Composite foundation for sealing carbon dioxide through seabed hydrate method and construction method

Abstract

The invention is suitable for the technical field of immersed tube tunnel construction, and provides a composite foundation for sealing carbon dioxide through a seabed hydrate method and a construction method.The hollow precast pile adopts a precast high-strength concrete hollow pipe pile, a pipe in the pile serves as a high-pressure sealed storage space to seal carbon dioxide, and the two ends of the pipe are sealed through expansion cement paste; wherein a pressure gauge valve is pre-buried at one end, so that the pipe pile forms a closed container capable of bearing high pressure. The hollow pipe pile can save the use amount of cement, carbon dioxide hydrate is sealed and stored through the seabed low-temperature environment and the hollow portion of the pipe pile, the requirement for foundation reinforcement is met, carbon dioxide is sealed and stored through the foundation, and the function of the foundation is expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of immersed tube tunnel construction, and in particular relates to a composite foundation for storing carbon dioxide using a seabed hydrate method and a construction method. Background Art

[0002] As an important transportation channel connecting the two sides of the water, immersed tube tunnels are widely used in submarine construction. However, they are extremely sensitive to differential settlement, so foundation treatment of the soft soil layer on the seabed is usually required. Composite foundation, as a common foundation treatment method, is widely used in immersed tube tunnel projects.

[0003] Commonly used composite foundations are divided into bulk material pile composite foundations (compacted sand piles, gravel piles), flexible pile composite foundations (deep cement mixing piles, lime soil piles, high-pressure rotary jet piles, etc.) and rigid pile composite foundations (PHC piles, reinforced concrete piles, steel pipe piles, thin-walled tube piles, etc.) according to the type of pile materials. Bulk material pile composite foundations replace bulk particles in the soil layer and use vibration and compaction to strengthen the surrounding soil. Its replacement rate is high, but the amount of replacement material required is large, and the depth of the applicable soil layer is shallow. It is also necessary to pay attention to the consolidation delay effect caused by the high replacement rate. Flexible pile composite foundations use curing agents (cement, lime) and soft soil for forced mixing, and use the physical and chemical reaction of curing agents and soft soil to solidify the soft soil. Its replacement rate is moderate, but the amount of cement required is large, and the leakage of cement needs to be paid attention to during the seabed spraying process. Rigid pile composite foundations use prefabricated concrete piles or steel piles, which are driven into the soil layer with underwater pile hammers to reinforce the soft soil. However, its replacement rate is low and it is suitable for deep soil layers, especially for foundations with weak underlying layers. In order to save cement, hollow concrete precast piles are usually used for construction.

[0004] The above three types of composite foundations all have shortcomings to varying degrees. Therefore, a new type of composite foundation is designed, which can save cement and achieve carbon sequestration without affecting its reinforcement of the soft soil foundation on the seabed. Summary of the invention

[0005] The purpose of the embodiments of the present invention is to provide a composite foundation and construction method for storing carbon dioxide using the seabed hydrate method, aiming to solve the problems raised in the above-mentioned background technology.

[0006] The embodiment of the present invention is implemented as follows: a composite foundation for storing carbon dioxide by a seabed hydrate method, comprising hollow prefabricated piles, a block stone ramming layer and a crushed stone cushion layer;

[0007] A plurality of hollow precast piles are provided, and a pile inner pipe is provided inside the hollow precast pile to form a hollow pipe structure. Both ends of the pile inner pipe are sealed by expanding cement slurry to form a cavity. A pile cap is provided on the top of each hollow precast pile. The hollow precast pile is arranged below the bottom surface of the foundation trench. A pile tip is welded at the lower end of the hollow precast pile, and an additive liquid is filled in the cavity of the hollow precast pile.

[0008] The block stone ramming layer is laid around the pile cap, and the top surface of the block stone ramming layer is rammed flat and connected to the bottom slope of the trench;

[0009] The crushed stone cushion layer is laid on the upper part of the block stone tamping layer, and the bottom surface width of the crushed stone cushion layer is smaller than the top surface width of the block stone tamping layer.

[0010] According to a further technical solution, the hollow prefabricated piles are prefabricated with reinforced concrete having a strength not less than C80.

[0011] According to a further technical solution, a pressure gauge valve is provided at the expansion cement slurry at the upper end, and the bottom of the expansion cement slurry at the upper end is made into a concave circular groove, the top of the concave circular groove corresponds to the bottom of the pressure gauge valve, and the bottom of the pressure gauge valve is connected to an inner tube connected to the cavity.

[0012] According to a further technical solution, end plates are provided at the upper and lower ends of the hollow prefabricated pile, and a steel sleeve is provided on the inner side of the end plate to clamp the steel bars inside the pile body, and a groove is reserved around the outer edge of the end plate;

[0013] The lower end plate needs to be sealed by welding the bottom after being sealed with expanding cement slurry. The bottom is a solid circular plate structure with a diameter equal to the inner diameter of the hollow precast pile. The bottom surface of the bottom is flush with the bottom surface of the lower end plate, and the upper end plate is not closed.

[0014] According to a further technical solution, pile sleeves are detachably mounted on both ends of the hollow prefabricated pile.

[0015] According to a further technical solution, the pile tip may be a cross-shaped pile tip, a conical pile tip or an open pile tip.

[0016] In a further technical solution, the pile cap is a rectangular body prefabricated from concrete and steel mesh, and its upper and lower surfaces are square;

[0017] Among them, the concrete strength is C30 or above, the steel mesh is made of multiple steel bars spot welded together, and the diameter is greater than or equal to 6mm; the pile cap is provided with through stepped holes, including the first-level holes on the upper part of the pile cap and the second-level holes on the lower part of the pile cap.

[0018] According to a further technical solution, the diameter of the first-level hole is smaller than that of the second-level hole; the diameter of the second-level hole is equal to the outer diameter of the hollow precast pile, and the diameter of the first-level hole is equal to the inner diameter of the hollow precast pile, or is smaller than the inner diameter of the hollow precast pile and the difference is within 50 mm.

[0019] The thickness of the pile cap is not less than 200 mm, wherein the height of the first-level hole is less than or equal to half of the thickness of the pile cap, and the height of the second-level hole is greater than or equal to half of the thickness of the pile cap.

[0020] According to a further technical solution, the pile cap is also provided with a connecting steel bar connected to the hollow precast pile, the diameter of which is greater than or equal to 6 mm; one end of the connecting steel bar is bent 90° to form a bending head, which extends into the inner cavity of the hollow precast pile in the bending direction.

[0021] According to a further technical solution, the steel mesh is arranged at a distance greater than or equal to 1 / 6 of the thickness of the pile cap downward from the upper part of the pile cap; the bent section of the connecting steel bar is also arranged at a distance greater than or equal to 1 / 6 of the thickness of the pile cap downward from the upper part of the pile cap, and passes through the hole wall of the first-level hole and bends toward the inner pipe of the hollow precast pile.

[0022] According to a further technical solution, the steel mesh comprises a plurality of parallel longitudinal steel bars and a plurality of parallel transverse steel bars welded at intersections;

[0023] The spacing of the steel bars in the longitudinal and transverse directions near the first-level holes in the steel mesh is greater than the spacing of other longitudinal and transverse steel bars, ensuring that the steel bars do not directly pass through the first-level holes.

[0024] A further technical solution is that the thickness of the stone tamping layer is 1.5m-5m, 10kg-100kg of stone is used, the mud content is controlled to be no more than 5%, and the saturated uniaxial ultimate compressive strength of the stone should be no less than 50Mpa.

[0025] A further technical solution is that a gravel ridge is arranged on the top of the gravel cushion layer, and the gravel ridge is laid along an S shape on the top plane of the gravel cushion layer, so that a plurality of V-shaped grooves are formed on the top of the gravel cushion layer;

[0026] The longitudinal width of the single ridge top is 1.5m-2.0m, the longitudinal width of the V-shaped trough top is 0.8m-1.2m, and the slope is calculated based on the natural underwater angle of repose.

[0027] Further technical solution, the selected crushed stone should meet the uneven coefficient C u >5 but does not meet the curvature coefficient C c =1-3; or select the condition that satisfies the curvature coefficient C c =1-3, but does not satisfy the non-uniformity coefficient C u >5 of gravel.

[0028] Another object of the embodiment of the present invention is to provide a construction method for a composite foundation for storing carbon dioxide using a submarine hydrate method. Based on the composite foundation for storing carbon dioxide using a submarine hydrate method, the pile driving equipment used includes a guide frame, an underwater hydraulic hammer and a pile delivery. The construction method specifically includes the following steps:

[0029] Step 1: Use a dredger to dig the foundation trench, lower the guide frame to the corresponding pile position, weld the pile tip on the construction ship, use a crane to lift the hollow prefabricated pile and lower it to the bottom of the foundation trench, and use an underwater robot (ROV) to guide the pile body into the guide frame. The pile body enters the mud to a certain depth under the action of gravity, and the hook is released. The guide frame should hold the hollow prefabricated pile. Use a crane to lift the underwater hydraulic hammer, connect it to the end of the pile delivery, and then lower it into the water. Under the guidance of the ROV, the bottom of the pile delivery is connected to the top of the hollow prefabricated pile. Under the action of the hollow prefabricated pile, underwater hydraulic hammer, pile delivery and pile tip, the hollow prefabricated pile is inserted into the soil to a certain depth. After releasing the hook, the guide frame should hold the hollow prefabricated pile, underwater hydraulic hammer and pile delivery to complete the underwater pile delivery operation.

[0030] Step 2: Start the underwater hydraulic hammer. Under the action of the hammer, the hollow prefabricated pile gradually penetrates into the soil layer. When the pile top is close to the top of the guide frame, turn off the underwater hydraulic hammer, use the ROV to open the pile delivery tube of the guide frame, and remove the guide frame. Continue to start the hydraulic hammer to drive the pile. When the distance between the pile top and the bottom of the foundation trench is close to the height of the second-level hole of the pile cap, stop the piling, retract the underwater hydraulic hammer and the pile delivery, and complete the piling operation.

[0031] Step 3: After the temperature of the hollow precast pile reaches the temperature of the seabed environment, the carbon dioxide hydrate sealing operation begins. Use a connecting pipe to access the pressure gauge valve reserved at the end of the hollow precast pile. One side of the connecting pipe is connected to a carbon dioxide storage tank. Open the valves of the storage tank and the pressure gauge valve in turn to slowly introduce carbon dioxide into the hollow precast pile. Observe through ROV. When the pressure gauge is stable and the amount of carbon dioxide introduced reaches the design value, stop introducing and end the sealing operation.

[0032] Step 4: Lower the pile cap, align the second-level hole of the pile cap with the pile head, so that the pile head can extend into the second-level hole, and fill the first-level hole with underwater concrete to make the pile cap and pile body a whole. The lowering, piling, carbon sequestration and pile cap installation operations of other pile bodies are completed in this way.

[0033] Step 5: Lay the rammed stone layer, use a riprap tamping boat to throw stones underwater, and when the height of the stone layer is 20% higher than the designed elevation of the rammed stone layer, use the tamping plate below to tamp and vibrate the stones to the designed elevation, thus completing the laying of the rammed stone layer.

[0034] Step 6: Lay the gravel cushion layer, use the gravel leveling ship to transport gravel to the underwater block stone tamping layer through the riprap pipe, control the travel speed of the riprap pipe at 0.8m / min-2m / min, and lay it in an S-shaped route along the horizontal direction of the foundation trench to complete the construction of the cushion layer.

[0035] According to a further technical solution, the additive liquid comprises 0.2%-1.2% surfactant, 4%-20% hydrate promoter, and the rest is water in terms of mass percentage.

[0036] According to a further technical solution, in step 3, after the pile body is lowered to the seabed, it is necessary to wait at least 24 hours before starting to introduce carbon dioxide into the inner cavity of the hollow prefabricated pile to ensure that the pile body reaches the seabed environment temperature.

[0037] The embodiment of the present invention provides a composite foundation and construction method for storing carbon dioxide by the seabed hydrate method. The hollow prefabricated piles use prefabricated high-strength concrete hollow pipe piles. The pipes in the piles are used as high-pressure sealed storage spaces to store carbon dioxide. Both ends of the pipes are sealed with cement, and a pressure gauge valve is pre-buried at one end, so that the pipe piles constitute a closed container that can withstand high pressure. The hollow pipe piles can save cement usage and use the low-temperature environment of the seabed and the hollow parts of the pipe piles to store carbon dioxide hydrates, thereby meeting the needs of foundation reinforcement and using the foundation to store carbon dioxide, thereby expanding the function of the foundation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A schematic diagram of the structure of a composite foundation for storing carbon dioxide using a seabed hydrate method provided in an embodiment of the present invention;

[0039] Figure 2 A longitudinal cross-sectional view of a hollow prefabricated pile in a composite foundation for storing carbon dioxide using a submarine hydrate method provided by an embodiment of the present invention;

[0040] Figure 3 A schematic diagram of the structure of a pile tip in a composite foundation for storing carbon dioxide using a seabed hydrate method provided by an embodiment of the present invention;

[0041] Figure 4 A schematic diagram of the structure of a pile cap in a composite foundation for storing carbon dioxide using a submarine hydrate method provided by an embodiment of the present invention;

[0042] Figure 5 A schematic diagram of the structure of a steel mesh in a composite foundation for storing carbon dioxide using a seabed hydrate method provided by an embodiment of the present invention;

[0043] Figure 6 A schematic diagram of the structure of a crushed stone cushion layer in a composite foundation for storing carbon dioxide using a seabed hydrate method provided by an embodiment of the present invention;

[0044] Figure 7 A flow chart of a construction method of a composite foundation for storing carbon dioxide using a submarine hydrate method provided in an embodiment of the present invention;

[0045] Figure 8 The following is a detailed diagram of the piling process;

[0046] Fig. 9 Schematic diagram of the carbon dioxide sequestration and pile capping of hollow prefabricated piles;

[0047] Fig.10 Schematic diagram of the pile driving sequence.

[0048] In the attached drawings: crushed stone cushion layer 1; block stone tamping layer 2; pile cap 3; hollow precast pile 4; carbon dioxide hydrate 5; bottom surface of foundation trench 6; trench bottom slope 7; seabed surface 8; mean sea level 9; pile tip 10; end plate 11; steel sleeve 12; pressure gauge valve 13; expansion cement slurry 14; inner pipe 15; bottom cover 16; fillet weld 17; steel mesh 18; connecting steel bar 19; first-level hole 20; second-level hole 21; crushed stone ridge 22; top edge line of crushed stone ridge layer 23; V-shaped groove 24; guide frame 25; underwater hydraulic hammer 26; pile delivery 27; connecting pipe 28; additive liquid 29; underwater concrete 30. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0050] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0051] like Figure 1-3 As shown, a composite foundation for storing carbon dioxide by a seabed hydrate method provided by an embodiment of the present invention comprises hollow prefabricated piles 4, a block stone ramming layer 2 and a crushed stone cushion layer 1;

[0052] The hollow precast piles 4 are provided in plurality, and a pile inner pipe is provided inside the hollow precast piles 4 to form a hollow pipe structure, and both ends of the pile inner pipe are blocked by expanding cement slurry 14 to form a cavity, and a pile cap 3 is provided on the top of each hollow precast pile 4, and the hollow precast pile 4 is arranged below the bottom surface 6 of the foundation trench, and a pile tip 10 is welded at the lower end of the hollow precast pile 4, and an additive liquid 29 is filled in the cavity of the hollow precast pile 4;

[0053] The block rammed layer 2 is laid around the pile cap 3, and the top surface of the block rammed layer 2 is rammed flat and connected to the trench bottom slope 7;

[0054] The crushed stone cushion layer 1 is laid on the upper part of the block stone tamping layer 2, and the bottom surface width of the crushed stone cushion layer 1 is smaller than the top surface width of the block stone tamping layer 2.

[0055] In the embodiment of the present invention, the hollow prefabricated pile 4 is prefabricated with reinforced concrete having a strength not less than C80, preferably C80. The hollow prefabricated pile 4 is driven into the bottom surface 6 of the foundation trench by an underwater hydraulic hammer 26, and the driving process will have a certain density effect on the soil around the pile; before the hollow prefabricated pile 4 is lowered to the seabed, an additive liquid 29 will be added to the cavity in advance, and carbon dioxide will be introduced into the cavity for storage after it is lowered. The pile not only uses less cement, but also seals carbon dioxide in the form of hydrates while reinforcing the soft soil layer on the seabed. In addition, the crushed stone cushion layer 1 has a certain siltation capacity, which can prevent the loss of foundation bearing capacity caused by silting.

[0056] In addition, for the attached Figure 1 For example, the seabed surface 8 and the mean sea level 9 are used to indicate the seabed surface and the mean sea level, respectively.

[0057] like Figure 2 As shown, as a preferred embodiment of the present invention, a pressure gauge valve 13 is provided at the expansion cement slurry 14 at the upper end, and the bottom of the expansion cement slurry 14 at the upper end is made into a concave circular groove shape, and the top of the concave circular groove corresponds to the bottom of the pressure gauge valve 13. After blocking, a closed space is formed inside the hollow pile body to seal carbon dioxide hydrate; the bottom of the pressure gauge valve 13 is connected to an inner tube 15, which mainly guides the flow direction of carbon dioxide gas during the process of introducing carbon dioxide so that it can be more fully in contact with the added liquid 29.

[0058] like Figure 2 and 3 As shown, as a preferred embodiment of the present invention, the upper and lower ends of the hollow prefabricated pile 4 are both provided with end plates 11, and the inner side of the end plate 11 is provided with a steel sleeve 12 for clamping the steel bars inside the pile body. The outer edge of the end plate 11 is reserved with a groove for welding during docking. The function of the end plate 11 is to fix the prestressed tendons inside the pile body and buffer the impact of the pile driving process;

[0059] Among them, the lower end plate 11 needs to be sealed by welding the bottom seal 16 after being plugged with the expansion cement slurry 14. The bottom seal 16 is a solid circular plate structure, and its diameter is the inner diameter of the hollow prefabricated pile 4. The bottom surface of the bottom seal is flush with the bottom surface of the lower end plate 11. The upper end plate 11 does not seal the leaking pressure gauge valve 13.

[0060] like Figure 2 and 3As shown, as a preferred embodiment of the present invention, pile collars are detachably mounted on both ends of the hollow prefabricated pile 4. After the pile body is formed, the pile collars are mounted on both ends to prevent damage to the pile head during transportation, stacking and pile sinking.

[0061] In the embodiment of the present invention, the outer diameter of the hollow prefabricated pile 4 can be specifically set to 300 mm, and the inner diameter is 80 mm.

[0062] like Figure 3 As shown, as a preferred embodiment of the present invention, the pile tip 10 is a steel cross pile tip, which is connected to the bottom of the hollow prefabricated pile 4 by fillet welding. The fillet weld 17 formed by welding is triangular and circumferentially along the top of the pile tip 10.

[0063] In the embodiment of the present invention, the form of the pile tip 10 is not qualitatively specified. In specific implementation, various forms can be adopted according to engineering geological conditions. Commonly used forms include cross pile tips, conical pile tips and open pile tips.

[0064] like Figure 4 and 5 As shown, as a preferred embodiment of the present invention, the pile cap 3 is a rectangular body prefabricated from concrete and a steel mesh 18, and its upper and lower surfaces are square;

[0065] Among them, the concrete strength is C30 or above, specifically C60, the steel mesh 18 is made of multiple steel bars spot welded, with a diameter greater than or equal to 6mm, specifically 8mm; the pile cap 3 is provided with through stepped holes, including a first-level hole 20 at the upper part of the pile cap and a second-level hole 21 at the lower part of the pile cap.

[0066] As a preferred embodiment of the present invention, the aperture of the first-level hole 20 is smaller than the aperture of the second-level hole 21; the aperture of the second-level hole 21 is equal to the outer diameter of the hollow precast pile 4, ensuring that when the pile cap 3 is placed on the upper part of the hollow precast pile 4, the pile head can extend into the second-level hole 21; the aperture of the first-level hole 20 is equal to the inner diameter of the hollow precast pile 4, or is smaller than the inner diameter of the hollow precast pile 4 and the difference is within 50 mm.

[0067] The thickness of the pile cap 3 is not less than 200 mm, wherein the height of the first-level hole 20 is less than or equal to half of the thickness of the pile cap 3 , and the height of the second-level hole 21 is greater than or equal to half of the thickness of the pile cap 3 .

[0068] In the embodiment of the present invention, the shape of the pile cap 3 is not specifically specified. The side length of the pile cap 3 should not be less than 1000 mm, wherein the side length of the pile cap should also be greater than or equal to 1.5 times the outer diameter of the hollow pipe pile.

[0069] In a specific implementation, the pile cap 3 can be prefabricated into a cylinder with round upper and lower surfaces, wherein the diameter of the cylinder is ensured to be greater than or equal to 1.5 times the outer diameter of the hollow prefabricated pile 4 .

[0070] When the pile cap 3 is a rectangular body, its side length is 2000 mm and its thickness is set to 600 mm; wherein the height of the first-level hole 20 is 200 mm, and the height of the second-level hole 21 is 400 mm.

[0071] As a preferred embodiment of the present invention, the pile cap 3 is further provided with a connecting steel bar 19 connected to the hollow prefabricated pile 4, and the diameter thereof is greater than or equal to 6 mm, and specifically may be 8 mm;

[0072] The connecting steel bar 19 is tied to the corresponding position together with the steel mesh 18 before the pile cap 3 is cast. One end of the connecting steel bar 19 is bent 90° to form a bent head, which extends into the inner cavity of the hollow precast pile 4 in the bending direction. The length of the extended end is controlled above the expansion cement slurry 14 on the upper part of the hollow precast pile 4, and the other end extends to the outer edge of the steel mesh 18.

[0073] As a preferred embodiment of the present invention, the steel mesh 18 is arranged at a distance greater than or equal to 1 / 6 of the pile cap thickness downward from the upper part of the pile cap 3; the bent section of the connecting steel bar 19 is also arranged at a distance greater than or equal to 1 / 6 of the pile cap thickness downward from the upper part of the pile cap 3, and passes through the hole wall of the first-level hole 20, and is bent toward the pile inner pipe of the hollow precast pile 4.

[0074] like Figure 5 As shown, as a preferred embodiment of the present invention, the steel mesh 18 includes a plurality of parallel longitudinal steel bars and a plurality of parallel transverse steel bars welded at the intersections;

[0075] The spacing of the steel bars in the longitudinal and transverse directions near the first-level holes 20 in the steel mesh 18 is greater than the spacing of other longitudinal and transverse steel bars, so as to ensure that the steel bars do not directly pass through the first-level holes 20 .

[0076] In the embodiment of the present invention, the steel mesh 18 is respectively formed by 10 parallel longitudinal steel bars and 10 parallel transverse steel bars crossing and welding at the intersection. Except for the two steel bars near the first-level hole, the spacing is 300mm, and the other spacings are set to 200mm. The position of the connecting steel bar 19 is set around the first-level hole 20, specifically in the middle of the two longitudinal and transverse steel bars near the first-level hole 20. The arrangement of the connecting steel bars 19 is not less than 2, and in this embodiment, it is set to 4.

[0077] As a preferred embodiment of the present invention, the thickness of the stone tamping layer 2 is 1.5m-5m, 10kg-100kg of stone is used, the mud content is controlled to be no more than 5%, and the saturated uniaxial ultimate compressive strength of the stone should be no less than 50Mpa.

[0078] In the embodiment of the present invention, the bottom width of the dumped stone is the excavation width of the bottom surface 6 of the foundation trench, and the top width is connected to the bottom slope 7 of the trench. After dumping, the stone is tamped, and the lateral width of the tamped stone is not less than the bottom width of the crushed stone cushion layer 1, and is symmetrical with the center line of the immersed tube. The function of the tamped stone layer is to protect the bottom surface of the foundation trench from the influence of siltation, and it has a certain ability to absorb siltation. Secondly, it provides a platform for laying the crushed stone cushion layer.

[0079] like Figure 6 As shown in FIG. 1 , as a preferred embodiment of the present invention, a crushed stone ridge 22 is provided on the top of the crushed stone cushion layer 1. The crushed stone ridge 22 is laid along an S shape on the top plane of the crushed stone cushion layer 1. The laying direction is as follows: Figure 6 As shown by the arrows, a plurality of V-shaped grooves 24 are formed on the top of the crushed stone cushion layer 1;

[0080] The longitudinal width of a single ridge top can be 1.5m-2.0m, and the longitudinal width of a V-shaped trough top can be 0.8m-1.2m. The slope is calculated based on the natural underwater angle of repose.

[0081] In the embodiment of the present invention, the longitudinal width of the top edge line 23 of the adjacent gravel ridge layer can be 1.8m, the longitudinal width of the top of the V-shaped groove 24 is 1.2m, and the slope is considered based on the underwater natural repose angle of 1:1.5.

[0082] As a preferred embodiment of the present invention, the thickness of the crushed stone cushion layer 1 is 0.5m-2m, and the crushed stone material is freely scattered, uncontaminated, clean, durable and well-graded. The gradation is 20mm-60mm, and the mud content of the crushed stone should be strictly controlled to be no more than 2%, and the saturated uniaxial ultimate compressive strength of the stone should be no less than 50MPa.

[0083] As a preferred embodiment of the present invention, considering the requirement of seabed siltation, gravel with relatively uniform gradation should be selected, and the selected gravel should satisfy the uneven coefficient C u >5 but does not meet the curvature coefficient C c =1-3, in the specific implementation, you can also choose to satisfy the curvature coefficient C c = 1-3 but does not satisfy the non-uniformity coefficient C u >5 crushed stone, the purpose is to ensure that the crushed stone materials used cannot meet the uneven coefficient C at the same time u >5 and curvature coefficient C c =1-3 conditions.

[0084] like Figure 7-9As shown, a construction method of a composite foundation for storing carbon dioxide by a submarine hydrate method is provided in another embodiment of the present invention. Based on the composite foundation for storing carbon dioxide by a submarine hydrate method, the pile driving equipment used includes a guide frame 25, an underwater hydraulic hammer 26 and a pile delivery 27. The construction method specifically includes the following steps:

[0085] Step 1: Use a dredger to dig the foundation trench, lower the guide frame 25 to the corresponding pile position, weld the pile tip 10 on the construction ship, lift the hollow prefabricated pile 4 with a crane and lower it to the bottom surface 6 of the foundation trench, and use an underwater robot (ROV) to guide the pile body into the guide frame 25. The pile body enters the mud to a certain depth under the action of gravity, and the hook is released. The guide frame 25 should support the hollow prefabricated pile 4. Lift the underwater hydraulic hammer 26 with a crane, connect it to the end of the pile delivery 27, and lower it into the water. Under the guidance of the ROV, the bottom of the pile delivery 27 is connected to the top of the hollow prefabricated pile 4. Under the action of the self-weight of the hollow prefabricated pile 4, the underwater hydraulic hammer 26, the pile delivery 27 and the pile tip 10, the hollow prefabricated pile 4 is inserted into the soil to a certain depth. After the hook is released, the guide frame 25 should support the hollow prefabricated pile 4, the underwater hydraulic hammer 26 and the pile delivery 27 to complete the underwater pile delivery operation.

[0086] Step 2: Start the underwater hydraulic hammer 26. Under the hammering action, the hollow prefabricated pile 4 gradually penetrates into the soil layer. When the pile top is close to the top of the guide frame 25, turn off the underwater hydraulic hammer 26, open the pile delivery tube of the guide frame 25 by ROV operation, and remove the guide frame 25. Continue to start the hydraulic hammer 26 for piling. When the distance between the pile top and the bottom surface 6 of the foundation trench is close to the height of the second-level hole 21 of the pile cap 3, the piling is stopped, and the underwater hydraulic hammer 26 and the pile delivery 27 are retracted to complete the piling operation.

[0087] Step 3: After waiting for the temperature of the hollow prefabricated pile 4 to reach the temperature of the seabed environment, the carbon dioxide hydrate sealing operation is started. The connecting pipe 28 is used to connect to the pressure gauge valve 13 reserved at the end of the hollow prefabricated pile 4. One side of the connecting pipe 28 is connected to a carbon dioxide storage tank. The valves of the storage tank and the pressure gauge valve 13 are opened successively to slowly introduce carbon dioxide into the hollow prefabricated pile 4. Through observation by an underwater robot, when the pressure gauge is stable and the amount of carbon dioxide introduced reaches the designed value, the introduction is stopped and the sealing operation is ended;

[0088] Step 4: Lower the pile cap 3, align the second-level hole 21 of the pile cap 3 with the pile head, so that the pile head can extend into the second-level hole 21, and fill the first-level hole 20 with underwater concrete 30, so that the pile cap 3 and the pile body are integrated. The lowering, piling, carbon sequestration and pile cap installation operations of other pile bodies are completed in this way.

[0089] The strength of the underwater concrete 30 is the same as that of the pile cap 3, and both can be selected as C60. An accelerating setting agent is added to the underwater concrete 30 to ensure that the underwater concrete 30 solidifies quickly on the seabed to prevent the concrete from flowing out of the hole and speed up the construction progress to prevent the bottom surface 6 of the foundation trench from being exposed to seawater for too long to affect its strength.

[0090] Step 5: Lay the rammed stone layer 2, use a riprap tamping boat to throw stones underwater, and when the height of the stone layer is 20% higher than the designed elevation of the rammed stone layer 2, the tamping plate below tamps and vibrates the stones to the designed elevation, completing the laying of the rammed stone layer 2.

[0091] Step 6: Lay the gravel cushion layer 1, use the gravel leveling ship to transport gravel to the underwater block stone tamping layer 2 through the riprap pipe, control the travel speed of the riprap pipe at 0.8m / min-2m / min, and lay it in an S-shaped route along the horizontal direction of the foundation trench to complete the construction of the cushion layer.

[0092] In the embodiment of the present invention, the average stable temperature of the seabed is measured to be 10 degrees Celsius, at which time the stable pressure of the carbon dioxide hydrate 5 is 3MPa. As carbon dioxide is introduced into the pile body, the pressure gradually increases and can be read from the pressure gauge valve. However, when carbon dioxide is converted into hydrates, the pressure will drop slightly. Through observation by an underwater robot, the pressure is stopped until it stabilizes in the range of 3MPa. Considering that the pile body contains an additive 29 that promotes the formation of carbon dioxide hydrates, the actual hydrate formation pressure will decrease, ensuring that the hydrate can still exist stably when encountering changes in seabed temperature during long-term storage.

[0093] When the height of the rocks thrown into the seabed reaches 1.8m, the tamping plate below tamps them until the thickness of the rock tamping layer 2 reaches 1.5m.

[0094] As a preferred embodiment of the present invention, in step 1, before the hollow prefabricated pile 4 below, an additive liquid 29 for promoting the formation of carbon dioxide hydrate needs to be prepared in advance, and its composition is 0.2%-1.2% surfactant, 4%-20% hydrate promoter, and the rest is water according to mass percentage; specifically, it can be: surfactant (dodecyltrimethylammonium chloride) 1.2%, hydrate promoter (tetrahydrofuran) 19%, and the rest is water. According to the fact that 1 volume of water can seal 0.85 times the volume of carbon dioxide hydrate, it can be known that the volume will shrink after the hydrate is formed, and it is selected to fill the closed cavity with the additive liquid 29 or inject an amount of additive liquid that accounts for 90% of the cavity volume.

[0095] As a preferred embodiment of the present invention, in step 3, after the pile body is lowered to the seabed, it is necessary to wait at least 24 hours before starting to introduce carbon dioxide into the inner cavity of the hollow precast pile to ensure that the pile body reaches the seabed environment temperature.

[0096] As a preferred embodiment of the present invention, in step 4, the pile driving sequence of the pile body is constructed according to the center line of the immersed tube, such as Fig.10 As shown, first drive the piles close to the center line, and after completing one row, move away from the center line to drive the next row, until the farthest piles are driven, and then return to the center line to drive the piles.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A composite foundation for storing carbon dioxide using the seabed hydrate method, characterized in that: It includes hollow precast piles, rammed stone layer and crushed stone cushion layer; A plurality of hollow prefabricated piles are provided, and a pile inner pipe is provided inside the hollow prefabricated pile to form a hollow pipe structure. Both ends of the pile inner pipe are sealed by expanding cement slurry to form a cavity. A pile cap is provided on the top of each hollow prefabricated pile. The hollow prefabricated pile is arranged below the bottom surface of the foundation trench. A pile tip is welded at the lower end of the hollow prefabricated pile. An additive liquid for promoting the formation of carbon dioxide hydrate is contained in the cavity of the hollow prefabricated pile. The block stone ramming layer is laid around the pile cap, and the top surface of the block stone ramming layer is rammed flat and connected to the bottom slope of the trench; The crushed stone cushion layer is laid on the upper part of the block stone tamping layer, and the bottom surface width of the crushed stone cushion layer is smaller than the top surface width of the block stone tamping layer.

2. The composite foundation for storing carbon dioxide by the seabed hydrate method according to claim 1, characterized in that: The hollow prefabricated piles are prefabricated with reinforced concrete having a strength not less than C80.

3. The composite foundation for storing carbon dioxide by the seabed hydrate method according to claim 1, characterized in that: A pressure gauge valve is arranged at the expansion cement slurry at the upper end, and the bottom of the expansion cement slurry at the upper end is made into a concave circular groove, the top of the concave circular groove corresponds to the bottom of the pressure gauge valve, and the bottom of the pressure gauge valve is connected with an inner tube communicating with the cavity.

4. The composite foundation for storing carbon dioxide by the seabed hydrate method according to claim 2, characterized in that: The upper and lower ends of the hollow prefabricated pile are both provided with end plates, the inner side of the end plates is provided with steel sleeves for clamping the steel bars inside the pile body, and a groove is reserved around the outer edge of the end plates; The lower end plate needs to be sealed by welding the bottom after being sealed with expanding cement slurry. The bottom is a solid circular plate structure with a diameter equal to the inner diameter of the hollow precast pile. The bottom surface of the bottom is flush with the bottom surface of the lower end plate, and the upper end plate is not closed.

5. The composite foundation for storing carbon dioxide by the seabed hydrate method according to claim 1, characterized in that: The pile tip may be a cross-shaped pile tip, a conical pile tip or an open pile tip.

6. The composite foundation for storing carbon dioxide by the seabed hydrate method according to claim 4, characterized in that: The pile cap is a rectangular body prefabricated from concrete and steel mesh, and its upper and lower surfaces are square; Among them, the concrete strength is C30 or above, the steel mesh is made of multiple steel bars spot welded together, and the diameter is greater than or equal to 6mm; the pile cap is provided with through stepped holes, including the first-level holes on the upper part of the pile cap and the second-level holes on the lower part of the pile cap.

7. The composite foundation for storing carbon dioxide by the seabed hydrate method according to claim 6, characterized in that: The aperture of the first-level hole is smaller than that of the second-level hole; the aperture of the second-level hole is equal to the outer diameter of the hollow precast pile, and the aperture of the first-level hole is equal to the inner diameter of the hollow precast pile, or smaller than the inner diameter of the hollow precast pile and the difference is within 50 mm; The thickness of the pile cap is not less than 200 mm, wherein the height of the first-level hole is less than or equal to half of the thickness of the pile cap, and the height of the second-level hole is greater than or equal to half of the thickness of the pile cap; The side length of the pile cap is not less than 1000 mm, and the side length of the pile cap is greater than or equal to 1.5 times the outer diameter of the hollow precast pile.

8. The composite foundation for storing carbon dioxide by the seabed hydrate method according to claim 6, characterized in that: The pile cap is also provided with connecting steel bars for connecting the hollow precast pile. The diameter of the connecting steel bars is greater than or equal to 6 mm, and the number is not less than 2. One end of the connecting steel bar is bent 90° to form a bending head, which extends into the inner cavity of the hollow precast pile in the bending direction.

9. The composite foundation for storing carbon dioxide by the seabed hydrate method according to claim 8, characterized in that: The steel mesh is arranged at a distance greater than or equal to 1 / 6 of the pile cap thickness downward from the upper part of the pile cap; the bent section of the connecting steel bar is also arranged at a distance greater than or equal to 1 / 6 of the pile cap thickness downward from the upper part of the pile cap, and passes through the hole wall of the first-level hole and bends toward the inner pipe of the hollow precast pile.

10. A construction method for a composite foundation for storing carbon dioxide using a submarine hydrate method, based on the composite foundation for storing carbon dioxide using a submarine hydrate method according to any one of claims 7 to 9, characterized in that: The pile driving equipment used includes a guide frame, an underwater hydraulic hammer and a pile delivery, and the construction method specifically includes the following steps: Step 1: Use a dredger to dig the foundation trench, lower the guide frame to the corresponding pile position, weld the pile tip on the construction ship, lift the hollow prefabricated pile with a crane and lower it to the bottom of the foundation trench, and use ROV to guide the pile body into the guide frame; the pile body enters the mud to a certain depth under the action of gravity, release the hook, and the guide frame should hold the hollow prefabricated pile; lift the underwater hydraulic hammer with a crane, connect it to the end of the delivery pile, and lower it into the water. Under the guidance of ROV, the bottom of the delivery pile is connected to the top of the hollow prefabricated pile; under the action of the hollow prefabricated pile, underwater hydraulic hammer, delivery pile and pile tip, the hollow prefabricated pile is inserted into the soil to a certain depth. After releasing the hook, the guide frame should hold the hollow prefabricated pile, underwater hydraulic hammer and delivery pile to complete the underwater delivery operation; Step 2: Start the underwater hydraulic hammer. Under the action of the hammer, the hollow prefabricated pile gradually penetrates into the soil layer. When the pile top is close to the top of the guide frame, turn off the underwater hydraulic hammer, use the ROV to open the pile delivery tube of the guide frame, and remove the guide frame; continue to start the hydraulic hammer to drive the pile. When the distance between the pile top and the bottom of the foundation trench is close to the height of the second-level hole of the pile cap, stop the piling, retract the underwater hydraulic hammer and the pile delivery, and complete the piling operation; Step 3: After the temperature of the hollow precast pile reaches the temperature of the seabed environment, the carbon dioxide hydrate sealing operation begins. Use a connecting pipe to access the pressure gauge valve reserved at the end of the hollow precast pile. One side of the connecting pipe is connected to a carbon dioxide storage tank. Open the valves of the storage tank and the pressure gauge valve in turn to slowly introduce carbon dioxide into the hollow precast pile. Observe through ROV. When the pressure gauge is stable and the amount of carbon dioxide introduced reaches the design value, stop introducing and end the sealing operation. Step 4: Lower the pile cap, align the second-level hole of the pile cap with the pile head so that the pile head can extend into the second-level hole, and fill the first-level hole with underwater concrete so that the pile cap and the pile body become a whole; and similarly complete the lowering, piling, carbon sequestration and pile cap installation operations of other pile bodies; Step 5: Lay the rammed stone layer, use the riprap ramming boat to throw stones underwater, and when the height of the stone layer is 20% higher than the designed elevation of the rammed stone layer, use the ramming plate below to tamp and compact the stones to the designed elevation, and the paving of the rammed stone layer is completed; Step 6: Lay the gravel cushion layer, use the gravel leveling ship to transport gravel to the underwater block stone tamping layer through the riprap pipe, control the travel speed of the riprap pipe at 0.8m / min-2m / min, and lay it in an S-shaped route along the horizontal direction of the foundation trench to complete the construction of the cushion layer.

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