PLC cofferdam hoist mold dry bottom structure and construction method

Abstract

This application discloses a PLC-based cofferdam dry sealing structure and construction method, relating to the field of cofferdam construction technology. The method includes the following steps: support assembly and lowering, pile connector installation, waler base plate fixing construction, support conversion risk control, and subsequent dismantling. First, the hanging legs are welded to the casing, completing the assembly and layered lowering of the three-layer support. Then, steel sheet piles and steel pipe piles are driven and precisely aligned with the bridge pile foundation, and connectors are installed. Next, connecting plates are welded layer by layer to fix the walers, and a cast-in-place C40 base plate serves as the core structure for sealing the bottom, with internal supports added to enhance support stability. Then, the support replacement operation is completed, and steel wire ropes are secured with rope clamps for typhoon protection. Finally, the cofferdam water level is balanced, and the walers, internal supports, and combined piles are dismantled. This method features clear connection procedures, a stable support structure, and good water-stopping effect, improving the efficiency and safety of cofferdam construction. It is suitable for dry sealing projects of cofferdams under complex hydrological conditions.

Description

Technical Field

[0001] This invention relates to the field of bridge construction technology, specifically to a PLC-based cofferdam formwork dry sealing structure and construction method. Background Technology

[0002] In the construction of high-speed railway bridge piers and abutments, cofferdams serve as temporary support structures for foundation construction. Their stability, water-stopping effect, and construction safety directly determine the project's quality and progress. Especially in complex hydrogeological environments such as shallow water areas and bays, cofferdam construction faces multiple challenges, including complex geological conditions, high water flow velocity, strong wave action, and high scour risk.

[0003] In existing technologies, the dry sealing construction of PLC-supported cofferdams using suspended formwork generally suffers from the following problems: First, the support system design is unreasonable, the connection strength between the walers and steel pipe piles / sheet piles is insufficient, and the support conversion sequence is chaotic, often involving the illegal operation of dismantling before supporting. This leads to excessive displacement of the cofferdam structure due to stress imbalance during dewatering and concrete pouring, and may even cause collapse accidents. According to industry statistics, approximately 35% of cofferdam construction safety accidents are directly related to the instability of the support system. Second, improper water level control during the sealing construction results in excessive water pressure differences inside and outside the cofferdam, and the interlocking seals are not tight, which can easily lead to water seepage and drowning risks. At the same time, the sealing around the casing is not tight before the bottom sealing concrete is poured, and water is pumped out before the concrete reaches the design strength, resulting in cracking and leakage of the bottom slab, affecting the quality of subsequent pier construction. Third, the technology is not adaptable to the construction environment. Existing technologies do not fully consider the differences between actual hydrogeology and design parameters. For example, when the scour depth exceeds the design expectation, protective measures are not taken in time, or the steel sheet pile extension position is unreasonable, which leads to a decrease in the overall anti-seepage and anti-overturning capacity of the cofferdam.

[0004] Therefore, there is an urgent need for a PLC cofferdam dry sealing structure and construction method that is adaptable to complex hydrogeological environments, provides stable support, ensures reliable water stoppage, and allows for orderly construction, in order to solve the technical problems of instability of the support system, water seepage and collapse of the sealing bottom, and poor environmental adaptability in existing technologies. Summary of the Invention

[0005] This application proposes a PLC cofferdam formwork dry sealing structure and construction method, aiming to solve the technical problems of high risk of support system conversion and easy water permeability and collapse of the sealing concrete in the existing PLC cofferdam formwork dry sealing construction, and to achieve safe, stable and efficient progress of cofferdam construction under complex hydrogeological conditions.

[0006] To achieve the above objectives, this application adopts the following technical solution: a construction method for a PLC-based cofferdam formwork dry sealing structure, comprising the following steps: S1 Design Preparation: Based on the geological survey report and hydrological specifications of the construction area, design parameters are determined, and a steel sheet pile-steel pipe pile combined support structure and a 3-layer waler support system are designed. S2 support and pile construction: During the low tide window, complete the installation of hanging legs, the assembly and layered lowering of the three-layer walers and inner supports, weld the limiting beam to fix the walers and casing, drive the combined piles from upstream to downstream until they are closed and set up the connecting device. S3 Waler Fixing and Base Slab Construction: Layered pumping and welding of replacement corbels and connecting plates for each layer. After removing the temporary structure, pump water to the design elevation to complete the installation of base slab steel, formwork, and C40 concrete pouring and curing. S4 Support Transformation and Risk Prevention: The support system transformation was completed according to the principle of "support first, dismantle later," and special protective measures were taken in response to severe weather such as typhoons; S5 Subsequent Construction and Cofferdam Removal: Pour the foundation and pier body until water flows out, balance the water levels inside and outside the cofferdam, and then remove the walers, inner supports and piles in layers. Before removal, check the scouring of the trestle bridge and the structural stress.

[0007] Furthermore, in S2, the assembly and lowering of the three-layer walers and internal supports specifically includes: S2.1 After the inner side of the casing is reinforced with a plate, the hanging leg is welded during the low tide window, and pads and pad beams are set on the bottom bracket. The third layer of waler and inner support are assembled on the upper bracket, and the vertical temporary support is welded. The bottom of the vertical temporary support is fully welded to the waler. After the crawler crane lifts the third layer of walers and inner supports, remove the upper bracket bolts and lower the third layer of inner supports to the bottom bracket at low tide. S2.3 Reinstall the upper bracket and assemble the second layer of support on the upper bracket; S2.4 After lifting the second-layer waler and inner supports using a crawler crane, remove the upper bracket bolts; at low tide, lower the second-layer inner supports onto the vertical temporary supports. S2.5 Reinstall the upper bracket, assemble the first layer of walers and inner supports on the upper bracket; after the hanging leg is installed, install the protective casing reinforcement measures, and weld the top limiting beam to connect the walers and the protective casing.

[0008] Furthermore, in step S3, the waler fixing specifically includes: S3.1 Check the fit between the waler and the pipe pile, and insert steel plates into any areas that are not tightly fitted; weld the first layer of waler onto the pipe pile to replace the corbel, and weld the waler to the pipe pile through the connecting plate; S3.2 Close the communicating vessel during high tide, pump water into the cofferdam to 1m below the center line of the second waler, weld the corbel of the second waler onto the pipe pile, and weld the waler to the pipe pile through the connecting plate; S3.3 Pump water into the cofferdam to 1m below the center line of the third waler, weld the corbel of the third waler onto the pipe pile, weld the waler to the pipe pile through the connecting plate, and remove the vertical temporary support; S3.4 Remove the hanging leg, install reinforcement measures for the bottom limit sleeve, and weld the bottom limit beam to connect the waler and the sleeve.

[0009] Furthermore, in S4, the support for conversion specifically includes: S4.1 Remove the limiting beam and cut off the steel casing. S4.2 Remove the third layer of support at low tide; S4.3 First, install the second layer of long diagonal bracing, and remove the second layer of short diagonal bracing and the opposing bracing; then install the first layer of long diagonal bracing, and remove the first layer of short diagonal bracing and the opposing bracing.

[0010] Furthermore, in S5, the subsequent construction and demolition specifically include: S5.1 Remove pile heads, tie reinforcing bars, erect formwork, and pour foundation; After the S5.2 pier cap reaches its design strength, the formwork is removed, and log supports are installed at intervals between the pier cap and the pipe piles. The pier body is then constructed until it reaches the water outlet. S5.3 Open the communicating vessel to balance the water level. When the water level is low, remove the two layers of walers and inner supports from bottom to top in sequence, and finally remove the steel sheet pile-steel pipe pile combination pile. S5.4 During the entire construction process, wave height and current velocity shall be monitored. If the wave height is greater than 1m or the current velocity is greater than 3m / s, personnel shall be stopped and evacuated.

[0011] Furthermore, in S2, the construction of combined piles specifically includes: steel pipe piles with a length of 35m and steel sheet piles with a length of 27m, with no less than 8 steel pipe piles on the short side and no less than 11 on the long side, strict control of the verticality of the steel pipe piles, layout, measurement and adjustment of the corner positions to close the steel sheet piles, and no less than 4 connecting devices.

[0012] Furthermore, in S3, the construction of the base plate specifically includes: S3.5 Pump water to the design elevation, weld the bottom plate brackets and shear reinforcements onto the casing, and install the bottom plate steel and formwork; S3.6 Lay and tie the bottom slab reinforcement and reinforcing bars, pour 60cm thick C40 concrete in place, and cure it to a strength of ≥30MPa before proceeding with subsequent procedures.

[0013] Furthermore, in S4, the specific protective measures during the typhoon season include: S4.4.1 Before the typhoon arrives, check the strength of the bottom sealing concrete. If it does not meet the standard, retain the casing and the limiting beam. S4.4.2 Stop construction and remove equipment. The water level inside the cofferdam should be the same as the water level outside. Install steel wire ropes on the walers and casing. S4.4.3 Inspect the quality of the connecting plates at the wire rope installation points, replace or weld any substandard connecting plates, and add new vertical stiffening plates; S4.4.4 Weld steel plates on both sides of the wire rope to limit its movement and protect the wire rope at the sharp points of the waler.

[0014] A PLC-based cofferdam formwork dry sealing structure includes the following steps: support assembly, lowering, and connection of piles and communicating vessels: After the inner side of the casing is reinforced with a plate, the hanging leg is welded to the casing during the low tide window, and pads and pad beams are set on the bottom corbel; the upper corbel is assembled with the third layer of support, the bottom of the vertical temporary support is fully welded to the third layer of support, the third layer of support is lifted by a crawler crane and lowered onto the bottom corbel; the upper corbel is reinstalled and assembled with the second layer of support, the second layer of support is lifted by a crawler crane and lowered onto the vertical temporary support; the upper corbel is reinstalled and assembled with the first layer of support, after the casing is reinforced, the top limiting beam is welded to connect the first layer of support and the casing; steel sheet pile-steel pipe pile combination piles are driven from upstream to downstream until they are closed, and no less than 4 communicating vessels are installed. After the steel sheet pile-steel pipe pile combination piles are constructed, their positions are precisely aligned with the pile bodies of the bridge pile foundation.

[0015] Furthermore, the construction steps include waler fixing, temporary structure removal, and bottom slab connection: checking the tightness of the waler and pipe piles, inserting steel plates into areas where they are not tightly fitted, welding replacement corbels onto the pipe piles, welding the waler and pipe piles sequentially through the first layer connecting plate, the first and second layer connecting plates, and the first, second, and third layer connecting plates, respectively, pumping water in layers to 1m below the corresponding waler centerline during welding, closing the connecting device during high tide, removing the vertical temporary support after welding the third layer connecting plate; removing the hanging legs, installing the bottom limiting sleeve reinforcement, and welding the bottom limiting beam to connect the waler and the sleeve; pumping water into the cofferdam to the design elevation, welding the bottom slab corbels and bottom slab shear reinforcements to the sleeve, installing the concrete bottom slab formwork, laying the bottom slab reinforcement and binding the reinforcing reinforcement, casting a 60cm thick C40 bottom slab as the core structure for sealing the bottom, and waiting for it to reach the design strength; internal supports are set between the waler and each layer of support to enhance the overall stability of the support system.

[0016] Furthermore, it also includes support conversion, risk prevention and control, and subsequent structural and cofferdam dismantling connection steps: dismantle the limiting beam and steel casing, and dismantle the third layer of support at low tide; install the second layer of long diagonal bracing and the first layer of support after replacement (both belong to the first and second layers of support) in sequence, and then dismantle the corresponding short diagonal bracing and counter-bracing respectively; before the typhoon arrives, install steel wire ropes on the walers and casing, and use rope clamps to fasten the steel wire ropes to the pre-set points on the walers and casing, add stiffening plates at the installation points of the steel wire ropes, and weld steel plates on both sides to limit and protect the steel wire ropes at the sharp points of the walers; chisel off the pile heads of the bridge pile foundation and pour the pile cap, remove the formwork after the pile cap reaches the design strength, set log supports at intervals between the pile cap and the pipe pile, and construct the pier body until it is above water; open the communicating vessel to balance the water level, and dismantle the walers and inner supports from bottom to top at low water level, and finally dismantle the steel sheet pile-steel pipe pile combination pile.

[0017] The present invention has the following beneficial effects: 1. This application provides a PLC cofferdam formwork dry sealing structure and construction method, which overcomes the limitations of traditional support installation being greatly affected by water flow by adopting the technology of low tide window operation + layered assembly and lowering of waler support. It avoids the problems of waler support placement deviation and structural loosening. The application also introduces vertical temporary support and double limit beam reinforcement technology to achieve precise assembly and stable connection of the support system.

[0018] 2. The PLC cofferdam formwork dry sealing structure and construction method provided in this application overcomes the limitations of traditional support transformation and weak resistance to severe weather by using the technology of first supporting and then dismantling and replacing the support, plus special protection during the typhoon season. It avoids the problem of sudden load changes caused by support transformation and structural damage caused by typhoons. It introduces technologies such as water level balance control, steel wire rope reinforcement, and connecting plate reinforcement to achieve a smooth transition of the support system and upgrade the typhoon resistance of the cofferdam.

[0019] 3. The PLC cofferdam formwork dry sealing structure and construction method provided in this application overcomes the limitations of traditional bottom sealing construction, such as improper water pressure control and easy cracking of the bottom plate, by adopting the technology of layered dewatering and welding + bottom plate strength meeting the standard construction. It avoids the risk of bottom sealing water seepage and drowning. It introduces a reinforced design of 60cm thick C40 concrete bottom plate + shear reinforcement + reinforcing steel bars to improve the water-stopping reliability and structural bearing capacity of dry sealing construction. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, illustrate embodiments disclosed in this application and, together with the specification, serve to explain the principles disclosed in this application.

[0021] This disclosure will become clearer with reference to the accompanying drawings and the following detailed description, wherein: Figure 1 This is a flowchart of the construction steps of the present invention; Figure 2 This is a schematic diagram of S2.1; where (a) is an elevation view and (b) is a plan view. Figure 3 This is a schematic diagram of S2.2; where (a) is an elevation view and (b) is a plan view. Figure 4 This is a schematic diagram of S2.3; where (a) is an elevation view and (b) is a plan view. Figure 5 This is a schematic diagram of S2.4; where (a) is an elevation view and (b) is a plan view. Figure 6 This is a schematic diagram of S2.5; where (a) is an elevation view and (b) is a plan view. Figure 7 Here is a schematic diagram of S2.6; where (a) is an elevation view and (b) is a plan view; Figure 8Here is a schematic diagram of S3.1; where (a) is an elevation view and (b) is a plan view; Figure 9 This is a schematic diagram of S3.2; where (a) is an elevation view and (b) is a plan view. Figure 10 This is a schematic diagram of S3.3; where (a) is an elevation view and (b) is a plan view. Figure 11 This is a schematic diagram of S3.4; where (a) is an elevation view and (b) is a plan view. Figure 12 This is a schematic diagram of S3.5; where (a) is an elevation view and (b) is a plan view. Figure 13 Here is a schematic diagram of S3.6; where (a) is an elevation view and (b) is a plan view; Figure 14 This is a schematic diagram of S4.1; where (a) is an elevation view and (b) is a plan view. Figure 15 This is a schematic diagram of S4.2; where (a) is an elevation view and (b) is a plan view. Figure 16 This is a schematic diagram of S4.3; where (a) is an elevation view and (b) is a plan view. Figure 17 This is a schematic diagram of S4.4; where (a) is an elevation view and (b) is a plan view. Figure 18 This is a schematic diagram of S5.1; where (a) is an elevation view and (b) is a plan view. Figure 19 This is a schematic diagram of S5.2; where (a) is an elevation view and (b) is a plan view. Figure 20 Here is a schematic diagram of S5.3; where (a) is an elevation view and (b) is a plan view.

[0022] In the diagram: 1. Hanging leg; 2. Vertical temporary support; 3. Third layer support; 4. Upper corbel; 5. Pad beam; 6. Bottom corbel; 7. Pad block; 8. Casing; 9. Second layer support; 10. First layer support; 11. Limiting beam; 12. Casing reinforcement; 13. Steel sheet pile-steel pipe pile combination pile; 14. Communicating device; 15. Replacement corbel; 16. First layer connecting plate; 17. First and second layer connecting plates; 18. First, second, and third layer connecting plates; 9. Base plate corbel; 20. Concrete base plate formwork; 21. C40 base plate; 22. Bridge pile foundation; 23. First and second layer supports; 24. First layer replacement support; 25. Pipe pile; 26. Stiffening plate; 27. Internal support; 28. Rope clamp; 29. ​​Wire rope; 30. Bottom sealing; 31. Pier cap; 32. Pier body; 33. Log; 34. Waler; 35. Wire rope protection component; 43. Stiffening plate limiting steel plate; 44. Wire rope clamping steel plate. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0024] Please see the appendix Figure 1 -Appendix Figure 20 As shown, a PLC-based cofferdam formwork dry sealing structure includes the following steps: support assembly, lowering, and connection of piles and communicating vessels: After the inner side of the casing 8 is reinforced with plates, the hanging leg 1 is welded to the casing 8 during the low tide window, and pad blocks 7 and pad beams 5 are set on the bottom corbel 6; the upper corbel 4 is assembled with the third layer support 3, the bottom of the vertical temporary support 2 is fully welded to the third layer support 3, the third layer support 3 is lifted by a crawler crane and lowered onto the bottom corbel 6; the upper corbel 4 is reinstalled and connected to the second layer support. 9. Assemble the second layer support 9 using a crawler crane and lower it onto the vertical temporary support 2; reinstall the corbel 4 and assemble it with the first layer support 10; after installing the protective casing reinforcement 12, weld the top limiting beam 11 to connect the first layer support 10 and the protective casing 8; drive the steel sheet pile-steel pipe pile combination pile 13 from upstream to downstream of the water flow until they are closed, and install no less than 4 connecting devices 14. After the construction of the steel sheet pile-steel pipe pile combination pile 13 is completed, it is precisely aligned with the pile body position of the bridge pile foundation 22.

[0025] The process also includes the following steps: waler fixing, temporary structure removal, and base plate connection: Check the tightness of the waler 34 and pipe pile 25; insert steel plates into any gaps; weld replacement brackets 15 onto the pipe pile 25; weld the waler 34 and pipe pile 25 sequentially using the first connecting plate 16, the first and second connecting plates 17, and the first, second, and third connecting plates 18; during welding, pump water in layers down to 1m below the center line of the corresponding waler; close the communicating vessel 14 during high tide; remove the vertical temporary support 2 after welding the third connecting plate; dismantle... After installing the hanging leg 1 and the bottom limiting sleeve reinforcement 12, the bottom limiting beam 11 is welded to connect the waler 34 and the sleeve 8. The water in the cofferdam is pumped to the design elevation. The bottom plate corbel 19 and the bottom plate shear reinforcement are welded to the sleeve 8 respectively. The concrete bottom plate formwork 20 is installed, the bottom plate reinforcement is laid and the reinforcing reinforcement is tied. The 60cm thick C40 bottom plate 21 is cast in place as the core structure of the bottom sealing 30 and is left to reach the design strength. The waler 34 and each layer of support are provided with internal supports 27 to enhance the overall stability of the support system.

[0026] It also includes support conversion, risk prevention and control, and subsequent structural and cofferdam dismantling connection steps: dismantle the limiting beam 11 and steel casing 8; dismantle the third layer support 3 at low tide; install the second layer, the first layer long diagonal brace, and the first layer replacement support 24 in sequence, all of which belong to the first and second layer supports 23, and then dismantle the corresponding short diagonal brace and counter-brace respectively; before the typhoon arrives, install steel wire ropes 29 on the waler 34 and casing 8, and use rope clamps 28 to fasten the steel wire ropes 29 to the waler 34 and casing 8 at the preset points. A stiffening plate 26 is added at the installation location of the wire rope 29, and steel plates are welded on both sides to limit and protect the wire rope 29 at the sharp point of the waler 34; the pile head of the bridge pile foundation 22 is removed and the pile cap 31 is poured. After the pile cap 31 reaches the design strength, the formwork is removed. Logs 33 are set at intervals between the pile cap 31 and the pipe pile 25 for support, and the pier body 32 is constructed until the water level is reached; the communicating vessel 14 is opened to balance the water level. When the water level is low, the waler 34 and the inner support 27 are removed from bottom to top, and finally the steel sheet pile-steel pipe pile composite pile 13 is removed.

[0027] Please see the appendix Figure 1 -Appendix Figure 20 As shown, a construction method for a PLC-based cofferdam with suspended formwork and dry sealing structure includes the following steps: S1 Design Preparation: Based on the geological survey report and hydrological specifications of the construction area, design parameters are determined, and a steel sheet pile-steel pipe pile combined support structure and a 3-layer waler support system are designed. S2 support and pile construction: During the low tide window, complete the installation of hanging legs, the assembly and layered lowering of the three-layer walers and inner supports, weld the limiting beam to fix the walers and casing, drive the combined piles from upstream to downstream until they are closed and set up the connecting device. S3 Waler Fixing and Base Slab Construction: Layered pumping and welding of replacement corbels and connecting plates for each layer. After removing the temporary structure, pump water to the design elevation to complete the installation of base slab steel, formwork, and C40 concrete pouring and curing. S4 Support Conversion and Risk Control: The support system conversion was completed according to the principle of supporting first and then dismantling, and special protective measures were taken in response to severe weather such as typhoons; S5 Subsequent Construction and Cofferdam Removal: Pour the foundation and pier body until water flows out, balance the water levels inside and outside the cofferdam, and then remove the walers, inner supports and piles in layers. Before removal, check the scouring of the trestle bridge and the structural stress.

[0028] The detailed steps are as follows: S2 includes the following steps: S2.1: Install the hanging legs, assemble the third layer of walers and internal supports. S2.1.1 After the inner side of the casing is reinforced with a plate, during the low tide window, weld hanging legs onto the casing, and pre-install pads and pad beams on the bottom brackets to support the bottom waler and limit its position. S2.1.2 Assemble the third layer of walers and inner supports on the upper corbel, weld the vertical temporary supports, and fully weld the bottom of the vertical temporary supports to the walers; S2.2: Lower the third layer of walers and inner supports S2.2.1 After using a crawler crane to lift the third layer of walers and inner supports, remove the upper bracket bolts; S2.2.2, Lower the third layer of inner support to the bottom corbel at low tide; S2.3: Assemble the second layer of walers and internal supports. S2.3.1 Reinstall the bracket; S2.3.2 Assemble the second layer of support on the upper bracket; S2.4: Lower the second layer of walers and inner supports S2.4.1 After using a crawler crane to lift the second layer of walers and inner supports, remove the upper bracket bolts; S2.4.2. At low tide, lower the second layer of inner support to the vertical temporary support; S2.5: Assemble the first layer of walers and inner supports, and weld the top limiting beam. S2.5.1 Reinstall the upper bracket, and assemble the first layer of walers and inner supports on the upper bracket; S2.5.2 After the hanging leg is installed, the protective casing is installed to strengthen it. The top limiting beam is welded to connect the waler and the protective casing. S2.6: Driven pipe piles and sheet piles S2.6.1 According to the plan layout, starting from the upstream of the water flow, a combination of steel pipe piles and steel sheet piles will be driven downstream until they are closed. The pipe piles are 35m long and the sheet piles are 27m long. S2.6.2. The verticality of the steel pipe piles should be checked to ensure the watertightness of the cofferdam. The corner positions should be laid out and measured. If necessary, the closure steel sheet piles should be adjusted. S2.6.3, Install communicating vessels, and the number of communicating vessels shall not be less than 4; S3 includes the following steps: S3.1: Weld the first layer replacement bracket and the first layer connecting plate. S3.1.1 Check whether the walers and pipe piles of each layer are tightly attached. Steel plates should be inserted into the parts that are not in close contact. S3.1.2 Weld the first layer of walers to the pipe pile to replace the corbels, and weld the walers to the pipe pile through the connecting plate; S3.2: Weld the second layer replacement bracket and connecting plate. S3.2.1. Close the communicating vessel during high tide to ensure that the water level on the inside is lower than the water level on the outside. S3.2.2. Pump water into the cofferdam to 1m below the center line of the second waler, weld the corbel of the second waler onto the pipe pile, and weld the waler to the pipe pile through the connecting plate; S3.3: Weld the third layer replacement bracket and connecting plate S3.1.1. Pump water into the cofferdam to 1m below the center line of the third waler, weld the corbel of the third waler onto the pipe pile, weld the waler to the pipe pile through the connecting plate, and remove the vertical temporary support. S3.4: Remove the hanging leg and weld the bottom limiting beam. S3.4.1 Remove the hanging leg; S3.4.2. Install reinforcement measures for the protective casing at the bottom limit point, and weld the bottom limit beam to connect the waler and the protective casing; S3.5: Weld the base plate brackets, install the base plate steel and formwork. S3.5.1, Pump water out of the cofferdam to the design elevation; S3.5.2 Weld the bottom plate brackets onto the casing, and install the bottom plate steel and template; S3.6: Casting the base slab S3.6.2 Weld the bottom plate shear reinforcement to the casing; S3.6.3 Lay the bottom slab reinforcement bars, install the reinforcing reinforcement bars, and tie the reinforcing reinforcement bars to the top reinforcement bars of the bottom slab; S3.6.4. Cast a 60cm thick C40 base slab in place and wait for the base slab to reach the design strength; S4 includes the following steps: S4.1: Remove the limiting beam and cut off the steel casing. S4.1.1 Remove the limiting beam and cut off the steel casing; S4.1.2 During subsequent construction, wave height and flow velocity should be monitored. If the wave height is >1m or the flow velocity is >3m / s, personnel operations should be stopped and personnel should be evacuated. S4.2: Remove the third layer of support S4.2.1 At low tide, remove the third layer of support; S4.3: Change support S4.3.1 Install the second layer of long diagonal bracing, and then remove the second layer of short diagonal bracing and the opposing bracing; S4.3.2 Install the first layer of long diagonal bracing, and then remove the first layer of short diagonal bracing and the opposing bracing; S4.4: Supplementary Measures During Typhoon Season S4.4.1 Before the typhoon arrives, check the strength of the bottom sealing concrete. If it does not meet the standard, retain the casing and the limiting beam. S4.4.2 Before a typhoon arrives, all construction inside the cofferdam must be stopped, equipment removed, and measures such as installing steel wire ropes on the walers and casings must be taken to ensure that the water level inside the cofferdam is the same as the water level outside. S4.4.3 At the location where the steel wire rope is installed on the waler, check the deformation and welding quality of the connecting plate between the adjacent pipe pile and the waler. Replace or repair the weld if the requirements are not met, and add a vertical stiffening plate. S4.4.4 At the location where the wire rope is installed on the waler, steel plates are welded on both sides of the wire rope to limit its movement, and the wire rope is protected at sharp points on the waler. S5 includes the following steps: S5.1: Casting of foundation cap S5.1.1 Remove the pile head, tie the reinforcing bars, erect the formwork, and pour the foundation. S5.2: Construction Pier Body S5.2.1 After the foundation reaches the design strength, remove the foundation formwork and install log supports at intervals between the foundation and the pipe piles; S5.2.2 Construction of the pier body until it emerges from the water; S5.3: Remove the cofferdam S5.3.1 Open the communicating vessel to maintain the balance of internal and external water levels. When the water level is low, remove the two layers of walers and internal supports from bottom to top in sequence, and finally remove the steel sheet pile-steel pipe pile combination pile. S5.4 During the entire construction process, wave height and current velocity shall be monitored. If the wave height is greater than 1m or the current velocity is greater than 3m / s, personnel shall be stopped and evacuated.

Claims

1. A construction method for a PLC-based cofferdam formwork dry sealing structure, characterized in that, Includes the following steps: S1 Design Preparation: Based on the geological survey report and hydrological specifications of the construction area, design parameters are determined, and a steel sheet pile-steel pipe pile combined support structure and a 3-layer waler support system are designed. S2 support and pile construction: During the low tide window, complete the installation of hanging legs, the assembly and layered lowering of the three-layer walers and inner supports, weld the limiting beam to fix the walers and casing, drive the combined piles from upstream to downstream until they are closed and set up the connecting device. S3 Waler Fixing and Base Slab Construction: Layered pumping and welding of replacement corbels and connecting plates for each layer. After removing the temporary structure, pumping water to the design elevation to complete the installation of base slab steel, formwork, and concrete pouring and curing. S4 Support Conversion and Risk Control: The support system conversion was completed according to the principle of support first and then dismantling, and protective measures were taken in response to severe weather such as typhoons; S5 Subsequent Construction and Cofferdam Removal: Pour the foundation and pier body until water flows out, balance the water levels inside and outside the cofferdam, and then remove the walers, inner supports and piles in layers. Before removal, check the scouring of the trestle bridge and the structural stress.

2. The construction method of the PLC cofferdam formwork dry sealing structure according to claim 1, characterized in that, In S2, the assembly and lowering of the three-layer walers and internal supports specifically includes: S2.1 After the inner side of the casing is reinforced with a plate, the hanging leg is welded during the low tide window, and pads and pad beams are set on the bottom bracket. The third layer of waler and inner support are assembled on the upper bracket, and the vertical temporary support is welded. The bottom of the vertical temporary support is fully welded to the waler. After the crawler crane lifts the third layer of walers and inner supports, remove the upper bracket bolts and lower the third layer of inner supports to the bottom bracket at low tide. S2.3 Reinstall the upper bracket and assemble the second layer of support on the upper bracket; S2.4 After lifting the second-layer waler and inner supports using a crawler crane, remove the upper bracket bolts; at low tide, lower the second-layer inner supports onto the vertical temporary supports. S2.5 Reinstall the upper bracket, assemble the first layer of walers and inner supports on the upper bracket; after the hanging leg is installed, install the protective casing reinforcement measures, and weld the top limiting beam to connect the walers and the protective casing.

3. The construction method of the PLC cofferdam formwork dry sealing structure according to claim 1, characterized in that, In S3, the waler fixing specifically includes: S3.1 Check the fit between the waler and the pipe pile, and insert steel plates into any areas that are not tightly fitted; weld the first layer of waler onto the pipe pile to replace the corbel, and weld the waler to the pipe pile through the connecting plate; S3.2 Close the communicating vessel during high tide, pump water into the cofferdam to 1m below the center line of the second waler, weld the corbel of the second waler onto the pipe pile, and weld the waler to the pipe pile through the connecting plate; S3.3 Pump water into the cofferdam to 1m below the center line of the third waler, weld the corbel of the third waler onto the pipe pile, weld the waler to the pipe pile through the connecting plate, and remove the vertical temporary support; S3.4 Remove the hanging leg, install reinforcement measures for the bottom limit sleeve, and weld the bottom limit beam to connect the waler and the sleeve.

4. The construction method of the PLC cofferdam formwork dry sealing structure according to claim 1, characterized in that, In S4, the support for conversion specifically includes: S4.1 Remove the limiting beam and cut off the steel casing; S4.2 Remove the third layer of support at low tide; S4.3 First, install the second layer of long diagonal bracing, and remove the second layer of short diagonal bracing and the opposing bracing; then install the first layer of long diagonal bracing, and remove the first layer of short diagonal bracing and the opposing bracing.

5. The construction method of the PLC cofferdam formwork dry sealing structure according to claim 1, characterized in that, In S5, the subsequent construction and demolition specifically include: S5.1 Remove pile heads, tie reinforcing bars, erect formwork, and pour foundation; After the S5.2 pier cap reaches its design strength, the formwork is removed, and log supports are installed at intervals between the pier cap and the pipe piles. The pier body is then constructed until it reaches the water outlet. S5.3 Open the communicating vessel to balance the water level. When the water level is low, remove the two layers of walers and inner supports from bottom to top in sequence, and finally remove the steel sheet piles and steel pipe piles. S5.4 During the entire construction process, wave height and current velocity shall be monitored. If the wave height is greater than 1m or the current velocity is greater than 3m / s, personnel shall be stopped and evacuated.

6. The construction method of the PLC cofferdam formwork dry sealing structure according to claim 1, characterized in that, In S2, the construction of combined piles specifically includes: steel pipe piles with a length of 35m and steel sheet piles with a length of 27m. The number of steel pipe piles on the short side is not less than 8 and the number of steel pipe piles on the long side is not less than 11. The verticality of the steel pipe piles is controlled, the corner positions are laid out, measured and adjusted to close the steel sheet piles, and the number of connecting devices is not less than 4.

7. The construction method of the PLC cofferdam formwork dry sealing structure according to claim 1, characterized in that, In S3, the base plate construction specifically includes: S3.5 Pump water to the design elevation, weld the bottom plate brackets and shear reinforcements onto the casing, and install the bottom plate steel and formwork; S3.6 Lay and tie the bottom slab reinforcement and reinforcing bars, pour 60cm thick C40 concrete in place, and cure it to a strength of ≥30MPa before proceeding with subsequent procedures.

8. The construction method of the PLC cofferdam formwork dry sealing structure according to claim 1, characterized in that, In S4, the specific protective measures during the typhoon season include: Before Typhoon S4.41 arrives, check the strength of the bottom sealing concrete. If it does not meet the standard, retain the casing and the limiting beam. S4.42 Stop construction and remove equipment. The water level inside the cofferdam is the same as the water level outside. Install steel wire ropes on the walers and casing. S4.43 Inspect the quality of the connecting plate at the wire rope installation point, replace or weld any substandard connecting plates, and add a vertical stiffening plate; S4.44 Steel plates are welded to both sides of the wire rope to limit its movement and protect the wire rope at the sharp points of the waler.

9. A PLC-based cofferdam formwork dry sealing structure, applied to the construction method of the PLC-based cofferdam formwork dry sealing structure according to any one of claims 1-8, characterized in that, The process includes the following steps: supporting assembly, lowering, and connecting the pile body with the communicating vessel: After the inner side of the casing is reinforced with a plate, the hanging leg is welded to the casing during the low tide window, and pads and pad beams are set on the bottom corbel; the upper corbel is assembled with the third layer of support, the bottom of the vertical temporary support is fully welded to the third layer of support, the third layer of support is lifted by a crawler crane and lowered onto the bottom corbel; the upper corbel is reinstalled and assembled with the second layer of support, the second layer of support is lifted by a crawler crane and lowered onto the vertical temporary support; the upper corbel is reinstalled and assembled with the first layer of support, after the casing is reinforced, the top limiting beam is welded to connect the first layer of support and the casing; steel sheet pile-steel pipe pile combination piles are driven from upstream to downstream until they are closed, and no less than 4 communicating vessels are installed. After the steel sheet pile-steel pipe pile combination piles are constructed, their positions are precisely aligned with the pile body of the bridge pile foundation.

10. The PLC cofferdam formwork dry sealing structure according to claim 9, characterized in that, The construction process also includes waler fixing, temporary structure removal, and base plate connection: Check the tightness of the waler and pipe piles; insert steel plates into any gaps; weld replacement corbels onto the pipe piles; weld the waler and pipe piles sequentially using the first layer connecting plate, the first and second layer connecting plates, and the first, second, and third layer connecting plates; during welding, pump water in layers to 1m below the corresponding waler centerline; close the connecting device during high tide; remove the vertical temporary support after welding the third layer connecting plate; remove the hanging legs; install the bottom limiting sleeve reinforcement; weld the bottom limiting beam to connect the waler and the sleeve; pump water into the cofferdam to the design elevation; weld the base plate corbels and base plate shear reinforcement to the sleeve; install the concrete base plate formwork; lay the base plate reinforcement and tie reinforcing bars; cast a 60cm thick C40 base plate as the core structure for sealing the bottom, and wait for it to reach its design strength; internal supports are installed between the waler and each layer of support to enhance the overall stability of the support system.

11. The PLC cofferdam formwork dry sealing structure according to claim 10, characterized in that, It also includes support conversion, risk prevention and control, and subsequent structural and cofferdam dismantling connection steps: dismantle the limiting beam and steel casing, and dismantle the third layer of support at low tide; install the second layer of long diagonal bracing and the first layer of support after replacement in sequence, all of which belong to the first and second layers of support, and then dismantle the corresponding short diagonal bracing and counter-bracing respectively; before the typhoon arrives, install steel wire ropes on the walers and casing, and use rope clamps to fasten the steel wire ropes to the pre-set points on the walers and casing, add stiffening plates at the installation points of the steel wire ropes, and weld steel plates on both sides to limit and protect the steel wire ropes at the sharp points of the walers; chisel off the pile heads of the bridge pile foundation and pour the pile cap, remove the formwork after the pile cap reaches the design strength, set log supports at intervals between the pile cap and the pipe pile, and construct the pier body until it is above water; open the communicating vessel to balance the water level, and dismantle the walers and inner supports from bottom to top at low water level, and finally dismantle the steel sheet pile-steel pipe pile combination pile.

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