JP3608539B2 - How to use upsoil generated during offshore improvement work - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for effectively using upsoil generated in offshore ground improvement work.
[0002]
[Prior art]
As shown in FIG. 2 and FIG. 3, a caisson 15 is constructed in a predetermined range in a shallow 11 portion relatively close to the land 12, and a space between the caisson 15 and the land 12 is reclaimed. In the case of use, it is necessary to improve the soft ground 111 near the caisson construction area 13 where the caisson 15 is constructed. Such a marine ground improvement work is performed by using a SCP (sand compaction pile) ship 14 and placing a number of compacted sand piles 51 on the soft ground 111 of a viscous soil. In this case, since materials such as sand and gravel used for the compacted sand pile 51 are introduced from the outside, when the substitution rate between the viscous soil and the sand pile, which is soft ground at sea, increases, The surface 111a is raised, and the raised soil 1 is generated. Since the embankment 1 becomes an obstacle to the construction of the caisson 15 in the subsequent process, it is necessary to hesitate and remove it to the planned height.
[0003]
[Problems to be solved by the invention]
The raised soil 1 is a viscous soil having a high water content ratio of 50 to 200%, so it is difficult to use it for other purposes. Except for a small portion of its effective use, it is taken out of the field and disposed of after disposal. It was. However, it is often difficult to secure a disposal site because of its impact on the natural environment. Therefore, the problem of securing a disposal site can be solved if the rising soil 1 generated in the offshore ground improvement work can be effectively used. Further, if the raised soil 1 can be effectively used on the spot, the cost for carrying it out of the hall can be reduced, which is more convenient.
[0004]
Accordingly, an object of the present invention is to reduce the amount of disposal by effectively using the uplifted soil generated in the offshore ground improvement work, and another object of the present invention is to use the uplifted soil on the spot. It is used to reduce the cost of carrying out to the outside.
[0005]
[Means for Solving the Problems]
Under such circumstances, the present inventors have conducted intensive studies, and as a result, mixed with appropriate amounts of modifiers and coarse particles in the high water content swell generated by the offshore ground improvement work, and having specific physical properties. When the soil was obtained, a filling material suitable for compacting sand piles was obtained, and it was found that the raised soil could be used effectively, and the present invention was completed.
[0006]
That is, the present invention is a mixed soil having a water content ratio of 25% or less, a plasticity index of 20 or less, and a fine particle content of 15% or more by mixing uplifted soil, reforming material and coarse-grained material generated in offshore ground improvement work. And providing a method for utilizing the uplifted soil generated in the offshore ground improvement work that uses the mixed soil as a filling material for compacting sand piles.
Further, the present invention mixes uplifted soil generated in offshore ground improvement work and a modifying material to obtain a modified soil, and then mixes the modified soil with a coarse material, and the moisture content is 25% or less. A method for using uplifted soil generated in offshore ground improvement work in which a mixed soil having a plasticity index of 20 or less and a fine particle content of 15% or more is obtained and the mixed soil is compacted and used as a filling material for sand pile formation It is to provide.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the rising soil refers to the raised soil that is generated when a large number of compacted sand piles are formed on the viscous ground at sea. The uplifting soil generated by the offshore ground improvement work is a viscous soil having a water content of 50 to 200%, and most of which is 80 to 150%. The water content ratio refers to the ratio of the weight of water contained in the soil to the weight of the dry soil, and is a value obtained by JIS A1203 “Test method for water content of water”. This uplifting soil has been dredged and shipped to a disposal site outside the site. In the present invention, after dredging to the planned height of the offshore ground, it is mixed with the reforming material and coarse-grained material, so that it is transported to a mixing place on a marine reforming ship, a mixer or a predetermined mixing place on land. Is done.
[0008]
Any modifier may be used as long as it reduces the water content of the raised soil, and examples thereof include dehydrated materials such as quicklime, polymer-based hygroscopic material, and cement. Among these, quick lime is suitable because it is easily available and the mixed soil is easily adjusted to a specific physical property value. Coarse-grained material is blended in order to lower the water content ratio and lower the plastic index. Examples of the coarse-grained material include artificial coarse-grained components such as natural sandy soil and crushed stone mainly composed of sand and gravel. The coarse-grained material may contain fine-grain components such as clay and silt at a maximum of about 15%. However, it is preferable that the fine-grained components are as small as possible because the amount of the coarse-grained material can be reduced. .
[0009]
In the present invention, the method of mixing the embankment soil, the modifying material and the coarse material is not particularly limited, the method of mixing the three raw materials at once, mixing the embankment soil and the modifying material, Examples include a method in which a modified soil excellent in handling is produced in advance, and then the modified soil and coarse particles are mixed to obtain a mixed soil. Among these, the method of mixing modified soil and the modified material to produce modified soil excellent in handling, and then mixing the modified soil and the coarse-grained material has good handling and will be described later. This is preferable in that adjustment for obtaining specific physical properties of the mixed soil is easy.
[0010]
As a blending ratio of the three raw materials, a blending ratio capable of obtaining predetermined physical properties described later is appropriately selected. For example, 50 to 200 kg of a modifying material, usually about 100 kg, is mixed with 1 m ^{3 of} the rising soil to obtain a modified soil having a reduced water content ratio, and then to 100 parts by weight of the modified soil. In contrast, 40 to 150 parts by weight of the coarse material may be mixed.
[0011]
The mixed soil obtained by the above method has a water content of 25% or less, a plasticity index of 20 or less, and a fine particle content of 15% or more. Usually, the water content is 5 to 25%, the plasticity index is 0 to 20, and the fine particle content is 15-70%. The plasticity index is expressed by the difference between the water content ratio (liquidity limit) at the boundary between the plastic state and the liquid state of the soil and the water content ratio (plasticity limit) at the boundary between the semisolid state and the plastic state of the soil. The plasticity index correlates with the water permeability coefficient, and when the plasticity coefficient is 20 or less, a predetermined water permeability coefficient is ensured, thereby improving the discharge of the soil from the casing. On the other hand, when the plastic index exceeds 20, a predetermined water permeability coefficient cannot be ensured, and the material does not easily escape from the casing. This is because, when a predetermined water permeability coefficient is ensured, the air permeability required for discharging from the soil casing is ensured. The plasticity index is determined according to JIS A1205 “Soil liquid limit / plastic limit test method”. In addition, if the physical properties of the mixed soil are within the above range, it can be easily charged into and discharged from the casing used in sand pile construction, and the movement within the casing is smooth, making it suitable as a filling material. Become. The fine particles are clay and silt, and have a particle size of 0.075 mm or less. In addition, a particle size is calculated | required by JIS A1204 "Soil particle size test method".
[0012]
The mixed soil having the above physical properties is used as a filling material in a sand pile type ground improvement method on land or on the sea. As a sand pile type ground improvement method, a compacted sand pile method can be mentioned. Furthermore, if this mixed soil is used as an intermediate filling material for compacted sand piles to be created in the above-mentioned offshore ground improvement work, it is preferable in that the cost of carrying out the rising soil to the outside can be reduced. The target ground of the land sand pile-based ground improvement method is not particularly limited, but if the soil has a slightly higher water content, the mixed material having specific physical property values according to the present invention is used as a filling material for the method. Can be used effectively as
[0013]
Next, a method of using the raised soil generated in the offshore ground improvement work as an filling material for compacted sand piles created in the offshore ground improvement work will be described with reference to FIG. FIG. 1 (A) is a schematic diagram for explaining the offshore ground improvement work of this example, and FIG. 1 (B) is a schematic view showing a completed state of the offshore ground improvement work. In FIG. 1, the arrow pointing to the right indicates the direction of sand pile placement.
[0014]
In the ground improvement work of this example, a modified earth ship 2, a mixed earth ship (hereinafter also referred to as an SCP ship) 3, a coarse material ship 4 and a dredger omitted in the figure are used. The modified earth ship 2 serves as a place for producing the modified earth and serves to transport the modified earth to the mixed earth ship 3, and includes a modified material storage tank 21, a mixer (not shown), and a crane with a grab. The mixed earth ship 3 is a place for producing mixed soil, and includes a mixing facility 31 and a compacted sand pile driving machine 32. Coarse-grained material ship 4 stores coarse-grained material, serves to convey the coarse-grained material to mixed earth vessel 3, and includes a coarse-grained material storage tank 41 and a crane with a grab (not shown). When the scale of construction is large, a gut ship that temporarily stocks the coarse grain material loaded on the coarse grain ship 4 is further used, and the coarse grain ship 4 reciprocates between the gut ship and the land. It is good.
[0015]
A large number of sand piles are formed on the soft ground 111 at sea by a compacted sand pile driving machine 32 attached to a mixed earth ship. A known method can be used as the compacting sand pile placing method. That is, the compacted sand pile driving method is, for example, the process of drawing the casing to the ground surface after penetrating the casing to the design depth in the sea ground, and pulling the casing to a certain depth, where the sand introduced into the pipe, etc. By repeatedly performing the drawing process for discharging the filling material and the re-penetration process for re-penetrating the casing and compacting the discharged sand, etc., a sand pile compacted to a predetermined strength is created, and the softness at sea This is a method of improving the ground. If the replacement rate of the sea ground and sand pile, that is, the ground improvement rate of the sea ground is 30 to 95%, especially 50 to 95%, the ground improvement is sufficiently performed and the raised soil 1 can be used effectively. This is effective in the present invention because it generates a quantity. In the early days of offshore ground improvement work, sand, crushed stone, etc., which are conventionally used, are used as the filling material for sand piles. Due to the sand pile construction in the initial stage, the raised soil is generated on the improved ground.
[0016]
The raised soil 1 generated is conveyed to the mixer of the modified earth ship 2 by a dredger (not shown) (arrow a). In the modified earth ship 2, the modified material (arrow b) stored in the modified material storage tank 21 and the raised soil are mixed by the mixer to produce modified soil. Since this modified soil has a reduced water content, it has excellent handling properties. The modified soil is conveyed to the SCP ship 3 by a crane with a grab (arrow c), and mixed with the coarse material (arrow d) transferred from the coarse material ship 4 by a crane with a grab by a mixing facility 31. A mixed soil having predetermined physical properties.
[0017]
The obtained mixed soil is suitable as an intermediate filling material for sand pile construction, and this intermediate filling material is used for the subsequent placement of the sand pile. As mentioned above, the above-mentioned cycle of uplifting dredging, mixed soil production, sand pile placement using this mixed soil as a filling material, and generation of uplifted soil accompanying this sand pile placement is repeated. By doing so, the ground improvement work in this example is performed. At the end of the construction, the surging soil will remain and will be disposed of, but it is much smaller than the conventional disposal amount.
[0018]
Thus, according to the offshore ground improvement work of this example, as shown in FIG. 1 (B), the soft ground at the sea is improved and the disposal amount of the raised soil 1 is reduced as much as possible to effectively use it. it can. The improved ground has a substitution rate of 30 to 50% of medium substitution, preferably 50 to 95% of high substitution, and can obtain a ground having excellent strength. Moreover, since the raised soil which generate | occur | produces can be used on the spot without carrying out outside, the carrying-out cost can be reduced.
[0019]
【The invention's effect】
According to the present invention, it is possible to reduce the amount of disposal by effectively using the rising soil generated in the offshore ground improvement work. Moreover, if this uplifting soil is used on the spot, the carrying-out cost to the outside of a field can be reduced. Moreover, when the ground improvement rate of the marine ground is 50 to 95%, it is effective in the present invention because an excellent ground strength can be obtained and a sufficient amount of the raised soil 1 can be effectively used.
[Brief description of the drawings]
FIG. 1A is a schematic diagram for explaining an offshore ground improvement work of this example, and FIG. 1B is a schematic view showing a completed state of an offshore ground improvement work.
FIG. 2 is a plan view for explaining a region where a conventional marine ground improvement work is performed.
FIGS. 3A and 3B are diagrams for explaining conventional offshore ground improvement work, where FIG. 3A shows a state during the improvement work, and FIG. 3B shows a state after the completion of the improvement work.
[Explanation of symbols]
1 Rise soil 2 Modified soil vessel 3 Mixed earth vessel (SCP vessel)
4 Coarse Grain Material 5 Improved Area 11 Sea Shallow 12 Land 13 Caisson Construction Area 14 SCP Ship 15 Caisson 16 Landfill 21 Reformer Storage Tank 31 Mixing Equipment 32 Compacting Sand Pile Driver 41 Coarse Grain Storage Tank 51 Compaction Sand pile 111 Soft ground 151 Foundation made of gravel or crushed stone

Claims (5)

Mixing uplifted soil, reforming material and coarse-grained material generated in marine ground improvement work to obtain a mixed soil with a water content ratio of 25% or less, a plasticity index of 20 or less, and a fine grain content of 15% or more. Is used as a filling material for the formation of compacted sand piles. Mixing uplifted soil and reforming material generated in offshore ground improvement work to obtain modified soil, then mixing the modified soil and coarse grain material, water content ratio 25% or less, plastic index 20 or less, A method for using uplifted soil generated in offshore ground improvement work, characterized in that a mixed soil having a fine particle content of 15% or more is obtained and the mixed soil is compacted and used as a filling material for sand pile construction. The uplifted soil generated by the improvement work at the sea is transported to the mixer of the modified earth ship 2 by a dredger with a dredger, and the reformer stored in the reformer storage tank 21 and the uplifted soil are transferred by the mixer. The modified soil is produced by mixing, the modified soil is transported to the SCP ship 3 by a crane with a grab, and mixed with the coarse material transferred by the crane with the grab from the coarse material ship 4 by the mixing facility 31. Obtaining mixed soil with a water content of 25% or less, a plasticity index of 20 or less, and a fine particle content of 15% or more, and using the mixed soil as a filling material for compacting sand piles How to use the raised soil generated during construction. The mixed soil is used as a filling material for compacted sand piles to be created in the offshore ground improvement work, which occurs in the offshore ground improvement work according to any one of claims 1 to 3. How to use uplifting soil. The ground improvement rate of the offshore ground improvement work is 30 to 95%, and the method of using the raised soil generated by the offshore ground improvement work according to any one of claims 1 to 4 .

Images