JPH0663213B2 - Landfill method with improved sediment - Google Patents

Description

The present invention relates to an improved soil reclamation method.

Currently used landfill methods include a method of discharging sediment directly to a landfill by a pump ship, dredging and removing soil with a grab ship, dipper ship, bucket ship, etc. Alternatively, a method of dumping soil into a pocket with a pump ship, a method of landfilling with mountain soil, and a method of simultaneously mixing and dropping earth and sand, a hydraulic substance and a thickener are used.

Among these known landfill methods, as a landfill method performed by mixing the chemical substances intended by the present invention with the landfill material and utilizing the above method, for example, from Japanese Patent Publication No. 40-21902, dredged sand is used. A method of forming a raised ground layer by dropping it into water together with a coagulant, and from JP-A-51-39939, a polymer coagulant and an inorganic coagulant such as cement are mixed in a discharge suspension of a sand pump. A method for constructing a temporary revetment or a temporary breakwater, and from JP-A-58-139775, a slurry composed of fly ash is added with a surfactant,
A landfill method using a tremie tube mixed with a hydraulic substance, aggregate, etc. is known.

The known landfill construction methods including these have the following drawbacks. With the method of dropping directly into the water, classification and diffusion of sediments on the bottom of the water is unavoidable.

As landfill material when constructing landfill with a dredger,
Dredged soil (clay, silt, sand) is used, but when this landfill method is used to reclaim dredged sand with a pump ship, clay,
Silt is easy to classify. In order to prevent classification, an aggregating material is added in the vicinity of the sand discharge pipe (sediment transport pipe) and the discharge pipe as disclosed in the known landfill method. But,
This landfill method is also disadvantageous in that soil and sand are classified in the upper and lower parts of the sediment deposited by dredging, and clay and sild pools are partially formed. In addition, it has been confirmed that the sediment deposited on the bottom of the water by the above-mentioned landfill method will cause unevenness due to classification and diffusion, which will cause uneven settlement of the ground after completion of the landfill, which will adversely affect the structure.

In the case of the landfill method in which the landfill material is directly dropped into the water using an earthmoving ship, a sandy material having a smaller compressibility and a larger bearing capacity than clay or silt such as sludge is generally used. The sandy material dropped in water is classified and deposited according to the difference in particle size when it falls in water and when it collides with the bottom.
In addition, the fine sand adhering to the surface of the sand and debris is washed away by tidal currents, piles up on top of the sediment to form a layer, and a fine sand puddle with a low density partially forms in the landfill. It is formed.

The ground constructed by the above-mentioned landfill method is extremely loose ground, and in terms of strength, the N value often fluctuates to 5 or less in the standard penetration test, and to prevent uneven settlement and liquefaction of the structure after construction. The ground improvement method is being carried out. When improving the ground, it is difficult to perform the conventional ground improvement method, which involves vibration, such as the vibro flotation method, near the existing structure.
Further, when a large amount of gravel or the like is mixed in the landfill material, it is necessary to excavate the landfill land of the conventional ground improvement method. For example, it becomes difficult to implement the sand compaction method.

Under these circumstances, ground improvement requires a great deal of cost.

Further, the post-ground improvement method in the conventional landfill method is performed after the landfill construction, so that the construction period becomes long.

In addition, a method of mixing at the same time (for example, Japanese Patent Laid-Open No. 62-
55325), there is a large variation in the cement content, the effect of the thickener is reduced, and the cement particles are left in the thickener solution, causing uneven distribution of the cement particles, and There is a drawback in that the cement is released in water and partly scatters because the molecular string is broken.

The subject of the present invention does not have the drawbacks of the conventional landfill method,
It is to provide a landfill method that does not require improvement of the ground after landfill.

The feature of this landfill method is that the hydraulic material is premixed into the soil before landfill, and the whole is mixed by time-dependent mixing with a thickener added to it.
It is to put the particles of sand and sand together to form aggregates, and to drop them directly into water.

The premixing of the sediment and the hydraulic substance may be carried out before the condensation by the hydraulic substance at the time of dropping in water, for example, when the dropping is carried out by an earth transporter, either on land, at the time of loading or on board.

The sandy material used in the present invention is a sandy material containing fine particles of 74 μm or less and granular material of 2 mm or more.

The addition of the thickener is carried out after the soil and the hydraulic substance are mixed almost uniformly.

In the landfill method according to the present invention, as the hydraulic material, for example, cement, granulated blast furnace slag, coal ash, etc. are used, and as the thickener, for example, cellulose ether, carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide, etc. are used.

The advantage of the present invention is that by adding a thickening agent to the sand premixed with the hydraulic material and then remixing, a bond is generated between the particles of the sandy material, which is the sand with the hydraulic material attached, to form aggregates. Since it settles and is landfilled, it is possible to form a strong solid ground that is uniform and stable.

Further, by using a thickener, it becomes possible to reduce pollution. In addition, land reclamation of deep water can also be done by the direct-draining method of earthmoving vessels, which enables large-scale and rapid construction. By using the mixed earth and sand, ground improvement after landfill (for example, dynamic consolidation, sand compaction, pipe rofation, etc.) is not required, and the construction period can be shortened. Furthermore, it is possible to simultaneously improve the ground while constructing the landfill land. It can also be applied to the landfill method near existing structures.

The landfill method according to the present invention will be described below based on an example of landfill construction by an earthmoving ship shown in FIG.

In FIG. 1, reference numeral 1 is an earth carrier, and 2 is a sand pre-mixed with a hydraulic substance and a thickener.

The mixed sand 2 is directly dropped into the water by the earth carrier 1. The earth and sand 2'dropped in the water is formed into aggregates of gravel, sand and fine sand, to which hydraulic material is attached, as seen in the drawing, forming ridges 4 at the bottom 3 of the water.

In this case, a uniform and stable strong ground is formed without classifying or diffusing when falling into water or colliding with the bottom of the water.

The ridges 4 formed in this way form sand or fine sand particles adhering to the surface of the gravel, which may be washed away by tidal currents, pile up on the accumulated sediment and form a layer, or form loose sand puddles. And a fine sand pool is not partially formed in the landfill.

2 to 6 show the results of a comparative test of a naturally collected sandy material and earth and sand improved by the present invention.

The test was carried out by mixing 4 parts by weight of cement as a hydraulic material and using polyacrylamide as a thickener in an experimental water tank.
The dimensions are converted from the model conversion rate.

Fig. 2 shows the particle size distribution of the naturally collected sandy material used in the comparative test.

FIG. 3 shows the relationship between the concentration of the thickener and the shape of sediment accumulation using earth and sand mixed with 4 parts by weight of cement, with the dropping center as the vertical axis. It is clear from FIG. 3 that when the thickener is not added, the sediment height at the dropping center is low, the swelling of the sediment caused by the diffusion of the sand is pushed outward, and the sand diffusion width becomes large. Is.

FIGS. 4a and 4b show a comparison of the particle size distribution of deposited sediment on the dropping center shown in FIG. From this figure, it is recognized that classification is occurring in the upper and lower parts of the sediment when the thickener is not added.

FIG. 5 shows the amount of cement remaining in the sediment deposited on the dropping center of FIG. 3 in percentage. From this figure, when the thickener is not added, the residual cement percentage is as low as about 50%, and the cement component flows out due to diffusion and separation. From this, it is confirmed that in the sand containing the thickener, classification does not occur, the diffusion of the sand is small, and the amount of cement remaining in the sediment is large. .

As shown in Fig. 6, when the thickener is not added, the cement separates in water, while the thickener is added, the cement adheres to the soil and settles in the aggregated state, so a uniform sample is obtained. (See FIGS. 4a and 4b) and the strength is increased.

On the other hand, as the concentration of the thickener is increased, the agglomeration becomes remarkable, and the dry density of the deposited earth and sand is reduced, so that the strength may be reduced. Therefore, in order to form a stable and strong ground, it is necessary to select the concentration of the thickener and the cement addition rate in consideration of the change in the collision velocity caused by the change in the depth of the sediment. In addition, in that case, it is necessary to determine the composition in consideration of the decrease in the dry density of the deposited soil caused by the addition of the thickener.

The particle size distribution of the upper part and the lower part of the deposited sediment is almost the same. That is, FIG. 5 illustrates the relationship between the depth of the deposited sand without classification and the concentration of the thickener. From this figure, it is clear that the concentration of the thickener increases as the depth of sedimentation increases.

That is, as the depth of water to which the sand is dropped increases, the collision speed at the bottom of the water increases, and it is necessary to naturally increase the concentration of the thickener that suppresses classification and diffusion.

[Brief description of drawings]

FIG. 1 is a diagram showing a premixing step of the landfill method according to the present invention, and FIGS. 2 to 6 are characteristic comparison diagrams of the improved soil and the naturally collected sandy material used according to the present invention. In the figure, the reference numerals are: 1 ... earthenship 2 ... earth and sand 2 '... earth and sand 3 ... water bottom 4 ... uplift

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akitomo Tamai 4-9-9 Akasaka, Minato-ku, Tokyo Within Japan Land Development Co., Ltd. (72) Innovator Hidenobu Kuroyama 4-9-9 Akasaka, Minato-ku, Tokyo Within Japan Land Development Co., Ltd. (56) Reference JP-A-62-55325 (JP, A) JP-A-51-62556 (JP, A)

Claims (1)

[Claims] 1. When a landfill site is constructed by using earth and sand as a landfill material, a hydraulic substance is premixed with the earth and sand before the landfill is dropped, and a thickener is added to this to mix the whole material with time. An improved method of landfill with earth and sand, characterized in that the particles of earth and sand are made into agglomerate by adding cohesiveness between the particles of the earth and then dropped directly into water.