Buoyancy countermeasure and construction method thereof

Abstract

To prevent floating by buoyancy acting on an undersea tunnel without using heavy concrete.SOLUTION: A plurality of buoyancy counterparts 30 for preventing floating due to buoyancy acting on an undersea tunnel T are constructed at a plurality of locations inside the undersea tunnel T. The buoyancy counterpart 30 is formed of a reinforcing bar laminate 31 formed by piling up a plurality of reinforcing bars 31a, and a hardening material 32 placed so as to embed the reinforcing bar laminate 31 therein. Mortar using only sand as an aggregate is applied to the hardening material 32.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a buoyancy countermeasure and a construction method thereof, and more particularly to a technique for preventing underwater and underground structures from floating up due to buoyancy acting on them. [Background technology]

[0002] When renovating underwater structures such as underwater tunnels, which are tunnels built under the bottom of bodies of water such as rivers, canals, or the sea, or underground structures (railways, roads, water supply and sewerage, and communication pipelines) built in soil that contains a lot of groundwater, removing the ceiling panels used as counterweights may cause the underwater or underground structure itself to float up.

[0003] Similarly, when constructing new underwater or underground structures, there is a risk of them floating up if there is not enough soil cover or the ground is very soft and the weight is not sufficient to resist buoyancy.

[0004] Therefore, in the past, as described in Patent Document 1 (JP Patent Publication No. 2000-034158), for example, a technology has been known to prevent the tunnel from floating up by constructing walls out of heavy concrete with a high specific gravity, for example by mixing iron powder, between pillars in a management area for maintenance and inspection located beneath a tunnel, which is an underground structure.

[0005] Here, when constructing the above-mentioned wall, in order to use as much heavy-duty concrete as possible to ensure that the tunnel does not rise up, the amount of reinforcing bars placed in the formwork is less than that used in the construction of a general wall. Then, heavy-duty concrete is poured into the formwork surrounding the reinforcing bars. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2000-034158 A Summary of the Invention [Problem to be solved by the invention]

[0007] Now, when pouring heavy concrete, the heavy concrete is brought in while being mixed with a mixer truck (truck mixer), and the heavy concrete is pumped out by a concrete pump truck and poured into the aforementioned formwork. To do this, one lane of the main road for general vehicles located above the controlled area must be restricted, and mixer trucks and concrete pump trucks must be positioned in a way that improves workability.

[0008] In addition, because the main line is restricted in this way, construction work will be carried out at night when the volume of general traffic is relatively low. This means that heavy concrete, which is a special material, will be difficult to obtain when construction work is carried out at night, creating problems with the supply itself.

[0009] Furthermore, in order to connect the main line above and the controlled area below, hatches will be opened at regular intervals to introduce piping from the concrete pump truck into the controlled area (for example, the maximum piping length will be about 70 m) and pour heavy concrete, so it will be necessary for workers on the main line and those in the controlled area to communicate with each other as they carry out the work.

[0010] Furthermore, heavy-duty concrete is not made by mixing sand and gravel into the cement as with regular concrete, but by mixing heavy aggregates with high specific gravity such as iron ore and barium ore, which means that there is a risk of problems such as the heavy concrete clogging the pipes when it is pumped.

[0011] The present invention has been made in light of the above-mentioned technical background, and aims to provide a technology that can prevent underwater and underground structures from floating up due to buoyancy acting on them without using heavy concrete. [Means for solving the problem]

[0012] In order to solve the above problems, the buoyancy countermeasure of the present invention described in claim 1 is a buoyancy countermeasure that prevents an underwater structure or an underground structure from floating up due to buoyancy acting on the underwater structure or underground structure, The buoyancy countermeasure portion is Inside the underwater structure or the underground structure Between some of the posts installed at specified intervals Built on It is made up of multiple reinforcing bars arranged in parallel with each other at a certain interval in the horizontal direction and stacked in a cross pattern with alternating different orientations in the vertical direction. A reinforcement bar laminate and a hardening material poured so as to embed the reinforcement bar laminate. and post-installed anchors are installed between the buoyancy countermeasure portion and the support column and between the buoyancy countermeasure portion and a bottom portion on which the buoyancy countermeasure portion is constructed. It is characterized by:

[0014] Claim 2 The buoyancy countermeasure of the present invention described in Claim 1 In the described invention, the hardening material is characterized by comprising cement paste and aggregate mixed into the cement paste.

[0015] Claim 3 The buoyancy countermeasure of the present invention described in Claim 2 In the invention described above, the hardening material is a mortar using only sand as an aggregate.

[0016] Claim 4 The buoyancy countermeasure of the present invention described in Claim 2 or 3 In the described invention, the horizontal spacing of the reinforcing bars is wider than the maximum particle size of the aggregate.

[0018] Claim 5 The buoyancy countermeasure of the present invention described in the above claims Any one of 1 to 4 In the invention described, the hardening material at the top is formed to the same height as the support and is non-shrinkable.

[0019] Claim 6 The buoyancy countermeasure of the present invention described in the above claims Any one of 1 to 5 In the described invention, the underwater structure or the underground structure is a road tunnel having a main line area formed on the upper side where a main line on which general vehicles run is provided, and a management area having the support pillars on the lower side for carrying out maintenance and inspection of the structure.

[0020] In order to solve the above problems, Claim 7 The construction method of the buoyancy countermeasure of the present invention described in is a construction method of the buoyancy countermeasure for preventing floating up due to buoyancy acting on an underwater structure or an underground structure, in which four angle bars are erected inside the underwater structure or the underground structure so that the corners of the angle bars face outward to form the four corners of a rectangle, and the angle bars are arranged in parallel with each other at a predetermined interval in the horizontal direction so as to be restricted by the inside of the angle bars, and are arranged in alternating different directions in the vertical direction. Orthogonal The method is characterized in that a reinforcing bar stack is constructed by arranging and stacking multiple reinforcing bars, a formwork is assembled to surround the reinforcing bar stack, a hardening material is poured into the formwork to embed the reinforcing bar stack, and the formwork is removed after the hardening material has hardened.

[0021] Claim 8 The construction method of the buoyancy countermeasure part of the present invention described in Claim 7 In the invention described above, the underwater structure or the underground structure has a main line area on the upper side where a main line on which general vehicles run is provided, and a main line area on the lower side. A plurality of electrodes are provided at predetermined intervals. The road tunnel has a management area for carrying out maintenance and inspection of the structure, and the buoyancy Opposition The present invention is characterized in that the section is constructed using only the management area.

[0022] Claim 9 The construction method of the buoyancy countermeasure part of the present invention described in Claim 7 or 8 In the described invention, the buoyancy countering portion is constructed prior to removal of the counterweight during renovation work on the underwater structure or the underground structure. Effect of the Invention

[0023] According to the present invention, a buoyancy-resistant section formed of a reinforcing bar stack formed by stacking a number of reinforcing bars and a hardening material poured so as to embed this reinforcing bar stack is constructed inside an underwater structure or an underground structure, making it possible to prevent underwater structures or underground structures from floating up due to buoyancy acting on them without using heavy concrete containing heavy aggregate. [Brief description of the drawings]

[0024] [Figure 1] 1 is a cross-sectional view showing the interior of an undersea tunnel in which a buoyancy countermeasure section according to one embodiment of the present invention is being constructed, viewed from the extension direction. [Diagram 2] FIG. 2 is a plan view showing the lower part of the undersea tunnel in FIG. 1. [Diagram 3] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 4] 2 is a cross-sectional view taken from a radial direction showing a buoyancy countermeasure portion constructed in the undersea tunnel of FIG. 1. [Diagram 5] 5 is an enlarged cross-sectional view showing a portion indicated by the symbol E in FIG. 4. [Figure 6] FIG. 6 is a cross-sectional view taken along line BB in FIG. 5. [Figure 7] 1 is a cross-sectional view showing the interior of an undersea tunnel in which a buoyancy countermeasure portion according to one embodiment of the present invention is constructed, viewed from the extension direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings for explaining the embodiment, the same components are generally designated by the same reference numerals, and the repeated description will be omitted.

[0026] FIG. 1 is a cross-sectional view showing the interior of an undersea tunnel from the extension direction in which a buoyancy countermeasure portion, which is one embodiment of the present invention, is being constructed; FIG. 2 is a plan view showing the lower part of the undersea tunnel of FIG. 1; FIG. 3 is a cross-sectional view along line AA of FIG. 1; FIG. 4 is a cross-sectional view from the radial direction showing the buoyancy countermeasure portion constructed in the undersea tunnel of FIG. 1; FIG. 5 is an enlarged cross-sectional view showing the part marked E in FIG. 4; FIG. 6 is a cross-sectional view along line BB of FIG. 5; and FIG. 7 is a cross-sectional view showing the interior of an undersea tunnel from the extension direction in which a buoyancy countermeasure portion, which is one embodiment of the present invention, has been constructed.

[0027] The buoyancy countermeasure section can be constructed during either the renewal or new construction of an undersea tunnel, but in this embodiment it is constructed during renewal work prior to the removal of the counterweight ceiling panel (counterweight) 11 used to prevent the undersea tunnel T, which is a type of road tunnel, from floating up.

[0028] In Figures 1 to 3, the undersea tunnel (underwater structure) T of this embodiment, which was constructed through the sea, has a main line area t1 on the upper side where a main line 10 on which general vehicles run is provided, and a management area t2 on the lower side for carrying out maintenance and inspection of the undersea tunnel T.

[0029] Above the main line area t1, a counterweight ceiling plate 11 for preventing the undersea tunnel T from floating up and a dust collector ceiling plate 12 for forming an exhaust duct 12a are installed and supported by hanging brackets 12b (Fig. 4). In addition, a dust collector 13 is installed at the end of the dust collector ceiling plate 12 to suck in dust and exhaust gas from the undersea tunnel T and send it into the exhaust duct 12a.

[0030] The management area t2 is divided into three areas, as shown in Figure 3, and is composed of a management passage (first lower area) 20 located in the center and having a height and width sufficient to allow vehicles such as a 2-ton truck to pass through, an equipment placement space (second lower area) 22 separated from the management passage 20 by multiple pillars 21 and in which various equipment necessary for the maintenance and inspection of the undersea tunnel T is placed, and a tunnel (third lower area) 24 separated from the management passage 20 by a partition wall 23 and in which communication cables, power transmission lines, etc. are laid.

[0031] In this embodiment, the width of the pillars 21 provided along the extension direction of the undersea tunnel T is 350 mm, and the distance between the pillars 21 is 3150 mm. However, the dimensions of the pillars 21 can be freely set and are not limited to the values ​​shown in this embodiment.

[0032] In this embodiment, as shown in Fig. 3, in the radial cross section of the undersea tunnel T, the management passage 20 is in the center, the equipment arrangement space 22 is provided to the right of it, and the tunnel 24 is provided to the left of it, but the positional relationship is not limited to these. Furthermore, it is sufficient that the tunnel is divided into a plurality of areas via the supports 21, and it is not necessary that the tunnel is divided into three or more areas or that partition walls 23 are provided.

[0033] In the renewal work of the undersea tunnel T, if the existing counterweight ceiling plate 11 is removed to renew the tunnel inner wall, there is a risk that the weight balance of the undersea tunnel T against buoyancy will be lost and it will float up. Therefore, in order to construct a buoyancy countermeasure 30 (Figs. 4 and 5) that prevents such floating up, as shown in Figs. 1 to 3, multiple trucks V loaded with necessary materials (reinforcing bars, cement, aggregate, water, formwork (concrete panels), etc.) and a small crawler crane CC with four foldable outriggers supporting the vehicle body are brought into the management passage 20.

[0034] Next, the buoyancy countering portion 30 of the present embodiment will be described with reference to FIGS.

[0035] The buoyancy countermeasures 30 in this embodiment are constructed inside the undersea tunnel T, specifically, between the supports 21 provided at a predetermined interval between the management passage 20 and the equipment arrangement space 22, as shown in FIG. 4. However, if the buoyancy countermeasures 30 are constructed between all the supports 21, the management passage 20 and the equipment arrangement space 22 will be blocked, and if an excessive number of buoyancy countermeasures 30 are constructed in succession, there is a risk that workers will have to make a detour when moving between the management passage 20 and the equipment arrangement space 22, which will be inconvenient. Therefore, as long as the buoyancy countermeasures 30 can secure a predetermined weight, there may be places between the supports 21 where the buoyancy countermeasures 30 are not constructed at appropriate intervals (see FIG. 7).

[0036] In this embodiment, the buoyancy countering portion 30 is thicker than the struts 21 (see Figs. 3 and 4), but the struts 21 and the buoyancy countering portion 30 may be the same thickness, or the struts 21 may be thicker than the buoyancy countering portion 30. In this embodiment, the buoyancy countering portion 30 is constructed between the struts 21, but it may be constructed in a location other than between the struts 21.

[0037] As shown in FIG. 5, the buoyancy countermeasure portion 30 is formed of a reinforcing bar stack 31 formed by stacking a plurality of reinforcing bars 31a in multiple stages, and a hardening material 32 poured so as to embed the reinforcing bar stack 31.

[0038] In this embodiment, the reinforcing bars 31a constituting the reinforcing bar stack 31 of the buoyancy countering section 30 are deformed reinforcing bars (bar-shaped reinforcing bars formed by rolling steel to form uneven protrusions on the surface) of D32 (diameter 32 mm). As shown in Figs. 5 and 6, the reinforcing bars 31a are arranged in parallel to each other at a predetermined interval (for example, 5 cm intervals) in the horizontal direction and are arranged perpendicular to each other in the vertical direction. The size and type of the reinforcing bars 31a are not limited to those described above and can be freely selected. The intervals between the reinforcing bars 31a in the horizontal direction do not need to be 5 cm intervals, and it is sufficient that the reinforcing bars 31a are arranged in different directions in the vertical direction and do not need to be perpendicular to each other.

[0039] The hardening material 32 in which the reinforcing bar stack 31 is embedded is composed of a cement paste made by mixing water and cement, and aggregate mixed into the cement paste. The horizontal intervals between the reinforcing bars 31a are wider than the maximum particle size of the aggregate so that the hardening material 32 can be distributed throughout the entire interior of the reinforcing bar stack 31.

[0040] As the aggregate, gravel (coarse aggregate) or sand (fine aggregate) can be used, but it is preferable to use only sand. This is because the cement paste does not contain gravel, which is a coarse aggregate (i.e., only sand, which is a fine aggregate), so the gap between the reinforcing bars 31a can be narrowed to a degree that sand can pass through, which means that the reinforcing bars 31a can be densely arranged, making the reinforcing bar stack 31 heavier.

[0041] In addition, in the case of concrete using sand as aggregate, a mixer truck must enter the undersea tunnel, but it is often not possible to enter the management passage 20 due to space restrictions. In other words, in the case of concrete, a mixer truck must enter the upper main line 10, a hatch communicating with the lower side is opened, and concrete is pumped and poured by a concrete pump truck, which requires lane restrictions on the main line 10 and the workers on the main line area t1 side and the workers on the management area t2 side to communicate with each other about the progress of work. In contrast, in the case of mortar using only sand as aggregate, if the mortar materials (cement, sand, water) are brought in by a truck V that has entered the management passage 20, the workers can mix them manually on-site to prepare mortar and pour it, which eliminates the above-mentioned need and makes construction easier.

[0042] Here, the construction of the buoyancy countering portion 30 will be described with reference to FIGS.

[0043] When constructing the reinforcing bar stack 31, first, four angle irons (equal leg angle steel) 33 are erected with the corners of the angle facing outward so as to form the four corners of the rectangular reinforcing bar stack 31 in a plan view (FIG. 6). The angle irons 33 are installed, for example, by welding to anchors buried in the bottom surface on the undersea tunnel T side.

[0044] Next, the reinforcing bars 31a are arranged in parallel with each other at a predetermined interval in the horizontal direction so as to be restricted by the inside of these angle bars 33, and are arranged alternately at right angles in the vertical direction to construct a reinforcing bar stack 31 formed by stacking a plurality of reinforcing bars 31a. Specifically, using a long ruler or a long plate with markings at predetermined intervals (in this embodiment, the intervals between the reinforcing bars 31a are 5 cm pitch), the reinforcing bars 31a are laid out at predetermined intervals in the horizontal direction in an area surrounded by four angle bars 33. Next, on top of the laid out reinforcing bars 31a, reinforcing bars 31a are laid out at predetermined intervals in the horizontal direction so as to be perpendicular to the reinforcing bars 31a. This is repeated in sequence to construct a reinforcing bar stack 31 in which a plurality of reinforcing bars 31a are stacked.

[0045] Once the reinforcing bar stack 31 has been constructed, a formwork (not shown) is assembled to surround the reinforcing bar stack 31. The hardening material 32 described above is then poured into the formwork to embed the reinforcing bar stack 31. At this time, if post-installed anchors are installed in the supports 21 and the bottom, it becomes possible to firmly integrate the buoyancy countermeasure section 30 to be constructed with the submarine tunnel T, which is an existing structure.

[0046] Here, buoyancy Opposition The portion 30 can also be formed with a gap provided between it and the support 21 or the ceiling surface.

[0047] Furthermore, as shown in FIG. 5, when the hardening material 32 is poured up to the ceiling surface of the control area t2 to form the buoyancy-resistant portion 30 at the same height as the support 21, it is desirable to use a material having non-shrinkage properties (for example, non-shrinkage mortar) for the uppermost hardening material 32.

[0048] In this way, the non-shrinkable hardening material 32 hardens in the same shape as when it was poured, so that no gaps are formed at the top of the buoyancy-counteracting part 30 (i.e., between the upper surface of the buoyancy-counteracting part 30 and the ceiling surface), and the adhesion to the ceiling surface is improved, resulting in integration and increased durability.

[0049] Finally, once the hardening material 32 poured into the formwork has hardened, the formwork is removed, thereby forming the buoyancy countermeasure 30 shown in Figs.

[0050] Such a buoyancy countermeasure 30 is constructed between the supports 21 provided in the management area t2 along the extension direction of the undersea tunnel T. In this embodiment, as shown in Fig. 7, the areas where the buoyancy countermeasure 30 is constructed between the supports 21 are continuous with the areas where it is not constructed. In this way, workers only have to make a slight detour when moving between the management passage 20 and the equipment arrangement space 22, and workability is not impeded.

[0051] The construction pattern of the buoyancy countering parts 30 is not limited to that of the present embodiment, and may be such that the parts where the buoyancy countering parts 30 are constructed and the parts where they are not constructed are alternated. Also, in the present embodiment, the buoyancy countering parts 30 are constructed in a plurality of places, but they may be constructed in only one place.

[0052] In this way, according to this embodiment, a buoyancy-resistant section 30 formed of a reinforcing bar stack 31 formed by stacking a plurality of reinforcing bars 31a and a hardening material 32 poured so as to embed this reinforcing bar stack 31 is constructed inside the undersea tunnel T, so that it is possible to prevent the undersea tunnel T from floating up due to buoyancy acting on it without using heavy concrete containing heavy aggregate.

[0053] As a result, the buoyancy control area t2 formed under the undersea tunnel T was used only. Opposition Therefore, unlike the case of pouring heavy concrete by pumping, it is no longer necessary to restrict lanes on the main line 10 for general vehicles provided in the main line area t1 formed above the undersea tunnel T, and to arrange mixer trucks and concrete pump trucks to improve workability.

[0054] In addition, since there is no longer a need to restrict lanes on the main line 10, construction work can be carried out even at times other than at night when the amount of general vehicle traffic is relatively low, and there is no need to procure special heavy concrete at night when it is difficult to obtain it.

[0055] In addition, since there is no need to open a hatch and introduce piping from the concrete pump truck to the controlled area to connect the upper main area t1 and the lower controlled area t2, there is no need for workers in the main area t1 and the lower controlled area t2 to communicate with each other while working.

[0056] In addition, because the heavy concrete contains heavy aggregates with a high specific gravity (such as iron ore and barium ore), there is no risk of problems such as the heavy concrete clogging the pipes during pumping.

[0057] Furthermore, since the buoyancy countering portion 30 is formed of the reinforcing bar stack 31 formed by stacking a plurality of reinforcing bars 31a, the desired weight can be achieved even with a relatively thin thickness, so that the wall thickness formed by the buoyancy countering portion 30 can be thin. This allows the passage width to be secured, and the wall thickness does not increase, resulting in a deterioration in workability during maintenance.

[0058] The invention made by the inventor has been specifically described above based on the embodiment, but the embodiment disclosed in this specification is illustrative in all respects and is not limited to the disclosed technology. In other words, the technical scope of the present invention should not be interpreted restrictively based on the description in the above embodiment, but should be interpreted strictly according to the description in the claims, and includes technologies equivalent to the described technologies in the claims and all modifications that do not deviate from the gist of the claims.

[0059] For example, the rectangle expressing the shape of the reinforcing bar laminate 31 in plan view is not limited to the rectangle shown in FIG. 6, but also includes a square. [Industrial Applicability]

[0060] In the above explanation, the present invention has been described as being applied to the construction of a buoyancy countermeasure section during the renewal work of an undersea tunnel. However, the present invention can be widely applied not only to undersea tunnels (tunnels), but also to renewal and new construction work of various underwater structures constructed under the bottom of bodies of water such as rivers, canals, and the sea, and various underground structures (tunnels, water supply and sewerage, communication pipelines) constructed in the ground containing a large amount of groundwater. [Explanation of symbols]

[0061] 10 Main Line 11 Counterweight ceiling plate 12 Ceiling plate for dust collector 20 Management passage 21 Post 22 Equipment placement space 23 Compartment Wall 24 Tunnel 30 Buoyancy counter part 31 Reinforced Concrete 31a Steel Bar 32 Hardening materials 33 Angle iron CC Crawler Crane T Undersea tunnel (underwater structure) V-Track t1 Main Line Area t2 Management Area

Claims

1. A buoyancy countermeasure that prevents an underwater structure or an underground structure from floating up due to buoyancy acting on the underwater structure or the underground structure, The buoyancy countermeasure portion is The underwater structure or the underground structure is constructed between some of the supports provided at predetermined intervals between the supports, The reinforcing bar stack is made up of a plurality of reinforcing bars arranged in parallel to each other at a predetermined interval in the horizontal direction and stacked in a cross pattern with alternating different orientations in the vertical direction, and a hardening material is poured in so as to embed the reinforcing bar stack. post-installed anchors are installed between the buoyancy countermeasure portion and the support column and between the buoyancy countermeasure portion and a bottom portion on which the buoyancy countermeasure portion is constructed; A buoyancy countermeasure portion characterized by:

2. The hardening material comprises a cement paste and an aggregate mixed into the cement paste.

2. The buoyancy countermeasure portion according to claim 1.

3. The hardening material is a mortar using only sand as an aggregate.

3. The buoyancy countermeasure according to claim 2.

4. The horizontal spacing of the reinforcing bars is wider than the maximum particle size of the aggregate.

4. The buoyancy countermeasure portion according to claim 2 or 3.

5. The buoyancy counteracting portion is The hardening material is formed to the same height as the support and has non-shrinkage properties. The buoyancy countermeasure part according to any one of claims 1 to 4.

6. The underwater structure or the underground structure is A road tunnel in which a main line area is formed on the upper side, where a main line on which general vehicles run is provided, and a management area having the support pillars and for carrying out maintenance and inspection of the structure is formed on the lower side. The buoyancy countermeasure part according to any one of claims 1 to 5.

7. A method for constructing a buoyancy countermeasure part that prevents an underwater structure or an underground structure from floating up due to buoyancy acting on the underwater structure or the underground structure, comprising: Inside the underwater structure or the underground structure, four angle bars are erected so that the angled corners face outward to form the four corners of a rectangle, and a reinforcing bar stack is constructed by stacking a plurality of reinforcing bars in such a way that the reinforcing bars are arranged in parallel to each other at a predetermined interval in the horizontal direction and arranged perpendicularly in different directions in the vertical direction so as to be restricted by the inside of the angle bars, Assemble a formwork to surround the reinforcing bar stack; A hardening material is poured into the formwork to embed the reinforcing bar stack; removing the formwork after the hardening material has hardened; A construction method for a buoyancy-resistant portion.

8. The underwater structure or the underground structure is a road tunnel having a main line area formed on the upper side with a main line on which general vehicles run, and a management area formed on the lower side with a plurality of supports arranged at predetermined intervals for carrying out maintenance and inspection of the structure, The buoyancy countermeasure portion is constructed using only the management area.

8. The method for constructing a buoyancy-opposing portion according to claim 7.

9. The buoyancy countermeasure portion is constructed prior to removal of the counterweight in the renewal work of the underwater structure or the underground structure.

9. The method for constructing a buoyancy-opposing portion according to claim 7 or 8.

Images