JP3114076B2 - Sand compaction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing liquefaction of sand ground and compacting the ground.

[0002]

2. Description of the Related Art There are two methods for preventing liquefaction of a sand ground: a method of compacting the ground and a method of lowering the groundwater level to maintain the lowered water level. However, when using the method of lowering the groundwater level, it was necessary to construct a cutoff wall and keep the water level low. In other words, it was necessary to construct a wall on the ground between the area where the ground improvement is to be made and the surrounding area, and to constantly lower the groundwater level so that the effect of the lowering of the groundwater level would not reach outside the ground to be compacted.

[0003]

SUMMARY OF THE INVENTION The above prior arts include:
The following problems exist. <B> The water barrier needed to be flexible enough to withstand an earthquake, and the groundwater level had to be permanently lowered. <B> In the compacting method, impact was applied to the ground, so that it was not possible to compact under the ground with the existing structure.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and does not use a water stop plate and can tighten a sand ground which can be constructed even on a ground having an existing structure. The purpose is to provide a hardening method. That is, the present invention relates to a method of compacting a sandy ground for preventing liquefaction of the sandy ground and compacting the ground, wherein an airtight film is laid on the surface of the sandy ground to block a permeable layer below the airtight film from the outside air, Pumping groundwater under the ground to lower the groundwater level, discharging air in the permeable layer to apply atmospheric pressure to the sandy ground, and repeating the above operation until a predetermined settlement amount occurs This is a method of compacting the sand ground.

[0005]

An embodiment of the present invention will be described below with reference to the drawings. <B> Groundwater pumping (Fig. 1) Drilling multiple holes in the sand ground, and drain pipes 1
Buried. In addition, a well 3 is dug, and a submersible pump 2 is installed therein. The submersible pump 2 is connected to a pumping pipe 9, and the free end of the pumping pipe 9 projects above the ground.
After the installation of the drain pipe 1 and the submersible pump 2 is completed, an exhaust pipe 5 having a large number of openings is installed inside the permeable layer 4 on the sandy ground. At this time, if the state of the permeable layer 4 is not good, or if the work of bleeding air from the permeable layer 4 by the exhaust pipe 5 is hindered as described later, it may be possible to artificially make the permeable layer 4. Then, an airtight sheet 6 is provided on the surface layer of the ground, that is, on the upper surface of the water permeable layer 4, to completely cover and seal the surface of the sand ground. The airtight sheet 6 is a permeable layer 4
Since it is intended to block the air from the outside air, it is made of vinyl or the like.

<B> Compaction by Atmospheric Pressure (FIG. 3) A vacuum pump 7 is attached to the free end side of the exhaust pipe 5, and the vacuum pump 7 is operated to evacuate the air in the permeable layer 4. Since the exhaust pipe 5 has a large number of openings, the air around the exhaust pipe 5 can be discharged to the outside. By evacuating air in this way, the airtight seal
A negative pressure is generated between the ground 6 and the sand ground, and the atmospheric pressure can be applied. In other words, when the air disappears, the space between the airtight sheet 6 and the sand ground becomes closer to a vacuum state, and the airtight sheet 6 is pressed against the sand ground. The sandy ground is compacted by the pressure of the atmosphere.

<C> Lowering of groundwater level (FIG. 2) After exhausting, the submersible pump 2 is operated to pump up the groundwater.
The groundwater is sent from the submersible pump 2 to the pumping pipe 9 and discharged to the ground. The groundwater around the well 3 is collected in the well 3 by such pumping, and the groundwater around the drain pipe 1 is also drained by the deep well effect.
Water is collected and discharged. That is, groundwater in the sandy ground is collected over a wide area and discharged to the outside through the pumping pipe 9 and the drain pipe 1. As the groundwater in the sandy ground is discharged in this way, the groundwater level 8 decreases as shown in the figure, and when the water content disappears, the load increases and the ground compacts. The above-mentioned work to reduce groundwater is performed for about 20 days.

<D> Cycle of compaction work The above two works, that is, the work of applying pressure by atmospheric pressure and the work of lowering the groundwater level are repeated five to ten times. That is, after the air in the permeable layer is evacuated, the groundwater level is lowered while maintaining low pressure. With the water level lowered, wait for land subsidence to stop, then return the water level. At this time, air may be returned. Next, after the air is exhausted, the water level is lowered. Due to this lowering effect, the so-called sand particle immersion phenomenon occurs, so that the ground subsides and compacts again. By repeating the work in this manner, the sand ground can be effectively and uniformly compacted over a wide range.

<E> Other embodiments (FIG. 4) When the structure 10 is constructed on sandy ground,
The pipe 1 is buried at an angle. That is, a hole for the drain pipe 1 is excavated from the sand ground without the existing structure 10, and the hole is dug to the ground below the structure 10. Then, the drain pipe 1 is buried in the hole. Drain like this
By locating the pipe 1, groundwater can be collected from the sand ground below the structure 10, and the groundwater level can be lowered. Therefore, even in the sand ground under the structure, the ground can be compacted by the same effect as in the above embodiment.

[0010]

Since the present invention has been described above, the following effects can be obtained. <A> The work of applying pressure by atmospheric pressure is,
After that, the operation for lowering the groundwater level is performed, for example, for about 20 days. These operations are repeated, for example, 5 to 10 times until the predetermined settlement is completed, thereby compacting the sandy ground. Therefore, the sand ground can be compacted effectively and uniformly over a wide range. <B> In the case of performing without using the waterproof plate between the compaction area and the surrounding area, which has been conventionally used, the sand ground can be compacted by constructing the recharge well at the boundary. Therefore, the manufacture and construction of the water stop plate become unnecessary, and the cost can be reduced and the working time can be shortened. <C> The drain pipe for collecting water can be buried from the sandy ground with no structure to the ground under the existing structure. Therefore, it is possible to compact under the ground with the existing structure, which could not be performed conventionally.

[Brief description of the drawings]

Fig. 1 Cross section of groundwater pumping

Fig. 2 Cross section of groundwater level drop

FIG. 3 is a sectional view of the atmospheric pressure action.

FIG. 4 is an explanatory view of construction of an existing structure base plate.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-50-7309 (JP, A) JP-A-3-206210 (JP, A) JP-A-48-6210 (JP, A) JP-A-5-205 33329 (JP, A) JP-B-48-11614 (JP, B1) JP-B-46-7348 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) E02D 3/00-3 / 02 E02D 3/08-3/10

Claims (1)

(57) [Claims] 1. A method of compacting a sandy ground for preventing liquefaction of the sandy ground and compacting the ground, wherein an airtight film is laid on the surface of the sandy ground to block a permeable layer below the airtight film from the outside air. The underground water is pumped to lower the groundwater level, and the air in the permeable layer is discharged to apply atmospheric pressure to the sandy ground. A method of compacting sandy ground, wherein the method is repeated until the amount of settlement of the sand is generated.