JPH0645927B2 - Ground compaction method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method of compacting ground for improving soft ground.

“Conventional Technology” Conventionally, for example, a vibro flotation method or a sand compaction pile method is known as a method for improving so-called soft ground such as sandy ground and cohesive ground.

In the vibro flotation method, a bar-shaped vibrator is penetrated into the ground, the ground is vibrated and compacted while ejecting water to the vibrator part, and sand and crushed stones are put into the voids near the vibrator. This is a construction method for increasing the vibration effect and the press-fitting effect.

Further, the sand compaction pile method is a method for increasing the relative density of the ground by injecting sand into the ground by using vibration or impact load and creating a compressed sand column.

"Problems to be solved by the invention" By the way, in the vibro flotation method, the sand is compacted and the sand is slightly pulled out alternately while vibrating the ground, and the sand compaction pile method is also used. Then, sand input and compression are alternately repeated.
Therefore, these construction methods have the drawback of prolonging the construction period, and also have the drawback that the construction cost is increased due to the need for sand or the like for sand column formation or as an input material. In addition, in the case of the vibro flotation method, it is intended to be applied to sandy ground, and there is no effect on the ground where the content ratio of soil particles below silt is 40% or more.
Further, there is a problem that a commercially available vibration exciter cannot be used because horizontal vibration is required.

The present invention has been made in view of the above circumstances, and an object thereof is to reliably compact the ground and prevent liquefaction of the ground particularly during an earthquake, and realize a significant reduction in construction period and construction cost. It is to provide a completely new ground compaction method.

“Means for Solving Problems” In order to achieve the above-mentioned object, in the ground compaction method of the present invention, a vertical hole is excavated in the ground, and a drain pillar is formed in the vertical hole, and then the drain pillar and its surroundings. The ground is compacted by vibrating the pillar into the ground while vibrating.

[Operation] According to the ground compaction method of the present invention, when the pillar penetrates into the ground while vibrating, the vibration of the pillar causes excessive water pressure in the ground, and this excessive water pressure causes water in the ground But,
The water is horizontally drained toward the drain pillars arranged around the pillar body, which causes the ground to sink and is compressed in the vertical direction.

Then, by adopting such a construction method, when a plurality of drain pillars are arranged around the pillar body and the pillar body is penetrated into the ground, groundwater can be efficiently supplied to these drain pillars. It can be discharged, and as a result, the work of compressing the ground can be performed in a relatively wide range by one penetration and vibration of the column body, and the compaction work can be efficiently performed.

[Examples] Hereinafter, the present invention will be described based on examples shown in the drawings.

1 to 7 show one embodiment of the present invention,
In these figures, FIGS. 1 to 3 show the outline of a compaction device applied to the soil compaction method of the present invention.

First, a crawler crane is denoted by reference numeral 1 in FIG. The crawler crane 1 supports a guide mast 2, and a pillar 4 is vertically hung on the upper end of the guide mite 2 via a hanging jig 3. The column 4 is, for example, a large H-shaped steel, and its cross section is substantially H-shaped as shown in FIG. A vibrator (so-called vibro hammer) 5 is attached to the upper end thereof as shown in FIG. The vibration exciter 5 applies vertical vibration to the columnar body 4. Further, on the surface of the columnar body 4, a large number of projecting portions (projections) 6 projecting in a direction intersecting the length direction thereof are provided. These protrusions 6 are, for example, angle steels cut into pieces and welded to the columnar body 4.

Next, a method of compacting the soft ground by using the device having the above-mentioned configuration will be described.

First, as shown in FIG. 4, a large number of drain columns D reaching a predetermined depth are formed in the ground G. The drain pillars D are arranged such that a grid pattern is drawn on the ground G as shown in FIG. 5, for example. Each drain pillar D is formed by, for example, penetrating a pipe whose tip is closed into the ground G, opening the tip of the pipe, and, while pulling out the pipe, introducing a drain material into the vertical hole after the pipe is pulled out. Further, as the drain material, for example, cut gravel, crushed stone, gravel, slag, cinder ash, bottom ash (a large block of fly ash), or incineration ash of sewer is used. Then, the crawler crane 1 is operated to hang the pillar 4 on the ground G between the drain pillars D, that is, at a position shown by a chain line in FIG. 5, and the lower end of the pillar 4 is grounded as shown in FIG. G
Abut. Then, the vibration exciter 5 is operated to give vibration to the columnar body 4, and as a result, the columnar body 4 penetrates to a predetermined depth in the ground G as shown in FIG. At this time, the vibration of the column 4
Due to the large surface area of the column 4 itself and the presence of the protrusions 7, the column body 4 is satisfactorily transmitted to the ground G, and this vibration causes excess water pressure in the ground G. Then, due to this excess water pressure, the ground G
The water inside is horizontally drained into the drain pillar D around the intrusion site. Therefore, the drained ground G sinks and is vertically compressed and compacted. Subsequently, while continuously vibrating the pillar body 4, the pillar body 4 is pulled out from the ground G by the crawler crane 1, and the pillar body 4 is moved to another position on the ground G, that is, between the drain pillars D and the above. Repeat the same work. That is, by performing such an operation on the ground G around each drain pillar D, the ground G in the vicinity where the many drain pillars D are arranged is compacted. By the way, if it is necessary to recover the ground surface (such as locally generated holes) subsided by the above construction method to the original altitude, mechanical rolling, compaction, or dynamic consolidation should be performed from another location. All you have to do is compact the transported soil.

On the other hand, FIGS. 8 to 10 show another embodiment of the present invention. In these figures, FIG. 8 and FIG.
The compaction apparatus applied to the ground compaction method of the present invention is shown. The column 7 of this embodiment is a large-diameter steel pipe. As shown in FIG. 9, this column 7 is provided with a vibrochuck plate 8 at its upper end that traverses the inside of the column 7 in its radial direction.
The vibrator 5 is attached to the vibro chuck plate 8. In addition, a large number of water-permeable holes 9 are formed through the tube wall of the columnar body 7, and a large number of protrusions 6 are provided on the outer surface of the columnar body 7.

When compacting the soft ground using the apparatus having such a structure, first, like the construction method of the above-described embodiment, first, a large number of drain pillars D are formed in the ground G, and then the pillar body 7 is formed by the crawler crane 1. Is hung on one drain pillar D. And
Vibration is applied to the columnar body 7 by the vibration exciter 5, and the columnar body 7 penetrates to a predetermined depth as shown in FIG. 10 by this vibration. That is, the drain pillar D is included inside the pillar body 7.
At this time, the vibration is satisfactorily transmitted to the ground G inside the pillar body 7 by surrounding the entire circumference by the pillar body 7, and the presence of the protrusion 6 in the ground G outside the pillar body 7. Vibration is transmitted satisfactorily. Therefore, excess water pressure is generated in the ground G inside and outside the pillar body 7, and due to this excess water pressure, the water in the inner ground G enters the drain pillar D in the pillar body 7, and the water in the outer ground G penetrates around the location. The water is horizontally drained into the drain pillar D inside the pillar body 7 or through the water permeable hole 9 into the drain pillar D inside the pillar body 7. Then, while continuously vibrating the pillar 7, the pillar 7 is pulled out from the ground G by the crawler crane 1, the pillar 7 is moved onto another drain pillar D, and the same work as above is repeated. .

Next, some experimental results will be shown to clarify the effect of the present invention. However, the experiment was 1200 mm in diameter and 1 in length
A 2,000 mm steel pipe (column, but no water-permeable holes and protrusions) was included by a method of enclosing a gravel drain (drain column) having a diameter of 500 mm and a depth of 11,000 mm. A vibro hammer VM2-25000A was used as the vibration exciter.

Fig. 11 shows a standard penetration test for the ground before the steel pipe penetration (dotted line) and the ground after the penetration (solid line), and shows the relationship between each test result, that is, the N value and the depth of the ground. It is shown together with the stratum condition of. The N value before penetration was 4.55 on average, and the N value after penetration was 23.6 on average. As is clear from this figure, the ground after intrusion is significantly compacted with respect to the ground before intrusion.

FIG. 12 shows the calculation of the liquefaction resistance strength R based on the road bridge specifications using the N value before penetration and the N value after penetration. It can be seen that R after penetration (average 0.384) is significantly higher than R before penetration (average 0.16). However, the upper and lower limits of the graph are values of ± σ (: average value of R, σ: standard deviation). In addition, the coefficient of variation of R after penetration σ / (0.283) is the coefficient of variation of R before penetration σ
It is much smaller than /(0.403), and it can be seen that the ground after intrusion uniformly compacts.

FIG. 13 shows the relationship between the content of fine particles (particle size 74 μ or less) and R after penetration. The ground in this experiment is a ground with a fine particle content rate of 38% or less, but the R value does not decrease even if the fine particle content rate increases. It can be said that an increase in (or N value) can be expected.

FIG. 14 shows the relationship between the steel pipe penetration time and the penetration depth. From the figure, it can be seen that it takes 3 to 12 minutes to penetrate 11 m, but it can be seen that the construction speed is considerably increased because the cycle time of the conventional construction method is about 20 minutes.

Although the H-shaped steel is used as the columnar body 4 in the above-described embodiment, the columnar body 4 is not limited to this.
Alternatively, it is also possible to use a shape having a flange portion at the tip of each arm portion that crosses in a cross shape. Further, in the other embodiments described above, a steel pipe having a circular cross section is used as the columnar body 7, but a square steel pipe may be used. Furthermore, in both of the embodiments, the protrusion 6 is a protrusion, but for example, a rod-shaped member (steel rod or the like) along the length direction of the pillars 4 and 7, or a shape along the periphery of the pillars 4 and 7. It may be a thing (steel ring or the like in the case of the column 7).

"Effects of the Invention" According to the ground compaction method as described in detail above,
When the pillar penetrates into the ground while vibrating, the vibration of the pillar causes excess water pressure in the ground, and this excess water pressure causes the water in the ground toward the drain pillars arranged around the pillar. It is drained horizontally, which sinks the ground and compresses it vertically.

By adopting such a construction method, the following excellent effects can be obtained.

With a plurality of drain pillars arranged around the pillar body, if the pillar body is penetrated into the ground, groundwater can be efficiently discharged to these drain pillars, and as a result,
It is possible to compress the ground in a relatively wide range by a single penetration of the pillar and vibration, and it is possible to efficiently perform the compaction work, and it is possible to realize a significant reduction in construction period and cost. Become.

Since the ground is only compressed in the vertical direction, there are no voids in the ground and it is not necessary to add sand or crushed stone. Therefore,
Combined with the effect of reducing the construction period, the construction cost can be significantly reduced. Especially when it is not necessary to restore the subsided ground surface to its original altitude, for example, in the case of construction work that involves excavation to build a basement, the N value of the improved ground is around 40 or more. Since it can be used directly as a foundation for the foundation, the foundation construction cost can be significantly reduced.

The ground can be reliably compacted to prevent liquefaction of the ground during an earthquake.

[Brief description of drawings]

FIGS. 1 to 7 explain one embodiment of the present invention.
FIG. 1 is a schematic view showing the overall structure of the compaction device, FIG. 2 is a side view of the main part, FIG. 3 is a view taken along the line III-III of FIG. 2, FIG. 4, FIG. 6 and FIG. FIG. 7 is a vertical sectional view showing a compaction method using the apparatus of FIG. 1 in the order of steps, FIG. 5 is a plan view showing an arrangement example of drain columns, and FIGS. 8 to 10 are other embodiments of the present invention. To explain an example, FIG. 8 is a longitudinal sectional view of the main part,
FIG. 9 is a view taken along the line IX-IX of FIG. 8, FIG. 10 is a vertical sectional view for explaining the compaction method using the apparatus of FIG. 8, and FIGS. 11 to 14 are the functions of the present invention. It is a graph which shows the experimental result for clarifying an effect. 1 ... crawler crane, 4, 7 ... pillars, 5 ... vibrator, 6 ... protrusion, 9 ... water permeation hole, G ... ground.

Front Page Continuation (72) Inventor Nobuo Mori 2-16-1, Kyobashi, Chuo-ku, Tokyo Shimizu Construction Co., Ltd. (72) Inventor Takuro Odawara 2-16-1, Kyobashi, Chuo-ku, Tokyo Shimizu Construction Stock In-company (72) Inventor Katsuhiko Yokoyama 2-16-1, Kyobashi, Chuo-ku, Tokyo Shimizu Construction Co., Ltd. (56) References JP-A-57-119012 (JP, A) SAIKAI 52-65006 (JP) , U)

Claims (2)

[Claims] 1. A pit is excavated in the ground, a drain pillar is formed in the pit, and the pillar is vibrated and penetrated into the ground around the drain pillar to compact the ground. A method for compacting the ground. 2. The columnar body has a tubular shape and is provided with a large number of water permeable holes penetrating through the tube wall, and the columnar body is inserted so that the drain column is contained in the columnar body. The method for compacting the ground according to claim 1, wherein