A construction method for double-wall steel cofferdam under complex conditions

Abstract

The application provides a double-wall steel cofferdam construction method suitable for complex conditions, which comprises the following steps: S1, splitting the double-wall steel cofferdam into block units; S2, inserting and driving steel pipe piles; S3, assembling the first section of the steel cofferdam; S4, setting up jacks to form a bearing system for bearing the steel cofferdam; S5, dividing the steel cofferdam into multiple sections, and sequentially assembling and lowering the multiple sections of the steel cofferdam; and when the steel cofferdam is lowered, pouring concrete into the wall bin to make the steel cofferdam sink to a preset position, and continuing to suck mud to sink after the steel cofferdam is bedded, so that the construction efficiency is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of steel cofferdam construction technology, specifically relating to a construction method for double-walled steel cofferdams suitable for complex conditions. Background Technology

[0002] A cofferdam is a temporary retaining structure built in water conservancy projects to construct permanent water facilities. Its function is to prevent water and soil from entering the construction site of the structure, so as to facilitate drainage, excavation of the foundation pit, and construction of the structure within the cofferdam.

[0003] In the construction of existing bridge foundations in water, double-walled steel cofferdams are often used. However, the traditional method of lowering the cofferdam by suction is difficult to achieve. The cofferdam is prone to deviation during construction, resulting in low construction efficiency. In addition, when constructing cofferdams next to existing bridges, it is easy to disturb the old bridge and affect the stability of the old bridge foundation.

[0004] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art. This invention designs a construction method for double-walled steel cofferdams suitable for complex conditions.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A construction method for double-walled steel cofferdams suitable for complex conditions includes:

[0008] Step S1: The double-walled steel cofferdam is broken down into block units and transported to the stockpiling platform via the river.

[0009] Step S2: Lay out and position the steel retaining piles, and drive the steel pipe piles using the full casing drilling method;

[0010] Step S3: Weld brackets onto the steel casing to serve as a splicing platform for constructing the steel cofferdam. The first section of the steel cofferdam is then assembled on the splicing platform.

[0011] Step S4: Install the lowering system on the steel casing and set up jacks on the six steel casings around the cofferdam to form the load-bearing system for the corresponding steel cofferdam.

[0012] Step S5: Use the lowering system to lift the first section of the steel cofferdam, detach it from the assembly platform and level it. Before lowering the first section of the steel cofferdam, mark the scale lines on the steel strands. Lower the six jacks simultaneously until the first section of the steel cofferdam stops sinking and reaches self-floating balance. Then pour the double-walled concrete of the cofferdam to put the first section of the cofferdam into the water.

[0013] Step S6: Using the first section of the steel cofferdam as a reference, assemble the second section of the steel cofferdam. After the assembly is completed, pour concrete symmetrically and evenly into the double-walled chamber of the cofferdam to make the cofferdam sink until the second section of the steel cofferdam sinks to the preset position, so that the bottom cutting edge of the first section of the steel cofferdam enters the soil.

[0014] Step S7: Assemble the third section of the steel cofferdam on top of the second section of the steel cofferdam. After the third section of the steel cofferdam is assembled, pour concrete into the double-walled chamber of the cofferdam symmetrically and evenly to make the cofferdam sink so that the bottom cutting edge of the first section of the steel cofferdam is in the gravelly soil layer. Pour the remaining concrete into the double-walled chamber of the cofferdam in multiple batches. At the same time, start the excavation and soil removal operation to assist the steel cofferdam in sinking.

[0015] Step S8: The fourth section of the steel cofferdam is spliced ​​and lowered using the method in step S7. After the bottom cutting edge of the first section of the steel cofferdam is in the completely weathered sandy mudstone, a platform is built on the cofferdam. A mud mixer is used to loosen the soil layer, and a mud suction machine is used to remove soil while divers remove rocks for the sinking operation.

[0016] Step S9: Install single-wall steel cofferdams in sections on the fourth section of the steel cofferdam. After confirming that the cofferdam has landed, carry out mud suction and sand dredging.

[0017] Step S10: The bottom of the cofferdam is sealed by multi-point underwater grouting using vertical ducts. After the bottom sealing concrete reaches more than 90% of the design strength, water is pumped out from inside the cofferdam.

[0018] Step S11: As water is pumped out of the cofferdam, the inner support of the cofferdam is installed layer by layer. After the inner support is installed, the pile head concrete is cut. After the cutting is completed, the foundation construction is carried out.

[0019] Preferably, the steel cofferdam is divided into 18 sections in the circumferential direction. The first section of the steel cofferdam to the fourth layer of the steel cofferdam are all composed of inner wall plates and outer wall plates. A horizontal ring plate and a partition plate are set between the two layers of steel walls. The horizontal ring plate is a U-shaped or C-shaped plate set between the two layers of steel walls. Vertical ribs are set on the inner walls of the two layers of steel walls. The horizontal ring plate is slotted at the position of the vertical ribs and the vertical ribs are welded together with the horizontal ring plate.

[0020] Horizontal inner diagonal braces are welded onto the horizontal ring plate. The horizontal inner diagonal braces are distributed in a V-shape, and their two ends are supported between the two layers of steel walls.

[0021] The partition plates are spaced apart between the two layers of steel walls. The length of the partition plates is adapted to the corresponding steel cofferdam segments. The partition plates are reinforced with stiffening ribs on both sides.

[0022] Preferably, a cutting edge is provided below the first section of the cofferdam, with the cutting edge tip angle being 45°. The inner and outer wall plates of the cutting edge are thickened, and a cutting edge reinforcement is provided inside the cutting edge. The cutting edge is then filled with fine stone concrete to ensure it is dense.

[0023] Preferably, each segment has multiple internal and external connecting pipes distributed circumferentially. The internal and external connecting pipes pass through the two layers of steel walls of the steel cofferdam. The steel pipes are equipped with connecting flanges and removable steel plate plugs at the ends of the steel pipes that extend into the cofferdam.

[0024] At least the inner steel wall has corresponding internal support points reinforced with steel plates.

[0025] Preferably, a guiding device is provided between the steel casing and the cofferdam. The guiding device is a guide pile, which is filled with concrete. A lifting point is set on the side of the guide pile. In use, the guide pile is horizontally suspended between the inner wall of the steel cofferdam and the steel casing by a steel wire rope, and the steel wire rope is attached to the top of the steel cofferdam.

[0026] Preferably, after the existing bridge is riprapped, a row of interlocking steel pipe piles is driven into the existing bridge abutment on the side closest to the new abutment to protect the existing abutment.

[0027] Preferably, before assembling the first section of the steel cofferdam, the assembly outline and the assembly connection lines between each adjacent block are laid out on the assembly platform, and positioning codes are welded on the outer outline edge to control the planar position of the lower edge of the steel cofferdam.

[0028] During the assembly of the first section of the steel cofferdam, temporary brackets were welded at the support points to serve as support points for the steel cofferdam, and temporary supports were also welded inside the steel cofferdam.

[0029] The first section of the steel cofferdam is assembled starting from the two corners, and then assembled clockwise at the two corners.

[0030] Preferably, the lower system includes hydraulic jacks, a lowering beam fixed to the steel casing, and steel strands. The lowering beam is installed on the top of the steel casing, the jacks are installed on the lowering beam, and the steel strands pass through the lowering beam and are anchored to the lifting points on the side wall of the cofferdam. The lifting and lowering points of the steel cofferdam are all welded inside the cofferdam partition plate, and their positions correspond one-to-one with the lifting points set on the top surface of the steel casing.

[0031] Preferably, the steel cofferdam is divided into multiple segments around its circumference by wall panels. When pouring concrete, a symmetrical pouring method is adopted, and the elevation difference between the top surfaces of the concrete filling of adjacent compartments should not exceed 1m.

[0032] Preferably, a total station is used to monitor the attitude of the cofferdam in real time during the sinking process. When the cofferdam tilts or deviates, an additional ring of guide piles is added to the upper layer of the cofferdam to form upper and lower support points to maintain the attitude of the cofferdam.

[0033] The deviation of the steel cofferdam is adjusted by pouring concrete into the compartment. If the deviation still exists after the concrete is poured, water or sand will be poured into the corresponding compartment to correct the deviation.

[0034] Beneficial effects: The steel cofferdam is divided into multiple sections, which are assembled and lowered sequentially. During lowering, concrete is poured into the wall chamber to make the cofferdam sink to the preset position. After the cofferdam lands, the sludge is sucked down to continue sinking, which effectively improves the construction efficiency. Attached Figure Description

[0035] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0036] Figure 1 This is a schematic diagram of the distribution of steel cofferdams in a specific embodiment provided by the present invention;

[0037] Figure 2 This is a schematic diagram of the steel cofferdam construction in a specific embodiment provided by the present invention;

[0038] Figure 3 for Figure 1 Enlarged view of point A in the middle;

[0039] Figure 4 This is a simplified cross-sectional view of the steel casing in a specific embodiment provided by the present invention;

[0040] Figure 5 This is a simplified structural diagram of the cutting head in a specific embodiment of the present invention;

[0041] Figure 6 This is a simplified structural diagram of the guide pile in a specific embodiment of the present invention.

[0042] In the diagram: 1. Steel casing; 2. Steel cofferdam; 3. Steel pipe pile; 4. Existing bridge; 5. Trestle platform; 6. Guide pile; 101. Alloy cutting edge; 102. Reinforcing ring; 103. Reinforcing ring; 104. Backing steel plate; 105. Fixing ring; 106. Extension section; 107. Base; 108. Cutting tool holder; 201. Cutting foot; 202. First section of steel cofferdam; 203. Second section of steel cofferdam; 204. Third section of steel cofferdam; 205. Fourth section of steel cofferdam; 206. Single-wall steel cofferdam; 207. Outer wall plate; 208. Inner wall plate; 209. Horizontal ring plate; 210. Horizontal inner diagonal bar; 211. Vertical rib; 212. Divider plate. Detailed Implementation

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0044] In the description of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. The terms "connected" and "linked" used in this invention should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through intermediate components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0045] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0046] like Figure 1-6 As shown, a construction method for double-walled steel cofferdams under complex conditions is described. The double-walled steel cofferdam 2 is a fully welded watertight structure, comprising four sections of double-walled cofferdam and one section of single-walled cofferdam. The main pier bored pile construction utilizes an erected trestle platform 5.

[0047] The specific construction steps include: Step S1, dividing the double-walled steel cofferdam 2 into block units, connecting the blocks of the steel cofferdam 2 with welded seams, and transporting them to the stockpiling platform via the river.

[0048] Step S2 involves laying out and positioning the steel retaining piles, then driving the steel pipe piles three times using the full casing drilling method. A cutting drill bit reinforced at the bottom of the casing is used to cut and break up the boulders directly below the casing. Simultaneously, a full-rotation drilling rig applies downward pressure to the casing to improve the cutting efficiency. Due to the protective effect of the casing, the broken boulders will not cause collapse of the surrounding boulder area, and the amount of boulder removal work is controllable. The broken boulders inside the steel casing are removed by excavating inside the steel casing using a grab bucket or rotary drilling rig.

[0049] The steel casing 1 consists of multiple sections. When extending it, a ring of steel plates 104 are first applied around the joint on the outer wall of the casing. The upper and lower casing sections are then aligned and positioned. All contact surfaces between the steel plates 104 and the outer wall of the casing are fully welded and secured. During this process, the crane must not unhook the second casing section. A pulling force is applied to the top of the casing to ensure its verticality and prevent it from tipping over during the connection process, thus avoiding safety accidents. After all the steel plates 104 are welded, the joint of the casing is fully welded to ensure welding quality and prevent detachment during drilling.

[0050] Step S3: Weld brackets onto the steel casing 1, and weld an operating platform onto the brackets to serve as a splicing platform for constructing the steel cofferdam 2. Assemble the first section of the steel cofferdam 202 on the assembly platform. When the inner and outer wall steel plates of the first section of the steel cofferdam 202 cannot be butt welded, lap welding or plate welding is allowed, but full welding is required, and the reliability of the fully welded watertight structure must be guaranteed.

[0051] Step S4: Install the lowering system on the steel casing 1. Install the hoisting equipment on the steel casing 1 according to the construction design drawings to prepare for lowering the steel cofferdam. Steel sections are used as distribution beams on the steel casing 1. Jacks are set on the six steel casings 1 around the cofferdam to form the corresponding load-bearing system for the steel cofferdam; before the cofferdam is lowered into the water, its weight is entirely borne by the jacks.

[0052] Step S5: Using the lowering system, lift the first section of the steel cofferdam 202, detaching it 0.5m from the assembly platform. After standing for 30 minutes, level it and remove the portion of the temporary assembly platform that obstructs the lowering of the steel cofferdam. Retain the section between the steel casing 1 and the inner wall of the cofferdam as a platform for future assembly and welding. Weld the outer side using a suspended basket method, and finally lower the entire cofferdam.

[0053] Before lowering the first section of the steel cofferdam 202, mark the scale lines on the steel strands. Adjust the verticality of the cofferdam every 15cm or so to ensure a smooth lowering process.

[0054] Six hydraulic jacks were lowered simultaneously until the first section of the steel cofferdam, 202, stopped sinking and reached self-buoyancy equilibrium. Then, the double-walled concrete of the cofferdam was poured to submerge the first section. As the depth of the cofferdam increased and buoyancy improved, coupled with the impact of the water flow, the cofferdam became unstable. To ensure the assembly of the second section, the final submerged state of the cofferdam was 5.5 meters, with 3 meters above the water surface.

[0055] The steel cofferdam has three lifting points on each side, and each lifting point consists of a 350t jack and a lowering beam. The lifting rod uses 14 steel strands.

[0056] Step S6: Using the first section of steel cofferdam 202 as a reference, assemble the second section of steel cofferdam 203. The assembly sequence of the second section of steel cofferdam 203 is the same as that of the first section of steel cofferdam 202. After the cofferdam wall panels are hoisted into place, weld the joint between the cofferdam and the top surface of the first section. First, align the partition plate 212 inside the upper section of cofferdam with the lower section, then attach the cofferdam wall panels to the connecting plate on the top surface of the bottom section wall panels, ensuring that the inclination angles of the upper and lower sections of the cofferdam are the same to ensure the straightness of the cofferdam. After alignment, weld a clamping plate to the top surface of the lower section of cofferdam to fix the position of the upper section of cofferdam, and then weld and fix the partition plate 212 of the cofferdam. After the cofferdam wall panels are assembled and fixed, the welders can begin welding the vertical joints of the cofferdam wall panels.

[0057] After the assembly is completed, concrete is poured symmetrically and evenly into the double-walled chambers of the cofferdam. At this point, the first section of the cofferdam is submerged 5.5m in the water, and the cutting edge 201 is in the water layer, in a self-floating state. Concrete is poured symmetrically and evenly into the double-walled chambers of the cofferdam, causing the cofferdam to sink slowly and evenly. This continues until the second section of the steel cofferdam 203 sinks to the preset position, specifically, so that the top of the second section of the cofferdam is 3m above the water surface, and the cutting edge 201 at the bottom of the first section of the steel cofferdam 202 is buried in the soil.

[0058] Step S7: Assemble the third steel cofferdam 204 on top of the second steel cofferdam 203. The unit division and assembly steps of the third steel cofferdam 204 are the same as those of the first and second steel cofferdams. During assembly, pay attention to reserving the bottom support for the inner wall plate 208 for easy installation later. After the third steel cofferdam 204 is assembled, pour concrete symmetrically and evenly into the double-walled chamber of the cofferdam to make the cofferdam sink, so that the top of the third cofferdam is 2.5m above the water surface, and the bottom cutting edge 201 of the first steel cofferdam 202 is in the gravelly soil layer.

[0059] In this embodiment, the flatness of the top surface of the cofferdam is measured every 50cm of sinking. If tilting or deviation occurs, the cofferdam wall is adjusted by locally pouring concrete into the cofferdam wall. After horizontal adjustment, concrete is poured again to sink the cofferdam by 50cm, and this process is repeated.

[0060] The remaining concrete was poured into the double-walled chambers of the cofferdam multiple times. Each subsequent pour was allowed to solidify completely before the next was poured to prevent excessive pouring that could deform the cofferdam walls. Simultaneously, excavation and soil removal operations began to assist in the sinking of the steel cofferdam.

[0061] If the concrete inside the cofferdam reaches the designed height during this process, water needs to be poured into the cofferdam to increase its weight.

[0062] Step S8: The steps for dividing and assembling the fourth steel cofferdam unit 205 are the same as those for the first, second, and third steel cofferdams. The fourth steel cofferdam 205 is spliced ​​and lowered using the method in step S7. First, the cofferdam is lowered by pouring concrete into the silo. If the concrete in the silo reaches the design height, water needs to be poured into the silo to increase the weight of the cofferdam.

[0063] After the bottom cutting edge 201 of the first steel cofferdam 202 is in the completely weathered sandy mudstone, a platform is built on the cofferdam, and a mud mixer is used to loosen the soil layer. A mud suction machine is used to remove soil and divers cooperate to remove rocks for sinking operations.

[0064] Step S9: Install single-wall steel cofferdam 206 on the fourth section of steel cofferdam 205 in the same order as the fourth section of cofferdam. After the cofferdam is in place, temporarily fix the top of the cofferdam to the steel casing 1. After confirming that the cofferdam is in place, carry out mud suction and sand pumping. Analyze the stress situation of the cofferdam when it is lowered into place. The cofferdam cannot sink into place by its own weight. It is necessary to take auxiliary sinking measures to sink the cofferdam into place.

[0065] Step S10: The cofferdam bottom sealing is carried out by multi-point underwater grouting using vertical ducts. The cofferdam bottom sealing construction process is as follows: construction preparation → cleaning of the outer wall of the casing and the inner wall of the cofferdam → erection of the bottom sealing platform → installation of ducts → layout of measuring points → placement of hoppers → preparation of materials at the concrete plant and preparation for concrete production → grouting of underwater concrete → measuring the elevation of the top surface of the concrete → completion of the entire bottom sealing.

[0066] After the bottom sealing concrete reaches more than 90% of its design strength, water will be pumped out from inside the cofferdam.

[0067] Step S11: As water is pumped out of the cofferdam, the internal supports are installed layer by layer. The internal supports use A630mm and A800mm steel pipes. For the underwater installation, the base supports are prepared in advance when the cofferdam is lowered. Divers descend into the water to weld pads and joints onto the inner wall of the cofferdam, and then install the underwater internal support steel pipes. The steel pipe internal supports are bolted to the pads. 20mm steel plates are used to make pads and joints to connect the cofferdam wall panels to the internal supports. After the underwater parts are installed, water is pumped out of the cofferdam, and the above-water parts are installed sequentially from bottom to top.

[0068] After the internal support is installed, the pile head concrete is cut, and then the pile cap is constructed.

[0069] Before cutting off the casing, use a crawler crane to hold the top of the casing with a little force to prevent the casing from affecting the pile head after it is cut off, and cut it in sections.

[0070] In this embodiment, the portion above the riverbed can be dismantled and recycled after construction. The steel cofferdam is divided into an above-water cutting section and an underwater cutting section, with the water level at the time of cutting as the dividing line. The above-water cutting section is, in principle, cut along the original vertical joints, first cutting the horizontal welds, then the vertical welds. The cofferdam is dismantled from top to bottom and from one side to the other. The cofferdam dismantling begins with the downstream side plate on the east side and proceeds clockwise.

[0071] In this embodiment, the steel casing 1 is reinforced by setting a reinforcing ring 102 with a height of 50cm, a thickness of 4cm, and a diameter of 2.8m at the bottom of the casing. At the same time, a reinforcing ring 102 with a height of 15cm, a thickness of 1cm, and a diameter of 2.764m is set every meter on the inner wall of the original steel casing 1. This increases the strength of the contact surface between the bottom of the steel casing 1 and the rock, preventing deformation of the casing bottom during rotary drilling.

[0072] Specifically, such as Figure 1-2 As shown, the lower end of the steel casing 1 is provided with multiple cutting heads. The cutting heads extend along the axial direction of the steel casing 1. The multiple cutting heads are evenly distributed around the circumference of the steel casing 1, and the cutting edge of the cutting head points to the tangential direction of the steel casing 1. In this embodiment, the diameter of the steel casing 1 is 2800mm, and the distance between two adjacent cutting heads is 130mm.

[0073] A reinforcing ring 102 is provided at the bottom opening of the steel casing 1. The reinforcing ring 102 is located on the inner wall of the steel casing 1, and its outer diameter is adapted to the inner diameter of the steel casing 1. The reinforcing ring 102 has a height of 50cm and a thickness of 4cm in the axial direction of the steel casing 1. The lower edge of the steel casing 1 is close to the cutting head, and can even touch the end of the cutting head, and is welded and fixed to the cutting head. The addition of a cutting head at the bottom of the steel casing 1 is used to break up underwater rocks.

[0074] To further enhance the strength of the steel casing 1, multiple reinforcing rings 103 are provided on the inner wall of the steel casing 1, equidistantly distributed along its axial direction. The outer diameter of the reinforcing rings 103 is adapted to the inner diameter of the steel casing 1. The reinforcing rings 103 are formed by bending steel bars, or by steel plates with a height of 15cm and a thickness of 1cm. The spacing between two adjacent reinforcing rings 103 is 50-100cm.

[0075] In another optional embodiment, the reinforcing ring 103 is an annular steel ring corresponding to the inner wall of the steel casing 1, and is fixed to the steel casing 1 by full welding. In order to reduce the difficulty of production, the reinforcing ring 103 can be strip-shaped, such as steel bars, formed by bending equipment. The two ends of the steel bars form cuts on the side of the reinforcing ring 103. During production, the outer diameter of the reinforcing ring 103 can be slightly larger than the inner wall of the steel casing 1. After the reinforcing ring 103 is pressed into the steel casing 1 by the pressing equipment, the reinforcing ring 103 can fit tightly against the inner wall of the steel casing 1 through deformation. Two adjacent reinforcing rings 103 in the longitudinal direction are staggered in the circumferential direction of the steel casing 1 to ensure the strength of the steel casing 1.

[0076] In another optional embodiment, a reinforcing rib is provided between any two adjacent reinforcing rings 103. The reinforcing rib is fully welded to the steel casing 1. The reinforcing rib extends along the generatrix of the steel casing 1. The reinforcing rib can be a steel bar or a steel plate, and its two ends extend to the two adjacent reinforcing rings 103 respectively.

[0077] In this embodiment, the reinforcing ribs on both sides of the same reinforcing ring 103 are staggered in the circumferential direction of the steel casing 1.

[0078] In another alternative embodiment, an extension section 106 is connected to the top of the steel casing 1. The extension section 106 has the same diameter and wall thickness as the steel casing 1, and is welded and fixed to the steel casing 1. This allows for lengthening according to the needs of the immersed tunnel to meet the requirements of immersed tunnel construction.

[0079] In this embodiment, the steel casing 1 and the extension section 106 are fixed together by a plurality of backing steel plates 104. The backing steel plates 104 are 400mm*200mm*16mm arc-shaped plates, and their inner diameter is adapted to the outer diameter of the steel casing 1. In this way, the backing steel plates 104 can be placed on the outer wall of the steel casing 1 and can be tightly attached to the steel casing 1 and the extension section 106. The number of backing steel plates 104 can be 8, which are evenly distributed around the circumference of the steel casing 1 and are fully welded to the steel casing 1 and the extension section 106.

[0080] When connecting the extension section 106 and the steel casing 1, the extension section 106 and the steel casing 1 are positioned and then fully welded to the contact surface between the backing steel plate 104 and the outer wall of the steel casing 1. During this process, the crane operating the extension section must not be unhooked. A pulling force is applied to the top of the steel casing 1 to ensure its verticality and prevent it from tipping over during the connection process, thus avoiding a safety accident. After all the backing steel plates 104 are welded, the joint of the steel casing 1 is fully welded to ensure welding quality and prevent detachment during drilling.

[0081] In this embodiment, the inner wall of the steel casing 1 is provided with a fixing ring 105 corresponding to the joint between the steel casing 1 and the extension section 106. The outer diameter of the fixing ring 105 is adapted to the inner diameter of the steel casing 1. The fixing ring 105 has a height of 15cm and a thickness of 1cm, which is used to fix the steel casing 1 and the extension section 106 on the inner side.

[0082] In some embodiments, the extension section 106 has multiple sections, each of which is provided with a reinforcing ring 103, and a backing steel plate 104 and a fixing ring 105 are provided between two adjacent extension sections 106.

[0083] The extension sections 106 and 106, and 106, and 106, and 106, are connected in the same way as the steel casing 1 and 106. The lengths of the 106 sections can be the same, or they can be designed to be different lengths according to the actual needs of the immersed tunnel.

[0084] In some embodiments, the extension section 106 is provided with a lifting point, which may be a lifting ring provided inside the extension section 106, or a through hole provided on the side wall at the upper end of the extension section 106 as a lifting point.

[0085] In some embodiments, the cutting head includes a base 107, a blade holder 108, and an alloy blade body 101. The base 107 is square and is fixed to the bottom of the steel casing 1 by welding. Furthermore, a notch is provided on one side of the base 107 corresponding to the steel casing 11, which can be snapped onto the end of the steel casing 1 and fixed by welding.

[0086] The inner side of the base 107 is provided with a corresponding mounting position for the tool holder 108. The tool holder 108 has a square structure. The mounting position is adapted to the tool holder 108. The tool holder 108 is fixed to the mounting position by bolts. The alloy blade 101 is fixed to the tool holder 108 by welding. All alloy blades 101 are located on one side of the tool holder 108 corresponding to the rotation direction.

[0087] Based on the cofferdam's settlement, observe the area where the cofferdam's misalignment is squeezing the casing. If this causes deformation of the casing, construct a cross-shaped support system using I20a steel at the deformed elevation and install it inside the casing, connecting the casings. Remove the system after the cofferdam is leveled and install internal supports.

[0088] In an optional embodiment, the steel cofferdam is divided into 18 sections in the circumferential direction. The first section of the steel cofferdam 202 to the fourth layer of the steel cofferdam are all composed of two layers of steel walls, with a horizontal ring plate 209 and a partition plate 212 set between the two layers of steel walls. The partition plate 212 is composed of a 16mm thick steel plate and is a single piece of steel plate. The long side of the stiffening rib of the partition plate 212 at the horizontal ring rib position is close to the lower edge of the horizontal ring rib, and the end is welded to the inner and outer wall plates 207 of the double-wall steel cofferdam.

[0089] The horizontal ring plate 209 is a U-shaped or C-shaped plate correspondingly set between two layers of steel walls. Vertical ribs 211 are correspondingly set on the inner walls of the two layers of steel walls. The horizontal ring plate 209 is slotted at the position of the vertical ribs 211, and the vertical ribs 211 are welded together with the horizontal ring plate 209.

[0090] A horizontal inner diagonal brace 210 is welded onto the horizontal ring plate 209. The horizontal inner diagonal brace 210 is distributed in a V-shape, and its two ends are supported between the two layers of steel walls to serve as the inner support of the steel cofferdam.

[0091] The partition plates 212 are spaced apart between the two layers of steel walls. The length of the partition plates 212 is adapted to the corresponding steel cofferdam segment. The partition plates 212 are provided with stiffening ribs on both sides.

[0092] In this embodiment, the cofferdam is divided into 52 segments based on the cofferdam slabs. Each cofferdam is not interconnected. When pouring concrete, a symmetrical pouring method is adopted, and the elevation difference between the top surfaces of the concrete filling of adjacent compartments should not exceed 1m.

[0093] Concrete pouring should be uniform and continuous, and the interval should not exceed the initial setting time of the concrete.

[0094] In an optional embodiment, a cutting edge 201 is provided below the first section of the cofferdam. The included angle of the cutting edge of the cutting edge 201 is 45°. The inner and outer wall plates 207 of the cutting edge portion should be thickened to 20mm. The cutting edge 201 is reinforced with a 10mm steel plate and filled with fine stone concrete.

[0095] In one optional embodiment, each segment is circumferentially distributed with multiple internal and external connecting pipes, which pass through the two layers of steel walls of the steel cofferdam and are tightly welded to the well wall.

[0096] The steel pipe extending into the cofferdam is equipped with a connecting flange and a removable steel plate plug; it must be plugged during pumping operations. After the flange is bolted together, a rubber pad should be placed under the cover plate to prevent leakage.

[0097] At least the inner steel wall has corresponding internal support points reinforced with steel plates.

[0098] In an optional embodiment, a guiding device is provided between the steel casing 1 and the cofferdam. The guiding device is a guide pile 6, which is a columnar, sealed metal shell filled with concrete. Lifting points are provided on the side of the guide pile 6. In use, the guide pile 6 is horizontally suspended by steel wire ropes onto the lifting lugs on the upper edge of the inner wall of the steel cofferdam, positioned between the steel cofferdam and the steel casing 1. The steel wire ropes are attached to the top of the steel cofferdam, ensuring the guide piles 6 are horizontally distributed. This roller-type guiding device is simple to manufacture, low in cost, high in strength, and reusable, and performs well in cofferdams using the "pile-then-cofferdam" method.

[0099] In another embodiment, there are two lifting points, located at both ends of the guide pile 6. A sleeve that can rotate relative to the guide pile 6 is fitted onto the outer wall of the guide pile 6. The sleeve is located between the two lifting points. The lifting points can be hooks or lifting lugs.

[0100] In another embodiment, two horizontally spaced corbels are welded to the inner wall of the surrounding rock. A support plate is provided above the two corbels. The support plate is supported by a longitudinal hydraulic cylinder on the side of the corbel. The width of the support plate is smaller than the distance between the inner wall of the steel cofferdam and the steel casing 1, and the length is larger than the distance between the two corbels. The guide pile 6 is placed on the support plate. The hydraulic cylinder can make the support plate move longitudinally above the corbel by extending and retracting. The hydraulic cylinder is controlled by a solenoid valve. If the steel cofferdam tilts during the downward process, the hydraulic cylinder corresponding to the guide pile 6 at the higher point slowly extends upward to the highest point, and then the hydraulic pump quickly retracts, so that the guide pile 6 has a downward movement tendency. This gives the guide pile 6 downward inertia, and through the blocking relationship between the support plate and the upper surface of the corbel, it generates an impact on the corbel, thereby realizing the downward settlement of the higher point of the steel cofferdam due to vibration impact, and leveling the steel cofferdam.

[0101] In this embodiment, when the guide pile 6 is placed on the corbel, the distance between the lifting point of the guide pile 6 and the lifting lug of the inner wall of the surrounding rock is less than the length of the wire rope, so as to prevent the guide pile 6 from falling off.

[0102] The upper surface of the corbel is flat. The hydraulic cylinder is welded to the inner wall of the steel cofferdam via the mounting base and is located on both sides of the corbel that are close to each other. The guide pile 6 moves downward and impacts the corbel through the support plate, thus impacting the steel cofferdam.

[0103] The attitude control of the steel cofferdam during the sinking process can also be achieved by adding this guiding device. The method is to use a total station to detect the attitude of the cofferdam in real time during the sinking process. Once the cofferdam is found to be tilted or deviated, an additional layer of roller guide is immediately added to the upper layer of the cofferdam to form upper and lower support points to control the attitude of the cofferdam.

[0104] In one optional embodiment, after the existing bridge 4 is riprap-filled, a row of interlocking steel pipe piles 3 are driven into the existing bridge 4 abutment on the side closest to the newly built abutment, 3m away from the old bridge abutment, to protect the existing abutment. The steel pipe piles 3 are driven using a "fishing method," employing a vibratory hammer for vibratory driving, and are installed one by one after positioning.

[0105] In an optional embodiment, before assembling the first section of the steel cofferdam 202, the assembly outline and the assembly connection lines between each adjacent block are laid out on the assembly platform, and positioning codes are welded on the outer outline edge to control the planar position of the lower edge of the steel cofferdam.

[0106] During the assembly of the first section of the steel cofferdam 202, temporary brackets were welded at the support to serve as support points for the steel cofferdam, and temporary supports were also welded inside the steel cofferdam. The upper opening of the steel cofferdam was fixed and controlled by a guide device welded to the outside of the steel casing 1. The guide device served as both a temporary support during the assembly of the steel cofferdam wall and a control over the verticality of the steel cofferdam.

[0107] The first section of the steel cofferdam, 202, is assembled starting from the two corners. It is then assembled clockwise at the two corners, with angle steel welded at the bottom for temporary fixation to prevent displacement of the cofferdam. The upper part of the unit plate is temporarily welded with steel profiles and casing. The planar position and verticality are checked by measuring instruments. After the requirements are met, the wall panels are connected.

[0108] In an optional embodiment, the lower system includes a hydraulic jack, a lowering beam fixed to the steel casing 1, and steel strands. The lowering beam is installed on the top of the steel casing 1, and the jack is installed on the lowering beam. The steel strands pass through the lowering beam and are anchored to the lifting points on the side wall of the cofferdam. The lifting and lowering points of the steel cofferdam are all welded inside the cofferdam partition plate 212, and their positions correspond one-to-one with the lifting points set on the top surface of the steel casing 1. The lowering points are welded and installed during the processing of the cofferdam at the processing plant.

[0109] The steel cofferdam is lowered by using the extension and retraction of the continuous jack cylinder and the cooperation of the upper and lower clamps to exchange the load. During installation, the position deviation of the lowering beam should be within 5cm. On the other hand, the lowering beam should be adjusted according to the theoretical position of the jack axis to ensure that the jack position is vertically aligned with the theoretical position of the cofferdam lifting point.

[0110] In an optional embodiment, a total station is used to monitor the attitude of the cofferdam in real time during the sinking process. When the cofferdam tilts or deviates, an additional ring of guide piles 6 is added to the upper layer of the cofferdam to form upper and lower support points to maintain the attitude of the cofferdam.

[0111] The deviation of the steel cofferdam is adjusted by pouring concrete into the compartment. If the deviation still exists after the concrete is poured, water or sand will be poured into the corresponding compartment to correct the deviation.

[0112] The cofferdam uses guide structures for limiting and correcting deviation. Two layers of guide structures, each with 14 guides, are installed inside the cofferdam. Deviation in silt can be corrected by lifting the cofferdam or adjusting with unbalanced concrete weights. Correction in gravelly soil layers is more difficult and may require excavation within the inner wall or even applying horizontal force at the top. After the cofferdam is inserted into the rock, the deviation is checked; if it does not exceed the allowable value specified in the code, no correction is necessary.

[0113] Concrete is poured into the cofferdam chambers according to the design requirements. The pouring height is detailed in the cofferdam lowering section. The deviation of the steel cofferdam is adjusted by pouring concrete into the chambers. If the cofferdam still deviates after the concrete is poured and the design position is reached, water will be injected into the corresponding chambers to correct the deviation. If the effect is still not achieved, sand is poured in the tremie pipe method to counterweight the cofferdam and finally achieve the cofferdam deviation correction.

[0114] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A construction method for double-walled steel cofferdams suitable for complex conditions, characterized in that, include: Step S1: The double-walled steel cofferdam is broken down into block units and transported to the stockpiling platform via the river. Step S2: Lay out and position the steel casing, and drive the steel casing using the full casing drilling method; Step S3: Weld brackets onto the steel casing to serve as a splicing platform for constructing the steel cofferdam. The first section of the steel cofferdam is then assembled on the splicing platform. Step S4: Install the lowering system on the steel casing and set up jacks on the six steel casings around the cofferdam to form the load-bearing system for the corresponding steel cofferdam. Step S5: Use the lowering system to lift the first section of the steel cofferdam, remove it from the assembly platform and level it. Before lowering the first section of the steel cofferdam, mark the scale lines on the steel strands. Lower the six jacks simultaneously until the first section of the steel cofferdam stops sinking and reaches self-floating balance. Then pour the double-walled concrete of the cofferdam to put the first section of the steel cofferdam into the water. Step S6: Using the first section of the steel cofferdam as a reference, assemble the second section of the steel cofferdam. After the assembly is completed, pour concrete symmetrically and evenly into the double-walled chamber of the cofferdam to make the cofferdam sink until the second section of the steel cofferdam sinks to the preset position, so that the bottom cutting edge of the first section of the steel cofferdam enters the soil. Step S7: Assemble the third section of the steel cofferdam on top of the second section of the steel cofferdam. After the third section of the steel cofferdam is assembled, pour concrete into the double-walled chamber of the cofferdam symmetrically and evenly to make the cofferdam sink so that the bottom cutting edge of the first section of the steel cofferdam is in the gravelly soil layer. Pour the remaining concrete into the double-walled chamber of the cofferdam in multiple batches. At the same time, start the excavation and soil removal operation to assist the steel cofferdam in sinking. Step S8: The fourth section of the steel cofferdam is spliced ​​and lowered using the method in step S7. After the bottom cutting edge of the first section of the steel cofferdam is in the completely weathered sandy mudstone, a platform is built on the cofferdam. A mud mixer is used to loosen the soil layer, and a mud suction machine is used to remove soil while divers remove rocks for the sinking operation. Step S9: Install single-wall steel cofferdams in sections on the fourth section of the steel cofferdam. After confirming that the cofferdam has landed, carry out mud suction and sand dredging. Step S10: The bottom of the cofferdam is sealed by multi-point underwater grouting using vertical ducts. After the bottom sealing concrete reaches more than 90% of the design strength, water is pumped out from inside the cofferdam. Step S11: As water is pumped out of the cofferdam, the inner support of the cofferdam is installed layer by layer. After the inner support is installed, the pile head concrete is cut. After the cutting is completed, the pile cap is constructed. A guide device is installed between the steel casing and the cofferdam. The guide device is a guide pile with concrete inside. A lifting point is set on the side of the guide pile. When in use, the guide pile is horizontally suspended between the inner wall of the steel cofferdam and the steel casing by a steel wire rope, and the steel wire rope is attached to the top of the steel cofferdam. Two horizontally spaced brackets are welded to the inner wall of the steel cofferdam. A support plate is installed above each bracket. The support plate is supported by a longitudinal hydraulic cylinder on the side of the bracket. The width of the support plate is smaller than the distance between the inner wall of the steel cofferdam and the steel casing, while its length is greater than the distance between the two brackets. Guide piles are placed on the support plate. The hydraulic cylinders extend and retract, allowing the support plate to move longitudinally above the brackets. The hydraulic cylinders are controlled by a solenoid valve. If the steel cofferdam tilts during lowering, the hydraulic cylinder corresponding to the guide pile at the higher point slowly extends upwards to its highest point, then quickly retracts, causing the guide pile to move downwards. The impact between the support plate and the upper surface of the bracket impacts the bracket, causing it to vibrate and sink downwards, thus leveling the steel cofferdam.

2. The construction method for double-walled steel cofferdams under complex conditions according to claim 1, characterized in that, The steel cofferdam is divided into 18 sections in the circumference. The first section of the steel cofferdam to the fourth layer of steel cofferdam are composed of inner wall plates and outer wall plates. A horizontal ring plate and a partition plate are set between the two layers of steel walls. The horizontal ring plate is a U-shaped or C-shaped plate set between the two layers of steel walls. Vertical ribs are set on the inner walls of the two layers of steel walls. The horizontal ring plate is slotted at the position of the vertical ribs and the vertical ribs are welded together with the horizontal ring plate. Horizontal inner diagonal braces are welded onto the horizontal ring plate. The horizontal inner diagonal braces are distributed in a V-shape, and their two ends are supported between the two layers of steel walls. The partition plates are spaced apart between the two layers of steel walls. The length of the partition plates is adapted to the corresponding steel cofferdam segments. The partition plates are reinforced with stiffening ribs on both sides.

3. The construction method for double-walled steel cofferdams under complex conditions according to claim 2, characterized in that, The first section of the steel cofferdam is equipped with a cutting edge at the bottom. The included angle of the cutting edge tip is 45°. The inner and outer wall plates of the cutting edge are thickened. The cutting edge is reinforced inside the cutting edge and filled with fine stone concrete.

4. The construction method for double-walled steel cofferdams under complex conditions according to claim 2, characterized in that, Each segment has multiple internal and external connecting pipes distributed circumferentially. The internal and external connecting pipes pass through the two layers of steel walls of the steel cofferdam. The steel pipes are equipped with connecting flanges and removable steel plate plugs at the ends of the steel pipes that extend into the cofferdam. At least the inner steel wall has corresponding internal support points reinforced with steel plates.

5. The construction method for double-walled steel cofferdams under complex conditions according to claim 1, characterized in that, After the existing bridge is riprapped, a row of interlocking steel pipe piles is driven into the existing bridge abutment on the side closest to the new abutment to protect the existing abutment.

6. The construction method for double-walled steel cofferdams under complex conditions according to claim 1, characterized in that, Before assembling the first section of the steel cofferdam, the assembly outline and the assembly connection between each adjacent block are laid out on the assembly platform, and positioning codes are welded on the outer outline to control the planar position of the lower edge of the steel cofferdam. During the assembly of the first section of the steel cofferdam, temporary brackets were welded at the support points to serve as support points for the steel cofferdam, and temporary supports were also welded inside the steel cofferdam. The first section of the steel cofferdam is assembled starting from the two corners, and then assembled clockwise at the two corners.

7. The construction method for double-walled steel cofferdams under complex conditions according to claim 2, characterized in that, The lowering system includes hydraulic jacks, a lowering beam fixed to the steel casing, and steel strands. The lowering beam is installed on the top of the steel casing, and the jacks are installed on the lowering beam. The steel strands pass through the lowering beam and are anchored to the lifting points on the side wall of the cofferdam. The lifting and lowering points of the steel cofferdam are all welded inside the cofferdam partition plate, and their positions correspond one-to-one with the lifting points set on the top surface of the steel casing.

8. The construction method for double-walled steel cofferdams under complex conditions according to claim 1, characterized in that, The steel cofferdam is divided into multiple segments around its circumference by wall panels. When pouring concrete, a symmetrical pouring method is adopted, and the elevation difference between the top surfaces of the concrete filling of adjacent compartments should not exceed 1m.

9. The construction method for double-walled steel cofferdams under complex conditions according to claim 1, characterized in that, The attitude of the cofferdam during the sinking process is monitored in real time using a total station. When the cofferdam tilts or deviates, an additional ring of guide piles is added to the upper layer of the cofferdam to form upper and lower support points to maintain the attitude of the cofferdam. The deviation of the steel cofferdam is adjusted by pouring concrete into the compartment. If the deviation still exists after the concrete is poured, water or sand will be poured into the corresponding compartment to correct the deviation.

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