Negative buoyancy submerged tube and prefabrication method thereof

Abstract

The present invention relates to the technical field of immersed tube tunnel construction, and in particular to a negative buoyancy immersed tube and a prefabrication method thereof, wherein the immersed tube comprises a main body, and the designed freeboard value of the main body is less than 0. There is no need to design the pipe section to be self-floating in the corresponding water area, and therefore, there is no need to increase the cross-sectional height of the immersed tube to ensure the minimum freeboard value during floating, thus avoiding the design contradiction between the freeboard value and the anti-floating during the operation period in the design link, and no need to set the dry dock detection freeboard value, which is particularly suitable for engineering projects with limited sites. The present application breaks the design concept that a self-floating immersed tube must be adopted in the prior art, and can reduce the structural height to the maximum extent, saving the engineering volume of the main structure, foundation trench backfilling, etc., without setting a freeboard adjustment layer, effectively saving the prefabrication cost and construction cost, and helping to reduce the difficulty of design and prefabrication, avoiding the cumbersome operation of adjusting the freeboard value in the water during the floating link, and helping to shorten the transportation time, and has important promotion significance and good application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of immersed tube tunnel construction, and in particular to a negative buoyancy immersed tube and a prefabrication method thereof. Background Art

[0002] Buoyancy design must be considered in the design of immersed tube structures, including the selection of freeboard and the verification of anti-floating safety factor. The existing immersed tube prefabrication methods mainly include dry dock method and factory method. Since the factory method has high prefabrication efficiency, it is often suitable for projects with tight construction schedules. The prefabricated pipe segments are transported to the designed construction location by floating for sinking. At present, no matter which prefabrication method is used, positive freeboard pipe segments are used, that is, when the pipe segments are floated, the pipe segments can float in the water, and the top surface of the pipe segments must be exposed above the water surface. In order to ensure the safety and stability of the pipe segments during floating, the pipe segments must be adjusted to the designed freeboard value through the ballast water tank system installed inside the pipe segments before floating. The designed freeboard value (exposed height) is usually around 10-30cm. Then, the self-floating characteristics of the immersed tube are utilized, and the immersed tube is floated from the prefabrication site to the installation site by a tugboat group.

[0003] Therefore, in order to meet the minimum positive freeboard value, the cross-sectional height of the pipe segment is often larger, which in turn increases the amount of work such as the main structure and foundation pit backfill, and increases the prefabrication cost and construction cost. Moreover, after the pipe segment is floated, not only is it necessary to test the freeboard value, but also during the floating and sinking process, in order to meet the corresponding anti-buoyancy coefficient requirements in the existing specifications, it is also necessary to adjust the negative buoyancy of the pipe segment in the water through the ballast water tank system. The precision control is complex and the construction difficulty can be imagined. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned shortcomings that the designs of immersed tubes in the prior art all need to meet the minimum freeboard value, resulting in a larger cross-sectional height of the pipe segment, which in turn increases the amount of engineering such as the main structure and foundation trench backfill, increases the prefabrication cost and construction cost, and increases the difficulty of construction, and to provide a negative buoyancy immersed tube and a prefabrication method thereof.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] A negative buoyancy submerged tube comprises a body, wherein the designed freeboard value of the body is less than 0.

[0007] The negative buoyancy submerged tube described in the present invention is adopted. The existing pipe sections are all designed with positive freeboard values. The present application adopts a design freeboard value less than 0, that is, it is a negative freeboard pipe section relative to the positive freeboard pipe section in the prior art. That is, it is not necessary to design the pipe section to be self-floating in the corresponding waters, but to form a negative buoyancy state of the submerged tube in the prior art during the sinking and docking process. Therefore, it is not necessary to increase the cross-sectional height of the submerged tube to ensure the minimum positive freeboard value during floating, avoiding the design contradiction between the freeboard value and the anti-floating during the operation period in the design process, and there is no need to set up a dry dock to detect the freeboard value. It is particularly suitable for engineering projects with limited sites. The present application breaks the design concept that self-floating submerged tubes must be adopted in the prior art, can reduce the structural height to the maximum extent, save the main structure, foundation trench backfill and other engineering quantities, does not need to set up a freeboard adjustment layer, effectively saves prefabrication costs and construction costs, is conducive to reducing the difficulty of design and prefabrication, avoids the cumbersome operation of adjusting the freeboard value in the water during the floating process, is conducive to shortening the transportation time, and has important promotion significance and good application prospects.

[0008] Preferably, the deadweight of the main body includes the designed structural deadweight G0 of the main body and the designed deadweight of the ballast concrete inside the main body, the designed deadweight of the ballast concrete includes the designed deadweight G1 of the first ballast concrete and the designed deadweight G2 of the second ballast concrete, the sum of G0 and G1 is greater than the designed buoyancy F of the main body, and the first ballast concrete is poured when the main body is prefabricated.

[0009] The designed structural deadweight G0 of the main body is the deadweight calculated according to the cross-sectional dimensions.

[0010] More preferably, It is 1.02-1.05.

[0011] In order to save costs to the maximum extent and ensure that the anti-buoyancy coefficient requirements during the sinking and docking construction stage are met, according to the existing design specifications, the anti-buoyancy coefficient of 1.02 during sinking and docking and 1.05 after sinking in place or stable ballasted sections can be used as control indicators.

[0012] In the prior art, after the pipe segment is sunk, ballast concrete needs to be poured to replace the ballast water tank. Due to the underwater operation, the construction is difficult and there is a certain risk of floating. It is difficult to test and verify after pouring. Increasing the pouring amount will increase the cost and waste materials. In order to ensure the clearance, the clearance height of the submerged pipe is increased in the design stage, thereby increasing the structural size. This application uses the existing ballast concrete poured after sinking, and pours the first ballast concrete in advance as a partial ballast layer in the prefabrication stage, so that the pipe segment cannot float in the construction water area, which is conducive to reducing the design difficulty. At the same time, it meets the anti-buoyancy coefficient requirements when replacing the ballast water tank after sinking and docking. There is no need to introduce additional equipment or structure, and the ballast water tank system can be cancelled, reducing construction costs, avoiding floating when replacing the water tank, and the installation process has low risks. The pouring process is carried out in the factory, with low operation difficulty and low risk. It is easy to accurately control the weight of the pipe segment after pouring and avoid waste of additional materials.

[0013] More preferably, The anti-buoyancy coefficient requirements of the main body during operation are met.

[0014] Further preferably, the second ballast concrete is poured after the main body is sunk.

[0015] It is helpful to reduce the weight of pipe sections during transportation and save transportation costs.

[0016] Preferably, the ballast concrete is arranged on the top surface of the carriageway, and the ballast concrete is plain concrete.

[0017] Further preferably, the concrete strength of the ballast concrete is less than the concrete strength of the body.

[0018] It is beneficial to reduce the prefabrication cost, and the concrete strength of the ballast concrete must meet the driving requirements of the road surface.

[0019] A method for prefabricating a negative buoyancy submerged tube, using any of the negative buoyancy submerged tubes described above, comprises the following steps:

[0020] a. Prefabricated body;

[0021] b. pouring a first ballast concrete in the body, and measuring whether the weight of the body satisfies a first anti-buoyancy coefficient;

[0022] c. After meeting the requirements, install the primary outfitting parts and embedded parts;

[0023] d. Install the end sealing wall to complete the prefabrication of the negative buoyancy submerged tube.

[0024] By adopting the method for prefabrication of a negative buoyancy submerged tube described in the present invention, the ballast concrete poured after the existing pipe segment is sunk is used, and the first ballast concrete is poured in advance in the prefabrication stage in the factory as a partial ballast layer, so that the pipe segment cannot float on its own in the construction waters. The operation is easy and the risk is small. It is convenient to accurately control the weight of the pipe segment after pouring, avoid the waste of extra materials, and is conducive to reducing construction costs. It will not significantly increase the prefabrication period, and provides technical guidance and operation procedures for the construction of a new type of negative buoyancy submerged tube, which is worthy of wide promotion and application.

[0025] Preferably, before step b, the method further comprises determining the dry bulk density of concrete used for the body and calculating the theoretical weight of the body.

[0026] It is convenient to accurately control the pouring amount of ballast concrete.

[0027] Further preferably, the step b comprises the following steps:

[0028] b1. After reaching a predetermined strength, the body is moved to the outfitting area by a trolley, and the weight of the body before pouring the first ballast concrete is measured by a pressure sensor of the trolley;

[0029] b2. According to the theoretical weight of the body and in combination with step b1, determine the pouring volume of the first ballast concrete, pour the first ballast concrete, and then measure by the pressure sensor of the trolley whether the weight of the body meets the first anti-buoyancy coefficient and whether the weight distribution is uniform;

[0030] Wherein, each of the trolleys is provided with a pressure sensor.

[0031] By adopting the above method, the casting area can be vacated as soon as possible so that the casting of the next pipe section can be carried out as soon as possible, shortening the construction period. At the same time, the trolley for transferring the pipe section is used as a weighing device, and the measurement process is simple and convenient, which is convenient for adjusting the first ballast concrete pouring amount according to actual conditions. Since the trolleys are widely and evenly distributed, it is beneficial to detect the uniformity of the weight of the pipe section, ensure transportation safety, and reduce the construction risk of the underwater process.

[0032] Further preferably, the first ballast concrete is poured at least three times, and the weight distribution is measured after each pouring.

[0033] Preferably, the first anti-buoyancy coefficient is 1.02-1.05.

[0034] Preferably, the order of steps b and c can be interchanged or performed simultaneously.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. It breaks the design concept of self-floating sinking tubes that must be adopted in the existing technology, can reduce the structural height to the maximum extent, save the main structure, foundation pit backfill and other engineering quantities, does not need to set up a freeboard adjustment layer, effectively saves prefabrication costs and construction costs, is conducive to reducing the difficulty of design and prefabrication, avoids the tedious operation of adjusting the freeboard value in the water during the floating link, is conducive to shortening the transportation time, and has important promotion significance and good application prospects.

[0037] 2. The existing ballast concrete poured after sinking is used, and the first ballast concrete is poured in advance in the prefabrication stage as a partial ballast layer, so that the pipe segment cannot float by itself in the construction waters, which is conducive to reducing the design difficulty and meeting the anti-buoyancy coefficient requirements after sinking and docking. There is no need to introduce additional equipment or structures, and the ballast water tank system can be cancelled, which reduces construction costs and avoids floating when replacing the water tank. The risk of floating in the operation stage is small. The pouring process is carried out in the factory, with low operation difficulty and risk, and it is easy to accurately control the weight of the pipe segment after pouring to avoid waste of extra materials.

[0038] 3. The pouring area can be vacated as soon as possible so as to start pouring the next pipe section as soon as possible, shortening the construction period. At the same time, the trolley for transferring the pipe section is used as a load-bearing device, and the measurement process is simple and convenient, which is convenient for adjusting the first ballast concrete pouring amount according to actual conditions. Since the trolleys are widely and evenly distributed, it is conducive to detecting the uniformity of the weight of the pipe section, ensuring transportation safety, and reducing the construction risk of the underwater process. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the state of a negative buoyancy submerged tube according to the present invention;

[0040] Figure 2 It is a schematic diagram of the cross-sectional structure of a negative buoyancy submerged tube described in the embodiment.

[0041] Markings in the figure: 1-main body, 21-first ballast concrete. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with test examples and specific implementation methods. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the content of the present invention belong to the scope of the present invention.

[0043] Example

[0044] like Figure 1As shown, a negative buoyancy submerged tube according to the present invention comprises a body 1, wherein the design freeboard value of the body 1 is less than 0. That is, a negative freeboard pipe section, that is, a design without considering positive freeboard, and it is not necessary to design the pipe section to be self-floating in the corresponding waters, but to form a negative buoyancy state of the existing submerged tube in the sinking and docking links, breaking the design concept of self-floating submerged tubes in the prior art, which can reduce the structural height to the maximum extent, save the engineering workload of the main structure, foundation trench backfilling, etc., and there is no need to set a freeboard adjustment layer.

[0045] Specifically, the deadweight of the main body 1 includes the designed structural deadweight G0 of the main body 1 and the designed deadweight of the ballast concrete inside the main body 1, wherein the designed structural deadweight G0 of the main body 1 can be calculated according to the cross-sectional dimensions, the designed deadweight of the ballast concrete includes the designed deadweight G1 of the first ballast concrete 21 and the designed deadweight G2 of the second ballast concrete, the sum of G0 and G1 is greater than the designed buoyancy F of the main body 1, the first ballast concrete 21 is cast when the main body 1 is prefabricated, such as after the main body 1 is cast in the casting area and moved to the outfitting area, the first ballast concrete 21 is cast, which is conducive to vacating the casting area as soon as possible for the casting of the next section of the main body 1. The ballast concrete is arranged on the top surface of the carriageway, and the ballast concrete is plain concrete. Preferably, the concrete strength of the ballast concrete is less than the concrete strength of the main body 1. The thickness of the ballast concrete must meet the minimum thickness requirement jointly controlled by the wastewater pump room and the cross-ditch arrangement, and the slope adjustment of the ballast concrete is carried out when the second ballast concrete is cast.

[0046] According to current regulations, the anti-buoyancy coefficient of the immersed tube must be 1.01-1.02 during the sinking stage, so the sum of G0 and G1 is at least 1.01 times the design buoyancy F, which can effectively ensure that the freeboard value of the body 1 after actually entering the corresponding waters is less than 0. If 1.02 times is selected, the body 1 will achieve a negative buoyancy of 1.02 by its own weight during installation, and a negative buoyancy of 1.05 will be achieved through a simple ballast water bag after installation, which can appropriately reduce costs and construction difficulties. The anti-buoyancy coefficient requirement of the main body 1 during operation is met. According to existing specifications, the anti-buoyancy coefficient during operation needs to be greater than 1.06. The second ballast concrete is poured after the main body 1 is sunk, which is conducive to reducing the weight of the pipe section during transportation and saving transportation costs.

[0047] Of course, the preferred That is, according to the existing design specifications, the anti-buoyancy coefficient of 1.05 of the section after sinking or stable ballast is used as the control index, which can save costs to the maximum extent, while ensuring that the anti-buoyancy coefficient requirements of the sinking and docking construction stage are met, completely eliminating the ballast water tank system, and no additional ballast device is required. If the specifications adjust the above indicators, they will be adjusted accordingly. Use the existing ballast concrete poured after sinking, and pour the first ballast concrete 21 in advance in the prefabrication stage as a partial ballast layer, such as Figure 2 As shown, the pipe segment cannot float by itself in the construction waters, which is conducive to reducing the difficulty of design and meeting the requirements of the anti-buoyancy coefficient after sinking and docking. There is no need to introduce additional equipment or structure, and the ballast water tank system can be cancelled, thereby reducing construction costs and avoiding floating when replacing the water tank. The risk of floating during the operation phase is small, and the casting process is carried out in the factory, with low operating difficulty and risk, and it is easy to accurately control the weight of the pipe segment after casting to avoid waste of additional materials.

[0048] Taking Qianhaiwan as an example, the construction environment in Qianhaiwan can be summarized as follows:

[0049] The wave height in the foundation channel is less than 0.2m, and there are many days without waves, accounting for 29% of the whole year. The wave height is less than 0.5m, accounting for more than 90% of the waves. The sand content gradually decreases from the mouth to the inside. The seawater density: the seawater density gradually decreases from the outside of the bay to the inside of the bay, between 1.00 and 1.015. The design high tide level in Qianhai Bay is +1.62m, and the design low tide level is -0.83m. The annual average number of days with strong winds above level 6 is 20 days, and the guarantee rate of working days with winds less than level 6 is 94%. The ebb and flow tide in Qianhai Bay is affected by the excavation of the foundation channel. The maximum flow velocity of the ebb and flow tide in the foundation channel is about 0.1m / s, and the flow velocity in some confluence areas is relatively large, about 0.4m / s.

[0050] The design dimensions and other parameters of the submerged tube in the prior art (positive freeboard submerged tube) and the negative buoyancy submerged tube (negative freeboard submerged tube) of the present application are compared as shown in Table 1 below:

[0051] Table 1 Parameter comparison table

[0052]

[0053]

[0054] According to the above table, it can be seen that the use of negative freeboard immersed tubes means that there is no need to consider the design freeboard value. The design freeboard value can be negative, which can effectively reduce the cross-sectional height of the immersed tube and thus reduce the engineering workload of the structure and foundation pit.

[0055] The negative buoyancy submerged tube prefabrication method comprises the following steps:

[0056] a. Prefabricated body 1;

[0057] b. pouring a first ballast concrete 21 in the body 1, and measuring whether the weight of the body 1 satisfies a first anti-buoyancy coefficient;

[0058] c. After meeting the requirements, install the primary outfitting parts and embedded parts;

[0059] d. Install the end sealing wall to complete the prefabrication of the negative buoyancy submerged tube, such as Figure 2 As shown (outfitting parts, embedded parts and end sealing walls are not shown).

[0060] First, the prefabrication of the main body 1 is the same as the prefabrication process of the positive freeboard pipe segment in the prior art in terms of steel bar binding, formwork installation, and concrete pouring. The existing immersed tube prefabrication process can be used. To ensure accuracy, the dry bulk density of the concrete used in the main body 1 can be determined in advance, and the theoretical weight of the main body 1 can be calculated. In order to avoid large errors that cause the weight of the immersed tube to increase or decrease, and thus cause the immersed tube to fail to achieve an anti-buoyancy coefficient of 1.05, it is necessary to strictly test the slump of the concrete before pouring into the mold, as well as the weight of the freshly mixed concrete (the test value before entering the mold) and the weight of the hardened concrete (the test value 28 days after hardening).

[0061] For example, the seawater density in Qianhai Bay is affected by the river and varies between 1.00 and 1.015 g / cm3. When prefabricating the immersed tube, the seawater density should take the upper limit value to ensure that the immersed tube meets the predetermined anti-buoyancy coefficient requirements after hydraulic crimping during the construction phase. For example, if the anti-buoyancy coefficient is 1.05, the theoretical weight of the prefabricated pipe section = drainage volume V × seawater density 1.015 × 1.05 (anti-buoyancy coefficient).

[0062] Then the first ballast concrete 21 is poured. The main body 1 can be moved to the outfitting area by a trolley to vacate the pouring area as soon as possible so as to start pouring the next pipe segment as soon as possible and shorten the construction period. The weight of the main body 1 before pouring the first ballast concrete 21 is then measured by the pressure sensor of the trolley. The trolley is a pipe segment transfer equipment commonly used in the prior art, which is widely and evenly distributed under the pipe segment. Each trolley is provided with a pressure sensor for easy weighing.

[0063] According to the theoretical weight of the main body 1 and the weight of the first weighing, the pouring volume of the first ballast concrete 21 is checked to ensure 1.05 times the negative buoyancy. Then, after pouring the first ballast concrete 21, the pressure sensor of the trolley is used to measure again whether the weight of the main body 1 meets the first anti-buoyancy coefficient and whether the weight distribution is uniform.

[0064] When pouring the first ballast concrete 21, it is advisable to adopt layered pouring, at least three times, with the thickness of each pouring being roughly the same. After each pouring, the weight distribution of the pipe section is measured. The hydraulic jack of the trolley can be used for weighing at the same time, and the pressure sensor thereon can be used to measure the weight, and then the weighing accuracy can be ensured through filtering and calibration.

[0065] After the requirements are met, the primary outfitting parts and embedded parts are installed; this step can also be carried out simultaneously with the pouring of the first ballast concrete 21, or installed first and then poured. Since the weight of the primary outfitting parts and embedded parts can be measured in advance and there is basically no change after installation, if measured again after installation, the weight of the primary outfitting parts and embedded parts can be subtracted to determine whether the anti-buoyancy coefficient meets the standard.

[0066] Finally, the end sealing wall is installed to complete the prefabrication of the negative buoyancy submerged tube.

[0067] After the main body 1 is transported to the corresponding installation position and is sunk, that is, when the ballast concrete is poured to replace the ballast water tank in the prior art, the second ballast concrete is poured to meet the anti-buoyancy coefficient requirements during the operation period of the immersed tube and achieve the corresponding negative buoyancy level, which is beneficial to reducing the equipment requirements for transportation equipment and the difficulty of transportation and installation.

[0068] The process comparison between the prefabrication method of the present invention and the prefabrication method of the positive freeboard pipe segment in the prior art is shown in Table 2 below:

[0069] Table 2 Prefabrication process comparison table

[0070]

[0071] According to the above table, the prefabrication method of the present application continues to use the ballast concrete poured after the existing pipe segment is sunk, and the first ballast concrete 21 is poured in advance in the factory prefabrication stage as a partial ballast layer, so that the pipe segment cannot float on its own in the construction waters. The operation is easy and the risk is small. It is convenient to accurately control the weight of the pipe segment after pouring, avoid the waste of extra materials, and help reduce construction costs. It will not significantly increase the prefabrication period, and provides technical guidance and operating procedures for the construction of new negative buoyancy submerged tubes, which is worthy of wide promotion and application.

[0072] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art who is familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for prefabricating a negative buoyancy submerged tube, characterized in that: The steps include: a. Prefabricated body (1); b. pouring a first ballast concrete (21) in the body (1), and measuring whether the weight of the body (1) satisfies a first anti-buoyancy coefficient; c. After meeting the requirements, install the primary outfitting parts and embedded parts; d. Install the end sealing wall to complete the prefabrication of the negative buoyancy submerged tube; before step b, it also includes determining the dry bulk density of the concrete used in the body (1) and calculating the theoretical weight of the body (1); step b includes the following steps: b1. After reaching a predetermined strength, the main body (1) is moved to an outfitting area by a trolley, and the weight of the main body (1) before pouring the first ballast concrete (21) is measured by a pressure sensor of the trolley; b2. According to the theoretical weight of the body (1), in combination with step b1, determine the pouring volume of the first ballast concrete (21), pour the first ballast concrete (21), and then measure by the pressure sensor of the trolley whether the weight of the body (1) meets the first anti-buoyancy coefficient and whether the weight distribution is uniform; Wherein, each of the trolleys is provided with a pressure sensor.

2. The prefabrication method according to claim 1, characterized in that: The first ballast concrete (21) is poured at least three times, and the weight distribution is measured after each pouring.

3. The prefabrication method according to any one of claims 1-2, characterized in that: The first anti-buoyancy coefficient is 1.02-1.

05.

4. The prefabrication method according to any one of claims 1-2, characterized in that: The order of steps b and c can be interchanged or performed simultaneously.

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