JPS5952013A - Improvement work for soft ground - Google Patents

Abstract

PURPOSE:To raise the efficiency of draining from soft ground by providing a small-diameter tube having a high pressure resistance against consolidation loads and a high flexibility, and also having large numbers of small holes in its periphery into a sand pillar formed in the soft ground in such a way as to insert it longitudinally into the sand pillar. CONSTITUTION:A pit 2 is drilled in soft ground 1, and a sand pillar 3 protected with a water-permeable bag 6 is formed in the pit 2. A flexible small-diameter tube 7 having large numbers of small holes impervious to sand on its periphery and also having a high pressure resistance against consolidation pressure is longitudinally inserted into the sand pillar 3. A sand layer 4 and a banking 5 are formed on the ground. The water discharged from the soft ground 1 by the load of the banking 5 goes into the small-diameter tube 7 through the sand pillar 3 and then is discharged through the tube 7 to the ground's surface.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground improvement method for soft ground, and more specifically to a method for improving soft ground made of highly water-containing clay, corroded ground, etc. by a drainage method. In order to improve the ground and use it as a foundation, various methods such as replacement, drainage, compaction, and consolidation methods are used to improve the ground depending on the condition of the ground. One of the drainage methods is to drill a vertical hole in soft ground, form a sand column inside the hole, then consolidate the soft ground and drain the water contained in the ground to the outside through the sand column. There is a construction method. The construction method will be explained based on FIG.

In FIG. 1, reference numeral 1 indicates soft ground, and reference numeral 2 indicates vertical holes drilled in the soft ground 1 at required intervals.

The spacing between the vertical holes 2 is determined by calculation based on the state of the soft ground 1, consolidation load, desired consolidation settlement time, etc., or by actual volume values. The vertical holes 2 are filled with sand to form sand columns 3. The depth of the hole 2 depends on the length L of the sand column 3 and the layer thickness of the soft ground to be improved, but generally the limit is about 15,711 mm. Further, it is preferable that the diameter of the hole 2, that is, the diameter f of the sand column 3, be larger than the drainage effect, but the larger the diameter, the larger the scale of the construction work, which is inconvenient.

Generally, the diameter is about 15 on.

A sand layer 4 having a thickness of I1'18) is provided on the soft ground 1 on which the sand columns 3 have been formed, and an embankment 5 having a thickness that produces a required consolidation load on the soft ground 1 is further placed on top of the sand layer 4. The soft ground 1 drains the water contained in it due to the load of the embankment 5, sinks, and is consolidated. Drainage from the soft ground l reaches sand pillar 3, sand pillar 3V'3
The water passes through the sand layer 4 and is discharged from the sand layer 4 to the outside by side force or a pump.

The above-mentioned sand pillar drainage method is widely used, but due to the condition of soft ground, when deep strata are improved, or when sand pillars with a relatively small diameter are used, the drainage effect may be insufficient even if the water collection capacity is sufficient. There was a problem that I could not get it. That is, there is a problem that the sand pillars are deformed due to subsidence due to ground consolidation, and are further cut and lose their function as a nine-channel waterway, and another problem is that the sand pillars do not exhibit sufficient water flow function.

The former problem can be prevented by protecting the sand column with a flexible, water-permeable mesh bag that is resistant to bending, such as a synthetic fiber mesh bag with openings that do not allow sand particles to pass through. It is often used as a sand pillar drainage method that does not require bagging.

The latter problem of sand pillars failing to provide sufficient water passage cannot be solved even by this bagged sand pillar drainage method. Water in soft ground due to consolidation can easily reach the surface of the sand pillars by placing sand pillars at appropriate intervals.
A sand column is an aggregation of sand particles that are significantly larger than clay, etc., so numerous pore spaces are formed between the sand particles throughout the sand column, and because these are connected, it has an excellent water permeation function. It is something. However, in an actual sand column, even if it appears to be a uniform sand column, if you look closely at the flow of water in the sand column, you will find that it is caused by fine heterogeneity [Water permeability occurs]. . Since the existence probability of this "water path" is almost constant, its number is proportional to the cross-sectional area of the sand column. , it is possible to think that the sand column is continuous over the entire length, but if the diameter of the sand column is made small, this ``water hole'' may disappear in some places,
[There was a tendency for the large flow of water caused by the water to be interrupted. Therefore, the conventional bagged sand pillar drainage method
It was difficult to use a packed sand column with a diameter of about 15 m and a length of about 15 m to allow sufficient water flow and to bring about a sufficient consolidation effect on soft ground. It is necessary to use mountain sand, etc., which is difficult to obtain and has poor water permeability, which causes the water permeability of the sand column described by FiFiJ to further decrease.

An object of the present invention is to provide a ground improvement method using a sand column drainage method that has excellent drainage efficiency from soft ground.

The ground improvement method for soft ground according to the present invention involves drilling vertical holes in the soft ground at required intervals, forming sand columns in the holes, providing a sand layer on the soft ground, and then placing an embankment on top of the vertical holes. In the ground improvement method for soft ground, the soft ground is consolidated by the load of embankment, and the drained water is guided through the sand column to the sand layer and discharged from the sand layer to the outside. This is a ground improvement method characterized by inserting a pressure-resistant, flexible, small-diameter pipe with many pores on the surface vertically across the sand column.

In a preferred embodiment of the ground improvement method according to the present invention, s
The riiJ period sand column is packed in a bag made of permeable material.

In a more preferred embodiment of the ground improvement method according to the present invention, the small-diameter tube iiJ is sewn to a bag made of water-permeable material.

In another preferred embodiment of the ground improvement method according to the present invention, F! iJ Me small diameter pipe is made of plastic corrugated pipe,
Or it is a braided tube made of elastic linear material such as metal or plastic.

In another preferred embodiment of the ground improvement method according to the present invention, the area of the small diameter pipe (iii) increases toward the upper sand layer.

The following is a second drawing showing an example of the ground improvement method of the present invention.
This will be explained based on the diagram. In this construction method, as well as the conventional construction method shown in Fig. 1, a vertical hole 2 is drilled in the soft ground 1, a sand column 3 is formed in the vertical hole, and a sand layer 4 is formed on the soft ground 1. Furthermore, an embankment 5 is placed on top of it. Three pillars of sand are protected by a bag 6 made of water-permeable material.

In this construction method, a small diameter pipe 7 is inserted into the sand column 3 so as to traverse the sand column 3 longitudinally. The small diameter pipe 7 needs to have pressure resistance against the consolidation load, and must have enough strength to not be crushed by the consolidation load. For this purpose, it is advantageous to make the diameter as small as possible within the range that maintains the water permeability. Furthermore, since the consolidation load decreases in the upper layer and the amount of water passing through the small diameter pipe 7 increases, it is an appropriate measure to increase the cross-sectional area of the small diameter pipe 7 toward the upper sand layer 4. be. In response to deformation of the sand column 3 due to subsidence due to consolidation of the soft ground 1, this small diameter pipe 7 also needs to have flexibility so that it can be bent without breaking. Historically, there were many pores on the periphery that did not allow sand to pass through. An example of a suitable small diameter tube 7 is a corrugated plastic tube with a large number of pores (
Examples include corrugate vibrator), braided tubes made of elastic linear materials such as metals and plastics.

When the sand column 3 is packed in a bag, as shown in Fig. 3, if the small diameter pipe 7 is sewn together when the bag 6 made of water-permeable material is sewn together, there is no manufacturing complexity and the construction is easy. There is no need to modify conventional construction machinery in any way. Even if sand with poor permeability is used for the sand column 3, the water discharged from the wall of the hole 2 can be made to flow horizontally across the diameter of the sand column 3, and the pores on the surface of the small diameter pipe 7 Since it is easy to reach the small diameter pipe 7
There is no doubt that there is pressure at the periphery of sand column 3. The one-dot chain line in FIG. 3 indicates the suture surface of the small diameter tube 7.

In this construction method, the soft ground 1 receives the load of the embankment 5.
The water discharged from the hole 2 passes horizontally through the water-permeable sandbag 6 and the sand column 3, and reaches the circumferential surface of the small diameter tube 7.
The wastewater enters the small diameter pipe 7 from the pore, and flows in the sand layer 4 only by receiving low flow resistance in the small diameter pipe 7.

Therefore, even if the length of the sand column 3 is increased, sufficient drainage can be achieved. Since the ground improvement method for soft ground according to the present invention is configured as described above, drainage and consolidation of soft ground can proceed smoothly. This allows the construction period to be shortened and the depth of the soft ground to be improved to be increased. Furthermore, even if good quality sand material for the sand pillar cannot be obtained, drainage can be carried out smoothly.

In addition, when the sand column is used as a bagging sand column and a small diameter pipe for water passage is sewn together at the same time as the water-permeable material for bagging is sewn, the work of preparing materials for carrying out the construction method of the present invention becomes easier. This is advantageous in terms of construction because it can be carried out without making any changes to conventional construction machinery.

As described above, the method of the present invention makes it possible to efficiently implement the sand column drainage method as a soil improvement method for soft ground, expands its scope of application, and significantly improves economic efficiency, workability, etc. That will happen.

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views of soft ground constructed by the conventional method and the embodiment of the present invention, respectively, and Figure 3 is a small diameter sutured bag of sand pillars used in the present invention. A cross-sectional view of an example of a pipe 0 1... Soft ground 2... Vertical hole 3...
・Sand column 4...Sand layer 5...Embankment 6...Bag of permeable material 7...Engraving of drawing of small diameter pipe for water flow (no change in content) Figure 1 Figure 2 Figure 3 Procedures Written amendment (method) % formula % 1 Display of the case Showa 5 Fi 1 Patent 1 No. 161486 Shiji 3 Relationship with the person making the amendment e1 Patent applicant 4 Agent Publication 03 6 Number of inventions increased by the amendment

Claims (1)

[Claims] (1) Vertical holes are drilled at required intervals in soft ground. A sand column is formed in the hole, a sand layer is placed on the soft ground, and an embankment is placed on top of it, the soft ground is consolidated by the load of the embankment, and the discharged water is passed through one sand column and deposited on the sand layer. guidance,
In a ground improvement method for soft ground that discharges water from a sand layer to the outside, a small diameter pipe that has pressure resistance against consolidation loads, is flexible, and has many pores on the circumferential surface is installed inside the sand column. A ground improvement method for soft ground, which is characterized by inserting it vertically. (2) The ground improvement method according to claim 1, wherein the separately mentioned sand pillar is packed in a bag made of water-permeable material. (3) The ground improvement method according to claim 2, wherein the small diameter pipe Mlj is sewn to a bag made of water permeable material IJ. (4) The ground improvement method according to claim 1, 2 or 3, wherein the small diameter pipe is a plastic corrugated pipe. (6) Claims 1, 2, or 1, wherein the small diameter tube is a braided tube made of an elastic linear material such as metal or plastic.
; is the ground improvement method described in Section 3. (6) The ground improvement method according to claim 1, wherein the cross-sectional area of the small diameter pipe increases toward the upper sand layer.