JPH03217513A - Vertical drain method - Google Patents

Abstract

PURPOSE:To shorten term of works and to reduce costs for execution of work by a method wherein a first hole for excavation is bored and a first drain material is inserted therein, and a second hole for excavation is bored so that it intersects the first hole at its optional position, and a second drain material is inserted therein. CONSTITUTION:A first hole 1 for excavation is bored obliquely with an excavator 10 from the surface of the earth toward a water-permeable layer S. The boring is made with an excavating means 11 and bore wall of the first hole 1 is maintained by a bore wall-maintaining means 12. Then a water-permeable first drain material 2 is inserted into the first hole 1 while the excavating means 11 and the bore wall-maintaining means 12 are being extracted and retreated, and thereby a first drainage 3 is formed. A second hole 5 for excavation is then bored by similar means of excavation from the surface of the earth toward the front end of the first drainage 3, and is made to communicate with the first drainage 3 at its front end 4. After inserting a second drain material 6 into the second hole 5, a second drainage 7 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ground improvement method. More specifically, it relates to improvements in the vertical drain construction method.

[Conventional technology]

Vertical drain methods such as sand drain method and paper drain method are conventionally known as ground improvement methods for soft ground, especially cohesive soil.

The vertical drain method is a construction method in which water-absorbing materials such as sand, cardboard, or nonwoven fabric are inserted vertically into the ground to reach the permeable layer. This construction method creates vertical drainage channels (made of water-absorbing material) in the ground.
drain) is formed. Water in the ground is squeezed out through this drain. Along with this drainage, consolidation of the ground is promoted.

The effect of consolidating the ground can be further enhanced by placing the drains closer together on the ground surface, or by using the method in combination with a preloading method in which a load of earth and sand is applied to the ground surface. This vertical drainage method is
It is particularly effective when used on viscous soil with a high moisture content.

[Problem to be solved by the invention]

However, in the above-mentioned conventional vertical drain construction method, it usually takes about 100 days to obtain the required amount of consolidation, although it depends on the spacing between the drains and other factors.

On the other hand, in civil engineering work, structures built on the ground are required to be put into service as soon as possible. Furthermore, construction costs are often determined by the construction period, and shortening the construction period has a large effect in reducing construction costs. Therefore, there are many benefits to shortening the construction period for ground improvement work in foundation work.

However, in the conventional vertical drainage method, although the consolidation time becomes shorter as the spacing between the drains becomes closer, there is a problem in that it is not economically advantageous to increase the number of drains without limit.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a vertical drain method that can improve drainage and consolidation effects without making the drains spaced too closely.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a first step of drilling a first borehole from the ground surface to a permeable layer in the ground;
a second step of inserting a first water-absorbing drain material into the first borehole; a third step of drilling a second borehole so as to intersect any part of the first borehole; and a fourth step of inserting a second drain material having water absorbing properties into the second excavated hole.

[Effect]

According to the present invention having the above configuration, one of the first drain or the second drain can be used as the main drain to reach the water permeable layer in the ground from the ground surface, and the other drain can be branched from the middle of the main drain. Due to this,
Not only vertical drains but also horizontal or diagonal drains can be formed in the ground.

In general, clay layers often have a higher hydraulic conductivity in the horizontal direction than in the vertical direction due to their deposition process. Therefore, by combining a drain with a horizontal component with a vertical drain, the drainage effect of the drain can be further enhanced.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

First Embodiment FIG. 1 shows a first embodiment of the vertical drain construction method according to the present invention. In Fig. 1, C indicates the stratum in which the vertical drain construction method is applied, and S indicates the permeable layer.

First, as a first step, a first excavation hole 1 is excavated in an oblique direction from the ground surface toward the permeable layer S using the excavation device 10 (FIG. 1(a)). This excavation is performed by an excavation means 11 such as an earth auger attached to the front part of the excavation device 10 so as to be movable prone. The hole wall of the first excavated hole 1 after being excavated by the excavating means 11 is held by a hole wall holding means 12 such as a casing or a mandrel. As the hole wall holding means 12,
Usually, a steel pipe is used. In this case, the hole wall holding means 12 may be a single long piece with no seams, or may have a structure in which pieces of a predetermined length are successively added to and extended as the excavation progresses. You can. The excavation means 11 may be of a type such as a water jet type provided at the tip of the hole wall holding means 12, or may be inserted into a hollow cavity of the hole wall holding means 12.
It may be of any type, such as an earth auger type, which protrudes from the tip of the earth auger and excavates. Furthermore, muddy water such as bentonite may be used to hold the hole wall of the first excavation hole and to discharge waste. In this way, the first excavation hole 1 is excavated to a predetermined depth (FIG. 1(b)).

Next, as a second step, the first drain material 2 is inserted into the first excavation hole 1 while pulling out and retreating the excavation means 11 and the hole wall holding means 12 from the tip of the first excavation hole 1 (
Figure 1 (C)). As the first drain material 2, absorbent sand, cardboard, nonwoven fabric, or the like is used. Further, the first drain material 2 may be inserted using a bag (pack). In this way, the first drain 3 is formed underground (FIG. 1(d)).

Next, as a third step, a second excavation hole 5 is vertically excavated from the ground surface toward the tip 4 of the first drain 3 using the same excavation method as described above (FIG. 1(e)). In this case, since the direction is vertical, the casing or the mandrel may be driven in using a diesel hammer or a pipe opening. In this drilling process, the second drilling hole 5 is
The first drain 3 communicates with the distal end 4 in an intersecting manner. (Figure 1(f)). Further drilling progressed to the second drilling hole 5.
excavate until reaching the permeable layer S (Fig. 1 (g)).

Next, as a fourth step, while pulling out the excavation means 11 and the hole wall holding means 12 from the tip of the second excavation hole 5 and retreating them, a second drain material 6 such as water-absorbent sand, cardboard, or nonwoven fabric is poured into the second excavation hole 5. 2 Insert into the drilling hole 5 and
A drain 7 is formed (FIG. 1(h)). Even in this case, the second drain material 6 may be inserted using a bag (pack).

In the vertical drain construction method of the present invention shown in FIG. 1, the first drain or the second drain may have an embodiment as shown in FIG.

That is, the direction of the second drain 7 is not limited to only the vertical direction, but may be an oblique direction (FIG. 2(a)).

Moreover, not only the second drain 7 but also the first drain 3 may be made to reach the water permeable layer S (FIG. 2(b)).

The diameters or drain materials of the first drain 3 and the second drain 7 may be made different (see FIG. 2).
C)).

Furthermore, a plurality of first drains 3 and second drains 7 may be combined (FIG. 2(d)).

In these cases, the arrangement of drains on the ground surface is
It may be grid-like, staggered, radial, or the like.

In addition, the intersection point between the first drain 3 and the second drain 7,
That is, the position of the point of intersection between the first excavated hole 1 and the second excavated hole 5 is arbitrary.

Second Embodiment FIG. 3 shows a second embodiment of the vertical drain construction method according to the present invention.

First, as a first step, a first excavation hole 21 is excavated vertically from the ground surface toward the permeable layer S by manual excavation such as a deep foundation method or by a drilling device (FIG. 3(a)). At this time, the hole wall of the first excavation hole 21 is held by a first excavation hole wall holding means 22 such as a sea cucumber board, a steel sheet pile, or a steel shoring to prevent collapse.

Next, as a third step, a second excavation hole 25 is excavated horizontally from the hole wall of the first excavation hole 21 (FIG. 3(b)).

The second excavation hole 25 is excavated by an excavation means 3 such as an earth auger.
1 and a second borehole wall holding means 32 such as a casing. In this way, the second excavation hole 25 is excavated to a predetermined depth position.

Next, as a fourth step, the excavation means 31 and the second excavation hole wall holding means 32 are pulled out and retreated from the tip of the second excavation hole 25, while the second drain material 26, such as water-absorbing sand, cardboard, or nonwoven fabric, is removed. is inserted into the second excavated hole 25 (FIG. 3(C)), and a second drain 27 is formed (FIG. 3(d)). In this case, the second drain material 26 may be inserted using a bag.

Next, the first step, which is the excavation of the first borehole 21, is performed until the permeable layer S is reached (FIG. 3(e)).

Next, as a second step, a first drain material 23 such as water-absorbing sand, cardboard, or nonwoven fabric is inserted into the first borehole 2 while removing the first borehole wall holding means 22 from the bottom.
1 to form the first drain 24 (see Fig. 3).
f)). In this case as well, the first drain material 23 may be inserted using a bag (pack).

In this case, in the third step of drilling the second drill hole 25, the first step of drilling the first drill hole 21 until reaching the permeable layer S is completed, and then the second drill hole 25 is drilled into the first drill hole 21. Hole 25
It is also possible to erect shoring for the excavation.

In the vertical drain method of the present invention shown in FIG. 3, the first drain or the second drain may have an embodiment as shown in FIG.

That is, the direction of the second drain 27 is not limited to only the horizontal direction, but may be an oblique direction (FIG. 4(a)).

In particular, when considering downstream drainage, it is desirable to provide the first excavation hole 21 in an oblique direction toward the ground surface.

Further, a plurality of first drains 24 may be connected by a second drain 27 (FIG. 4(b)).

Furthermore, the first drain and the second drain may have different diameters or different drain materials.

In this case as well, the arrangement of the drains on the ground surface may be in a grid pattern, staggered pattern, radial pattern, or the like.

Furthermore, the first drain 24 may be formed in the shape of a trench, and the second drain 27 may be formed by excavating horizontally from the hole wall (FIG. 4(C)).

Further, the position of the point of intersection between the first drain 24 and the second drain 27, that is, the point of intersection between the first excavation hole 21 and the second excavation hole 25, is arbitrary.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to form a drainage channel in the ground that has not only a vertical component but also a horizontal component, so that the drainage speed can be increased compared to the conventional vertical drain construction method. can.

Therefore, it has the advantage that not only rapid construction is possible in foundation work, but also the economical efficiency of the construction work can be improved.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing a first embodiment of the present invention, Fig. 2 is a diagram showing another aspect of the first embodiment of the invention, and Fig. 3 is a schematic diagram showing a second embodiment of the invention. The configuration diagram, FIG. 4, is a diagram showing another aspect of the second embodiment of the present invention. 1... First excavation hole 2... First drain material 3... First drain 5... Second excavation hole 6... Second drain material 7... Second drain 10... Drilling device 11...Drilling means 12...Bore wall holding means 21...First drill hole 23...First drain material 24...First drain 25...Second drill hole 26... -Second drain material 27...Second drain 30...Drilling equipment 31...First borehole wall holding means 32...Second borehole wall holding means

Claims (1)

[Claims] a first step of excavating a first borehole from the ground surface to a permeable layer in the ground; a second step of inserting a first drain material having water absorbing properties into the first borehole; A third step of drilling a second borehole so as to intersect any part of the borehole, and a fourth step of inserting a second drain material having water absorbing properties into the second borehole. The characteristic vertical drain construction method.