JPH0547683B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a construction method for consolidating soft ground.

[Conventional technology] Generally, soft ground is a soft soil layer (soft soil layer) that contains a lot of clay and organic matter, and also has a high water content.
Because the soil is thickly deposited, the amount of ground subsidence is large, and it is extremely vulnerable to external forces such as earthquake motion. Therefore, when creating a housing site on soft ground and building a structure on it, it is necessary to take measures such as increasing the strength of the ground and increasing its resistance to external forces. must be done.

As a means of improving such soft ground,
Conventionally, a consolidation method called the preload method is widely used. In the preload method, embankment of an appropriate thickness is placed on soft ground, and the weight of this embankment compresses the soft soil layer to compact it, increasing the density of the soil and increasing its strength, that is, consolidation. It is something.

When performing the preload method, at the same time, drain material such as paper drain material is driven into the soft soil layer to drain pore water in the soil, lowering the groundwater level and reducing the water content of the soil. It is also common practice to increase the strength of soil.

[Problems to be Solved by the Invention] However, the above preload construction method has the following problems.

In other words, when soft ground is consolidated by the preload method, the load (embankment) first closes the gaps between soil particles, and the pore water between the soil particles is drained, causing the soil to weaken. Generally, soil particles undergo a process of increasing density (primary consolidation) and then a process in which the skeletal structure of the soil particles themselves changes due to the creep phenomenon (secondary consolidation). Therefore, in the preload method, after the ground has largely settled due to primary consolidation and is almost compacted, it will further settle slightly due to secondary consolidation, and this subsidence due to secondary consolidation will be the cause of the construction of residential land. Even after completion of the project, problems such as subsidence of the developed residential land occurred gradually.

The reason why this secondary consolidation occurs is that the pressure applied to soil particles during the primary consolidation process acts mainly in the vertical direction, and only about half the pressure is applied in the horizontal direction compared to the vertical direction (i.e., anisotropy of consolidation pressure). It is said that this is especially true for gender. Therefore, the occurrence of secondary consolidation is unavoidable not only in the preload method but also in all construction methods that attempt to consolidate a soft soil layer by applying a load only from above the ground. Therefore, in order to prevent secondary consolidation and the resulting settlement, it is necessary to apply approximately the same pressure to the soil particles in the horizontal direction as in the vertical direction (i.e., isotropy of consolidation stress). is necessary.

However, as mentioned above, no effective and suitable means for applying horizontal pressure to the soft soil layer has yet been provided.

This invention has been made in view of the above circumstances, and an object of the present invention is to provide a consolidation method that does not cause subsidence of the ground due to secondary consolidation by applying pressure in the horizontal direction when consolidating soft ground. With the goal.

[Means for Solving the Problems] This invention compresses the soft ground in the vertical direction by carrying out a loading embankment on the soft ground, and at least the lower part of the soft ground is formed of an elastic material such as a rubber membrane. The lower part of the hollow cylindrical body is arranged almost vertically, and the upper part is made of a rigid material.
The upper part is made to protrude upright by a predetermined length from the above-mentioned loading embankment, and by injecting and filling the inside of the cylindrical body with liquid to a height above the ground surface, the pressure of the liquid causes the cylindrical body to Press the soft ground horizontally through the lower side.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 4.

In these figures, reference numeral A indicates a soft ground in which a soft soil layer 2 is deposited on a stable ground 1. To improve this soft ground A by consolidating and compacting the soft soil layer 2, first, sand mats 3 are laid on top of the soft soil layer 2 to a predetermined thickness,
A drainage pipe 4 made of a perforated pipe is installed inside the sand mat 3.
Lay down. Furthermore, an embankment 5 of a predetermined thickness is placed on the top of the sand mat 3. This embankment 5 serves as a load that mainly applies compressive force in the vertical direction to the soft soil layer 2.

Next, a plurality of compaction devices 6 are installed in the soft soil layer 2...
are arranged over the entire soft ground A at predetermined intervals both in the left-right direction and in the direction orthogonal to the plane of the drawing in FIG.

This compaction device 6 consists of a hollow cylindrical body made of a rubber membrane, that is, a rubber tube 7, and a drain drainage material 8 attached to the outer surface of the rubber tube 7. As shown in FIG. 4, the drain drainage material 8 is made of a resin corrugated plate 8a.
Water-permeable membranes 8b made of non-woven fabric are attached to both sides of the corrugated plate 8a, and the recesses of the corrugated plate 8a form the water-permeable grooves 8.
This is what forms c. (This drain drainage material 8 is similar to the plastic drain material commonly used in the past.) This drain drainage material 8... is a rubber tube 7 on the outer surface of the lower part near the center in the length direction of the rubber tube 7. They are attached at approximately equal intervals along the axial direction.

As shown in FIG. 1, the consolidation device 6 configured as described above is arranged so that its lower part is located under the soft soil layer 2, and the part that projects above the embankment 5 is made of a rigid steel cylindrical shape. It is supported by a casing 9 and placed almost vertically on soft ground A. At this time, the upper end portion of the drain drainage material 8 is positioned within the sand mat 3. Then, by injecting bentonite muddy water 10 into the rubber tube 7 of this compaction device 6 and keeping the water level at a predetermined height, the rubber tube 7 bulges outward due to the head pressure of the bentonite muddy water 10, as shown in FIG. (At this time, the drain drainage material 8 attached to the rubber tube 7 is also slightly curved.) The soft soil layer 2 in contact with the outer surface of the rubber tube 7 is indicated by the solid line arrow in FIGS. 1 and 2. In this way, it is compressed by pressing horizontally.

In addition, as the soft soil layer 2 is consolidated, pore water in the soil passes through the permeable membrane 8a of the drain drainage material 8,
The water rises in the water channel 8c, flows out into the sand mat 3, and is discharged through the drain pipe 4. (This flow of water is shown by the dashed arrow in Figure 1.) That is,
This compaction device 6 is capable of simultaneously compacting the soft soil layer 2 and discharging pore water in the soil.

As is clear from the above explanation, rubber tube 7
The pressure with which the soft soil layer 2 is pressed in the horizontal direction is determined by the water level of the bentonite slurry 10 in the rubber tube 7. Therefore, this pressure is applied to the embankment 5, especially at the bottom of the soft soil layer 2.
If the length of the rubber tube 7 and the water level of the bentonite slurry 10 are set to be approximately equal to the vertical pressure applied by the soft soil layer 2,
Because it is compressed with almost equal pressure in the vertical and horizontal directions, the primary consolidation and associated ground subsidence can be completed early, and
Secondary consolidation can be prevented from occurring, and settlement due to it can be reduced.

After the soft soil layer 2 has been sufficiently consolidated after a predetermined period of time, cement is poured into the rubber tube 7 to solidify the bentonite slurry 10, and the casing 9 is removed from the rubber tube 7.
The portion of the rubber tube 7 that protrudes above the embankment 5 may be cut off.

The embodiments of this invention have been described above, but
This invention is not limited to the above embodiments. For example, the upper part of the rubber tube 7 (the part above the soft soil layer 2) may be formed of a rigid material and the casing 9 may be omitted, and the liquid injected into the rubber tube 7 may be bentonite slurry 1.
It is not limited to 0. Further, the drain drainage material 8 may be used alone without being attached to the rubber tube 7, or drainage may be carried out by other means without using the drain drainage material 8.

[Effects of the Invention] As described in detail above, according to the present invention, a hollow cylindrical body, at least the lower part of which is formed of an elastic material such as a rubber membrane, is placed in soft ground with the lower part thereof substantially vertically disposed. By injecting liquid into the cylindrical body, the hydraulic pressure of the liquid causes
Since the soft ground is pressed horizontally through the lower side of the cylindrical body, subsidence of the ground due to secondary consolidation can be prevented.

In addition, a rigid material is used for the upper part of the cylindrical body, and the upper part is made to protrude upright from the above-mentioned loading embankment by a predetermined length. By setting appropriately, the horizontal pressing force applied to the soft ground can be easily adjusted. Therefore, the compressive force applied vertically to the soft ground by the loaded embankment and the compressive force applied to the cylindrical body in the vertical direction can be easily adjusted. As a result, the applied horizontal compressive forces can be easily set to be equal, primary consolidation and the resulting ground subsidence can be terminated early, and secondary consolidation and the resulting ground subsidence can be prevented.

Furthermore, once the cylindrical body is filled with liquid, the horizontal pressing force applied to the soft ground can be maintained almost constant for a long period of time without requiring any power. Furthermore, even when improving soft ground over a wide area, it is only necessary to erect a corresponding number of cylindrical bodies, and there is no need to install other piping or equipment, so there is no need to maintain them. Therefore, the cost of ground improvement can be reduced by reducing the cost of piping equipment and maintenance work required for ground improvement.

[Brief explanation of the drawing]

1 to 4 are diagrams showing embodiments of the present invention. Figure 1 is an elevational cross-sectional view showing the state in which soft ground is being consolidated by the consolidation method of this embodiment;
Figures 2 to 4 are diagrams showing the schematic structure of the consolidation device used in the consolidation method of this embodiment, in which Figure 2 is a plan sectional view, Figure 3 is a partial elevation view, and Figure 4 is a partial elevation view. is an enlarged perspective view (partially cut away) of the drain drainage material. A: Soft ground, 5: Embankment, 7: Rubber tube (cylindrical body), 10: Bentonite mud (liquid).

Claims (1)

[Claims] 1 Load embankment is carried out on the soft ground to compress the soft ground in the vertical direction, and at the same time, a hollow cylindrical body with at least the lower part made of an elastic material such as a rubber membrane is placed in the soft ground almost vertically. and using a rigid material for the upper part, the upper part is made to protrude upright by a predetermined length from the above-mentioned loading embankment,
By injecting and filling the inside of the cylindrical body with liquid to a height above the ground surface, the pressure of the liquid can push the soft ground horizontally through the lower side of the cylindrical body. A special feature is the consolidation method for soft ground.