Ground materials and seabed reclamation methods

Abstract

We propose a ground material using crushed clay tiles that can reduce turbidity when used underwater, and a method for reclamating seabeds using this ground material. [Solution] This is a ground material made by mixing crushed clay tiles and sand. The fine-grained content of the crushed clay tiles, including silt and clay, is 20% or less, the maximum particle size is 30 mm or less, and the 50% particle size is 10 mm or less. The maximum particle size of the sand is 2.0 mm, and the mixing ratio of sand to dry weight is in the range of 20% to 60%. When filling the bottom of a body of water with this ground material, it is moistened by soaking it in water before being placed in the water.

Description

Technical Field

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[0001] The present invention relates to a ground material using crushed clay tiles and a submerged landfill method for filling this ground material underwater.

Background Art

[0002] As a ground material used for landfill and the like, crushed clay tiles may be used. For example, Patent Document 1 discloses a backfill material (ground material) made of crushed clay tiles obtained by crushing clay tiles as a ground material used for backfilling around and above buried objects.

[0003] Since the interior of the particles of crushed clay tiles is porous and the particle shape is pointed, the particles are likely to catch on each other, resulting in easy bulking and large friction. Therefore, the ground material containing crushed clay tiles has a lower unit weight than general sandy soil, while having a larger shear strength (shear resistance angle).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when using crushed clay tiles as a backfill material for underwater structures or a fill material for underwater embankments, the particles are less likely to sink due to the influence of internal air bubbles, and the water becomes turbid for a longer time than general sandy soil. From such a perspective, an object of the present invention is to propose a ground material using crushed clay tiles capable of reducing turbidity when used underwater and a submerged landfill method for filling this ground material underwater.

Means for Solving the Problems

[0006] The present invention, which solves the aforementioned problems, is a ground material obtained by mixing crushed clay tiles and sand. It is desirable that the fine-grained content of the crushed clay tiles, including silt and clay, is 20% or less, and that the maximum particle size is 30 mm or less, preferably 20 mm or less. It is also desirable that the 50% particle size of the crushed clay tiles is 10 mm or less, and that the maximum particle size of the sand is 2 mm or less. Furthermore, it is desirable that the mixing ratio of the sand to the total dry weight of the ground material be in the range of 20% to 60%.

[0007] With this type of ground material, the fine particles of crushed clay tiles (small-particle crushed clay tiles) and sand intertwine, so even when added to water, they settle together, preventing the clay tile particles from floating. As a result, turbidity of the water over a long period of time is suppressed. Furthermore, because the ground material is mixed with crushed clay tiles that have a pointed particle shape, the shear strength (shear resistance angle) of the soil increases proportionally to the mixing ratio of the crushed clay tiles until the mixing ratio reaches approximately 85%, and can increase by more than 1.4 times compared to when sand is used alone.

[0008] The method for burying the ground material in the seabed includes the steps of immersing the ground material in water and introducing the ground material into the water. With this method, the ground material is introduced into the water as a mass and buried in a state in which separation is suppressed, thus suppressing turbidity of the water during reclamation. [Effects of the Invention]

[0009] According to the ground material of the present invention, since sand is mixed with crushed clay tiles, turbidity of the water can be suppressed even when used underwater. [Brief explanation of the drawing]

[0010] [Figure 1] This graph shows examples of crushed clay tiles used as ground material and their particle size range. [Figure 2] This is a diagram showing the test results of soil materials, specifically a graph illustrating the relationship between turbidity and elapsed time. [Figure 3] Figure 2 is a log-log graph showing the test results. [Figure 4] This graph shows the relationship between turbidity and elapsed time, with the turbidity 10 minutes after the start of the test set to 1. [Figure 5] This graph shows the relationship between turbidity and the sand content. [Figure 6] This graph shows the relationship between the turbidity ratio and the sand mixing ratio, with the turbidity of only crushed clay tiles (where the sand mixing ratio is 0) set to 1. It also shows the rate of decrease in turbidity according to the sand mixing ratio. [Figure 7] This graph shows the relationship between the sand mixing ratio and the internal friction angle. [Figure 8] This graph shows the relationship between the sand mixing ratio and the coefficient of friction. [Figure 9] This graph shows the relationship between the friction coefficient ratio of the ground material and the sand mixing ratio, assuming a sand mixing ratio of 100, i.e., a friction coefficient of 1 for sand alone. [Modes for carrying out the invention]

[0011] In this embodiment, the ground material to be used for reclamation at the bottom of the sea will be described. The ground material is a mixture of crushed clay tiles and sand. The sand is mixed in such a way that its mixing ratio is within the range of 20% to 60% of the total dry weight of the ground material. That is, when the total dry weight of the ground material is 100, the dry weight of the crushed clay tiles is 80 to 40, and the dry weight of the sand is 20 to 60. In this embodiment, sand with a maximum particle size of 2 mm or less is used.

[0012] The crushed clay tiles used include discarded tiles generated during roof replacement, non-standard tiles that do not meet the required performance specifications even though they are unused, and damaged tiles that have become unusable due to natural disasters such as earthquakes and typhoons. These tiles are crushed so that the fine particle content (percentage of particles smaller than 0.075 mm) of the combined silt and clay is 20% or less, the maximum particle size is 30 mm or less, preferably 20 mm or less, and the 50% particle size is 10 mm or less.

[0013] The method of underwater landfill using ground material includes a mixing process of manufacturing the ground material by mixing crushed clay tiles and sand, a dipping process of dipping the ground material in water, and a landfill process of putting the ground material into water.

[0014] In the mixing process, the crushed clay tiles and sand are mixed in a dry state and then wetted by adding water, or the crushed clay tiles and sand in a wet state are mixed from the beginning, etc., so that mixing is performed so that there is no bias in the materials. By making the ground material in a wet state before being put into water, when the ground material is put into water in the landfill process, it is more difficult to separate than when used in a dry state, and it can be dropped to the bottom of the water in a lump state.

[0015] According to the ground material of the present embodiment, since the particles of the crushed clay tiles and the sand are intertwined, even when put into water, it is possible to prevent only the particles of the crushed clay tiles from floating, and as a result, the turbidity of the water is suppressed.

[0016] In addition, since the ground material is put into water as a lump and landfill is performed in a state where separation is suppressed, turbidity of water during landfill can be suppressed. Furthermore, since the ground material uses crushed clay tiles with pointed particle shapes, the ground strength increases according to the mixing ratio of the crushed clay tiles, and the shear strength of the ground material also becomes larger than in the case of only sand.

[0017] Hereinafter, the test results of examining the turbidity when the ground material of the present embodiment is put into water will be described. Table 1 shows examples of crushed clay tiles with a smaller particle size and crushed clay tiles with a larger particle size used as the ground material. Among these, in this test, crushed clay tile 1 with a small particle size and a high content of fine particles, which is likely to cause turbidity, is used. Also, FIG. 1 shows examples of the particle size distributions of crushed clay tiles with a smaller particle size and a larger particle size. In this test, ground materials (wet soil mass samples) were prepared with sand mixing ratios of 0% (comparative example), 20% (Example 1), 40% (Example 2), and 60% (Example 3), and the turbidity when each was put into water was measured. The test results are shown in Figure 2. Note that since particle sedimentation was intense immediately after the start of the test and measurement was unstable, measurement was carried out starting 10 minutes after the start.

[0018]

Table 1

[0019] As shown in Figure 2, in all samples, the turbidity decreased with the sedimentation of soil particles over time and eventually approached 0. Also, the turbidity decreased significantly at an early stage after the start of the test and then decreased slowly.

[0020] The test results in Figure 2 are shown in a double logarithmic graph in Figure 3. Since the turbidity gradually approaches 0 according to the elapsed time, it is appropriate to represent it as a power function of the elapsed time. Here, the power function becomes a straight line in a double logarithmic graph. Therefore, as shown in Figure 3, when the results in Figure 2 are represented in a double logarithmic graph, the relationship between time and turbidity became linear for all samples. Also, as shown in Figure 3, regardless of the sand mixing ratio, the relationship between turbidity and time had a similar tendency.

[0021] Figure 4 shows the turbidity change rate when 10 minutes after the start is set to 1. As shown in Figure 4, the relationship between the turbidity with the value 10 minutes after the start of each formulation set to 1 and the elapsed time was the same regardless of the sand mixing ratio. That is, the change rate of turbidity (dissipation of turbidity) was independent of the sand mixing ratio.

[0022] Next, the influence of the mixing ratio of crushed clay tiles in the ground material on turbidity was examined. Figure 5 shows the relationship between the proportion of sand (sand mixing ratio) in the ground material and turbidity. As shown in Figure 5, it was confirmed that the higher the sand mixing ratio, the lower the turbidity at all times.

[0023] Figure 6 shows the turbidity ratio based on a sand mixing ratio of 0% (clay tile fragments only). As shown in Figure 6, the results were consistent across all time points, represented by a single curve. This confirms that the sand mixing ratio can be uniquely determined by setting the target turbidity reduction rate, regardless of the time elapsed since the material was introduced into the water. For example, to reduce turbidity by half compared to a 0% sand mixing ratio (comparative example), the sand mixing ratio should be set to approximately 20%, and to reduce turbidity by approximately 1 / 3, the sand mixing ratio should be set to approximately 30%.

[0024] Since the turbidity of crushed clay tiles 2, which has fewer fine particles, decreases faster than that of crushed clay tiles 1, which has more fine particles, the ground material made by mixing crushed clay tiles 2 with sand decreases in turbidity faster than the ground material made by mixing crushed clay tiles 1 with sand. Also, since crushed clay tiles with smaller particle sizes and a higher proportion of fine particles have higher turbidity than crushed clay tiles with larger particle sizes and a lower proportion of fine particles, in the ground material of this embodiment, even if the maximum particle size of the crushed clay tiles is 30 mm or less, preferably 20 mm or less, it is possible to reduce the turbidity by mixing in sand, similar to the test results (under stricter conditions) using crushed clay tiles with smaller particle sizes and a higher proportion of fine particles.

[0025] Next, we present the results of our investigation into the internal friction angle, which is a strength constant of the ground material, and the coefficient of friction (calculated as the tangent of the internal friction angle), which represents the shear strength of sandy soil. The test results (internal friction angle) are shown in Figure 7. Here, the internal friction angle of only crushed clay tiles (0% sand) is 45.1° when the particle size is 0-5 mm, and 44.6° when the particle size is 0-20 mm. Generally, the upper limit of the internal friction angle is 45 degrees from a physical standpoint of the coefficient of friction (the upper limit of the coefficient of friction is 1), so the internal friction angle when sand is 0% was set to 45°.

[0026] As shown in Figure 7, since the ground material uses crushed clay tiles with pointed particle shapes, the internal friction angle, which is the strength constant of the soil, increases in proportion to the mixing ratio of the crushed clay tiles compared to when sand is used alone. Figure 8 shows the relationship between the mixing ratio of sand and the friction coefficient of the soil. As shown in Figure 8, it was confirmed that mixing in crushed clay tiles also increases the friction coefficient, which is the shear strength of the soil. Furthermore, Figure 9 shows the ratio of the soil friction coefficient normalized by the friction coefficient of sand alone (friction coefficient of sand alone set to 1) to the mixing ratio of sand. As shown in Figure 9, it was confirmed that mixing crushed clay tiles with sand increases the ground strength in proportion to the mixing ratio of crushed clay tiles, and the shear strength of the ground material can be up to 1.4 times or more compared to sand alone.

[0027] Therefore, with the ground material of this embodiment, compared to the case of sand alone, it was confirmed that turbidity could be reduced to less than half when the sand content was 20% or more, and that the strength was increased by approximately 1.2 times when the sand content was 60% or less. Thus, it was confirmed that in the ground material of this embodiment, it is desirable in terms of reducing turbidity and developing strength by setting the mixing ratio of sand to dry weight within the range of 20% to 60%.

[0028] Furthermore, as shown in Figure 1, it is desirable that the fine particle content of the crushed clay tiles be 20% or less, the maximum particle size be 30 mm or less, and the 50% particle size be 10 mm or less, as values ​​encompassing the upper and lower limits of the particle size distribution.

[0029] Embodiments of the present invention have been described above. However, the present invention is not limited to the embodiments described above, and each of the above-described components can be modified as appropriate without departing from the spirit of the present invention.

Claims

1. A ground material made by mixing crushed clay tiles and sand, A ground material characterized in that the fine-grained content, which is the sum of silt and clay in the crushed clay tile material, is 20% or less.

2. The ground material according to claim 1, characterized in that the maximum particle size of the crushed clay tiles is 30 mm or less.

3. The ground material according to claim 1, characterized in that 50% of the crushed clay tiles have a particle size of 10 mm or less.

4. The ground material according to claim 1, characterized in that the maximum particle size of the sand is 2.0 mm or less.

5. The ground material according to any one of claims 1 to 4, characterized in that the mixing ratio of the sand to the dry weight is in the range of 20% to 60%.

6. A method for burying the ground material described in claim 1 in the seabed, The process of immersing the aforementioned ground material in water, A method for reclamating a seabed, characterized by comprising the step of introducing the aforementioned ground material into water.

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