone cages, and the weir slope protection is made of a second geomembrane.

[0050] In the above embodiments, the toe protection of the weir body uses gabion stone cages. Gabion stone cages have good natural resistance and can withstand large-scale deformation without collapsing. Therefore, they also have good stability on the soft soil foundation within the river channel, preventing water flow from directly eroding the toe of the weir body and improving the stability of the cofferdam. Furthermore, gabion stone cages have good integrity, and their filling and dismantling are relatively simple and easy to construct. The slope protection of the weir body uses a second geomembrane. The second geomembrane can be used to prevent external water flow from seeping into the first weir body 1 and the second weir body 2 from the water-facing and back-facing sides. The geomembrane has the advantages of low specific gravity, high elongation, high adaptability to changes, corrosion resistance, low temperature resistance, and good frost resistance, and has a good seepage prevention effect when used in the cofferdam structure.

[0051] The present invention also provides a construction method for the above-mentioned composite cofferdam structure, comprising:

[0052] Step 1: Construct the first weir 1 and the second weir 2 along the width of the river channel;

[0053] Specifically, both the first weir body 1 and the second weir body 2 are composed of stacked sand-filled pipe bags. When constructing the weir body, multiple layers of sand-filled pipe bags are laid on both sides of the riverbed above the weir foundation, using the full-section advance method, advancing forward along the axis of the cofferdam during the laying process.

[0054] Step 2: Drain the water out of the trench formed by the first weir 1 and the second weir 2, and drive trough-shaped steel sheet piles 301 into the trench. Drive several trough-shaped steel sheet piles 301 along the width of the river channel and splice adjacent trough-shaped steel sheet piles 301 together.

[0055] Step 3: Insert flat steel plates 303 into the water-facing and back-facing sides of several channel-shaped steel sheet piles 301 located in the river channel, and lay a top plate 306 on top of the channel-shaped steel sheet piles 301 and the flat steel plates 303 to form a sheet pile wall 3.

[0056] In some superior technical solutions, the top and two sides of the sheet pile wall 3 can be covered with a first geomembrane to enhance the seepage prevention effect of the sheet pile wall 3.

[0057] Step 4: Backfill plain soil 4 on both sides of the sheet pile wall 3, and backfill impermeable clay 5 on the top of the sheet pile wall 3.

[0058] In some better technical solutions, weir toe protection can be set at the slope toe of the first weir body 1 and the second weir body 2 to prevent the slope toe of the weir body from being eroded and unstable by water, thereby enhancing the stability of the weir body. Weir slope protection can be set at the slope surface of the first weir body 1 and the second weir body 2 to enhance the seepage prevention effect of the weir body slope surface.

[0059] Specifically, the toe protection of the dam body can be made of gabion stones, and the slope protection of the dam body can be made of a second geomembrane.

[0060] The above construction method uses two weirs and a sheet pile wall 3 is driven into the trench formed by the two weirs, forming a multi-layered waterproof structure. The weirs are on both sides of the sheet pile wall 3, which provides a relatively stable construction site for the sheet pile wall 3 and also weakens the impact of water flow. The sheet pile wall 3 is driven deep into the riverbed to play a good role in positioning and preventing seepage. Furthermore, the sheet pile wall 3 is composed of channel steel sheet piles 301, flat steel plates 303, and a top plate 306. Flat steel plates 303 are installed on the water-facing and back-facing sides of the channel steel sheet piles 301, and a top plate 306 is installed on the top of the channel steel sheet piles 301. The resulting sheet pile wall 3 structure is more stable. Even if uneven settlement of the riverbed causes the top height of several channel steel sheet piles 301 to be different, since the top plate 306 is located on the top of multiple channel steel sheet piles 301 and is connected to different flat steel plates 303, the top plate 306 on the top of the channel steel sheet piles 301 with more severe settlement will be supported by the surrounding channel steel sheet piles 301. The channel steel sheet piles 301 move down along the slot 302, while the overall structure of the top plate 306 and flat steel plates 303 is strong and the height change is not obvious. At the same time, it can also avoid local depression defects on the surface of the impermeable clay 5 at the top of the sheet pile wall 3. Furthermore, some of the channel-shaped steel sheet piles 301 move down along the interlock 305, while the top plate 306 and the flat steel plate 303 remain basically unchanged. This can better ensure the stability of the internal structure of the cofferdam and minimize the possibility of the backfill soil becoming loose and leaking as the channel-shaped steel sheet piles 301 move.

[0061] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A composite cofferdam structure on soft soil foundation in a river channel, comprising a first cofferdam body on the water side and a second cofferdam body on the land side, a trench formed between the first cofferdam body and the second cofferdam body, a sheet pile wall arranged in the trench, and backfilling of the sheet pile wall with soil on both sides and backfilling of the top of the sheet pile wall with impermeable clay, characterized in that, The sheet pile wall comprises: a plurality of channel steel sheet piles arranged along the width direction of the river, and adjacent two channel steel sheet piles are spliced with each other, and a slot is arranged in the middle of the inner wall of the channel bottom of the channel steel sheet pile in the vertical direction; a plurality of flat steel plates arranged close to the outer wall of the channel bottom of the channel steel sheet pile, and the two side ends of the flat steel plate extend to the middle of the slot of the adjacent two channel steel sheet piles, and the two side ends of the flat steel plate are provided with a connecting plate extending to the slot of the channel bottom of the adjacent channel steel sheet pile, and the end of the connecting plate is provided with a lock opening matched with the slot, and the lock opening is inserted into the slot of the channel bottom of the adjacent channel steel sheet pile, and a plurality of flat steel plates are arranged on the water-facing surface and the backwater surface of the channel steel sheet pile in the river, and the top of the flat steel plate is flush with the top of the channel steel sheet pile; a plurality of top plates arranged on the top of the channel steel sheet pile and the flat steel plate, and the length of the top plate is the same as the length of the flat steel plate, and the width of the top plate covers the opposite flat steel plates arranged on the water-facing surface and the backwater surface, and the top plate is fixedly connected with the opposite flat steel plates arranged on the water-facing surface and the backwater surface; wherein, the inner wall of the channel bottom of the channel steel sheet pile is provided with a corbel on both sides of the slot, and a support assembly is arranged on the corbel, and the support assembly comprises: a cylinder, and a piston is arranged in the cylinder; a support rod connected to the top of the piston at the lower end, and the upper end of the support rod is connected to the top plate; wherein, a through hole is formed in the bottom of the side wall of the cylinder, and a one-way valve is arranged in the through hole and opens from the outside of the cylinder to the inside of the cylinder.

2. The composite cofferdam structure of claim 1, wherein, The outer wall surface of the top plate and the flat steel plate is covered with a first geomembrane.

3. The composite cofferdam structure of claim 2, wherein, The outer wall surface of the top plate and the flat steel plate is uniformly and spacedly provided with a plurality of magic tape male surfaces, and the inner surface of the first geomembrane is provided with a plurality of magic tape female surfaces corresponding to the plurality of magic tape male surfaces respectively, and the magic tape female surfaces are pasted on the corresponding magic tape male surfaces to cover the first geomembrane on the outer wall surface of the top plate and the flat steel plate.

4. The composite cofferdam structure of claim 1, wherein, The cavity surrounded by the flat steel plate and the channel steel sheet pile is provided from bottom to top with a gravel layer, a sand gravel layer, a coarse sand layer, a medium sand layer and a fine sand layer.

5. The composite cofferdam structure of claim 1, wherein, The first weir body and the second weir body are both stacked by sand-filled pipe bags filled with sand.

6. The composite cofferdam structure of claim 1, wherein, The first weir body and the second weir body are both provided with weir body toe and weir body slope, the weir body toe adopts gabion, and the weir body slope adopts a second geomembrane.

7. The method of constructing a composite cofferdam structure according to claim 1, wherein It comprises: Step one, building a first weir body and a second weir body along the width direction of the river; Step two, draining the water in the groove formed by the first weir body and the second weir body, arranging channel steel sheet piles in the groove, arranging a plurality of channel steel sheet piles along the width direction of the river, and splicing adjacent two channel steel sheet piles with each other; Step three, inserting flat steel plates on the water-facing surface and the backwater surface of the channel steel sheet piles in the river, and laying top plates on the top of the channel steel sheet pile and the flat steel plate to form a sheet pile wall; Step four, backfilling the sheet pile wall with soil, and backfilling the top of the sheet pile wall with impermeable clay.

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