Construction method of recoverable double-layer steel casing for underwater pile foundation construction

Abstract

The invention provides a construction method of a recoverable double-layer steel casing for underwater pile foundation construction. The double-layer steel casing comprises an inner-layer steel casing body and an outer-layer steel casing body. The construction method comprises the steps that the outer-layer steel casing and the inner-layer steel casing are sequentially immersed; counter-force devices are installed on the inner-layer steel casing and the drilling platform, the percussion drill conducts drilling construction, and meanwhile the counter-force devices apply downward pressure to the inner-layer steel casing to drive the inner-layer steel casing to move along with the inner-layer steel casing; a second drill bit of the percussion drill is used for continuing drilling construction until a pile foundation hole is drilled, drilling slag and slurry between the outer-layer steel casing and the inner-layer steel casing are pumped out, and a gap between the outer-layer steel casing and the inner-layer steel casing is filled with clay; concrete is poured into the pile foundation hole, the inner-layer steel casing is pulled out before initial setting of the concrete, and the outer-layer steel casing is pulled out after final setting of the concrete. Safety construction of the pile foundation in water can be achieved, the steel pile casing can be recycled, reutilization is achieved, resources are saved, the construction cost is reduced, and great economic benefits and implementation value are achieved.

Description

Technical Field

[0001] This invention generally relates to the field of bridge pile foundation construction technology, and specifically to a recyclable double-layer steel casing construction method for underwater pile foundation construction. Background Technology

[0002] Steel casings play a crucial role in the entire process of underwater bored pile foundation construction, determining the quality of the pile foundation. Typically, the steel casing for underwater bridges must penetrate the silt cover layer of the seabed and be driven into stable geological strata to ensure that there is no seepage, leakage of mud, or reverse drilling during the drilling process. According to conventional techniques, steel casings for underwater pile foundations are typically installed once and not removed after pile completion, leading to waste and increased construction costs. Furthermore, the long-term presence of steel casings in the water can easily disturb the benthic habitat. Summary of the Invention

[0003] In view of the above-mentioned defects or deficiencies in the existing technology, it is desirable to provide a recyclable double-layer steel casing construction method for underwater pile foundation construction, which can realize safe and reliable construction of underwater pile foundations, and at the same time, the steel casing can be recycled, achieving reuse, saving resources, reducing construction costs, and having significant economic benefits and implementation value.

[0004] In a first aspect, the present invention provides a method for constructing a recyclable double-layer steel casing for underwater pile foundation construction. The double-layer steel casing includes an inner steel casing and an outer steel casing that are nested together. The inner diameter of the outer steel casing is 100-200 cm larger than the outer diameter of the inner steel casing, and the length of the inner steel casing is greater than the length of the outer steel casing. The wall thickness of the inner steel casing is 8-12 mm. The construction method includes: The outer steel casing and the inner steel casing were laid in sequence, with the bottom ends of both the outer and inner steel casings penetrating into the first stable geological layer. A reaction device is installed on the inner steel casing and the drilling platform. The percussion drill is then used for drilling. Simultaneously, the reaction device applies downward pressure to the inner steel casing, causing it to move until the bottom end of the inner steel casing penetrates into the second stable geological layer. During the percussion drill, a mud pump is used to pump drill cuttings into the gap between the inner and outer steel casings. The diameter of the first drill bit of the percussion drill is larger than the diameter of the underwater pile foundation but smaller than the inner diameter of the inner steel casing. The bottom depth of the inner steel casing is greater than that of the outer steel casing, and the top of the outer steel casing is 20-40 cm higher than the top of the inner steel casing. The drilling continues using the second drill bit of the impact drill until the pile foundation hole is drilled. Then, the drill cuttings and mud between the outer and inner steel casings are extracted, and clay is filled into the gap between the outer and inner steel casings. After concrete is poured into the pile foundation hole, the inner steel casing and the outer steel casing are pulled out in sequence to complete the construction of the underwater pile foundation.

[0005] As an alternative, the inner diameter of the inner steel casing is 10-20 cm larger than the diameter of the designed underwater pile foundation.

[0006] As an optional solution, a reaction device is installed at the top of the inner steel casing and on the drilling platform. During the drilling operation, the reaction device applies downward pressure to the inner steel casing, causing it to move along with the casing until the bottom of the inner steel casing penetrates into the second stable geological layer. In this process, the diameter of the first drill bit of the impact drill is 5-10 cm larger than the diameter of the underwater pile foundation, and the diameter of the first drill bit of the impact drill is 5-10 cm smaller than the inner diameter of the inner steel casing.

[0007] As an optional solution, the reaction device includes: The reaction base is fixed to the drilling platform; The reaction frame is clamped on the outer periphery of the top of the inner steel casing and is located above the reaction base; At least three hydraulic jacks are located between the reaction frame and the reaction base, and are evenly distributed around the outer perimeter of the inner steel casing. A hydraulic system is connected to at least three hydraulic jacks to drive the at least three hydraulic jacks to move synchronously.

[0008] As an optional solution, the hydraulic jacks include four, which are evenly distributed at intervals on the outer periphery of the top of the inner steel casing.

[0009] As an alternative, during the process of filling the gap between the outer and inner steel casings with clay, the height of the clay filling is 2m-5m higher than that of the underwater pile foundation.

[0010] As an alternative, when filling the gap between the outer and inner steel casings with clay, the thickness of the clay filling is 50-100 cm.

[0011] As an optional solution, after the concrete is poured into the pile foundation hole, the inner steel casing and the outer steel casing are pulled out in sequence. The inner steel casing is pulled out within 0.5h-1h after the concrete is poured into the pile foundation hole, and the outer steel casing is pulled out by vibration after the concrete has finally set.

[0012] As an alternative, during the process of continuing drilling using the second drill bit of the impact drill until the pile foundation hole is drilled, the diameter of the second drill bit of the impact drill is equal to the diameter of the pile foundation in the water.

[0013] As an alternative, during the process of sequentially lowering the outer and inner steel casings, the outer steel casing is lowered using a conventional crawler crane in conjunction with a vibratory hammer.

[0014] This invention provides a recyclable double-layer steel casing construction method for underwater pile foundation construction. By utilizing a double-layer steel casing, the outer steel casing is installed first, followed by the inner steel casing. The diameter of the inner steel casing is larger than that of the underwater pile foundation, while the diameter of the outer steel casing is larger than that of the inner steel casing. This provides a stable operating space for construction and can accommodate different pile diameter requirements. During the drilling operation of the first drill bit of the impact drill, the inner steel casing moves under the drive of the reaction device, allowing it to penetrate deeper into the stable geological layer, effectively preventing grout leakage and perforation. Drill cuttings and mud generated during drilling can be discharged between the inner and outer steel casings. In the gaps, a "ring"-shaped drill cuttings wall is formed. The double-layer steel casing can temporarily store drill cuttings and circulate mud, eliminating the need for a separate mud circulation device. Then, the drill bit of the impact drill is replaced, and the second drill bit is used to drill to form the pile foundation hole and extract the drill cuttings and mud between the outer and inner steel casings. Clay is then backfilled. After concrete is poured into the pile foundation hole, the concrete will not collapse when the inner steel casing is pulled out due to the clay wall. The outer casing is slowly pulled out after the concrete has fully set, protecting the concrete structure. This achieves safe and reliable construction of pile foundations in water, while also enabling the recycling and reuse of the double-layer steel casing, saving resources, reducing costs and increasing efficiency, and reducing interference with the underwater environment. Attached Figure Description

[0015] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the structure of a double-layer steel casing according to an embodiment of this application; Figure 2 This is a schematic flowchart illustrating a recyclable double-layer steel casing construction method for underwater pile foundation construction, as described in an embodiment of this application. Detailed Implementation

[0016] The present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present application will now be described in detail with reference to embodiments.

[0017] To address the aforementioned problems, embodiments of this application provide a method for constructing a recyclable double-layer steel casing for underwater pile foundation construction, such as... Figure 1As shown, the double-layer steel casing includes an inner steel casing 10 and an outer steel casing 20 that are nested together. The inner diameter of the outer steel casing 20 is 100-200 cm larger than the outer diameter of the inner steel casing 10, and the length of the inner steel casing 10 is greater than the length of the outer steel casing 20. The wall thickness of the inner steel casing 10 is 8 mm-12 mm. Figure 2 As shown, the construction methods include: S10. The outer steel casing 20 and the inner steel casing 10 are laid in sequence, with the bottom ends of the outer steel casing 20 and the inner steel casing 10 penetrating into the first stable geological layer. S20. Install reaction devices on the inner steel casing 10 and the drilling platform. Perform percussion drilling. Simultaneously, the reaction devices apply downward pressure to the inner steel casing 10, causing it to move until the bottom of the inner steel casing 10 penetrates into the second stable geological layer. During percussion drilling, a mud pump is used to pump drilling cuttings into the gap between the inner steel casing 10 and the outer steel casing 20. The diameter of the first drill bit of the percussion drill is larger than the diameter of the underwater pile foundation and smaller than the inner diameter of the inner steel casing 10. The bottom depth of the inner steel casing 10 is greater than the bottom depth of the outer steel casing 20, and the top of the outer steel casing 20 is 20-40 cm higher than the top of the inner steel casing 10. S30. Continue drilling using the second drill bit of the impact drill until the pile foundation hole is drilled. Then, remove the drill cuttings and mud between the outer steel casing 20 and the inner steel casing 10, and fill the gap between the outer steel casing 20 and the inner steel casing 10 with clay. S40. After pouring concrete into the pile foundation hole, the inner steel casing 10 and the outer steel casing 20 are pulled out in sequence to complete the construction of the underwater pile foundation.

[0018] It is understood that the double-layer steel casing, comprising an inner steel casing 10 and an outer steel casing 20 nested together, refers to the outer steel casing 20 being positioned outside the inner steel casing 10. In actual construction, the outer steel casing 20 is located outside the inner steel casing 10, and there is no connection between the two. The inner diameter of the outer steel casing 20 is 100-200 cm larger than the outer diameter of the inner steel casing 20, thus creating a gap between the outer steel casing 20 and the inner steel casing 10. This gap can be used to store drill cuttings and drilling mud during actual construction. Specifically, the difference between the inner and outer diameters of the outer steel casing 20 can be, but is not limited to, 100 cm, 120 cm, 150 cm, 180 cm, or 200 cm, depending on the actual construction conditions.

[0019] The inner steel casing 10 has a greater height than the outer steel casing 20, meaning its total length is greater than the outer steel casing 20. During actual construction, the casing can be gradually lengthened according to the actual construction depth. This ensures that even if the top of the inner steel casing 10 has sunk below the platform during subsequent construction, it still has sufficient reserve length to continue being pressed downwards, always maintaining its bottom ahead of the drill bit. This allows it to cover all unfavorable geological sections from the pile top to above the second stable geological layer. The wall thickness of the inner steel casing 10 can be, but is not limited to, 8mm, 10mm, 11mm, or 12mm, giving it sufficient rigidity and strength to resist complex external forces. The diameter of the outer steel casing 20 is selected based on the diameter of the underwater pile foundation.

[0020] It is also understandable that in step S10, the outer steel casing 20 is first lowered until the bottom end of the outer steel casing 20 extends into the first stable geological layer. Then, the inner steel casing 10 is lowered using the same process, and the bottom end of the inner steel casing 10 can extend into the first stable geological layer. During this process, it is necessary to ensure the accuracy requirements of the design and specifications to ensure the safe and reliable lowering of the outer steel casing 20 and the inner steel casing 10.

[0021] In step S20, the first drill bit of the impact drill moves, and under the action of the reaction device, it drives the inner steel casing 10 to move. The purpose is to allow the bottom end of the inner steel casing 10 to extend into a deeper second stable geological layer, thereby ensuring the stability of the underwater pile foundation construction. The diameter of the first drill bit is larger than the diameter of the underwater pile foundation but smaller than the inner diameter of the inner steel casing 10. On the one hand, during the drilling process of the first drill bit, the downward pressure of the reaction device forces the inner steel casing 10 to be squeezed / vibrated into a hole slightly smaller than its own outer diameter. The inner steel casing 10 will violently compress the soil around the borehole wall, making it more compact and greatly enhancing the temporary stability of the borehole wall, preventing collapse during the drilling process. On the other hand, the gap between the inner steel casing 10 and the first drill bit allows the first drill bit to be lifted and lowered inside the inner steel casing 10, and can also avoid mechanical accidents caused by scraping and collision between the drill bit and the inner steel casing 10. In addition, the gap can also allow the mud to have a sufficient flow rate to carry and extract larger drill cuttings into the gap between the inner steel casing 10 and the outer steel casing 20.

[0022] In this process, the bottom depth of the inner steel casing 10 is deeper than that of the outer steel casing 20. This means that the second stable geological layer is deeper than the first stable geological layer. In this way, the inner steel casing 10 can provide advanced protection and avoid the risk of collapse, thereby ensuring the safety of the pile foundation hole formation. The top of the outer steel casing 20 is 20-40 cm higher than the top of the inner steel casing 10. Specifically, it can be, but is not limited to, 20 cm, 30 cm or 40 cm. This can prevent debris from falling in during construction and provide visual and physical warnings, improving construction safety. It can also accommodate drill cuttings between the outer steel casing 20 and the inner steel casing 10, and can accommodate more backfill clay during the backfilling process.

[0023] In step S30, after the inner steel casing 10 moves into the second stable geological layer, completely avoiding the risk of geological layer collapse, the second drill bit is used to drill and form the pile foundation hole. Due to the protection of the inner steel casing 10, the risk of collapse during the drilling process of the second drill bit can be reliably avoided. The diameter of the second drill bit is the same as the diameter of a normally designed underwater pile foundation.

[0024] It is also understandable that after the pile foundation hole is formed, the drilling cuttings and mud between the inner steel casing 10 and the outer steel casing 20 are extracted using a mud pump. The drilling cuttings are discarded, and the mud can be recycled. Then, clay is backfilled into the gap between the inner steel casing 10 and the outer steel casing 20 to form a protective geological layer, so as to facilitate the extraction of the inner steel casing 10.

[0025] In step S40, concrete is poured into the pile foundation hole to form a pile foundation in water. Before the concrete initially sets, i.e. when the concrete is in a plastic state with low frictional resistance, the inner steel casing 10 is pulled out. After the concrete has fully set, the outer steel casing 20 is pulled out, thus realizing the recycling of the inner steel casing 10 and the outer steel casing 20.

[0026] The recyclable double-layer steel casing construction method for underwater pile foundation construction disclosed in this application solves the problems of grout leakage or reverse perforation in existing drilling methods, as well as the inability to recycle the steel casing. This application utilizes a double-layer steel casing. During construction, the outer steel casing 20 is installed first, followed by the inner steel casing 10. The diameter of the inner steel casing 10 is larger than that of the underwater pile, while the diameter of the outer steel casing 20 is larger than that of the inner steel casing 10. This provides a stable operating space for construction and can accommodate different pile diameter requirements. During the drilling operation of the first drill bit of the impact drill, the inner steel casing 10 moves under the drive of the reaction device, allowing it to penetrate deeper into the stable geological layer, effectively preventing grout leakage and perforation. Drill cuttings and mud generated during drilling can be discharged into the gap between the inner steel casing 10 and the outer steel casing 20. The drilling cuttings are formed in a "ring" shape, and the double-layer steel casing can temporarily store the drilling cuttings and circulate the mud, eliminating the need for a separate mud circulation device. Then, the drill bit of the impact drill is replaced, and the second drill bit is used to drill into the pile foundation hole and extract the drilling cuttings and mud between the outer steel casing 20 and the inner steel casing 10. Clay is then backfilled, and after concrete is poured into the pile foundation hole, the concrete will not collapse when the inner steel casing 10 is pulled out due to the clay wall. The outer casing is slowly pulled out after the concrete has fully set, protecting the concrete structure. This achieves safe and reliable construction of the pile foundation in the water, while also enabling the recycling and reuse of the double-layer steel casing, saving resources, reducing costs and increasing efficiency, and reducing interference with the underwater environment.

[0027] As a feasible approach, the inner diameter of the inner steel casing 10 is 10-20 cm larger than the diameter of the designed underwater pile foundation.

[0028] In a preferred embodiment, the inner diameter of the inner steel casing 10 is 10 centimeters larger than the diameter of the designed underwater pile foundation.

[0029] In this embodiment, the difference between the inner diameter of the inner steel casing 10 and the diameter of the designed underwater pile foundation is beneficial for the inner steel casing 10 to move into a deeper second stable geological layer, thereby improving the structural stability of the pile foundation hole and avoiding collapse.

[0030] In some embodiments, S20, a reaction device is installed at the top of the inner steel casing 10 and on the drilling platform, and the impact drill is drilled. At the same time, the reaction device applies downward pressure to the inner steel casing 10, causing the inner steel casing 10 to move along with it until the bottom end of the inner steel casing 10 penetrates into the second stable geological layer. During this process, the diameter of the first drill bit of the impact drill is 5 cm to 10 cm larger than the diameter of the underwater pile foundation, and the diameter of the first drill bit of the impact drill is 5 cm to 10 cm smaller than the inner diameter of the inner steel casing 10.

[0031] Specifically, the difference between the diameter of the first drill bit of the impact drill and the diameter of the underwater pile foundation can be, but is not limited to, 5 cm, 6 cm, 7 cm, 9 cm or 10 cm, etc.; the difference between the diameter of the first drill bit of the impact drill and the inner diameter of the inner steel casing 10 can be, but is not limited to, 5 cm, 6 cm, 7 cm, 9 cm or 10 cm, etc.

[0032] This embodiment helps to ensure the reliable lifting and lowering of the first drill bit during construction, and also avoids the first drill bit from colliding or scraping with the inner steel casing 10, thereby helping to ensure that the inner steel casing 10 can safely follow the movement to a deeper second stable geological layer.

[0033] As a feasible approach, the reaction device includes: The reaction base is fixed to the drilling platform; The reaction frame is clamped on the outer periphery of the top of the inner steel casing 10 and is located above the reaction base; At least three hydraulic jacks 30 are located between the reaction frame and the reaction base, and are evenly distributed around the outer periphery of the inner steel casing 10. A hydraulic system is connected to at least three hydraulic jacks 30 to drive the at least three hydraulic jacks 30 to move synchronously.

[0034] The reaction base can be a sturdy frame formed by welding steel sections (such as I-beams and H-beams), which is mainly used to evenly and safely transfer the reaction force generated by the jacks to the entire construction platform; the reaction frame mainly clamps or holds the top of the inner steel casing 10; the hydraulic jacks 30 are distributed between the reaction frame and the reaction base, and generate downward pressure under the drive of the hydraulic system, so that the inner steel casing 10 can move to a deeper second stable geological layer.

[0035] Among them, there can be three or more hydraulic jacks 30, which are evenly distributed around the outer periphery of the inner steel casing 10, which helps to ensure that the downward pressure on the inner steel casing 10 is uniform.

[0036] In a preferred embodiment, the hydraulic jacks 30 include four, which are evenly distributed at intervals on the outer periphery of the top of the inner steel casing 10.

[0037] In some embodiments, during the process of filling the gap between the outer steel casing 20 and the inner steel casing 10 with clay, the height of the clay filling is 2m-5m higher than the underwater pile foundation.

[0038] Specifically, the height of the clay filling can be, but is not limited to, 2m, 3m, 4m or 5m higher than the underwater pile foundation.

[0039] Clay has water-stopping, stabilizing and buffering functions, and is mainly used to form a protective wall around the pile foundation hole, providing support for the subsequent extraction of the inner steel casing 10 and the outer steel casing 20.

[0040] In this embodiment, the height of the clay filling helps to achieve reliable seepage prevention and support, while avoiding the problem of excessive clay usage leading to high costs.

[0041] In some embodiments, during the process of filling the gap between the outer steel casing 20 and the inner steel casing 10 with clay, the thickness of the clay filling is 50 cm to 100 cm.

[0042] Specifically, the thickness of the clay can be, but is not limited to, 50 cm, 60 cm, 70 cm, 80 cm, or 100 cm.

[0043] In this embodiment, the thickness of the clay helps to form reliable protection and avoids the risk of collapse after the inner sleeve is pulled out.

[0044] In some embodiments, during the process of sequentially pulling out the inner steel casing 10 and the outer steel casing 20 after concrete is poured into the pile foundation hole, the inner steel casing 10 is pulled out within 0.5h-1h after the concrete is poured into the pile foundation hole, and the outer steel casing 20 is pulled out by vibration after the concrete has finally set.

[0045] Understandably, the inner steel casing 10 is vibrated and pulled out during the window period after concrete pouring but before the initial setting of the concrete. At this time, the concrete is still in a plastic state, with low frictional resistance, and there is also a protective wall formed by clay. Pulling out the inner steel casing 10 will not cause collapse. The window period can be within 0.5h-1h after the concrete pouring is completed, specifically, but not limited to 0.5h, 0.6h, 0.8h, or 1h, depending on the actual concrete properties during construction.

[0046] As a feasible method, during the sequential lowering of the outer steel casing 20 and the inner steel casing 10, the outer steel casing 20 is lowered using a conventional crawler crane in conjunction with a vibratory hammer.

[0047] In summary, the recyclable double-layer steel casing construction method for underwater pile foundation construction according to the embodiments of this application has the following beneficial effects: Significant economic benefits: All steel casings can be recycled and reused, which can save resources and reduce construction costs, resulting in significant economic benefits and implementation value; The casing design is reasonable: it has a double-layer steel casing structure. The inner diameter of the inner steel casing 10 is 10cm larger than the designed pile diameter, and the inner diameter of the outer steel casing 20 is 100cm larger than the outer diameter of the inner steel casing 10. The outer wall thickness is selected according to the pile diameter. This design provides a stable operating space for construction and can adapt to different pile diameter requirements. Accuracy assurance during installation: Using a conventional crawler crane in conjunction with a vibratory hammer to install the inner and outer steel casings 20mm thick ensures that the casings are installed with the accuracy required by the design and specifications, thus guaranteeing the quality of the pile foundation construction. Effective follow-up device: When the inner steel casing 10 is followed up, a reaction device consisting of a large-tonnage hydraulic jack 30 and a special reaction frame is installed. It is safe, stable and reliable, and can apply downward pressure to press the inner casing along the hole wall into the bottom of the hole to the stable geological layer, effectively preventing grout leakage and perforation.

[0048] Scientific Drill Cutting Treatment: A high-power cutting mud pump is prepared to pump the drilling cuttings into the gap between the double-layer casing to form a "ring"-shaped drilling cuttings wall. The double-layer steel casing can serve as a temporary storage for drilling cuttings and a circulation system for mud, thus avoiding the need for a separate mud circulation system. Proper protection during casing removal: After drilling, the drill cuttings and mud are removed, and clay is backfilled to 2m above the designed pile top elevation. After concrete pouring, the clay wall prevents the concrete from collapsing when the inner casing is removed, and the removal rate is controlled; the outer casing is slowly removed after the concrete has initially set, protecting the concrete structure.

[0049] The following specific embodiment illustrates the construction method of the recyclable double-layer steel casing for underwater pile foundation construction according to the present invention.

[0050] The double-layer steel casing includes an outer steel casing 20 and an inner steel casing 10. The inner steel casing 10 has a diameter 10cm larger than the designed diameter of the underwater pile foundation and a wall thickness of 12mm. The outer steel casing 20 has a diameter 100cm larger than the inner steel casing 10, and the wall thickness is selected according to the different underwater pile foundations. The top opening of the outer steel casing 20 is about 30cm higher than the inner steel casing 10. After the underwater pile foundation is poured, the inner steel casing and the outer steel casing 20 are pulled out in two separate stages. Laying double-layer steel casing: First, use a conventional crawler crane with a vibratory hammer to lay the outer steel casing 20. The bottom of the casing must penetrate into a stable geological layer. Use the same process to lay the inner steel casing 10. The laying of the steel casing must ensure the accuracy requirements of the design and specifications.

[0051] Inner steel casing 10 follow-up: The impact drilling rig is positioned on the drilling platform. The diameter of the first drill bit of the impact drill is 5cm larger than the designed underwater pile diameter and 5cm smaller than the inner diameter of the inner steel casing 10. At the same time, a reaction device is installed at the top of the inner steel casing 10 and on the drilling platform. This reaction device consists of 4 large-tonnage hydraulic jacks 30 and a specially made reaction frame, which are respectively set at 1 / 4 of the circumference of the casing. The installation must be safe, stable and reliable. The impact drill begins drilling. As the borehole advances, the reaction device is activated to apply downward pressure. The inner steel casing 10 is simultaneously subjected to downward pressure and its own weight, gradually being pressed into the bottom of the hole, achieving a "follow-up" effect. The inner casing continues to "follow" into deeper, stable geological layers, stopping once there is no slurry leakage or perforation. Simultaneously, a high-powered cuttings pump is prepared to pump drill cuttings from the borehole into the gap between the two casings, forming a ring-shaped cuttings wall. Because the diameter difference between the inner and outer steel casings 10 and 20 is designed to be 100cm, there is sufficient space to store a large amount of drill cuttings and mud, solving the mud circulation problem.

[0052] Normal drilling construction: After the inner steel casing 10 stops "following up", replace the drill bit of the impact drill with the normal design pile diameter and carry out construction until the hole is completed; Remove the double-layer steel casing: After drilling, use a mud pump to remove the drill cuttings and mud between the inner and outer casings. The drill cuttings are discarded, while the mud can be recycled. Then, backfill the gap between the inner steel casing 10 and the outer steel casing 20 with clay until it reaches 2m above the design elevation of the top of the underwater pile foundation.

[0053] After the concrete pouring is completed, the inner steel casing 10 must be removed using a vibratory hammer during the window period before initial setting (on site, this is generally controlled to begin within 0.5 to 1 hour after pouring, when the concrete is still in a plastic state and frictional resistance is low). Because there is a 50cm thick clay wall between the inner and outer casings, the concrete will not scatter or collapse. It is important to note that the removal rate should not be too fast; the outer steel casing 20 should be slowly removed using vibration after the concrete has fully set.

[0054] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A method for constructing a recyclable double-layer steel casing for underwater pile foundation construction, characterized in that, The double-layer steel casing includes an inner steel casing and an outer steel casing that are nested together. The inner diameter of the outer steel casing is 100-200 cm larger than the outer diameter of the inner steel casing, and the length of the inner steel casing is greater than the length of the outer steel casing. The wall thickness of the inner steel casing is 8-12 mm. The construction method includes: The outer steel casing and the inner steel casing are laid in sequence, with the bottom ends of both the outer and inner steel casings penetrating into the first stable geological layer. A reaction device is installed on the inner steel casing and the drilling platform. During percussion drilling, the reaction device applies downward pressure to the inner steel casing, causing it to move until its bottom end penetrates into the second stable geological layer. Simultaneously, a mud pump pumps drill cuttings into the gap between the inner and outer steel casings. The diameter of the first drill bit of the percussion drill is larger than the diameter of the underwater pile foundation but smaller than the inner diameter of the inner steel casing. The bottom depth of the inner steel casing is greater than that of the outer steel casing, and the top of the outer steel casing is 20-40 cm higher than the top of the inner steel casing. The drilling continues using the second drill bit of the impact drill until the pile foundation hole is drilled. Then, the drill cuttings and mud between the outer steel casing and the inner steel casing are extracted, and clay is filled into the gap between the outer steel casing and the inner steel casing. After concrete is poured into the pile foundation hole, the inner steel casing and the outer steel casing are pulled out in sequence to complete the construction of the underwater pile foundation.

2. The method for constructing a recyclable double-layer steel casing for underwater pile foundation construction according to claim 1, characterized in that, The inner diameter of the inner steel casing is 10-20 cm larger than the diameter of the designed underwater pile foundation.

3. The method for constructing a recyclable double-layer steel casing for underwater pile foundation construction according to claim 1, characterized in that, A reaction device is installed at the top of the inner steel casing and on the drilling platform. The impact drill is then used for drilling. At the same time, the reaction device applies downward pressure to the inner steel casing, causing it to move along with the casing until the bottom of the inner steel casing penetrates into the second stable geological layer. During this process, the diameter of the first drill bit of the impact drill is 5-10 cm larger than the diameter of the underwater pile foundation, and the diameter of the first drill bit of the impact drill is 5-10 cm smaller than the inner diameter of the inner steel casing.

4. The method for constructing a recyclable double-layer steel casing for underwater pile foundation construction according to claim 1, characterized in that, The reaction device includes: The reaction base is fixed to the drilling platform; The reaction frame is clamped around the outer periphery of the top of the inner steel casing and is located above the reaction base; At least three hydraulic jacks are located between the reaction frame and the reaction base, and are evenly distributed around the outer periphery of the inner steel casing. A hydraulic system is connected to the at least three hydraulic jacks to drive the at least three hydraulic jacks to move synchronously.

5. The method for constructing a recyclable double-layer steel casing for underwater pile foundation construction according to claim 4, characterized in that, The hydraulic jacks include four, which are evenly distributed at intervals on the outer periphery of the top of the inner steel casing.

6. The method for constructing a recyclable double-layer steel casing for underwater pile foundation construction according to claim 1, characterized in that, During the process of filling the gap between the outer steel casing and the inner steel casing with clay, the height of the clay filling is 2m-5m higher than the underwater pile foundation.

7. The method for constructing a recyclable double-layer steel casing for underwater pile foundation construction according to claim 1, characterized in that, During the process of filling the gap between the outer steel casing and the inner steel casing with clay, the thickness of the clay filling is 50 cm to 100 cm.

8. The method for constructing a recyclable double-layer steel casing for underwater pile foundation construction according to claim 1, characterized in that, During the process of sequentially pulling out the inner steel casing and the outer steel casing after pouring concrete into the pile foundation hole, the inner steel casing is pulled out within 0.5h-1h after the concrete is poured into the pile foundation hole, and the outer steel casing is pulled out by vibration after the concrete has finally set.

9. The method for constructing a recyclable double-layer steel casing for underwater pile foundation construction according to claim 1, characterized in that, During the process of continuing drilling using the second drill bit of the impact drill until the pile foundation hole is drilled, the diameter of the second drill bit of the impact drill is equal to the diameter of the underwater pile foundation.

10. The method for constructing a recyclable double-layer steel casing for underwater pile foundation construction according to any one of claims 1-9, characterized in that, During the process of sequentially lowering the outer steel casing and the inner steel casing, the outer steel casing is lowered using a conventional crawler crane in conjunction with a vibratory hammer.

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