A construction method of a lock steel pipe pile cofferdam suitable for high-strength bare rock deep water sea area

Abstract

The application discloses a kind of suitable for high-strength bare rock deepwater sea area lock steel pipe pile cofferdam construction method, comprising: S1, construction water operation platform;S2, along cofferdam design position section is carried out into groove operation: after each slot section is into groove, sequentially carry out hole cleaning, slot section inner cement mixed soil backfill, slot section inner temporary positioning Larsen steel pipe pile insertion and hit, then carry out the construction of next slot section;S3, to each temporary positioning Larsen steel pipe pile in secondary drilling hole, and replace with the same type Larsen steel pipe pile with steel reinforcement cage fixed at bottom, form steel pipe pile cofferdam;S4, install two layers of steel encloses purlin and steel support located at top;S5, pour anti-scour layer on the inside and outside of steel pipe pile cofferdam bottom;S6, pour underwater concrete into Larsen steel pipe pile to bare rock surface;S7, water is pumped out in steel pipe pile cofferdam, and remaining steel encloses purlin and steel support are sequentially installed from top to bottom.The application effectively solves the problem of hole forming, seepage prevention and embedded fixation in bare rock, and realizes the construction of Larsen steel pipe pile cofferdam under harsh conditions.

Description

Technical Field

[0001] This invention relates to the field of cofferdam construction technology. More specifically, this invention relates to a method for constructing a cofferdam using interlocking steel pipe piles in deep waters with high-strength bare rock. Background Technology

[0002] Currently, two common construction methods for deep-water cofferdams in China are double-walled steel cofferdams and interlocking steel pipe pile cofferdams. Existing interlocking steel pipe pile cofferdam construction techniques involve using a vibratory hammer to forcefully drive each interlocking steel pipe pile into the ground to form a single unit. Therefore, this construction technique is suitable for soft soils (silty soil, silty clay, silt, etc.), sandy soils, or strongly weathered soft rock with a strength below 5 MPa, where the interlocking steel pipe piles can be driven in forcefully without severe deformation, allowing for successful implementation of interlocking steel pipe pile cofferdam construction. When the thickness of the overburden layer cannot meet the lateral embedment requirements of the interlocking steel pipe piles, and the overburden layer is below strong weathered rock, moderate weathered rock or pebbles with relatively low strength, the steel pipe piles cannot be forcibly driven into such strata with a vibratory hammer. The current technology is to drive steel casings through the overburden layer to the rock surface, then drill holes in the steel casing with a rotary drilling rig, enlarge the holes, backfill sandy soil one by one, and then insert the interlocking steel pipe piles. Then, double high-pressure jet grouting pipe piles are used to reinforce the soil in the backfilled sand outside the steel pipe piles. The existing interlocking steel pipe pile cofferdam construction method has the following obvious shortcomings: (1) The cofferdam is located in a water area with an overburden layer, but the thickness of the overburden layer cannot meet the requirements of the lateral embedment force of the steel pipe piles, and the rock strength below the overburden layer is not very high. A rotary drilling rig can be used to drill into such rocks. (2) The steel pipe piles are embedded in the rock by backfilling sand into the steel casing after drilling, and then driving steel pipe columns into the rock one by one after pulling out the steel casing. Double-pipe high-pressure jet grouting piles and grouting are used to reinforce the backfilled sand outside the steel pipe piles. Since this type of cofferdam only has one layer of lateral embedment, the embedment requirements of the cofferdam are relatively low. No special measures are taken for leakage and piping at the bottom of the pile. The rock layer is simply replaced with highly permeable sand and then grouting is carried out for reinforcement. The inside of the steel pipe pile, the bottom of the steel pipe pile and the surrounding area are all sandy soil. Under high water pressure, leakage and piping are easy to occur. Therefore, this type of single-layer embedded interlocking steel pipe pile cofferdam is not suitable for water areas with high water pressure in deep water areas. It is only suitable for water areas with shallow water depth and low water pressure. (3) Since the cofferdam support was not specially designed during the design of the cofferdam, and no two layers of walers and supports were set above the water surface to resist wind and waves, this type of cofferdam is only suitable for still water or water pressure with low wind and waves and low flow velocity. (4) Cofferdams typically use "CT" type interlocking. This type of cofferdam is easy to drive and close, and is easy to construct, but its disadvantage is that there is a large leakage at the interlocking point, making it unsuitable for deep water construction. (5) There is no special anti-scour treatment outside the cofferdam, so this type of cofferdam cannot meet the requirements of water areas with scour. In summary, the existing technology of "CT" type interlocking steel pipe piles involves drilling holes in the rock strata to replace sand, and then using double-pipe high-pressure jet grouting piles for reinforcement. The pile bottom adopts a single layer of lateral embedment. This type of cofferdam is suitable for areas with shallow water depth, low water pressure, low water flow or still water, and where the riverbed surface has a certain overburden layer, the rock strength below the overburden layer is not high, and the requirements for pile bottom embedment are not high. It cannot meet the requirements of deep-sea areas with water depth exceeding 20 meters, strong winds and waves, strong scour, and no overburden layer, where the rock is exposed to high strength. 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 method for constructing interlocking steel pipe pile cofferdams suitable for high-strength bare rock deep-water areas is provided, comprising the following steps:

[0005] S1, Construction water-based operation platform;

[0006] S2. Trenching operations are carried out in sections along the design location of the cofferdam: after each trench section is completed, the holes are cleaned, the cement-soil mixture in the trench section is backfilled, and the temporary positioning Larssen steel pipe piles in the trench section are driven in sequence before the construction of the next trench section is carried out.

[0007] S3. Drill secondary holes in each of the temporary positioning Larssen steel pipe piles and replace them with Larssen steel pipe piles of the same type with steel cages fixed at the bottom to form a steel pipe pile cofferdam.

[0008] S4. Install the two layers of steel walers and steel supports at the top;

[0009] S5. Pour an anti-scouring layer on both the inner and outer sides of the bottom of the steel pipe pile cofferdam.

[0010] S6. Pour underwater concrete into the Larsen steel pipe pile replaced in step S3 up to the bare rock surface.

[0011] S7. Carry out dewatering operations inside the steel pipe pile cofferdam, and install the remaining steel walers and steel supports from top to bottom.

[0012] S8. Construction of the main structure, and gradual removal of each layer of steel walers and steel supports from bottom to top;

[0013] S9. Dismantle the steel pipe pile cofferdam.

[0014] Preferably, in step S2, the construction of each trench segment specifically includes: using an impact drill to form a hole, the diameter of the impact drill bit being 50cm larger than the diameter of the temporary positioning Larssen steel pipe pile; and using skip-hole construction, after two adjacent pile holes are formed, the pile hole between these two pile holes is constructed, and the construction of one trench segment is completed in this order.

[0015] Preferably, in step S2, the cement-mixed soil is composed of the following components by mass percentage: 8% cement, 52%~62% yellow sand and 30%~40% clay.

[0016] Preferably, step S3 specifically includes:

[0017] S31. Drill a second hole in the temporary positioning Larssen steel pipe pile and clean the hole;

[0018] S32. Slowly pull out the temporary positioning Larssen steel pipe pile;

[0019] S33. Another Larssen steel pipe pile of the same type with a steel cage fixed at the bottom is driven into the corresponding trench section again. The bottom of the Larssen steel pipe pile is driven to the rock surface at the bottom of the trench section, and the steel cage is inserted into the hole obtained by secondary drilling in step S31.

[0020] S34. Repeat steps S31 to S33 until all the temporary positioning Larssen steel pipe piles have been replaced, forming the steel pipe column cofferdam.

[0021] Preferably, the length and diameter of the reinforcing cage are the same as the hole depth and diameter obtained by secondary drilling in step S31.

[0022] Preferably, in step S4, the top layer of steel walers and steel supports are first installed symmetrically in sections using a crawler crane, and then the second layer of steel walers and steel supports are installed symmetrically in sections during low tide. The steel walers and the Larssen steel pipe piles are connected as a whole by welding arc-shaped steel plates, and then fine stone concrete is backfilled between the steel walers and the Larssen steel pipe piles.

[0023] Preferably, in step S5, during low tide, an anti-scouring layer 80-100 cm thick and 100 cm wide is poured on the inner and outer sides of the steel pipe pile cofferdam, wherein the anti-scouring layer is underwater early-strength concrete.

[0024] Preferably, in step S8, after each section of the main structure is constructed, water is pumped back into the steel pipe pile cofferdam or soil is backfilled, and the steel supports and steel walers at the corresponding height are removed simultaneously.

[0025] Preferably, step S1 specifically includes the following steps:

[0026] S11. Using anchored vessels for positioning, underwater drilling with impact drills is performed in clear water to form holes;

[0027] S12. Lower the guide pipe into the hole and pour underwater concrete;

[0028] S13. Use a small floating crane to lift a vibratory hammer and drive the platform steel pipe piles to the bottom of the hole where the concrete has just been poured.

[0029] S14. Repeat steps S11 to S13 until 6 to 8 platform steel pipe piles are constructed. Use these platform steel pipe piles to erect the starting work platform using a floating crane.

[0030] S15. Install a 100-ton crawler crane on the starting platform; using the starting platform as a base, construct the remaining part of the water-based work platform using the 100-ton crawler crane and impact drill with the fishing method.

[0031] The present invention has at least the following beneficial effects:

[0032] 1. The present invention provides a method for constructing cofferdams using interlocking steel pipe piles in deep waters with high-strength bare rock. This method employs a dual seepage prevention technology that combines the integral backfilling of cement-mixed soil within the trench section with the backfilling of underwater concrete with strong seepage prevention capabilities within the Larssen steel pipe piles. It also employs a double-layer embedding technology that embeds the steel pipes in the cement-mixed soil and embeds the steel cage at the bottom of the Larssen steel pipe piles. This effectively solves the problems of drilling, seepage prevention, and embedding in bare rock, enabling the construction of cofferdams using Larssen steel pipe piles under the conditions of high-strength bare rock in deep waters with strong winds and waves.

[0033] 2. The construction method of interlocking steel pipe pile cofferdams for high-strength bare rock deep-sea areas provided by the present invention has strong resistance to scour, wind and waves and water flow, and has a wide range of applications. It can be constructed in the harsh hydrological conditions of deep-sea areas, and can also be used in rivers with relatively good water wave and water flow conditions.

[0034] 3. The construction method of interlocking steel pipe pile cofferdams for high-strength bare rock deep waters provided by this invention eliminates the need for complex processes such as underwater blasting, waterborne transportation of large components, hoisting with large floating cranes, and setting up large platforms for large-area and large-volume underwater sealing construction. The construction process is simple and the construction difficulty is significantly reduced.

[0035] 4. The construction method of interlocking steel pipe pile cofferdams for high-strength bare rock deep-water areas provided by this invention uses Larssen steel pipe piles, steel walers and steel supports, which are standard products on the market and can be reused multiple times. They can be invested through leasing, resulting in low construction costs.

[0036] 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

[0037] Figure 1 This is a top view of the water-based work platform and the steel pipe column cofferdam described in this invention;

[0038] Figure 2 This is a side view of the water-based work platform and the steel pipe column cofferdam described in this invention.

[0039] Figure 3 for Figure 1 Enlarged view of section A in the image;

[0040] Figure 4 This is a schematic diagram of the pile hole construction sequence in step S2 of the cofferdam construction method for high-strength bare rock deep-water areas described in this invention;

[0041] Figure 5 This is a schematic diagram of the connection structure between the Larsen steel pipe pile and the reinforcing cage described in this invention. Detailed Implementation

[0042] 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.

[0043] 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.

[0044] like Figures 1 to 5 As shown, this invention provides a method for constructing interlocking steel pipe pile cofferdams suitable for high-strength bare rock deep-water areas, comprising the following steps:

[0045] S1, Construction Waterway Operation Platform 1;

[0046] S2. Trenching operations are carried out in sections along the design location of the cofferdam: After each trench section is completed, the following steps are performed in sequence: cleaning the holes, backfilling the trench section with cement-mixed soil, driving the temporary positioning Larssen steel pipe piles in the trench section, and then proceeding to the construction of the next trench section.

[0047] S3. Drill secondary holes in each of the temporary positioning Larssen steel pipe piles and replace them with Larssen steel pipe piles of the same type 21 with steel cages fixed at the bottom to form a steel pipe pile cofferdam 2.

[0048] S4. Install the two layers of steel walers 3 and steel supports 4 located at the top;

[0049] S5. Pour an anti-scouring layer 6 on both the inner and outer sides of the bottom of the steel pipe pile cofferdam 2.

[0050] S6. Pour underwater concrete into the Larsen steel pipe pile 21 after the replacement in step S3 up to the bare rock surface.

[0051] S7. Carry out dewatering operations inside the steel pipe pile cofferdam 2, and install the remaining steel walers 3 and steel supports 4 from top to bottom.

[0052] S8. Construction of the main structure 5, and gradual removal of each layer of steel walers 3 and steel supports 4 from bottom to top;

[0053] S9. Remove the steel pipe pile cofferdam 2.

[0054] In this technical solution, a dual seepage prevention technology is employed, combining the integral backfilling of the trench section with cement-mixed soil with the backfilling of the Larssen steel pipe piles 21 with highly seepage-proof underwater concrete. This solves the problem of seepage prevention difficulties in the construction of deep-water cofferdams on bare rock with high water pressure. Furthermore, a double-layer embedding technology, where the cement-mixed soil is used to embed the steel pipes and the reinforcing cage 8 at the bottom of the Larssen steel pipe piles 21, solves the problem of lateral embedding at the pile bottom in deep-water bare rock. Before dewatering the steel pipe pile cofferdam 2, the top two layers of steel walers 3 and steel supports 4 are constructed to ensure the early stability of the steel pipe pile cofferdam 2 and reduce the swaying effects of wind, waves, and water flow. The scour protection layer 6, constructed on the inner and outer sides of the steel pipe pile cofferdam 2, effectively mitigates the impact of strong wave scouring. The Larssen steel pipe piles 21 are used, referring to… Figure 3 It includes a steel pipe pile body 211 and Larssen locks 212 disposed on both sides of the steel pipe pile body 211. Two adjacent Larssen steel pipe piles 21 are connected by the Larssen locks 212, which have excellent waterproof performance and can effectively solve the leakage problem caused by high water pressure at the CT lock connection. The Larssen locks 212 are lock structures used on both sides of the Larssen steel sheet pile.

[0055] The dimensions of the steel pipe pile cofferdam are determined based on the structure 5. If the structure 5 is a bridge abutment, the inner dimension of the steel pipe pile cofferdam 2 is approximately 4 meters larger than the abutment dimension, and the bottom of the Larssen steel pipe piles 21 is 4-5 meters deeper than the abutment bottom. If the structure 5 is a water intake of a water intake tunnel, the inner dimension of the steel pipe pile cofferdam 2 is approximately 8 meters larger than the water intake outer dimension, and the bottom of the Larssen steel pipe piles 21 penetrates 4-5 meters into the moderately weathered rock. The diameter of the Larssen steel pipe piles 21 is 80-100 cm, a standard product on the market. The steel walers 3 and steel supports 4 are arranged in 4-6 layers, with two layers of steel walers 3 and steel supports 4 positioned above the low tide level. These two layers of steel supports 4 are connected by upper and lower horizontal bracing and scissor bracing to form a whole, ensuring that the steel pipe pile cofferdam 4 can stabilize as early as possible and reducing the swaying effects caused by wind, waves, and water flow. The water-based work platform 1 is arranged in a circle around the steel pipe pile cofferdam 2. The width and force of the water-based work platform 1 must meet the requirements for the movement and operation of a 100-ton crawler crane. The water-based work platforms 1 are connected to form a whole to meet the requirements for scouring and resistance to wind, waves and water flow. The distance between the water-based work platform 1 and the steel pipe pile cofferdam 2 is about 1.5 meters.

[0056] In step S1, the above-water work platform 1 is first constructed, and the specific construction steps include:

[0057] S11. Using anchored vessels for positioning, underwater drilling with impact drills is performed in clear water to form holes;

[0058] S12. Lower the guide pipe into the hole and pour underwater concrete;

[0059] S13. A small floating crane is used to lift a vibratory hammer to drive the platform steel pipe pile 11 to the bottom of the hole where the concrete has just been poured.

[0060] S14. Repeat steps S11 to S13 until 6 to 8 platform steel pipe piles are constructed. Use these platform steel pipe piles 11 to erect the starting work platform using a floating crane.

[0061] S15. Install a 100-ton crawler crane on the starting platform; using the starting platform as a base, construct the remaining part of the water-based work platform using the 100-ton crawler crane and impact drill with the fishing method.

[0062] By constructing the above-mentioned water-based work platform 1 through the above steps, the problems of driving high-strength bare rock steel pipe piles and erecting water-based steel platforms can be effectively solved.

[0063] In step S2, the construction of each trench segment specifically includes: using an impact drill to create holes, with the drill bit diameter being 50cm larger than the diameter of the temporary positioning Larssen steel pipe pile; and employing a skip-hole construction method, where after two adjacent pile holes 7 are completed, the pile hole between these two pile holes 7 is constructed, and the construction of one trench segment is completed in this sequence. The skip-hole construction sequence is as follows: Figure 4 As shown, Figure 4 The numbers above each of the pile holes 7 indicate their construction sequence. Two adjacent pile holes 7 interlock, and three pile holes 7 form a continuous arc-shaped trench segment. This process is repeated to construct one trench segment. Then, an air compressor is used for air-lift reverse circulation cleaning to remove boulders and stones from the bottom of the trench segment. The cement-soil mixture 7 is then backfilled into the trench segment. The cement-soil mixture 7 consists of the following components by mass percentage: 8% cement, 52%~62% yellow sand, and 30%~40% clay. Before backfilling, a trial mix of the cement-soil mixture 7 is conducted to ensure that its solidified strength is 3~5 MPa, possessing certain consolidation and embedding capabilities, erosion resistance, and seepage prevention capabilities, without affecting the forced driving and extraction of the Larssen steel pipe piles 21. To prevent the cement-soil mixture 7 from being diluted into mud during backfilling, a steel pipe with an inner diameter of 800 mm is used as a guide pipe for backfilling, following a process similar to underwater concrete pouring.

[0064] After backfilling is completed, a temporary positioning guide frame is set up using the above-water operation platform 1. A crawler crane is used to lift a DZ60 vibratory hammer to drive each of the temporary positioning Larssen steel pipe piles into the trench section one by one until the bottom of the pile hole. Steel sections are then used to temporarily fix the piles to the above-water operation platform 1. After completing the hole cleaning, backfilling, and driving of the temporary positioning Larssen steel pipe piles for one trench section, construction of the next trench section begins. This process is repeated to complete the trenching operation and driving of the temporary positioning Larssen steel pipe piles for one ring of the steel pipe pile cofferdam 2. This ensures that all the temporary positioning Larssen steel pipe piles are successfully driven into place to form a complete structure.

[0065] Then, in step S3, each of the temporary positioning Larssen steel pipe piles is replaced with Larssen steel pipe piles 21 of the same type with a steel reinforcement cage 8 fixed at the bottom to obtain the steel pipe pile cofferdam 2, which specifically includes the following steps:

[0066] S31. Drill a second hole in the temporary positioning Larssen steel pipe pile and clean the hole;

[0067] S32. Slowly pull out the temporary positioning Larssen steel pipe pile;

[0068] S33. Another Larssen steel pipe pile 21 of the same type with a steel cage fixed at the bottom is driven back into the corresponding trench section. The bottom of the Larssen steel pipe pile 21 is driven to the rock surface at the bottom of the trench section, and the steel cage is inserted into the hole obtained by secondary drilling in step S31.

[0069] S34. Repeat steps S31 to S33 until all the temporary positioning Larssen steel pipe piles have been replaced, forming the steel pipe column cofferdam 2.

[0070] A small impact drill was used to perform secondary impact drilling inside the temporarily positioned Larssen steel pipe pile. The drill bit was 10 cm smaller than the inner diameter of the temporary positioning Larssen steel pipe pile. After cleaning the hole, the temporary constraint on the temporary positioning Larssen steel pipe pile was released, and a crawler crane was used to slowly pull out the temporary positioning Larssen steel pipe pile. Another Larssen steel pipe pile 21 of the same type was then driven back into the trench section. A short reinforcing cage 8 was fixed to the bottom of the Larssen steel pipe pile 21. The bottom of the Larssen steel pipe pile 21 was driven into the rock surface of the trench section, and the bottom reinforcing cage 8 extended into the hole formed by the second impact drilling. (Refer to...) Figure 5 The bottom of the Larssen steel pipe pile 21 is welded and fixed to the reinforcing cage 8 via connecting steel bars 213, which effectively prevents the reinforcing cage from floating due to impact during the first concrete pouring. The temporarily positioned Larssen steel pipe pile after being pulled out can then have a reinforcing cage 8 welded to its bottom as a temporary positioning Larssen steel pipe pile to replace the Larssen steel pipe pile 21 at the next hole location. Furthermore, the length and diameter of the reinforcing cage 8 are the same as the hole depth and diameter obtained from the secondary drilling in step S31.

[0071] In step S4, the top layer of steel walers 3 and steel supports 4 are first installed symmetrically in sections using a crawler crane. Then, during low tide, the second layer of steel walers 3 and steel supports 4 are installed symmetrically in sections. The steel walers 3 and the Larssen steel pipe piles 21 are connected as a whole by welding arc-shaped steel plates. Then, fine stone concrete is backfilled between the steel walers 3 and the Larssen steel pipe piles 21 to compact the gap.

[0072] In step S5, to prevent erosion by sea waves, an anti-erosion layer 6 with a thickness of 80-100 cm and a width of 100 cm is poured on the inner and outer sides of the steel pipe pile cofferdam during low tide. The anti-erosion layer 6 is underwater early-strength concrete.

[0073] In step S6, the guide pipe is lowered and underwater concrete is poured into the Larssen steel pipe pile 21 replaced in step S3 up to the bare rock surface. This can effectively prevent piping and leakage at the bottom of the steel pipe pile, and can also effectively embed the steel pipe pile and improve its bending resistance.

[0074] In step S7, after the underwater concrete pouring inside all the Larssen steel pipe piles 21 is completed, the water is pumped out inside the steel pipe pile cofferdam 2, and the remaining steel walers 3 and steel supports 4 are installed from top to bottom.

[0075] In step S8, after the water in the steel pipe pile cofferdam 2 is pumped to the bottom, the base is simply leveled and the leveling concrete of the cushion layer is poured, and then the construction of the main structure 5 inside the cofferdam can be carried out. After each section of the main structure 5 is constructed, water is pumped back into the steel pipe pile cofferdam 2 or soil is backfilled, and the steel supports 4 and steel walers 3 of the corresponding height are removed at the same time.

[0076] In step S9, a 100-ton crawler crane and a DZ120 vibratory hammer are used to extract each of the Larssen steel pipe piles 21, and the steel pipe column cofferdam 2 is dismantled. For deep-water areas, if the design requires an underwater scour wall several meters high to protect the main structure, a combination of permanent and temporary measures can be adopted. The Larssen steel pipe piles 21 are cut underwater along the top elevation of the scour wall, and the remaining steel pipe pile structure serves as part of the scour wall structure.

[0077] 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 construction method suitable for high-strength bare rock deepwater sea area lock steel pipe pile cofferdam, characterized in that, The method comprises the following steps: S1, constructing a water operation platform; S2, performing groove forming operation along the cofferdam design position in sections: after groove forming of each groove section, sequentially performing hole cleaning, backfilling of cement mixed soil in the groove section, temporary positioning and driving of Larsen steel pipe pile in the groove section, and then performing construction of the next groove section; the cement mixed soil is composed of the following components in mass percentage: cement 8%, yellow sand 52%-62%, and clay 30%-40%; S3, sequentially drilling holes in each temporary positioning Larsen steel pipe pile, and replacing the temporary positioning Larsen steel pipe pile with a same type of Larsen steel pipe pile with a steel reinforcement cage fixed at the bottom to form a steel pipe pile cofferdam; Step S3 specifically comprises: S31, drilling holes in the temporary positioning Larsen steel pipe pile, and cleaning the holes; S32, slowly pulling out the temporary positioning Larsen steel pipe pile; S33, re-driving another same type of Larsen steel pipe pile with a steel reinforcement cage fixed at the bottom into the corresponding groove section, the Larsen steel pipe pile is driven to the rock surface at the bottom of the groove section, and the steel reinforcement cage is inserted into the hole drilled in step S31; S34, repeating steps S31 to S33 until the replacement of all the temporary positioning Larsen steel pipe piles is completed to form the steel pipe pile cofferdam; S4, installing two layers of steel enclosing purlins and steel supports at the top; S5, pouring anti-scouring layers on the inner and outer sides of the bottom of the steel pipe pile cofferdam; S6, pouring underwater concrete into the replaced Larsen steel pipe pile in step S3 to the bare rock surface; S7, performing water pumping operation in the steel pipe pile cofferdam, and sequentially installing the remaining steel enclosing purlins and steel supports from top to bottom; S8, constructing the main structure, and sequentially removing each layer of steel enclosing purlins and steel supports from bottom to top; S9, removing the steel pipe pile cofferdam.

2. The method for high-strength bare rock deep water sea area lock steel pipe pile cofferdam construction method suitable for claim 1, characterized in that, In step S2, the construction of each groove section comprises: using an impact drill to impact hole forming, the diameter of the impact drill bit is 50 cm larger than the diameter of the temporary positioning Larsen steel pipe pile; and using skip hole construction, when two adjacent pile holes are formed, the pile hole between the two pile holes is constructed, and the construction of a groove section is completed in this order.

3. The method for high-strength bare rock deep water sea area lock steel pipe pile cofferdam construction method suitable for claim 1, characterized in that, The length and diameter of the steel reinforcement cage are the same as the depth and diameter of the hole drilled in step S31.

4. The method for high-strength bare rock deep water sea area lock steel pipe pile cofferdam construction method suitable for claim 1, characterized in that, In step S4, the top layer of steel enclosing purlins and steel supports are first symmetrically hoisted and installed in blocks by using a crawler crane, then the second layer of steel enclosing purlins and steel supports are symmetrically installed in blocks during low tide, the steel enclosing purlins and the Larsen steel pipe piles are welded and connected into a whole by using arc-shaped steel plates, and fine stone concrete is backfilled between the steel enclosing purlins and the Larsen steel pipe piles.

5. The method for high strength bare rock deep water sea area lock catch steel pipe pile cofferdam construction method according to claim 1, characterized in that, In step S5, during low tide, an anti-scouring layer with a thickness of 80-100 cm and a width of 100 cm is poured on the inner and outer sides of the steel pipe pile cofferdam, and the anti-scouring layer is underwater early strength concrete.

6. The method for high strength bare rock deep water sea area lock catch steel pipe pile cofferdam construction method according to claim 1, characterized in that, In step S8, after construction of a section of the main structure, water or soil is backfilled into the steel pipe pile cofferdam, and the steel supports and steel enclosing purlins of the corresponding height are removed synchronously.

7. The method for high strength bare rock deep water sea area lock catch steel pipe pile cofferdam construction method according to claim 1, characterized in that, Step S1 specifically comprises the following steps: S11, positioning by using an anchor throwing ship, and performing underwater clean water drilling by using an impact drill; S12, lowering a guide pipe in the hole to pour underwater concrete; S13, using a small floating crane to hoist a vibrating hammer to drive the platform steel pipe pile to the bottom of the hole in which the concrete is just poured; S14, repeat steps S11 to S13 until 6 to 8 platform steel pipe piles are constructed, and the starting work platform is erected by using the floating crane and the platform steel pipe piles; S15, install 1 100-ton crawler crane on the starting platform; and use the 100-ton crawler crane and the impact drill to construct the remaining part of the water work platform by using the fishing method.

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