On-water cast-in-place construction method for large deepwater caisson

Abstract

The present application relates to an on-water cast-in-place construction method for a large deepwater caisson, comprising: first casting a caisson bottom slab in a dry dock, and mounting a double-wall steel cofferdam on the bottom slab; then injecting water into the dock to float the bottom slab and tow same to a pier site; using the steel cofferdam as a temporary water blocking structure, and using a cast-in-place method to construct a caisson; and once the construction of the caisson is completed, sinking and seating the caisson in place by means of water injection. The present application can greatly reduce the requirement on the excavation depth of a dry dock, and can also reduce the dredging workload of an undocking and floating-towing channel, thereby reducing construction costs, and shortening the construction period of a caisson.

Description

A method for on-site construction of large deep-water caissons.

[0001] Cross-referencing

[0002] This application claims priority and benefit to patent application 202410902397.7, filed with the China National Intellectual Property Administration on July 6, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application belongs to the field of deep-water bridge construction technology, specifically relating to a method for on-site construction of large deep-water caissons used as pier or tower foundations. Background Technology

[0004] When constructing bridges across the sea or river, in deep water, it is difficult to use conventional cofferdam or steel caisson methods for the construction of piers or tower foundations. Using large caisson foundations is a better option. A caisson is a concrete box structure, usually prefabricated in a temporary dry dock, transported to the pier location by water transport, and then sunk to serve as the pier foundation. After sinking, the top of the caisson rises above the water surface, facilitating the construction of the superstructure of the pier.

[0005] When constructing caissons in a dry dock, the depth of the temporary dry dock must be compatible with the height of the caisson. Therefore, for large deep-water caissons, they need to be prefabricated in an ultra-large and ultra-deep dry dock, which presents problems such as deep dock excavation depth, long construction period, and high investment cost. Moreover, large caissons have a large draft, and a lot of dredging work is often required when the caissons are moved from the dock to the waterway, which further increases the construction cost.

[0006] To address the aforementioned issues, patent CN112878357A proposes a caisson foundation structure and construction method for a deep-water cross-sea bridge exceeding 100 meters in depth. The caisson employs a stepped structure with a cross-sectional area gradually decreasing from bottom to top. The caisson is prefabricated and towed in a horizontal position, and after floating to its designated location, it is adjusted to a vertical position and sunk. While this solution reduces the excavation depth of the dry dock and the draft during caisson floating, the increased floor space required for horizontal prefabrication due to the caisson's height means that the construction workload, construction period, and cost of the dry dock are not significantly reduced. Furthermore, during floating, the large length of the caisson and the significant difference in volume and weight between its front and rear ends make it difficult to control its balance, resulting in low safety. Summary of the Invention

[0007] One of the purposes of this application is to address the above-mentioned problems by providing a method for on-site construction of large deep-water caissons. This method involves prefabricating the caisson bottom plate only in a dry dock, then floating the bottom plate to the pier and completing the main structure of the caisson by on-site casting. This reduces the excavation depth of the dry dock and the amount of dredging required for the floating transport channel, thereby lowering construction costs.

[0008] The technical solution of one embodiment of this application is as follows:

[0009] A method for on-site construction of a large deep-water caisson, wherein the lower half of the caisson is a large-diameter cylindrical reinforced concrete foundation, and the upper half is a conical reinforced concrete pier, wherein the lower cylindrical foundation includes a base plate, an annular side plate, and an inner partition plate, characterized by comprising the following steps:

[0010] Step 1: Construct a shallow dry dock and supporting facilities for caisson construction;

[0011] Step 2: Pour the bottom plate of the caisson in the dry dock, and install a double-walled steel cofferdam on the bottom plate to form an open box structure; the height of the steel cofferdam shall not be less than the height of the lower foundation side plate of the caisson.

[0012] Step 3: The container is undocking and towed to the pier.

[0013] Step 4: Complete the caisson construction using cast-in-place concrete; precisely adjust the caisson's position, inject water, and sink it into place.

[0014] According to one embodiment of this application, in step 1 of the construction method for the large deep-water caisson, the construction of the shallow dry dock and supporting facilities follows the specific construction process as follows:

[0015] Construction of dock cofferdam → Construction of dock perimeter walls within the dock cofferdam → Dewatering of the dock area → Excavation of dock foundation pit → Pouring of dock chamber floor slab → Construction of ancillary facilities → Demolition of dock cofferdam.

[0016] Depending on the topography, geomorphology, and hydrogeological conditions of the dock site, the cofferdam may be an earth dam, a double-row steel sheet pile cofferdam, or a steel sheet pile foundation pit cofferdam.

[0017] Ancillary facilities include a concrete mixing plant, a steel reinforcement / steel structure processing area, and office and living areas.

[0018] According to one embodiment of this application, in step 2 of the above-mentioned construction method for large deep-water caissons, steel cofferdam connecting steel plates are pre-embedded around the top surface of the concrete bottom plate of the caisson. After the concrete bottom plate reaches the design strength, the double-walled steel cofferdam is installed.

[0019] According to one embodiment of this application, in the above-mentioned construction method of large deep-water caisson, the double-walled steel cofferdam is prefabricated into multiple steel cofferdam unit plates in a processing plant using steel profiles and steel plates, and then assembled into a whole on the bottom plate of the caisson; the joints between the steel cofferdam unit plates and between the steel cofferdam and the bottom plate are sealed with rubber waterstop strips.

[0020] According to one embodiment of this application, step 3 of the above-mentioned construction method for large deep-water caissons is specifically constructed as follows:

[0021] (31) Conduct a sealing inspection on the joints between the steel cofferdam unit plates and the joints between the steel cofferdam and the concrete bottom plate to ensure that the steel cofferdam is impermeable;

[0022] (32) Four winches are symmetrically arranged on the top of the dock walls on both sides of the dock. The winches are connected to the steel cofferdam by cables to limit the cable position of the box.

[0023] (33) Remove the dock gate and fill the dock with water to make the container float;

[0024] (34) Use two tugboats to tow the container, and at the same time control the position of the container by four winches set on the dock wall to prevent collision with the dock wall. Slowly drag the container out of the dock and then transport it to the pier.

[0025] According to one embodiment of this application, in the above-mentioned construction method of large deep-water caisson, the difference in water head between the inside and outside of the dock should be measured before the dock gate is removed. The part in the center of the dock gate is removed first, and after the difference in water head between the inside and outside is consistent, the part is removed from the middle to both sides.

[0026] According to one embodiment of this application, in the above-mentioned construction method of large deep-water caissons, during the towing of the caisson, two tugboats are used behind the caisson to provide a certain counter-pull force to prevent the caisson from deviating due to the impact of water flow and waves.

[0027] According to one embodiment of this application, step 4 of the above-mentioned construction method for large deep-water caissons is specifically constructed as follows:

[0028] (41) After the caisson is floated to the predetermined position, it is anchored and positioned, and the caisson is cast on the bottom plate inside the steel cofferdam by cast-in-place method.

[0029] (42) The caisson reinforcement is modularly tied in the field and transported to the site by barge for installation; the concrete is supplied by the mixing ship and directly pumped into the formwork for pouring; when the caisson is poured to a height exceeding the height of the double-walled steel cofferdam, the steel cofferdam is dismantled in sections and symmetrically using a large floating crane, and then the caisson is poured to the design height.

[0030] (43) After the caisson is poured, the caisson is precisely positioned by tugboats, anchoring systems and positioning piles, and then sunk into place by water injection.

[0031] According to one embodiment of this application, in the above-mentioned construction method for large deep-water caissons, when the outer wall panel of the caisson is cast below the top height of the steel cofferdam, the steel cofferdam is directly used as the outer template for casting the side panel of the caisson.

[0032] This application proposes a method to construct the caisson by pouring concrete only for the bottom slab of the caisson in a dry dock, installing a double-walled steel cofferdam around the bottom slab as a waterproof structure, and then towing the bottom slab to the vicinity of the bridge site to complete the caisson construction using a concrete casting method. This method can significantly reduce the excavation depth requirement of the dry dock, thereby reducing the amount of construction work and construction costs. On the other hand, it reduces the amount of dredging work required for the floating transport channel after the dock is opened, further reducing construction costs. At the same time, the reduction in the amount of dock construction and dredging work also helps to shorten the caisson construction period. Attached Figure Description

[0033] Figure 1 is a construction flowchart of an embodiment of this application;

[0034] Figure 2 is a schematic diagram of the elevation structure of the steel cofferdam installed on the bottom plate of the caisson;

[0035] Figure 3 is a schematic diagram of the plan structure of the steel cofferdam installed on the bottom plate of the caisson;

[0036] Figure 4 is a schematic diagram of the state when the bottom plate of the caisson is being towed out of the dock.

[0037] Figure 5. Schematic diagram of the caisson bottom plate during floating;

[0038] Figure 6 is a schematic diagram of the plan structure for anchoring the caisson at the caisson casting location;

[0039] Figure 7 is a schematic diagram of the construction status of the lower foundation structure of the caisson being poured inside the steel cofferdam.

[0040] Figure 8 is a schematic diagram of the construction process of dismantling the steel cofferdam and continuing to raise the caisson. Detailed Implementation

[0041] The construction method of this application is described below through a specific embodiment. In this embodiment, the lower half of the caisson structure to be constructed is a large-diameter cylindrical reinforced concrete foundation, and the upper half is a conical reinforced concrete pier; wherein the lower cylindrical part includes a bottom plate, side plates, and inner partitions.

[0042] Figure 1 is a construction flowchart of this embodiment, which is divided into 4 stages. The specific construction process is as follows:

[0043] Step 1: Construct a shallow dry dock and supporting facilities for caisson construction; the specific construction process is as follows:

[0044] Construction of dock cofferdam → Construction of dock perimeter walls within the dock cofferdam → Dewatering of the dock area → Excavation of dock foundation pit → Pouring of dock chamber floor slab → Construction of ancillary facilities → Demolition of dock cofferdam.

[0045] The dock site should be located as close as possible to the shore where the bridge is being constructed. The dock cofferdam should be an earth dam, a double-row steel sheet pile cofferdam, or a steel sheet pile foundation pit cofferdam, depending on the topography, geomorphology, and hydrogeological conditions of the dock site. The size and elevation of the dry dock should be selected based on factors such as the vessels to be transported, the size of the caisson bottom plate, the transport process, and the hydrological conditions of the dock site.

[0046] Ancillary facilities include a concrete mixing plant, a steel reinforcement / steel structure processing area, and office and living areas.

[0047] Step 2, as shown in Figures 2 and 3, pour the bottom plate 1 of the caisson in the dry dock, and install the double-walled steel cofferdam 2 on the bottom plate to form an open box structure. The double-walled steel cofferdam 2 serves as a temporary water barrier. The height of the steel cofferdam is not less than the height of the lower cylindrical side plate of the caisson.

[0048] Due to the large area of ​​the base slab, the vertical concrete of the base slab is poured in one go during the construction process, while the horizontal concrete can be poured in four stages, with two 2m wide post-pouring strips set in the middle.

[0049] Steel cofferdam connecting plates are pre-embedded around the top surface of the caisson's bottom concrete slab. Bolts are threaded through these connecting plates, with the lower ends embedded in the bottom concrete and the upper ends protruding a certain length for connection to the steel cofferdam. After the bottom concrete reaches its design strength, the double-walled steel cofferdam is installed.

[0050] The double-walled steel cofferdam is made by prefabricating multiple steel cofferdam unit panels using steel profiles and steel plates in the processing plant, and then assembling them into a whole on the bottom plate of the caisson; the joints between the steel cofferdam unit panels and between the steel cofferdam and the bottom plate are sealed with rubber waterstop strips.

[0051] Step 3, as shown in Figures 4 and 5, involves undocking the container and transporting it to the pier location; the specific construction method is as follows:

[0052] (31) Conduct a sealing inspection on the joints between the steel cofferdam unit plates and the joints between the steel cofferdam and the concrete bottom plate to ensure that the steel cofferdam is impermeable;

[0053] (32) Four winches 4 are symmetrically arranged on the top of the dock walls 3 on both sides of the dock. The winches 4 are connected to the steel cofferdam 2 by cables 5 to limit the cable of the box.

[0054] (33) Remove the dock gate and fill the dock with water to make the hull float. Before removing the dock gate, the difference in water head between the inside and outside of the dock should be measured. First, remove part of the dock gate in the center. After the difference in water head between the inside and outside is consistent, remove it from the middle to both sides.

[0055] (34) Use two tugboats 6 to tow the container, and at the same time control the position of the container by four winches 4 set on the dock wall to prevent collision with the dock wall. Slowly pull the container out of the dock and then transport it to the pier. The speed of leaving the dock is controlled at about 1 knot.

[0056] During the towing process after the container is undocking, to prevent it from veering off course due to water currents and waves, two tugboats can be used behind the container to provide some counter-pull. Furthermore, a tugboat can be positioned close to the container on each side to accompany it, serving a navigation and correction function.

[0057] Step 4: Construct the caisson using cast-in-place concrete; precisely adjust the caisson's position, inject water, and sink it into place. The specific construction method is as follows:

[0058] (41) As shown in Figures 6 and 7, after the box body is floated to the predetermined position, it is anchored and positioned by the anchoring system 7, and the outer wall panel 8 and inner partition 9 of the caisson are cast on the bottom plate 1 of the caisson inside the steel cofferdam 2 by the cast-in-place method.

[0059] (42) The steel reinforcement of the caisson is modularly tied in the field and transported to the site by barge for installation; the concrete is supplied by the mixing ship and directly pumped into the formwork for pouring.

[0060] When the outer wall panel of the caisson is located below the top height of the steel cofferdam, the steel cofferdam 2 can be directly used as the outer formwork for casting the side panel 8 of the caisson.

[0061] As shown in Figure 8, after the caisson is poured to a height exceeding that of the double-walled steel cofferdam, the steel cofferdam 2 is dismantled symmetrically in 10 sections using a large floating crane, and then the caisson is poured to the design height.

[0062] (43) After the caisson is poured, the caisson is precisely positioned by tugboats, anchoring systems and positioning piles, and then sunk into place by water injection.

[0063] This application proposes a method to construct the caisson by pouring concrete only for the bottom slab of the caisson in a dry dock, installing a double-walled steel cofferdam around the bottom slab as a waterproof structure, and then towing the bottom slab to the vicinity of the bridge site to complete the caisson construction using a concrete casting method. This method can significantly reduce the excavation depth requirement of the dry dock, thereby reducing the amount of construction work and construction costs. On the other hand, it reduces the amount of dredging work required for the floating transport channel after the dock is opened, further reducing construction costs. At the same time, the reduction in the amount of dock construction and dredging work also helps to shorten the caisson construction period.

Claims

1. A method for on-site construction of a large deep-water caisson, wherein the lower half of the caisson is a large-diameter cylindrical reinforced concrete foundation, and the upper half is a conical reinforced concrete pier, wherein the lower cylindrical foundation includes a base plate, annular side plates, and an inner partition plate, characterized in that... Includes the following steps: Step 1: Construct a shallow dry dock and supporting facilities for caisson construction; Step 2: Pour the bottom plate of the caisson in the dry dock, and install a double-walled steel cofferdam on the bottom plate to form an open box structure; the height of the steel cofferdam shall not be less than the height of the lower foundation side plate of the caisson. Step 3: The container is undocking and towed to the pier. Step 4: Complete the caisson construction using cast-in-place concrete; precisely adjust the caisson's position, inject water, and sink it into place.

2. The method for on-site construction of large deep-water caissons by cast-in-place concrete according to claim 1, characterized in that, In step 1, the construction of the shallow dry dock and supporting facilities follows a specific construction process: Construction of dock cofferdam → Construction of dock perimeter walls within the dock cofferdam → Dewatering of the dock area → Excavation of dock foundation pit → Pouring of dock chamber floor slab → Construction of ancillary facilities → Demolition of dock cofferdam. Depending on the topography, geomorphology, and hydrogeological conditions of the dock site, the cofferdam may be an earth dam, a double-row steel sheet pile cofferdam, or a steel sheet pile foundation pit cofferdam. Ancillary facilities include a concrete mixing plant, a steel reinforcement / steel structure processing area, and office and living areas.

3. The method for on-site construction of large deep-water caissons by cast-in-place concrete according to claim 1, characterized in that: In step 2, steel cofferdam connecting steel plates are pre-embedded around the top surface of the concrete bottom plate of the caisson. After the bottom plate concrete reaches the design strength, the double-walled steel cofferdam is installed.

4. The method for on-site construction of large deep-water caissons by cast-in-place concrete according to claim 3, characterized in that: The double-walled steel cofferdam is made by prefabricating multiple steel cofferdam unit panels using steel profiles and steel plates in the processing plant, and then assembling them into a whole on the bottom plate of the caisson; the joints between the steel cofferdam unit panels and between the steel cofferdam and the bottom plate are sealed with rubber waterstop strips.

5. The method for on-site construction of large deep-water caissons by cast-in-place concrete according to claim 1, characterized in that, The specific construction method for step 3 is as follows: (31) Conduct a sealing inspection on the joints between the steel cofferdam unit plates and the joints between the steel cofferdam and the concrete bottom plate to ensure that the steel cofferdam is impermeable; (32) Four winches are symmetrically arranged on the top of the dock walls on both sides of the dock. The winches are connected to the steel cofferdam by cables to limit the cable position of the box. (33) Remove the dock gate and fill the dock with water to make the container float; (34) Use two tugboats to tow the container, and at the same time control the position of the container by four winches set on the dock wall to prevent collision with the dock wall. Slowly drag the container out of the dock and then transport it to the pier.

6. The method for on-site construction of large deep-water caissons by cast-in-place concrete according to claim 5, characterized in that: Before dismantling the dock gate, the difference in water head between the inside and outside of the dock should be measured. First, dismantle the part in the center of the dock gate. After the difference in water head between the inside and outside is consistent, dismantle from the center outwards to both sides.

7. The method for on-site construction of large deep-water caissons by cast-in-place concrete according to claim 5, characterized in that: During the container transport, two tugboats are used behind the container to provide a certain amount of counter-pull force to prevent the container from deviating due to the impact of water flow and waves.

8. The method for on-site construction of large deep-water caissons by cast-in-place concrete according to claim 1, characterized in that, The specific construction method for step 4 is as follows: (41) After the caisson is floated to the predetermined position, it is anchored and positioned, and the caisson is cast on the bottom plate of the steel cofferdam using the cast-in-place method. (42) The caisson reinforcement is modularly tied in the field and transported to the site by barge for installation; the concrete is supplied by the mixing ship and directly pumped into the formwork for pouring; when the caisson is poured to a height exceeding the height of the double-walled steel cofferdam, the steel cofferdam is dismantled in sections and symmetrically using a large floating crane, and then the caisson is poured to the design height. (43) After the caisson is poured, the caisson is precisely positioned by tugboats, anchoring systems and positioning piles, and then sunk into place by water injection.

9. The method for on-site construction of large deep-water caissons by cast-in-place concrete according to claim 8, characterized in that: When the side panels of the caisson are cast below the top height of the steel cofferdam, the steel cofferdam is used directly as the outer formwork for casting the side panels of the caisson.

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