Double-wall steel cover box cofferdam construction method

Abstract

The invention discloses a double-wall steel jacket box cofferdam construction method, which belongs to the field of civil engineering, and comprises the following steps: S1, mounting a first section splicing platform and a bottom compartment splicing platform; s2, an inner support, a ring beam, a steel cofferdam and a guide device are transported to a target pier position, and in-situ assembly is conducted through a crawler crane; s3, a hydraulic pump station is selected and assembled; then, a first section of assembly platform bracket is cut off, and a steel pile casing is used as a steel cofferdam sinking hanging system for sinking of the steel cofferdam; s4, after the first section of steel cofferdam is lowered to reach a self-floating state, the temporary inner support is welded, after welding is completed, water is continuously injected into the partition bin, a proper assembling height is kept, and the subsequent steel cofferdams and the temporary inner support are assembled in place; and S5, compartment concrete is poured into the compartments of the steel cofferdam or water is slowly injected for sinking, the steel cofferdam is assisted to sink to the designed bottom elevation through sand pumping of a dredge pipe and a grab bucket, the remaining compartment concrete is poured, foundation cleaning is conducted in the steel cofferdam to the designed base elevation position, and bottom sealing concrete is poured.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering, and in particular, to a construction method for a double-wall steel casing cofferdam. Background Art

[0002] According to different construction and geological conditions, the water retaining structures for deep-water foundations of bridges include various forms such as double-wall steel casing cofferdams, steel sheet pile cofferdams, and reinforced concrete cofferdams. The double-wall steel casing cofferdam is a water retaining and soil retaining structure for bridge pile caps and also serves as a formwork for pile cap construction. It has no bottom and no cover and is generally composed of parts such as blade feet, inner and outer wall plates, diaphragm plates, vertical ribs, circumferential stiffening plates, and stiffening column joints. There are generally two construction methods for double-wall steel casing cofferdams. One is to float the whole in place, and the other is to assemble in situ. The double-wall steel casing cofferdam generally needs to sink through the water flow layer and soil layer, and different sinking methods are adopted according to different soil geological conditions. For sandy pebble strata, the method of sucking mud with a sand suction pipe is generally adopted, and for rock strata, methods such as blasting and impact are generally adopted; after the cofferdam sinks to the design position, underwater blinding concrete is poured to form a water-stop and soil-retaining cofferdam. The steel sheet pile realizes water retaining and soil retaining for deep foundation pits through its own stiffness and tight lock joints.

[0003] With the rapid development of infrastructure fields such as bridges, the requirements for the construction period progress of bridges are getting higher and higher. The construction period of underwater cofferdams and foundations of bridges is often difficult to control due to many uncertain factors. Especially for the mud suction sinking speed of double-wall steel casing cofferdams in soil layers for bridge foundations, after the traditional double-wall steel casing cofferdam sinks and lands, it directly sucks mud and sinks to the design position, and the actual mud suction volume is far greater than the vertical volume under the cofferdam. Especially for strata with good fluidity such as sandy pebbles, mud suction construction is often time-consuming and laborious. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a construction method for a double-wall steel casing cofferdam, including the steps of:

[0005] S1: Loft and position the construction location of the cofferdam above the bored pile, weld platform brackets on the steel casing, and install the first-section assembly platform and the bottom diaphragm assembly platform on the platform brackets. The first-section assembly platform of the cofferdam is set 1.5 m above the water surface;

[0006] S2: Measure and loft the position of the blade feet on the first-section assembly platform, then transport the internal support, ring beam, steel cofferdam, and guiding device to the target pier position, and perform in-situ assembly using a crawler crane; then set the guiding device on the steel casing;

[0007] S3: Select and match a hydraulic pump station according to the requirements of the lifting and lowering speeds and the operating efficiency of the hydraulic pump station; then cut off the brackets of the first-section assembly platform, and use the steel casing as the hanging system for the steel cofferdam to sink, and perform the sinking of the steel cofferdam;

[0008] S4: After the first - stage steel cofferdam is lowered to the self - floating state, water is injected into the compartments of the steel cofferdam to lower the top of the first - stage steel cofferdam to a suitable assembly height. After considering the assembly of the second stage, the circumferential weld is 1 - 1.5 m above the water surface. During the assembly process of each stage of the cofferdam, the temporary internal supports are welded. After the welding is completed, water is continuously injected into the compartments to maintain a suitable assembly height, and the subsequent steel cofferdams and temporary internal supports are assembled in place.

[0009] S5: After the blade foot of the steel cofferdam touches the riverbed surface, partial compartment concrete is poured into the compartments of the steel cofferdam or water is slowly injected to sink it, and the suction pipe + grab bucket is used to assist the steel cofferdam in sinking to the designed bottom elevation. The remaining compartment concrete is poured, the foundation in the steel cofferdam is cleared to the designed base elevation position, and the bottom - sealing concrete is poured. After the bottom - sealing concrete reaches the designed strength, the water is pumped out layer by layer and the temporary internal supports are cut off, and the permanent supports are installed and welded.

[0010] Furthermore, in step S1, a personnel access ladder is set on the side of the steel casing. A platform is set on each steel pipe pile passed by the ladder. The platform uses I20 I - shaped steel as the support corbel and is welded and fixed to the steel pipe pile, and is arranged at intervals of 30 cm along the length direction of the corbel; a 1.2 - m - high railing is set on the outside of the ladder.

[0011] Furthermore, in step S1, HN700×300 I - shaped steel corbels are installed by opening holes on the steel casing. The corbels on both sides of the steel casing are strengthened with 16 - mm - thick steel plates as vertical rib plates. The fillet weld thickness between the vertical rib plates, the steel casing and the corbels is 12 mm, and then the first - stage assembly platform and the bottom - compartment assembly platform are installed on the corbels.

[0012] Furthermore, the installation and welding operation of the corbels is carried out by using a floating box method; the floating box is a sealed box made of waste steel plates from the cofferdam processing factory, with dimensions of 1.5×1.5×1.0 m, and a 1.2 - m - high railing is set on its surface.

[0013] Furthermore, in step S2, a 150t crawler crane is used for assembly.

[0014] Furthermore, in step S2, the guiding device is made of I40b I - shaped steel and 12 - mm - thick steel plates. The guiding device consists of a guiding base and a guiding mechanism arranged on the guiding base; the guiding base is fixed on the surface of the steel casing through the stiffening plates on the inner wall of the cofferdam; a 50 - mm - thick rubber cushion block is provided at one end of the guiding mechanism far from the steel casing.

[0015] Further, in step S3, several steel casing pipes on the long and short sides outside the bearing platform are used as the main force-bearing carriers of the sinking system. A lifting point is arranged at the corresponding position on the inner and outer side walls of the steel cofferdam. The lifting point is provided with a lifting lug corresponding to the top ring frame of the first section of the cofferdam. The lifting lug is made of 10 mm, 16 mm or 20 mm steel plate.

[0016] Further, the lifting point is composed of a lifting lug, a hanging beam, a temporary corbel, a hanging beam, a hanging beam, a jack, and high-strength precision rolled threaded steel from bottom to top; HN700×300 steel hanging beams are arranged by grooving on both sides of the steel casing pipe. A 28b I-beam hanging beam is arranged on the upper part of the hanging beam. A jack is installed on the hanging beam, and a 28b I-beam hanging beam is installed on the jack.

[0017] In summary, the present invention has the following beneficial effects compared with the prior art:

[0018] (1) A steel section ring beam is added at the internal support of the double-wall steel cofferdam, reducing the wall thickness of the cofferdam and dispersing the stress of the cofferdam wall plate. On the premise of ensuring the structural safety of the cofferdam, the steel consumption of the cofferdam is saved.

[0019] (2) The structure at the four corners of the cofferdam adopts the form of concealed columns, effectively enhancing the uneven stress at the four corners of the cofferdam and strengthening the integrity of the cofferdam.

[0020] (3) The internal horizontal ring frame and vertical ribs of the double-wall steel cofferdam are replaced with T-shaped steel instead of angle steel, reducing the steel consumption without affecting the structural stress. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0022] Figure 1 is a plan view of the double-wall steel casing cofferdam provided by the present invention;

[0023] Figure 2 is an elevation view of the double-wall steel casing cofferdam provided by the present invention;

[0024] Figure 3 is a schematic diagram of the lowering system of the double-wall steel casing cofferdam provided by the present invention.

[0025] Among them, the above-mentioned drawings include the following reference numerals:

[0026] 1. Steel cofferdam; 2. Steel concealed column; 3. Ring beam; 4. Bottom compartment; 5. Internal support; 6. Steel casing pipe; 7. Guide device; 71. Guide base; 72. Guide mechanism; 8. Hydraulic pump station; 9. Platform corbel. DETAILED DESCRIPTION OF THE INVENTION

[0027] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The following will describe the present invention in detail with reference to the drawings and in combination with the embodiments.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form can also include the plural form. In addition, it should also be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or their combinations.

[0029] See Figures 1 to 3 As shown, the present invention provides a construction method for a double-wall steel cofferdam, including the steps:

[0030] S1: Loft and position the construction location of the cofferdam above the bored piles, weld platform brackets 9 on the steel casing 6, and install the first-section assembly platform and the bottom compartment 4 assembly platform on the platform brackets 9. The first-section assembly platform of the cofferdam is set 1.5 m above the water surface;

[0031] In actual operation, after the demolition of the drilling platform within the cofferdam is completed, the installation of the first-section assembly platform of the cofferdam is carried out. The first-section assembly platform uses the outermost pile foundation steel casing 6 as the bearing structure. The first-section assembly platform of the steel cofferdam 1 adopts the form of pile foundation steel casing 6 + temporary brackets, and the elevation of the assembly platform is controlled at 1.5 m above the water surface, and the specific elevation is adjusted in real time according to the river water level. To ensure the walking safety of personnel on the assembly platform, I10 steel beams are welded on the outside of the brackets and on the side close to the steel casing 6 as guardrail columns, and three layers of safety ropes are set on the columns.

[0032] The bottom compartment 4 assembly platform uses the steel casings 6 on both sides of the compartment as the bearing structure of the assembly platform, and the compartments are assembled by welding brackets between the casings. A pedestrian passage and guardrails are provided on both sides of the brackets of the bottom compartment 4 assembly platform. The form of the guardrails is the same as that of the first-section assembly platform, and the bottom compartment 4 assembly platform is connected to the first-section assembly platform.

[0033] S2: Measure and loft the position of the blade foot on the first-section assembly platform, then transport the internal support 5, the ring beam 3, the steel cofferdam 1, and the guiding device 7 to the target pier position, and perform in-situ assembly using a crawler crane; the guiding device 7 is arranged on the steel casing 6;

[0034] Precautions during the assembly of the cofferdam:

[0035] ① The assembly support platform at the bottom section of the cofferdam should be firm, and the top plane should be leveled during measurement; deformed steel members should be corrected before assembly;

[0036] ② After the trial assembly of the cofferdam side plates is qualified, the block joints can be welded officially.

[0037] ③ The cofferdam assembly should be carried out symmetrically in zones and the measurement should be reviewed in a timely manner.

[0038] ④ During splicing, the levelness of the horizontal ring plate must be well controlled.

[0039] ⑤ When hoisting the cofferdam, it should be hoisted at the designated position without any arbitrary change and without collision during hoisting.

[0040] In addition to meeting the design requirements, all splicing welds should also be subject to a kerosene test uniformly before launching after the welding of all the large closure welds of the steel cofferdam. Brush the external welds of the shell with lime water. After drying, apply kerosene to the corresponding welds inside. Observe the penetration visually after 15 minutes. If there is penetration to the reverse side, the weld at that place should be removed and re-welded according to the regulations.

[0041] S3: Cut off the bracket 9 of the first-stage assembly platform, and use the steel casing 6 as the hanging system for the sinking of the steel cofferdam 1 to sink the steel cofferdam 1.

[0042] S4: After the first-stage steel cofferdam 1 is lowered to the self-floating state, inject water into the compartments of the steel cofferdam 1 to lower the top of the first-stage steel cofferdam 1 to a suitable assembly height. Considering the circumferential weld is 1 - 1.5 m above the water surface after the second-stage assembly on the top of the first-stage steel cofferdam 1. During the assembly of each stage of the cofferdam, weld the temporary internal support 5. After the welding is completed, continue to inject water into the compartments to maintain a suitable assembly height and assemble the subsequent steel cofferdam 1 and the temporary internal support 5 in place.

[0043] S5: After the blade foot of the steel cofferdam 1 touches the riverbed surface, pour partial compartment concrete or slowly inject water into the compartments of the steel cofferdam 1 to sink it, and assist the sinking of the steel cofferdam 1 to the design bottom elevation by using a suction pipe + grab bucket to draw sand. Pour the remaining compartment concrete, clear the foundation inside the steel cofferdam 1 to the design base elevation position, pour the bottom sealing concrete. After the bottom sealing concrete reaches the design strength, pump out water layer by layer and cut off the temporary internal support 5 and install and weld the permanent support.

[0044] As a preferred embodiment, in step S1, in order to facilitate personnel to go up and down the first section assembly platform, a personnel access ladder is set on the side of the steel casing 6 of the construction platform outside the cofferdam. The ladders are respectively set on the steel pipe pile side of the long side of the cofferdam. The ladder section beam adopts 22b channel steel, and the step adopts ∠10 angle steel. In order to ensure the stability of the stairs, a platform is set on each steel pipe pile passed by the ladder. The platform adopts I20 I-beam as a supporting bracket and is welded and fixed with the steel pipe pile. The platform adopts I20 I-beam and is arranged at intervals of 30cm along the length direction of the bracket. A 1.2m high railing is set on the outside of the ladder, and the railing is connected to the ∠10 angle steel by welding. The railing is set with 3 horizontal rails, which are evenly distributed with 48mm×3.5mm steel pipes, and the vertical columns are made of 100mm×100mm I-beams, with holes in the middle, and the steel pipes are inserted and welded with the I-beams. The bottom adopts 0.5mm thick steel plate and an 18cm high skirting board is set.

[0045] As a preferred embodiment, in step S1, the assembly platform is installed with HN700×300 I-steel brackets by drilling holes on the steel casing 6. The brackets are reinforced with 16mm steel plates as vertical ribs on both sides of the steel casing 6. The thickness of the fillet welds between the vertical ribs, the steel casing 6 and the brackets is 12mm. The assembly platform of the bottom compartment 4 is similar to the assembly platform of the first cofferdam. Holes are drilled on the steel casing 6 on both sides of the bottom compartment 4 to install HN700×300 I-steel brackets.

[0046] When installing the assembly platform bracket 9, the operators use the pontoon to perform welding operations. The pontoon is made of discarded steel plates from the cofferdam processing plant into a sealed box. The size of the pontoon is 1.5×1.5×1.0m, and a 1.2m high railing is set on the pontoon. The pontoon is hoisted into the water by a crawler crane. After entering the water, it is observed whether it can float steadily on the water surface. Then, the pontoon is connected to the steel pipe piles of the working platform with a guy rope to prevent water impact. The operators climb up and down the platform and the pontoon by climbing the ladder, and use the pontoon to row to the working position, weld a temporary hanging point on the steel casing 6, and use the guy rope to fix the pontoon to the steel casing 6, and then perform welding operations.

[0047] As a preferred embodiment, in step S2, a 150t crawler crane is used for assembly; before the cofferdam is hoisted, when the cofferdam is processed in the processing yard, lifting points are set at the cofferdam wall plate and the top ring rib, and a total of 8 lifting points are set for each cofferdam to meet the horizontal lifting and vertical lifting conditions. When the cofferdam is lifted vertically. Four vertical lifting points are set at the inner and outer ring frames at the top of each cofferdam, and the lifting points are set at 2.2m on both sides of the center line of each cofferdam. The vertical lifting lugs are made of 22mm steel plates. The lifting lugs are fully welded to the cofferdam wall plate and channel steel at the top of each cofferdam, and a 4cm hole is opened in the lifting lug to hang the shackle. The shackle is connected to the lifting lug and the wire rope for vertical lifting. Due to the large weight of a single cofferdam, a trial lift is carried out before lifting. After the cofferdam is lifted by 5cm, the state of the wire rope and the sling is observed, and the lifting is carried out after it is stable.

[0048] When the cofferdam is transported from the processing plant to the pier position and unloaded from the flatbed truck, a horizontal hoisting method is adopted. During the processing of the cofferdam, 4 lifting points are set at the outer wall plate. The lifting points are symmetrically arranged on the channel steel of the cofferdam ring frame 2.2 m on both sides of the center line of each cofferdam. The lifting lugs are made of 22-mm steel plates. Since the lifting points need to pass through the wall plate, the wall plate needs to be perforated according to the position of the lifting points during the assembly of the wall plate. The lifting lugs are passed through the wall plate. After the cofferdam is hoisted in place, the lifting lugs are cut off, and the holes at the wall plate are plugged. During horizontal hoisting, shackles are used to connect with the lifting lugs and steel wire ropes, and the cofferdam is unloaded onto the platform, and square timbers are laid on the platform for support.

[0049] When the cofferdam is hoisted, there is a situation where the cofferdam flips. When the cofferdam is changed from horizontal hoisting to vertical hoisting, the main hook is hung on the top lifting lug of the cofferdam through the sling shackle, and the auxiliary hook is hung on the lifting lug of the bottom horizontal hoisting. The conversion of the steel cofferdam 1 is carried out in cooperation with the main hoisting cable and the auxiliary hoisting cable. By raising the main hoisting cable and lowering the auxiliary hoisting cable, as the lowering degree progresses, when the cofferdam is in a vertical state, the auxiliary hoisting cable is released. After erection, the steel cofferdam 1 is hoisted to the first-stage assembly platform.

[0050] As an optimization, in step S2, the guiding device 7 is made of I40b I-beams and 12-mm steel plates. The guiding device 7 consists of a guiding base 71 and a guiding mechanism 72 arranged on the guiding base 71. The guiding base 71 is fixed on the surface of the steel casing 6 through the stiffening plates on the inner wall of the cofferdam. One end of the guiding mechanism 72 away from the steel casing 6 is provided with a 50-mm rubber cushion block to increase the contact area with the steel cofferdam 1 and ensure that the wall plate is not damaged. To prevent the casing from being offset too much due to pile foundation construction, which may cause an obstacle to the lowering of the cofferdam by the guiding frame, before the guiding installation, the offset and inclination of the steel casing 6 where the guiding device 7 is located are measured, and the guiding device 7 is appropriately processed according to the offset distance to ensure the smooth sinking of the cofferdam.

[0051] As an optimization, in step S3, several steel casings 6 on the long and short sides outside the pile cap are used as the main force-bearing carriers of the sinking system. A set of lifting points is set at the corresponding hanging beam positions in the vertical direction of the steel cofferdam 1, that is, one lifting point is set at the corresponding positions of the inner and outer wall plates respectively. The lifting points are provided with lifting lugs corresponding to the top ring frame of the first-stage cofferdam. The lifting lugs are made of 10-mm, 16-mm, and 20-mm steel plates. Each lifting point consists of a lifting lug, a hanging beam, a temporary corbel (with the same structure as the hanging beam), a hanging beam, a hanging beam, a jack, and a high-strength threaded steel bar from bottom to top. HN700×300 steel hanging beams are arranged by grooving on both sides of the steel casing 6. A 28b I-beam hanging beam is arranged on the upper part of the hanging beam. Jacks are installed on the hanging beam, and a 28b I-beam hanging beam is installed on the jack.

[0052] Select the hydraulic pump station 8 according to the requirements of hoisting and lowering speeds, and also consider the operating efficiency of the hydraulic pump station 8. Take the example of selecting 4 hydraulic pump stations 8 with a flow rate of 80 L / min, where the hoisting speed is 8 m / h and the lowering speed is 6 m / h when driving 8 hoisting cylinders. Each hydraulic pump station 8 controls 2 hoisting cylinders, and the hydraulic oil circuits are independent of each other and can independently control the pressure and flow rate. Adopt a decentralized control mode, where the main controller, sub-controllers, and sensor modules are interconnected through a bus network. The control system mainly includes 1 main controller, 8 sets of cylinder sensors, 16 sets of anchor sensors, 8 sets of pressure sensors, 8 sets of long-distance sensors, and electrical accessories such as wires and cables. The electric control system processes and stores various monitoring data.

[0053] To ensure the safe and smooth sinking of the cofferdam, before the official lowering of the cofferdam, a hoisting test is carried out on the overall cofferdam. That is, simultaneously lift 8 jacks to make the cofferdam 5 cm away from the assembly platform and hold the load for several minutes to check if there are any abnormalities in the cofferdam.

[0054] Lowering operation steps: Loosen the double nuts of the hanging beam 2, jack up 15 cm, then tighten the double nuts of the hanging beam 2, the jack continues to jack up 1 cm, the jack is stressed, then loosen the double nuts of the hanging beam 3, and 8 jacks return oil synchronously, and the cofferdam is lowered. Repeat the above process to complete the entire cofferdam lowering operation.

[0055] The above is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A double-wall steel box cofferdam construction method, characterized in that: Includes steps: S1: Locate and locate the construction position of the cofferdam above the bored piles, weld the platform bracket (9) on the steel casing (6), install the first section assembly platform and the bottom compartment (4) assembly platform on the platform bracket (9), and the first section assembly platform of the cofferdam is set at 1.5m above the water surface; S2: measuring and setting out the position of the blade foot on the first assembly platform, then transporting the inner support (5), the ring beam (3), the steel cofferdam (1), and the guide device (7) to the target pier position, and assembling them in situ using a crawler crane; then setting the guide device (7) on the steel casing (6); S3: Select the hydraulic pump station (8) according to the speed requirements for lifting and lowering and the operating efficiency of the hydraulic pump station (8); then cut off the first section of the assembly platform bracket (9), and use the steel casing (6) as the steel cofferdam (1) sinking and hanging system to sink the steel cofferdam (1); S4: After the first section of the steel cofferdam (1) is lowered to a self-floating state, water is injected into the compartment of the steel cofferdam (1) to lower the top of the first section of the steel cofferdam (1) to a suitable assembly height. After the second section is assembled, the circumferential weld of the top of the first section of the steel cofferdam (1) is 1-1.5 m away from the water surface. During the assembly process of each section of the cofferdam, the temporary inner support (5) is welded. After the welding is completed, water is continuously injected into the compartment to maintain a suitable assembly height, and the subsequent steel cofferdams (1) and the temporary inner support (5) are assembled in place. S5: After the blade of the steel cofferdam (1) touches the riverbed, pour part of the compartment concrete into the compartment of the steel cofferdam (1) or slowly inject water to sink it, and use the suction pipe + grab bucket to pump sand to assist the steel cofferdam (1) to sink to the designed bottom elevation, pour the remaining compartment concrete, clear the foundation inside the steel cofferdam (1) to the designed bottom elevation, pour the bottom sealing concrete, and after the bottom sealing concrete reaches the designed strength, pump out water layer by layer, cut off the temporary internal support (5), and install the welded permanent support.

2. The double-wall steel box cofferdam construction method according to claim 1 is characterized in that: In step S1, a ladder for personnel passage is arranged on the side of the steel casing (6), and a platform is arranged on each steel pipe pile that the ladder passes through. The platform uses I20 I-beams as supporting brackets and is welded and fixed to the steel pipe piles, and is arranged at intervals of 30 cm along the length direction of the brackets; a 1.2m high railing is arranged on the outside of the ladder.

3. The double-wall steel box cofferdam construction method according to claim 1 is characterized in that: In step S1, a hole is opened on the steel casing (6) to install an HN700×300 I-beam corbel. The corbel is reinforced with 16 mm steel plates as vertical ribs on both sides of the steel casing (6). The thickness of the fillet weld between the vertical ribs, the steel casing (6) and the corbel is 12 mm. Then, the first section assembly platform and the bottom bulkhead (4) assembly platform are installed on the corbel.

4. The double-wall steel box cofferdam construction method according to claim 3 is characterized in that: The installation and welding of the corbels are carried out by means of a pontoon; the pontoon is a sealed box made of discarded steel plates from a cofferdam processing plant, with dimensions of 1.5×1.5×1.0m, and a 1.2m high railing is provided on its surface.

5. The double-wall steel box cofferdam construction method according to claim 1 is characterized in that: In step S2, a 150t crawler crane is used for assembly.

6. The double-wall steel box cofferdam construction method according to claim 1 is characterized in that: In step S2, the guide device (7) is made of I40b I-beam and 12mm steel plate, and the guide device (7) is composed of a guide base (71) and a guide mechanism (72) arranged on the guide base (71); the guide base (71) is fixed to the surface of the steel casing (6) through a stiffening plate on the inner wall of the cofferdam; and a 50mm rubber pad is provided at one end of the guide mechanism (72) away from the steel casing (6).

7. The double-wall steel box cofferdam construction method according to claim 1 is characterized in that: In step S3, a plurality of steel casings (6) on the long and short sides of the outer side of the pedestal are used as the main load-bearing bodies of the sinking system, and a hanging point is set at the corresponding position of the inner and outer side wall panels of the steel cofferdam (1). A hanging ear is set at the top ring frame of the first section of the cofferdam corresponding to the hanging point, and the hanging ear is made of 10mm, 16mm or 20mm steel plate.

8. The double-wall steel box cofferdam construction method according to claim 7 is characterized in that: The hanging point is composed of a hanging lug, a hanging beam, a temporary bracket, a hanging beam, a hanging beam, a jack, and a precision-rolled threaded steel bar from bottom to top; HN700×300 steel hanging beams are arranged in grooves on both sides of the steel casing (6), a 28b I-beam hanging beam is arranged on the upper part of the hanging beam, a jack is installed on the hanging beam, and a 28b I-beam hanging beam is installed on the jack.

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