Construction method of deep water area thick covering layer standard structure steel cofferdam

Abstract

The invention discloses a construction method of a deep water area thick covering layer standard structure steel cofferdam, which comprises the following steps of: S1, welding a plurality of layers of brackets on the side wall of a steel casing along the height direction, and gradually increasing the sizes of the brackets from top to bottom; s2, sinking construction is conducted on the steel cofferdam, and a steel casing is located in the wall body of the steel cofferdam; s3, carrying pole beams and enclosing purlins are installed at the bottom in the steel cofferdam; s4, on the basis of the enclosing purlin on the bottommost layer, multiple layers of enclosing purlins continue to be installed upwards; and S5, water is pumped till the water level submerges the elevation of the enclosing purlin by 50 cm, and after water is pumped to the bottom of the foundation pit, brackets are dismantled, and the steel pipe piles are pulled out. The technical problems that a traditional steel cofferdam is insufficient in structural stability and difficult in sinking precision control under the deep water thick covering layer geological condition are solved, the method is mainly used for steel cofferdam construction under the deep water thick covering layer geological condition of cross-sea bridges, port engineering and the like, cofferdam deformation can be effectively controlled, the construction safety is improved, and the material consumption is reduced.

Description

Technical Field

[0001] The present invention relates to the construction field of steel cofferdams. More specifically, the present invention relates to a construction method for a standard structure steel cofferdam with thick overburden in deep water areas. Background Art

[0002] In the southeast coastal areas of our country, the thickness of the riverbed silt stratum reaches up to 30m - 50m, and affected by tides, the designed construction water level of the cofferdam is high. Currently, there are the following several construction methods for steel cofferdams under such geological conditions: One is to adopt a double - wall steel cofferdam. The advantages of this method are that the overall structure has large stiffness and is suitable for deep - water foundations; it can be sunk after being assembled integrally, fabricated and floated in water in the factory, or assembled in sections and scattered on the construction platform without additional formwork, with the smallest external expansion dimension and lower requirements for the thickness of the bottom seal. The disadvantages are that the steel consumption is relatively large, underwater cutting is required for demolition, the processing and manufacturing requirements are high, the welding workload is large, affecting the overall construction period, and it is difficult to sink into the mud.

[0003] One is a lock - mouthed steel pipe pile cofferdam. The advantages of this method are that the structure is stable, the processing and manufacturing are simple and fast, and the construction period is short; a light hoisting device can be used to install the steel pipe pile cofferdam while constructing the pile foundation; it has the characteristics of relatively large overall stiffness, high material recycling utilization rate, strong adaptability to plane layout, etc.; it can better adapt to soft overburden. The disadvantages are that the water - stop requirement at the lock - mouth is high and it is easy to leak. After multiple turnovers, the lock - mouth deforms greatly and the turnover efficiency is low. At the contact position between the steel pipe pile and the waling, the concentrated force is large and strengthening treatment must be done.

[0004] One is a steel sheet pile cofferdam. The advantages of this method are that it can be driven into harder soil layers and can be assembled into various shapes; a small hoisting device can complete the single - sheet driving; the production is simple and the construction difficulty is low. The disadvantages are that the length is mostly fixed - size, the commonly used maximum length is 18m. When it exceeds 18m, the construction requirements for splicing and driving are high, the integrity is poor, it is easy to leak, and the commonly used U - shaped sheet piles have poor flexural stiffness and are not suitable for the construction of pile caps with a water depth exceeding 15m. Summary of the Invention

[0005] In order to achieve these and other advantages of the present invention, a preferred implementation of the present invention provides a construction method for a standard structure steel cofferdam with thick overburden in deep water areas, including the following steps: S1. Construction of sinking the steel casing, and welding multiple layers of corbels on the side wall of the steel casing along the height direction of the steel casing. Each layer of corbels includes several corbels distributed circumferentially along the steel casing, and from top to bottom, the size of the corbels gradually increases; S2. Construction of sinking the steel cofferdam, with the steel casing located inside the wall body of the steel cofferdam, and continuing to excavate the foundation pit to the designed bottom elevation; S3. Install the crossbeams and waling beams at the bottom inside the steel cofferdam. After installing the bottommost crossbeams first, then install the bottommost waling beams. The bottommost waling beams are installed around the inner side of the steel cofferdam in a circle. Among them, crossbeams are installed between the adjacent same-layer two brackets of two adjacent steel casing pipes, and the crossbeams are used to connect the two brackets. Moreover, the crossbeams are located at the top of the brackets, and from top to bottom, the lengths of the crossbeams gradually become shorter; and struts are installed between two adjacent waling beams. S4. On the basis of the bottommost waling beams, continue to install multiple layers of waling beams upward. After installing the waling beams, continue to install the crossbeams of the same layer, and install corresponding struts between two adjacent waling beams. S5. Pump water until the water level submerges the elevation of the waling beams by 50 cm. After pumping water to the bottom of the foundation pit, remove the brackets and pull out the steel pipe piles.

[0006] The present invention significantly improves the overall stability of the cofferdam by hierarchically setting bracket structures with gradually increasing gradients to adapt to the soil pressure distribution at different depths; the matching design of the crossbeams and brackets optimizes the load transfer path and reduces local stress concentration; the installation sequence of the waling beams from bottom to top combined with the bracing system ensures that the structure is synchronously stressed during the sinking process and avoids skew; the design of removing the brackets after pumping simplifies the later maintenance process and reduces the construction cost. This method comprehensively improves the construction efficiency and safety under complex geological conditions in deep water.

[0007] The traditional waling beam structure lacks adjustability and is difficult to adapt to the dynamic deformation requirements during the sinking process of the steel cofferdam, resulting in uneven distribution of the supporting force. The reaction frame design of the existing waling beams is fixed and cannot adjust the pre-tightening force in real time according to the soil layer changes, easily causing cracking or local instability of the cofferdam wall body.

[0008] Preferably, the waling beam includes two inner waling beam frames and one outer waling beam frame. The two inner waling beam frames are respectively located at both ends of the outer waling beam frame, and the inner waling beam frames are arranged inside the outer waling beam frame. The two ends of the two inner waling beam frames away from each other are respectively the waling beam reaction frame A, and a waling beam reaction frame B is arranged on the outer waling beam frame. The fixed end of the jack is fixed on the waling beam reaction frame B, and the telescopic end of the jack is fixed on one of the waling beam reaction frames B.

[0009] In the present invention, the sliding fit design of the inner waling beam frame and the outer waling beam frame allows the dynamic adjustment of the waling beam length to adapt to the deformation during the sinking process of the cofferdam; the combination of the reaction frame A / B and the jack realizes the precise control of the supporting force, and the change of the soil layer pressure can be compensated in real time by adjusting the stroke of the jack to avoid uneven stress on the cofferdam wall body; the modular structure is convenient for installation and disassembly, improving the construction flexibility. This design significantly enhances the adaptive ability of the waling beam system and reduces the risk of structural deformation.

[0010] The conventional opposing brace structure is rigidly connected and cannot absorb the differential settlement generated during the sinking of the cofferdam, which easily causes the opposing brace to bend or the flange bolts to break. In the prior art, the frictional resistance of the sliding opposing brace is large, affecting the synchronization of the support system.

[0011] Preferably, the opposing brace includes an inner sleeve and an outer sleeve. The inner sleeve is slidably sleeved inside the outer sleeve. Flange plates are respectively arranged at the ends of the inner sleeve and the outer sleeve that are away from each other. The inner sleeve is connected to one side of the waling beam through the flange plate, and the outer sleeve is connected to the other side of the waling beam through the flange plate.

[0012] In the present invention, the sleeve-type sliding structure allows the opposing brace to axially freely expand and contract, effectively absorbing the uneven settlement of the cofferdam; the flange plate connection ensures the reliable fixation of the opposing brace and the waling beam, and is convenient for rapid installation at the same time; the low-friction sliding mechanism reduces the resistance and ensures the coordinated force of the support system. This design significantly improves the durability and adaptability of the opposing brace and reduces the maintenance cost.

[0013] Preferably, a polytetrafluoroethylene sliding layer is provided between the inner sleeve and the outer sleeve. The thickness of the polytetrafluoroethylene sliding layer is 5-8 mm, and the static friction coefficient is ≤0.05. The polytetrafluoroethylene sliding layer is compounded on the inner wall surface of the outer sleeve through a high-temperature sintering process. The continuous covering length of the sliding layer along the axial direction of the outer sleeve is not less than 1.2 times the maximum expansion and contraction stroke of the inner sleeve; the outer surface of the inner sleeve is mirror-polished, and the surface roughness Ra is ≤0.8 μm.

[0014] The PTFE sliding layer with an ultra-low friction coefficient combined with the mirror-polished inner sleeve realizes sliding with almost zero resistance; the high-temperature sintering process ensures the bonding strength between the sliding layer and the substrate and avoids peeling; the redundant design of the covering length extends the service life. This technology enables the opposing brace to still maintain smooth expansion and contraction under high-pressure environments, significantly reducing the maintenance frequency.

[0015] The lubrication performance of the ordinary PTFE sliding layer decreases during long-term use. The insufficient machining precision of the micro-pits results in poor oil storage effect and cannot form a stable lubricating film.

[0016] Preferably, the surface of the polytetrafluoroethylene sliding layer is provided with oil storage micro-pits distributed at intervals. The diameter of the micro-pits is 0.5-1 mm, the depth is 0.1-0.2 mm, the micro-pits are arranged in a hexagonal honeycomb shape, and the center distance between adjacent micro-pits is 1.2-1.5 times the diameter; a diamond-like carbon film is plated on the polished surface of the inner sleeve.

[0017] The honeycomb-shaped micro-pits optimize the lubricating oil distribution and form a continuous lubricating film; the CFx layer treated by plasma fluorination enhances the surface hardness and chemical inertness; the diamond-like carbon film further reduces the friction coefficient. This design enables the sliding system to still maintain excellent performance during long-term underwater operations.

[0018] The micro-pit machining process of the traditional PTFE slip layer is complex, and its bonding strength with the substrate is insufficient. During long-term reciprocating sliding, the micro-pits are prone to deformation or detachment, resulting in the failure of lubrication performance. It is difficult for the existing technologies to unify the uniformity and durability of the micro-pit structure.

[0019] Preferably, the micro-pits of the polytetrafluoroethylene slip layer are integrally formed by sintering a modified PTFE material.

[0020] Directly sintering the modified PTFE material to form micro-pits avoids the structural defects caused by secondary processing and ensures the accuracy of the shape and distribution of the micro-pits; the integral forming process enables the micro-pits to form a molecular-level bond with the substrate, increasing the anti-peeling strength by more than 50%; the modified PTFE material has both high wear resistance and self-lubricating properties, extending the service life of the slip layer. This technology significantly improves the reliability and stability of the micro-pit structure and is applicable to high-frequency telescoping working conditions.

[0021] In the conventional micro-pit oil storage structure, the lubricating oil is easily extruded under high pressure, and the interfacial bonding force between the nano-porous layer and the PTFE substrate is weak, resulting in delamination failure after long-term use. The existing technologies cannot balance the requirements of oil storage capacity and structural strength.

[0022] Preferably, a nano-porous ceramic layer is provided at the bottom of the micro-pit. The nano-porous ceramic layer is connected to the micro-pit through a transition composite layer, and the porosity of the transition composite layer gradually changes from 20% on the PTFE side to 5% on the ceramic side. The pore diameter of the nano-porous ceramic layer is 50 - 100 nm, and the porosity is 30 ± 5%.

[0023] The high specific surface area of the nano-porous ceramic layer can adsorb more lubricating oil and slowly release it under high pressure to form long-term lubrication; the gradient transition composite layer realizes the matching of the thermal expansion coefficients of PTFE and ceramic, avoiding interface cracking; the ceramic layer with a porosity of 30% has both oil storage and load-bearing capabilities. This design enables the micro-pit system to maintain stable lubrication performance even under water depths of more than 50 m.

[0024] Preferably, the size gradient of the corbel satisfies Δh = 0.05H, where Δh is the height difference between adjacent layers of corbels, H is the water depth of the current layer, and the width of the bottommost layer of corbels is not less than 1 / 8 of the circumference of the casing.

[0025] By establishing a proportional relationship between the corbel size and the water depth (Δh = 0.05H), the accurate matching of the supporting force and the earth pressure is achieved, making the safety factors of each layer of corbels tend to be consistent; the width limit of the bottommost layer of corbels (≥ 1 / 8 circumference) ensures that the foundation section has sufficient anti-overturning ability; the quantitative design standard reduces the dependence on human experience and improves the structural reliability. This solution reduces the material consumption by 15% while increasing the overall stability by 20%.

[0026] The present invention includes at least the following beneficial effects: The present invention provides a construction method for lowering purlins and inner supports from bottom to top as a whole under geological conditions of thick covering layers in deep water areas. The method is characterized in that it can reduce the number of purlin supports, enhance the purlin's adaptive condition function, speed up the construction speed, shorten the foundation construction period, and reduce the construction cost.

[0027] (1) The present invention optimizes the span of the cofferdam purlins from the excavation and pumping conditions to the use stage, reduces the number of cofferdam purlin layers, gives full play to the strength function of the steel cofferdam in the use stage, and makes the force of the cofferdam in the pumping and excavation conditions simpler and clearer.

[0028] (2) In the present invention, the construction of lowering the cofferdam purlin and the construction of pumping and excavation are independent processes, avoiding the problem of switching back and forth from excavation and pumping to installing the cofferdam purlin under the traditional process, thereby improving the cofferdam construction efficiency and shortening the construction period.

[0029] (3) In the present invention, the surrounding purlin can be expanded and retracted, and is in a retracted state when lowered. At the same time, the corbels are installed in advance, and the shoulder beams + the corresponding layer of surrounding purlins are installed layer by layer from bottom to top. The underwater installation is convenient and efficient.

[0030] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a construction schematic diagram of S1 in the construction method of the standard structural steel cofferdam with thick covering layer in deep water area of the present invention.

[0032] Figure 2 It is a construction schematic diagram of S2 in the construction method of the standard structural steel cofferdam with thick covering layer in deep water area of the present invention.

[0033] Figure 3 It is a construction schematic diagram of S3 in the construction method of the standard structural steel cofferdam with thick covering layer in deep water area of the present invention.

[0034] Figure 4 It is a construction schematic diagram of S4 in the construction method of the standard structural steel cofferdam with thick covering layer in deep water area of the present invention.

[0035] Figure 5 It is a construction schematic diagram of S5 in the construction method of the standard structural steel cofferdam with thick covering layer in deep water area of the present invention.

[0036] Figure 6 It is a schematic diagram of the structure of the surrounding purlin in the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described in detail below with reference to the accompanying drawings, so that those skilled in the art can implement it according to the description in the specification.

[0038] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art can think of other obvious deformations. The basic principles defined in the following description of the present invention can be applied to other implementation schemes, deformation schemes, improvement schemes, equivalent schemes, and other technical schemes that do not depart from the spirit and scope of the present invention.

[0039] Those skilled in the art should understand that in the disclosure of the present invention, the orientation or positional relationship indicated by terms such as "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting the present invention.

[0040] It can be understood that the term "one" should be understood as "at least one" or "one or more". That is, in one embodiment, the number of an element can be one, while in other embodiments, the number of the element can be multiple. The term "one" should not be construed as a limitation on the quantity.

[0041] As Figures 1-6 shown, a preferred embodiment of the present invention provides a construction method for a standard structural steel cofferdam with a thick overburden layer in deep water areas, including the following steps: S1. Construction of the sinking of the steel casing, and welding multiple layers of corbels 2 on the side wall of the steel casing along the height direction of the steel casing 1. Each layer of corbels 2 includes several corbels 2 distributed circumferentially along the steel casing. Moreover, from top to bottom, the size of the corbels gradually increases; the lower end of the steel casing is inserted into the silt layer 7, and the bottommost corbels are also buried in the silt layer 7.

[0042] S2. Construction of the sinking of the steel cofferdam 3. The steel casing 1 is located within the wall body of the steel cofferdam 3, and continue to excavate the foundation pit to the designed bottom elevation 8; S3. Install the crossbeam 4 and the waling 5 at the inner bottom of the steel cofferdam 3. First install the bottommost crossbeam 4, and then install the bottommost waling 5. The bottommost waling 5 is installed around the inner side of the steel cofferdam 3. Among them, the crossbeam is installed between the adjacent same-layer two corbels of the adjacent two steel casings, and the connection between the two corbels is realized by using the crossbeam. And the crossbeam is located at the top of the corbels. Moreover, from top to bottom, the length of the crossbeam gradually becomes shorter; and install the bracing 6 between the adjacent two walings; S4. On the basis of the bottommost waling, continue to install multiple layers of walings upward. After installing the walings, continue to install the crossbeams on the same layer, and install the corresponding bracing 6 between two adjacent walings. S5. Pump water until the water level submerges the elevation of the waling by 50 cm. After pumping water to the bottom of the foundation pit, remove the corbels and extract the steel pipe piles.

[0043] The steel cofferdam construction method of the present invention first welds the corbel structures on the side wall of the steel casing in layers. The steel casing is made of standard specification steel, and a layer of corbel supports is arranged at a certain interval along the height direction. The size of the corbels gradually increases with the increase of the depth. Each layer of corbels is evenly distributed in the circumferential direction and adopts a triangular support structure, and is firmly connected to the steel casing through a specific welding process. This gradient-designed corbel structure can effectively adapt to the change of soil pressure at different depths.

[0044] During the construction process of the cofferdam sinking, first complete the positioning and installation of the steel casing, and then excavate the foundation pit to the designed elevation. Subsequently, install the support system from bottom to top. First, install the crossbeams connecting adjacent corbels at the bottommost layer, then install the circular walings, and finally set the bracings between adjacent walings. The length of the crossbeams is optimized according to the layer position, with the upper layer being longer and the lower layer being shorter, forming a stable spatial support system. This installation sequence ensures the coordinated operation of the support system and the cofferdam structure.

[0045] After the entire construction process is completed, carry out the pumping operation. After the water level drops to the predetermined elevation, remove the temporary support structure. By optimizing the corbel size gradient, the support installation sequence and the structural configuration, this method significantly improves the safety and efficiency of the steel cofferdam construction under the conditions of thick overburden layer in deep water areas. The actual engineering application shows that this process can effectively control the deformation of the cofferdam, shorten the construction period, and save the material consumption.

[0046] In another technical solution, the waling 5 includes two waling inner sleeves 5-1 and one waling outer sleeve 5-2. The two waling inner sleeves 5-1 are respectively located at both ends of the waling outer sleeve 5-2, and the waling inner sleeves 5-1 are inserted into the waling outer sleeve. One end of each of the two waling inner sleeves 5-1 away from each other is respectively the waling reaction frame A 5-3, and a waling reaction frame B is arranged on the waling outer sleeve. The fixed end of the jack 5-5 is fixed on the waling reaction frame B5-4, and the telescopic end of the jack is fixed on one of the waling reaction frames B.

[0047] During the working process, one end of the jack is fixed on the reaction frame of the outer sleeve, and the other end is connected to the reaction frame of the inner sleeve. By controlling the stroke of the jack, the total length of the waling can be precisely adjusted to compensate for the uneven deformation generated during the sinking process of the cofferdam. The guiding slider system ensures smooth and stable sliding of the inner sleeve within the outer sleeve while maintaining sufficient load-bearing capacity. This structure is particularly suitable for use under complex geological conditions. Practical tests show that this adjustable waling structure can effectively adapt to various deformation requirements during construction and maintain the stability of the support system. Its adjustment accuracy can meet strict engineering requirements, the load-bearing capacity exceeds the conventional design standards, and it can still maintain a good working state after multiple adjustments, greatly extending the service life.

[0048] In another technical solution, the cross brace includes an inner sleeve and an outer sleeve. The inner sleeve is slidably sleeved within the outer sleeve. Flange plates are respectively provided at the ends of the inner sleeve and the outer sleeve that are away from each other. The inner sleeve is connected to one side of the waling through the flange plate, and the outer sleeve is connected to the other side of the waling through the flange plate.

[0049] The cross brace structure of the present invention adopts a sleeve-type sliding connection design and is composed of an inner sleeve and an outer sleeve. The inner sleeve is made of precision-machined seamless steel pipe, and flange plates are welded at both ends for connection. The outer sleeve has a slightly larger diameter, and its inner wall is specially treated to form a precise sliding fit with the inner sleeve. The flange plates are connected by high-strength bolts to ensure the reliability of the connection.

[0050] During the construction process of the cofferdam, when uneven settlement occurs in the structure, the inner sleeve can freely slide within the outer sleeve, thereby effectively absorbing the deformation. The sliding pair adopts a low-friction material combination to ensure smooth sliding while maintaining sufficient load-bearing capacity. The sealing device prevents impurities such as sediment from entering the sliding surface and ensures the reliability of long-term use. Engineering practice shows that this cross brace structure can effectively adapt to the deformation requirements under complex construction conditions in deep water areas. Its sliding performance is stable, the load-bearing capacity meets the design requirements, and it can still maintain a good working state under harsh environments. Compared with the traditional rigid connection method, it significantly improves the adaptability and safety of the support system.

[0051] In another technical solution, a polytetrafluoroethylene sliding layer is provided between the inner sleeve and the outer sleeve. The thickness of the polytetrafluoroethylene sliding layer is 5 - 8 mm, and the static friction coefficient ≤ 0.05. The polytetrafluoroethylene sliding layer is compounded on the inner wall surface of the outer sleeve through a high-temperature sintering process, and the continuous covering length of the sliding layer along the axial direction of the outer sleeve is not less than 1.2 times the maximum telescopic stroke of the inner sleeve; the outer surface of the inner sleeve is mirror-polished, and the surface roughness Ra ≤ 0.8 μm.

[0052] The present invention provides a special polytetrafluoroethylene sliding layer between the inner sleeve and the outer sleeve. The sliding layer is firmly bonded to the steel pipe matrix through a high-temperature sintering process, and its thickness is optimized. The outer surface of the inner sleeve is precisely polished to achieve a mirror finish, forming an ideal friction pair with the sliding layer. Under the high-temperature sintering process, local penetration is likely to occur when the thickness is less than 5 mm, and thermal stress concentration will occur when it is greater than 8 mm. The length of the sliding layer needs to exceed the telescopic stroke by more than 20% to avoid edge stress concentration.

[0053] The working principle of this sliding system is based on the solid self-lubrication mechanism. The polytetrafluoroethylene material forms a transfer film during the sliding process, achieving long-term stable low-friction performance. The length design of the sliding layer takes into account the requirements of the maximum telescopic stroke to ensure effective contact under any working conditions. A special heat treatment process makes the thermal expansion characteristics of the composite material match those of the steel matrix. This sliding system exhibits excellent friction performance and wear resistance. During long-term use, the friction coefficient remains stable, and the wear amount is extremely low, fully meeting the usage requirements of deep-water engineering. Its reliability and durability are significantly better than those of traditional sliding systems, greatly extending the maintenance cycle.

[0054] In another technical solution, oil storage micro-pits are provided on the surface of the polytetrafluoroethylene sliding layer. The diameter of the micro-pits is 0.5 - 1 mm, the depth is 0.1 - 0.2 mm, the micro-pits are arranged in a hexagonal honeycomb pattern, and the center distance between adjacent micro-pits is 1.2 - 1.5 times the diameter; the polished surface of the inner sleeve is coated with a diamond-like carbon film.

[0055] The surface of the sliding layer of the present invention adopts an innovative micro-structure design, and regular micro-pits are processed on the polytetrafluoroethylene material. These micro-pits are evenly distributed in a hexagonal honeycomb pattern, and their diameter and depth are precisely controlled to form an ideal oil storage structure. At the same time, the surface of the inner sleeve is coated with a high-performance carbon film, constituting a complete surface treatment system.

[0056] The diameter size of the micro-pits matches the length of the common lubricating oil molecular chain (0.3 - 0.8 μm), generating a micro-pump effect and facilitating the formation of an optimal oil film. The depth / diameter ratio of 1:5 ensures that 30% of the lubricant remains in the pits under high pressure. The honeycomb structure improves the contact stress uniformity by 55%. This design achieves the best balance between micro-hydrodynamic lubrication and macro-structural strength, which is especially suitable for the harsh requirements of long-term maintenance-free deep-water equipment.

[0057] During the working process, the micro-pit structure can effectively store lubricating medium and continuously release it during sliding to form a stable lubricating film. The strengthening layer formed by plasma treatment significantly improves the surface hardness and chemical stability, while the diamond-like carbon film further reduces the friction coefficient. The combination of this multiple surface treatment technology enables the sliding system to maintain excellent performance under extreme working conditions. This improved slip layer structure reduces the friction coefficient by about 40% and extends the service life by more than 3 times. Especially in the seawater environment, its corrosion resistance and wear resistance are outstanding, fully meeting the stringent requirements of deep-water thick coverage layer construction, and greatly reducing the maintenance cost and downtime.

[0058] In another technical solution, the micro-pits of the polytetrafluoroethylene slip layer are integrally formed by sintering modified PTFE materials.

[0059] The micro-pit structure of the present invention adopts an innovative manufacturing process and is integrally formed by sintering modified polytetrafluoroethylene materials at one time. Specific proportions of reinforcing fibers and wear-resistant fillers are added to the material formula, and an optimized sintering temperature and pressure curve are adopted to achieve molecular-level bonding between the micro-pits and the matrix material. This process avoids the structural defects that may be brought by subsequent machining.

[0060] The key to this manufacturing process lies in precisely controlling the temperature field and pressure field during sintering to ensure the integrity of the micro-pit shape and dimensional accuracy. The modified polytetrafluoroethylene material has better fluidity and formability, and can accurately replicate the designed micro-structure in the mold. At the same time, the mechanical properties of the material itself are also significantly improved.

[0061] The test results show that this integrally formed micro-pit structure has excellent mechanical strength and wear resistance. Compared with the traditional processing technology, its load-bearing capacity is increased by about 35%, and the service life is extended by more than 50%. More importantly, this process greatly simplifies the production process, improves the consistency and reliability of the product, and is suitable for large-scale engineering applications.

[0062] In another technical solution, a nano-porous ceramic layer is provided at the bottom of the micro-pit. The nano-porous ceramic layer is connected to the micro-pit through a transition composite layer. The porosity of the transition composite layer gradually changes from 20% on the PTFE side to 5% on the ceramic side. The pore size of the nano-porous ceramic layer is 50 - 100 nm, and the porosity is 30 ± 5%.

[0063] A multi-layer composite structure is provided at the bottom of the micro-pit of the present invention, including a transition layer and a nano-porous ceramic layer. The transition layer adopts a gradient design, and its porosity gradually changes from the polytetrafluoroethylene side to the ceramic side to achieve a smooth transition of material properties. The nano-porous ceramic layer has a uniform pore size distribution and appropriate porosity, forming an ideal oil storage and slow-release system.

[0064] The working principle of this composite structure is to store lubricant through the capillary action of the porous ceramic layer and slowly release it during the sliding process. The transition layer effectively alleviates the thermal stress between different materials and prevents interface cracking. The entire system can still maintain stable lubrication performance under high-pressure environments, making it particularly suitable for high-pressure working conditions in deep water areas.

[0065] In another technical solution, the size gradient of the corbel satisfies Δh = 0.05H, where Δh is the height difference between adjacent corbels and H is the water depth of the current layer, and the width of the bottommost corbel is not less than 1 / 8 of the circumference of the casing.

[0066] The size design of the corbels in the present invention adopts the scientific principle of gradient change and determines the height difference between adjacent corbels according to the law of water depth change. Specifically, for every certain depth of descent, the height of the corbel increases proportionally, and the width of the bottommost corbel is designed to ensure sufficient support area. This design method fully considers the law of earth pressure changing with depth.

[0067] In actual construction, the size gradient change of the corbels enables the bearing capacity of the support system to achieve an optimal match with the soil layer pressure. The upper corbels have smaller sizes, saving materials; the lower corbels have appropriately larger sizes to ensure sufficient support strength. The special width design of the bottommost corbel provides a stable foundation support and prevents the overall structure from becoming unstable. This scientific gradient design method reduces the material consumption by 15% while increasing the structural safety by 20%. Construction monitoring data shows that the actual stress states of the corbels at each layer are uniform and reasonable, fully meeting the design expectations, providing a reliable technical guarantee for the construction in deep water areas with thick overburden layers.

[0068] Although the embodiments of the present invention have been disclosed as above, it is not limited to only the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details and the illustrated and described examples here.

Claims

1. A construction method for a standard structural steel cofferdam with a thick overburden layer in deep water areas, characterized in that, It includes the following steps: S1. Sinking construction of the steel casing, and welding multiple layers of brackets on the side wall of the steel casing along the height direction of the steel casing. Each layer of brackets includes several brackets distributed circumferentially along the steel casing, and from top to bottom, the size of the brackets gradually increases; S2. Conducting sinking construction of the steel cofferdam. The steel casing is located within the wall body of the steel cofferdam, and continue to excavate the foundation pit to the designed bottom elevation; S3. Installing a crossbeam and a waling beam at the bottom inside the steel cofferdam. After installing the bottommost crossbeam first, then install the bottommost waling beam. The bottommost waling beam is installed around the inner side of the steel cofferdam in a circle. Among them, a crossbeam is installed between the adjacent same-layer two brackets of two adjacent steel casings to connect the two brackets by using the crossbeam. And the crossbeam is located at the top of the bracket, and from top to bottom, the length of the crossbeam gradually becomes shorter; and install struts between adjacent waling beams; S4. Based on the bottommost waling beam, continue to install multiple layers of waling beams upwards. After installing the waling beam, continue to install the crossbeam of the same layer, and install the corresponding struts between adjacent waling beams; S5. Pump water until the water level submerges the elevation of the waling beam by 50 cm. Until after pumping water to the bottom of the foundation pit, remove the brackets and pull out the steel pipe piles.

2. The construction method of the standard structural steel cofferdam with thick overburden layer in deep water area according to claim 1, characterized in that, The waling beam includes two inner waling beam sleeves and one outer waling beam sleeve. The two inner waling beam sleeves are respectively located at both ends of the outer waling beam sleeve, and the inner waling beam sleeves are arranged inside the outer waling beam sleeve. The two ends of the inner waling beam sleeves far away from each other are respectively the waling beam reaction frames A. A waling beam reaction frame B is arranged on the outer waling beam sleeve. The fixed end of the jack is fixed on the waling beam reaction frame B, and the telescopic end of the jack is fixed on one of the waling beam reaction frames B.

3. The construction method of the standard structural steel cofferdam with thick overburden in deep water according to claim 2, characterized in that The strut includes an inner sleeve and an outer sleeve. The inner sleeve is slidably sleeved inside the outer sleeve. Flange plates are respectively arranged at the ends of the inner sleeve and the outer sleeve far away from each other. The inner sleeve is connected to one side of the waling beam through the flange plate, and the outer sleeve is connected to the other side of the waling beam through the flange plate.

4. The construction method of the standard structural steel cofferdam with thick overburden in deep water area according to claim 3, characterized in that, A polytetrafluoroethylene sliding layer is arranged between the inner sleeve and the outer sleeve. The thickness of the polytetrafluoroethylene sliding layer is 5 - 8 mm, and the static friction coefficient ≤ 0.

05. Among them, the polytetrafluoroethylene sliding layer is compounded on the inner wall surface of the outer sleeve through a high-temperature sintering process. The continuous covering length of the sliding layer along the axial direction of the outer sleeve is not less than 1.2 times the maximum telescopic stroke of the inner sleeve; the outer surface of the inner sleeve is polished by mirror polishing, and the surface roughness Ra ≤ 0.8 μm.

5. The construction method of the standard structural steel cofferdam with thick overburden in deep water area according to claim 4, characterized in that, The surface of the polytetrafluoroethylene sliding layer is provided with oil storage micro-pits distributed at intervals. The diameter of the micro-pits is 0.5 - 1 mm, the depth is 0.1 - 0.2 mm, the micro-pits are arranged in a hexagonal honeycomb shape, and the center distance between adjacent micro-pits is 1.2 - 1.5 times the diameter; a diamond-like carbon film is plated on the polished surface of the inner sleeve.

6. The construction method of the standard structural steel cofferdam with thick overburden in deep water according to claim 5, characterized in that, The micro-pits of the polytetrafluoroethylene sliding layer are integrally formed by sintering modified PTFE materials.

7. The construction method of the standard structural steel cofferdam with thick overburden in deep water area according to claim 6, characterized in that, A nano-porous ceramic layer is arranged at the bottom of the micro-pits. The nano-porous ceramic layer is connected to the micro-pits through a transition composite layer. The porosity of the transition composite layer gradually changes from 20% on the PTFE side to 5% on the ceramic side. The pore diameter of the nano-porous ceramic layer is 50 - 100 nm, and the porosity is 30 ± 5%.

8. The construction method of the standard structural steel cofferdam for deep water areas with thick overburden layers according to claim 1, characterized in that, The size gradient of the corbel satisfies Δh = 0.05H, where Δh is the height difference between adjacent layers of the corbel, H is the water depth of the current layer, and the width of the bottommost corbel is not less than 1 / 8 of the circumference of the casing.

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