JP3866848B2 - Suspended semi-submersible structure - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a suspended semi-submersible structure, for example, a building such as an airport constructed on an offshore artificial island or a terminal facility constructed adjacent to a harbor or a building constructed adjacent to a coastal landfill. Used as a seismic isolation and settlement measure.
[0002]
[Prior art]
In recent years, many offshore artificial islands have been planned, but large buildings such as airports and port terminal facilities are generally built on the soft ground of artificial islands, and are therefore affected by earthquakes and land subsidence. Cheap. For this reason, countermeasures against earthquakes and countermeasures for uneven settlement are important technical issues, and due to consideration of the foundation structure such as ground improvement and jack-up construction, the construction period and construction costs are increasing.
[0003]
Making a building a floating structure has the advantages of reducing the effects of earthquakes and reducing the effects of subsidence due to the seismic isolation effect of water. Since the structure is affected by fluctuations in tide level, loading load, wind and waves, the displacement of the floating structure due to fluctuations in tide level, etc. should be reduced, and the level difference between the ground and the surrounding ground must be minimized. It is a construction method that can not be used because it interferes with the entry of the means and the connection of the lifeline.
[0004]
A method has been proposed to eliminate the effects of tidal fluctuations by installing a water shielding wall around the floating structure, but for large buildings such as terminal facilities adjacent to an airfield constructed on an offshore artificial island, the water shielding wall is used. In addition to the enormous cost of construction, the impact of the land subsidence caused by the load of the artificial island landfilled with a large amount of earth and sand is so great that the impermeable wall breaks down due to the unsettled settlement of the impermeable wall over a long period of time. It is difficult to cope with the case where the impervious wall breaks down.
[0005]
In a floating structure such as an oil mining platform, as shown in Japanese Patent Laid-Open No. 61-49029, it uses a frictional resistance between a pile and the ground, and a foundation having a plurality of cylindrical pile fixing members around it. The main body is installed at the bottom of the water, the lower end of the tensile material is connected to the center of the foundation main body, the upper end of the tensile material is connected to the floating structure, and each cylindrical pile fixing member is inserted into the bottom of the water. Injecting and filling the coupling grout material between the head of the ready-made pile and the cylindrical pile fixing member, and forcibly sinking the lower part of the floating structure into the water with the tensile material to A towed floating structure that is not affected by fluctuations of wind, waves or waves has also been proposed, but it was difficult to adopt when the bottom of the ground was soft. In other words, when the water bottom ground into which the ready-made piles are driven is soft ground such as alluvial clay, the peripheral frictional strength of the piles is small, so the number of piles and the pile length need to be remarkably increased. Because of the repeated tides and high tides, a large pulling force acts periodically on the pile, so in soft ground such as alluvial cohesive soil, the ground around the pile deteriorates due to this cyclic load, reducing the frictional strength, This is because there is a high possibility of missing.
[0006]
A soft landing method is also possible, in which the floating structure is lightly grounded at the bottom of the water and the buoyancy reduction at low tide (that is, the increase in vertical load) is received by the bottom of the ground. It is expected that the advantages of the floating structure, which can reduce the effects of earthquakes, are hindered by the effect, and that countermeasures against uneven settlement will be difficult.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned problems, and the object of the present invention can be adopted even when the bottom of the ground is soft ground such as alluvial cohesive soil, and fluctuations in tide level. Suspension type semi-submersible structure that can reliably suppress the displacement and shaking of semi-submersible structures due to fluctuations in load and load, the effects of wind and waves, is less affected by seismic forces, and can easily cope with uneven settlement of the ground It is to provide a submersible structure.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the technical means taken by the present invention are as follows. That is, the suspended semi-submersible structure according to the present invention includes a semi-submersible structure disposed on the surface of the sea where the tide level fluctuates, a mooring device constructed around the structure, and a lower end side connected to the semi-submersible structure. And a tension member connected to the mooring device at the upper end side higher than the water surface, and the semi-submersible structure is loaded on the semi-submersible structure with the lowest tide level by the tension material to the mooring device. When the load is the maximum, the tensile force of the tensile material is maximized, and when the tide level is the highest and the load load on the floating structure is minimum, the suspension is lightly suspended and supported so that the tensile force of the tensile material is minimized. It is characterized by that.
[0009]
According to the above configuration, a large buoyancy acts on the semi-submersible structure due to fluctuations in tide level, load load, waves during typhoons, etc., but instead of completely floating the semi-submersible structure in the water, When the tide level is the lowest and the load on the semi-submersible structure is the maximum, the tensile force of the tensile member is the highest and the tide level is the highest and the semi-submersible structure. When the load on the load is minimum, it is supported by hanging lightly so that the tensile force of the pulling material is minimized, so the semi-submersible structure has the highest tide level and is loaded on the semi-submersible structure. Even when the load is minimized (in other words, when the semi-submersible structure is lightest), it is diving without floating, the tide level is the lowest, and the load on the semi-submersible structure is low Even if the maximum (in other words, the semi-submersible structure is the heaviest Even) without sinking, always to be kept at a constant level.
[0010]
Therefore, the pulling force due to the buoyancy of the semi-submersible structure does not act on the mooring device, and even if the mooring device is made up of pre-made piles driven into the bottom of the ground, the piles are pulled out due to the cyclic load acting on the piles. In principle, the possibility of doing so is eliminated, and safety and reliability can be significantly increased.
[0011]
Although it is lightly suspended and supported, it is basically a floating structure that uses a large buoyancy, so the impact of the earthquake can be reduced by the seismic isolation effect of water.
[0012]
Uneven subsidence of the mooring device due to consolidation subsidence of the bottom and surrounding ground can be dealt with by adjusting the length of the tensile material by loosening the fixing of the upper end side of the tensile material to the mooring device. In this case, since the upper end side of the tensile material is connected to the mooring device at a position higher than the water surface, the length of the tensile material is adjusted at a position higher than the water surface, so that it is easy to take measures against uneven settlement.
[0013]
In addition, as in the invention described in claim 2, the semi-submersible structure includes a lower structure having a large horizontal area that is always located below the water surface and an upper structure having a large horizontal area that is always located above the water surface. And a plurality of column portions having a small horizontal area connecting the two, fluctuations in buoyancy due to fluctuations in tide level can be minimized.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
1 to 4 show an example of a suspended semi-submersible structure according to the present invention. In FIG. 1, reference numeral 1 denotes a water channel formed between a coastal landfill 2 that was previously landfilled and a coastal landfill 3 that was lately landfilled. In FIG. 4, L ₁ indicates the water surface at the low tide (lowest tide level), L ₂ indicates the water surface at high tide, and L ₃ indicates the abnormally high water surface (highest tide level) due to storm surges, storms, waves, and the like during typhoons.
[0015]
In this suspended semi-submersible structure, the semi-submersible structure 4 is arranged on the water surface with the tide level fluctuations (L _{1 to} L ₃ ) as described above, and the semi-submersible structure 4 is constructed around it. When the mooring device 5 is made of a tensile material 6 such as a PC steel wire or a PC steel bar, the tide level is at least L ₁ and the load on the semi-submersible structure 4 is maximum, the tensile force of the tensile material 6 When the tide level is maximum, the maximum tide level is L ₃ , and the load on the semi-submersible structure 4 is minimum, the suspension is lightly suspended and supported so that the tensile force of the tensile material is minimum (a value close to zero). Therefore, the lower end side of the tension member 6 is connected to the semi-submersible structure 4 under the water surface, but the upper end side of the tension member 6 is connected to the mooring device 5 at a position higher than the water surface. a is a communication path with the seaside landfills 2 and 3 on both sides.
[0016]
The mooring device 5 is constructed by driving a ready-made pile 8 such as a steel pipe pile or a PC pile into the water bottom ground 7 and building a support base 9 on a pile head protruding upward from the water surface. Although not shown, in order to suppress horizontal displacement (swaying) of the semi-submersible structure 4, tension using a fender or a hydraulic mechanism is provided between the mooring device 5 and the semi-submersible structure 4. A horizontal displacement prevention mechanism of a system or a compression system may be provided.
[0017]
The semi-submersible structure 4 has a lower horizontal structure (a part with a large amount of drainage to ensure buoyancy) that is always located below the water surface in order to minimize fluctuations in buoyancy due to fluctuations in the tide level. An upper structure 4B with a large horizontal area located above the water surface and a plurality of thin column parts with a small horizontal area connecting both 4A and 4B (a columnar shape that requires less fluctuation in the amount of drainage even if the tide level changes) Part) 4C. The illustrated semi-submersible structure 4 is made of prestressed concrete from the viewpoint of corrosion prevention / durability, but may be made of steel if there is no problem with corrosion prevention / durability and cost.
[0018]
The construction procedure of the suspended semi-submersible structure will be described as follows. The semi-submersible structure 4 is manufactured by dividing it into small blocks by a shipbuilding dock or the like for shortening the construction period, towing them appropriately to the construction point, and combining them at the construction point.
[0019]
When temporary closing of the waterway 1 is impossible, a part of the mooring device 5 is constructed at a predetermined position of the waterway 1, while the semi-submersible structure 4 is constructed at the construction point, and then the remaining mooring device 5 is constructed. Then, after surrounding the semi-submersible structure 4 and connecting the semi-submersible structure 4 to the mooring device 5 with a tension member 6, a ballast including a mechanical device is placed inside the semi-submersible structure 4. Then, the semi-submersible structure 4 is submerged to a predetermined position, and the mooring device 5 is lightly suspended and supported by the tension member 6.
[0020]
When temporary closing of the water channel 1 is possible, first, a necessary number of mooring devices 5 are constructed at a predetermined position of the water channel 1, and then the temporary closing of the water channel 1 is performed, and after draining, the work surrounded by the mooring device 5 A working base is created by carrying out sand of the required thickness for the yard (temporary dock).
[0021]
After manufacturing the semi-submersible structure 4 on the work base, attaching one end of the tension member 6 to the semi-submersible structure 4, water is poured into the work yard (temporary dock), and the semi-submersible structure 4 is levitated. .
[0022]
Thereafter, an upper building (not shown) of the semi-submersible structure 4 is constructed with the other end of the tensile member 6 temporarily fixed to the mooring device 5, and the tensile member 6 is firmly fixed to the mooring device 5. Thereafter, a ballast including a mechanical device is placed inside the semi-submersible structure 4, and the semi-submersible structure 4 is submerged to a predetermined position, and is supported by the mooring device 5 by being suspended by a tension member 6. .
[0023]
According to the above configuration, a large buoyancy acts on the semi-submersible structure 4 due to fluctuations in the tide level, load load, waves during a typhoon, etc., but the semi-submersible structure 4 cannot be completely floated in water. In the mooring device 5 constructed in the surrounding area, when the tide level is at least L ₁ and the loading load on the semi-submersible structure 4 is the maximum, the tensile force of the tensile material 6 is the maximum and the tide level is Since the maximum load is applied to the semi-submersible structure 4 at the maximum L ₃ and the tensile force of the tensile material 6 is minimized (zero or close to it), the suspension is lightly suspended. The submersible structure 4 does not rise or sink due to the influence of tide level fluctuations, load changes, wind and waves, and is always kept at a constant level in this range.
[0024]
Accordingly, the mooring device 5 is not subjected to the pulling force due to the buoyancy of the semi-submersible structure 4 and acts on the pile even though the mooring device 5 is composed of the ready-made pile 8 driven into the bottom bottom ground 7. Since the cyclic load to be performed is always compression, the possibility of the occurrence of pile detachment is eliminated in principle, and safety and reliability can be significantly improved.
[0025]
Although it is lightly suspended and supported, it is basically a structure that is close to a floating body that uses a large buoyancy. Therefore, the effect of the earthquake can be reduced by the seismic isolation effect of water. For the unsettled settlement of the mooring device 5 due to the consolidation settlement of the submarine ground 7 and the coastal landfills 2 and 3 on both sides, the length of the tensile material 6 is adjusted by loosening the fixing of the upper end side of the tensile material 6 to the mooring device 5. It can be dealt with by doing. In this case, since the upper end side of the tension member 6 is connected to the mooring device 5 at a position higher than the water surface, the length of the tension member 6 is adjusted at a position higher than the water surface, so that it is easy to take measures against uneven settlement. is there.
[0026]
【The invention's effect】
The present invention has the above-described configuration, and can be adopted even when the bottom of the ground is soft ground such as alluvial cohesive soil, and is a floating structure that is affected by fluctuations in tide level, load load, wind and waves. It is possible to realize a suspended semi-submersible structure that can reliably suppress the displacement and shaking of the earth, is less affected by the seismic force, and can easily cope with the uneven settlement of the ground.
[Brief description of the drawings]
FIG. 1 is a schematic plan view of a suspended semi-submersible structure showing an embodiment of the present invention.
FIG. 2 is a schematic side view of the suspended semi-submersible structure.
FIG. 3 is a plan view of a main part of the suspended semi-submersible structure.
FIG. 4 is a longitudinal side view of a main part of the suspended semi-submersible structure.
[Explanation of symbols]
4 ... semi submersible structure, 5 ... mooring device, 6 ... tension _{members, L 1, L 2, L} 3 ... tide.

Claims (2)

A semi-submersible structure located on the water surface with tidal fluctuations, a mooring device built around it, and a lower end side connected to the semi-submersible structure, with the upper end side being a mooring device at a position higher than the water surface. The tension material has a maximum tensile force when the tide level is the lowest and the load on the semi-submersible structure is the maximum. Suspended semi-submersible structure characterized in that it is lightly suspended and supported so that the tensile force of the tensile material is minimized when the tide level is the highest and the load on the semi-submersible structure is minimal. . The semi-submersible structure consists of a lower structure with a large horizontal area that is always located below the water surface, an upper structure with a large horizontal area that is always located above the water surface, and a plurality of small structures that connect the two with a small horizontal area. The suspended semi-submersible structure according to claim 1, comprising a column portion.

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