A method for sealing the bottom of a cofferdam in deep silt geology

Abstract

This invention discloses a method for constructing a cofferdam bottom sealing system in deep silt geological conditions. The successful application of this method solves the problem of insufficient bearing capacity in deep silt layers. Previous methods used the original foundation surface as the reference elevation for the bottom concrete, increasing the bond strength between the concrete and the sheet pile cofferdam / steel casing to meet the concrete's anti-buoyancy and anti-sinking requirements. However, large-scale application of this method leads to increased concrete usage and lower safety performance in subsequent construction. This invention further removes silt from the original foundation to ensure no silt deposition on the bottom sealing base surface, preventing the bottom sealing concrete from mixing with deposited silt and reducing its strength. Furthermore, it uses replacement filling to form a new base structure, increasing the bearing capacity of the bottom sealing base surface and enhancing the safety of subsequent pile cap construction. Overall, it reduces material waste and significantly saves economic costs.

Description

Technical Field

[0001] This invention specifically relates to a method for constructing a cofferdam for sealing the bottom of a deep silt geological formation. Background Technology

[0002] As bridge construction projects expand to more extensive areas and cross increasingly longer distances of rivers, seas, and mountains,...

[0003] The geological environment of the substructure foundation of bridges on water is complex. For example, a deep silt layer or silty clay layer cannot meet the load requirements of subsequent substructure construction. At the same time, the substructure foundations of bridges are designed with different shapes and structural dimensions, which makes the control of the sealing area more demanding. In order to meet the requirements of the bridge construction environment and the bearing capacity of subsequent substructure construction, the thickness and quality of the sealing are extremely important.

[0004] The existing construction process is as follows: dredging of the foundation area → driving of sheet pile cofferdam → waler installation → underwater concrete sealing → dewatering and foundation construction. This process has the following problems: ① The sealing concrete mixes with the silt during sealing, resulting in insufficient concrete strength; ② Due to the long interval between dredging and underwater concrete sealing, silt deposition or backfilling may occur, leading to insufficient concrete thickness or repeated dredging; ③ Severe silt compression on one side of the concrete during sealing, resulting in localized silt-like structures. All three problems can lead to: ① rupture of the sealing concrete due to hydrostatic pressure difference after dewatering, even causing seepage and resulting in sealing failure; ② In subsequent foundation construction under load, insufficient strength of the sealing concrete or insufficient bearing capacity of the silt layer or silty clay layer beneath the sealing concrete can cause soft soil subsidence, resulting in discrepancies between the foundation construction and design parameters. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for constructing a cofferdam with a bottom sealing layer in deep silt geology. On the original basis, further sludge removal and dredging are carried out to ensure that there is no silt deposit on the bottom sealing base surface, avoiding the mixing of the bottom sealing concrete with the deposited silt and reducing its strength. Furthermore, by replacing the fill to form a new base structure, the bearing capacity of the bottom sealing base surface is increased, and the bearing safety of subsequent pier construction is enhanced. Overall, material consumption is reduced, and economic costs are significantly saved.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] A method for sealing the bottom of a cofferdam in deep silt geology includes the following steps:

[0008] S1. Clearing the foundation within the cofferdam:

[0009] S11. After the cofferdam is formed, a long-arm excavator or grab bucket is used for bottom cleaning, and a sludge suction machine is used in conjunction to initially clean it to the bottom sealing elevation. The elevation can be adjusted appropriately according to the actual bearing capacity required by the foundation. Therefore, the initial cleaning is done using a long-arm excavator and grab bucket. After cleaning, mud and sand will settle on the base, which is not conducive to the subsequent bottom sealing. At the same time, there are many obstacles around the steel casing that are difficult to clean. Therefore, after the cofferdam is formed, a sludge suction equipment is used for secondary cleaning of the base. High-pressure water jetting can be used to clean the area around the steel casing. No part of the entire cofferdam should be missed. After cleaning, divers need to go underwater to inspect it. When inspecting, divers need to pay special attention to all corners, especially the steel casing and steel sheet pile surfaces within the bottom sealing concrete area. Mud and sand must not be adhering to them.

[0010] S12. After the cofferdam foundation is cleared, crushed stone is dumped in the lower area, and then crushed stone or rubble is dumped in further according to the requirements of subsequent concrete filling, and leveled.

[0011] S2. Construction platform erection:

[0012] S21. The bottom sealing platform of the cofferdam for the approach bridge in the water adopts a Bailey beam platform. The bottom sealing platform adopts the form of steel casing plus distribution beam plus Bailey frame. The bottom sealing guide platform adopts a single-layer standard Bailey beam structure, that is, Bailey beams are used as bottom sealing supports. Bailey beams are connected with standard support frames to form a whole. Due to the large volume of concrete, the bottom of the bottom sealing platform pouring frame should be set on the bottom sealing platform corresponding to the steel casing, and the Bailey beam support frames at the corresponding positions should be added according to the actual situation.

[0013] S22. After the construction platform is erected, the guide pipe positioning frame is set up. Scaffold boards are laid around the positioning frame as a personnel operating platform and construction passage. The scaffold boards are made of 50mm thick wooden boards or steel fixed scaffold boards. To ensure construction safety, the platform is required to be fully covered with scaffold boards except for the guide pipe positioning frame and observation points. Fall protection nets are set up at the measuring points. After the bottom platform is set up and the guide pipe is installed in place, guardrails are installed around the platform and safety green nets are hung to close it off to ensure construction safety.

[0014] S23. The on-site distribution beam model and the steel casing reinforcement structure or reserved slot should correspond to each other. The top surface elevation of the four distribution beams should be consistent to ensure that the construction platform is flat.

[0015] S3. Layout of observation points and conduits:

[0016] S31. Layout of guide pipes: The guide pipes for sealing the bottom are selected based on the maximum two-way slab area of ​​the sealing area. The diameter of the guide pipes is sufficient to meet the maximum two-way slab area, and the length of the guide pipes is sufficient to meet the height from the bottom sealing platform elevation to the bottom sealing ground. The same number of guide pipes are equipped on both the north and south banks. A 75t crawler crane is used to lower the guide pipes one by one. During the construction process, chain hoists are used for tipping and lifting.

[0017] S32. To facilitate the observation of the bottom sealing concrete elevation, the location and number of observation points are arranged as follows: Considering the influence of the tremie pipe on the radius of concrete bottom sealing diffusion, the highest observation point is arranged at the location of the tremie pipe, with the observation point located at the top of the tremie pipe. Then, taking the tremie pipe as a circle, fixed observation points are arranged at the contact points of the concrete bottom sealing diffusion between two adjacent tremie pipes. These observation points are the lowest observation points. At the same time, observation points are added at the edge of the steel casing and on the side of the steel sheet pile cofferdam to ensure that the thickness of the bottom sealing concrete in the construction blind spot meets the requirements. In addition, to better ensure the thickness of the bottom sealing concrete around the steel sheet piles of the approach bridge in the water, moving measuring points are set within a 0.9m range inside the cofferdam. The moving measuring points should be frequently and closely measured during the bottom sealing construction process.

[0018] S4. Concrete ball extraction and pouring, the specific steps are as follows:

[0019] S41. Selection of ball extraction point: First, the interference from the inner support, steel casing, and Bailey beam support frame of the cofferdam needs to be considered. After eliminating the interference factors of the inner support, steel casing, and Bailey beam support frame, for larger steel cofferdams, the corresponding areas can be divided according to the area. Ball extraction is carried out symmetrically within the area. Simulation is used to determine whether the concrete is pushed to the other side in an "S" shape on one side of the inner wall of the cofferdam to ensure the continuity of the concrete. Finally, the first extraction position is determined by selecting the corner where the minimum amount of first concrete is required, that is, the place where the space between the steel casing and the inner wall of the cofferdam is the smallest, thus completing the selection of the ball extraction sequence.

[0020] S42. Before removing the ball, the base should be cleaned, the guide tube slots should be installed, and the lower end of the assembled guide tube should be placed on the base according to the base elevation of each guide tube. Check the left and right sides using measuring ropes;

[0021] S43. After completing the base cleaning and guide pipe verification, the first batch of sealing concrete is poured according to the ball removal sequence selected in specific step S41. To ensure the first batch of concrete is poured, the pouring frame and hopper must be filled with concrete before the ball can be removed for pouring. A small hopper is installed at the top of the guide pipe, and the pouring frame is arranged next to the small hopper as a storage hopper. The truck pump pumps the concrete into the pouring frame. First, the pouring frame valve is opened, and the concrete flows into the small hopper through the chute, filling the small hopper with concrete. Then, the pouring frame valve is closed. When the concrete in the pouring frame is almost full, the pouring frame valve is opened, and the plug in the small hopper is pulled out at the same time to pour the first batch of sealing concrete.

[0022] S431. When pulling the ball for the first time, the concrete in the storage hopper should be continuously, quickly and controlledly fed into the guide pipe without interruption to prevent water from entering the guide pipe and causing the ball pulling failure. After pulling the ball, the ball pulling of the next guide pipe can only be carried out after the burial depth of the guide pipe is confirmed by measurement. Specifically, the actual burial depth should be related to the thickness of the bottom sealing concrete. It can be considered that this is the highest point. After the highest point meets the thickness of the bottom sealing concrete, the ball pulling of the next guide pipe can be carried out.

[0023] S432. After the second guide pipe is removed, concrete should be poured into the first guide pipe once, then the third guide pipe should be removed. After the third guide pipe is removed, concrete should be poured into the first and second guide pipes once, then the fourth guide pipe should be removed, and so on, until the last guide pipe in the segmented pouring is removed. The pouring of subsequent guide pipes should be carried out sequentially, ensuring that the burial depth of the guide pipes after removal meets the minimum guide pipe burial depth of 0.3–0.4 m. Within the specified range, during normal pouring, the interval between concrete pours for the duct that has been removed from its ball should not exceed 30 minutes. If material cannot be supplied within 30 minutes, the duct should be repeatedly raised and lowered several times, with each rise and fall approximately 0.1 meters. Each duct must guarantee at least one concrete supply per hour.

[0024] S44. Normal bottom sealing concrete pouring: After the first batch of concrete is successfully poured, the normal pouring stage begins. The hopper is removed, and the pump pipe is inserted into the guide pipe to pour concrete.

[0025] Furthermore, in step S31, to ensure good bonding between the sheet piles, steel casing, and bottom sealing concrete, the guide pipes should be arranged close to the perimeter of the cofferdam and the steel casing. The guide pipes should be laid out with an influence radius of 4.5m, and the influence range should be adjusted appropriately according to the concrete slump and initial setting. When the measured influence radius is less than 4.5m, a temporary guide pipe should be added at the observation point between the two guide pipes in the longitudinal direction of the bridge. For blind spots in the construction process due to obstructions such as the bottom sealing platform and steel casing, the ball-pulling points should be appropriately increased. Secondly, to ensure the bonding force between the concrete and the steel casing and sheet pile cofferdam, divers should go underwater to check whether the bottom sealing thickness of the structure meets the requirements.

[0026] Furthermore, in step S31, a water tightness test should be performed on the conduit before use. The test pressure should be 1.5 times the hydrostatic pressure. After pressing in the calculated water pressure, hold the load for 15 minutes and observe for leakage. If there is no leakage, it is considered qualified.

[0027] Furthermore, in step S31, the interference from the cofferdam support, steel casing, and Bailey beam support frame must be considered when laying the conduit to facilitate the movement and lifting of the conduit.

[0028] In step S41, the formula for calculating the volume of the ball-lifting concrete in the first batch of bottom sealing concrete pouring is as follows:

[0029]

[0030]

[0031] in;

[0032] R is the radius, in meters (m).

[0033] H2 is the height from the bottom of the conduit to the bottom of the sealing surface, which should be 0.3 to 0.4 m according to the specifications.

[0034] H1 is the height from the bottom of the guide pipe to the centroid of the concrete cone during the first ball extraction. According to the specifications, it should be 1 to 1.5m, but can be changed according to the actual sealing thickness on site. The unit is meters.

[0035] d is the diameter of the catheter, in meters (m).

[0036] γ w The specific weight of the concrete mixture;

[0037] γ c The unit weight of water inside the cofferdam is kN / m³. 3 ;

[0038] H w The height is the distance from the horizontal plane inside the cofferdam to the centroid of the first concrete cone extracted from the spherical pile, in meters.

[0039] h1 is the height required for the concrete column inside the conduit to balance the external pressure when the conduit is buried at a depth of H1, in meters;

[0040] V represents the volume of concrete used for the initial bottom sealing concrete pour, measured in meters. 3 .

[0041] Furthermore, in step S43, when the total volume of the pouring frame and the small hopper is less than the calculated volume of the first batch of concrete, the pouring frame and the small hopper are filled with concrete and the ball is pulled out. After the ball is pulled out, the truck pump should continuously pump concrete into the pouring frame to ensure that the actual volume of the first batch of concrete meets the calculation requirements.

[0042] Furthermore, in step S43, for the conduits that have not yet had their balls removed, the conduits should be raised above the concrete surface at any time based on the measurement data of the rising height of the bottom concrete surface to prevent concrete from entering the conduits and causing blockage when the balls are removed. The height of the bottom of these conduits from the concrete surface must be re-determined before removing the balls.

[0043] Furthermore, in step S44, to ensure a certain burial depth at the duct opening, the duct should not be lifted as much as possible while the concrete pouring is proceeding smoothly. When it is necessary to lift the duct, a guide chain should be used to lift it slowly, and the lifting height should be controlled so that the bottom of the duct is 1m below the concrete surface. After lifting, concrete pouring should continue. At the same time, the concrete height at the lifting point should be frequently measured to prevent the duct from being lifted out of the concrete. The actual measured depth should be strictly used as the basis for lifting the duct. The duct should be lifted in a timely manner based on the concrete pouring volume and the measured pouring height. At the same time, attention should be paid to coordinating the pouring speed of each duct to keep the concrete inside the cofferdam at approximately the same elevation.

[0044] The main technical effects of this invention are reflected in the following aspects:

[0045] ① The successful application of the cofferdam sealing construction method for deep silt geology has solved the problems of insufficient bearing capacity of deep silt layer sealing and large amount of sealing concrete. It has strong operability and practicality, good overall application prospects, and the construction has become standardized.

[0046] ②Previous methods used the original foundation surface as the reference surface for the bottom elevation of the sealing concrete. By increasing the bond strength between the concrete and the sheet pile cofferdam and steel casing, the requirements for concrete anti-buoyancy and anti-sinking were achieved. However, if this method was used on a large scale, it would lead to an increase in concrete volume and lower safety performance in subsequent construction. On the original basis, further dredging and silt removal were carried out to ensure that there was no silt deposit on the bottom sealing base surface, thus avoiding the mixing of the sealing concrete with the deposited silt and reducing its strength. Furthermore, a new base structure was formed by replacement filling, which increased the bearing capacity of the bottom sealing base surface and increased the bearing safety of subsequent pile cap construction. Overall, this reduced material waste and significantly saved economic costs. Detailed Implementation

[0047] The specific embodiments of the present invention will be further described below to make the technical solution of the present invention easier to understand and master.

[0048] A method for sealing the bottom of a cofferdam in deep silt geology includes the following steps:

[0049] S1. Clearing the foundation within the cofferdam:

[0050] S11. After the cofferdam is formed, a long-arm excavator or grab bucket is used for bottom cleaning, and a sludge suction machine is used in conjunction to initially clean it to the bottom sealing elevation. The elevation can be adjusted appropriately according to the actual bearing capacity required by the foundation. Therefore, the initial cleaning is done using a long-arm excavator and grab bucket. After cleaning, mud and sand will settle on the base, which is not conducive to the subsequent bottom sealing. At the same time, there are many obstacles around the steel casing that are difficult to clean. Therefore, after the cofferdam is formed, a sludge suction equipment is used for secondary cleaning of the base. High-pressure water jetting can be used to clean the area around the steel casing. No part of the entire cofferdam should be missed. After cleaning, divers need to go underwater to inspect it. When inspecting, divers need to pay special attention to all corners, especially the steel casing and steel sheet pile surfaces within the bottom sealing concrete area. Mud and sand must not be adhering to them.

[0051] S12. After the cofferdam foundation is cleared, crushed stone is dumped in the lower area, and then crushed stone or rubble is dumped in further according to the requirements of subsequent concrete filling, and leveled.

[0052] S2. Construction platform erection:

[0053] S21. The bottom sealing platform of the cofferdam for the approach bridge in the water adopts a Bailey beam platform. The bottom sealing platform adopts the form of steel casing plus distribution beam plus Bailey frame. The bottom sealing guide platform adopts a single-layer standard Bailey beam structure, that is, Bailey beams are used as bottom sealing supports. Bailey beams are connected with standard support frames to form a whole. Due to the large volume of concrete, the bottom of the bottom sealing platform pouring frame should be set on the bottom sealing platform corresponding to the steel casing, and the Bailey beam support frames at the corresponding positions should be added according to the actual situation.

[0054] S22. After the construction platform is erected, the guide pipe positioning frame is set up. Scaffold boards are laid around the positioning frame as a personnel operating platform and construction passage. The scaffold boards are made of 50mm thick wooden boards or steel fixed scaffold boards. To ensure construction safety, the platform is required to be fully covered with scaffold boards except for the guide pipe positioning frame and observation points. Fall protection nets are set up at the measuring points. After the bottom platform is set up and the guide pipe is installed in place, guardrails are installed around the platform and safety green nets are hung to close it off to ensure construction safety.

[0055] S23. The on-site distribution beam model and the steel casing reinforcement structure or reserved slot should correspond to each other. The top surface elevation of the four distribution beams should be consistent to ensure that the construction platform is flat.

[0056] S3. Layout of observation points and conduits:

[0057] S31. Layout of guide pipes: The guide pipes for sealing the bottom are selected based on the maximum two-way slab area of ​​the sealing area. The diameter of the guide pipes is sufficient to meet the maximum two-way slab area, and the length of the guide pipes is sufficient to meet the height from the bottom sealing platform elevation to the bottom sealing ground. The same number of guide pipes are equipped on both the north and south banks. A 75t crawler crane is used to lower the guide pipes one by one. During the construction process, chain hoists are used for tipping and lifting.

[0058] S32. To facilitate the observation of the bottom sealing concrete elevation, the location and number of observation points are arranged as follows: Considering the influence of the tremie pipe on the radius of concrete bottom sealing diffusion, the highest observation point is arranged at the location of the tremie pipe, with the observation point located at the top of the tremie pipe. Then, taking the tremie pipe as a circle, fixed observation points are arranged at the contact points of the concrete bottom sealing diffusion between two adjacent tremie pipes. These observation points are the lowest observation points. At the same time, observation points are added at the edge of the steel casing and on the side of the steel sheet pile cofferdam to ensure that the thickness of the bottom sealing concrete in the construction blind spot meets the requirements. In addition, to better ensure the thickness of the bottom sealing concrete around the steel sheet piles of the approach bridge in the water, moving measuring points are set within a 0.9m range inside the cofferdam. The moving measuring points should be frequently and closely measured during the bottom sealing construction process.

[0059] S4. Concrete ball extraction and pouring, the specific steps are as follows:

[0060] S41. Selection of ball extraction point: First, the interference from the inner support, steel casing, and Bailey beam support frame of the cofferdam needs to be considered. After eliminating the interference factors of the inner support, steel casing, and Bailey beam support frame, for larger steel cofferdams, the corresponding areas can be divided according to the area. Ball extraction is carried out symmetrically within the area. Simulation is used to determine whether the concrete is pushed to the other side in an "S" shape on one side of the inner wall of the cofferdam to ensure the continuity of the concrete. Finally, the first extraction position is determined by selecting the corner where the minimum amount of first concrete is required, that is, the place where the space between the steel casing and the inner wall of the cofferdam is the smallest, thus completing the selection of the ball extraction sequence.

[0061] S42. Before removing the ball, the base should be cleaned, the guide tube slots should be installed, and the lower end of the assembled guide tube should be placed on the base according to the base elevation of each guide tube. Check the left and right sides using measuring ropes;

[0062] S43. After completing the base cleaning and guide pipe verification, the first batch of sealing concrete is poured according to the ball removal sequence selected in specific step S41. To ensure the first batch of concrete is poured, the pouring frame and hopper must be filled with concrete before the ball can be removed for pouring. A small hopper is installed at the top of the guide pipe, and the pouring frame is arranged next to the small hopper as a storage hopper. The truck pump pumps the concrete into the pouring frame. First, the pouring frame valve is opened, and the concrete flows into the small hopper through the chute, filling the small hopper with concrete. Then, the pouring frame valve is closed. When the concrete in the pouring frame is almost full, the pouring frame valve is opened, and the plug in the small hopper is pulled out at the same time to pour the first batch of sealing concrete.

[0063] S431. When pulling the ball for the first time, the concrete in the storage hopper should be continuously, quickly and controlledly fed into the guide pipe without interruption to prevent water from entering the guide pipe and causing the ball pulling failure. After pulling the ball, the ball pulling of the next guide pipe can only be carried out after the burial depth of the guide pipe is confirmed by measurement. Specifically, the actual burial depth should be related to the thickness of the bottom sealing concrete. It can be considered that this is the highest point. After the highest point meets the thickness of the bottom sealing concrete, the ball pulling of the next guide pipe can be carried out.

[0064] S432. After the second guide pipe is removed, concrete should be poured into the first guide pipe once, then the third guide pipe should be removed. After the third guide pipe is removed, concrete should be poured into the first and second guide pipes once, then the fourth guide pipe should be removed, and so on, until the last guide pipe in the segmented pouring is removed. The pouring of subsequent guide pipes should be carried out sequentially, ensuring that the burial depth of the guide pipes after removal meets the minimum guide pipe burial depth of 0.3–0.4 m. Within the specified range, during normal pouring, the interval between concrete pours for the duct that has been removed from its ball should not exceed 30 minutes. If material cannot be supplied within 30 minutes, the duct should be repeatedly raised and lowered several times, with each rise and fall approximately 0.1 meters. Each duct must guarantee at least one concrete supply per hour.

[0065] S44. Normal bottom sealing concrete pouring: After the first batch of concrete is successfully poured, the normal pouring stage begins. The hopper is removed, and the pump pipe is inserted into the guide pipe to pour concrete.

[0066] In step S31, to ensure good bonding between the sheet piles, steel casing, and bottom sealing concrete, the guide pipes should be arranged close to the perimeter of the cofferdam and the steel casing. The guide pipes should be laid out with an influence radius of 4.5m. The influence range should be adjusted appropriately according to the concrete slump and initial setting. When the measured influence radius is less than 4.5m, a temporary guide pipe should be added at the observation point between the two guide pipes in the longitudinal direction of the bridge. For blind spots in the construction process due to obstructions such as the bottom sealing platform and steel casing, the ball-pulling points should be appropriately increased. Secondly, to ensure the bonding force between the concrete and the steel casing and sheet pile cofferdam, divers should go underwater to check whether the bottom sealing thickness of the structure meets the requirements.

[0067] In step S31, a water tightness test should be performed on the conduit before use. The test pressure should be 1.5 times the hydrostatic pressure. After pressing in the calculated water pressure, hold the load for 15 minutes and observe for leakage. If there is no leakage, it is considered qualified.

[0068] In step S31, the interference from the cofferdam support, steel casing, and Bailey beam support frame must be considered when laying the conduit to facilitate the movement and lifting of the conduit.

[0069] In step S41, the formula for calculating the volume of the ball-lifting concrete in the first batch of bottom sealing concrete pouring is as follows:

[0070]

[0071]

[0072] in;

[0073] R is the radius, in meters (m).

[0074] H2 is the height from the bottom of the conduit to the bottom of the sealing surface, which should be 0.3 to 0.4 m according to the specifications.

[0075] H1 is the height from the bottom of the guide pipe to the centroid of the concrete cone during the first ball extraction. According to the specifications, it should be 1 to 1.5m, but can be changed according to the actual sealing thickness on site. The unit is meters.

[0076] d is the diameter of the catheter, in meters (m).

[0077] γ w The specific weight of the concrete mixture;

[0078] γ c The unit weight of water inside the cofferdam is kN / m³. 3 ;

[0079] H wThe height is the distance from the horizontal plane inside the cofferdam to the centroid of the first concrete cone extracted from the spherical pile, in meters.

[0080] h1 is the height required for the concrete column inside the conduit to balance the external pressure when the conduit is buried at a depth of H1, in meters;

[0081] V represents the volume of concrete used for the initial bottom sealing concrete pour, measured in meters. 3 .

[0082] In step S43, when the total volume of the pouring frame and the small hopper is less than the calculated volume of the first batch of concrete, the pouring frame and the small hopper are filled with concrete and the ball is pulled out. After the ball is pulled out, the truck pump should continuously pump concrete into the pouring frame to ensure that the actual volume of the first batch of concrete meets the calculation requirements.

[0083] In step S43, for the conduits that have not yet had their balls removed, the conduits should be raised above the concrete surface at any time based on the measurement data of the rising height of the bottom concrete surface to prevent concrete from entering the conduits and causing blockage when the balls are removed. The height of the bottom of these conduits from the concrete surface must be re-determined before removing the balls.

[0084] In step S44, to ensure a certain burial depth at the tremie pipe opening, the tremie pipe should not be lifted as much as possible while the concrete pouring is proceeding smoothly. When it is necessary to lift the tremie pipe, a guide chain should be used to lift it slowly, and the lifting height should be controlled so that the bottom of the tremie pipe is 1m below the concrete surface. After lifting, concrete pouring should continue. At the same time, the concrete height at the lifting point should be frequently measured to prevent the tremie pipe from being lifted out of the concrete. The actual measured depth should be strictly used as the basis for lifting the pipe. The tremie pipe should be lifted in a timely manner based on the concrete pouring volume and the actual pouring height. At the same time, attention should be paid to coordinating the pouring speed of each tremie pipe to keep the concrete inside the cofferdam at approximately the same elevation.

[0085] Experimental example: Take the Niutianyang Bridge project in Shantou City as an example.

[0086] Niutianyang Grand Bridge Approach Bridge The foundation is constructed using bored cast-in-place piles, and the pile cap is constructed using a steel sheet pile cofferdam or a combination cofferdam consisting of a bottomless steel caisson and steel sheet piles.

[0087] For underwater approach bridges, long-arm excavators or grab buckets are used to clean the bottom, with sludge suction machines working in conjunction. When the base elevation is lower than the design elevation, crushed stone or rubble is thrown into the lower area. To avoid concrete layering caused by subsequent ball removal, resulting in failure of concrete sealing, about 20cm of crushed stone or rubble should be thrown in and leveled to ensure that the base elevation is close to the design elevation.

[0088] After the bottom of the cofferdam is cleared, the cofferdam needs to be sealed before the foundation construction. The main function of the sealing concrete is to form a water-retaining cofferdam together with the side wall of the sheet pile cofferdam. After the sealing is successful, the water in the cofferdam is pumped out, thus forming a dry foundation pit foundation. In addition, as the "bottom formwork" for foundation construction, the sealing concrete should meet the requirements for buoyancy resistance and stress.

[0089] The underwater cofferdam bottom sealing concrete pouring for the approach bridge is completed in one go. The theoretical value of the concrete volume for a single cofferdam bottom sealing may have a 10% error compared to the actual construction volume; therefore, material preparation is necessary. The underwater concrete pouring for bottom sealing is carried out using the vertical tremie method, with the cofferdam's piers being removed sequentially from the downstream side. The radius of influence of the bottom sealing concrete is considered to be 4.5m. During the cofferdam bottom cleaning and sealing processes, attention should be paid to the installation of connecting pipes. Flange steel pipes can be welded to the side of the sheet piles. During the bottom sealing concrete pouring, the internal and external water levels should be kept consistent. Before proceeding with subsequent construction after the bottom sealing concrete has reached the design strength, the connecting pipes should be closed at low tide, and pumping operations should be carried out. The specific steps are as follows:

[0090] S1. Clearing the foundation within the cofferdam:

[0091] S11. After the cofferdam is formed, a long-arm excavator or grab bucket is used for bottom cleaning, with the assistance of a sludge suction machine. The initial cleaning is carried out to about 20cm below the bottom elevation of the sealing layer. After cleaning with a long-arm excavator and grab bucket, mud and sand will settle at the base, which is not conducive to the subsequent sealing. At the same time, there are many obstacles around the steel casing that are difficult to clean. Therefore, after the cofferdam is formed, a second cleaning of the base is required using a sludge suction machine. High-pressure water jetting can be used to clean around the steel casing. No part of the entire cofferdam should be missed. After cleaning, divers need to go underwater to inspect. When inspecting, divers need to pay special attention to all corners, especially the surface of the steel casing and steel sheet piles within the sealing concrete area. Mud and sand must not be adhering to them.

[0092] S12. After the cofferdam foundation is cleared, crushed stone or rubble is thrown into the lower area. In order to avoid the concrete layering caused by the subsequent ball removal, which would result in the failure of the concrete bottom sealing, crushed stone or rubble about 20cm should be thrown in and leveled. The particle size of the crushed stone or rubble should not be too large, so as to reduce the impact of concrete on the base when the ball is removed, which would turn up the mud and sand in the base and cause mud and sand to be mixed between the two layers of concrete during the second ball removal.

[0093] S2. Construction platform erection:

[0094] S21. The bottom sealing platform of the cofferdam for the approach bridge in the water adopts a Bailey beam platform. The bottom sealing platform is in the form of a steel casing with a top elevation of 5.5m, a distribution beam with a height of 0.5m, and a Bailey frame with a height of 1.5m. The bottom sealing guide platform adopts a single-layer standard Bailey beam structure. The Bailey beams serve as the bottom sealing support, and the Bailey beams are connected by standard support frames to form an integral whole. Due to the large volume of concrete, the bottom of the bottom sealing platform pouring frame should be set on the bottom sealing platform corresponding to the steel casing, using the steel casing as the support to meet the stress requirements of the platform erection. The Bailey beam support frames at the corresponding positions should be added according to the actual situation.

[0095] S22. After the platform is erected, the guide pipe positioning frame is set up, and scaffold boards are laid around the positioning frame as a personnel operating platform and construction passage. The scaffold boards are made of 50mm thick wooden boards or steel fixed scaffold boards. To ensure construction safety, the platform is required to be fully covered with scaffold boards except for the guide pipe positioning frame and observation points. Fall protection nets are set up at the observation points. After the bottom platform is set up and the guide pipe is installed in place, guardrails are installed around the platform and safety green nets are hung to close it off to ensure construction safety.

[0096] S23. The on-site distribution beam model and the steel casing reinforcement structure or reserved slot should correspond to each other. The top surface elevation of the four distribution beams should be consistent to ensure that the construction platform is flat.

[0097] S3. Layout of measuring points and conduits:

[0098] S31. Conduit Layout: The bottom sealing conduit uses a conduit diameter of 377 x 6 mm selected based on the maximum bidirectional slab area of ​​the bottom sealing region. The conduit diameter expansion must meet the maximum bidirectional slab area, and the steel pipe length... The length of the guide pipes must meet the elevation requirements from the bottom sealing platform to the bottom sealing ground level. Twelve sets are provided on both the north and south banks. Six sets of guide pipes are required for the bottom sealing of a single cofferdam for the underwater approach bridge. Each guide pipe is lowered one by one using a 75t crawler crane, with chain hoists used for tipping and lifting during construction. Before use, the guide pipes should undergo a watertightness test. The test pressure should be 1.5 times the hydrostatic pressure, and the load should be held for 15 minutes after being pressurized with the calculated water pressure. n. Observe the leakage situation; no leakage is acceptable. To ensure good bonding between the sheet piles, steel casing, and bottom sealing concrete, the guide pipes should be arranged close to the perimeter of the cofferdam and the steel casing. The guide pipes should be laid out with an influence radius of 4.5m. The influence range should be adjusted appropriately according to the concrete slump and initial setting. When the measured influence radius is less than 4.5m, a temporary guide pipe should be added at the observation point between the two guide pipes in the longitudinal direction of the bridge. For blind spots in the construction process due to obstructions such as the bottom sealing platform and steel casing, the ball-pulling point should be appropriately increased. Secondly, ensure the bonding force between the concrete and the steel casing and sheet pile cofferdam. Divers should go underwater to check whether the bottom sealing thickness of the structure meets the requirements. At the same time, when laying the guide pipes, the interference of the cofferdam support, steel casing, and Bailey beam support frame should be considered to facilitate the movement and lifting of the guide pipes.

[0099] S32. To facilitate the observation of the bottom sealing concrete elevation, the location and number of observation points are arranged as follows: Considering the influence of the duct on the radius of concrete bottom sealing diffusion, the highest observation point is arranged at the location of the duct. There are 12 sets of ducts, so there are 12 highest observation points. The observation point is located at the top of the duct. Then, taking the duct as a circle, fixed observation points are arranged at the contact points of the concrete bottom sealing diffusion between two adjacent ducts. The fixed observation points can be arranged according to actual needs. This observation point is the lowest observation point. At the same time, observation points are added at the edge of the steel casing and on the side of the steel sheet pile cofferdam to ensure that the thickness of the bottom sealing concrete in the construction blind spot meets the requirements. In addition, to better ensure the thickness of the bottom sealing concrete around the steel sheet piles of the approach bridge in the water, mobile measuring points are set within 0.9m of the inner circumference of the cofferdam. The mobile measuring points should be measured frequently and closely during the bottom sealing construction.

[0100] S4. Concrete ball extraction and pouring, the specific steps are as follows:

[0101] S41. Selection of ball extraction point: First, the interference from the inner support, steel casing, and Bailey beam support frame of the cofferdam area needs to be considered. After eliminating the interference factors of the inner support, steel casing, and Bailey beam support frame, for larger steel cofferdams, the corresponding areas can be divided according to the area. Ball extraction is carried out symmetrically within the area. Simulation is used to determine whether the concrete is pushed to the other side in an "S" shape on one side of the inner wall of the cofferdam to ensure the continuity of the concrete. Finally, the first extraction position is determined by selecting the corner where the minimum amount of first concrete is required, that is, the place where the space between the steel casing and the inner wall of the cofferdam is the smallest, thus completing the selection of the ball extraction sequence.

[0102] S42. Before removing the ball, the base should be cleaned, the guide tube slots should be installed, and the lower end of the assembled guide tube should be placed on the base according to the base elevation of each guide tube. Check the left and right sides using measuring ropes;

[0103] S43. After completing the base cleaning and guide pipe calibration, pour the first batch of sealing concrete according to the ball removal sequence selected in specific step S41. The storage hopper should be filled to 18m of the pouring frame. 3 3m hopper 3 After the concrete is poured, the ball can be removed and the grouting can begin. A 3m diameter pipe should be installed at the top of the guide pipe. 3 Small hopper, 18m 3 The pouring frame, acting as a storage hopper, is positioned next to the small hopper. The truck-mounted concrete pump delivers the concrete to a height of 18m. 3Inside the pouring frame, first open the pouring frame valve, and concrete flows into the small hopper through the chute until the small hopper is full of concrete. Then close the pouring frame valve. When the pouring frame is almost full of concrete, open the pouring frame valve again and simultaneously pull out the plug in the small hopper to pour the first batch of sealing concrete. In this step, it is important to note that if the total volume of the pouring frame and the small hopper is less than the calculated volume of the first batch of concrete, the ball should be pulled out after the pouring frame and the small hopper are full of concrete. After the ball is pulled out, the truck pump should continuously pump concrete into the pouring frame to ensure that the actual volume of the first batch of concrete meets the calculation requirements.

[0104] S431. During the initial ball extraction, the concrete slump can be appropriately reduced, controlled at 180-200mm. During extraction, the concrete in the storage hopper should be continuously, rapidly, and in a controlled manner fed into the guide pipe without interruption to prevent water ingress into the guide pipe, which could lead to extraction failure. After extraction, the burial depth of the guide pipe should be measured and confirmed. The lower tube can be removed from the left, right, and rear sides;

[0105] S432. After the second guide pipe is removed, concrete should be poured into the first guide pipe once, and then the third guide pipe should be removed. After the third guide pipe is removed, concrete should be poured into the first and second guide pipes once, and then the fourth guide pipe should be removed, and so on, until the last guide pipe in the segmented pouring is removed. The pouring of subsequent guide pipes should be carried out sequentially, and the burial depth of the guide pipes after removal should be controlled within [specific parameters]. Within the specified range, during normal pouring, the interval between concrete pours for the duct that has been removed from the ball should not exceed 30 minutes. If material cannot be supplied within 30 minutes, the duct should be raised and lowered repeatedly several times, with each raising and lowering increment being approximately 0.1 meters. Each duct must guarantee at least one concrete supply per hour. Under normal circumstances, the concrete pouring interval for a duct that has already had its ball removed should not exceed 30 minutes. If material cannot be supplied within 30 minutes, the duct should be raised and lowered repeatedly three times, with each rise and fall approximately 0.1 meters. During normal pouring, the duct's embedment depth should be controlled at... For each conduit, at least one concrete supply must be guaranteed per hour, each time... For guide pipes that have not yet had their balls removed, the guide pipes should be raised to a certain height above the concrete surface at any time, based on the measurement data of the rising height of the bottom concrete surface, to prevent concrete from entering the guide pipes and causing blockage when removing the balls. The height of the bottom of these guide pipes from the concrete surface must be re-determined before removing the balls.

[0106] S44. Pouring of Normal Bottom Sealing Concrete: After the first batch of concrete is successfully poured, the normal pouring stage begins. The hopper is removed, and concrete is poured into the guide pipe using a pump pipe. To ensure a certain burial depth at the guide pipe opening, the guide pipe should not be raised as much as possible while the concrete pouring is progressing smoothly. If it is necessary to raise the guide pipe, it should be raised slowly using a chain conveyor, with the raising height controlled so that the bottom of the guide pipe is 1m below the concrete surface. After raising, concrete pouring continues. The concrete height at the raising point should be frequently measured to prevent leakage of the guide pipe. The actual measured depth should be strictly used as the basis for raising the pipe. The guide pipe should be raised in a timely manner based on the volume of concrete poured and the measured pouring height. Attention should be paid to coordinating the pouring speed of each guide pipe to keep the concrete elevation within the cofferdam approximately the same.

[0107] The main technical effects of this invention are reflected in the following aspects:

[0108] ① The successful application of the cofferdam sealing construction method for deep silt geology has solved the problems of insufficient bearing capacity of deep silt layer sealing and large amount of sealing concrete. It has strong operability and practicality, good overall application prospects, and the construction has become standardized.

[0109] ②Previous methods used the original foundation surface as the reference surface for the bottom elevation of the sealing concrete. By increasing the bond strength between the concrete and the sheet pile cofferdam and steel casing, the requirements for concrete anti-buoyancy and anti-sinking were achieved. However, if this method was used on a large scale, it would lead to an increase in concrete volume and lower safety performance in subsequent construction. On the original basis, further dredging and silt removal were carried out to ensure that there was no silt deposit on the bottom sealing base surface, thus avoiding the mixing of the sealing concrete with the deposited silt and reducing its strength. Furthermore, a new base structure was formed by replacement filling, which increased the bearing capacity of the bottom sealing base surface and increased the bearing safety of subsequent pile cap construction. Overall, this reduced material waste and significantly saved economic costs.

[0110] Of course, the above are just typical examples of the present invention. In addition, the present invention may have many other specific embodiments. All technical solutions formed by equivalent substitution or equivalent transformation fall within the scope of protection claimed by the present invention.

Claims

1. A method for sealing the bottom of a cofferdam in deep silt geology, characterized in that, Includes the following steps: S1. Clearing the foundation within the cofferdam: S11. After the cofferdam is formed, a long-arm excavator or grab bucket is used for bottom cleaning, and a sludge suction machine is used in conjunction to initially clean to the bottom elevation of the sealing base. The elevation is adjusted according to the actual bearing capacity required by the foundation. Therefore, the initial cleaning is done using a long-arm excavator and grab bucket. After cleaning, mud and sand will settle on the base, which is not conducive to the subsequent sealing. At the same time, there are many obstacles around the steel casing that are difficult to clean. Therefore, after the cofferdam is formed, a secondary cleaning of the base is carried out using a sludge suction machine. High-pressure water jetting is used to clean around the steel casing. No part of the entire cofferdam must be missed. After cleaning, divers go underwater to inspect and focus on checking the surfaces of the steel casing and steel sheet piles in various corners and within the sealing concrete area. No mud or sand should adhere to the surfaces of the steel casing and steel sheet piles. S12. After the cofferdam foundation is cleared, crushed stone is dumped in the lower area, and then crushed stone is further dumped and leveled according to the requirements of subsequent concrete filling. S2. Construction platform erection: S21. The bottom sealing platform of the cofferdam for the approach bridge in the water adopts a Bailey beam platform. The bottom sealing platform adopts the form of steel casing plus distribution beam plus Bailey frame. The bottom sealing guide platform adopts a single-layer standard Bailey beam structure, that is, Bailey beams are used as bottom sealing supports. Bailey beams are connected with standard support frames to form a whole. Due to the large volume of concrete, the bottom of the bottom sealing platform pouring frame should be set on the bottom sealing platform corresponding to the steel casing, and the Bailey beam support frames at the corresponding positions should be added according to the actual situation. S22. After the construction platform is erected, the guide pipe positioning frame is set up. Scaffold boards are laid around the positioning frame as a personnel operating platform and construction passage. The scaffold boards are made of 50mm thick wooden boards or steel fixed scaffold boards. To ensure construction safety, the platform is required to be fully covered with scaffold boards except for the guide pipe positioning frame and observation points. Fall protection nets are set up at the measuring points. After the bottom platform is set up and the guide pipe is installed in place, guardrails are installed around the platform and safety green nets are hung to close it off to ensure construction safety. S23. The on-site distribution beam model and the steel casing reinforcement structure should correspond to the reserved slots. The top surface elevation of the four distribution beams should be consistent to ensure that the construction platform is flat. S3. Layout of observation points and conduits: S31. Layout of guide pipes: The guide pipes for sealing the bottom are selected based on the maximum two-way slab area of ​​the sealing area. The diameter of the guide pipes is sufficient to meet the maximum two-way slab area, and the length of the guide pipes is sufficient to meet the height from the bottom sealing platform elevation to the bottom sealing ground. The same number of guide pipes are equipped on both the north and south banks. A 75t crawler crane is used to lower them one by one. During the construction process, chain hoists are used for temporary fixing and lifting. S32. To facilitate the observation of the bottom sealing concrete elevation, the location and number of observation points are arranged as follows: Considering the influence of the tremie pipe on the radius of concrete bottom sealing diffusion, the highest observation point is arranged at the location of the tremie pipe, with the observation point located at the top of the tremie pipe. Then, taking the tremie pipe as a circle, a fixed observation point is arranged at the contact point of the concrete bottom sealing diffusion between two adjacent tremie pipes. This observation point is the lowest observation point. At the same time, observation points are added on the edge side of the steel casing and the side of the steel sheet pile cofferdam to ensure that the thickness of the bottom sealing concrete in the construction blind spot meets the requirements. In addition, to better ensure the thickness of the bottom sealing concrete around the steel sheet piles of the approach bridge in the water, a moving measuring point is set within 0.9m of the inner circumference of the cofferdam. The moving measuring point should be frequently and closely measured during the bottom sealing construction process. S4. Concrete ball extraction and pouring, the specific steps are as follows: S41. Selection of ball extraction point: First, the interference from the inner support, steel casing, and Bailey beam support frame of the cofferdam needs to be considered. After eliminating the interference factors of the inner support, steel casing, and Bailey beam support frame, for larger steel cofferdams, the corresponding areas are divided according to the area. Ball extraction is carried out symmetrically within the area. Simulation is used to determine whether the concrete moves in an "S" shape from one side of the inner wall of the cofferdam to the other side to ensure the continuity of the concrete. Finally, the first extraction position is selected at the point where the space between the steel casing and the inner wall of the cofferdam is the smallest, thus completing the selection of the ball extraction sequence. S42. Before removing the ball, clean the base, install the guide slots, and place the lower end of the assembled guide 20-30cm above the base according to the base elevation of each guide, and check it with a measuring rope. S43. After completing the base cleaning and guide pipe verification, the first batch of sealing concrete is poured according to the ball removal sequence selected in specific step S41. To ensure the first batch of concrete pouring, the pouring frame and hopper need to be filled with concrete before the ball is removed and poured. A small hopper is installed at the top of the guide pipe, and the pouring frame is arranged next to the small hopper as a storage hopper. The truck pump pumps the concrete into the pouring frame. First, the pouring frame valve is opened, and the concrete flows into the small hopper through the chute, filling the small hopper with concrete. Then, the pouring frame valve is closed. When the concrete in the pouring frame is almost full, the pouring frame valve is opened, and the plug in the small hopper is pulled out at the same time to pour the first batch of sealing concrete. S431. When pulling the ball for the first time, the concrete in the storage hopper should be continuously, quickly and controlledly fed into the guide pipe without interruption to prevent water from entering the guide pipe and causing the ball pulling failure. After pulling the ball, the ball pulling of the next guide pipe can be carried out after the burial depth of the guide pipe is confirmed by measurement. Specifically, the ball pulling of the next guide pipe can be carried out after the top elevation of the bottom sealing concrete design meets the thickness of the bottom sealing concrete. S432. After the ball is removed from the second guide pipe, concrete should be poured into the first guide pipe once, and then the ball should be removed from the third guide pipe. After the ball is removed from the third guide pipe, concrete should be poured into the first and second guide pipes once, and then the ball should be removed from the fourth guide pipe, and so on, until the last guide pipe of the segmented pouring is removed. The pouring of each guide pipe shall be carried out in sequence thereafter. It is required that the burial depth of the guide pipe after the ball is removed meets the minimum guide pipe burial depth within the range of 0.3 to 0.4 m. During the normal pouring process of the guide pipes that have been removed, the concrete pouring interval shall not exceed 30 minutes. If the material cannot be supplied after 30 minutes, the guide pipe shall be raised and lowered repeatedly several times, with each raising and lowering range of 0.1 m. Each guide pipe must ensure at least one concrete supply per hour, with each concrete supply volume of 4 to 8 m³. S44. Normal bottom sealing concrete pouring: After the first batch of concrete is successfully poured, the normal pouring stage begins. The hopper is removed, and the pump pipe is inserted into the guide pipe to pour concrete.

2. The method for sealing the bottom of a cofferdam in deep silt geology according to claim 1, characterized in that, In step S31, to ensure good bonding between the sheet piles, steel casing, and bottom sealing concrete, the guide pipes are arranged close to the perimeter of the cofferdam and the steel casing. The guide pipes are laid out with an influence radius of 4.5m, which is adjusted appropriately according to the concrete slump and initial setting. When the measured influence radius is less than 4.5m, a temporary guide pipe should be added at the observation point between the two guide pipes in the longitudinal direction of the bridge. For blind spots in the construction process due to obstruction by the bottom sealing platform and steel casing, the ball-pulling points should be appropriately increased to ensure the bonding force between the concrete and the steel casing and sheet pile cofferdam. Divers will go underwater to check whether the bottom sealing thickness of the structure meets the requirements.

3. The method for sealing the bottom of a cofferdam in deep silt geology according to claim 1, characterized in that, In step S31, a water tightness test should be performed on the conduit before use. The test pressure is 1.5 times the hydrostatic pressure. After pressing in the calculated water pressure, hold the load for 15 minutes and observe for leakage. If there is no leakage, it is qualified.

4. The method for sealing the bottom of a cofferdam in deep silt geology according to claim 1, characterized in that, In step S31, the interference from the cofferdam support, steel casing, and Bailey beam support frame must be considered when laying the conduit to facilitate the movement and lifting of the conduit.

5. The method for sealing the bottom of a cofferdam in deep silt geology according to claim 1, characterized in that, In step S41, the formula for calculating the volume of the ball-lifting concrete in the first batch of bottom sealing concrete pouring is as follows: ； ； in; R is the radius, in meters (m). H2 is the height from the bottom of the conduit to the bottom of the sealing surface, which is 0.3~0.4m according to the specifications, in meters; H1 is the height from the bottom of the guide pipe to the centroid of the concrete cone during the first ball extraction, which is 1 to 1.5m according to the specifications, in meters; d is the diameter of the catheter, in meters (m). γ w The specific weight of the concrete mixture; γ c The unit weight of water inside the cofferdam is KN / m³. H w The height is the distance from the horizontal plane inside the cofferdam to the centroid of the first concrete cone extracted from the spherical pile, in meters. h1 is the height required for the concrete column inside the conduit to balance the external pressure when the conduit is buried at a depth of H1, in meters; V represents the volume of concrete used for the initial bottom sealing concrete pour, measured in meters. 3 .

6. The method for sealing the bottom of a cofferdam in deep silt geological conditions according to claim 1, characterized in that: In step S43, when the total volume of the pouring frame and the small hopper is less than the calculated volume of the first batch of concrete, the pouring frame and the small hopper are filled with concrete and the ball is pulled out. After the ball is pulled out, the truck pump should continuously pump concrete into the pouring frame to ensure that the actual volume of the first batch of concrete meets the calculation requirements.

7. The method for sealing the bottom of a cofferdam in deep silt geology according to claim 1, characterized in that: In step S43, for the conduits that have not yet had their balls removed, the conduits should be raised above the concrete surface at any time based on the measurement data of the rising height of the bottom concrete surface to prevent concrete from entering the conduits and causing blockage when the balls are removed. The height of the bottom of these conduits from the concrete surface must be re-determined before removing the balls.

8. The method for sealing the bottom of a cofferdam in deep silt geological conditions according to claim 1, characterized in that: In step S44, to ensure a certain burial depth at the tremie pipe opening, the tremie pipe should not be lifted as much as possible while the concrete pouring is proceeding smoothly. When it is necessary to lift the tremie pipe, a guide chain should be used to lift it slowly, and the lifting height should be controlled so that the bottom of the tremie pipe is 1m below the concrete surface. After lifting, concrete pouring should continue. At the same time, the concrete height at the lifting point should be frequently measured to prevent the tremie pipe from being lifted out of the concrete. The actual measured depth should be strictly used as the basis for lifting the pipe. The tremie pipe should be lifted in a timely manner based on the concrete pouring volume and the actual pouring height. At the same time, attention should be paid to coordinating the pouring speed of each tremie pipe to keep the concrete inside the cofferdam at approximately the same elevation.

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