JP2601702B2 - Soft ground improvement method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a soft ground improvement method suitable as a measure against liquefaction of low-rise structures.

"Conventional technology" Conventionally, ground improvement methods performed for the purpose of increasing the bearing capacity of soft ground and preventing liquefaction during an earthquake include, for example,
A compaction pile method for stabilizing the ground by forming a number of compacted piles (compaction piles) by compressing sand, gravel, crushed stone, or ore sill, etc. in soft ground is known. As a typical method, there is a vibro composer method.

When the soft ground is improved by the vibro composer method, first, as shown in FIG. 2 (a), the hollow pipe 2 on which the vibrator 1 is fixed is connected to the soft ground G
By placing the vibrator 1 in the upper construction position and then driving the vibrator 1, as shown in FIG.
Into the soft ground G. After the hollow pipe 2 is driven to a predetermined depth in this way, as shown in FIG. 2 (c), sand 4 is introduced into the hollow pipe 2 from a hopper 3 provided above the hollow pipe 2. And put
As shown in FIGS. 2 (c), (d), (e) and (f),
Sand 4 is discharged from the lower end of the hollow pipe 2 and the hollow pipe 2 is pulled out while being vibrated up and down, so that the side compaction pile 5 shown in FIG.
To create.

[Problems to be solved by the invention] By the way, when the ground is improved by the compaction pile method described above, in sandy ground, effects such as enhancement of ground support capacity, reduction of settlement, and prevention of fluidization during an earthquake are expected. In the case of viscous soil, it has the excellent characteristics that it can be expected to increase the bearing capacity of the ground and the shear strength against slip failure, reduce settlement and promote consolidation, etc. When preventing compaction, it is necessary to build a large number of compaction piles densely.Therefore, if the soft ground layer is thick and the compaction pile must be cast deep into the underground, the construction cost will be high. is there.

However, since the seismic force is relatively small in the deep underground, it is considered that there is little danger of liquefaction in the deep part even if the ground is thick and soft. In such cases, it has been desired to reduce the construction cost as much as possible.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a low-cost soft ground improvement method that is particularly suitable as a measure against liquefaction of a low-rise structure.

"Means for solving the problem" The soft ground improvement method of the present invention, when laying a number of compaction piles in the soft ground, while laying several compaction piles to a comparatively deep layer, these By placing the remaining compaction pile shallower than the compaction pile between each compaction pile, the compaction pile is densely formed in the shallow part of the soft ground, and the compaction pile is formed in the deep part of the soft ground. It is created sparsely.

[Operation] In the soft ground improvement method of the present invention, when a number of compaction piles are driven into the soft ground, several compaction piles are driven to a relatively deep layer, and each of these compaction piles is formed. The compaction pile is densely formed in the shallow part of the soft ground by driving the remaining compaction pile in shallower than the compaction pile in between, so it has a sufficient compaction effect in the shallow part with large seismic force The compaction pile is sparsely formed in the deep part where the seismic force is small, so that the construction cost can be reduced while the liquefaction prevention effect during the earthquake is sufficiently secured.

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

In the soft ground improvement method of this embodiment, the sand compaction piles 5 are cast at a large number of working positions on the soft ground G at predetermined intervals in the vertical and horizontal directions. Assuming that the pile 5 is cast to a relatively deep layer, the sand compaction pile 5 is cast shallower than the sand compaction pile 5 at four construction positions adjacent to the construction position of the sand compaction pile 5. And
At the construction position adjacent to the construction position of the sand compaction pile 5, the sand compaction pile 5 is cast again to a deep layer, so that the sand compaction pile 5 is densely formed at the shallow portion of the soft ground G, and In the deep part of the soft ground, the sand compaction pile 5 is sparsely formed.

As a method of forming the compaction pile 5, for example, there is a vibro composer method of a conventional method.

When the soft ground is improved by the vibro composer method, as described above, first, as shown in FIG. 2 (a), the hollow pipe 2 on which the vibrator 1 is fixed is placed on the soft ground G. Then, by driving the vibrator 1, the hollow pipe 2 is driven into the soft ground G as shown in FIG. 2 (b). And
After the hollow pipe 2 is driven to a predetermined depth in this manner, sand 4 is put into the hollow pipe 2 from a hopper 3 provided on the upper part of the hollow pipe 2 as shown in FIG. Then, as shown in FIGS. 2 (c), (d), (e) and (f), the sand 4 is discharged from the lower end of the hollow pipe 2 and the hollow pipe 2 is pulled out while vibrating up and down. Thus, a sand compaction pile 5 as shown in FIG. 2 (g) is formed.

In this example, the sand compaction pile 5 was formed by the vibro composer method, but the sand compaction pile 5 may be formed by another method, and instead of the sand compaction pile 5, gravel, crushed stone, or A compaction pile may be formed by compressing ore mining. Then, when creating a compaction pile using gravel or the like, after drilling the ground to a predetermined depth with a machine such as an earth auger, an appropriate amount of gravel is dropped into the hole, and the gravel is used by the weight. All you have to do is hit the top and compact the gravel.

[Effects of the Invention] The soft ground improvement method of the present invention, when placing a number of compaction piles in the soft ground, places several compaction piles to a relatively deep layer, and each of these compaction piles The remaining compaction pile is cast at a shallower depth than the compaction pile, so that the compaction pile can be densely formed in the shallow part of the soft ground. The compaction pile can be sparsely formed in the deep part where the seismic force is small.
The construction cost can be reduced while the effect of preventing liquefaction during an earthquake is sufficiently ensured.

[Brief description of the drawings]

1 and 2 are views showing one embodiment of the present invention. FIG. 1 is an explanatory view for explaining a soft ground improvement method, and FIG.
The figure is an explanatory view for explaining the vibro composer method. 1 ... vibrator, 2 ... hollow pipe, 3 ... hopper, 4 ... sand, 5 ... sand compaction pile, G ... soft ground.

Claims (1)

(57) [Claims] When a large number of compaction piles are cast in soft ground, some compaction piles are cast to a relatively deep layer, and the remaining compaction piles are interposed between each compaction pile. A soft ground improvement method characterized by forming a compaction pile densely in the shallow part of the soft ground and sparsely forming a compaction pile in the deep part of the soft ground by placing it shallower than the compaction pile. .