Environment-friendly and economical hydraulic reclamation cofferdam and construction method thereof

Abstract

The invention belongs to the technical field of hydraulic reclamation cofferdams, and provides an environment-friendly and economical hydraulic reclamation cofferdam and a construction method thereof.The environment-friendly and economical hydraulic reclamation cofferdam comprises a double-layer cofferdam, the double-layer cofferdam comprises a main cofferdam body and a sub-cofferdam body, the main cofferdam body is arranged on the elevation line of + / -0 m, the top face elevation of the main cofferdam body is 5 m, the top width of the main cofferdam body is 15 m, the coastal side slope is 1: 1.5, and the inner side slope The top surface elevation of the sub cofferdams is 5 m, the top width is 16.25 m, and the ratio of side slopes on the two sides of the sub cofferdams is 1: 1; the bottom width of the overflow channel is 40m, and the bottom elevation of the overflow channel is 5m; a tidal channel; according to the method, a line production mode is realized through the grab ships, the land machinery and the auxiliary construction calculation platform, partitioned construction and synchronous propulsion can be realized, overflow channels are simultaneously excavated by the large grab ships in a plurality of areas, and then subsequent procedures are sequentially carried out, so that the construction efficiency is further improved, the completion speed of the whole cofferdam and hydraulic reclamation project is accelerated, and the construction cost is reduced. Operation conditions can be monitored in real time, and efficient and continuous construction is ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of blown-fill cofferdams, and in particular relates to an environmentally friendly and economical blown-fill cofferdam and a construction method thereof. Background Art

[0002] In island countries such as the Maldives, coral reef resources are abundant, but the land area is decreasing due to the impact of global warming and rising sea levels. In addition to raising the elevation of existing island land through filling, these countries also need to develop and build new land on the existing coral reefs. However, the ecology around the coral reefs is fragile, and during filling construction, cofferdams must be built to prevent the diffusion of suspended matter in the filling materials to avoid the death of corals and fish. At the same time, the cofferdam structure and construction methods must be environmentally friendly. Moreover, the coral reefs are located in the far sea, and it is inconvenient to transport materials, so materials need to be saved. In addition, the construction environment is harsh, which is not conducive to the work of land workers.

[0003] The existing construction plan only has a single-layer cofferdam and no overflow channel, which has limited ability to control the tailwater and suspended solids of the fill. It also adopts a method that mainly relies on workers and supplemented by suction dredgers, with a low degree of mechanization. The workers are limited by their physical strength and skills, and are inefficient in high-intensity links such as large-scale reef sand excavation and transportation, making it difficult to ensure construction quality and progress.

[0004] To this end, those skilled in the art have proposed an environmentally friendly and economical blown-fill cofferdam and a construction method thereof to solve the problems raised by the background technology. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides an environmentally friendly and economical blown-fill cofferdam and a construction method thereof, so as to solve the problems in the prior art that the cofferdam structure has limited control ability over blown-fill tail water and suspended solids, requires large manpower and is difficult to operate, and has a low degree of construction mechanization.

[0006] An environmentally friendly and economical dredger-filled cofferdam comprises: a double-layer cofferdam, which comprises a main cofferdam and a sub-cofferdam, wherein the main cofferdam is arranged on a ±0m elevation line, has a top elevation of 5m, a top width of 15m, a sea-facing side slope of 1:1.5, and an inner side slope of 1:1; the sub-cofferdam has a top elevation of 5m, a top width of 16.25m, and side slopes on both sides of the sub-cofferdam are both 1:1;

[0007] Overflow channel, the bottom width of the overflow channel is 40m, and the bottom elevation is -5m;

[0008] Tidal channels are arranged on the atoll platform, with 3-5 channels in number and a bottom elevation of -5m.

[0009] Preferably, the sea-side slope adopts large coral rocks with a diameter of more than 1m and a thickness of 1.5m to enhance wave resistance; the core of the main cofferdam adopts coral rocks with a diameter of 0.1m-1m; the inner slope and top surface adopt relatively broken coral rocks with a diameter of less than 0.1m and a thickness of 1m.

[0010] Preferably, the core of the sub-cofferdam is made of coral rock with a diameter of 0.1m-1m; the side slopes and the top surface are made of relatively broken coral rock with a diameter of less than 0.1m and a thickness of 1m.

[0011] Preferably, a temporary drainage ditch is provided between the main cofferdam and the sub-cofferdam, and the bottom width of the temporary drainage ditch is 40m and the bottom elevation is -5m.

[0012] An environmentally friendly and economical hydraulic filling cofferdam construction method, comprising:

[0013] S1. Collect basic data on coral islands and reefs and their surrounding waters, and determine the location of tidal channels, reclamation areas and cofferdam structure parameters;

[0014] S2. Topographic survey: using unmanned equipment to obtain accurate topographic data and transmit it to the auxiliary construction computing platform;

[0015] S3. Planning and layout: arrange several tidal channels on the atoll platform to connect the lagoon with the open sea and divide the atoll platform into several reclamation areas; and set up a double-layer cofferdam, including a main cofferdam and a sub-cofferdam, with a temporary drainage channel between the main cofferdam and the sub-cofferdam.

[0016] S4. Configure construction equipment, all of which are equipped with auxiliary construction computing platforms:

[0017] S5. Configure the process flow and import the planning layout files into the auxiliary construction calculation platform

[0018] S6. Carry out work in a flow-like manner according to the construction steps.

[0019] Preferably, the basic data include wave, hydrological, silt, topographic, geological and ecological data.

[0020] Preferably, in the topographic survey, unmanned aerial vehicles are used to measure the topography and elevation of the reef platform; and unmanned boats are used to measure the underwater topography and elevation of the lagoon and the sea area near the reef.

[0021] Preferably, S301, the number of tidal channels is 3-5, and the filling area is divided into 3-5;

[0022] The main cofferdam has a top elevation of 5m, a top width of 15m, a seaward side slope of 1:1.5, an inner side slope of 1:1, and a core of coral rock with a diameter of 0.1m-1m;

[0023] The top surface elevation of the sub-cofferdam is 5m, the top width is 16.25m, and the side slopes of the sub-cofferdam are 1:1. The core and slope materials are similar to those of the main cofferdam but with different specifications. The bottom width of the overflow channel is 40m, the bottom elevation is -5m, and the cofferdam material uses coral rock excavated from the overflow channel.

[0024] Preferably, S6 comprises the following steps:

[0025] S601, excavation and filling by large grab boat;

[0026] S602, medium grab boat repairs cofferdam;

[0027] S603, land mechanical leveling and slope adjustment;

[0028] According to the S601, S602 and S603 flow operation, the process proceeds according to the set partitions and routes. Each step is closely connected, and the previous step creates a working surface for the next step.

[0029] Preferably, the filling area is provided with a sub-drainage outlet and a main drainage outlet, and the filling tail water is discharged into the overflow channel through the sub-drainage outlet, and is discharged into the open sea through the main drainage outlet after sedimentation; after the filling is completed in each filling area, the overflow channel of each area is filled again.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] This method forms a double-layer cofferdam through construction and reasonably plans tidal channels, thereby enhancing the overall stability and wave resistance of the cofferdam, effectively preventing the diffusion of suspended matter in the filling material during the filling process, and protecting the living environment of the surrounding coral reefs and marine life; there is no need to purchase geotextiles and other materials, saving material procurement costs and transportation costs, and realizing the maximum utilization of resources; through grab ships, land machinery and auxiliary construction computing platforms, a flow operation mode is realized, and construction and synchronous advancement can be carried out in different areas. Large grab ships in multiple areas simultaneously excavate overflow channels, and then carry out subsequent processes in sequence, further improving construction efficiency and accelerating the completion speed of the entire cofferdam and filling project. The operation status can be monitored in real time to ensure efficient and continuous construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is an example diagram of the cross section of the cofferdam and spillway structure;

[0033] Figure 2 This is an example diagram of the tidal channel structure section;

[0034] Figure 3 This is an example diagram of the cofferdam plan layout;

[0035] Figure 4 A schematic diagram of the process flow. DETAILED DESCRIPTION

[0036] The following is a further detailed description of the embodiments of the present invention in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0037] Embodiment 1: As shown in the attached Figure 1 To Attachment Figure 4 As shown: The present invention provides an environmentally friendly and economical blown-fill cofferdam, comprising a double-layer cofferdam, an overflow channel and a tidal channel;

[0038] The double-layer cofferdam includes the main cofferdam and the sub-cofferdam. The main cofferdam is arranged on the ±0m elevation line, with a top elevation of 5m, a top width of 15m, a side slope of 1:1.5 on the sea (lake) side, and a side slope of 1:1 on the inner side; the sub-cofferdam has a top elevation of 5m, a top width of 16.25m, and side slopes on both sides of the sub-cofferdam are 1:1;

[0039] The seaside (lake) side slopes are made of large coral rocks with a diameter of more than 1m and a thickness of 1.5m to enhance wave resistance; the core of the main cofferdam is made of coral rocks with a diameter of 0.1m-1m; the inner side slopes and top surface are made of relatively broken coral rocks with a diameter of less than 0.1m and a thickness of 1m.

[0040] The core of the sub-cofferdam is made of coral rock with a diameter of 0.1m-1m; the side slopes and top surface are made of relatively broken coral rock with a diameter of less than 0.1m and a thickness of 1m.

[0041] A temporary drainage channel is set between the main cofferdam and the sub-cofferdam. The bottom width of the temporary drainage channel is 40m and the bottom elevation is -5m. It is used to guide the discharge of the tail water of the filling. The double-layer cofferdam structure design not only enhances the overall stability and wave resistance of the cofferdam, but also further intercepts the suspended matter in the filling process through the sub-cofferdam. At the same time, the temporary drainage channel provides the necessary space and path for the sedimentation of the tail water of the filling, effectively preventing the suspended matter from spreading to the lagoon and nearby sea areas.

[0042] The bottom width of the overflow channel is 40m, and the bottom elevation is -5m. The excavated coral reef rocks are used to build the cofferdam, so that materials can be sourced locally, reducing material transportation costs and dependence on external materials. At the same time, the overflow channel provides a sedimentation and discharge channel for the blown-fill tailwater. When the blown-fill tailwater flows in the overflow channel, due to its length, depth and the adsorption and sedimentation effects of the coral reef rocks, the suspended matter in the tailwater is fully precipitated, ensuring that the tailwater discharged to the open sea is discharged cleanly and protecting the surrounding marine ecological environment.

[0043] Tidal channels are arranged on the ring-shaped reef platform, with a number of 3-5, a bottom elevation of -5m, and a bottom width designed according to the specific project. The cofferdams on both sides refer to the main cofferdam structure. The tidal channels connect the lagoon and the open sea to ensure normal water exchange in the lagoon and avoid the deterioration of the lagoon's ecological environment due to filling construction. The setting of tidal channels is crucial to maintaining the balance of the marine ecosystem. It can ensure the normal migration and survival of marine organisms between the lagoon and the open sea. It also helps to regulate environmental factors such as water quality and water temperature in the lagoon, ensuring that the impact of filling construction on the surrounding marine ecological environment is minimized.

[0044] An environmentally friendly and economical hydraulic filling cofferdam construction method, comprising:

[0045] S1. Collect basic data on coral islands and reefs and their surrounding waters, and determine the location of tidal channels, reclamation areas and cofferdam structure parameters;

[0046] Basic data include wave, hydrological, sediment, topographic, geological, and ecological data;

[0047] Hydrological data include tidal fluctuations, seawater flow rate, etc. Topographic data include the ups and downs of the reef platform, slope, and areas with slow currents, etc. Geological data include reef hardness and stratum stability, etc. Ecological data include marine life migration routes, coral reef distribution, etc.

[0048] S2. Topographic survey: using unmanned equipment to obtain accurate topographic data and transmit it to the auxiliary construction computing platform; using drones to measure the topography and elevation of reef platforms; using unmanned boats to measure the underwater topography and elevation of lagoons and reef areas;

[0049] S3. Planning and layout: 3-5 tidal channels are arranged on the atoll platform to connect the lagoon with the open sea to ensure water exchange, and the atoll platform is divided into 3-5 reclamation areas; the tidal channels avoid areas with dense marine life and coral reef growth areas; and the advantageous terrain positions (such as areas with low terrain and slow water flow) are obtained through terrain data, and the reclamation areas are divided according to the advantageous terrain positions to minimize the impact of reclamation construction on the ecological environment and facilitate material stacking and construction operations;

[0050] A double-layer cofferdam is set up, including a main cofferdam and a sub-cofferdam. A temporary drainage channel is set up between the main cofferdam and the sub-cofferdam to extend the discharge path of the blown fill tailwater;

[0051] The top elevation of the main cofferdam is 5m, the top width is 15m, the side slope on the sea (lake) side is 1:1.5 (using large coral rocks with a diameter of more than 1m and a thickness of 1.5m), the inner side slope is 1:1 (using broken coral rocks with a diameter of less than 0.1m and a thickness of 1m), and the core of the embankment is made of coral rocks with a diameter of 0.1m-1m;

[0052] The top surface elevation of the sub-cofferdam is 5m, the top width is 16.25m, and the side slopes on both sides of the sub-cofferdam are 1:1. The core and slope materials are similar to those of the main cofferdam but with different specifications; the bottom width of the overflow channel is 40m, the bottom elevation is -5m, and the cofferdam material uses coral rock excavated from the overflow channel.

[0053] The cofferdam structural parameters are obtained by analyzing hydrological data (such as tidal variation, seawater flow rate, etc.) and geological data (such as reef hardness, formation stability, etc.), and determining the elevation, top width, side slope gradient of the main cofferdam and sub-cofferdam as well as the specifications of the coral reef rock used.

[0054] S4. Configure construction equipment. All construction equipment is equipped with auxiliary construction computing platform:

[0055] Construction equipment includes large grab boats, medium grab boats, crawler long-arm hook machines and crawler forklifts;

[0056] The construction equipment is as follows: 1 large grab ship with a capacity of 100 cubic meters or more, using steel piles for positioning, equipped with hydraulic grabs and auxiliary construction calculation platforms;

[0057] 1 medium-sized grab vessel of 18 cubic meters or less, equipped with hydraulic grab and auxiliary construction computing platform;

[0058] 2 crawler-type long-arm cranes of 1 cubic meter or more, equipped with satellite positioning navigation system;

[0059] 2 crawler forks of 3 cubic meters or more, equipped with satellite positioning navigation system.

[0060] S5. Configure the process flow and import the planning layout files into the auxiliary construction calculation platform to provide accurate route guidance for construction;

[0061] Large grab boats are put into place for construction: With the help of Beidou positioning and navigation system, they reach the designated location, excavate the spillway according to the layout route, and fill the cofferdams on both sides;

[0062] The medium-sized grab boat is put into place for construction: the large grab boat will follow after advancing 100m, and the cofferdam will be repaired according to the block specifications;

[0063] Land machinery in place for construction: After the medium-sized grab boat moves forward 100m, a long-arm hook machine and a forklift are arranged to level the top surface and trim the slope respectively; each process is carried out in sequence until the cofferdam (overflow channel) is completed, and then the tidal channel is excavated, and the excavated coral rock is piled near the cofferdam and pushed to the filling area by land machinery;

[0064] S6. Work in a flow-line according to the construction steps;

[0065] S601, excavation and filling by large grab boat;

[0066] S602, medium grab boat repairs cofferdam;

[0067] S603, land mechanical leveling and slope adjustment;

[0068] According to the S601, S602 and S603 flow operation, the process proceeds according to the set partitions and routes. Each step is closely connected, and the previous step creates a working surface for the next step.

[0069] Sub-drainage outlets and main drainage outlets are set up in the reclamation area. The tail water of reclamation is discharged into the overflow channel through the sub-drainage outlet, and is discharged into the open sea through the main drainage outlet after sedimentation. After the reclamation in each reclamation area is completed, the overflow channel of each area will be filled.

[0070] Example 2: Detailed information on a group of island coral reefs and their surrounding waters was collected; through long-term observation, it was learned that the average wave height in the area was 1-2 meters, the maximum wave height could reach 3 meters, the tidal range was 2-3 meters, the seawater flow rate could reach 1-1.5 meters per second at high tide and 0.5-1 meters per second at low tide.

[0071] Topographic surveys show that the reef platform has obvious ups and downs, with a slope between 5° and 15°, and some areas with slow water flow; geological exploration has found that the reef is relatively hard and the stratum is relatively stable. Ecological surveys have made it clear that the migration routes of marine organisms are mainly concentrated on the south side of the island, and coral reefs are distributed on the edge of the reef and in some shallow areas. Based on these data, it was determined to arrange tidal channels on the east and west sides of the island to avoid biological migration routes and coral reef-dense areas, divide the reef into three reclamation areas, and design the structural parameters of the main cofferdam and sub-cofferdam according to the topographic and hydrological conditions. For example, the slope of the main cofferdam on the sea side is set at 1:1.5, and large coral rocks with a diameter of 1.2 meters and a thickness of 1.5 meters are used to enhance the wave resistance.

[0072] The reef platform was measured using drones, and terrain and elevation data with a resolution of 0.1 meters were obtained. Unmanned boats measured the underwater topography of the lagoon and nearby waters with an accuracy of 0.5 meters. The measurement data was transmitted in real time to the auxiliary construction computing platform, providing accurate terrain basis for subsequent construction.

[0073] Three tidal channels are arranged on the atoll platform, with a bottom elevation of -5 meters and a bottom width of 30 meters designed according to water flow calculations, connecting the lagoon and the open sea to ensure water exchange. When planning the reclamation area, choose an area with low terrain and close to the material stacking point to facilitate reclamation construction and material management.

[0074] A double-layer cofferdam is set up. The main cofferdam is arranged on the ±0m elevation line, with a top elevation of 5 meters and a top width of 15 meters. Large coral rocks are used on the seaside, coral rocks with a diameter of 0.5 meters are used in the core of the embankment, and broken coral rocks are used on the inner slope; the sub-cofferdam has a top elevation of 5 meters and a top width of 16.25 meters. The structure is similar to the main cofferdam, but the specifications have been adjusted. The temporary drainage channel between the main cofferdam and the sub-cofferdam has a bottom width of 40 meters and a bottom elevation of -5 meters, which is used to guide the discharge of the blown fill tailwater.

[0075] One 120-cubic-meter large grab ship was deployed, which was positioned using steel piles and equipped with advanced hydraulic grabs and an auxiliary construction computing platform; one 15-cubic-meter medium-sized grab ship was also equipped with the corresponding system; two 2-cubic-meter crawler long-arm hook machines were equipped with a high-precision satellite positioning and navigation system; and two 5-cubic-meter crawler forklifts were equipped with a satellite positioning and navigation system.

[0076] Import the planned CAD layout file into the grab boat auxiliary construction calculation platform; the large grab boat reaches the designated location according to the Beidou positioning navigation system, excavates the overflow channel according to the layout route, and fills the cofferdams on both sides with the excavated coral reef rocks. When the large grab boat advances 100 meters, the medium grab boat follows up and trims the cofferdam according to the block specifications. After the medium grab boat advances another 100 meters, long-arm hooks and forklifts are arranged on both sides of the cofferdam. The long-arm hooks level the top surface, and the forklifts clean up the debris and assist in slope trimming. Each process is carried out in sequence until the cofferdam and overflow channel are completed, and then the tidal channel is excavated, and the excavated coral rocks are piled near the cofferdam and pushed to the filling area by the forklift.

[0077] The operation is carried out in strict accordance with the steps of large grab boats for excavation and filling, medium grab boats for cofferdam trimming, and land machinery for leveling and slope adjustment. Sub-drainage outlets and main drainage outlets are set up in the filling area. During the filling process, the tail water is discharged into the overflow channel through the sub-drainage outlet, and discharged into the open sea through the main drainage outlet after sedimentation. When each filling area is completed, the overflow channel of each area is filled.

[0078] In the embodiment, since the tidal channel avoids biological migration routes and coral reef-dense areas, and the double-layer cofferdam intercepts most of the suspended matter, the coral reefs and marine life around the construction area are minimally affected.

[0079] Compared with the traditional construction method that requires a large amount of geotextiles, the material cost alone saves about 30%; in this island project, all the excavated coral reef rocks are reasonably used in engineering construction, reducing resource waste.

[0080] The construction process, which mainly relies on grab ships and is supplemented by a small amount of land machinery, has improved the level of construction mechanization and automation; large grab ships are used for efficient excavation and filling, medium-sized grab ships are used for fine finishing, and crawler long-arm hook machines and forklifts work in coordination, which greatly shortens the construction period; in the embodiment, compared with the traditional construction method that mainly relies on manpower, the construction efficiency is improved by about 50%.

[0081] In this island project, facing the impact of waves with a maximum wave height of 3 meters, the cofferdam remained stable, ensuring the safe progress of the reclamation construction; the reasonable setting of temporary drainage channels and overflow channels provided good discharge and sedimentation conditions for the reclamation tail water, ensuring the clean discharge of the tail water that was finally discharged into the open sea, while also ensuring the dryness and stability of the reclamation area, which was conducive to subsequent project construction.

[0082] By setting up a double-layer cofferdam and rationally planning the tidal channel, the overall stability and wave resistance of the cofferdam are enhanced, effectively preventing the diffusion of suspended matter in the filling material during the filling process, and protecting the living environment of the surrounding coral reefs and marine life; the cofferdam is built using coral reef rocks excavated from the overflow channel, avoiding transportation pollution caused by a large amount of purchased materials, while reducing environmental impacts such as carbon emissions in the material production process; there is no need to purchase geotextiles and other materials, saving material procurement costs and transportation costs; all the earth and stone generated during construction are used in the cofferdam and filling area, without any external waste materials, thus maximizing the utilization of resources.

[0083] By adopting drone measurement, computer layout and Beidou positioning navigation, surveyors no longer need to board the coral reef platform, reducing the risk of personnel working in dangerous waters and ensuring construction safety.

[0084] The construction process is carried out in three steps: excavation and filling by large grab boats, cofferdam trimming by medium grab boats, and leveling and slope adjustment by land machinery. The previous process creates a good working surface for the next process. For example, when the large grab boat moves forward 100 meters, the medium grab boat can follow up and trim. After the medium grab boat moves forward another 100 meters, the land machinery enters the site for operation. The various processes are closely connected, avoiding pauses and waiting time during construction, making the entire construction process as smooth as flowing water, and greatly shortening the construction period.

[0085] The annular reef platform is divided into 3-5 filling areas (such as the 3 filling areas in the embodiment), and construction can be carried out in each filling area at the same time. The same processes in different areas are carried out simultaneously. For example, large grab ships in multiple areas excavate spillways at the same time, and then carry out subsequent processes in sequence, which further improves the construction efficiency and speeds up the completion of the entire cofferdam and filling project.

[0086] The CAD file is imported into the grab boat auxiliary construction calculation platform through computer layout, providing accurate route guidance for construction. Operators work according to the route and parameters displayed on the screen, reducing the measurement and positioning time during construction and improving the accuracy of operation. The application of Beidou positioning and navigation system (such as large grab boats use it to accurately reach the construction location from the sea side, with the error controlled within 1 meter) and satellite positioning and navigation system (such as long-arm hook machines and forklifts use it to accurately locate the operation area) ensures the rapid positioning and accurate operation of construction equipment in complex marine environments, avoids rework and delays caused by inaccurate positioning, and effectively improves the construction speed.

[0087] During the construction process, the auxiliary systems equipped on each piece of equipment can monitor the operation in real time, such as the grab boat recording the excavation progress, the hook machine and the forklift detecting the flatness of the operation area, etc., and comparing them with the plan. Once a problem is found (such as the excavation depth not meeting the requirements, the slope flatness deviation, etc.), it can be adjusted back in time, ensuring the construction quality while avoiding the impact of the accumulation of problems on subsequent construction, ensuring efficient and continuous construction.

[0088] The embodiments of the present invention are provided for the purpose of illustration and description. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations of the present invention. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. An environmentally friendly and economical dredger, characterized in that: include: Double-layer cofferdam, including main cofferdam and sub-cofferdam, the main cofferdam is arranged on the ±0m elevation line, with a top elevation of 5m, a top width of 15m, a sea-facing side slope of 1:1.5, and an inner side slope of 1:1; the sub-cofferdam has a top elevation of 5m, a top width of 16.25m, and the slopes on both sides of the sub-cofferdam are 1:1; Overflow channel, the bottom width of the overflow channel is 40m, and the bottom elevation is -5m; Tidal channels are arranged on the atoll platform, with 3-5 channels in number and a bottom elevation of -5m.

2. An environmentally friendly and economical dredger-fill cofferdam as claimed in claim 1, characterized in that: The sea-facing side slope is made of large coral rocks with a diameter of more than 1m and a thickness of 1.5m; the core of the main cofferdam is made of coral rocks with a diameter of 0.1m-1m; the inner side slope and top surface are made of relatively broken coral rocks with a diameter of less than 0.1m and a thickness of 1m.

3. An environmentally friendly and economical dredger-fill cofferdam as claimed in claim 2, characterized in that: The core of the sub-cofferdam is made of coral rock with a diameter of 0.1m-1m; the side slopes and top surface are made of relatively broken coral rock with a diameter of less than 0.1m and a thickness of 1m.

4. An environmentally friendly and economical dredger-fill cofferdam as claimed in claim 3, characterized in that: A temporary drainage ditch is provided between the main cofferdam and the sub-cofferdam, and the bottom width of the temporary drainage ditch is 40m and the bottom elevation is -5m.

5. An environmentally friendly and economical dredger-fill cofferdam construction method, used in conjunction with any one of the environmentally friendly and economical dredger-fill cofferdams of claims 1 to 4, characterized in that: include: S1. Collect basic data on coral islands and reefs and their surrounding waters, and determine the location of tidal channels, reclamation areas and cofferdam structure parameters; S2. Topographic survey: using unmanned equipment to obtain accurate topographic data and transmit it to the auxiliary construction computing platform; S3. Planning and layout: arrange several tidal channels on the ring-shaped reef platform to connect the lagoon with the open sea, and divide the ring-shaped reef platform into several reclamation areas; and set up a double-layer cofferdam, including a main cofferdam and a sub-cofferdam, with a temporary drainage channel between the main cofferdam and the sub-cofferdam; S4. Configuring construction equipment, wherein the construction equipment is equipped with an auxiliary construction computing platform; S5. Configure the process flow and import the planning layout and layout files into the auxiliary construction calculation platform; S6. Carry out work in a flow-like manner according to the construction steps.

6. An environmentally friendly and economical method for constructing a hydraulically filled cofferdam as claimed in claim 5, characterized in that: The basic data include wave, hydrological, sediment, topographic, geological and ecological data.

7. An environmentally friendly and economical method for constructing a hydraulically filled cofferdam as claimed in claim 6, characterized in that: In the topographic survey, drones are used to measure the topography and elevation of the reef platform; unmanned boats are used to measure the underwater topography and elevation of the lagoon and the sea area near the reef.

8. An environmentally friendly and economical method for constructing a hydraulically filled cofferdam as claimed in claim 6, characterized in that: S301, the number of tidal channels is 3-5, and the filling area is divided into 3-5; The main cofferdam has a top elevation of 5m, a top width of 15m, a seaward side slope of 1:1.5, an inner side slope of 1:1, and a core of coral rock with a diameter of 0.1m-1m; The top surface elevation of the sub-cofferdam is 5m, the top width is 16.25m, and the side slopes of the sub-cofferdam are 1:

1. The core and slope materials are similar to those of the main cofferdam but with different specifications. The bottom width of the overflow channel is 40m, the bottom elevation is -5m, and the cofferdam material uses coral rock excavated from the overflow channel.

9. An environmentally friendly and economical method for constructing a hydraulically filled cofferdam as claimed in claim 8, characterized in that: The S6 comprises the following steps: S601, excavation and filling by large grab boat; S602, medium grab boat repairs cofferdam; S603, land mechanical leveling and slope adjustment; According to the S601, S602 and S603 flow operation, the process proceeds according to the set partitions and routes. Each step is closely connected, and the previous step creates a working surface for the next step.

10. An environmentally friendly and economical method for constructing a hydraulically filled cofferdam as claimed in claim 9, characterized in that: The filling area is provided with a sub-drainage outlet and a main drainage outlet. The filling tail water is discharged into the overflow channel through the sub-drainage outlet, and is discharged into the open sea through the main drainage outlet after sedimentation. After the filling is completed in each filling area, the overflow channel of each area is filled again.

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