JPH0639772B2 - Ground compaction method and compaction device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for compacting ground for improving soft ground, and a compacting device.

“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.

The vibro flotation method is to penetrate a bar-shaped vibrator into the ground, vibrate the ground in a horizontal direction while ejecting water to the vibrator to compact it, and sand and crush stones in the voids near the vibrator. It is a construction method that aims to increase the vibration effect and press-fitting effect by adding the like.

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 and compaction device.

"Means for Solving Problems" The construction method of the present invention creates a high-density soil column compressed in the pipe axis direction inside the pipe by vibrating the pipe while penetrating the ground. At the same time, the ground reaction force under the soil pillar is compressed by the compression reaction force of the soil pillar.

Further, the device of the present invention comprises a tube body having an open tip driven into the ground, and a vibration exciter for imparting vibration to the tube body in the tube axis direction, and at least one of an inner surface and an outer surface of the tube body. A steel rod having substantially the same length as the tubular body is provided on the surface.

[Operation] According to the method of the present invention, the soil that the pipe body enters into the ground when it penetrates into the ground is compressed in the vertical direction (pipe axis direction), and this soil is compressed by the reaction force at the time of compression. The lower ground is compressed vertically. Therefore, one compaction work is completed by one penetration and one extraction, and since it only compresses in the vertical direction, there is no void in the ground,
No need to add sand or crushed stone.

Further, according to the device of the present invention, the vibration exciter vibrates the tubular body and penetrates it into the ground, and the steel rod increases the compressibility of the soil pillar in the tubular body. Moreover, since the steel rod has substantially the same length as the tubular body, the soil rod is continuously compressed by the steel rod, further increasing the compression ratio of the soil column.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an outline of a ground compaction device according to the present invention, in which reference numeral 1 is a crawler crane. The crawler crane 1 supports a guide mast 2, and a pipe body (a steel pipe having a large diameter in this embodiment) 4 is vertically hung on an upper end of the guide mast 2 via a suspension jig 3. As shown in FIGS. 2 and 3, the tube body 4 is provided with a vibro chuck plate 5 that traverses the inside of the tube body 4 in the radial direction at its upper end, and the vibro chuck plate 5 has a vibrating machine (so-called vibro hammer). 6 is attached. The vibration exciter 6 gives vibration to the tube body 4 along its axial direction (pipe axis direction). Further, on the inner surface and the outer surface of the tube body 4, a plurality of protruding portions (for example, steel rods) 7 extending along the tube axis direction are provided at intervals in the circumferential direction of the tube body 4 (third part). See figure).

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

First, the crawler crane 1 is operated to hang the pipe 4 at a predetermined position on the ground G, and the lower end of the pipe 4 is brought into contact with the ground G as shown in FIG. Then, the vibration exciter 6 is actuated to give vibration to the pipe body 4, whereby the pipe body 4 penetrates to a predetermined depth in the ground G as shown in FIG. At this time, the soil coming into the pipe body 4 is the pipe body 4 and the protruding portion 7 inside thereof.
Further, the pressing force of (3) further compresses in the vertical direction due to the frictional force generated between the tube body 4 and the inner protruding portion 7, and closes the inside of the tube body 4 to form the high density soil column P. Further, the high density soil pillar P is compressed by the compression reaction force.
The ground G below the ground is compressed vertically as indicated by the arrow. On the other hand, the protrusion 7 on the outer side of the pipe body 4 compresses the ground G around the pipe body 4 in the vertical direction and the horizontal direction by the pressing force and the frictional force at the time of penetration. Subsequently, the tube body 4 is pulled out from the ground G by the crawler crane 1 while continuously vibrating the tube body 4, the tube body 4 is moved to another position on the ground G, and the same work as above is repeated. That is, the ground G is compacted by performing such an operation on a large number of places on the ground G so as to draw a grid pattern, for example.

Next, some experimental results will be shown to clarify the effect of the present invention. However, the vibrating machine used in the experiment was a vibro hammer VM2-25000A, and the tube was 1200 mm in diameter and 12 in length.
000mm steel pipe, projection 50mm diameter, length 11000
mm steel rod. A total of 16 steel rods were welded only to the inner surface of the steel pipe.

Fig. 6 shows a standard penetration test for the ground before the steel pipe intrusion (dotted line) and the ground after the intrusion (solid line), and shows the test results, that is, the relationship between the N value and the depth of the ground. It is shown with the stratum condition of the ground. N after penetration
The values are those at the center of the steel pipe after drawing. The N value before penetration is 4.55 on average, and the N value after penetration is 15.89 on average.
Met. As is clear from this figure, the ground after intrusion is significantly compacted with respect to the ground before intrusion.

FIG. 7 is calculated using the liquefaction resistance strength R based on the road bridge specification for the N value before penetration and the N value after penetration. R after penetration (average 0.281) is R before penetration (average 0.1
6) It can be seen that it increases more significantly. 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 /
(0.499) is slightly higher than the coefficient of variation of R before penetration, σ / (0.403).

FIG. 8 shows the relationship between the content of fine particles (particle size 74 μ or less) and R after penetration. From this figure, it can be seen that R has a large value when the content of fine particles is 50% or less. That is, if the sandy soil has a fine particle content of 50% or less, an increase in R (or N value) can be expected by this method.

FIG. 9 shows the relationship between the N value and the depth at each location by applying the construction method according to the present invention so as to draw an equilateral triangle as shown in FIG. 11 at three locations on the ground. However, the ● mark shows the part of the code a, the x mark shows the part of the code a, and the Δ mark shows the part of the code c. As is clear from this figure, an N value that is approximately the same as the N value inside the steel pipe is obtained outside the steel pipe, and the compaction effect extends outside the pipe. However, depth 7-
The range where the N value is relatively small at 10 m is a stratum with a large amount of silt, so R is not small, so there is no problem if the N value is not increased.

Fig. 10 shows the relationship between the penetration time of steel pipe and the penetration depth. It can be seen from this figure that it takes 3 to 15 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. However, in the figure, the X mark is the result obtained by experimenting with an eccentric moment (magnitude of power of the vibration exciter) of 15000 kg · cm, and the ○ mark is the result obtained by experimenting with 25000 kg · cm.

By the way, the ratio (S / L) of the subsidence amount S of the soil in the pipe due to the penetration and withdrawal of the steel pipe (S / L) is 20% to 50%, and the subsidence occurs particularly in the steel pipe as shown in FIG. The backfilling of this portion may be carried out by bull compaction or dynamic compaction in which the weight is dropped only in this portion.

In the above embodiment, the tubular body has a circular cross section, but the tubular body is not limited to this and may have a rectangular cross section, for example. Further, the protruding portion 7 may be provided only on one of the inner and outer surfaces of the tubular body 4, and as the protruding portion 7, for example, a simple protrusion or a ring-shaped one along the circumferential direction of the tubular body 4 is used. May be.

"Effect of the invention" As described above, according to the construction method of the present invention, by penetrating the pipe body into the ground, a high-density soil column compressed in the pipe axis direction is formed inside the pipe body. Since the ground below the soil pillar is compressed by the compression reaction force of the soil pillar, the following excellent effects can be obtained.

One compaction work is completed by one penetration and one extraction, and it is not necessary to repeat the steps of inserting sand etc. and extracting the vibrator as in the vibro flotation method, thus significantly reducing the construction period. You can

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.

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

On the other hand, the device of the present invention includes a tube body when the tip driven into the ground is opened, and a vibrating machine that applies vibration to the tube body in the tube axis direction, and at least one of the inner and outer surfaces of the tube body. Further, since the steel rod having substantially the same length as the tubular body is provided, the following excellent effects can be obtained.

An exciter vibrates the pipe vertically and penetrates it into the ground, and the steel rod increases the compressibility of the soil inside or outside the pipe, so the ground is reliably compacted and the ground Liquefaction can be prevented. Moreover, since the steel rod is approximately the same length as the tubular body, the soil rod is continuously compressed by the steel rod, and the compressibility of the soil column can be further increased, preventing liquefaction of the ground. The effect can be further enhanced.

Since the structure is simple and the vertical vibration is used, a commercially available vibration exciter can be used. Therefore, the equipment cost can be significantly reduced.

[Brief description of drawings]

1 to 11 illustrate one embodiment of the present invention.
FIG. 1 is a schematic view showing the overall structure of the compaction device, FIG. 2 is a longitudinal sectional view of a main part, FIG. 3 is a view taken along the line III-III in FIG.
FIGS. 4 and 5 are vertical sectional views showing the compaction method in the order of steps, FIGS. 6 to 10 are graphs showing experimental results for clarifying the action and effect of the present invention, and FIG. It is explanatory drawing of the experiment which produced the result of the figure. 1 ... Crawler crane, 4 ... Tube, 6 ... Exciter,
7 ... Projection, G ... Ground, P ... Clay pillar.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Nobuo Mori No. 16-1 Kyobashi, Chuo-ku, Tokyo Shimizu Construction Co., Ltd. (72) Takuro Odawara No. 16-1 Kyobashi, Chuo-ku, Tokyo Shimizu Construction Co., Ltd. (72) Inventor Katsuhiko Yokoyama 2-16-1, Kyobashi, Chuo-ku, Tokyo Shimizu Construction Co., Ltd. (56) References: Development 52-7904 (JP, U) Development 52- 151606 (JP, U)

Claims (3)

[Claims] 1. A high-density soil column compressed in the axial direction of the pipe is created by oscillating the pipe into the ground while vibrating the pipe, and the compression reaction force of the soil column is used. A method of compacting the ground characterized by compressing the ground below the soil pillar. 2. A steel rod having substantially the same length as that of the tubular body is provided on at least one of the inner and outer surfaces of the tubular body. The method of compacting the ground. 3. A pipe body having a tip end that is driven into the ground and having an opening, and a vibration exciter that applies vibration to the pipe body in the pipe axis direction. At least one of the inner and outer surfaces of the pipe body is provided with:
A ground compaction device, characterized in that a steel rod having substantially the same length as the tubular body is provided.