JP2620628B2 - Method of forming foundation ground using sludge layer - Google Patents

Description

The present invention relates to a method for forming a sludge layer as a foundation ground, and more particularly, to removing water in a sludge layer through a perforated pipe embedded in the sludge layer. And forming a hard base on the sludge layer.

(B) Conventional technology Conventionally, an extremely soft ground such as a sludge layer has not been utilized by itself. For example, a sludge layer deposited on the sea floor is only used as an original ground at the time of landfill. Further, when such an ultra soft ground is used as the original ground, various displacements occur due to compaction and plastic deformation. For this reason, in general, measures have been taken to give the strength as the original ground while naturally draining the water of the sludge layer by the pressure of the embankment at the time of landfill.

For example, as a method of using the sludge layer as the original ground, there is a method of drying naturally as it is for a long period of time, or a method of putting a cement-based solidifying agent into the sludge layer and hardening the surface. Also, by laying a synthetic resin net, sheet or non-woven fabric on the seabed sludge layer, uneven settlement of the sludge layer is prevented and so-called sheet method or net method for uniform consolidation settlement (hereinafter referred to as “sheet method”). "). This sheet method is a method in which displacement due to uneven settlement is limited to the displacement amount of the sheet or the like itself, and is a method for preventing debris from sinking into a sludge layer in the seabed.

(C) Problems to be Solved by the Invention The above-mentioned method of curing by natural drying has a problem that it takes more than 5 years, and the method of adding a cement-based solidifying agent has a short construction period. However, there is a disadvantage that a large amount of a solidifying agent is required, and a huge cost is required.

In addition, the sheet method requires a lot of time and has the following problems. That is, in order to prevent uneven settlement of the ground by laying a sheet or the like, it is a precondition that there is no breakage of the sheet or the like and no movement of the sheet or the like in the buried layer. In other words, when a sheet is damaged, the original ground is destroyed by the pressure of the embankment on the sheet, etc., and a part of it is blown up as a mud and the strength of the landfill is significantly reduced. I do. When the sheet or the like moves, there is a problem that the original ground receives an eccentric load and uneven settlement occurs.

In addition, the sheet method using the sludge layer itself as the original ground also requires a sheet and the like that can cope with the drop of sand and debris and the load during embankment by marine earthwork, and the construction cost is relatively high. there were.

(D) Means for Solving the Problems Therefore, as a result of intensive studies to solve the above problems, the present inventor has found that by arranging a plurality of perforated pipes having a surface filter in the sludge layer, A method for forming the sludge layer as the foundation ground has been developed. That is, the method of the present invention is a method of forming a hardened material layer at least on the upper part of the sludge layer by draining the water in the sludge layer from the sludge layer. The feature is that a plurality of perforated pipes with a surface filter are arranged in parallel in the sludge layer in the area to be constructed, and the water in the sludge layer is perforated due to the pressure difference between the inside and outside of the pipe. While penetrating into the pipe and discharging through the pipe to the outside, solids in the sludge layer are sequentially laminated around individual perforated pipes to form a cured body, and the upper layer of the sludge layer is formed by the cured body. After the cured body layer is formed so as to cover, the surface layer of the cured body layer is dried.

Here, the outline of the present invention will be described. First, after damming by a method such as constructing a dike around the area to be constructed, a perforated pipe provided with a filter is provided throughout the sludge layer deposited on the water bottom. I do. When constructing the whole pond or the area where the sludge layer is exposed, simply install a perforated pipe without damming. Then, the water in the sludge layer is caused to flow out from one end of the perforated tube protruding outside the sludge layer by a method such as a natural flow, a pump, or a reduced pressure.

In this manner, the drainage from the perforated pipe is promoted by utilizing the pressure difference between the inside and outside of the perforated pipe, and the solid content in the sludge layer is gradually laminated around each perforated pipe to form a concentric circle. A cured body is formed. After the cured body is further grown to form a cured body layer covering the entire surface layer portion of the sludge layer, the surface layer portion of the cured body layer is dried in the sun. If water is present on the cured body layer, the water is removed and then dried on the sun. In this case, it is preferable to remove the water after the hardened material layer is generated over the entire sludge layer. However, the water is removed at a stage where the hardened material is generated to some extent, and the formation of the hardened material layer and solar radiation May be performed in parallel. After drying, sand or soil may be laminated on the cured body layer.

The “sludge layer” in this specification refers to a soft mud or organic / inorganic layer that is deposited on the bottom of rivers, lakes and marshes and contains a large amount of water.

The "perforated pipe" is one in which a number of holes are provided on the peripheral surface of the pipe, and is usually made of synthetic resin. For example, it seems that a corrugated pipe made of polyethylene, vinyl chloride, or the like is preferable in terms of strength and cost. Also, a tube wall made of a mesh is used. The diameter depends on the construction conditions,
It is about 20cm.

In order to dispose the perforated tube in the sludge layer, a method of placing it on the sludge layer and pushing it in from above, or a method of pushing horizontally into the sludge layer from the tip portion in the horizontal direction can be considered. The placement depth and spacing vary depending on the moisture content and thickness of the sludge layer, but usually the cured body formed around the perforated pipe has a diameter
It is preferable to arrange them so that they are connected to each other when they have grown to about 3 m. This is because a sufficient pressure resistance can be obtained if the cured body layer formed by connecting the cured bodies is about 3 m. It takes about 6 months for the cured product to grow to this extent.

Of course, in order for the cured body layers to be interconnected,
It is possible to select the depth and spacing of the perforated pipes in any way.However, if they are connected to each other at the stage where the diameter of the hardened material is small, the hardened material layer can be generated quickly throughout the sludge layer. However, it is necessary to reduce the layer thickness and increase the number of perforated pipes to be provided. In the opposite case, the cured layer becomes thicker and the number of perforated tubes can be reduced, but it takes time to form the layer. Therefore, generally, when the cured layer having a diameter of about 3 m is formed, it is connected to each other at a point of time when the
It is preferable to arrange them at an interval of about and a depth of about 1.5 to 3 m. The layer thickness is also affected by the moisture content of the sludge layer.

"Surface filter" is installed around the perforated pipe to prevent sludge from directly penetrating the perforated pipe,
For example, a nonwoven fabric wound around a perforated tube is used.

The "pressure difference between the inside and outside of the perforated pipe" refers to a difference caused by making the pressure inside the perforated pipe disposed in the sludge layer lower than the pressure applied to the sludge layer. For example, water is left on the sludge layer, pressure is applied to the sludge layer by the weight of the water, and one end of the perforated tube is made to protrude outside the sludge layer to make the inside of the tube an atmospheric pressure, thereby causing a pressure difference. To do. Of course, the weight of the sludge layer itself may be used, but this takes time. In addition to the natural drainage due to the pressure difference, a method of connecting a pump to a perforated pipe to reduce the pressure may be used.

"Solid content" refers to components other than water in the sludge layer.
For example, inorganic particles such as sand particles and soil, and organic substances.

The “hardened body layer” is such that the hardened body in which solids are gradually laminated around each perforated pipe as the water is drained from the perforated pipe in the sludge layer covers the surface layer of the sludge layer. What has grown. This cured layer need not be formed on the entire sludge layer. In other words, if the sludge layer is thick,
If there is also about m, a perforated pipe is provided so that a hardened material layer is formed on the upper part of the sludge layer. In such a case, a soft sludge layer still remains under the formed hardened material layer, but if the thickness of the hardened material layer is formed up to about 3 m, it is sufficient as a foundation ground. High strength can be obtained.

(E) Example Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

First, as shown in FIG. 1, an embankment (2) is built in an area (1) where the method of the present invention is to be applied, and the embankment is dammed. Then, a perforated pipe (P) provided with a surface filter (F) is disposed all over the inside of the sludge layer (3) deposited on the water bottom. This state is shown in FIGS. 2 (a) and 2 (b).

In this example, partitions are provided on the inner part of the embankment (2) built around the dovetails at intervals of several tens to several hundreds of centimeters by a row of sheet piles (4), and the gap between them is used as a drainage channel (5). The end of (P) faces the catchment channel (5). Water discharged from the perforated pipe (P) is collected in the water collecting channel (5) and discharged out of the area (1) by a pump or the like. Incidentally, reference numeral (6) in the figure
Is a hard base layer, (7) is an aqueous layer, and (8) is a sheet pile support. The sheet piles may be provided in two rows, or a concrete wall may be provided instead of the sheet piles.

As a method for disposing the perforated pipe (P) in the sludge layer (3), the perforated pipe (P) is settled on the sludge layer (3) as shown in FIG. The method of pushing it into) is simple. In this case, a weight may be attached to an appropriate portion of the perforated pipe (P). In addition, as shown in FIG. 4, the tip of the perforated pipe (P) may be horizontally pushed into the sludge layer (3). In this case, it is preferable to use a flexibility of the perforated pipe (P) to extend a curved portion of a root portion thereof, and to gradually push a distal end portion into a deep portion. Further, the pipes may be pushed in while being connected sequentially.

The perforated pipe (P) in the present embodiment is a pipe having a large number of holes on the peripheral surface as shown in FIG. 5 (a), and a surface filter (F) is wound therearound to form a sludge layer. It is arranged in (3). Also, as shown in FIG. 2B, a branch pipe (P ₁ ) or a branch-like water-permeable material (not shown) such as a nonwoven fabric is provided at an appropriate place in the perforated pipe (P) so as to enhance drainage efficiency. You may.

FIG. 6 (a) shows a state where the perforated pipe (P) is laid in the sludge layer (3). In this example, a perforated pipe (P) having a diameter of about 15 cm is laid on a sludge layer (3) having a water content of about 150% and a thickness of about 10 m. In this case, a perforated pipe (P)
Is laid at a depth of about 2m from the sludge layer surface, and the distance between each is 3m.

In this way, by draining the sludge layer (3), solids (9) are gradually laminated from the peripheral portion of the perforated pipe (P), and a hardened body (10) is formed. The hardened body (10) is formed in a columnar shape (concentric) around the perforated pipe (P) as shown in FIG. The sludge layer (3) forms a cured body layer (11) covering the entire surface layer portion. This cured body layer (1
1) becomes the ground with high strength.

What promotes drainage in the sludge layer (3) is the pressure of the water layer (7) above the sludge layer (3). That is, by making the sludge layer (3) filled with water, pressure is applied to the sludge layer (3), and drainage from the perforated pipe (P) is promptly and reliably performed.

Then, as shown in FIG. 7, the cured body layer (11) is
After being formed to a thickness of, the water on the cured body layer (11) is removed, and the surface layer is dried in the sun to be used as a foundation ground. An earth and sand layer (12) may be further provided on the cured body layer (11). The part of the water collecting channel (5) removes water and partial sludge, fills the part with earth and sand (13), and then removes sheet pile.

(F) Effects of the Invention As described in detail above, the method for forming a foundation ground using a sludge layer according to the present invention uses a perforated pipe submerged in the sludge layer to remove the water in the sludge layer using a pressure difference. It is to be removed.

Therefore, since it is only necessary to arrange a perforated pipe with a surface filter in the construction area, it is possible to form the foundation ground at a very low cost with little effort and compared with the conventional natural drainage and drying method. Reliable drainage and drying in a short time.

Further, as compared with the conventional sheet construction method or net construction method, there is no accident such as destruction of the original ground caused by the failure of the sheet or net. Moreover, since the sludge layer itself is formed as an independent foundation ground after blocking the construction water area, there is no problem of environmental pollution due to sludge or solidifying agent, and uneven settlement is suppressed even when reclaiming. This is a construction method having an extremely useful effect in practical use.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a construction area of the construction method according to the present invention, FIG. 2 (a) is a schematic cross-sectional view showing a state in which a perforated pipe is disposed in a sludge layer, and FIG. FIGS. 3 and 4 are schematic cross-sectional views each showing a state in which a perforated pipe is disposed in the sludge layer, and FIGS. 5 (a) and 5 (a).
(B) is a perspective view showing one embodiment of a perforated pipe, FIGS. 6 (a) and (b) are cross-sectional views each showing a state where a perforated pipe is laid in a sludge layer, and FIG. It is a schematic sectional drawing of the state where the water on the sludge layer was removed and the foundation ground was completed. P ... perforated pipe, F ... surface filter 1 ... construction area 2 ... embankment 3 ... sludge layer 4 ... sheet pile row 5 ... catchment channel 6 ... base layer 9 ... solid content, 10: cured body 11: cured body layer

Claims (1)

(57) [Claims] 1. A plurality of perforated pipes having a surface filter are disposed in parallel in a sludge layer in an area to be constructed, and water in the sludge layer is introduced into the perforated pipe by a pressure difference between the inside and the outside of the pipe. The hardened body is formed by infiltrating and discharging to the outside through the pipe, and sequentially laminating the solids in the sludge layer around each perforated pipe to form a hardened body, and further growing the hardened body to form a surface layer of the sludge layer. A method for forming a foundation ground using a sludge layer, comprising forming a hardened material layer covering a portion, and then drying a surface portion of the hardened material layer.